• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.757-762
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• 2011

We investigate the transient temperature response in biological tissue whose surface is exposed to alternately varying sinusoidal oscillation. Based on the Pennes bio-heat equation, we apply numerical analysis using a finite element method to find the effects of the physical properties of the skin layers. Three layers of tissue-epidermis, dermis, and subcutaneous-are considered as the solution region. We investigate the effects of different properties of the skin layers on the temperature profile. We also investigate the effects of the perfusion rate for the dermis, which is the most sensitive layer. The results show that the temperature profile of tissue depth has a discontinuous point when different physical properties are used.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.27-35
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• 2006

It has been observed in experiments that combustion instability of low frequency (${\sim}$ 10Hz) results form the modulation of equivalence ratio at fuel injection hole when a pressure fluctuation propagates upwards along the channel of the burner under an unchoked fuel flow condition. In this study, a commercial program was used to determine how the fuel flow rate changed with respect to the pressure, velocity of the fuel flow and the mass fraction in a choked and an unchoked condition. The calculation focus on the upstream of the dump plane to know how the forced pressure with the fuel injection conditions affects the modulation of the equivalence ratio. Therefore, it is found that pressure fluctuation leads to oscillation of mass flow rate and then results in equivalence ratio modulation under the unchoked fuel flow condition.

• Journal of computational fluids engineering
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• v.19 no.3
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• pp.85-90
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• 2014

The purpose of this study is to develop a new Meshless Method to solve 2-D compressible flow problems numerically. This paper includes a revised Least Square method that improves robustness compared with its original version by removing excessive numerical oscillation which occurs when points are randomly distributed. Numerical analyses of hypersonic flow over a blunt body were carried out using the method, then robustness, accuracy and convergence of their results were compared with those obtained from the original method.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.177-184
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• 2002

Large amplitude sloshing can occur in contained fluid region due to the seismic ground motion. Also, The pressure by large amplitude sloshing damages the connections between the wall and roof of a fluid container and causes outflow of contained fluid. Therefore, to predict the dynamic behavior accurately, three dimensional analysis with the nonlinear boundary condition must be performed. In this study, the numerical solution procedure is developed using the boundary element method with the Lagrangian particle approach. In order to demonstrate the accuracy and validity of the developed method, the fluid motion for a free oscillation with small amplitude and a forced vibration are analyzed. And the numerical results are compared with the linear theory results and the previous studies with the nonlinear boundary condition.

• Journal of computational fluids engineering
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• v.13 no.3
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• pp.8-13
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• 2008

We present a numerical simulation technique and some preliminary results of the impact and spreading of a droplet containing particles on the solid substrate in 2D. We used the 2nd-order Adams-Bashforth / Crank-Nicholson method to solve the Navier-Stokes equation and employed the level-set method with the continuous surface stress for description of droplet spreading with interfacial tension. The impact velocity has been generated by the instantaneous gravity. The distributed Lagrangian-multipliers method has been combined for the implicit treatment of rigid particles and the discontinuous Galerkin method has been used for the stabilization of the interface advection equation. We investigated the droplet spreading by the inertial force and discussed effects of the presence of particles on the spreading behavior using an example problem. We observed reduced oscillation and spread for the particulate droplet.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.189-196
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• 2004

A modified generalized particle algorithm, MGPA, was suggested to improve the calculation efficiency of standard SPH Method in numerical analysis of high speed impact behavior. MGPA had a new weight function to reduce computation time. The efficiency of this method was proven through calculation for the sample problems of one dimensional rod impact problem and two dimensional plate impact problem. The MGPA method reduced the calculation error and stress oscillation near the boundaries. The validity of this approach was shown by the comparison with ABAQUS results in two dimensional plate impact problem.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1264-1275
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• 2002

This paper is concerned with the investigation on the stability and convergence characteristics of the Crank-Nicolson-Galerkin scheme that is widely being employed for the numerical approximation of parabolic-type partial differential equations. Here, we present the theoretical analysis on its consistency and convergence, and we carry out the numerical experiments to examine the effect of the time-step size △t on the h- and P-convergence rates for various mesh sizes h and approximation orders P. We observed that the optimal convergence rates are achieved only when △t, h and P are chosen such that the total error is not affected by the oscillation behavior. In such case, △t is in linear relation with DOF, and furthermore its size depends on the singularity intensity of problems.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.261-267
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• 2005

A comprehensive DES quality numerical analysis has been carried out for reacting flows in constant-area and divergent scramjet combustor configuration with and without a cavity. Transverse injection of hydrogen is considered over a broad range of injection pressure. The corresponding equivalence ratio of the overall fuel-air mixture ranges from 0.167 to 0.50. The work features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the pervious studies. Much of the flow unsteadiness is related not only the cavity, but also to the intrinsic unsteadiness in the flowfield. The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The roles of the cavity, injection pressure, and heat release in determining the flow dynamics are examined systematically.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.11
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• pp.538-543
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• 2006

A high-Power continuous-wave (CW) ten-vane double-strapped magnetron oscillator has been investigated using three-dimensional (3D) particle-in-cell (PIC) numerical simulation code, MAGIC3D. The resonant modes and their resonant frequencies of the ten-vane strapped magnetron resonator were obtained to show a large mode separation near the ${\pi}$-mode. An electron cloud formed in an anode-cathode gap, called an interaction space was confined well enough to result in no leakage current. Five spokes were clearly observed in the electron cloud, which definitely ensured the ${\pi}$-mode oscillation in the ten-vane magnetron. Numerical simulations predicted that the saturated microwave output power measured at the coaxial output port was 5.41 kW at the microwave frequency of 893 MHz, corresponding to a power conversion efficiency of 72.6% when the external axial magnetic field was 1150 gauss and the electron beam voltage and current were 6 kV and 1.25 A, respectively.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.459-462
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• 2006

In this study, the characteristic of a vane pump of an automative power steering system is numerically analyzed. The vane pump changes the energy level of operation fluid by converting mechanical input power to hydraulic output. To simulate this mechanism, moving mesh technique is adopted. As a result, the flow rate and pressure are obtained by numerical analysis. The flow rate agrees well with the experimental data. Moreover, the variation and oscillation of the pressure around the rotating vane are confirmed. The difference of pressure appears in the vane tip as a result of the flow characteristics. Furthermore, the back flow into the rotor was observed.