Sharif Digital Repository

This article describes the results of experimental observations in pulsating Simple Shear Flows (SSF). A uniform-mean-gradient shear flow was generated within the test section of an open circuit wind tunnel. Transverse arrays of honeycomb channels with differing resistances were used to generate shear flow at low shear rates (less than 20 s-1). A set of rotating vanes pulsated the flow field at 8.5 Hz and 18 Hz. Instantaneous velocity was measured by employing a two-component hot wire anemometry technique. The experimental credibility of the facility was established in stationary SSF. In pulsating flows the pulsation effects on mean shear rate, the kinetic energy of turbulence, Reynolds... 

In this paper, pulsating grid-generated turbulence is studied. A two-component hot wire anemometry technique is used. The pulsation effects on characterizing lenght scales and the statistical description of fluctuations are studied in comparison with their stationary counterparts. No significant change in the character of the turbulent flow with pulsation is observed  

In this study, polypropylene/carbon nanotube nanocomposites were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. In this system, magnesium ethoxide and multiwall carbon nanotubes (MWCNTs) are jointly used as catalyst supports. SEM images reveal the distribution and quite good dispersion of MWCNTs throughout the polypropylene (PP) matrix. The thermal properties of the samples were examined using DSC and TGA tests. The results show that the crystallization temperature of the nanocomposites significantly increases while the melting point is not markedly affected. In addition, the thermal stability is improved. The melt rheological properties of PP/MWCNT... 

The results of several monotonioc push-out tests on polypropylene concrete with channel shear connectors are presented in this research. The results are compared with ordinary concrete specimens with the same test setup. The effect of confining reinforcement on the shear capacity and ductility of polypropylene concrete composite system is investigated  

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. In fact such methodologies consider cavitation flow statically, rather than taking dynamic effects of overall flow into account. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Thereby, in order to configure the system conditions which may be cause of cavity perturbation and so system oscillation, we need to use proper methodologies in which... 

We use coarse grained molecular dynamics simulations to investigate diffusion properties of sheared lipid membranes with embedded transmembrane proteins. In membranes without proteins, we find normal in-plane diffusion of lipids in all flow conditions. Protein embedded membranes behave quite differently: by imposing a simple shear flow and sliding the monolayers of the membrane over each other, the motion of protein clusters becomes strongly superdiffusive in the shear direction. In such a circumstance, the subdiffusion regime is predominant perpendicular to the flow. We show that superdiffusion is a result of accelerated chaotic motions of protein-lipid complexes within the membrane voids,... 

Recorded accelerograms in the regions near active faults may have specific characteristics that inclusion of their effects on the response of structures is necessary. Of particular importance are permanent displacement, i.e. fling-step, rupture directivity pulses and high-frequency content. Several researchers have focused on the effects of rupture directivity pulses on response of structures. They have shown that long-period structures are severely affected by these types of excitations. However, in near-fault regions, the question 'which building structures are long period?' has not been clearly and quantitatively answered. In this paper, responses of 10-, 20-, 30- and 40-story steel... 

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... 

A damage-plasticity based mixed axial-shear-flexural (PVM) link element for the inelastic analysis of frames is introduced in this paper. The multi-surfaces yield concept is utilized in the definition of the element. The yield surfaces are defined in deformation space and interaction of axial-shear-flexural deformations is considered by defining non-rectangular yield surfaces. The element is capable of considering damage and post-peak softening behavior. The analytical results of introduced element are verified by existing experimental results of steel beam to column connection and it is indicated that the analytical results have reasonable agreement with the test results. Nonlinear dynamic... 

Standard Penetration Test (SPT) is the most commonly used insitu test for soil characterization, including the liquefaction resistance. Many studies have sought to correlate SPT number to cyclic resistance ratio (CRR) as a frequently-used approach for assessment of liquefaction potential. However, it has been shown that SPT has major deficiencies (e.g., inaccuracy in coarse sands and clays) which have given rise to development and utilization of new characterization methods such as geophysical tests (e.g., down-hole and cross-hole). In this paper, a comparison is made between the results of SPT and geophysical tests in three boreholes through the body and foundation of Mahabad Dam (located... 

Diversion in heterogeneous carbonate reservoirs plays the most important role to the success of acidizing. Without the use of diversion, more acid preferentially flows into the high-permeability region and leaves the low-permeability region underreacted. But a clear understanding of diverting agents, such as polymer-based in-situ-gelled acids, can help uniformly stimulate the near-wellbore region. In this paper, we correct the rheological model that was developed by Ratnakar et al. (2013) according to experimental data from Gomaa and Nasr-El-Din (2010b) by considering shear-rate effect in a two-scale continuum model. It is found that the rheology parameters and shear rate are influential... 

We report the observation of the oscillatory and irregular motion of solid spheres settling under the influence of gravity in a thixotropic yield-stress fluid, namely, a suspension of Laponite. The size of the ball and the aging time of the Laponite suspension are found to be two important parameters that determine whether oscillations occur. The irregular motion may be related to the existence of an unstable flow region and shear banding as is concluded from comparisons with rheological measurements, namely, the flow curve and creep tests, using the same Laponite suspensions. © 2017 The Japan Society of Applied Physics  

Based on the results of recent studies, comprehensive characterization of the behavior of infilled rock fractures under saturated and unsaturated conditions requires knowledge of morphological details of fracture surface, as well as state of stress of infill materials and their initial innate conditions (e.g., void ratio, water content, degree of saturation and dry density). This paper describes a semi-empirical equation to interpret the effects of wall-roughed nature of the fractures and presence of partially saturated fine materials within the fractures on the behavior of infilled rock fractures during shear. The proposed equation incorporates the soil-water retention curve parameters as... 

We present a quantitative analysis on the response of a dilute active suspension of self-propelled rods (swimmers) in a planar channel subjected to an imposed shear flow. To best capture the salient features of the shear-induced effects, we consider the case of an imposed Couette flow, providing a constant shear rate across the channel. We argue that the steady-state behavior of swimmers can be understood in the light of a population splitting phenomenon, occurring as the shear rate exceeds a certain threshold, initiating the reversal of the swimming direction for a finite fraction of swimmers from down- to upstream or vice versa, depending on the swimmer position within the channel.... 

To investigate the influences of microstructure changes on dilatancy of unsaturated loess at high suctions, a direct shear box device using the vapour equilibrium technique was used. Through conducting two series of direct shear tests on both intact and recompacted loess specimens and also investigating microstructural changes using the mercury intrusion porosim-etry (MIP) technique, a linear increase in dilatancy with suctions ranging from 8 to 230 MPa can be identified at different net stresses. The enhanced dilatancy observed is mainly attributed to desiccation-induced high suctions as the reduction in void ratio due to enhancement of suction was negligible. A macrovoid ratio, eM, may be... 

The dynamic response of a one-dimensional distributed parameter system subjected to a moving mass with constant speed is investigated. An Euler-Bernoulli beam with the uniform cross-section and finite length with specified boundary support conditions is assumed. In this paper, rather a new method based on the time dependent series expansion for calculating the bending moment and the shear force due to motion of the mass is suggested. Governing differential equations of the motion are derived and solved. The accuracy of the numerical results primarily is verified and further the rapid convergence of this new technique was illustrated over other existing methods. Finally, it is shown that a... 

Linear and nonlinear (in both steady and transient shear flows) rheological properties of polyamide 6/acrylonitrile-butadiene-styrene (PA6/ABS) nanocomposite blends have been investigated. Characterization of nanocomposite samples morphology by scanning electron microscopy revealed that with increasing nanoclay loading, size of dispersing phase droplets decreases significantly and their uniformity improved considerably. Transmission electron microscopy observations clearly display a coexistence of intercalate and exfoliate structure for nanoclay in the polymer-blend nanocomposite. On the other hand, we see that the tactoids are collected of a few silicate layers and possibly also of a single... 

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...