• 한국기계연구소 소보
• /
• 통권13호
• /
• pp.87-98
• /
• 1984

An experimental study carried out to predict the performance characteristics of a high speed planing boat at the two displacements whose hull form shows hard chines form transom to bow. In the resistance test the planing hull model was porpoising at and above 30 knots for both displacements of 30 tons and 24 tons. A small stern wedge was newly designed and attached across hull bottom. The planing hull model with the stern sedge did not show any porpoising up to the speed of 45 knots for both displacements and it analysed results shows the improvement of resistance performance and planing performance comparing with those of original hull form; i.e. for displacement of 30 tons the effective power and trim angle were reduced by 18.9% and 5.71 degrees at the speed of 28 knots, and for the displacement of 24 tons the effective power and trim angle were reduced by 23.63% and 4.37 degrees at the speed of 28 knots, respectively.

• 대한지하수환경학회지
• /
• 제4권1호
• /
• pp.5-13
• /
• 1997

제주도는 예상되는 물 부족분을 충당하기 위하여 대규모 지하수 개발을 계획하고 있다. 효율적인 지하수 자원의 관리를 위해서는 개발에 대한 영향평가가 선행되어야 하는데 제주도에서는 지역의 특성상 해수의 영향을 고려해야 한다. 본 연구에서는 가상의 지하수 개발에 대한 중-동제주 수역의 해수쐐기의반응을 해석하였다. 해석 방법으로는 담수와 해수의 동수역학을 동시에 고려하는 비확산 전산모형(sharp interface numerical model)을 이용하였다. 모델링에서 사용된 단계적 지하수 개발 일정은 제주도 광역상수도개발 계획과 동일한 비율과 시간 간격에 따라 설정되었다. 모델링 결과 해수쐐기(saltwater wedge)는 지역에 따라 1km이상 침투하는 것으로 예측되었다. 이러한 결과는 해수쐐기를 고정된 것으로 가정하여 담수의 흐름만을 고려한 모델링을 바탕으로 한 영향평가의 신뢰성에 의문을 가지게 한다.

• 대한조선학회논문집
• /
• 제56권4호
• /
• pp.308-315
• /
• 2019

In this study, numerical simulations of slamming impact pressure acting on the flat plate and wedge type models using the cartesian-grid system and Modified Marker-Density Method (MMD method) were performed and the results were examined. The flat plate and wedge type models were selected as target objects, the turbulence characteristics were considered by applying the Sub-Grid Scale (SGS) turbulence model. Through this study, how the pressure acting on the target objects according to the incident angle influences the slamming impact pressure was examined and the results were compared with the flow characteristics of other experimental results. Also, the degree of slamming impact pressure is evaluated with respect to the cartesian-grid system and MMD method, which is easy to use and has a high degree of calculation for free surface.

• 한국의학물리학회지:의학물리
• /
• 제10권2호
• /
• pp.103-114
• /
• 1999

본 연구에서는 외부조사 광자선에 대한 3차원 선량계산 알고리즘 모델을 개발하기 위한 기초 연구로서 기존의 2D 선량 계산 알고리즘을 확장시켜 비동일 평면 조사가 가능한 2.5D 선량계산 모델을 개발하였다. 이를 위해 3차원 치료계획 및 선량계산에 적합하도록 환자 및 조사빔에 대한 3차원 좌표계 시스템을 정의하고, 이들 간의 좌표변환식을 유도하였다. 선량계산 알고리즘으로는 "Clarkson-Cunningham" 의 2D 광자선량 계산 알고리즘을 3차원으로 확장시켜 정형 조사면 및 비정형 조사면에 대한 선량계산과 wedge filter에 대한 선량계산이 가능하도록 하였고, Batho 방식을 적용하여 비 균질 보정을 구현하였다. 선량계산의 정확도를 평가하기 위해, AAPM TG #23 에 제시된 절차에 따라 자료에 제시된 4MV 광자선에 대한 실험 값과 본 연구에서 계산된 결과를 비교한 결과, 정형조 사면에 대한 PDD(percent depth dose)는 buildup 영역을 제외하면 $\pm$1% 이내, 비정형 조사면의 경우 $\pm$3% 이내에서 실험값과 일치하였다. 또한, wedge filter에 대한 PDD 및 profile은 $\pm$3% 이내, 45$^{\circ}$ oblique 입사빔에 대한 선량은 $\pm$4% 이내에서 실험값과 일치하였다. 비균질 보정의 경우 Lung/water 경계에서 7% 과소 평가되었고, Bone/water 경계에서 3% 과대 평가되는 것으로 나타났다. 이들 결과를 종합해 볼 때, 비균질 보정을 제외하고는 비교적 정확하게 선량을 계산하는 것으로 평가되었다. 추후 대부분의 상용 2.5D 치료계획시스템 (radiation treatment planning system; RTP)들이 비균질 보정 방법으로 사용하고 있는 Equivalent TAR(tissue-air ratio) 방식을 구현시키고자 하며, 본 연구에서 구현된 선량계산 모듈을 교육 및 연구용으로 활용할 수 있을 것으로 기대 한다.것으로 기대 한다.

• Computers and Concrete
• /
• 제18권3호
• /
• pp.337-354
• /
• 2016

To study the influence on fracture properties of reinforced concrete wedge splitting test specimens by the addition of reinforcement, and the restriction of steel bars on crack propagation, 7 groups reinforced concrete specimens of different reinforcement position and 1 group plain concrete specimens with the same size factors were designed and constructed for the tests. Based on the double-K fracture criterion and tests, fracture toughness calculation model which was suitable for reinforced concrete wedge splitting tensile specimens has been obtained. The results show that: the value of initial craking load Pini and unstable fracture load Pun decreases gradually with the distance of reinforcement away from specimens's top. Compared with plain concrete specimens, addition of steel bar can reduce the value of initial fracture toughness KIini, but significantly increase the value of the critical effective crack length ac and unstable fracture toughness KIun. For tensional concrete member, the effect of anti-cracking by reinforcement was mainly acted after cracking, the best function of preventing fracture initiation was when the steel bar was placed in the middle of the crack, and when the reinforcement was across the crack and located away from crack tip, it plays the best role in inhibiting the extension of crack.

• Asian Pacific Journal of Cancer Prevention
• /
• 제17권4호
• /
• pp.1685-1689
• /
• 2016

Physical wedges still can be used as missing tissue compensators or filters to alter the shape of isodose curves in a target volume to reach an optimal radiotherapy plan without creating a hotspot. The aim of this study was to investigate the dosimetric properties of physical wedges filters such as off-axis photon fluence, photon spectrum, output factor and half value layer. The photon beam quality of a 6 MV Primus Siemens modified by 150 and 450 physical wedges was studied with BEAMnrc Monte Carlo (MC) code. The calculated present depth dose and dose profile curves for open and wedged photon beam were in good agreement with the measurements. Increase of wedge angle increased the beam hardening and this effect was more pronounced at the heal region. Using such an accurate MC model to determine of wedge factors and implementation of it as a calculation algorithm in the future treatment planning systems is recommended.

• Imaging Science in Dentistry
• /
• 제31권1호
• /
• pp.17-22
• /
• 2001

Purpose: To compare the film density of Insight dental X-ray film (Eastman Kodak Co., Rochester, NY, USA) with that of Ektaspeed Plus film (Eastman Kodak) under manual and automatic processing conditions. Materials and Methods : Insight and Ektaspeed Plus films were exposed at three different exposure conditions with an aluminum step wedge on the films under the three different exposure times. The exposed films were processed by both manual and automatic ways. The Base plus fog density and the optical density made by exposing step wedge were calculated using a digital densitometer (model 07-443, Victoreen Inc, Cleveland, Ohio, USA). The optical densities of the Insight and Ektaspeed film versus thickness of alumimun wedge at the same exposure time were plotted on the graphs. Statistical analyses were applied for comparing the optical densities of the two films. Results: The film density of both Insight films and Ektaspeed Plus films under automatic processing condition was significantly higher over the manual processing. The film density of Insight films was significantly higher than that of Ektaspeed Plus films on both automatic and manual processing conditions. Conclusion: The radiation exposure time can be reduced when using Insight over Ektaspeed Plus film. To take the full advantage of reducing exposure time, Insight film should be processed automatically.

• 대한기계학회논문집B
• /
• 제25권3호
• /
• pp.285-295
• /
• 2001

The transport phenomena in a wedge-shaped pool of twin-roll continuous caster are affected by the various operating parameters such as the melt-feed pattern, roll-gap thickness, melt-superheat, and casting speed. A computer program has been developed for analyzing the two-dimensional, steady conservation equations for transport phenomena during twin-roll continuous casting process in order to estimate the turbulent melt-flow, temperature fields, and solidification in the wedge-shaped pool. The turbulent characteristics of the melt-flow were considered using a low-Reynolds-number K-$\xi$ turbulence model. Based on the computer program, the effects of the different melt-feed patterns, roll-gap thicknesses, and superheats of melt on the variations of the velocity and temperature distributions, and the mushy solidification were examined. The results show that the liquidus line is located considerably at the upstream region, and in the lower region appear the well-mixed melt-flow and most widely developed mushy zone. Besides, the variation of melt-flow due to varying melt-feed patterns, affects mainly the liquidus line, and scarcely has effects on the solidus line in the outlet region.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제6권3호
• /
• pp.638-651
• /
• 2014

Main aim of this paper is to find the best combination of numerical schemes for 2-D SPH simulation of wedge water entry. Diffusion term is considered as laminar, turbulent, and artificial viscosity. Density filter that seriously affects the pressure distribution is investigated by adopting no filter, first order filter, and second order filter. Validation of the results indicates that turbulent model and first order density filter can lead to more reasonable solutions. This simulation was then conducted for wedge water entry with wide range of deadrise angles including 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees and 81 degrees, with extreme deadrise angles of 10 degrees, 60 degrees and 81 degrees being considered. Comparison of SPH results with BEM solutions has displayed favorable agreement. In two particular cases where experimental data are available, the SPH results are shown to be closer to the experiments than BEM solution. While, accuracy of the obtained results for moderate deadrise angles is desirable, numerical findings for very small or very large deadrise angles are also very reasonable.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2004년도 춘계 학술대회논문집
• /
• pp.113-118
• /
• 2004

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.