Sardar Malekmohammadi

An experimental study of laminar displacement flows in narrow vertical eccentric annuli

We present an experimental study of slow laminar miscible displacement flows in vertical narrow eccentric annuli. We demonstrate that for suitable choices of viscosity ratio, density ratio and flow rate, we are able to find steady travelling wave displacements along the length of the annulus, even when strongly eccentric. Small eccentricity, increased viscosity ratio, increased density ratio and slower flow rates all appear to favour a steady displacement for Newtonian fluids. Qualitatively similar effects are found for non-Newtonian fluids, although the role of flow rate is less clear. These results are largely in line with predictions of a Hele-Shaw style of displacement model (Bittleston et al ., J. Engng Math ., vol. 43, 2002, pp. 229–253). The experiments also reveal interesting phenomena caused largely by secondary flows and dispersion. In the steady displacements, eccentricity drives a strong azimuthal counter-current flow above/below the advancing interface. This advects displacing fluid to the wide side of the annulus, where it focuses in the form of an advancing spike. On the narrow side we have also observed a spike, but only in Newtonian fluid displacements. For unsteady displacements, the azimuthal currents diminish as the interface elongates. With a strong enough yield stress and with a large enough eccentricity, unyielded fluid remains behind on the narrow side of the annulus.

Multiscale Stochastic Modeling of the Elastic Properties of Strand-Based Wood Composites

AbstractThis paper introduces a novel modeling approach for wood composites using concepts of numerical homogenization employed in synthetic composites. It describes a multiscale model based on a unit cell that incorporates both the wood and resin phases for simulating structural composite lumber made of strands. In this approach, constant resin thickness and strand geometry, elastic properties of constituents, and perfect bonding between wood and resin are assumed. The multiscale modeling is composed of two steps. The first step estimates the effective elastic properties of a unit cell based on the numerical homogenization with periodic boundary conditions. The second step consists of a macroscopic finite element structural analysis of a beam (assembly of several unit cells) under three-point bending. Random distribution of strand orientation that may be encountered in an actual composite beam is introduced at this stage. Results indicate a significant influence of the resin. The first step of the approa...

Analytical micromechanics equations for elastic and viscoelastic properties of strand-based composites

Using the principles of classical micromechanics, analytical equations are developed in this paper to estimate the effective orthotropic properties of a unit cell of strand-based composites according to their constituent phase properties and their microstructural features such as resin thickness, void content and strand geometrical characteristics. Although a special type of strand-based wood composite product, Parallel Strand Lumber, is considered here as an illustrative example, the methodology can be used for other wood composites consisting of high volume fraction of wood strands. The predictive accuracy of the derived analytical equations is investigated through comparisons with numerical results. Finally, applications of these equations in a linear viscoelastic analysis are discussed. The analytical micromechanics models developed here provide an efficient means of computing effective properties of a unit cell of strand-based composites. These models can then be used within a multi-scale modelling framework that has been developed previously to simulate the macroscopic behaviour of structures made of such materials.

A comprehensive multi-scale analytical modelling framework for predicting the mechanical properties of strand-based composites

A multi-scale modelling framework was developed for predicting the mechanical properties of strand-based wood composites. This framework is based on closed-form analytical models at three different resolution levels; micro-, meso- and macro-mechanical. A preprocessing step was performed to provide the input data for the three main modelling steps in this framework. Finite element-based mechanical analyses were employed to verify the accuracy of the analytical models developed for the first two steps. The predictive capability of the entire framework was validated using a set of experimental data reported in the literature. Although the methodology presented is general, it has specifically been applied here to predict an important structural property (modulus of elasticity, MOE) of a special strand-based wood composite product, namely, oriented strand board (OSB). The MOE predictions of OSB panels showed reasonable agreement with the available experimental data, thus providing confidence in the practical utility of this easy-to-use and efficient analytical modelling tool for predicting the properties of wood composites employed in structural members.

An experimental study of two multi-fluid flows of interest to the oilfield cementing industry

In this work two multi-fluid flows are studied. In the first project, displacement flows in an eccentric annulus were studied experimentally. Displacement flows occur in the oil and gas industry during well construction when drilling mud is displaced by a cement slurry. To remove mud effectively, it is important to design the fluid rheology so that a steady displacement front can be achieved when displacing along an eccentric annulus. In our research, we have investigated the effects of viscosity, density and eccentricity of inner pipe on the interface dynamics. An experimental matrix is devised in a manner to capture the boundary between steady and unsteady displacements for specific pairs of fluids, and to compare against previously published models. Reasonable qualitative agreement was achieved however a systematic discrepancy was observed due to the presence of secondary flows and dispersion in the experiments. These effects have not been studied carefully so far and more sophisticated models are needed to predict this type of flow. In the second project, slumping flows of two non-Newtonian fluids in horizontal closed pipes were studied. This type of flow occurs during the abandonment of horizontal oil and gas wells, when sealing the well through the setting of cement plugs. We have studied the effects of changes in density difference and of small deviations from a perfectly horizontal inclination. The effects of these parameters on the slump length versus time were analyzed. Comparison of numerical and experimental results shows broadly similar trends, but with some qualitative differences also observed, possibly due to interfacial effects.

Slump Flows inside Pipes: Numerical Results and Comparison with Experiments

In this work an analysis of the buoyancy‐driven slumping flow inside a pipe is presented. This flow usually occurs when an oil well is sealed by a plug cementing process, where a cement plug is placed inside the pipe filled with a lower density fluid, displacing it towards the upper cylinder wall. Both the cement and the surrounding fluids have a non Newtonian behavior. The cement is viscoplastic and the surrounding fluid presents a shear thinning behavior. A numerical analysis was performed to evaluate the effects of some governing parameters on the slump length development. The conservation equations of mass and momentum were solved via a finite volume technique, using Fluent software (Ansys Inc.). The Volume of Fluid surface‐tracking method was used to obtain the interface between the fluids and the slump length as a function of time. The results were obtained for different values of fluids densities differences, fluids rheology and pipe inclinations. The effects of these parameters on the interface shape and on the slump length versus time curve were analyzed. Moreover, the numerical results were compared to experimental ones, but some differences are observed, possibly due to chemical effects at the interface.In this work an analysis of the buoyancy‐driven slumping flow inside a pipe is presented. This flow usually occurs when an oil well is sealed by a plug cementing process, where a cement plug is placed inside the pipe filled with a lower density fluid, displacing it towards the upper cylinder wall. Both the cement and the surrounding fluids have a non Newtonian behavior. The cement is viscoplastic and the surrounding fluid presents a shear thinning behavior. A numerical analysis was performed to evaluate the effects of some governing parameters on the slump length development. The conservation equations of mass and momentum were solved via a finite volume technique, using Fluent software (Ansys Inc.). The Volume of Fluid surface‐tracking method was used to obtain the interface between the fluids and the slump length as a function of time. The results were obtained for different values of fluids densities differences, fluids rheology and pipe inclinations. The effects of these parameters on the interface sh...