• Journal of Mechanical Science and Technology
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• 제20권1호
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• pp.158-166
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• 2006

Extended Graetz problem in microtube is analyzed by using eigenfunction expansion to solve the energy equation. For the eigenvalue problem we applied the shooting method and Galerkin method. The hydrodynamically isothermal developed flow is assumed to enter the microtube with uniform temperature or uniform heat flux boundary condition. The effects of velocity and temperature jump boundary condition on the microtube wall, axial conduction and viscous dissipation are included. From the temperature field obtained, the local Nusselt number distributions on the tube wall are obtained as the dimensionless parameters (Peclet number, Knudsen number, Brinkman number) vary. The fully developed Nusselt number for each boundary condition is obtained also in terms of these parameters.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.797-804
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• 2003

본 연구에서는 진동대 실험을 실시하여 매립지에서 널리 사용되고 있는 지오멤브레인과 지오텍스타일 사이의 동적 접촉 마찰 특성을 살펴보았다. 연직응력, 진동 주파수, 건조/수침 상태의 영향에 대해서 평가하였으며, 또한 지오멤브레인과 지오텍스타일 사이의 상대적인 미끄러짐의 정도를 측정하였다. 실험 결과, 지오멤브레인과 지오텍스타일 사이를 통해 전달되는 한계 가속도(limited acceleration)가 있음을 확인할 수 있었으며, 이를 통해 지오멤브레인과 지오텍스타일 사이의 동적 접촉 마찰각을 산정할 수 있었다. 이러한 가속도는 수침상태의 경우 건조상태보다 더 작게 산정되었으며, 변위의 경우 수침상태에서 더 크게 발생함을 관찰하였다. 또한 실험조건에 따라 지오멤브레인과 지오텍스타일 사이에 발생하는 상대적인 미끄러짐의 정도가 다르게 측정되었다. 본 연구에서는 지오멤브레인과 지오텍스타일 사이의 slip equation을 제안하였으며, 이 식을 통해 주어진 가속도와 주파수에서 지오멤브레인과 지오텍스타일 사이를 따라 발생되는 최대 미끄러짐의 정도를 예측 가능하게 하였다.

• 조명전기설비학회논문지
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• 제20권4호
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• pp.117-122
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• 2006

입력이 최소가 되는 자속의 값을 찾는 유도전동기 고정자자속기준제어의 최대효율제어방법을 제안한다. 제안한 방법에서, 정해진 자속의 값만큼씩 기준자속의 값을 변화시키면서 직류링크에서 측정된 입력의 값이 최소가 되는 기준자속의 값을 찾는다. 또한 철손저항을 고려한 유도전동기의 모델을 이용하여 철손저항을 고려한 토크, 슬립각 속도, 비간섭 보상전류식을 사용한다. 시뮬레이션 및 실험결과를 통해서 제안한 방법의 효과를 입증한다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.206-218
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• 2014

The wave attenuation by floating breakwaters in high amplitude waves, which can lead to wave overtopping and breaking, is examined by numerical simulations. The governing equations, the Navier-Stokes equations and the continuity equation, are calculated in a fixed Cartesian grid system. The body boundaries are defined by the line segment connecting the points where the grid line and body surface meet. No-slip and divergence free conditions are satisfied at the body boundary cell. The nonlinear waves near the moving body is defined using the modified marker-density method. To verify the present numerical method, vortex induced vibration on an elastically mounted cylinder and free roll decay are numerically simulated and the results are compared with those reported in the literature. Using the present numerical method, the wave attenuations by three kinds of floating breakwaters are simulated numerically in a regular wave to compare the performance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 추계학술대회 논문집 학회본부
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• pp.45-48
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• 1990

This paper deals with the control strategy for constant voltage, constant frequency (CVCF) generation of doubly-fed Induction generator. As induction machine is a nonlinear and multivariable machine, so, the influential factors for CVCF generation of induction generator are the magnitude of output voltage, load current and its power factor, slip of the machine, etc. To get appropriate control scheme and to research the effect of its parameters, the control equation of induction machine is derived and tested. The derived condition is very useful for the CVCF control of the machine and for determing the characteristics of the system. The simulation results show that magnetizing reactance and rotor resistance is a very important parameter in this control system.

• 대한전기학회논문지
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• 제40권6호
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• pp.567-573
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• 1991

Full direct digital control of induction motor driver is implemented with a minimal hardware structure. This paper deals with the presentation of a low-cost single-chip microprocessor-based control system for three-phase PWM generation and vector control that control speed of the induction motor using the field-oriented control method. Rotor flux is estimated using the indirect sensing method based on the rotor circuit equation in the synchronously rotation reference frame, and slip angle and rotor position are calculated from rotor angular velocity and stator current. Through simulation and experiment, it is shown that the proposed scheme gives good static and dynamic performance to the induction motor drive.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.903-908
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• 2001

This paper deals with the estimation of the maximum flexural crack widths using minimum crack spacing for reinforced concrete members. The proposed method utilizes the conventional crack and bond-slip theories as well as bonding transfer length and effects of creep and shrinkage between the reinforcement and concrete. An analytical equation for the estimation of the maximum flexural crack width is formulated as a function of mean bond stress. The validity, accuracy and efficiency of the proposed method are established by comparing the analytical results with the experimental data and the major code specifications (e.g., ACI, CEB-FIP Model code, Eurocode 2, etc.). The analytical results of analysis presented in this paper indicate that the proposed method can be effectively estimated the maximum flexural crack width of the reinforced concrete members.

• 한국해양공학회지
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• 제10권3호
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• pp.62-73
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• 1996

Numerical simulation is made of the three-dimensional wave breaking motion about a part of a floating offshore structure containing a circular cylinder mounted vertically onto a lower hull in regular periodic gravity wave generated by a numerical wave maker. TUMMAC-VIII finite-difference method is newly developed for such a problem. By use of density-function technique the three-dimensional wave breaking motion is approximately implenented in the framework of rectangular grid system. A porosity technique is devised for the implementation of the no-slip bydy boundary conditions. The generation of breaking waves by the interaction of incident waves with the structure is well simulated and interesting features of breaking waves are revealed with containing degree of quantitative and qualitative accuracy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.366-368
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• 1994

This paper deals with the vector control that control of torque and speed of the induction motor using field-oriented control method. Rotor flux is estimated using the indirect sensing method based on the rotor circuit equation in the synchronously rotation reference frame, and slip angle and rotor position are caculated from rotor angular velocity and stator current. Through modeling and digital simulation with a voltage source inverter, it is shown that the proposed scheme gives good static and dynamic performance to the induction motor drive.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 추계 학술대회논문집
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• pp.195-199
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• 2005

Wave breaking phenomenon near the fore body of a ship is numerically simulated. The ship advance with uniform velocity in calm water. For the simulation, incompressible Navier-Stokes equations and continuity equation are adopted as governing equations. The simulation is carried out in staggered variable mesh system with finite difference method. Marker and Cell(MAC) method and Marker-Density method are employed to track the free surface. Body boundary conditions are satisfied with the adoption of porosity method and no-slip condition on the hull surface. The ship model has a wedge type fore-body, and the computational domain is an appropriate region around the fore-body. The computation results are compared with some experimental results. Also the difference of the free surface tracking methods are discussed.