Hydrodynamic Wave Loading on Offshore Structures Simulated by a Two-Phase Flow Model

The numerical simulation of hydrodynamic wave loading on different types of offshore structures is important to predict forces on and water motion around these structures. This paper presents a numerical study of two-phase flow over a sloping bottom with the presence of breaking waves. The details of the numerical model, an improved Volume Of Fluid (iVOF) method, are presented in the paper. The program has been developed initially to study the sloshing of liquid fuel in satellites. This micro-gravity environment requires a very accurate and robust description of the free surface. Later, the numerical model has been used for calculations of green water loading and the analysis of anti-roll and sloshing tanks, including the coupling with ship motions. The model has been extended recently to take two-phase flow effects into account. Two-phase flow effects are particularly important near the free surface, where loads on offshore structures strongly depend on the interaction between different phases like air and water. Entrapment of air pockets and entrainment of bubble clouds have a cushioning effect on breaking wave impacts. The velocity field around the interface of air and water, being continuous across the free surface, requires special attention. By using a newly-developed gravity-consistent discretisation, spurious velocities at the free surface are prevented. Thus far, the second air phase has been treated as incompressible. Taking compressibility effects into account requires a pressure-density relation for grid cells containing air. The expansion and compression of air pockets is considered as an adiabatic process. The numerical model is validated on several test cases. In this paper special attention will be paid to the impact of a breaking wave over a sloping bottom.

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Numerical Simulation of Sloshing in LNG Tanks With a Compressible Two-Phase Model

Volume 3: Pipeline and Riser Technology; CFD and VIV ◽

10.1115/omae2007-29294 ◽

2007 ◽

Cited By ~ 5

Author(s):

Rik Wemmenhove ◽

Roel Luppes ◽

Arthur E. P. Veldman ◽

Tim Bunnik

Keyword(s):

Numerical Simulation ◽

Free Surface ◽

Numerical Model ◽

Pressure Distribution ◽

Two Phase Flow ◽

Phase Model ◽

Phase Flow ◽

Two Phase ◽

Model Scale ◽

Flow Effects

The study of liquid dynamics in LNG tanks is getting more and more important with the actual trend of LNG tankers sailing with partially filled tanks. The effect of sloshing liquid in the tanks on pressure levels at the tank walls and on the overall ship motion indicates the relevance of an accurate simulation of the fluid behaviour. This paper presents the simulation of sloshing LNG by a compressible two-phase model and the validation of the numerical model on model-scale sloshing experiments. The details of the numerical model, an improved Volume Of Fluid (iVOF) method, are presented in the paper. The program has been developed initially to study the sloshing of liquid fuel in spacecraft. The micro-gravity environment requires a very accurate and robust description of the free surface. Later, the numerical model has been used for calculations for different offshore applications, including green water loading. The model has been extended to take two-phase flow effects into account. These effects are particularly important for sloshing in tanks. The complex mixture of the liquid and gas phase around the free surface imposes a challenge to numerical simulation. The two-phase flow effects (air entrapment and entrainment) are strongly affected by both the filling ratio of the tank and the irregular motion of the tank in typical offshore conditions. The velocity field and pressure distribution around the interface of air and LNG, being continuous across the free surface, requires special attention. By using a newly-developed gravity-consistent discretisation, spurious velocities at the free surface are prevented. The equation of state applied in the compressible cells in the flow domain induces the need to keep track on the pressure distribution in both phases, as the gas density is directly coupled to the gas pressure. The numerical model is validated on a 1:10 model-scale sloshing model experiment. The paper shows the results of this validation for different filling ratios and for different types of motion of the sloshing tank.

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A numerical model for simulating two-phase flow through porous media

Applied Mathematical Modelling ◽

10.1016/0307-904x(89)90070-x ◽

1989 ◽

Vol 13 (5) ◽

pp. 268-281 ◽

Cited By ~ 6

Author(s):

Anant R. Kukreti ◽

Yatendra Rajapaksa

Keyword(s):

Porous Media ◽

Numerical Model ◽

Two Phase Flow ◽

Phase Flow ◽

Flow Through Porous Media ◽

Two Phase ◽

Flow Through

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A three-dimensional numerical model for incompressible two-phase flow of a granular bed submitted to a laminar shearing flow

Computer Methods in Applied Mechanics and Engineering ◽

10.1016/j.cma.2009.07.007 ◽

2010 ◽

Vol 199 (9-12) ◽

pp. 439-449 ◽

Cited By ~ 31

Author(s):

Julien Chauchat ◽

Marc Médale

Keyword(s):

Numerical Model ◽

Two Phase Flow ◽

Three Dimensional ◽

Phase Flow ◽

Granular Bed ◽

Two Phase ◽

Shearing Flow

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On shock waves in two-phase flow: effects of inter-phase heat transfer and slip

Acta Astronautica ◽

10.1016/s0094-5765(99)00181-2 ◽

1999 ◽

Vol 45 (11) ◽

pp. 687-696

Author(s):

W.E. Lear ◽

C.R. Jackson ◽

S.A. Sherif

Keyword(s):

Heat Transfer ◽

Shock Waves ◽

Two Phase Flow ◽

Phase Flow ◽

Two Phase ◽

Flow Effects

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Two-Phase Flow Considerations in PEMFC Design and Operation

ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2008-62037 ◽

2008 ◽

Cited By ~ 2

Author(s):

Jon P. Owejan ◽

Jeffrey J. Gagliardo ◽

Jacqueline M. Sergi ◽

Thomas A. Trabold

Keyword(s):

Liquid Water ◽

Proton Exchange Membrane ◽

Two Phase Flow ◽

Bipolar Plate ◽

Gas Diffusion ◽

Proton Exchange ◽

Phase Flow ◽

Two Phase ◽

Flowing Hydrogen ◽

Flow Effects

A proton exchange membrane fuel cell (PEMFC) must maintain a balance between the hydration level required for efficient proton transfer and excess liquid water that can impede the flow of gases to the electrodes where the reactions take place. Therefore, it is critically important to understand the two-phase flow of liquid water combined with either the co-flowing hydrogen (anode) or air (cathode) streams. In this paper, we describe the design of an in-situ test apparatus that enables investigation of two-phase channel flow within PEMFCs, including the flow of water from the porous gas diffusion layer (GDL) into the channel gas flows; the flow of water within the bipolar plate channels themselves; and the dynamics of flow through multiple channels connected to common manifolds which maintain a uniform pressure differential across all possible flow paths. These two-phase flow effects have been studied at relatively low operating temperatures under steady-state conditions and during transient air purging sequences.

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Gradient-Augmented Level Set Two-Phase Flow Method With Pretreated Reinitialization for Three-Dimensional Violent Sloshing

Journal of Fluids Engineering ◽

10.1115/1.4044823 ◽

2019 ◽

Vol 142 (1) ◽

Cited By ~ 1

Author(s):

Jianjian Xin ◽

Fulong Shi ◽

Qiu Jin ◽

Lin Ma

Keyword(s):

Free Surface ◽

Level Set ◽

Two Phase Flow ◽

Three Dimensional ◽

Surface Shape ◽

Phase Flow ◽

Two Phase ◽

Correction Technique ◽

Highly Nonlinear ◽

Violent Sloshing

Abstract A three-dimensional (3D) gradient-augmented level set (GALS) two-phase flow model with a pretreated reinitialization procedure is developed to simulate violent sloshing in a cuboid tank. Based on a two-dimensional (2D) GALS method, 3D Hermite, and 3D Lagrange polynomial schemes are derived to interpolate the level set function and the velocity field at arbitrary positions over a cell, respectively. A reinitialization procedure is performed on a 3D narrow band to treat the strongly distorted interface and improve computational efficiency. In addition, an identification-correction technique is proposed and incorporated into the reinitialization procedure to treat the tiny droplet which can distort the free surface shape, even lead to computation failure. To validate the accuracy of the present GALS method and the effectiveness of the proposed identification-correction technique, a 3D velocity advection case is first simulated. The present method is validated to have better mass conservation property than the classical level set and original GALS methods. Also, distorted and thin interfaces are well captured on all grid resolutions by the present GALS method. Then, sloshing under coupled surge and sway excitation, sloshing under rotational excitation are simulated. Good agreements are obtained when the present wave and pressure results are compared with the experimental and numerical results. In addition, the highly nonlinear free surface is observed, and the relationship between the excitation frequency and the impulsive pressure is investigated.

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Numerical and Mechanistic Modelling of Two-Phase Liquid-Gas Flow’s Pressure Drop Across Sharp-Edged Orifices

Volume 2: CFD and FSI ◽

10.1115/omae2019-96305 ◽

2019 ◽

Author(s):

Zurwa Khan ◽

Reza Tafreshi ◽

Matthew Franchek ◽

Karolos Grigoriadis

Keyword(s):

Numerical Model ◽

Pressure Drop ◽

Relative Error ◽

Two Phase Flow ◽

Mechanistic Model ◽

Gas Mixture ◽

Phase Flow ◽

Two Phase ◽

Pressure Drops ◽

Phase Liquid

Abstract Pressure drop estimation across orifices for two-phase liquid-gas flow is essential to size valves and pipelines and decrease the probability of unsafe consequences or high costs in petroleum, chemical, and nuclear industries. While numerically modeling flow across orifices is a complex task, it can assess the effect of numerous orifice designs and operation parameters. In this paper, two-phase flow across orifices has been numerically modeled to investigate the effect of different fluid combinations and orifice geometries on pressure drop. The orifice is assumed to be located in a pipe with fully-developed upstream and downstream flow. Two liquid-gas fluid combinations, namely water-air, and gasoil liquid-gas mixture were investigated for different orifice to pipe area ratios ranging from 0.01 to 1 for the superficial velocity of 10 m/s. Volume of Fluid multiphase flow model along with k-epsilon turbulence model were used to estimate the pressure distribution of liquid-gas mixture along the pipe. The numerical model was validated for water-air with mean relative error less than 10.5%. As expected, a decrease in orifice to pipe area ratio resulted in larger pressure drops due to an increase in the contraction coefficients of the orifice assembly. It was also found that water-air had larger pressure drops relative to gasoil mixture due to larger vortex formation downstream of orifices. In parallel, a mechanistic model to directly estimate the local two-phase pressure drop across orifices was developed. The gas void fraction was predicted using a correlation by Woldesemayat and Ghajar, and applied to separated two-phase flow undergoing contraction and expansion due to an orifice. The model results were validated for different orifices and velocities, with the overall relative error of less than 40%, which is acceptable due to the uncertainties associated with measuring experimental pressure drop. Comparison of the developed numerical and mechanistic model showed that the numerical model is able to achieve a higher accuracy, while the mechanistic model requires minimal computation.

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Study on the internal two-phase flow of the inverted-umbrella aerator

Advances in Mechanical Engineering ◽

10.1177/1687814019871731 ◽

2019 ◽

Vol 11 (8) ◽

pp. 168781401987173 ◽

Cited By ~ 3

Author(s):

Liang Dong ◽

Jiawei Liu ◽

Houlin Liu ◽

Cui Dai ◽

Dmitry Vladimirovich Gradov

Keyword(s):

Free Surface ◽

Velocity Distribution ◽

Surface Deformation ◽

Two Phase Flow ◽

Back Surface ◽

High Speed Photography ◽

Aeration Tank ◽

Phase Flow ◽

Two Phase ◽

Radial Profiles

In order to reveal the gas–liquid two-phase flow pattern of inverted-umbrella aerator, the high-speed photography technology, particle image velocimetry, and Volume of Fluid model are employed to capture the free-surface dynamics and velocity distribution. The Computational Fluid Dynamics simulations are validated by experimental data and the results are in good agreement with experiment. The simulation results of flow field, streamline distribution, velocity distribution, free-surface deformation, and turbulence kinetic energy are analyzed at in time and at radial profiles sampled at several vertical positions. Back surface of each blade revealed the area of low-pressure, which can drag air into water directly from surface and thus enhance liquid aeration and oxygenation capacity. Lifting capacity of the inverted-umbrella aerator is enough to get the liquid at the bottom of the aeration tank accelerated toward liquid surface generating the hydraulic jump. As a result, liquid phase splashes capture portions of air promoting aeration of the solution. A clear circulation whirlpool is formed during the process. The circulation whirlpool starts at the bottom of the impeller moving upward along the plate until the outer edge of the impeller, which is close to the free surface. The circulation whirlpool indicates that the inverted-umbrella aerator plays a significant role in shallow aeration. The turbulence intensity created by the impeller gradually reduces with depth. The position ( z = 0.65 H) is the watershed in the tank. The oxygen mass transfer mainly occurs in the layer above watershed.

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The Numerical Simulation of the Water Jet in Hydroentanglement

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.189-193.2181 ◽

2011 ◽

Vol 189-193 ◽

pp. 2181-2184

Author(s):

Heng Zhang ◽

Xiao Ming Qian ◽

Zhi Min Lu ◽

Yuan Bai

Keyword(s):

Numerical Simulation ◽

Numerical Model ◽

Multiphase Flow ◽

Flow Model ◽

Two Phase Flow ◽

Water Jet ◽

Phase Flow ◽

Governing Equations ◽

Two Phase ◽

Set Up

The functions of hydroentangled nonwovens are determined by the degree of the fiber entanglement, which depend mainly on parameters of the water jet. According to the spun lacing technology, this paper set up the numerical model based on the simplified water jetting model, establishing the governing equations, and the blended two-phase flow as the multiphase flow model. This paper simulation the water needle after the water jetting from the water needle plate in the different pressure (100bar, 60bar, 45bar, 35bar).

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