• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.37-43
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• 2000

The effect of the alignment of the contacting bodies is concerned. Tilting of a body (indenter) is regarded as a mis-alignment. Recently developed method fur evaluating the contact normal traction is introduced and discussed, in which piecewise parabolic profile is considered as a generalized contact profile. Indentation by a wedge with rounded apex is solved as an example problem. In the case of partial slip regime, the variation of shear traction is examined during the closed path of shear force by using the efficient numerical technique. Concentration of the slip region is also investigated. By evaluating the energy dissipation from the contact surface, the effect of the mis-alignment-alignment on wear is discussed.

• 대한기계학회논문집
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• 제18권1호
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• pp.150-155
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• 1994

An Approximate solution for plane two-dimensional incompressible laminar jet issuing from a finite opening with arbitrary initial profile into the same ambient fluid is proposed. For an arbitrary initial velocity profile, the problem is generated from the well known similarity solution for the jet of infinitesimal opening and provides good approximations in the region where the similarity solution cannot be used as an approximation. The asymptotic behavior of this solution is investigated and it is shown that, as goes downstream, the present solution approachs the similarity solution.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제24권3호
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• pp.293-303
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• 2020

The present work aims to analyzed the transient thermoelastic stress analysis of a thin circular plate with uniform internal heat generation. Initially, the plate is characterized by a parabolic temperature distribution along the z-direction given by T = T₀(r, z) and perfectly insulated at the ends z = 0 and z = h. For times t > 0, the surface r = a is subjected to convection heat transfer with convection coefficient h_c and fluid temperature T_∞. The integral transform method used to obtain the analytical solution for temperature, displacement, and thermal stresses. The associated thermoelastic field is analyzed by making use of the temperature and thermoelastic displacement potential function. Numerical results are carried out with the help of computational software PTC Mathcad Prime-3.1 and shown in figures.

• Smart Structures and Systems
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• 제16권1호
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• pp.27-46
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• 2015

Active surface adjustment of cable net structures is becoming significant when large-size cable net structures are widely applied in various fields, especially in satellite antennas. A general-duty adjustment method based on active cables is proposed to achieve active surface adjustment or surface profile reconfiguration of cable net structures. Piezoelectric actuators and voice coil actuators are selected for constructing active cable structures and their simplified mechanical models are proposed. A bilevel optimization model of active surface adjustment is proposed based on the nonlinear static model established by the direct stiffness method. A pattern search algorithm combined with the trust region method is developed to solve this optimization problem. Numerical examples of a parabolic cable net reflector are analyzed and different distribution types of active cables are compared.

• 대한설비공학회지:설비저널
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• 제10권3호
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• pp.185-219
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• 1981

To analyze two dimensional incompressible laminar natural convection in a rectangular enclosure heated from below and cooled by a horizontal ceiling and two vertical walls, he primitive Navier-Stokes equations and the energy equation were solved numerically in time dependent form by a marker and cell method. A successive over-relaxation method for the elliptic portion of the problem and an explicit method for the parabolic portion were applied for the range of Grashoff number of $5{\times}10^3\;to\;5{\times}10^4$ to get the transient and steady state dimensionless temperature and velocity profiles. For the range of aspect ratio $L/H{\leqq}2.4$ in which only a pair of convection rolls exists mean Nusselt number calculated are as follows : $$N_{NU}0.89\;N_{Gr}^{0.2}(H/L)^{0.45}$$ By path lines drawn by marker particle trajectories roll number of cellular motion were observed for various aspect ratio of the enclosure.

• 한국해안해양공학회지
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• 제4권2호
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• pp.59-62
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• 1992

경사가 일정한 해안에서 단조파의 쇄파조건을 다룬 Carrier-Greenspan 이논을 일반화시켜 복잡한 실제 지형에까지 적용시킬 수 있게 하였으며 따라서 종래 주로 경험에만 의존하던 쇄파대내의 파낭변형에 이논적 배경을 제공하였다. 포물선형태의 지형을 대상으로 계산하였으며 이들 결과로부터 비선형성이 강한 쳐오름(run-up) 문제를 선형화시킴으로 나타나는 영향에 대하여도 검토하였다.

• Journal of applied mathematics & informatics
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• 제40권3_4호
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• pp.491-505
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• 2022

This paper is concerned with singularly perturbed convection-diffusion parabolic partial differential equations which have time-delayed. We used the Crank-Nicolson(CN) scheme to build a fitted operator to solve the problem. The underling method's stability is investigated, and it is found to be unconditionally stable. We have shown graphically the unstableness of CN-scheme without fitting factor. The order of convergence of the present method is shown to be second order both in space and time in relation to the perturbation parameter. The efficiency of the scheme is demonstrated using model examples and the proposed technique is more accurate than the standard CN-method and some methods available in the literature, according to the findings.

• 한국학교수학회논문집
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• 제24권2호
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• pp.173-190
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• 2021

본 연구는 Newton의 의 핵심으로 일컬어지는 역제곱 법칙의 증명을 기하학적 극한과 관련하여 분석하고, 이를 수학교육에 활용하는 방안과 관련한 교육적 시사점을 제공하고자 하였다. Newton은 무한소에 대한 논쟁을 의식하여 전통적인 Euclid의 기하 방식으로 역학 문제를 해결하였다. Newton은 힘, 시간, 관성 궤도 이탈 정도 등을 기하 선분으로 표현함으로써 역학을 기하의 차원에 포함시키는 결과를 이뤄냈다. Newton은 특히 포물선 근사, 다각형 근사, 선분의 비의 극한이라는 기하학적 극한을 도입함으로써 Euclid 기하를 역학을 아우르는 새로운 차원으로 발전시킬 수 있었다. 이러한 분석을 바탕으로 Newton의 기하학적 극한을 수학의 유용성을 보여주는 도구로 활용, 곡선면적은 정적분이라는 통념을 깨는 수단으로 활용할 것을 제안하였다. 더불어 학교수학에서 기하학적 극한의 바람직한 활용을 돕기 위해서는 미시 세계에서의 동등성 확대 강조, 발견술로서 활용하게끔 유도하는 질문 활용, 미시 세계에서 선분의 동등성 파악에는 비의 접근이 유용하다는 인식을 돕는 과정이 필요할 것이라는 교육적 시사점을 제안하였다.

• Tribology and Lubricants
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• 제1권1호
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• pp.46-58
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• 1985

피스톤링과 실린더벽 사이의 윤활이 왕복운동을 하며 동하중을 받는 포물선형의 슬라이드 베어링의 유체 윤활로 보고 전개하였다. 싸이클 상의 유막 두께의 변화, 윤활유 운반과 마찰력을 계산하는 과정이 개략적으로 설명되었고, 이들 성능 특성들에 대한 링 높이, 링 앞면 곡률반경과 링의 비대칭의 영향을 고찰하였다. 단독링에 대한 해석결과를 조금 더 복잡한 링 팩에 대해 확대 적용하였다. 링의 부하가 되는 링 주위의 압력들은 실험적으로 또는 가스 흐름 해석으로부터 얻을 수 있는데 본 연구에서는 후자를 택하였다. 링팩에서의 유체 연속 및 윤활유 부족에 따른 수치 해석에 주안점을 두었다.

• 제어로봇시스템학회논문지
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• 제21권12호
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• pp.1193-1200
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• 2015

An effective swing trajectory of legged robots is different from the swing trajectories of humans or animals because of different dynamic characteristics. Therefore, it is important to find optimal parameters through experiments. This paper proposes a real-time nonlinear programming (RTNLP) method for optimization of the swing trajectory of the legged robot. For parameterization of the trajectory, the swing trajectory is approximated to parabolic and cubic spline curves. The robotic leg is position-controlled by a high-gain controller, and a cost function is selected such that the sum of the motor inputs and tracking errors at each joint is minimized. A simplified dynamic model is used to simulate the dynamics of a robotic leg. The purpose of the simulation is to find the feasibility of the optimization problem before an actual experiment occurs. Finally, an experiment is carried out on a real robotic leg with two degrees of freedom. For both the simulation and the experiment, the design variables converge to a feasible point, reducing the cost value.