• Journal of Computational Design and Engineering
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• v.1 no.2
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• pp.96-102
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• 2014

In the field of design and manufacturing, there are many problems with managing dynamic states of three-dimensional (3D) objects. In order to solve these problems, the four-dimensional (4D) mesh model and its modeling system have been proposed. The 4D mesh model is defined as a 4D object model that is bounded by tetrahedral cells, and can represent spatio-temporal changes of a 3D object continuously. The 4D mesh model helps to solve dynamic problems of 3D models as geometric problems. However, the construction of the 4D mesh model is limited on the time-series 3D voxel data based method. This method is memory-hogging and requires much computing time. In this research, we propose a new method of constructing the 4D mesh model that derives from the 3D mesh model with continuous rigid body movement. This method is realized by making a swept shape of a 3D mesh model in the fourth dimension and its tetrahedralization. Here, the rigid body movement is a screwed movement, which is a combination of translational and rotational movement.

• KIEAE Journal
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• v.16 no.1
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• pp.89-94
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• 2016

This study is part of three-dimensional(3D) heat transfer analysis program developmental process. The program is being developed without it's own built in 3D-modeller. So 3D-model must be created from another 3D-modeller such as generic CAD programs and imported to the developed program. After that, according to the 3D-geometric data form imported model, 3D-mesh created for numerical calculation. But the 3D-model created from another 3D-modeller is likely to have errors in it's geometric data such as mismatch of position between vertexes or surfaces. these errors make it difficult to create 3D-mesh for calculation. These errors are must be detected and cured in the pre-process before creating 3D-mesh. So, in this study four kinds of filters and functions are developed and tested. Firstly, 'vertex error filter' is developed for detecting and curing for position data errors between vertexes. Secondly, 'normal vector error filter' is developed for errors of surface's normal vector in 3D-model. Thirdly, 'intersection filter' is developed for extracting and creating intersection surface between adjacent objects. fourthly, 'polygon-line filter' is developed for indicating outlines of object in 3D-model. the developed filters and functions were tested on several shapes of 3D-models. and confirmed applicability. these developed filters and functions will be applied to the developed program and tested and modified continuously for less errors and more accuracy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.247-256
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• 2019

In this study, 2-D Godunov type finite volume model which can apply the mixed mesh including triangular and quadrilateral meshes for flood inundation modeling is used to compare and analyze the flood height, flood extent and model execution time according to mesh type and resolution. The study area is the Upton-upon Severn watershed in Great Britain, where the flood occurred for 22 days from October 29 to November 19, 2000. For the flood modeling, topographic data were constructed using high resolution LiDAR (Light Detection And Ranging). The results of the 2-D flood modeling by the mesh type and resolution were compared with four ASAR (Airborne Synthetic Aperture Radar) images captured during the flood period. This study has shown that flood height and extent can vary greatly depending on the mesh type and resolution, even if identical topography and boundary conditions are used, and that the selection of appropriate mesh type and resolution for the purpose and situation of the 2-D flood modeling is necessary.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.935-937
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• 1993

This paper presents a three dimensional automatic mesh generation scheme for the boundary element method, and this scheme can be applicable to practical problems of complex shape. The geometry of the problem is expressed as an assemblage of linear Coon's surfaces, and each surface is made up of four edge curves which are defined in the form of a parametric function. Curves are automatically segmented according to their characteristics. With these segments of curves, interior points and triangular mesh elements are generated in the parametric plane using Lindholm's method, and then their projection on the real surface forms the initial mesh. The refinement of initial mesh is performed so that the discrete triangular planes are close to the real continuous surfaces. The bisection method is used for the refinement. Finally, interior points in the refined mesh are rearranged so as to make each element be close with an equilateral triangle. An attempt has been made to apply the proposed method to a DY(Deflection Yoke) model.

• Restorative Dentistry and Endodontics
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• v.20 no.2
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• pp.655-669
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• 1995

Restorative procedures can lead to weakening tooth due to reduction and alteration of tooth structure. It is essential to prevent fractures to conserve tooth. Among the several parameters in cavity designs, cavity isthmus is very important. In this study, amalgam 0 cavity was prepared on maxillary first premolar. Two dimensional finite element models were made by serial photographic method and isthmus(1/4, 1/3, 1/2, 2/3 of intercuspal distance) were varied. Three or four-nodal mesh were used for the two dimensional finite element models. The periodontal ligament and alveolar bone surrounding the tooth were excluded in these models. 1S model was sound tooth with no amalgam cavity. B model was assumed perfect bonding between the restoration and cavity wall. Both compressive and tensile forces were distributed directly to the adjacent regions. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed von Mises stress, 1 and 2 directional normal stress and Y and Z axis translation with FEM software Super SAPII Version 5.2 (Algor Interactive System Co.) and hardware 486 DX2 PC. The results were as :follows : 1. 1S model was slightly different with 1B model in stress distibution. 1S, 2B, 3B, 4B models showed similiar stress distribution. 2. 1S model and four B models showed similiar pattern in Y axis and Z axis translation. 3. 1S model and four B models showed the bending phenomenon in the translation. 4. As increasing of the width of the cavity, experimental group was similiar with the control group in stress distribution. 5. As increasing of the width of the cavity, experimental group was similiar with the control group in Y and Z axis tranlation.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.10
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• pp.46-55
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• 1996

As industrial standard data, the STL format which approximates three dimensional CAD model to triangular facets, is used for RP(Rapid Prototyping) system in recent days. Because most RP system take the only form of two dimensional line segments as an input stream inspite of its imperfectness while converting into STL format, a CAD model is converted into a standard industrial format which is composed of many triangular facets. The error verifying process is composed of four main steps, and these are 1) Remove facets with two or more vertices equal to each other. 2) Fix overlapping error such as more than three facets adjacent to anedge. 3) Fill holes in the mesh by using Delaunay triangulation method. 4) Correct the wrong direction and normal vectors. This paper is concerned with serching the mentioned errors in advance and modifying them.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.325-333
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• 2000

The aerodynamics of the Wells turbine has been studied using a 3-dimensional, unstructured mesh flow solver for the Reynolds-averaged Navier-Stokes equations. The basic feature of the Wells turbine is that even though the cyclic airflow produces oscillating axial forces on the airfoil blades, the tangential force on the rotor is always in the same direction. Geometry used to define the 3-dimensional numerical grid is based upon that of an experimental test rig. The 3-dimensional Wells turbine model, consisting of approximate 220,000 cells is tested at four axial flow rates. In the calculations the angle of attack has been varied between $10^{\circ}$ and $30^{\circ}$ of blades. Representative results from each case are presented graphically and analyzed. It is concluded that this method holds much promise for future development of Wells turbines.

• Structural Engineering and Mechanics
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• v.83 no.4
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• pp.435-449
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• 2022

Constitutive modeling that could reasonably predict and effectively evaluate the post-peak structural behavior while eliminating the mesh-dependency in numerical simulation remains to be developed for general engineering applications. Based on the previous work, a simple one-dimensional modeling procedure is proposed to predict and evaluate the post-peak response, as characterized by the evolution of localized strain field, of a steel member to monotonically uniaxial tension. The proposed model extends the classic one-dimensional softening with localization model as introduced by (Schreyer and Chen 1986) to account for the localization length, and bifurcation and rupture points. The new findings of this research are as follows. Two types of strain-softening functions (bilinear and nonlinear) are proposed for comparison. The new failure criterion corresponding to the constitutive modeling is formulated based on the engineering strain inside the localization zone at rupture. Furthermore, a new mathematical expression is developed, based on the strain rate inside and outside the localization zone, to describe the displacement field at which bifurcation occurs. The model solutions are compared with the experimental data on four low-carbon cylindrical steel bars of different lengths. For engineering applications, the model solutions are also compared to the experimental data of a cylindrical steel bar system (three steel bars arranged in series). It is shown that the bilinear and nonlinear softening models can predict the energy dissipation in the post-peak regime with an average difference of only 4%.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.2
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• pp.121-129
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• 1992

A two-dimensional numerical tidal model is formulated to reproduce tides in the northeastern Yellow-Sea, Seohan Bay. The model was formulated on spherical grid system with mesh resolution of 1' latitude by 4/3' longitude. As a first step, tidal distribution of four major tidal constituents are computed and compared with coastal observation. Independent tidal charts for the M$_2$, S$_2$, $K_1$, and $O_1$ tides were presented. Residual tidal currents and tidal energy flux were also computed.

• Wind and Structures
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• v.28 no.1
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• pp.31-47
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• 2019

The accurate prediction of snow distributions under the wind action on roofs plays an important role in designing structures in civil engineering in regions with heavy snowfall. Affected by some factors such as building shapes, sizes and layouts, the snow drifting on roofs shows more three-dimensional characteristics. Thus, the research on three-dimensional snow distribution is needed. Firstly, four groups of stepped flat roofs are designed, of which the width-height ratio is 3, 4, 5 and 6. Silica sand with average radius of 0.1 mm is used to model the snow particles and then the wind tunnel test of snow drifting on stepped flat roofs is carried out. 3D scanning is used to obtain the snow distribution after the test is finished and the mean mass transport rate is calculated. Next, the wind velocity and duration is determined for numerical simulations based on similarity criteria. The adaptive-mesh method based on radial basis function (RBF) interpolation is used to simulate the dynamic change of snow phase boundary on lower roofs and then a time-marching analysis of steady snow drifting is conducted. The overall trend of numerical results are generally consistent with the wind tunnel tests and field measurements, which validate the accuracy of the numerical simulation. The combination between the wind tunnel test and CFD simulation for three-dimensional typical roofs can provide certain reference to the prediction of the distribution of snow loads on typical roofs.