• Journal of KSNVE
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• v.8 no.4
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• pp.700-705
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• 1998

Recent past work has demonstrated that hydraulic semiactive vibration absorbers hold the promise of providing an ideal means of mitigating structural vibration. This paper examines a factor that must be treated when designing a hydraulic semiactive vibration absorber for application to a full scale structure; fluid compressibility. An expanded and consistent dynamic model of the flow process is first established. A simple feedback control is then tested on a single degree of freedom laboratory structure to verify the findings.

• The KSFM Journal of Fluid Machinery
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• v.6 no.1 s.18
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• pp.44-50
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• 2003

Flow through a turbine flow meter is simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo-compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved steadily in rotating reference frames, and the centrifugal force and the Coriolis force are added to the equation of motion. The standard $k-{\epsilon}$model is employed to evaluate turbulent viscosity. Computational results yield quantitative as well as qualitative information on the design of turbine flow meters by showing the distributions of pressure and velocity around the turbine blades.

• International Journal of Fluid Machinery and Systems
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• v.8 no.4
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• pp.240-253
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• 2015

The objective of this paper is to evaluate the applicability of mass transfer cavitation models and determine appropriate numerical parameters for cavitating flow simulations. CFD simulations were performed for a NACA66 hydrofoil at cavitation numbers of 1.49 and 1.00, corresponding to steady sheet and unsteady sheet/cloud cavitating regimes using the Kubota and Merkle cavitation models. The Merkle model was implemented into CFX by User Fortran code. The Merkle cavitation model is found to give some improvements for cavitating flow simulation results for these cases. Turbulence modeling is also found to have an important contribution to the prediction quality of the simulations. The relationship between the turbulence viscosity modification, in order to take into account the local compressibility at the vapor/liquid interfaces, and the predicted numerical results is clarified. The limitations of current cavitating flow simulation techniques are discussed throughout the paper.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.1
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• pp.56-65
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• 2018

Pressure oscillation caused by the compressibility of entrapped air in dam break flow is analyzed using an open source code, which is a two-phase compressible code for non-isothermal immiscible fluids. Since compressible flows are computed based on a pressure-based method, the code can handle the equation of state of barotropic fluid, which is virtually incompressible. The computed time variation of pressure is compared with other experimental and computational results. The present result shows good agreements with other results until the air is entrapped. As the entrapped air bubbles pulsate, pressure oscillations are predicted and the pressure oscillations damp out quickly. Although the compressibility parameter of water has been varied for a wide range, it has no effects on the computed results, because the present equation of state for water is so close to that of incompressible fluid. Grid independency test for computed time variation of pressure shows that all results predict similar period of pressure oscillation and quick damping out of the oscillation, even though the amplitude of pressure oscillation is sensitive to the velocity field at the moment of the entrapping. It is observed that as pressure inside the entrapped air changes quickly, the pressure field in the neighboring water adjusts instantly, because the sound of speed is much higher in water. It is confirmed that the period of pressure oscillation is dominated by the added mass of neighboring water. It is found that the temperature oscillation of the entrapped air is critical to the quick damping out of the oscillations, due to the fact that the time averaged temperature inside the entrapped air is higher than that of surrounding water, which is almost constant.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.5
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• pp.735-745
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• 1997

In this study, the compressibility of resin was considered in filling analysis to account for the possible packing type flow. A numerical simulation program employing a hybrid finite element/finite difference scheme was developed to solve Hele-Shaw flow of the compressible viscous fluid at non-isothermal conditions. To advance the melt front, a control volume approach was adopted. Thin complex 3-D shapes of cavities, runners, and sprues were discretized by employing triangular, cylindrical and/or rectangular strip elements. Mass conservation was applied to each control volume to solve for the pressure distribution. Directly applying a constant mass flow rate at the inlet removes calculation of the apparent pressure boundary conditions, resulting in better simulation condition. The Cross model was used to model viscosity and the Tait equation was employed to represent density as a function of temperature and pressure. The validity of the developed program was verified through comparisons with available data in the literature and the effect of compressibility on the pressure distribution was discussed. To reduce computation time, 1-D and 2-D elements were used instead of applying triangular elements and the numerical results were compared to each other.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.229-240
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• 1991

The large camber angle theory of turbomachine blade of compressor has been developed recently for the two-dimensional flow by Hawthorn, et al. However, in the above theory it was assumed that the fluid was incompressible and inviscid, and the blades had no thickness. In this study, the flow in a blade cascade being mounted in parallel fashion with blade of arbitrary thickness is studied in order to determine the effects of the camber angle on the performance characteristic of the blade section under the consideration of compressibility and viscosity of fluid. The panel method is used for potential flow analysis. The flow in the boundary-layer is obtained by solving the integral boundary-layer structure through the laminar, transitional , and turbulent flow using the pressure field determined from the potential flow. And then the viscous-inviscid interaction scheme is used for interaction of these two flows. For the determination of the variation in the outlet fluid angle influenced by deviation in cascade flow, the superposition method which is used for single foil is introduced in this analysis. By the introduction of this method, the effects of the deviation on outlet fluid angle and the resulting fluid angle are made to adjust for oneself through the calculation. As the result of this study, the blade of large camber angle, large incidence angle, large pitch-chord ratio has large viscous and compressible effect than those of small camber angle. Lift force increase as camber angle increases, but above 60.deg. of camber angle, lift force decrease as camber angle increases. But drag force increases linearly with camber angle increases in the entire region.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.10a
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• pp.168-175
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• 1996

This paper reports on theoretical study of the pressure overshoot in the delivery ports and pressure rising within balanced type vane pump. Pressure overshoot occur due to the accelerated fluid through the notch, so, result in pressure ripple, flow ripple, and noise. For calculating the pressure rising and fluctuations of pressure, we have modeled mathematically used continuity equation based on compressibility and momentum equation considered fluid inertia in the notch, and analyzed simultaneously. As a results of analysis, we have found oscillation of pressure and compression chamber pressure depend on the rotational speeds, bulk modulus of working fluid, notches, number of vane and camring. Using the model, notches have been shown to be important design factor in relaxing the rapid pressure rising and reducing the amplitudes of pressure overshoot.

• Transactions of The Korea Fluid Power Systems Society
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• v.1 no.1
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• pp.17-22
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• 2004

The goal of this paper is to improve the position control performance of pneumatic rotary actuator with variable brake using Magneto-Rheological Fluid. The air compressibility and the lack of damping of the pneumatic actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. In this study, a variable rotary brake comprising Magneto-Rheological Fluid is equipped to the joint of a pneumatic manipulator. Experiments of step response have proved that the transient response of the manipulator could be improved compared with that of the conventional control algorithm by using a phase plane switching control algorithm.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1841-1850
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• 1993

A simplified one-dimensional analysis has been performed to predict the local pressure distributions in Y-Jet twin-fluid atomizers. Fluid compressibility was considered both in the gas(air) and two-phase(mixing) ports. The annular-mist flow model was adopted to analyze the flow in the mixing port. A series of experiments also has been performed; the results show that the air flow rate increases and the liquid flow rate decreases with the increase of the air injection pressure and/or with the decrease of the liquid injection pressure. From the measured injection pressures and flow rates, the appropriate constants for the correlations of the pressure loss coefficients and the rate of drop entrainment were decided. The local pressures inside the nozzle by prediction reasonably agree with those by the experiments.

• Ocean Systems Engineering
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• v.13 no.1
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• pp.57-77
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• 2023

In the present study, the total hydrodynamic pressure exerted by the fluid on walls of rectangular tanks due to horizontal excitations of different frequencies, is investigated by pressure based finite element method. Fluid within the tanks is invisid, compressible and its motion is considered to be irrotational and it is simulated by two dimensional eight-node isoparametric. The walls of the tanks are assumed to be rigid. The total hydrodynamic pressure increases with the increase of exciting frequency and has maximum value when the exciting frequency is equal to the fundamental frequency. However, the hydrodynamic pressure has decreasing trend for the frequency greater than the fundamental frequency. Hydrodynamic pressure at the free surface is independent to the height of fluid. However, the pressure at base and mid height of vertical wall depends on height of fluid. At these two locations, the hydrodynamic pressure decreases with the increase of fluid depth. The depth of undisturbed fluid near the base increases with the increase of depth of fluid when it is excited with fundamental frequency of fluid. The sloshing of fluid with in the tank increases with the increase of exciting frequency and has maximum value when the exciting frequency is equal to the fundamental frequency of liquid. However, this vertical displacement is quite less when the exciting frequency is greater than the fundamental frequency.