Search

An analytical model is developed in this article to study the effects of liquid sloshing on dynamics of articulated vehicle carrying liquid in turning maneuver. To investigate the interaction betwe...

International audience; In this study, we have introduced two new iterative density-based Smoothed Particle Hydrodynamics (SPH) methods to model incompressible flows, namely, preconditioned dual time-stepping, and augmented Lagrangian method. The performance of these new methods are compared with each other and also with a modified version of the well-known weakly compressible SPH (WC-SPH) method through solving three carefully chosen incompressible flow problems: a laminar incompressible channel flow over a backward-facing step, a 2D stiff pressure decay problem and Taylor-Green vortices flow. For the first test problem, the results are compared with available data in literature. Moreover, it is observed that the two iterative methods provide a better accuracy in terms of smoother pressure field and also smaller magnitude of the velocity divergence across the computational domain. In the second test problem, it is shown that the preconditioned dual time-stepping and the augmented Lagrangian SPH methods yield rather smooth pressure fields, and converge to the exact solution, while the pressure field computed by the WC-SPH method oscillates even after very long time. As for the third test case, the iterative methods are compared with WC-SPH method for different iteration numbers and particle resolutions.

Summary Although the use of radial logarithmic-distributed grids are popular in the case of the reservoir simulation with high saturation changes around the wells, this method is limited to the reservoirs with single-well. On the other hand, the necessity of applying fine-grid around the wellbore is approved in such phenomena. Therefore, a robust solution may be using both the Cartesian and the radial grid. In this paper, a Double-Scale method by using the concept of overlapping grids is presented. The main idea in this method is a coarse Cartesian grid overlapped by a radial grid connected by using the interpolation between the results of grids on the outer boundary of the radial grid. The method is implemented in the open-source Matlab Reservoir Simulation Toolbox (MRST). To show the performance of the presented Double-Scale method, the results of the second SPE comparative study simulation are compared with those obtained by PEBI (perpendicular-bisectional) grid. The results clearly show the good agreement between these methods in case of water cut and oil production rate while the advantage of the new Double-Scale method is in computational time which is about 1.7 times faster than PEBI.

Summary Gravity drainage is an effective recovery mechanism in the majority of fractured reservoirs. In this study, the effects of matrix and fracture orientation, and 0–20 degrees’ deviation from vertical alignment on recovery factors were investigated during free fall gravity drainage (FFGD) and forced gravity drainage (FGD). Experiments were conducted in a novel fractured sand pack with a different number of fractures. Water was used as the wet phase, and during the FGD process, nitrogen at a constant rate of 10 cc/min was used as the non-wet phase. Results demonstrated that final recovery factors in FGD were almost 3% more than FFGD experiments. Also, it is found that depend on the number, position, and orientation of fractures, the final recovery factor by increasing deviation from vertical alignment can increase or decrease. In other words, the position of matrix and fractures and their orientation have an important effect on the rule of fluid flow mechanisms and enhance oil recovery.

Gas injection is a proven economical process that significantly increases oil and condensate recovery from hydrocarbon reservoirs. Relative permeability is an important parameter in modeling, simulation, and evaluation of gas injection. In this study, new empirical-mathematical models are developed to predict the relative permeability of gas-oil systems in different rock and fluid systems. The Multi-Gene Genetic Programming (MGGP) technique is employed to develop relative permeability equations. The smart correlations presented in this work require capillary number, interfacial tension, API, gas molecular weight, and viscosity ratio as extra input variables to improve its precision and accuracy. The significance of each parameter is evaluated by statistical approach and Taguchi experimental design. The new models are evaluated by experimental data extracted from literature and validated by extensive error analysis. Additionally, laboratory tests were performed for determining gas-oil relative permeability which were used to check the accuracy of new developed correlations. In relative permeability curves for different gas flow rates, the coupling effect becomes strong and, in competition with the inertia effect, causes changes in the relative permeability with flow rate. The comparison of the experimental results of this study with the new proposed correlation resulted in a root-mean-square error (RMSE) of 0.0796 for gas relative permeability and 0.0564 for oil relative permeability. The results strongly admit the MGGP approach and high accuracy of developed mathematical correlations.

In this paper, we propose two consistent incompressible Smoothed Particle Hydrodynamics (ISPH) methods, namely explicit ISPH (EISPH) and iterative implicit ISPH (IISPH) for simulating free surface flow as challenging complex and highly nonlinear problem. Both methods employ new consistent spatial derivatives schemes, boundary conditions free of dummy or mirror particle. In the explicit method, a projection approach is used with one pressure Poisson equation solution at each time-step. In this work, it is shown that this approach does not guarantee the incompressibility. The suggested iterative implicit approach is a remedy for this difficulty. Both methods showed satisfactory results in comparison with the available experimental and numerical solutions of the well-known 2-D dam breaking problem over dry and wet beds. However, the proposed IISPH method yields more accurate and stable results rather than EISPH even with a lower number of particles and greater time-step sizes.

Fluid flow in porous media is extensively associated with Darcy's law. Deviations from Darcy's law and its limitations result in modifications known as non-Darcy flow at high velocity and Pre-Darcy flow at low velocity. In this paper, experiments were conducted to explore significance of departure from linearity at low fluid velocity (Pre-Darcy flow) in porous media. Effect of different liquid and gas types on the onset of Pre-Darcy flow were studied for water, condensate, n-hexane and n-heptane as liquid phase and CH4, CO2 and N2 as gas phase. Superficial velocity versus pressure gradient was measured and different onset values were reported. The minimum observed Darcy velocity was 0.189 × 10−05 m/s, below which Pre-Darcy flow prevails. Analysis was performed in terms of friction factor and Reynolds number for different particle size of 0.15, 0.25 and 0.3 mm. Pre-Darcy, Darcy and Non-Darcy flow regimes were observed and characterized in terms of R e √ k , Red and Rep. The range of Reynolds number were reported for different flow regimes, different particle sizes and different types of liquids. For the case of condensate in 0.15 mm sand pack, Pre-Darcy flow was observed in the range of R e √ k

Simulation of near-well flow around a single well in reservoirs is normally studied using radial logarithmic grids. A promising method for more complicated, multi-well cases is a combined approach of using a Cartesian and a radial grid. In this paper, a new method of overlapping grids is introduced in which a radial grid is overlapped on a coarse Cartesian grid in the area around a well. Connectivity between the two grids is established using an appropriate boundary condition. Five different algorithms of grids connectivity with internal boundary conditions are presented in which the data are transferred between the grids by interpolation pressure and saturations in each grid. This method is implemented in the open-source Matlab Reservoir Simulation Toolbox (MRST) using the modified black-oil model. The proposed approach is validated by simulation of a reference fine radial grid model on a gas-condensate reservoir. Comparing the results with the reference model indicates that the proposed Double-Scale method using a 21 × 21 coarse Cartesian grid is as accurate as a 1001 × 1001 simple Cartesian fine grid model. Then, a double-layer numerical problem with two production wells was simulated and sensitivity analysis was conducted to investigate the effect of critical condensate saturation and vertical permeability. Finally, the second SPE comparative solution project was simulated to compare the performance of the proposed method with the use of the perpendicular bisector (PEBI) grids around the well. Results showed that the accuracy of the PEBI grid and Double-Scale method are comparable. However, the proposed Double-Scale method is almost 2 times faster in this specific problem.

Gravity is one of the major driving forces for fluid flow in naturally fractured reservoirs. Gravity drainage appears to be a vital recovery mechanism over the oil production process in a majority of fractured reserves. In this paper, free-fall gravity drainage (FFGD) and forced gravity drainage (FGD) production approaches are investigated through employing a new fractured sand pack with a rectangular geometry. Distilled water and condensate are used as the wetting phase. Nitrogen, carbon dioxide, and air are also utilized as the non-wetting phase. A systematic sensitivity analysis is conducted to find the effects of the key factors such as fracture blockage, injection rate, dip angle, and type of wetting phase and injection fluid on the performance of FFGD and FGD processes. Also, a numerical simulation is performed to simulate the experiments. Results reveal that the FGD has a better performance under controlled process conditions, compared to the FFGD so that gas injection with a controlled rate improves the recovery. Moreover, it was found that increasing the gas injection rate improves the recovery factor (RF) of wetting-phase when the up and bottom sides of the fractures are blocked; the RF is decreased in the case with open fracture sides. The recovery of the wetting phase decreases in both FFGD and FGD modes when the porous system has a deviation from the vertical orientation. According to the study outcomes, the immiscible gas-assisted gravity drainage offers a higher condensate recovery, compared to water recovery, due to lower viscosity and interfacial tension (IFT) of the condensate phase. The comparison of the experimental data and simulation results implies that the simulation approach can satisfactorily predict the performance of the FGD process. Based on the error analysis, there is a good match between the simulation results and the experimental measurements; the fluid pair of CO2-condensate exhibits the highest accuracy with an R-squared of 0.9961 and an average relative error (ARE) of 0.0054.

Various methods are devised to capture renewable energy or waste heat from different sectors, where among all, waste heat capturing from the generator of a wind turbine through the cooling process for freshwater and cooling production is paid less attention in Iran, in spite of the fact that many wind farms in Iran are in hot and humid regions and the residents nearby the farms desperately need freshwater and cooling load. To surmount this problem, waste heat extraction from a wind turbine (Enercon 70 Model) for freshwater and cooling production is proposed in this study. Instead of dissipating this thermal energy of the wind turbine into the environment, it can be used for freshwater and cooling production. Meantime, the use of nanoparticles increases the heat transfer rate of the cooling process in the wind turbines, and hence more freshwater and cooling can be obtained. This concept is also accounted for in this study by presenting thermodynamic and thermoeconomic modeling of a new trigeneration system, using three types of nanoparticle namely Cu, CuO, and TiO2 in the base fluid of water. The results showed that Cu/water nanofluid had the highest performance since it produced more freshwater and cooling capacity, while TiO2/water mixture had the lowest performance. In comparison with the reference system, 7.135 kW power can be saved for a cooling capacity of 56.6 kW if the proposed system is used at a wind speed of 12 m/s. Increasing Cu concentration from 0.5% to 7% increases the freshwater rate from 126.9 L/day to 144.5 L/day, cooling load from 5.1 kW to 5.8 kW, supply air volume rate from 9.27 m 3 / m i n to 10.56 m 3 / m i n , energy efficiency from 45.47% to 51.68%, and exergy efficiency from 11.04% to 12.12%. At last, two cities of Manjil and Kahak are selected as case study benchmarks and the results are further expanded for each case.

The Smoothed Particle Hydrodynamics (SPH) method is extended to solve magnetostatic problems involving magnetically interacting solid bodies. In order to deal with the jump in the magnetic permeability at a fluid-solid interface, a consistent SPH scheme is utilized and a modified formulation is proposed to calculate the magnetic force density along the interface. The results of the magnetostatic solver are verified against those of the finite element method. The governing fluid flow equations are discretized using the same SPH scheme, developing an efficient method for simulating the motion of paramagnetic solid bodies in a fluid flow. The proposed algorithm is applied to a benchmark problem including a suspended paramagnetic solid body moving under the influence of a non-uniform magnetic field and the result is validated against literature. The proposed method is further verified by simulating the magneto-hydrodynamic interaction of two suspended circular cylinders. As a more complex test-case, the evolution of a suspended magnetic chain under the influence of a rotating magnetic field is also simulated. The deformation of a chain formed by a number of paramagnetic solid bodies in a shear flow is simulated. Steady state and dynamic responses of the magnetic chain are investigated under steady and oscillatory shear flows. The effects of Reynolds number, solid volume fraction, strength of the external magnetic field and the number of solid bodies forming the chain, are discussed.

Altering the wettability of a gas-liquid system from liquid-wetting to intermediate gas-wetting is a novel strategy for removing condensate from gas condensate reservoirs. In this paper, the role of a silica nanofluid modified by fluorine groups in the wettability alteration of seven carbonate samples was investigated. An acid test and Energy Dispersive X-ray Spectroscopy analysis were carried out to identify the levels of calcite and dolomite as dominant carbonate minerals and evaluate the coating ability of the proposed chemical used on carbonate surfaces. Contact angle measurements and spontaneous imbibition experiments were conducted before and after wettability alteration. In addition, gas flooding experiments were conducted on three permeable core samples to investigate the effect of the nanofluid on the fluid flow at the core scale. Contact angle measurements demonstrated that the wetting tendency of core samples altered from liquid-wetting into gas-wetting after surface treatment, and a higher contact angle was achieved for carbonate cores with less dolomite than calcite. EDX analysis showed more fluorine and silica adsorption on calcite, compared to dolomite cores. After surface modification, the brine imbibed into carbonate core samples 1 to 7 decreased by 0.104, 0.174, 0.0016, 0.773, 0.355, 0.056, and 0.279, respectively. Core flooding results demonstrated that the recovery factor of three permeable core samples increased from 56.52%, 49.69%, and 65.33%–69.34%, 56.75%, and 76.72%, respectively.

Fluid flow in porous media is extensively associated with Darcy's law. Deviations from Darcy's law and its limitations result in modifications known as non-Darcy flow at high velocity and Pre-Darcy flow at low velocity. In this paper, experiments were conducted to explore significance of departure from linearity at low fluid velocity (Pre-Darcy flow) in porous media. Effect of different gas types on the onset of Pre-Darcy flow were studied for CH4, CO2 and N2 as gas phase. Superficial velocity versus pressure gradient was measured and different onset values were reported. The minimum observed Darcy velocity was 0.189 x10-05 m/s, below which Pre-Darcy flow prevails. Dimensional analysis was performed in terms of friction factor and Reynolds number for different particle size of 0.15, 0.25 and 0.3 mm. Pre-Darcy, Darcy and Non-Darcy flow regimes were observed and characterized in terms of Re√k, Red and Rep. The range of Reynolds number were reported for different flow regimes, different particle sizes and different types of fluids.

In the present study, a robust Incompressible smoothed particle hydrodynamics (ISPH) method, based on an advanced Smoothed particle hydrodynamics (SPH) discretization, is introduced to study the effects of the non-Newtonian power-law index and stirrer frequency on fluid mixing in an active micromixer that uses an oscillating stir-bar. Two Reynolds numbers (20 and 72) are considered, and more than 70 SPH simulations are carried out, in order to investigate the effects of the power-law index and stirrer frequency on fluid mixing. The results show that this active micromixer is more efficient at the lower power-law indices.

Carbon Capture and Storage is developed as state-of-the-art method to bring CO 2 emissions under control. Among different options, saline aquifers are viable choices to sequestrate CO 2 in which this gas can be dissolved in the pertinent brine through a gradual progressive diffusive layer and subsequent possible density-induced convection. Quantification of CO 2 dissolution rate in saline aquifers is dependent on the true estimation of CO 2 diffusivity in brine. In this work, equilibrium dissolution and diffusion coefficient of CO 2 in water-saturated porous medium is modeled. The simple and well-known pressure-decay method is applied numerically in different porous systems. Also, interference of density-driven convection using different permeability values is addressed and the idea of using a porous medium such as glass bead model is proposed to block convective swirls or postpone onset of convection. Convective currents are suppressed at Rayleigh numbers (Ra) fewer than 40. For controlled convective dissolution, the onset of convection should be late enough for that early diffusive dissolution to dominate. Also, convective dissolution should deviate from diffusive dissolution to find the onset of convection and time at the end of early convection. The former and latter require Ra 150, respectively. Under these circumstances, pressure decay results can be analyzed to estimate the gas–liquid diffusion coefficient using early pressure–time data, onset of convection, the maximum Sherwood and time at the end of early convection.

This paper presents a linear perturbation analysis of natural convection in porous media due to density change caused by dissolution of an injected carbon dioxide in saline aqueous phase. The main application is in geological sequestration of CO 2 in deep aquifer. In this study, both density and viscosity of the fluid in the medium are functions of the dissolved substance concentration. Effects of concentration-dependent viscosity and density on the stability of the system are studied parametrically. By linearizing the system of equations, a set of governing equations for perturbed concentration and velocity is derived as a function of density and viscosity derivatives. Then, the eigenvalue problem is solved numerically to obtain growth rate of waves as a function of wave-number. From a quantitative analysis on the onset of instability, it is found that the system is more stable when the viscosity increases more rapidly with concentration. In addition, parametric analysis of density–concentration relationship shows that the form of density–concentration relationship affects the prediction of onset of instability. In this way, concavity of density–concentration function decreases the weight of the top layer and lowers the destabilizing effect of the layer. These findings provide a more realistic outlook to recognize the onset of convection and long-term fate of disposed gas in large-scale geological sequestration of CO 2 .

In this work, dissolution of CO 2 in bulk water is simulated under isothermal pressure decay. Different boundary conditions (BCs) including equilibrium, semi-equilibrium and non-equilibrium are examined at gas/liquid interface. Comparison of our simulated and measured experimental data shows that the non-equilibrium BC can predict dissolution behavior reliably. Other boundary conditions show considerable deviation between model predictions and experimental measurements. On the other side, convective dissolution is found much more active than diffusive mixing, so that the role of diffusive transport is overshadowed. Mass transfer coefficient is highest at the start of dissolution and decreases with time. Results show that when convection is the active mechanism even at late times, it interferes with diffusivity measurements and makes interpretation of diffusion experiment results difficult both at early and later times.

Purpose – The purpose of this paper is to present a detailed algorithm for simulating three-dimensional hydrocarbon reservoirs using the blackoil model. Design/methodology/approach – The numerical algorithm uses a cell-centred structured grid finite volume method. The blackoil formulation is written in a way that an Implicit Pressure Explicit Saturation approach can be used. The flow field is obtained by solving a general gas pressure equation derived by manipulating the governing equations. All possible variations of the pressure equation coefficients are given for different reservoir conditions. Key computational details including treatment of non-linear terms, expansion of accumulation terms, transitions from under-saturated to saturated states and vice versa, high gas injection rates, evolution of gas in the oil production wells and adaptive time-stepping procedures are elaborated. Findings – It was shown that using a proper linearization method, less computational difficulties occur especially when free gas is released with high rates. The computational performance of the proposed algorithm is assessed by solving the first SPE comparative study problem with both constant and variable bubble point conditions. Research limitations/implications – While discretization is performed and implemented for unstructured grids, the numerical results are presented only for structured grids, as expected, the accuracy of numerical results are best for structured grids. Also, the reservoir is assumed to be non-fractured. Practical implications – The proposed algorithm can be efficiently used for simulating a wide range of practical problems wherever blackoil model is applicable. Originality/value – A complete and detailed description of ingredients of an efficient finite volume-based algorithm for simulating blackoil flows in hydrocarbon reservoirs is presented.

In the present study, a robust modified weakly compressible smoothed particle hydrodynamics (SPH) method is introduced in order to examine the micromixing phenomena within a cylindrical paddle mixer. Because it has a Lagrangian nature and it is based on particles, smoothed particle hydrodynamics is an appropriate and convenient method for simulating the moving boundary problems and tracking the particles in the mixing process. The present study thus introduces a convenient SPH method for modelling the mixing process. The straight and cross-shaped blades are considered, and the effects of the fixed rotation, planetary motion of the blade, and position of the blade on the mixing rate are studied. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Date palm trees (Phoenix dactylifera L.) produce approximately 40 kg of burnable waste including dried leaves, spathes, sheaths, and petioles annually. In this paper, the potential of date palm waste as a bioenergy source has been investigated. As a sample project, a power plant has been preliminary designed to simultaneously generate electrical power using a steam Rankine cycle and distilled water by the thermal desalination of seawater using a multiple effect evaporator. The results indicated that a small plant in Bushehr Province in southern Iran which burns 140,000 tons of waste annually can produce approximately 62 GWh of electricity in conjunction with 2.27 million tons of distilled water. This production is equivalent to 75 GWhe/year. Environmental assessments revealed that the use of this amount of biomass leads to a net green-house gas (GHG) reduction of 40,500 tCO2/year.

Instability of the interface between two immiscible fluids representing the so-called Kelvin–Helmholtz instability problem is studied using smoothed particle hydrodynamics method. Interfacial tension is included, and the fluids are assumed to be inviscid. The time evolution of interfaces is obtained for two low Richardson numbers [Formula: see text] and [Formula: see text] while Bond number varies between zero and infinity. This study focuses on the effect of Bond and Richardson numbers on secondary instability of a two-dimensional shear layer. A brief theoretical discussion is given concerning the linear early time regime followed by numerical investigation of the growth of secondary waves on the main billow. Results show that for [Formula: see text], at all Bond numbers, secondary instabilities start in the early times after a perturbation is imposed, but they grow only for Bond numbers greater than 1. For [Formula: see text], however, secondary instabilities appear only at Bond numbers greater than 10. Finally, based on numerical simulations and using an energy budget analysis involving interfacial potential energy, a quantitative measure is given for the intensity of secondary instabilities using interfacial surface area.

A weakly compressible smoothed particle hydrodynamics (WCSPH) method is used along with a new no-slip boundary condition to simulate movement of rigid bodies in incompressible Newtonian fluid flows. It is shown that the new boundary treatment method helps to efficiently calculate the hydrodynamic interaction forces acting on moving bodies. To compensate the effect of truncated compact support near solid boundaries, the method needs specific consistent renormalized schemes for the first and second-order spatial derivatives. In order to resolve the problem of spurious pressure oscillations in the WCSPH method, a modification to the continuity equation is used which improves the stability of the numerical method. The performance of the proposed method is assessed by solving a number of two-dimensional low-Reynolds fluid flow problems containing circular solid bodies. Wherever possible, the results are compared with the available numerical data.

An explicit weakly compressible SPH method is introduced to study movement of suspended solid bodies in Oldroyd-B fluid flows. The proposed formulation does not need further stabilizing treatments and can be efficiently employed to study particulate flows with Deborah to Reynolds number ratios up to around 10. A modified boundary treatment technique is also presented which helps to deal with the movement of solid particles in the flow. The technique is computationally efficient and gives an improved evaluation of fluid-solid interaction forces. A number of test cases are solved to show performance of the proposed method in simulating particulate viscoelastic flows containing circular and non-circular cylinders. The effect of Deborah number on the particle trajectory has been investigated.

SUMMARY A modified weakly compressible smoothed particle hydrodynamics (WCSPH) is presented, which utilizes consistent discretization schemes for spatial derivatives in the flow equations. Here, each SPH particle is considered as a computational point that represents a specific part of the fluid. To overcome non-physical oscillations that usually arise in standard WCSPH, we modified the mass conservation equation by using a numerical filter. This modification is based on the difference between two discretization schemes used for the term ∇⋅∇Pρ. Furthermore, a new implementation of wall boundary condition in SPH is introduced. This condition is imposed on the pressure of wall boundary particles to ensure that the acceleration of each boundary particle in normal direction to the wall is zero. Thus, no penetration through walls will occur. To examine the performance of the modified method, we solved a series of two-dimensional incompressible internal flow benchmark problems. By comparing the result with analytical solutions and the results of the standard WCSPH, we show that the use of consistent schemes in conjunction with the proposed numerical filter improves both accuracy and speed of the numerical method. Copyright © 2011 John Wiley & Sons, Ltd.

Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) can lead to non-physical oscillations in the pressure and density fields when simulating incompressible flow problems. This in turn may result in tensile instability and sometimes divergence. In this paper, it is shown that this difficulty originates from the specific form of spatial discretization used for the pressure term when solving the mass conservation equation. After describing the pressure–velocity decoupling problem associated with the so-called colocated grid methods, a modified approach is presented that overcomes this problem using a different discretization scheme for the second derivative of pressure. The modified scheme is employed for solving a number of benchmark problems including both single-phase and two-phase test cases. Copyright © 2010 John Wiley & Sons, Ltd.

In this paper, a modified finite-volume Eulerian–Lagrangian localized adjoint method (FVELLAM) extended for convection–diffusion problems with a non-linear flux function is introduced. Tracking schemes are discussed using viscous Burgers’ equation. It is shown that in order to have smooth results, only the new time level values should be used in tracking process. Then, the proposed method is employed to study immiscible incompressible two-phase flows in porous media. Various one- and two-dimensional test cases involving internal sources and sinks are solved and accuracy of solution and performance of the method are investigated by comparing the results obtained using FVELLAM with those of fine grid solutions. Finally, it is concluded that although proposed FVELLAM produces satisfactory results even on coarse grids and allows fairly large time-steps, its major advantage is in solving convection-dominated problems in heterogeneous media.

A direct numerical simulation approach is used to investigate the effective non-linear viscoelastic stress response of non-gap-spanning magnetic chains suspended in a Newtonian fluid. The suspension is confined in a channel and the suspended clusters are formed under the influence of a constant external magnetic field. Large amplitude oscillatory shear (LAOS) tests are conducted to study the non-linear rheology of the system. The effect of inertia on the intensity of non-linearities is discussed for both magnetic and non-magnetic cases. By conducting magnetic sweep tests, the intensity and quality of the non-linear stress response are studied as a function of the strength of the external magnetic field. The Chebyshev expansion of the stress response is used to quantify the non-linear intra-cycle behaviour of the suspension. It is demonstrated that the system shows a strain-softening behaviour while the variation of the dynamic viscosity is highly sensitive to the external magnetic field. In a series of strain sweep tests, the overall non-linear viscoelastic behaviour of the system is also investigated for both a constant frequency and a constant strain-rate amplitude. It is shown that the intra-cycle behaviour of the system is different from its inter-cycle behaviour under LAOS tests.A direct numerical simulation approach is used to investigate the effective non-linear viscoelastic stress response of non-gap-spanning magnetic chains suspended in a Newtonian fluid. The suspension is confined in a channel and the suspended clusters are formed under the influence of a constant external magnetic field. Large amplitude oscillatory shear (LAOS) tests are conducted to study the non-linear rheology of the system. The effect of inertia on the intensity of non-linearities is discussed for both magnetic and non-magnetic cases. By conducting magnetic sweep tests, the intensity and quality of the non-linear stress response are studied as a function of the strength of the external magnetic field. The Chebyshev expansion of the stress response is used to quantify the non-linear intra-cycle behaviour of the suspension. It is demonstrated that the system shows a strain-softening behaviour while the vari...

A robust modified weakly compressible smoothed particle hydrodynamics (WCSPH) method based on a predictive corrective scheme is introduced to model the fluid flows engaged with stationary and moving boundary. In this paper, this model is explained and practically verified in three distinct laminar incompressible flow cases; the first case involves the lid driven cavity flow for two Reynolds numbers 400 and 1000. The second case is a flow generated by a moving block in the initially stationary fluid. The third case is flow around the stationary and transversely oscillating circular cylinder confined in a channel. These results in comparison with the standard benchmarks also confirm the good accuracy of the present solution algorithm.

Summary During depletion of gas condensate reservoir, bottom hole pressure falls below dew point pressure and condensate starts to form around well bore. These phenomena reduce gas production significantly. Altering the wettability of gas-liquid system from liquid wetting to intermediate gas wetting is a permanent strategy for removing condensate and achieving high gas recovery. In this paper, Performance of modified silica nanofluid on wettability alteration of carbonate rock types from Iranian gas reservoir is investigated. Carbonate rock types are characterized based on porosity, permeability and rock mineralogy. EDAX analysis and acid test are used to recognize calcite and dolomite as dominate carbonate minerals. Contact angle experiments are conducted before and after wettability alteration to determine surface wetting behaviour due to nanofluid adsorption. In addition, core flooding experiments are conducted on high permeable rock types to investigate effect of nanoparticles on fluid flow at core scale. It is inferred from contact angle results that higher contact angle is achieved for carbonate rock types which have more calcite respect to dolomite. EDAX analysis also showed more adsorption silica and fluorine on these rock types. Core flood experiments demonstrated Enhancement in recovery factor due to improvement gas and condensate relative permeability after surface treatment.

Discretization of spatial derivatives is an important issue in meshfree methods especially when the derivative terms contain non-linear coefficients. In this paper, various methods used for discretization of second-order spatial derivatives are investigated in the context of Smoothed Particle Hydrodynamics. Three popular forms (i.e. "double summation", "second-order kernel derivation", and "difference scheme") are studied using one-dimensional unsteady heat conduction equation. To assess these schemes, transient response to a step function initial condition is considered. Due to parabolic nature of the heat equation, one can expect smooth and monotone solutions. It is shown, however in this paper, that regardless of the type of kernel function used and the size of smoothing radius, the double summation discretization form leads to non-physical oscillations which persist in the solution. Also, results show that when a second-order kernel derivative is used, a high-order kernel function shall be employed in such a way that the distance of inflection point from origin in the kernel function be less than the nearest particle distance. Otherwise, solutions may exhibit oscillations near discontinuities unlike the "difference scheme" which unconditionally produces monotone results., {"references":["L. Lucy, \"A numerical approach to the testing of fission hypothesis,\"\nAstrophysical Journal, vol. 82, pp. 1013-1020, 1977.","R. Gingold and J. Monaghan, \"Smoothed particle hydrodynamics:\nTheory and application to nonspherical stars,\" Astrophysical Journal,\nvol. 181, pp. 275-389, 1977.","ÔÇöÔÇö, \"Kernel estimates as a basis for general particle methods in\nhydrodynamics,\" Journal of Computational Physics, vol. 46, pp. 429-\n453, 1982.","J. Monaghan, \"Simulating free surface flows with sph,\" Journal of\nComputational Physics, vol. 110, pp. 399-406, 1994.","H. Takeda, S. Miyama, and M. Sekiya, \"Numerical simulation of viscous\nflow by smoothed particle hydrodynamics,\" Progress of Theoretical\nPhysics, vol. 92, no. 5, pp. 939-960, 1994.","J. Morris, P. Fox, and Y. Zhu, \"Modeling low reynolds number incompressible\nflows using sph,\" Journal of Computational Physics, vol. 136,\nno. 1, pp. 214-226, 1997.","J. Monaghan, \"Smoothed particle hydrodynamics,\" Reports on Progress\nin Physics, vol. 68, pp. 1703-1759, 2005.","O. Flebbe, S. Munzel, H. Herold, H. Riffert, and H. Ruder, \"Smoothed\nparticle hydrodynamics-physical viscosity and the simulation of accretion\ndisks,\" The Astrophysical Journal, vol. 431, pp. 214-226, 1994.","S. Watkins, A. Bhattal, N. Francis, T. J.A., and Whitworth, \"A new prescription\nfor viscosity in smoothed particle hydrodynamics,\" Astronomy\nand Astrophysics, vol. 119, pp. 177-187, 1996.\n[10] J. Jeong, M. Jhon, J. Halow, and J. van Osdol, \"Smoothed particle\nhydrodynamics: Applications to heat conduction,\" Computer Physics\nCommunications, vol. 153, no. 1, pp. 71-84, 2003.\n[11] J. Bonet and T. Lok, \"Variational and momentum preservation aspects\nof Smooth Particle Hydrodynamic formulations,\" Computer Methods in\nApplied Mechanics and Engineering, vol. 180, no. 1-2, pp. 97-115,\n1999.\n[12] S. Nugent and H. Posch, \"Liquid drops and surface tension with\nsmoothed particle applied mechanics,\" Physical Review E, vol. 62, no. 4,\npp. 4968-4975, 2000.\n[13] J. Bonet, S. Kulasegaram, M. Rodriguez-Paz, and M. Profit, \"Variational\nformulation for the smooth particle hydrodynamics (SPH) simulation of\nfluid and solid problems,\" Computer Methods in Applied Mechanics and\nEngineering, vol. 193, no. 12-14, pp. 1245-1256, 2004.\n[14] Y. Mele'an, L. Sigalotti, and A. Hasmy, \"On the SPH tensile instability\nin forming viscous liquid drops,\" Computer Physics Communications,\nvol. 157, no. 3, pp. 191-200, 2004.\n[15] H. L'opez and L. Sigalotti, \"Oscillation of viscous drops with smoothed\nparticle hydrodynamics,\" Physical Review E, vol. 73, no. 5, p. 51201,\n2006.\n[16] A. Chaniotis, D. Poulikakos, and P. Kououtsakos, \"Remeshed smoothed\nparticle hydrodynamics for the simulations of viscous and heat conducting\nflows,\" Journal of Computational Physics, vol. 182, pp. 67-90,\n2002.\n[17] P. Cleary, \"Modelling confined multi-material heat and mass flows using\nsph,\" Applied Mathematical Modelling, vol. 22, pp. 981-993, 1998.\n[18] J. Monaghan and J. Lattanzio, \"A refined particle method for astrophysical\nproblems,\" Astronomy and Astrophysics, vol. 149, no. 1, pp.\n135-143, 1985.\n[19] I. Schoenberg, \"Contributions to the problem of approximation of\nequidistant data by analytic functions. Part A - On the problem of\nsmoothing or graduation. A first class of analytic approximation formulas,\"\nQuarterly of Applied Mathematics, vol. 4, pp. 45-99, 1946."]}

In the present study, we apply a robust Incompressible Smoothed Particle Hydrodynamics method improved by advanced second-order discretization in order to examine active micromixers equipped with a rotating or an oscillating stir-bar. Since it has a Lagrangian nature and it is based on particles, Smoothed Particle Hydrodynamics is an appropriate and convenient method for the moving boundary and for one-way coupled fluid- solid interactions. However, this method has not been applied to simulate active micromixers. The present study thus introduces a convenient Smoothed Particle Hydrodynamics method for modelling active micromixers. In addition, mixing flow is investigated by considering the vorticity field. Cross-shaped and straight stir-bars are also examined and evaluated. The presented results show that the cross-shaped stir-bar is more efficient than the straight stir-bar. In addition, the rotating cross-shaped stir-bar can be introduced as an appropriate stirrer, while the rotating straight stir- bar demonstrates weak performance.