• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.55-62
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• 2006

The natural frequency of a beam plays a critical role in the dynamic analysis of beams. Especially it is a complicated and difficult task to analyse the natural frequency of a stepped beam with an irregularly varying section. The lumped mass methods, multi-degree of freedom analyses, are mainly used for the analysis of this kind of stepped beams. The accuracy of these methods are determined by the number of the partitions of elements, the number of the iterations in calculation, and the accuracy of assumed mode shapes. This study presents a method of transformation from symmetrically stepped beams to an equivalent beam and a method of the eigenvalue analysis. Appropriateness and utility of this method are demonstrated by comparing examples from other literatures and various models.

• Journal of KSNVE
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• v.9 no.1
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• pp.206-213
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• 1999

In the beam-like ship vibration analysis. three-dimensional correction factor(J-factor) can be calculated by considering the three-dimensional effect of the two-dimensional added mass. However, existing method is time-consuming with low accuracy in respect of global vibration analyses for vessels with large breadth. In this paper, to improve the demerit of the previous method, a new method of the beam-like ship vibration analysis is introduced In this method. the three-dimensional fluid added mass of surrounding water is calculated directly by solving the velocity potential problem using the Boundary Element Method (BEM). Then the three-dimensional added mass is evaluated as the lumped mass for each strip. Also, the beam-like ship vibration analysis for the structural beam model if performed with the lumped mass considered. It was verified that this new method is useful for the beam-like ship vibration analysis by comparing results obtained from both the existing method and the new method with experimental measurements for the open top container model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.251-258
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• 2009

At the stage conceptual design, combat vehicle is classified into three general categories of fire power, mobility and physical properties of system. The present research is restricted to fire power and its optimization. At the stage of conceptual designing of system, it is appropriate to consider major variables affecting fire power - including the weight of bullet, which exerts a direct influence on destroying effect, maximum range which takes long range firing in consideration. To estimate the maximum firing range, a simple interior ballistic and an exterior ballistic model were built by using the lumped parameter method, Le Duc method and point mass trajectory model. Design of experiment and regression analysis was used to derive simulations of fire power. Finally, response surface models were built and design variables were analyzed.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.108-116
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• 2015

An acoustic vector sensor is a device that is capable of measuring the direction of wave propagation and the acoustic pressure. In this paper, the modeling of micro-cantilever sensor for the vector sensor are proposed by consideration of acoustic phenomenon in water. Two models based on unimorph structure are proposed in this paper and corresponding transfer function which describes the relation between input pressure wave and output voltage depending on incidence angle and frequency of pressure wave is derived based on lumped model. It has been shown that very thin and flexible micro-cantilever can be used to measure directly the particle velocity component in water.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.48-54
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• 2015

In this study, we propose an innovative lateral force distribution building system between tall buildings by utilizing the difference of moment of inertia, resulting the reduction of lateral displacement and the lateral forces in terms of an alternative for the dense human and increased cost of lands in highly integrated city area. A successive collapse prevention means by providing additional bearing plate between connections is proposed. In addition to that, a more economical vibration reduction is expected due to the suggested tuned mass damper on the surface of spacial structure. In the considered verification examples, reduced drifts at the top location of the building systems are validated against static wind pressure loads and static earthquake loads. The suggested hybrid building system will improve the safety and reliability of the new or existing building system in terms of more than 30% reduced drift and vibration through the development of convergence of tall buildings and spatial structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.495-501
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• 2001

In this paper, a new technique which models the joints characteristics through reduction of DOFs of structures with joints using component mode synthesis (CMS) method is proposed. Bolt joints are modeled by mass-spring systems. Also generalized mass and stiffness matrices for this models are introduced. Because bolt joints have influence on eigenvalues of structures, exact eigenvalues from modal test are used. The results show that the behaviors of structures with bolt joints depend to a large extent on the translational DOFs and not on rotational DOFs of mass and stiffness matrices of bolts. Furthermore it is confirmed that lumped mass-spring systems as models of bolt joints are effective models considering the facts that joint characteristics converged to constant values in some iterations and eignevalues from proposed method are in good agreement with ones from modal test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.307-312
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• 1995

장거리 시스템의 경우에 있어서 기동과 정지 시의 동적하중은 구동부 입력크기의 변화와 구동부간이 기동 시간차이로부터 발생되며, 벨트로 전파되어 장력변화를 일으키고, 과도한 장력의 변화는 인장과 압축의 탄성파로 벨트요소의 응력을 증가시키며, 벨트, 풀리, 아이들러(idler)등의 벨트요소들을 파괴시킨다. 따라서 동적해석에 의한 설계가 필수적으로 요구되어 벨트의 동적거동 해석에 대한 연구가 많이 수행되고 있다. 본 연구에서는 벨트 컨베이어 시스템을 집중질량모델(lumped mass model)로 근사하여 모델링하는 방법을 도입하여 세부요소에 대한 운동방정식을 유도하고, 각 요소 모델링을 결합하여 전체 운동방정식을 수립하였으며, 예제 시스템에 적용하여 동적거동을 해석하였다. 예제 시스템에 있어서 기동시의 구동입력을 두 가지 형태의 입력을 이용하였고, 정지시에는 구동부 브레이크가 없는 경우로 정상운전상태에서 순간적으로 구동부의 동력을 제거하는 방법을 적용하였다. 시뮬레이션 결과를 통하여 기동시의 구동입력을 적절히 제어하므로 벨트 속도와 장력의 변화를 줄일 수 있는 입력형태를 결정할 수 있었고, 이 때의 테이크업의 운동도 구할 수 있었다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.2 s.95
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• pp.219-224
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• 2005

Vibration response of the tower structure of a 750kW wind turbine (W/T) generator is investigated by measurement and analysis. Acceleration response of the W/T tower under various operation condition is monitored in real time by the vibration monitoring system using LabVIEW. Resonance state of the tower structure is diagnosed in the operating speed range. Resonance frequency range of the test model is investigated with the wind speed data of the test site. To predict the tower resonance frequency, tower is modeled as an equivalent beam with a lumped mass and Rayleigh energy method is applied. Calculated tower bending frequency is in good agreement with the measured value and the result shows that the simplified model can be used in the design stage of the W/T tower.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.58-58
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• 2011

고밀도 플라즈마는 재료의 표면 처리, 박막의 증착, 식각 등에 집중적으로 응용되어 왔다. 주요이슈들은 전자기적 관점에서 바라본 전력 전달 메커니즘, 전자 충돌 과정을 포함하는 원자물리학적 과정들, 흡착, 탈착, 스퍼터링 등의 표면 화학 공정들이다. 각각을 이해하는 도구들은 주로 플라즈마 진단 장치(전기탐침, 분광기, 질량분석기, 전압-전류측정기)와 초고진공 표면 분석 장치(XPS, AES)및 실시간 표면 분광 해석기등이 이용되어 왔다. 여기에 유체 모델을 이용한 3차원 수치 해석이 가능해지면서 균일한 공정 결과를 얻기 위한 플라즈마 증착/식각 시스템 디자인 원리의 많은 부분의 이해가 진전을 이루고 있다. 본 발표에서는 고밀도 유도 결합 플라즈마 발생 시스템, 마그네트론 스퍼터링, 펄스 전원 등의 영향이 어떻게 박막 가공 시스템의 성능에 영향을 주고 있으며 이에 대한 해결 노력들이 갖는 학문적, 실제적인 의미에 대해서 고찰한다.

• Journal of the Korean Society for Railway
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• v.6 no.4
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• pp.279-285
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• 2003

In an electric traction system in which power is supplied from a catenary via a pantograph, the mechanical design of the catenary and pantograph is clearly of importance in relation to the problem of current collection at high speed. A computer-simulation technique is used to study the effects of changing parameters of pantograph and catenary on the quality of current collection at high speed. The current collection system is evaluated on the basis of the contact-force variations and displacement responses of the pantograph and contact wire. This study shows that current-collection quality is determined primarily by the overhead line parameters rather than by the pantograph. The results can be applied to optimize the design of current-collection systems.