• Structural Engineering and Mechanics
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• 제33권6호
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• pp.709-724
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• 2009

In this paper a free-free uniform beam with damping effects subjected to follower and transversal forces at its end is considered as a model for a space structure. The effect of damping on the stability of the system is first investigated and the effects of the follower and transversal forces on the vibration of the beam are shown next. Proportional damping model is used in this work, hence, the effects of both internal (material) and external (viscous fluid) damping on the system are noted. In order to derive the frequency of the system, the Ritz method has been used. The mode shapes of the system must therefore be extracted. The Newmark method is utilized in the study of the system vibration. The results show that an increase in the follower and transversal forces leads to an increase of the vibrational motion of the beam which is not desirable.

• Structural Engineering and Mechanics
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• 제8권3호
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• pp.299-310
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• 1999

One problem with base isolators of the sliding type is that their dynamic responses are nonlinear, which cannot be solved in an easy manner, as distinction must be made between the sliding and non-sliding phases. The lack of a simple method for analyzing structures installed with base isolators is one of the obstacles encountered in application of these devices. As an initial effort toward simplification of the analysis procedure for base-isolated structures, an approach will be proposed in this paper for computing the equivalent damping for the resilient-friction base isolators (R-FBI), based on the condition that the sum of the least squares of errors of the linearized response with reference to the original nonlinear one is a minimum. With the aid of equivalent damping, the original nonlinear system can be replaced by a linear one, which can then be solved by methods readily available. In this paper, equivalent damping curves are established for all ranges of the parameters that characterize the R-FBI for some design spectra.

• 소음진동
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• 제9권2호
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• pp.258-264
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• 1999

The purpose of this paper is to investigate the damping behavior of a flexible joint. The slip at a structrual joint is selected at the tips of two identical cantilever beams adjoining each other. Both the direction of normal force and its magnitude varies due to the global deformation of the structure from mode to mode in the friction model. The friction dependent on vibration displacements resultsin the same functional behavior of the hysteretic material damping. Linearized energy loss factors are obtained as functions of both linear and torsional spring stiffness for their groups of symmetric and anti-symmetric modes, respectively. Experimental measurements as made for comparisons with analytical estimations by controlling the magnitude of fastening torque in the fastener, Hi-Lite. Trends on damping levelsmeasured in a very common vibration test method make an excellent agreement on the estimated damping levels.

• 한국구조물진단유지관리공학회 논문집
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• 제22권5호
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• pp.23-30
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• 2018

최근 들어 건물의 내진 및 내풍 성능을 향상시키기 위하여 감쇠구조에 대한 관심이 높아지고 있다. 감쇠장치 중 저렴한 비용과 높은 에너지소산능력을 발휘하며, 설치와 유지관리가 용이하다는 장점이 있어 강재이력형 감쇠장치를 이용한 수동형 감쇠구조시스템이 널리 사용되고 있다. 본 논문에서는 라멘구조 또는 무량판 구조에 적합한 계단 설치형 카고메 감쇠시스템(SKDS)을 제안하고자 하며, 제안된 감쇠시스템의 지진응답 개선효과에 대하여 해석적으로 검토하고자 한다. 비선형 동적해석결과 최대응답변위, 최대응답가속도 및 밑면전단력 감소로 살펴볼 때 내진구조와 비교하여 더 향상된 거동이 기대된다는 점에서 SKDS의 효과를 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제24권3호
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• pp.375-393
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• 2006

Under high velocity, pulse type near source earthquakes semi-active control systems are very effective in reducing seismic response base isolated structures. Semi-active control systems can be classified as: 1) independently variable stiffness, 2) independently variable damping, and 3) combined variable stiffness and damping systems. Several researchers have studied the effectiveness of independently varying damping systems for seismic response reduction of base isolated structures. In this study effectiveness of a combined system consisting of a semi-active independently variable stiffness (SAIVS) device and a magnetorheological (MR) damper in reducing seismic response of base isolated structures is analytically investigated. The SAIVS device can vary the stiffness, and hence the period, of the isolation system; whereas, the MR damper enhances the energy dissipation characteristics of the isolation system. Two separate control algorithms, i.e., a nonlinear tangential stiffness moving average control algorithm for smooth switching of the SAIVS device and a Lyapunov based control algorithm for damping variation of MR damper, are developed. Single and multi degree of freedom systems consisting of sliding base isolation system and both the SAIVS device and MR damper are considered. Results are presented in the form of nonlinear response spectra, and effectiveness of combined variable stiffness and variable damping system in reducing seismic response of sliding base isolated structures is evaluated. It is shown that the combined variable stiffness and variable damping system leads to significant response reduction over cases with variable stiffness or variable damping systems acting independently, over a broad period range.

• Steel and Composite Structures
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• 제26권6호
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• pp.771-791
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• 2018

This paper deals with the low velocity impact response and dynamic stresses of composite sandwich truncated conical shells (STCS) with compressible or incompressible core. Impacts are assumed to occur normally over the top face-sheet and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring-mass-damper (SMD) model. The displacement fields of core and face sheets are considered by higher order and first order shear deformation theory (FSDT), respectively. Considering continuity boundary conditions between the layers, the motion equations are derived based on Hamilton's principal incorporating the curvature, in-plane stress of the core and the structural damping effects based on Kelvin-Voigt model. In order to obtain the contact force, the displacement histories and the dynamic stresses, the differential quadrature method (DQM) is used. The effects of different parameters such as number of the layers of the face sheets, boundary conditions, semi vertex angle of the cone, impact velocity of impactor, trapezoidal shape and in-plane stresses of the core are examined on the low velocity impact response of STCS. Comparison of the present results with those reported by other researchers, confirms the accuracy of the present method. Numerical results show that increasing the impact velocity of the impactor yields to increases in the maximum contact force and deflection, while the contact duration is decreased. In addition, the normal stresses induced in top layer are higher than bottom layer since the top layer is subjected to impact load. Furthermore, with considering structural damping, the contact force and dynamic deflection decrees.

• 한국소음진동공학회논문집
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• 제25권2호
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• pp.108-115
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• 2015

Electro-mechanical actuator installed on aircraft consists of a decelerator which magnifies the torque in order to rotate an axis connected with aircraft control surface, a control section which controls the motor assembly through receiving orders from cockpit and a motor assembly which rotates the decelerator. Electro-mechanical actuator controls aircraft altitude, position, landing, takeoff, etc. It is an important part of a aircraft. Aircraft maneuvering causes vibrations to electro-mechanical actuator. Vibrations may result in structural fatigue. For that reason, it is necessary to analyze the system structural safety. In order to analyze the system structural safety. It is needed reasonable finite element model and structural response stress closed to real value. In this paper, analytic model is derived by using the simplified finite element model, and damping ratio which is closely related to response stress is derived by using modal test. So, we developed analytic model in less than 10 % error rate, compared with modal test. Vibration response stress close to real value was estimated from analytic model modified with modal experimental damping ratio. Estimation method for damping ratio with empirical formula was suggested partly. Finally, It was proved that electro-mechanical actuator had reasonable structure margin of safety at environmental random $3{\sigma}$ stress during life cycle.

• 한국전산구조공학회논문집
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• 제12권3호
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• pp.281-292
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• 1999

지반-기초 상호작용계를 해석할 때 실제로 지반은 다양한 지반종류와 다층으로 형성되어 있으므로 지반 특성의 변화를 고려해야 한다. 초기의 대부분의 상호작용계의 정·동적 해석은 지반의 복잡한 성질을 역학적으로 탄성거동을 한다고 가정한 Winkler 지반모델 혹은 지반을 등방성이고 균질한 반무한 탄성체로 가정한 반무한 탄성지반 모델로 보아 수행되었다. 본 연구는 유한 요소법을 이용하여 지반-기초 상호작용계의 동적 거동을 해석하기 위해 기초는 4절점 후판요소를 사용하고 지반은 지반특성을 고려할 수 있도록 8절점 6면체 요소를 사용하였고, 지반의 감쇠효과 및 지반특성을 고려한 지반-기초 상호작용계의 동적 거동을 유한요소법으로 해석하고 지반의 영향범위를 결정하는 것이다.

• 산업기술연구
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• 제22권A호
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• pp.137-144
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• 2002

A series of wind tunnel tests was conducted to investigate the existence of the galloping instability of inclined dry cables and also to Identify the influence of some parameters on it. These parameters are the structural damping and cable surface roughness, which may have significant impact on the vibration characteristics. The test results showed both the divergent type of galloping instability and the limited amplitude high wind speed vortex shedding excitation. Galloping instability was observed in only one case. Parametric study shows that the vortex shedding oscillation can be easily suppressed with an increase of structural damping. It was also shown that the instability criterion indicated by earlier research was too conservative compared to the results obtained from the present study.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.296-303
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• 2004

In this study, equivalent linear damping and stiffness of a single-degree-of-freedom (SDOF) structure with a rotational friction damper are estimated using the result of experiments and compared with those obtained from non-linear time history analyses. First, the transfer function of the test model is constructed and then the equivalent stiffness and damping are calculated, using the half-power bandwidth (HPB) method. For comparative study, those properties are estimated based on stochastic theory in the time domain. Both equivalent linear systems identified from experiments and numerical analyses correspond well. Further, it is observed that there exists an optimal clamping force on the rotational friction damper from estimated equivalent damping.