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  <doc>
    <id>50765</id>
    <completedYear/>
    <publishedYear>2020</publishedYear>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst>571</pageFirst>
    <pageLast>574</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>conferenceobject</type>
    <publisherName>Deutsche Gesellschaft für Akustik e.V.</publisherName>
    <publisherPlace>Berlin</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Bestimmung von Materialparametern aus dem dispersiven Verhalten geführter Wellen mittels neuronaler Netze</title>
    <abstract language="deu">Damit eine Simulationsrechnung, beispielsweise mit einer FEM-Software, eine ausreichend hohe Genauigkeit erreicht, muss vorausgesetzt werden, dass die Modellparameter eine sehr hohe Güte aufweisen. Die genaue Kenntnis der Materialparameter ist dabei von besonderer Bedeutung. Um diese Parameter bestimmen zu können, müssen die verwendeten Werkstoffe messtechnisch charakterisiert werden. Neben anderen Ansätzen sind dafür akustische Verfahren im Ultraschallbereich geeignet. Für dünnwandige und plattenförmige Materialien können aus den sich ausbreitenden geführten Wellen messtechnisch Dispersionskurven bestimmt und aus diesen die Materialparameter abgeleitet werden.&#13;
Da für die Signalverarbeitung und für Optimierungsaufgaben aktuell zunehmend Machine Learning Tools zum Einsatz kommen, stellt sich die Frage, ob diese Werkzeuge auch für die Ermittlung der Materialparameter aus den gemessenen Dispersionskurven eingesetzt werden können.&#13;
In der vorgestellten Untersuchung soll ein Convolutional Neural Network aufgestellt werden, welches aus Dispersionsbildern Muster extrahiert und aus diesen eine Schätzung für die Materialparameter ermittelt. Um die Machbarkeit dieses Ansatzes zu prüfen, werden zunächst nur isotrope Materialien betrachtet. Für das Netz werden mit der Scaled-Boundary-Finite-Element-Methode synthetische Daten für das Trainieren und Validieren generiert. Zusätzlich werden die Hyperparameter des neuronalen Netzes variiert, um ein optimales Model für die Schätzung zu finden. Anschließend kann das Netz mit experimentellen Daten getestet und das Ergebnis hinsichtlich der Genauigkeit bewertet werden.</abstract>
    <parentTitle language="deu">DAGA 2020 - 46. Jahrestagung für Akustik</parentTitle>
    <identifier type="isbn">978-3-939296-17-1</identifier>
    <enrichment key="eventName">DAGA 2020 - 46. Jahrestagung für Akustik</enrichment>
    <enrichment key="eventPlace">Meeting was canceled</enrichment>
    <enrichment key="eventStart">16.03.2020</enrichment>
    <enrichment key="eventEnd">19.03.2020</enrichment>
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    <author>Maik Lauschkin</author>
    <author>Jannis Bulling</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>P. Wasmer</author>
    <author>Jens Prager</author>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Machinelles Lernen</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Geführte Ultraschallwellen</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Materialcharakterisierung</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Elastische Konstanten</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Isotrope Materialien</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>53304</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst/>
    <pageLast/>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>lecture</type>
    <publisherName/>
    <publisherPlace/>
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    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Ein inverses Verfahren zur Schadensrekonstruktion mittels geführter Wellen</title>
    <abstract language="deu">Eine zentrale Aufgabe der zerstörungsfreien Prüfung und der Strukturüberwachung (engl. Structural Health Monitoring - SHM) mit Ultraschallwellen ist die Bewertung von Schäden in Bauteilen. In vielen Bauteilen, wie zum Beispiel platten- und schalenförmigen Strukturen, Rohrleitungen oder Laminaten, breitet sich der Ultraschall in Form geführter Wellen aus. Zwar haben geführte Wellen eine relativ große Reichweite innerhalb des Bauteils und ermöglichen so eine großflächige Prüfung, ihre multimodalen und dispersiven Eigenschaften erschweren jedoch die Analyse der vom Schaden kommenden Reflexionen. Eine Möglichkeit, die Messsignale zu interpretieren und die Schäden zu charakterisieren, ist deren Vergleich mit der Wellenausbreitung in einem digitalen Modell. Hierbei stellt sich die Aufgabe, den Schaden im digitalen Modell anhand der Messdaten zu rekonstruieren. Diese Rekonstruktion beschreibt ein inverses Problem, das mehrere Vorwärtsrechnungen braucht, um das Schadensmodell an die Messdaten anzupassen.Durch die kleine Wellenlänge von Ultraschallwellen sind klassische Vorwärtsmethoden wie die Finte Elemente Methode rechenintensiv, weshalb die Autoren die semi-analytische Scaled Boundary Finite Element Method (SBFEM) benutzen, um den Rechenaufwand zu verringern. Im Beitrag wird ein inverses Verfahren basierend auf dem Automatischen Differenzieren in Kombination mit der SBFEM vorgestellt und an verschiedenen Schadenstypen in 2D-Querschnittmodellen von Wellenleitern getestet. In der präsentierten Vorstudie werden dafür „Messdaten“ aus unabhängigen Simulationen verwendet.</abstract>
    <enrichment key="eventName">DAGA 2021 - 47. Jahrestagung für Akustik</enrichment>
    <enrichment key="eventPlace">Vienna, Austria</enrichment>
    <enrichment key="eventStart">15.08.2021</enrichment>
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    <author>Jannis Bulling</author>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>SBFEM</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Inverse Verfahren</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>AD</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>SHM</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>NDT</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Präsentation</collection>
  </doc>
  <doc>
    <id>53305</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst>1</pageFirst>
    <pageLast>4</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>conferenceobject</type>
    <publisherName>Deutsche Gesellschaft für Akustik (DEGA)</publisherName>
    <publisherPlace>Berlin</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Ein inverses Verfahren zur Schadensrekonstruktion mittels geführter Wellen</title>
    <abstract language="deu">Eine zentrale Aufgabe der zerstörungsfreien Prüfung und der Strukturüberwachung (engl. Structural Health Monitoring - SHM) mit Ultraschallwellen ist die Bewertung von Schäden in Bauteilen. In vielen Bauteilen, wie zum Beispiel platten- und schalenförmigen Strukturen, Rohrleitungen oder Laminaten, breitet sich der Ultraschall in Form geführter Wellen aus. Zwar haben geführte Wellen eine relativ große Reichweite innerhalb des Bauteils und ermöglichen so eine großflächige Prüfung, ihre multimodalen und dispersiven Eigenschaften erschweren jedoch die Analyse der vom Schaden kommenden Reflexionen. Eine Möglichkeit, die Messsignale zu interpretieren und die Schäden zu charakterisieren, ist deren Vergleich mit der Wellenausbreitung in einem digitalen Modell. Hierbei stellt sich die Aufgabe, den Schaden im digitalen Modell anhand der Messdaten zu rekonstruieren. Diese Rekonstruktion beschreibt ein inverses Problem, das mehrere Vorwärtsrechnungen braucht, um das Schadensmodell an die Messdaten anzupassen. Durch die kleine Wellenlänge von Ultraschallwellen sind klassische Vorwärtsmethoden wie die Finte Elemente Methode rechenintensiv, weshalb die Autoren die semi-analytische Scaled Boundary Finite Element Method (SBFEM) benutzen, um den Rechenaufwand zu verringern. Im Beitrag wird ein inverses Verfahren basierend auf dem Automatischen Differenzieren in Kombination mit der SBFEM vorgestellt und an verschiedenen Schadenstypen in 2D-Querschnittmodellen von Wellenleitern getestet. In der präsentierten Vorstudie werden dafür „Messdaten“ aus unabhängigen Simulationen verwendet.</abstract>
    <parentTitle language="deu">Tagungsband DAGA 2021</parentTitle>
    <enrichment key="eventName">DAGA 2021 - 47. Jahrestagung für Akustik</enrichment>
    <enrichment key="eventPlace">Vienna, Austria</enrichment>
    <enrichment key="eventStart">15.08.2021</enrichment>
    <enrichment key="eventEnd">18.08.2021</enrichment>
    <enrichment key="opus.source">publish</enrichment>
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    <author>Jannis Bulling</author>
    <author>B. Jurgelucks</author>
    <author>Jens Prager</author>
    <author>A. Walther</author>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>SBFEM</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Inverse Probleme</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>SHM</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>NDT</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>AD</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>51986</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>759</pageFirst>
    <pageLast>768</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>127</volume>
    <type>conferenceobject</type>
    <publisherName>Springer</publisherName>
    <publisherPlace>Cham</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Sensitivity of Ultrasonic Guided Waves to Elastic Constants: A Numerical Study</title>
    <abstract language="eng">The dispersive properties of Lamb waves can be utilised for material characterisation because the frequency-wavenumber-relationship, as well as the group velocity, depend on material parameters. These dependencies make a non-destructive estimation of an elastic constant possible. This preliminary study investigates the sensitivity of dispersion curves caused by a change in elastic constants. The Scaled Boundary Finite Element Method is used to compute special dispersion curves, which show the sensitivity value of the frequency and group velocity as a colour value. This representation allows for easy identification of patterns and local effects. Two sets of dispersion curves are presented, one set for a steel plate and the other set for a plate made of a carbon fibre reinforced polymer. In general, we notice that the sensitivity often increases with the frequency and that higher-order modes seem to be more suitable for material characterisation. Moreover, specific modes respond to material changes while others are relatively unaffected, which must be taken into consideration for material characterisation.</abstract>
    <parentTitle language="eng">Lecture Notes in Civil Engineering</parentTitle>
    <identifier type="isbn">978-3-030-64593-9</identifier>
    <identifier type="doi">10.1007/978-3-030-64594-6_73</identifier>
    <enrichment key="eventName">European Workshop on Structural Health Monitoring (EWSHM 2020)</enrichment>
    <enrichment key="eventPlace">Online meeting</enrichment>
    <enrichment key="eventStart">06.07.2020</enrichment>
    <enrichment key="eventEnd">09.07.2020</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">true</enrichment>
    <author>Jannis Bulling</author>
    <author>Georg Franosch</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jens Prager</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scaled Boundary Finite Element Method</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Lamb waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Dispersion curves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Carbon fibre reinforced polymer</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Transverse isotropy</value>
    </subject>
    <collection role="ddc" number="53">Physik</collection>
    <collection role="ddc" number="620">Ingenieurwissenschaften und zugeordnete Tätigkeiten</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Material</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>53492</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst>659</pageFirst>
    <pageLast>662</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>47</volume>
    <type>conferenceobject</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Inverse Bestimmung elastischer Materialparameter aus dem Ausbreitungsverhalten geführter Ultraschallwellen mittels eines Convolutional Neuronal Networks</title>
    <abstract language="deu">Detailliertes Wissen über die mechanischen Eigenschaften verwendeter Materialien ist Grundvoraussetzung für viele ingenieurtechnische Aufgaben und Dienstleistungen. Zur Bestimmung der elastischen Materialparameter gibt es verschiedene klassische, zerstörende Prüfverfahren. Eine Möglichkeit der zerstörungsfreien Bestimmung liegt in der Auswertung von Messergebnissen, die auf Basis des Ausbreitungsverhaltens geführter Ultraschallwellen gewonnen wurden. Das Ausbreitungsverhalten geführter Ultraschallwellen kann mittels Dispersionsabbildungen dargestellt werden.&#13;
&#13;
Um aus messtechnisch ermittelten Dispersionsabbildungen Rückschlüsse auf die Materialparameter zu ziehen, werden in der aktuellen Forschung verschiedene inverse Methoden diskutiert. Maschinelles Lernen und insbesondere Convolutional Neural Networks (CNNs) stellen eine Möglichkeit der automatisierten inversen Modellierung und Evaluierung von Bilddaten dar.&#13;
&#13;
In diesem Beitrag wird gezeigt, wie das Ausbreitungsverhalten von geführten Ultraschallwellen unter Verwendung von CNNs genutzt werden kann, um die isotropen elastischen Konstanten einer plattenförmigen Struktur zu bestimmen. Hierfür werden die verwendeten Daten analysiert, das Preprocessing erläutert und eine grundlegende CNN-Architektur gewählt. Zur Auswertung des generierten Modells werden verschiedene Verfahren wie Gradienten-Mapping und die Visualisierung der verschiedenen Schichten vorgestellt. Die Anwendbarkeit der Methode wird anhand synthetischer Daten demonstriert.</abstract>
    <parentTitle language="deu">Tagungsband DAGA 2021 - 47. Jahrestagung für Akustik</parentTitle>
    <identifier type="isbn">978-3-939296-18-8</identifier>
    <enrichment key="eventName">DAGA 2021</enrichment>
    <enrichment key="eventPlace">Vienna, Austria</enrichment>
    <enrichment key="eventStart">15.08.2021</enrichment>
    <enrichment key="eventEnd">18.08.2021</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <author>Mathias Held</author>
    <author>Abdalla Rashwan</author>
    <author>Jannis Bulling</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Maik Lauschkin</author>
    <author>Jens Prager</author>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Geführte Ultraschallwellen</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Inverse Probleme</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Materialcharakterisierung</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Maschinelles Lernen</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Dispersion</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Lamb Wellen</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>52820</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>2472</pageFirst>
    <pageLast/>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>122</volume>
    <type>article</type>
    <publisherName>Elsevier Ltd.</publisherName>
    <publisherPlace>Amsterdam, Netherlands</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>1</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Damage quantification in an aluminium-CFRP composite structure using guided wave wavenumber mapping: Comparison of instantaneous and local wavenumber analyses</title>
    <abstract language="eng">Composite-overwrapped pressure vessels (COPV) are increasingly used in the transportation industry due to their high strength to mass ratio. Throughout the years, various designs were developed and found their applications. Currently, there are five designs, which can be subdivided into two main categories - with a load-sharing metal liner and with a non-load-sharing plastic liner. The main damage mechanism defining the lifetime of the first type is fatigue of the metal liner, whereas for the second type it is fatigue of the composite overwrap. Nevertheless, one damage type which may drastically reduce the lifetime of COPV is impact-induced damage. Therefore, this barely visible damage needs to be assessed in a non-destructive way to decide whether the pressure vessel can be further used or has to be put out of service. One of the possible methods is based on ultrasonic waves. In this contribution, both conventional ultrasonic testing (UT) by high-frequency bulk waves and wavenumber mapping by low frequency guided waves are used to evaluate impact damage. Wavenumber mapping techniques are first benchmarked on a simulated aluminium panel then applied to experimental measurements acquired on a delaminated aluminium-CFRP composite plate which corresponds to a structure of COPV with a load-sharing metal liner. The analysis of experimental data obtained from measurements of guided waves propagating in an aluminium-CFRP composite plate with impact-induced damage is performed. All approaches show similar performance in terms of quantification of damage size and depths while being applied to numerical data. The approaches used on the experimental data deliver an accurate estimate of the in-plane size of the large delamination at the aluminium-CFRP interface but only a rough estimate of its depth. Moreover, none of the wavenumber mapping techniques used in the study can quantify every delamination between CFRP plies caused by the impact, which is the case for conventional UT. This may be solved by using higher frequencies (shorter wavelengths) or more advanced signal processing techniques. All in all, it can be concluded that imaging of complex impact damage in fibre-reinforced composites based on wavenumber mapping is not straightforward and stays a challenging task.</abstract>
    <parentTitle language="eng">NDT &amp; E International</parentTitle>
    <identifier type="issn">0963-8695</identifier>
    <identifier type="doi">10.1016/j.ndteint.2021.102472</identifier>
    <identifier type="urn">urn:nbn:de:kobv:b43-528203</identifier>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="date_peer_review">12.08.2021</enrichment>
    <licence>Creative Commons - CC BY-NC-ND - Namensnennung - Nicht kommerziell - Keine Bearbeitungen 4.0 International</licence>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>O. Mesnil</author>
    <author>Jens Prager</author>
    <author>Dirk Gohlke</author>
    <author>C. Boller</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasonic guided waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Instantaneous wavenumber analysis</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Local wavenumber analysis</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Signal processing</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="literaturgattung" number="">Verlagsliteratur</collection>
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    <file>https://opus4.kobv.de/opus4-bam/files/52820/Damage quantification in an aluminium-CFRP composite structure.pdf</file>
  </doc>
  <doc>
    <id>52271</id>
    <completedYear/>
    <publishedYear>2020</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst/>
    <pageLast/>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>lecture</type>
    <publisherName/>
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    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Numerical methods (part II) Finite element method (FEM), Spectral element method (SEM) and Scaled Boundary FEM (SBFEM)</title>
    <abstract language="eng">A general presentation on numerical methods. In particular, the Finite Element Method, the Spectral Element Method, and the Scaled Boundary Finite Element Method.</abstract>
    <enrichment key="eventName">ITN-Trainingsevent</enrichment>
    <enrichment key="eventPlace">Online meeting</enrichment>
    <enrichment key="eventStart">22.11.2020</enrichment>
    <enrichment key="opus.source">publish</enrichment>
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    <author>Jannis Bulling</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>FEM</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>SBFEM</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>SEM</value>
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    <collection role="literaturgattung" number="">Präsentation</collection>
  </doc>
  <doc>
    <id>52275</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst/>
    <pageLast/>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>lecture</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">A Combination of the Scaled Boundary Finite Element Method with the Mortar Method</title>
    <abstract language="eng">The simulation of ultrasonic waves in a linearly elastic body can be computationally intensive. The reason is the relatively short wavelength compared to the body size for high frequencies. One possible approach to counteract the high computational costs is to decompose the domain into small parts and strive for parallelization. The Mortar Method is a well-established approach for domain decomposition.&#13;
A rather new approach to discretize the emerging subdomains is the Scaled Boundary Finite Element Method. This semi-analytical method has many attractive properties. Some of these properties are listed subsequently. The grid consists of polygonal elements, which leaves much freedom in the meshing process. A variety of material distributions, including anisotropic materials, can be considered. High-order shape functions can be used for optimal convergence properties. The approach treats singularities at crack tips and corners analytically. Especially in the frequency domain, the Scaled Boundary Finite Element Method reduces the dimension of the approximation because only degrees of freedom which are associated with the boundary of a polygonal element are necessary. Those desirable properties make the method particularly suitable for calculating the dynamic responses in bodies with cracks, as it is essential for many non-destructive testing and structural health monitoring applications. &#13;
In this contribution, we present a combination of the Scaled Boundary Finite Element Method with the Mortar Method in two dimensions. The presentation starts with a theoretical overview of both approaches. Subsequently, numerical examples demonstrate the stability of the combination for the polygonal boundary of the elements. The numerical examples increase in complexity and are compared to results computed on non-divided domains with the Finite Element Method.</abstract>
    <enrichment key="eventName">WCCM-ECCOMAS CONGRESS</enrichment>
    <enrichment key="eventPlace">Online meeting</enrichment>
    <enrichment key="eventStart">11.01.2021</enrichment>
    <enrichment key="eventEnd">15.01.2021</enrichment>
    <enrichment key="opus.source">publish</enrichment>
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    <author>Jannis Bulling</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasound</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Numerical Simulation</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scaled Boundary Finite Element Method, Mortar Method</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
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    <collection role="literaturgattung" number="">Präsentation</collection>
  </doc>
  <doc>
    <id>52618</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>239</pageFirst>
    <pageLast>240</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>2021</volume>
    <type>conferenceobject</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation>AMA Service GmbH, Von-Münchhausen-Straße 49 31515 Wunstorf</creatingCorporation>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Inverse determination of elastic material parameters from ultrasonic guided waves dispersion measurements using Convolutional Neuronal Networks</title>
    <abstract language="eng">In the context of Industry 4.0 and especially in the field of Structural Health Monitoring, Condition Monitoring and Digital Twins, simulations are becoming more and more important. The exact determination of material parameters is required for realistic results of numerical simulations of the static and dynamic behavior of technical structures. There are many possibilities to determine&#13;
elastic material parameters. One possibility of non-destructive testing are ultrasonic guided waves. For the evaluation of the measurement results, mostly inverse methods are applied in order to be able to draw conclusions about the elastic material parameters from analysing the ultrasonic guided wave propagation. For the inverse determination of the elastic material Parameters with ultrasonic guided waves, several investigations were carried out, e.g. the determination of the isotropic material parameters through the point of zero-groupvelocity or anisotropic material parameters with a simplex algorithm. These investigations are based on the evaluation of dispersion images. Machine learning and in particular Convolutional Neural Networks (CNN) are one possibility of the automated evaluation from Image data, e.g. classification or object recognition problems. This article shows how the dispersive behavior of ultrasonic guided waves and CNNs can be used to determine the isotropic elastic constants of plate-like structures.</abstract>
    <parentTitle language="eng">SMSI 2021 - Measurement Science</parentTitle>
    <identifier type="isbn">978-3-9819376-4-0</identifier>
    <identifier type="doi">10.5162/SMSI2021/A10.2</identifier>
    <enrichment key="eventName">SMSI 2021 2021-05-03 - 2021-05-06 digital</enrichment>
    <enrichment key="eventPlace">Online meeting</enrichment>
    <enrichment key="eventStart">03.05.2021</enrichment>
    <enrichment key="eventEnd">06.05.2021</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <author>Mathias Held</author>
    <author>Abdalla Rashwan</author>
    <author>Maik Lauschkin</author>
    <author>Jannis Bulling</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jens Prager</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Convolutional Neuronal Networks</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Inverse Probleme</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Materialcharakterisierung</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>guided waves</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Dispersion</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>54504</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst/>
    <pageLast/>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>researchdata</type>
    <publisherName>Zenodo</publisherName>
    <publisherPlace>Geneva</publisherPlace>
    <creatingCorporation>Bundesanstalt für Materialforschung und -prüfung (BAM)</creatingCorporation>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Dataset on full ultrasonic guided wavefield measurements of a CFRP plate with fully bonded and partially debonded omega stringer</title>
    <abstract language="eng">The fourth dataset dedicated to the Open Guided Waves platform presented in this work aims at a carbon fiber composite plate with an additional omega stringer at constant temperature conditions. The dataset provides full ultrasonic guided wavefields. &#13;
&#13;
A chirp signal in the frequency range 20-500 kHz and Hann windowed tone-burst signal with 5 cycles and carrier frequencies of 16.5 kHz, 50 kHz, 100 kHz, 200 kHz and 300kHz are used to excite the wave. The piezoceramic actuator used for this purpose is attached to the center of the stringer side surface of the core plate.&#13;
&#13;
&#13;
Three scenarios are provided with this setup: (1) wavefield measurements without damage, (2) wavefield measurements with a local stringer debond and (3) wavefield measurements with a large stringer debond. The defects were caused by impacts performed from the backside of the plate. As result, the stringer feet debonds locally which was verified with conventional ultrasound measurements.&#13;
&#13;
The dataset can be used for benchmarking purposes of various signal processing methods for damage imaging.&#13;
&#13;
The detailed description of the dataset is published in Data in Brief Journal.</abstract>
    <identifier type="doi">10.5281/zenodo.5105861</identifier>
    <enrichment key="ScientificResourceTypeGeneral">Datensatz</enrichment>
    <enrichment key="ScientificDateCreatedStart">2021</enrichment>
    <enrichment key="ScientificGeolocation">Institute of Fluid-Flow Machinery Polish Academy of Sciences, Generała Józefa Fiszera 14, 80-231 Gdańsk, Poland</enrichment>
    <enrichment key="ScientificNote">The detailed description of the dataset is published in the journal "Data in Brief".</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="RelatedIdentifier">https://opus4.kobv.de/opus4-bam/frontdoor/index/index/docId/54524</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
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    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>P. Kudela</author>
    <author>M. Radzienski</author>
    <author>M. Moix-Bonet</author>
    <author>C. Willberg</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>K. Tschöke</author>
    <author>J. Moll</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Open data</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasonic guided waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Experimental data</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei für die Öffentlichkeit verfügbar ("Open Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
    <collection role="unnumberedseries" number="">Forschungsdatensätze der BAM</collection>
  </doc>
  <doc>
    <id>54524</id>
    <completedYear/>
    <publishedYear>2022</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1</pageFirst>
    <pageLast>13</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>42</volume>
    <type>article</type>
    <publisherName>Elsevier</publisherName>
    <publisherPlace>Amsterdam</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>1</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Dataset on full ultrasonic guided wavefield measurements of a CFRP plate with fully bonded and partially debonded omega stringer</title>
    <abstract language="eng">The fourth dataset dedicated to the Open Guided Waves platform presented in this work aims at a carbon fiber composite plate with an additional omega stringer at constant temperature conditions. The dataset provides full ultrasonic guided wavefields. Two types of signals were used for guided wave excitation, namely chirp signal and tone-burst signal. The chirp signal had a frequency range of 20-500kHz. The tone-burst signals had a form of sine modulated by Hann window with 5 cycles and carrier frequencies 16.5kHz, 50kHz, 100kHz, 200kHz, 300kHz. The piezoceramic actuator used for this purpose was attached to the center of the stringer side surface of the core plate. Three scenarios are provided with this setup: (1) wavefield measurements without damage, (2) wavefield measurements with a local stringer debond and (3) wavefield measurements with a large stringer debond. The defects were caused by impacts performed from the backside of the plate. As result, the stringer feet debonds locally which was verified with conventional ultrasound measurements.</abstract>
    <parentTitle language="eng">Data in brief</parentTitle>
    <identifier type="doi">10.1016/j.dib.2022.108078</identifier>
    <identifier type="issn">2352-3409</identifier>
    <identifier type="urn">urn:nbn:de:kobv:b43-545242</identifier>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="RelatedIdentifier">https://opus4.kobv.de/opus4-bam/frontdoor/index/index/docId/54504</enrichment>
    <enrichment key="date_peer_review">20.04.2022</enrichment>
    <licence>Creative Commons - CC BY-NC-ND - Namensnennung - Nicht kommerziell - Keine Bearbeitungen 4.0 International</licence>
    <author>P. Kudela</author>
    <author>M. Radzienski</author>
    <author>M. Moix-Bonet</author>
    <author>C. Willberg</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>K. Tschöke</author>
    <author>J. Moll</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Lamb waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Composite panel</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Impact damage</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Damage detection</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scanning laser Doppler vibrometry</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Structural health monitoring</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Non-destructive evaluation</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Open data</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="literaturgattung" number="">Verlagsliteratur</collection>
    <collection role="fulltextaccess" number="">Datei für die Öffentlichkeit verfügbar ("Open Access")</collection>
    <collection role="unnumberedseries" number="">Wissenschaftliche Artikel der BAM</collection>
    <thesisPublisher>Bundesanstalt für Materialforschung und -prüfung (BAM)</thesisPublisher>
    <file>https://opus4.kobv.de/opus4-bam/files/54524/1-s2.0-S235234092200289X-main.pdf</file>
  </doc>
  <doc>
    <id>54206</id>
    <completedYear/>
    <publishedYear>2022</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1</pageFirst>
    <pageLast>19</pageLast>
    <pageNumber/>
    <edition/>
    <issue>1</issue>
    <volume>22</volume>
    <type>article</type>
    <publisherName>MDPI</publisherName>
    <publisherPlace>Basel</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>1</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Towards interpretable machine learning for automated damage detection based on ultrasonic guided waves</title>
    <abstract language="eng">Data-driven analysis for damage assessment has a large potential in structural health monitoring (SHM) systems, where sensors are permanently attached to the structure, enabling continuous and frequent measurements. In this contribution, we propose a machine learning (ML) approach for automated damage detection, based on an ML toolbox for industrial condition monitoring. The toolbox combines multiple complementary algorithms for feature extraction and selection and automatically chooses the best combination of methods for the dataset at hand. Here, this toolbox is applied to a guided wave-based SHM dataset for varying temperatures and damage locations, which is freely available on the Open Guided Waves platform. A classification rate of 96.2% is achieved, demonstrating reliable and automated damage detection. Moreover, the ability of the ML model to identify a damaged structure at untrained damage locations and temperatures is demonstrated.</abstract>
    <parentTitle language="eng">Sensors</parentTitle>
    <identifier type="doi">10.3390/s22010406</identifier>
    <identifier type="issn">1424-8220</identifier>
    <identifier type="urn">urn:nbn:de:kobv:b43-542060</identifier>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="date_peer_review">21.01.2022</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>C. Schnur</author>
    <author>P. Goodarzi</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>Jens Prager</author>
    <author>K. Tschöke</author>
    <author>J. Moll</author>
    <author>A. Schütze</author>
    <author>T. Schneider</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Composite structures</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Structural health monitoring</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Carbon fibre-reinforced plastic</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Interpretable machine learning</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Automotive industry</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="literaturgattung" number="">Verlagsliteratur</collection>
    <collection role="fulltextaccess" number="">Datei für die Öffentlichkeit verfügbar ("Open Access")</collection>
    <collection role="unnumberedseries" number="">Wissenschaftliche Artikel der BAM</collection>
    <thesisPublisher>Bundesanstalt für Materialforschung und -prüfung (BAM)</thesisPublisher>
    <file>https://opus4.kobv.de/opus4-bam/files/54206/Schnur - 2022 - Machine Learning on OGW Dataset (MDPI Sensors).pdf</file>
  </doc>
  <doc>
    <id>57768</id>
    <completedYear/>
    <publishedYear>2023</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1</pageFirst>
    <pageLast>20</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>120</volume>
    <type>article</type>
    <publisherName>Elsevier B.V.</publisherName>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>1</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">3D simulations of ultrasonic waves in plates using the scaled boundary finite element method and high-order transition elements</title>
    <abstract language="eng">It can be difficult to efficiently model ultrasonic waves in 3D structures, especially when the computational model needs to account for complex geometries. This contribution presents a solution based on the Scaled Boundary Finite Element Method (SBFEM). It is a numerical tool suitable for elastodynamic problems. A space-tree discretisation, namely quad-trees, is used. This technique allows the decomposition of an image into quadrilaterals or quads, which are extruded to generate the 3D plate geometry. In particular, small quads resolve regions with discontinuities, allowing them to represent fine details in the structure. Moreover, this meshing technique allows for exploiting cell similarities, making the calculation procedure more efficient. The space-tree discretisations are generated from a high-resolution image containing all the information about damaged regions or boundary conditions. The resulting SBFEM polyhedral domains employ transition elements to ensure correct coupling between cells of different sizes. The analytical solution of a cylindrical scatterer serves as a reference to validate the proposed approach. Other examples also demonstrate the validity of the methodology and its flexibility.</abstract>
    <parentTitle language="eng">Wave Motion</parentTitle>
    <identifier type="doi">10.1016/j.wavemoti.2023.103158</identifier>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="date_peer_review">26.06.2023</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">true</enrichment>
    <author>Daniel Lozano</author>
    <author>Jannis Bulling</author>
    <author>A. Asokkumar</author>
    <author>H. Gravenkamp</author>
    <author>C. Birk</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>High-order transition elements</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Image-based models</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Wave propagation</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scaled boundary finite element method</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="literaturgattung" number="">Verlagsliteratur</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
  </doc>
  <doc>
    <id>57338</id>
    <completedYear/>
    <publishedYear>2023</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1</pageFirst>
    <pageLast>11</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume>72</volume>
    <type>article</type>
    <publisherName>IEEE</publisherName>
    <publisherPlace>Piscataway Township, New Jersey, USA</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>1</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Polar Coordinate for Damage Imaging of Adhesively Bonded Plates Using Ultrasonic Guided Waves and Laser Doppler Vibrometer Measurements</title>
    <abstract language="eng">Wavefield measurements by a scanning laser Doppler vibrometer are generally carried out in a cartesian coordinate. As a piezoelectric transducer generates Lamb waves following radial paths, the use of a polar coordinate can be a suitable alternative to the use of a cartesian coordinate. Therefore, in the proposed method, using a single transducer placed on the center of the specimen, the measured wavefields are transformed into polar coordinates, making several identical radial line inspections from the center in a direction of incident waves. Taking advantage of the properties of the polar coordinates, a signal processing technique is proposed through a frequency-wavenumber filtering process in these coordinates. In this technique, by using proper filters, unwanted wave modes of the incident wave along with all reflected waves are filtered out. In addition, the conventional features of RMS and Euclidean distance are adapted for the polar coordinate system to image the bonded plate. The proposed signal processing and damage imaging are first introduced through a numerical simulation. Then, the performance of the proposed technique is presented by experimental measurements of two specimens including adhesively bonded carbon fiber-reinforced plastic composite plates and bonded aluminum plates.</abstract>
    <parentTitle language="eng">IEEE Transactions on Instrumentation and Measurement</parentTitle>
    <identifier type="doi">10.1109/TIM.2023.3267528</identifier>
    <identifier type="urn">urn:nbn:de:kobv:b43-573386</identifier>
    <identifier type="issn">0018-9456</identifier>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="date_peer_review">19.06.2023</enrichment>
    <licence>Creative Commons - CC BY - Namensnennung 4.0 International</licence>
    <author>M. Barzegar</author>
    <author>D. J. Pasadas</author>
    <author>A. L. Ribeiro</author>
    <author>H. G. Ramos</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Lamb waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Composites</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Disbond</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="literaturgattung" number="">Verlagsliteratur</collection>
    <collection role="fulltextaccess" number="">Datei für die Öffentlichkeit verfügbar ("Open Access")</collection>
    <collection role="unnumberedseries" number="">Wissenschaftliche Artikel der BAM</collection>
    <thesisPublisher>Bundesanstalt für Materialforschung und -prüfung (BAM)</thesisPublisher>
    <file>https://opus4.kobv.de/opus4-bam/files/57338/Barzegar - 2023 - Polar Coordinate for Damage Imaging of Adhesively Bonded Plates using UGW.pdf</file>
  </doc>
  <doc>
    <id>57340</id>
    <completedYear/>
    <publishedYear>2021</publishedYear>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst>52</pageFirst>
    <pageLast>55</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>conferenceobject</type>
    <publisherName>Deutsche Gesellschaft für Akustik (DEGA)</publisherName>
    <publisherPlace>Berlin</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Akustische Bestimmung der Werkstoffparameter faserverstärkter Kunststoffe durch Auswertung der Dispersionseigenschaften geführter Wellen</title>
    <abstract language="deu">Akustische Verfahren eignen sich hervorragend zur Bestimmung der Werkstoffeigenschaften. Die Verfügbarkeit derartiger Verfahren ist vor allem für Kunststoffe wichtig, da deren Eigenschaften stark abhängig vom jeweiligen Herstellungsprozess und vom Alterungszustand sind. Exakte und vollständige Werte sind daher in Datenbanken oder von Herstellern nur begrenzt zu finden. Insbesondere die Entwicklung von Methoden zur Charakterisierung faserverstärkter Kunststoffe (FKV) ist nach wie vor Gegenstand der Forschung. Hier müssen anisotropiebedingt mehrere Kennwerte bestimmt werden. Da FKV zumeist als dünnwandige Bauteile zum Einsatz kommen, können die Werkstoffparameter aus den Dispersionseigenschaften der Lamb-Wellen, die sich in diesen Strukturen ausbreiten, abgeleitet werden. Dazu ist eine räumliche Abtastung des sich ausbreitenden Schallfelds erforderlich.&#13;
In der vorliegenden Untersuchung wird dieser Ansatz für die relativ neue Werkstoffklasse der faserverstärkten Thermoplaste angewendet. Diese zeichnet ein ausgeprägtes Dämpfungsverhalten und eine Anisotropie der Materialparameter aus. Dazu wurde das Schallfeld im Ultraschallbereich mit einem Laser-Doppler-Vibrometers vermessen. Rechnerisch bestimmte Dispersionskurven wurden dann an die gemessenen Werte angepasst, womit die richtungsabhängigen Materialparameter bestimmt werden konnten.&#13;
Im Vortrag wird das Messverfahren vorgestellt und auf spezielle Probleme, die sich z.B. aus dem Dämpfungsverhalten des Werkstoffs ergeben, eingegangen. Ausgewählte gemessene Werte werden mit den Ergebnissen von Referenzverfahren verglichen.</abstract>
    <parentTitle language="deu">Tagungsband DAGA 2021</parentTitle>
    <enrichment key="eventName">DAGA 2021 - 47. Jahrestagung für Akustik</enrichment>
    <enrichment key="eventPlace">Vienna, Austria</enrichment>
    <enrichment key="eventStart">15.08.2021</enrichment>
    <enrichment key="eventEnd">18.08.2021</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">true</enrichment>
    <author>Jens Prager</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>Mathias Held</author>
    <author>M. Klärner</author>
    <author>T. Winkler</author>
    <author>L. Kroll</author>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Ultraschall</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Composites</value>
    </subject>
    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Thermoplastische Kunststoffe</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>57378</id>
    <completedYear/>
    <publishedYear>2023</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>823</pageFirst>
    <pageLast>826</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>conferenceobject</type>
    <publisherName>Deutsche Gesellschaft für Akustik e.V.</publisherName>
    <publisherPlace>Berlin</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Characterization of adhesion strength using guided ultrasonic waves</title>
    <abstract language="deu">Klebeverbindungen sind aus vielen Anwendungen wie dem Leichtbau nicht mehr wegzudenken. Durch die Verklebung gleicher oder ungleicher Materialien entstehen viele Vorteile gegenüber konservativen Fügeverfahren. Jedoch stellen schwache Haftfestigkeiten eine sehr unbeliebte Fehlerart dar, die schlecht zu detektieren sind und zu einem frühzeitigen Versagen der Verklebung bei vergleichsweise geringen Belastungen führen können. Aufgrund hoher Sicherheits- und Qualitätsansprüche wird die Haftfestigkeit dieser Verbindungen jedoch noch immer zerstörend geprüft. Zufriedenstellende zerstörungsfreie Verfahren, um Haftfestigkeiten zu prüfen, sind nicht vorhanden und Thema gegenwärtiger Forschung. Ein Ansatz, der in diesem Projekt verfolgt wird, liegt in der Verwendung geführter Ultraschallwellen.&#13;
Hierzu wird anhand von Simulationen mittels der Scaled Boundary Finite Element Methode gezeigt, dass die gezielte Auswertung bestimmter Bereiche des Dispersionsdiagrams, den sogenannten vermiedenen Kreuzungen (engl. mode repulsion regions), eine Charakterisierung der Haftfestigkeiten zulassen könnten. Dies liegt darin begründet, dass die mittleren mechanischen Belastungen der Kleberschicht in diesen Bereichen ein lokales Maximum aufweisen und daher eine erhöhte Sensitivität auf Materialänderungen haben. Es wird gezeigt, wie sensitiv diese Bereiche auf Materialänderungen in der Klebergrenzschicht sind und welche potenziellen Fehlergrößen existieren.</abstract>
    <parentTitle language="deu">Fortschritte der Akustik - DAGA 2023</parentTitle>
    <identifier type="isbn">978-3-939296-21-8</identifier>
    <identifier type="url">https://pub.dega-akustik.de/DAGA_2023</identifier>
    <enrichment key="eventName">DAGA 2023</enrichment>
    <enrichment key="eventPlace">Hamburg, Germany</enrichment>
    <enrichment key="eventStart">06.03.2023</enrichment>
    <enrichment key="eventEnd">09.03.2023</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">true</enrichment>
    <author>Marcel Nicolai</author>
    <author>H. Zeipert</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>S. Johannesmann</author>
    <author>Jens Prager</author>
    <author>B. Henning</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>SBFEM</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Adhesive Bonding</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Kissing Bonds</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>NDT</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasonic Guided Waves</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>57379</id>
    <completedYear/>
    <publishedYear>2023</publishedYear>
    <thesisYearAccepted/>
    <language>deu</language>
    <pageFirst/>
    <pageLast/>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>lecture</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="deu">Charakterisierung von Haftfestigkeiten mittels geführter Ultraschallwellen</title>
    <abstract language="deu">Klebeverbindungen sind aus vielen Anwendungen wie dem Leichtbau nicht mehr wegzudenken. Durch die Verklebung gleicher oder ungleicher Materialien entstehen viele Vorteile gegenüber konservativen Fügeverfahren. Jedoch stellen schwache Haftfestigkeiten eine sehr unbeliebte Fehlerart dar, die schlecht zu detektieren sind und zu einem frühzeitigen Versagen der Verklebung bei vergleichsweise geringen Belastungen führen können. Aufgrund hoher Sicherheits- und Qualitätsansprüche wird die Haftfestigkeit dieser Verbindungen jedoch noch immer zerstörend geprüft. Zufriedenstellende zerstörungsfreie Verfahren, um Haftfestigkeiten zu prüfen, sind nicht vorhanden und Thema gegenwärtiger Forschung. Ein Ansatz, der in diesem Projekt verfolgt wird, liegt in der Verwendung geführter Ultraschallwellen.&#13;
Hierzu wird anhand von Simulationen mittels der Scaled Boundary Finite Element Methode gezeigt, dass die gezielte Auswertung bestimmter Bereiche des Dispersionsdiagrams, den sogenannten vermiedenen Kreuzungen (engl. mode repulsion regions), eine Charakterisierung der Haftfestigkeiten zulassen könnten. Dies liegt darin begründet, dass die mittleren mechanischen Belastungen der Kleberschicht in diesen Bereichen ein lokales Maximum aufweisen und daher eine erhöhte Sensitivität auf Materialänderungen haben. Es wird gezeigt, wie sensitiv diese Bereiche auf Materialänderungen in der Klebergrenzschicht sind und welche potenziellen Fehlergrößen existieren.</abstract>
    <enrichment key="eventName">Schall 23</enrichment>
    <enrichment key="eventPlace">Wetzlar, Germany</enrichment>
    <enrichment key="eventStart">20.03.2023</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">true</enrichment>
    <enrichment key="InvitedTalks">0</enrichment>
    <author>Marcel Nicolai</author>
    <author>H. Zeipert</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>Jens Prager</author>
    <author>B. Henning</author>
    <author>Daniel Hernando Lozano Duarte</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Adhesive Bonding</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Kissing Bonds</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>NDT</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasonic Guided Waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>SBFEM</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Präsentation</collection>
  </doc>
  <doc>
    <id>57354</id>
    <completedYear/>
    <publishedYear>2023</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>88</pageFirst>
    <pageLast>91</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>conferenceobject</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation>Deutsche Gesellschaft für Akustik e.V. (DEGA)</creatingCorporation>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Comparative Study Between Simulation and Experimental Guided Ultrasonic Wave Propagation on a Plate Like Structure</title>
    <abstract language="eng">In plate-like structures, ultrasonic waves propagate as Lamb waves. Their use is important for many applications from non-destructive testing to structural health monitoring. Efficient simulation tools contribute to a significant value add e.g. in designing systems for these applications. Under which conditions an acceptable accuracy of these models with affordable computational costs can be achieved is an open question. Many of these applications include the usage of a plane wavefront, simulated in 2D crossesctional models to reduce complexity. In this contribution, a comparative case study between simulations and experiments is presented. The aim is to verify and compare a 2D cross-sectional model with experimental data. The experimental setup for this case study consists of an aluminum plate. A rectangular piezoelectric transducer is mounted for guided wave excitation. A laser Doppler vibrometer (LDV) measures out-of-plane velocities on the plate. A 2D cross-sectional model based on the Scaled Boundary Finite Element Method (SBFEM) is used to simulate the wave propagation of the experimental setup. The first data points near the transducer are used to fit the excitation tractions of the model, while additional points further away from the source are used to validate the model. The comparison between the recorded measurements and the simulated velocities shows a high degree of compatibility.</abstract>
    <parentTitle language="deu">Fortschritte der Akustik - DAGA 2023</parentTitle>
    <identifier type="isbn">978-3-939296-21-8</identifier>
    <enrichment key="eventName">DAGA 2023 - 49. Jahrestagung für Akustik</enrichment>
    <enrichment key="eventPlace">Hamburg, Germany</enrichment>
    <enrichment key="eventStart">06.03.2023</enrichment>
    <enrichment key="eventEnd">09.03.2023</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
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    <author>A. Bayoumi</author>
    <author>Daniel Lozano</author>
    <author>Jannis Bulling</author>
    <author>I. Mueller</author>
    <author>Jens Prager</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scaled Boundary Finite Element Method</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Guided Ultrasonic Wave</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Laser Doppler Vibrometer</value>
    </subject>
    <collection role="ddc" number="543">Analytische Chemie</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Chemie und Prozesstechnik</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Graue Literatur</collection>
  </doc>
  <doc>
    <id>59775</id>
    <completedYear/>
    <publishedYear>2023</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst/>
    <pageLast/>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>lecture</type>
    <publisherName/>
    <publisherPlace/>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">The SBFEM to simulate the scattering of ultrasonic guided waves interacting with defects in plate structures</title>
    <abstract language="eng">In the field of guided waves for non-destructive testing, the interaction of these waves with damages or other discontinuities in a structure is critical. When a guided wave mode travels and hits a defect, it scatters in all directions, converting to other modes and reflecting the existing one. These interactions are captured in scattered far field complex amplitudes. The amplitudes are stored in scattering matrices, which characterise the elastodynamic behaviour of a defect completely. Scattering matrices are also useful to simulate backpropagation from a defect using ray-tracing methods.&#13;
&#13;
Simulating these interactions is challenging, and analytical solutions only exist for simple geometries. Still, using general tools like the finite element method results in large, usually costly models. Recently, researchers proposed a method based on a numerical implementation of the Kirchhoff–Helmholtz integral that allows the computation of the scattering matrices using a model containing only the damaged region. However, classical methods to resolve the far field and low-order elements were used, leading to large models yet more efficient than using other techniques.&#13;
&#13;
We propose using the SBFEM as an alternative to enhance the computation of the far field scattering. The damaged region is discretised using high-order polyhedral elements, while the far field is constructed using a modified version of the SBFEM. Examples compared to the literature demonstrate the validity of the approach.</abstract>
    <enrichment key="eventName">Doktorandentreffen</enrichment>
    <enrichment key="eventPlace">Attendorn, Germany</enrichment>
    <enrichment key="eventStart">16.10.2023</enrichment>
    <enrichment key="InvitedTalks">0</enrichment>
    <enrichment key="opus.source">publish</enrichment>
    <enrichment key="opus.doi.autoCreate">false</enrichment>
    <enrichment key="opus.urn.autoCreate">true</enrichment>
    <author>Daniel Lozano</author>
    <author>Jannis Bulling</author>
    <author>Hauke Gravenkamp</author>
    <author>Jens Prager</author>
    <author>Carolin Birk</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>SBFEM</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Guided Waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scattering</value>
    </subject>
    <collection role="ddc" number="624">Ingenieurbau</collection>
    <collection role="institutes" number="">8 Zerstörungsfreie Prüfung</collection>
    <collection role="institutes" number="">8.4 Akustische und elektromagnetische Verfahren</collection>
    <collection role="themenfelder" number="">Infrastruktur</collection>
    <collection role="themenfelder" number="">Security</collection>
    <collection role="fulltextaccess" number="">Datei im Netzwerk der BAM verfügbar ("Closed Access")</collection>
    <collection role="literaturgattung" number="">Präsentation</collection>
  </doc>
  <doc>
    <id>59776</id>
    <completedYear/>
    <publishedYear>2023</publishedYear>
    <thesisYearAccepted/>
    <language>eng</language>
    <pageFirst>1035</pageFirst>
    <pageLast>1038</pageLast>
    <pageNumber/>
    <edition/>
    <issue/>
    <volume/>
    <type>conferenceobject</type>
    <publisherName/>
    <publisherPlace>Hamburg</publisherPlace>
    <creatingCorporation/>
    <contributingCorporation/>
    <belongsToBibliography>0</belongsToBibliography>
    <completedDate>--</completedDate>
    <publishedDate>--</publishedDate>
    <thesisDateAccepted>--</thesisDateAccepted>
    <title language="eng">Modeling guided waves interacting with arbitrarily shaped inhomogeneities using SBFEM in combination with an extruded quadtree decomposition for 3D plates</title>
    <abstract language="eng">For structural health monitoring systems or non-destructive testing, it is crucial to study the interactions of ultrasonic-guided waves with inhomogeneities or damage in structural components. Simulation of these interactions poses a challenge.&#13;
&#13;
After the wave-damage interaction, the numerical model must reproduce features like mode conversion or wave scattering. Mathematically, damages are discontinuities in a computational domain, and each wave interacts differently because of the geometrical features. We propose a quadtree-based meshing in the current contribution to capture these geometrical characteristics.&#13;
&#13;
This kind of discretisation approach requires special techniques to couple cells of different sizes since, after a quadtree decomposition, the problem of so-called hanging nodes may arise. Transition elements based on high-order transfinite shape functions are used to solve this issue. The advantage is that these elements allow the correct coupling of the cells while retaining a high-order interpolation. Moreover, the reuse of the dynamic stiffness matrices can be exploited based on the similarity of the cells. This procedure makes the approach very efficient.&#13;
&#13;
Examples show the scattering characteristics of different guided wave modes after interacting with inhomogeneities and discontinuities in a plate.</abstract>
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    <author>Daniel Lozano</author>
    <author>Jannis Bulling</author>
    <author>Jens Prager</author>
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      <value>SBFEM</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Quadtree</value>
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    <subject>
      <language>eng</language>
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      <value>Ultrasound</value>
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    <title language="eng">Experimental Study of Ultrasonic Guided Waves in a Bipolar Plate of a Fuel Cell</title>
    <abstract language="eng">Water management in proton-exchange membrane fuel cells (PEMFCs) is critical for efficient operation. However, in-situ measurements of the water distribution in an operating PEMFC are challenging. In this study, we investigate key aspects of ultrasonic guided wave (UGW) propagation through the bipolar plate of a PEMFC using 3D scanning laser Doppler vibrometry (3D LDV). Our results provide insights for the design and optimization of UGW-based sensor systems for water detection in PEMFCs.</abstract>
    <parentTitle language="eng">2023 IEEE International Ultrasonics Symposium (IUS)</parentTitle>
    <identifier type="doi">10.1109/IUS51837.2023.10307327</identifier>
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    <author>J. Sablowski</author>
    <author>Yevgeniya Lugovtsova</author>
    <author>Jannis Bulling</author>
    <author>C. Kupsch</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasonic guided waves</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Laser Doppler vibrometry</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Fuel cells</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Water management</value>
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    <title language="eng">Adhesive Porosity Analysis of Composite Adhesive Joints Using Ultrasonic Guided Waves</title>
    <abstract language="eng">Adhesively bonded composite joints can develop voids and porosity during fabrication, leading to stress concentration and a reduced load-carrying capacity. Hence, adhesive porosity analysis during the fabrication is crucial to ensure the required quality and reliability. Ultrasonic-guided wave (UGW)-based techniques without advanced signal processing often provide low-resolution imaging and can be ineffective for detecting small-size defects. This article proposes a damage imaging process for adhesive porosity analysis of bonded composite plates using UGWs measured by scanning laser Doppler vibrometer (LDV). To implement this approach, a piezoelectric transducer is mounted on the composite joint specimen to generate UGWs, which are measured over a densely sampled area. The signals obtained from the scan are processed using the proposed signal processing in different domains. Through the utilization of filter banks in frequency and wavenumber domains, along with the root-mean-square calculation of filtered signals, damage images of the adhesive region are obtained. It has been observed that different filters provide information related to different void sizes. Combining all the images reconstructed by filters, a final image is obtained which contains damages of various sizes. The images obtained by the proposed method are verified by radiography results and the porosity analysis is presented. The results indicate that the proposed methodology can detect the pores with the smallest detectable pore area of 2.41 mm^2, corresponding to a radius of 0.88 mm, with an overall tendency to overestimate the pore size by an average of 11%.</abstract>
    <parentTitle language="eng">IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control</parentTitle>
    <identifier type="doi">10.1109/TUFFC.2024.3371671</identifier>
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Transactions on Ultrasonics, Ferroelectrics, and Frequency Control"],"original-title":[],"link":[{"URL":"http:\/\/xplorestaging.ieee.org\/ielx7\/58\/10484993\/10454005.pdf?arnumber=10454005","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2024,4,1]],"date-time":"2024-04-01T15:14:58Z","timestamp":1711984498000},"score":1,"resource":{"primary":{"URL":"https:\/\/ieeexplore.ieee.org\/document\/10454005\/"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,4]]},"references-count":35,"journal-issue":{"issue":"4"},"URL":"http:\/\/dx.doi.org\/10.1109\/tuffc.2024.3371671","relation":{},"ISSN":["0885-3010","1525-8955"],"issn-type":[{"value":"0885-3010","type":"print"},{"value":"1525-8955","type":"electronic"}],"subject":[],"published":{"date-parts":[[2024,4]]}}}</enrichment>
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    <author>M. Barzegar</author>
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    <author>Tatiana Mishurova</author>
    <author>Dario J. Pasadas</author>
    <author>Artur L. Ribeiro</author>
    <author>Helena G. Ramos</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Adhesives</value>
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    <subject>
      <language>eng</language>
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      <value>Damage imaging</value>
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    <subject>
      <language>eng</language>
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      <value>Nondestructive testing (NDT)</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Porosity analysis</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Signal processing</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasonic guided waves (UGWs)</value>
    </subject>
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    <title language="eng">Automatic improved-resolution imaging of composite adhesive joints using time-frequency-wavenumber filtering applied to ultrasonic guided wavefields</title>
    <abstract language="eng">This paper presents an automatic damage imaging technique by employing a signal processing approach based on applying hierarchically clustered filters across different domains. The technique involves time-frequency-wavenumber filter banks which are applied sequentially to ultrasonic guided wave (UGW) data. The study is conducted for a single lap joint composite specimen with a special focus on small voids which were formed due to manual adhesive component mixing. UGW data are acquired with a 3D Scanning Laser Doppler Vibrometer (LDV) over the scan area of the bonded plate. UGWs are excited at the central frequency of 100 kHz by a single piezoelectric transducer mounted on the surface of the single plate. Within each domain of time, frequency, and wavenumber, four filters are designed which results in 64 distinct filtered wavefields. From each filtered wavefield, an image is obtained by using root-mean-square (RMS) calculation of the signals. The obtained results are then combined to create a final, improved-resolution image of the scan area. The final image is compared to the image obtained through RMS calculation of full wavefield with interpolation through Delaunay triangulation and the image obtained by X-ray radiography. The results show that the smallest void that could be detected has a diameter of 2.14 mm.</abstract>
    <parentTitle language="eng">2023 IEEE International Ultrasonics Symposium (IUS)</parentTitle>
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    <author>Yevgeniya Lugovtsova</author>
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    <author>Tatiana Mishurova</author>
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    <title language="eng">Domain decoupling implementation for efficient ultrasonic wave simulations using scaled boundary finite elements and the mortar method</title>
    <abstract language="eng">We introduce a novel approach that combines the scaled boundary finite element method (SBFEM) with a mortar coupling to enhance the computational modelling of elastic wave propagation and interaction with local features in the ultrasonic range. The key objective is to achieve decoupling between different regions of interest, enabling independent meshes for the zones where waves either propagate or interact with localised discontinuities in the elastic media. This decoupling allows us to exploit the benefits offered by various SBFEM formulations. Thus, we can select the most suitable solution for each specific region. An important concept we emphasise is the differentiation between the near field and far field regions. The near field encompasses zones where the precise representation of small features compared to the wavelength is crucial. At the same time, the far field comprises homogeneous regions where the waves propagate without interactions, eventually radiating towards infinity if the domain is unbounded. By separating these two zones, we can improve the computational performance by employing finer discretisation only where necessary. Furthermore, this decoupling enables the reuse of far field models in parametric analyses, making it highly valuable for scenarios focused particularly on local elastic wave interactions. This approach offers considerable potential in such cases. The modelling technique is validated, and its potential is demonstrated through practical applications.</abstract>
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All rights reserved.","name":"copyright","label":"Copyright"}],"article-number":"116465"}}</enrichment>
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    <author>Daniel Lozano</author>
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    <author>Hauke Gravenkamp</author>
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    <subject>
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      <value>Mechanics of Materials</value>
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    <subject>
      <language>eng</language>
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      <value>Computational Mechanics</value>
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    <title language="eng">Defect Characterization in Plate Models Facilitated by Algorithmic Differentiation</title>
    <abstract language="eng">In non-destructive testing and structural health monitoring with ultrasonic waves, the quantification of damage in components is one of the main tasks. In many shell-like structures, such as plates, pipes, or laminate components, ultrasonic waves propagate as guided waves. Although guided waves enable the testing of large areas, their multimodal and dispersive properties make it challenging to analyze signals. So, there is a need for more advanced algorithms to handle these properties, especially when reconstructing damage position and geometry.&#13;
&#13;
The reconstruction can be formulated as an inverse problem where the measured signals are fitted with a simulative forward model. Due to the small wavelength of ultrasonic waves, classic forward models based on, e.g., the Finite Element Method are computationally intensive. In contrast, the authors use the semi-analytical Scaled Boundary Finite Element Method (SBFEM) to reduce the computational effort. The SBFEM approximates arbitrary long, undamaged parts of the structure with only a few degrees of freedom.&#13;
&#13;
This contribution summarizes a general inverse procedure based on algorithmic differentiation in combination with the SBFEM. Results are presented for damaged 2D cross-sectional models of waveguides. These results include an analysis of the robustness of the proposed algorithms against noise.</abstract>
    <parentTitle language="deu">Tagungsband zur DAGA 2022</parentTitle>
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      <value>Structural health monitoring</value>
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      <value>SBFEM</value>
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      <value>Algorithmic Differentiation</value>
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    <subject>
      <language>eng</language>
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      <value>Non-destructive testing</value>
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    <title language="eng">Defect reconstruction in a two-dimensional semi-analytical waveguide model via derivative-based optimization</title>
    <abstract language="eng">This paper considers an indirect measurement approach to reconstruct a defect in a two-dimensional waveguide model for a non-destructive ultrasonic inspection via derivative-based optimization. The propagation of the mechanical waves is simulated by the scaled boundary finite element method that builds on a semi-analytical approach. The simulated data are then fitted to given data associated with the reflected waves from a defect which is to be reconstructed. For this purpose, we apply an iteratively regularized Gauss-Newton method in combination with algorithmic differentiation to provide the required derivative information accurately and efficiently. We present numerical results for three kinds of defects, namely, a crack, delamination, and corrosion. The objective function and the properties of the reconstruction method are investigated. The examples show that the parameterization of the defect can be reconstructed efficiently as well as robustly in the presence of noise.</abstract>
    <parentTitle language="eng">The Journal of the Acoustical Society of America</parentTitle>
    <identifier type="doi">10.1121/10.0013574</identifier>
    <identifier type="urn">urn:nbn:de:kobv:b43-565485</identifier>
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    <author>Jannis Bulling</author>
    <author>B. Jurgelucks</author>
    <author>Jens Prager</author>
    <author>A. Walther</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Mechanical waves</value>
    </subject>
    <subject>
      <language>eng</language>
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      <value>Corrosion</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Finite-element analysis</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Ultrasonic testing</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Nondestructive testing techniques</value>
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    <subject>
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      <value>Symbolic computation</value>
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    <subject>
      <language>eng</language>
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      <value>Materials analysis</value>
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    <subject>
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    <subject>
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      <value>Newton Raphson method</value>
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  <doc>
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    <language>eng</language>
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    <title language="eng">Quadtree decomposition as a meshing strategy for guided waves simulations using the scaled boundary finite element method</title>
    <abstract language="eng">Structural health monitoring techniques associate strongly with damage detection and characterization. Ultrasonic guided waves (UGW), for such scope, arise as one of the most promising methods for many reasons i.e. UGW are able to travel long distances and they have high sensitivity to damage. In this context, the necessity to model realistic wave-defect interaction occurs to be critical.&#13;
Realistic damage scenarios can be modeled through the usage of image-based quadtree meshes. Images, such as the outcome from X-ray scans, C-scans, etc., can be converted into meshes for further integration in a computational domain. Quadtree meshes are created by converting the intensity of the pixels to quadrilateral cells. Homogeneous regions inside one image result in one quad, whereas fine features such as discontinuities can be described with smaller quads.&#13;
This contribution proposes an efficient methodology to model wave defect interaction, using as a framework the scaled boundary finite element method (SBFEM) and quadtree meshes. Problems as non-conforming regions in the mesh due to the space tree decomposition can be easily avoided using SBFEM’s polygonal elements. Moreover, the semi-analytical nature of the SBFEM allows the modeling of arbitrarily long prismatic/undamaged regions of the waveguides without an increase in the computational burden.</abstract>
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    <author>Daniel Lozano</author>
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      <language>eng</language>
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      <value>Wave defect interaction</value>
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    <subject>
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      <value>Scaled Boundary Finite Element Method</value>
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    <subject>
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      <value>Quadtree meshes</value>
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    <subject>
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      <value>Image-based models</value>
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    <subject>
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      <value>Transient analysis</value>
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    <title language="deu">Schadensrekonstruktion mittels geführter Wellen in Stahlplatten</title>
    <abstract language="deu">Ein Hauptziel der zerstörungsfreien Prüfung und der Strukturüberwachung (engl. Structural Health Monitoring - SHM) mit Ultraschallwellen ist die Charakterisierung von Schäden in Bauteilen. In vielen schalenförmigen Bauteilen, wie zum Beispiel Rohrleitungen, Laminaten und Platten, breitet sich der Ultraschall in Form geführter Wellen aus. Zwar erlauben geführte Wellen eine großflächige Prüfung durch das langsame Abklingen der Wellen. Jedoch breiten sich die Wellen in verschiedenen dispersiven Moden aus, was die Analyse der vom Schaden erzeugten Reflexionen erschwert. Eine Möglichkeit, die Messsignale zu interpretieren, um Schäden zu charakterisieren, ist der direkte Vergleich mit einem Simulationsmodell. Die Rekonstruktion des Schadens stellt ein inverses Problem dar. Das inverse Problem kann als Optimierungsproblem formuliert werden. Für die Optimierung werden mehrere Vorwärtsrechnungen gebraucht, um das Schadensmodell an die Messdaten anzupassen.&#13;
Aufgrund der kurzen Wellenlängen von Ultraschallwellen sind klassische Methoden für die Vorwärtsrechnung, wie z.B. die Finite Elemente Methode (FEM), rechenintensiv. Eine Möglichkeit den Rechenaufwand zu reduzieren, bietet die Approximation der Wellenausbreitung mittels der semi-analytischen Scaled Boundary Finite Element Method (SBFEM). Frühere Untersuchungen haben gezeigt, dass die benötigten Freiheitsgrade im Vergleich zur FEM wesentlich geringer sind [1]. &#13;
Im Beitrag wird eine Optimierung basierend auf einem Gradientenverfahren in Kombination mit der SBFEM vorgestellt und an verschiedenen Schadenstypen in 2D-Querschnittsmodellen von Stahlplatten getestet. Der Gradient des Vorwärtsmodells wird durch Algorithmisches Differenzieren berechnet, wodurch eine genaue und schnelle Optimierung ermöglicht wird. Es werden Untersuchungen zum inversen Problem und das Finden einer geeigneten Zielfunktion präsentiert. Es wird verdeutlicht, dass der entwickelte Algorithmus robust gegenüber von Rauscheinflüssen ist. In diesen Untersuchungen werden zunächst „Messdaten“ aus unabhängigen Simulationen verwendet [2]. Erste Schritte für die experimentelle Validierung und Erweiterung auf 3D Modelle werden anschließend vorgestellt.</abstract>
    <enrichment key="eventName">Doktorandenworkshop in Kloster Lehnin</enrichment>
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    <enrichment key="eventStart">19.10.22</enrichment>
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    <author>Jannis Bulling</author>
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      <value>SBFEM</value>
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    <subject>
      <language>deu</language>
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      <value>Zerstörungsfreie Prüfung</value>
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      <value>Structural Health Monitoring</value>
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    <subject>
      <language>deu</language>
      <type>uncontrolled</type>
      <value>Ultraschallwellen</value>
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    <pageFirst>636</pageFirst>
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    <title language="eng">The SBFEM to simulate the scattering of ultrasonic guided waves interacting with defects in 3D plate structures</title>
    <abstract language="eng">In the field of guided waves for non-destructive testing, the interaction of these waves with damages or other discontinuities in a structure is critical. When a guided wave mode travels and hits a defect, it scatters in all directions, converting to other modes and reflecting the existing one. These interactions are captured in scattered far field complex amplitudes and characterise the elastodynamic behaviour of a defect completely. Simulating these interactions is challenging, and analytical solutions only exist for simple geometries. Still, using general tools like the finite element method results in large, usually costly models. We employ a method based on a numerical implementation of the Kirchhoff–Helmholtz integral that allows the computation of the scattering matrices using a model containing only the damaged region. However, classical techniques to resolve the far field and low-order elements are commonly used, leading to large models yet more efficient than using other strategies.We propose using the SBFEM as an alternative to enhance the computation of the far field scattering. The damaged region is discretised using high-order polyhedral elements, while the far field is constructed using a modified version of the SBFEM. Examples compared to the literature demonstrate the validity of the approach.</abstract>
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    <author>Daniel Lozano</author>
    <author>Jannis Bulling</author>
    <subject>
      <language>eng</language>
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      <value>Simulations</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Guided waves</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>SBFEM</value>
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    <title language="eng">On the efficient simulation of ultrasonic waves on polygonal meshes</title>
    <abstract language="eng">At many stages of technology development in ultrasonic Non-Destructive Testing (NDT) and Structural Health Monitoring (SHM), simulation tools are essential. Many modern approaches to ultrasonic testing, such as Model Assisted Probability of Detection, inverse problems with iterative optimization, or the generation of data for AI training, benefit from highly effcient simulation tools in terms of simulation time. In this talk, we investigate explicit time stepping with the Scaled Boundary Finite Element Method (SBFEM) for approximating the linear elastic wave equation on 2D polygonal meshes, enhanced with a mass lumping technique for faster simulation times. We present the proposed changes to the formulation to successfully use mass lumping. Examples are used to demonstrate that there is no loss of quality due to the approximated mass matrix. Furthermore, mass lumping reduces the simulation time and makes the simulation more effcient. In addition, the proposed simulation method has the advantages of SBFEM meshing techniques. These advantages include fast meshing using an image-based quadtree algorithm or polygonal meshing by transforming triangular meshes based on a CAD model. The latter meshing method can include special crack tip elements that effciently handle the crack tip singularity.</abstract>
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    <author>Jannis Bulling</author>
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      <type>uncontrolled</type>
      <value>Non-Destructive Testing (NDT)</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scaled Boundary Finite Element Method (SBFEM)</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Structural Health Monitoring (SHM)</value>
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    <title language="eng">On the efficient simulation of ultrasonic waves on polygonal meshes</title>
    <abstract language="eng">At many stages of technology development in ultrasonic Non-Destructive Testing (NDT) and Structural Health Monitoring (SHM), simulation tools are essential. Many modern approaches to ultrasonic testing, such as Model Assisted Probability of Detection, inverse problems with iterative optimization, or the generation of data for AI training, benefit from highly efficient simulation tools in terms of simulation time. In this talk, we investigate explicit time stepping with the Scaled Boundary Finite Element Method (SBFEM) for approximating the linear elastic wave equation on 2D polygonal meshes, enhanced with a mass lumping technique for faster simulation times. We present the proposed changes to the formulation to successfully use mass lumping. Examples are used to demonstrate that there is no loss of quality due to the approximated mass matrix. Furthermore, mass lumping reduces the simulation time and makes the simulation more efficient. In addition, the proposed simulation method has the advantages of SBFEM meshing techniques. These advantages include fast meshing using an image-based quadtree algorithm or polygonal meshing by transforming triangular meshes based on a CAD model. The latter meshing method can include special crack tip elements that efficiently handle the crack tip singularity.</abstract>
    <parentTitle language="eng">Proceedings of DAS|DAGA 2025</parentTitle>
    <identifier type="isbn">978-3-939296-23-2</identifier>
    <identifier type="url">https://pub.dega-akustik.de/DAS-DAGA_2025/imprint.html</identifier>
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    <author>Jannis Bulling</author>
    <author>H. Gravenkamp</author>
    <author>C. Birk</author>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Non-Destructive Testing (NDT)</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Scaled Boundary Finite Element Method (SBFEM)</value>
    </subject>
    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Structural Health Monitoring (SHM)</value>
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    <subject>
      <language>eng</language>
      <type>uncontrolled</type>
      <value>Numerical simulation</value>
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    <title language="eng">Mass Lumping for Scaled Boundary Polygonal Elements</title>
    <abstract language="eng">Many modern ultrasonic methods in the fields of Non-Destructive Testing (NDT) and Structural Health Monitoring (SHM) require simulations in research. Researchers either use simulation data initially during development to investigate certain aspects, or the simulation process is directly part of the research task. Examples of the second case are inverse methods for parameter estimation, model-assisted probability of detection analysis or the generation of training data for AI algorithms. All these applications require algorithms that are as efficient as possible. For methods based on explicit time-step methods, a significant increase in efficiency can be achieved if a so-called lumped mass matrix can be used, which approximates the consistent mass matrix but is easier to invert.&#13;
&#13;
The finite element method has been the subject of many studies on approximations of the mass matrix. In contrast, the lumped mass matrix in the context of the Scaled Boundary Finite Element Method (SBFEM) is a current field of research [1,2]. In the time domain, the semi-analytical SBFEM is notable for its flexibility to be applied to polygonal meshes. In particular, image-based mesh generation using a quadtree algorithm is possible. In general, polygonal meshes have the same flexibility as triangular meshes, but polygonal meshes can have additional advantages such as greater tolerance to distortion.&#13;
&#13;
In this contribution, the SBFEM formulation based on bubble functions [3] for the time domain is presented for two-dimensional elastic waves. The adjustments necessary for a good approximating lumped mass matrix are emphasized. Several grid generation methods for polygonal elements are shown. Figure 1 depicts the difference between the consistent mass matrix and the lumped mass matrix for a normal polygonal mesh. Finally, the accuracy of mass lumping for linear, quadratic and cubic shape functions is presented and the computational efficiency is demonstrated using exemplary waveguide geometries.</abstract>
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      <value>Mass lumping</value>
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      <value>Guided waves</value>
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    <title language="eng">Determination of isotropic elastic constants from dispersion images based on ultrasonic guided waves by using neural networks</title>
    <abstract language="eng">This article presents a method to use the dispersive behavior of ultrasonic guided waves and neural networks to determine the isotropic elastic constants of plate-like structures through dispersion images. Therefore, two different architectures are compared: one using convolutions and transfer learning based on the EfficientNetB7 and a Vision Transformer-like approach. To accomplish this, simulated and measured dispersion images are generated, where the first is applied to design, train, and validate and the second to test the neural networks. During the training of the neural networks, distinct data augmentation layers are employed to introduce artifacts appearing in measurement data into the simulated data. The neural networks can extrapolate from simulated to measured data using these layers. The trained neural networks are assessed using dispersion images from seven known material samples. Multiple variations of the measured dispersion images are tested to guarantee the prediction stability. The study demonstrates that neural networks can learn to predict the isotropic elastic constants from measured dispersion images using only simulated dispersion images for training and validation without needing an initial guess or manual feature extraction, independent of the measurement setup. Furthermore, the suitability of the different architectures for generating information from dispersion images in general is discussed.</abstract>
    <parentTitle language="eng">Ultrasonics</parentTitle>
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    <title language="deu">Modellierung und Validierung eines inversen Verfahrens zur Schadensrekonstruktion mittels Lamb-Wellen im Ultraschallbereich</title>
    <abstract language="deu">Das Ausbreitungsverhalten geführter Ultraschallwellen ermöglicht die großflächige Prüfung von Platten und schalenförmigen Bauteilen wie Rohren und Laminaten auf Fehlstellen von wenigen Prüfpunkten aus. Während die beschränkte Divergenz der geführten Wellen die Ultraschallprüfung begünstigt, erschwert das dispersive und multimodale Verhalten der Lamb-Wellen die Auswertung der Ultraschallsignale. Die dispersive und multimodale Wellenausbreitung verkompliziert die Bestimmung der Fehlerposition bei der Auswertung der Geschwindigkeiten einzelner Wellenpakete. Zudem ist es herausfordernd, einen einfachen Zusammenhang zwischen den Reflexionen der Fehlstelle und deren Größe und Form herzustellen. Eine Möglichkeit zur genauen Bestimmung der Fehlerposition und -geometrie bietet der direkte Vergleich der Messsignale mit den Signalen aus einem Simulationsmodell. Die Nachbildung des Schadens im Simulationsmodell stellt ein inverses Problem dar, das iterativ gelöst werden kann, indem ein Vorwärtsmodell immer weiter optimiert wird. Klassische Ansätze wie die Finite Elemente Methode (FEM) sind für die Simulation von Ultraschallwellen aufgrund der kleinen Wellenlängen im Vergleich zur Bauteilgröße meist ineffizient. Aus diesem Grund basiert das vorgestellte Vorwärtsmodell auf der semi-analytischen Scaled Boundary Finite Element Method (SBFEM), die große Teile der Wellenausbreitung analytisch berechnet. In diesem Beitrag wird die Validierung des zweidimensionalen Modells an Platten mit einer rechteckigen Nut als Ersatzfehler präsentiert und es werden erste Schritte zur Validierung von 3D-Modellen vorgestellt.</abstract>
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    <title language="deu">Modellierung und Validierung eines inversen Verfahrens zur Schadensrekonstruktion mittels Lamb-Wellen im Ultraschallbereich</title>
    <abstract language="deu">Das Ausbreitungsverhalten geführter Ultraschallwellen ermöglicht die großflächige Prüfung von Platten und schalenförmigen Bauteilen wie Rohren und Laminaten auf Fehlstellen von wenigen Prüfpunkten aus. Während die beschränkte Divergenz der geführten Wellen die Ultraschallprüfung begünstigt, erschwert das dispersive und multimodale Verhalten der Lamb-Wellen die Auswertung der Ultraschallsignale. Die dispersive und multimodale Wellenausbreitung verkompliziert die Bestimmung der Fehlerposition bei der Auswertung der Geschwindigkeiten einzelner Wellenpakete. Zudem ist es herausfordernd, einen einfachen Zusammenhang zwischen den Reflexionen der Fehlstelle und deren Größe und Form herzustellen. Eine Möglichkeit zur genauen Bestimmung der Fehlerposition und -geometrie bietet der direkte Vergleich der Messsignale mit den Signalen aus einem Simulationsmodell. Die Nachbildung des Schadens im Simulationsmodell stellt ein inverses Problem dar, das iterativ gelöst werden kann, indem ein Vorwärtsmodell immer weiter optimiert wird. Klassische Ansätze wie die Finite Elemente Methode (FEM) sind für die Simulation von Ultraschallwellen aufgrund der kleinen Wellenlängen im Vergleich zur Bauteilgröße meist ineffizient. Aus diesem Grund basiert das vorgestellte Vorwärtsmodell auf der semi-analytischen Scaled Boundary Finite Element Method (SBFEM), die große Teile der Wellenausbreitung analytisch berechnet. In diesem Beitrag wird die Validierung des zweidimensionalen Modells an Platten mit einer rechteckigen Nut als Ersatzfehler präsentiert und es werden erste Schritte zur Validierung von 3D-Modellen vorgestellt.</abstract>
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    <abstract language="eng">Defect reconstruction is essential in non-destructive testing and structural health monitoring with guided ultrasonic waves. This paper presents an algorithm for reconstructing notches in steel plates, which can be seen as artificial defects representing cracks by comparing measured results with those from a simulation model. The model contains a parameterized notch, and its geometrical parameters are to be reconstructed. While the algorithm is formulated and presented in a general notation, a special case of guided wave propagation is used to investigate one of the simplest possible simulation models that discretizes only the cross section of the steel plate. An efficient simulation model of the plate cross section is obtained by the semi-analytical scaled boundary finite element method. The reconstruction algorithm applied is gradient-based, and algorithmic differentiation calculates the gradient. The dedicated experimental setup excites nearly plane wave fronts propagating orthogonal to the notch. A scanning laser Doppler vibrometer records the velocity field at certain points on the plate surface as input to the reconstruction algorithm. Using two plates with notches of different depths, it is demonstrated that accurate geometry reconstruction is possible.</abstract>
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    <title language="eng">On the repulsion effect of coupled Lamb wave modes</title>
    <abstract language="eng">Lamb waves, recognized for their significance in material characterisation, structural health monitor-ing, and non-destructive testing, exhibit complex behaviours that are crucial for industrial applica-tions. This paper delves into the mathematical and physical principals of the repulsion effect that can be observed in the dispersion curves of coupled Lamb wave modes. This effect is the result from the mechanical coupling of thin-walled solid plates and prevents the crossing of the dispersion curves. The study employs the Scaled Boundary Finite Element Method to calculate the dispersion curves of coupled plates and to simulate their interaction for a weak and ideal coupling. Through a mathemati-cal framework and a physical analogy with simple harmonic oscillators, the paper elucidates the un-derlying principals of this effect. Furthermore, the paper highlights the practical significance of the repulsion effect in Lamb waves, suggesting its application for testing and monitoring the integrity of multi-layer structures like adhesive bonds, which are important for various industrial applications. A deepened understanding of this effect could contribute to the enhancement of non-destructive evalua-tion techniques.</abstract>
    <parentTitle language="eng">Proceedings of the 30th International Congress on Sound and Vibration</parentTitle>
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    <title language="eng">On the repulsion effect of coupled Lamb wave modes</title>
    <abstract language="eng">This work investigates the phenomenon of mode repulsion in coupled Lamb wave systems. By mechanically coupling two dissimilar plates using spring elements, it is shown that previously intersecting Lamb wave modes are repelled, avoiding any crossing in the dispersion curves. The effect, rooted in eigenvalue theory and first observed in quantum systems, is explained through both mathematical models and classical analogies with coupled harmonic oscillators. Numerical simulations using the Scaled Boundary Finite Element Method validate the theoretical predictions, revealing a correlation between strain distribution and frequency splitting. The observed mode repulsion provides new insights into interface properties and offers potential for applications such as monitoring adhesive degradation in layered structures.</abstract>
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    <title language="eng">Dynamic interface behavior in coupled plates: Investigating Lamb wave mode repulsion with a spring-based model</title>
    <abstract language="eng">This study investigates the phenomenon of mode repulsion in Lamb waves propagating through two coupled plates with an elastic interface. Using a spring-based coupling model and the Scaled Boundary Finite Element Method, the dispersion curves of the coupled system are analyzed under various interface conditions—weak coupling, sliding boundary, and perfect coupling. This research highlights how the mechanical stiffness of the interface influences the separation of modes and the emergence of repulsion regions. A novel focus on interface displacements reveals a unique dynamic behavior within the repulsion regions, driven by in-phase and out-of-phase oscillations of the coupled plates. The findings provide a physically grounded explanation of mode repulsion, linking it to the strain patterns in the interface. This insight lays the theoretical groundwork for future applications in material characterization and non-destructive evaluation, enabling more precise selection of Lamb wave modes for scientific and industrial purposes.</abstract>
    <parentTitle language="eng">Ultrasonics</parentTitle>
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