• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.39-44
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• 2008

Stress wave propagation plays an important role in many engineering problems for reducing industrial noise and vibrations. In this paper, the dispersion-corrected finite element model is proposed for reducing the dispersion error in simulation of stress wave propagation. At eliminating the numerical dispersion error arising from the numerical simulation of stress wave propagation, numerical dispersion characteristics of the wave equation based finite element model are analyzed and some dispersion control scheme are proposed. The validity of the dispersion correction techniques is demonstrated by comparing the numerical solutions obtained using the present techniques.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.1
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• pp.75-82
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• 2004

With an aim at eliminating the numerical dispersion error arising from the numerical simulation of stress wave propagation, numerical dispersion characteristics of the wave equation based one-dimensional finite element model are analyzed and some dispersion control scheme are proposed in this paper The dispersion analyses are carried out for two types of mass matrix, namely the consistent and the lumped mass matrices. Based on the finding of the analyses, dispersion correction techniques are developed for both the implicit and explicit schemes. For the implicit scheme, either the weighting factor for the spatial derivatives of each time level or the lumping coefficient for mass matrix is adjusted to minimize the numerical dispersion. In the case of the explicit scheme an artificial dispersion term is introduced in the governing equation. The validity of the dispersion correction techniques proposed in this study is demonstrated by comparing the numerical solutions obtained using the Present techniques with the analytical ones.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.5
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• pp.383-396
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• 1997

Numerical prediction of the pollutant dispersion over a two-dimensional hilly terrain is presented. The dispersion model used in the present work is based on the gradient diffusion theory and the finite-volume method on a non-orthogonal boundary-fitted grid system. The numerical model is validated by comparing the results with the available experimental data for the flat-floor dispersion within a turbulent boundary-layer. The numerical error analysis is performed based on the guideline of Kasibhatla et al.(1988) for the elevated-source dispersion in the flat-floor boundary layer having a power-law velocity and linear eddy-diffusivity profile. The influences of the two-dimensional hilly terrain on the dispersion from a continuously released source are numerically investigated by changing the emission locations and heights. It is found that the distributions of ground-level concentration are strongly influenced by the source location and the emission height. Hence, the terrain amplification factor is greatly enhanced when the pollutant source is located within a flow separation region. Dispersion from a source of short duration is also simulated and the duration time of the pollutant is compared at several downstream locations on a hilly terrain. The results of the numerical prediction are applied to the evaluation of environmental impacts due to the automobile exhausts at the seashore highway with a parallel mountain range.

• Journal of Soil and Groundwater Environment
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• v.20 no.2
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• pp.10-21
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• 2015

The present study introduces a novel numerical approach for solving dispersion dominated problems with Cauchy boundary condition in an Eulerian-Lagrangian scheme. The study reveals the incapability of traditional Neuman approach to address the dispersion dominated problems with Cauchy boundary condition, even though it can produce reliable solution in the advection dominated regime. Also, the proposed numerical approach is applied to a real field problem of radioactive contaminant migration from radioactive waste repository which is a major current waste management issue. The performance of the proposed numerical approach is evaluated by comparing the results with numerical solutions of traditional FDM (Finite Difference Method), Neuman approach, and the analytical solution. The results show that the proposed numerical approach yields better and reliable solution for dispersion dominated regime, specifically for Peclet Numbers of less than 0.1. The proposed numerical approach is validated by applying to a real field problem of radioactive contaminant migration from radioactive waste repository of varying Peclet Number from 0.003 to 34.5. The numerical results of Neuman approach overestimates the concentration value with an order of 100 than the proposed approach during the assessment of radioactive contaminant transport from nuclear waste repository. The overestimation of concentration value could be due to the assumption that dispersion is negligible. Also our application problem confirms the existence of real field situation with advection dominated condition and dispersion dominated condition simultaneously as well as the significance or advantage of the proposed approach in the real field problem.

• Membrane and Water Treatment
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• v.9 no.3
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• pp.173-179
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• 2018

Microcystin-LR, one of algal toxins induced by the eutrophication of a reservoir, is known to be harmful to human by adversely affecting our liver and brain. Hypochlorous acid is very efficient to remove Microcystin-LR in a clear well. The previous researches showed that CT, pH and temperature affected removal rate in batch tests. It was noted that hydrodynamic properties of clear well could also influence its removal rate. A mathematical model was built using an axial dispersion reactor model and software was used to simulate the removal rate. The model consisted of the second order differential equations including dispersion, convection, Microcystin-LR reaction with chlorine. Kinetic constants were obtained through batch tests with chlorine. They were $0.430{\times}10^{-3}L/mg/sec$ and $0.143{\times}10^{-3}L/mg/sec$ for pH 7.0 and 8.1, respectively. The axial dispersion reactor model was shown to be useful for the numerical model through conservative tracer tests. The numerical model successfully estimated the removal rate of Microcyctin-LR in a clear well. Numerical simulations showed that a small dispersion number, low pH and long hydraulic retention time were critical for higher removal rate with same chlorine dosage. This model could be used to optimize the operation of a clear well during an eutrophication season.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1935-1939
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• 2006

In this study, the new dispersion-correction terms are added to leap-frog finite difference scheme for the linear shallow-water equations with the purpose of considering the dispersion effects such as linear Boussinesq equations for the propagation of tsunamis. And, dispersion-correction factor is determined to mimic the frequency dispersion of the linear Boussinesq equations. The numerical model developed in this study is tested to the problem that initial free surface displacement is a Gaussian hump over a constant water depth, and the results from the numerical model are compared with analytical solutions. The results by present numerical model are accurate in comparison with the past models.

• Journal of Radiation Industry
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• v.2 no.3
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• pp.135-140
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• 2008

A field tracer experiment using radioisotope was carried out to investigate the characteristics of a pollutant transport and a determination of the dispersion coefficients in a river system. The dispersion coefficients in the longitudinal and transverse directions were determined by using the measured concentration of a radioisotope. The two-dimensional numerical models were applied to calculate the flow and concentration fields at the experimental site. Several numerical simulations were performed to investigate the effects of the numerical results according to variations of the dispersion coefficients. The calculated concentrations agreed well with the measured ones.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.2
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• pp.116-127
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• 2002

Most of finite difference numerical models for the simulation of tsunami propagation developed so for are based on the shallow-water equations which are frequently solved by the leap-frog scheme. If the grid size is properly selected, this numerical scheme gives a correct dispersion effect fur constant water depth. However, if the water depth changes, the dispersion effect of tsunamis can not be accurately considered at every grid point in the whole computational domain. In this study we improved the existing two-dimensional dispersion-correction finite difference numerical scheme. The present scheme satisfies the local dispersion relationships of tsunamis propagating over a slowly varying topography while using uniform grid size and time step. To verify the applicability of the improved numerical model, a tsunami due to 1983 East Sea central earthquake is simulated for Korean harbors with the tide gage records such as Sokcho, Mukho, Pohang and Ulsan in the East Sea. Numerical results of the 1983 tsunami are compared with the measured data and the accuracy of the present numerical model is evaluated.

• Journal of Mechanical Science and Technology
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• v.17 no.7
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• pp.1054-1062
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• 2003

The numerical simulations of flow and pollutant particle dispersion are described for two-dimensional bell shaped hills with various aspect ratios. The Reynolds-averaged incompressible Navier-Stokes equations with low Reynolds number $\kappa$-$\varepsilon$ turbulent model are used to simulate the flowfield. The gradient diffusion equation is used to solve the pollutant dispersion field. The code was validated by comparison of velocity, turbulent kinetic energy, Reynolds shear stress, speed-up ratio, and ground level concentration with experimental and numerical data. Good agreement has been achieved and it has been found that the pollutant dispersion pattern and ground level concentration have been strongly influenced by the hill shape and aspect ratio, as well as the location and height of the source.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.6
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• pp.651-657
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• 2010

Solute transport through a groove is affected by its vortices. Our laboratory and numerical experiments of dye transport through a single axisymmetric groove reveal evidence of enhanced spreading and mixing by the vortex, i.e., a new kind of dispersion called here the vortex dispersion. The uptake and release of contaminants by vortices in porous media is affected by the flow Reynolds number. The larger the flow Reynolds number, the larger is the vortex dispersion, and the larger is the mass-transfer rate between the mobile zone and the vortex. The long known dependence of the mass-transfer rate between the mobile and "immobile" zones in porous media on flow velocity can be explained by the presence of vortices in the "immobile" zone and their uptake and release of contaminants.