• Journal of the Society of Naval Architects of Korea
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• v.42 no.4 s.142
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• pp.307-314
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• 2005

In recent years, many environmentally disastrous oil spill accidents from damaged vessels become worse especially when the early treatment is not prompt enough. To properly handle this type of accidents and prevent further disasters, international organizations establish and impose various rules and regulations. In assessing the damages and providing salvage operations, the propulsive performance of damaged vessels is of great importance, as well as for containing oil spill while the vessels are being towed or self-propelled. Until now, many naval hydrodynamics researches have focused on the propulsive performance in normal operating conditions and only a few studies for damaged vessels are found in literature. In this paper experimental method is used to study the Propulsive performance of a very large crude-oil carrier (VLCC) in .heeled and/or trimmed conditions.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.3 s.147
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• pp.275-284
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• 2006

In recent years, many environmentally disastrous maritime accidents resulted from oil or fuel spills from damaged vessels. The situation becomes worse especially when the early counter treatment is not prompt enough. To properly handle this type of accidents and prevent further disasters, the propulsive performance of damaged vessels must be better understood for salvage operations, as well as for containing oil spills while the vessels are being towed or self-propelled. Until now, many hydrodynamic studies have focused on the propulsive performance of undamaged vessels but only a few studies on that of damaged vessels. in this paper, both experimental and computational methods are used to study the propulsive performance of a VLCC in heeled and/or trimmed conditions. For experimental studies, measurement systems should be modified to adapt to the variations of attitude of a damaged vessel. For numerical studies, CFD programs should be also extended to be applied to asymmetrically floating conditions.

• Journal of computational fluids engineering
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• v.8 no.2
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• pp.24-32
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• 2003

In this work, we propose a new idea of flapping airfoil design for optimal aerodynamic performance from detailed computational investigations of flow physics. Generally, flapping motion which is combined with pitching and plunging motion of airfoil, leads to complex flow features such as leading edge separation and vortex street. As it is well known, the mechanism of thrust generation of flapping airfoil is based on inverse Karman-vortex street. This vortex street induces jet-like flow field at the rear region of trailing edge and then generates thrust. The leading edge separation vortex can also play an important role with its aerodynamic performances. The flapping airfoil introduces an alternative propulsive way instead of the current inefficient propulsive system such as a propeller in the low Reynolds number flow. Thrust coefficient and propulsive efficiency are the two major parameters in the design of flapping airfoil as propulsive system. Through numerous computations, we found the specific physical flow phenomenon which governed the aerodynamic characteristics in flapping airfoil. Based on this physical insight, we could come up with a new kind of airfoil of tadpole-shaped and more enhanced aerodynamic performance.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.291-293
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• 2003

This paper deals with a thrust generation of flapping-airfoil by dynamic stall. From many other previous research results, phase angle $ between pitching and plunging mode of flapping motion must be 90 deg. to satisfy maximum propulsive efficiency. In this case, leading edge vortex is relatively small. This phenomenon is related dynamic stall. So preventing leading edge vortex induced by dynamic stall guarantees maximum propulsive efficiency. But, in this paper we insist the leading edge vortex yields quite a positive influence on thrust generation and propulsive efficiency. In order to certify our opinion, pitching and plunging motions were calculated with the parameter of amplitude and frequency by using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation, it is parallelized by MPI programming method.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.89-99
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• 1990

It is required to develop a hull form with low resistance and high propulsive efficiency for the improvement of the ship-board operational economy. Since the hull forms with low resistance frequently have lower propulsive efficiency and on the other hand the hull forms with higher propulsive efficiency don't show good resistance characteristics, it is always very difficult to obtain economical hull forms which require less propulsive power accordingly. Efforts have been made to pursue a stern form with excellent resistance and propulsion characteristics together by shaping the run of the so-called buttock-flow type stern, which is known to have good viscous resistance performance, like that of conventional aftbody(U-type or Hogner type) featured by high propulsive efficiency. First model tests confirmed that the above concept can be one of the alternative approaches to the design of the good stern form and by the continuing efforts thereafter for the refining of the concept, propelled by the first promising results, stern form of good resistance performance together with good propulsive efficiency has been realized to some extent. In addition, it is confirmed that the new new stern can have better cavitation and vibration characteristics due to uniform wake-fields and the compact engine room arrangement can be possible due to it's larger floor area in way of engine room double bottom as compared with usual barge stern.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.1-6
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• 2015

In this study, a numerical prediction on propulsive performance of a ducted propeller in open water condition was carried out by solving Reynolds averaged Navier-Stokes(RANS) equation using computational fluid dynamics(CFD). A configuration of propeller Ka-470 inside duct 19A was considered. Hexahedral grid system was generated by dividing whole computational domain into three separate regions; propeller, duct and outer flow region. A commercial CFD software, ANSYS-CFX was used for numerical simulations. Results were compared with experimental data and showed considerable improvement in accuracy, in comparison to those from surface panel method which is based on potential flow assumption. The results also exhibited the importance of grid system within the gap between the inner surface of duct and blade tip for accurate prediction of propulsive performance of ducted propeller.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.151-159
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• 1999

A self-propulsive polishing robot is proposed as a method which automates a floor polisher. The proposed robot with two rotary brushes does not require any mechanism such as wheels to obtain driving forces. When the robot polishes a floor with its two brushes rotating, friction forces occur between the two brushes and the floor. These friction forces are used to move the robot. Thus, the robot can move in any direction by controlling the two rotary brushes properly. In this paper, firstly a dynamics model of a brush is presented. It computes the friction force between the brush and the floor. Secondly, the dynamics of the proposed robot is presented by using the bush dynamics. Finally, the inverse dynamics is solved for the basic motions, such as the forward, backward, leftward, rightward motions and the pure rotaion. This paper will contribute to realize a self-propulsive polishing robot as proposed above, In addition, this paper will give basic ideas to automate the concrete floor finishing trowel, because its basic idea for motion is similar to that of the proposed robot.

• The Journal of Korea Robotics Society
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• v.11 no.4
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• pp.285-292
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• 2016

For articulated swimming robots, there have been no researches about controlling the motion or trajectory following. A control method for articulated swimming robot is suggested by extending a previous algorithm, ESPG (Extended Swimming Pattern Generator). The control method focuses on the situation that continuous pre-determined swimming pattern is applied for long range travelling. In previous studies, there has not been a way to control the propulsive force when a swimming pattern created by ESPG was in progress. Hence, no control could be made unless the swimming pattern was completed even though an error occurred while the swimming pattern was in progress. In order to solve this problem, this study analyzes swimming patterns and suggests a method to control the propulsive force even while the swimming pattern was in progress. The angular velocity of each link is influenced and this eventually modifies the propulsive force. However, The angular velocity is changed, a number of problems can occur. In order to resolve this issue, phase compensation method and synchronization method were suggested. A simple controller was designed to confirm whether the suggested methods are able to control and a simulation has affirmed it. Moreover, it was applied to CALEB 10 (a biomimetic underwater articulated robot) and the result was verified.

• Korean Journal of Applied Biomechanics
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• v.14 no.2
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• pp.85-103
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• 2004

This study was conducted to determine what effects would the midsole hardness of running shoes have on shoe flex angle and maximum propulsive force. Furthermore, the relationship between the shoes flex angle and maximum propulsive force was elucidated in order to provide basic data for developing running shoes to improve sports performances and prevent injuries. The subjects employed in the study were 10 college students majoring in physical education who did not have lower limbs injuries for the last one year and whose running pattern was rearfoot strike pattern of normal foot. The shoes used in this study had 3different hardness, shore A 40(soft), 50(medium) and 60(hard). The subjects were asked to run at a speed of $4{\pm}0.08m/sec$, and their movements were videotaped with 2 S-VHS video-cameras and measured with a force platform. And the following results were obtained after analyzing and comparing the variables. 1. Although the minimum angle of shoes flex angle was estimated to appear at SFA4, it appeared at SFA2 except in those shoes with the hardness of 40. 2. The minimum angle of shoes flex angle was $145.1^{\circ}$ with barefoot. Among the shoes with different hardness, it was the smallest when the hardness was 50 at $149.9^{\circ}$. The time to the minimum angle was 70.7% of the total ground contact time. 3. Maximum propulsive force according to midsole hardness was the largest when the hardness was 50 at $1913.9{\pm}184.3N$. There was a low correlation between maximum propulsive force and shoes flex angle.

• Korean Journal of Applied Biomechanics
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• v.17 no.4
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• pp.27-36
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• 2007

The purpose of this study was to investigate the effect of the upper body in order to increase a propulsive force in the old's walking. The subjects were each 10 males, the latter term of the aged and former term of the aged. There were three walking speeds of slow(about 5km/h), medium(about 6km/h), and maximum speed(about 7km/h). The subjects walking 11m were filmed the 5m section (from 3m to 8m) by 2-video cameras using three dimensional cinematography. And we computed different mechanical quantities and especially computed the relative momentum in order to achieve this study's aim. In this study, we was able to acquire some knowledge. The step length and step frequency increased in proportion to the walking speed, and the faster walking speed, the shorter ratio of supporting time( both legs supporting time/one step length time). When it was one leg support phase, the torso was indicated to generate the momentum in order to produce the propulsive force of walking. The upper and lower body had a cooperative relation for walking such as keeping step rate with the arms to legs and maintaining the body balance. The opposition phase for upward-and-downward direction of the torso and arms in walking was functioned to prevent the increase rapidly toward vertical direction of the center of gravity. The arms had contributed to coordinate the tempo of legs and the posture maintenance of the upper body. And by absorbing the relative momentum from the upper torso with arms to the lower torso, it had the rhythmical movement on upward-and-downward direction reducing the vertical reaction force. On account of the relations of absorption and generation of the propulsive force and the production of vertical impulse in the lower torso when walking by maximum speed, it was showed that the function of lower torso was come up as important problem for the mechanical posture stability and propulsive force coordination.