• 대한조선학회논문집
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• 제54권6호
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• pp.447-452
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• 2017

A rigid body supported by 4 linear springs has been analyzed, to investigate the effects of eccentricities on the vibration responses for naval shipboard equipments supported by elastic mounts. Considering mount eccentricity (the location of the center of spring reaction forces relative to the mass center) and excitation force eccentricity (the location of the center of the excitation force relative to the mass center), the vibration phenomena have been formulated and discussed. Also, the effects of the eccentricities have been evaluated and discussed for the elastically mounted naval shipboard equipment. Results show that the mount eccentricity has little effects on the structure-borne noise above the natural frequency of the system, however the excitation force eccentricity has significant effects all over the frequency range.

• 한국통신학회논문지
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• 제26권12C호
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• pp.218-224
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• 2001

분산병렬처리의 목적은 다양한 내재 병렬 형태의 특징을 갖는 연산 집약적 문제를 고속 네트웍으로 연결되어진 다수의 고성능 및 병렬 컴퓨터들의 각기 다른 능력을 최대한 이용하여 해결함에 있다. 본 논문에서는 분산병렬시스템을 이용하는 경우의 성능 향상 분석을 위해 일반적인 그래프 표현 방법을 포함하는 계산 모델을 제안하고 프로그램의 수행을 위한 스케쥴링 시에 성능 향상이 어떠한 요인에 의해 달성되는지를 분석한다. 제안된 표현 방법은 동기종 및 이기종 시스템 모두에 적용되어질 수 있다. 분산병렬 시스템에서 스케줄링을 통하여 더 많은 속도향상을 얻기 위해서는 태스크와 병렬 컴퓨터간의 병렬특성의 일치가 주의 질게 다루어져야 하며 태스크의 이동으로 인한 통신 오버 헤드가 최소화 되어야 한다.

• International Journal of Fluid Machinery and Systems
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• 제8권2호
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• pp.94-101
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• 2015

To investigate the influence of blade profiles on cavitation behavior in impeller of centrifugal pump, a centrifugal pump with five different blade profiles impellers are studied numerically. The impellers with five different blade profiles (single arc, double arcs, triple arcs, logarithmic spiral and linear-variable angle spiral) were designed by the in-house hydraulic design code using geometric parameters of IS 150-125-125 centrifugal pump. The experiments of the centrifugal pump have been conducted to verify numerical simulation model. The numerical results show that the blade profile lines has a weak effect on cavitation inception near blade inlet edge position, however it has the key effect on the development of sheet cavitation in impeller, and also influences the distribution of sheet cavitation in impeller channels. A slight changing of blade setting angle will induce significant difference of cavitation in impeller. The sharp changing of impeller blade setting angle causes obvious cavitation region separation near the impeller inlet close to blade suction surface and much more flow loss. The centrifugal pump with blade profile of setting angle gently changing (logarithmic spiral) has the super cavitation performance, which means smaller critical cavitation number and lower vapor cavity volume fraction at the same conditions.

• 반도체디스플레이기술학회지
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• 제8권4호
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• pp.53-58
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• 2009

A SMT mounter is a kind of equipment that mounts SMD parts quickly on the printed circuit board. By using linear motors, it is controlled with high speed and precision, which is similar to semi-conductor and display process equipment. It is necessarily used in an assembly process of an electronic device. Mobile devices such as a mobile phone and PDA are required to reduce mount areas due to the demands for high performance and small size. Hence, super small sized and complex mobile devices have been developed. To improve the productivity of the corresponding equipment, designs with large sized, high speed, and multidisciplinary functions have been consistently performed. Meanwhile, a design trend of large size and light-weight on SMT mounter causes a low natural frequency of systems and vibration problems at the high speed operation. In this paper, the dynamic characteristics of the SMD mounter system were investigated through a modal test and transmissibility test, and verified by finite element method. Also, various design improvement was performed to avoid the resonance phenomena.

• 한국해양공학회지
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• 제19권2호
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• pp.12-18
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• 2005

Typhoon Maemi landed on the southeast coast of Korea and caused a severe storm surge in Jinhae Bay and Masan Bay. The tide gage in Masan Port recorded the storm surge of a maximum of more than 2m and the area of more than 700m from the Seo Hang Wharf was flooded by the storm surge. They had not met such an extremely severe storm surge since the opening of the port. Then storm surge was hindcasted with a numerical model. The typhoon pressure was approximated by Myers' empirical model and super gradient wind around the typhoon eye wall was considered in the wind estimation. The land topography surrounding Jinhae Bay and Masan Bay is so complex that the computed wind field was modified with the 3D-MASCON model. The motion of seawater due to the atmospheric forces was simulated using a one-layer model based on non-linear long wave approximation. The Janssen's wave age dependent drag coefficient on the sea surface was calculated in the wave prediction model WAM cycle 4 and the coefficient was inputted to the storm surge model. The result shows that the storm surge hindcasted by the numerical model was in good agreement with the observed one.

• 원자력산업
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• 제20권6호통권208호
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• pp.31-44
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• 2000

본 연구에서 액체금속로의 노심용융(core meltdown)으로 인한 초 즉발 임계(super-prompt critical)의 출력 폭주 사고시, 노심의 반응도 및 열수력 특성 변화와 에너지 방출량등을 계산하기 위하여, Bethe-Tait 방버론을 수정, 보완한 분석 모델이 개발되었다. 주요 보완 내용으로서는, 금속 연료 노심의 단상 액체 영역에서의 선형의(Linear) threshold 형태의 상태 방정식뿐만 아니라 포화 증기(saturated fuel vapor) 영역에서의 상태 방정식이 개발되었고, 이에 따른 노심 붕괴 반응도(disassembly reactivity)의 분석 모델이 개발되었다. 또한 도플러 반응도 효과를 고려하기 위한 분석모델도 아울러 개발되었다. 상기 보완 모델을 실행할 수 있는 수치 해석 프로그램이 개발되었고, 이를 활용하여 KALIMER에서 HCDA가 발생하였을 경우 노심에서의 에너지 방출량 계산이 수행되었다. 분석결과 도플러 효과와 포화 증기 영역에서의 압력 증가 및 노심팽창의 중요성이 확인되었다. 도플러 효과가 고려되지 않을 경우 HCDA는 분석된 모든 반응도 삽입률에 대하여 폭발적인 에너지 방출과 함께 사고가 종결되는 것으로 평가되었다. 그러나 도플러 상수가 최적 평가치인 -0.002인 경우 50$/s이하의 반응도 삽입률에서는 노심은 비등점(0.8KJ/g)에 도달치 않았으며, 설계 기준 사고인 100$/s의 경우에도 노심은 포화 증기 영역에 머물고 압력이 급격히 증가하는 단상(single phase)액체 영역의 threshold 값에 미치지 않기 때문에 사고는 핵연료 증기(vapor)의 점진적인 분산과 함께 종결되는 것으로 분석되며, 총 에너지 발생량은 약 1,800MJ로서 기계적 손상 에너지로 전환되는 분율을 고려할 때 KALIMER 원자로 용기의 구조 설계 기준치에 비해 상당한 여유도를 갖는 것으로 평가되었다.

• Environmental Analysis Health and Toxicology
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• 제23권2호
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• pp.67-77
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• 2008

It has been observed that the linear relationship between the logarithm of bioconcentration factor (log BCF) of highly hydrophobic chemicals and their log $K_{ow}$ breaks when log $K_{ow}$ becomes greater than 6.0. Consequently, super hydrophobic chemicals were not thought to cause baseline toxicity as a single compound. Researchers often call this phenomenon as "hydrophobicity cutoff" meaning that bioconcentration or corresponding baseline toxicity has a certain cutoff at high log $K_{ow}$ value of hydrophobic organic pollutants. The underlying assumption is that the increased molecular size with increasing hydrophobicity prohibits highly hydrophobic compounds from crossing biological membranes. However, there are debates among scientists about mechanisms and at which log $K_{ow}$ this phenomenon occurs. This paper reviews three hypotheses to explain observed "cutoff": steric effects, kinetic or physiological limitations, and chemical activity cutoff. Although the critical molecular size that makes biological membranes not permeable to hydrophobic organic chemicals is uncertain, size effects in combination with kinetic limitation would explain observed non-linearity between log BCF and log $K_{ow}$. Chemical activity of hydrophobic chemicals generally decreases with increasing melting point at their aqueous solubility. Thus, there may be a chemical activity cutoff of baseline toxicity if there is a critical chemical activity over which baseline effects can be observed.

• Journal of Biosystems Engineering
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• 제32권6호
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• pp.395-402
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• 2007

This study was carried out as basic researches to develop the leaf vegetable harvester. This study was conducted to investigate physical and rheological properties of bundled leaf vegetables with stem (Chinese leek, Crown daisy and Chamnamul) as test materials held and picked-up by a machine. Stress-strain behavior, stress relaxation, and strain recovery for the bundled materials were analyzed using simple Maxwell model. Physical and rheological properties of the materials were investigated by measuring rupture load, deformation and stress experimentally. Also, strain recovery time when unloading was measured using super high speed camera. Recorded recovery time for stress-strain behavior was0.026 s for Chinese leek with liner strain recovery, 0.046 s for Crown daisy and 0.05 s for Chamnamul with non-linear strain recovery. Furthermore, the strain recovery time for permanent deformation was 0.026 s, 0.046 s, and 0.05 s for Chinese Leek, Crown daisy and Chamnamul, respectively. Finally, strain recovery time and strain recovery ratio for the test materials were 0.17 s, 60.4% in Chinese leek, 0.12 s, 55.3% in Crown daisy, 0.15 s, 58.7% in Chamnamul. Here strain recovery time means that how fast the test materials are recovered from initial deformation and strain recovery ratio means how much the test materials are recovered from initial deformation. The above results show that the test materials can be held enough and moved by the belts.

• Journal of Astronomy and Space Sciences
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• 제29권4호
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• pp.363-374
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• 2012

This paper studies the problem of tracking a re-entry vehicle (RV) in order to predict its impact point on the ground. Re-entry target dynamics combined with super-high speed has a complex non-linearity due to ballistic coefficient variations. However, it is difficult to construct a database for the ballistic coefficient of a unknown vehicle for a wide range of variations, thus the reliability of target tracking performance cannot be guaranteed if accurate ballistic coefficient estimation is not achieved. Various techniques for ballistic coefficient estimation have been previously proposed, but limitations exist for the estimation of non-linear parts accurately without obtaining prior information. In this paper we propose the ballistic coefficient ${\beta}$ model-based interacting multiple model-extended Kalman filter (${\beta}$-IMM-EKF) for precise tracking of an RV. To evaluate the performance, other ballistic coefficient model based filters, which are gamma augmented filter, gamma bootstrapped filter were compared and assessed with the proposed ${\beta}$-IMM-EKF for precise tracking of an RV.

• 한국통신학회논문지
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• 제22권9호
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• pp.1985-1997
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• 1997

공액 경사법을 이용한 정칙화 반복 복원 방법에 관하여 논하였다. 기존의 반복 복원 방법에 비하여, 공액 경사법을 이용한 반복 복원 방법은 초선형적인 속도로 해에 수렴한다는 장점을 지닌다. 그러나, 이와 같은 성질로 인해 잡음과 흐려짐현상으로 훼손된 영상을 복원하는 과정에서 잡음의 증폭이나 파문현상과 같은 결합을 갖게된다. 본 논문은 구속 조건을 적용한 정칙화 공액 경사법을 제안한다. 정칙화 공액 경사법에 정칙화 구속 조건과 정칙화 변수를 적용함으로서, 영상에서 윤곽 부분의 평활화없이 파문 현상을 감소시킬 수 있을 뿐 아니라, 가산 잡음의 증폭을 억제할 수 있다는 장점을 지닌다. 실험 결과를 통하여 기존의 정칙화 반복 복원 방법에 비해 본 논문에서 제안한 방법이 수렴비에 우수함을 증명하였다.