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.     

Feasibility of operating air cushion vehicle in wetland paddy field

The problem of sinkage of machinery, poor trafficability and compaction of soil in wetland paddy fields has stimulated new interest to make an investigation of a new device for performing the field operations. Since an Air Cushion Vehicle (ACV) has the ability to travel unimpeded over a variety of difficult surfaces, whose load-bearing properties make it difficult for other vehicles to move, this may be a suitable device for overcoming the above problems. The air cushion concept has been considered for application to off-road transport ever since the early days of its development, but so far it has not been employed for wetland paddy field operations. Therefore, a study of this type was undertaken at the Asian Institute of Technology, Bangkok. This paper describes the feasibility of using an ACV in wetland paddy fields. It shows that there is a reduction of drag force of about 60%, which is quite significant.     

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.     

Field tests and theoretical analyses concerning the rolling resistance of a track-laying vehicle due to plastic deformation

Submerged vehicles, especially those with floating tanks, are subjected to rolling resistance due to soil under various vehicle operating conditions, soils, and external forces. It is desirable to obtain simple, general solutions for the peak contact pressure and rolling resistance due to plastic deformation. In this paper, these theoretical analyses for a track-laying vehicle are presented and related to tests on submerged sands.     

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.     

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.     

The effect of drawbar pull on the rolling resistance of track-laying tractors

Theoretical expression for the rolling resistance of crawler tractors have been derived on the basis that a trapezoidal contact pressure distribution exists under the tracks when a tractor operates with a drawbar load. Experimental investigations carried out with a special 500 h.p. research and experimental tractor are described. These investigations show that as predicted, the rolling resistance increases with drawbar load although there is a small initial load range in which the rolling resistance actually decreases.     

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.     

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.     

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.     

Air cushion vehicles and soil erosion

The use of aerostatically supported vehicles is particularly interesting in agriculture, principally because the tractive effort required to pull implements may be reduced. Then the tractor used for driving can be lighter or its outer dimensions may be more appropriate to European land ownership structures.

This study verifies that the induced effects in the soil when repetitive passes of an ACV occur, do not include damage to the substrate by aeolian erosion. The main ACV characteristics influencing erosion are the speed of the air at the outlet under the skirt and the angle of incidence of the jet on the soil. The effect of the escaping air is in proportion to the square of its velocity. The angle of incidence must be chosen in relation to an equilibrium between induced erosion and operating height. The ACV with peripheral jet seems to be more appropriate when applied in agriculture. Soil resistance to erosion is a function of moisture content and of compaction. During the passage of an ACV, erosion happens in two phases. Initially, erosion is high, then the process reaches a certain level at which it remains stable. Having measured the extent of a major disadvantage of ACV's for work on agricultural land, i.e. the induced erosion, it appears that such equipment shows some promise for special conditions of use.     

Development of a new type of electric off-road vehicle powered by microwaves transmitted through air

Needless to say, we are now facing a critical state in the global environment, i.e. global warming. We have to change our way of thinking and our economic systems from those dependent on fossil resources to those dependent on renewable energy resources, such as solar energy. In our field of research, electric vehicles are considered the best choice for reducing carbon dioxide emissions. A battery is not an adequate energy source for electric vehicles, because batteries quickly get depleted because of its low energy and power density. A fuel cell is a more favorable alternative to the battery; however, it has large mass and can only replace the internal combustion engine, but the power transmission mechanisms are still necessary. The new concept of an electric off-road vehicle proposed here is entirely different from those mentioned above. The vehicle has neither a combustion engine nor a battery but only electric motors. Energy to drive the motors is transmitted through air as microwaves at 2.45 GHz. This technology was developed at the Research Institute for Sustainable Humanosphere, Kyoto University, as a method for transmitting electricity from a large-scale solar power station (SPS) orbiting in space to the Earth. We have constructed some models of electric off-road vehicles and investigated their adoptability to microwave power transmission. In this paper, some experimental results on the use of microwave power transmission for powering the vehicles are presented, and some problems such as low energy transmission efficiency are also discussed.     

Adaptive vehicle posture and height synchronization control of active air suspension systems with multiple uncertainties

This paper addresses the tasks of height and posture motion control for an electronically controlled active air suspension (AAS) system. A mathematical model of a vehicle body with AAS system is established to describe the dynamic characteristics and then formulated into a multi-input multi-output nonlinear system by considering parametric uncertainties and unmodelled dynamics. Based on this mathematical model, a synchronization control strategy is proposed to adjust the heights of adjacent AASs simultaneously, driving the pitch and roll angles closely to an arbitrarily neighborhood of zero, achieving global uniform ultimate boundedness. The proposed controller is robust to parametric uncertainties and external disturbances. A projection operator is utilized to limit the estimated parameters to their corresponding prescribed bounds in finite time. A co-simulation is conducted by combining a virtual vehicle plant with ASS system in AMEsim with the proposed synchronization controller in MATLAB/Simulink. Simulation results demonstrate that the proposed synchronization controller is effective and robust.     

A study of vehicle performance in snow

The snow trafficability problem is studied by calculating the energy absorbed by snow while being compacted by vehicle tracks. Using a constitutive law for snow which is valid for large volumetric strains and high strain rates, the rate of energy dissipation due to viscoplastic compaction of the snow is calculated and related parametrically to vehicle speed, track loading and snow density. Energy dissipated by shear effects is neglected. The results indicate that such studies can provide design guidelines for track geometry, track loading, and vehicle speed in terms of snowpack properties.     

Design,manufacturing, and flight testing of a fixed wing micro air vehicle with Zimmerman planform

An optimized and comprehensive method is used to design and manufacture a fixed wing micro air vehicle (MAV) with Zimmerman planform. The design process includes four stages which are the specification of the flight mission, determination of the best aspect ratio, identification of the optimum wing loading and thrust loading values, and estimation of the weight of the structural components of the MAV. To do this, various statistical and analytical methods are utilized. Based on an aerodynamic analysis, the results show that an optimum aspect ratio that maximizes the performance of the Zimmerman MAV for a well-defined cruise speed is determined. Considering six possible flights, a constraint analysis is performed and an optimum wing loading value is determined. It is shown that the computational method is beneficial to determine the exact masses for the structural components including the wing, fuselage, and vertical tail. Using the 3D panel method, the determination of the shape of the reflexed airfoil for the MAV is successfully done by minimizing the drag force and the angle of attack to use less powerful motor and avoid any stall effect, respectively. A stability analysis is then performed to check the safe flight of the designed vehicle. During test flight, the results show that the designed Zimmerman MAV satisfies the pre-defined specification. The final characteristics of the manufactured MAV are: wingspan of 44 cm, weight of 450 g, aspect ratio of 1.51, cruise speed of 20 m/s, and flight endurance of 20 min.     

A multiaxial-failure test vehicle for filament-wound pressure vessels

A test vehicle to obtain multiaxial failure envelopes for filamentary composites was designed. The test sample consisted of a filament-wound pressure vessel with the dome and tangent line regions of the chamber reinforced with low-modulus cast-epoxy pieces. Finite-element stress analysis was used to design the shape of the epoxy so that the maximum stress and strains and, thus, the failure, would occur in the cylindrical section of the chamber. The device was proven in initial tests.