Modal testing

About: Modal testing is a research topic. Over the lifetime, 4047 publications have been published within this topic receiving 64772 citations.

Computing fluid-coupled resonance frequencies, mode shapes, and damping loss factors using the singular value decomposition

Abstract: In many acoustic design problems, it would be useful to be able to compute fluid-coupled resonance frequencies, mode shapes, and their associated damping levels. Unfortunately, conventional eigenvalue solution procedures are either computationally inefficient, unreliable, or have limited applicability. Sophisticated methods for identifying modal parameters using the singular value decomposition have recently emerged in the area of experimental modal analysis, where the available data typically consists of velocity-to-force transfer functions for several drive point locations. In this paper, we show that these techniques can be applied to numerically generated frequency domain data and are even more effective because full matrices of transfer function data are available. This typically allows the modes to be completely separated from each other, such that the modal parameters can be identified using analytical formulas. Several benchmark example problems are solved numerically, including a rectangular cantilever plate, a baffled circular plate, and a baffled circular plate covered by an open-ended rigid-walled pipe.

Optimization of actuator placement in a truss-cored sandwich plate with independent modal space control

Abstract: The determination of optimal locations of actuators is an important issue in the field of vibration control in structures. In this paper, a practical method for the optimal actuator placement in a truss-cored sandwich plate based on independent modal space control (IMSC) is proposed. It is shown that the modal strain energy (MSE) alone is not enough to determine the actuator locations since the system may become uncontrollable, especially when the structure is symmetrical. Moreover, it is found that the controllability can be measured through the singular values of the input matrix. Therefore the singular values of the input matrix together with the modal strain energy may serve as an effective optimization index for actuator placement. Numerical examples are presented to show that the maximal actuator force can be significantly reduced after the optimization in order to achieve an equal modal control force.

Experimental Investigation of the Cross-Sensitivity and Size Effects of Polyvinylidene Fluoride Film Sensors on Modal Testing

Abstract: Due to advantages such as light weight, flexibility, and low cost, polyvinylidene fluoride (PVDF) films have been widely used in engineering applications as sensors for detecting strain, pressure, or micro-force. However, it is known that PVDF strain sensors have strain cross-sensitivity in mutually orthogonal directions. Furthermore, the size of the PVDF film sensor would also affect the dynamic strain sensing performance. In this paper, to investigate the cross-sensitivity and size effects experimentally, we employ PVDF film sensors to perform dynamic measurements on a cantilever beam. Since the vibrations of the cantilever beam are excited by impacts of a steel ball, the induced highly repeatable transient responses contain a wide range of resonant frequencies and thus can be used to investigate both the size and cross-sensitivity effects of the PVDF film sensors in a dynamic sensing environment. Based on the experimental results of the identified resonant frequencies compared with results obtained from a strain gauge, finite element calculations, and theoretical predictions, suggestions for the use of the PVDF strain sensor in modal testing are given in this paper.

Modal parameter extraction of Z24 bridge data

Abstract: The vibration data obtained from ambient, drop-weight, and shaker excitation tests of the Z24 Bridge in Switzerland are analyzed to extract modal parameters such as natural frequencies, damping ratios, and mode shapes. Two system identification techniques including Frequency Domain Decomposition and Eigensystem Realization Algorithm are employed for the extraction of modal parameters and the stationarity of the bridge is also investigated using time-frequency analysis.