• Journal of Advanced Marine Engineering and Technology
• /
• v.36 no.4
• /
• pp.497-503
• /
• 2012

The aim of this study was to optimize S-tube shape of heat exchanger in term of reducing the size of tube bundle and improving the mechanical properties such as the thermal stress and resonance. The geometric parameters such as offset length, the straight distance between one end and other end of tube, the tube length in straight portion and fillet radius was assessed as a valid parameters. The structural analysis was performed to estimate the structural characteristics. Main effect analysis was performed to investigate the main effect for the various geometric parameters. The response surface methodology was employed to establish mathematical approximation models as a function of the geometric parameters of the S-tube. Also, The optimization was performed to optimize geometric parameters of S-tube using the regression equations and optimization tool. The optimized tube shape has been proposed. Those could be used in the heat exchanger design used in high temperature.

• Journal of the Korea Computer Graphics Society
• /
• v.25 no.3
• /
• pp.143-152
• /
• 2019

This paper presents two new techniques for solving the two problems of the water curtain: 'shape distortion' caused by gravity and 'resolution degradation' caused by fine satellite droplets around the shape. In the first method, when the user converts a three-dimensional model to a vertical sequence of slices, the slices are evenly spaced. The method is to adjust the time points at which the equi-distance slices are created by the nozzle array. In this method, even if the velocity of a water drop increases with time by gravity, the water drop slices maintain the equal interval at the moment of forming the whole shape, thereby preventing distortion. The second method is called the minimum time interval technique. The minimum time interval is the time between the open command of a nozzle and the next open command of the nozzle, so that consecutive water drops are clearly created without satellite drops. When the user converts a three-dimensional model to a sequence of slices, the slices are defined as close as possible, not evenly spaced, considering the minimum time interval of consecutive drops. The slices are arranged in short intervals in the top area of the shape, and the slices are arranged in long intervals in the bottom area of the shape. The minimum time interval is pre-determined by an experiment, and consists of the time from the open command of the nozzle to the time at which the nozzle is fully open, and the time in which the fully open state is maintained, and the time from the close command to the time at which the nozzle is fully closed. The second method produces water drop sculptures with higher resolution than does the first method.

• Journal of Aerospace System Engineering
• /
• v.16 no.5
• /
• pp.8-16
• /
• 2022

This paper presents the orbital control for positioning micro synthetic aperture radar (SAR) satellites for all-weather monitoring around the Korean Peninsula. In Small SAR technology experimental project (S-STEP) developed in Korea, multiple satellites are placed at equal intervals in multiple orbital planes to secure an average revisit period for the region around the Korean Peninsula. Satellites entering the same orbital plane use ion thrusters to control their orbits and the separation velocity from the launch vehicle to distribute them evenly across the orbit. For an orbital that places the satellites equally spaced in the same orbital plane, the shape of the satellite constellation is formed by adjusting the difference in drift rates between the satellites. This paper presents, different types of satellite constellations, and the results of satellite constellation placement according to launch strategies are presented. In addition, a method and limitations in shortening the duration of orbital deployment are presented.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.28 no.6A
• /
• pp.819-825
• /
• 2008

This paper describes the shaping formation and the erection of SCST structure by cable-tensioning. It could be a fast and economical method for constructing the space structure consisted with uniform pyramids by cable-tensioning of the cable in bottom chords. In the initial layout, the top chords and web members are left at their true length, the bottom chords are given gaps in proportion to the desired final shape. The feasibility of the proposed shaping method and the reliability of the established geometric model were confirmed with nonlinear finite element analysis and an experimental investigation on small scale and full size test models. As a result, the behaviour characteristic of MERO joint is very significant in shaping analysis of space structure. This study suggests the most reasonable modeling technique for the prediction of shaping in practices. And it is shown the characteristic of the behavior in shaping test for practical design purposes.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.24 no.3
• /
• pp.267-274
• /
• 2011

The effect of internal ring stiffeners is numerically evaluated for reinforcement of tubular K-joints. Finite element analyses are performed to compute stress of un-stiffened and ring-stiffened K-joints subjected to axial loading. The influence of loading condition and geometrical parameters of ring stiffener on joint behavior is assessed to determine the installation effect of single and double ring stiffeners. The arrangement effect of ring stiffener are evaluated using quantitative analysis compared single ring with double ring stiffeners. Based on the numerical results, practical size of ring stiffener is proposed for design of tubular K-joints.

• The Journal of the Acoustical Society of Korea
• /
• v.23 no.1
• /
• pp.40-46
• /
• 2004

The equivalent source method (ESM) uses two groups of equivalent source positions. One group includes the first order images of the sound source inside the enclosure. The positions of the other group are usually on a spherical surface some distance outside the enclosure. A proper selection of the positions for the far field sources could greatly improve the performance of the modeling accuracy and reduce the number of the sources to achieve the required accuracy. This study uses optimally distributed far field source positions on the surface of enlarged version of the rectangular enclosure instead of using typical spherical distribution. Simulations using various sizes of the box shaped distribution are executed and optimal positions are searched using an optimization technique from the larger number of candidate positions. The results of using these far field source positions are compared and analyzed.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.5 no.6
• /
• pp.613-619
• /
• 2010

The stationary discontinuous armatures that are used in permanent magnet linear synchronous motors (PM-LSMs) have been proposed as a driving source for transportation systems. However, the stationary discontinuous armature PM-LSM contains the outlet edges which always exist as a result of the discontinuous arrangement of the armature. For this reason, the outlet edge cogging force generated between the armature's core and the mover's permanent magnet. This paper contemplated the outlet cogging for ceaccording to 2-D numerical analysis by FEM. We installed the auxiliary pole for in order to minimize the outlet cogging force.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2020.06a
• /
• pp.222-222
• /
• 2020

급격한 기후변화와 도시화, 산업화로 인해 도시지역의 홍수피해가 증가하고 있다. 기후변화로 인한 재해 중 45%가 극한 강우 또는 홍수로 인한 재해로 확인되었으며, 급속도로 확장되고 있는 도시화 추세로 인해 도시지역의 홍수피해가 더욱 심화되고 있다(UNISDR, 2016). 기후변화 및 도시화로 인한 도시지역의 홍수피해가 증가하면서 시가지 건물 배치 및 도로망과 같은 복잡한 지역특성이 침수에 주는 영향을 분석할 필요성이 점차 증가하고 있다. 도시지역에서 홍수가 발생할 경우 복잡한 도로망은 배수로 역할을 하며 건물의 밀집도와 배치는 골목길 등에서 침수심을 증가시켜 안전한 구역이 좁아지는 효과를 발생시키고 있다. 본 연구에서는 우선 복잡한 시가지를 특성화하여 분석 할 수 있도록 이상화된 시가지 모형을 설계하고 제작한 후 유량에 따른 흐름 특성 변화를 분석하였으며, 기초 실험 결과를 바탕으로 강우강도에 따른 유황 변화와 연계할 예정이다. 기초 실험 수행을 위하여 먼저 건물 배치 밀집도를 고려하여 주거구역을 불록화하여 직선형의 이상적인 도시지역의 시가지 모형을 설계한 후 실험 모형을 제작하였다. 하천 범람으로 인한 침수발생을 재현하기 위해 상류 도로망에서 유량이 유입되도록 제작하였으며, 유입조건에 따라 변화하는 시가지 내부 침수 흐름은 LSPIV 기법을 이용하여 분석하였다. 유입조건에 따른 시가지 내 침수 특성을 분석한 결과 지형적 경사 특성에 의해 시가지 내부에서 흐름이 가속되며, 모형의 사거리 구간에서는 흐름 유입 방향에 대해 횡방향으로 흐름이 합류하는 경우에는 합류 흐름이 유속이 더 높은 것으로 분석되었다. 따라서 합류 이후 유속이 증가하면서 피해 발생 가능성이 높은 것으로 나타났다.

• 한국공간정보시스템학회:학술대회논문집
• /
• 2004.05a
• /
• pp.255-263
• /
• 2004

광명시 경륜 경기장은 국민 체육진흥공단에서 턴키(Turn key)공사로 발주하였고, CS구조+공간건축+대우건설, 삼성건설, 태영건설의 제출안이 당선되어 현재 시공중에 있다. 경기장의 저층부는 PC로 설계되었고, 지붕은 철골 트러스를 사용한 Dome 형상으로 이루어져 있다. 돔 지붕의 개념은 지붕에 물을 부었을 때 가장 흘러가기 쉬운 방향으로 트러스를 배치하여 유연한 힘의 흐름을 유도하는 것이다. 143.6m(폭)${\times}$183.5m(길이)${\times}$21m(높이)의 지붕엔 지붕의 개념인 Flow Truss를 물이 흐르는 방향의 방사형으로 배치하고, 내부에 압축링(Compression Ring Truss)과 외부에 인장링(Tension Ring Truss)를 설치하여 힘의 흐름을 단순화시켰고, 실내에서 보기에 플로우 트러스의 간격을 넓게 유지함으로써 개방감을 극대화시켰다. 또한 Flow Truss는 동일한 곡률과 길이로 설계하여 표준화시킴으로써 시공성과 경제성을 동시에 만족토록 하였다. 현재 저층부 시공은 거의 완료된 상황이고, 곧 지붕을 설치할 예정이다. 본 고에서는 돔 지붕의 형성 개념과 설계 과정을 살펴보고, 접합상세 등의 해결에 대해 살펴보겠다.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2011.05a
• /
• pp.144-149
• /
• 2011

합류부에서의 수공구조물의 설치는 수리학적으로는 매우 불리하며, 최근 심각해지고 있는 국지성 집중호우로 인한 과중한 유량이 합류부에 집적되어 홍수위를 상승시킴으로써 하천 범람 피해의 주원인이 된다. 본 연구에서는 1차원 HEC-RAS 및 2차원 수치모형 CCH2D을 이용하여 합류부에서의 교각설치에 따른 하천흐름 변화를 분석하고 각 모형의 성과를 비교 검토한다. 또한 2차원 모형인 CCHE2D 모형의 원형교각 배치에 대한 단점을 보완하고자 2차원 수리해석 모형인 FLUMEN모형과 함께 비교 분석하여 실제 교각의 배치, 형상 및 제원이 고려된 격자망을 이용하여 합류부 주변에 위치한 교량에 의한 흐름 유동특성을 평가한다.