• 대한기계학회논문집
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• 제17권2호
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• pp.248-256
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• 1993

본 연구에서는 연속계의 진동모드를 구하여 일반질량(generalize mass)을 유 동하였으며 집중, 분포질량 변경에 따른 일반질량 변화량을 산출하여 감도계수를 구하 는 새로운 연속계 감도해석 방법을 제안하였고, 타당성을 검증하기 위해 외팔보, 계단 보에 적용하여 감도계수, 고유진동수, 진동모드, 전달함수의 변화량을 예측하고 이론 치와 비교하였다. Fig.1은 본 연구의 흐름도를 나타낸다.

• 한국생산제조학회지
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• 제6권3호
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• pp.82-88
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• 1997

This paper derives the generalized stiffness to find dynamic characteristics and its derivatives of a continuous system. And a new sensitivity analysis method is presented by using the amount of change of generalized stiffness and vibrational mode caused by the variation of stiffness. In this paper, to get or detect appropriate results, cantilever beam and stepped beam and stepped beam are used. Deviations of sensitivity coefficient, natural frequency, and vibrational mode are calculated as result, and compared with the theoretical exact values.

• 대한기계학회논문집A
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• 제27권4호
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• pp.585-592
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• 2003

Among various sensitivity evaluation techniques, semi-analytical method(SAM) is quite popular since this method is more advantageous than analytical method(AM) and global finite difference method(FDM). However, SAM reveals severe inaccuracy problem when relatively large rigid body motions are identified fur individual elements. Such errors result from the numerical differentiation of the pseudo load vector calculated by the finite difference scheme. In the present study, an iterative method combined with mode decomposition technique is proposed to compute reliable semi-analytical design sensitivities. The improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes and the error of SAM caused by numerical difference scheme is alleviated by using a Von Neumann series approximation considering the higher order terms for the sensitivity derivatives.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.359-369
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• 1999

The paper describes the study of concurrent subspace optimization(CSSO) for coupled multidisciplinary design optimization (MDO) techniques in mechanical systems. This method is a solution to large scale coupled multidisciplinary system, wherein the original problem is decomposed into a set of smaller, more tractable subproblems. Key elements in CSSO are consisted of global sensitivity equation(GSE), subspace optimization (SSO), optimum sensitivity analysis(OSA), and coordination optimization problem(COP) so as to inquiry valanced design solutions finally, Automatic differentiation has an ability to provide a robust sensitivity solution, and have shown the numerical numerical effectiveness over finite difference schemes wherein the perturbed step size in design variable is required. The present paper will develop the automatic differentiation based concurrent subspace optimization(AD-CSSO) in MDO. An automatic differentiation tool in FORTRAN(ADIFOR) will be employed to evaluate sensitivities. The use of exact function derivatives in GSE, OSA and COP makes Possible to enhance the numerical accuracy during the iterative design process. The paper discusses how much influence on final optimal design compared with traditional all-in-one approach, finite difference based CSSO and AD-CSSO applying coupled design variables.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.530-533
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• 2004

It is well known that many real systems have asymmetric mass, damping and stiffness matrices. In this case, the method for calculating eigenpair sensitivity is different from that of symmetric system. To determine the derivatives of the eigenpairs in asymmetric damped case, a modal method was recently developed by Adhikari. When a dynamic system has many degrees of freedom, only a few lower modes are available, and because the higher modes should be truncated to use the modal method, the errors may become significant. In this paper a procedure for determining the sensitivities of the eigenpairs of asymmetric damped system using a few lowest set of modes is proposed. Numerical examples show that proposed method achieves better calculating efficiency and highly accurate results when a few modes are used.

• 한국항공우주학회지
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• 제30권8호
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• pp.10-20
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• 2002

본 논문에서는 최적화 방법을 이용하여 동적 실속을 제어하는 방법을 제시하고자 한다. 비정상 공력 민감도 해석코드는 2 방정식 난류 모델을 사용한 비정상 압축성 Navier-Stokes 해석코드로부터 직접 미분법을 사용하여 개발되었다. 목적함수는 해석이 수행되는 전시간에 대한 것보다는 매 순간의 값을 사용하였다. 매 순간의 목적함수에 대한 구배값은 민감도 해석코드를 사용하여 얻었고, 최적화는 매 시간마다 간단한 건형 직선 조사방법(linear line search)을 이용하였다. 제어 변수는 익형의 노즈 반경, 최대 두께와 흡입을 사용하였다. 계산결과는 동적 실속을 제어하는데, 본 논문에서 제시한 최적화 방법이 효과적이라는 것을 보여주고 있다.

• Communications for Statistical Applications and Methods
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• 제15권4호
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• pp.563-585
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• 2008

본 연구는 다양하고 복잡해지는 파생상품 추세에 상응하는 적절한 가치평가에 대한 연구의 필요성을 인지하고 가격 및 민감도 평가에 있어서 속도와 정확도를 향상시키는데 그 의의를 두고자 한다. 몬테카를로 시뮬레이션에서 의사난수 대신 저불일치수열인준난수를 이용하면 시행횟수의 감소와 정확도 개선이 가능한데, 미국형 옵션이나 경로의존형 상품 등 다차원의 난수가 필요할 경우 기존의 준난수를 사용하면 상관관계가 증가하는 문제로 적용에 한계가 있다. 이런 단점을 보완하기 위해 문제를 발생시키는 차원의 난수를 제외시켜 상관계수를 특정값 이하로 제어하는 새로운 방법을 고안하여 다차원 상품에 적용이 가능토록 하였고 미국형 풋옵션에 적용하여 새로운 방법의 유용성을 검증하였다. 또한, 몬테카를로 시뮬레이션에서 민감도 계산방법으로 우도비율법과 경로의존형 근사방법을 사용하면 속도 및 정확도가 개선됨을 보인다. 이러한 결과는 최근 시장의 추세인 기초자산이나 위험요소가 여러 개인 경우 그리고 경로의존형 및 조기상환형 상품 등에 적용 가능토록하여 몬테카를로 시뮬레이션 방법에 있어 가장 큰 단점으로 지적되는 수행시간을 단축시키고 민감도 계산의 오차를 줄여줌을 보여준다. 또한, 2개 이하의 기초자산으로 이루어진 파생상품의 가치 및 민감도 평가에 가장 효율적인 수치해석적 방법론으로 알려져 있는 유한차분법의 적용시 격자생성구간의 설정이 매우 중요하다는 사실을 비대칭 나비형스프레드에 적용하여 실증적으로 보인다.

• 대한기계학회논문집A
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• 제21권5호
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• pp.707-718
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• 1997

This paper presents an efficient numerical method for the computation of eigenpair derivatives for a real symmetric eigenvalue problem with distinct and multiple eigenvalues. The method has a very simple algorithm and gives an exact solution. Furthermore, it saves computer sotrage and CPU time. The algorithm preserves not only the symmetricity but also the band width of the matrices, allowing efficient computer storage and solution techniques. Results from the proposed method for calculating the eigenpair derivatives are compared with those from Rudisill and Chu's method and Nelson's method which is known efficient one in the case of distinct natural frequencies. As an example to demonstrate the efficiency of the proposed method in the case of distinct eigenvalues, a cantilever plate is considered. The design parameter of the cantilever plate is its thickness. For the eigenvalue problem with multiple natural frequencies, the adjacent eigenvectors are used in the algebraic equation as side conditions, lying adjacent to the multiplicity of multiple natural frequency distinct eigenvalues, which appear when design parameter varies. A cantilever beam is used to demonstrate the efficiency of the proposed method in the case of multiple natural frequencies. Results form the proposed method for calculating the eigenpair derivatives are compared with those from Dailey's method(an amendation of Ojalvo's work) which finds the exact eigenvector derivatives. The design parameter of the cantilever beam is its height. Data is presented showing the amount of CPU time used to compute the first ten eigenpair derivatives by each method. It is important to note that the numerical stability of the proposed method is proved.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.299-306
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• 2006

Using a level set method and topological derivatives, a topological shape optimization method that is independent of an initial design is developed for linearly elastic structures. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. The 'Hamilton-Jacobi (H-J)' equation and computationally robust numerical technique of 'up-wind scheme' lead the initial implicit boundary to an optimal one according to the normal velocity field while minimizing the objective function of compliance and satisfying the constraint of allowable volume. Based on the asymptotic regularization concept, the topological derivative is considered as the limit of shape derivative as the radius of hole approaches to zero. The required velocity field to update the H -J equation is determined from the descent direction of Lagrangian derived from optimality conditions. It turns out that the initial holes is not required to get the optimal result since the developed method can create holes whenever and wherever necessary using indicators obtained from the topological derivatives. It is demonstrated that the proper choice of control parameters for nucleation is crucial for efficient optimization process.

• International Journal of Oral Biology
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• 제43권1호
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• pp.29-35
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• 2018

It is noted that chalcone derivatives have characteristic diverse pharmacological properties, and that precise evidence has been growing that they could regulate a tumor necrosis $factor-{\alpha}$ ($TNF-{\alpha}$) induced insulin resistance. The purpose of the present investigation is to elucidate the effects of the identified chalcone derivatives on adipogenesis, and to find the underlying mechanism of action in that case. Consequently, we first investigated whether the chalcone derivatives could affect the identified $PPAR{\gamma}$-induced transcriptional activity on the proliferator-activated receptor response elements (PPRE) at target promoters, and find that trans-chalcone most significantly increased the $PPAR{\gamma}$-induced transcriptional activity. Additionally, we confirmed that there were up-regulatory effects of trans-chalcone during the adipogenesis and lipid accumulation, and on the mRNA of adipogenic factors in 3T3-L1 cells. Next, we examined the effect of trans-chalcone on the inhibition induced by $TNF-{\alpha}$ on adipogenesis. To that end, we noted that the treatment with trans-chalcone attenuated the effect of $TNF-{\alpha}$ mediated secretion of various adipokines that are involved in insulin sensitivity. For this reason, we noted that this study clearly demonstrates that trans-chalcone enhanced adipogenesis, in part, by its potent effect on $PPAR{\gamma}$ activation and by its reverse effect on $TNF-{\alpha}$.