• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.46.1-46.1
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• 2019

We present an accurate and efficient method to calculate the gravitational potential of an isolated system in three-dimensional Cartesian and cylindrical coordinates subject to vacuum (open) boundary conditions. Our method consists of two parts: an interior solver and a boundary solver. The interior solver adopts an eigenfunction expansion method together with a tridiagonal matrix solver to solve the Poisson equation subject to the zero boundary condition. The boundary solver employs James's method to calculate the boundary potential due to the screening charges required to keep the zero boundary condition for the interior solver. A full computation of gravitational potential requires running the interior solver twice and the boundary solver once. We develop a method to compute the discrete Green's function in cylindrical coordinates, which is an integral part of the James algorithm to maintain second-order accuracy. We implement our method in the {\tt Athena++} magnetohydrodynamics code, and perform various tests to check that our solver is second-order accurate and exhibits good parallel performance.

• Structural Engineering and Mechanics
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• v.43 no.3
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• pp.321-336
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• 2012

As an improvement on the isoparametric element method, the derivation presented in this paper is close to that done by Wang (1990) for the 2-D finite element. We extend this idea to solve 3-D crack problems in this paper. A new displacement modelling is constructed with local solutions of three-dimensional cracks and a quasi-compatible isoparametric element for three-dimensional fracture mechanics analysis is presented. The stress intensity factors can be solved directly by means of the present method without any post-processing. A new method for calculating the stress intensity factors of three-dimensional cracks with complex geometries and loads is obtained. Numerical examples are given to demonstrate the validity of the present method. The accuracy of the results obtained by the proposed element is demonstrated by solving several crack problems. The results illustrate that this method not only saves much calculating time but also increases the accuracy of solutions. Because this quasi-compatible finite element of 3-D cracks contains any singularities and easily meets the requirement of compatibility, it can be easily implemented and incorporated into existing finite element codes.

• Nuclear Engineering and Technology
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• v.27 no.6
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• pp.870-876
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• 1995

In this paper, a new three-dimensional nodal diffusion code which is based on the AFEN methodology is described and tested. The method expands the homogeneous flux within a node in ter-ms of eighteen analytic basis functions satisfying the diffusion equation at any point of the node. And the nodal coupling equations are derived such that nodal balance, current continuity and leakage balance within an infinitesimally small box around the edge are satisfied. To verify its accuracy, the code was applied to the well-known static LMW benchmark problem and a small core benchmark problem that has the same material properties as the three-dimensional IAEA benchmark problem and compared with two other codes (QUANDRY, VENTURE). The results show that the code provides good accuracy both in the power distribution and in the effective multiplication factor.

• Journal of Welding and Joining
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• v.13 no.3
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• pp.77-88
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• 1995

A prediction method for determining the welding residual stress by artificial neural network is proposed. A three-dimensional transient thermomechanical analysis has been performed for the CO$_{2}$ arc welding using the finite element method. The first part of numerical analysis performs a three-dimensional transient heat transfer analysis, and the second part then uses the results of the first part and performs a three-dimensional transient thermo-elastic-plastic analysis to compute transient and residual stresses in the weld. Data from the finite element method are used to train a backpropagation neural network to predict the residual stress. Architecturally, the fully interconnected network consists of an input layer for the voltage and current, a hidden layer to accommodate the ailure mechanism mapping, and an output layer for the residual stress. The trained network is then applied to the prediction of residual stress in the four specimens. It is concluded that the accuracy of the neural network predicting method is fully comparable with the accuracy achieved by the traditional predicting method.

• Journal of Conservation Science
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• v.36 no.4
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• pp.264-274
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• 2020

The Choijin Lama Temple is a representative example of 19th- to 20th-century architecture. The temple has been damaged by various development pressures and the effect of a harsh continental climate. This study digitalized the entire temple site using three-dimensional scanning to establish the basic data of conservational management and monitoring for spatial changes. A terrestrial laser scanning model of the temple was completed, which showed low registering error vectors (3.73 mm average) and dense point distances. Unmanned aerial vehicle (UAV) photogrammetry was also applied to verify its applicability to the spatial and environmental monitoring of the temple. The results showed that the overall point density of the UAV photogrammetry model is similar within a 10 mm resolution. The relatively low RMSE of UAV photogrammetry from the ground to the uppermost roof indicates the high applicability of integrating it with the terrestrial laser scanning model. The digital documentation of the Choijin Lama Temple is expected to have a great ripple effect on the documentation, conservation, and utilization of Mongolian cultural heritage sites.

• Journal of the Society of Disaster Information
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• v.10 no.1
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• pp.1-14
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• 2014

This paper presents the three-dimensional stress analysis of orthotropic thick plates using the three-dimensional spline strip method based on the theory of elasticity. The orthotropic plates are made of Aragonite crystal and sitka spruce. To demonstrate the convergence and accuracy of the present method, several examples are solved, and results are compared with those obtained by other exact and numerical methods based on the theory of elasticity. Good convergence and accuracy are obtained. The effects of thickness/width ratio, aspect ratio and boundary conditions on normal stress distributions of Aragonite crystal plates and sitka spruce plates are investigated. Moreover, the difference of weak orthotropic and strong orthotropic properties given to the characteristics of stress distributions are also shown.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.12-26
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• 2004

A new treatment of cell-interface flux in AUSM-type methods is introduced to reduce the numerical dissipation. Through analysis of TVD limiters, a criterion for the more accurate prediction of cell-interface state is found out and M-AUSMPW+ is developed by determining the transferred property newly and appropriately within the criterion. The superiority of M-AUSMPW+ is clearly revealed in multi-dimensional flow problems. It can eliminate numerical dissipation effectively in a non-flow aligned grid system. As a result, M-AUSMPW+ is shown to be much more accurate and effective than other previous schemes in multi-dimensional problems. Through a stationary contact discontinuity, a vortex flow, a shock wave/boundary layer interactions and viscous shock tube problems, it is verified that accuracy of M-AUSMPW+ is improved.

• Journal of IKEEE
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• v.14 no.4
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• pp.339-345
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• 2010

So far, many researches have been done to index high-dimensional feature values for fast content-based image retrieval. Still, many existing indexing schemes are suffering from performance degradation due to the curse of dimensionality problem. As an alternative, heuristic algorithms have been proposed to calculate the result with 'high probability' at the cost of accuracy. In this paper, we propose a new extendible hash-based indexing scheme for high-dimensional feature values. Our indexing scheme provides several advantages compared to the traditional high-dimensional index structures in terms of search performance and accuracy preservation. Through extensive experiments, we show that our proposed indexing scheme achieves outstanding performance.

• Structural Engineering and Mechanics
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• v.3 no.2
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• pp.121-133
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• 1995

It is well known that two-dimensional simplified third-order theories satisfy the layer interface continuity of transverse shear strains, thus these theories violate the continuity of transverse shear stresses when two consecutive layers differ either in fibre orientation or material. The third-order theories considered herein involve four/or five dependent unknowns in the displacement field and satisfy the condition of vanishing of transverse shear stresses at the bounding planes of the plate. The objective of this investigation is to examine (i) the flexural response prediction accuracy of these third-order theories compared to exact elasticity solution (ii) the effect of layer interface continuity conditions on the flexural response. To investigate the effect of layer interface continuity conditions, three-dimensional elasticity solutions are developed by enforcing the continuity of different combinations of transverse stresses and/or strains at the layer interfaces. Three dimensional twenty node solid finite element (having three translational displacements as degrees of freedom) without the imposition of any of the conditions on the transverse stresses and strains is also employed for the flexural analysis of the laminated plates for the purposes of comparison with the above theories. These shear deformation theories and elasticity approaches in terms of accuracy, adequacy and applicability are examined through extensive numerical examples.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.4 no.1
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• pp.25-36
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• 1986

Minimum three pairs of model are necessary to determine absolute coordinates of three-dimensional objects. This paper researches the method of analyzing three-dimensional coordinates of all sides of objects by photographing a pair of stereo model through the medium of mirror. An objective lies in improving the accuracy and the efficiency of mirror images method by introducing an error correction function for distortion of the mirror. Projected-onto-mirror points are transformed on the object plane through mirror plane equation. As the result, X-coordinates error is the largest and Y, Z-coordinates error represents about 1mm. Also, accuracy can be improved by introducing correction function for left and right mirror and correcting the distortion of mirror.