• 한국해양공학회지
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• 제28권5호
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• pp.452-465
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• 2014

The application of friction stir welding (FSW) technology has been extended to all industries, including shipbuilding. A heat transfer analysis evaluates the weldability of a welded work piece, and elasto-plastic analysis predicts the residual stress and deformation after welding. A thermal elasto-plastic analysis based on the heat transfer analysis results is most frequently used today. However, its application to large objects such as offshore structures and hulls is impractical owing to its long computational time. This paper proposes a new method, namely an equivalent strain method using the inherent strain, to overcome the disadvantages of the extended analysis time. In the present study, a residual stress analysis of FSW was performed using this equivalent strain method. Additionally, in order to reflect the external constraints in FSW, the reaction force was predicted using a neural network, Finally, the approach was verified by comparing the experimental results and thermal elasto-plastic analysis results for the calculated residual stress distribution.

• 대한기계학회논문집A
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• 제28권1호
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• pp.48-54
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• 2004

Generally, structural optimization is carried out based on external static loads. All forces have dynamic characteristics in the real world. Mathematical optimization with dynamic loads is extremely difficult in a large-scale problem due to the behaviors in the time domain. In practical applications, it is customary to transform the dynamic loads into static loads by dynamic factors, design codes, and etc. But the optimization results with the unreasonably transformed loads cannot give us good solutions. Recently, a systematic transformation has been proposed as an engineering algorithm. Equivalent static loads are made to generate the same displacement field as the one from dynamic loads at each time step of dynamic analysis. Thus, many load cases are used as the multiple loading conditions which are not costly to include in modem structural optimization. In this research, the proposed algorithm is applied to the optimization of flexible multibody dynamic systems. The equivalent static load is derived from the equations of motion of a flexible multibody dynamic system. A few examples that have been solved before are solved to be compared with the results from the proposed algorithm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 B
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• pp.635-637
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• 2000

To analyze the transient state of an induction motor, there have been studies for using the magnetic equivalent circuit method (MECM) instead of the time differential finite-element method, MECM which analyzes magnetic equivalent circuits after converting each part of an electric machine into the magnetic circuit elements. has the merits of short calculation-time and comparatively accurate results. To analyze an electric machine with MECM, we have to replace stator and rotor with the magnetic elements and express the air gap, where electromechanical energy conversion takes place, with the permeance. So in this paper, to analyze an Induction Motor with MECM, we express the magnetic equivalent circuit as algebraic equations and then as the matrix for solving easily them.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 B
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• pp.330-332
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• 2000

To analyze the transient state of an induction motor, there have been studies for using the magnetic equivalent circuit method(MECD) instead of the time differential finite-element method. MECD which analyzes magnetic equivalent circuits after converting each part of an electric machine into the magnetic circuit elements, has the merits of short calculation-time and comparatively accurate results. To analyze an electric machine with MECM, we have to replace stator and rotor with the magnetic elements and express the air gap, where electromechanical energy conversion takes place, with the permeance. So in this study, to analyze an Induction Motor with HECM, we express the magnetic equivalent circuit as algebraic equations and then as the matrix for solving easily them. In particular, all relations are formed with matrixes to solve Mathematically them in the programming process later. As a result, this theory will be the basis on the static and dynamic analysis of an Induction Motor.

• 한국군사과학기술학회지
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• 제3권1호
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• pp.26-37
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• 2000

This research paper deals with the problem of determining the optimal life time in terms of economical sense for a self-propelled artillery. Equivalent Annual Cost Method(EACM) is used to evaluate the optimal life time, based on the acquisition cost, and the operation and maintenance cost. It is assumed that the operation and maintenance cost includes the costs for spare parts, petroleum and ammunition for training. From the result of this study, the optimal life time for a self-propelled artillery is between 13.9 years and 16.1 years with 95% confidence interval.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 B
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• pp.506-508
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• 1998

In this paper, the optimal digital redesign is studied within the framework of fuzzy systems and dual-rate sampling control theory. An equivalent fast-rate discrete-time state-space model of the continuous-time system is constructed by using fuzzy inference systems. To obtain the optimal feedback gains developed in the continuous-time system, the constructed fuzzy system is converted into a continuous-time system. The developed continuous-time control law is converted into an equivalent slow-rate digital control law using the proposed digital redesign method. The digital redesign technique using a fuzzy model is employed to simulate the inverted pendulum dynamics.

• 한국산학기술학회논문지
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• 제12권1호
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• pp.32-37
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• 2011

본 연구에서는 구조해석을 통하여 차체의 전복 시에 있어서의 차체의 두께에 따른 변형량과 응력 변화를 고찰하여 보았다. 차체의 두께가 5t인 자동차에서는 2초일 때에 차체의 오른쪽 천장에서 7.5024mm의 최대변형이 일어났으며, 차체의 왼쪽 밑 부분에서 113.69 MPa의 최대응력을 받았다. 차체의 두께가 10t인 자동차에서는 2초일 때에 차체의 오른쪽 천장에서 1.2557mm로 최대의 변형이 일어났으며 차체의 왼쪽 밑 부분에서 15.134 MPa의 최대응력이 발생했다. 차체의 두께가 15t인 자동차에서는 2초일 때에 0.42529mm로서 차체의 오른쪽 천장에서 최대의 변형이 일어났으며 응력은 2초일 때에 차체의 왼쪽 밑 부분에서 4.405MPa의 최대응력이 작용되었다. 두께가 15mm보다 커지는 경우에는 시간에 따른 응력 및 변형율의 분포가 고르게 나타나고 있어 설계의 안전성을 보이고 있다.

• 한국전산구조공학회논문집
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• 제22권3호
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• pp.231-242
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• 2009

스카이브릿지의 연결시스템은 일반적으로 매우 큰 비선형성을 가지고 있으므로 연결된 건물의 동적거동을 정확하게 예측하여 스카이브릿지를 설계하기 위해서는 경계비선형 시간이력해석이 필요하다. 그러나 일반적인 유한요소 해석모델을 사용하여 전체 고층건물을 모형화하고 설계를 위하여 반복적인 경계비선형 시간이력해석을 수행한다면 해석에 소요되는 노력과 시간이 매우 클 것이다. 따라서 본 연구에서는 스카이브릿지로 연결된 고층건물의 효율적인 동적해석 및 진동제어 성능 평가를 위하여 벨트월의 효과를 고려한 등가의 캔틸레버모델을 제안하였다. 제안된 등가모델의 효율성 및 정확성을 검토하기 위하여 스카이브릿지로 연결된 49층과 42층 건물을 예제구조물로 사용하였고 풍하중에 대한 경계비선형 시간이력해석을 수행하였다. 해석결과 제안된 등가모델을 사용하면 스카이브릿지로 연결된 고층건물의 동적응답을 매우 효율적으로 파악할 수 있다는 것을 확인하였다.

• 한국식품과학회지
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• 제25권6호
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• pp.643-648
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• 1993

표준온도 상당시간을 이용하여 규칙적인 온도변화 조건에서 식품의 품질변화를 간편하게 예측하는 근사식의 유효성을 밝히기 위하여, 비등온 가속조건 및 상온저장 조건에서 Sucrose 가수분해속도를 측정한 설험자료로 비교, 분석을 분석하였다. 정속가열 (定速加熱) 가속(加速)실험을 통해 구한 sucrose의 가수분해 반응은 1차 반응이고, 활성화에너지는 25.84kcal/mol이었으며, 반응속도상수는 pH가 감소함에 따라 직선적으로 증가하였다. 하루 동안의 온도변화를 sine wave 형태 온도변화로 가정하고 하루 동안에 일어난 품질변화를 표준온도 $T_{ref}$에서 몇일 동안에 일어난 변화에 상당하는가를 의미하는 표준온도 상당시간 $T_{eq.i}$를 이용하여 품질변화를 근사적으로 간단히 예측하는 방법을 제안하였다. Sucrose 액체 모델 시스템을 sine wave 형태의 규칙적인 온도변화 조건에서의 가속 가수분해실험 결과와 $T_{eq.i}$를 이용하여 품질변화를 computer simulation한 결과, 실험값과 예측값과의 상관계수는 0.99로서 잘 일치하였으므로 표준온도상당시간을 이용한 예측 모델의 유효함을 확인하였다. 뿐만 아니라 sucrose 모델 시스템을 실제 상온 저장한 실험결과와 계절적 온도변화를 computer simulation하여 예측한 값과는 상관계수가 0.92로서 잘 일치하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.109-114
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• 2002

The purpose of this study is to propose the general method for evaluating the equivalent damping ratios of a structure with supplemental response control dampers. We define Lyapunov function of which derivative can be expressed in autoregressive form and evaluate the equivalent damping ratios by using Lyapunov function and its derivative. This Lyapunov function may be called as generalized structural energy. In this study, it is assumed that the response of a structure is stationary random process and control dampers do not affect the modal shapes of a structure, and the structure has proportional damping. Proposed method can be used to get the equivalent damping ratios of a structure with non-linear control dampers such as friction dampers as well as linear control dampers. To show the effectiveness of the proposed method. we evaluate the equivalent damping ratios of a structure with viscous dampers. AMDs. and friction dampers. The equivalent damping ratios from proposed method are compared to those from eigenvalue analysis for linear control dampers. and those from time history analysis for non-linear control dampers. respectively.