Studies of the Ionospheric Horizontal Gradient and Its Influence on Propagating Wave Vector

The ionosphere is a three dimensional inhomogeneous and time-variational medium, therefore the ray path is not in the great circle determined by the wave vector and the earth center, but have a deviation. Under some approximations, starting from Maxwell equation, the two special case of the original wave vector in the equator plane and in the meridian plane are studied. Finally in general case, through coordinates system transformation, the trajectory’s lateral deviation is solved.

Control for Underactuated Reentry Aircraft in Small Angle of Attack

The control problem for under-actuated reentry vehicle like HTV-2 is considered with small angle of attack.The control strategy for an aircraft with positive lateral control departure parameter relies on strong lateral stability,which declines with the decrease of the angle of attack.Thus,to control the lateral-directional motion in a stable state is hard and even impossible in some scenarios where the under-actuated reentry vehicle,like HTV-2,flies in a low angle of attack.To address this problem,the lateral-directional open-loop motion characteristics are analyzed.The results show that in an uncontrolled state,the lateral-directional motion can automatically converge to stabilization thanks to the aerodynamic damping effect.Therefore,a method of turning-off the lateral-directional control and inviting aerodynamic damping to control can achieve stability.The six-degree-of-freedom simulation show that the lateral-directional motion can be stabilized by the aerodynamic damping,and the lateral position error caused by the bank angle deviation is limited near the zero-rise angle of attack.The control strategy is effective.

Design and experiment evaluation of furrow compaction device with opener for maize

The double-disc opener of maize precision seeder is an important component which affects sowing quality.After the double-disc opening operation,there will be many unfavorable phenomena such as a W-shaped bottom with pointed ridge,returning soil to furrow,loose and rough furrow sidewall,and large soil blocks in the furrow bottom.These phenomena often cause the problems of poor sowing depth consistency and seed spacing uniformity.In order to solve the above problems,the furrow compaction device with opener was designed to compact and reshape the original seed furrow,eventually forming a smooth and flat V-shaped seed furrow.Through theoretical calculations and kinematic analysis,the main structural parameters of the device were limited to a small range:the spring stiffness coefficient k=0.96-4.19 N/mm and the angle of the furrow compaction wheelφ=30°-60°.In the soil-bin experiment,the rotary combination design was adopted to study the effects of the parameters of the furrow compaction device with opener on the seeds location variation.The regression model of two factors with respect to each indicator was established in the Design-Expert software,revealing the effects of two factors on the indicators.Finally,the optimal structural parameters obtained were:the spring stiffness coefficient k=4.0 N/mm,and the angle of furrow compaction wheelφ=42.4°.The field test was carried out to verify the effect of the furrow compaction device with opener on the performance of precision seeder.The results showed that the average values of the sowing depth variable coefficient,the lateral deviation and the seed spacing variable coefficient respectively were 5.77%,5.1 mm and 9.54%in the treatment of the furrow compaction device with opener.All indicators were superior to the traditional double-disc opener.This research can provide references for the design of furrow opening device and maize precision seeder.

Numerical and theoretical investigation on three-dimensional trajectory characteristics of skipping stones

An in-depth study of the complicated trajectory characteristics of skipping stones is carried out in the present work.A three-dimensional numerical simulation validated by acquiring good agreement with experimental results is established.It is devoted to illustrating five different types of motion responses after the stone impacts the water surface in the o-xy plane,including“dive”,“hydroplaning trout”,“hydroplaning skip”,“stable skip”,and“skipping trout”.Then,the lateral deviations are investigated quantitatively based on dimensionless parameter sin(α+β)cosαin the o-yz plane.Steady interval and linear interval are divided for lateral deviation Z1/D and Z2/D based on the values of(α+β)andα,respectively.The results reveal that(1)Z1/D increases almost linearly with the increasing sin(α+β)cosαat different slopes in different(α+β)intervals;(2)Z2/D increases almost linearly with the increasing sin(α+β)cosαat different slopes in differentαintervals;(3)in linear interval,numerical lateral deviations are much larger than the fitting values at pointsβ/α≥4.5,and much smaller than the fitting values at points 2.3≤β/α<4.3.Finally,a theoretical approach is proposed to predict the maximum immersion depth of trailing edge point P.