• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.6B
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• pp.507-514
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• 2011

A numerical model has been developed by employing a finite element method to simulate the depth-averaged 2-D dispersion of the heat pollutant, which is an important pollutant material in natural streams. Among the finite element methods, the Streamline Upwind/Petrov Galerkin (SUPG) method was applied. Also both linear and quadratic elements can be applied so that irregular river boundaries can be easily represented. To show the movement of heat pollutants, the reaction term describing heat transfer was represented as an equation in which sink/source term is proportional to the difference between the equilibrium temperature and water surface temperature. The equation was expressed so that the water surface temperature changes according to the temperature transfer coefficient and the equilibrium temperature. For the calibration of the model developed, analytic and numerical results from a case of rectangular channel with full width continuous injection have been compared in a steady state. The comparisons showed that the numerical results were in good agreement with analytical solutions. The application site was selected from the downstream of Paldang dam to Jamsil submerged weir, and overall length of this site is about 22.5 km. The change of water temperature caused by the discharge from the Guri sewage treatment plant has been simulated, and results were similar to the observed data. Overall it is concluded that the developed model can represent the water temperature changes due to heat transport accurately. But the verification using observed data will further enhance the validity of the model.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.747-769
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• 2020

This paper provides a semi-analytical approach to investigate the variations of 3D displacement components, electric potential, stresses, electric displacements and transverse vibration frequencies in laminated piezoelectric composite plates based on the scaled boundary finite element method (SBFEM) and the precise integration algorithm (PIA). The proposed approach can analyze the static and dynamic responses of multilayered piezoelectric plates with any number of laminae, various geometrical shapes, boundary conditions, thickness-to-length ratios and stacking sequences. Only a longitudinal surface of the plate is discretized into 2D elements, which helps to improve the computational efficiency. Comparing with plate theories and other numerical methods, only three displacement components and the electric potential are set as the basic unknown variables and can be represented analytically through the transverse direction. The whole derivation is built upon the three dimensional key equations of elasticity for the piezoelectric materials and no assumptions on the plate kinematics have been taken. By virtue of the equilibrium equations, the constitutive relations and the introduced set of scaled boundary coordinates, three-dimensional governing partial differential equations are converted into the second order ordinary differential matrix equation. Furthermore, aided by the introduced internal nodal force, a first order ordinary differential equation is obtained with its general solution in the form of a matrix exponent. To further improve the accuracy of the matrix exponent in the SBFEM, the PIA is employed to make sure any desired accuracy of the mechanical and electric variables. By virtue of the kinetic energy technique, the global mass matrix of the composite plates constituted by piezoelectric laminae is constructed for the first time based on the SBFEM. Finally, comparisons with the exact solutions and available results are made to confirm the accuracy and effectiveness of the developed methodology. What's more, the effect of boundary conditions, thickness-to-length ratios and stacking sequences of laminae on the distributions of natural frequencies, mechanical and electric fields in laminated piezoelectric composite plates is evaluated.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.63-77
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• 1990

The combined deckstructure-car system of a car carrier is especially sensitive to hull girder vibrations due to mechanical excitations and wave loads. For the free and forced vibration analysis of the system, the analytical methods based on the receptance method and two schemes for efficient applications of the methods are presented. The methods are especially relevant to dynamical reanalysis of the system subject to design modification or to dynamic optimization. The deck-car system is modelled as a combined system consisting of a stiffened plate representing deck, primary structure, and attached subsystems such as pillars, additional stiffeners and damped spring-mass systems representing cars/trucks. For response calculations of the system subjected to displacement excitations along the boundaries, the support displacement transfer ratio conceptually similar to the receptance is introduced. For the verification of accuracy and calculation efficiency of the proposed methods, numerical and experimental investigations are carried out.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1244-1254
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• 1992

This paper investigates the vibrational damping characteristics of laminated plates composed of elastic, viscoelastic and elastic layers by theoretical and experimental methods. Laminated plates are in cylindrical bending and visco-elastic adhesive layer is assumed as the visco-elastic spring which takes damping effect through both shear and normal deformations. Governing equations oof laminated plates are derived in the form of simultaneous first order differential equations, which account for the longitudinal displacements, rotary inertia and shear deformations of elastic base plate and elastic constraining plate. The numerical calculations of the equations are illustrated by the applications to the cantilever beam in transverse vibration. The results of the solutions agree well with the experimental measurements in general. The damping effects due to the shear and thickness deformations in the adhesives are analyzed and it is shown that for thicker adhesives, the damping effect due to thickness deformation becomes significant and for thinner adhesives, due to shear deformation.

• Journal of Biomedical Engineering Research
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• v.28 no.1
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• pp.8-16
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• 2007

Finite element analysis (FEA) is an effective means for the analysis of bioelectromagnetism. It has been successfully applied to various problems over conventional methods such as boundary element analysis and finite difference analysis. However, its utilization has been limited due to the overwhelming computational load despite of its analytical power. We have previously developed a novel mesh generation scheme that produces FE meshes that are content-adaptive to given MR images. MRI content-adaptive FE meshes (cMeshes) represent the electrically conducting domain more effectively with far less number of nodes and elements, thus lessen the computational load. In general, the cMesh generation is affected by the quality of feature maps derived from MRI. In this study, we have tested various feature maps created based on the improved differential geometry measures for more effective cMesh head models. As performance indices, correlation coefficient (CC), root mean squared error (RMSE), relative error (RE), and the quality of cMesh triangle elements are used. The results show that there is a significant variation according to the characteristics of specific feature maps on cMesh generation, and offer additional choices of feature maps to yield more effective and efficient generation of cMeshes. We believe that cMeshes with specific and improved feature map generation schemes should be useful in the FEA of bioelectromagnetic problems.

• Archives of Plastic Surgery
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• v.34 no.1
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• pp.44-51
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• 2007

Purpose: Blow-out fracture is one of the most common fractures in facial trauma. It is diagnosed by Computed Tomography(CT) scan, which is considered as the most effective diagnostic tool. Since, the Picture Archiving Communication System(PACS) has been provided recently to many hospitals, doctors are more familiar with imaging software of PACS. Because this software has many useful measuring tools, doctors can measure orbital structure easily and make a plan for treatment with its data. Therefore, authors intended to analyze the data of orbital structure measured with PACS imaging software and evaluate its usefulness. Methods: The charts and CT images of 100 patients, which were 50 patients with medial wall fracture and 50 patients with floor fracture, were reviewed. Patients were selected by pre-determined criteria and their CT images were measured with image software of PACS. 'Extraocular muscle thickness', 'Defect ratio'(ratio of defect area to normal area) and 'Globe position index' were measured and analyzed statistically. Results: The thickness of inferior rectus muscle and medial rectus muscle was simultaneously increased in acute-stage of blow-out fracture. The medial rectus muscle was more thickened in medial wall fracture and inferior rectus was more thickened in floor fracture, respectively. In acute blow-out fracture, globe position is exophthalmic rather than enophthalmic. Especially in floor fracture, numerical value summed up thickness of all extraocular muscle is correlated to the defect ratio and globe position index. Conclusion: Clinicians can decide globe position or presume defect ratio in inferior wall fracture by measurement of CT image in acute blow-out fracture using PACS.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.1
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• pp.33-40
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• 2013

Since most of yacht sails are made of thin fabric, they form cambered sail shape that can efficiently generate lift power by aerodynamic interaction and by external force delivered from supporting structures such as mast and boom. When the incident flow and external force alter in terms of volume or condition, the shape of sail also change. This deformation in shape has impact on the peripheral flow and aerodynamic interaction of the sail, and thus it is related to the deformation of the sail in shape again. Therefore, the precise optimization of aerodynamic performance of sail requires fluid-structure interaction (FSI) analysis. In this study, the simplified sail without camber was under experiment for one-way FSI that uses the result of flow analysis to the structural analysis as load condition in an attempt to fluid-structure interaction phenomenon. To confirm the validity of the analytical methods and the reliability of numerical computation, the difference in deformation by the number of finite element was compared. This study reproduced the boundary conditions that sail could have by rigs such as mast and boom and looked into the deformation of sail. Sail has non-linear deformation such as wrinkles because it is made of a thin fabric material. Thus non-linear structural analysis was conducted and the results were compared with those of analysis on elastic material.

• Tunnel and Underground Space
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• v.10 no.4
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• pp.533-543
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• 2000

Deformation behavior and stability of vertical pipeline subjected to underground excavation have been studied by means of numerical analysis. Vortical ground displacements cause the pipe to be compressed, while horizontal ones cause it to be bent. In that region the vertical pipeline meets with the induced compressive stress and bending stress. In addition horizontal rock stress subjected to underground excavation may press the tube in its radial direction and it finally produces the tangential stress of pipe. In this study active gas well system is considered as an example of vertical pipelines. Factor analysis has been conducted which has great influence on the pipeline behavior. Three case studies are investigated which have the different pillar widths and gas well locations in pillar. For example, where overburden depth is 237.5 m and thickness of coal seam is 2.5 m, chain pillar of 45.8 m width in the 3-entry longwall system is proved to maintain safely the outer casing of gas welt which is made of API-55 steel, 10$\frac{3}{4}$ in. diameter and 0.4 in. thickness. Finally an active gas well which was broken by longwall mining is analyzed, where the induced shear stress turn out to exceed the allowable stress of steel.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.42 no.4
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• pp.183-193
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• 2019

Process mining is an analytical technique aimed at obtaining useful information about a process by extracting a process model from events log. However, most existing process models are deterministic because they do not include stochastic elements such as the occurrence probabilities or execution times of activities. Therefore, available information is limited, resulting in the limitations on analyzing and understanding the process. Furthermore, it is also important to develop an efficient methodology to discover the process model. Although genetic process mining algorithm is one of the methods that can handle data with noises, it has a limitation of large computation time when it is applied to data with large capacity. To resolve these issues, in this paper, we define a stochastic process tree and propose a tabu search-genetic process mining (TS-GPM) algorithm for a stochastic process tree. Specifically, we define a two-dimensional array as a chromosome to represent a stochastic process tree, fitness function, a procedure for generating stochastic process tree and a model trace as a string of activities generated from the process tree. Furthermore, by storing and comparing model traces with low fitness values in the tabu list, we can prevent duplicated searches for process trees with low fitness value being performed. In order to verify the performance of the proposed algorithm, we performed a numerical experiment by using two kinds of event log data used in the previous research. The results showed that the suggested TS-GPM algorithm outperformed the GPM algorithm in terms of fitness and computation time.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.12
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• pp.1343-1352
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• 1992

This paper presents a new and easy method to obtain the Fourier transforms of the n-th order cosine-pulses whose maximum amplitudes are uniform. The new method is focused on deriving a formula which is recursively related following their orders and can be well applied to some numerical solutions. On the other hand, this method also offers more compact procedures in view of analytical solutions than the conventional methods because the results are consist of the sum of two functions which are easily calculated. Especially, the formula can be represented as a complete recursion by the separation of coefficients originated by the authors and the resulting difference equation is given by the sum of the original 'sinc' functions shifted by some symmetrical factors and multiplied by some constants. The constants are easily decided from the binomial coefficients and the shifting factors from the corresponding exponential differences in the expansion of $(a+b)^n$.