• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1058-1063
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• 2004

This paper presents a new approach regarding thermal characteristics associated with a design of the high efficiency motor. Electrical conduction materials, such as coil and aluminum embedded in the core generate high heat exerting negative influence on both lifetime and performance of machine. Thus, it is necessary to design high efficiency motor considering heat transfer in order to improve motor performance and to be protected against overheating. In this paper, firstly, numerical analysis of electromagnetic field is carried out by the nonlinear transient finite element method (FEM). Secondly, the linear static FEA of magneto-thermal field is implemented by applying source current computed by the nonlinear transient analysis. FE results are validated in terms of electromagnetics and heat transfer by experiments. And then, the pseudo-transient topology optimization using a multi-objective function is performed. The proposed method is applied to a squirrel cage single-phase induction motor of the scroll compressor.

• The KSFM Journal of Fluid Machinery
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• v.7 no.5 s.26
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• pp.20-28
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• 2004

Static and dynamic structural analyses of a turbine bladed-disk for a liquid rocket turbopump are performed to investigate the safety level of strength and vibration at design point. During operation, turbopump is exposed to various external loads. Therefore, the effects of them should be carefully considered and properly modeled. First, due to the high rotational speed of the turbopump, effects of centrifugal forces are considered in the structural analysis. Thermal load caused by severe temperature differences is also considered. A three dimensional finite element method (FEM) is used for linear and nonlinear structural analyses with modified Newton-Raphson iteration method. After the nonlinear solution is obtained from the structural analysis, dynamic characteristics are obtained as a function of rotational speed from the linearized eigenvalue analysis at an equilibrium position. From the analysis results, characteristics of stress distribution and vibration were thoroughly examined and investigated.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.69-76
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• 2000

In this study, an improved analysis model for the more efficient and accurate structural analysis of cable-stayed bridges is presented. In this model, beam elements, of which stability functions are stabilized by the use of Taylor's series expansions, are used to model space frame structures, and truss elements, of which equivalent elastic moduli are evaluated on the assumption that the deflected shape of a cable has a catenary function, are used to model cables. By using the proposed analysis model, nonlinear static analysis and natural vibration analysis of 2-dimensional and 3-dimensional cable-stayed bridges are carried out and are compared with the analysis results reported by other researchers.

• Journal of applied mathematics & informatics
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• v.26 no.1_2
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• pp.75-106
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• 2008

In this paper, we derive necessary optimality conditions for a continuous programming problem in which both objective and constraint functions contain support functions and is, therefore, nondifferentiable. It is shown that under generalized invexity of functionals, Karush-Kuhn-Tucker type optimality conditions for the continuous programming problem are also sufficient. Using these optimality conditions, we construct dual problems of both Wolfe and Mond-Weir types and validate appropriate duality theorems under invexity and generalized invexity. A mixed type dual is also proposed and duality results are validated under generalized invexity. A special case which often occurs in mathematical programming is that in which the support function is the square root of a positive semidefinite quadratic form. Further, it is also pointed out that our results can be considered as dynamic generalizations of those of (static) nonlinear programming with support functions recently incorporated in the literature.

• Wind and Structures
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• v.6 no.5
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• pp.357-386
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• 2003

A number of methods based on various ideas have been proposed for simulating the non-Gaussian stationary process. However, these methods have some limitations. This paper reviewed several simulation methods based on the translation method using logarithmic and polynomial functions, which have emerged in the history of statistics and in the field of civil engineering. The applicability of each method is discussed from the viewpoint of the reproducibility of higher order statistics of the object function in the simulated sample functions, and examined using pressure signals measured from wind tunnel experiments for various shapes of buildings. The parameter estimation methods, i.e. the method of moments and quantile plot, are also reviewed, and the useful aspects of each method are discussed. Additionally, a simple worksheet for parameter estimation is derived based on the method of moment for practical application, and the accuracy is discussed comparing with a set of previously proposed formulae.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.336-340
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• 1998

In this paper, an effective control scheme of a single phase UPS inverter is proposed to have no steady state error of the output voltage and the fast response for the load request. The cosine wave tranfer function is proposed to control the output voltage. This controller clearly removes errors of magnitude and phase both in the steady state. On the other hand, a current controller is proposed to reduce the transient time of the voltage control and to improve the bad distorted factor of the output voltage waveform by the load fluctuation and the presences of nonlinear parameters in the plant. The current controller is designed parallel to the voltage controller and performs separately from it.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.750-755
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• 2012

In this study we conduct the optimal spot-weld layout design of vehicle body structure considering dynamic stiffness and side impact. We conduct both linear static analysis and nonlinear analysis with a baseline model to verify the process. 13 design variables will be selected for the effect analysis. Then, topology optimization is conducted to each selected design variable. The design constraints are formulated to improve the dynamic stiffness and side impact performance. Objective function is to set the density of weld component. Optimal spot-weld layout design are compared with the baseline model to show the improvement.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.2
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• pp.114-120
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• 2004

Propeller blades have complex airfoil section type geometry and the thickness is continuously varied to both its length and cord-wise direction. in the present research, the finite element analysis program PROSTEC (Propeller Stress Evaluation Code) is developed to calculate the structural responses of propeller blades in irregular ship wake field. To represent the curved and skewed geometry of propeller blades accurately, 20-node curved solid element using the quadratic shape function is adopted. Input data for the analysis including the geometry and pressure distribution of propeller blades can be generated automatically from the propeller design program. And to visualize the results of analysis on windows system conveniently, the post processor PROSTEC-POST is developed.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.393-400
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• 1998

In this study, the crash situations and general crash analysis methods of railway rolling stocks were explained. To calculate the applied load and the maximum stress in the carbody when two aluminum railway vehicles were shunted, the finite element models for the carbody and the coupling system were made. The characteristic curve of draft gear which had a function to reduce impact force was modeled by nonlinear bar elements and the carbody was modeled by shell elements. Two shunting speeds, 5km/h and 8km/h, were considered and the results were analyzed and compared with static analysis case. Also, the aluminum railway vehicle with 60km/h was crashed against rigid wall to examine the global behavior of the carbody.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.10
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• pp.999-1008
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• 2007

The spacer grid set is a component in the nuclear fuel assembly. The set supports the fuel rods safely. Therefore, the spacer grid set should have sufficient strength for the external impact forces such as earthquake. The fretting wear occurs between the spring of the fuel rod and the spacer grid due to flow-induced vibration. Conceptual design of the spacer grid set is performed based on the Independence Axiom of axiomatic design. Two functional requirements are defined for the impact load and the fretting wear, and corresponding design parameters are selected. The overall flow of design is defined according to the application of axiomatic design. Design for the impact load is carried out by using nonlinear dynamic analysis to determine the length of the dimple. Topology optimization is carried out to determine a new configuration of the spring. The fretting wear is reduced by shape optimization using the homology theory. The deformation of a structure is called homologous if a given geometrical relationship holds before, during, and after the deformation. In the design to reduce the fretting wear, the deformed shape of the spring should be the same as that of the fuel rod. This condition is transformed to a function and considered as a constraint in the shape optimization process. The fretting wear is expected to be reduced due to the homology constraint. The objective function is minimizing the maximum stress to allow a slight plastic deformation. Shape optimization results are confirmed through nonlinear static analysis.