• 대한기계학회논문집
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• 제15권2호
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• pp.575-583
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• 1991

The weld pool convection problem that occurs during the stationary GTA welding has been studied, considering the four driving forces for weld pool convection, i.e., the electromagnetic force, the buoyancy force, the aerodynamic drag force, and the surface tension force at the weld pool surface. In the numerical simulation, the difficulties associated with the irregular moving liquid-solid interface have been successfully overcome by adopting a Boundary-Fitted Coordinate system. In the experiments to show the validity of the numerical analysis, a deep periphery and shallow centerpentrated weld pool shape was observed from the etched specimen. It could be revealed that this type of weld pool shape could be simulated, only when some of aerodynamic drag force distributions are considered. Although slight disagreement arose, the calculated and the observed weld pool shapes were in a reasonable agreement.

• International Journal of Control, Automation, and Systems
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• 제4권1호
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• pp.42-52
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• 2006

In order to utilize hydrodynamic drag force on articulated robots moving in an underwater environment, an optimum motion planning procedure is proposed. The drag force acting on cylindrical underwater arms is modeled and a directional drag measure is defined as a quantitative measure of reaction force in a specific direction in a workspace. A repetitive trajectory planning method is formulated from the general point-to-point trajectory planning method. In order to globally optimize the parameters of repetitive trajectories under inequality constraints, a 2-level optimization scheme is proposed, which adopts the genetic algorithm (GA) as the 1st level optimization and sequential quadratic programming (SQP) as the 2nd level optimization. To verify the validity of the proposed method, optimization examples of periodic motion planning with the simple two-link planner robot are also presented in this paper.

• 한국터널지하공간학회 논문집
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• 제14권3호
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• pp.277-292
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• 2012

본 논문에서는 쉴드 TBM 커터비트의 절삭력 평가를 위한 기초적 연구를 실시하였다. 기존 커터비트 절삭력 분석을 위한 여러 이론식이 존재하지만 기존이론식은 실제 커터비트 절삭력과 차이를 보인다. 따라서 실제 커터비트의 절삭력을 분석하기위하여 축소모형실험을 실시하였으며, 축소모형시험에서 얻은 결과는 기존 이론식과 비교 분석하였다. 이 연구로부터 얻은 결과는 TBM 커터헤드 설계에 있어 기본적으로 매우 필수적인 자료로 활용될 것이라 판단된다.

• 대한기계학회논문집B
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• 제20권1호
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• pp.369-376
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• 1996

Variations of the drag and lift forces of a circular cylinder in a planar turbulent jet were experimentally investigated. The force was directly measured using the load cell and estimated by integrating the pressure distribution on the cylinder. As the cylinder moves outward from the center of the jet, the direction of lift force changes and the drag force decreases. Reynolds number, the ratio of cylinder's diameter to half width of jet had effect on maximum drag coefficient and the location where the direction of lift changes.

• 천문학회보
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• 제35권1호
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• pp.72.2-72.2
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• 2010

We use three-dimensional hydrodynamic simulations to investigate nonlinear gravitational responses of gas to, and the resulting drag force on, a massive perturber moving on a circular orbit through a uniform gaseous medium. We assume that the background medium is non-rotating and adiabatic with index 5/3, and represent the perturber using a Plummer potential with softening radius a. This work extends our previous study where we showed that the drag force on a straight-line trajectory is proportional to a0.45 if the perturber is massive enough. This indicates that the orbital decay of supermassive black holes (SMBHs) near galaxy centers may take much longer than the prediction of the linear force formula applicable for low-mass perturbers. For the circular orbits are considered, however, we find that the nonlinear drag force becomes independent of a, but dependent instead on the orbital radius R as $\varpropto$ R0.5. This suggests not only that the choices of large values of a, for resolution issues, in recent numerical experiments for mergers of SMBH, are marginally acceptable, but also that the gaseous drag indeed provides an efficient mean for the orbtial decay of SMBHs.

• 한국진공학회지
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• 제9권2호
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• pp.172-178
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• 2000

반도체 제조공정 중 플라즈마 반응기 내에서 입자오염을 유발하는 입자들의 거동과 성장을 모델식을 사용하여 이론적으로 고찰하였다. 플라즈마 반응기 내에서 입자 거동에 영향을 미치는 힘들로 유체 대류, 입자 확산 및 외부힘 (ion drag force, electrostatic force, 중력) 등을 고려하였다. 플라즈마 벌크 영역에서 전하를 가진 입자들간의 충돌에 의한 입자 성장을 고려하기 위해 모델식에 입자 전하 분포를 고려하였다. 대부분의 입자들은 ion drag force와 electrostatic force가 균형을 이루고 있는 두 sheath 경계 영역에 존재하였으며 두 sheath 영역과 벌크 플라즈마에서의 입자 농도는 0에 접근하였다. 시간이 지남에 따라 입자 충돌로 인한 입자들의 크기는 증가하였으며 입자가 성장함에 따라 입자 표면적의 증가와 더불어 입자가 가지는 평균 전하량도 증가하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 추계 학술대회논문집
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• pp.132-138
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• 2003

The optimal design for a leading car considering the aerodynamic resistance is required on the high-speed train due to increasing of ratio of drag force with proportion for the square of velocity. The aerodynamic analysis using CFD in the stage of concept design offers more economical analysis method which is used to estimate the influence of flow and pressure around the leading car than the experimental method using the Mock-up. In this study, we want to assist the artistic design with aerodynamics analysis in order to get the optimal design for leading car with the operation speed of 180km/h. The results of aerodynamic analysis for two leading car models which one is expressed with lineal beauty and the other is with curvaceous beauty are compared with each other and they offer the proposal of modification for two models in order to decrease the drag force. The shape of curvaceous model is better for the pressure force but slightly worse for the viscous force than the other. The Fluent software is used for the calculation of flow profile in this study.

• 한국산업융합학회 논문집
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• 제2권2호
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• pp.173-180
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• 1999

When Automobile runs high velocity, it causes sleepy velocity profile then that generates lift force and drag force. Lift force reduce tire friction force. Drag force increase consumed power. For improve automobile performance, reduction of Lift force and Drag force was seriously considered. It measured experimently using wind tunnel, numerically using numerical analysis. Finite difference method is using difference equation and simplifed mesh. This method require less calculation time and computer power than other method.

• 한국항공우주학회지
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• 제42권7호
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• pp.616-621
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• 2014

저궤도에서 운용되는 위성은 대기 저항에 의한 연료소모가 크며, 연료소모는 임무수명 및 발사무게에 영향을 미치게 되어 위성 형상에 따른 항력의 예측이 중요하다. 본 논문에서는 직접모사법을 이용하여 파라볼릭 안테나를 탑재한 저궤도 위성의 임무고도의 변화와 받음각에 따른 항력 및 항력 계수의 변화를 살펴보았다. 저궤도의 희박 기체의 거동을 모사하는 직접모사법의 적용성을 검증하기 위해 스타샤인(Starshine) 위성의 비행데이터를 이용하여 고도, 대기와 표면의 상호작용에 따른 항력 계수를 비교하였다. 결론적으로 계산결과로부터 저궤도 위성의 정밀한 궤도수명 계산에 적합한 항력 계수를 도출하였다.

• 대한기계학회논문집
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• 제15권2호
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• pp.488-496
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• 1991

Dynamic chanracterisitcs and control of a submerged working robot manipulator have been investigated for articulated type robot manipulator with three revoluted joints. A dynamic equation of the manipulator has been derived. The dynamic equation includes not only mass matrix, centrifugal and Coriolis terms and gravity terms but also added mass, buoyant force and drag force terms, which are important terms for underwater motion description. A series of simulations using computed torque method have been performed for the cases of straight and circular trajectory motion controls. The results of this study show that the dynamic characteristics of the submerged working robot manipulator are very different from that of the manipulator which works in air. The influences of added mass, buoyant force and drag force terms to the total required torques have been discussed as distribution ratios to the total required torques.