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    Akustische isogeometrische Analysen mit der Boundary-Elemente-Methode
    (Shaker Verlag, 2025)
    Beiroth, Kim Marcel
    ;
    Estorff, Otto von
    Publicationtype: Doctoral Thesis
      19
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    Helmholtz resonators with integrated vibrating cantilevers for low-frequency noise control in aircraft sidewalls
    (2025)
    Hoppen, Hannah
    ;
    Estorff, Otto von
    This work presents a novel resonator type combining a Helmholtz resonator and a cantilever to achieve two resonance frequencies. An analytical model for the Helmholtz resonator with integrated cantilever is developed in this thesis. This model allows accurate determination of the acoustic behavior of the resonator. When the resonator is integrated into an aircraft-like double wall the sound transmission loss is improved broadband in the low-frequency region.
    Publicationtype: Doctoral Thesis
      99  50
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    Scaling laws for mitigated pile driving: dependence of underwater noise on strike energy, pile diameter, ram weight, water depth, and mitigation system
    (American Institute of Physics (AIP), 2024-09-01)
    Pein, Jonas von
    ;
    Lippert, Tristan
    ;
    Lippert, Stephan
    ;
    Estorff, Otto von
    Sound induced by impact pile driving is a possible risk to marine life. Therefore, it is common practice to use noise mitigation systems during piling to reduce the respective impact and to fulfill the prescribed noise limits. Scaling laws for the estimation of the underwater noise from unmitigated impact pile driving have been presented in von Pein, Lippert, Lippert, and von Estorff, "Scaling laws for unmitigated pile driving: Dependence of underwater noise on strike energy, pile diameter, ram weight, and water depth," Appl. Acoust. 198, 108986 (2022). This contribution shows how these scaling laws need to be changed if noise mitigation systems are considered. Scaling laws are developed for four different kinds of noise mitigation system setups. These include big bubble curtains, double big bubble curtain combinations, a fully absorbing system directly at the pile, and the combination of a system close to the pile and a double big bubble curtain. The derived scaling laws are verified and compared to publicly available measurement data.
    Publicationtype: Journal Article
      16  105
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    Vibo-acoustic metamaterial model in energy based finite element method applied to automotive structures
    (Society of Acoustics, 2024)
    Lohmann, Henning
    ;
    Dilba, Boris
    ;
    Rehbein, Nicolai
    ;
    Keuchel, Sören
    ;
    Zaleski, Olgierd
    Classical numerical methods such as the finite element method (FEM) or the boundary element method (BEM) are limited in the frequency domain due to its need of frequency dependent discretization. In contrast to this, energy based methods use a formulation that is independent from kinematic degrees of freedom. Instead, energy density and energy flow are used as primary variables. This allows solving large acoustic problems in the high frequency domain up to 20 kHz or higher. Vibro-acoustic metamaterials allow optimizing properties like group speed and structural damping coefficient at specific frequency bands. To improve the assessment of the impact on more complex structures numerical simulation is helpful. Combining energy based methods with a metamaterial model provides the possibility to analyze the impact of metamaterials on larger structures such as full car models. This includes effects such as reflections on the interface between isotropic material and metamaterial and the influence of secondary paths on the target variable. Coupling fluid and structure via transmission coefficients provides the possibility to predict noise levels inside and outside of the car cabin. In this contribution a method of taking into account metamaterials in energy based finite element simulations is presented. This method is based on analytical descriptions of the energetic properties like wave number and structural damping coefficient of the metamaterial. The results are compared to results of FEM for academic structures and more advanced application-related structures.
    Publicationtype: Conference Paper
      59
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    Designing impact hammers to reduce offshore pile driving noise
    (Shaker Verlag, 2024)
    Klages, Elin
    ;
    Estorff, Otto von
    Publicationtype: Doctoral Thesis
      43
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    Erweiterung energiebasierter Boundary-Elemente-Methoden für Hochfrequenzprobleme
    (Shaker Verlag, 2024)
    Ram, Matthias Wolf Christian
    ;
    Estorff, Otto von
    The energy boundary element method is a numerical prediction method for acoustic high-frequency problems. By employing averaged energetic quantities as primary field variables, it allows for an almost frequency-independent discretization. In the present work the method is enhanced by an isogeometric formulation, where both the geometry and the boundary values are described using non-uniform rational B-splines (NURBS). In addition, the method is implemented as a fast multipole method, thus achieving a significant acceleration while simultaneously reducing the memory consumption.
    Publicationtype: Doctoral Thesis
      55  31
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    Helmholtz resonator with two resonance frequencies by coupling with a mechanical resonator
    (2023-09-01)
    Hoppen, Hannah
    ;
    Langfeldt, Felix
    ;
    Gleine, Wolfgang
    ;
    Estorff, Otto von
    This contribution presents the acoustical properties and corresponding theoretical descriptions of a Helmholtz resonator with an integrated cantilever inside the Helmholtz resonator neck. The advantage of this resonator design is a second resonance frequency, which leads to a supplemental frequency region with high sound absorption properties. An analytical model is derived to calculate the resonance frequencies and the absorption coefficient of the resonator system. This model has been verified with finite element simulations for the resonance frequencies, taking into account several geometric parameter variations. It has been validated experimentally for the calculated absorption coefficients by impedance tube measurements. In conclusion, it has been found a high influence of the geometric parameters on the resonance frequencies and a broader sound absorption performance of the coupled resonator system.
    Publicationtype: Journal Article
      143