![]() ![]() A gradual change of the strain rate would not incur the stress over/undershoot phenomenon. The latter can be in the order of milliseconds or below. ![]() For it to be better observed, or to have any important effects on the flow behaviors, with a small change of the strain rate, a short time interval may be required. The manifestation of the stress over/undershoot would depend on how fast and how much the strain rate is changed. Likewise, a stress undershoot corresponds to a sudden decrease of the shear rate. As time goes on, the material is broken, which eases the stress and results in a smaller value of λ a steady state is approached after a certain time. When γ ̇ 1 is suddenly increased to γ ̇ 2 within a short time, λ would remain constant as the microstructure needs time to respond to this sudden change, the shear stress is therefore increased abruptly. (3), the shear stress is calculated as τ = K γ ̇ + λ τ y for a Bingham fluid. For one-dimensional (1D) problem, from Eq. 6 investigated submarine landslide kinematics and tsunami the Bingham model was employed in the former for the muddy debris flow, and the Herschel–Bulkley (HB) model in the latter as the material contained mostly small blocks and soil.Īn interesting characteristic of thixotropic fluids is stress overshoot when they are subjected to a sudden jump in the strain rate. ![]() Thixotropy was not considered, as the problem was limited to low clay concentrations. It was applied to a problem of sediment bed–plate interaction, in which only the yield stress characteristic was taken into account using the Bingham–Papanastasiou model, though experimental data of the sediment suspension exhibited complex behaviors with a yield stress, viscoelasticity, and thixotropy. 4 adopted a two phase mixture model in the framework of Smoothed Particle Hydrodynamics (SPH) to simulate turbulent sediment transport. The simulation was validated using experimental data of Mossaz et al. 1,2 simulated a nonthixotropic yield stress fluid flow over a circular cylinder at several (moderate) Reynolds and Oldroyd numbers. There have been few studies of viscoplastic fluid flows over an obstacle in the literature. The simulation results show that the size and shape of both static and moving unyielded zones are considerably affected by the thixotropic parameters. Various flow characteristics, such as the microstructure evolution and the flow field including the yielded and unyielded zones, are analyzed and discussed in detail. ![]() In addition, the Bingham and/or Herschel–Bulkley model with Papanastasiou’s regularization is utilized. This work aims at investigating the influence of the parameters that control the recovery and breakdown rates on the flow of a thixotropic fluid past a circular cylinder. It is then assumed that the recovery rate depends linearly on the structural parameter, and the breakdown one is a complex function of it and the shear rate. A brief review on thixotropic models for different materials is first carried out. The microstructure is characterized by a dimensionless structural parameter, whose evolution is modeled by a rate equation consisting of two terms representing the rate of the two mechanisms. During a flowing process, two microstructure transition mechanisms are considered to take place simultaneously: the recovery and the breakdown the former makes the materials more solid, while the latter makes them more liquid. Thixotropy is a time-dependent shear thinning property, associated with the microstructural evolution of materials. Non-Newtonian fluids exhibiting complex rheological characteristics, such as yield stress and thixotropy, are frequently encountered in nature and industries. ![]()
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