• Structural Engineering and Mechanics
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• v.54 no.5
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• pp.909-922
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• 2015

The dynamic response and the mooring line tension of a 1/75 scale model of spar-type platform for 2.5 MW floating offshore wind turbine subject to one-dimensional regular harmonic wave are investigated numerically and verified by experiment. The upper part of wind turbine which is composed of three rotor blades, hub and nacelle is modeled as a lumped mass the scale model and three mooring lines are pre-tensioned by means of linear springs. The coupled fluid-rigid body interaction is numerically simulated by a coupled FEM-cable dynamics code, while the experiment is performed in a wave tank with the specially-designed vision and data acquisition system. The time responses of surge, heave and pitch motions of the scale platform and the mooring line tensions are obtained numerically and the frequency domain-converted RAOs are compared with the experiment.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.542-547
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• 2010

Recently, thanks to advanced computational power and numerical techniques, it is made possible to analyze the flow around moving bodies using computational fluid dynamics techniques. In those simulations, moving mesh techniques should be able to represent both the body motion and boundary deformation which are frequently encounterd in fluid-structure interaction and/of six degree-of-freedom problems. There are several moving mesh techniques such as the Laplacian operator based, tension spring based and elastic deformation based methods. In the present study, the Laplacian operator based method was utilized and the results were validated. For the validation, the flow around an oscillating two-dimensional cylinder was simulated and analyzed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.233-240
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• 2017

The flowfield around transonic wing-body configuration was simulated using in-house CFD code and compared with the experimental data to understand the influence of several features of CFD(Computational Fluid Dynamics) ; grid dependency, turbulence models, spatial discretization, and viscosity. The wing-body configuration consists of a simple planform RAE Wing 'A' with an RAE 101 airfoil section and an axisymmetric body. The in-house CFD code is a compressible Euler/Navier-Stokes solver based on unstructured grid. For the turbulence model, the $k-{\omega}$ model, the Spalart-Allmaras model, and the $k-{\omega}$ SST model were applied. For the spatial discretization method, the central differencing scheme with Jameson's artificial viscosity and Roe's upwind differencing scheme were applied. The results calculated were generally in good agreement with experimental data. However, it was shown that the pressure distribution and shock-wave position were slightly affected by the turbulence models and the spatial discretization methods. It was known that the turbulent viscous effect should be considered in order to predict the accurate shock wave position.

• Journal of the Korean Ceramic Society
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• v.55 no.2
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• pp.145-152
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• 2018

Although many bone graft materials have been developed, powder graft materials are somewhat difficult to use in surgery. To solve this problem, a bone graft material in the form of a viscous paste was prepared. Hydroxyapatite was used as a bone graft material, and methyl cellulose was used to impart viscosity. Three cases of samples were prepared, and freeze-dried block type and sintered specimens were made from the paste. The recrystallization of the graft material in a simulated body fluid and the degree of graft adhesion with a tooth were observed by scanning electron microscopy (SEM). The test for cytotoxicity was carried out and the sample was grafted into the back of a mouse to confirm the presence or absence of side effects in the animal's body. Based on these investigations, composites of this type are expected to be applicable for bone grafts.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.214-218
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• 2000

Hydroxyapatite (HA) and $\beta$-tricalcium phosphate ($\beta$-TCP) are bio-compatible materials with bones and teeth. HA has been widely applied as bone substitutes because of chemical stability in vivo, while $\beta$-TCP has higher resorbability than HA when the material is implanted in a bone defect. In the present study, both HA and $\beta$-TCP porous ceramics were soaked in the simulated body fluid in order to investigate the reaction between the materials and the fluid. After the soaking test, carbonate hydroxyapatite was formed on HA surface at 1 week, and then the amount of precipitates increased with increasing period of the soaking test. While $\beta$-TCP was not dissolved in the fluid, carbonate hydroxyaopatite was also formed on $\beta$-TCP surface after 12 weeks, and the amount of precipitates was less than that on HA. In vitro behavior of HA was similar to that in vivo, but in vitro behavior of $\beta$-TCP was not similar to that in vivo.

• The KSFM Journal of Fluid Machinery
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• v.14 no.3
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• pp.33-38
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• 2011

Medicated water electrolysis apparatus, which electrolyzes water into acidic water and alkaline water, was in the spotlight as becoming known the effect of alkaline water. It is known as good for health as removing active oxygen in the human's body and promoting digestion. But, the customers could not get that desired water temperature because these apparatuses are directly connected with a water pipe. So, the cooling system was developed for controlling the temperature of the alkaline water. One of the typical way is to store water in water tank and control the temperature. But, in this way, storing water can be polluted impurities coming from outside. For protecting this pollution, the cooling system based on indirect heat exchange method through phase change between water and ice was developed. In this study, we have calculated efficiency of the cooling system with phase change by experiment and commercial CFD(Computational Fluid Dynamics) code, ANSYS CFX. To consider the effect of latent heat that is generated by melting ice, we have simulated two phase numerical analyses used enthalpy method and found the temperature, velocity, and ice mass distribution for calculating the efficiency of cooling. From the results of numerical analysis, we have obtained the relationship between the cooling efficiency and each design factor.

• International Journal of Ocean System Engineering
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• v.1 no.3
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• pp.136-143
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• 2011

In this paper, three-dimensional free-surface flows are simulated by using two different numerical methods, the constrained interpolation profile (CIP)-based and finite volume (FV)-based methods. In the CIP-based method, the governing equations are solved on stationary staggered Cartesian grids by a finite difference method, and an immersed boundary technique is applied to deal with wave-body interactions. In the FV-based method, the governing equations are solved by applying collocated finite volume discretization, and body-fitted meshes are used. A free-surface boundary is considered as the interface of the multi-phase flow with air and water, and a volumeof-fluid (VOF) approach is applied to trace the free surface. Among many variations of the VOF-type method, the tangent of hyperbola for interface capturing (THINC) and the compressive interface capturing scheme for arbitrary meshes (CICSAM) techniques are used in the CIP-based method and FV-based method, respectively. Numerical simulations have been carried out for dam-breaking and wave-body interaction problems. The computational results of the two methods are compared with experimental data and their differences are observed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.203-211
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• 2021

Octacalcium phosphate(OCP, Ca₈H₂(PO₄)₆·5H₂O) is one of biodegradable calcium phosphate materials with osteoconductivity and biocompatibility. It has the advantage of rapid bone formation and resorption due to the property of stimulating stromal cells to differentiate into osteoblasts. However, if OCP is inserted in body, it is immediately decomposed without maintaining of its shape as scaffolds due to their weak cohesive force between powder. On the other hand, hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), which has a crystal structure similar to that of OCP, remains in the body without decomposition until the bone defect is restored. In this study, the degradation behavior of OCP/HA disc with different amount of HA in SBF (simulated body fluid) solution was characterized in terms of the weight loss, pH variation and microstructure change with immersion duration in SBF solution. As a result, the OCP/HA disc was not quickly decomposed and maintained its own shape for 2 weeks regardless of HA content. In particular, the surface of 40HA specimen was uniformly dissolved and then CDHA (calcium deficient hydroxyapatite) phase were formed onto the surface of disc after 7 days in SBF solution. It would be suggested that the 40HA specimen would be suitable candidate material as the scaffolds for the restoration of bone defect.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.259-267
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• 2017

Flow fields around a KARI-11-180 airfoil, SDM and transonic body are numerically simulated by using an unstructured meshes based compressible flow solver developed at KAIST. RANS equations are solved to analyse the flow fields and Roe's FDS method is adopted to evaluate convective fluxes. Turbulence effect of the flow fields is modeled by a SA model, SST model and ${\gamma}-{\widetilde{Re}}_{{\theta}t}$ model. It is found that smaller drag coefficients are predicted for the KARI-11-180 airfoil when a transition phenomenon is considered and small deviations exist between CFD and EFD results. For the SDM, flow separation is observed at a leading edge and calculated aerodynamic properties show similar tendencies to experimental results. A shock wave on main wings of the transonic body is successfully captured by the present flow solver at a Mach number 0.9. Estimated pressure profiles by means of the present CFD method also agree well with those of wind tunnel results.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.4
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• pp.81-87
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• 2007

In this study, analysis of structural design criteria for the canopy actuating device has been conducted considering the aerodynamic breakaway capabilities of jettisonable canopy system. Unsteady aerodynamic loads for the opened canopy configuration at passively controlled jettision mode were computed using CFD method. The general purpose multi-body finite element code, SAMCEF Mecano, is used in the implemented analyses for the passive jettision condition. The recommended altitude and speed of aircraft was suggested as design criteria of aerodynamic breakaway capability of jettisonable canopy system as a bakup egress method when normal canopy jettison sequence malfunctioned. Aerodynamic breakaway condition of jettisonable canopy was also simulated and the fracture load conditions of canopy actuator were investigated.