• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.575-582
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• 2005

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.3
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• pp.22-30
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• 2006

In this paper, a systematic design method on an IPMC(ionic polymer-metal composite)-driven ZNMF(zero-net-mass-flux) pump is introduced for the flow control of an MAV's (micro air vehicle) wing. Since the IPMC is able to generate a large deformation under a low input voltage along with its ability to operate in air, and is easier to be manufactured in a small size, it is considered to be an ideal material of the actuating diaphragm. Through the numerical methods, an optimal shape of the IPMC　diaphragm was found for maximizing the stroke volume. Based on the optimal IPMC diaphragm, a proto-type ZNMF pump with a slot, was designed. By using the flight speed of the MAV considered in this work, the driving frequencies(~ 40 Hz) of IPMC diaphragm, and the flow velocity through the pump's slot, the calculated non-dimensional frequency and the momentum coefficient ensure the feasibility of the designed ZNMF pump as a flow control device.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.243-253
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• 1999

The dual reciprocity boundary element method (DRBEM) is used to solve the Graetz problem of laminar flow inside circular duct. In this method the domain integral tenn of boundary integral equation resulting from source term of governing equation is transformed into equivalent boundary-only integrals by using the radial basis interpolation function, and therefore complicate domain discretization procedure Is completely removed. Velocity profile is obtained by solving the momentum equation first and then, using this velocities as Input data, energy equation Is solved to get the temperature profile by advancing from duct entrance through the axial direction marching scheme. DRBEM solution is tested for the uniform temperature and heat flux boundary condition cases. Local Nusselt number, mixed mean temperature and temperature profile inside duct at each dimensionless axial location are obtained and compared with exact solutions for the accuracy test Solutions arc in good agreement at the entry region as well as fully developed region of circular duct, and their accuracy are verified from error analysis.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1093-1100
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• 2004

Numerical analysis of the heat transfer associated with droplet impact on a hot solid surface is performed by solving the equations governing conservation of mass, momentum and energy in the liquid and gas phases. The deformed droplet shape is tracked by a level set method which is modified to achieve volume conservation and to include the effect of contact angle at the wall. The numerical method is validated through the calculations for the cases reported in the literature. Based on the numerical results, the heat transfer rate is found to depend strongly on the droplet spread radius. Decreased advancing/receding contact angles enlarge the splat radius and in turn enhance the wall heat flux. The effect of impact velocity on the droplet spread is reduced as the droplet size decreases. Also, droplet atomization is observed to significantly enhance the heat transfer rate and the effect is pronounced for a smaller size of droplet. An existing model equation to predict the maximum spread radius is improved for application to a micro droplet.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.178-187
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• 2010

The performance of the waterjet system of a patrol boat has been experimentally studied. A waterjet propulsion system has many advantages comparing with a conventional screw propeller especially for high speed craft because of its good cavitation performance. This paper describes experimental procedure and analysis method of self-propulsion tests with a 1/12-scale model. Experimental results were analyzed according to ITTC 96 standard method. The full-scale effective power and delivered power of the ship were also analyzed and the full-scale speed predicted from the model test compares reasonably with the measured full-scale results of the sea trial.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.39-46
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• 2011

A numerical study of a turbulent natural convection in an enclosure with the lattice Boltzmann method (LBM) is presented. The primary emphasis of the present study is placed on investigation of accuracy and numerical stability of the LBM for the turbulent natural convection flow. A HYBRID method in which the thermal equation is solved by the conventional Reynolds averaged Navier-Stokes equation method while the conservation of mass and momentum equations are resolved by the LBM is employed in the present study. The elliptic-relaxation model is employed for the turbulence model and the turbulent heat fluxes are treated by the algebraic flux model. All the governing equations are discretized on a cell-centered, non-uniform grid using the finite-volume method. The convection terms are treated by a second-order central-difference scheme with the deferred correction way to ensure accuracy and stability of solutions. The present LBM is applied to the prediction of a turbulent natural convection in a rectangular cavity and the computed results are compared with the experimental data commonly used for the validation of turbulence models and those by the conventional finite-volume method. It is shown that the LBM with the present HYBRID thermal model predicts the mean velocity components and turbulent quantities which are as good as those by the conventional finite-volume method. It is also found that the accuracy and stability of the solution is significantly affected by the treatment of the convection term, especially near the wall.

• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2276-2296
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• 2022

This study validates the applicability of the CUPID code for simulating subcooled wall boiling under high-pressure conditions against number of DEBORA tests. In addition, a new numerical technique in which the interfacial momentum non-drag forces are calculated at the cell faces rather than the center is presented. This method reduced the numerical instability often triggered by calculating these terms at the cell center. Simulation results showed good agreement against the experimental data except for the bubble sizes in the bulk. Thus, a new model to calculate the Sauter mean diameter is proposed. Next, the effect of the relationship between the bubble departure diameter (D_dep) and the nucleation site density (N) on the performance of the Wall Heat Flux Partitioning (WHFP) model is investigated. Three correlations for D_dep and two for N are grouped into six combinations. Results by the different combinations show that despite the significant difference in the calculated D_dep, most combinations reasonably predict vapor distribution and liquid temperature. Analysis of the axial propagations of wall boiling parameters shows that the N term stabilizes the inconsistences in D_dep values by following a behavior reflective of D_dep to keep the total energy balance. Moreover, ratio of the heat flux components vary widely along the flow depending on the combinations. These results suggest that separate validation of D_dep correlations may be insufficient since its performance relies on the accompanying N correlations.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.3
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• pp.137-151
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• 1991

The motion of two-dimensional floating breakwaters with rectangular clots-section which are moored tautly in shallow water has been analyzed using a velocity potential matching method in which the fluid region is devided into sub-regions and then unknown coefficients of velocity potentials are determined from the continuity condition of mass and momentum flux of fluid at imaginary boundaries between sub-regions. The method originally suggested by Ijima et al.(1972) for the motion of submerged body has been modified to analyze the motion of floating body. The total fluid region has been divided into three sub-regions : the incident wave region, the transmitted wave region and the region below the floating breakwater. The restoring forces induced by mooring lines which were ignored by Ijima et al.(1972) have been modeled as linear springs with the initial tension effects. This method has been verified through the comparions with results from hydraulic expriments. Applications to various conditions of floating breakwater have been performed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.262-270
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• 1987

A numerical method is presented which can solve the unsteady momentum and thermal boundary layers, coupled through the agency of buoyancy force, over a heated circular cylinder impulsively started from rest. By linearizing the nonlinear finite difference equations without sacrificing accuracy, numerical solutions are obtained at each time step without iteration. To get rid of the requirement of excessive number of grid points in the region of reversed flow, special form of transformed variables are used, by which the computational boundary layer thickness is maintained almost constant. These numerical properties enable the method to easily handle the region of reversed flow and how the singularity develops in the interior of the boundary layer. In order to investigated the thermal effects on the skin friction, heat flux, displacement thickness and on the separation, we have successfully solved three different cases of the buoyancy parameter .alpha.(Gr/Re$^{2}$).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1089-1095
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• 2011

Numerical simulation is performed for nucleate boiling on a micro-finned surface, which has been widely used to enhance heat transfer, by solving the equations governing the conservation of mass, momentum, and energy in the liquid and vapor phases. The bubble motion is determined by a sharp-interface level-set method, which is modified to include the effect of phase change and to treat the no-slip and contact-angle conditions, as well as the evaporative heat flux from the liquid microlayer on immersed solid surfaces such as micro fins and cavities. The numerical results for bubble formation, growth, and departure on a microstructured surface including fins and cavities show that the bubble behavior during nucleate boiling is significantly influenced by the fin-cavity arrangement and the fin-fin spacing.