RESUMEN
To explore the influence of different wax components and the shear effect exerted by the pump and pipe wall in the process of crude oil pipeline transportation on the microbehavior of wax aggregation in crude oil at low temperatures, molecular dynamics models of binary and multivariate systems of crude oil with different wax components are established in this paper. The simulation results are compared with the existing experimental results and the NIST database to verify the rationality and accuracy of the models. By using the established binary model to simulate four crude oil systems containing different wax components, it can be found that the longer the wax molecular chain, the more easily the wax molecules aggregate. The influence of temperature on the aggregation process of wax molecules with different chain lengths is also studied. The lower the temperature, the greater the difference in wax molecular aggregation degree caused by the difference in molecular chain length. Nonequilibrium molecular dynamics is used to simulate the shear process of a multivariate system of crude oil, and the micromechanisms of the shear effect on the aggregation process of wax molecules are studied. Shearing can destroy the stable structure of crude oil, resulting in the orientation and conformational transformation of wax molecules, and obtaining the region of wax molecules sensitive to temperature and shear effects, the temperatures of which are below the wax precipitation point and the shear rate of which is lower than the maximum shear rate to prevent the molecular structure from being destroyed. At the same time, the sensitivity of wax components with different chain lengths to the shear effect is studied. The research results provide theoretical guidance for ensuring the safe and economic operation of waxy crude oil production.
RESUMEN
The effect of shear on heat-induced changes in milk protein concentrate suspensions was examined at different pH levels, revealing novel insights into micellar dissociation and protein aggregation dynamics. Milk protein concentrate suspensions, adjusted to pH of 6.1, 6.4, 6.8, or 7.5, underwent combined heat (90 °C for 5 min or 121 °C for 2.6 min) and shear (0, 100, or 1000 s-1) treatment. The fragmentation of protein aggregates induced by shear was evident in the control MPC suspensions at pH 6.8, irrespective of the temperature. At pH 7.5, shear increased the heat-induced micellar dissociation. This effect was particularly pronounced at 121 °C and 1000 s-1, resulting in reduced particle size and an elevated concentration of κ-casein (κ-CN) in the non-sedimentable phase. At pH 6.1 or 6.4, shear effects were dependent on sample pH, thereby modifying electrostatic interactions and the extent of whey protein association with the micelles. At pH 6.1, shear promoted heat-induced aggregation, evidenced by an increase in particle size and a significant decline in both whey proteins and caseins in the non-sedimentable phase. At pH 6.4, shear-induced fragmentation of aggregates was observed, prominently due to comparatively higher electrostatic repulsions and fewer protein interactions. The influence of shear on heat-induced changes was considerably impacted by initial pH.
RESUMEN
This paper proposes a method to evaluate the effect of shear on the deflection of reinforced concrete (RC) beams. The deflection of RC beams due to the effects of flexural and shear cracks shows different results from those obtained from the elastic theory. The effect of shear on deflection was compared and analyzed in this study, on the basis of experimental results and elastic theory using the virtual work method. The shear effect on the deflection of RC beams by elastic theory was extremely small. However, experimental results showed a difference of over 40% from the results predicted by elasticity theory. In this study, a new method was developed to reasonably predict the deflection of flexure-critical RC beams using the deflection incremental coefficient due to shear. The proposed method was compared with the existing experimental results obtained from the literature for verification. As a result of the comparison, the deflection obtained using ACI 318-19 underestimated the actual deflection by approximately 33%, whereas the deflection obtained by the proposed method predicted the experimental results relatively accurately.
RESUMEN
In the rolling process of heavy cylinders, the deformation section is subjected to the effects of compression and shear. In order to analyze the influences of the shear effect on the microstructure evolution characteristics, a mathematical model was established and the rolling process was simulated. Firstly, shear-compression specimen (SCS) and ordinary cylinder specimens were designed, high-temperature compression experiments were carried out and the mathematical model of microstructure evolution considering shear effect was established; then, a program based on finite element software was developed to simulate the microstructure evolution process, and the feasibility of the development program was verified by compression experiments. Finally, a macro-micro coupling model based on the development program was established to simulate the microstructure evolution of the heavy cylinder during the rolling process. Then, the influence of the shear effect on the microstructure evolution was analyzed. The results showed that the shear effect had a great influence on the heavy cylinder. Dynamic recrystallization was more likely to occur in the heavy cylinder during the rolling process and the grain refinement was more obvious; compared with the case without considering the shear effect, the volume fraction of dynamic recrystallization was increased by 0.25%, and the grain size was refined by 30 µm.