• Journal of the Speleological Society of Korea
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• no.82
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• pp.17-25
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• 2007

The use of a low-frequency cave radio can also verify survey accuracy. A receiving unit on the surface can pinpoint the depth and location of a transmitter in a cave passage by measurement of the geometry of its radio waves. A survey over the surface from the receiver back to the cave entrance forms an artificial loop with the underground survey, whose loop-closure error can then be determined. In the past, caves were reluctant to redraw complex cave maps after detecting survey errors. Today, computer cartography can automatically redraw cave maps after data has been corrected.

• Journal of Korea Multimedia Society
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• v.13 no.12
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• pp.1748-1759
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• 2010

We extend the octree subdivision process from Cartesian coordinates to spherical coordinates to develop more efficient space-partitioning structure for surface models. As an application of the proposed structure, we apply the octree subdivision in spherical coordinates ("S-Octree") to geometry compression in progressive mesh coding. Most previous researches on geometry-driven progressive mesh compression are devoted to improve predictability of geometry information. Unlike this, we focus on the efficient information storage for the space-partitioning structure. By eliminating void space at initial stage and aligning the R axis for the important components in geometry information, the S-Octree improves the efficiency in geometry information coding. Several meshes are tested in the progressive mesh coding based on the S-Octree and the results for performance parameters are presented.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.409-414
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• 2010

This paper describes the surface form measurement of a spherical smooth surface by using single shot off-axis Fizeau interferometry. The demodulated phase map is obtained and unwrapped to remove the $2\pi$ ambiguity. The unwrapped phase map is converted to height and the 3D surface height of the surface object is reconstructed. The results extracted from the single shot off-axis geometry are compared with the results extracted from four-frame phase shifting in-line interferometry, and the results are in excellent agreement.

• Journal of the Korean Mathematical Society
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• v.43 no.6
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• pp.1339-1355
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• 2006

This paper develops in detail the differential geometry of ruled surfaces from two perspectives, and presents the underlying relations which unite them. Both scalar and dual curvature functions which define the shape of a ruled surface are derived. Explicit formulas are presented for the computation of these functions in both formulations of the differential geometry of ruled surfaces. Also presented is a detailed analysis of the ruled surface which characterizes the shape of a general ruled surface in the same way that osculating circle characterizes locally the shape of a non-null Lorentzian curve.

• Tribology and Lubricants
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• v.25 no.3
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• pp.141-149
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• 2009

The effect of micro-cavities fabricated using laser surface texturing (LST) technique on polyoxymethylene (POM) surface was studied in terms of heat affected zone (HAZ), cavity geometry, surface roughness, deformation of cavity along with sliding cycles, and tribological characteristics. Cavity process parameters were lamp current, process time, and the stream of air used to minimize the flow of molten polymer into cavity. Especially, the deformation of cavity geometry was extensively studied to provide deep insight into morphological analysis of the cavities. Also, this paper presents the behavior of friction and wear of POM specimens as a function of sliding cycles.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.401-407
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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 state variables calculated from its original mesh geometry are mapped into the new mesh geometry for the next stage or incremental step of a forming analysis. 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.

• Journal of Industrial Technology
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• v.14
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• pp.109-117
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• 1994

To satisfy the requirement for the precision and productivity of machine tools, we need the technique to predict the surface roughness of workpiece under various cutting conditions. The surface roughness is mainly influenced by the ideal roughness i. e., the roughness by feeding quantity and geometry of the tool. In this paper, the surface roughness is divided into three zones and the mathematical models of the three zones are obtained, in consideration of the feeding conditions and tool geometry. Using the mathematical models, we developed a program to calculate the maximum feeding quantity satisfying the required surface roughness of the workpiece. The program is used to calculate the maximum feed for two kinds of the bites used under the real cutting condition.

• Journal of Ocean Engineering and Technology
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• v.14 no.1
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• pp.29-36
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• 2000

Surface micro-crack grows along intergranular or transgranular region of crystal grains. But if it meets the barrier such as sessile dislocation and precipitates it loses straightness and deflects. Investigators had many difficulties in estimating fatigue life of smooth specimen because of the random distribution growth and coalescence of surface micro-cracks. The path of surface micro-crack has irregularity due to nonhomogeneous microstructure. Euclidian geometry can't quantify the shape of surface micro-crack but fractal geometry can. Therefore in this paper fractal dimension is measured at various stage of cycle ratio and estimated cycle ratio in 2024-T3 aluminium, alloy.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.27-33
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• 2000

This paper presents a method for determining machining parameters in 3-dimentional electrical discharge machining(EDM). The parameters are the peak value of currents, the pulse-on time, and the pulse-off time. It is known that they influence the performance of EDM more than the other else. The parameters are determined from the discharge area between a tool electrode and a work piece. The discharge area is directly influenced by the geometry of a tool surface and the tool discharge position. The discharge area on a tool discharge position is calculated from intersection curves between the tool surface and a horizontal plane. The grid search method is applied to determine the intersection curves. An example is introduced to show that the machining parameters are obtained from the surface geometry of a tool electrode.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.3
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• pp.35-47
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• 1996

A surface panel method treating a boundary-value problem of the Dirichlet type is presented to design a three dimensional body with free surface corresponding to a prescribed pressure distribution. An integral equation is derived from Green's theorem, giving a relation between total potential of known strength and the unknown local flux. Upon discretization, a system of linear simultaneous equations is formed including free surface boundary condition and is solved for an assumed geometry. The pseudo local flux, present due to the incorrect positioning of the assumed geometry, plays a role f the geometry corrector, with which the new geometry is computed for the next iteration. Sample designs for submerged spheroids and Wigley hull and carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. For the calculation of the wave resistance, normal dipoles and Rankine sources are distributed on the body surface and Rankine sources on the free surface. The free surface boundary condition is linearized with respect to the oncoming flow. Four-points upwind finite difference scheme is used to compute the free surface boundary condition. A hyperboloidal panel is adopted to represent the hull surface, which can compensate the defects of the low-order panel method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but by experiment.