Particle Kinematics Analysis of Droplet Drift in Spraying Operation of Plant Protection UAV

[Objectives]The paper was to study the effect of droplet drift on spray quality of plant protection UAV.[Methods]Based on the theory of multiphase flow and the method of particle kinematics,the force and motion trajectory of droplet sprayed by plant protection UAV were theoretically analyzed and mathematically modeled.On the basis of the assumption of wind speed in the ground layer and the laminar sublayer,that is,it is assumed that the wind speed in the area of wind measurement was approximately a linear distribution,the coupling iterative solution of the equations was carried out.The influence of droplet diameter,flight height,flight speed of plant protection UAV,course angle,wind speed,wind direction,initial droplet velocity and direction of initial velocity on droplet drift were analyzed.The influence of the coupling effect of each factor on droplet drift was further discussed and the distribution of droplet drift concentration was obtained.[Results]The wind speed and direction had much influence on the drift distance of droplets,and the drift distance and the initial velocity angle show a quadratic function distribution.Under the given conditions,the drift distance was the closest when the initial velocity angle was about 20°.The droplet drift was mainly distributed scatteredly around the nozzle.[Conclusions]The study provides a reference for improving the spraying quality of plant protection UAV.

Variable elliptical vibrating screen: Particles kinematics and industrial application

Traditional vibrating screen usually adopts the linear centralized excitation mode,which causes the difficulty in particles loosening and low screening efficiency.The variable elliptical vibrating screen(VEVS)trajectory is regulated to adapt the material mass along the direction of the screen length,improving the particles distribution as well as the screening efficiency.In this work,a theoretical model was developed for analyzing the screen surface motion law during VEVS-based screening process.An equation was obtained to show the relationship between the horizontal amplitude and the vertical amplitude.The materials kinetic characteristics were studied by using high-speed camera during screening process.Compared with equal-amplitude screen(EAS),the material moving velocity was increased by 13.03%on the first half but decreased by 3.52% on the second half,and the total screening time was reduced by 9.42% by using VEVS.In addition,-6 mm screening test was carried out.At the length of VEVS equaled to 1.2 m,the screening efficiency and the total misplaced material content were 92.50% and 2.90%,respectively.However,the screening efficiency was 89.91% and the total misplaced material content was 3.76% during EAS-based screening process.Furthermore,when external moisture is 5.96%,the screening efficiency of VEVS could reach 86.95%.The 2 TKB50113 type VEVS with double-layered screen surface used in Huoshizui Coal Mine was 5.0 m in width and 11.3 m in length.The areas of single layer and double layer were 56.5 and 113 m~2,respectively.In industrial production,the processing capacity was 2500-3000 t/h and the screening efficiency was larger than 90%.

Variation of Flow Field Around Twin Cylinders with and Without the Outer Perforated Cylinder ? Numerical Study

Presence of the outer perforated cylinder reduces the direct wave impact on the inner cylinder, which has been testified by many researchers. However, the force reduction mechanism, which is complicated due to the wave-porous structure interaction, needs to be addressed in detail. The present study explains the mechanism with the aid of the computational fluid dynamics （CFD） tool STAR CCM＋. This package is chosen for its capabilities to simulate viscous and turbulence effects caused by passage of waves. For the present study, flow fields around the twin cylinders with different orientations are examined with and without the outer perforated cover. Mechanism contributing to the reduction of force on the existing structure is explained in physical terms, and force reduction is quantified. The present study has direct application in the retrofitting application of offshore members.

A Conceptual Deficiency for the Use of Christoffel Connection in Gravity Theories

Christoffel connection (or Levi-Civita affine connection) did not enter gravity as an axiom of minimal length for the free fall of particles (where anyway length action is not defined for massless particles), nor out of economy, but from the weak equivalence principle (gravitational force is equivalent to acceleration according to Einstein) together with the identification of the local inertial frame with the local Lorentz one. This identification implies that the orbits of all particles are given by the geodesics of the Christoffel connection. Here, we show that in the presence of only massless particles (absence of massive particles), the above identification is inconsistent and does not lead to any connection. The proof is based on the existence of projectively equivalent connections and the absence of proper time for null particles. If a connection derived by some kinematical principles for the particles is to be applied in the world, it is better for these principles to be valid in all relevant spacetime rather than different principles to give different connections in different spacetime regions. Therefore, our result stated above may imply a conceptual insufficiency of the use of the Christoffel connection in the early universe where only massless particles are expected to be present (whenever at least some notions, like orbits, are meaningful), and thus of the total use of this connection. If in the early universe, the notion of a massive particle, which appears latter in time, cannot be used, in an analogous way in a causally disconnected high-energy region (maybe deep interior of astrophysical objects or black holes), the same conclusions could be extracted if only massless particles are present.

Kinematics and dynamics of a particle on a non-simple harmonic vibrating screen

The motion of a particle on a screen is directly affected by the motion of the screen if airflow and inter- granular friction are ignored. To study this effect, a mathematical model was established to analyze the motion of a planar reciprocating vibrating screen, and a matrix method was employed to derive its equa- tion of motion. The motion of the screen was simulated numerically and analyzed using MATLAB. The results show that the screen undergoes non-simple harmonic motion and the law of motion of each point in the screen is different. The tilt angle of the screen during screening is not constant but varies according to a specific periodic function. The results of numerical simulations were verified through experiments. A high-speed camera was used to track the motion of three points in the longitudinal direction of the screen. The balance equation for forces acting on a single particle on the screen was derived based on the non-simple harmonic motion of the screen, These forces were simulated using MATLAB. Different types of particle motion like slipping forward, moving backward, and being tossed to different parts of the screen were analyzed. A vibro-impact motion model for a particle on the non-simple harmonic vibrating screen was established based on the nonlinear law of motion of the particle. The stability of fixed points of the map is discussed. Regimes of different particle behaviors such as stable periodic motion, period-doubling bifurcation motion, Hopf bifurcation motion, and chaotic motion were obtained. With the actual law of motion of the screen and the behavior of a particle on the screen, a theoretical basis for design optimization of the screen is provided.