Modal testing

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

Material characterization for orthotropic shells using modal analysis and Rayleigh-Ritz models

Abstract: Using the method of Bayesian estimation, the elastic constants of specially orthotropic cylindrical composite shells with balanced symmetric lamination were characterized based on their natural frequencies obtained from free-free configuration modal testing Estimation of the various elastic constants of each cylinder involved an iterative tuning of a mathematical model describing its modal response Formulation of the model was accomplished with the Rayleigh-Ritz method in conjunction with characteristic beam functions For a prescribed circumferential wave pattern of the vibration modes, a five-term series was sufficient to describe the deflection shapes By carrying out sensitivity analysis, the natural frequencies of the cylindrical shells were found to have a high dependence on the circumferential and in-plane shear moduli rendering an accurate characterization for these moduli On the contrary, the Poisson's ratios of the specimens cannot be accurately determined

Three-phase squirrel-cage induction motor modal analyses. Theoretical and experimental aspects

Abstract: The vibrations developed during the work represent one of the main mechanical problems of the electric motors. Their frequencies and levels can cause large damages of different electrical motors parts. This is the reason why even in the design phase it is useful to be known the values of the natural frequencies of the parts. This can be made in two different ways: using modern capabilities of finite element method (FEM) or doing experimental modal analysis. The study developed in the present paper refers to the modal analysis of a three-phase squirrel cage induction of 1.5 kW, for both, for its elements and, for motor and the electric motor as an assembly. The FEM modal analysis was applied using ABAQUS software for assembly of the 7 elements of the motor. The 3D model was developed, mechanical connections being of screw type. The theoretical model was validated by experiments, with impact hammer test method. The validation confirms the assumptions made for the 3D model and the designed model can be use, as example, for other FEM based modal analysis. The natural frequencies obtained both by FEM and experimental method does not overlap on the working frequencies.

Enhanced optimization-based structural damage detection method using modal strain energy and modal frequencies

Abstract: To identify the location and severity of structural damages precisely, a two-stage damage detection method is proposed here. In the first stage, the most probable elements that maybe damaged are determined using the modal strain energy concept of structure. For such purpose, an efficient modal strain energy conversion-based index is proposed. In the second stage, the structural damage identification problem is defined as an optimization problem that to be solved by a modified genetic algorithm. In the optimization problem, the damage extents of structure’s elements which are determined in the previous stage are considered as the variables. An efficient objective function considering the first few modal frequencies of the structure, before and after damage occurrence, is utilized for optimization. The robustness of the proposed method is assessed by several benchmark examples. The numerical results exhibit the effectiveness of the proposed method for precisely determining the location and severity of multiple structural damages.

Vibration and actuation characteristics of composite structures with a bonded piezo-ceramic actuator

Abstract: For the design of vibration control systems of composite structures using piezo-ceramic actuators, it is necessary to obtain an accurate system model. Especially, the information related to natural modes, damping ratios and modal actuation forces appears in the governing state space equations. A refined finite element analysis based on the layerwise displacement plate theory has been performed to obtain the system parameters of composite plates with piezoelectric actuators. In this study, the present finite element method has the capability to take account of the stepped effect due to partly bonded piezo-ceramics. Also modal testing techniques have been applied to identify the system parameters experimentally. Through the comparison of numerical results with experimental data, the validity of the numerical procedures has been proved.