• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.310-313
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• 2007

This paper covers finite element simulations to evaluate the bending limit of double pipe for tube-hydroforming. The tube-hydroforming process starts with a straight precut tube. The tube is often prebent in a rotary draw bending machine to fit the hydroforming tool. During the bending the tube undergoes significant deformation. So forming defects such as wrinkling, thinning and flattening are generated in the tube. Consequently we analyzed the effect of process parameters in rotary draw bending process and searched the optimized combination of process parameters to minimize the forming defects using orthogonal arrays. The characteristic to evaluate the effects of the process parameters is the bending angle which wrinkling is generated, we define the bending angle at that time as bending limit. Of many process parameters, the process parameters of the bending process such as gab between inner and outer tube, boosting force, dimensions of mandrel were analyzed. And we observed the deformation modes of bent double pipe at specific bending angle in each parameter combination.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.45-50
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• 2011

Hot-Press-Forming (HPF), an advanced sheet metal forming method using stamping at a high temperature of about $900^{\circ}C$ and quenching in an internally cooled die set, is one of the most successful forming process in producing crash-resistant parts such as pillars and bumpers with complex shape, ultrahigh strength, and minimum springback. To optimize conditions of a forming quality in HPF process and secure a safe product without any failures, such as fractures and wrinkling, the simulations based on the coupled thermo-mechanical analysis for a hot-press-formed lower control arm are applied with Taguchi's orthogonal array experiment. Three factor variables - the friction coefficient, blank shape, and hole location for burring - are selected to be optimized. The most effective condition of a forming quality for a hot-press-formed lower control arm is suggested. The simulation results are confirmed with experimental ones.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2246-2256
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• 1996

To investigate the effect of material and precess variables on stamping formability of sheet materials, simulations for the cup drawing and the Yoshida buckling test were carried out using ABAQUS, commercial nonlinear finite element analysis code. The various factor effects on stamping formability of sheet materials were analyzed by the designed process according to Taguch's orthogonal array experiment. Cup drawing simulation showed that local neckling was very sensitive to plastic anisotropy parameter of sheet material and friction coefficient between sheet and tool interface. Simulations for the Yoshida buckling test have clarified that buckling behaviour of sheet material was mostly susceptible to yield stress and sheet thickness mostly. However, plastic anisotropy parameter and strain hardening coefficient affect moderately buckling behaviour of steel sheets after the buckling initiation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.64-69
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• 2011

Magnesium alloy has been known as lightweight material in automobile and electronic industry with aluminum alloy, titanium alloy and plastic material. Friction welding is useful to join different kinds of metals and nonferrous metals they are difficult to be joined by such as gas welding, resistance welding and electronic beam welding. In this study, friction welding was performed to investigate optimization process of Mg alloy with a 20mm diameter solid bar. For that, the orthogonal array $(L_{9}(3^{4}))$ was used that contained four factors and each factor had three levels. Control factors were heating pressure, heating time, upsetting pressure and upsetting time. Also tensile tests were carried out to measure mechanical properties for welded conditions. The levels of heating pressure and upsetting pressure used were 15, 25, 35MPa, and 30, 50, 70MPa, respectively. In addition those of heating time and upsetting time were 0.5, 1, 1.5 sec and 3, 4, 5 sec., respectively, rotating speed of 2000rpm. From the experimental results, optimization condition was estimated as follows; heating pressure=35MPa, upsetting pressure=70MPa, heating time=1.5sec, upsetting time=3sec.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12A
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• pp.1161-1167
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• 2005

In this Paper, a concept of virtual smart antenna (SA) is introduced for orthogonal Sequency division multiplexing (OFDM)-based cellular systems with a frequency reuse factor equal to 1. The OFDM-based cellular system is robust to multipath channels but has a disadvantage that the intercell interference (ICI) caused by adjacent base stations is large at the edge of a cell. In this paper, after deriving the symbol timing offset estimation scheme for the OFDM signal received from multiple base stations in a quasi-static fading channel, the ICI cancellation method based on virtual smart antenna is proposed using the steering vector formed by the symbol timing offset of the desired signal and interference signals.

• Journal of Power System Engineering
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• v.18 no.3
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• pp.106-111
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• 2014

Welding is very popular method for joining two or more metals. However, welding causes residual stress and distortion and these give a bad influence to the structure strength. In this paper, TIG welding technique was performed to investigate the joint characteristics of AISI321 steel. For its evaluation, the orthogonal array method and variance analysis were applied with three factors of electric current, travel speed and argon gas and also three levels of each factor to tensile tests for optimum design. From the results, the increaser weld speed the narrower bead width and the lower weld penetration. The increaser electric current the brighter argon gas and the wider bead width. Also weld speed influenced most on the tensile strength and presumption range of tensile strength at optimal condition from reliability 95% was estimated to $635.02{\pm}14.64$. In addition the increaser weld speed and electric current the fracture occurred around bead vicinity.

• Journal of Communications and Networks
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• v.12 no.3
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• pp.222-230
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• 2010

In this paper, we present a closed-form approximation of the average sum rate of zero-forcing (ZF) beamforming (BF) with semi-orthogonal user selection (SUS). We first derive the survival probability associated with the SUS that absolute square of the channel correlation between two users is less than the orthogonalization level threshold (OLT).With this result, each distribution for the number of surviving users at each iteration of the SUS and the number of streams for transmission is calculated. Secondly, the received signal power of ZF-BF is represented as a function of the elements of the upper triangular matrix from QR decomposition of the channel matrix. Thirdly, we approximate the received signal power of ZF-BF with the SUS as the maximum of scaled chisquare random variables where the scaling factor is approximated as a function of both OLT and the number of users in the system. Putting all the above derivations and order statistics together, the approximated ergodic sum rate of ZF-BF with the SUS is shown in a closed form. The simulation results verify that the approximation tightly matches with the sample average for any OLT and even for a small number of users.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.9
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• pp.1207-1214
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• 1995

We present an optimized integer cosine transform(OICT) as an alternative approach to the conventional discrete cosine transform(DCT), and its fast computational algorithm. In the actual implementation of the OICT, we have used the techniques similar to those of the orthogonal integer transform(OIT). The normalization factors are approximated to single one while keeping the reconstruction error at the best tolerable level. By obtaining a single normalization factor, both forward and inverse transform are performed using only the integers. However, there are so many sets of integers that are selected in the above manner, the best OICT matrix obtained through value minimizing the Hibert-Schmidt norm and achieving fast computational algorithm. Using matrix decomposing, a fast algorithm for efficient computation of the order-8 OICT is developed, which is minimized to 20 integer multiplications. This enables us to implement a high performance 2-D DCT processor by replacing the floating point operations by the integer number operations. We have also run the simulation to test the performance of the order-8 OICT with the transform efficiency, maximum reducible bits, and mean square error for the Wiener filter. When the results are compared to those of the DCT and OIT, the OICT has out-performed them all. Furthermore, when the conventional DCT coefficients are reduced to 7-bit as those of the OICT, the resulting reconstructed images were critically impaired losing the orthogonal property of the original DCT. However, the 7-bit OICT maintains a zero mean square reconstruction error.

• Solar Energy
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• v.20 no.1
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• pp.91-96
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• 2000

This study was performed to find out how much experimental factors influence on regeneration performance in a solar air conditioning system. The experimental apparatus was set up in a climate-controlled chamber where temperature and humidity could be kept constant. In order. to investigate factors' influence on the regeneration performance of the solar air conditioning system, the model experiment was done using the 600mm $\times$ 600mm black painted aluminum regenerator. The design and analysis of experiment were done by the design of experiments, especially the table of orthogonal arrays. In order to find out how much experimental factors influence on regeneration performance, the table of orthogonal arrays $L_8(2^7)$ was used. According to the results, it was found that the most influential factor to affect regeneration performance was the concentration of LiCl solution. The next influential factors were a solar radiation, an air velocity, and the temperature of LiCl solution in order.

• Corrosion Science and Technology
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• v.20 no.2
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• pp.77-84
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• 2021

This study aims to optimize the DL-EPR test solution for duplex stainless steel S31083 using the Taguchi design. The test solution parameters applied to the Taguchi design are H₂SO₄, NaCl, KSCN concentration, and temperature. In the experimental design, an orthogonal array of 4 levels 4 factor L₁₆(4⁴) was used. Output values for the orthogonal array were used for resolution (degree of sensitization) and selective etch (I_a) values. The optimal test solution conditions were selected by comparing the normalized S/N ratio for the two reaction properties. As a result, the H₂SO₄ and NaCl were identified as the main factors influencing the sensitivity measurement, but the delta statistics showed that the KSCN concentration and temperature had relatively low influence. The optimal condition was identified as 1.5 M H₂SO₄+0.03 M KSCN+1.5M NaCl at 30 ℃. The degree of sensitization presented a tendency to depend on the heat treatment temperature and time in the optimal test solution. This investigation confirmed the possibility of optimizing the experiment solution for the DL-EPR test of stainless steel using the Taguchi technique.