• Smart Structures and Systems
• /
• v.18 no.4
• /
• pp.819-837
• /
• 2016

The quality of vibration pattern reproduction of elastic structures by the modal expansion method is influenced by the modal expansion method and the sensor placement as well as the accuracy of measured natural modes and the total number of vibration sensors. In this context, this paper presents an improved numerical method for reproducing the vibration patterns by introducing a block-wise modal expansion method (BMEM), together with the genetic algorithm (GA). For a given number of vibration sensors, the sensor positions are determined by an evolutionary optimization using GA and the modal assurance criterion (MAC). Meanwhile, for the proposed block-wise modal expansion, a whole frequency range of interest is divided into several overlapped frequency blocks and the vibration field reproduction is made block by block with different natural modes and different modal participation factors. A hollow cylindrical tank is taken to illustrate the proposed improved modal expansion method. Through the numerical experiments, the proposed method is compared with several conventional methods to justify that the proposed method provides the improved results.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2006.04a
• /
• pp.778-785
• /
• 2006

In this paper, two possible ways for mode shape expansion are proposed and opened for discussion for future use. The first method minimizes the modal flexibility error between the experimental and analytical mode shapes corresponding to the measured DOFs to find the multiplication matrix which can be treated as the least-squares minimization problem. In the second method, Normalized Modal Difference (NMD) is used to calculate multiplication matrix using the analytical DOFs corresponding to measured DOfs. This matrix is then used to expand the measured mode shape to unmeasured DOFs. A simulated simply supported beam is used to demonstrate the performance of the methods. These methods are then compared with two most promising existing methods namely Kidder dynamic expansion and Modal expansion methods. It is observed that the performance of the modal flexibility method is comparable with existing methods. NMD also have the potential to expand the mode shapes though it is seen more sensitive to the distribution of error between FEM and actual test data.

• Journal of KSNVE
• /
• v.8 no.4
• /
• pp.654-662
• /
• 1998

To predict the radiating noise from the vibrating surface, it is required to know the velocity distribution of vibrating surface exactly as possible as it can. Although it can be obtained by finite element method, their accuracy is limited by theuncertainty of preparing input data such as material propoerties, damping, excitation, and the actual boundary conditions. Experimental values are accurate but are seldom available as many asthe data points compared to FEM mesh. Therefore, hybrid method of experiment and finite element method, called modal expansion technique, is investigated for the preparatin of accurate element method at specified frequencies and for the verification of this scheme, related experiment is performed. In high frequency range above 2000 Hz, piezo-electric material is used as an actuator.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.25 no.10
• /
• pp.677-684
• /
• 2015

It is often necessary to predict the vibration patterns of the structures from the signals of finite number of vibration sensors. This study presents the optimal placement of vibration sensors by applying the genetic algorithm and the modal expansion method. The modal expansion method is used to estimate the vibration response of the whole structure. The genetic algorithm is used to estimate the optimal placement of vibration sensors. Optimal sensor placement can be obtained so that the fitness function is minimized in the genetic algorithm. This paper discusses the comparison of the performances of two types of fitness functions, modal assurance criteria(MAC) and condition number( CN). As a result, the estimation using MAC shows better performance than using CN.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2014.04a
• /
• pp.227-228
• /
• 2014

• Structural Engineering and Mechanics
• /
• v.14 no.1
• /
• pp.1-20
• /
• 2002

Investigated in this study are the modal characteristics of the eccentric cylindrical shells with fluid-filled annulus. Theoretical method is developed to find the natural frequencies of the shell using the finite Fourier expansion, and their results are compared with those of finite element method to verify the validation of the method developed. The effect of eccentricity on the modal characteristics of the shells is investigated using a finite element modeling.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1718-1723
• /
• 2003

This paper presents a computational method for deformation modes of a flexible body in multibody system from the experimental modal analysis and an efficient method for flexible multibody dynamic analysis by use of the modes. It is difficult to directly use experimental modal parameters in flexible multibody dynamic analysis. The major reasons are that there are many inconsistencies between experimental and analytical modal data and experimental noises are inherent in the experimental data. So two methods, such as, a method for ortho-normalization of experimental modes and the other one for mode expansion, are suggested to gain deformation modes of a flexible body from the experimental modal parameters. Using the virtual work principle, the equation of motion of a flexible body is derived. The effectiveness of the proposed method will be verified in the numerical example of cab vibration of a truck by comparing analysis and test results.

• Structural Engineering and Mechanics
• /
• v.64 no.3
• /
• pp.279-285
• /
• 2017

Modal expansion technique (MET) is a method to estimate the vibration fields of flexible structures by using eigenmodes of the structure and the signals of sensors. It is the useful method to estimate the vibration fields but has the truncation error since it only uses the limit number of the eigenmodes in the frequency of interest. Even though block-wise MET performed frequency block by block with different valid eigenmodes was developed, it still has the truncation error due to the absence of other eigenmodes. Thus, this paper suggested an improved block-wise modal expansion technique. The technique recovers the truncation errors in one frequency block by utilizing other eigenmodes existed in the other frequency blocks. It was applied for estimating the vibration fields of a cylindrical shell. The estimated results were compared to the vibration fields of the forced vibration analysis by using two indices: the root mean square error and parallelism between two vectors. These indices showed that the estimated vibration fields of the improved block-wise MET more accurately than those of the established METs. Especially, this method was outstanding for frequencies near the natural frequency of the highest eigenmode of each block. In other words, the suggested technique can estimate vibration fields more accurately by recovering the truncation errors of the established METs.

• Journal of KSNVE
• /
• v.7 no.5
• /
• pp.737-746
• /
• 1997

The substructure synthesis method is used for making it easy to analyze vibration systems generally in vibration field. In the past, this method has been to be used mainly because of shortage of computer memory and CPU time. But recently this method is used for analyzing complex structure or identifying the characteristics of systems precisely. The purpose of this study is to develop acoustic substructure synthesis method that can be applied to acoustic modal analysis of complex acoustic systems. Acoustic modal analysis method to be introduced here is a method that analyze acoustic natural mode shape of the complex acoustic system by the principle of CMS(component mode synthesis method). This paper describes the acoustic modal analysis of the acoustic finite element model of simple expansion pipe by acoustic substructure synthesis method. The resutls of acoustic modal analysis analyzed by Acoustic substructure synthesis method and the results by FEM(finite element method) shows good agreement.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.19 no.9
• /
• pp.1802-1811
• /
• 1994

In this paper, the corrugated horn antenna used in the reflector feed horn of satellite is analyzed using the modal expansion method. The modal expansion method is represented by the summations of modals at each point so the exact prediction of field and phase patterns can be obtained. The least number of iterations to compute field patterns is proposed. By using this number. calculation of accurate near and far field patterns without comsuming a lot of computational effort is available. Three kinds of corrugated horn antenna is designed to verify the method and experimented. The VSWR of designed frequency is from 1.04 to 1.1. The input impedance is nearly matched to $50\Omega$.