• 대한기계학회논문집A
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• 제26권5호
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• pp.851-863
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• 2002

Recent industrial requirements for highly precise shape processing have brought the electric discharge machining (EDM) in great need. High precision in EDM is primarily achieved by high performance controllers. However there exists inherent precision loss due to structural micro-deformation. On this background, we study structural deformation characteristics of wire cut EDM via finite element (FE) analysis and axiomatic design. Two different wire cut EDMs are selected as analysis models. 3D CAD package I-Deas is first used to construct FE models of wire cut EDMs, and then ABAQUS FE code is used for following structural analysis. Pertinency of FE mesh refinement is discussed in terms of η -factor. It is shown that performance accuracy of EDM depends strongly on the structural characteristics. Some design enhancements are suggested in an axiomatic design point of view. Finally we provide weight and temperature induced displacement discrepancies between wire end points as position functions of each subframe.

• Advances in aircraft and spacecraft science
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• 제5권1호
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• pp.129-139
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• 2018

The composite materials are widely used in aircraft structures. Their relative rigidity/weight gives them an important advantage over the metal structures. The objective of this work is to analyze by the finite element method the mechanical behavior of composite plate type notched with various forms under tensile load. Two basic parameters were taken into consideration. The first, the form of the notch in order to see its effect on the stress and the failure load. The second, we studied the influence of the locale orientation of fiber around the plate's notch. These parameters are studied in order to see their effects on the distribution stress and failure load of the plate. The calculation of the failure load is determined numerically with the numerical code ABAQUS using the XFEM (extended Finite Element Modeling) based on the fracture mechanics. The result shows clearly that it is important to optimize the effect of fiber orientation around the notch.

• International Journal of Aeronautical and Space Sciences
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• 제1권1호
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• pp.21-28
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• 2000

The flowfield of hypersonic shock-shock interaction has been simulated using a two-dimensional Navier-Stokes code based on AUSMPW+ scheme. AUSMPW+ scheme is a new hybrid flux splitting scheme, which is improved by introducing pressure-based weight functions to eliminate the typical drawbacks of AUSM-type schemes, such as non-monotone pressure solutions. To study the real gas effects, three different gas models are taken into account in the present paper: perfect gas, equilibrium flow and non equilibrium flow. It has been investigated how each gas model influences on the peak surface loading, such as wall pressure and wall heat transfer, and unsteady structure of flowfield in the region of shock-shock interaction. With the results, the value of peak pressure is not sensitive to the real gas effects nor to the wall catalyticity. However, the value of peak heat transfer rates is affected by the real gas effects and the wall catalyticity. Also, the structure of the flowfield changes drastically in the presence of real gas effects.

• 한국미생물·생명공학회지
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• 제22권2호
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• pp.134-142
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• 1994

The neucleotide sequences of the xylA gene encoding $\beta $-xylosidase of Bacillus stearothermophilus and is its flanking regions were datermined. Three open reading frame(ORFs) were found, one of which(ORF1) appeared to code for the $\beta $-xylosidase. The 1830 base pair ORF1 encoded 609 amino acids starting from a TTG initiation codon. The molecular weight deduced from the nucleotide sequence(68 KD) was in agreement with that estimated by SDS-polyacrylamide gel electrophoresis of the purified enzyme(66 KD). The Shine-Dalgarno sequence(5'-AGGAGG-3') was found 11 bp upstream of the initiation codon. Further 15 bp upstream, there observed a potential transcription initiation signals. The putative -10 sequence(CATAAT) and -35 sequence(TTGTTA) coresponded closely to the consensus sequences for Bacillus subtilis RNA polymerase with major sigma factor. The guanine-plus-cytosine content of the coding region of the xylA gene was 56mol% while that of the third position of the codons was 63 mol%. Based on the comparison with the amino acid sequences of several other carbohydrate degrading enzymes, two conserved regions, possibly participating in the catalytic mechamism of $\beta $-xylosidase xylA, were identified in 278-298 and 329-350 regions of the translated xylA gene. The nucleotide sequence of the xylA was found to exhibit no homology to any other genes so far reproted.

• 한국해양공학회지
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• 제26권1호
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• pp.17-26
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• 2012

A coupled analysis of a floating crane barge with a crane wire and hanging structure is carried out in thetime domain. The motion analysis of the crane barge is based on the floating multi-body dynamics, and thecrane wire is modeled as a simple spring tension. The hanging structure is assumed to be a rigid body with 3 degree-of-freedom translational motion. In this study, numerical simulations were conducted at three different stages. First, the developed code was validated by comparing the time-domain motion response of a crane barge with the frequency-domain results. Then, a coupled analysis of a crane barge and simple structure hanging by the crane wire was performed using the present scheme. The motion response and wire tension from the present calculations are compared with the results of OrcaFlex. The agreement between the two sets of results isfairly good. Last, lowering simulations in regular and irregular waves were conducted considering buoyancy changes in the hanging structure. The effects of the wave conditions, structure's weight, wire length, and lowering speed on the wire tension are considered.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 춘계학술대회 논문집
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• pp.81-88
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• 2000

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid-structure interaction is understood, as the whole or part of the structure is in contact with water. Specially, the importance of the added mass is not necessary to say like the submerged vehicle, all of the hull body, is positioned in the water. This paper introduce two method to find natural frequency in consideration of fluid-structure modal coupled vibration analysis. The purpose of this study is to analyze of the vibration characteristic of submerged vehicle to obtain the anti-vibration design data, which could be used in the preliminary design stage data. Underwater pressure hull of submerged vehicle is used as the model of this study. The F.E.M model is meshed by shell and beam element. Also, considering of the inner hull weight, mass element is distributed in the direction of hull length. Numerical calculations are accomplished using the commercial B.E.M code. The characteristics of natural frequency(eigenvalues), mode shape(eigenvectors) and frequency-displacement response are analyzed. The results of this study will be used as the useful design data in preliminary anti-vibration design stage.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 봄 학술발표회 논문집
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• pp.262-271
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• 1998

Recent, more and more steel deck bridges are adopted for the design of long span bridges and the upgrading of existing concrete deck bridges, mainly because of reduced self weight, higher stiffness and efficient erection compared to concrete decks. The main objective of this study is to propose on formulation of the design optimizations to develop an optimal desist program required for optimum desist for orthotropic steel-deck bridges. The objective function of the optimization is formulated as a minimum initial cost design problem. The behavior and design constraints are formulated based on the ASD and LRFD criteria of the Korean Bridge Design Code(1996). The optimum design program developed in this study consists of two steps. In the first step the system optimization of the steel box girder bridges is carried out. And in the second step the program provided the optimum design of the orthotropic steel-deck with close ribs. In the optimal design program the analysis module for the deck optimization is based on the Pelican Esslinger method. The optimizer module of the program utilizes the ADS(Automated Desist Synthesis) routines using the optimization techniques fuor constrained optimization. From the results of real application examples, The cost effectiveness of optimum orthotropic steel-deck bridges designs based on both ASD and LRFD methods is investigated by comparing the results with those of conventional designs, and it may be concluded that the design developed in this study seems efficient and robust for the optimization of orthotropic steel-deck bridges

• Steel and Composite Structures
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• 제13권3호
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• pp.295-308
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• 2012

This paper experimentally investigated the buckling capacity of built-up steel columns mainly, Cruciform Columns (CC) and Side-to-Side (SS) columns fabricated from two Universal Beam (UB) sections. A series of nine experimental tests comprised of three UB sections, three CC sections and three SS sections with different lengths were tested to failure to measure the ultimate axial capacity of each column section. The lengths used for each category of columns were 1.8, 2.0, and 2.2 m with slenderness ratios ranging from 39-105. The measured buckling loads of the tested specimens were compared with the predicted ultimate axial capacity using Eurocode 3, AISC LRFD, and BS 5959-1. It was observed that the failure modes of the specimens included flexural buckling, local buckling and flexural-torsional buckling. The results showed that the ultimate axial capacity of the tested cruciform and side-by-side columns were higher than the code predicted design values by up to 20%, with AISC LRFD design values being the least conservative and the Eurocode 3 design values being the most conservative. This study has concluded that cruciform column and side-to-side welded flange columns using universal beam sections are efficient built-up sections that have larger ultimate axial load capacity, larger stiffness with saving in the weight of steel used compared to its equivalent universal beam counterpart.

• 한국해양공학회지
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• 제15권1호
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• pp.19-25
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• 2001

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid-structure interaction is understood, as the whole or part of the structure is in contact with water. This paper introduces two methods to find natural frequency in consideration of fluid-structure interaction, direct coupled vibration analysis and fluid-structure modal coupled vibration analysis. The purpose of this study is to analyze the vibration characteristic of a submerged vehicle to obtain the anti-vibration design data, which could be used in the preliminary design stage. The underwater pressure hull of submerged vehicle is used as the model of this study. The F.E.M. model is meshed by shell and beam elements. Also, considering the inner hull weight, the mass element is distributed in the direction of hull length. Numerical calculations are accomplished by using the commercial B.E.M. code. The characteristics of natural frequency, mode shape and frequency-displacement response are analyzed.

• 한국환경보건학회지
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• 제41권2호
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• pp.82-89
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• 2015

Objectives: This study was performed to investigate the effect of cooking time on the internal temperature and color of cutlets and the reduction of indicator organisms in cutlets by cooking. Methods: Three kinds of commercially packed frozen cutlets (pork, chicken and fish cutlets), were purchased from local markets. The cutlets were cooked in a frying pan at $180^{\circ}C$ for four minutes. Internal temperature was measured with a food thermometer. Color was measured using a Hunter spectrocolorimeter. Aerobic colony counts, coliforms, and Escherichia coli were determined according to the Food Code of Korea. Results: The internal cooked temperature of every cutlet reached over $74^{\circ}C$, the temperature considered safe, after three minutes, while external temperature reached this level in two minutes (p < 0.001). The instrumental color value as lightness (L) in the cooked cutlets significantly changed (p < 0.001) after one minute. The level of aerobic colony counts of fresh cutlets was under the specification and was reduced to one tenth its level in the cooked cutlets. Coliforms and E. coli were not detected in all samples. The internal temperature of the cutlets was significantly affected by cooking time and weight (p < 0.001). The interaction effect of time and weight was also significant (p < 0.001), and time was the more influential factor. Conclusion: The results of this study indicate that the sampled cutlets should be cooked for a minimum of three minutes or more in order to ensure food safety. The results also indicate that if consumers cease cooking based on external temperature or color, there will be a risk of inadequate cooking.