• Progress in Superconductivity and Cryogenics
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• v.13 no.1
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• pp.31-35
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• 2011

A Hybrid Fault Current Limiter(FCL) which has more advantages in fast response and thermal characteristics than a simple resistive FCL had been proposed by our group. The Hybrid FCL consists of a resistive FCL for the magnitude of the first peak of fault current, and a fast switch for detecting fault current and generating the repulsive force within a cycle in fault situation. In ideal case, the impedance of the fast switch wound with two other kinds of HTS tape is negligibly zero in normal operation. But, during the fault situation, each HTS tape has different quench characteristics because of asymmetric current distribution. And this phenomenon causes effective flux and this flux opens the switch through the repulsive force applied to a metal plate of the fast switch. The magnitude of the repulsive force affects the switching characteristics of the fast switch. It should be large enough to raise the metal plate up. Otherwise the arc re-out break which are caused by not enough repulsive force to raise the metal plate up can cause unintended operation of the fast switch. In this paper, the numerical calculation of the repulsive force applied to the metal plate of the fast switch in various combinations of HTS tapes was performed by using the short-circuit test and finite element method.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.146-153
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• 2004

The Numerical study has been carried out to investigate the effects of chemical reaction and thermal radiation on the rocket plume flow-field at various altitudes. The theoretical formulation is based on the Navier-Stokes equations for compressible flows along with the infinitely fast chemistry and thermal radiation. The governing equations were solved by a finite volume fully-implicit TVD(Total Variation Diminishing) code which uses Roe's approximate Riemann solver and MUSCL(Monotone Upstream-centered Schemes for Conservation Laws) scheme. LU-SGS (Lower Upper Symmetric Gauss Seidel) method is used for the implicit solution strategy. An equilibrium chemistry module for hydrocarbon mixture with detailed thermo-chemical properties and a thermal radiation module for optically thin media were incorporated with the fluid dynamics code. In this study, kerosene-fueled rocket was assumed operating at O/F ratio of 2.34 with a nozzle expansion ratio of 6.14. Flight conditions considered were Mach number zero at ground level, Mach number 1.16 at altitude 5.06km and Mach number 2.9 at altitude 17.34km. Numerical results gave the understandings on the detailed plume structures at different altitude conditions. The diffusive effect of the thermal radiation on temperature field and the effect of chemical recombination during the expansion process could be also understood. By comparing the results from frozen flow and infinitely fast chemistry assumptions, the excess temperature of the exhaust gas resulting from the chemical recombination seems to be significant and cannot be neglected in the view point of performance, thermal protection and flow physics.

• Computational Structural Engineering
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• v.3 no.3
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• pp.113-123
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• 1990

The paper is concerned with the elasto-plastic and geometrically nonlinear analysis of shell structures using an improved degenerated shell element. In the formulation of the element stiffness, the combined use of three different techniques was made. They are; 1) an enhanced interpolation of transverse shear strains in the natural coordinate system to overcome the shear locking problem ; 2) the reduced integration technique in in-plane strains to avoid the membrane locking behavior ; and 3) selective addition of the nonconforming displacement modes to improve the element performances. This element is free of serious shear/membrane locking problems and undesirable compatible/commutable spurious kinematic deformation modes. In the formulation for plastic deformation, the concept of a layered element model is used and the material is assumed von Mises yield criterion. An incremental total Lagrangian formulation is presented which allows the calculation of arbitrarily large displacements and rotations. The resulting non-linear equilibrium equations are solved by the Netwon-Raphson method combined with load or displacement increment. The versatility and accuracy of this improved degenerated shell element are demonstrated by solving several numerical examples.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1163-1169
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• 2014

In this study, a fatigue assessment method for vehicle suspension systems having welded geometries was established under a bending loading condition. For the fatigue life estimation of the actual product's welded joints made of different steels, bending fatigue tests were performed on welded specimens with a simplified shape for obtaining the moment-fatigue-life plot. Further, geometry modeling of the simplified welded specimens was conducted. Results of finite element analysis were used to obtain the stress-fatigue-life plot. The analysis results were also used to calculate the stress concentration factors for notch-factor-based fatigue life estimation. The test results were compared with results of the general notch-factor-based fatigue life estimation for improving fatigue assessment. As a result, it was concluded that both the welded fatigue tests and the notch-factor-based fatigue life estimation are necessary for accurate fatigue assessment.

• Journal of Korean Society of Steel Construction
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• v.18 no.3
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• pp.373-383
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• 2006

In a steel structural system, noncomposite form deck one-way slab is the plate element supported by four-edged steel beams with unequaled stiffness. However, design criterion has analyzed the one-way slab as the continuous beam. Because the end beams that support the one-way slab have elastic supports t hat cause different deflections according to the support conditions and locations, the bending moments corresponding to the support ic support effect is not considered in the design criterion. Accordingly, to conduct a reasonable estimation of approximate moment coefficients considering the unequaled elastic support conditions, this study analyzes and estimates various models with varia bles for the ratios of live load to dead load and pattern arangements of live loads and span lengths. The analytical methods considering the finite three-dimensional plate element, the two-dimensional elastic support and the infinite stifnes suport are performed.

• Advances in environmental research
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• v.3 no.1
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• pp.45-69
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• 2014

The groundwater has been a major source of water supply throughout the ages. Around 50% of the rural as well as urban population in the developing countries like India depends on groundwater for drinking. The groundwater is also an important source in the agriculture and industrial sector. In many parts of the world, groundwater resources are under increasing threat from growing demands, wasteful use and contamination. A good planning and management practices are needed to face this challenge. A key to the management of groundwater is the ability to model the movement of fluids and contaminants in the subsurface environment. It is obvious that the contaminant source activities cannot be completely eliminated and perhaps our water bodies will continue to serve as receptors of vast quantities of waste. In such a scenario, the goal of water quality protection efforts must necessarily be the control and management of these sources to ensure that released pollutants will be sufficiently attenuated within the region of interest and the quality of water at points of withdrawal is not impaired. In order to understand the behaviour of contaminant transport through different types of media, several researchers are carrying out experimental investigations through laboratory and field studies. Many of them are working on the analytical and numerical studies to simulate the movement of contaminants in soil and groundwater of the contaminant transport. With the advent of high power computers especially, a numerical modelling has gained popularity and is indeed of particular relevance in this regard. This paper provides the state of the art of contaminant transport and reviews the allied research works carried out through experimental investigation or using the analytical solution and numerical method. The review involves the investigation in respect of both, saturated and unsaturated, porous media.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.3
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• pp.345-356
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• 2013

Numerical simulation on rock cutting by a TBM disc cutter was carried out using SPH (Smoothed Particle Hydrodynamics) code. AUTODYN3D, a commercial software program based on finite element method, was used in this study. The three-dimensional geometry of a disc cutter and a rock specimen were modeled by Lagrange and SPH code respectively. The numerical simulation was carried out for Hwangdeung granite for 10 different cutting conditions. The results of the numerical simulation, i.e. the relation between cutter force and failure behavior, had a good agreement with those from LCM test. The cutter forces measured in the numerical simulation had 10% deviation from the LCM test results. Moreover, the optimum cutter spacing was almost identical with the experimental results. These results indicate that SPH code can be successfully used had applicability for simulation on rock cutting by a TBM disc cutter. However, further study on Lagrange-SPH coupled modelling would be necessary to reduce the computation time.

• Wind and Structures
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• v.26 no.5
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• pp.331-341
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• 2018

A numerical study on the flow over a square cylinder in the vicinity of a wall is conducted for different Couette-Poiseuille-based non-uniform flow with the non-dimensional pressure gradient P varying from 0 to 5. The non-dimensional gap ratio L (=$H^{\ast}/a^{\ast}$) is changed from 0.1 to 2, where $H^{\ast}$ is gap height between the cylinder and wall, and $a^{\ast}$ is the cylinder width. The governing equations are solved numerically through finite volume method based on SIMPLE algorithm on a staggered grid system. Both P and L have a substantial influence on the flow structure, time-mean drag coefficient ${\bar{C}}_D$, fluctuating (rms) lift coefficient ($C_L{^{\prime}}$), and Strouhal number St. The changes in P and L leads to four distinct flow regimes (I, II, III and IV). Following the flow structure change, the ${\bar{C}}_D$, $C_L{^{\prime}}$, and St all vary greatly with the change in L and/or P. The ${\bar{C}}_D$ and $C_L{^{\prime}}$ both grow with increasing P and/or L. The St increases with P for a given L, being less sensitive to L for a smaller P (< 2) and more sensitive to L for a larger P (> 2). A strong relationship is observed between the flow regimes and the values of ${\bar{C}}_D$, $C_L{^{\prime}}$ and St. An increase in P affects the pressure distribution more on the top surface than on bottom surface while an increase in L does the opposite.

• Advances in nano research
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• v.6 no.3
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• pp.243-255
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• 2018

Polystyrene granules were combined with nanosilver to form a nanocomposite film. One-side migration was conducted to test into three food simulants (3% acetic acid, 10% ethanol and 95% ethanol) at $40^{\circ}C$ temperature on different period of time (2, 4, 6, 8 and 10 days). It was found that, among the simulants, the highest migration amount was obtained with 3% acetic acid, while the 95% ethanol revealed the least migration level. Diffusion coefficients of nanosilver particles into simulants were estimated by inverse simulation using experimental data of concentration variation in the simulants. The finite element method used to solve the mass transfer equation and the numerical results indicates the sameresponse with the experimental data. The numerical results confirmed that the highest diffusion coefficient for acetic acid 3% (1.82E-10 to $1.76E-9m^2\;s^{-1}$) and the lowest diffusion coefficient for ethanol 95% from 2 to 10 days were obtained, respectively. Also, results of diffusion coefficient - concentration relation showed, the diffusion coefficient had in direct correlation with time and concentration. The results indicated that, in the 3% acetic acid, due to the increasing of diffusion coefficient of silver nanoparticles, they are released faster and distributed uniformly.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.9
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• pp.5467-5473
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• 2014

This study examined the numerical analysis results with respect to the thermal behavior of a natural convection cooled pin-fin heat sink. The heat sink consisted of pin fins integrated with plate fins. The heat sinks were designed with two different types to fit the limited internal space. The two types of heat sinks designed were analyzed using the ANSYS software package, and the numerical analysis results were compared with the cooling performance of the two types of heat sinks. The results of the simulation were analyzed according to the temperature distribution and air flow characteristics, heat flux etc. This study examined the correlation of the cooling performance with the heat sink internal structure and fin shape. FEM (Finite Element Method) confirmed the cooling performance of heat sink type A under natural convection conditions as the best results. The results of the numerical simulation showed that the heat sink type A shape showed an approximately 70 percent better heat transfer rate with natural convection than that of type B.