Methods for generalization of experimental results in terramechanics

G. Sitkei, G. Pillinger, L. Máthé, L. Gurmai, P. Kiss,

Journal of Terramechanics, Volume 81, 2019, Pages 23-34, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2018.05.004.(http://www.sciencedirect.com/science/article/pii/S0022489817302690)

Abstract: Due to the extreme variability of soils and different tillage and settling conditions, measurements made under a single set of conditions have little practical applicability under arbitrary conditions. Results of more general usefulness require systematic measurements to be carried out over suitable ranges of the main influencing variables. The results can then be processed to obtain dimensionally homogeneous equations, i.e. similarity equations. This method was first proposed a century ago (Buckingham, 1914) [1], and one year later, Nusselt published a fundamental paper showing how it could be used to generalize the results of heat transfer experiments and to plan new experiments (Nusselt, 1915) [2]. The method is based on the postulate that all physical processes can be expressed as relationships among dimensionless parameters, and it specifies how to find those parameters. We describe new experimental results and generalize the results using dimensional analysis to obtain similarity plots and equations that are generally applicable within the feasible range of variables.

Keywords: Terramechanics; Generalization; Tyre-soil interaction

Real-time side-slip angle measurements using digital image correlation

Devin K. Johnson, Theunis R. Botha, P. Schalk Els,

Journal of Terramechanics, Volume 81, 2019, Pages 35-42, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2018.08.001.(http://www.sciencedirect.com/science/article/pii/S002248981730263X)

Abstract: In vehicle dynamics there are many parameters that are desired for vehicle control and modelling. One of the most important parameters for handling and stability is the vehicle side-slip angle. The ability to directly measure the vehicle side-slip in real-time will aid and improve many driver assist systems such as stability control schemes and roll-over mitigation, especially over rough terrain. Commercial side-slip angle solutions are available but they are prohibitively expensive and are only suitable for use during vehicle development and performance evaluation. They are also restricted to small side-slip angles and give unsatisfactory results at low speeds and over uneven terrain. Previous research has proven that digital image correlation can be used to accurately measure vehicle side-slip angle over rough off-road terrain using inexpensive, off-the-shelf cameras. However, side-slip angle calculations were performed in post processing from pre-recorded footage and not implemented in real time due to the large computational times of the novel algorithms developed. This paper describes the improvements made to the algorithms that enable real-time implementation. The side-slip angle is measured using a single camera pointing downwards to the terrain and digital image correlation. The sensor is tested on a flat surface using a rig that allows for validation. The maximum sampling frequency and accuracy are investigated. The system is shown to measure accurately and in real-time up to 100 km/h speeds.

Keywords: Computer vision; Side-slip angle; Off road; Image correlation

Towards a real-time pneumatic tire performance prediction using an advanced tire-ice interface model

Emilio Jimenez, Corina Sandu,

Journal of Terramechanics, Volume 81, 2019, Pages 43-56, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2018.04.004.(http://www.sciencedirect.com/science/article/pii/S0022489817302653)

Abstract: Icy road conditions and tire operational parameters play a vital role in determining the overall performance of a vehicle. This study builds on prior work in the researchers’ group. The Advanced Tire-Ice Interface Model (ATIIM) simulates the temperature rise in the contact patch based on the measured pressure distribution and the thermal properties of the tread compound and of the ice surface. It has the capability to simulate the height of the thin water film created from the melted ice, to predict the tractive performance, and to estimate the viscous friction due to the water layer and the influence of braking operations, including the locked wheel condition. The experimental investigation included measuring the bulk temperature distribution in the contact patch to validate the temperature rise simulations of the ATIIM. As shown by the simulations and the test data, a rise in temperature was observed from the leading edge to the trailing edge of the contact patch. As the wheel load increases, the difference in temperature rise increases, as also reflected in the experimental study. When the temperature difference was significant, a thin water film was observed that resulted in a reduction of friction, which was simulated using the ATIIM.

Keywords: Tire-ice interface; Contact patch temperature; Traction performance

A comparative study of destructive effects resulting from road profile acting on off-road towed vehicles

László Gurmai, Péter Kiss,

Journal of Terramechanics, Volume 81, 2019,Pages 57-65, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2018.06.002.

(http://www.sciencedirect.com/science/article/pii/S0022489817302719)

Abstract: The more extreme conditions the vehicle is exposed to, the sooner it wears out and deteriorates. In order to determine the forces affecting the lifespan of vehicles we need to know the environmental conditions eliciting these forces. This research aims at elaborating and testing a method which can help to conduct a comparative analysis of forces acting on towed vehicles used in different terrain conditions. Excitation forces acting on a vehicle being towed across terrain cause vibrations which lead to wear and structural deterioration. The rate of deterioration depends on the activating forces resulting from the road profile geometry and the dynamic properties of the vehicle. A knowledge of the relationship between the towed vehicle and the terrain profile will enable the design of an artificial road profile for fatigue testing with which similar stresses arise as during normal use. With the developed comparative method, a connection can be established between stochastic road profiles and road profiles containing artificially built obstacles.

Keywords: Towed vehicle; Terrain profile; Transfer function; Fatigue test; Power spectral density; Root mean square; Characteristic frequency

ABS braking on rough terrain

Nico A. van der Merwe, P. Schalk Els, Vidas Žuraulis,

Journal of Terramechanics, Volume 80, 2018, Pages 49-57, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2018.10.003.(http://www.sciencedirect.com/science/article/pii/S0022489818301526)

Abstract: The performance of Anti-lock Brake Systems (ABS) for vehicles deteriorate on rough terrains, due to fluctuations in the angular wheel speeds and in the vertical loading conditions of the tyre caused by the terrain inputs. In this paper, ABS braking performance on non-deformable rough terrain is investigated by performing experiments and simulations using a testing trailer and a validated multi-body dynamics model. The trailer was constructed using a Land Rover Defender chassis and installed with standard Land Rover braking components including an ABS modulator. It was found in the ABS tests performed, while using a standard Bosch ABS algorithm, that the ABS algorithm failed to perform optimally due to oscillations and irregularities that were present in the measurement of angular wheel speeds. Good correlation is found between the tyre forces measured and the forces simulated using an FTire model in MSC ADAMS software. A powerful platform was created for future off-road ABS investigation and development using both experiments and a simulation platform.

Keywords: Anti-lock braking system; ABS; Rough terrain; ADAMS; FTire; Belgian paving

Comparison of simulation models NRMM and NTVPM for assessing military tracked vehicle cross-country performance

J.Y. Wong, P. Jayakumar, E. Toma, J. Preston-Thomas,

Journal of Terramechanics, Volume 80, 2018, Pages 31-48, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2018.10.002.(http://www.sciencedirect.com/science/article/pii/S0022489817300538)

Abstract: Mobility of ground vehicles is an important issue for defence operations. In the United States and some other NATO countries, the NATO Reference Mobility Model (NRMM) is currently used to evaluate military ground vehicle mobility. The cross-country performance prediction module of NRMM is based on empirical relations established with test data primarily collected decades ago. It has inherent limitations, such as the uncertainty whether the empirical relations can be extrapolated beyond the test conditions upon which they were derived. This paper describes a comparison of the empirically-based NRMM with the physics-based Nepean Tracked Vehicle Performance Model (NTVPM) for assessing the cross-country performance of military tracked vehicles. It examines the soundness of the methodologies of NRMM and NTVPM, the adequacy of the vehicle design parameters and terrain characteristics that they take into account, the user friendliness of their operations, and the correlations between the measured cross-country performance of a notional tracked vehicle (an armoured personnel carrier) and that predicted by the two simulation models on sandy terrain, muskeg and snow-covered terrain. Based on the results of the evaluation, it appears that the physics-based NTVPM has potential as the basis for the development of the next generation simulation model for assessing the cross-country performance of military tracked vehicles.

Keywords: Coefficient of correlation; Coefficient of variation; Computer simulation models; Cross-country performance; Empirical models; Mean maximum pressure; Measured data; Physics-based models; Predicted performance; Tracked vehicles

Road profile reconstruction using connected vehicle responses and wavelet analysis

Zhiming Zhang, Chao Sun, Raj Bridgelall, Mingxuan Sun

Journal of Terramechanics, Volume 80, 2018, Pages 21-30, ISSN 0022-4898,

https://doi.org/10.1016/j.jterra.2018.10.004.(http://www.sciencedirect.com/science/article/pii/S0022489818300107)

Abstract: Practitioners analyze the elevation profile of a roadway to detect localized defects and to produce the international roughness index. The prevailing method of measuring road profiles uses a specially instrumented vehicle and trained technicians, which usually leads to a high cost and an insufficient measurement frequency. The recent availability of probe data from connected vehicles provides a method that is cost-effective, continuous, and covers the entire roadway network. However, no method currently exists that can reproduce the elevation profile from multi-resolution features of the vehicle inertial response signal. This research uses the wavelet decomposition of the vehicle inertial responses and a nonlinear autoregressive artificial neural network with exogenous inputs to reconstruct the elevation profile. The vehicle inertial responses are a function of both the vehicle suspension characteristics and its speed. Therefore, the authors normalized the vehicle response models by the traveling speed and then numerically solved their inertial response equations to simulate the vehicle dynamic responses. The results demonstrate that applying the artificial neural network to the wavelet decomposed inertial response signals provides an effective estimation of the road profile.

Keywords: Road roughness; Profile reconstruction; Vehicle response; Wavelet analysis; Neural network

Evaluating mobility vs. latency in unmanned ground vehicles

David J. Gorsich, Paramsothy Jayakumar, Michael P. Cole, Cory M. Crean, Abhinandan Jain, Tulga Ersal

Journal of Terramechanics, Volume 80, 2018, Pages 11-19, ISSN 0022-489

https://doi.org/10.1016/j.jterra.2018.10.001.(http://www.sciencedirect.com/science/article/pii/S0022489818300971)

Abstract: As the penetration levels of unmanned ground vehicles (UGVs) in military applications increase, there is a growing need to evaluate their mobility across different latencies and various modes of operation ranging from pure teleoperation to full autonomy. State-of-the-art tools to evaluate mobility of ground vehicles do not address this need due to their not accounting for UGV technologies and the associated latencies. Although the trade-off between latency and performance has been thoroughly studied in the telerobotics literature and the results may qualitatively shed light onto the UGV domain, as well, a quantitative generalization is not possible due to the differences in context. Recognizing this gap, this paper presents a functional relationship between mobility and latency in high-speed, teleoperated UGVs under the context of path following. Specifically, data from human-in-the-loop simulations performed in this paper are combined with data from prior studies to span three vehicle types, three courses, and teleoperation latencies ranging from 0 s to 1 s. This combination yields for the first time a diverse data set for the context of path following in high speed, teleoperated UGVs. Based on this data set, empirical relationships are derived to quantify the trade-off between latency versus average speed and lane keeping error. These relationships can be used to establish a benchmark to evaluate the performance of autonomy-enabled UGV systems.

Keywords: Mobility; Latency; Unmanned ground vehicles; Teleoperation

Use of explicit finite-element formulation to predict the rolling radius and slip of an agricultural tire during travel over loose soil

Dror Rubinstein, Itzhak Shmulevich, Nicolay Frenckel,

Journal of Terramechanics, Volume 80, 2018, Pages 1-9, ISSN 0022-4898,https://doi.org/10.1016/j.jterra.2018.09.002.(http://www.sciencedirect.com/science/article/pii/S0022489818301319)

Abstract: Theoretically, there is zero slip between two bodies when there is no relative motion in their contact points. In the contact between a wheel and a surface, zero slip can be obtained only in the case of a single contact point. In this case, the wheel and the surface must be rigid. The theoretical zero-slip condition can’t be obtained in the contact between tire and terrain surface. In much of the scientific literature, two alternatives are suggested for a practical definition of the zero-slip condition: the point at which the gross traction force is equal to zero, or the point at which the net traction force is equal to zero. In the ASABE (2013), there is still no unique definition for the practical zero-slip condition. According to the definition of zero-slip condition, the rolling radius is not constant and depends on the slip. A detailed finite-element model using Lagrangian elements was built for each tire, taking into account the effect of all tire materials and their arrangement, lug shape, and inflation pressure. The soil model was built with Eulerian elements, which allow a large degree of deformation and flow of the soil. The initial verification experiments of the tire models were conducted by pressing the tires against a rigid plane. Each tire was examined under several different inflation pressures. Very good correlations were obtained between the experimental and model results. The verification test for the gross and net traction forces was performed in the soil-bin laboratory at the Technion. Special equipment was built, including a heavy dragging platform and a cell to hook the tire. This equipment allows control of the tire slip. The net traction force, gross traction force, and vertical load were measured in each test. Good correlations were obtained between the experimental and model results. Using the FEM model developed, some definitions for zero-slip condition were examined. The results indicate that the best criterion for zero-slip condition is definition of the point at which the gross traction force is equal to zero.

Keywords: Soil wheel interaction; Gross traction; Net traction; Finite element; Eulerian; Lagrangian; Zero slip