• 한국전산유체공학회지
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• 제11권1호
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• pp.21-28
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• 2006

Reliability Based Design Optimization(RBDO) is one of the optimization methods that minimize the product failure due to small changes of operating conditions or process errors. It searches the optimum that satisfies the safety margin of each constraint, and it gives stable and reliable designs. However, RBDO requires many times oj computational efforts compared with the conventional deterministic optimization(DO) to evaluate the probability of failure about each constraint, therefore it is hard to apply directly to large-scaled problems such as a flexible wing shape design optimization. For the efficient reliability analysis, the approximate reliability analysis method with the two-point approximation(TPA) is proposed In this study, the lift-to-drag ratio maximization designs are performed with 3-dimensional Navier-Stokes analysis and NASTRAN structural analysis, and the optimization results about the deterministic, FORM and SORM are compared.

• 한국전산구조공학회논문집
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• 제22권4호
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• pp.299-306
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• 2009

최적설계는 설계자가 요구하는 제한조건을 만족시키는 범위에서 목적함수가 최소가 되는 설계점을 찾는 방법이다. 그러나 기존의 최적설계는 설계변수의 불확실성을 고려하지 않아 최적해가 제한조건의 경계에 위치하고, 이것은 모델링과정이나 가공 등으로 인한 오차의 영향을 고려하지 않는 문제점이 있다. 신뢰성 기반 최적설계는 불확실성을 정량화하면서 신뢰도를 계산하는 신뢰도 해석과정과 최적설계 과정을 포함한다. 일반적으로 신뢰성 해석은 크게 추출법, 급속 확률 적분법, 모멘트 기반 신뢰성 해석이 있다. 가장 널리 사용되는 급속 확률 적분법 중 최대 손상 가능점(MPP) 방법은 많은 MPP점이 존재하는 경우 수치적 비용이 증가하는 문제점과 표준 정규분포 공간으로 변환하는 과정에서 제한조건의 비선형성을 증가시켜 큰 오차를 발생시키는 문제점이 있다. 본 논문에서는 RBDO를 수행하기에 앞서 선행되어야 할 신뢰성 해석 방법으로 곱분해기법을 사용하였고, 이로부터 민감도 정보를 유도하여 기울기 기반 최적화 알고리즘을 적용하였다.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.268-283
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• 2016

Aircraft manufacturing companies have to consider multiple derivatives to satisfy various market requirements. They modify or extend an existing aircraft to meet new market demands while keeping the development time and cost to a minimum. Many researchers have studied the derivative design process, but these research efforts consider baseline and derivative designs together, while using the whole set of design variables. Therefore, an efficient process that can reduce cost and time for aircraft derivative design is needed. In this research, a more efficient design process is proposed which obtains global changes from local changes in aircraft design in order to develop aircraft derivatives efficiently. Sensitivity analysis was introduced to remove unnecessary design variables that have a low impact on the objective function. This prevented wasting computational effort and time on low priority variables for design requirements and objectives. Additionally, uncertainty from the fidelity of analysis tools was considered in design optimization to increase the probability of optimization results. The Reliability Based Design Optimization (RBDO) and Possibility Based Design Optimization (PBDO) methods were proposed to handle the uncertainty in aircraft conceptual design optimization. In this paper, Collaborative Optimization (CO) based framework with RBDO and PBDO was implemented to consider uncertainty. The proposed method was applied for civil jet aircraft derivative design that increases cruise range and the number of passengers. The proposed process provided deterministic design optimization, RBDO, and PBDO results for given requirements.

• Composites Research
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• 제26권1호
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• pp.29-35
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• 2013

복합재료 샌드위치 구조는 굽힘 강성을 향상시키고 복합재 적층판에 비해 30% 이상의 무게를 절감할 수 있다. 그러나 일반 금속에 비해 제작과정에서 발생되는 재료물성의 불확실성이 많이 내재되어 있으므로 신뢰성 기반 확률론적 설계방법이 요구된다. 본 논문에서는 안전계수를 이용한 고전적인 설계 방법이 구조물의 안전을 보장하지 않는다는 확률론적 증거를 제시하기 위하여 단순화된 복합재 샌드위치 동체에 대해 PMS(Probabilistic Margin of Safety)를 계산하였다. 이 과정에서 CMCS(Crude Monte-Carlo Simulation)에 의해 계산된 확률밀도함수를 이용하였다. 더 나아가 신뢰성 기반 최적설계를 수행하고 효율적인 계산을 위해 RBDO-MPDF(RBDO by Moving PDF) 방법을 제시하였다. 본 논문의 결과는 구조물의 신뢰성을 보장하기 위한 개선된 설계 방법과 효율적인 신뢰성 기반 최적설계 방법 연구에 유용할 것이다.

• 한국공작기계학회논문집
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• 제13권6호
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• pp.107-113
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• 2004

This paper presents the pillar section optimization technique considering the reliability of the vehicle body structure consisted of complicated thin-walled panels. The response surface method is utilized to obtain the response surface models that describe the approximate performance functions representing the system characteristics on the section properties of the pillar and on the mass and the natural frequencies of the vehicle B.I.W. The reliability-based design optimization on the pillar sections Is performed and compared with the conventional deterministic optimization. The FORM is applied for the reliability analysis of the vehicle body structure. The developed optimization system is applied to the pillar section design considering the fundamental natural frequencies of passenger car body structure. By applying the proposed RBDO technique, it can be possible to optimize the pillar sections considering the reliability that engineers require.

• 기계저널
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• 제54권2호
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• pp.28-34
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• 2014

이 글에서는 신뢰성 기반 최적설계(RBDO: Reliability-Based Design Optimization)의 필요성을 설명하고, RBDO를 위해 필요한 기술을 소개하며, RBDO기술이 산업계에 적용되는 사례연구를 통해 기술적 어려움과 향후 연구방향을 제시하고자 한다.

• 한국항공우주학회지
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• 제34권7호
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• pp.18-27
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• 2006

일반적인 신뢰성 최적 설계는 결정론적 최적 설계에 비해 매우 많은 계산비용이 필요하므로 공력 형상 최적화와 같은 큰 문제에 직접 적용하기는 매우 어렵다. 본 연구에서는 이러한 한계를 극복하기 위하여 이점 근사화 기법과 adjoint 민감도 해석 기법을 결합한 효율적인 신뢰성 설계 과정을 제안한다. 이 방법은 계산비용은 결정론적 방법과 거의 동일하지만 계산 결과에 있어서는 기존의 신뢰성 설계 기법과 유사한 결과를 얻을 수 있다. 이를 이용하여 3차원 공력 형상 최적 설계를 매우 효율적으로 수행할 수 있었다.

• Structural Engineering and Mechanics
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• 제52권6호
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• pp.1099-1120
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• 2014

In this paper, reliability-based design optimization (RBDO) of structures is addressed. For this purpose, the global search and optimization capabilities of genetic algorithm (GA) are combined with the efficiency and reasonable accuracy of an advanced moment-based finite element reliability method. For performing RBDO, three variants of GA including a real-coded, a binary-coded and an improved binary-coded GA are developed. In these methods, GA performs (finite element) reliability analyses to evaluate reliability constraints. For truss structures which include finite element modeling, reliability constraints are evaluated using finite element reliability analysis. Response sensitivity required for finite element reliability analysis is obtained by direct differentiation method (DDM) rather than finite difference method (FDM). The proposed methods are examined within four standard test examples and real-world design problems. The results illustrate the superiority and efficiency of the improved binary-coded GA. Results also illustrate that DDM significantly reduces the computational cost and improves the efficiency of the optimization procedure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.753-758
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• 2004

This study is to suggest a probabilistic design determining configurations of slider air bearings with the dimensional manufacturing tolerances of the ABS. The probabilistic design problem is formulated to minimize the variation in flying height from a target value while satisfying the desired probabilities keeping the pitch and roll angles within suitable range. The proposed approach first solves the deterministic optimization problem. Then, beginning with this solution, the RBDO is continued with the probabilistic constraints affected by the random variables with a fixed standard deviation in normal distribution. The RBDO results are directly compared with the values of the initial design and the results of the deterministic optimization, respectively. The reliability analyses are performed by the descriptive sampling (DS) to show the effectiveness and accuracy of the proposed approach. It is demonstrated that the proposed RBDO approach can efficiently obtain an optimum solution satisfying all the desired probabilistic constraints.

• 한국소음진동공학회논문집
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• 제14권8호
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• pp.695-701
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• 2004

This study is to suggest a Probabilistic design determining configurations of slider air bearings with the dimensional manufacturing tolerances of the ABS. The probabilistic design problem is formulated to minimize the variation in flying height from a target value while satisfying the desired probabilities keeping the pitch and roll angles within a suitable range. The proposed approach first selves the deterministic optimization problem. Then, beginning with this solution, the RBDO is continued with the probabilistic constraints affected by the random variables with a fixed standard deviation in normal distribution. The RBDO results are directly compared with the values of the initial design and the results of the deterministic optimization, respectively. The reliability analyses are performed by the descriptive sampling (DS) to show the effectiveness and accuracy of the proposed approach. It is demonstrated that the Proposed RBDO approach can efficiently obtain an optimum solution satisfying all the desired probabilistic constraints.