Physical models of off-road vehicles moving on loose soils

International audienceThis short text is illustrated by a video about physically-based particle simulations of various off-road moving on deformable soils, leaving tyre traces, spinning, skidding and even sinking

Modeling of the interaction of rigid wheels with dry granular media

We analyze the capabilities of various recently developed techniques, namely Resistive Force Theory (RFT) and continuum plasticity implemented with the Material Point Method (MPM), in capturing dynamics of wheel--dry granular media interactions. We compare results to more conventionally accepted methods of modeling wheel locomotion. While RFT is an empirical force model for arbitrarily-shaped bodies moving through granular media, MPM-based continuum modeling allows the simulation of full granular flow and stress fields. RFT allows for rapid evaluation of interaction forces on arbitrary shaped intruders based on a local surface stress formulation depending on depth, orientation, and movement of surface elements. We perform forced-slip experiments for three different wheel types and three different granular materials, and results are compared with RFT, continuum modeling, and a traditional terramechanics semi-empirical method. Results show that for the range of inputs considered, RFT can be reliably used to predict rigid wheel granular media interactions with accuracy exceeding that of traditional terramechanics methodology in several circumstances. Results also indicate that plasticity-based continuum modeling provides an accurate tool for wheel-soil interaction while providing more information to study the physical processes giving rise to resistive stresses in granular media

Where geology meets pedology: Late Quaternary tephras, loess, and paleosols in the Mamaku Plateau and Lake Rerewhakaaitu areas

On this trip we focus on tephrostratigraphy and soil stratigraphy together with aspects of palaeoenvironmental reconstruction over long and short time-spans. We will examine the relationship between the deposition of tephras and tephric loess and the formation of soils in these deposits as they accumulate, either incrementally (millimetre by millimetre) or as thicker layers, in a process known as upbuilding pedogenesis. Development of age models for the eruption of marker tephras, and of the new climate event stratigraphy for New Zealand within the NZ-INTIMATE project (Integration of ice-core, marine, and terrestrial records for New Zealand since 30,000 years ago), will also be touched upon

Managing Dust on Unpaved Roads and Airports

INE/AUTC 14.1

Modeling of Terrain Impact Caused by Off-road Vehicles

Terrain impact models were developed for both wheeled vehicles and tracked vehicles based on the analysis of vehicle dynamics, soil mechanics, and geometric relationships between vehicle parameters and the disturbed width. The terrain impact models, including both disturbed width models and impact severity models, were developed separately for tracked vehicles and wheeled vehicles. The disturbed width models of both vehicle types were primarily based on the geometric relationship between vehicle contact width and vehicle dynamic parameters. For both vehicle types, the impact severity was defined as the ratio between soil shear stress and soil shear strength. The impact severity model of wheeled vehicles was based on the balance between the centrifugal force of the vehicle and the soil shearing force that was related to vehicle dynamic parameters. For tracked vehicles, the soil shear stress was primarily de- rived from the lateral displacement of the tracks, not the centrifugal force, thus the impact severity model of tracked vehicles was based on the relationship between soil shear stress and soil lateral displacement caused by the lateral movement of the tracks. Field tests of both wheeled vehicles and tracked vehicles were conducted at different test sites with different soil types and soil strength. The wheeled vehicles included a High Mobility Multipurpose Wheeled Vehicle (HMMWV), and a Light Armored Vehicle (LAV). The tracked vehicles included an M1A1 tank, an M577 armored personal carrier (APC), and an M548 cargo carrier. The field test data supported the prediction of terrain impact models. The average per- centage errors of the disturbed width model of the LAV and the HMMWV were 19.5 % and 8.6 %, respectively. The average percentage errors of the impact severity model for the LAV were 48.5 % and 34.2 % for the high-speed (9.6 m/s) test and low-speed (5.4 m/s) test, respectively. The average percentage errors of the disturbed width model for the M1A1, M577, and the M548 were 10.0 %, 27.3 %, and 8.5 %, respectively. The average percent- age errors of the impact severity model of the M1A1 and M577 were 25.0 % and 21.4 %, respectively

Influence of Turning on Military Vehicle Induced Rut Formation

Rut formation can severely influence soil conditions and vegetation, and reduce vehicle mobility. Vehicle operations can affect rut formation. Ruts formed in straight vehicle paths are different than when the vehicle turns. This research is mainly to investigate the effects of vehicle turning maneuvers on soil rut formation, including field tests, lab tests, and model development. Field tests were conducted at Yuma Training Center, Fort Riley and Fort Lewis on wheeled and tracked military vehicles. In field tests, rut depth, rut width and rut index were used as the main indicators to quantify a rut. A Vehicle Tracking System was mounted onto each vehicle to utilize the Global Positioning System. The vehicles were operated in spiral patterns to get constantly decreasing turning radius. The Vehicle Terrain Interaction terrain mechanics model was chosen to modify to predict rut formation during vehicle turning operations on yielding soils. In the modified VTI model, the resultant force on a single wheel is a dynamic variable correlated with the vehicle’s weight, velocity, and turning radius. In addition, lab tests were conduced on a tire and a track shoe in sand. Lateral forces and lateral displacements were applied under constant normal forces. The tire was pulled laterally and the track shoe was pulled back and forth to represent actual movement during vehicle turning. Results indicate that (1) rut depth, rut width and rut index increase with the decrease of TR, especially when TR is less than 20 meters; (2) vehicle parameters and soil parameters are statistically significant to affect rut formation; (3) the modified VTI model is able to predict rut formation when turning, with an improved R square of 0.43; (4) in lab tests, the final sinkage caused by the lateral force or displacement is 3 to 5 times the static sinkage; (5) rut depths increase from 65% to 548% of the initial rut depths under the effects of the combination of the multi-pass and turning maneuvers after multiple passes. This dissertation is a collection of five individual papers. More detailed description of test procedures and conclusions are found in these papers

Analytical and finite element modelling of the dynamic interaction between off-road tyres and deformable terrains

Automotive tyres are one of the main components of a vehicle and have an extremely complex structure consisting of several types of steel reinforcing layers embedded in hyperelastic rubber materials. They serve to support, drive – accelerate and decelerate – and steer the vehicle, and to reduce transmitted road vibrations. However, driving is associated with certain types of pollution due to CO2 emissions, various particles due to tyre wear, as well as noise. The main source of CO2 emissions is the tyre rolling resistance, which accounts for roughly 30% of the fuel consumed by cars. The phenomenon becomes more pronounced in off-road conditions, where truck vehicles are responsible for about a quarter of the total CO2 emissions. Appropriate legislation has been introduced, to control all of these pollution aspects. Therefore, tyre simulation (especially in off-road conditions) is essential in order to achieve a feasible design of a vehicle, in terms of economy and safety. [Continues.

Terramechanics and soil–wheel interactions for road vehicle applications

The current research concerns the analysis and development of a soil-wheel interaction model intended for application in road vehicles, in order to support virtual vehicle development processes. As a first step, a review of the literature is conducted which reveals the absence of a reliable tyre model for off-road applications. In addition, it highlights two critical performance items for the soil-wheel interaction; tractive effort and rolling resistance. The rolling resistance is generated by soil compaction, horizontal soil displacement and tyre flexibility, while the tractive effort is generated by the soil shearing behaviour at the soil-wheel interface. Existing models for soil compaction (i.e. pressure-sinkage) are initially evaluated for their accuracy and applicability using literature data, but their performance is unsatisfactory. In addition, a large experimental campaign is conducted using two soil types and various experimental processes such as pressure-sinkage on flat and curved plates, shear tests, rolling wheel tests. [Continues.