Topology optimisation of the damping medium for an acoustic silencer
Translated title
Topologi optimering af dæmpnings materialet for akustisk lyddæmper
Authors
Rey Romero, Daniel ; Kleppe, Håvard Borvik ; Julsgaard, Rasmus
Term
4. term
Education
Publication year
2015
Submitted on
2015-06-03
Pages
70
Abstract
This thesis develops and demonstrates a topology optimization tool for a dissipative muffler in collaboration with Lloyd’s Register ODS, aiming to determine the minimum amount and optimal placement of absorbing material that meets a 17 dB transmission loss target at three preset frequencies. The work begins with an analytical model based on linear acoustics of a simplified cylindrical geometry to obtain eigenfrequencies and modes and to validate element type and mesh density for a numerical FEM model in ANSYS APDL; transmission loss from the analytical and numerical models agrees well below 300 Hz. The full geometry is then implemented, and damping material is introduced using the Delany–Bazley porous material model in a 3D setup. A manually defined design domain is parameterized with design variables that scale flow resistivity between air and porous material; a thickness filter ensures contiguous, void-free distributions for manufacturability. The topology optimization is implemented in MATLAB and solved with a Sequential Linear Programming (SLP) algorithm, supported by tools to improve robustness. Results show a substantial reduction in damping material while satisfying the transmission loss requirement; material placement strongly influences transmission loss, distributions differ markedly between single- and multi-frequency targets, and the initial design affects the outcome. The proposed designs, however, require some post-processing before production.
Dette speciale udvikler og demonstrerer et topologi‑optimeringsværktøj til en dissipativ lyddæmper i samarbejde med Lloyd’s Register ODS med det formål at bestemme den minimale mængde og optimale placering af dæmpningsmateriale, der opfylder en transmissionstabsgrænse på 17 dB ved tre foruddefinerede frekvenser. Arbejdet begynder med en analytisk model baseret på lineær akustik af en forenklet cylindrisk geometri for at bestemme egenfrekvenser og -modes samt validere elementtype og maske-tæthed til en numerisk FEM-model i ANSYS APDL; transmissions tabet sammenlignes mellem modellerne, med god overensstemmelse under 300 Hz. Den fulde geometri implementeres herefter, og dæmpningsmateriale indføres via Delany–Bazley-materialemodellen i en 3D-opsætning. Et manuelt defineret designdomæne parameteriseres med designvariable, der skalerer flowresistiviteten mellem luft og porøst materiale; et tykkelsesfilter sikrer sammenhængende, hulfrie fordelinger for bedre fremstillbarhed. Topologioptimeringen er implementeret i MATLAB og løses med en Sequential Linear Programming (SLP) algoritme, suppleret med robuste numeriske værktøjer. Resultaterne viser en markant reduktion af materialeforbruget samtidig med, at transmissionskravet overholdes; placeringen af materialet er afgørende for transmissions tabet, fordelingerne varierer betydeligt mellem enkelt- og flerfrekvensmål, og startdesignet har stor indflydelse. De foreslåede design kræver dog vis efterbehandling før produktion.
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Keywords