• Proceedings of the KWS Conference
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• 2009.11a
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• pp.24-24
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• 2009

현재 조선소를 비롯하여 각종 산업 전반적으로 기존의 SCR 용접기를 대체하여 용접품질이 우수한 인버터 용접기가 널리 사용되고 있는 실정이다. 그러나 기존 인버터 용접기의 전원은 Mono 타입으로 이루어져 있어 대용량 인버터 용접기의 경우 대용량 스위칭 소자가 요구되어 제조원가가 높다. 그리고 문제 발생 시 용접기의 사용이 불가능하게 된다. 개발된 단위모듈을 병렬로 연결하여 대용량 용접기를 구성하게 되면 제조원가를 절감할 수 있으며 병렬로 연결되어 단위 모듈에 문제가 발생하여도 계속적인 사용이 가능하고, 주 회로를 작은 용량으로 분산시켜 전력을 제어하므로 높은 에너지 효율을 가지게 된다. 또한 인버터 용접기의 가장 중요한 성능인 스위칭 주파수에 있어서도 기존의 인버터 용접기는 20kHz의 스위칭 주파수를 가지지만 본 기술은 낮은 전력을 병렬로 연결하여 대용량을 동시에 제어가능 하므로 약 70kHz의 고속제어가 가능하다. 본 연구에서는 개발된 용량 170A단위모듈을 병렬로 연결하여 단위모듈 집적형 인버터 아크용접기 510A, 680A급의 부하테스트 실시 및 기본출력특성에 대하여 실험하였으며, GMAW에서 ${\Phi}1.6$ 솔리드 와이어를 이용하여 두께 20t의 후판 맞대기 용접에 적용실험을 실시하였다. 그 결과 모든 전류영역에서의 부하특성 및 출력특성이 양호하게 나타났으며, 후판 맞대기 용접에서는 SAW에 버금가는 생산성과 용접특성을 얻을 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.565-572
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• 2009

This work intends to establish the reliability and fracture toughness $K_{IC}$ criterion of welded joints by EGW for high strength EH36-TMCP ultra thick plate. For this, firstly thermo elasto-plastic analysis has been carried out on two pass X-groove butt joint model to clarify the thermal and mechanical behaviour(residual stress, plastic strain, magnitude of stress and their distribution and production mechanism). Moreover, to establish fracture criterion, analysis of fracture toughness $K_{IC}$ has been performed under the notch machined and residual stress with the load condition on EGW welded joints. A quantitative fracture criterion for EGW welded joints is suggested by using $K_{IC}$.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.7
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• pp.585-596
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• 2013

This study introduces a hybrid approach combining numerical results with pre-developed analytical calculations for the sound radiation from the modal vibration of a thick, finite length cylinder with various boundary conditions. Structural vibrations of the cylinder are numerically investigated with the finite element method, and distributions of vibratory displacements on the cylinder surface are idealized as simple mathematical expressions based on the numerical results. Sound radiations from the normal vibration of the cylinder are calculated based on idealized modal displacements using a previously introduced theoretical solution. The results are confirmed with numerical analyses using the boundary element method. Based on these results, it can be concluded that the solutions suggested in this study have good accuracies in calculating the vibro-acoustic properties of a thick, finite cylinder with various boundary conditions. Also, the sound radiation characteristics of many practical components such as brake drums and motor housings are expected to be investigated using the procedure proposed in this study.

• Korean Journal of Metals and Materials
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• v.46 no.4
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• pp.257-266
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• 2008

AHydrogen induced cracking (HIC) was phenomenologically studied in terms of the effect of nonmetallic inclusions and hot rolling process parameters. By comparing the level of non-metallic inclusions in two different kinds of commercial grade steels having different HIC resistance, the role of non-metallic inclusions in HIC occurrence was investigated. Change in inclusion morphology and distribution during hot rolling was also studied throughout slab, rolling at austenite recrystallization region (roughing mill; RM) and rolling at austenite non-recrystallization region (finish mill; FM). In addition, the contribution of RM and FM parameters to HIC was investigated from the standpoint of change in inclusion morphology during hot rolling processes. As a result, HIC was closely related to the separation of large complex inclusion during hot rolling process. Large complex inclusions originated from the improper Ca treatment, after which equilibrium composition of slag should have resulted in eutectoid composition. By controlling the equilibrium slag composition equivalent to eutectoid one, HIC resistance could be improved due to the reduced size of inclusions. In addition, change in reduction/pass in RM had an effect on HIC resistance of steels while that in FM did not. Increase in the reduction/pass in the latter stage of RM improved HIC resistance of steels by enhancing the void enclosure around inclusions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.67-74
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• 2006

The use of steel plates has been greatly increased in bridge construction, particularly for long-span bridges. For connections of those steel plates in the field, application of high-tension bold, such as M30, is highly demanded. However, the current steel construction specifications in Korea do not provide information for large-sized bolt connections. In order to evaluate the applicability of the large-sized high-tension bolt, this study experimentally investigates relaxation and slip behavior of M30 bolts with varying bolt size and plate thickness. In addition, internal compressive stress was computed using FEM analysis. The analyzed results were compared with the stress distribution measured from strain gages attached on bolts and bolt holes. From the study presented herein, the M30 high-tension bolts are anticipated to be successfully used with the relaxation less than 10% and the slip coefficient satisfying the specified limit.

• Korean Journal of Ichthyology
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• v.34 no.3
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• pp.153-159
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• 2022

The olfactory organ of a Korean endemic species, Pseudobagrus koreanus, was investigated to describe its morphology and histology and analyze correlation between habitat environment and its ecological habits and characters, using a stereo microscope, a light microscope, and a scanning electron microscope. Its external morphology showed tubular anterior nostril at the tip of the snout and slit posterior nostril at the base of the nasal barbel. The olfactory chamber showed the rosette structure consisting of numerous lamellae radial and parallel to the medium raphe. The olfactory lamella has the sensory epithelium with olfactory receptor nuerons, supporting cells, basal cells, lymphatic cells, plasma cells and the non-sensory epithelium with stratified epithelial cells, mucous cells, lymphatic cells. In particular, 1) 41~43 (n=20) lamellae, 2) lymphatic cells and plasma cells, 3) mucous cells including neutral polysaccharid may be olfactory characteristics relevant to a stagnant or a standing habitat environment, nocturnal habit dependent on olfaction, and taxonomic characters compared at least to other catfish species.

• Korean Journal of Ichthyology
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• v.32 no.2
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• pp.49-54
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• 2020

The morphometry and morphology of the olfactory organ of the southern king spine loach Iksookimia hugowolfeldi were investigated by stereo microscopy and statistical analysis. Its external morphology consists of two holes, the anterior and posterior nostrils. The anterior nostril (0.35~0.53 mm in diameter) forms tubular process protruding vertically from each side of the snout. The posterior nostril (0.32~0.68 mm in major diameter) is a eye-like hole parallel to the skin. Internally, the rosette structure is set with 14 to 21 lamellae and medium raphe on the inner floor. In morphometry, its lamellar number (male vs. female; 18±1.8 vs. 17±1.6, P<0.05) and lamellar number to standard length ratio (24.2±1.3% vs. 21.7±2.5%, P<0.05) was larger in male than female. The lamellar number and standard length have high correlation in male (P<0.001) but not in female (P=0.170). It seems that such characteristics of the olfactory organ of I. hugowolfeldi are related to its bottom-dwelling life which digs and takes a rest under sand and sexual dimorphism by a distinct degree in olfactory dependence for reproduction of each sex.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.407-418
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• 2014

As a continuing work of previously conducted standard tension tests, full-scale flexural tests were conducted in this study to assess the structural performance the CJP groove welded joints connecting thick HSA800 plates. Two welding electrodes were available at the time of this experimental research; one was GMAW-based electrode A and the other FCAW-based electrode B. Three full-scale box-type beam specimens with single bevel- and V-groove CJP welded joints were fabricated from 60mm and 25mm thick HSA800 plates according to the AWS-prequalified groove welded joint details. In designing the specimens, all possible limit states like local and lateral torsional buckling were carefully controlled in order to induce flexural plastic yielding or eventual joint fracture. All the CJP joints made by both welding electrodes showed satisfactory performance and were able to transfer the tensile flange forces higher than that corresponding to the measured tensile strength of HSA800 flange plates. However, it should be noted that, during fabrication, serious concerns about the welding efficiency and workability of the GMAW-based electrode were raised by a certified welder. The fracture occurred at the unbeveled (or vertical) interface between the weldment and the base metal when the GMAW-based electrode was used in the single-bevel joint, implying the possibility of insufficient melting. Thus, the FCAW-based electrode B is again recommended as the choice of welding electrode for HSA800 plates. The limited test data of this study implies that the V-groove CJP joint should be used in favor of the single bevel CJP joint, if possible.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1519-1520
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• 2013

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.269-270
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• 2010