• 한국정밀공학회지
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• 제20권8호
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• pp.175-184
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• 2003

A method of the shape design sensitivity analysis based on the boundary integral equation formulation is presented for two-dimensional inhomogeneous thermal conducting solids with multiple domains. Shape variation of the external and interface boundary is considered. A sensitivity formula of a general performance functional is derived by taking the material derivative to the boundary integral identity and by introducing an adjoint system. In numerical analysis, state variables of the primal and adjoint systems are solved by the boundary element method using quadratic elements. Two numerical examples of a compound cylinder and a thermal diffuser are taken to show implementation of the shape design sensitivity analysis. Accuracy of the present method is verified by comparing analyzed sensitivities with those by the finite difference. As application to the shape optimization, an optimal shape of the thermal diffuser is found by incorporating the sensitivity analysis algorithm in an optimization program.

• 한국지반공학회논문집
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• 제22권6호
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• pp.51-61
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• 2006

말뚝-지반의 상호거동과 다양한 설계변수들의 불확실성을 고려한 축하중을 받는 단말뚝의 위험도를 정량화하기 위하여 효율적이고 정확한 복합 신뢰성해석 기법이 본 논문에서 제안되었다. 제안된 신뢰성해석 기법은 응답면기법, 유한차분법, 일차신뢰도법과 반복 선형보간기법의 개념들을 지능적으로 결합하였다. 단말뚝-지반계의 확정적 해석을 위해서 하중전이법과 유한차분법을 통합하였다. 하중조건, 말뚝의 재료와 단면특성, 그리고 지반특성과 관련된 불확실성을 명확하게 고려하였다. 말뚝과 지반의 사용성 한계상태 및 강도 한계상태에 대한 위험도를 평가하였다. 축하중을 받는 사실적인 말뚝-지반계의 안전성평가에 대한 제안기법의 적용성, 정확성 및 효율성을 몬테카를로 시뮬레이션의 결과와 비교함으로써 검증하였다.

• 대한의용생체공학회:의공학회지
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• 제13권1호
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• pp.33-38
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• 1992

A new approach to texture classification for quantitative ultrasound liver diagnosis using run difference matrix was developed. The run difference matrix comprised the gray level difference along with a distances. From this run difference matrix, we defined several vectors and parameters such as DOD, DGD, DAD vector, SHP, SMO, SMG, LDE, LDEL etc. Each parameter values calculated in fatty, cirrhotic, normal and chronic hepatitic liver images were plotted in a plane and we found that RDM method was more sensitive to small structural changes than the conventional run length method and showed improved classification ability between the diseases.

• 천문학회보
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• 제24권2호
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• pp.105-105
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• 1999

• 경영과정보연구
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• 제2권
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• pp.237-266
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• 1998

The purpose of this study was to analyze the differences of application level the computer programming languages in major. The method of this study is the empirical method based on theoretical one with the previous bibliographical suduies. The sample consists of 268 listed university disclosing over the period of Dec. 1. 1997 to Du. 15. 1997. The samples were 10 university in university of Seoul, Pusan, Masan City, Korea. The data were collected by questionnaire research through interview with each person. The analysis data was carried to 268 samples by using SPSS/PC for Windows Version 7.5 statistical package. Statistical methods such as frequency analysis, chi-square test, ANOVA test, correlation analysis were used to test the research questions. This paper focuses on the design of the hypothesis test show that the 2 type are significantly different in major of university students. Before the test of research questions performed it frequency analysis by using the factor score that bring each items. The research type of 2 guoups, that is, BA Group(business administration group) and NBA Group(non-business administration guoup). To summarize the result of this study is as follows ; (1) Hypothesis 1 : Concerning about computer programming language in major, the significant difference is application the present condition. (2) Hypothesis 2 : Concerning about computer programming language in major, the significant difference is application level. (3) Hypothesis 3 : Concerning about each application software in major, the significant difference is application level. According to the results of this study, it is found that (1) Hypothesis 1 related In application the present condition of computer programming language was accepted its all at 0.05 % significance level. (2) Hypothesis 2 related to application level of computer programming language was accepted its all at 0.05 % significance level. (3) Hypothesis 3 related to application level of each application software was rejected its all. at 0.05 % significance level.

• 대한기계학회논문집
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• 제18권3호
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• pp.653-661
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• 1994

In this paper the CSCM type upwind flux difference splitting Navier-Stokes method has been applied to study the ARL-SL19 supersonic/transonic compressor cascade flow. H-type grid was chosen for its simplicity in applying cyclic tridiagonal matrix algorithm along with conventional slip/no-slip boundary conditions. The thin-layer algebraic model of Baldwin-Lomax was employed for the calculation of turbulent flows. The test case inlet Mach No. was 1.612 and inlet/exit pressure ratio($P_2/P_1$) was 2.15. The results were compared with experimental results from current method were compared well in suction surface with the experiments and other computational results; however, not well in pressure surface. It might be due to the complex flowfields such as shock/boundary layer interaction, turbulence, and flow separation, etc. In the future, a proper turbulence modelling and adaptive grid system will be studied to improve the solution quality.

• 대한조선학회논문집
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• 제57권3호
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• pp.160-167
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• 2020

A two-stroke diesel engine and a propeller normally adopted in large merchant ships are regarded as major ship vibration sources. They are directly connected and generate various excitation components proportional to the rotating speed of diesel engine. Among the components, the magnitude of two excitation components with the same frequency generated by both engine and propeller can be compensated by the adjustment of their phase difference. It can be done by the optimization of propeller assembly angle but requires a number of burdensome trials to find the optimal angle. In this paper, the efficient estimation method to determine optimal propeller assembly angle is proposed. Its application requires the axial vibration measurement in sea trial and the numerical vibration analysis for propulsion shafting which can be substituted by additional vibration measurement after one-trial modification of propeller assembly angle. In order to verify the validity of the proposed method, the phase difference between two fifth order excitation components generated by both diesel engine and propeller of a real ship is calculated by the finite element analysis and its result is indirectly validated by the comparison of axial vibration responses at intermediate shaft obtained by the numerical analysis and the measurement in sea trial. Finally, it is numerically confirmed that axial vibration response at intermediate shaft at a resonant speed can be decreased more than 87 % if the optimal propeller assembly angle determined by the proposed method is applied.

• 통상정보연구
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• 제6권1호
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• pp.25-50
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• 2004

This study attempts to find out what kind of service quality is considered important by customers in using the Internet shopping mall and suggests the way to activate the customer relationship. The findings based on empirical analysis are shown here. First, empirical analysis of the contextual factors such as gender, education, and experience levels, shows that what customers perceive as most important in the product purchase is security in terms of the payment and personal information service. The second important service quality factor perceived by customers is responsiveness, particularly the rapidity and accuracy of response to their needs and wants. The customers also considered price, quality and diversity of the product as being important. Furthermore, there is no big difference among other service quality factors. Second, in the different gender context, there is no significant difference between the genders. However, the male group shows an even distribution of factors valued in the service quality, whereas female respondents placed stronger emphases on particular aspects of service, such as security, response, reliability and product quality. Third, in the context of different education level, the payment method between graduates and non-graduates has a significant difference. That is, the non-graduates prefer the credit card and saving through ATM, while the graduates use dual payment method using credit card and another payment method together. Therefore, the various payment methods should be considered according to the customer type, namely graduates or non-graduates. Fourth, in the context of different experience level, the result of the empirical analysis of the factors of the service quality shows no great difference between experienced and inexperienced customers. Both types of customer perceive security as the most important. To sum up, the service quality perceived by the customers of Internet shopping malls is empirically analyzed in different contexts such as gender, education, and experience. Then, the device for the customer relationship activation is suggested. It can be utilized as a guideline for the continuing diffusion of the Internet shopping mall, giving it a competitive advantage against other companies.

• 대한기계학회논문집
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• 제18권7호
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• pp.1738-1750
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• 1994

Both cylindrical cup drawing and square cup drawing are analyzed using membrane analysis as well as shell analysis by the elastic-plastic finite element method. An incremental formulation incorporating the effect of large deformation and normal anisotropy is used for the analysis of elastic-plastic non-steady deformation. The computed results are compared with the existing experimental results to show the validity of the analysis. Comparisons are made in the punch load and distribution of thickness strain between the membrane analysis and the shell analysis for both cylindrical and square cup drawing processes. In punch load, both analyses show very little difference and also show generally good agreement with the experiment. For the cylindrical cup deep drawing, the computed thickness strain of a membrane analysis, however, shows a wide difference with the experiment. In the shell analysis, the thickness strain shows good agrement with the experiment. For the square cup deep drawing, both membrane and shell analyses show a wide difference with experiment, this may be attributable to the ignorance of the shear deformation. Concludingly, it has been shown that the membrane approach shows a limitation for the deep drawing process in which the effect of bending is not negligible and more exact information on the thickness strain distribution is required.

• Nuclear Engineering and Technology
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• 제16권1호
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• pp.21-28
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• 1984

수치확산을 포함한 truncation오차의 줄임은 수치해석의 중요한 과제가 되어왔다. Stream line방법이 교차수치 확산과 비확산형의 truncation 오차를 제거하기 위하여 고안되었다. 또한, stream line방법과 유한 차분법이 합쳐진 2단계 stream line방법이 비압축성 난류유동의 지배 방정식을 풀기 위하여 고안되었다. 이 방법은 유한 차분법과 비교되었으며, 두 방법 모두 실험자료와 비교되었다. 그리고, 두 방법의 truncation 오차를 비교하기 위하여 truncation 오차 분석이 행해졌다