Simple Fluid Model Research Articles

Axial force imparted by a current-free magnetically expanding plasma

The axial force imparted from a magnetically expanding, current-free, radiofrequency plasma is directly measured. For an argon gas flow rate of 25 sccm and an effective rf input power of ∼800W, a maximum force of ∼6mN is obtained; ∼3mN of which is transmitted via the expanding magnetic field. The measured forces are reasonably compared with a simple fluid model associated with the measured electron pressure. The model suggests that the total force is the sum of an electron pressure inside the source and a Lorentz force due to the electron diamagnetic drift current and the applied radial magnetic field. It is shown that the Lorentz force is greatest near the magnetic nozzle surface where the radial pressure gradient is largest.

Stochastic Dynamic Response of a Simplified Nonlinear Fluid Model for Viscoelastic Materials

AbstractIn the present study, we propose a simplified nonlinear fluid model to characterize the complex nonlinear response of some viscoelastic materials. Recently, the viscoelastic modeling has been utilized by many researchers to simulate some parts of human body in bioengineering and to represent many material properties in mechanical engineering, electronic engineering and construction engineering. Occasionally it is almost impossible to evaluate the constant parameters in the model in the deterministic sense, therefore, the damping coefficient of the dashpot and the spring constants of the linear and nonlinear springs are considered as stochastic to model the stochastic properties of the viscoelastic materials. After some transformations, the closed-form solution can be obtained for the mean value of the displacement of the simplified nonlinear fluid model, subjected to constant rate of displacement. Based on the closed-form solution, the proposed method generates the stochastic dynamic response of the simplified nonlinear model, which plays an important role in performing the reliability analysis of the nonlinear system.

Caching for BitTorrent-Like P2P Systems: A Simple Fluid Model and Its Implications

Peer-to-peer file-sharing systems are responsible for a significant share of the traffic between Internet service providers (ISPs) in the Internet. In order to decrease their peer-to-peer-related transit traffic costs, many ISPs have deployed caches for peer-to-peer traffic in recent years. We consider how the different types of peer-to-peer caches--caches already available on the market and caches expected to become available in the future--can possibly affect the amount of inter-ISP traffic. We develop a fluid model that captures the effects of the caches on the system dynamics of peer-to-peer networks and show that caches can have adverse effects on the system dynamics depending on the system parameters. We combine the fluid model with a simple model of inter-ISP traffic and show that the impact of caches cannot be accurately assessed without considering the effects of the caches on the system dynamics. We identify scenarios when caching actually leads to increased transit traffic. Motivated by our findings, we propose a proximity-aware peer-selection mechanism that avoids the increase of the transit traffic and improves the cache efficiency. We support the analytical results by extensive simulations and experiments with real BitTorrent clients.

Experimental and Numerical Investigation of Single Bubble Dynamics in a Two-Phase Bubbly Medium

The dynamics of a bubble in a dilute bubbly water-air mixture is investigated experimentally and the results compared with a simple homogeneous compressible fluid model in order to elucidate the requirements from a better advanced numerical solution. The experiments are conducted in view of providing input and validation for an advanced bubbly flow numerical model we are developing. Corrections for classical approaches where in the two-phase flow modeling the dynamics of individual bubble is based on spherical isolated bubble dynamics in the liquid or an equivalent homogeneous medium are sought. The main/primary bubble is produced by an underwater spark discharge from charged capacitors, while the bubbly medium is generated using electrolysis. The size of the main bubble is controlled by the discharge voltage, the capacitors size, and the ambient pressure in the container. The size and concentration of the fine bubbles is controlled by the electrolysis voltage, the length, diameter, arrangement, and type of the wires, and also by the pressure imposed in the container. This enables parametric study of the factors controlling the dynamics of the primary bubble and development of relationships between the primary bubble characteristic quantities such as achieved maximum bubble radius and bubble period and the characteristics of the surrounding two-phase medium: micro bubble sizes and void fraction. The dynamics of the main bubble and of the mixture is observed using high speed video photography. The void fraction of the bubbly mixture in the fluid domain is deduced from image analysis of the high speed movies and obtained as a function of time and space. The interaction between the primary bubble and the bubbly medium is analyzed using both field pressure measurements and high-speed videography. Parameters such as the primary bubble energy and the bubble mixture density (void fraction) are varied, and their effects studied. The experimental data is then compared to a simple compressible fluid medium model which accounts for the change in the medium properties in space and time. This helps illustrate where such simple models are valid and where they need improvements. This information is valuable for the parallel development of an Eulerian-Lagrangian code, which accounts for the dynamics of bubbles in the field and their interaction.

Internal Flow Characteristics of a Plastic Kaolin Suspension During Extrusion

The internal flow characteristics of a kaolin suspension were examined via magnetic resonance imaging (MRI) in a flow regime for which the material behaves as an almost pure plastic material. The paste also showed a significant tendency toward liquid phase migration under squeezing tests. The MRI measurements produced a 2D slice of the 3D velocity field near the entrance of the cylindrical extrusion die, as well as the relative liquid–solid ratio within the cylindrical extrusion cartridge. Finite element simulations were also carried out using a simple yield stress fluid model, i.e. Herschel–Bulkley model, which was fit to rheometrical data obtained from independent experiments. A relatively good agreement between numerical simulations and the measured velocity field was obtained. In addition, the clay concentration of the paste within the extrusion column was imaged before and after extrusion experiments displaying a migration of water from the dead zones toward the entrance of the die. It is remarkable, however, that this phenomenon does not significantly affect the velocity distribution.

Numerical analysis of plasma evolution on dielectric barrier discharge plasma actuator

Time evolution of the discharge plasma in the dielectric barrier discharge (DBD) plasma actuator was simulated by the simple fluid model in which the electron and single positive ion species were considered. The characteristics of the discharge plasma evolution were investigated in detail, and the following results were obtained. When the positive-going voltage is applied, the streamer discharge is formed periodically. The periodically formed streamer expands from the exposed electrode, and its length becomes longer than the previous one. Periodic breakdown of the gas and step-by-step plasma expansion are also observed during the negative-going voltage; however, the streamer is not formed and the breakdown frequency is much higher. The simulation results with a triangular applied voltage waveform show the same characteristics as observed in the experiment; large discharge current spikes are observed during both the positive- and negative-going voltage phase, and the plasma in the negative-going voltage phase expands more smoothly than that in the positive phase because of its higher breakdown frequency. It was shown that even the simple numerical model could provide valuable insights into the physics of DBD plasma actuator; this indicates that the positive ions and electrons play a prominent role in determining the general characteristics of the plasma evolution.

Dynamic response of a simplified nonlinear fluid model for viscoelastic materials under random parameters

In this paper, a simplified spring-dashpot model is proposed to represent the complicated nonlinear response of some viscoelastic materials. Recently, the viscoelastic modeling has been adopted by many researchers to characterize some parts of the human body in bioengineering and to simulate many material properties in mechanical engineering, electronic engineering and construction engineering. Sometimes it is impossible to estimate the constant parameters in the model deterministically, therefore, the damping coefficient of the dashpot and the spring constants of the linear and nonlinear springs are considered as stochastic to characterize the random properties of the viscoelastic materials. The mean value of the displacement of the nonlinear model, subjected to constant rate displacement, can be solved analytically. Based on the closed-form solution, the proposed method produces the statistical dynamic response of the simplified nonlinear fluid model, which is fairly useful in estimating the reliability of the nonlinear system.

Simple flow models of accretionary prisms: Predictions for coexisting arc-normal compression and extension, and implications for locked zones on the interplate megathrust

In accretionary prisms formed in subduction zones, accreted sediments deform due to the drag of the subducting plate, resulting in arc-normal compression. In the Cascadia and eastern Nankai subduction zones, however, arc-parallel normal faults, which indicate the occurrence of arc-normal extension, have been observed at the rear of the accretionary prisms. In this study, the deformation caused by the subducting plate in the accretionary prism is calculated using a simple fluid model that considers temperature-dependent rheology. The qualitative results show that a circulating flow is induced by the subducting plate under a lid formed at the rear of the accretionary prisms at higher temperatures, while, in lower-temperature prisms, the flow pattern is analogous to a simple corner flow, and the circulating flow is not induced. Prism materials flow trenchward just under the lid, and this return flow may be the cause of the arc-normal extension observed in the accretionary prisms. Most of the subduction velocity is accommodated by ductile deformation at the rear of the accretionary prisms, resulting in lower seismic coupling at the deeper interplate megathrusts. In the frontal part of the accretionary prisms, where imbricate thrusts develop, low rigidity due to high porosity and pore fluid pressure in the compacting sediment, together with higher concentrations of clay minerals with low frictional coefficients, probably prevents seismic slip at the interplate megathrusts. Locked zones develop between the extensional and imbricate thrust regions in the subduction zones. For low-temperature prisms, locked zones are located arc side of the imbricate thrust region. The fore-arc basin is thus formed above the locked zone in accretionary prisms. In the eastern Nankai subduction zone, another locked zone is estimated to be located in the lower crust. The location of the arc side of the imbricate thrust region in the western and central Nankai subduction zones may be controlled by the thrust intersection with the top of the lower crust and the splay-fault, respectively.

Optimization of the separation of sulfur hexafluoride and nitrogen by selective adsorption using monte carlo simulations

AbstractWe present molecular simulations to find the optimal conditions for the separation by adsorption of SF6 from a gaseous mixture with N2, a mixture of key interest in electrical applications. The effect of pore size, pressure, and mixture compositions on the selective adsorption of SF6 was investigated by using Grand Canonical Monte Carlo simulations with simple fluid models and a simplified model of MCM‐41. Simulations performed with multisite fluid models confirm that general trends are predicted using simple models, including a maximum in SF6 selectivity for pore diameters around 1.1 nm. Simulations were also performed using two atomistic models of zeolite‐templated carbon (ZTC), FAU‐ZTC, and EMT‐ZTC, materials with average pore sizes close to 1.1 nm, obtaining high selectivities for both materials. Selectivities for FAU‐ZTC are approximately four times higher than the best materials published for this mixture separation, opening excellent opportunities to use it for recovering SF6 from SF6/N2 mixtures. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Understanding the fluid phase behaviour of crude oil: Asphaltene precipitation

We present a simplified but consistent picture of asphaltene precipitation from crude oil from a thermodynamic perspective, illustrating its relationship to the familiar bubble curve via the calculation of constant-composition p– T phase diagrams that incorporate both the bubble curve and the asphaltene precipitation boundary. Using the statistical associating fluid theory (SAFT) we show that the position of the precipitation boundary can be explained using a very simple fluid model including relatively few components. Our results support the view that the precursor to asphaltene precipitation is a liquid–liquid phase separation due to a demixing instability in the fluid. Moreover, the bubble curve for these systems is seen to represent a boundary between regions of two-phase (liquid–liquid) and three-phase (vapour–liquid–liquid) equilibria.

Application of the dynamic compliance method for fluid–structure interaction

This article is focused on application of the dynamic compliance method for fluid–structure interaction. The dynamic compliance method is in principle a method which provided reduction of the order in the frequency domain. This method has been implemented in MATLAB and tested on a relatively simple structure and fluid models. Results were compared with the exact solution and a good agreement was found.

Scale-Up Correlation for the Flow of Surfactant-Based Fluids in Circular Coiled Pipes

This study involves experimental investigation on the flow properties of aqueous surfactant-based (SB) fluids in small and large-scale coiled tubing. It aims at understanding the viscoelastic properties and its effect on the flow behavior of SB fluids in coiled tubing. In spite of SB fluids wide use as friction reducer and/or fracturing fluid in the oil and gas industry, the flow data in large pipe sizes as well as coiled tubing are very scarce. Majority of the available flow data are gathered in straight pipes with small sizes. The scale-up of small-scale flow data is questionable due to the pronounced diameter effect. Furthermore, previous studies have correlated flow behavior of these fluids only through simple power-law model parameters. Limited work with polymeric fluids has been reported that includes fluid elasticity in scale-up procedure and it is nonexistent for highly elastic SB fluids. In this study, the properties of widely used Aromox APA-T, a highly active surfactant used as gelling agent in aqueous and brine base fluids, are thoroughly investigated. Rheological measurements are conducted using Bohlin rheometer for SB fluid concentration of 1.5 vol %, 2 vol %, 3 vol %, and 4 vol %. Flow data are gathered using 1.27 cm, 3.81 cm, 6.03 cm, and 7.30 cm OD coiled tubing with various curvature ratios. This study presents the first attempt to investigate the flow behavior SB fluids in large-scale coiled tubing. The results show that SB fluids exhibit non-Newtonian pseudoplastic behavior. Elastic and viscous properties of SB fluids are very sensitive to surfactant concentration. Friction losses in coiled tubing are significantly higher than those in straight pipes due to secondary flow effect. Increasing curvature ratio yields higher friction pressure loss. Also, small-scale data correlations using only simple power-law model fluid rheological parameters lead to erroneous results when scaled-up to large pipe sizes. New technique, based on the modified Deborah number, which includes fluid elasticity and pipe shear effect, has been developed to correlate data from the small laboratory-scale tubing and large field-scale pipes. Correlation to predict Fanning friction factor of SB fluids in coiled tubing as a function of Deborah number and fluid flow behavior index is presented. Correlation is validated by comparing predictions with the experimental data. It is shown that the new correlation accurately predicts friction factor of SB fluids and thus alleviates the scale-up issue.

Correlation between laser accelerated MeV proton and electron beams using simple fluid model for target normal sheath acceleration

High density energetic electrons that are created by intense laser plasma interactions drive MeV proton acceleration. The correlation between accelerated MeV protons and escaped electrons is experimentally investigated at laser intensities in the range of 1018–1019 W/cm2 with S-polarization. Observed proton maximum energies are linearly proportional to escaped electron slope temperatures with a scaling coefficient of about 10. In the context of the simple analytical fluid model for transverse normal sheath acceleration, hot electron sheath density near the target rear surface can be estimated if an empirical acceleration time is assumed.

Ion jet generation in the ultraintense laser interactions with rear-side concave target

AbstractIn this paper, the ion jet generation from the interaction of an ultraintense laser pulse and a rear-side concave target is investigated analytically using a simple fluid model. We find that the ion expanding surface at the rear-side is distorted due to a strong charge-separation field, and that this distortion becomes dramatic with a singular cusp shown on the central axis at a critical time. The variation of the transverse ion velocity and the relative ion density diverge on the cusp, signaling the emergence of an on-axis ion jet. We have obtained analytical expressions for the critical time and the maximum velocity of the ion jet, and suggested an optimum shape for generating a collimated energetic ion jet. The above theoretical analysis has been verified by particle-in-cell (PIC) numerical simulations.

Investigation of the Complex Flow Behaviour of Surfactant-Based Fluids in Straight Tubing

Summary In spite of their wide use in hydraulic fracturing and gravel-pack operations, the complex flow behaviour of surfactant-based (SB) fluids in straight tubing is rarely investigated. Accurate prediction of friction-pressure is essential for proper treatment design. Previous correlations from small tubing data and using simple power-law fluid model parameters alone do not scaleup to large tubing sizes for field application. The properties of one of the most popular surfactants, Aromox APA-T, are thoroughly investigated. It is a highly-active surfactant used as the gelling agent in aqueous and brine solutions. Commonly used surfactant concentrations (1.5%, 2%, 3% and 4% by volume) are studied. Rheological and viscoelastic measurements are conducted using the Bohlin rheometer. Flow tests are conducted using 1.27-cm, 3.81-cm, 6.03-cm and 7.30-cm tubing. The results show SB fluid exhibiting a non-Newtonian pseudo-plastic behaviour. Fluid concentration and pipe shear have a significant effect on fluid elasticity. The conventional Fanning friction factor vs. Reynolds number correlation is improved by including a new dimensionless group that accounts for both fluid elasticity and pipe diameter. A new definition of Deborah number is introduced. Thus, a new correlation for predicting friction factors of SB fluid in straight tubing is developed. The scaleup problem is thus alleviated with the present analysis and this provides more accurate friction-pressure estimates.

A simple phenomenological non-Newtonian fluid model

In this work, a simple phenomenological generalized Newtonian law model has been proposed and tested for different polymer melts by using rheological data taken from the open literature. Viscosity is given as a specific function of three principal invariants of the deformation rate tensor, D, and its absolute value defined as D ⋅ D . It has been found that the model predictions are in very good agreement with the strain rate dependent steady shear and uniaxial extensional viscosities for linear and branched polyolefines. The model behaves correctly in description of steady planar and equibiaxial extensional viscosities and allows their independent strain hardening level control with respect to uniaxial extensional viscosity.

A numerical investigation of electric current conservation associated with solar wind plasma under GES-model approach

A plasma-based Gravito-Electrostatic Sheath (GES) model for theoretical description of the basic physics of the surface emission mechanism of the quasi-neutral Solar Interior Plasma (SIP) on a bounded scale, and subsequently, its transonic transition into Solar Wind Plasma (SWP) on an unbounded scale with a simplified field-free fluid model approach has already been proposed. An autonomous closed set of self-consistently coupled nonlinear eigenvalue equations for analyzing the dynamical stability of the steady GES model on both the scales is developed. The focussed aim of the present contribution is only to study the electric current profiles associated with the SIP as well as SWP, and hence to investigate conservative dynamical features thereof. Applying the developed set of coupled nonlinear dynamical evolution equations, the profiles of electric currents associated with both SIP as well as SWP have been obtained numerically under a wide range spectrum of initial values of relevant physical parameters (by nonlinear stability analysis). Interestingly, it is conjectured that the dynamical evolution of solar electric currents is found fairly to be conservative (divergence-free) in nature except some deviations near the defined solar surface boundary. Results, discussions and conclusions on the basis of the obtained numerical results are presented in brief.

Effective charge of photons and plasmons

AbstractWe review the concept of photon effective charge in a plasma, and extend it to the case of longitudinal photons or plasmons. A simple electrostatic fluid model is considered in a non-magnetized and non-relativistic plasma. The contribution of the ions to the plasmon charge is also considered.

Effect of nonlinear Landau damping in plasma-based backward Raman amplifier

A plasma wave can mediate laser coupling in a plasma-based resonant backward Raman amplifier for high power amplification of short laser pulses. The resonant nature of amplification requires a long lifetime of the plasma wave. However, the plasma wave can be heavily Landau damped in warm plasma. On the other hand, Landau damping can be saturated in the presence of a strong plasma wave. We study backward Raman amplifier in the nonlinear regime of Landau damping using a simplified fluid model. We find the regime in which initially high linear Landau damping can be significantly saturated. Because of the saturation effect, higher temperatures can be tolerated in achieving efficient amplification. The plasma temperature can be as much as 50% larger compared to the case of unsaturated Landau damping.

Experimental Determination of Relative Permeabilities for a Rich Gas/Condensate System Using Live Fluid

Summary Measurement of gas and condensate relative permeabilities typically is performed through steady-state linear coreflood experiments using model fluids. This study addresses experimental measurement of relative permeabilities for a rich gas/condensate reservoir using a live, single-phase reservoir fluid. Using a live, single-phase reservoir fluid eliminates the difficulties in designing a relatively simple model fluid that replicates the complicated thermodynamic and transport properties of a near-critical fluid. Two-phase-flow tests were performed across a range of pressures and flow rates to simulate reservoir conditions from initial production through depletion. A single-phase multirate experiment was also performed to assess inertial, or non-Darcy, effects. Correlations were developed to represent both the gas and condensate relative permeabilities as a function of capillary number. A nearly 20-fold increase in gas relative permeability was observed from the low- to high-capillary-number flow regime. Compositional simulations were performed to assess the impact of the experimental results for vertical- and horizontal-well geometries.