• Journal of Energy Engineering
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• v.11 no.4
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• pp.283-290
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• 2002

Numerical calculations have been carried out for the mixed convection flow in a concentric curved annulus with constant heat flux boundary condition at inner wall. The flow is assumed to be fully developed so as to maintain a constant streamwise pressure and temperature gradient. Computations have been performed for flows of radius ratio 0.2 and 0.5 with the Dean number lying in the range 0$K^{1/2}$ for the wide range of the Dean number considered here.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.447-457
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• 2018

In this study, a two-dimensional fully nonlinear transient wave numerical tank was developed using a desingularized indirect boundary integral equation method. The desingularized indirect boundary integral equation method is simpler and faster than the conventional boundary element method because special treatment is not required to compute the boundary integral. Numerical simulations were carried out in the time domain using the fourth order Runge-Kutta method. A mixed Eulerian-Lagrangian approach was adapted to reconstruct the free surface at each time step. A numerical damping zone was used to minimize the reflective wave in the downstream region. The interpolating method of a Gaussian radial basis function-type artificial neural network was used to calculate the gradient of the free surface elevation without element connectivity. The desingularized indirect boundary integral equation using an isolated point source and radial basis function has no need for information about the element connectivity and is a meshless method that is numerically more flexible. In order to validate the accuracy of the numerical wave tank based on the desingularized indirect boundary integral equation method and meshless technique, several numerical simulations were carried out. First, a comparison with numerical results according to the type of desingularized source was carried out and confirmed that continuous line sources can be replaced by simply isolated sources. In addition, a propagation simulation of a $2^{nd}$-order Stokes wave was carried out and compared with an analytical solution. Finally, simulations of propagating waves in shallow water and propagating waves over a submerged bar were also carried and compared with published data.

• Ocean Systems Engineering
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• v.2 no.2
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• pp.147-158
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• 2012

A time-domain simulation of a land-based Oscillating Water Column (OWC) with various irregular waves as a form of PM spectrum is performed by using a two-dimensional fully nonlinear numerical wave tank (NWT) based on the potential theory, mixed Eulerian-Lagrangian (MEL) approach, and boundary element method. The nonlinear free-surface condition inside the OWC chamber was specially devised to describe both the pneumatic effect of the time-varying pressure and the viscous energy loss due to water column motions. The quadratic models for pneumatic pressure and viscous loss are applied to the air and free surface inside the chamber, and their numerical results are compared with those with equivalent linear ones. Various wave spectra are applied to the OWC system to predict the efficiency of wave-energy take-off for various wave conditions. The cases of regular and irregular waves are also compared.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.1020-1028
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• 2012

This work compares various models for geminate reversible diffusion influenced reactions. The commonly utilized contact reactivity model (an extension of the Collins-Kimball radiation boundary condition) is augmented here by a volume reactivity model, which extends the celebrated Feynman-Kac equation for irreversible depletion within a reaction sphere. We obtain the exact analytic solution in Laplace space for an initially bound pair, which can dissociate, diffuse or undergo "sticky" recombination. We show that the same expression for the binding probability holds also for "mixed" reaction products. Two different derivations are pursued, yielding seemingly different expressions, which nevertheless coincide numerically. These binding probabilities and their Laplace transforms are compared graphically with those from the contact reactivity model and a previously suggested coarse grained approximation. Mathematically, all these Laplace transforms conform to a single generic equation, in which different reactionless Green's functions, g(s), are incorporated. In most of parameter space the sensitivity to g(s) is not large, so that the binding probabilities for the volume and contact reactivity models are rather similar.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.56-64
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• 2000

A friction force measurement system using the floating liner method was developed to study the frictional behavior of piston rings. The measurement system was carefully designed to control the effect of the piston secondary motion and the temperature of cylinder wall and oil. The friction force between the barrel shaped piston ring and the cylinder liner, was measured under the condition of flooded oil supply. The measured friction forces were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(midstroke and dead centers). The modes could be identified on the Stribeck diagram of the friction coefficients and the dimensionless number of ㎼/p, where the friction coefficients are evaluated at near the midstroke and dead centers.

• Journal of Wetlands Research
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• v.5 no.1
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• pp.67-78
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• 2003

The unsteady 2D convection and diffusion equation is solved numerically for the real-time simulation of suspended load propagation. The streamlined upwind scheme efficiently reduces numerical oscillations due to the high Peclet number in the convection dominant flow. By using the mixed boundary condition to express the external source terms or externally induced suspended load as a function of time in the algorithm, the model is capable of handling not only continuous load cases but also non-continuous suspended load influx. The suspended load transport modelwas verified using a case study for which an analytical exact solution is available and was applied to the real-time simulation of a suspended load influx case on the Mississippi River. The model algorithm can provide a framework upon which water quality as well as contaminant transport models can be built.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1275-1281
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• 2001

Aqueous polymer solutions are known to have small pressure reduction. Paraffin slurries are known to have high thermal capacity. Paraffin particles are mixed into an aqueous polymer solution to make a new heat transfer fluid having high thermal capacity but low pressure reduction. The heat transfer characteristics of the new slurry was tested in a circular tube having a constant heat transfer boundary condition. The new slurry was found to have high Nusselt numbers as well as high thermal capacity and low pressure reduction in the laminar flow. The trends of the Nusselt numbers along the heating test section were studied for various heating conditions.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.6
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• pp.21-30
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• 2019

Livestock odor is comprised of mixed type of odorous compounds. Among these, ammonia ($NH_3$) and hydrogen sulfide ($H_2S$) are the two known major odor causing substances. Because high odor concentration reduces productivity of livestock and causes damage to the surrounding communities, quantitative analysis is needed to manage the odor inside and outside the livestock facilities. It is also necessary to evaluate odor dispersion according to the distance between the receptors taking into account the influence of odor source and weather condition. Therefore, in this study, we tried to evaluate the internal environment and odor dispersion from experimental pig house considering weather conditions. An experimental farm was specifically selected to eliminate the interference of odors generated by adjacent farms. $NH_3$ and complex odor were quantitatively analyzed using a gas detector and air dilution sensory method. The concentration of $NH_3$ and complex odor in pig house showed a distinct concentration difference according to the cleaning and ventilation conditions. $NH_3$ concentration and complex odor was lower than emission standard in the pig house and at the site boundary. The average $NH_3$ concentration (P1~P3) and the $NH_3$ concentration at the site boundary (S1) were strongly correlated with R=0.77. While the correlation for complex odor inside and at the site boundary had R=0.52. The correlation coefficient between $NH_3$ and the complex odor was 0.80.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.549-560
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• 2021

Forces exerted on a shield TBM (tunnel boring machine) such as cutter head torque, thrust force, chamber pressure, and upward force are key factors determining TBM performance. However, the forces acting on the TBM when tunnelling the mixed ground have different tendencies compared to that of the uniform ground, which could impair TBM performance. In this study, the effect of mixed ground tunnelling was numerically investigated with torque, thrust force, chamber pressure, and upward force. A coupled discrete element method (DEM) and finite difference method (FDM) model for TBM driving model was used. This numerical study simulates TBM tunnelling in mixed ground composed of upper weathered granite soil and lower weathered rock. The effect on the force acting on the TBM according to the location and slope of the boundary of the mixed ground was numerically examined.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2226-2240
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• 1992

This paper studies the applicability of the method of caustics into anisotropic materials under mode I and mixed static loading conditions and introduces the procedure to obtain stress intensity factors(S.I.F.) in anisotropic materials by the method of caustics. The mapping equations for initial and caustic curves in anisotropic materials were introduced and their computer graphical images were compared to the experimental ones to check the validity of the mapping equations proposed in this paper. The agreement between them was found to satisfactory. Two kinds of method to determine S.I.F. in anisotropic materials by the method of caustics were proposed in this paper and applied into the orthotropic materials under various loading conditions. In the case of mode I loading condition, the S.I.F.'s obtained by this paper's methods were found to be quite similar to the results by other method, boundary element method(B.E.M) and in the case of mixed loading condtion, the S.I.F's by this paper and B.E.M. showed a little differences(2.2-24.4%) with respect to the slanted angle of crack.