Search

Aircraft icing is formed dynamically and appears with porous structure in microcosmic view. This structure directly influences the physical properties of ice, and varies with different icing conditions. In order to know this influence law better, the paper focuses on the difficult about question how micro features changed quantitatively at different temperatures. At the beginning, an information extraction approach is presented based on the image segmentation method. Secondly, some assumptions arc given following the quantitative results of ice in microcosmic view, and then the 3D mathematical model is built based on them. In order to measure distribution characteristics of air pores in the model quantitatively, a computational density is proposed. Finally, take micro-images of ice formed in icing wind tunnel as objects, the feasibility and rationality of the proposed information extraction method and mathematical model are demonstrated. Pores distribution and computational density of ice at different temperatures are also discussed, and the results show highly consistent with the macroscopic viewpoints. Through this paper, it provides quantitative basis for deep understanding of physical phenomenon and properties, and a new way to ice study in microscopic view can be given. [ABSTRACT FROM AUTHOR]

Wheat is one of the main grain crops in China. It has a great significance to ensure its sustained high and stable yield for maintenance food security in China. Studies have shown that the traditional wheat drill sowing technology is not suitable for the requirement of high and stable yield due to the bareness between rows, the insufficient utilization of land resources, the crowding between rows and plants, and the competing for water and fertilizer. Wide-boundary sowing was a new planting type of wheat, which can effectively improve the utilization rate of light, heat, water, fertilizer and land, it is meaningful to develop mechanized wide-boundary sowing technology. Wide-boundary sowing device is a core component of the technology. Structure and parameters optimization of wide-boundary sowing device were studyed based on the discrete element simulation technology, soil tank test and orthogonal test in this paper. The mathematical structure model of seed separated plate was established, spherical radius, installation angle and span were 3 key structural parameters of mathematical structure model. The discrete element simulation platform for wide-boundary sowing device, which mainly consists of particle factory, seed tube, cover plate for protect seed, side plate for support, seed separated plate and seedbed was set up. Taking the coefficient variation of wheat transverse uniformity as evaluation index, the influence of 3 key structural parameters on the performance of wide-boundary sowing device was analyzed, and the structure of seed separated plate was optimized according to the simulation results. The results of single factor simulation test showed that wide-boundary sowing device had relatively small coefficient variation of wheat lateral uniformity when spherical radius, installation angle and span at 130-150 mm, 30°-40° and 80°-100° respectively. According to the results of single factor experiment, the quadratic orthogonal rotation combination simulation experiments were conducted, and the regression equations of 3 key structural parameters and coefficient variation of wheat lateral uniformity were established. The orthogonal results showed that the main and secondary factors affecting coefficient variation of wheat lateral uniformity were installation angle, spherical radius, span, interaction between installation angle and span, and there was a certain interaction between installation angle and span. When spherical radius, installation angle and span were 141.26 mm, 35.53° and 90.72° respectively, coefficient variation of wheat lateral uniformity was minimum. in this case, the coefficient variation of wheat lateral uniformity of theoretical calculation value and simulation test value were 10.58% and 9.21%, respectively, and the deviation was only 1.37%, the regression model was accurate and credible. In order to validate the regression model established by simulation test and the optimization effect of structure parameters, a bench test of wide-boundary sowing device with the structure parameters optimization combination of seed separated plate was carried out. The results showed that the average coefficient variation of wheat lateral uniformity was 13.40%, and the deviation with simulation experiment results was 4.19%, which less than 5%, and considering there may be some errors in the bench test, so it was believed that the results of bench test was basically consistent with simulation test. This paper proved that the discrete element method was feasible to optimize the structural parameters of seed separated plate, the research results could provide references for optimizing the structural parameters of seed separated plate of wide-boundary sowing device and improving the performance of the wide-boundary sowing. [ABSTRACT FROM AUTHOR]

The diffusion angle of forebay of most positive inflow pumping stations is controlled according to 40°, but some projects cannot meet the design code due to the site conditions, it makes the flow patterns in the forebay disordered and affects the operation of water pump. Adding the diversion pier, bottom sill, water pressure plate and slope are used to improve the flow pattern of the forebay with large diffusion angle. In this paper, a pumping station with counter-slope of the South-to-North Water Transfers was studied numerically based on the unsteady Reynolds averaged N-S equation and the Standard k-e turbulence model. Based on the initial design of the project, the flow pattern was calculated by adjusting the diffusion angle. The results show that when the diffusion angle is greater than 80°, the flow in the forebay cannot be effectively diffused, the backflow on both sides is obvious, and the suction condition of side hole water pump is poor and even the water depth is large in the forebay. When the diffusion angle is 50°, the flow pattern in forebay is stable and the flow diffusion is uniform. The counter-slope structure of forebay intake section is conducive to the uniform diffusion of water flow in forebay and the diffusion angle of forebay can be increased to 50° under reverse slope condition. [ABSTRACT FROM AUTHOR]

The final form of blueberry picking is to separate the blueberry fruit growing on the blueberry branch from its branches, so the vibration force produced by picking is greater than the bearing capacity of the fruit handle itself. In order to better achieve the purpose of mechanized blueberry picking, this paper studies the damped vibration inertial force of the blueberry side branch in the blueberry picking. Aiming at the radial vibration of blueberry lateral branches, in order to get closer to the actual vibration situation of lateral branches, the damping coefficient is considered in the mathematical formula derivation, and the influence of damping ratio on vibration force and amplitude is studied emphatically. The experimental data of the vibration inertia force, action position and displacement of the side branches are measured by experiments, and a series of mathematical formulas are derived to establish a mathematical model of the damped free vibration inertial force of the lateral branches. Based on the measured data and mathematical model, the simulation is verified by MATLAB software. The results show that the application of the inertial force with radial damping and free vibration can realize the picking of blueberry in the middle of the side branches. This result can guide the position and direction of the vibration force, and provide a theoretical basis for the mechanized selection of blueberry equipment. [ABSTRACT FROM AUTHOR]

Winter wheat is the most important crop in China, which has a large planting area, a high per unit area yield and a high total output. This is important to the maintenance of national food security. Base-fertilizer application is an important process of winter wheat production, which directly affects the yield of crops, and reasonable and effective use of chemical fertilizer can improve the yield of crops. At present, base-fertilizer of winter wheat is applied to the surface of farmland by manure spreader or laborers. Then the rotary tiller or moldboard plow is used to bury the fertilizer underground. The method has the problems of disordered fertilizer, excessive fertilizer delivery and low utilization efficiency. The depth-setting fertilizer application for winter wheat is an ideal way of fertilization. It can carry out a uniform fertilization to the winter wheat’s underside position with a certain depth, which can reduce fertilizer amount of 10%-20% compared with the traditional fertilization operation. It is a fertilization technique with high output, stable yield and low cost. Combined with the characteristics of rotary tillage fertilizing of winter wheat in Huanghe-Huaihe-Haihe (HHH) zone of China, this paper proposes a precise depth-setting fertilizer application method based on principle of rotary tillage. From the kinematics analysis of rotary blade and soil block respectively, the mathematical model of the positions of fertilizer outlet orifice of steel pipe and the target depth of fertilization was established. In order to validate this mathematical model, a precision rotary tillage fertilization test platform was set up. The test platform includes tractor, depth-controlled component, rotary tillage device, fertilizer ejecting device, precision hydraulic control system and press device. The fertilizer ejecting device is the key part of the test platform. It includes longitudinal beam, fastening bolt, steel pipe of fertilizer ejecting, U-shaped bolt and sleeve. The steel pipe of fertilizer ejecting can be adjusted longitudinally and laterally according to the requirements of the test. In order to accurately validate the mathematical model, 2 groups of progressive experiments were designed and conducted at the National Experiment Station for Precision Agriculture in Xiaotangshan Town, Beijing City in October 2017. After testing, the hardness, humidity and temperature of soil in the test area at the depth of 0-10 cm were 615.0 MPA, 10.9% and 17.6 °C, respectively. In the experiment, the IT245 rotary blade cutting operation parts were selected, and power transfer mechanism used John Deal 1204 tractor. The tractor was controlled at the speed of 1.5 m/s, the rotational speed of rotary blade was stable at 180 r/min, and the rotary tillage depth was set to 200 mm in the verification test. The experiment selected blue fertilizer as the application object. Target fertilization depth was set as 80, 100, 120, 140, and 160 mm, respectively, for the precision fertilization field test, and the actual depth of fertilization was 73, 92, 111, 132 and 151 mm, respectively. The maximum offset deviation of fertilization depth was 9 mm, and the maximum deviation ratio of fertilization depth was 8.75%, which could meet the requirement of the actual production. The results of these experiments show that the mathematical model of the positions of fertilizer outlet orifice of steel pipe and the target depth of fertilization established is trustworthy. The results can be a theoretical basis for design and development of rotary tillage and fertilization equipment. [ABSTRACT FROM AUTHOR]

Mathematical modeling plays an important role in promoting the quality of education and in promoting the cultivation of innovative talents. This paper proposes a teaching and practical teaching system that includes knowledge popularization, classroom teaching, research, discussion and specialization. Based on the guiding ideologies of innovation and creativity, we combine teaching and practical training together to cultivate multidisciplinary and all-round talents in finance, economics and management. Through ten years of exploration and practice, we have formed a series of teaching reform achievements and practical results. [ABSTRACT FROM AUTHOR]