• The Journal of the Acoustical Society of Korea
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• v.18 no.4
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• pp.71-77
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• 1999

Exact forward modeling of acoustic propagation is crucial in MFP such as inverse problems and various other acoustic applications. As acoustic propagation in shallow water environments become important, range dependent modeling has to be considered of which PE method is considered as one of the most accurate and relatively fast. In this paper higher order numerical rode employing the PE method is developed. To approximate the depth directional operator, Galerkin's method is used with partial collocation to lessen necessary calculations. Linearization of tile depth directional operator is achieved via expansion into a multiplication form of (equation omitted) approximation. To approximate the range directional equation, Crank-Nicolson's method is used. Final1y, numerical self stater is employed. Numerical tests are performed for various occan environment scenarios. The results of these tests are compared to exact solutions, OASES and RAM results.

• Journal of Power System Engineering
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• v.19 no.4
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• pp.36-42
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• 2015

TMixed convective flow in a bottom heated and top cooled rectangular channel can be significantly affected by the channel aspect ratio, Prandtl number, Reynolds number, Rayleigh number and angle of inclination. In such a mixed convection, the flow pattern plays an important role in various technological processes. In this study, a numerical investigation is carried out to explore mixed convection in a three-dimensional rectangular channel with bottom heated and top cooled uniformly. The three-dimensional governing equations are discretized using the finite volume method. In the range of low Reynolds number($0{\leq}Re{\leq}9.6{\times}10^{-2}$), the effects of the aspect ratio($2{\leq}AR{\leq}12$) and Gr/Re are presented and discussed. The longitudinal roll number in the channel is increased with increasing aspect ratio, and the roll number induced, regardless of the aspect ratio number, is even in the range of aspect ratios between 2 and 12, New vortex flow structure containing inclined longitudinal rolls is found, which is affected by aspect ratio and Reynolds number. The ratio Gr/Re is used to check the relative magnitudes of forced and natural convection in the mixed convective flow of high viscous fluid.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.6
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• pp.860-869
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• 2000

Numerical and experimental investigations are performed for the molecular transition and slip flows in pumping channels of a disk-type drag pump. The flow occurring in the pumping channel develops from the molecular transition to the slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier-Stokes equations with slip boundary conditions, and the second one is a stochastic approach through the use of the direct simulation Monte Carlo method. In the experimental study, the inlet pressures are measured for various outlet pressures in the range of 0.1{\sim}4Torr. From the present study, the numerical results of predicting the performance, obtained by both methods, agree well with the experimental data for the range of Knudsen number $Kn{\leq}0.1$ (i.e., the slip flow regime). But the results from the second method only agree with the experimental data for Kn>0.1(i.e., the molecular transition regime)

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.3
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• pp.638-651
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• 2014

Main aim of this paper is to find the best combination of numerical schemes for 2-D SPH simulation of wedge water entry. Diffusion term is considered as laminar, turbulent, and artificial viscosity. Density filter that seriously affects the pressure distribution is investigated by adopting no filter, first order filter, and second order filter. Validation of the results indicates that turbulent model and first order density filter can lead to more reasonable solutions. This simulation was then conducted for wedge water entry with wide range of deadrise angles including 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees and 81 degrees, with extreme deadrise angles of 10 degrees, 60 degrees and 81 degrees being considered. Comparison of SPH results with BEM solutions has displayed favorable agreement. In two particular cases where experimental data are available, the SPH results are shown to be closer to the experiments than BEM solution. While, accuracy of the obtained results for moderate deadrise angles is desirable, numerical findings for very small or very large deadrise angles are also very reasonable.

• Structural Engineering and Mechanics
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• v.35 no.3
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• pp.283-299
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• 2010

This paper addresses the numerical simulation of fatigue crack growth in arbitrary 2D geometries under constant amplitude loading by the using a new finite element software. The purpose of this software is on the determination of 2D crack paths and surfaces as well as on the evaluation of components Lifetimes as a part of the damage tolerant assessment. Throughout the simulation of fatigue crack propagation an automatic adaptive mesh is carried out in the vicinity of the crack front nodes and in the elements which represent the higher stresses distribution. The fatigue crack direction and the corresponding stress-intensity factors are estimated at each small crack increment by employing the displacement extrapolation technique under facilitation of singular crack tip elements. The propagation is modeled by successive linear extensions, which are determined by the stress intensity factors under linear elastic fracture mechanics (LEFM) assumption. The stress intensity factors range history must be recorded along the small crack increments. Upon completion of the stress intensity factors range history recording, fatigue crack propagation life of the examined specimen is predicted. A consistent transfer algorithm and a crack relaxation method are proposed and implemented for this purpose. Verification of the predicted fatigue life is validated with relevant experimental data and numerical results obtained by other researchers. The comparisons show that the program is capable of demonstrating the fatigue life prediction results as well as the fatigue crack path satisfactorily.

• Current Optics and Photonics
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• v.5 no.1
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• pp.66-71
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• 2021

The resonance characteristics of H-shaped metamaterials, whose widths were varied while keeping the height constant, were investigated in the terahertz (THz) frequency range. The H-shaped metamaterials were numerically analyzed in two modes in which the polarization of the incident THz electric field was either parallel or perpendicular to the width of the H-shaped structure. The resonant frequency of the metamaterial changed stably in each mode, even if only the width of the H shape was changed. The resonant frequency of the metamaterial operating in the two modes increases without significant difference regardless of the polarization of the incident electromagnetic wave as the width of the H-shaped metamaterial increases. The electric field distribution and the surface current density induced in the metamaterial in the two modes were numerically analyzed by varying the structure ratio of the metamaterial. The numerical analysis clearly revealed the cause of the change in the resonance characteristics as the width of the H-shaped metamaterial changed. The efficacy of the numerical analysis was verified experimentally using the THz-TDS (time-domain spectroscopy) system. The experimental results are consistent with the simulations, clearly demonstrating the meaningfulness of the numerical analysis of the metamaterial. The analyzed resonance properties of the H-shaped metamaterial in the THz frequency range can be applied for designing THz-tunable metamaterials and improving the sensitivity of THz sensors.

• Journal of the Korean Society of Groundwater Environment
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• v.4 no.1
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• pp.54-59
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• 1997

The river and groundwater are contaminated by pollution source of a waste landfill and others near river. The contaminant transport and response of aquifer parameters are studied in the aquifer affected by variation of river stage. First, the equation for component of variation velocity with river stage is developed by using the analytical solution of groundwater governing equation. The numerical model which considered component of variation velocity is constructed for the transport of mass by advection and dispersion. In order to verify a numerical scheme, the analytical solution is used. The numerical solution is coincided with the analytical one. Aquifer parameters of Nanjido are used as the data for numerical experiment. Second, the range of aquifer parameters is established in order to reponse contaminant transport in aquifer with river stage. The result of numerical experiment shows that the range of the storage coefficient except hydraulic conductivity and effective porosity is relatively sensitive to the contaminant transport. When the storage coefficient is the order of 10$\^$－2/, the response is very sensitive to the variation of river stage.

• Journal of Power System Engineering
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• v.13 no.2
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• pp.30-35
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• 2009

Numerical Calculations for dimensionless pressure drop (friction factor times Reynolds number) have been obtained for fully developed laminar flow of MPL(Modified Power Law) fluid in isosceles triangle pipes. The solutions are valid for Pseudoplastic fluids over a wide range from Newtonian behavior at low shear rates through transition region to power law behavior at higher shear rates. The analysis identified a dimensionless shear rate parameter which for a given set of operating conditions specifies where in the shear rate range a particular system is operating, i.e., Newtonian, transition or power law region. The numerical calculation data of the dimensionless pressure drop for the Newtonian and power law regions are compared with previously published asymptotic results presenting within 0.16 % in Newtonian region and 2.98 % in power law region.

• Wind and Structures
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• v.15 no.3
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• pp.247-261
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• 2012

Some numerical investigations are presented concerning the response of a given plate under turbulence driven excitations. Three different input loads are simulated according to the wall pressure distributions derived from the models proposed by Corcos, Efimtsov and Chase, respectively. Modal solutions (finite element based) are used for building the modal stochastic responses in the sub-critical aerodynamic frequency range. The parametric investigations concern two different values of the structural damping and three values of the boundary layer thickness. A final comparison with available experimental data is also discussed. The results demonstrate that the selection of the adequate TBL input model is still the most critical step in order to get a good prediction.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.681-687
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• 2002

The cumulative, shrinkage plastic strains and their distributions in the weld joint after completion of the welding process determine welding-induced distortion. Although the weldment undergoes many complex physical and metallurgical changes during welding, only the material plastic temperature range and its cooling history below this temperature range influence the [mal state of the cumulative shrinkage plastic strains. In addition, for structural welds, these plastic strains are uniform, except in the arc start and stop regions, along the weld. Therefore, the plastic strain-based "inherent shrinkage model" is effective and accurate to describe welding-induced distortion. This paper presents the theoretical background and numerical verification of this root cause.