• Journal of Korean Association for Spatial Structures
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• v.8 no.1
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• pp.49-56
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• 2008

A multi-objective optimization approach is presented for force design of tensegrity structures. The geometry of the structure is given a priori. The design variables are the member forces, and the objective functions are the lowest eigenvalue of the tangent stiffness matrix that is to be maximized, and the deviation of the member forces from the target values that is to be minimized. The multi-objective programming problem is converted to a series of single-objective programming problems by using the constraint approach. A set of Pareto optimal solutions are generated for a tensegrity grid to demonstrate the validity of the proposed method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1077-1082
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• 2013

To improve cycling performance, the power output of the rider and the sources of resistance (e.g., air resistance, frame stiffness, and cycle mass) must be considered. From a mechanical viewpoint, we consider how the bike frame performance can be increased while decreasing the resistance. First, to improve the competitive ability of a racing track cycle, we should consider the stiffness of the bike frame including the pedal loading and aerodynamic effects when riding. Therefore, we obtained the cross-sectional area of each part of the bike frame and then aimed to minimize the drag force through an aerodynamic parametric study. In addition, the frame should remain safe under the loading applied by the rider. Under the guidelines of the UCI (union Cycliste Internationale) regulations, the bike frame has been evaluated under the proposed loading condition, and we developed a racing track cycle for elite cyclists.

• Composites Research
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• v.16 no.3
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• pp.18-24
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• 2003

Sandwich structures have been widely used in the applications of vessel industry, where high structural stiffness is required with small addition of weight. It is so significant to think of the effect of the variables in the design process of the sandwich structure for the concentrated loads. This paper describes the influence of design variables, such as core density, core thickness and face thickness ratio, on the strength of sandwich beam. The theoretical failure loads based on the 2-D elasticity theory agree well with the experimental yield or failure loads, which are measured at the three point bending laboratory test using AS4/3501-6 facing and polyurethane foam core sandwich beam. The comparison of those yield or failure loads was also done with the ratio of the top to bottom face thickness. The theoretical optimum condition is obtained by finding the intersection point of failure modes involved, which gives optimum core density of the sandwich beam for strength and stiffness. In the addition, the effect of unequal face thickness for the optimized and off-optimized sandwich beams for the strength was compared with the ratio of loading length to beam length, and the variations of strength and stiffness were discussed with the relative ratio of core to face mass.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.201-213
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• 2005

The automotive door has a large finite element model in analysis and many design requirements such as stiffness, natural frequency, side intrusion, etc. Thus, various related governing equations should be solved for systematic analysis and design. Because each governing equation has different characteristics, it is almost impossible to solve them simultaneously. Instead, they are separately handled and the analysis results are incorporated into the design separately. Currently, the design is usually conducted by trials and errors with engineering intuition in design practice. In this research, MDO methods are proposed to solve the problems that share design variables in disciplines. The idea is from the Gauss-Seidel type method for multi-discipline analysis. The developed methods show stable convergence and the weight of the door is reduced by fifteen percent.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.9
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• pp.1432-1440
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• 1997

The flexibility as well as the stiffness is required to perform mechanical function of a structure such as compliant mechanisms, which can be applied to MEMS(Micro-Electro-Mechanical Systems), flexible manufacturing devices, and design for no assembly. In this paper, the optimal design problem to achieve both structural flexibility and stiffness is formulated using multi-objective function, and the optimization problem is resolved by using Finite Element Method(FEM) and Sequential Linear Programming(SLP). Design examples of compliant mechanisms are presented to validate the design method.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.6
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• pp.145-152
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• 1998

This paper presents an optimum design of a rotor-bearing spindle system for a ultra centrifuge (80,000 RPM) supported by ball bearings with nonlinear stiffness characteristics. To obtain the nonlinear bearing stiffnesses, a ball bearing is modeled in five degrees of freedom and is analyzed quasi-statically. The dynamic behaviors of the nonlinear rotor-bearing system are analyzed by using a transfer-matrix method iteratively. For optimization. we use the cost function that simultaneously minimizes the weight of a rotor and maximizes the separation margins to yield the critical speeds as far from the operating speed as possible. Augmented Lagrange Multiplier (ALM) method is employed for the nonlinear optimization problem. The result shows that the rotor-bearing spindle system is optimized to obtain 9.5％ weight reduction and 21％ separation margin.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.269-276
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• 2007

Optimal thickness and shape of the pedal arm of an automotive clutch is determined, using the numerical optimization technique, by solving the size and shape optimization problems to minimize its weight. For the optimization problems, two cases of stress and displacement constraints are considered: one from the vertical, and the other from the transverse stiffness test condition. The result of the transverse case is shown to be more conservative than that from the vertical case, being determined as the final optimum.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.431-432
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• 2020

철도차량 하부에 부착되는 전장품 무게는 차량의 바퀴 및 베어링 등 철도차량 수명에 큰 영향을 주기 때문에 경량화는 필수적이다. 본 논문에서는 철도 차량용 보조전원장치의 경량화를 위해 LLC 공진형 컨버터를 적용한 보조전원장치 시스템과 제어알고리즘을 제안한다. 제안하는 알고리즘은 고속스위칭을 위해 입력단 벅 컨버터를 이용하여 가선 전압을 감압시키고 이후 LLC 공진형 컨버터를 통해 인버터 입력단 전압을 제어한다. 또한, 공진형 컨버터 손실을 최소화하기 위해 ZVS(Zero Voltage Switching) 동작을 하며, 공진 탱크의 최적 설계도 제안한다. 본 논문에서 제안하는 알고리즘은 시뮬레이션 및 실험으로 검증한다.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.5-14
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• 2018

Recently, method of reinforced earth retaining wall have been proposed according to the material of facing, geosynthetic, construction method, and facing slope. However, the regulations such as the design method and detailed review items according to each construction method are not clear, and collapse due to heavy rainfall frequently occurs. In this study, to obtain a more stable technical approach in the design of reinforced earth retaining wall, the combination of the pullout failure of reinforced earth retaining wall and the optimal reinforcement ratio of height using reinforced earth retaining wall using a single strength reinforcement is assumed, optimum design of stiffener, optimal design of superimposed wall and optimum length ratio of reinforcement material of geosynthetics are proposed through safety factor according to reinforcement length ratio (L/H).

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.70-78
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• 2018

This research was carried out to develop an integrated folding wing made from carbon composite materials. Design requirements were reviewed and composite wing sizing was conducted using design optimization with commercial software. Three composite manufacturing processes including hot-press, pultrusion, and autoclave were evaluated and the most suitable processes for the integrated wing fabrication were selected, with consideration given to performance and cost. The determined manufacturing process was verified by two design development tests for selecting the design concept. Stiffness and strength of the composite wing were estimated through structural analyses. The test loads were calculated and static tests about design limit load and design ultimate load were performed using both wings. As a result, the evaluation criterions of the tests were satisfied and structural safety was verified through the series of structural analyses and testing.