• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.8-15
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• 2002

A two-dimensional higher order panel method using B-splines has been developed to overcome the disadvantages of the low order panel method and to obtain more accurate solution. The sources and the normal dipoles are distributed on both the body and the free surface. Instead of applying the upwind finite difference schemes to satisfy the linearized free surface and the radiation condition, the derivatives of the basis functions of the B-splines are directly applied to the linearized free surface condition. Numerical damping in the Dawson's method are avoided in the Present computations. In order to validate the present method, numerical computations are carried out for a submerged cylinder and a two-dimensional hydrofoil steadily moving beneath a free surface. The numerical results show that fast convergence and better accuracies have been achieved by the present method.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.2
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• pp.77-87
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• 2000

The water entry forces acting on an air-dropped torpedo are of the restrictions on launch speed and launch altitude, because it could cause the structural damage to components of torpedo. Therefore, it is necessary to estimate the water entry forces with confidence according to launch conditions. In this study, an approximation method for water entry forces is presented, and the results using this approximation are compared with those of other numerical methods. The magnitude and duration of impact forces estimated by the present approximation agree with those of impact by the analysis of ideal or viscous flow. This method can give useful tools to select the launch in initial design stage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1371-1378
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• 1999

Flow through turbomachinery has a very complex structure and Is Intrinsically unsteady. In addition, trend to highly loaded turbomachinery makes the flow extremely complex due to the interaction between rotor and stator. In this study, flows through UTRC LSRR turbine are numerically analyzed using 2 dimensional Navier-Stokes equations. The convective terms of the governing equations are discretized using the Van-Leer's FVS(Flux vector splitting) with an upwind TVD scheme. The conventional central differencing is used to discretize the diffusion terms on the finite volume. The accurate unsteady motion is achieved by using a 2nd order accurate, 3-point Euler implicit scheme. The quasi-conservative zonal scheme is used for calculating the flow variables on the zonal interface between the rotor and stator. The axial gap between stator and rotor has been configured in two variations, 15% and 65% of average chord length. The analysis program is validated using experimental results and the effect of axial gap is examined. The numerical analysis results are presented by time averaged pressure coefficient and pressure magnitude coefficient and compared with experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.924-929
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• 1994

In using a performance model of a torque converter determined by its gemetric condition, it is possible that the analysis of two arbitrary converters produces the the same results because of the same value of equivalent parameters despite their different shapes. Therefore, it is necessary to understand the effect of shape factor on dynamic perfomance, and equivalent parameters reoresenting a performace model of a converter should into its defined by the behavior of flow field. In this study, torus flow of a torque converter is changed into its equivalent system defined by the behavior of flow, and govering equations for the system are presented and used for analysis. Equivalent parameters are obtained from the results of flow analysis and are compared with parameters of one dimensional performance model. The influence that shape change of a converter has on the behavior of flow and the equivalent parameters is studied qualitatively.

• Journal of Ocean Engineering and Technology
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• v.21 no.3 s.76
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• pp.16-25
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• 2007

A comparative study on the turbulent flaw simulation and the potential flaw analysis has been performed. A law Mach number preconditioned Navier-Stokes solver, using the multi-block grid method and a panel method based on the velocity potential, have been developed and validated by comparison to the experimental data. The present numerical analysis methods are applied to the ground effect problem around the NACA 4412 airfoil. It has been confirmed that the potential flaw analysis on the ground effect, using the image method, is consistent, to some degree, with the viscous calculations for high Reynolds number flows.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.2
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• pp.156-162
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• 1995

A numerical method for a 2-D oil boom model considering the flexibility of skirt has been developed The neater is assumed rigid and the skirt is tensioned membrane having a point mass at its end The fluid motion is potential. The kinematic condition which demands the continuity of the displacement is imposed at the joint between the floater and the skirt. The dynamic condition for the point mass is imposed at the bottom end of the skirt. The numerical method is based on the Green's function method in the frame of linear potential theory. It finds it's solution simultaneously from the total system of three equations, integral equation, the equation of motion of the floater and the equilibrium equation of the deformation of the skirt. Integral equation is derived by applying the Green's theorem to radiation potential and Green's function. Proper descretization of those three equations leads to the system of a linear algebraic equation. Due to the flexibility of skirt the motion of floater can be diminished in some range of wave frequency and furthermore the mechanism of resonance of the oil boom can be changed. The motion responses of various oil booms have been compared varying the length of the skirt and the point mass. The numerical method has been validated indirectly from the good correspondence between the motion responses of the flexible skirt model and the rigid skirt model in low frequency limit.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.127-138
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• 1999

In this study steady state solutions of cavity flows driven by two moving walls are studied. The north and east walls of the cavity are movable where as the remaining two walls are fixed in space. Numerical experiments for three different driving schemes for moving walls are done at two different Reynolds numbers of Re=40 and 400. The first scheme is to accelerate north and east walls simultaneously. In the second one, the north wall is started first and the east wall is accelerated later. In the third one the east wall starts first. It is usually expected that all these three cases yield the same steady state solution after sufficiently long time. However, present numerical experiments show that such a usual belief is valid only when the Reynolds number is low enough (Re=40). At higher Reynolds number (Re=400), the flow develops to three different steady states depending on the history of the boundary condition change.

• Computational Structural Engineering
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• v.9 no.1
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• pp.55-64
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• 1996

Sloshing frequencies of the fluid in rectangular tanks with a bottom-mounted rectangular block are determined by linear water wave theory. Velocity potential is decomposed into those for the wall-induced waves, and the reflected, transmitted, and scattered waves by the block. The reflection and transmission coefficients are determined using the continuity conditions of mass flux and energy flux on the common vertical boundaries of the fluid regions, and the boundary conditions on the both sides of the block. The analysis results indicate that the sloshing frequencies reduce, as the block becomes tall and vade and as the block moves toward the center. The variations of the sloshing frequencies due to the block are found to be more sensitive in broad thanks than is tall tanks.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.12
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• pp.931-939
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• 2013

In this paper, we try to find the lifting-line method which is applicable to the conceptual design of aircraft wings, and analyze the accuracy and coverage of the method. Two methods that are extended from the lifting-line theory of Prandtl are selected. One of the methods is Weissinger's method which imposes the velocity boundary condition at the control points located at the quarter chord, and the other is Phillips's method which combines the three-dimensional vortex lifting law. Calculations are performed for an elliptic wing, a swept back wing, and a tapered unswept wing with dihedral angle and geometric twist. The aerodynamic data of the potential flow such as spanwise distributions of circulation and downwash, lift and induced drag are obtained through calculations, and these data are compared with theoretical results and wind tunnel test data. As a result, Weissinger's method showed good accuracy and reliability regardless of wing shapes, but Phillips's method revealed inaccurate results for a swept back wing.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.255-263
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• 2005

This paper proposes an efficient boundary-based technique for the shape design sensitivity analysis in various disciplines. An analytical sensitivity formula in the form of a boundary integral is derived based on the continuum formulation for a general functional defined in the problems. The formula can be conveniently used for gradient computation in a variety of shape design problems. The advantage of using a boundary-based method is that the shape variation vectors are needed only on the boundary, not over the whole domain. The boundary shape variation vectors are conveniently computed by using finite. Perturbations of the shape geometry instead of complex analytical differentiation of the geometry functions. The potential flow problems and fillet problem are chosen to illustrate the efficiency of the proposed methodology.