• Computational Structural Engineering
• /
• v.11 no.4
• /
• pp.187-196
• /
• 1998

불연속 갤러킨 정식화에 기초를 둔 시간적분법에 대하여 시간을 변수로 한 유한요소적 접근법을 시도하였다. 단일 형상함수와 두 형상함수 정식화에 대해 각각 선형, 이차 형상함수를 적용하여 모두 네 종류의 시간적분법을 유도하였으며, 각 방법에 대하여 시간시텝의 증가에 따른 변위와 속도의 관계를 나타내는 증폭행렬을 계산하였다. 유도된 방법들의 성능을 평가하기 위하여 부하가 갑자기 변화는 진동 문제를 해석하고 변위의 오차를 비교하였다. 네 가지의 방법에 대하여 국부 오차 추정치를 개발하였으며, 오차 추정치의 정확도를 수치예를 이용하여 평가하였다. 단일 형상함수 정식화에서 이차 형상함수를 이용한 오차 추정치가 실제 국부오차를 잘 나타내었으며 유도된 오차 추정치는 시간간격제어 기법에서 시간간격의 크기를 결정하는 척도로 이용 가능하다.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.11 no.5
• /
• pp.15-22
• /
• 2002

A study is the selection of optimum forming condition for RP system. We develop the Automatic design program for machine element using visual LISP program in AutoCAD. Automatic design program reduces the required time for feedback between design and manufacturing of workpiece. Also we investigate the relationship between circularity of 3D solid model and circularity of rapid prototype using RP system and we will find optimum forming condition in RP system.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.19 no.2
• /
• pp.230-235
• /
• 2009

This paper describes an automatic finite element mesh generation for finite element analysis of three-dimensional structures. It is consisting of fuzzy knowledge processing, bubble meshing and solid geometry modeler. This novel mesh generation process consists of three subprocesses: (a) definition of geometric model, i.e. analysis model, (b) generation of bubbles, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Bubble is generated if its distance from existing bubble points is similar to the bubble spacing function at the point. The bubble spacing function is well controlled by the fuzzy knowledge processing. The Delaunay method is introduced as a basic tool for element generation. Automatic generation of finite element for three-dimensional solid structures holds great benefits for analyses. Practical performances of the present system are demonstrated through several mesh generations for 3D geometry.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.10
• /
• pp.1748-1753
• /
• 2003

This paper describes the forming of fine gear housing using RP system. In order to apply 3D model formed through CAD software to RP system, it is necessary of transforming 3D model into STL file format. Besides, when the same shape is formed repetitively, we must solve the program that the shape accuracy of prototype is irregular. Therefore, we will make an experiment on influence of 3D model, file transformation and prototype on facetres, AutoCAD system value. On the basis of experimental result, we will develop an automatic file transformation program for RP. In the final process, we will manufacture on a better prototype according to the experiment result of fine gear housing.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2021.06a
• /
• pp.433-433
• /
• 2021

본 연구는 개수로 흐름에서 조류발전단지의 터빈 최적 배열의 거시적 특성에 관한 연구를 수행하였다. 천수방정식을 통해 직사각형 개수로의 흐름장을 해석하였고, 상류와 하류단에 대해 각각 유입경계조건(inlet boundary condition)과 Flather 형식의 개방경계조건(open boundary condition)을 부여하여 일정 유량으로 흐르는 개수로 흐름을 구현하였다. 더불어, Strickler의 법칙을 확장한 반력공식을 연계하여, 개수로 흐름에 대한 조류 터빈의 영향을 반영하였다. 주어진 상류의 흐름 조건에 대해 조류발전량을 최대로 하는 최적 배열을 구하기 위해 터빈 반력모형을 연계한 천수방정식, 터빈간 최소간격, 그리고 발전단지영역을 제한조건으로 하는 발전량 최대화 문제를 구성하였다. 여기서 조류 터빈의 위치를 나타내는 벡터를 설계변수로 두었는데, 설계되는 터빈의 수가 증가함에 따라 최적화 문제의 계산량이 증가하지 않도록 수반법(adjoint method)을 경사도기반법(gradient-based method)에 연계한 방법이 이용되었다. 다수의 터빈초기배치로 상당한 수치실험이 수행되었고, 발전량 최대화를 이루도록 최적화된 터빈의 배치들이 큰 규모에서 고유한 형상으로 수렴함을 확인하였다. 이러한 특성은 발전단지의 너비와 터빈의 최소간격의 함수로 정의된 무차원수 E를 바탕으로 설명되었다. 구체적으로, E가 1보다 작을 때에는 선형배열이 최적배열로 나타났고, E가 1을 넘어 점차 커짐에 따라 하류에 오목한 형상을 보이다가 V-형태로 발전하는 양상을 보였다. 또한, 어느 임계 수 이상의 터빈이 배치되는 경우 일열 배열을 유지하지 못하고 이열 배열로 분리됨이 관찰되었다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.4
• /
• pp.335-341
• /
• 2015

In this study, we analyzed a two-dimensional Stokes flow through a microchannel containing projections with constant spacing attached to each wall. The projections on the top and bottom walls were semi-circular in shape, with in-phase locations. By considering the periodicity and symmetry of the flow, the eigenfunction expansion and least squared error method were applied to determine the stream function and pressure distribution. For some typical radius and spacing values, the streamline patterns and pressure distributions in the flow field are shown, and the shear stress distributions on the boundary walls are plotted. In addition, the average pressure gradients in the microchannel are also calculated and shown with the radius and spacing of the projections. In particular, the results for the case of extremely small gaps between the projections on the top and bottom walls are in good agreement with the lubrication results.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2003.04a
• /
• pp.441-447
• /
• 2003

In the study, we described on the 3D solid model be made on the AutoCAD haved an effect on the deviation of form as RP manufactures the facetres. The STL file improved the deviation of form as the facetres value but the deviation of form have the difference a little as the RP system. In result, we ruled the correlation with the 3D solid model and the RP sample manufacturing, with manufacture RP sample according to facetres value in complex shape. And we developed the program which recombination the STL file that we make use of the AutoLISP.

• Aerospace Engineering and Technology
• /
• v.9 no.1
• /
• pp.78-83
• /
• 2010

In the present paper, a flap was optimized to maximize the lift. A 2-element fowler flap system was utilized for optimization with an initial shape of general aviation airfoil and a flap shape designed by Wentz. Response surface method and Hicks-Henne shape function were implemented for optimization. 2-D Navier-Stokes method was used to solve flow field around aGA(W)-1 airfoil with a fowler flap. Commercial programs including Visual-Doc, Gambit/Tgridand Fluent were used. Upper surface shape and the flap gap were optimized and lift for landing condition was improved considerably. The original and optimized flaps were tested in the KARI's 1-m low speed wind tunnel to examine changes in aerodynamic characteristics. For optimized flap tests, the similar trend to prediction could be seen but stall angle of attack was lower than what was expected. Also, less gap than optimized design delayed stall and produced better lift characteristics. This is believed to be the effect of turbulence model.

• Journal of Korea Water Resources Association
• /
• v.40 no.11
• /
• pp.899-908
• /
• 2007

In this study, wave reflection due to depression of seabed is calculated by using eigenfunction expansion method. The proper numbers of steps and evanescent modes needed for analysis are suggested by applying the eigenfunction expansion method to bottom topography of which slope or curvature varies. While satisfying shallow or intermediate water depth condition, the optimal figure of depression of seabed is obtained by calculating reflection coefficient for various depressions of seabed. The reflection coefficient with distance between the depression of seabeds is then calculated after arraying the optimal geometry in two and three rows.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.9 no.6
• /
• pp.566-572
• /
• 2016

Software Reliability implemented in software development is one of the most important issues. In finite failure NHPP software reliability models for software failure analysis, the hazard function that means a failure rate may have constant independently for failure time, non-increasing or non-decreasing pattern. In this study, software development cost analysis considering the variable shape parameter of Erlang distribution as the failure life distribution in the software product testing process was studied. The software failure model was applied finite failure Non-Homogeneous Poisson Procedure and the parameters approximation using maximum likelihood estimation was accompanied. Thus, this paper was presented comparative analysis by applying a software failure time data to the software, considering the shape parameter of Erlang distribution for development cost model analysis. When compared to the cost curve in accordance with the shape parameter, the model of smaller shape can be seen that the optimal software release time delay and more cost. Through this study, it is thought that it can serve as a preliminary information which can basically help the software developers to search for development cost according to software shape parameters.