• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1198-1203
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• 2008

An efficient sequential optimization approach for metamodel was presented by Choi et al [6]. This paper describes a new approach of the multilevel optimization method studied in Refs. [5] and [21-25]. The basic idea is concerned with multilevel iterative methods which combine a descent scheme with a hierarchy of auxiliary problems in lower dimensional subspaces. After fitting a metamodel based on an initial space filling design, this model is sequentially refined by the expected improvement criterion. The advantages of the method are that it does not require optimum sensitivities, nonlinear equality constraints are not needed, and the method is relatively easy to understand and use. As a check on effectiveness, the proposed method is applied to a classical cantilever beam.

• Transactions of Materials Processing
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• v.19 no.4
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• pp.236-241
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• 2010

The frictional behavior of bare steel sheet highly depends on surface roughness. It was investigated that the change of surface roughness of bare steel sheet due to deformation for each forming mode. The flat type friction test was done to check the effect of surface roughness change on frictional characteristics of bare steel sheet. As increasing the deformation, the Ra value was increased at stretching forming mode and drawing forming mode, however the change of Pc showed different trends. The Pc was decreased as increasing stretch deformation but increased at compression deformation. At drawing forming mode, the friction coefficient was increased as deformation was increased after initial big drop with drawing oil. As deformation was increased, the friction coefficient was decreased with drawing oil at stretching forming mode. The results show that the deformation changes the surface roughness and frictional characteristics of steel sheet but the effect depends on the forming mode.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.280-283
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• 2003

To enhance the performance of superconducting motor, the flux which links the stator windings needs to be increased as much as possible. In this paper we redistributed the field winding to increase the flux-linkage. This paper introduces an algorithm that modifies the rotor winding shape to increase the flux-linkage to stator winding, satisfying both the constant superconductor volume and HTS tape characteristic (I$_{c}$-B curve) constraints. To check the validness of the proposed algorithm, it was applied to the 100 Hp HTS motor model, and about 21 % increase of flux-linkage was confirmed depending on the initial winding shape.e.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.4
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• pp.71-78
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• 2017

New concept rotary engine initial prototype has been developed. Engine motoring, compressor pressure and fuel combustion were tested for engine mechanism and operability check. Merits and demerits, applicable areas of the engine have been investigated against reciprocating and Wankel rotary engines. It was found that this engine is best fit for small aircraft and it is better than existing engines for motorcycle, portable and hybrid car Genset too.

• Transactions of Materials Processing
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• v.5 no.1
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• pp.8-17
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• 1996

In the present study SEAM (Shear Energy Augmented Membrane) elements have been devel-oped. Maintaining the numerical efficiency of conventional membrane elements the effect of out-of-plane deformation (transverse shear deformation) has been incorporated for the purpose of computational stabilization without introducing additional degrees of freedom. Computations are carried out for the deep drawings of square cup to check the validity and the effectiveness of proposed SEAM elements. The computational results are compared with both the existing results. And the effects of process variables like initial sheet thickness punch & die round and clearance are checked

• Transactions of Materials Processing
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• v.9 no.6
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• pp.615-623
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• 2000

The industrial application of hydroforming has a great potential in saying cost and achieving dimensional accuracy in automotive industry presently. The aim of the following article is to investigate the effect of process parameters on hydroformed part. Firstly, we have to investigate the change of mechanical properties for sheet and pipe material according to various radius/thickness ratio(r/t). The change of mechanical properties affects the yield stress more than the total elongation. Increase of yield stress for pipe has a bad influence on formability of hydroforming. Among the roll-forming process, the sizing process didn't change mechanical properties. The process parameters such as the initial pressure, mandrel shape and friction have seriously influenced on formability of hydroforming. Therefore we need to check formability of given material through the FE analysis in the beginning stage of process design and the predicted hydroforming process parameters ate generally a good starting point for the prototype tryout stage. The results of pretending, hydroforming analysis using FE model are good agreement with experimental results.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.9-12
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• 2005

In this study, to investigate shrinkage and cracking behavior of 120MPa UHSC, free and restrained drying shrinkage test were performed. Three strength levels(50MPa, 80MPa, 120MPa) were used and the effect of mineral admixtures(fly ash, slag) on free and restrained shrinkage was investigated. From comparing the result of pin -penetration test with the result of ring test, Time-Zero was determined as initial set. Shrinkage test results show that autogenous shrinkage of UHSC was much higher than that of HSC, VHSC and fly ash delayed cracking age in UHSC by decreasing autogenous shrinkage. Additional free concrete rings(with restraint removed) were also tested to check the influence of the geometry of the specimens on free shrinkage. And then the relationship between free shrinkage and restrained shrinkage was investigated.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1903-1910
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• 2012

This paper presents a data based low-order controller design algorithm for a linear time-invariant process with a time delay. The algorithm is composed by combining an identification step based on open loop pulse test with a low-order controller design step to obtain the entire set of controllers achieving multiple performance specifications. The initial information necessary for this algorithm are merely the width and amplitude of a rectangular pulse, a controller of four types (PI, PD, PID, first-order), and design objectives. Various parametric approaches that have been developed are merged in the controller design algorithm. The resulting controller set satisfying the design objectives are displayed on the 2D and 3D graphics and thus it is very easy for us to pick a controller inside the admissible set because we can check the corresponding closed-loop performances visually.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.10a
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• pp.133-140
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• 2000

A suspension bridge with long span is distinguished by aesthetic point of view, but it is difficult to analyze the structural behaviors due to its geometric nonlinear characteristics. Futhermore, because the chance of design such special bridges is very rare, the assumption of initial dimensions of geometrical shapes and structural sections may be much difficult also. In this paper, the brief data base on the important structural dimensions of suspension bridges is constructed after the informations on existing suspension bridges are collected and classified from various texts and internet web sites. Therefore this data base may be utilized very easily by the designers who tries to design such bridges in the preliminary design step. Also the static geometric nonlinear analysis program is added to assist the designer in simple decision of safety check for assumed dimensions.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.32-38
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• 1999

Fatigue crack propagation behavior for block load in high strength aluminum alloys was investigated in this study. The materials used in this study are aluminum alloy 5052-H32. Initial crack was made by applying cyclic load to a through crack with chevron notch. Crack length was measured from calibration curve, which was plotted by known crack length and resistance of standard specimens. Load was obtained from linear regression formula. Unloading elastic compliance method was applied to check the crack closure and cracked area. The present study results can be usefully applied to predicting the change of crack propagation rate, the crack closure, and the delay of crack propagation.