Determination the ability of military vehicles to override vegetation

Military operations usually include movement over existing roads and also through natural terrain. Wooded terrain is one of the most challenging environments which affect vehicle mobility. The ability of a vehicle to cross a forest area depends on the possibility of determining if the vehicle is able to manoeuvre between tree stems or can override individual trees. Overriding tree obstacles can be more effective if a vehicle needs a shorter time to cross some tree stems rather than manoeuvring around them. Vehicle movement to cross a forest stand depends on vegetation factors as the stem diameter, stem spacing, and also on tree root parameters, which determine the mechanical tree stability, and a vehicle’s ability to override the trees. Also, the technical parameters (width, length, turning radius, weight, traction force) of the selected military vehicle are important to classify the cross-country movement options. This study describes both the theoretical predictions of the movement of vehicles in forest stands and summarizes the results of one of the most extensive testing of vehicles’ ability to cross individual trees.     

An efficient method for increasing the accuracy of mobility maps for ground vehicles

This paper presents an efficient method for increasing the accuracy of one key step regarding the process of determining a mobility map. That is, the interpolation of the original Digital Elevation Model (DEM) to a finer resolution before running multi-body-dynamics simulations. Specifically, this paper explores the use of fractal dimension and elevation range metrics for increasing the accuracy and reducing the computation time associated with the spatial interpolation ordinary kriging method. The first goal is to ensure the stationary variogram requirement. The second goal is to reduce kriging error or variance in the new predicted values. A novel segmentation-based approach has been proposed to divide the regions of interest into segments where stationarity is ensured. Empirical investigation based on real DEMs indicates the generality of the segmentation approach when natural and man-made terrains are considered. The proposed method leads to a more efficient computation burden and to more accurate results than the traditional approach.     

Determining unsteady aerodynamic forces for three-dimensional plate cascade in subsonic gas flow

The general solution for the problem of three-dimensional gas flow through a cascade of plates was obtained in [1], It is shown below that in the considered direct and inverse aerodynamic problems there may exist nontrivial solutions for uniform boundary conditions. The flow regimes for which such solutions exist may be treated as aerodynamic resonance.The examples presented of the calculation for a plate cascade illustrate the behavior of the unsteady aerodynamic forces near the aerodynamic resonance regimes and make it possible to evaluate the limits of applicability of the hypothesis of plane sections. In addition, the calculation results show the possibility of self-induced vibrations of plate cascades with a single degree of freedom in a subsonic gas stream.     

A mathematical model for spatial motion of tracked vehicles on soft ground

A mathematical model which predicts spatial motion of tracked vehicles on non-level terrain has been developed. The motion of the vehicle is represented by three translational and three rotational degrees of freedom. In order to incorporate the inelastic deformation of soil, a soil-track interaction model is introduced; this constitutive model relates the traction exerted on the track by soil to the slip velocity and sinkage of the track. The model is based upon available soil plasticity theories and furnishes mechanics-based interpretation of Bekker's empirical relations. For planar motion the proposed model reduces to the existing equations of motion by introducing kinematic constraints on the vertical translation, pitching and rolling degrees-of-freedom.     

Prediction of track forces in skid-steering of military tracked vehicles

Track forces for outer and inner tracks have been calculated for a military tracked vehicle in a skid-steer situation. The present work is an attempt to improve the understanding of track force variation with turning radius. Furthermore, a reasonable estimate of transmission loads is required for the design of steering transmission for turning a tracked vehicle. This may also be obtained from the track forces. The understanding of track force variation with turning radius has been rather poor. In literature, the reason for lower track force at larger turning radius has been explained in terms of the deflection of the various suspension components like the track shoes, bushings, etc., which are associated with steer action. Deflection of the suspension components does not seem to be an adequate explanation for the variation of track forces with turning radius. In the present work, track forces have been obtained from the dynamics of the moving vehicle. The variation of tractive coefficient (coefficient of friction) due to lateral track slippage has also been considered. This is where the present work differs from the conventional track force estimation where a constant value of coefficient of lateral friction has been used. The estimation of tractive coefficient is made by using pull-slip equation found in literature. The explanation of decreasing track force with increasing radius is given in terms of variation of slip with speed and turning radius. It is found from the study that the concept of variation of coefficient of friction (tractive coefficient) is very important and probably a realistic one in the prediction of track forces. The results of the calculations compare reasonably well with the trends of test result plots obtained in the literature.     

Determining the constraint forces for a two-link robotic vehicle with three steerable wheels

Exact formulas to determine the reactions of nonholonomic constraints for a two-link robotic vehicle with three steerable wheels are derived. The simplest (asymptotic) approximations of these formulas are presented. The results are illustrated by a numerical example     

Prediction of ground pressure distribution under tracked vehicles—I. An analytical method for predicting ground pressure distribution

An analytical method for predicting the pressure distribution beneath a tracked vehicle under static conditions is presented. In the analysis, the track-suspension system which consists of the track, the suspension and the track tensioning device, is considered inits entirety. All major design parameters of the vehicle, as well as terrain characteristics, are taken into consideration. It is shown that the analytical method proposed can provide a means whereby the effects of vehicle design parameters and terrain conditions on ground pressure distribution can be assessed quantitatively.     

An automated vane shear test tool for environmental monitoring with unmanned ground vehicles

The present work describes the development of a novel robotic vane shear test tool for characterization of soil parameters with high precision and accuracy. The tool automates industrial standards for testing procedures. The proposed system is capable of performing high resolution torque measurements, which are then used to estimate the shear strength of the soil. The design of the instrument and its advantages over traditional manual instruments are discussed, after which error sources, calibration, and test procedures are described. The developed tool was successfully validated against high-end commercial equipment. The built unit was employed for characterizing mine waste in a laboratory setting and also deployed in the field on board an Unmanned Ground Vehicle for remote soil characterization.     

A simulation model for the prediction of the ground pressure distribution under tracked vehicles

A computer based simulation model for the prediction of the ground pressure distribution beneath tracked vehicles under static conditions has been developed. The model can differentiate between various track designs and is based on an analytical method developed and described by Garber and Wong. Simulating the model with the parameters of a rubber tracked forestry vehicle (FARMI TRAC 5000) led to several conclusions. The road wheel arrangement has a considerable effect on the ground pressure distribution: increasing the number of road wheels reduces the maximum ground pressure and improces the uniformity of the pressure distribution. The radius of the road wheel, the stiffness of the suspension and the stiffness of the track tensioning device have an insignificant effect on the ground pressure distribution. In contrast, the initial track tension and the width of the track have a significant effect on the ground pressure distribution: increasing the initial track tension reduces the maximum ground pressyre and improves the uniformity of the pressure distribution. The same conclusions are valid for an increase of the track width. This model can be used as a tool to assist in the design of off-road vehicles, and is currently being used in the design of forestry vehicles in Ireland.     

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 approach to computer control for legged vehicles

Observation of the locomotion of animals and human beings in difficult terrain makes it quite obvious that legged locomotion offers substantial mobility advantages over conventional wheeled or tracked systems. However, effective adaptation of legged locomotion principles to off-road vehicles has to date been frustrated by the complexity of the joint coordination control problem and by the lack of suitable sources of power for individual leg joints. This paper is addressed to the first problem and is intended to show that some of the techniques used in aircraft autopilots can be adapted to legged vehicle control. The main results presented are derived from a computer simulation study of a system in which vehicle speed and direction are determined by a human operator while individual joint commands are generated automatically by a digital computer. Present indications are that such a vehicle might be as easy to control as a conventional wheeled or tracked automotive system.     

Investigation of the soil thrust interference effect for tracked unmanned ground vehicles (UGVs) using model track tests

The traction force of a tracked unmanned ground vehicle (UGV) depends on the soil thrust generated by the shearing action on the soil-track interface. In the development of soil thrust, because the continuous-track system consists of a number of single-track systems connected to each other, interference occurs between the adjacent single-track systems through the surrounding soil. Thus, the total soil thrust of the continuous-track system is not equal to the sum of the soil thrust of each single-track system, and the interference effect needs to be carefully considered. In this study, model track tests were conducted on model single-, double-, and triple-track systems according to relative density of soil and shape ratio (i.e., the length of the track plate to grouser depth). The test results indicated that the interference effect reduced soil thrust due to the overlapping shear zones between adjoining single-track systems. The loss of soil thrust increased as the relative density of the soil increased and the shape ratio decreased. Based on these findings, a soil thrust multiplier that can be utilized to assess the soil thrust of a continuous-track system was developed.     

Extracting micro air vehicles aerodynamic forces and coefficients in free flight using visual motion tracking techniques

This paper describes a methodology to extract aerial vehicles’ aerodynamic characteristics from visually tracked trajectory data. The technique is being developed to study the aerodynamics of centimeter-scale aircraft and develop flight simulation models. Centimeter-scale aircraft remains a largely unstudied domain of aerodynamics, for which traditional techniques like wind tunnels and computational fluid dynamics have not yet been fully adapted and validated. The methodology takes advantage of recent progress in commercial, vision-based, motion-tracking systems. This system dispenses from on-board navigation sensors and enables indoor flight testing under controlled atmospheric conditions. Given the configuration of retro-reflective markers affixed onto the aerial vehicle, the vehicle’s six degrees-of-freedom motion can be determined in real time. Under disturbance-free conditions, the aerodynamic forces and moments can be determined from the vehicle’s inertial acceleration, and furthermore, for a fixed-wing vehicle, the aerodynamic angles can be plotted from the vehicle’s kinematics. By combining this information, we can determine the temporal evolution of the aerodynamic coefficients, as they change throughout a trajectory. An attractive feature of this technique is that trajectories are not limited to equilibrium conditions but can include non-equilibrium, maneuvering flight. Whereas in traditional wind-tunnel experiments, the operating conditions are set by the experimenter, here, the aerodynamic conditions are driven by the vehicle’s own dynamics. As a result, this methodology could be useful for characterizing the unsteady aerodynamics effects and their coupling with the aircraft flight dynamics, providing insight into aerodynamic phenomena taking place at centimeter scale flight.     

Determining the shear angle,forces, and sizes of shearing elements during metal cutting

A new solution for the shear angle is proposed which is a generalization of the solution Lee-Shaffer solution and allows the determination of the cutting force and the shearing-element size. Merchant’s experimental data are processed taking into account the resistance force at the cutting edge, and it is shown that accounting for this force leads to the need to increase the internal friction angle in the calculated dependences in order to match theory with experiment. It is shown that the obtained theoretical results agree well with experimental results. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 177–186, January–February, 2009.     

Drift due to two obstacles in different arrangements

We study the drift induced by the passage of two cylinders through an unbounded extent of inviscid incompressible fluid under the assumption that the flow is two dimensional and steady in the moving frame of reference. The goal is to assess how the resulting total particle drift depends on the parameters of the geometric configuration, namely the distance between the cylinders and their angle with respect to the direction of translation. This problem is studied by numerically computing, for different cylinder configurations, the trajectories of particles starting at various initial locations. The velocity field used in these computations is expressed in closed form using methods of the complex function theory, and the accuracy of calculations is carefully verified. We identify cylinder configurations which result in increased and decreased drift with respect to the reference case when the two cylinders are separated by an infinite distance. Particle trajectories shed additional light on the hydrodynamic interactions between the cylinders in configurations resulting in different drift values. This ensemble of results provides insights about the accuracy of models used to study biogenic transport.     

Prediction of ground pressure distribution under tracked vehicles—II. Effects of design parameters of the track-suspension system on ground pressure distribution

The effects of vehicle design parameters on ground pressure distribution and track tension are evaluated quantitatively using the analytical method described in Part I of this paper. The ground pressure distribution of a vehicle is closely related to vehicle sinkage and external motion resistance, while the track tension affects the internal resistance of the track-suspension system. It is found that the number of road wheels on the track has a significant effect on both ground pressure distribution and track tension. On the other hand, the diameter of the road wheels has only a moderate influence on track tension and a rather insignificant effect on ground pressure distribution. The stiffnesses of the suspension and the track tensioning springs have varying degrees of influence on ground pressure distribution and track tension dependent upon terrain stiffness. It is also found that the initial track tension has a significant effect on the actual track tension over a wide range of terrain and a slight to moderate influence on ground pressure distribution, dependent upon terrain stiffness.It should be noted that although individually some of the design parameters have only a slight or moderate effect on ground pressure distribution and track tension, their combined effects may be significant. Therefore, in the selection of design parameters of the track-suspension system, their combined influence must be carefully examined.