• Journal of Korean Association for Spatial Structures
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• v.7 no.4
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• pp.89-96
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• 2007

The fundamental frequency maximization of beam structures is carried out by using strain energy based topology optimization technique. It mainly uses the modal strain energy distributions induced by the mode shapes of the structures. The modal strain energy to be minimized is employed as the objective function and the initial volume of structures is adopted as the constraint function. The resizing algorithm devised from the optimality criteria method is used to update the hole size of the cell existing in each finite element. The beams with three different boundary conditions are used to investigate the optimum topologies against natural mode shapes. From numerical test, it is found to be that the optimum topologies of the beams produced by the adopted technique have hugh increases in some values of natural frequencies and especially the technique is very effective to maximize the fundamental frequency of the structures.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.7
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• pp.574-579
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• 2016

Grid systems used in previous studies were determined to be valid only if the length between the perpendiculars in a model ship was in the range of 6-8 m, and the maximum dynamic trim angle was smaller than $1^{\circ}$. The application of the grid system to a small fishing boat can create numerical instability because the dynamic trim of small boats is generally larger than $3^{\circ}$, and their Froude numbers are in the range of 0.3-0.8. In the present study, resistances of a small fishing boat were stably obtained by reducing the length between the center of buoyancy and the inlet boundary of the numerical domain, and by refining grid cells vertically in a region that would be swept by a free surface. The effective power of the small fishing boat was predicted based on the ITTC-1978 two-dimensional analysis. By using the results of previous towing tank tests, the coefficient of quasi-propulsive efficiency and the brake horsepower at a design draft were calculated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.895-906
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• 2014

A fundamental study of the dynamically penetrating anchor (DPA - colloquially known as torpedo anchor) embedded into deep seabed was conducted using measurement data and numerical approaches. Numerical simulation of such a structure penetration was often suffered by severe mesh distortion arising from very large soil deformation, complex contact condition and nonlinear soil behavior. In recent years, a Coupled Eulerian-Lagrangian method (CEL) has been used to solve geomechanical boundary value problems involving large deformations. In this study, 3D finite element analyses using the CEL formulation are carried out to simulate the construction process of dynamic anchors. Through comparisons with results of field measurements, the CEL method in the present study is in good agreement with the general trend observed by in-situ measurements and thus, predicts a realistic large deformation movement for the dynamic anchors by free-fall dropping, which the conventional FE method cannot. Additionally, the appropriate parametric studies needed for verifying the characteristic of dynamic anchor are also discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.484-491
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• 2007

Numerical experiments using a numerical wave tank have been performed to verier the nonlinear interaction between monochromatic waves and a submerged horizontal plate. As a model for numerical wave tank, we used a higher-order Boundary Element Method(BEM) based on fully nonlinear potential flow theory and CADMAS-SURF for solving Navier Stokes equations and exact free surface conditions. Both nonlinear models are able to predict the higher harmonic generation in the shallow water region over a submerged horizontal plate. CADMAS-SURF, which involves the viscous effect, can evaluate the higher harmonic generation by flow separation and vortices at the each ends of plate. The comparison of reflection and transmission coefficients with experimental results(Patarapanich and Cheong, 1989) at different lengths and submergence depths of a horizontal plate are presented with a good agreement. It is found that the transfer of energy from the incident fundamental waves to higher harmonics becomes larger as the submergence depth ratio decreases and the length ratio increases.

• Journal of the Korean Society of Groundwater Environment
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• v.4 no.2
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• pp.61-72
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• 1997

With increasing activities for groundwater withdrawal and for the construction of underground cavern in the coastal areas, the seaward flow of groundwater has been disturbed or even reversed, resulting in seawater intrusion in aquifers. This phenomenon would be attributed to the freshwater contamination and the corrosion of steel materials. The hydrogeological and geochemical investigations have performed to characterize the seawater intrusion into the underground caverns located in the coastal area. Assumimg the inland aquifer as unconfined one, we have found out that the theoretical interface of freshwater-seawater is far different from the pathways identified. In the study site, the main pathways of seawater intrusion into the underground cavern are characterized as the sub-horizontal fractures (zones). The seawater intrusion in granitic terrane would depend mainly on the characteristics of conductive fracture system developed along the coastal area.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.39-46
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• 2019

A three-dimensional flow simulation model for high flow concrete was developed using Incompressible Smoothed Particle Hydrodynamics (ISPH), which can solved Navier-Stokes equation with the assumption of a fluid to be incompressible. For the simulation, a computer program code for ISPH was implemented with MATALB programming code. A piecewise cubic spline function was used for the kernel function of ISPH. Projetion method was used to calculate the velocity and pressure of particles as a function of time. Fixed ghost particle was used for wall boundary condition. Free surface boundaries were determined by using virtual density of particles. In order to validate the model and the code, the simulation results of slump flow test, $T_{500}$ test and L-box test were compared with experimental ones. The simulation results were well matched with the experimental results. The simulation described successfully the characteristics of the flow phenomenon according to the change of the viscosity and yield stress of high flow concrete.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.581-592
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• 2007

This paper deals with the elastica of deflected cantilever column with the constant volume. The columns are subjected to combined loads consisted of an axial compressive load and a couple moment at the free end. Differential equations governing the elastica of such column are derived, in which both the effects of taper type and shear deformation are included. Three kinds of taper types are considered: linear, parabolic and sinusoidal tapers. Differential equations are solved numerically to obtain the elastica of objective columns. The effects of various system parameters on the elastica are investigated extensively. Experimental studies were carried out in order to verify the theoretical results of non-linear behavior of the elasticas.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.114-119
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• 2007

This paper introduces modal test of the 2nd stage structure of KSLV-I which is composed to satellite, PLA(Payload Adapter), EB(Equipment Bay), KMS(Kick Motor Support) and KM(Kick Motor) without PLF(Payload Fairing). In this test, to simulate free-free boundary condition, test object was hung by 4 bungee cords and excited by using impact hammer. From this test, dynamic properties of the 2nd stage structure of KSLV-I can be obtained. Modal test data are analyzed by using TDAS(Test Data Analysis Software). As the result, modal parameters and mode shapes below 100Hz of the 2nd stage of KSLV-I were identified.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.65-73
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• 1987

An efficient plate bending finite element has been developed using higher-order inplane displacement profiles of the plate. The 6-noded, 21-d.o.f. triangular element including shear deformation effect has been derived from the plate-like continuum by the Galerkin's weighted residual method. Square plate examples were tested with selected element meshes and several aspect ratios for their static behavior under uniformly distributed load. The result of the example tests indicated consistently good performance of the present higher-order plate bending element in comparison with the thin and thick plate solution and other existing finite element solutions.

• Composites Research
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• v.12 no.4
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• pp.17-24
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• 1999

Finite element analysis and experiment are performed to investigate residual deformation induced by the repair of composite shell structures using a prepreg patch method. The finite element program is developed on the basis of a three-dimensional degenerated shell element and the first order shear deformation theory. The results analyzed for the laminated shell with free boundary conditions are compared with strains measured during the prepreg patch repair. Final residual stresses occur greatly near the patch when the laminated shell with all edges clamped is repaired using the prepreg patch. Stacking sequences of the laminated shell and patch affect significantly the residual stresses which occur even if they are the same.