• Journal of applied mathematics & informatics
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• v.38 no.5_6
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• pp.489-506
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• 2020

The spatial fractional diffusion equation can be discretized by employing the implicit finite difference scheme using the shifted Grünwald formula. The discretized linear system is obtained, whose the coefficient matrix has a diagonal-plus-Toeplitz structure. In order to solve the diagonal-plus-Toeplitz linear system, on the basis of circulant and skew-circulant splitting (CSCS splitting), we construct a new and efficient iterative method, called DSCS iterative methods, which have two parameters. Than we prove the convergence of DSCS methods. As a focus, we derive the simple and effective values of two optimal parameters under some restrictions. Some numerical experiments are carried out to illustrate the validity and accuracy of the new methods.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1995.03a
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• pp.9-16
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• 1995

The thermal deformation of machine tool spindle influences the performance of the manufacturing systems for precision products. In this research thermal analysis of a high speed machine tool spindle with the rolling bearing and the built-in motor is carried out using Finite Difference Method. The thermal boundary conditions describing the hear generation in the bearing and built-in motor are considered in the simulation. And various convective boundary conditions are assumed with the empirical formula in the references. From the simulation results the characteristics of each element affecting the dynamic thermal behaviour of the machine tool spindle systems have been clarified. This model can be well applied to the future development of the high speed spindle systems.

• Computers and Concrete
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• v.16 no.5
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• pp.775-793
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• 2015

Moisture transport in concrete in atmospheric environment was studied in this paper. Based on the simplified formula of the thickness of the adsorbed layer, the pore-size distribution function of cement paste was calculated utilizing the water adsorption isotherms. Taking into consideration of the hysteresis effect in cement paste, the moisture diffusivity of cement paste was obtained by the integration of the pore-size distribution. Concrete is regarded as a two-phase composite with cement paste and aggregate, neglecting the moisture diffusivity of aggregate, then moisture diffusivity of concrete was evaluated using the composite theory. Finally, numerical simulation of humidity response during both wetting and drying process was carried out by the finite difference method of partial differential equation for moisture transport, and the numerical results well capture the trend of the measured data.

• Bulletin of the Society of Naval Architects of Korea
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• v.20 no.1
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• pp.29-33
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• 1983

The loading condition, of a ship, especially a multi-purpose cargo carrier, in service, is often changed. Then, the prediction of natural frequency changes is necessary to provide measures for prevention of ship vibrations. In this paper a simplified method for the above purpose is presented. The bases of the method are analytical solutions for the lateral vibrations of uniform Timoshenko beams carrying a concentrated mass and the Dunkerley's formula. In this method a ship in the standard ballast condition is reduced to a uniform Timoshenko beam having same system parameters as those of the midship section. To investigate the validity of the proposed method, numerical calculations are carried out for a 46,000 DWT bulk carrier and compared with detailed calculations based on the finite difference method. Even in cases those the cargoes in a hold, length of which is about 13% of the ship's length, are reduced to a concentrated mass, the proposed method gives results of several percent differences from the detailed calculations up to the six-noded mode.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.5 no.4
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• pp.90-97
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• 1996

The thermal deformation of a machine tool spindle influences the performance of the manufacturing systems for precision products. In this research, thermal analysis of a high speed machine tool spindle with the rolling bearing and the built-in motor is carried out by using Finite Difference Method. The thermal boundary conditions describing the heat generation in the bearing and built-in motor are considered in the simulation. And various convective boundary conditions are assumed with the empirical formula in the references. From the simulation results, the characteristics of each element affecting the dynamic thermal behaviour of the machine tool spindle system have been clarified. Therefore, this model can be well applied to the future development of the high speed spindle systems.

• Journal of the Chungcheong Mathematical Society
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• v.33 no.1
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• pp.165-171
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• 2020

In this paper we consider a mixed fractional Brownian motion (mfBm) with jumps. The prices of European barrier options can be evaluated by solving a partial integro-differential equation (PIDE) with variable coefficients, which is derived from the mfBm with jumps. The 2-step backward differentiation formula (BDF2 method) proposed in [6] is applied with the second-order convergence rate in the time and spatial variables. Numerical simulations are carried out to observe the convergence behaviors of the BDF2 method under the mfBm with the Kou model.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.8
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• pp.175-184
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• 2003

A method of the shape design sensitivity analysis based on the boundary integral equation formulation is presented for two-dimensional inhomogeneous thermal conducting solids with multiple domains. Shape variation of the external and interface boundary is considered. A sensitivity formula of a general performance functional is derived by taking the material derivative to the boundary integral identity and by introducing an adjoint system. In numerical analysis, state variables of the primal and adjoint systems are solved by the boundary element method using quadratic elements. Two numerical examples of a compound cylinder and a thermal diffuser are taken to show implementation of the shape design sensitivity analysis. Accuracy of the present method is verified by comparing analyzed sensitivities with those by the finite difference. As application to the shape optimization, an optimal shape of the thermal diffuser is found by incorporating the sensitivity analysis algorithm in an optimization program.

• Journal of Korean Association for Spatial Structures
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• v.23 no.4
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• pp.71-79
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• 2023

In this study, a prefabricated buckling brace (PF-BRB) was proposed, and a test specimen was manufactured based on the design formula for the initial shape and structural performance tests were performed. As a result of the experiment, all standard performance requirements presented by KDS 41 17 00 and MOE 2021 were satisfied before and after replacement of the reinforcement module, and no fracture of the joint module occurred. As a result of the incremental load test, the physical properties showed a significant difference in the stiffness ratio after yielding under the compressive load of the envelope according to the experimental results. It is judged necessary to further analyze the physical properties according to the experimental results through finite element analysis in the future.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.2
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• pp.135-146
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• 2003

This paper presents the effect of ground vibration induced by vibrohammer and RCD on adjancent subway tunnel performance using FDM program. Firstly, the stability criteria for structures near vibration source were proposed according to existing data, then peak particle velocity around tunnel was estimated based on detailed information of vibrohammer and existing formula for dynamic loads through numerical analysis. The peak particle velocity induced by RCD bit rotation was also estimated using surveyed data and formula. Consequently, displacement and stress responses were obtained at crown, shoulder and spring line and compared with the criteria to check stability of tunnel.

• Journal of KSNVE
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• v.6 no.5
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• pp.607-616
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• 1996

A combined computational fluid dynamics(CFD)-Kirchhoff method is presented for predicting high-speed impulsive noise generated by a hovering blade. Two types of Kirchhoff integral formula are used; one for the classical linear Kirchhoff formulation and the other for the nonlinear Kirchhoff formulation. An Euler finite difference solver is solved first to obtain the flow field close to the blade, and then this flow field is used as an input to a Kirchhoff formulation to predict the acoustic far-field. These formulas are used at Mach numbers of 0.90 and 0.95 to investigate the effectiveness of the linear and nonlinear Kirchhoff formulas for delocalized flow. During these calculiations, the retarded time equation is also carefully examined, in particular, for the cases of the control surface located outside of the sonic cylinder, where multiple roots are obtained. Predicted results of acoustic far-field pressure with the linear Kirchhoff formulation agree well with experimental data when the control surface is at the certain location(R=1.46), but the correlation is getting worse before or after this specific location of the control surface due to the delocalized nonlinear aerodynamic flow field. Calculations based on the nonlinear Kirchhoff equation using a linear sonic cylinder as a control surface show a reasonable agreement with experimental data in negative amplitudes for both tip Mach numbers of 0.90 and 0.95, except some computational integration problems over a shock. This concliudes that a nonlinear formulation is necessary if the control surface is close to the blade and the flow is delocalized.