An Object-Oriented Programming for the Boundary Element Method in Plane Elastostatic Contact Analysis

김문겸,윤익중,Kim, Moon-Kyum,Yun, Ik-Jung Computational Structural Engineering Institute of 2011 한국전산구조공학회논문집 Vol.24 No.2

본 논문에서는 경계요소법으로 평면 탄성 접촉문제를 해석하기 위하여 객체지향기법을 이용하여 프로그램을 구성하였다. 개발된 프로그램의 상세는 UML을 통하여 기술함으로써, C++로 구현된 프로그램이 일반적인 객체지향기법을 통해 구현될수 있도록 하였다. 개발된 프로그램은 접촉해석의 비선형성과 모퉁이 문제를 포괄할 수 있도록 추상화된 객체로 구현되었다. 접촉해석에 관련된 객체의 상세를 기술하였으며, 수치해석 예제를 통하여 개발된 프로그램의 정확성을 검증하였다. An object oriented programming(OOP) framework is presented to solve plane elastostatic contact problems by means of the boundary element method(BEM). Unified modeling language(UML) is chosen to describe the structure of the program without loss of generality, even though all implemented codes are written with C++. The implementation is based on computational abstractions of both mathematical and physical concepts associated with contact mechanics involving geometrical nonlinearities and the corner node problems for multi-valued traction. The overall class organization for contact analysis is discussed in detail. Numerical examples are also presented to verify the accuracy of the developed BEM program.

경계요소법을 이용한 접촉해석의 효율적인 접촉면 검출기법

김문겸,윤익중,Kim, Moon-Kyum,Yun, Ik-Jung 한국전산구조공학회 2009 한국전산구조공학회논문집 Vol.22 No.5

본 논문에서는 경계요소법의 평면 접촉해석에 사용될 수 있는 효율적인 접촉면 검출 알고리즘을 제시하였다. 접촉면 검출 알고리즘을 경계요소법에 적용하기 위하여, 경계요소법이 가지는 자료구조를 분석하였다. 경계요소법의 특징 중 하나인 모퉁이 문제를 고려하여 전역검색, 지역검색, 접촉관계식 설정의 3단계로 접촉면 검출기법을 구현하였다. 전역검색은 접촉 주요소, 부요소 개념을 도입하였으며, 지역검색에 있어서는 공간분할기법인 사지트리를 이용하였다. 접촉관계식의 설정을 위하여 요소수준에서 절점의 접촉여부를 검토하고 최종계의 방정식에 구속조건을 할당하도록 하였다. 제시된 알고리즘을 이용한 프로그램의 정확성과 효율성을 입증하기 위하여 수치해석을 실시하여 결과를 비교하였다. This paper presents an efficient contact detection algorithm for the plane elastostatic contact problem of the boundary element method(BEM). The data structures of the boundary element method are dissected to develop an efficient contact detection algorithm. This algorithm is consists of three parts as global searching, local searching and contact relation setting to reflect the corner node problem. Contact master and slave type elements are used in global searching step and quad-tree is selected as the spatial decomposition method in local searching step. To set up contact relation equations, global contact searching is conducted at node level and local searching is performed at element level. To verify the efficiency of the proposed contact detection algorithm of BEM, numerical example is presented.

시간의존 비탄성 문제의 유한요소-경계요소 조합에 의한 해석

김문겸,허택녕,장정범,오세호,Kim, Moon Kyum,Huh, Taik Nyung,Jang, Jung Bum,Oh, Se Ho 대한토목학회 1993 대한토목학회논문집 Vol.13 No.3

The long-term behavior, such as in excavation problems of weak medium, can be dealt with by the elasto-viscoplasticity models. In this paper, a combined formulation of elasto-viscoplasticity using boundary elements and finite elements without using internal cells is presented. The domain integral introduced due to the viscoplastic stresses is transformed into a boundary integral applying direct integration in cylindrical coordinates. The results of the developed boundary element analysis are compared with those from the explicit solution and from the finite element analysis. It is observed that the boundary element analysis without internal cells results in some error because of its deficiency in handling the nonlinearity in local stress concentration. Therefore, a coupled analysis of boundary elements and finite elements, in which finite elements are used in the area of stress concentration, is developed. The coupled method is applied to a time dependent inelastic problem with semi-infinite boundaries. It results in reasonable solution compared with other methods where relatively higher degree of freedoms are employed. Thus, it is concluded that the combined analysis may be used for such problems in the effective manner. 지하구조물은 일반적으로 영역의 무한성, 다양한 하중, 복합적인 구성재료 등으로 인하여 그 거동의 해석이 난이하다. 특히, 장기거동이 중요시되는 연약지반의 굴착문제 등에 있어서는 시간에 의존하는 점탄소성거동을 해석에 고려하여야만 한다. 본 연구에서는 점탄소성거동을 해석하는 방법으로서, 내부요소를 사용하지 않은 경계요소 해석방법을 유도하고, 정계요소와 유한요소를 조합하여 해석하는 방법을 도출하였다. 점탄소성을 고려한 지배적분방정식에서 점소성응력에 대한 영역적분은 극좌표를 이용한 직접적분방법을 적용하여 경계적분화하였고, 이에 따른 계방정식을 이용하여 프로그램화하였다. 또한 경제요소 프로그램을 점소성 유한요소 프로그램과 조합하여 굴착면 주위에 발생하는 시간의존 비탄성거동을 합리적으로 해석하도록 하였다. 경계요소해석 및 조합해석 결과는 정해 및 유한요소해석의 결과와 비교하여 검토하였다. 비교결과 내부요소를 사용하지 않은 경계요소법으로는 국부적인 응력집중으로 인한 비선형성이 충분히 고려되지 못함을 알 수 있었다. 반면에 유한요소-경계요소 조합방법으로는 상대적으로 많은 자유도를 가진 타 방법에 비교하여 합리적인 결과를 얻음을 알 수 있었다. 따라서 시간에 의존되는 비탄성체의 해석에 있어서 조합방법을 사용하면 하중조건과 경계조건에 따르는 구조물의 거동을 합리적으로 예측할 수 있으며, 유한요소와 경계요소의 장점을 살려 보다 효용적인 해석의 수행이 가능할 것으로 판단된다.

강-콘크리트 혼합거더 접합부의 정적 거동에 관한 연구

김문겸(Kim, Moon-Kyum),노병철(Lho, Byeong-Cheol),김정훈(Kim, Jeong-Hoon),박현철(Park, HyunChul) 한국콘크리트학회 2006 한국콘크리트학회 학술대회 논문집 Vol.2006 No.5

건설 R&D 활성화를 위하여

김문겸(Moon Kyum Kim) 대한토목학회 2005 대한토목학회지 Vol.53 No.8

2005년도 정기학술대회 및 Civil Expo 행사 보고

김문겸(Moon Kyum Kim),최성욱(Sung-Uk Choi),김철영 대한토목학회 2005 대한토목학회지 Vol.53 No.11

입력정보가 배제된 구조물 동특성 응답해석기법을 적용한 실험적 모우드해석에 관한 연구

김문겸(Kim Moon Kyum),임윤묵(Lim Yun Mook),박종헌(Park Jong Heon) 대한토목학회 2002 대한토목학회논문집 A Vol.22 No.4A

액상화ㆍ영구지반변형을 고려한 지중 매설관로의 지진피해평가

김문겸(Kim Moon Kyum),김태욱(Kim Tae Wook),신인나(Shin In Na),정재광(Jueng Jae Kwang) 대한토목학회 2004 대한토목학회 학술대회 Vol.2004 No.10

일반 논문 : 관계금융이 중소기업 대출구조와 경영성과에 미치는 영향에 관한 연구

김문겸 ( Moon Kyum Kim ),이규옥 ( Kyoo Ok Lee ),김순철 ( Soon Choul Kim ) 한국중소기업학회 2011 中小企業硏究 Vol.33 No.2

본 연구는 중소기업에 있어서 관계금융의 효과가 대출구조와 경영성과에 어떠한 영향을 미치는지에 대해 기업의 규모와 업력으로 구분하여 살펴보았다. 본 연구는 관계금융의 편익과 비용 측면에서 벗어나 중소기업의 금융에서 중요한 역할을 하는 규모와 업력에 따라 관계금융이 금리수준과 금융비용에 미치는 영향에 있어 유의미한 차이가 있는지와 관계금융이 중소기업의 규모와 업력에 따라 수익성과 성장성에 차별적인 영향이 있는지를 분석하였다. 연구결과를 요약하면 다음과 같다. 첫째, 관계금융은 중소기업 창업 초기에 자금의 가용성 확보를 위한 유인으로 작용하게 된다. 둘째, 중소기업은 관계금융 형성 시 은행의 우월적 지위를 수용하게 된다는 것이다. 이는 창업 초기의 중소기업이 다양한 방법으로 자금을 조달할 수 없기 때문에 이를 극복하기 위해서는 금융기관과의 유대가 절대적으로 필요하기 때문인 것으로 판단된다. 셋째, 중소기업은 규모가 커지고 성장함에 따라 관계금융의 효익이 낮아진다는 것이다. The fact asymmetric information problems are apt to be much more serious in SMEs than in large companies makes the ways in which they raise debt capital differ significantly. In other words, SME financing through commercial banks often involves a long-term relationship that may mitigate these information problems. As Berger and Udell (2002) mentioned, one of the features of small and medium enterprise (SME) financing is that personal experience and subjective judgment of loan officer in financial intermediaries, particularly commercial banks, can affect decisions and terms of loan for SMEs while large companies typically obtain credit in the public debt markets. This close relationship between banks and companies in financing is called ``relationship banking`` and Boot (2000) mentioned that the relationship banking is established when banks make investments to get clients` information exclusively and provide various financial services through consistent and a wide range of interactions. The relationship banking in Korea has evolved from the one which resembles the ``main-bank system`` in Japan. Korea had adopted the main-bank system to control credit for large business conglomerates in 1982. Those main-banks played roles of controlling client companies financing plans and investments, performing financial analyses, and even promoting the improvements of capital structures. This study tried to investigate how the relationship banking affects financing costs of SMEs and SME performance from perspectives of traditional corporate finance and SME theories. Most existing researches have tried to figure out which party in the relationship banking, between companies and banks, has a superior position in terms of marginal profits and costs. They used the data of public companies, which usually are not SMEs, to analyze the relationship banking. We, however, believe that there must be a different shape of the relationship banking for SMEs and try to find impacts on the level of interest rates charged by banks, the size of interest payments by SMEs, and the managerial performance of SMEs from the perspective of the relationship banking. This study has several features differentiating it from other researches. First, this study has used only non-public SMEs in analysis, which expands our understanding of the relationship banking into the area of non-listed SMEs. Second, we tested if there exists any difference in effects of the relationship banking according to the capitalization size and ages of SMEs. Lastly, this study tried to see not only how the relationship banking affects the level of financial cost, but also the performance of SMEs, which would be the first attempt to relate relationship banking to company performance like profitability and growth. The data used in this study were obtained from the Industrial Bank of Korea data base. The Industrial Bank of Korea is a commercial bank with a focus on SME financing, so it maintains a consistent and complete database for SMEs. The data analyzed in this study was three year panel from 2006 through 2008 which encompasses a total of 7,618 SMEs with more than debt of about 0.9 million US dollars (1 billion Korean won). Classification of firms is made by capitalization size of 6.5 million US dollars (7 billion Korean won), which requires external auditing. If the size of capitalization is greater than 6.5 million US dollars, firms are categorized as a medium firm and a small firm with less capitalization. Also each category is divided into two subsequent categories, so that a total of four categories are involved in the analyses. Also, another classification was introduced in terms of age: one to five years, six to ten years, eleven to twenty years and more than twenty years. Spread between interest rate charged to SMEs and three month-KORIBOR (CDS) and ratio of interest payment and total borrowing (RAB) are employed as dependent variables to figure out how relationship banking affects interest payments of SMEs. Two other dependent variables, ratio of operating income to total assets (INR) and growth rate of assets (GRO), are adopted to investigate a relationship between SMEs` performance and relationship banking. A dummy variable of DBANK as an independent variable is included specifically to see if one main-bank relation has any peculiar impact on the level of interest and company performance. Proxies for relationship banking are borrowing period (LLT), degree of client contribution to bank (CGI), portion of loans without collaterals (NLL), and number of client`s accounts (CRS). It is found that as Pertersen and Rajan (1994), Berger and Udell (1995), and D`Auria et al. (1999) reported, an effect of lowering interest rate through one bank relationship is significant for SMEs with more than 7 billion KRW capitalization, which is required to be externally audited. But, in the group of less than 2 billion KRW, a positive relationship between a one bank-relationship and the level of interest payment is evident. This complies with the arguments of Sharpe (1990) and Rajan (1992) which reported a one bank relationship raised interest rates charged to small firms because banks monopolized information. Banks may require a risk premium based upon their monopolized information when they make loans to SMEs which do not have credit records or collateral, but SMEs can expand their availability of funds through a one bank relationship. Thus, these contradicting results from those previous researches indicate that the effects of relationship banking on the level of interest rates are different depending upon the size of firms. Also, other proxy variable such as CGI (client contribution) reassures that benefits of relationship banking exists for SMEs over a certain size while small firms can not enjoy the benefits of relationship banking in terms of the level of interest rates. Relationship banking, however, increases the availability of funds, especially for smaller firms. Also, as previous studies show, TAR (ratio of tangible assets to total assets) has a meaningful negative relationship with the level of interest rates and the size of interest payments, and OCF (ratio of operating cash flow to total assets) has a meaningful negative relationship with the level of interest rates, which implies that SMEs with larger fixed assets and operating cash flow have more debt capacities. The one bank relationship does not have a clear impact on the actual size of the interest payment. But, other proxies of LLT and NLL indicate the benefits of relationship banking exist in expanding availability of funds, especially for smaller firms. There are not many differential effects of relationship banking on the level of interest rates and the size of interest payments according to the different ages of SMEs. The results of analysis investigating effects of relationship banking on SME performance indicates that there exists differential effects of relationship banking according to the different sizes of SMEs. The one-bank relationship has a generally negative effect on profitability while any significant effect is not found in the largest group with more than 20 billion KRW capitalization. When this is combined with the relationship between proxies of relationship banking (LLT and CGI) and company growth, we can derive another implication that banks tend to maintain long time relationships with clients which are rather stable in their performance. Banks prefer stability of SMEs to growth. Also, the positive coefficient of NLL with company growth indicates that SMEs utilize augmented fund availability through relationship banking to raise their profitability in all groups. It is found that while CDS (level of interest rates) has a negative effect on profitability in the group of greater than 7 billion KRW, RAB (size of interest payment) contributes to increasing profitability in the group of less than 7 billion KRW. This implies that smaller SMEs raise profitability by taking advantage of financial leverage obtained through relationship banking. Meanwhile, it fails to find any meaningful relationship between the number of banks and growth, so that the one-bank relationship does not affect the growth of SMEs, which is contrary to Houston and James (1996).

변위구속조건을 받는 경계요소법의 최외측 절점 처리 기법

김문겸(Kim Moon Kyum),윤익중(Yun Ik Jung) 대한토목학회 2010 대한토목학회논문집 A Vol.30 No.2A

본 논문에서는 경계요소법의 모서리 문제(corner problem)의 해결책으로 제시된 다양한 알고리즘을 비교하였다. 비교를 위해 각각 기법을 반영한 프로그램을 작성하고, 이론적 바탕을 토대로 하여 기존의 방법 중 상호간에 새롭게 조합될 수 있는 추가조건식(auxiliary equation)을 찾아 새로운 알고리즘을 구성하였다. 새롭게 구성된 알고리즘과 기존 알고리즘에 대하여 3 가지 종류의 수치 실험을 수행하였다. 수치해석모형은 정해가 알려진 2개의 문제와 기존 연구에서 제시된 한 개의 예제에 대하여 수행하였다. 이상을 바탕으로 기존 알고리즘의 특성을 기술하고 새롭게 제시된 알고리즘이 다양한 형태의 표면력을 반영할 수 있음을 보였다. In this study, most of famous algorithms for the comer problem are listed. By comparing these with implemented codes and theoretical dissections, new algorithms are developed. These algorithms are combined by the existing auxiliary equations. All relating algorithms are numerically tested with 3 problems. Two problems have well-known analytical solutions and the result of another example is compared with the one of the published paper. The conducted research reveals the characteristics of existing algorithms and demonstrates newly developed algorithms can produce a reasonable solution by reflecting various type of boundary conditions.