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    Item type:Publication, Access status: without files ,
    Reduced order structural models for the calculation of wet contact forces due to impacts in hydraulic valves
    (Springer, 2015-01-07)
    Koreck, Jürgen
    ;
    Estorff, Otto von
    Impacts in hydraulic valves generate structure-borne sound. Numerical methods are applied to calculate the contact forces, which are related to the acoustic noise generation. The fluid between the moving valve stem and the end stop creates a squeeze film force. A model order reduction technique in two steps is applied to capture the flexibility of the impact bodies in a multi-physics system simulation. The first reduction step is based on modal truncation using normal and attachment modes. The second step aims to select the important states or modes within the model bandwidth based on Hankel singular values, where two selection procedures are compared. The squeeze film effect is represented by an analytical formula which is closely incorporated to the compliant contact model. This contact deformation relation for the wet impact has to account for the transition between the pure squeeze motion and the structural collision. Measurements are used to support the calculation results. The coupled calculation of elastic and hydraulic effects leads to improved models for predicting the noise design and the functionality of hydraulic valves.
    Publicationtype: Journal Article
      39
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    Item type:Publication, Access status: without files ,
    Frequency-dependent damping model for the hydroacoustic finite element analysis of fluid-filled pipes with diameter changes
    (Elsevier, 2011)
    Herrmann, Jan
    ;
    Koreck, Jürgen
    ;
    Maess, Matthias
    ;
    Gaul, Lothar
    ;
    Estorff, Otto von
    The integration of a model for longitudinal hydroacoustic fluid damping in thin hydraulic pipes in 3D finite element models is presented in this paper. In order to perform quantitative prediction of the vibroacoustic behavior and resulting noise levels of such fluidstructure coupled system due to hydraulic excitation, an accurate frequency-dependent fluid damping model including friction effects near the pipe wall is required. This step is achieved by matching complex wave numbers from analytical derivation into a parameterized damped wave equation and consecutive translation into finite element modeling. Since the friction effect close to the pipe wall changes locally with the inner pipe radius, the fluid damping model is applied segment-wise in order to model the influence of cross-sectional discontinuity, such as orifices, on the oscillating pressure pulsations. A component synthesis approach, which uses pipe segments as substructures, allows a simple model generation and fast computation times. The numerical harmonic results are compared to experimental frequency response functions, which are performed on a hydraulic test bench driven by a dynamic pressure source in the kHz-range.
    Publicationtype: Journal Article
      9