• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.05a
• /
• pp.82-85
• /
• 2008

When a projectile travels at high speed underwater, supercavitating flowarises, in which a huge cavity is generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape optimization technique is employed to determine the optimum cavitator shape for minimum drag, given certain operating conditions. Simultaneous optimization technique is proposed for efficient cavitator shape optimization, in which the cavity and cavitator shape are determined in a single optimization routine.

• Journal of Korea Water Resources Association
• /
• v.37 no.9
• /
• pp.729-736
• /
• 2004

Analysis of reflection of random waves propagating over rectangular submerged non-porous breakwaters was performed by using the eigenfunction expansion method. In this study, random waves were generated by superposition of several monochromatioc waves. Reflection coefficients were calculated by summing each numerical results of regular waves. Predicted results from the eigenfunction expansion method were in a good agreement with the results of laboratory measurements. Reflection coefficients of random waves were also resonated at the Bragg reflection condition.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.14 no.1
• /
• pp.21-27
• /
• 2008

Triangular structure is used as basic shape of artificial structures for generating the upwelling current in order to make rich fishing ground at sea. Artificial upwelling current could bring the deep sea water containing a lot of nutrients from the bottom up to the surface. The purpose of this study is to examine the flow characteristics around underwater triangular structure with various stratification parameter. An experimental study was carried out for the triangular structure model in the circulating water channel to investigate flow characteristics by flow visualization method. A velocity fields around the underwater structure were measured by particle image velocimetry(PIV). The experimental results showed that the upwelling effect at the back and upper region of the structure could be best when the water depth was 2 times of the structure height and the stratification parameter was approximately 3.0. These quantitative data will be useful to determine the functional efficiency cf artificial upwelling structures.

• Journal of Korea Water Resources Association
• /
• v.36 no.5
• /
• pp.741-749
• /
• 2003

This study presents a combined experimental and numerical effort to investigate experimentally and numerically the Bragg reflection of sinusoidal waves due to trapezoidal submerged porous breakwaters. Numerical predictions of the study are verified by comparing to laboratory measurements. In the numerical model, the flow in porous structures is described by the spatially averaged Navier-Stokes equations and the volume of fluid method is employed to track the free surface displacements. Numerical solutions are agree well with laboratory measurements. The reflection coefficients of porous structures are smaller than those of non-porous structures and become stronger in proportion to the increase of number of submerged breakwaters.

• Journal of the Society of Naval Architects of Korea
• /
• v.28 no.2
• /
• pp.159-173
• /
• 1991

This paper describes a potential-based panel method formulated for the analysis of a super-cavitating two-dimensional hydrofoil. The method employs normal dipoles and sources distributed on the foil and cavity surfaces to represent the potential flow around the cavitating hydrofoil. The kinematic boundary condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the fictitious inner flow region of the foil, and the dynamic boundary condition on the cavity surface is satisfied by requiring thats the potential vary linearly, i.e., the tangential velocity be constant. Green's theorem then results in a potential-based integral equation rather than the usual velocity-based formulation of Hess & Smith type. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with improved accuracy compared to those of the linearized lilting surface theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. This iteration process is repeated until the results are converged. Characteristics of iteration and discretization of the present numerical method are much faster and more stable than the existing nonlinear theories. The theory shows good correlations with the existing theories and experimental results for the super-cavitating flow. In the region of small angles of attack, the present prediction shows and excellent comparison with the Geurst's linear theory. For the long cavity, the method recovers the trends of the Wu's nonlinear theory. In the intermediate regions of the short super-cavitation, the method compares very well with the experimental results of Parkin and also those of Silberman.

• Proceedings of the Korean Society of Fisheries Technology Conference
• /
• 2002.05a
• /
• pp.43-44
• /
• 2002

• Proceedings of the Korean Society of Fisheries Technology Conference
• /
• 1995.06a
• /
• pp.293-294
• /
• 1995

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.34 no.4
• /
• pp.359-365
• /
• 1998

• Proceedings of the Korea Water Resources Association Conference
• /
• 2003.05b
• /
• pp.1043-1046
• /
• 2003

• Journal of the Korean Magnetics Society
• /
• v.23 no.5
• /
• pp.159-165
• /
• 2013

A active magnetic sensor has been widely used in the underwater guided weapon system because it is able to detect a target accurately in close range, but the target doesn't have any good countermeasure to overcome the threat from the active magnetic sensor. Recently, in order to increase the damage area of target by shock wave with explosion of the underwater weapon system and to detect small target, the maximum target detection range of the active magnetic sensor needs to be increased. One method for improving maximum target detection range is to improve output power from transmitter through demagnetization factor minimization of a transmitting core. Thus, in this paper, we describe the study results on the transmitter core shape design to enhance output power of the active magnetic sensor.