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.     

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.     

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.     

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.     

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.     

Demonstration of a portable device for predicting vehicle tractive performance in snow

This workshop study program which was sponsored by the ISTVS Snow Mechanics Committee examined the problems of snow traction and methods of predicting vehicle mobility on snow. This study presents one aspect of the field prediction problem where a portable, hand-held instruments is used and prescribed by requirements for simplicity, portability and facility.     

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.     

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.     

Steering performance of an inverted pendulum vehicle with pedals as a personal mobility vehicle

From the viewpoints of environmental protection, support for the aged and ensuring the right to mobility, there is a need to develop a new type of mobility vehicle that provides more effective transportation. The authors propose an inverted pendulum vehicle with pedals as one of the forms of personal mobility vehicles (PMVs). In this paper, the steering performance of the inverted pendulum vehicle with pedals is discussed based on experiments on a prototype. From the experimental results, it was confirmed that the errors from the five subjects for the target trajectory and the five-grade evaluation of the maneuverability were similar. Finally, we created an inverted pendulum vehicle with pedals to which was added a reaction actuator for the steering system. From the experimental results, it was found that setting appropriate feedback gains for the handle steering angle and its rate of rotation, which control the right and left wheel driving torques, resulted in greatly improved maneuverability.     

Bubble generation and transport in a microfluidic device with high aspect ratio

Bubble generation and transport in a micro-device composed of a micro-T-junction and a following serpentine micro-channel was experimentally investigated. It has a rectangular cross-sectional with an aspect ratio of 7.425. Air and water were used as gas and liquid, respectively. Mixtures of water–glycerol and water–Tween-20 were used to study the effects of liquid viscosity and surface tension. Compared with previous T-junction bubble generation, the liquid and gas inlets orientation was switched in this work. The continuous flow was driven from the perpendicular channel and the dispersion flow was from the main channel. It shows that the break-up process has three periodic steps under certain operating conditions. The dimensionless bubble length L/w in the micro-channel with high aspect ratio is much larger than that in square microchannels. A correlation is proposed to correlate L/w with liquid flow rate J_L, gas flow rate J_G, and liquid viscosity μ_L. Surface tension σ can change the bubble shape but almost does not affect the bubble length in this fast break-up process. Additionally, a long bubble may be broken up at the corners at the same time because the locations of gas and liquid are exchanged relative to the concave and convex portions of an elbow after a turn which may result in the change of fluid velocities and gas–liquid pressure drop.     

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。     

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.     

The brachistochronic motion of a wheeled vehicle

The paper considers the brachistochronic motion of a wheeled vehicle on a horizontal plane surface. The objective is to transfer the vehicle from the specified initial position with given initial kinetic energy to the specified terminal position in minimum time with conserved total mechanical energy of the vehicle. The problem is solved by applying Pontryagin’s maximum principle and singular optimal control theory. The projection of the reaction force of the horizontal plane applied on the front vehicle wheels onto the axis of the front vehicle axle is taken for a control variable. The cases of unbounded and bounded value of this projection are considered. The shooting method is used to solve the two-point boundary value problem arising from Pontryagin’s maximum principle and singular optimal control theory.     

Numericalmodeling of vehicle exhaust gas transport and dispersion by an airflow over a city block

The vehicle exhaust gas concentration field in the atmosphere of a city block is described by means of solving the system of Euler’s partial differential equations (those of continuity, motion, energy, and state) with the corresponding boundary conditions. The numerical solution is obtained by Davydov’s large particle method. The numerical experiment made it possible to determine the distributions of the main gasdynamic parameters of the gas-air mixture flow and the distribution of the concentration of carbon monoxide entering in the composition of the exhaust gases throughout a three-dimensional domain of complicated shape.     

The development of acoustic generators and their application as a boundary layer transition control device

An experimental investigation of a controllable artificial boundary layer transition by means of electro-acoustic generators was carried out in flat-plate boundary layers. The acoustic generators were flush mounted with the model surface in order to minimize local surface roughnesses which may cause flow instabilities in the laminar boundary layer. The dependence of the input power, pulse ratio, and input frequency of the acoustic generators on the transition threshold values of the input power were determined with surface hot films. In addition, the functional application of the acoustic generators for a controllable artificial boundary layer transition was examined qualitatively by flow visualizations applying the liquid crystal technique.List of symbols A fluctuating component of the hot film anemometer output voltage - time mean hot film anemometer output voltage - ₀ time mean hot film anemometer output voltage at zero velocity - B spectral component of any measured quantity (the used dB-scale is referred to 1 Volt) - time mean hot wire anemometer output voltage - ₀ time mean hot wire anemometer output voltage at zero velocity - f frequency - I _av average input current of the acoustic generator - P mean input power of the acoustic generator - p pressure - Re Reynolds number, Re=U x t/ - t time - t _i period of pulse signal - t _p pulse width of input power - t _s time after switching off heating lamp - U freestream velocity - blowing or sucking velocity produced by the acoustic generator - x longitudinal coordinate from the leading edge (Fig. 2) - x _t distance from the flat plate to the transition location - y coordinate normal to the wall (Fig. 2) - z spanwise coordinate (Fig. 2) - angle of incidence - pulse ratio t _p /t _I - kinematic viscosity - density - ₀ wall shear stress     

Convective transport of air bubbles in strong hydraulic jumps

A hydraulic jump is a flow singularity characterised by a significant amount of air entrainment in the shear zone. The air is entrapped at the jump toe that is a discontinuity between the impinging flow and the roller. The impingement point is a source of air bubbles, as well as a source of vorticity. Herein the convective transport of air bubbles in the jump roller is re-visited. Some analytical extension is presented and the theoretical results are compared with some laboratory experiments conducted in a large-size facility operating at large Froude numbers. The turbulent air bubble mixing coefficient was found to increase linearly with increasing distance and be independent of the Froude and Reynolds numbers. Overall the study highlighted some seminal features of the air–water shear layer in hydraulic jumps with large Froude numbers (5.1 < Fr₁ < 11.2). The air bubble entrainment in the mixing zone was a convective transport process, although there was some rapid flow de-aeration for all Froude numbers.     

The hull starting resistance of a boat-type vehicle

This paper makes an analysis of the hull starting resistance of a boat-type vehicle. It demonstrates that the soil cohesion and friction change along with the changes in the soil moisture content. A mathematical model of the hull starting resistance of a boat-type vehicle by theoretical and experimental inference is obtained. A forecast, tests and verification of the hull starting resistance were carried out and experimental results that tallied with the forecast ones were obtained. The hull starting resistance using the model was forecast for a real vehicle and methods were explored for reducing the hull starting resistance of a boat-type vehicle along a beach and in a swamp.     

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.