• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1465-1477
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• 1993

Powder Injection Molding(PM) is an advanced and complicated technology for manufacturing ceramic or metal products making use of a conventional injection molding process, which is generally used for plastic products. Among many technologies involved in the successful PIM, injection molding process is one of the key steps to form a desired shape out of powder/binder mixtures. Thus, it is of great importance to have a numerical tool to predict the powder injection molding filling process. In this regard, a finite element analysis system has been developed for numerical simulations of filling process of powder injection molding. Powder/polymer mixtures during the filling pro cess of injection molding can be rheologically characterized as Non-Newtonian fluids with a so called yield phenomena and have a peculiar feature of apparent slip phenomena on the wall boundaries surrounding mold cavity. Therefore, in the present study, a physical modeling of the filling process of powder/polymer mixtures was developed to take into account both the yield stress and slip phenomena and a finite element formulation was developed accordingly. The numerical analysis scheme for filling simulation is accomplished by combining a finite element method with control volume technique to simulate the movement of flow front and a finite difference method to calculate the temperature distribution. The present study presents the modeling, numerical scheme and some numerical analysis results showing the effect of the yield stress and slip phenomena.

• Bulletin of the Society of Naval Architects of Korea
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• v.13 no.1
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• pp.17-23
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• 1976

Some methods of analysis of rectangular plates under distributed load of various intensity with interior supports are presented herein. Analysis of many structures such as bottom, side shell, and deck plate of ship hull and flat slab, with or without internal supports, Floor systems of bridges, included crthotropic bridges is a problem of plate with elastic supports or continuous edges. When the four edges of rectangular plate is simply supported, the double Fourier series solution developed by Navier can represent an exact result of this problem. If two opposite edges are simply supported, Levy's method is available to give an "exact" solution. When the loading condition and supporting condition of a plate does not fall into these cases, no simple analytic method seems to be feasible. Analysis of a simply supported rectangular plate under irregularly distributed loads of various intensity with internal supports is carried out by applying Navier solution well as the "Principle of Superposition." Finite difference technique is used to solve plates under irregularly distributed loads of various intensity with internal supports and with various boundary conditions. When finite difference technique is applied to the Lagrange's plate bending equation, any of fourth order derivative term in this equation produces at least five pivotal points leading to some troubles when the resulting linear algebraic equations are to be solved. This problem was solved by reducing the order of the derivatives to two: the fourth order partial differential equation with one dependent variable, namely deflection, is changed to an equivalent pair of second order partial differential equations with two dependent variables. Finite difference technique is then applied to transform these equations to a set of simultaneous linear algebraic equations. Principle of Superposition is then applied to handle the problems caused by concentrated loads and interior supports. This method can be used for the cases of plates under irregularly distributed loads of various intensity with arbitrary conditions such as elastic supports, or continuous edges with or without interior supports, and this method can also be solve the influence values of deflection, moment and etc. at arbitrary position of plates under the live load.

• Steel and Composite Structures
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• v.27 no.3
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• pp.255-271
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• 2018

This paper deals with the transient dynamic analysis and elastic wave propagation in a functionally graded graphene platelets (FGGPLs)-reinforced composite thick hollow cylinder, which is subjected to shock loading. A micromechanical model based on the Halpin-Tsai model and rule of mixture is modified for nonlinear functionally graded distributions of graphene platelets (GPLs) in polymer matrix of composites. The governing equations are derived for an axisymmetric FGGPLs-reinforced composite cylinder with a finite length and then solved using a hybrid meshless method based on the generalized finite difference (GFD) and Newmark finite difference methods. A numerical time discretization is performed for the dynamic problem using the Newmark method. The dynamic behaviors of the displacements and stresses are obtained and discussed in detail using the modified micromechanical model and meshless GFD method. The effects of the reinforcement of the composite cylinder by GPLs on the elastic wave propagations in both displacement and stress fields are obtained for various parameters. It is concluded that the proposed micromechanical model and also the meshless GFD method have a high capability to simulate the composite structures under shock loadings, which are reinforced by FGGPLs. It is shown that the modified micromechanical model and solution technique based on the meshless GFD method are accurate. Also, the time histories of the field variables are shown for various parameters.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.291-302
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• 2000

In recent years the development of high modulus, high strength and low density boron and graphite fibers bonded together has brought renewed interestes in structural elements. When a plate with arbitrarily oriented layers and clamped boundary conditions is subjected to uniform loading, it is difficult to analyze and apply, compared with isotropic and orthotropic cases. Therefore the numerical methods, such as finite difference method or finite element method, should be emloyed to analyse such problems. In this study the finite difference technique is used to formulate the bending analysis of symmetric composite laminated skew plates. When this technique is used to solve the problem, it is desirable to reduce the order of the derivatives in order to minimize the number of the pivotal points involved in each equation. The 4th order partial differential equations of laminated skew plates are converted to an equivalent three of 2nd order partial differential equations with three dependant variables.

• Structural Engineering and Mechanics
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• v.19 no.6
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• pp.603-618
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• 2005

The split Hopkinson pressure bar (SHPB) technique is widely used to characterize the dynamic mechanical response of engineering materials at high strain rates. In this paper, attendant problems associated with testing 70 mm diameter concrete specimens are considered, analysed and resolved. An adaptation of a conventional solid circular striker bar, as a means of achieving reliable and repeatable SHPB tests, is then proposed. In the analysis, a pseudo one-dimensional model is used to analyse wave propagation in a non-uniform striker bar. The stress history of the incident wave is then obtained by using the finite difference method. Comparison was made between incident waves determined from the simplified model, finite element solution and experimental data. The results show that the simplified method is adequate for designing striker bar shapes to overcome difficulties commonly encountered in SHPB tests. Using two specifically designed striker bars, tests were conducted on 70 mm diameter steel fibre reinforced concrete specimens. The results are presented in the paper.

• Journal of applied mathematics & informatics
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• v.25 no.1_2
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• pp.269-282
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• 2007

In this paper, we consider a two-dimensional fractional space-time diffusion equation (2DFSTDE) on a finite domain. We examine an implicit difference approximation to solve the 2DFSTDE. Stability and convergence of the method are discussed. Some numerical examples are presented to show the application of the present technique.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1590-1597
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• 2004

Three methods of design sensitivity analysis for structures such as numerical method, analytical method and semi-analytical method have been developed for the last three decades. Although analytical design sensitivity analysis can provide very exact result, it is difficult to implement into practical design problems. Therefore, numerical method such as finite difference method is widely used to simply obtain the design sensitivity in most cases. The numerical differentiation is sufficiently accurate and reliable fur most linear problems. However, it turns out that the numerical differentiation is inefficient and inaccurate in nonlinear design sensitivity analysis because its computational cost depends on the number of design variables and large numerical errors can be included. Thus the semi-analytical method is more suitable for complicated design problems. Moreover, semi-analytical method is easy to be performed in design procedure, which can be coupled with an analysis solver such as commercial finite element package. In this paper, implementation procedure fur the semi-analytical design sensitivity analysis outside of the commercial finite element package is studied and the computational technique is proposed for evaluating the partial differentiation of internal nodal force, so called pseudo-load. Numerical examples coupled with commercial finite element package are shown to verify usefulness of proposed semi-analytical sensitivity analysis procedure and computational technique for pseudo-load.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.585-592
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• 2003

Among various sensitivity evaluation techniques, semi-analytical method(SAM) is quite popular since this method is more advantageous than analytical method(AM) and global finite difference method(FDM). However, SAM reveals severe inaccuracy problem when relatively large rigid body motions are identified fur individual elements. Such errors result from the numerical differentiation of the pseudo load vector calculated by the finite difference scheme. In the present study, an iterative method combined with mode decomposition technique is proposed to compute reliable semi-analytical design sensitivities. The improvement of design sensitivities corresponding to the rigid body mode is evaluated by exact differentiation of the rigid body modes and the error of SAM caused by numerical difference scheme is alleviated by using a Von Neumann series approximation considering the higher order terms for the sensitivity derivatives.

• Journal of electromagnetic engineering and science
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• v.9 no.1
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• pp.12-16
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• 2009

This paper presents a new iterative locally one-dimensional [mite-difference time-domain(LOD-FDTD) method that has a simpler formula than the original iterative LOD-FDTD formula[l]. There are fewer arithmetic operations than in the original LOD-FDTD scheme. This leads to a reduction of CPU time compared to the original LOD-FDTD method while the new method exhibits the same numerical accuracy as the iterative ADI-FDTD scheme. The number of arithmetic operations shows that the efficiency of this method has been improved approximately 20 % over the original iterative LOD-FDTD method.

• Journal of Magnetics
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• v.21 no.3
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• pp.442-449
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• 2016

In this paper, an effective numerical analysis method is proposed for calculating dosimetry of the wireless power transfer system operating low-frequency ranges. The finite-difference time-domain (FDTD) method is widely used to analyze bio-electromagnetic field problems, which require high resolution, such as a heterogeneous whole-body voxel human model. However, applying the standard method in the low-frequency band incurs an inordinate number of time steps. We overcome this problem by proposing a modified finite-difference time-domain method which utilizes a quasi-static approximation with the surface equivalence theorem. The analysis results of the simple model by using proposed method are in good agreement with those from a commercial electromagnetic simulator. A simulation of the induced electric fields in a human head voxel model exposed to a wireless power transmission system provides a realistic example of an application of the proposed method. The simulation results of the realistic human model with the proposed method are verified by comparing it with the conventional FDTD method.