• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.496-500
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• 1997

This paper describes an automated system for analyzing the stress intensity factors(SIFs) of three-dimensional (3D) cracks. A geometry model, i.e.a solid containing one or several 3D cracks is defined. Several distributions of local node density are chosen, and then automatically superposed on one another over the geometry model by using the fuzzy knowledge processing. Nodes are generated by the bucketing method, and ten-noded quadratic tetrahedral solid elements are generated by the Delauuay triangulation techniques. The singular elements such that the mid-point nodes near crack fornt are shifted at the quarter-points are automatically placed along the 3D crack front. THe complete finite element (FE) model generated, i.e the mesh with material properties and boundary conditions is given to one of the commercial FE codes, and a stress analysis is performed. The SIFs are calculated using the displacement extrapolation method. To demonstrate practical performance of the present system, a semi- elliptical surface crack in a plate subjected to tension is solved.

• 대한기계학회논문집A
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• 제33권11호
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• pp.1187-1194
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• 2009

During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.

• 한국CDE학회논문집
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• 제4권4호
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• pp.381-390
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• 1999

In this study, a pseudo ship structure data model for the :.hip cargo hold structure based on STEP is proposed. The proposed data model is based on Application Reference Model of AP218 Ship Structure which is the model that specifies conceptual structures and constraints used to describe the information requirements of an application. And the proposeddata model refers the Ship Common Model framework for the model architecture which is the basis for ongoing ship AP development within the ISO ship-building group and the ship product definition information model of CSDP research project for analyzing the relationship between ship structure model entities. The proposed data model includes Space, Compartment. Ship Structural System, Structural Part and Structural Feature of cargo hold. To generate this data model schema in EXPRESS format, ‘GX-Converter’was used which enables user to edit a model in EXPRESS format and convert schema file in EXPRESS format. Using this model schema, STEP physical file containing design data for ship cargo hold data structure was generated through SDAI programming. The another STEP physical file was also generated containing geometry data of ship cargo hold which was extracted and calculated by SDAI and external surface/surface intersection program. The geometry information of ship cargo hold can be then transferred to commercial CAD system, for example, Pro/Engineer. Examples of the modification of the design information are also Presented.

• 소성∙가공
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• 제21권8호
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• pp.493-498
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• 2012

A wheel nut wrench is one of the hand tools used to loosen and tighten lug nuts on automobile wheels and it has generally a solid-type geometry for commercial vehicles. However, the solid-type wheel nut wrenches manufactured by hot forging processes exhibit several drawbacks such as heavy weight and rough surface finish. Thus, many efforts have been devoted to change the part geometry and improve the manufacturing process. For this purpose, the weight of the final product can be reduced drastically using a hollow tube as the initial stock, which can be manufactured by the more economical manufacturing process of cold forging. In this study, the cold forging of a hollow-type wheel nut wrench for commercial vehicles was designed based on the results of fundamental experiments and CAE analyses using the commercial finite element code DEFORM-3D. In addition, cold forging experiments were conducted on a special-purpose forming machine for hollow wheel nut wrenches in order to validate the designed process sequence. As results, it was found that the final products with a weight reduction of 39% and better surface appearance can be manufactured without any defect with the newly designed cold forging process.

• 대한조선학회논문집
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• 제29권1호
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• pp.29-42
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• 1992

Spade Type 타의 단독 특성을 추정하기 위하여 3차원 Panel Method를 사용하였다. 입사류는 균일하며 시간에 따라 변하지 않는다고 가정하였고, 타 표면에 쏘오스 및 다이폴을 분포하였다. 후류면은 타의 뒷날에서 물체로부터 떨어져 나간다고 가정하였으며, 후류면에는 다이폴을 분포하였다. 후류면은 물체의 뒷날과 무한 원방에서 적당한 조건을 부여함으로써 그 형상을 가정하였으며, 후류 형상의 차이가 최종 결과에 미치는 영향을 고찰하였다. 뒷날에서는 3차원 압력 Kutta 조건을 적용하였으며, 2차원 Kutta조건을 적용한 결과와 비교하여 보았다. Spade Type 타에 대한 계산을 수행하였으며, 실험 결과와 전반적으로 잘 일치함을 확인하였다. 본 연구에서 사용한 방법은 타의 초기 설계 단계에서 유용하게 사용할 수 있을 것이다.

• Bulletin of the Korean Chemical Society
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• 제34권4호
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• pp.1043-1046
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• 2013

Prediction of physicochemical properties of organic molecules is an important process in chemistry and chemical engineering. The MSEP approach developed in our lab calculates the molecular surface electrostatic potential (ESP) on van der Waals (vdW) surfaces of molecules. This approach includes geometry optimization and frequency calculation using hybrid density functional theory, B3LYP, at the 6-31G(d) basis set to find minima on the potential energy surface, and is known to give satisfactory QSPR results for various properties of organic molecules. However, this MSEP method is not applicable to screen large database because geometry optimization and frequency calculation require considerable computing time. To develop a fast but yet reliable approach, we have re-examined our previous work on organic molecules using two semi-empirical methods, AM1 and PM3. This new approach can be an efficient protocol in designing new molecules with improved properties.

• Journal of Welding and Joining
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• 제28권5호
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• pp.86-92
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• 2010

In GMAW processes, bead geometry is a criterion to estimate welding quality. Bead geometry is affected by welding current, arc voltage, welding speed, shielding gas and so on. Thus the welding condition has to be selected carefully. In this paper, an experimental method for the selection of optimal welding condition was proposed in the root pass welding which was done along the GMA V-grooved butt weld joint. This method uses the response surface analysis in which the width and height of back bead were chosen as the quality variables of the weld. The overall desirability function, which is the combined desirability function for the two quality variables, was used as the objective function for getting the optimal welding condition. Through the experiments, the target values of the back bead width and the height were chosen as 4mm and 1mm respectively for the V-grooved butt weld joint. From a series of welding test, it was revealed that a uniform weld bead can be obtained by adopting the optimal welding condition which was determined according to the method proposed.

• 한국음향학회지
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• 제29권7호
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• pp.431-438
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• 2010

곡면에 지지된 음원의 경우 음원의 배열 방식에 따라 방사되는 음장이 매우 복잡한 특성을 가진다. 본 연구에서는 곡면 배열 트랜스듀서를 구성하는 음원을 등각, 등간격 그리고 geodesic dome 형태로 배열하여, 각각의 배열 방식에 따른 음향 방사 패턴 함수를 유도하고, 그에 따라 방사 패턴을 해석하였다. 해석 결과를 바탕으로 3가지 배열 방법 가운데 상대적으로 주엽의 빔 폭이 크고 부엽의 크기가 작은 경향을 보이는 등간격 배열을 곡면 배열 트랜스듀서의 구조로 선정하였다. 본 연구 결과는 곡면 배열 트랜스듀서의 구조 설계에 활용될 수 있을 것으로 기대된다.

• 한국음향학회지
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• 제31권4호
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• pp.214-224
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• 2012

The objective of this paper is to design multichannel spherical loudspeaker array by considering various positioning methods such as Gaussian grid, Lebedev grid and packing method. For the spatial sound manipulation, which is to make desired sound field by controling multiple sound sources, the Kirchhoff-Helmholtz integral states that sound fields can be reproduced in terms of infinite control sources on the integral surface. But since we cannot control infinite number of sources for the implementation, we have to allocate finite number of sound sources which can approximately act as infinite number of sources. To manipulate sound field inside of a sphere (which is typical example of three dimensional array) by controlling sound sources on the surface, three methods of allocating sound sources, which are Gaussian grid, Lebedev grid and packing method, are reviewed. For each geometry, the performances of manipulation rendered by time-reversal operator and higher-order ambisonics are compared.

• 한국전자파학회논문지
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• 제28권1호
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• pp.80-83
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• 2017

본 논문에서는 휘어짐이 가능한 유연한 기판 위에 X-대역에서 동작하는 PIN 다이오드 기반 재구성 주파수 선택 표면구조 (RFSS)를 설계하였다. 제안된 구조는 윗면에 십자형 루프 패턴과 인덕턴스 성분의 스터브 사이에 위치한 PIN 다이오드의 전기적 제어를 통해 C-대역(OFF)과 X-대역(ON)에 대한 주파수 재구성이 가능하며, 그리드 형태의 전원 바이어스 회로와 비아홀구성을 통해 기생 결합을 최소화함으로써 단위구조와의 격리도를 확보하였다. 설계한 결과를 바탕으로 유연한 필름기판위에 제안한 RFSS 를 제작하고, 측정 실험을 통해 입사파의 편파와 입사각 그리고 단일 곡률을 갖는 곡면에 대한 안정적인 투과 특성을 확인하였다.