• Journal of the Korean Mathematical Society
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• v.59 no.3
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• pp.519-548
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• 2022

In this paper, a stabilized-penalized collocated finite volume (SPCFV) scheme is developed and studied for the stationary generalized Navier-Stokes equations with mixed Dirichlet-traction boundary conditions modelling an incompressible biological fluid flow. This method is based on the lowest order approximation (piecewise constants) for both velocity and pressure unknowns. The stabilization-penalization is performed by adding discrete pressure terms to the approximate formulation. These simultaneously involve discrete jump pressures through the interior volume-boundaries and discrete pressures of volumes on the domain boundary. Stability, existence and uniqueness of discrete solutions are established. Moreover, a convergence analysis of the nonlinear solver is also provided. Numerical results from model tests are performed to demonstrate the stability, optimal convergence in the usual L² and discrete H¹ norms as well as robustness of the proposed scheme with respect to the choice of the given traction vector.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3197-3202
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• 2007

An analysis program for pedestrian flow has been developed to investigate the flow patterns of passenger in railway stations. Analysis algorithms for pedestrian flow based on DEM(Discrete Element Method) are newly developed. There are lots of similarity between particle-laden two phase flow and passenger flow. The velocity component of 1st phase corresponds to the unit vector of calculation cell, each particle to passenger, volume fraction to population density and the particle velocity to the walking velocity, etc. And, the walking velocity of passenger is also represented by the function of population density. Key algorithms are developed to determine the position of passenger, population density and numbering to each passenger. By using the developed program, we compared the simulation results of the effects of the location and size of exit and elapsed time.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.276-286
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• 1995

In this study, pressure drop and heat transfer coefficients were measured in tubes with three dimensional roughness. Dimples were made by rotating the saw-tooth shaped finning disc on the outer tube surface. Resultant dimple shape was oval. Friction and heat transfer tests were performed with a range of roughness variables-roughness height 'e', axial roughness pitch 'p', circumferential roughness pitch 'z'. Within the test range, tube with e=0.5mm, z=5mm, p=3mm performed best. The efficiency ratio(rati of the heat transfer improvement and the pressure drop increase) of the tube approached 1.0 at low Reynolds number, and it was higher than that of the two-dimensional roughess tube of the same roughness height. Test data were predicted by 'discrete element method'. Results show that discrete element method underpredicts the friction data by 2% to 32%, and overpredicts the heat transfer data by-12% to 113%.

• Journal of KSNVE
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• v.10 no.3
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• pp.523-530
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• 2000

In this paper we present an efficient method for finite element vibration analysis of a structure with cyclic symmetry and applied it to calculating the natural vibration characteristics for a blower impeller. Blower impeller having a cyclically symmetric structure is composed of circumferentially repeated substructures., The whole-structure is partitioned into substructures and then finite element vibration analysis is performed for a substructure using transformed equations for each number of nodal diameter which are derived from discrete Fourier transform in consideration of the cyclic symmetry. natural vibration characteristics for three kinds of models which are blower impeller without support ring with small support ring and with large support ring are numerically analyzed and compared. Accuracy and efficiency of the present method are verified by comparison of results of the analysis with substructure and with whole-structure. Also the results of the analysis by cyclic symmetry module(SOL 115) of MSC/NASTRAN are presented and compared.

• Journal of KSNVE
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• v.8 no.6
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• pp.1150-1157
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• 1998

In this Paper, we present an efficient method for finite element vibration analysis of constantly rotating structures with cyclic symmetry, which are deformed to some considerable extent by centrifugal force, Coriolis force and operating load, and vibrate due to several types of exciting forces. A structure with cyclic symmetry is composed of circumferentially repeated substructures with the same geometry. Being only one substructure modeled. the dynamic characteristics of the structure can be analyzed systematically. rapidly and exactly using discrete Fourier transform by means of a computer with small memory.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.117-123
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• 2000

Using the modified DEM (Discrete Element Method), which we proposed in order to improve the accuracy of the simulation, soil behavior and reaction by lugs of rotating wheel and a soil cutting process by a high speed blade were calculated and compared with experimental data. The DEM is one of computational mechanics, where the object body is supposed as an assembly of small particles called elements and not a continuum as in the case of FEM. We can easily treat some discrete phenomena such as cracking, separating and sliding by the DEM. We had to modify the original mechanical model, which induced too free movement of elements, adding a tension spring, which would display the role of soil adhesion. The results of DEM simulations were successful from both the soil behavior and reaction points of view.

• Geomechanics and Engineering
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• v.2 no.3
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• pp.161-176
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• 2010

Discrete Element Method (DEM) simulations were developed to investigate the effectiveness of geosynthetic reinforcement and the effectiveness of maintenance techniques performed on a simulated ballast bed subjected to dynamic loading. The results from four samples subjected each one to a total of 425 load cycles are presented: one unreinforced and unmaintained sample, one unmaintained but reinforced sample, one unreinforced sample subjected to maintenance in the form of stoneblowing after 200 load cycles, and one unreinforced sample subjected to maintenance in the form of tamping after 200 load cycles. The obtained values of permanent deformation as a function of the applied number of load cycles for the four cases are presented together allowing a comparison of the effectiveness of each technique. Moreover, snapshots of the simulated track sections are presented at different moments of the simulations. The simulations indicated that the geosynthetic reinforcement may not be beneficial for the analyzed case while stoneblowing was the most effective maintenance technique.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.475-480
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• 2008

A pre/post processor program based GUI(Graphic User Interface) by using the MFC and OpenGL library in the Windows OS have been developed for the analysis of the passenger flow. Using this program, users are able to generate and modify the meshes of multi-storied subway station, set all the parameters for the solver, and obtain the results of the simulation such as transient passenger motions and passenger streak lines in 3-dimensional graphic view.

• Structural Engineering and Mechanics
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• v.59 no.5
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• pp.921-932
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• 2016

This paper presents a theoretical analysis for determining the transverse deflection of simply supported battened beams subjected to a uniformly distributed transverse quasi-static load. The analysis considers not only the shear effect but also the discrete effect of battens on the transverse deflection of the battened beam. The analytical solution is obtained using the principle of minimum potential energy. Numerical validation of the present analytical solution is accomplished using finite element methods. The present analytical solution shows that the shear effect on the transverse deflection of battened beams increases with the cross-section area of the main member but decreases with the cross-section area of the batten. The longer the battened beam is, or the larger the moment of inertia of the main member is, the smaller the shear effect will be.

• Structural Engineering and Mechanics
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• v.71 no.1
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• pp.65-75
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• 2019

In this article, the dynamic fracture instability characteristics, including dynamic crack propagation and crack branching, in PMMA brittle solids under dynamic loading are investigated using the discrete element method (DEM) simulations. The microscopic parameters in DEM are first calibrated using the comparison with the previous experimental results not only in the field of qualitative analysis, but also in the field of quantitative analysis. The calibrating process illustrates that the selected microscopic parameters in DEM are suitable to effectively and accurately simulate dynamic fracture process in PMMA brittle solids subjected to dynamic loads. The typical dynamic fracture behaviors of solids under dynamic loading are then reproduced by DEM. Compared with the previous experimental and numerical results, the present numerical results are in good agreement with the existing ones not only in the field of qualitative analysis, but also in the field of quantitative analysis. Furthermore, effects of dynamic loading magnitude, offset distance of the initial crack and initial crack length on dynamic fracture behaviors are numerically discussed.