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Institute of Machine Design and Hydraulic Drives
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The following publications have been published in the FWF project "Model updating of coupled hydraulic-mechanical systems":

Energy related model correlation criteria for modal analysis of fluid-structure interaction systems

G. Mikota, J. Mikota

Vibroacoustical problems are sometimes treated by modal analyis, which has been applied to air-filled shells. It is suggested to use the method for various types of liquid-structure interaction systems. Potential applications are water or oil hydraulic pipelines and heavy machinery actuated by fluid power. Modal testing of such systems should be accompanied by sensor placement strategies, test data assessment, and comparisons between theoretical and experimental mode shapes. In structural dynamics, these issues are covered by model correlation criteria like the classicalmodal assurance criterion (MAC). From the orthogonality relations of undamped vibroacoustical systems, two new criteria are developed. Their respective formulations are related to potential energy (POTMAC) and kinetic energy (KINMAC). Both criteria assume real values between zero and one. In practical applications of model correlation, it should be understood which values are acceptable. An approximation indicates that the limits for individualmatrix elements can be adopted fromthe MAC. Numerical examples of  POTMAC and KINMAC matrices are given for two different hydraulic press models. Analogies between POTMAC, KINMAC, and the rotor modal assurance criterion (RMAC) are pointed out. The new criteria can help to develop modal testing into a useful tool for systems with a vibroacoustical model structure.

Modal testing and model correlation of a lumped parameter vibroacoustical system

G. Mikota, A. Brandl, P. Treml

Vibroacoustical modal analysis is applied to a lumped parameter coupled hydraulic-mechanical system. Hydraulic excitation is realized by a chirp flow rate signal through a servovalve. Mechanical force excitation is applied by an impact hammer. In each case, five pressures and two accelerations are measured. For further processing, the signals are weighted by the square roots of the mean hydraulic capacity and the mean stiffness, respectively. A lumped parameter theoretical model is set up and frequency response functions are compared to measurements. An eigenvalue analysis results in six mode shapes, which are compared to those extracted from servovalve and impact hammer excitation. Recently presented model correlation criteria are applied to assess the autocorrelation of measured modes and their agreement with theoretical ones.

Coupled mode shapes