• 대한기계학회논문집
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• 제14권1호
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• pp.13-22
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• 1990

본 연구에서는 일반적인 셸 요소에 대해 von Mises의 항복조건에 입각한 탄소 성 구성방정식과 total Lagrangian식을 바탕으로한 비선형 해석이론에 Lagrange Mult- iplier식을 이용한 구속조건(constraints)을 도입하여, 중첩된 비선형 구조물이 갖고 있는 제반 비선형성을 고려할 수 있도록 수식화하였으며, 이를 엄밀해를 구할 수 있는 두개의 외팔보가 중첩된 경우에 적용하여 엄밀해와 비교하였으며, 또한 실제적으로 국 산 핵연료 집합체에 사용되는 각 홀드다운 스프링 집합체에 대한 특성 해석을 수행하 여 그 결과를 실험치와 비교하여 그 비교치가 근사함을 보임으로써 본 방법의 신뢰성 과 효용성을 보였다.

• Nuclear Engineering and Technology
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• 제52권3호
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• pp.621-625
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• 2020

Cast austenitic stainless steel (CASS) is used for fabricating different components of the primary reactor coolant system of pressurized water reactors. However, the thermal embrittlement of CASS resulting from long-term operation causes structural safety problems. Ultrasonic testing for flaw detection has been used to assess the thermal embrittlement of CASS; however, the high scattering and attenuation of the ultrasonic wave propagating through CASS make it difficult to accurately quantify the flaw size. In this paper, we present a different approach for evaluating the thermal embrittlement of CASS by assessing changes in the material properties of CASS using a nonlinear ultrasonic technique, which is a potential nondestructive method. For the evaluation, we prepared CF8M specimens that were thermally aged under four different heating conditions. Nonlinear ultrasonic measurements were performed using a contact piezoelectric method to obtain the relative ultrasonic nonlinearity parameter, and a mini-sized tensile test was performed to investigate the correlation of the parameter with material properties. Experimental results showed that the ultrasonic nonlinearity parameter had a correlation with tensile properties such as the tensile strength and elongation. Consequently, we could confirm the applicability of the nonlinear ultrasonic technique to the evaluation of the thermal embrittlement of CASS.

• 한국지능시스템학회논문지
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• 제21권3호
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• pp.372-377
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• 2011

본 논문에서는 하이브리드 자기베어링 시스템의 효과적인 제어 방안 마련을 위한 기법 제안을 목표로 한다. 자기베어링 시스템에서의 제어 목적이란, 회전자(rotor)의 회전을 외부의 물리적 접촉 없이 자기장의 힘만으로 동작하도록 베어링의 위치를 최대한 센터에 위치케 하는 것이다. 기본적으로 자기베어링 시스템은 비선형적 동적방정식으로 구성되기 때문에, 제어 목적을 달성하기 위한 제어 입력 신호의 설계가 쉽지 않으며, 외부 환경의 영향에 따른 시스템 파라미터 변화율에도 많이 민감한 편이다. 본 논문에서는 자기베어링 시스템의 비선형성에 대한 해석 방안으로 퍼지 모델링을 통해 시스템을 재해석하게 되며, 제어 목적에 대한 설정은 선형행렬 부등식 기반 안정화 문제로 변환하여 제어 입력을 설계하고자 한다. 해당 퍼지 모델링 및 제어 알고리즘의 정당성은 시뮬레이션을 통해 검증된다.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1540-1546
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• 2000

Recently, force measurement systems are commonly used in many industrial fields and the precision of the measurement system is getting more important as the industry needs more precise tools and in struments to make high quality products. However, a high precision force measurement system is hard to make unless we know precisely the causes, quality and quantity of measurement errors in advance. In this work, many possible mechanical causes of measurement errors are reviewed including ratio of length to diameter of sensing part, radius of contact area, radius of bearing part, ratio of material properties and change of boundary conditions. Also, the measurement errors are analyzed by nonlinear finite element method and the nonlinear behavior of the errors are investigated. The results can be used to design force measurement systems and expected to be very useful especially for compact type load cells.

• 대한기계학회논문집A
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• 제20권10호
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• pp.3186-3198
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• 1996

When a robot is to have contact with its enviornment, such as a medi-care robot, it would be advantageous for the robot to have a high compliance. For this reason, a robot having not only a flexible link but also an actuator with compliance, is desirable. This paper is concerned with the position and vibration control of 1 degree of freedom flexible robot using a pneumatic artificial muscle actuator. The dynamics of the manipulator assumed to be and Euler-Bernoulli beam are derived on the basis of the linear mathematical modle. Although this pneumatic artifical muscle actuator has many merits for the compliance robot, it is difficult to make an effective control scheme of this system because of ths nonlinearity and uncertainty on the dynamics of the actuator. By designing a controller using .mu.-synthesis, robust performance against measurement noise, various modeling uncertainties on the dynamics of the servo valve, actuator and mainpulator, is achieved. The effectiveness of the proposed control method is illustrated through simulations and experiments.

• 대한기계학회논문집A
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• 제33권11호
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• pp.1202-1208
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• 2009

An inverse finite element (FE) model parameter estimation algorithm can be used to characterize mechanical properties of biological tissues. Using this algorithm, we can consider the influence of material nonlinearity, contact mechanics, complex boundary conditions, and geometrical constraints in the modeling. In this study, biomechanical experiments on macro and micro samples are conducted and characterized with the developed algorithm. Macro scale experiments were performed to measure the force response of porcine livers against mechanical loadings using one-dimensional indentation device. The force response of the human liver cancer cells was also measured by the atomic force microscope (AFM). The mechanical behavior of porcine livers (macro) and human liver cancer cells (micro) were characterized with the algorithm via hyperelastic and linear viscoelastic models. The developed models are suitable for computing accurate reaction force on tools and deformation of biomechanical tissues.

• Steel and Composite Structures
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• 제22권1호
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• pp.91-112
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• 2016

In this paper, post-buckling behavior of sandwich plates with functionally graded (FG) face sheets under uniform temperature rise loading is examined based on both sinusoidal shear deformation theory and stress function. It is supposed that the sandwich plate is in contact with an elastic foundation during deformation, which acts in both compression and tension. Thermo-elastic non-homogeneous properties of FG layers change smoothly by the variation of power law within the thickness, and temperature dependency of material constituents is considered in the formulation. In the present development, Von Karman nonlinearity and initial geometrical imperfection of sandwich plate are also taken into account. By employing Galerkin method, analytical solutions of thermal buckling and post-buckling equilibrium paths for simply supported plates are determined. Numerical examples presented in the present study discuss the effects of gradient index, sandwich plate geometry, geometrical imperfection, temperature dependency, and the elastic foundation parameters.

• Geomechanics and Engineering
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• 제20권5호
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• pp.433-445
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• 2020

A new code, called PRaFULL (Piled Raft Foundation Under Lateral Load), was developed for the analysis of laterally loaded Combined Pile Raft Foundation (CPRF). The proposed code considers the contribution offered by the raft-soil contact and the interactions between all the CPRF system components. The nonlinear behaviour of the reinforced concrete pile and the soil are accounted. As shallower soil layers are of great relevance in the lateral response of a pile foundation, PRaFULL includes the possibility to consider layered soil profiles with appropriate properties. The shadowing effect on the ultimate soil pressure is accounted, when dealing with pile groups, as proposed by the Strain Wedge Model. PRaFULL BEM code obviously requires less computational resources compared to FEM (Finite Element Method) or FDM (Finite Difference Method) codes. The proposed code was validated in the linear elastic range by comparisons with the code APRAF (Analysis of Piled Raft Foundations). The reliability of the procedure to predict piled raft performance was then verified in nonlinear range by comparisons with both centrifuge tests and computer code PRAB.

• 대한기계학회논문집A
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• 제21권2호
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• pp.261-271
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• 1997

This paper presents the design process and characteristic test results of tension sensors for measuring the ultimate tension forces of surgical wires. Three types of sensor were designed and tested for calibration. The first two types which transfer the wire tension to the sensing element by direct contact have too much hysterisis errors due to the firctional effect. This error can be considerably reduced in the modified structure, where a cover and a loading button is used to transfer force and moment to the sensing element. The strains predicted by theoretical equations agree well with those by finite element calculations neglecting friction and the strains by finite element analysis considering friction are in good agreement with those measured by four strain gages. The modified ring type tension sensor developed in this paper is expected to be useful for measuring the tension of surgical wires with nonlinearity of 1.31%FS, hysterisis of 5.74%FS and repeatability of 0.19%FS.

• Steel and Composite Structures
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• 제7권5호
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• pp.405-419
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• 2007

This paper presents the development of some numerical models based on the results of laboratory tests performed on axially loaded RC columns strengthened with steel angles and strips. These numerical models consider the nonlinearity of the building materials and the effects of the contact interfaces between different materials. The results of the finite element models accurately describe the general behaviour of the strengthened columns. This study allows engineers to assess the relative importance of the mechanisms acting on the strengthened RC columns. Constructive recommendations are also provided in this paper.