• Journal of the Korean Society for Precision Engineering
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• 제14권3호
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• pp.50-56
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• 1997

본 논문은 다물체동역학에서의 민감도해석을 위하여 개발된 혼합법(Mixed method)을 보여준다. 이 방법은 해석적인 미분의 유도와 수치적인 미분의 장점을 함께 사용한다. 해석적인 유도는 기본적인 전체의 미분에서 사용 되며 여기서 나온 각 세부 미분항은 수치적인 미분방법에 의존한다. 이로인하여 세부미분항을 다물체의 운동방정식 에서 유도할 때 발생하는 어려움을 제거한다. 여기서 사용되는 운동 방정식은 Joint Coordinate 방정식을 사용하며, 이 방정식의 계산시간과 정확도에 의해 민감도해석에서도 정확도와 계산시간의 효율을 향상시킬 수 있게 된다. 예제로서 자동차 Suspension 시스템의 승차감을 최적화하기 위한 민감도 해석을 수행하였으며, 여기서 혼합법이 차등미분법과 상응한 결과를 보였다.

• Proceedings of the Korea Contents Association Conference
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• 한국콘텐츠학회 2011년도 춘계 종합학술대회 논문집
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• pp.549-550
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• 2011

본 논문은 다구찌 설계방법을 이용하여 이동식 정수 시스템의 구조물에 대한 최적설계 조건을 확보하기 위하여 유한요소해석을 수행하였다. 다구찌 설계방법은 이동식 정수 시스템 구조물의 설계인자 중 가장 큰 영향을 미치는 파라미터를 고찰하고 최적화 하는데 유용한 결과를 제시 하였다. 다구찌 설계방법으로 수행된 민감도 해석 결과에 따르면 이동식 정수 시스템 구조물의 최적설계에 필요한 중요 인자로 세로방향 보강빔의 수량을 보여주고 있다. 결과적으로 안전하면서 효율적인 이동식 정수 시스템 구조물을 제작하기 위한 최적설계 시 가로방향 보강빔 수량과 바닥판의 두께보다는 세로방향 보강빔의 수량이 매우 중요한 설계인자라는 해석결과를 제시하였다.

• The Korean Journal of Applied Statistics
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• 제33권5호
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• pp.541-553
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• 2020

The receiver operating characteristic (ROC) curve is expressed as both sensitivity and specificity; in addition, some optimal thresholds using the ROC curve are also represented with both sensitivity and specificity. In addition to the sensitivity and specificity, the expected usefulness function is considered as disease prevalence and usefulness. In particular, partial the area under the ROC curve (AUC) on a certain range should be compared when the AUCs of the crossing ROC curves have similar values. In this study, partial AUCs representing high sensitivity and specificity are proposed by using sensitivity and specificity lines, respectively. Assume various distribution functions with ROC curves that are crossing and AUCs that have the same value. We propose a method to improve the discriminant power of the classification models while comparing the partial AUCs obtained using sensitivity and specificity lines.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제27권1호
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• pp.9-16
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• 2014

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 are 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.

• Transactions of the Korean Society of Mechanical Engineers
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• 제15권6호
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• pp.2109-2124
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• 1991

A simulation program is developed to analyse the performance of an axial flow turbine stage based on the meanline prediction method. The gradient projection method is utilized to minimize the aerodynamic losses under the specified constraints on such as flow coefficient, total pressure ratio, stage power and blade loading coefficient. After obtaining the optimum point for minimizing the stage loss, a sensitivity analysis is carried out ground the optimum point to find the effects of the design variables and the design constraints on the stage performance. The result of the senitivity analysis under a constant blade loading coefficient shows that the total loss is more sensitive to the mean diameter, the absolute flow angle at nozzle outlet, the relative flow angle at rotor outlet and the axial mean velocity compared to the chords and the pitches. Moreover, the design constraints on the degree of reaction at root and the blade length-to-diameter ratio are found to be most influencial on the maximization of the overall aerodynamic efficiency.

• Journal of Korean Society of Transportation
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• 제19권1호
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• pp.89-99
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• 2001

The conventional studies on equilibrium network design problem(ENDP) with fixed travel demand models assume that the future OD travel demand might not be changed even if the structure and the capacity of the network are improved. But this fixed demand assumption may loose its validity in the long-range network design because OD travel demand actually shifts with the network service level. Thus, it is desirable to involve the variable travel demand which is determined endogenously in the model in the optimal network design. In this paper a hi-level model formulation and solution procedure for ENDP with variable travel demand are presented. Firstly It is considered how to measure the net user benefits to be derived from the improved in link capacities, and the equilibrium network design problem considered here is to maximize the increase of net user benefit which results from a set of lift capacity enhancements within the budget constraints, while the OD travel demands and link travel times are obtained by solving the lower level network equilibrium problem with variable demand. And secondly sensitivity analysis is carried out to find the links to which the network equilibrium flow pattern is the most sensitive. Finally numerical example with simple network is carried out to test the validity of the model.

• Journal of Navigation and Port Research
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• 제48권4호
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• pp.249-260
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• 2024

This paper aimed to summarize research on technologies that could efficiently reduce wave-making resistance of container ships. Tto develop wave resistance reduction technology that could be applied to container ships and use it in real ship design, hull-form optimal design was performed by applying optimization algorithms, hull-form change algorithms, ship performance prediction algorithms, automation algorithms, and iterative optimal design techniques. A computer program was also developed. To properly set design variables known to be important elements in hull-form optimal design and to efficiently set lower and upper limits of design variables, a sensitivity analysis algorithm was developed and applied to hull-form optimal design. To predict the reliability and applicability of the developed computer program for real ships, hull-form optimal design was performed for a KRISO Container Ship (KCS), a container ship with various studies conducted worldwide. Hull-form optimal design was performed at Fn=0.26, the design speed of the KCS ship. Numerical analysis was performed on the hull-form of the target ship, the KCS ship, and the hull-form of the ship derived as a result of the hull-form optimal design to determine wave resistance, wave system, and wave height. The optimal ship's wave resistance was found to be reduced by 80.60% compared to the target ship. The displacement and wetted surface area were also found to be reduced by 1.54% and 1.21%, respectively.

• Journal of Korea Water Resources Association
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• 제37권12호
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• pp.1009-1018
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• 2004

A systematic method using an optimal estimation algorithm is presented for simultaneous estimation of diffuse pollution distributed along a stream reach and model parameters for a stream water quality model. It was applied with the QVAL2E model to the South Han River for optimal estimation of kinetic constants and diffuse loads along the river. Initial calibration results for kinetic constants selected from a sensitivity analysis reveal that diffuse source inputs for nitrogen and phosphorus are essential to satisfy the system mass balance. Diffuse loads for total nitrogen and total phosphorus were estimated solving the expanded inverse problem. Comparison of kinetic constants estimated simultaneously with diffuse sources to those estimated without diffuse loads, suggests that diffuse sources must be included in the optimization not only for its own estimation but also for adequate estimation of the model parameters. Application of optimization method to river water quality modeling is discussed in terms of the sensitivity coefficient matrix structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제21권3호
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• pp.239-245
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• 2008

A level set based topological shape optimization using extended B-spline basis functions is developed for steady-state heat conduction problems. The only inside of complicated domain identified by the level set functions is taken into account in computation, so we can remove the effects of domain outside parts in heat conduction problem. The solution of Hamilton-Jacobi equation leads to an optimal shape according to the normal velocity field determined from the sensitivity analysis, minimizing a thermal compliance while satisfying a volume constraint. To obtain exact shape sensitivity, the precise normal and curvature of geometry need to be determined using the level set and B-spline basis functions. Using topological derivative concept, the nucleation of holes for topological changes can be made whenever and wherever necessary during the optimization.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제20권5호
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• pp.1458-1467
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• 1996

A direct differentiationmethod is presented for the shape design sensitivity analysis of axisymmeetric elastic solids. Based on the exisymmetric boundary integralequaiton formulation, a new boundary ntegral equatio for sensitivity analysis is derived by taking meterial derivative to the same integral identity that was used in the adjoint variable melthod. Numerical implementation is performed to show the applicaiton of the theoretical formulation. For a simple example with analytic solution, the sensitivities by present method are compared with analytic sensitivities. As an application to the shape optimization, an optimal shape of a gas turbine disc toinimize the weight under stress constraints is found by incorporating the sensitivity analysis algorithm in an optimizatio program.