Using Hybrid Modal Substructuring with a Complex Transmission Simulator to Model an Electrodynamic Shaker

Abstract

When conducting a vibration test on an electrodynamic shaker or shaker table, the layout of fixtures and test components on the shaker adapter changes the vibration modes and anti-resonances of the system. During a test, these dynamics can be excited by the shaker itself, leading to an invalid test if the desired environment is exceeded at some points, and potentially damaging the shaker or test components. A high-fidelity shaker model would allow for accurate pretest planning, in which test component layout and control accelerometer placement can be optimized to mitigate problem areas. However, shaker systems are notoriously difficult to model analytically due to a multitude of joints with indefinite properties, unknown stiffness and damping of the magnetic field, and the scarcity of available technical drawings for the internal components. This work explores the use of hybrid modal substructuring to create a test-based model of a shaker table with a dynamically complex shaker fixture. The transmission simulator method is used with an experimentally derived modal model of the shaker and a fixture to decouple a finite element model of the fixture and replace it with a finite element model of the fixture with an attached test article. Special care is taken to ensure that an optimized test layout and accurate FEMs are created. The resultant modal model for the total system is shown to accurately retain the fixture dynamics while successfully adding the test component dynamics through the usable frequency range of the shaker.