• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.133-140
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• 2019

In this paper, the penetration process of Shaped charge jet(SCJ) was simulated through finite element analysis to obtain physical quantities such as jet incidence velocity, penetration rate, and penetration increment. As a result of applying these physical quantities to the hydrodynamic theory, it was confirmed that the penetration efficiency of the jet with a high incident velocity is higher than that of the following slow jet. This efficiency decreased sharply when the jet was slower than the hydrodynamic limit(HL). On the other hand, the comparison of penetration increment and jet consumption over time showed that the length extension effect should be considered for SCJ's theoretical penetration analysis.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.369-374
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• 2000

The buckling of two elastic layers bonded to a semi-infinite substrate under a transverse compressive plane strain is investigated. Incremental deformation theory is employed to describe the buckling behavior of both two isotropic layers and the semi-infinite substrate. The problem is converted to an eigenvalue-eigenvector case, from which the critical buckling strain and the wavelength of the buckled shape are obtained. The results are presented on the effects of the layer geometries and material properties on the buckling behavior.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.177-184
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• 2000

In this work, some inaccuracies and limitation of prior indentation theory, which is based on the deformation theory of plasticity and experimental observations, are first investigated. Then effects of major material properties on the configuration of indentation load-deflection curve are examined via incremental plasticity theory based finite element analyses. It is confirmed that subindenter deformation and stress-strain distribution from the deformation theory of plasticity are quite dissimilar to those from incremental theory of plasticity. We finally suggest the optimal data acquisition location, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.166-171
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• 1998

본 논문에서는 고체구조물의 비선형변형해석에 대하여 일반이론으로 개발된 수치해법을 단순 고체 구조물인 일차원 봉 문제에 적용하여 그 변형해석을 수행 하였다. 정확한 해를 구하기 위하여 증분 뉴톤-랩슨방법이 수정 보완 사용되었다. 또한 개발된 비선형유한요소법의 검증을 위하여 수학적인 정해가 존재하는 균일한 체력이 작용하는 단순봉의 변형을 해석하여 그 결과를 수학적인 정해와 비교하였다. 비교 결과 본 논문을 통하여 개발된 비선형 유한요소법의 정확성이 입증되었다.

• Journal of the Korean Institute of Intelligent Systems
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• v.21 no.2
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• pp.230-236
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• 2011

This paper proposes the possibility which the fuzzy theory can be used to improve the performance of the parabolic SAR(Stop-And-Reverse) indicator in the trading systems for stock market. The simulation results with data of the KOSPI 200 future show that the occurred number of trading signals and the false signals in the proposed fuzzy SAR indicator is less than that in the conventional SAR indicator. In the conventional SAR system, the incremental value of the acceleration factor is usually setted as 0.02 and the maximum value of the acceleration factor is usually limited as 0.2. But in the proposed fuzzy SAR system, the incremental value and the maximum value of the acceleration factor are automatically adjusted by using the fuzzy rules, which are designed based-on the difference between short-term moving average and medium-term moving average and also based-on the slope of short-term moving average.

• Journal of Korean Society of Steel Construction
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• v.12 no.1 s.44
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• pp.29-43
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• 2000

In this study, the computationally efficient inelastic buckling analysis program is developed to be used as the research tool in finding buckling strength of inelastic members. The program can determine buckling loads and buckled shapes of elastic and inelastic members which failed by flexural, lateral-torsional and/or local buckling. It can analyze singly and doubly symmetric I-shape members. In the program, the web of the member is modeled using the plate element and the flanges are modeled by beam elements. Multilinear isotropic hardening rule and the incremental theory of plasticity are used to simulate the inelastic stress-strain relationship from material tests. The program is verified using theoretical solutions and experimental results. The results from the program show good agreement with those from experiments and theory.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.159-164
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• 1988

The directions of the principal strain increment, stress, and stress increment during rotation of the principal stress axes at any stress level was studied for $K_0$-consolidated clay using torsion shear apparatus with individual control of the vertical stress, the confining pressure, and the shear stress on hollow cylinder specimens under undrained and drained condition. The torsion shear tests were performed according to predetermined stress-paths, which were chosen to cover over the full range of rotation of principal stress axes. The test results indicated that the strain increment vectors at failure coincided with the stress vectors. That is, the direction of strain increment coincided with the direction of stress increment at small stress levels and with the direction of stress at higher stress levels, which indicated that the behavior of clay was transfered from elastic to plastic as the stress level was increased. The applicability of the elastoplastic theory for modeling of the behavior of clay during rotation of the principal stress axes was given.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.3-17
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• 1999

Torsion shear tests under various stress paths were performed to study the behavior of sand during large stress reversal. The stress paths can be classified into the clockwise and the counterclockwise according to torque applied to specimen, and the directions of plastic strain incremental on the stress paths including large stress reversal are compared with the direction of stress state and stress incremental. From test results, the isotropic hardening theory using the principle of St. Venant desirably showed that direction of plastic strain incremental coincided with stress state on primary loading part and nearby failure point, but it might result in a rough approximation on part of unloading and reloading by stress reversal.

• Computational Structural Engineering
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• v.11 no.4
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• pp.155-168
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• 1998

보강된 판 및 쉘구조의 안정성 및 후좌굴을 포함하는 기하학적 비선형 해석을 수행하기 위하여, total Lagrangian formulation에 근거한 연속체의 증분평형방정식으로부터 변형된 쉘요소인 유한요소이론을 제시하였다. 쉘구조의 곡률이 불연속적으로 변하거나 쉘부재들이 유한한 각도로 만나는 보강된 판 및 쉘구조의 비선형 해석이 가능하도록 주부재와 보강재 간의 연결점에 대한 일반적인 변환관계를 제시하였으며 좌굴해석 및 기하학적 비선형해석의 경우에 해의 정확성 및 수렴성을 개선시키기 위하여 접선강도행렬 산정시 회전각의 2차항을 포함시켰다. 또한, shear locking 현상을 극복하기 위하여 감차적분을 적용하였고 쉘구조의 좌굴해석에서는 power method를 적용하여 해석의 효율을 높였으며, 후좌굴해석에서는 변위 및 하중증분법을 적절히 결합시켜 보강된 쉘구조의 후좌굴 거동추적이 용이하였다. 또한, 입력자료를 손쉽게 준비하고 좌굴모드 및 후좌굴거동을 효율적으로 분석하기 위하여 전, 후 처리 프로그램을 개발하였고 다양한 해석예제를 통하여 다른 문헌의 해석결과를 비교함으로써 본 연구에서 개발된 유한요소 해석프로그램의 타당성 및 정확성을 입증하였다.

• Computational Structural Engineering
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• v.10 no.4
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• pp.205-216
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• 1997

In order to trace the lateral post-buckling behaviors of thin-wafled space frames, a geometrically nonlinear finite element formulation is presented by applying incremental equilibrium equations based on the updated Lagrangian formulation and introducing Vlasov's assumption. The improved displacement field for symmetric thin-walled cross sections is introduced based on inclusion of second order terms of finite rotations, and the potential energy corresponding to the semitangential rotations and moments is consistently derived. For finite element analysis, tangent stiffness matrices of the thinwalled space frame element with 7 degrees of freedom including the restrained warping for each node are derived by using the Hermition polynomials as shape functions. A co-rotational formulation in order to evaluate the unbalanced loads is presented by separating the rigid body rotations and pure deformations from incremental displacements and evaluating the updated direction cosines of the frame element due to rigid body rotations and incremental member forces from pure deformations. Finite element solutions for the spatial buckling and post-buckling analysis of thin-walled space frames are presented and compared with available solutions and other researcher's results.