• Journal of Energy Engineering
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• v.12 no.1
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• pp.29-34
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• 2003

Thermo-acoustic waves can be generated in a compressible fluid by rapid heating and cooling near the boundary walls. These phenomena are very important mechanism of heat transfer in the space environment in which natural convection does not exist. In this study, the generation and transmission characteristics of thermo-acoustic waves in an air filled enclosure with rapid wall heating are studied numerically. The governing equations were discretized using control volume method, and were solved using PISO algorithm and second-order upwind scheme. For the stable solution time step were considered as t=1$\times$$10^{-9}$ order, and grids are 50$\times$800. The induced thermo-acoustic wave propagates through the fluid until it decays due to viscous and heat dissipation. The wave showed sharp front shape and decreased with long tail.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.567-576
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• 2003

In this study, a robust controller to control pressure in a pneumatic pressure vessel with a long transmission line is proposed. Frequency response of transmission line using compressible fluid is changed by the flowing state of the fluid. So, it a fixed gain controller designed based on a model supposed the flowing state to a specific state, the performance of the control system could be degraded because of the modelling error. The controller designed in this study is composed of two parts. One is a feedback controller to improve a feedback characteristics and to compensate the influence of the variation of transfer characteristics of a transmission line owing to the change of flowing state and the other is a feedforward controller to regulate command fallowing performance. The experimental results with the designed controller show that the robustness of the control system is achieved regardless of the change of the model or the transmission line. Therefore, the designed controller can be utilized for the Performance improvement of a Pressure control system with a long transmission line using compressible fluid.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.914-922
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• 2002

Thermo-acoustic waves can be thermally generated in a compressible flow field by rapid heating and cooling, and chemical reaction near the boundary walls. This mechanism is very important in the space environment in which natural convection does not exist. Also this may be a significant factor for heat transfer when the fluids are close to the thermodynamic critical point. In this study, the generation and transmission characteristics of thermo-acoustic waves in an air-filled confined domain with two-step pulsed heating are studied numerically. The governing equations are discretized using control volume method, and are solved using PISO algorithm and second-order upwind scheme. For the purpose of stable solution, time step was set to the order of $1\times10_-9s,\;and\;grids\;are\;50\times2000$. Results show that temperature and pressure distributions of fluid near the boundary wall subjected to a rapid heating are increased abruptly, and the induced thermo-acoustic wave propagates through the fluid until it decays due to viscous and heat dissipation. Pressure waves have sharp front shape and decay with a long tail in the case of step heating, but these waves have sharp pin shape in the case of pulsed heating.

• Structural Engineering and Mechanics
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• v.22 no.6
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• pp.719-739
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• 2006

An analytical method for the free vibration of two circular plates coupled with an inviscid and compressible fluid is developed by the Rayleigh-Ritz method. The fluid is bounded by a rigid cylindrical vessel and two circular plates with an unequal thickness and diameter. It was found that the theoretical results could predict well the fluid-coupled natural frequencies with an excellent accuracy when compared with the finite element analysis results. As the fluid thickness increases or the plate thickness difference increases, an abrupt curve veering in the natural frequency loci of the neighboring modes and drastic changes in the corresponding mode shapes are observed. The mode localization frequently appears in the higher modes and in the wide gap between the plates because of a decrease in the fluid coupling owing to the fluid dispersion effect.

• Structural Engineering and Mechanics
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• v.20 no.4
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• pp.389-403
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• 2005

In the present paper it is aimed to perform the stochastic dynamic analysis of fluid and fluidstructure systems by using the Lagrangian approach. For that reason, variable-number-nodes twodimensional isoparametric fluid finite elements are programmed in Fortran language by the authors and incorporated into a general-purpose computer program for stochastic dynamic analysis of structure systems, STOCAL. Formulation of the fluid elements includes the effects of compressible wave propagation and surface sloshing motion. For numerical example a rigid fluid tank and a dam-reservoir interaction system are selected and modeled by finite element method. Results obtained from the modal analysis are compared with the results of the analytical and numerical solutions. The Pacoima Dam record S16E component recorded during the San Fernando Earthquake in 1971 is used as a ground motion. The mean of maximum values of displacements and hydrodynamic pressures are compared with the deterministic analysis results.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.17 no.3
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• pp.209-219
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• 2013

The present paper deals with the extension of AUSMPW+ scheme into two-fluid model for multiphase flow. AUSMPW+ scheme is the improvement of a single-phase AUSM+ scheme by designing pressure-based weighting functions to prevent oscillations near a wall and shock instability after a strong shock. Recently, Kitamura and Liou assessed a family of AUSM-type schemes with two-fluid model governing equations [K. Kitamura and M.-S. Liou, Comparative study of AUSM-Family schemes in compressible multi-phase flow simulations, ICCFD7-3702 (2012)]. It was observed that the direct application of the single-phase AUSMPW+ did not provide satisfactory results for most of numerical test cases, which motivates the current study. It turns out that, by designing pressure-based weighting functions, which play a key role in controlling numerical diffusion for two-fluid model, problems reported in can be overcome. Various numerical experiments validate the proposed modification of AUSMPW+ scheme is accurate and robust to solve multiphase flow within the framework of two-fluid model.

• Journal of applied mathematics & informatics
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• v.25 no.1_2
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• pp.51-66
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• 2007

A layer of compressible, rotating, elastica-viscous fluid heated & soluted from below is considered in the presence of vertical magnetic field to include the effect of Hall currents. Dispersion relation governing the effect of viscoelasticity, salinity gradient, rotation, magnetic field and Hall currents is derived. For the case of stationary convection, the Rivlin-Erickson fluid behaves like an ordinary Newtonian fluid. The compressibility, stable solute gradient, rotation and magnetic field postpone the onset of thermosolutal instability whereas Hall currents are found to hasten the onset of thermosolutal instability in the absence of rotation. In the presence of rotation, Hall currents postpone/hasten the onset of instability depending upon the value of wavenumbers. Again, the dispersion relation is analyzed numerically & the results depicted graphically. The stable solute gradient and magnetic field (and corresponding Hall currents) introduce oscillatory modes in the system which were non-existent in their absence. The case of overstability is discussed & sufficient conditions for non-existence of overstability are derived.

• Honam Mathematical Journal
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• v.36 no.1
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• pp.11-27
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• 2014

In this paper, we propose closures for multi-phase flow models, which satisfy boundary conditions and conservation constraints. The models governing the evolution of the fluid mixing are derived by applying an ensemble averaging procedure to the microphysical equations characterized by distinct phases. We consider compressible multi species multi-phase flow with surface tension and transport.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.572-583
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• 2019

This paper aims to assess the applicability of the Runge Kutta Discontinuous Galerkin-Direct Ghost Fluid Method to the internal explosion inside a water-filled tube, which previously was studied by many researchers in separate works. Once the explosive charge located at the inner center of the water-filled tube explodes, the tube wall is subjected to an extremely high intensity fluid loading and deformed. The deformation causes a modification of the field of fluid flow in the region near the water-structure interface so that has substantial influence on the response of the structure. To connect the structure and the fluid, valid data exchanges along the interface are essential. Classical fluid structure interaction simulations usually employ a matched meshing scheme which discretizes the fluid and structure domains using a single mesh density. The computational cost of fluid structure interaction simulations is usually governed by the structure because the size of time step may be determined by the density of structure mesh. The finer mesh density, the better solution, but more expensive computational cost. To reduce such computational cost, a non-matched meshing scheme which allows for different mesh densities is employed. The coupled numerical approach of this paper has fewer difficulties in the implementation and computation, compared to gas dynamics based approach which requires complicated analytical manipulations. It can also be applied to wider compressible, inviscid fluid flow analyses often found in underwater explosion events.

• Journal of computational fluids engineering
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• v.8 no.2
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• pp.33-41
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• 2003

A simplified simulation model is designed to investigate the vacuum-driven bonding of glass panels in the cell process for LCD manufacturing. The bonding process is modelled by the transient flow of a weakly-compressible fluid in a very thin channel between two horizontal glass panels. An order of magnitude scaling analysis is conducted based on the characteristic feature of the channel of which height is much smaller than the horizontal length scales. It is revealed that the flow in the channel is represented by a Poiseuille flow of a compressible fluid. A finite volume model has been constructed to acquire the numerical solution to the derived simplified equations. For a simple test problem of pressure-driven microchannel flow, an assessment is made of the accuracy and validity of the proposed model. The basic aspects of vacuum-driven bonding are examined numerically, and the applicability of the present simulation model is illustrated.