A track-laying air cushion vehicle

Almost no previous research has dealt with the design of a track-laying air cushion vehicle. Preliminary estimates indicated that the total power requirement would be high, so means of reducing the likely power consumption were studied. An analysis of the behaviour of three track layouts made it possible to compare their power efficiencies under a wide range of operating conditions. A two track articulated configuration was generally the most efficient. To minimize loss pressurised air the exit gap height between track and side skirt must be small, but an unstable heave motion is prone to develop under these conditions. The heave motion characteristics of a plenum air cushion were, therefore, investigated theoretically and guidelines for design established. These were used in the design of a $\text{3}\text{4}$ scale model of one track of a 20,000 N air track vehicle. The model incorporated a new type of side skirt assembly which can react automatically to vertical motion of the lower track run. The new skirt was stable in heave and was reasonably effective in avoiding local closure of the air exit gap when the track belt was raised on small simulated bumps. It was confirmed that the original estimates of blower power required by an air cushion track were of the right order.     

The air cushion vehicle as a load-spreading transport device

The most effective fields of operation of the ACV are discussed, and it is shown that the vehicle effectively fills the role of a heavy transporter over weak terrain. A speculative discussion of the interaction between ACV skirts and various terrain is given in some detail. In conclusion short notes are given on some current experimental programmes, and on the work of some actual vehicles in the field.     

Static roll stiffness characteristics of two multicell type air cushion systems

Although there is growing interest in the use of flexible skirted air cushions for various off-road and other over-land transportation tasks, relatively little data on their suspension properties are available in the open literature. This paper presents the results of some experimental studies of the static roll stiffness of two resistance orifice-fed multicellular cushion designs. The conditions for scaling the tests to full-size behaviour are discussed. A simple theory, based on the assumptions that the skirt material is an inelastic membrane and that the cushion air flow can be described by one-dimensional orifice flow laws, is developed for one of the cushion systems.Good agreement between theory and experiment is obtained under certain restricted conditions, but in general the experimental results show that the skirt material properties can play an important role. This manifests itself in two ways: as a potential scaling problem, and the appearance of hysteresis in the rolling moment produced by the cushion. The latter can, under certain circumstances, be so large as to completely destroy its stiffness when rolled. At least two hysteresis mechanisms are indicated, and one has been observed. This is a buckling failure of the cells leading to large-scale venting and consequent loss of pressure. A detailed explanation of the other mechanism has not been obtained, but it is noted that skirt-ground friction does not appear to be important. It is concluded that a careful study of the structural properties of air-inflated cones is required. In particular, buckling phenomena need clarification.     

Fuzzy clustering of paddy field soils in South China

Various paddy field soils in South China were measured during the rice-growing season and numerous data were collected concerning soil composition, water content and soil strength. A similarity matrix of 16 samples was constructed, by means of which the soils were clustered at λ = 0.75 into four groups.     

Rural road characteristics and vehicle operating costs in developing countries

The primary phase of transportation at the smallholder level, from village to local market, is a particularly important aspect of increasing agricultural production in developing countries. The realistic prediction of vehicle operating costs on the (largely) unsurfaced roads in this sector is a useful input to development planning and a computer program has been developed to produce such predictions from first principles. When compared with survey results obtained by the Transport and Road Research Laboratory in Kenya, it is found that correlation is satisfactorily close. The program can also be used to predict the effects, on the operating costs of various vehicles, of changing road characteristics (gradient, curvature, roughness, rolling resistance and traction). It is found that rolling resistance and road roughness are the factors most likely to influence operating costs, due to their effects on vehicle speeds, fuel consumption and service/repair costs. Small, cheap machines are not necessarily superior to larger vehicles in terms of costs per tonne kilometre and fuel, particularly where the available load is sufficient to allow the larger vehicle to be utilized reasonably fully.     

Comparison of different bogie configurations for a vehicle operating in rough terrain

Conventional wheeled vehicles have serious mobility limitations in rough terrain while walking vehicles have inherent drawbacks such as a high number of DOF and actuators, control complexity and low energy efficiency. Vehicles that passively fit the position of multiple wheels to maintain contact with the ground can be a good solution to this problem. The present work aims to comparatively quantify the ability of overcoming obstacles that is achieved by using different configurations of vehicles with bogies. Different configurations of vehicles facing obstacles when climbing along ramps of different longitudinal slope have been modeled. Further analyses have been done in order to investigate the influence of the position of the center of gravity and obstacle traversing speed. Different asymmetrical bogie configurations have also been proposed to further improve the obstacle surmounting capacity of the 4-axle vehicle. The results show a clear improvement in the ability to overcome obstacles when using bogies. Compromise solutions can be found for the obstacle traversing speed and position of the center of gravity. Asymmetrical bogie geometry can provide an improvement in the obstacle surmounting ability, although vehicle application has to be taken into account to find the best solution.     

A laboratory investigation of ground erosion and dust generation by air cushion vehicles

The erosion process which occurs when an air cushion vehicle (ACV) passes over certain types of surface material has been investigated. Experiments were conducted in laboratory apparatus which simulates conditions under the edge of an ACV skirt.

Tests were carried out on three samples of dry erodible materials for a variety of cushion parameters. Representative photographs and data on time rates of erosion are presented. The results indicate that erosion rates are proportional to cushion pressure to the power 3/2 and that skirt angle, hoverheight and time since start of a run are of secondary importance. The results and analysis indicate that erosion rates are independent of particle size when this exceeds about 0.1 mm.     

Active bogies and chassis levelling for a vehicle operating in rough terrain

Four axle vehicles with bogies can adapt the position of the wheels to follow irregularities in the terrain, having an obstacle surpassing ability far greater than conventional 2-axle vehicles. Still, the ability to overcome discrete obstacles on a steep slope is very different depending on the wheel that is facing the obstacle. A possible solution to diminish this variation can be found if the vehicle is able to actively redistribute the load on each wheel. One strategy is to design the suspension mechanism so it can regulate its height, being able to level the chassis. Also, an active torque on the pin join between the bogie and the chassis can be applied with the same goal, adopting a system of active bogies. Both solutions have been parametrically studied in a bi-dimensional multibody model of a 4-axle vehicle with double bogies. The results show an improvement independent of obstacle position and terrain angle when using active bogies. With height regulation, this improvement is limited to the rear bogie wheels, but the obstacle surmounting capacity of the vehicle as a whole can be considerably increased if the optimal regulation point is found. Possible applications for such enhanced vehicles with bogies are performing different tasks in forest areas with obstacles on steep slopes or unstructured terrain exploration.     

Numerical simulation of the flow in a conduit,in the presence of a confined air cushion

A rectangular conduit with a closed end has water flowing in/out at the other end. The water level at the open end has an imposed sinusoidal movement. When this level is higher than the ceiling of the conduit, a certain mass of air is trapped under the ceiling. In a previous article (T.D. Nguyen, La Houille Blanche, No. 2, 1990), it was supposed that this air is flowing out freely through the ceiling, so the relative pressure at the water surface is zero, and the water hammer at the dead end of the conduit was calculated when the conduit was thoroughly filled. In this article, it is supposed that the trapped air is compressed isothermally or adiabatically. The set of equations is resolved (water continuity and movement equations, air state equation) by supposing a regime of flow at each section (section submerged or not), a certain value for the air pressure and by using the sweep method to determine the water flow characteristics. The air volume calculated by iteration must converge, and the calculated regimes at each section (submerged or free) must agree with the supposed regimes. The simulation is performed first with a horizontal conduit then with an inclined conduit. As expected, adiabatic compression gives higher pressure than isothermal compression. The simulation shows also that when there is an air cushion, compared with the case when air is flowing out freely, the shock of the water hammer at the closed end of the conduit is significantly reduced. This method is aimed at calculating the flow with entrapped air in the inlet/outlet tunnel of a hydroelectric plant, or in sewer system pipe when a sudden discharge surge (due to turbin opening/closing or to urban storm) changes a previously free‐surface flow in a mostly full‐pipe flow, but with some air entrapped under the ceiling. Copyright © 1999 John Wiley & Sons, Ltd.     

爆轰产物驱动飞片运动数值模拟研究

利用数值模拟方法,研究了主装药与飞片之间的空气隙厚度变化对飞片中载荷幅度和载荷上升时间、飞片速度和飞片变形量的影响。数值模拟与验证实验结果吻合得较好。结果表明,带空气隙的化爆加载装置可以在飞片中获得较小的载荷幅度和较长的载荷上升时间,并且可以降低飞片击靶速度,从而实现较低的冲击压力,但飞片变形量随着空气隙厚度增大而增大。     

Virtual flight simulation of a dual rotor micro air vehicle

In this paper, a new computational method is developed based on computational fluid dynamics (CFD) coupled with rigid body dynamics (RBD) and flight control law in an in-house programmed source code. The CFD solver is established based on momentum source method, preconditioning method, lower–upper symmetric Gauss–Seidel iteration method, and moving overset grid method. Two-equation shear–stress transport k ? ω turbulence model is employed to close the governing equations. Third-order Adams prediction-correction method is used to couple CFD and RBD in the inner iteration. The wing-rock motion of the delta wing is simulated to validate the capability of the computational method for virtual flight simulation. Finally, the developed computational method is employed to simulate the longitudinal virtual flight of a dual rotor micro air vehicle (MAV). Results show that the computational method can simulate the virtual flight of the dual rotor MAV.     

Electrical breakdown in air in a transverse magnetic field

The electrical breakdown of gases in a transverse magnetic field is discussed in references [1–16]. Attention has mainly been concentrated on the case of coaxial electrode geometry [1–10]. The existing experimental data on breakdown between plane-parallel electrodes [11–14] relate to a narrow range of variation of the parameters characterizing breakdown (P, d, H, U). The author has made an experimental study of the process of electrical breakdown in air in a transverse magnetic field between plane-parallel electrodes of finite size in the pressure interval from 650 to 5·10^–3 mm Hg at gap lengths of from 1 to 140 mm and magnetic inductions from 0 to 10 600 G.     

Effects of camber angle on aerodynamic performance of flapping-wing micro air vehicle

This study investigates the unsteady aerodynamic characteristics of the cambered wings of a flapping-wing micro air vehicle (FW-MAV) in hover. A three-dimensional fluid–structure interaction solver is developed for a realistic modeling of large-deforming wing structure and geometry. Cross-validation is conducted against the experimental results obtained also in the present study to establish more accurate analyses of cambered wings. An investigation is carried out on the unsteady vortex structures around the wings caused by the passive twisting motion. A parametric study is then conducted to evaluate the aerodynamic performance with respect to the camber angle at three different flapping frequencies including normal operating conditions. The camber angles producing the largest thrust and highest propulsive efficiency are estimated at each flapping frequency, and their effects on aerodynamic performance are analyzed in terms of the stroke phase. The timing and magnitude of the passive twisting motion, which are dependent on the camber angle at the operating frequency, greatly affects the unsteady vortex structure. Consequently, the camber angle designed at the operating frequency plays a key role in enhancing the aerodynamic performance of FW-MAVs.     

Electric field excited in air by a pulse of gamma rays

The characteristics of the electric field produced by air polarization during the passage of nonstationary Compton currents excited by a -ray pulse in low-density air are discussed. The influence of the field on the motion of the Compton electrons is taken into account. The amplitude and relaxation time of the field are evaluated. A polarization electric field is created through the action of a directed current of -rays in air because of the movement of the Compton electrons. This paper discusses the basic characteristics of the resultant field in low-density air. A similar problem was raised in [1], where the electromagnetic field excited by a nonstationary source of -radiation in the upper atmosphere was considered. In that case, the Compton-electron currents were specified and their magnitude was assumed to be proportional to the ratio between the gas kinetic ranges of Compton electron and -ray (this ratio is of the order of 0.01 and is indepenent of height). With an increase in electron range, however, the decelerating action of the resultant electric field on the motion of the Compton electron becomes important (eE/ is a criterion for the effect; E is the field intensity, and and are the range and energy of the Compton electron).Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 3–8, July–August, 1970.In conclusion, the authors thank G. M. Gandel'man for several discussion.     

Statistics of the surface temperature field of an air/water interface under air flow

Experimental results are presented that reveal the relationship between the root mean square of the surface temperature field of an air/water interface (σ) and the heat flux (q′′) emanating from that interface, over a range of wind speeds. Experiments were conducted for wind speeds ranging from 1.0 to 4.0 m/s to determine if and how the σ versus q′′ relationship was affected by wind speed. Consistent surfactant coverage conditions were maintained for wind speeds ranging from 1.0 to 2.6 m/s, and these are the focus of the results presented herein. For wind speeds above 2.6 m/s the surfactant was consistently pushed downstream, resulting in an inhomogeneous surface condition for the air/water interface. For wind speeds less than 2.6 m/s the relationship between σ and q′′ is approximately linear and is weakly dependent on wind speed. The surface temperature field was obtained by infrared (IR) imaging. Sample IR images are presented in addition to the σ versus q′′ data. IR images are presented for surfaces covered with insoluble surfactants (liquid phase and solid phase), a soluble surfactant, and a clean water surface.

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An experimental study of a bio-inspired corrugated airfoil for micro air vehicle applications

An experimental study was conducted to investigate the aerodynamic characteristics of a bio-inspired corrugated airfoil compared with a smooth-surfaced airfoil and a flat plate at the chord Reynolds number of Re _C  = 58,000–125,000 to explore the potential applications of such bio-inspired corrugated airfoils for micro air vehicle designs. In addition to measuring the aerodynamic lift and drag forces acting on the tested airfoils, a digital particle image velocimetry system was used to conduct detailed flowfield measurements to quantify the transient behavior of vortex and turbulent flow structures around the airfoils. The measurement result revealed clearly that the corrugated airfoil has better performance over the smooth-surfaced airfoil and the flat plate in providing higher lift and preventing large-scale flow separation and airfoil stall at low Reynolds numbers (Re _C  < 100,000). While aerodynamic performance of the smooth-surfaced airfoil and the flat plate would vary considerably with the changing of the chord Reynolds numbers, the aerodynamic performance of the corrugated airfoil was found to be almost insensitive to the Reynolds numbers. The detailed flow field measurements were correlated with the aerodynamic force measurement data to elucidate underlying physics to improve our understanding about how and why the corrugation feature found in dragonfly wings holds aerodynamic advantages for low Reynolds number flight applications.     

Increasing the efficiency of the resonance method for breaking an ice cover with simultaneous movement of two air cushion vehicles

This paper describes a study on the possibility of increasing the efficiency of the resonance method for breaking an ice cover due to the flexural-gravitational wave interference arising during simultaneous movement of several air cushion vehicles.