• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 가을 학술발표회 논문집
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• pp.535-540
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• 2003

The objective of this paper is to assess the variability of modal properties caused by temperature effects and to adjust modal data used for frequency-based damage detection in plate-girder bridges. First, experiments on model plate-girder bridges are described. Next, the relationship between temperature and natural frequencies is assessed and a set of empirical frequency-correction formula are analyzed for the test structure. Finally, a frequency-based method is used to locate and estimate severity of damage in the test structure using experimental modal data which are adjusted by the frequency-correction formula. Here, local damage in beam-type structures is detected by using measured frequencies and analytical mode shapes.

• 한국군사과학기술학회지
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• 제2권2호
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• pp.251-260
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• 1999

The stiffness of joint parts in the finite element beam model are corrected by the direct comparison between the modal test and analysis model. The corrected stiffness are reviewed according to the boundary conditions of modal testing. For the improved modal test/analysis correction, more modes measured than acceleration sensors are used to make a minimal order system model. In addition, the initial F.E. model is reduced to the degrees of freedom of a minimal order system model, keeping the dynamics of the initial model. Finally, for the parametric correction of the reduced model, the submatrices are used to model the initially assumed stiffness.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.840-845
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• 2004

Development of the linear motors is recently required to control a high-speed and high-resolution in the high-integrated and speed process industry. This paper presents vibration analyses as well as measurement standards of the newly developed linear motors through analyzing the vibration characteristics of the advanced products. Vibration experiments are conducted for identifying vibration level during operation. They are also included in the modal test to analyze dynamic characteristics. Analytic data using Finite Element Method (FEM) are compared with the results of the modal. The FEM and experiments make it possible to understand these characteristics. Further, through computer simulation for the behavior of moving part to be vibration source, the best acceleration pattern of moving part movement can be verified to achieve effective moving part positioning and reduce the vibration due to moving part movement.

• 정보저장시스템학회논문집
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• 제9권2호
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• pp.51-55
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• 2013

HDD has been easily exposed to the external shock and vibration because HDD has to apply to mobile devices. Therefore, the stiffness of base has been the important factors for the design of HDD. To improve the stiffness of base, the frame was applied to the base. First, the finite element model of the base was constructed. Then, the FE model was verified by modal analysis. Drop test was performed to confirming the shock simulation model. The dynamic characteristic of original base which is verified is compared with the base which is applied the frame through modal analysis and shock analysis.

• 수산해양기술연구
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• 제29권1호
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• pp.39-55
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• 1993

Modal Analysis is the process of characterizing the dynamic properties of an elastic structure by identifying its modes of vibration. A mode of vibration is a global property of an elastic structure. That is, a mode has a specific natural frequency and damping factor which can be identified from response data at practically any point on a structure, and it has a characteristic mode shape which identifies the mode spatially over the entire structure. Modal testing is able to be performed on structural and mechanical structure in an effort to learn more about their elastic behavior. Once the dynamic properties of a structure are known its behavior can be predicted and therefore controlled or corrected. Resonant frequencies, damping factors and mode shape data can be used directly by a mechanical designer to pin point weak spots in a structure design, or this data can also be used to confirm or synthesize equations of motion for the elastic structure. These differential equations can be used to simulate structural response to know input forces and to examine the effects of pertubations in the distributed mass, stiffness and damping properties of the structure in more detail. In this paper the measurement of transfer functions in digital form, and the application of digital parameter identification techniques to identify modal parameters from the measured transfer function data are discussed. It is first shown that the transfer matrix, which is a complete dynamic model of an elastic plate structure can be written in terms of the structural modes of vibration. This special mathematical form allows one to identify the complete dynamics of the structure from a much reduced set of test data, and is the essence of the modal approach to identifying the dynamics of a structure. Finally, the application of transfer function models and identification techniques for obtaining modal parameters from the transfer function data are discussed. Characteristics on vibration response of elastic plate structure obtained from the dynamic analysis by Finite Element Method are compared with results of modal analysis.

• 대한토목학회논문집
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• 제26권4A호
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• pp.707-717
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• 2006

근래에 들어 기존의 PSC 거더 교량 외에 다양한 형태의 교량이 개발되고 있으며, 다단계 긴장에 의한 PSC 거더교는 대표적인 예이다. 다단계 긴장 PSC 거더교는 구조적 개념에 따라 자중을 줄이고 경간을 장대화할 수 있는 장점을 갖고 있다. 그러나, 이와 같은 장대화된 보다 유연한 교량은 구조적 안전성 및 사용성을 고려한 주행열차하중에 대한 동적거동 검토가 필수적이며, 철도교량의 주행열차하중에 대한 동적성능평가를 위한 정확한 동특성 입력은 매우 중요하다. 본 연구에서는 정확한 고유진동수 및 감쇠비 추출을 위하여 25m 실물 다단계 긴장 PSC 거더를 제작하여 시공단계별 모달테스트를 수행하였다. 모달테스트를 위한 가진방법으로 기존의 충격햄머에 의한 방법 외에 디지털 콘트롤에 의한 가진기를 사용하여 보다 정확한 주파수응답 함수를 얻고자 하였다. 또한, 시공단계별 구조계 변화 및 긴장에 의한 동특성 변화를 고찰하기 위하여 시공단계별 실험을 수행하였다. 모달테스트 결과에 의한 동특성 값을 주행열차하중 해석에 적용하여 다양한 매개변수연구를 통한 철도교량 동적성능평가를 수행하였다. 동적처짐, 충격계수, 바닥판의 연직가속도, 단부꺾임각 등에 대하여 열차별, 속도별 동적해석을 수행하여 국내외 철도교량 동적성능 평가기준과 비교하였다.

• 대한조선학회 특별논문집
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• 대한조선학회 2017년도 특별논문집
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• pp.14-18
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• 2017

The Lashing bridge and radar mast of ship are upright structures so they are generally exposed to excessive vibration. Recently, the use of low speed main engines for improving fuel efficiency has been increasing, and the excitation frequencies of the main engine are moving to the low frequency band. If the excitation frequencies are coincident with the natural frequencies of the local structure, excessive vibration occurs during main engine operating condition. The modal test is to experimentally determine resonance frequency, mode shape, and damping, which are vibration characteristics of a mechanical structure under dynamic external force. Through this study, the vibration characteristics of the structure are obtained by modal tests and the low vibration measure is applied to the local structures.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1159-1164
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• 2006

Torsional vibration is an important vibration mode when shafts, cylinders and pipes are considered. However, the modal testing of torsional vibrations is not an easy job to carry out because of the lack of proper transducers. This work presents a new torsional vibration transducer based on the magnetostrictive principle and its application to torsional modal testing. The transducer is so designed as to generate/measure only torsional vibrations excluding other vibration modes such as longitudinal and bending vibrations. The transducer is composed of ferromagnetic patches bonded to a test structure, permanent magnets, and a solenoid. Though patches and magnets are bonded to a structure, torsional vibrations are generated and measured wirelessly by a solenoid encircling a test structure. The proposed transducer works even at considerably high frequencies, say, tens of kilohertz. Furthermore, the transducer can be manufactured at a low price. To check the performance of the proposed method, the torsional modal testing on a hollow aluminum shaft was conducted. The results, such as eigenfrequencies, obtained by the proposed transducer agreed favorably with theoretical results.

• 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.

• 한국소음진동공학회논문집
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• 제16권8호
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• pp.879-885
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• 2006

Torsional vibration is an important vibration mode when shafts, cylinders and pipes are considered. However, the modal testing of torsional vibrations is not an easy task to carry out because of the lack of proper transducers. This work presents a new torsional vibration transducer based on the magnetostrictive principle and its application to torsional modal testing. The transducer is so designed as to generate/measure only torsional vibrations excluding other vibration modes such as longitudinal and bending vibrations. The transducer is composed of ferromagnetic patches bonded to a test structure, permanent magnets, and a solenoid. Though patches and magnets are bonded to a structure, torsional vibrations are generated and measured wirelessly by a solenoid encircling a test structure. The proposed transducer works even at considerably high frequencies, say, tens of kilohertz. Furthermore, the transducer can be manufactured at a low price. To check the performance of the proposed method, the torsional modal testing on a hollow aluminum shaft was conducted. The results, such as eigenfrequencies, obtained by the proposed transducer agreed favorably with theoretical results.