• Smart Structures and Systems
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• 제7권1호
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• pp.59-82
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• 2011

In this study, an output-only modal identification approach is proposed for decentralized wireless sensor nodes used for linear structural systems. The following approaches are implemented to achieve the objective. Firstly, an output-only modal identification method is selected for decentralized wireless sensor networks. Secondly, the effect of time-unsynchronization is assessed with respect to the accuracy of modal identification analysis. Time-unsynchronized signals are analytically examined to quantify uncertainties and their corresponding errors in modal identification results. Thirdly, a modified approach using complex mode shapes is proposed to reduce the unsynchronization-induced errors in modal identification. In the new way, complex mode shapes are extracted from unsynchronized signals to deal both with modal amplitudes and with phase angles. Finally, the feasibility of the proposed approach is evaluated from numerical and experimental tests by comparing with the performance of existing approach using real mode shapes.

• 한국정밀공학회지
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• 제8권2호
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• pp.57-68
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• 1991

In this study, to analyse the dynamic characteristics of a machine-tool spindle system, the spindle is mathematically represented by a Timoshenko beam including the internal damping of beam material, and each bearing by four bearing coefficients; stiffness and damping coefficients in moment and radial directions. And the dynamic compliance of the system is calculated by introducing the transfer matrix method, and the complex modal analysis method has been applied for the modal parameter identification. The influence of the bearing coefficients, material damping factor and bearing span on the dynamic characteristics of the system is parametrically examined.

• 소음진동
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• 제5권4호
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• pp.503-514
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• 1995

In the case of performing experimental modal analysis(EMA) and finite- element analysis(EFA) for a whole structure of automotive body that is composed of many complex parts, a trouble may arise from the calculation time, the capacity of memory in computers and the experimental conditions, etc. In this paper, for the vibrational analysis of automotive body model, the efficient modal synthesis method by means of dividing the whole structure into two parts and performing EMA and FEA for each part is studied. In addition, the method based on Lagrange interpolation is proposed for approximating rotational degrees-of-freedom information and linking FEA with EMA. In result, by measuring translational degrees-of-freedom information of only few points and adopting only few modes, the linking method based on Lagrange interpolation turned out to be efficient and accurate in the low frequency range.

• Structural Engineering and Mechanics
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• 제73권3호
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• pp.271-286
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• 2020

Passive control technologies are commonly used in several areas to suppress structural vibrations by the addition of supplementary damping, and some modal damping may be heavy beyond critical damping even for regular structures with energy dissipation devices. The design of passive control structures is typically based on (complex) mode superposition approaches. However, the conventional mode superposition approach is predominantly applied to cases of under-critical damping. Moreover, when any modal damping ratio is equal or close to 1.0, the system becomes defective, i.e., a complete set of eigenvectors cannot be obtained such that some well-known algorithms for the quadratic eigenvalue problem are invalid. In this paper, a generalized complex mode superposition method that is suitable for under-critical, critical and over-critical damping is proposed and expressed in a unified form for structural displacement, velocity and acceleration responses. In the new method, the conventional algorithm for the eigenvalue problem is still valid, even though the system becomes defective due to critical modal damping. Based on the modal truncation error analysis, modal corrected methods for displacement and acceleration responses are developed to approximately consider the contribution of the truncated higher modes. Finally, the implementation of the proposed methods is presented through two numerical examples, and the effectiveness is investigated. The results also show that over-critically damped modes have a significant impact on structural responses. This study is a development of the original complex mode superposition method and can be applied well to dynamic analyses of non-classically damped systems.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.359-364
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• 2002

Statistical energy method is widely used for the prediction of vibrational and acoustical behavior of complex structures, such as ship building and automobile in mid-, high frequency ranges. However. in order to convince this SEA result, it is important to verify estimated SEA parameters, e. g. modal density, energy in each subsystem, damping loss factor, coupling loss factor. with possible other method. For modal density parameter, the experimental estimations via Experimental Modal Analysis are checked with those from finite element method for both beam- plate and plate-plate cans. Loss factors are calculated by Lyon's simple method for the two subsystem. finally. modal experiments are carried out by varying the mass added on the junction of two subsystem for the purpose of investigating the influence on the coupling loss factor's behavior.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1999년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall
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• pp.186-192
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• 1999

Safety-related equipments of nuclear power plant must be seismically qualified to demonstrate their ability to function as required during and/or after the earthquake, The seismic qualification is usually achieved through analysis and testing. Analysis method is preferably adopted for structurally simple equipments which are easy to be mathematically modeled. However even for relatively complex equipments analysis method is occasionally used for computing the input motion or supporting information for the component test followed. Electrical cabinet is a typical example for which analysis method is combinedly used with test to get modal properties of the enclosing cabinet structure. Usually the structural elements and doors of the cabinet are loosely interconnected with small-size bolts or spot welding. Therefore cabinet-type equipment usually has high and complex nonlinear properties which are not easily idealized by simple practical modeling techniques. in this paper with respect to a typical cabinet-type structure(instrumentation cabinet of nuclear power plant) a comparative study has been performed between three different state-of-the -art modeling techniques: lumped mass model frame model and FEM modal. Form the study results it has been found that modal properties of the cabinet-type structure in the elastic behavior range can be reasonably computed through any type of modeling techniques in the practice with slight modification of model properties to get better accuracy. However it needs additional modeling techniques to get reasonable results up to nonlinear range.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.278-285
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• 2009

Operational modal analysis (OMA) allows modal parameters, such as natural frequencies and damping, to be estimated solely from data collected during operation. However, a main shortcoming of these methods resides in the evaluation of the accuracy of the results. This paper will explore the uncertainty and possible variations in the estimates of modal parameters for different operating conditions. Two algorithms based on the Least Square Complex Exponential (LSCE) method will be used to estimate the modal parameters. The uncertainties will be calculated using a Monte-Carlo approach with the hypothesis of constant modal parameters at a given operating condition. In collaboration with Andritz-Hydro Ltd, data collected on two different stay vanes from an Andritz-Hydro Ltd Francis turbine will be used. This paper will present an overview of the procedure and the results obtained.

• 소음진동
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• 제8권1호
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• pp.139-145
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• 1998

A great deal of effort has been invested in upgrading the performance and the efficiency of dynamic analysis of mechanical structures. Using experimental modal analysis(EMA) or finite element analysis(FEA) data of mechanical structures, the performance and efficiency can be effectively evaluated. In order to analyze complex structures such as automobiles and aircrafts, for the sake of computing efficiency, the dynamic substructuring techniques that allow to predict the dynamic behavior of a structure are widely used. Through linking a modal model obtained from EMA and an analytical model obtained from FEA, the best conditioned strucutres can be proposed. In this study, a new algorithm of substructre synthesis method, Multi-FRF synthesis method, is proposed to analyze a structure composed of many substructures.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.236-243
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• 2005

Nonlinear static analysis is used to quantify the resistance of the structure to lateral deformation and to gauge the mode of deformation and intensity of local demands. A simple method for the nonlinear static analysis of complex building structures subjected to monotonically increasing horizontal loading(pushover analysis) is presented. The method is designed to be a part of new methodologies for the seismic design and evaluation of structures. A variety of existing pushover analysis procedures are currently being consolidated under programs such as ATC 40 and FEMA 273. And various techniques have been recommended, including the use of constant lateral force profiles and the use of adaptive and multimodal approaches. In this paper a modal pushover analysis using design response spectra of UBC 97 is proposed. Proposed method is compared against the method in FEMA 273 and ATC 40, and results of time history analysis.

• 소음진동
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• 제8권6호
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• pp.1103-1112
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• 1998

A new time series method, directional ARMAX (dARMAX) model-based approach. is proposed for rotor dynamics identification. The dARMAX processes complex-valued signals, utilizing the complex modal testing theory which enables the separation of the backward and forward modes in the two-sided frequency domain and makes effective modal parameter identification possible, to account for the dynamic characteristics inherent in rotating machinery. This paper is divided into two parts : The dARMAX modeling, analysis. and fitting strategy are presented in the first part. whereas a evaluation of its performance characteristics based on both simulated and experimental data is presented in the second.