A macroscopic viscoelastic model of magnetorheological elastomer with different initial particle chain orientation angles based on fractional viscoelasticity

In this paper, a macroscopic viscoelastic modeling method for magnetorheological elastomer (MRE) based on fractional derivative model is presented to describe the dynamic viscoelastic properties of MRE with different initial particle chain orientation angles. The angle between the particle chain and the applied magnetic field is used as an indicator to describe the directionality of the particle chain. MRE samples with different initial inclination angles have been designed and fabricated. The dynamic viscoelastic properties of different MRE samples under shear working mode were measured using a parallel plate rheometer. The dynamic viscoelastic properties of MRE with different initial inclination angles are analyzed under the test conditions of different strain amplitude, frequency and magnetic flux density. The test results show that the initial inclination angle of the particle chain in the MRE has significant effect on the dynamic viscoelastic properties of the MRE. A polynomial function is used to describe the relationship between the initial particle chain orientation angle and the magneto-induced modulus of MRE. A phenomenological model of magneto-induced modulus is established based on the fractional derivative model. The model parameters are identified using the nonlinear least square method. The predicted values of the model are in good agreement with the experimental results, indicating that the model can well describe the dynamic viscoelastic properties of MRE.

Prediction of Surface Profile Evolution of Workpiece and Lapping plate in Lapping Process

Lapping has a history of hundreds of years, yet it still relies on the experience of workers. To improve the automaticity and controllability of the lapping process, a modeling method of friction and wear is developed to predict the surface profile evolution of the workpiece and lapping plate in the lapping process. In the proposed method, by solving the balance equations of resultant force and moment, the inclination angles of the workpiece can be calculated, thus more accurate contact pressure distribution of the workpiece/lapping plate interface can be calculated. Combined with the material removal rate model, the continuous evolution process of the workpiece and lapping plate can be predicted in the lapping process. The modeling method was validated by a lapping test of a flat optical glass (Φ 100 mm) with a composite copper plate. The results show that the proposed method can predict the evolution of the surface profile of the workpiece and lapping plate with high accuracy. Consequently, the lapping plate can be dressed at the right time point. Benefit from this, in the validation test the PV value of the workpiece (with 5 mm edge exclusion) was reduced from 5.279 μm to 0.267 μm in 30 min. The proposed surface profile evolution modeling method not only improves the lapping efficiency but also provides an opportunity to understand the lapping process.

Research on the Wing-Type Antiscour Device of Pier Based on Scour Test and Numerical Simulation

In order to reduce the local scour before the antiscour device of piers, this paper proposed an improvement on a “V-type” device. That was to say, wing plates were set on the surface of the “V-type” device to enhance the diversion and reduce the local scour. To explore the protection effect of the modified device, the inclination angles of the wing plates were set to three angles, and the scour characteristics around the device were studied through the flume scour test and numerical simulation test. The results showed that the wing plates can reduce the impact force of the diving flow which was at the front end of the protective device. Besides, they could also disturb the flow around both sides of the device and weaken its sediment carrying capacity. Thus, the local scour around the device was effectively reduced. Especially, when the wing plates were 30°, the performance of reducing the local scour was the best.

Binary Fractions of G and K Dwarf Stars Based on Gaia EDR3 and LAMOST DR5: Impacts of the Chemical Abundances

Based on the large volume Gaia Early Data Release 3 and LAMOST Data Release 5 data, we estimate the bias-corrected binary fractions of the field late G and early K dwarfs. A stellar locus outlier method is used in this work, which works well for binaries of various periods and inclination angles with single-epoch data. With a well-selected, distance-limited sample of about 90,000 GK dwarfs covering wide stellar chemical abundances, it enables us to explore the binary fraction variations with different stellar populations. The average binary fraction is 0.42 ± 0.01 for the whole sample. Thin-disk stars are found to have a binary fraction of 0.39 ± 0.02, thick-disk stars have a higher one of 0.49 ± 0.02, while inner halo stars possibly have the highest binary fraction. For both the thin- and thick-disk stars, the binary fractions decrease toward higher [Fe/H], [α/H], and [M/H] abundances. However, the suppressing impacts of [Fe/H], [α/H], and [M/H] are more significant for the thin-disk stars than those for the thick-disk stars. For a given [Fe/H], a positive correlation between [α/Fe] and the binary fraction is found for the thin-disk stars. However, this tendency disappears for the thick-disk stars. We suspect that it is likely related to the different formation histories of the thin and thick disks. Our results provide new clues for theoretical works on binary formation.

Choosing the flow part geometric shape of the dredge pumps for viscous fluids

Purpose. Search for the possibility of increasing the efficiency of dredge pumps for viscous fluids by determining the rational values of the blade-outlet inclination angles in the pump impellers. Methods. During the research, the following is used: theoretical studies of the structure of the viscous fluids flowing through the flow part of dredge pumps; the method of three-dimensional software-simulation modeling of hydrodynamic processes using the Ansys software package; the methods of rational experiment planning for selecting the values of the number of points in the computational grid when optimizing the geometric parameters of the dredge pump impellers; methods of mathematical statistics and correlation analysis. Findings. It has been proven that the main reason for the failure of the flow part components in the dredge pumps is the manifestation of the influence of cavitation processes, which can be eliminated by changing the blade-outlet inclination angles in the pump impellers. A software-simulation complex for the automated design of the flow parts in the dredge pumps has been developed based on the use of optimization algorithms and computational fluid dynamics methods, which makes it possible to design dredge pumps with optimal characteristics that ensure their efficient operation with maximum efficiency values. It has been determined that one of the main factors influencing the head developed by dredge pumps and the efficiency value is the blade-outlet inclination angle in the pump impellers. Originality. Scientific novelty is in the scientific substantiation and development of a simulation-mathematical method for calculating the geometric parameters of the flow part in dredge pumps for viscous fluids at the design stage. Practical implications. The developed method for determining the rational blade-outlet inclination angles of the impellers in the dredge pumps for viscous fluids can be recommended to scientific-research and industrial organizations for use in the improvement, design and operation of the dredge pumps.