• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.625-628
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• 1995

A static/implicit finite element code for sheet forming (ITAS3D) is parallelized on IBM SP 6000 multi-processor computer. Computing-load-balanced domain decomposition method and the direct solution method at each subdomain (and interface) equation are developed. The system of equations for each subdomain are constructed by condensation and calculated on each processor. Approximated operation counts are calculated to set up the nonlinear equation system for balancing the compute load on each subdomain. Th esquare cup tests with several numbers of elements are used in demonstrating the performance of this parallel implementation. This procedure are proved to be efficient for moderate number of processors, especially for large number of elements.

• KSTLE International Journal
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• 제2권1호
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• pp.46-54
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• 2001

The herringbone groove journal bearing (HGJB) has chevron type grooves on stationary or rotating member of the bearing so that they pump the lubricant inward the grooves when journal rotates. As a result, the pressure is generated around the journal so that the radial stiffness and dynamic stability are improved comparing to the plain journal bearing (PJB) when the bearing operates near the concentric condition. The narrow groove theory, conventionally adopted to simulate the concentric operation of HGJB, is limited to the infinite number of grooves. A numerical study of air-lubricated HGJB is presented for the finite number of grooves. The compressible isothermal Reynolds equation is solved by using Finite Element Method together with the Newton-Raphson iterative procedure and perturbation method. The solutions render the static and dynamic performances of HGJB. Comparison of present results with a PJB validates previously published finite difference solution. The HGJB's geometric parameters influence its static and dynamic characteristics. The optimum geometric parameters are presented for the air-lubricated HGJB in particular conditions.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.30-36
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• 1995

Conventionally design for multi-stage cold forging depends on the designer's experience and decision-making. Due to such non-deterministic nature of the process sequence design, a flexible inference engine is needed for process design expert system. In this study, A* searching algorithm was introduced to arrive at the vetter process sequence design considering the number of forming stages and levels of effective strain, effective stress, and forming load during the porcess. In order to optimize the process sequence in producing the final part, cost function was defined and minimized using the proposed A* searching algorithm. For verification of the designed forming sequences, forming experiments and finite element analyses were carried out in the present investigation. The developed expert system using A* searching algorithm can produce a flexible design system based on changes in the number of forming stages and weights.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.74-78
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• 2003

Stress analysis was conducted with finite element method to study the stress distributions in both single-pin and multi-pin loaded composite laminates. The various parameters involved in the design of the joint method were considered. The stress distributions in the vicinity of the holes were predicted considering the effects of various parameters such as the lay-ups, number of pins, number of rows, row spacing, and hole patterns. The results show that the performance of joint is greatly affected by these parameters.

• Geomechanics and Engineering
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• 제20권5호
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• pp.421-432
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• 2020

Cutting of rocks is very common encountered in tunneling and mining during underground excavations. A deep understanding of rock-tool interaction can promote industrial applications significantly. In this paper, a distinct element method based approach, PFC^3D, is adopted to simulate the rock cutting under different operation conditions (cutting velocity, depth of cut and rake angle) and with various tool geometries (tip angle, tip wear and tip shape). Simulation results showed that the cutting force and accumulated number of cracks increase with increasing cutting velocity, cut depth, tip angle and pick abrasion. The number of cracks and cutting force decrease with increasing negative rake angle and increase with increasing positive rake angle. The numerical approach can offer a better insight into the rock-tool interaction during the rock cutting process. The proposed numerical method can be used to assess the rock cuttability, to estimate the cutting performance, and to design the cutter head.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 추계학술대회논문집 - 한국공작기계학회
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• pp.428-433
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• 2000

A disassembility assessment has mostly depend on the subjective decision making from the qualitative element. The work of disassembly is already classified with given disassemble points from the symbolic chart method. It is not useful in the practical assessment because it is not specified. The new method of design for disassembility assessment(DFDA) is practical to introduce the fuzzy number as the conversion of quantitative element from qualitative. It is appled to compare the usefulness of air-cleaner in Korea-Japan passenger-vehicle.

• 한국분말재료학회지
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• 제29권4호
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• pp.303-308
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• 2022

The plastic deformation behavior of additively manufactured anisotropic structures are analyzed using the finite element method (FEM). Hill's quadratic anisotropic yield function is used, and a modified return-mapping method based on dual potential is presented. The plane stress biaxial loading condition is considered to investigate the number of iterations required for the convergence of the Newton-Raphson method during plastic deformation analysis. In this study, incompressible plastic deformation is considered, and the associated flow rule is assumed. The modified return-mapping method is implemented using the ABAQUS UMAT subroutine and effective in reducing the number of iterations in the Newton-Raphson method. The anisotropic tensile behavior is computed using the 3-dimensional FEM for two tensile specimens manufactured along orthogonal additive directions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.444-449
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• 2001

A numerical parametric study is conducted to simulate shock-induced combustion with a variation in freestream conditions. A steady combustion front is established if the freestream Mach number is above the Chapman-Jouguet speed of the mixture. On the other, an unsteady reaction front is established if the the freestream Mach number is below or at the Chapman-Jouguet speed of the mixture. The three cases have been simulated for Machs 4.18, 5.11, and 6.46 with a projectile diameter of 15 mm. Machs 4.18 and 5.11 shows an unsteady reaction front, whereas Mach 6.46 represents a steady reaction front. Thus Chapman-Jouguet speed is one of deciding factor for the instabilities to trigger.

• 한국수학사학회지
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• 제20권3호
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• pp.59-72
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• 2007

복소수 발견초기 수학자들은 복소수에 대한 거부감이 상당했으나 복소수의 대수적 연산에는 큰 어려움이 없었다. 복소수가 수학적 대상으로 인정받기까지 많은 시간이 필요했던 이유는 복소수의 기하적 해석에 많은 시행착오와 시간이 필요했기 때문이다. 본 논문은 복소수의 기하적 해석의 싹을 Euclid 원론에서 찾고, Descarte, Wallis, Wessel를 거치면서 그 싹이 틔어가는 과정을 밝히고 있다. 복소수의 기하적 해석에 대한 세 명의 수학자들의 생각은 서로 다르지만 밀접한 관계가 있다. 이들은 선분과 복소수의 관계에 주목하고, 곱셈 연산을 일반화하면서 복소수의 기하적 해석을 시도하였다.

• 한국수학사학회지
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• 제18권2호
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• pp.9-22
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• 2005

본 연구는 자연수 개념이 역사적으로 전개된 방식을 이해하는 것이 수학적$\cdot$ 교육적으로 매우 중요함에도 불구하고, 그 역사적 고찰이 미진한 상태에 있다는 데에 문제 의식을 갖고 출발하였다. 그리하여 자연수 개념이 역사적으로 어떻게 논의되어 왔는지 살펴보고자 하였다. 수학의 발달 과정에서 수가 어떤 의미를 지녔는지, 문화적$\cdot$사회적 요소가 수 개념을 이해하는 방식과 수 개념의 발달에 어떤 영향을 주었는지 밝힘으로써 자연수 개념에 대한 이해를 풍부하게 하고자 하였다. 그리고 자연수 개념의 역사에 나타난 특징을 드러내고자 하였다.