• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.279-287
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• 2019

This paper intends to introduce a near-tip grid refinement and to explore its usefulness in the crack analysis by the natural element method (NEM). As a sort of local h-refinement in FEM, a NEM grid is locally refined around the crack tip showing the high stress singularity. This local grid refinement is completed in two steps in which grid points are added and Delaunay triangles sharing the crack tip node are divided. A plane-state plate with symmetric edge cracks is simulated to validate the proposed local grid refinement and to examine its usefulness in the crack analysis. The crack analysis is also simulated using a uniform NEM grid for the sake of comparison. The near-tip stress distributions and SIFs that are obtained using a near-tip refined NEM grid are compared with the exact values and those obtained using uniform NEM grid. The convergence rates of global relative error to the total number of grid points between the refined and non-refined NEM grids are also compared.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.11-18
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• 2002

In this paper, the method calculating hydroelastic responses of very large floating structure close to a breakwater in waves is presented. The source-dipole distribution method is used to calculate the generalized radiation problem considering breakwater effects and the diffraction problem is analyzed by using the source-dipole distribution andvelocity potential continuation method. The response of a VLFS is approximated by anexpansion in terms of a free-free beam. Calculated model is a VLFS with 1000m in length in a sea with a straight breakwater. The vertical displacements and bonding moments around a VLFS are calculated by variations for distance between a VLFS and a breakwater and incident wave angle to know the effect of a breakwater.

• Journal of Distribution Science
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• v.11 no.12
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• pp.5-11
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• 2013

Purpose - The purpose of this study was to construct a turnover estimation model by investigating research by Park et al. (2006) on the market area of domestic distribution. The study investigated distribution by using a new tool for the turnover estimation technique. This study developed and discussed the turnover estimation technique of Park et al. (2006), applying it to a large-scale retailer in "D"city that was suitable for on-the-spot distribution. It constructed the new model in accordance with test procedures keeping to this retail business location, to apply its procedures to a specific situation and improve the turn over estimation process. Further, it investigated the analysis and procedures of existing turnover estimation cases to provide problems and alternatives for turnover estimation for a large-scale retailer in "D"city. Finally, it also discussed problems and scope for further research. Research design, data, and methodology - This study was conducted on the basis of "virtue" studies. In other words, it took into account the special quality of the structure of Korea's trade zones. The researcher sought to verify a sale estimate model for use in a distribution industry's location. The main purpose was to enable the sale estimate model (that is, the individual model's presentation) to be practically used in real situations in Korea by supplementing processes and variables. Results - The sale estimate model is constructed, first, by conducting a data survey of the general trading area. Second, staying within the city's census of company operating areas, the city's total consumption expenditure is derived by applying the large-scale store index. Third, the probability of shopping is investigated. Fourth, the scale of sales is estimated using the process of singularity. The correct details need to be verified for the model construction and the new model will need to be a distinct sale estimate model, with this being a special quality for business conditions. This will need to be a subsequent research task. Conclusions - The study investigated, tested, and supplemented the turnover estimation model of Park et al. (2006) in a market area in South Korea. Supplementation of some procedures and variables could provide a turnover estimation model in South Korea that would be an independent model. The turnover estimation model is applied, first, by undertaking an investigation of the market area. Second, a census of the intercity market area is carried out to estimate the total consumption of the specific city. Consumption is estimated by applying indexes of large-scale retailers. Third, an investigation is undertaken on the probability of shopping. Fourth, the scale of turnover is estimated. Further studies should investigate each department as well as direct and indirect variables. The turnover estimation model should be tested to construct new models depending on the type of region and business. In-depth and careful discussion by researchers is also needed. An upgraded turnover estimation model could be developed for Korea's on-the-spot distribution.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2001.11a
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• pp.168-182
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• 2001

A new concept of stock preparation for the increase of bending stiffness in paper and board was proposed. The 'stiff' fibers, which were mechanically not treated or treated slightly to remove fiber curls, were combined with extensively refined fibers (ERF) to produce higher stiffness papers than those where the whole fibers were refined. The combination of 'stiff' fibers and extensively refined fibers produced higher stiffness at the same tensile strength than the control furnish, in which all the fibers are refined together. In this concept, the fibers from recycled papers could be as much useful as the virgin fibers as long as they are stiff enough or they can produce highly bondable fiber fractions by extensive refining. Use of the concept in real paper mill needs considerations such as increase of refining energy, slower drainage, and added drying burden, but savings of wood fibers, utilization of more recycled fibers, and increase of physical properties may offset the negative concerns. The success of this concept implementation in mills, therefore, depends on the wood fiber market around the mills and the proper decision making for the papermakers about how to apply this concept.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.667-674
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• 1992

Recently advantages in composite and light weight material technique have led to the increased use of structural adhesives in various industries. In spite of such wide application of the adhesive joints, the evaluation method of fracture strength and design methodology of them, have not been established. In this study finite element method, theoretical and experimental analyses were investigated according to changes of lap length and adhesive for adhesive single-lap joint. As the results, the strength evaluation of adhesive joint by conventional nominal stress, was pointed out inadequate strength evaluation and design method regardless stress singularity, stress distribution and crack propagation in its adhesive layer. Also, it was examined the problems to apply fracture mechanics by means of static and fatigue test.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.1
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• pp.45-50
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• 2013

In this study, lumped-vortex element method and thin airfoil theory were used to analyze aerodynamic characteristics of airfoils with relative motion that had camber lines of NACA $44{\times}{\times}$ airfoil in 2-dimensional unsteady incompressible potential flow. Velocity disturbance due to airfoil was calculated by lumped-vortex element model and force distribution on airfoil by unsteady Bernoulli's equation. Variables in relative motion were considered the period p, the amplitude of flapping $A_f$ and pitching $A_p$, and the phase difference between flapping and pitching ${\phi}_p$ and the angle of attack ${\alpha}$. Due to movement of an airfoil, dag was induced in 2-dimensional unsteady incompressible potential flow. The numerical results show that the aerodynamic characteristics of the airfoil with flapping and pitching at the same time are illustrated. Especially the mean lift coefficient became smaller, but drag coefficient became larger.

• Journal of Ship and Ocean Technology
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• v.9 no.2
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• pp.21-28
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• 2005

Recently moored offshore vessels like as FPSO(Floating Production Storage Offloading) are frequently deployed in seas for a long time. For successful operation, the motion behavior of such a vessel in waves must be clarified in advance either theoretically or experimentally. It is of particular interest to examine the behavior, when swells are superposed to seas with different incident angle. Such a situation is actually reported in some offshore oilfield. In this paper, the motion of a FPSO in irregular waves including swells is studied in time domain. Hydrodynamic coefficients and wave forces are calculated in frequency domain using three-dimensional singularity distribution method. Time memory function and added mass at infinite frequency are derived by Fourier transform utilizing hydrodynamic damping coefficients. In the process, the numerical accuracy of added mass at infinite frequency is carefully examined in association with free decay simulations. It is found from numerical simulations that swells significantly affect the vertical motion of FPSO mainly because of their longer period compared to the ordinary sea waves. In particular, the roll motion is largely amplified because the dominant period of swell is closer to the roll natural period than that of seas.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.58-65
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• 1992

In this paper, wave resistance for a submerged body is calculated by a higher order panel method. The Neumann-Kelvin problem is solved by the source or normal dipole distribution method. The body surface is represented by a bicubic B-spline and the singularity strengths are approximated by a bilinear form. The results calculated by the higher order panel method are compared with those by the lowest order panel method developed by Hess & Smith. The convergence rate of the higher order panel method is much better than the lowest order panel method. But the wave resistance calculated by the higher order panel method still shows discrepancy with an analytic solution at low Froude number like that by the lowest order panel method.

• Bulletin of the Society of Naval Architects of Korea
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• v.19 no.4
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• pp.39-45
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• 1982

A floating rig, which has been used to develop the ocean resources has a common characteristics with the catamaran ship that it is composed of the two simple hulls. So the motion responses of the floating rig can be predicted theoretically with the aid of the strip method as those of the catamaran. And for the strip method, the two-dimensional hydrodynamic coefficients are the most important inputs to predict the results accurately. In this report, a theoretical method is proposed for calculating two-dimensional hydrodynamic forces and moments acting upon arbitrary shaped twin-hull cylinders, which are forced to make a heaving, swaying and rolling oscillation about their mean position on the free surface of a finite depth water. The theoretical results by making use of the singularity distribution method are presented. The accuracy of the coefficients was confirmed to be reasonable by the comparison with the Ohkusu's results for two circular cylinders in an infinite depth water. The depth effects on two-dimensional hydrodynamic coefficients for two circular cylinders are also checked. In some range of wave numbers, large differences in the behavior of hydrodynamic coefficients between for a finite depth and for an infinite depth are shown.

• Journal of Ocean Engineering and Technology
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• v.18 no.6 s.61
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• pp.16-21
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• 2004

This study presents the wave forces for spar platforms. The advantage of a spar platform is that it is easy to manufacture and has excellent to motion characteristics. It is important to precisely determine the wave force acting on spar platforms for their basic design of them. We measur the wave exciting force for both the classic spar and truss spar models, and accomplish the numerical calculation using diffraction theory. The results show that experimental values have good agreement with theoretical values. However it is difficult to accurately estimate the value considering the heave plate of truss spar due to the viscosity.