We propose a single chain slip-spring model, which is based on the slip-spring model by Likhtman [A. E. Likhtman, Macromolecules, 38, 6128 (2005)], for fast rheology simulations of entangled polymers on a GPU. We modify the original slip-spring model slightly for efficient calculations on a GPU. Our model is designed to satisfy the detailed balance condition, which enables us to analyze its static or linear response properties easily. We theoretically analyze several statistical properties of the model, such as the linear response, which will be useful to analyze simulation data. We show that our model can reproduce several rheological properties such as the linear viscoelasticity or the viscosity growth qualitatively. We also show that the use of a GPU can improve the performance drastically.
Laminar, two-dimensional flow of an incompressible thixotropic fluid obeying Moore's model is investigated numerically in a slipper-pad bearing using FVM method. Results will be presented addressing the effect of thixotropic properties and inclination angle on the pressure distribution and load-carrying capacity of the bearing. It is shown that the pressure distribution under the upper pad depends only on the buildup-to-breakdown ratio. It is also predicted that by increasing this ratio, the load-carrying capacity increases, but, the pressure distribution becomes more and more asymmetric with the maximum pressure shifting towards the outlet section of the bearing. Also, for any given set of Moore's model parameters, an increase in the inclination angle is shown to linearly increase the load-carrying capacity of the bearing at small angles. Above a critical inclination angle, however, the rise in the load-carrying capacity becomes nonlinear. Also, by increasing the inclination angle, the location for the occurrence of maximum pressure shifts towards the outlet section of the bearing.
Dynamic birefringence and viscoelasticity of cellulose acetate propionate were measured at various temperatures covering a wide frequency region from the rubbery plateau to the glassy zone in order to determine the viscoelastic segment size of cellulose. The complex Young's modulus was separated into two components, R and G components. From the limiting modulus at high frequencies of the R component, molecular weight of viscoelastic segment was determined as 3100. This value is the largest one among amorphous polymers previously determined. Larger dynamic segment size reflects the rigid chain structure of β linked D-glucose units (about 10 glucose units per segment). Number of segments per entanglement strand was also estimated to be 4. Reflecting the small segment number per entanglement strand, most of reorientation of segment (relaxation of stress) was found to be delayed until the terminal flow zone.
Mixtures of surfactants and polymers are known to reduce drag, but their use is limited because of environmental concerns. In this study, surfactant/nanobubble mixtures were passed through several sizes of micro-orifices, and the resultant pressure drops, as compared with water and only surfactant solution, were evaluated. For anionic surfactant/nanobubble mixtures, the experimentally observed pressure drop was less than that for water. However, it was found that the pressure drop was greater than that for only anionic surfactant solution. In the case of non-ionic and cationic surfactants, the experimental results of mixed nanobubble liquids were less than those for water and only surfactant solution. This phenomenon is considered in terms of interface behavior and attributed to the electrical interaction between an electric double layer and nanobubbles.
Concentrated suspensions of non-Brownian spheres dispersed in Newtonian / viscoelastic carrier liquids were placed under large amplitude oscillatory shear flows. Transient responses in shear rate and strain after each shear reversal were examined under sinusoidal stresses applied. The viscoelastic suspensions have showed similar transient responses with fluidity increase to those observed with Newtonian carrier liquids. It was considered that these responses were caused with collapse and rearrangement in the particulate microstructure. In order to clarify the influence of the viscoelasticity of carrier liquids on the fluidity increase, deviations in the shear rate from purely viscous predictions and characteristic strains were estimated. The flows of viscoelastic suspensions were reversed before stress reversal applied due to the elastic recoil of the polymers in the carrier liquid. Such kind of historical effects of viscoelasticity increased the fluidity at the first stage in the transient period and finished the whole transient phenomena with smaller strains. But, the viscoelasticity resisted the rearrangement in the latter half stage. Typical gap between the particles was introduced to obtain dependence of the volume fraction on the transient responses. The characteristic strains to the whole transient responses were normalized well with the gap both for Newtonian and viscoelastic cases.