• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.5
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• pp.388-397
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• 2012

In this study, 3D-NIT(3-Dimensional Numerical Irregular wave Tank) model in which regular wave as well as stable irregular wave can be generated in 3-dimensional numerical irregular wave tank was proposed. To verify validity, the following steps need to be conducted: 1) comparative analysis between calculated waveforms and targeted waveforms at the wave generating point, 2) comparative analysis with the existing experimental values of overtopping volume estimated, targeting shore protection structures installed on a slope bed, 3) comparison with the existing numerical and hydraulic experimental results through application in the analysis on the wave deformation by structures and wave force acting on the vertical cylindrical structures. Based on the results, characteristics of the breaking wave forces according to incident waves and interval distance of structures were identified through application of 3D-NIT model in the analysis on the breaking wave forces acting on the cylindrical structures installed on a slope bed, and reflection and overtopping was reviewed through application in the special breakwaters on the domestic fields. The numerical results obtained the 3D-NIT model are in good agreement with experimental results, and its applicaion to the complex-shpaed coastal structures is verified.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.206-216
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• 2002

The finite element method (FEM), a powerful numerical modeling tool for solving various engineering problems, is frequently applied to three-dimensional (3-D) modeling thanks to its capability of discretizing and simulating the shape of model with finite number of elements. Considering the accuracy of the solution and computing time in modeling of engineering problems, it is preferable to construct physical continuity and simplify mesh system. Although there exist systematic mesh generation systems for arbitrary shaped model, it is hard to model a simple cylinder in terms of 3-D coordinate system especially in the vicinity of the central axis. In this study I adopt cylindrical coordinate system for modeling the 3-D model space and define the origin of the coordinates with mathematically clear coordinate transformation. Since we can simulate the whole space with hexahedral elements, the cylindrical coordinate system is effective in handling the 3-D model structure. The 3-D do resistivity modeling scheme developed in this study provides basie principle for borehole-to-surface resistivity survey, which can be a useful tool for the application to environmental problem.

• Korean Journal of Optics and Photonics
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• v.28 no.6
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• pp.281-289
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• 2017

In the present research, the optical measurement error induced by vibration of the optical measurement tower for large mirrors at KRISS (Korea Research Institute of Standards and Science) is investigated. The vibrations of the tower structure, the interferometer, and the null lens are measured while the surface errors of the 600-mm-diameter on-axis aspheric mirror are measuring, under various environmental conditions. The increase of surface error induced by alignment error with respect to vibration is analyzed. As a result, the interferometer and the null lens, which are located on the top of the tower, are highly sensitive to vibration. Additionally, the surface error of the mirror is strongly increased when the vibration directions of the interferometer and the null lens are different. To reduce the alignment error and the surface error induced by vibration, the tower structure should be improved, to be insensitive to low-frequency vibration. Alternatively, optical measuring under stable conditions by vibration monitoring can improve the reliability of the surface error measurement.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.258-263
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• 1995

미래 정보와 시대에서 중추적인 역할을 할 광관련 멀티미디어 장비들은 최근 관련 산업계에서 주목을 받기 시작하고 있고 특히 기존 VTR(Video Tape Recorder) 시장을 대체할 차세대 DVDR(Digital Video Disk Recorder)는 기술전쟁이라고 할 정도로 선진 기업의 연구가 치열해지고 있다. DVDR 시스템에서는 필요한 정보들을 레이저빔을 이용한 광학신호로 바꾸어 광디스크에 기록, 재생하는 광픽업이 절대적으로 필요하게 된다. 그런데 광픽업의 위치추종기구인 Actuator는 정확한 위치추종(.+-.1.$\mu$m 오차이내)을 할 수 있는 성능이 요구되며 서보의 특성상 20KHz 이하에서 불필요한 모우드가 가진되지 않는 정밀부품이어야 하므로 Actuator 각 부품의 동적인 특성을 명확히 규명할 필요가 있다. 따라서 본 연구에서는 우선 Actuator 각 부품과 가동부 전체의 중량 및 진동해석을 통해 동특성을 조사하였다. 그리고 Actuator의 중요한 기본성능중 하나인 구동감도 확보여부를 검토할 필요가 있기 때문에 유한요소법 프로그램인 ANSYS를 이용하여 자기회로 부분에 대한 해석을 구하였다. 또한 가동부와 자기회로 등 하위부품을 조립하는 과정에서 발생하는 조립오차로 인해 불필요한 공진과 회전형상이 야기될 수 있으므로 동특성 및 문제점 파악을 위한 민감도 분석이 필요하다. 따라서 본 연구에서는 가동부의 관성 모멘트 값과 강체에 대한 일반식을 이용한 자체 프로그램을 작성하여 조립공차를 구하였다. 이와같은 과정을 통해 구해진 설계값을 바탕으로 실제 제작된 Actuator에 대해서는 비접촉식 측정방법을 통해 동특성값을 측정하였고 이를 해석값과 상호 비교하였다.동강성행렬법(dynamic stiffness matrix method)을 이용하여 해석하고자 한다. 수준임이 입증되었다. 본 연구의 결과를 토대로우리나라 젊고 건강한 남성에게 적합한 무게상수는 작업자군에 대하여 25.05kg, 학생군에 대하여 20.24kg 으로 나타나 이는 미국 NIOSH 안전기준과 대체로 일치함을 발견하였다.ive structures utilized in Client/server architecture for distribution and cooperative processing of application between server and client this study presents two different data management methods under the Client/server environment; one is "Remote Data Management Method" which uses file server or database server and. the other is "Distributed Data Management Method" using distributed database management system. The result of this study leads to the conclusion that in the client/server environment although distributed application is assumed, the data could become centralized (in the case of file server or database server) or decentralized (in the case of distributed

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.189-200
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• 2017

Nonplanar structural walls with C-shaped and H-shaped sections have been used as an efficient lateral force-resisting system for building structures. Since the nonplanar walls are subjected to axial load and bending moments about two orthogonal axes, complicated section analysis is required for flexure-compression design. In the present study, a straightforward design method for biaxially loaded C- and H-shaped walls was proposed by modifying the existing load contour method for columns with symmetric solid sections. For this, a strain compatibility section analysis program that can calculate biaxial moment strengths of arbitrary wall section was developed and its validity was verified by comparing with existing test results. Then, through parametric study, the interaction of biaxial moments at constant axial loads in prototype C- and H-shaped walls was investigated. The results showed that, due to unsymmetrical geometry of the wall sections, the biaxial interaction was significantly affected by the moment directions and axial loads. From those investigations, non-dimensional contour equations of the biaxial moments at constant axial loads for C- and H-shaped walls were suggested. Further, design examples using the proposed contour equations were given for engineering practice.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1093-1098
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• 2013

A single-crystal sapphire is used as a transparent bulletproof window material; however, few studies have investigated the dynamic behavior and fracture properties under high-speed impact. High-speed and high-resolution sequential images are required to study the interaction of the bullet with the brittle ceramic materials. In this study, a device is developed to capture the sequence of high-speed impact/penetration phenomena. This system consists of a speed measurement device, a microprocessor-based camera controller, and multiple CCD cameras. By using a linear array sensor, the speed-measuring device can measure a small (diameter: up to 1 2 mm) and fast (speed: up to Mach 3) bullet. Once a bullet is launched, it passes through the speed measurement device where its time and speed is recorded, and then, the camera controller computes the exact time of arrival to the target during flight. Then, it sends the trigger signal to the cameras and flashes with a specific delay to capture the impact images sequentially. It is almost impossible to capture high-speed images without the estimation of the time of arrival. We were able to capture high-speed images using the new system with precise accuracy.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.12
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• pp.1223-1231
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• 2010

The design is presented for a SATCOM antenna capable of simultaneous multi-band (X/Ku/Ka-Band) communications without replacement of feed horns or change of other parts in the application as a ground satellite terminal for large data transfer. The antenna is the offset configuration and consists of a dual-band(X/Ka-band) feed horn, a single-band(Ku-band) feed horn, a frequency selective surface(FSS) sub-reflector and a parabolic main-reflector. The antenna has a main reflector defining a prime focus and a frequency selective surface sub-reflector defining an image focus. A dual-band feed and a single-band feed are provided at each of the prime focus and image focus. The antenna is designed using 3D EM simulator and the gains measured in X/Ku/Ka-band of the complete antenna assembly is more than 31.6dBi, 36.8dBi, 40.8dBi, and the cross polarization is 21.7dB, 26.6dB, 25.2dB, respectively.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.4
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• pp.466-471
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• 2007

The purpose of study is to obtain basic but important information for the operation of the greenhouse facility located in the suburb of town. Special emphasis is given on the aspect of energy saving method, which can be easilyapplicable in a practical sense. For this end numerical calculation has been made systematically in order to increase the energy efficiency by the evaluation of the temperature distribution in greenhouse. Major parameters considered are primarily the overall shape of greenhouse together with the various conditions of baffle installion inside greenhouse. Further, the performance of heating system is also carefully compared each other for a number of typical arrangements of heating duct. The performance of the computer program developed in this study is evaluated by the observation of the famous fluid trapping phenomenon occurred in staggered baffle condition in the enclosure of greenhouse. Based on the this study, a number of useful conclusions can be drawn, that is, the installation of baffles are quite effective in energy saving method with a minor modification of facility. Also, it is found that the change of the heating duct system can contribute significantly to the uniform temperature distribution in greenhouse. Further other findings obtained by numerical calculation were not only physically consistent and meaningful but also useful for the determination of optimum condition of practical operation of greenhouse.

• Journal of Korean Society of Steel Construction
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• v.21 no.1
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• pp.37-44
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• 2009

A truss deck system that has replaced the slab form conventional method has become widely used in the construction of reinforced concrete structures as well as steel structures. The current commercial products, however, have some problems. The discontinuity between the lattice wires on the joint of the bottom wire induces vierendeel behavior, which increases the deflection of the system. In this research, a new truss deck system with continuous lattice wires on the level of the bottom wire was developed to reduce the system's vierendeel behavior and to improve its deformation capacity. To investigate the system's structural behavior, an experimental test and an analysis were performed. The main parameters of the test and analysis were the longitudinal shape and spacing of the lattices. To simulate the loading condition in the construction field, uniform construction loads were directly applied on the deck plates of the analysis model and the test specimens. The results of such analysis and test revealed that the longitudinal shape of the lattice wires is a major factor affecting the structural behavior of a steel wire truss deck. Thus, continuous lattice wires could result in decreased vierendeel behavior in the steel wire truss deck. It was also found that the truss deck system with lattices spaced longer than in the conventional products could be effectively used without increasing the member stresses.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.10
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• pp.530-540
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• 2005

Virtual colonoscopy is an easy and fast method to reconstruct the shape of colon and diagnose tumors inside the colon based on computed tomography images. This is a non-invasive method, which resolves weak points of previous invasive methods. The path for virtual colonoscopy should be generated rapidly and accurately for clinical examination. However, previous methods are computationally expensive because the data structure such as distance map should be constructed in the preprocessing and positions of all the points of the path needs to be calculated. In this paper, we propose the automatic path generation method based on visibility to decrease path generation time. The proposed method does not require preprocessing and generates small number of control points representing the Path instead of all points to generate the path rapidly. Also, our method generates the path based on visibility so that a virtual camera moves smoothly and a comfortable and accurate path is calculated for virtual navigation. Also, our method can be used for general virtual navigation of various kinds of pipes.