• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.21-30
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• 2001

The analysis system implementing a serial process from structural vibration to sound radiation has been developed using both the power flow finite element method (PFFEM) known as a new vibrational analysis technique in medium to high frequency ranges and the acoustic boundary element method (BEM) which is effective in analyzing the sound radiation problems. The vibration analysis for arbitrary shape structures composed of plates is performed, and using the vibration energy density obtained from this analysis as the velocity boundary conditions for an acoustic analysis, vibro-acoustic analysis has been processed. To verify the developed system, we select a simple structure model and compare the results of developed system with those of SYSNOISE, and also the developed system is applied for the vibro-acoustic analysis of various structures in shapes.

• Water for future
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• v.6 no.2
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• pp.60-73
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• 1973

• Journal of Astronomy and Space Sciences
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• v.18 no.2
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• pp.153-162
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• 2001

In this paper, space radiation environment and total ionizing dose(TID) effect have been analyzed for the KOMPSAT-2 operational orbit. It has been revealed that the trapped protons are concentrated in the SAA(South Atlantic Anomaly) area and that the trapped protons and electrons, and solar protons are main factors affecting TID. It turned out that low energy Particles can be effectively blocked by aluminum shielding thickness, but high energy Particles can not be effectively blocked by increasing aluminum shielding thickness. KOMPSAT-2 total radiation dose which is accumulated continuously to spacecraft electronics has been expressed as the function of aluminum thickness. These values ran be used as the criteria for the selection of electronic parts and shielding thinkness of the KOMPSAT-2 structure or electronic box.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.3
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• pp.128-137
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• 2013

Due to the global warming and air pollution, interest in renewable energies has increased in recent years. In particular, the crisis of the depletion of fossil energy resources in the near future has accelerated the renewable energy technologies. Among the renewable energy resources, oceans covering almost three-fourths of earth's surface have an enormous amount of energy. For this reason, various approaches have been made to harness the tremendous energy potential. In order to achieve two purposes: to improve harbor water quality and to use wave energy, this study proposed a sea water exchange structure applying an Oscillating Water Column (OWC) wave generation system that utilizes the air flow velocity induced by the vertical motion of water column in the air chamber as a driving force of turbine. In particular, the airflow velocity in the air chamber was estimated from the time variations of water surface profile computed by using 3D-NIT model based on the 3-dimensional irregular numerical wave tank. The relationship of the frequency spectrums between the computed airflow velocities and the incident waves was analyzed. This study also discussed the characteristics of frequency spectrums in the air chamber according to the presence of the structure, wave deformations by the structure, and the power of the water and air flows were also investigated. It is found that the phase difference exists in the time series data of water level fluctuations and air flow in the air chamber and the air flow power is superior to the fluid flow power.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.136-137
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• 2002

크롬-몰리브덴 강종들은 고온에서 우수한 기계적 성질을 나타내기 때문에 에너지 변환설비 및 압력용기 등에 폭넓게 사용되고 있다. 그러나 고온에서 장시간 사용됨에 따라 입계에 탄화물의 형성 및 조대화, 용질원자의 결핍, 불순물의 편석 등 미세조직의 변화에 의해 초기의 우수한 기계적 성질이 저하되는 경년열화 현상이 나타나고 있다. 따라서, 이들 대형기기 및 구조물의 보다 신뢰성 있는 품질보증과 정기적인 가동 중 검사가 요구되어지고 있다. (중략)

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.391-399
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• 2008

In this paper, we further generalize the work of Lin and Abel to the case of the first and the second order derivatives of energy release rates for two-dimensional, multiply cracked systems. The direct integral expressions are presented for the energy release rates and their first and second order derivatives. The salient feature of this numerical method is that the energy release rates and their first and second order derivatives can be computed in a single analysis. It is demonstrated through a set of examples that the proposed method gives expectedly decreasing, but acceptably accurate results for the energy release rates and their first and second order derivatives. The computed errors were approximately 0.5% for the energy release rates, $3\sim5%$ for their first order derivatives and $10\sim20%$ for their second order derivatives for the mesh densities used in the examples. Potential applications of the present method include a universal size effect model and a probabilistic fracture analysis of cracked structures.

• Journal of the Korean Institute of Gas
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• v.17 no.6
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• pp.52-57
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• 2013

In this study, the strain energy density, stress and deformation behaviors have been analyzed as functions of a thickness and a force area of protective helmets with and without an extruder on the top of the shell structure using the finite element method. The strain energy density in which is related to the absorption capacity of an impact energy transfer is one of a key element of the helmet safety. The FEM analyzed results show that when the impulsive force of 4,540N is applied on the top surface of the helmets, the maximum stress is linearly reduced for an increased area of impact forces. But, the maximum strain energy density has been reduced for the increased force area. The reduced strain energy density may increase the impulsive forces transferred to the head and neck of helmet wearers, which may decrease the impact energy absorption safety of the helmets. In thus, it is safer design of the helmet in which has an extruded structure on the summit surface, but the modified helmet may decrease the impact energy absorption capacity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.159-166
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• 2007

This paper evaluates the soundness of structural elements using Wavelet Packet Transform (WPT). WPT is applied to the response acceleration of a framed structure which is subjected to earthquake load to decompose the response acceleration, then the energy of each component is calculated. The first five largest components in energy magnitude among the decomposed components are selected as input to an ANN to identify the damage location and severity. Two nodes in output layer yield damaged element and damage severity respectively. This method successfully evaluates the amount of damage and its location in the structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.140-146
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• 2008

The damage evaluation method for framed structures using continuous wavelet transform (CWT) is proposed. CWT is applied to the response acceleration of a structure subjected to earthquake load to decompose the response acceleration corresponding to each scale, then the normalized energy value for each scale is calculated. The difference between the normalized energy curvature (NEC) in each node before and after damage indicates a damaged element, which makes it possible to assess the soundness of structural elements. As damage becomes more severe the difference in normalized energy curvature becomes larger. The NEC calculated from the signal corresponding to high scale in CWT analysis is found to be a good index that shows the location and severity of damage.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.11a
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• pp.85-87
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• 2018

전 세계적으로 온실가스 배출 규제가 강화되고 있고 에너지 절감 및 환경오염 문제가 없는 재생에너지에 대한 관심이 높아지고 있다. 육상 전력을 공급받기 어려움 해양 구조물의 경우에는 배터리와 같은 에너지 저장장치 또는 재생에너지를 활용하여 독립 전원 시스템을 구성하게 된다. 해양에서 활용이 가능한 재생에너지로는 태양광, 풍력, 파력, 조력등이 있으며 이러한 자연 에너지를 활용하는 재생에너지 발전 시스템의 경우 환경의 영향을 많이 받게 되므로 안정적인 전력 생산에 어려움이 있다. 예를 들어 태양광 발전 시스템의 경우 일조량에 따라 발전량이 결정되고, 풍력 발전 시스템의 경우 풍속 및 풍향이 발전량에 영향을 미친다. 따라서 독립전원시스템에서 태양광-풍력-파력의 멀티소스를 갖는 하이브리드 발전 시스템을 구성하여 기상상태에 따른 발전량을 보완가능하게 구성하면 보다 안정적으로 전력을 얻을 수 있다. 본 연구에서는 항만 및 협수로를 항해하는 선박 안전을 위해 설치된 등부표에 적용하는 해상하이브리드발전시스템을 설계하고 실증을 통해 하이브리드 발전시스템의 발전 특성을 확인한다.