• 전산구조공학
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• 제10권4호
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• pp.239-249
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• 1997

랜덤하중 하에서의 구분적선형시스템이 갖는 노이즈의 영향으로 인해 그 특성이 많이 감소되거나 소멸된 응답거동으로부터 chaos거동을 검출하는 방법을 개발, 분석하였다. 해양에서 구조물이 받는 파력은 결정론적이 아닌 추계론적이다. 바람, 파도 그리고 조류 등에 의한 파력은 유한도의 랜던성을 갖으며, 이러한 파력은 지배적인 조화가진하중과 정규 백색노이즈를 더함으로써 표현할 수 있다. 외적 동요를 받는 시스템의 응답거동은 그 거동이 방해를 받으며, 이로 인해 chaos응답거동을 확인하기가 어려우며, 그 거동의 특성이 일반적인 랜덤거동과 다를 바가 없다. 이러한 경우, 평균 포인케어맵을 이용하여 랜덤노이즈에 의해 발견되지 않는 chaos응답거동을 식별할 수 있다. 본 연구에서는 직접수치시뮬레이션상에서 이러한 평균 포인케어맵을 만드는 방법을 개발하였으며, 얻어진 평균 포인케어맵의 적용범위에 대하여 분석하였다. 평균 포인케어맵은 노이즈가 포함된 조화가진하중을 받는 시스템의 chaos응답거동을 확인하는데 있어서 노이즈의 강도가 높을 때 일반적인 포인케어맵만으로는 놓칠 수 있는 chaos응답거동을 성공적으로 확인할 수 있음을 알아내었다. 또한 시스템의 응답거동에서 chaos의 특성이 완전히 사라지는 노이즈의 강도를 얻을 수 있음도 알아내었다.

• Smart Structures and Systems
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• 제24권3호
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• pp.333-343
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• 2019

The possibility of adopting vibration-powered wireless nodes has been largely investigated in the last years. Among the available technologies based on the piezoelectric effect, the most common ones consist of a vibrating beam covered by electroactive layers. Another energy harvesting strategy is based on the use of piezoelectric strips attached to a hosting structure subjected to dynamic loads. The hosting structure, for example, can be the system to be equipped with wireless nodes. Such strategy has received few attentions so far and no analytical studies have been presented yet. Hence, the original contribution of the present paper is concerned with the development of analytical solutions for the electrodynamic analysis and design of piezoelectric polymeric strips attached to relatively large linear elastic structural systems subjected to random vibrations at the base. Specifically, it is assumed that the dynamics of the hosting structure is dominated by the fundamental vibration mode only, and thus it is reduced to a linear elastic single-degree-of-freedom system. On the other hand, the random excitation at the base of the hosting structure is simulated by filtering a white Gaussian noise through a linear second-order filter. The electromechanical force exerted by the polymeric strip is negligible compared with other forces generated by the large hosting structure to which it is attached. By assuming a simplified electrical interface, useful new exact analytical expressions are derived to assess the generated electric power and the integrity of the harvester as well as to facilitate its optimum design.

• Structural Engineering and Mechanics
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• 제20권6호
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• pp.655-672
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• 2005

Seismic random responses due to the wave passage effect are extensively investigated by using the pseudo excitation method (PEM). Two examples are used. The first is very simple but also very informative, while the second is a realistic suspension bridge. Numerical results show that the seismic responses vary significantly with wave speed, especially for low velocity or large span. Such variations are not monotonic, especially for flexible structures. The contributions of the dynamic and quasi-static components depend heavily on the seismic wave velocity and the natural frequencies of structures. For the lower natural frequency cases, the dynamic component has significant effects on the dynamic responses of the structure, whereas the quasi-static component dominates for higher natural frequencies unless the wave speed is also high. It is concluded that if insufficient data on local seismic wave velocity is available, it is advisable to select several possible velocity values in the seismic analysis and to choose the most conservative of the results thus obtained as the basis for design.

• Earthquakes and Structures
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• 제5권4호
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• pp.395-416
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• 2013

The magneto-rheological (MR) damper contributes to the new technology of structural vibration control. Its developments and applications have been paid significant attentions in earthquake engineering in recent years. Due to the shortages, however, inherent in deterministic control schemes where only several observed seismic accelerations are used as the trivial input and in classical stochastic optimal control theory with assumption of white noise process, the derived control policy cannot effectively accommodate the performance of randomly base-excited engineering structures. In this paper, the experimental and analytical studies on stochastic seismic response control of structures with specifically designed MR dampers are carried out. The random ground motion, as the base excitation posing upon the shaking table and the design load used for structural control system, is represented by the physically based stochastic ground motion model. Stochastic response analysis and reliability assessment of the tested structure are performed using the probability density evolution method and the theory of extreme value distribution. It is shown that the seismic response of the controlled structure with MR dampers gain a significant reduction compared with that of the uncontrolled structure, and the structural reliability is obviously strengthened as well.

• Composites Research
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• 제24권2호
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• pp.14-21
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• 2011

본 논문에서는 항공기에 장착되는 다축 구동 광학계에 대한 동역학 모델링을 하고, 다물체 동역학 해석프로그램을 사용하여 다축 구동 광학계의 모드해석, 사인파 해석 및 랜덤 진통해석을 하였다. 카메라 모듈의 물성으로는 Al6061-T6와 두 가지 형태의 강화 복합재 물성을 적용하였으며, x, y, z 축의 가진에 따른 각 축의 응답을 구하여 서로 비교하였다. 해석 결과는 카메라 모듈의 경량화를 위해 사용될 수 있을 것으로 사료된다.

• International Journal of Aeronautical and Space Sciences
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• 제17권4호
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• pp.551-564
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• 2016

High-speed flight vehicles (HSFVs) such as space launch vehicles and missiles undergo severe dynamic loads which are generated during the launch and in in-flight environments. A typical vehicle is composed of thin plate skin structures with high-performance electronic units sensitive to such vibratory loads. Such lightweight structures are then exposed to external dynamic loads which consist of random vibration, shock, and acoustic loads created under the operating environment. Three types of dynamic loads (acoustic loads, rocket motor self-induced excitation loads and aerodynamic fluctuating pressure loads) are considered as major components in this study. The estimation results are compared to the design specification (MIL-STD-810) to check the appropriateness. The objective of this paper is to study an estimation methodology which helps to establish design specification for the dynamic loads acting on both vehicle and electronic units at arbitrary locations inside the vehicle.

• 대한토목학회논문집
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• 제14권3호
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• pp.463-472
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• 1994

Random 지반운동에 대한 면진수조구조물 응답의 추계학적 해석방법을 연구하였다. 유연한 벽체와 내부유체간의 유체구조물 상호작용은 유체운동의 유한요소 모델링에 의하여 얻어지는 부가질량행렬 형태로 고려되었다. 정상(定常)(Stationary)지반운동으로는 수정된 Clough-Penzien Spectral Model이 사용되었으며, 비정상(非定常)(Nonstationary)지반운동으로는 상기모델에 포락함수를 적용한 모델을 사용하였다. 운동을 지배하는 Lyapunov Covariance Matrix 미분방정식의 해를 구하여 두 종류 면진시스템의 정상응답 및 비정상응답을 해석하였다.

• 한국음향학회지
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• 제20권6호
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• pp.9-16
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• 2001

본 논문에서는 음파를 이용하여 덕트 내 길이 방향으로의 불균일 단면적을 역문제적으로 측정하는 방법에 대해서 연구하였다. 음파를 사사용하여 덕트 단면적을 구하는 이론 및 실험방법 등에 대해서 많은 연구가 되어왔으나, 본 연구에서는 덕트 내 충격응답을 구하고 이를 재구성 알고리즘에 대입하여 덕트 내 단면적을 구하는 방법을 채택하였다. 충격 가진을 통하여 덕트 내 충격응답을 구하는 기존 방법의 문제점을 살펴보았고, 광대역 가진 방법을 새로 제안하였다. 실험 및 이론적 고찰을 통하여 새로운 방법이 기존의 방법보다 면적 재구성 오차가 적음을 보였다. 덕트 단면적을 재구성 할 때의 오차 원인과 불규칙 잡음에 의한 오차범위를 파악하기 위하여 오차해석을 수행하여 음파를 이용한 면적 재구성 방법의 적용범위 및 대상을 명확히 하였다.

• Structural Engineering and Mechanics
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• 제21권3호
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• pp.255-273
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• 2005

Based on the random vibration theory, a response spectrum method is developed for seismic response analysis of linear, multi-degree-of-freedom structures under multi-support excitations is developed. Various response quantities, including the mean and variance of the peak response, the response mean frequency, are obtained from proposed combination rules in terms of the mean response spectrum. This method makes it possible to apply the response spectrum to the seismic reliability analysis of structures subjected to multi-support excitations. Considering that the tedious numerical integration is required to compute the spectral parameters and correlation coefficients in above combination rules, this paper further offers simplified procedures for their computation, which enhance dramatically the computational efficiency of the suggested method. The proposed procedure is demonstrated for tow numerical examples: (1) two-span continuous beam; (2) two-tower cabled-stayed bridge by using Monte Carlo simulation (MC). For this purpose, this paper also presents an approach to simulation of ground motions, which can take into account both mean and variation properties of response spectrum. Computed results based on the response spectrum method are in good agreement with Monte Carlo simulation results. And compared with the MSRS method, a well-developed multi-support response spectrum method, the proposed method has an incomparable computational efficiency.

• 한국군사과학기술학회지
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• 제26권3호
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• pp.252-261
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• 2023

Analysis of dynamic characteristics and flight vibration test for unmanned aerial vehicles was studied by using dummy test body. The FEM model for dummy test body was supplemented by results of modal and random vibration test. The free end boundary condition to simulate flight environments was made by test setup using bungee cable. Prior to the flight vibration test using a dual electric vibration exciters, the test procedure to calculate quantitative vibration level was studied by using military specification. The actual test was successfully done by using the analysis and pretest results. From the analysis results, it was possible to determine the feasibility of the test by predicting the excitation force of the flight vibration test and to get the response of any point which could not be measured by the test. The results of this study will much contribute to the Test and Evaluation of unmanned aerial vehicles.