• 대한기계학회논문집A
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• 제26권7호
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• pp.1270-1279
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• 2002

Residual stress is a dominant obstacle to efficient production and safe usage of device by deteriorating the mechanical strength and failure properties. Therefore, we proposed a new thin film stress-analyzing technique using a nanoindentation method. For this aim, the shape change in the indentation load-depth curve during the stress-relief in film was theoretically modeled. The change in indentation depth by load-controlled stress relaxation process was related to the increase or decrease in the applied load using the elastic flat punch theory. Finally, the residual stress in thin film was calculated from the changed applied load based on the equivalent stress interaction model. The evaluated stresses for diamond-like carbon films from this nanoindentation analysis were consistent with the results from the conventional curvature method.

• Structural Engineering and Mechanics
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• 제33권5호
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• pp.589-604
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• 2009

In the field of predicting structural safety and reliability the operating conditions play an essential role. Since the time and cost limitations are a significant factors in engineering it is important to predict the future operating conditions as close to the actual state as possible from small amount of available data. Because of the randomness of the environment the shape of measured load spectra can vary considerably and therefore simple distribution functions are frequently not sufficient for their modelling. Thus mixed distribution functions have to be used. In general their major weakness is the complicated calculation of unknown parameters. The scope of the paper is to investigate the load spectra growth for actual operating conditions and to investigate the modelling and extrapolation of load spectra with algorithm for mixed distribution estimation, REBMIX. The data obtained from the measurements of wheel forces and the braking moment on proving ground is used to generate load spectra.

• 한국지열·수열에너지학회논문집
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• 제13권1호
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• pp.7-13
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• 2017

In order to use and manage the building energy efficiently, it is necessary to minimize building energy consumptions, and establish operation plans of various equipment. The maximum heating and cooling load calculation is an essential way in various equipment selections, and the annual building load calculation is used in forecasting & evaluating the LCC required for operation plan. In this study, noting that the annual building load changes depending on outside temperature around year, we propose a predicting method of annual building load. By using the $4^{th}$ polynomial function that have two double radix and a feature the $f(x)=a^4$ in x = 0 condition, we can calculate annual building load very easily only with the two result (maximum heating and cooling load) and a minimum parameters.

• Nuclear Engineering and Technology
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• 제52권1호
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• pp.78-86
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• 2020

The operation and monitoring (OM) interface is the digital medium between nuclear power system and operators. The cognitive load of OM interface has an important effect on the operation errors made by operator during OM task between operator and computer. The cognitive load model of OM interface is constructed for analysing the composition and influencing factors of OM interface cognitive load. And to study the coping strategies and methods for cognitive load of nuclear power system. An experiment method based on eye movement is proposed to measure the cognitive load of OM interface. Experiment case is carried out with 20 subjects and typical OM interface of a nuclear power system simulator. The OM interface is optimized based on the experiment results. And the results comparison between the original OM interface and the optimized OM interface shows that the cognitive load model and proposed method is valuable contributions in reducing the cognitive load and improving the interaction efficiency of OM tasks.

• Tribology and Lubricants
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• 제18권3호
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• pp.194-203
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• 2002

This paper is the first step fur thermo-mechanical stress analyses of part with coated layer under contact load. A lot of coated material is applied in many structures to endure severe situation, like thermal stresses, high temperature gradients, irradiation, impacts by microscopic meteorites, and so on. In this part we are going to apply the FEM to analyze space parts with a coated layer subjected to a contact load thermo-mechanically. Coating layer is very thin in comparision with the structure, therefore it should take more times and behaviors to analyze whole model. In these reason we develop the FEM method of analyzing part with coated layer under contact load using partial model. Steady state temperature distribution of the part is obtained first, and then we apply quasi-static external load on the part. To obtain the final stage of solution, we compute the total solution, and by subtracting the thermal strain from the total ones we get the mechanical strains to compute stresses of the parts. In using the FEM, one has to discretize the model into many sub-domain, finite elements. The method is consisited of two steps. First step is to analyze the whole model with rather coarse meshes. Second step we cut a small region near the loading point, and analyze with very fine meshes. This method is allowable by the Saint-Venant's principle. And then, we finally shall check the therma1 load on the stresses of the space part with coating layer with or without substrate cracks. Then, we predict the actual behaviors of the part used in space.

• Composites Research
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• 제27권6호
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• pp.213-218
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• 2014

본 논문에서는 특성길이 및 특성 곡선 방법을 굽힘 하중 상태의 복합재 기계적 체결부에 적용하여 강도를 예측하는 연구를 수행하였다. 선행 연구들이 특성길이 및 특성 곡선 방법을 인장과 압축 하중에만 적용한 것과 달리 본 연구에서는 굽힘 하중에 적용하고 그 가능성을 확인했다. 체결부 파손 해석을 위해 ABAQUS를 사용하여 핀과 모재의 접촉 및 마찰을 고려한 비선형 해석을 수행하였다. 해석결과를 이용하여 얻은 특성 곡선상에서 Tsai-Wu 이론을 적용하여 파손 및 파단 양상을 예측하였다. 또한 복합재 시편에 굽힘 하중을 가해 파손하중을 알아보는 실험을 통해 검증한 결과 해석으로 얻은 복합재 체결부의 파손하중이 실험 결과와 매우 잘 일치함을 확인하였다. 결론적으로 특성길이 및 특성 곡선 방법이 굽힘 하중 상태의 복합재 기계적 체결부의 강도를 비교적 잘 예측할 수 있다는 것을 알 수 있었다.

• 대한기계학회논문집A
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• 제20권6호
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• pp.1843-1853
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• 1996

The objective of this paper is to evaluate the crack stability of the nuclear main stresm pipes, considering the load reduction effect due to the presence of circumferential throuth-wall crack. Also, the optimization techniques are adoped tosimulate the crack effect on the elbow component of the piuping system. By using a general beam elemetn which contains a discontinuous cross-section, the piping analysis is accomplished to acquire the reduced load. Considering this reduced load, it is feasible for the LBB application in nuclear main stresm pipe. Also, by combining an optimization program and a genaral finite element analysis program, the appropriate dimensions of the simplified beam elemtn which represents the effect of crack in elbow could be successfully determined.

• 한국정밀공학회지
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• 제28권11호
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• pp.1316-1322
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• 2011

Most of the mechanical structures use bolting or spot welding for the whole structure. In recent years, bolting & rivets are used rather than the welding due to reassembly and repair. Analysis of bolted joints is so complicate that many conditions must be considered such as pre-load and contact, etc.. Bolted joint analysis is done by theoretical, experimental & numerical methods. However, numerical analysis in the bolted joint is used because the contact and stress in the joints are changed due to the pre-load. In this study, we analysis the slip and the deformation of the contact area in the joint depending on the pre-load and find the optimized bolting condition.

• 대한기계학회논문집B
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• 제37권11호
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• pp.1015-1022
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• 2013

본 연구에서는 현재 개발중인 200kW 급 마이크로 가스터빈의 운전 특성을 모사하였다. 세부적인 성능 데이터를 이용하여 부분부하 제어방식(터빈 입구온도 제어방식(constant TIT control)과 터빈 출구온도 제어방식(constant TET control))과 외기온도에 따른 성능 및 작동특성을 분석하였다. 넓은 운전 범위에 대하여 압축기 서지마진과 터빈 입출구 온도 같은 작동 파라미터의 민감도를 단위 연료량 변화에 따라 예측하였다. 정상상태 계산으로 부분부하 변동 시 최대서지마진의 감소에 대한 정보를 민감도 분석을 통해 알 수 있다.

• 대한기계학회논문집A
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• 제37권5호
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• pp.685-691
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• 2013

로드셀형 풍향풍속계는 바람의 벡터적 성질을 이용한다. 본 연구를 통해 개발된 풍향풍속계는 기존과 달리 풍속계의 날개부가 회전하지 않는 고정형이다. 로드셀형 풍향풍속계를 개발하기 위해서는 측정된 4개 날개의 압력비와 풍향, 압력합과 풍속사이의 관계식을 각각 도출해야 한다. 본 연구에서는 압력비와 풍향사이의 관계식을 도출하기 위하여 각각 ANSYS CFX를 이용한 해석적 접근과 풍동실험을 이용한 실험적 접근을 적용하였다. 해석시 $0^{\circ}$에서 $90^{\circ}$까지 $7.5^{\circ}$ 간격으로 풍향조건을, 실험시 $10^{\circ}$ 간격으로 10가지 풍향조건을 설정하였다. 또한 실험 및 해석적 접근을 통해 압력비와 풍향사이의 관계식을 도출하였다.