• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.59-69
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• 2019

This paper focuses on the numerical simulation of ice abrasion induced by unbreakable ice floe. Under the assumption that unbreakable floes behave as rigid body, the Discrete Element Method (DEM) was applied to simulate the interaction between a fixed structure and ice floes. DEM is a numerical technique which is eligible for computing the motion and effect of a large number of particles. In DEM simulation, individual ice floe was treated as single rigid element which interacts with each other following the given interaction rules. Interactions between the ice floes and structure were defined by soft contact and viscous Coulomb friction laws. To derive the details of the interactions in terms of interaction parameters, the Finite Element Method (FEM) was employed. An abrasion process between a structure and an ice floe was simulated by FEM, and the parameters in DEM such as contact stiffness, contact damping coefficient, etc. were calibrated based on the FEM result. Resultantly, contact length and contact path length, which are the most important factors in ice abrasion prediction, were calculated from both DEM and FEM and compared with each other. The results showed good correspondence between the two results, providing superior numerical efficiency of DEM.

• Advances in Computational Design
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• 제5권3호
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• pp.305-321
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• 2020

In this paper is presented the solution method for three-dimensional problem of transversely isotropic body's elastoplastic deformation by the finite element method (FEM). The process of problem solution consists of: determining the effective parameters of a transversely isotropic medium; construction of the finite element mesh of the body configuration, including the determination of the local minimum value of the tape width of non-zero coefficients of equation systems by using of front method; constructing of the stiffness matrix coefficients and load vector node components of the equation for an individual finite element's state according to the theory of small elastoplastic deformations for a transversely isotropic medium; the formation of a resolving symmetric-tape system of equations by summing of all state equations coefficients summing of all finite elements; solution of the system of symmetric-tape equations systems by means of the square root method; calculation of the body's elastoplastic stress-strain state by performing the iterative process of the initial stress method. For each problem solution stage, effective computational algorithms have been developed that reduce computational operations number by modifying existing solution methods and taking into account the matrix coefficients structure. As an example it is given, the problem solution of fibrous composite straining in the form of a rectangle with a system of circular holes.

• 소성∙가공
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• 제6권3호
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• pp.233-238
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• 1997

The estimation of the forming force required for metal forming process is unavoidable for selecting suitable machine and dimensioning die and punch parts. For this purpose the upper-bound method turns out to be very practical in simple two-dimensional cases under well-known boundary conditions. However, the application of this method for complicated two-or three-dimentional cases is very limited or practically impossible. The modified application of FEM in a manner of applying the upper bound method(the so-called Upper-bound Finite Element Simulation Method) fortunately provides the posibility of getting important information about the forming process in a simple and quick way before realizing the process on the machine. It is expected to function successfully even in three-dimentional cases. The application procedure has been explained for two-dimensional cases and its usefulness shown.

• 대한기계학회논문집A
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• 제20권6호
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• pp.1773-1783
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• 1996

Finite element method(FEM) is one of the most popularly used method analyzing the dynamic behaviors of structures. But unless number of finite elements is large enough, the results from FEM some what different from exact analytical solutions, especially at high frequency range. On the other hand, as the spectral analysis method(SAM) deals directly with the governing equations of a structure, the results from this melthod cannot but be exact regardless of any frequency range. However, the SAM can be applied only to the case where a structure is subjected to the concentrated loads, despite a structure could be unddergone distributed loads more generally. In this paper, therefore, new spectral analysis algorithm is introduced through the spectral element method(SEM), so that it can be applied to anlystructures whether they are subjected to the concentrated loads or to the distributed loads. The results from this new SEM are compared with both the results from FEM and the exact analytical solutions. As expected, the results from new SEM algorithm are found to be almost identical to the exact analytical solutions while those from FEM are not agreed well with the exact analytical solutions as the mode number increases.

• 대한기계학회논문집
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• 제18권7호
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• pp.1664-1673
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• 1994

As a fundamental study on effects of thermal-cycles on residual stress of ceramics/metal joints, residual stresses in $Si_3N_4$/SUS304 joint specimens were measured before and single thermal-cycle by X-ray diffraction method and finite element method(FEM). The residual stress was found to increase after single thermal-cycle, which was agreeable with the results of residual stress measurement by X-ray diffraction method and residual stress analysis by finite element method. After the residual stress measurement, 4-point bending tests were performed. The relationship between the bending strength, the thermal-cycle temperature and hold time was examined. The bending strength was found to decrease with the increase of residual stress in linear relation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.645-650
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• 2004

There have been lots of efforts to analyze the dynamic characteristics of mechanical systems. However, it is difficult to know the dynamic characteristics of mechanical systems composed of many parts with joints. Specially, in case of a bolted joint structure, no effective modeling method has been defined to acquire dynamic characteristics of the structure, using the finite element (FE) analysis. In this research, a linear dynamic model is developed for bolted joints and large interfaces using con frusta method and linear spring elements, respectively. The developed modeling method for bolted joints is verified based on the experimental result.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.217-227
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• 2019

The methodology known as "shape sensing" allows the reconstruction of the displacement field of a structure starting from strain measurements, with considerable implications for structural monitoring, as well as for the control and implementation of smart structures. An approach to shape sensing is based on the inverse Finite Element Method (iFEM) that uses a variational principle enforcing a least-squares compatibility between measured and analytical strain measures. The structural response is reconstructed without the knowledge of the mechanical properties and load conditions but based only on the relationship between displacements and strains. In order to efficiently apply iFEM to the most common structural typologies of civil engineering, its formulation according to the kinematical assumptions of the Bernoulli-Euler theory is presented. Two beam inverse finite elements are formulated for different loading conditions. Depending on the type of element, the relationship between the minimum number of required measurement stations and the interpolation order is defined. Several examples representing common applications of civil engineering and involving beams and frames are presented. To simulate the experimental strain data at the station points and to verify the accuracy of the displacements obtained with the iFEM shape sensing procedure, a direct FEM analysis of the considered structures is performed using the LUSAS software.

• 소성∙가공
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• 제4권3호
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• pp.267-281
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• 1995

Preform design is one of the critical fields in metal forming. The finite element method(FEM) has been effective in designing preforms and process sequence, for which the backward tracing scheme of the rigid-plastic FEM has been explored. In this work a program using the backward tracing scheme by the rigid-plastic FEM is developed for three-dimensional plastic deformation, which is an extension of the scheme from two-dimensional cases. The calculation of friction between workpiece and die, and handling of boundary conditions during backward tracing require sophisticated treatment. The developed program is applied to upsetting of a rectangular block and to side pressing of a cylindrical workpiece. The results of the two applications show feasibility of the program on three-dimensional plastic deformation.

• Structural Engineering and Mechanics
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• 제16권3호
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• pp.341-360
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• 2003

The goal of this paper is to determine the eigenvalues of a uniform rectangular plate carrying any number of spring-damper-mass systems using an analytical-and-numerical-combined method (ANCM). To this end, a technique was presented to replace each "spring-damper-mass" system by a massless equivalent "spring-damper" system with the specified effective spring constant and effective damping coefficient. Then, the mode superposition approach was used to transform the partial differential equation of motion into the matrix equation, and the eigenvalues of the complete system were determined from the associated characteristic equation. To verify the reliability of the presented theory, all numerical results obtained from the ANCM were compared with those obtained from the conventional finite element method (FEM) and good agreement was achieved. Since the order of the property matrices for the equation of motion obtained from the ANCM is much lower than that obtained from the FEM, the CPU time required by the ANCM is much less than that by the FEM.

• Korean Journal of Mathematics
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• 제13권2호
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• pp.127-137
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• 2005

The objective of numerical analysis is to devise and analyze efficient algorithms or numerical methods for equations arising in mathematical modeling for science and engineering. In this article, we present some recent topics in computational mathematics, specially in the finite element method and overview the development of the mixed finite element method in the context of second order elliptic and parabolic problems. Multiscale methods such as MsFEM, HMM, and VMsM are included.