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Abstract:To simulate the bending behavior of wheat straw, a flexible straw model was developed based on the Hertz-Mindlin with bonding model using discrete element method. The proposed model was constructed by bonding straw units (filled by multi-spherical method) through parallel bonding keys. By means of a three-point bending test, single-factor sensitivity analysis and calibration of bonding parameters were performed. Results showed that elastic modulus of the flexible straw enhanced with the increase of bonded disk radius, normal stiffness per unit area and shear stiffness per unit area. The three bonding parameters were respectively calibrated to be 2.11 mm, 9.48×10 9 N/m 3 and 4.67×10 9 N/m 3 by solving the regression equation developed from Box-Behnken design. The simulated elastic modulus (in terms of those three calibrated parameters) exhibited 4.20% difference with the measured one. It proved that the flexible straw could accurately demonstrate bending property of the wheat straw. This would not only help to improve accuracy in simulating wheat straw, but also provide references for flexible straw modeling and parameters calibration of other crops.

To accurately and efficiently remove unripe fruit, flowers, leaves, and other impurities in machine-harvested Lycium barbarum L., winnowing equipment for machine-harvested L. barbarum based on the principle that different materials have different flight coefficients was designed. To optimize the structure and working parameters of winnowing equipment, this study adopted the free flow resistance model to establish a horizontal airflow model based on C++ in Microsoft Visual Studio. A discrete element method (DEM) simulation of ripe fruit in the horizontal airflow was performed using EDEM software. Results showed that the optimal parameters included an airflow speed of 5-6 m/s, input conveyor speed of 0.4-0.6 m/s, and input-output conveyor distance of 260-270 mm. We used three factors and three levels in a quadratic orthogonal rotation design to establish mathematical models regarding the rate of impurity change and the clearance rate of ripe fruit based on the airflow speed, input conveyor speed, and input-output conveyor distance. We also analyzed the effects of all factors on the rate of impurity change and the clearance rate of ripe fruit. The optimal parameter combination was an airflow speed of 5.52 m/s, input conveyor speed of 0.5 m/s, and input-output conveyor distance of 265.04 mm. The field experiment showed that the rate of impurity change and the clearance rate of ripe fruit were 89.74% and 8.71%, respectively. Findings provide a design basis for future research on winnowing equipment for machine-harvested L. barbarum.

A broadband absorber composed of silicon rods and nickel ground is proposed in the visible band. The absorption above 98% can be obtained in the frequency range of [Formula: see text] THz with strong polarization independence and angle independence. The impedance matching theory and field distributions of eigenmodes are used to analyze the physical mechanism of the broadband absorption. The absorber has a simple structure with only two layers, which is composed of silicon and nickel. Nickel is a non-precious metal, which is cheaper than the precious metal materials commonly used in metamaterial absorber. The proposed cost-effective absorber with simple structure has great potential in the application of solar cells.

A broadband MoS2-based absorber composed of Ag rod/MoS2/dielectric/Ag is proposed in the visible band. The relative bandwidth is 65% for the absorption above 80%. The absorber also has the properties of polarization-independence and wide-angle absorption. Impedance matching theory is used to analyze the physical mechanism of the broadband absorption. By investigating the absorption property of each part of the absorber, it is found that the absorption is enhanced by introducing the two-dimensional material MoS2. The broadband absorber can be changed to be multiband absorber by changing the thickness of dielectric substrate. This structure provides a new perspective to enhance absorption in the visible band and has promising applications in solar cells.