• Journal of applied mathematics & informatics
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• v.27 no.5_6
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• pp.1411-1427
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• 2009

We propose a model based on Lotka-Volterra dynamics with two competing spices which are affected not only by harvesting but also by the presence of a predator, the third species. Hyperbolic and linear response functions are considered. We derive the conditions for global stability of the system using Lyapunov function. The optimal harvest policy is studied and the solution is derived in the interior equilibrium case using Pontryagin's maximal principle. Finally, some numerical examples are discussed. The nature of variations in the two prey species and one predator species is studied extensively through graphical illustrations.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.215-219
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• 2003

Buckling and post-buckling Analysis of Ludwick type and modified Ludwick type elastic materials was carried out. Because the constitutive equation, or stress-strain relationship is different from that of linear elastic one, a new governing equation was derived and solved by $4^{th}$ order Runge-Kutta method. Considered as a special case of combined loading, the buckling under both point and distributed load was selected and researched. The final solution takes distinguished behavior whether the constitutive relation is chosen to be modified or non-modified Ludwick type as well as linear or non-linear. We also derived strain energy function for non-linear elastic constitutive relationship. By doing so, we calculated the criterion function which estimates the stability of the equilibrium solutions and determines critical buckling load for non-linear cases. We applied this theory to the constitutive relationship of fabric, which also is the non-linear equation between the applied moment and curvature. This results has both technical and mathematical significance.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.167-171
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• 2006

The previous models for thermal behavior in the melting furnace were deterministic, composed of such a form that if the initial input conditions are determined, the results would have been come out by using the basic heat equilibrium equations. But making the experiment by trusting the analysis results, the melted slag is fortuitously set often, because temperature variation of the melted slag in the reaction process is not point function but path function. So in this study, a transient model was developed and verified by comparing with the experimental results.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.196-201
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• 2000

The influence of adsorption on cadmium toxicity to soil microorganisms in smectite-rich soils and sediments was quantified as a function of solution and sorbent characteristics. Adsorption and surface complexation experiments were conducted to infer Cd sorption mechanisms to a reference smectite and three fractions of a Veritsol soil, and to elucidate the effects of the surface complexation on Cd bioavailability and toxicity in soils and sediments. Cadmium adsorption isotherms conformed to the Langmuir adsorption model, with adsorptive capacities of the different samples dependent on their characteristics. Equilibrium geochemical modeling (MINTEQA2) was used to predict the speciation of Cd in the soil suspensions using Langmuir and Triple Layer surface complexation models. The influence of adsorption and surface complexation on cadmium toxicity to soil microorganisms was assessed indirectly through the relative change in microbial hydrolysis of fluorescein diacetate (FDA) as a function of total Cd concentration and sorbent characteristics. Adsorption decreased the toxicity of Cd to soil microorganisms. Inner-sphere complexation is more effective than outer-sphere complexation in reducing the bioavailability and toxicity of heavy metals in soils and sediments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.169-174
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• 1996

In this paper, the electron transport characteristic in CF$_4$has been analysed over the E/N range 1~300(Td) by a two-term approximation Boltzmann equation method and by a Monte Carlo simulation. The alteration of cross sections from the literature is avoided as much as possible in the analysis. The motion has been calculated to give swarm parameters for the electron drift velocity(W), diffusion coefficient(D$_{L}$), the ratio of the diffusion coefficient to the mobility(D$_{L}$/$\mu$), mean energy($\varepsilon$), the electron energy distribution function. The electron energy distribution function has been analysed in CF$_4$at E/N=50, 100 and 200(Td) for a case of the equilibrium region in the mean electron energy. The results of Boltzmann equation and Monte Carlo simulation have been compared with experimental data by Y. Nakamura and M. Hayashi.shi.

• Transactions of Materials Processing
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• v.9 no.6
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• pp.590-597
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• 2000

A finite element formulation lot the simulation of axisymmetric sheet hydroforming is proposed, and an implicit program is coded. In order to describe normal anisotropy of steel sheet, Hill's non-quadratic yield function (Hill, 1979) is employed. Frictional contacts among sheet surface, rigid tool surface, and flexible hydrostatic pressure are considered using mesh normal vectors based on finite element of the sheet. Applied hydraulic pressure is also considered as a function of forming rate and time and treated as an external loading. The complete set of the governing relations comprising equilibrium and interfacial equations is approximately linearized for Newton-Raphson algorithm. In order to verify the validity of the developed finite element formulation, the axisymmetric bulge test is simulated. Simulation results are compared with other FEM results and experimental measurements and showed good agreements. In axisymmetric hydroforming processes of a disk cover, formability changes are observed according to the hydraulic pressure curve changes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.2
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• pp.97-107
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• 2002

The continuous circular cylindrical shells are widely used for the high performance structures of aircraft, spacecraft, missile, nuclear fuel rod shell and so on. In this paper, a method for the vibrational analysis of the continuous circular cylindrical shells with the clamped-clamped supports at two end edges is developed by using the modal expansion method. Forces and/or moments acting on the shell surface are expressed in terms of the Dirac Delta Function. Frequency equation of the continuous shell is also derided by the application of the equilibrium of forces and the continuity of displacements at the boundary. Natural frequencies of the continuous shell are calculated numerically with mathematica 3.0 and they are compared with FEM results from the ANSYS 5.3 to improve the reliability of analytic solutions. Mode shares obtained by the FEM are Presented in this paper.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.615-617
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• 2003

In electricity market with a imperfect competition, participants make plans of biddings and transaction strategies to maximize their own profits. The market price and the quantity are determined by bidding systems and market demands. Practically the characteristics of power demand have rather two forms; elastic region and inelastic region, than constant slope elasticity. Furthermore the price cap in the market can be modelled as a region of perfect elasticity in the demand function. This paper analyses supplier's bidding strategies which are reflected the characteristics of practical demand. Equilibrium strategies are solved by using the Bertrand model and payoff matrices.

• Proceedings of the KIEE Conference
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• 2005.10a
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• pp.97-100
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• 2005

This paper describes the electron transport characteristics in SiH4 has been analysed over the E/N range 0.5${\sim}$300[Td] and Pressure value 0.5, 1, 2.5 [Torr] by a two-term approximation Boltzmann equation method and by a Monte Carlo simulation. The motion has been calculated to give swarm parameters for the electron drift velocity, diffusion coefficient, electron ionization, mean energy and the electron energy distribution function. The electron energy distribution function has been analysed in $SiH_4$ at E/N=30, 50[Td] for a case of the equilibrium region in the mean electron energy and respective set of electron collision cross sections. The results of Boltzmann equation and Monte carlo simulation have been compared with experimental data by Pollock, Ohmori, cottrell and Walker.

• Structural Engineering and Mechanics
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• v.54 no.4
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• pp.623-648
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• 2015

A numerical approach is presented for the analysis of the forced vibration of a rigid surface foundation with arbitrary shape. In the analysis, the foundation is discretized into a number of sub squaree-lements. The dynamic response within each sub-element is described by the Green's function, which is obtained by the Fourier-Bessel transform and Precise Integration Method (PIM). Incorporating the displacement boundary condition and force equilibrium of the foundation, it obtains a system of linear algebraic equation in terms of the contact forces within each sub-element. Solving the equation leads to the desired dynamic impedance functions of the foundation. Numerical results are obtained for foundation not only with simple geometrical configurations, such as rectangular and circular foundation, but also the case of irregularly shaped foundation. Several comparisons between the proposed approach and other methods are made. Very good agreement is reached. Also, parametric studies are carried out on the dynamic response of foundation. Addressed in this study are the effects of Poisson's ratio, material damping and contact condition of soil-foundation interface. Several conclusions are drawn the significance of the factors.