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.     

An experimental study of a vortex ring interacting with an inclined wall

An experimental study has been made on the interaction of a vortex ring with a plane solid boundary which is inclined to the axis of the ring. Dye visualizations of the ring during the interaction revealed (i) the formation of bi-helical vortex lines around the circumferential axis of the ring, and (ii) that these vortex lines were constantly being displaced along the circumferential axis on either side of the plane of symmetry and towards the region of the ring furthest away from the wall. Key factors which may be responsible for this phenomenon have been identified and are discussed in this paper.     

Development of a tracked vehicle to study the influence of vehicle parameters on tractive performance in soft terrain

This paper describes a new special tracked vehicle for use in studying the influence of different vehicle parameters on mobility in soft terrain; particularly muskegg and deep snow. A field test in deep snow was carried out to investigate the influence of nominal ground pressure on tractive performance of the vehicle. The vehicle proved useful for studying vehicle parameters influencing the tractive performance of tracked vehicles. The tests show that the nominal ground pressure has a significant effect on the tractive performance of tracked vehicles in deep snow. The decrease in drawbar pull coefficient when the nominal ground pressure is increased and originates at about the same amount from a decrease of the vehicle thrust coefficient, an increase of the belly drag coefficient and an increase of the track motion resistance coefficient.     

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.     

Long-term effects of off-road vehicle traffic on tundra terrain

Traffic tests were conducted at two sites in northern Alaska with an air cushion vehicle, two light tracked vehicles, and three types of wheeled Rolligon vehicles. The traffic impact (surface depression, effect on thaw depth, damage to vegetation, traffic signature visibility) was monitored for periods of up to 10 years. Data show the immediate and long-term effects from the various types of vehicles for up to 50 traffic passes and the rates of recovery of the active layer. The air cushion vehicle produced the least impact. Multiple passes with the Rolligons caused longer-lasting damage than the light tracked vehicles because of their higher ground contact pressure and wider area of disturbance. Recovery occurs even if the initial depression of the tundra surface by a track or a wheel is quite deep (15 cm), as long as the organic mat is not sheared or destroyed.     

Evaluation of fractal terrain model for vehicle dynamic simulations

Fractals are a popular method for modeling terrains that include various scales. This paper investigates the effectiveness of using fractals for generating artificial terrains which can be used for vehicle simulations. The 3-D Weierstrass–Mandelbrot function was used to generate surfaces based on experimentally measured terrains. There is an exponential relationship between the root means squared elevation of the surfaces and the fractal scaling parameter. This relationship was used to determine the required fractal parameters to generate a surface with a desired roughness. A light detection and ranging (LiDAR) sensor coupled with a global positioning system (GPS) and inertial navigation system (INS) was used to measure two off road surfaces. The experimental terrain was then compared to the simulated terrain. Based on the comparison, the fractal model can capture the general roughness of the experimentally measured terrains as determined by the dynamic response of a suspension model. However, the fractal model fails to capture some of the nuances and non-periodic events observed in experimental terrains.     

Automatic control system of a rear-wheel drive vehicle moving on a sloped weak sandy terrain

The general mechanism of tractive performance of a four-wheel vehicle with rear-wheel drive moving up and down a sloped sandy soil has been considered theoretically. For the given vehicle dimensions and terrain-wheel system constants, the relationships among the effective tractive or braking effort of the vehicle, the amount of sinkage of the front and rear wheels, and the slip ratio were analysed by simulation. The optimum eccentricity of the vehicle’s center of gravity and the optimum application height of the drawbar-pull for obtaining the largest value of maximum effective tractive or braking effort could be calculated by means of the analytical simulation program. For a 5.88 kN weight vehicle, it was found that the optimum eccentricity of the center of gravity e_opt was 1/6 for the range of slope angle—0βπ/24 rad during driving action of the rear wheel and e_opt was also 1/6 for the range of slope angle—π/24β0 rad during braking action of the rear wheel. The optimum application height H_opt was found to be 35 cm for the range of slope angle 0βπ/24 rad during driving action of the rear wheel and H_opt was 0 cm for the range of slope angle—π/24β0 rad during braking action of the rear wheel.     

Interaction of vehicle and terrain results from 10 years research at IKK

The IKK research program comprises:

• experimental evaluation of terrain data and formulation of analytical models for soil properties

• development of models for the different soil-wheel interactions

• development of a highly sophisticated model, ORIS, for off-road interactive simulation of the driver-vehicle-terrain system and the utilization for vehicle development and mission optimization

• development of finite element methods, e.g. VENUS, and their utilization for multiple terramechanical problems.

With these achievements, the team of scientists of the Institute of Automotive Engineering of the University of the Federal Armed Forces, Hamburg (IKK) could contribute essentially to the state of the art.It is the nature of scientific development that problems are recognized to be important and treated by several institutions in the world often at the same time. Also, in the case of the IKK research program, some problems may have been investigated in parallel by others. This indicates the actuality of the research program, and gives the chance for discussion and cooperation between the different scientific groups in the world, to ensure the dissemination of new pieces of knowledge.     

Vortex rings interacting with a wall

Accurate numerical simulations of vortex rings impinging on flat boundaries have revealed the same features observed in the experiment of Walkeret al. (1987). They observed atRe _v >1250 the formation of azimuthal instabilities in the secondary ring during its compression within the primary ring. In the present numerical simulation the number of waves agrees very well with those observed in the experiment. The distributions of the vorticities together with the distribution of each term in the vorticity equations give insights on the formation of azimuthal instabilities.     

Mechanical properties in relation to vehicle mobility of Sepang peat terrain in Malaysia

An analytical framework for determining the mechanical properties of peat and predicting the tractive performance of tracked vehicle is presented. It takes into account the load-sinkage and shearing characteristics of peat as well as all major design parameters of tracked vehicle. An experimental study on the mechanical properties of peat soil was conducted at Sepang area, Selangor, Malaysia. The stiffness values of surface mat and underlying weak peat deposit from load-sinkage test were determined by specially made bearing capacity apparatus. The mean values of surface mat stiffness before and after drainage were found to be 31 and 45.62 kN/m³, respectively and the mean values of underlying peat stiffness before and after drainage were found to be 252 and 380.20 kN/m³, respectively. The mean value of the internal frictional angle, cohesiveness and shear deformation modulus of the peat soil sample were determined using a direct shear box apparatus in the laboratory. The mean values of internal friction angle, cohesiveness and shear deformation modulus before and after drainage were found to be 22.80° and 24.31°, 2.63 and 2.89 kN/m², and 1.21 and 1.37 cm, respectively.     

Vehicle vibrating on a soft compacting soil half-space: Ground vibrations, terrain damage, and vehicle vibrations

The point of departure of the present work may be either an interest in vehicle vibrations themselves, or in ground vibrations and terrain damage due to vehicles traveling off-road. The vibrations of a vehicle traversing dry, soft terrain, which is either rough or undulating, may be significantly modified by the dynamic interaction of the vehicle with the soil, particularly due to losses of energy by soil compaction and as elastic waves. The present work provides a prediction methodology for both vehicle and soil vibrations, accounting for the effects mentioned above. An expedient linear method is compared to a rheologically-based non-linear method. In the linear method, the soil compaction is incorporated as a loss factor in the dynamic stiffness of the otherwise elastic half-space; the imaginary part of that dynamic stiffness already includes the effects of wave damping. The non-linear model treats the compaction using a general rheological model for soils exhibiting both viscous and thixotropic effects, and requires iterative solution. A key feature of the latter model is the hypothesis that the stress distribution may be approximately regarded as quasi-static when calculating compaction losses; that approximation is expected to hold at low frequencies, since the P-wavelength in the soil is then much greater than the dimensions of the zone in which most compaction occurs. The methods predict that the soil compaction and excited ground vibrations have maxima at the vehicle bounce and hop resonances, and at high frequencies at which the Rayleigh wavelength approaches the order of the contact patch diameter. Moreover, sufficiently soft, compactable soils, but fully realizable in nature, control the vehicle response at the hop resonance, and possibly also at the bounce resonance.     

Stable growth of a crack interacting with a circular inclusion

The problem of failure of a plate containing a circular inclusion and a crack is studied. The crack is oriented along a diameter of the inclusion and the plate is subjected to a remote uniaxial stress perpendicular to the crack axis. The process of slow stable crack growth from initiation to termination is studied by the strain energy density theory. The crack growth is simulated by predicting finite increments of crack extension when material elements near the crack tip absorb a critical amount of strain energy density level, . Unstable crack growth occurs when the strain energy density factor S reaches a critical value where r_c is the critical size of the final crack increment prior to instability. The stress at crack initiation and the critical stress and crack length at failure are determined. The influence of the mechanical properties of the plate and the inclusion, the relative position of the inclusion and the crack and the crack length on the characteristic quantities of stable crack growth is analyzed. The dependence of the stable crack growth process on the loading rate is also investigated. Results are displayed in graphical form.     

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.     

Hydrodynamics of a liquid with deformable and interacting particles

Interest in the hydrodynamics of a liquid with particle rotations and microdeformations has recently intensified [1–9] in connection with the technical applications of different artificially synthesized structured media. A model of a liquid with deformable microstructure was first proposed in [4] and was thermodynamically analyzed in [6], in which a model of a liquid was constructed by means of methods from the thermodynamics of irreversible processes. A model of a macro- and microincompressible liquid with particle rotations and deformations has been proposed [7, 8] based on constitutive equations from [6]. Below we will solve the sphere rotation problem in an infinite liquid given different boundary conditions on the rates of particle rotation and microdeformation within the context of the system of equations presented in [7]. The solution of an analogous problem for a micropolar liquid simulating a suspension with solid particles has been obtained [9] and the solution for a viscous liquid was found by Stokes in [10].Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnieheskoi Fiziki, No. 1, pp. 79–87, January–February, 1976.     

Numerical and experimental studies of natural convective heat transfer from vertical and inclined narrow isothermal flat plates

Natural convective heat transfer from an isothermal narrow flat plate embedded in a plane adiabatic surface and inclined at moderate positive and negative angles to the vertical has been numerically and experimentally studied. The solution has the Rayleigh number, the dimensionless plate width, the angle of inclination, and the Prandtl number as parameters. Attention was restricted to a Prandtl number of 0.7. The numerical results have been obtained for Rayleigh numbers between 10³ and 10⁷ for dimensionless plate widths of between 0.3 and 1.2 and for angles of inclination between +45° and −45°. In the experimental study, results have been obtained for Rayleigh numbers between 4 × 10² and 10⁵ for dimensionless plate widths of 0.4 and 2.5 and for angles of inclination between +45° and −45° to the vertical. Empirical equations for the heat transfer rate have been derived.     

Static analysis of a two-member linkage interacting with a given surface

Summary The static interaction of a two-member linkage with a given surface is investigated. Dry friction acts at the point of contact of the linkage with the surface. The linkage has two drives generating torques at its joints. The optimal distribution of the joint torques is determined to maximize the friction force at the point of contact. The dependence of this maximal force on the lengths of the links and on the linkage configuration is investigated. The results obtained can be applied to the analysis and optimization of various robotic systems, in particular, manipulators interacting with rough surfaces and walking machines, especially tube-crawling robots. Received 21 December 1998; accepted for publication 25 February 1999     

Aerodynamic assessment of a rotary entry vehicle for Mars landing: an experimental analysis

Meccanica - A theoretical and experimental study has been undertaken, under ESA contract, by a team including GMV, the University of Bologna and EADS-Astrium, to assess the feasibility of an entry...