• Transactions of Materials Processing
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• v.4 no.1
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• pp.92-104
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• 1995

It often happens some elements are so largely distorted during a large-deformation finite element analysis that further calculation becomes impossible or the approximation error increases rapidly. This problem can be overcomed only by remeshing at several suitable stages. The present study aimed to establish the criterion based on the error estimators, and examined in the simulation and posterior error analysis of ring compression test to demonstrate the usefulness of them. The distribution of each error estimator and its variation during deformation were investigated. All the error estimators were increased monotonously with deformation and decreased rapidly at remeshing stage. It was shown that the error estimators suggested in this study are good measures as remeshing criterion for large deformation finite element analyses.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.444-450
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• 1998

In the present investigation, it is attempted to derive a yield function and associated flow rules of loose metal powders to predict plastic deformation and density change during compaction. The loose metal powders yield by shear stress as well as hydrostatic stress and the yield strength is much smaller in tension than compression. Therefore, a yield function for the powders is expressed as a shifted ellipse toward the negative direction in the hydrostatic stress axis in the space defined by the two stresses. Each of parameters A, B and .delta. used in the yield function is expressed as a function of relative density and it is determined by uniaxial strain and hydrostatic compressions using Cu powder. Flow rules obtained by imposing the normality rule to the yield function are applied to the analyses of unidirectional, bidirectional and hydrostatic compressions, resulting in an excellent agreement with experiments. The yield function is further examined by checking volume changes in plane stain, uniaxial strain and shear deformations.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.67-75
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• 2002

A study to investigate the influence of combustion chamber shape, especially piston top face configuration, on the combustion stability is presented with CFD analysis and single cylinder GDI engine test. Initial configuration of the piston bowl was designed with CFD analysis and further parametric studies of the design factors on the piston top face were carried out through the single cylinder GDI engine test. It was found that both the geometry of piston top face and the compression ratio have great influences on the combustion stability. Of interest is that the design factors of the GDI piston to prevent mixture diffusion out of the piston bowl have important roles for the stable combustion at the stratified mixture condition. Also the relationship between spray impingement and flow pattern in a GDI piston bowl should be considered to design an optimal bowl configuration for stable stratified combustion.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1259-1265
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• 2007

This paper presents nonlinear vibration characteristics of a vertical passive zero stiffness isolator. The passive isolator can achieve zero stiffness through buckling of notched flexure caused by a compressive force. First, a simulation model of the isolator was built based on elastic beam theory. As increasing the compression force, time and frequency responses of the isolator were simulated. In addition, further nonlinear vibration characteristics were investigated through a bifurcation diagram and a Poincare's map, which shows that even chaostic vibration could happen. The simulations show that as the compressive force increases, the stiffness goes close to zero and the nonlinear characteristic becomes stronger to have a great effect on the isolation performance.

• The Transactions of the Korea Information Processing Society
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• v.7 no.6
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• pp.1956-1963
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• 2000

In this paper, a wavelet image coding scheme exploiting the correlation of neighboring VQ indices in eh wavelet domain is proposed. the codewords in each sub-codebook are re-ordered in terms of their energies in order to increase the correlation of he indices. Then, the generated indices after VQ can be further encoded by non-adaptive DPCM/Huffman method. LBG algorithm and a fast-PNN algorithm using k-d trees are used for generating a multiresolution codebook. Experimental results show that or scheme outperforms the ordinary wavelet VQ and JPEG at low bit rates.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.3
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• pp.51-58
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• 2004

Optimization of engine desist and operation parameters using a genetic algorithm was demonstrated for direct injection diesel engine combustion. A micro genetic algorithm and a modified KIVA-3V code were used for the analysis and optimization of the engine combustion. At each generation of the optimization step the micro genetic algorithm generated five groups of parameter sets, and the five cases of KIVA-3V analysis were to be performed either in series or in parallel. The micro genetic algorithm code was also parallelized by using MPI programming, and a multi-CPU parallel supercomputer was used to speed up the optimization process by four times. An example case for a fixed engine speed was performed with six parameters of intake swirl ratio, compression ratio, fuel injection included angle, injector hole number, SOI, and injection duration. A simultaneous optimization technique for the whole range of engine speeds would be suggested for further studies.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2001.10a
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• pp.386-389
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• 2001

The strength parameters of two different type of disturbed weathered soils were investigated by the triaxial tests in this study. Soil samples include granite soils from two different sites and non-granite soils from six sampling sites. The results of this study indicate that the triaxial tests could be employed for determining the strength parameters for disturbed soil samples. When additional parameters are obtained by further experiments, they could be utilized in various engineering design practices.

• Interaction and multiscale mechanics
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• v.4 no.3
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• pp.239-245
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• 2011

The dynamic mechanical behavior of silicone rubber reinforced with multi-walled carbon nanotubes (MWCNTs) has been investigated in this study. The MWCNT-reinforced nanocomposites are tested in compression mode through dynamic mechanical analysis (DMA). Multiple effects including MWCNT loading, testing frequency, dynamic strain amplitude, and pre-strain level are taken into consideration. Results show that, by adding 5 wt% of MWCNTs, the dynamic stiffness and damping coefficient of the silicone rubber are significantly enhanced. It is further observed that the dynamic mechanical properties of the nanocomposites are sensitive to dynamic strain amplitude but only slightly affected by pre-strains.

• International Journal of Concrete Structures and Materials
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• v.10 no.1
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• pp.99-112
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• 2016

During earthquake, reinforced concrete walls show complicated post-yield behavior varying with shear span-to-depth ratio, re-bar detail, and loading condition. In the present study, a macro-model for the nonlinear analysis of multi-story wall structures was developed. To conveniently describe the coupled flexure-compression and shear responses, a reinforced concrete wall was idealized with longitudinal and diagonal uniaxial elements. Simplified cyclic material models were used to describe the cyclic behavior of concrete and re-bars. For verification, the proposed method was applied to various existing test specimens of isolated and coupled walls. The results showed that the predictions agreed well with the test results including the load-carrying capacity, deformation capacity, and failure mode. Further the proposed model was applied to an existing wall structure tested on a shaking table. Three-dimensional nonlinear time history analyses using the proposed model were performed for the test specimen. The time history responses of the proposed method agreed with the test results including the lateral displacements and base shear.

• Journal of information and communication convergence engineering
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• v.13 no.3
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• pp.152-158
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• 2015

We consider the problem of designing independently operating local quantizers at nodes in distributed estimation systems, where many spatially distributed sensor nodes measure a parameter of interest, quantize these measurements, and send the quantized data to a fusion node, which conducts the parameter estimation. Motivated by the discussion that the estimation accuracy can be improved by using the quantized data with a high probability of occurrence, we propose an iterative algorithm with a simple design rule that produces quantizers by searching boundary values with an increased likelihood. We prove that this design rule generates a considerably reduced interval for finding the next boundary values, yielding a low design complexity. We demonstrate through extensive simulations that the proposed algorithm achieves a significant performance gain with respect to traditional quantizer designs. A comparison with the recently published novel algorithms further illustrates the benefit of the proposed technique in terms of performance and design complexity.