• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.65-73
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• 2004

CMG(Control Momentum Gyro) is a control device being used for spacecraft attitude control constructing relatively large amount of torque compared to conventional body-fixed reaction wheels. The CMG produces gyroscopic control torque by continuously varying the angular momentum vector direction with respect to the spacecraft body. The VSCMG(Variable Speed Control Momentum Gyro) has favorable advantages with variable speed to lead to better control authority as well as singularity avoidance capability. Attitude dynamics with a VSCMG mounted on a two-axis gimbal system are derived in this study. The dynamic equation may be considered as an extension of the single-axis counterpart. Also, a feedback control law design is addressed in conjunction with the dynamic equations of motion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.4
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• pp.490-498
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• 1993

A variety of methods for measuring the velocity from an image sequence use the relationship between the spatial and temporal gradients of image brightness function. In most situations, an additional constraint is required because the velocity is not determined uniquely by a above relationship. Horn and Schunch proposed a constraint that the velocity field should vary smoothly over the image. This requirement, however, forces the velocity field to vary smoothly even across motion boundaries. To complement this probe, Nagel introduced and 'oriented smoothness' constraint which restricts variations of velocity field only in directions with small or no variation of image brightness function. On the other hand, Paquin and Dubois proposed a different type of constraint that the velocity is constant in a small area of image. But, this constraint also creates difficulties at motion boundaries which large variations in velocity field often occur. We propose the method to overcome these difficulties by utilizing the information of discontinuities in image brightness function, and present the experimental results.

• Proceedings of the Korea Water Resources Association Conference
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• 1986.07a
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• pp.131-145
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• 1986

흐름수역에서 연직상향으로 방류되는 평면부력\ulcorner의 거동이 연속방정식, 운동량방정식 및 추적물수송식의 기본방정식에 의하여 수치적으로 해석된다. 난류확산에는 Prandtld의 혼합거리이론을 도입한 난류수송모형이 이용된다. 수치해 과정은 기본방정식을 유함수(stream function)식, 와도수송(vorticity transport)식으로 변환한 후, \ulcorner방류속도와, 방류구폭 등으로 표현되는 변수와 흐름을 지배하는 무차원 매개변수를 도입하여 무차원 형태로 표현하는 부분과 successive under-relaxation과 Gauss-Seidel반복법으로 수행하는 부분으로 이루어진다. 적절한 relaxation 계수를 선정하므로써 안정되고 수렴성이 좋은 계산이 수행된다. \ulcorner방류 속도와 가로흐름 속도의 비가 속도비(Velocity ratio)로 정의되며 속도비가 8 - 15의 범위에서 부력\ulcorner으로 인한 주변흐름수역의 속도변화 온도상승범위, 흐름상태(유선) 및 와도가 조사되었으며 \ulcorner의 경로에 대하여 속도비와 방류밀도후르드수의 영향이 또한 조사되었다. \ulcorner중심선의 속도와 온도변화, 국부밀도후르드수의 변화가 구해지며 퍼짐율(dispersion ratio), 확산비(spreading rate)가 방류밀도후르드수, 국부밀도후르드수 및 방류구로부터의 경로의 항으로 해석되었다. 또한 속도와 온도 분포에 상사(similarity)가 존재함이 밝혀졌으며 본 연구와 같은 조건의 범위에서는 Gaussian분포를 이용한 적분형해석(intergal type analysis)이 가능한 것으로 사료된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1470-1473
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• 2006

연속된 두 장의 레이더 반사도(합성 CAPPI)를 이용하여 설정된 두 윈도우 사이의 최대 상관계수를 찾아 냄으로써 강수의 움직임을 파악하는 기존의 TREC(Tracking Radar Echoes by Correlation) 기법은 단지 통계적인 상관법을 이용하여 산출된 TREC 벡터를 외삽하기 때문에 강우 시스템의 이동양상을 물리적으로 표현하는데 한계를 가질 뿐만 아니라 강수가 직선운동을 하는 것처럼 묘사될 수밖에 없는 기법의 한계성을지니고 있다. 본 연구에서는 도플러 레이더로부터 생산되는 시선속도를 이용하여 바람장을 산출하고 이를 TREC 벡터와 연계시켜 단시간 예보모형을 개선하고자 하였다. 시선속도는 레이더로부터 멀어지거나 다가오는 물체의 속도성분이며, 이를 이용하여 강수 영역 내의 바람장을 산출할 수 있다. 이러한 바람장 정보와 연계한 TREC 벡터의 개선은 단시간 강우 예보모형의 개선을 통하여 짧은 시간에 급격한 발달하는 집중호우 등에 대한 보다 정확한 예보를 가능하게 한다.

• Water for future
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• v.24 no.1
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• pp.73-81
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• 1991

The Saint-Venant equations of the continuity and momentum principles of one-dimensional, unsteady, open-channel flow are expressed in terms of the phase velocities of constant depth, velocity, and discharge, which results in unique relationships between these phase velocities and channel velocity. A case study shows that these unique relationships developed in this study can be used as an indicator of precision of numerical solutions of the Saint-Venant equations. Further physical interpretation of these relationships and utilization to the numerical analyses of the Saint-Venant equations are to be investigated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.213-216
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• 2010

A typical unsteady internal ballistic analysis model was proposed to take account of the erosive burning for a solid rocket motor. The variance of local velocity and pressure along grain surface are analyzed by using the continuity and momentum equation. The model introduced in this study showed good agreements with the results of previous internal ballistics program. It was investigated that the change of combustion pressure, gas velocity and regrestion rate along the grain axis.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.3
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• pp.137-151
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• 1991

The motion of two-dimensional floating breakwaters with rectangular clots-section which are moored tautly in shallow water has been analyzed using a velocity potential matching method in which the fluid region is devided into sub-regions and then unknown coefficients of velocity potentials are determined from the continuity condition of mass and momentum flux of fluid at imaginary boundaries between sub-regions. The method originally suggested by Ijima et al.(1972) for the motion of submerged body has been modified to analyze the motion of floating body. The total fluid region has been divided into three sub-regions : the incident wave region, the transmitted wave region and the region below the floating breakwater. The restoring forces induced by mooring lines which were ignored by Ijima et al.(1972) have been modeled as linear springs with the initial tension effects. This method has been verified through the comparions with results from hydraulic expriments. Applications to various conditions of floating breakwater have been performed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.2
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• pp.41-48
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• 2023

In this study, simplified linear numerical method that can simulate wave generation and transformation by a moving bottom is introduced. Numerical analysis is conducted in wave number domain after continuity equation, linear dynamic and kinematic free surface boundary conditions and linear kinematic bottom boundary condition are Fourier transformed, and the results are expressed in space domain by an inverse Fourier transform. In the wavenumber domain, the dynamic free water surface boundary condition and the kinematic free water surface boundary condition are numerically calculated, and the velocity potential in the mean water level (z = 0) satisfies the continuity equation and the kinematic bottom boundary condition. Wave generation and transformation are investigated when the triangular and rectangular shape of bottoms move periodically. The results of the simplified numerical method are compared with the results of previous analytical solutions and agree well with them. Stability of numerical results according to the calculation time interval (Δt) and the calculation wave number interval (Δk) was also investigated. It was found that the numerical results were appropriate when Δt ≤ T(period)/1000 and Δk ≤ π/100.

• Water for future
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• v.23 no.4
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• pp.435-444
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• 1990

The flow characteristics varying with the rate of the radius of curvature to width (Rc/B) in open channel bends are investigated with a simplified numerical model, briefly. Secondary flow velocity and transverse bed slope are formulated from the equations of moment of momentum and force balance analysis, respectively. The conservation equations of mass and streamwise momentum are simplified by depth integration and its solution could be obtained form explicit finite difference method. Three sets of computer simulation are executed. The rates of Rc/B adopted in simulations are 2.7, 5.4, 8.1 , respectively. The terms analyzed in this paper are secondary flow velocity, streamwise velocity, the path of maximum streamwise velocity, deviation angle, and mass-shift velocity.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.949-949
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• 2012

유출수문곡선은 강우량, 강우강도, 강우지속시간, 강우이동방향 및 이동속도와 같은 강우발생특성과 강수대의 공간적 이류방향과 유역형상과의 상호작용에 의하여 영향을 받으며, 특히 강우의 이류과정에서 나타나는 시간적, 공간적인 분포는 유출에 영향을 미치는 중요한 인자이다. 일반적으로 유출해석 기본이론은 연속방정식과 운동방정식으로서 운동파가정(kinematic wave analogy)을 기반으로 한 집중수문모형(lumped hydrologic model)에 의하여 수행되고 있지만 집중형 모형은 한 매개변수에 여러 가지의 물리적 과정을 개념화하여 담고 있기 때문에 유출과정에 대한 섬세한 모형화의 제약으로 인하여 강우의 이류과정에 따른 유출변화특성을 모의하기가 어렵다. 본 연구에서는 완전 분포형 수문동력학적 강우-유출 모형을 사용하여 강우의 이류특성을 반영할 수 있는 유출 모델을 구성하고, 강우의 이류특성에 따른 유역 출구에서의 유출수문곡선의 변화과정을 살펴보고 상관관계를 분석하였다.