• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.339-342
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• 2003

This paper newly proposes a mesh regularization method for the enhancement of the efficiency in sheet metal forming analysis. The regularization method searches for distorted elements with appropriate searching criteria and constructs patches including the elements to be modified. Each patch is then extended to a three-dimensional surface in order to obtain the information of the continuous coordinates. In constructing the surface enclosing each patch, NURBS(Non-Uniform Rational B-Spline) surface is employed to describe a three-dimensional free surface. On the basis of the constructed surface, each node is properly arranged to form unit elements as close as to a square. The analysis results with the proposed method are compared to the results from the direct forming analysis without mesh regularization in order to confirm the validity of the method.

• ETRI Journal
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• v.27 no.2
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• pp.235-238
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• 2005

A new mesh reconstruction scheme for approximating a surface from a set of unorganized 3D points is proposed. The proposed method, called a shrink-wrapped boundary face (SWBF) algorithm, produces the final surface by iteratively shrinking the initial mesh generated from the definition of the boundary faces. SWBF surmounts the genus-0 spherical topology restriction of previous shrink-wrapping-based mesh generation techniques and can be applied to any type of surface topology. Furthermore, SWBF is significantly faster than a related algorithm of Jeong and others, as SWBF requires only a local nearest-point-search in the shrinking process. Our experiments show that SWBF is very robust and efficient for surface reconstruction from an unorganized point cloud.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2242-2251
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• 1993

The mesh-based frictional contact model has been developed which does not rely on the spatial derivatives of the tool surface. Only points on the surface are evaluated from the description. which can then be simplified because of the relaxed demands placed on it. The surface tangents, normals, and corresponding derivatives at each finite-element node are evaluated directly from the finite-element mesh, in terms of the connecting nodal positions. The advantages accrue because there is no longer a need for a smooth tool surface to assure reasonable normals and derivatives. Furthermore, it can be shown that the equilibrium equations can only be properly written with a special normal derived from the mesh itself. The validity, accuracy, computation time, and stability of mesh-based contact model were discussed with the numerical examples of rounded flat-top and rough, flat-top rounded punch forming operations. Also, the forming process of a automobile inner panel section was simulated for testing the robustness of new contact model. In the discussion, the superiority of new model was examined, comparing with tool-based contact one.

• Journal of Ceramic Processing Research
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• v.23 no.4
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• pp.436-442
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• 2022

Gallium nitride (GaN) substrates were ground in two different grinding wheel abrasive sizes of 270 and 800-mesh, and thechange in surface morphologies of the substrates and the depth of subsurface damage (SSD) were observed. With the 800-meshgrinding wheel, the surface roughness (SR) and the depth of SSD of the sample tended to decrease, which was not the casewith the 270-mesh grinding wheel. In the X-ray rocking curve, the sample exhibited some compressive stress with the 270-meshgrinding wheel, but with the 800-mesh grinding wheel, it demonstrated the occurrence of tensile stresses in the sample and adecrease in full width at half maximum (FWHM), which confirms an improvement in the crystallinity. In the Raman spectra,the compressive stress of the 270-mesh grinding wheel and the tensile stress of the 800-mesh grinding wheel were confirmedthrough peak shifts. Photoluminescence (PL) spectra confirmed that the intensity ratio of the yellow luminescence increasedat the 800-mesh grinding wheel, and a blue shift occurred further. These results indicate that the SR and the depth of SSDwere proportional to the abrasive grain size of the grinding wheel. At the same time, the increase in PL intensity at specificpeak positions indicates that the stress stemming from the grinding process was concentrated at the crystal surface. The abovemechanism is illustrated in a schematic diagram, which confirms the possibility of improving the grinding efficiency andsubsequent polishing processes in future applications.

• Tribology and Lubricants
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• v.37 no.5
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• pp.189-194
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• 2021

A straightforward, yet effective surface modification method of stainless steel mesh and its interesting anti-wetting characteristics are reported in this study. The stainless steel mesh is electrochemically etched, and the specimen has both micro and nano-scale structures on its surface. This process transforms the two types of mesh specimens known as the regular and dense specimens into hydrophobic specimens without applying any hydrophobic chemical coating process. The fundamental wettability of the modified mesh is analyzed through a dedicatedly designed experiment to investigate the waterproof characteristics, for instance, the penetration threshold. The waterproof characteristics are evaluated in a manner that the modified mesh resists as high as approximately 2.7 times the pressure compared with the bare mesh, i.e., the non-modified mesh. The results show that the penetration threshold depends primarily on the advancing contact angles, and the penetration stop behaviors are affected by the contact angle hysteresis on the surfaces. The findings further confirm that the inexpensive waterproof meshes created using the proposed straightforward electrochemical etching process are effective and can be adapted along with appropriate designs for various practical applications, such as underwater devices, passive valves, and transducers. In general, , additional chemical coatings are applied using hydrophobic materials on the surfaces for the applications that require water-repelling capabilities. Although these chemical coatings can often cause aging, the process proposed in this study is not only cost-effective, but also durable implying that it does not lose its waterproof properties over time.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1564-1569
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• 2007

This study concerns an advanced NURBS surface reconstruction method, which is based on the NURBS surface model fitting to the unstructured point cloud measured from an arbitrary complex shape. The concept of generating a simple triangular mesh model was introduced to generate a quadrilateral mesh model well-representing the topological characteristics of point cloud. The NURBS surface reconstruction processes required the use of the various methodologies such as QEM algorithm, merging scheme of pair-wise triangular mesh, creation algorithm of $G^1$ continuous tensor product NURBS surface patch, and so on. The effectiveness and reliability of the proposed NURBS surface reconstruction method were validated through the simulation results for the geometrically and topologically complex shapes.

• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.592-601
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• 2001

An automatic mesh generation scheme with unstructured quadrilateral elements on trimmed NURBS surfaces has been developed. In this paper NURBS surface geometries in the IGES format have been employed to represent geometric models. For unstructured mesh generation with quadrilateral elements, a domain decomposition algorithm employing loop operators has been modified. As for the surface meshing, an indirect 2D approach is proposed in which both quasi-expanded planes and projection planes are employed. Sampled meshes for complex models are presented to demonstrate the robustness of the algorithm.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.351-358
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• 2001

In this study, for the investigation of effects of several parameters, such as fluid mesh boundary size, cylinder or block shape, dimensions of depth, breadth and length at free suface, and fluid mesh element size to the depth direction on a reliable shock response of finite element model under underwater explosion with consideration of the bulk cavitation analysis of a simplified surface ship was carried out using the LS-DYNA3D/USA code. The shock responses were not much affected by the fluid mesh parameters. The computational time was greatly dependent on the number of DAA boundary segments. It is desirable to reduce the DAA boundary segments in the fluid mesh model, and it is not necessary to cover the fluid mesh boundary to or beyond the bulk cavitation zone just for the concerns about an initial shock wave response. It is also the better way to prefer cylinder type of the fluid mesh model to the block one.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.705-711
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• 2000

This paper presents a fast 3D mesh generation method using a surface based method with a stitching algorithm. This method uses the surface based method since the volume based method that uses 3D Delaunay triangulation can hardly deal with a large scale of scanned points. To reduce the processing time, this method also uses a stitching algorithm: after dividing the whole point data into several sections and performing mesh generation on individual sections, the meshes from several sections are stitched into one mesh. Stitching method prevents the surface based method from increasing the processing time exponentially as the number of the points increases. This method works well with different types of scanned points: a scattered type points from a conventional 3D scanner and a cross-sectional type from CT or MRI.

• Journal of Surface Science and Engineering
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• v.38 no.6
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• pp.212-215
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• 2005

Novel continuous electroforming process equipped with a rotating patterned mandrel, soluble/insoluble anode and multiple stage of rolling wheels was proposed to produce precision nickel mesh, which is known as a very efficient electromagnetic interference (EMI) shielding material. Continuously electroformed nickel deposits showed a tendency to form small-sized particles as the plating solution temperature increased and mandrel rotation speeded up and the applied current density decreased. Along the honeycomb patterns of mandrel, nickel was accurately electrodeposited on the surface of rotating mandrel, but quite different visual/structural characteristics were measured on both sides.