@misc{LemkeSteinHoelteretal.2021, author = {Lemke, Mathias and Stein, Lewin and H{\"o}lter, Arne and Weinzierl, Stefan}, title = {Adjungierten-basierte Synthese und Bestimmung optimaler Treiberfunktionen von Lautsprechern mit komplexer Richtcharakteristik}, publisher = {Deutsche Gesellschaft f{\"u}r Akustik e.V.}, isbn = {978-3-939296-18-8}, doi = {https://doi.org/10.14279/depositonce-12515}, year = {2021}, abstract = {Die Bestimmung optimaler Treiberfunktionen von Lautsprechern mit frequenzabh{\"a}ngiger Richtcharakteristik ist ein schlecht gestelltes Optimierungsproblem. Zu dessen L{\"o}sung haben die Autoren in vorangegangenen Beitr{\"a}gen eine adjungierten-basierte Methode zur Optimierung von Lautsprecher-Arrays im Zeitbereich vorgestellt [5, 6, 8]. Diese erm{\"o}glicht unter anderem die Ber{\"u}cksichtigung von Berandungen und Umgebungseffekten wie Wind, war jedoch bisher auf monopol-artige Quellen beschr{\"a}nkt. Um diese Einschr{\"a}nkung zu beheben, haben die Autoren einen adjungierten-basierten Zeitbereichsansatz mit Finiten-Differenzen (FDTD) zur Synthese komplexer synthetischer Schallquellen durch diskrete, gitter-basierte Monopole vorgestellt [4, 9]. In diesem Beitrag demonstrieren die Autoren die entsprechende Modellierung eines realen Zweiwege-Monitors (A). Zudem wird gezeigt, wie sich die Vielzahl der zur Synthese verwendeten Monopole in eine Lautsprecher-Treiberfunktion {\"u}berf{\"u}hren lassen (B).}, language = {de} } @article{HoelterLemkeWeinzierletal.2025, author = {H{\"o}lter, Arne and Lemke, Mathias and Weinzierl, Stefan and Stein, Lewin}, title = {Non-Reflecting Characteristic Boundary Conditions for Adjoint Time-Domain Acoustic Simulations}, journal = {Journal of Theoretical and Computational Acoustics}, year = {2025}, abstract = {Accurate acoustic simulations in the free field require non-reflective boundary conditions to suppress spurious reflections at the computational domain boundaries. Although several characteristic-based formulations for direct (forward) simulations have been proposed in recent decades, the adjoint formulations of such characteristic-based boundary conditions (CBCs) have received limited atten- tion in the literature and lack a comprehensive analysis. This paper presents the derivation and evaluation of adjoint CBCs complementing the existing direct CBCs. Both the forward and adjoint CBCs are applied to the (nonlinear) Euler equations and linear acoustic equations in time-domain simulations. In this manner, the CBCs are investigated and subsequently compared to assess their respective accuracy and consistency. The CBCs were implemented using both a single-point and a zonal approach, with the former optionally combined with a sponge layer. Both approaches yielded comparable results in direct and adjoint simulations, while the zonal CBC exhibited improved ac- curacy at lower frequencies. Across the evaluated frequency range of approximately 350 - 5600 Hz, spurious reflections were attenuated by up to -70dB in both forward and adjoint cases, demon- strating the effectiveness and consistency of the proposed boundary treatment.}, language = {en} } @article{SteinStraubeWeinzierletal.2020, author = {Stein, Lewin and Straube, Florian and Weinzierl, Stefan and Lemke, Mathias}, title = {Directional sound source modeling using the adjoint Euler equations in a finite-difference time-domain approach}, volume = {148}, journal = {Acoustical Society of America}, number = {5}, publisher = {The Journal of the Acoustical Society of America}, doi = {https://doi.org/10.1121/10.0002425}, pages = {3075 -- 3085}, year = {2020}, abstract = {An adjoint-based approach for synthesizing complex sound sources by discrete, grid-based monopoles in finite-difference time-domain simulations is presented. Previously [Stein et al., 2019a, J. Acoust. Soc. Am. 146(3), 1774-1785] demonstrated that the approach allows to consider unsteady and non-uniform ambient conditions such as wind flow and thermal gradient in contrast to standard methods of numerical sound field simulation. In this work, it is proven that not only ideal monopoles but also realistic sound sources with complex directivity characteristics can be synthesized. In detail, an oscillating circular piston and a real 2-way near-field monitor are modeled. The required number of monopoles in terms of the SPL deviation between the directivity of the original and the synthesized source is analyzed. Since the computational effort is independent of the number of monopoles used for the synthesis, also more complex sources can be reproduced by increasing the number of monopoles utilized. In contrast to classical least-square problem solvers, this does not increase the computational effort, which makes the method attractive for predicting the effect of sound reinforcement systems with highly directional sources under difficult acoustic boundary conditions.}, language = {en} } @incollection{LemkeStein2020, author = {Lemke, Mathias and Stein, Lewin}, title = {Adjoint-Based Identification of Sound Sources for Sound Reinforcement and Source Localization}, volume = {145}, booktitle = {Notes on Numerical Fluid Mechanics and Multidisciplinary Design}, publisher = {Springer, Cham}, isbn = {978-3-030-52429-6}, doi = {https://doi.org/10.1007/978-3-030-52429-6_17}, pages = {263 -- 278}, year = {2020}, abstract = {The identification of sound sources is a common problem in acoustics. Different parameters are sought, among these are signal and position of the sources. We present an adjoint-based approach for sound source identification, which employs computational aeroacoustic techniques. Two different applications are presented as a proof-of-concept: optimization of a sound reinforcement setup and the localization of (moving) sound sources.}, language = {en} } @misc{LemkeSteinHoelteretal.2020, author = {Lemke, Mathias and Stein, Lewin and H{\"o}lter, Arne and Straube, Florian and Weinzierl, Stefan}, title = {Synthese komplexer Richtcharakteristiken f{\"u}r eine Schallfeldoptimierung im Zeitbereich}, editor = {Peissig, J{\"u}rgen}, publisher = {Deutsche Gesellschaft f{\"u}r Akustik e.V.}, isbn = {978-3939296171}, doi = {https://doi.org/10.14279/depositonce-9997}, year = {2020}, abstract = {Die Bestimmung optimaler Treiberfunktionen von Lautsprechern in beliebiger Anordnung ist ein schlecht gestelltes Optimierungsproblem, da die Anzahl der Quellen immer erheblich kleiner als die Anzahl der Empf{\"a}nger ist. Typischerweise werden frequenz-basierte L{\"o}ser eingesetzt. In einem vorangegangenen Beitrag haben die Autoren einen Adjungierten-basierten Ansatz vorgestellt, um optimale Treiberfunktionen im Zeitbereich zu bestimmen. Die Methode erlaubt es, inhomogene Windprofile und Temperaturschichtungen einzubeziehen, die typischerweise bei auf der Wellengleichung beruhenden L{\"o}sungen nicht ber{\"u}cksichtigt werden. Daru ̈ber hinaus k{\"o}nnen komplexe Geometrien und Randbedingungen ber{\"u}cksichtigt werden. Bisher war diese Methode auf Monopolquellen beschr{\"a}nkt. Hier stellen die Autoren eine Erweiterung des Ansatzes in Bezug auf eine Adjungierten-basierte Monopolsynthese vor, die es erm{\"o}glicht, auch Quellen mit komplexen Richtcharakteristiken zu betrachten. Das Verfahren wird f{\"u}r typische Quellsignale und ein repr{\"a}sentatives Lautsprechermodell mit komplexer Richtcharakteristik validiert.}, language = {de} } @inproceedings{BrookFullerSwinburneetal.2022, author = {Brook, Glenn and Fuller, Douglas and Swinburne, John and Christgau, Steffen and L{\"a}uter, Matthias and Rodrigues Pel{\´a}, Ronaldo and Lewin, Stein and Christian, Tuma and Steinke, Thomas}, title = {An Early Scalability Study of Omni-Path Express}, address = {Hamburg}, organization = {ISC 2022 IXPUG}, doi = {10.13140/RG.2.2.21353.57442}, pages = {8}, year = {2022}, abstract = {This work provides a brief description of Omni-Path Express and the current status of its development, stability, and performance. Basic benchmarks that highlight the gains of OPX over PSM2 are provided, and the results of an initial performance and scalability study of several applications are presented.}, language = {en} }