• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.2
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• pp.141-151
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• 2003

Railway bridges are subject to dynamic loads generated by the interaction between moving vehicles and the bridge structures. These dynamic loads result in response fluctuations in bridge members. To investigate the real dynamic behavior of the bridge, therefore, a number of analytical and experimental Investigations should be carried out. In this paper, a train/track/bridge interaction analysis program for evaluating the dynamic characteristics of bridges due to KTX operation in terms of structural safety, operational safety and passenger comfort is developed. To build a practical model of train/track/bridge, Hertzian spring for wheel/rail contact modeling and Winkler element for ballast are applied. This program also used torsional degree of freedom and constraint equation based on geometrical relationship in order to take into consideration three-dimensional eccentricity effect due to the operation on double track through quasi-three dimensional analysis. To verify the developed Program, comparison has been made between the measured results and those of simulation of the typical PSC box bridge(2@40m=80m) of the KHSR bridges.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1152-1155
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• 1995

An analytic model for the optimum design of the power MOSFET considering the degradation of the breakdown voltage by the three dimensional effect is proposed. The proposed method gives the optimum design parameters such as the lateral radius of window curvature and the doping concentration of the epi-layer, which does not minimize the on-resistance but also maintains the required breakdown voltage. The analytical results are verified by the quasi 3D simulation tools, MEDICI, and it is found that the proposed method may be a good guideline for the design of power MOSFET.

• Geomechanics and Engineering
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• v.21 no.3
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• pp.227-236
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• 2020

Non-destructive exploration using elastic waves has been widely used to characterize rock mass properties. Wave propagation in jointed rock masses is significantly governed by the characteristics and orientation of discontinuities. The relationship between spatial heterogeneity (i.e., joint spacing) and wavelength for elastic waves propagating through jointed rock masses have been investigated previously. Discontinuous rock masses can be considered as an equivalent continuum material when the wavelength of the propagating elastic wave exceeds the spatial heterogeneity. However, it is unclear how stress-dependent long-wavelength elastic waves propagate through a repetitive rock-joint system with multiple joints. A preliminary numerical simulation was performed in in this study to investigate long-wavelength elastic wave propagation in regularly jointed rock masses using the three-dimensional distinct element code program. First, experimental studies using the quasi-static resonant column (QSRC) testing device are performed on regularly jointed disc column specimens for three different materials (acetal, aluminum, and gneiss). The P- and S-wave velocities of the specimens are obtained under various normal stress levels. The normal and shear joint stiffness are calculated from the experimental results using an equivalent continuum model and used as input parameters for numerical analysis. The spatial and temporal sizes are carefully selected to guarantee a stable numerical simulation. Based on the calibrated jointed rock model, the numerical and experimental results are compared.

• Ocean Systems Engineering
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• v.8 no.3
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• pp.329-343
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• 2018

The inclination of seabed profile (sloped seabed) is one of the known topographic features which can be observed at different seabed level in the large offshore basin. A mooring system connected between the platform and global seabed is an integral part of the floating structure which tries to keep the floating platform settled in its own position against hostile sea environment. This paper deals with an investigation of the motion responses of an FPSO platform moored on the sloped seabed under the combined action of wave, wind and current loads. A three-dimensional panel discretization method has been used to model the floating body. To introduce the connection of multi-segmented non-linear elastic catenary mooring cables with the sloped seabed, a quasi-static composite catenary model is employed. The model and analysis have been completed by using hydrodynamic diffraction code AQWA. Validation of the numerical model has been successfully carried out with an experimental work published in the latest literature. The analysis procedure in this study has been followed time domain analysis. The study involves an objective oriented investigation on platform motions, in order to identify the effects of the slopped seabed, the action of the wave, wind and current loads and the presence of riser system. In the end, an effective analysis has been performed to identify a stable mooring model in demand of reducing structural responses of the FPSO.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.2
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• pp.12-23
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• 1994

In order to investigate the effect of turbulent intensity on combustion characteristics, new flame factor model was developed. The principal study is the evaluation of interaction of swirl, tumble and unstrutural component of flow characteristics and correlation between turbulent intensity and flame factor. Computational and experimental study has been, performed such as quasi-dimensional cycle simulation, three dimensional flow analysis, engine performance test and diagnostic simulation. From these studies, it was found that flame factor was a function of engine speed and turbulent intensity.

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.271-278
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• 2020

The investigation into a full-scale 27 m high, by 6 m wide, thermosyphon loop. The simulation model is based on a one-dimensional axially-symmetrical control volume approach, where the loop is divided into a series of discreet control volumes. The three conservation equations, namely, mass, momentum and energy, were applied to these control volumes and solved with an explicit numerical method. The flow is assumed to be quasi-static, implying that the mass-flow rate changes over time. However, at any instant in time the mass-flow rate is constant around the loop. The boussinesq approximation was invoked, and a reasonable correlation between the experimental and theoretical results was obtained. Experimental results are presented and the flow regimes of the working fluid inside the loop identified. The results indicate that a series of such thermosyphon loops can be used as a cavity cooling system and that the one-dimensional theoretical model can predict the internal temperature and mass-flow rate of the thermosyphon loop.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.305-306
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• 2006

Developed in this study is a nonlinear Ekman pumping model to be used in simulating the rotating flows with quasi-three-dimensional Navier-Stokes equations. In this model, the Ekman pumping velocity is given from the solution of the Ekman boundary-layer equations for the region adjacent to the bottom wall of the flow domain; the boundary-layer equations are solved in the momentum-integral form. The developed model is then applied to rotating flows in a rectangular container receiving a time-periodic forcing. By comparing our results with the DNS and experimental data we have validated the developed model. We also compared our results with those given from the classical Ekman pumping model. It was found that our model can predict tile rotating flows more precisely than the classical linear model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.568-577
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• 2006

Developed in this study is a nonlinear Ekman pumping model to be used in simulating the rotating flows with quasi-three-dimensional Navier-Stokes equations. In this model, the Ekman pumping velocity is given from the solution of the Ekman boundary-layer equations for the region adjacent to the bottom wall of the flow domain; the boundary-layer equations are solved in the momentum-integral form. The developed model is then applied to rotating flows in a rectangular container receiving a time-periodic forcing. By comparing our results with the DNS and experimental data we have validated the developed model. We also compared our results with those given from the classical Ekman pumping model. It was found that our model can predict the rotating flows more precisely than the classical linear model.

• Steel and Composite Structures
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• v.47 no.5
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• pp.551-568
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• 2023

In this research, a new two-dimensional (2D) and quasi three-dimensional (quasi-3D) higher order shear deformation theory is devised to address the bending problem of functionally graded plates resting on an elastic foundation. The displacement field of the suggested theories takes into account a parabolic transverse shear deformation shape function and satisfies shear stress free boundary conditions on the plate surfaces. It is expressed as a combination of trigonometric and exponential shear shape functions. The Pasternak mathematical model is considered for the elastic foundation. The material properties vary constantly across the FG plate thickness using different distributions as power-law, exponential and Mori-Tanaka model. By using the virtual works principle and Navier's technique, the governing equations of FG plates exposed to sinusoidal and evenly distributed loads are developed. The effects of material composition, geometrical parameters, stretching effect and foundation parameters on deflection, axial displacements and stresses are discussed in detail in this work. The obtained results are compared with those reported in earlier works to show the precision and simplicity of the current formulations. A very good agreement is found between the predicted results and the available solutions of other higher order theories. Future mechanical analyses of three-dimensionally FG plate structures can use the study's findings as benchmarks.

• Proceedings of the IEEK Conference
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• 2002.07c
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• pp.1404-1407
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• 2002

Although we look at objects as 2D images through our eyes, we can reconstruct the shape and/or depth of objects. In order to realize this ability using computers, it is required that the method which can estimate the 3D features of object from 2D images. As feature which represents 3D shapes effectively, three dimensional vector autoregressive model is pro- posed. If this feature is associated other feature of 2D shape, then above aim might be achieved. On the other hand, as feature which represents 2D shapes, quasi moment features is proposed. As the first step of association of these features, we constructed real time simulator that computes both of two features concurrently from object data (3D curves) . This simulator can also rotate object and estimate the rotation The method using 3D VAR model estimates the rotation correctly, but the estimation by quasi moment features includes much errors. This reason would be that projected images are constructed by the points only, and doesn't have enough sizes to estimate the correct 3D rotation parameters.