Modal testing

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

Modal analysis in the design of an automotive exhaust pipe

Abstract: The problem of mechanical vibration for an automotive exhaust system is investigated using the modal analysis method. Using a finite–element mathematical model it is possible to calculate the vibration eigenfrequencies and the medal shape. In assembling the mathematical model the major points are the correct evaluation of the excitation sources of the actual temperature and of the effects of the pipe bends. Moreover, through dynamical analysis the real displacement and the related stresses can be determined. Some calculated results are reported in order to illustrate the most specific aspects of the proposed method.

Dynamic Study of Bicycle Frame Structure

Abstract: Bicycle frames have to bear variety of loads and it is needed to ensure the frame can withstand dynamic loads to move. This paper focusing on dynamic study for bicycle frame structure with a purpose to avoid the problem regarding loads on the structure and to ensure the structure is safe when multiple loads are applied on it. The main objectives of dynamic study are to find the modal properties using two method; finite element analysis (FEA) and experimental modal analysis (EMA). The correlation between two studies will be obtained using percentage error. Firstly, 3D model of mountain bike frame structure has been draw using computer-aided design (CAD) software and normal mode analysis using MSC Nastran Patran was executed for numerical method meanwhile modal testing using impact hammer was performed for experimental counterpart. From the correlation result, it show that percentage error between FEA and EMA were below 10% due to noise, imperfect experiment setup during perform EMA and imperfect modeling of mountain bike frame structure in CAD software. Small percentage error differences makes both of the method can be applied to obtain the dynamic characteristic of structure. It is essential to determine whether the structure is safe or not. In conclusion, model updating method is required to reduce more percentage error between two results.

On the use of auto-and cross-correlation functions to extract modal parameters from output-only data

Abstract: Correlation functions can be treated as though they were free vibration responses, i.e. sums of decaying sinusoids. Consequently, feeding conventional time domain modal parameter extraction techniques with auto-and cross-correlation functions calculated between all responses and a set of responses which serve as references instead of impulse response functions, allows to identify the modal parameters from output-only data. Polyreference LSCE, a well-known and often used technique in classical modal analysis is well-suited for this purpose. It yields the natural frequencies and damping factors in one step, while the mode shapes need to be determined in a separate step. This paper gives a theoretical formulation for the extraction of mode shapes by fitting the auto-and crosspower spectra of the outputs in a least-squares sense. It is shown that this auto-and crosspower fit should be differently approached than the conventional modal FRF fit. Some practical examples are giving, illustrating the usefulness of the Polyreference LSCE and the auto-and crosspower fit for modal parameter extraction from output-only data.