• Journal of Ship and Ocean Technology
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• 제8권4호
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• pp.1-9
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• 2004

High lifting devices used for control purposes have received much attention in the marine field. Hydrofoils for supporting the hull, roll stabilizer fins for developing the motion damping performance, rudders for maneuverability are the well-known devices. In the present study, the ability of the rudder with flap to produce high lift was analyzed. The boundary layer control, one of the flow control techniques, was adopted. Especially, to build the blown flap, a typical and representative type of a boundary layer control, a flapped rudder was designed and manufactured so that it could eject the water jet from the gap between the main foil and the flap to the flap surface tangentially. And it was tested in the towing tank. Simultaneously, to know the information about the 2-dimensional flow field, a fin model with similar characteristics as the rudder model applicable for the motion control was made and tested in the cavitation tunnel. In addition, local flow measurements were carried out to obtain physical information, for example, a surface pressure measurement and flow visualization around the flap. And CFD simulation was used to obtain information difficult to collect from the experiment about the 2-dimensional flow.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
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• pp.25-32
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• 2002

Free vibration analysis of radialiy multi-delaminated beams with through-the-width multi-delamination is performed in the present study. The multiple delaminations are considered to be in a radial manner through the thickness from the top surface of the beam. The natural frequencies of the radially multi-delaminated beams are calculated from a new algorithm that is based on the single compound delaminated beam model. That is, beams with radial multi-delaminations are regarded as the sum of a single compound delamlnated beam that is the single sub-delaminated beam from the top surface of global beam. Each result of frequency equation for the single delaminated beam with unknown boundary conditions obtained through continuity conditions Is updated to the next one, With these sequential operations, the final frequency equation of radially multi-delaminated beams is obtained for both ends boundary conditions of global beam. The numerical results carried out for the beams are compared with those of some references to give the reliance on the proposed algorithm and to investigate the effects of the shape, number, size of multi-delaminations on the natural frequency. Compared with the other previously presented model, the proposed algorithm is more flexible in modeling and formulating as the total array size of frequency equation is always four by four. Therefore, the proposed algorithm will reduce the effort of user in formulating the physical model to the numerical model.

• Solar Energy
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• 제19권3호
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• pp.125-131
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• 1999

This paper deals with a novel structure of poly-Si solar cell. A grain boundary(GB) of poly-Si acts as potential barrier and recombination center for photo-generated carriers. To reduce unwanted side effects at the GB of poly-Si, we employed physical GB removal of poly-Si using chemical solutions. Various chemical etchants such as Sirtl, Yang, Secco, and Schimmel were investigated for the preferential GB etching. Etch depth about 10 ${\mu}m$ was achieved by a Schimmel etchant. After a chemical etching of poly-Si, we used $POCl_3$ for emitter junction formation. This paper used an easy method of top electrode formation using a RF sputter grown ITO film. ITO films with thickness of 300 nm showed resistivity of $1.26{\times}10^{-4}{\Omega}-cm$ and overall transmittance above 80%. Using a preferential GB etching and ITO top electrode, we developed a new fabrication procedure of poly-Si solar cells. Employing optimized process conditions, we were able to achieve conversion efficiency as high as 16.6% at an input power of 20 $mW/cm^2$. This paper investigates the effects of process parameters: etching conditions, ITO deposition factors, and emitter doping densities in a poly-Si cell fabrication procedure.

• Journal of Magnetics
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• 제22권2호
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• pp.181-187
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• 2017

Flow of electrically conducting nanofluids is of pivotal importance in countless industrial and medical appliances. Fluctuations in thermophysical properties of such fluids due to variations in temperature have not received due attention in the available literature. Present investigation aims to fill this void by analyzing the flow of copper-water nanofluid with temperature dependent viscosity past a Riga plate. Strong wall suction and viscous dissipation have also been taken into account. Numerical solutions for the resulting nonlinear system have been obtained. Results are presented in the graphical and tabular format in order to facilitate the physical analysis. An estimated expression for skin friction coefficient and Nusselt number are obtained by performing linear regression on numerical data for embedded parameters. Results indicate that the temperature dependent viscosity alters the velocity as well as the temperature of the nanofluid and is of considerable importance in the processes where high accuracy is desired. Addition of copper nanoparticles makes the momentum boundary layer thinner whereas viscosity parameter does not affect the boundary layer thickness. Moreover, the regression expressions indicate that magnitude of rate of change in effective skin friction coefficient and Nusselt number with respect to nanoparticles volume fraction is prominent when compared with the rate of change with variable viscosity parameter and modified Hartmann number.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제17권10호
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• pp.938-946
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• 2005

Shape optimization of internally finned circular tube has been peformed for periodically fully developed turbulent flow and heat transfer. The physical domain considered in this study is very complicated due to periodic boundary conditions both streamwise and circumferential directions. Therefore, Pareto frontier sets of a heat exchanger can be acquired by coupling the CFD and the multi-objective genetic algorithm, which is a global optimization technique. The optimal values of fin widths $(d_1,\;d_2)$ and fin height (H) are numerically obtained by minimizing the pressure loss and maximizing the heat transfer rate within ranges of $d_1=0.2\sim1.5\;mm,\;d_2=0.2\sun1.5\;mm,\;and\;H=0.2\sim1.5\;mm$. The optimal values of the design variables are acquired after the fifth generation and also compared to those of a local optimization algorithm for the same geometry and conditions.

• Nuclear Engineering and Technology
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• 제45권7호
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• pp.895-910
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• 2013

The reflood test data from the rod bundle heat transfer (RBHT) test facility showed that the grids in the upper portion of the rod bundle could become wet well before the arrival of the quench front and that the sizes of liquid droplets downstream of a wet grid could not be predicted by the droplet breakup models for a dry grid. To investigate the water droplet generation from a wet grid spacer, a viscous linear temporal instability model of the water sheet issuing from the trailing edge of the grid with the surrounding steam up-flow is developed in this study. The Orr-Sommerfeld equations along with appropriate boundary conditions for the flow are solved using Chebyshev series expansions and the Tau-Galerkin projection method. The effects of several physical parameters on the water sheet oscillation are studied by determining the variation of the temporal growth rate with the wavenumber. It is found that a larger relative steam velocity to water velocity has a tendency to destabilize the water sheet with increased dynamic pressure. On the other hand, a larger ratio of steam boundary layer to the half water sheet thickness has a stabilizing effect on the water sheet oscillation. Droplet diameters downstream of the spacer grid predicted by the present model are found to compare reasonably well with the data obtained at the RBHT test facility as well as with other data recently reported in the literature.

• Journal of Korean Society for Atmospheric Environment
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• 제27권4호
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• pp.416-425
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• 2011

To analyze the physical processes of sea-breeze development over a coastal urban area, numerical simulation for seabreeze (SB) and its frontogenesis was examined based on urbanized MM5 (uMM5) with urban canopy parameterization. On 6 August 2006, SB and its front were well developed in Busan under a weak offshore flow. As a result of wind vector, ZVB (Zero Velocity Boundary), potential temperature obtained the uMM5, at 0900 LST, SB advanced below 200 m height in the coastal areas and the internal boundary grew with the urban coastal region. At noon, the height of the SB head with updraft was approximately one and a half times (~600 m) higher than its depth in central urban. Applying the frontogenesis function, the SB structure for frontogenesis and frontolysis were complicated spatially; the dynamic effects of wind (i.e. convergence and tilting term) could play an important role in the growth of SB, especially the convergence effect.

• Journal of Environmental Impact Assessment
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• 제20권3호
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• pp.257-267
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• 2011

This paper examines the spatial and temporal variability in the shoreline boundary caused by artificial structures in Songdo Beach of South Korea. Quickbird Images of 2003, 2005, 2007, and 2010 extracted from Google Earth were used to identify changing trends of shoreline boundary. The most significant changes were observed in area where groins were extensively established, inducing the sand beach much narrower than before in almost 75% of the area($15070.72m^2$ in 2003 to $3877.46m^2$ in 2010). The Google Earth made it possible to identify area-wide patterns of shoreline change subject to many different type of artificial structures, which cannot be acquired by traditional field sampling. Groin heights, lengths and profiles can be modified during maintenance operations if the Google Earth monitoring indicates that the initial layout is not operating properly as a physical barrier to control sediment transport. It is anticipated that this research could be used as a valuable reference to confirm the outputs from past field researches for coastal processes to respond to storms in more visual and quantitative manner.

• Korean Institute of Interior Design Journal
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• 제18권1호
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• pp.64-71
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• 2009

The modern society is rapidly changing through the development of computer network technology. By generation a collapse of boundaries between may important social institutions, computer networking has affected culture, economy and the physical environment. Because of this, people face a switchover from a simple society, to a compound society. It will also increase the diversity if society's demand, though, and experience. This change is not an exception in the exhibition space. People are more interested in civilized pastimes and also demand diverse thinking. So as a necessary consequence, the function of museum space Is offended and that there are various attempt to increase information and demand of that space. The purpose of this study is try to find a solution a countermeasure of modern society's mobile situation. Researchers analyzed structural qualities of Hyper-text; non-boundary, interaction and nonlinear and deduce nine kinds of methods to apply in space. Also, Researchers looked at the examples in museum space and derived like this expression way; dynamics, mobility, a non-materiality, continuity, complexity from analysis of expression way.

• Fire Science and Engineering
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• 제8권1호
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• pp.9-20
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• 1994

To understand the phenomena of laminar diffusion flame along vortical walt, the numerical analysis has been performed. Keller-box method was used to solve the problem in the boundary layer. The governing equation is simplified by thin-flame approxiamtion. And energy and chemical species equations are normalized with Schvab-Zeldovich variables. A physical domain is divided the boundary layer along streamwise coordinate as the combustion region and the propagation region. And Radiation model is concerned in these region. As a result, typical phenomena have been observed. Comparison of the numerical results with experimental data shows that the present method can successfully predict phenomena of laminar diffusion flame along upright surface.