8.6 Faseroptische Sensorik
Filtern
Dokumenttyp
- Vortrag (81)
- Zeitschriftenartikel (55)
- Beitrag zu einem Tagungsband (51)
- Posterpräsentation (30)
- Buchkapitel (3)
- Forschungsdatensatz (3)
- Beitrag zu einem Sammelband (1)
- Dissertation (1)
- Sonstiges (1)
- Forschungsbericht (1)
Sprache
- Englisch (169)
- Deutsch (57)
- Mehrsprachig (1)
Schlagworte
- Distributed acoustic sensing (29)
- DAS (21)
- Structural health monitoring (20)
- Distributed fiber optic sensing (16)
- Distributed fiber sensing (15)
- Artificial neural networks (14)
- Machine learning (14)
- Verteilte faseroptische Sensorik (12)
- Acoustic sensing (11)
- Distributed sensing (11)
- BOFDA (10)
- Faseroptische Sensorik (10)
- Geometric Phase (10)
- Coherent Heterodyne (9)
- Distributed Fiber Optic Sensor (9)
- Fiber optics sensors (9)
- Monitoring (8)
- Distributed vibration sensing (7)
- Optical backscatter reflectometry (7)
- Zustandsüberwachung (7)
- Industry 4.0 (6)
- Optical fiber sensor (6)
- Verteilte faseroptische akustische Sensorik (6)
- Zerstörungsfreie Prüfung (6)
- Distributed humidity sensing (5)
- Fiber optic sensing (5)
- Fiber optic sensor (5)
- Infrastructure monitoring (5)
- OTDR (5)
- Optical time domain reflectometry (5)
- Pipeline monitoring (5)
- Polymer optical fibre (5)
- Rayleigh scattering (5)
- Structural health monitoring (SHM) (5)
- Artificial Neural Networks (4)
- Bridge monitoring (4)
- C-OTDR (4)
- Composite structures (4)
- DVS (4)
- Distributed fibre optic sensing (4)
- Distributed fibre optic sensors (4)
- Faseroptischer Sensor (4)
- Fiberoptic sensors (4)
- Fibre optic sensors (4)
- Gassensorik (4)
- Geophysics (4)
- H2Safety@BAM (4)
- Humidity (4)
- I-OFDR (4)
- Optical fibre (4)
- PMMA (4)
- POF (4)
- Smart geosynthetics (4)
- Structural Health Monitoring (4)
- Structural Health Monitoring (SHM) (4)
- Swept wavelength interferometry (SWI) (4)
- Acoustic emission (3)
- Acoustic emission analysis (3)
- All-optical switching (3)
- Automation (3)
- Bauwerksüberwachung (3)
- Brillouin (3)
- Brillouin distributed sensing (3)
- Brillouin sensing (3)
- Brückenmonitoring (3)
- Cyber-Physical Systems (3)
- Distribute fiberoptic sensor (3)
- Distributed Acoustic Sensing (DAS) (3)
- Distributed Brillouin sensing (3)
- Distributed fiber optic sensors (3)
- Distributed sensor (3)
- Distributed strain sensing (3)
- Distributed temperature gradient sensing (3)
- Faseroptik (3)
- Faseroptischer Strahlungssensor (3)
- Fiber optic sensors (3)
- Geführte Ultraschallwellen (3)
- Hochspannung (3)
- Hybrid composite pressure vessel (3)
- Infrastrukturmonitoring (3)
- Kavernenspeicher (3)
- Leak detection (3)
- Leakage detection (3)
- Leckdetektion (3)
- Magnetostriktive Beschichtung (3)
- Mass Spectrometry (3)
- Metrologie zur Wasserstoffspeicherung (3)
- Nuclear Magnetic Resonance Spectroscopy (3)
- Online NMR spectroscopy (3)
- Ortsauflösende Fasersensorik (3)
- Passive sensor interface (3)
- Polymer optical fiber (3)
- Polymer optical fibers (3)
- Process industry (3)
- RFID (3)
- Radiation sensing fibers (3)
- Radiation-induced attenuation (3)
- Rayleigh-Streuung (3)
- Real-time process monitoring (3)
- Rhodamine B (3)
- Rohrleitungen (3)
- Schallemissionsanalyse (3)
- SensRef (3)
- Solution doping (3)
- Spanndrahtbruchdetektion (3)
- Strahlungsinduzierte optische Dämpfung (3)
- Strain detection (3)
- Surface waves (3)
- Traffic monitoring (3)
- Wasserstoffspeicher (3)
- Acceleration sensors (2)
- Accelerometers (2)
- Alkali-Activated Mortars (2)
- Aqueous polymer solution (2)
- Asymmetric coupler (2)
- Bauteilmonitoring (2)
- Bending tests on pipe segments (2)
- Betriebsverhaltenskenngrößen (2)
- Blast experiment (2)
- Blast tests (2)
- Bridge (2)
- Brillouin distributed fiber sensor (2)
- Brillouin-Frequenzverschiebung (2)
- Brücke (2)
- Cladding-doped fibers (2)
- Composite (2)
- Concrete (2)
- Condition monitoring (2)
- Continous monitoring (2)
- Coupled generalized nonlinear Schrödinger equation (2)
- Digital I-OFDR (2)
- Digital image correlation (2)
- Distributed Acoustic Sensing (2)
- Distributed acoustic sensing (DAS) (2)
- Distributed acoustic sensor (DAS) (2)
- Distributed fiber-optic sensors (2)
- Distributed strain sensor (2)
- Druckbehältern (2)
- Dual-core photonic crystal fiber (2)
- Electrochemical deposition (ECD) (2)
- Embedded fiber optic sensor (2)
- Embedded sensors (2)
- Fading suppression (2)
- Faser-Bragg Gitter (2)
- Faseroptische Sensoren (2)
- Faserverbund (2)
- Fiber-optic sensors (2)
- Fibre optic acoustic sensing (2)
- Fluorescent optical fibers (2)
- Frequenzbereichsreflektometrie (2)
- Geomonitoring (2)
- Ground movement monitoring (2)
- Humidity sensing (2)
- Intelligente Geokunststoffe (2)
- Interferometer-based (2)
- Künstliche Neuronale Netze (2)
- LCST (2)
- Lebensdauerversuche (2)
- Magneto-optischer Sensor (2)
- Metrologie (2)
- Modular Production (2)
- Multiparameter sensing (2)
- Nuclear waste disposal (2)
- Optical fiber sensors (2)
- Optical fibers (2)
- Ortsaufgelöste Brillouin-Sensorik (2)
- Ortsaufgelöste Fasersensorik (2)
- PFGI-POF (2)
- Perfluorinated graded-index polymer optical fiber (2)
- Plastic optical fibers (2)
- Polyimide-coated fibers (2)
- Polymethyl methacrylate (2)
- Power cable monitoring (2)
- Process Analytical Technology (2)
- Radar (2)
- Response characterization (2)
- Road condition monitoring (2)
- Rotation (2)
- SEA (2)
- Schallemissionsprüfung (2)
- SealWasteSafe (2)
- Seismic measurement (2)
- Seismology (2)
- Selbstkalibrierung (2)
- Sensorbasierte Geokunststoffe (2)
- Simultaneous temperature and humidity sensing (2)
- Soft glass (2)
- Static load monitoring (2)
- Stimulated Brillouin scattering (2)
- Structural response (2)
- Structured fiber (2)
- Strukturüberwachung (2)
- TW-COTDR (2)
- Temperature and strain sensing (2)
- Temperature sensor (2)
- Thermoresponsive polymer (2)
- Tight-buffered fibers (2)
- Ultrafast soliton fission (2)
- Verteilte Fasersensorik (2)
- Verteilte Messverfahren (2)
- Verteilte akustische Sensorik (2)
- Verteilte faseroptische Temperaturmessung (2)
- Vibration (2)
- Water ingress detection (2)
- X-ray reflectivity (2)
- Փ-OTDR (2)
- 3D printing (1)
- Ageing (1)
- Akustische Sensorik (1)
- Alkali-Activated Material (1)
- Alkali-activated mortars (1)
- Artificial neural network (1)
- BOTDA (1)
- Backscatter measurement (1)
- Benchtop NMR Spectroscopy (1)
- Bending (1)
- Berry phase (1)
- Beschleunigungssensorik (1)
- Betriebsmittelüberwachung (1)
- Bio engineering (1)
- BioProScale (1)
- Biotechnology (1)
- Blast (1)
- Borehole monitoring (1)
- Brillouin Sensing (1)
- Brillouin distributed fiber optic sensors (1)
- Brillouin optical frequency-domain analysis (1)
- Brillouin sensor (1)
- Brillouin-Streuung (1)
- CFD (1)
- CFRP (1)
- Certified reference materials (1)
- Chemischer Angriff (1)
- Civil engineering (1)
- Coherent optical time domain reflectometry (1)
- Composite Overwrapped Pressure Vessel (1)
- Composite material (1)
- Composite-Druckgefäße (1)
- Composites (1)
- Concrete beam (1)
- Concrete drying (1)
- Convolutional neural networks (1)
- Cracks (1)
- DSS (1)
- DTGS (1)
- DTS (1)
- Data Analysis (1)
- Degradation (1)
- Dehnungsdetektion (1)
- Dehnungsmessung (1)
- Delay lines (1)
- Destructive testing (1)
- Digital Transformatioin (1)
- Digitale Transformation (1)
- Dispersion tailoring of optical fibres (1)
- Distributed Brillouin Sensing (1)
- Distributed POF sensor (1)
- Distributed fiber optic radiation sensing (1)
- Distributed fiber optic radiation sensors (1)
- Distributed fibre optic sensor (1)
- Distributed humidity sensor (1)
- Distributed radiation monitoring (1)
- Distributed temperature sensing (1)
- Distributed vibration sensor (1)
- Distributed vibrations sensing (DVS) (1)
- Distriubuted polymer optical fiber sensor (1)
- Dual sensing (1)
- Dual-core optical fibres (1)
- Dye-doped fiber (1)
- Dynamic strain sensing (1)
- Dynamic structural response (1)
- Dynamische Strukturantwort (1)
- ECD NiFe-layer (1)
- Earth (1)
- Earthquake Monitoring (1)
- Eddy current (1)
- Eingebettete Sensorik (1)
- Embedded humidity sensors (1)
- Energiekabel (1)
- Energiekabelmonitoring (1)
- Engineered barriers (1)
- Explosionswirkung (1)
- Explosivstoff (1)
- Explosivstoffe (1)
- FBG (1)
- FEM (1)
- Faser-Bragg-Gitter (FBG) (1)
- Faseroptische Sensorsysteme (FOS) (1)
- Fasersensorik (1)
- Fatigue (1)
- Fiber (1)
- Fiber Bragg grating (FBG) (1)
- Fiber optic (1)
- Fiber optic radiation sensor (1)
- Fiber optic radiation monitoring (1)
- Fiber structuring (1)
- Fiber- Bragg-gratings (FBG) (1)
- Fiber-optic sensing (1)
- Fiber-optic vibration monitoring (1)
- Fibre Optic Sensing (FOS) (1)
- Fibre bragg grating (1)
- Fibre-optic sensors (1)
- Fire resistance (1)
- Fluorescent optical fiber (1)
- Frequency Drift (1)
- Fs-inscription (1)
- Gammastrahlung (1)
- Gas analysis (1)
- Gas explosion (1)
- Gas monitoring (1)
- Gas purity (1)
- Gassensoren (1)
- Generalised nonlinear Schrödinger equation (1)
- Geometric phase (1)
- Geometric phase measurement (1)
- Glass optical fiber (GOF) (1)
- Glass-fiber-reinforced plastic transport tank (1)
- Ground motion detection (1)
- Grouted connection (1)
- HV cable accessories (1)
- Hazard monitoring (1)
- Hochspannungsanlagen (1)
- Hydrogen (1)
- Incoherent optical frequency domain reflectometry (1)
- Industrie 4.0 (1)
- Interferometric Sensor (1)
- KI (1)
- KTE (1)
- Kabelmonitoring (1)
- Kramers-Kronig detector (1)
- Künstliche Intelligenz (1)
- LSFD (1)
- Lebensdauerabschätzung (1)
- Leckage (1)
- Lichtwellenleiter (1)
- Long Period Grating (1)
- Machine Learning (1)
- Machine-Assisted Workflows (1)
- Magneto-optical coupling (MOC) (1)
- Magnetostrictive coating (1)
- Maschinelles Lernen (1)
- Material engineering (1)
- Material moisture (1)
- Mechanical characterization (1)
- Molecular semiconductor (1)
- Molecule (1)
- Monitoring Endlager (1)
- Monitoring von Rohrleitungen (1)
- Multi-functional coatings for sensors (1)
- NMR spectroscopy (1)
- Neural networks (1)
- Noise analysis (1)
- Nonlinear directional coupler (1)
- OFDR (1)
- Offshore (1)
- Online NMR Spectroscopy (1)
- Online-NMR-Spektroskopie (1)
- Optic (1)
- Optical frequency-domain reflectometry (1)
- Optical properties (1)
- Optische Fasern (1)
- Optische Frequenzbereichsreflektometrie (1)
- Optoelectronics (1)
- Ortsaufgelöste Messung (1)
- Ortsverteilte faseroptische Sensorik (1)
- Ortsverteilter Sensor (1)
- PF-POF (1)
- Pancharatnam–Berry phase (1)
- Perfluorinated polymer optical fiber (1)
- Perfluorinated polymer optical fiber (PF-POF) (1)
- Phase error (1)
- Phase unwrapping (1)
- Phase-sensitive (1)
- Phase-sensitive optical time-domain reflectometry (1)
- Photonic crytal fibers (1)
- Physical vapour deposition (PVD) (1)
- Pipeline integrity (1)
- Pipeline vibrations (1)
- Plastic Optical Fiber Sensor (1)
- Polycarbonate (1)
- Polyimide-coated optical fibers (1)
- Polymer optical fiber (POF) (1)
- Polymer optical fibers (POF) (1)
- Polymer optical fibres (1)
- Polzmethyl methacrylate (1)
- Practical application (1)
- Procee Analytical Technology (1)
- Process Control (1)
- Process Industry (1)
- Prozessanalytik (1)
- Prozessindustrie (1)
- Quasi-verteilte Messverfahren (1)
- Radiation monitoring (1)
- Radioactive Waste Disposal (1)
- Rayleigh Rückstreuung (1)
- Rayleigh Scattering (1)
- Rayleigh backscatter measurement (1)
- Real time measurement (1)
- Reflected pressure (1)
- Rehabilitation (1)
- Reinforced concrete (1)
- Repair (1)
- Reyleigh-Rückstreumessung (1)
- Rissbildung (1)
- Road construction (1)
- Rohrbiegeprüfstand (1)
- SHM (1)
- Scaling (1)
- Schadensursachen an Rohrleitungen (1)
- Schädigungscharakterisierung (1)
- Seismic measurements (1)
- Selbstdiagnose (1)
- Self-healing silicone rubber (1)
- Semiconductor (1)
- Sensor intergration (1)
- Sensor response (1)
- Sensorik (1)
- Sensorvalidierung (1)
- Signal processing (1)
- Simultaneous temperature and humidity sen (1)
- Smart Geosynthetics (1)
- Smart structures (1)
- Soft-glass optical fibres (1)
- Specialty Chemicals (1)
- Sprengversuche (1)
- Stahlbeton (1)
- Static loading (1)
- Stereophotogrammetry (1)
- Strain and temperature measurements (1)
- Strain measurement (1)
- Stree-strain curve (1)
- Stromkabelüberwachung (1)
- Stromnetzen (1)
- Structural health monitoring. (1)
- Structure health monitoring (1)
- Subsidence monitoring (1)
- Subsurface (1)
- Surface migration barriers (1)
- Surface plasmon resonance enhanced ellipsometry (SPREE) (1)
- Temperatur (1)
- Temperature and strain monitoring (1)
- Temperature sensing (1)
- Temperaturmessung (1)
- Tetracene (1)
- Thermomechanics (1)
- Thin magnetic films (1)
- Topas (1)
- Train monitoring (1)
- Train tracking (1)
- Ultrafast nonlinear propagation (1)
- Ultraschall (1)
- Ultrasonic Guided Waves (1)
- Ultrasonic imaging (1)
- Ultrasonic structure-scanner (1)
- Underground Repositories (1)
- Unterseekabel (1)
- Verbundwerkstoffe (1)
- Verpressanker (1)
- Verteilte Faseroptische Sensorik (1)
- Verteilte faseroptische Sensoren (1)
- Verteilten akustischen faseroptischen Sensorik (1)
- Verteilter Sensor (1)
- Vibration modes (1)
- Vibration sensing (1)
- WS-COTDR (1)
- Wasserstoff (1)
- Wasserstoff-Druckbehälter (1)
- X-ray DIFFRACTION (1)
- X-ray diffraction (1)
- Zeonex (1)
- zertifizierte Referenzmaterialien (1)
- Überwachung von Rohrleitungen (1)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (227)
- 8.6 Faseroptische Sensorik (227)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (28)
- 3 Gefahrgutumschließungen; Energiespeicher (20)
- 7 Bauwerkssicherheit (17)
- 2 Prozess- und Anlagensicherheit (16)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (16)
- 8.4 Akustische und elektromagnetische Verfahren (16)
- 7.4 Baustofftechnologie (14)
- 1 Analytische Chemie; Referenzmaterialien (13)
Protection against terroristic or accidental scenarios in industrial settings requires suitable designs of structures to resist blast loads. Field testing as well as finite element simulations are among the techniques available to engineers in the understanding of the structural behavior against blast loading.
As blast testing of complex scenarios can be very resource intensive, tests are generally performed for simplified scenarios. Numerical tools can be used to model these scenarios to get better insight into blast loading, structural response, and the resulting damage to the structure. During the next steps, the simplified scenario is successively modified in numerical simulations to incorporate complexities that cannot be covered in blast testing experiments. One of the conditions for this approach to work is that the original simplified numerical simulation is valid. The scopes and challenges encountered in such a validation are the focus of this presentation/article.
A relatively ‘simple’ field test of a horizontal reinforced concrete (RC) slab subjected to blast loading is taken as an example for validation of the performance of numerical tools. The blast test incorporated various measurement techniques to quantify the blast load as well as the behavior of the RC slab. Blast load was measured using flush mounted piezoelectric pressure gauges, whereas acceleration sensors and fiber-optic sensor cables were used to characterize the dynamic behavior of the slab under blast loading. Additionally, damage characteristics were ascertained also using fiber optic sensing. The application of such measurement techniques, along with different numerical software available for the analysis of the scenario in question, demonstrate the scope of our contribution.
When it comes to the challenges, it begins with proper instrumentation of the test specimen followed by the data processing. For numerical modelling, geometric conditions with appropriate boundary constraints, physical conditions such as the configuration of the rebars, as well as material parameters add to this challenge. The issues of choosing appropriate material models and comparison of results with multiple software tools will be discussed. This discussion forms the basis for a coherent approach to technical-safety assessment of blast effects on structures in its broader sense.
Current capabilities for full-scale field testing are highly resource intensive. Reliable small-scale experiments are an effective alternative. Characterization of the dynamic response and damage of RC elements to scaled blast loads was investigated in scaled-down field experiments. Spatially resolved information on the dynamic structural response using distributed fiber optic acoustic sensing (DAS) and acceleration as well as blast loading by piezoelectric pressure sensors.
Wir präsentieren unsere Forschungsergebnisse zur Entwicklung eines faseroptischen Sensorsystems mit polymeroptischen Fasern integriert in Geokunststoffe für die Überwachung von geotechnischen Anlagen. Das Sensorsystem dient der räumlichen Auflösung lokaler Dehnungsereignisse im für Anwender signifikanten Größenordnungsbereich von 3 % bis 10 %. Das gesamte Sensorkonzept besteht aus einem praxistauglichen Messsystem basierend auf der digitalen inkohärenten optischen Frequenzbereichsreflektometrie (I-OFDR) und einer Sensormatte in Form eines Geotextils mit integrierten faseroptischen perfluorierten polymeroptischen Fasern (PF-POFs).
Distributed fiber optic sensors for structural health monitoring of composite pressure vessels
(2024)
In diesem Beitrag geben wir einen umfassenden Überblick über unsere Forschung auf dem Gebiet der verteilten faseroptischen Sensorik für die strukturelle Zustandsüberwachung von Wasserstoffdruckbehältern aus Verbundwerkstoffen. Insbesondere zeigen wir, wie die Integration von faseroptischen Sensoren in Druckbehälter aus Verbundwerkstoffen die Sicherheit erhöht und gleichzeitig die Wartungskosten senkt. Die geringe Größe von Lichtwellenleitern ermöglicht ihre Integration in Verbundwerkstoffstrukturen während des Herstellungsprozesses, wodurch eine kontinuierliche Überwachung sowie eine präzise Erkennung und Lokalisierung von Strukturschäden während des Betriebs der Druckbehälter ermöglicht wird. Wir erörtern auch das Potenzial modernster Signalverarbeitungsmethoden und des maschinellen Lernens für die Weiterentwicklung der vorausschauenden Instandhaltung. Die von uns vorgestellten Anwendungen von faseroptischen Sensoren zeigen, dass sie einen wichtigen Beitrag zur Energiewende hin zu erneuerbaren Energien leisten können.
A novel distributed acoustic sensing technique is proposed that exploits both phase and amplitude of the Rayleigh backscattered light to quantify the environmental variation. The system employs a wavelength-scanning laser and an imbalanced Mach-Zehnder interferometer to acquire the reflection spectra and the phase of the detected light, respectively. Fading-free and low-frequency measurements are realized via the crosscorrelation of the reflection spectra. The discrete crosscorrelation is used to circumvent the nonlinear frequency sweeping of the laser. Based on the phase of the backscattered light, it is possible to quantify fast environmental variations. The whole system requires no hardware modification of the existing system and its functionality is experimentally validated. The proposed system has the potential to monitor ground motion/movement at very low frequency band like subsidence around mining areas and at high frequency band like earthquakes and vibrations induced by avalanches.
Die Nutzung von Sensortechnologien, insbesondere im Bereich der Gasdetektion mit einem Schwerpunkt auf Wasserstoff, spielt eine entscheidende Rolle in verschiedenen Anwendungsbereichen der Wasserstofftechnologie. Sicherheitsüberwachung, Leckdetektion und Prozesskontrolle gehören zu den prominenten Anwendungsgebieten dieser Sensortechnologien. Ein zentrales Ziel ist die Erkennung von freigesetztem Wasserstoff sowie die genaue Bestimmung des Wasserstoff-Luftverhältnisses mithilfe von Gassensoren. Dies ist von entscheidender Bedeutung, um potenzielle Gefahren frühzeitig zu erkennen und angemessene Maßnahmen zu ergreifen.
Ein weiterer Schwerpunkt dieses Beitrags liegt auf der Analytik und der Verwendung zertifizierter Referenzmaterialien in Verbindung mit Metrologie für die Wasserstoffspeicherung. Dies gewährleistet eine präzise und zuverlässige Charakterisierung von Wasserstoff und unterstützt die Entwicklung sicherer Speichertechnologien. Im Rahmen des Euramet-Vorhabens Metrology for Advanced Hydrogen Storage Solutions (MefHySto) wird eine Kurzvorstellung präsentiert.
Der Vortrag stellt zwei zerstörungsfreie Prüfverfahren zum strukturellen Zustandsüberwachung (Structural Health Monitoring, SHM) für Wasserstofftechnologien vor. Insbesondere die Fehlstellenerkennung mittels geführter Ultraschallwellen spielt eine bedeutende Rolle bei der Lebensdauerüberwachung von Wasserstoffspeichern. Ein weiterer Aspekt ist die Anwendung faseroptischer Sensorik zur Schadensfrüherkennung von Wasserstoffspeichern. Diese zerstörungsfreien Prüfverfahren ermöglichen eine präzise und frühzeitige Identifizierung von Schäden, was die Sicherheit und Effizienz von Wasserstoffspeichersystemen entscheidend verbessert.
A novel DAS setup based on geometric phases in coherent heterodyne detection is applied for the first time to the characterisation of the Earth’s subsurface. In addition, an optimisation of the proposed setup in terms of its spatial resolution is also presented for the first time. The surface waves are generated by strong blasts of 25 kg of explosives at a dedicated test site. A 10 km dark fiber link in the vicinity of the test site connected to the test setup records the resulting strain signals. The spike-free and low-noise strain data thus obtained minimize post-processing requirements, making the setup a candidate for real-time seismic monitoring. An analysis of the dispersion characteristics of the generated surface waves is performed using a recently reported optimised seismic interferometric technique. Based on the dispersion characteristics, the shear wave velocities of the surface waves as a function of the depth profile of the Earth’s crust are determined using an optimised evolutionary algorithm.