• Ocean Systems Engineering
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• 제6권4호
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• pp.305-324
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• 2016

Wave load prediction at zero forward speed using finite depth Green function is a well-established method regularly used in the offshore and marine industry. The forward speed approximation in deep water condition, although with limitations, is also found to be quite useful for engineering applications. However, analysis of vessels with forward speed in finite water depth still requires efficient computing methods. In this paper, a method for analysis of wave induced forces and corresponding motion on freely floating three-dimensional bodies with low to moderate forward speed is presented. A finite depth Green function is developed and incorporated in a 3D frequency domain potential flow based tool to allow consideration of finite (or shallow) water depth conditions. First order forces and moments and mean second order forces and moments in six degree of freedom are obtained. The effect of hull flare angle in predicting added resistance is incorporated. This implementation provides the unique capability of predicting added resistance in finite water depth with flare angle effect using a Green function approach. The results are validated using a half immersed sphere and S-175 ship. Finally, the effect of finite depth on a tanker with forward speed is presented.

• 풍력에너지저널
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• 제2권1호
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• pp.82-89
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• 2011

his dissertation is on power control system for MW-class wind turbine. Especially, the control purpose is reduction in electrical power and rotor speed. The base control structure is power curve tracking control using variable speed variable pitch operational type. For the reduction of fluctuations, more control algorithm is needed in above rated wind conditions. Because general pitch control system is low dynamic response as compared with the wind speed change. So, this paper introduces about the pitch feed forward control to minimize fluctuations of the electrical power and rotor speed. To maintain rated electrical power, the algorithm of feed forward control adds feed forward pitch amount to the pitch command of power curve tracking control. The effectiveness of the feed forward control is verified through the simulation.

• 한국운동역학회지
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• 제17권3호
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• pp.1-10
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• 2007

The purpose of this study was to examine the differences of lower limbs muscle activities depending on three walking speeds of 2.5km/h, 5.0km/h and 7.5km/h during forward walking and backward walking making 14 students the subjects of this study. To achieve this aim, surface electrodes for factor analysis of EMG were adhered to rectus femoris, biceps femoris, tibialis anterior and gastrocnemius medial head of right lower limbs. The conclusions through this study are as follows. 1) The muscle activity of rectus femoris was higher in backward walking group than in forward walking group and it was the highest at 7.5km/h walking speed. 2) The muscle activity of biceps femoris was higher in forward walking group than in backward walking group. It was the lowest at 5.0km/h walking speed and the highest at 7.5km/h walking speed. 3) The muscle activity of tibialis anterior was higher in backward walking group than in forward walking group. It was the lowest at 5.0km/h walking speed and the highest at 7.5km/h walking speed. 4) The muscle activity of gastrocnemius medial head was higher in backward walking group than in forward walking group except P2. It was the lowest at 5.0km/h walking speed and the highest at 7.5km/h walking speed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 The 8th Asian Symposium on Precision Forging ASPF
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• pp.162-166
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• 2003

In combined forward-backward extrusion with controlled forward speed by a counter punch, accurate parts with forward rod can be formed. As an extension of this method, reverse extrusion is proposed, in which the extruded forward rod is pushed back while the main punch is kept at the final position after the forward-backward extrusion process. The experiment is carried out using lead as a model material. With the reverse extrusion method, longer forward rods can be formed without under-filling defect than that by combined extrusion with controlling extrusion speed.

• Journal of Mechanical Science and Technology
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• 제18권6호
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• pp.972-978
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• 2004

Forward slip is an important parameter often used in rolling-speed control models for tandem hot strip rolling mills. In a hot strip mill, on-line measurement of strip speed is inherently very difficult. Therefore, for the set-up of the finishing mill, a forward slip model is used to calculate the strip speed from roll circumferential velocity at each mill stand. Due to its complexity, most previous researches have used semi-empirical methods in determining values for the forward slip. Although these investigations may be useful in process design and control, they do not have a theoretical basis. In the present study, a better forward slip model has been developed, which provides for a better set-up and more precise control of the mill. Factors such as neutral point, friction coefficient, width spread, shape of deformation zone in the roll bite are incorporated into the model. Implementation of the new forward slip model for the control of a 7-stand hot strip tandem rolling mill shows significant improvement in roll speed set-up accuracy.

• 대한조선학회논문집
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• 제56권5호
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• pp.396-409
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• 2019

In this paper, a comparative study on the radiation techniques for the motion analysis of the three dimensional floating structure with the forward speed was carried out. The Sommerfeld radiation condition, the damping technique, and the point shift technique were used for the comparative study. Radiated wave patterns and hydrodynamic coefficients of the heave motion of floating structure with the forward speed were compared and analyzed. The characteristics and limitations of each radiation technique were analyzed through the calculation results. To overcome the limitations of conventional radiation techniques, the hybrid radiation technique combining the Sommerfeld radiation condition with the damping technique was proposed. It is confirmed that the proposed method, the Hybrid radiation technique, improves the limitation of the speed range and the dissipation of the wave of the conventional radiation technique. The motion analysis code of the three dimensional floating structure with the forward speed based on the Rankine source method with hybrid radiation technique was developed. In order to validate the developed code, hydrodynamic analyses were carried and compared with published experiments.

• Journal of Ship and Ocean Technology
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• 제6권1호
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• pp.34-53
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• 2002

Numerical solution of the forward-speed radiation problem for a half-immersed cylinder advancing in regular waves is presented by making use of the improved Green integral equation in the frequency domain. The B-spline higher order panel method is employed stance the potential and its derivative are unknown at the same time. The present numerical solution of the improved Green integral equation by the B-spline higher order Kelvin panel method is shown to be free of irregular frequencies which are present in the Green integral equation using the forward-speed Kelvin-type Green function.

• 대한조선학회논문집
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• 제45권3호
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• pp.280-287
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• 2008

In this paper, a mathematical model for a ship manoeuvring with low forward speed in shallow water was suggested. Based on the cross flow model with low forward speed in deep sea, hull, propeller and rudder models were modified to consider the shallow water effects. Static drift and PMM tests were performed to obtain the cross flow drag coefficients and hydrodynamic coefficients. To validate suggested mathematical model, numerical simulation results were compared with those of sea-trials. Through comparisons, it was concluded that suggested mathematical model could give proper estimation on turning test results.

• 한국해안·해양공학회논문집
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• 제33권5호
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• pp.187-194
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• 2021

최근 기후변화에 의한 영향으로 태풍에 의한 피해가 점차 증가하고 있다. 이에 따라 폭풍해일의 특성을 결정하는 여러 요소에 대해 오랫동안 많은 연구가 수행되었으며, 대부분의 연관성들이 발견되었다. 폭풍해일은 여러 요소에 의해 복합적으로 결정되는 이유로 다른 결과를 보여주는 경우가 많아 연구마다 다른 결론을 내리는 경우가 많았다. 이런 이유로 태풍의 이동속도 변화에 의한 폭풍해일의 다양한 특성들을 이해하기 위해 본 연구를 수행하였다. 본 연구는 수치해석 프로그램을 이용하여 수행되었으며, 이동속도에 의한 영향을 분석하기 위해 다른 요소들을 최대한 단순화하였다. 수치해석 결과 태풍에 의한 폭풍해일은 이동속도가 빨라질 경우 점차 증가하는 경향을 보였다. 폭풍해일은 느린 이동속도에서는 넓고 완만하게 증가하였으며, 빠른 이동속도에서는 좁고 급하게 증가하는 형상을 보여주었다. 동일한 이동속도의 경우 실제 해역의 수심 영향이 폭풍해일에 크게 작용하는 것으로 판단된다. 제주도를 지나 이동속도가 변화하는 경우 남해안의 폭풍해일에 큰 영향을 미치지 못하는 것을 확인하였다.

• 한국운동역학회지
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• 제12권1호
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• pp.221-231
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• 2002

The purpose of this study was to clarify the differences in service patterns of a forward and backward soft tennis players using 3D motion analyzer. Subjects were 4 forward players of $24.0\pm5.23$yrs and 4 backward players of $23.5\pm1.73$yrs. The results were as following: 1. There was no difference among each positions on swinging-time. The longest racket swinging-time was in the phase of takeback, the second one was in follow-through. The shortest one was in the phase of forward-swing so called force production phase, which had an influence on ball's velocity. 2. The racket speed on impact was 16.3m/s in forward subject and 19.53m/s in backward subject, when each velocity of balls was 44.6m/s, 52.9m/s. Although there was no significant difference along by positions, backward subject showed faster result. 3. The maximum speed of each performance was reached before the impact, and the speed at impact along by positions did not show any significant difference. The summation of velocity was measured in good order as following; hip, shoulder, elbow, wrist, top of racket. 4. In the angular velocity of all examine except one, the angular velocity of forearm was bigger than the one of racket top although there was no statistically significant difference between forward and backward subject. 5. The service grip of the forward players was shorter than that of backward players.