• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.603-606
• /
• 2002

Numerical analysis and its inverse design process of 2nd stage of JT8D aircraft engine is described. One of the most important factors that affect the performante of turbomachine is secondary flow in the blade passage, so that the performance of turbomachine can be improved by controlling secondary flow. In this paper, as a method to control secondary flow, commercial inverse design program, TurboDesign is used. Meridional derivative of angular momentum is selected as a parameter to control blade leading in this program, To validate inverse designed model, computational analysis is applied which includes rotor-stator-interaction. In this paper, CFB results of both original and inverse designed model are compared to examine how much the performance improves without reduction of work output.

• 대한기계학회논문집B
• /
• 제30권1호
• /
• pp.16-23
• /
• 2006

The present study aims at establishing the design procedure of regenerative pumps. It is based on the new momentum exchange theory proposed in Yoo, Park and Chung. Salient feature of the present design procedure is that it does not require input of any kinds of empirical design data. Using the design procedure, a prototype regenerative pump has been designed and manufactured to confirm its validity. Comparison between the predicted performance and the experimental measurement reveals that the prototype pump has its maximum efficiency at the design flow rate and that the proposed performance analysis method satisfactorily predicts the machine performance.

• Nuclear Engineering and Technology
• /
• 제44권1호
• /
• pp.79-88
• /
• 2012

Migration tests were performed with conservative tracers in a fractured zone that had a single fracture of about 2.5 m distance at the KURT. To interpret the migration of the tracers in the fractured rock, a solute transport model was developed. A two dimensional variable aperture channel model was adopted to describe the fractured path and hydrology, and a particle tracking method was used for solute transport. The simulation tried not only to develop a migration model of solutes for open flow environments but also to produce ideas for a better understanding of solute behaviours in indefinable fracture zones by comparing them to experimental results. The results of our simulations and experiments are described as elution and breakthrough curves, and are quantified by momentum analysis. The main retardation mechanism of nonsorbing tracers, including matrixdiffusion, was investigated.

• Wind and Structures
• /
• 제17권6호
• /
• pp.589-608
• /
• 2013

A model is proposed to analyse the along-wind dynamic response of upwind turbines with horizontal axis under service wind conditions. The model takes into account the dynamic coupling effect between rotor blades and supporting tower. The wind speed field is decomposed into a mean component, accounting for the well-known wind shear effect, and a fluctuating component, treated through a spectral approach. Accordingly, the so-called rotationally sampled spectra are introduced for the blades to account for the effect of their rotating motion. Wind forces acting on the rotor blades are calculated according to the blade element momentum model. The tower shadow effect is also included in the present model. Two examples of a large and medium size wind turbines are modelled, and their dynamic response is analysed and compared with the results of a conventional static analysis.

• Journal of Power Electronics
• /
• 제17권4호
• /
• pp.953-962
• /
• 2017

Momentum flywheels are widely applied for the generation of small and precise torque for the attitude control and inertial stabilization of satellites and space stations. Due to its inherited system nonlinearity, the tracking performance of the flywheel torque/speed in dynamic/plug braking operations is limited when a conventional controller is employed. To take advantage of the well-separated two-time-scale quantities of a flywheel driving system, the singular perturbation technique is adopted to improve the torque tracking performance. In addition, the composite control law, which combines slow- and fast- dynamic portions, is derived for flywheel driving systems. Furthermore, a novel control strategy for plug braking dynamics, which considers couplings between the Buck converter and the three-phase inverter load, is designed with easy implementation. Finally, experimental results are presented to demonstrate the correctness of the analysis and the superiority of the proposed methods.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 2002년도 추계학술발표회요약집
• /
• pp.167-167
• /
• 2002

• 한국항공우주학회지
• /
• 제38권5호
• /
• pp.437-444
• /
• 2010

본 논문에서는 한 개의 1축 가변속 CMG를 장착한 부족구동 위성의 자세제어 문제를 다루고 있다. 이러한 부족구동 위성의 경우, 전체 모멘텀이 영(zero)이 아니면 자세를 임의로 취할 수 없다. 위성을 안정화 시키려면 가변속 CMG가 위성의 모멘텀 방향으로 정렬해야 하기 때문이다. 4가지의 다른 장착형상을 고려하였으며, 각각에 대해 제어가능 모멘텀 영역을 분석하였다. 또한 각 형상에 대해 백스테핑 기법을 이용하여 안정한 자세제어 법칙을 제시하고 자세제어 특성을 비교하였다.

• 대한기계학회논문집B
• /
• 제28권6호
• /
• pp.619-627
• /
• 2004

In most industrial applications, the geometrical complexity is combined with the moving boundaries. These problems considerably increase the computational difficulties since they require, respectively, regeneration and deformation of the grid. As a result, engineering flow simulation is restricted. In order to solve this kind of problems the immersed boundary method was developed. In this study, the immersed boundary method is applied to the numerical simulation of stationary, rotating and oscillating cylinders in the 2-dimensional square cavity. No-slip velocity boundary conditions are given by imposing feedback forcing term to the momentum equation. Besides, this technique is used with a second-order accurate interpolation scheme in order to improve the accuracy of flow near the immersed boundaries. The governing equations for the mass and momentum using the immersed boundary method are discretized on the non-staggered grid by using the finite volume method. The results agree well with previous numerical and experimental results. This study presents the possibility of the immersed boundary method to apply to the complex flow experienced in the industrial applications. The usefulness of this method will be confirmed when we solve the complex geometries and moving bodies.

• 한국운동역학회지
• /
• 제13권3호
• /
• pp.15-26
• /
• 2003

This study was conducted to investigate the performance times, CM position and CM speed, pole chord length and pole chord angle, whole body angular momentum(X axis), and grip width in pole vault event according to the event and phase; touch down, pole plant, take-off, maximum pole bending pole straight, pole release, peak height, and foot contact, pole contact, free flight. The pole vaulting of four male elite vaulters including six trial were filmed using two video digital cameras at 60 Hz at 56th national athletic match, and data were collected through the DLT method of three dimensional cinematography. In general the better jumper is, the longer the performance time is. And the greater CM speed is, and the better his transformation ability of CM horizontal speed into vertical speed is. As he uses a longer pole, his grip is higher, and it is a enough for him to rock back his body, so that he pulls and pushes the pole well keeping his hips close to. An greater maximum angular momentum and early positioning of the hips parallel to the bar makes his body far side of the bar and his bar clearance easier. Specially our national jumper needs to have more powerful braking force during foot contact phase, and take his body on the pole after maximum pole bending, and pull and push the pole strongly keeping his hips close to. Also he needs to have stronger muscular strength in order to control the longer pole and use the pole of proper tension more efficiently.

• Composites Research
• /
• 제14권5호
• /
• pp.26-37
• /
• 2001

본 연구에서는 복합재료 원통쉘의 구조해석을 통하여 구해진 원통쉘 경사면의 10등분 등간격 9지점의 변형율을 신경회로망의 입력패턴으로 활용하여 원통쉘에 가해진 중격하중 특성을 동시에 추론하였다. 적용된 신경회로망은 Momentum Backpropagation 알고리즘이며, 모멘텀 계수 및 학습율이 학습도에 따라 가변적으로 조정될 수 있도록 프로그램을 개발 적용하였다 Backpropagation 신경회로망의 은닉층은 1층에서 3층까지 별도 프로그램을 개발하여 충격하중 특성추론 학습을 시도하였다. 개발된 신경회로망 프로그램을 적용하여 원통쉘의 충격하중 특성추론 정확도는 1%이내로 학습에 성공하였다. 본 연구 결과 신경회로망을 이용한 복합재료 원통쉘의 충격하중 특성을 추론할 수 있는 역문제 해석이 가능해졌다.