• Proceedings of the KSME Conference
• /
• 2005.11a
• /
• pp.236.2-236.2
• /
• 2005

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2010.05a
• /
• pp.1197-1198
• /
• 2010

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.1
• /
• pp.1-10
• /
• 2005

An aerodynamic shape optimization technique has been developed for helicopter rotor blades in hover based on a continuous adjoint method on unstructured meshes. The Euler flow solver and the continuous adjoint sensitivity analysis were formulated on the rotating frame of reference for hovering rotor blades. In order to handle the repeated evaluation of the design cycle efficiently, the flow and adjoint solvers were parallelized using a domain decomposition strategy. A solution-adaptive mesh refinement technique was adopted for the accurate capturing of the tip vortex. Applications were made for the aerodynamic shape optimization of Caradonna-Tung rotor blades and UH60 rotor blades in hover. The results showed that the present method is an effective tool to determine optimum aerodynamic shapes of rotor blades requiring less torque while maintaining the desired thrust level.

• Journal of the Society of Naval Architects of Korea
• /
• v.37 no.2
• /
• pp.70-76
• /
• 2000

A numerical study on the viscous flow around a 2-dimensional circulation control foil is carried out for application on the field of naval architecture and ocean engineering. The governing equations are the RANS and the continuity equations. The equations are discretized by finite difference method and MAC method and the pressure poisson equation is calculate by a SOR method and an O-type non-staggered boundary fitted coordinate system which is overlapped near the slot is used to improve the numerical accuracy. Turbulence is approximated by a modified Baldwin-Lomax turbulence model. In the present paper, the Coanda effect on a 2-dimensional foil of a 20% thickness ellipse with modified rounded trailing edge has been numerically studied. The change in drag and lift of the foil with various jet momentums are calculated and compared to the experimental results to show good agreements.

• Korean Journal of Optics and Photonics
• /
• v.7 no.4
• /
• pp.314-321
• /
• 1996

In this paper, the chemical process of each step in fabricating the holographic phase diffraction grating with silver salt sensitive materials has been studied in detail. A new analysis of the bleaching methods have been made through the study. The result shows that among the types of bleaching methods, the reversal bleach can not be reacted chemically. And the experiments about the chemical reactions, the characteristics of the reaction products and the refractive modulation types by the bleaching methods have been done to prove the theory. It is investigated that the exposure acts as the catalyst of developing reaction and affects the developing reaction time conspicuously. At the optimum developing reaction times, which could be taken from the experiments, the holographic diffraction gratings with high diffraction efficiency over 70% could be obtained in the range of the exposure quantity 50~350 [$\mu$J/ $\textrm{cm}^2$]. From the experiments about the correlation of the chemical processing conditions of the composition of developers, the exposure, and the developing reaction time, it has proved that the enhancement of the diffraction efficiency is impossible in the limited exposure energy and conventional constant chemical reaction time.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.26 no.3
• /
• pp.145-152
• /
• 1989

Volume phase diffraction grating is formed in 5${mu}m$ Agfa 8E75 photographic emulsion film using He-Ne laser. It is dependent on the chemical processing rather than materials themselves that high diffraction efficiency can obtained in silver halide emulsions. With potassium dichromate bleach and alcohol drying, overall efficiency of 71% (81% after allowing for reflection at the two surfaces) has been achieved at an exposure of 180${mu}J/cm^2.$ Dichromate cross-linkage and air void by rapid dehydration increase refractive index modulation depth. The grating is swollen, which is newly identified by Scanning Electronic Microscope(SEM) photography, and it causes on-Bragg at larger angle than the recording angle. It is pointed out that controlling the emulsion thickness has an important role as a potential source for high diffraction efficiency.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.04a
• /
• pp.239-244
• /
• 2009

The gridless (or meshfree) methods, such as MPS, SPH, FPM an so forth, are feasible and robust for the problems with moving boundary and/or complicated boundary shapes, because these methods do not need to generate a grid system. In this study, a gridless solver, which is based on the combination of moving least square interpolations on a cloud of points with point collocation for evaluating the derivatives of governing equations, is presented for two-dimensional unsteady incompressible Navier-Stokes problem in the low Reynolds number. A MAC-type algorithm was adopted and the Poission equation for the pressure was solved by successively in the moving least square sense. Some weighing functions were tested in order to investigate the up-winding effect for the convection term. Some typical problems were solved by the presented solver for the validation and the results obtained were compared with analytic solutions and the numerical results by conventional CFD methods, such as FVM.

• Journal of computational fluids engineering
• /
• v.20 no.3
• /
• pp.20-26
• /
• 2015

This paper introduces a computational method for analysis of the 6-DOF motions of a ship in waves using an overset grid technique which consists of inner and outer domains for representing body motions and numerical wave tank, respectively. High order interpolation scheme is employed to increase numerical accuracy over the interface where physical values, such as velocities and pressure, interact between the inner and outer domains. The numerical schemes and algorithm are addressed in the present paper. An application to motion of KCS container carrier in head waves is presented, and the comparison of responses on heave and pitch motions shows good agreement with those of model tests.

• Journal of computational fluids engineering
• /
• v.16 no.1
• /
• pp.30-35
• /
• 2011

In this paper, our effort to apply 3-D Virtual Reality system for stereoscopic visualization of mesh data on the web is briefly described. This study is an extension of our previous and on-going research efforts to develop an automatic grid generation program specialized for wing mesh, named as eGWing. The program is developed by using JAVA programming language, and it can be used either as an application program on a local computer or as an applet in the network environment. In this research advancing layer method(ALM) augmented by elliptic smoothing method is used for the structured grid generation. And to achieve a stereoscopic viewing capability, two graphic windows are used to render its own viewing image for the left and right eye respectively. These two windows are merged into one image using 3D monitor and the viewers can see the mesh data visualization results with stereoscopic depth effects by using polarizing glasses. In this paper three dimensional mesh data visualization with stereoscopic technique combined with 3D monitor is demonstrated, and the current achievement would be a good start-up for further development of low-cost high-quality stereoscopic mesh data visualization system which can be shared by many users through the web.

• 한국전산유체공학회:학술대회논문집
• /
• 2006.10a
• /
• pp.193-198
• /
• 2006

It takes a lot of time and effort to generate grids for numerical analysis of problems with ground effect because the relative attitude and height of airfoil should be maintained to the ground as well as the inflow. A low Mach number preconditioned turbulent flow solver using the overlap grid technique has been developed and applied to the ground effect simulation. It has been validated that the present method using the multi-block grid gives us highly accurate solutions comparing with the experimental data of the RAE 101 airfoil in an unbounded condition. Present numerical method has been extended to simulate ground effect problems by using the overlapped grid system to avoid tedious work in generating multi-block grid system. An extended method using the overlapped grid has been verified and validated by comparing with results of multi-block method and experimental data as well. Consequently, the overlapped grid method can provide not only sufficiently accurate solutions but also the efficiency to simulate ground effect problems. It is shown that the pressure and aerodynamic centers move backward by the ground effect as the airfoil approaches to the ground.