• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.1152-1156
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• 2003

Hard disk drives (HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speeds requires an improved understanding of fluid motion in the space between disks. PIV measurement was used fer the unsteady flow between the center pair of four disks of four times larger than common radius of HDD disk at several rpm in a fixed cylindrical enclosure. The boundary between inner region and outer region is detected using PIV measurement and the number of dominant vortices s determined clearly. Tip vortices generated by an obstruction with actual-like configuration can be found at inner region. Oscillating flow from the obstruction appears at outer region with complex flow pattern.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1172-1177
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• 2004

The evolution of incipient soot particles has been examined by high resolution electron microscopy (HRTEM) and elemental analyzer in ethylene-air inverse diffusion flames. Laser Induced Incandescence(LII) and laser scattering methods were introduced for examining the change of soot volume fraction and morphological properties in combustion generated soot qualitatively. Soot particles, collected by thermophoretic sampling were analyzed by using HRTEM to examine the nano structure of precursor particles. HRTEM micrographs apparently reveal a transformation of condensed phase of semitransparent tar-like material into precursor particles with relatively distinct boundary and crystalline which looks like regular layer structures. During this evolution histories C/H analysis was also performed to estimate the chemical evolution of precursor particles. The changes of C/H ratio of soot particles with respect to residence time can be divided into two parts: one is a very slowly increasing regime where tar-like materials are transformed into precursor particles (inception process) the other is an increasing region with constant rate where surface growth affects the increase of C/H ratio dominantly (surface growth region). These results provide a clear picture of a transition to mature soot from precursor materials.

• 대한기계학회논문집B
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• 제30권9호
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• pp.921-928
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• 2006

Wake-induced boundary-layer transition on a NACA0012 airfoil with zero angle of attack is experimentally investigated in periodically passing wakes under the moderate level of free-stream turbulence. The periodic wakes are generated by rotating circular cylinders clockwise or counterclockwise around the airfoil. The free-stream turbulence is produced by a grid upstream of the rotating cylinder, and its intensities $(Tu_{\infty})$ at the leading edge of the airfoil are 0.5 and 3.5%, respectively. The Reynolds number (Rec) based on chord length (C) of the airfoil is $2.0{\times}10^5$, and Strouhal number (Stc) of the passing wake is about 1.4. Time- and phase-averaged streamwise mean velocities and turbulence fluctuations are measured with a single hot-wire probe, and especially, the corresponding wall skin friction is evaluated using a computational Preston tube method. The patch under the high free-stream turbulence $(Tu_{\infty}=3.5%)$ grows more greatly in laminar-like regions compared with that under the low turbulence $(Tu_{\infty}=0.5%)$ in laminar regions. The former, however, does not greatly change the turbulence level in very near-wall region while the latter does it. At further downstream, the former interacts vigorously with high environmental turbulence inside the pre-existing transitional boundary layer and gradually loses its identification, whereas the latter keeps growing in the laminar boundary layer. The calmed region is more clearly observed under the lower free-stream turbulence level and with the receding wakes.

• 동력기계공학회지
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• 제14권6호
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• pp.67-74
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• 2010

Many tanks are installed in ship and marine structures. They are often in contact with inner or outer fluid, like ballast, fuel and cargo tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks in contact with fluid near engine and propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tanks. Many authors have studied vibration of cylindrical and rectangular tanks containing fluid. Few research on dynamic interaction among tank walls through fluid are reported in the vibration of rectangular tanks recently. In case of rectangular tanks, structural coupling between adjacent panels and effect of vibration modes of multiple panels on added mass have to be considered. In the previous report, A numerical tool of vibration analysis of a 3-dimensional tank is developed by using finite element method for plates and boundary element method for fluid region. In this paper, the coupling effect between panels of a tank on added mass of containing fluid, the effect of structural constraint between panels on each vibration mode for fluid region and mode characteristics in accordance with changing breadth of the plates are investigated numerically and discussed.

• 한국소음진동공학회논문집
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• 제13권10호
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• pp.791-797
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• 2003

A liquid storage rectangular tank structures are used In many fields of civil, mechanical and marine engineering. Especially, Ship structures have many tanks In contact with Inner or outer fluid, like ballast, fuel and cargo tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks in contact with fluid near engine or propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tank structures. In the previous report, we have developed numerical tool of vibration analysis of 3-dimensional tank structure using finite elements for plates and boundary elements for fluid region. In the present report, using the numerical analysis, vibrations characteristics In deep water tank are investigated and discussed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.1079-1084
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• 2003

A liquid storage rectangular tank structures are used in many fields of civil, mechanical and marine engineering. Especially, Ship structures have many tanks in contact with inner or outer fluid, like ballast, fuel and cargo tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks ill contact with fluid near engine or propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tank structures. In the previous report, we have developed numerical tool of vibration analysis of 3-dimensional tank structure using finite elements for plates and boundary elements for fluid region. In the present report, using the numerical analysis, vibrations characteristics in deep water tank are investigated and discussed.

• 한국해양공학회지
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• 제18권2호
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• pp.10-17
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• 2004

In this research, a numerical simulation for the acoustic sounds around a two-dimensional circular cylinder in a uniform flaw was developed, using the finite difference lattice Boltzmann model. We examine the boundary condition, which is determined by the distribution function concerning density, velocity, and internal energy at the boundary node. Pressure variation, due to the emission of the acoustic waves, is very small, but we can detect this periodic variation in the region far from the cylinder. Daple-like emission of acoustic waves is seen, and these waves travel with the speed of sound, and are synchronized with the frequency of the lift on the cylinder, due to the Karman vortex street. It is also apparent that the size of the sound pressure is proportional to the central distance to the circular cylinder. The lattice BGK model for compressible fluids is shown to be a powerful tool for the simulation of gas flaws.

• Journal of Mechanical Science and Technology
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• 제17권11호
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• pp.1756-1766
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• 2003

Numerical modeling is carried out to investigate forced convective heat transfer to near-critical water in developing laminar flow through a circular tube. Due to large variations of thermo-physical properties such as density, specific heat, viscosity, and thermal conductivity near thermodynamic critical point, heat transfer characteristics show quite different behavior compared with pure forced convection. With flow acceleration along the tube unusual behavior of heat transfer coefficient and friction factor occurs when the fluid enthalpy passes through pseudocritical point of pressure in the tube. There is also a transition behavior from liquid-like phase to gas-like phase in the developing region. Numerical results with constant heat flux boundary conditions are obtained for reduced pressures from 1.09 to 1.99. Graphical results for velocity, temperature, and heat transfer coefficient with Stanton number are presented and analyzed.

• Structural Engineering and Mechanics
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• 제55권2호
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• pp.435-459
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• 2015

Parametric resonance of shear deformable composite skew plates subjected to non-uniform (parabolic) and linearly varying periodic edge loading is studied for different boundary conditions. The skew plate structural model is based on higher order shear deformation theory (HSDT), which accurately predicts the numerical results for thick skew plate. The total energy functional is derived for the skew plates from total potential energy and kinetic energy of the plate. The strain energy which is the part of total potential energy contains membrane energy, bending energy, additional bending energy due to additional change in curvature and shear energy due to shear deformation, respectively. The total energy functional is solved using Rayleigh-Ritz method in conjunction with boundary characteristics orthonormal polynomials (BCOPs) functions. The orthonormal polynomials are generated for unit square domain using Gram-Schmidt orthogonalization process. Bolotin method is followed to obtain the boundaries of parametric resonance region with higher order approximation. These boundaries are traced by the periodic solution of Mathieu-Hill equations with period T and 2T. Effect of various parameters like skew angle, span-to-thickness ratio, aspect ratio, boundary conditions, static load factor on parametric resonance of skew plate have been investigated. The investigation also includes influence of different types of linearly varying loading and parabolically varying bi-axial loading.

• Journal of Welding and Joining
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• 제29권4호
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• pp.48-53
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• 2011

A thermal distortion analysis which takes strains directly as boundary conditions removed barrier of analysis time for the evaluation of welding distortion in a large shell structure like ship block. If the FE analysis time is dramatically reduced, the structure modeling time or the input-value calculating time will become a new issue. On the contrary to this, if the calculation time of analysis input-value is dramatically reduced and its results also are more meaningful, a little longer analysis time could be affirmative. In this study, instead of using inherent strain based on elastic analysis, a thermal strain based on elasto-plastic analysis is used as the boundary condition of weldments in order to evaluate the welding distortion. Here, the thermal strain at the weldment was established by using a stress-strain curve established from the test results. It is possible to automatically recognize the modeling induced-stiffness in the shrinkage direction of welded or heated region. The validity of elasto-plastic thermal distortion analysis was verified through the experiment results with various welding sequence.