Estimation of plowing forces on vehicles driving through deep snow

Orian Welling, Sally Shoop, Ted Letcher, Bruce Elder, Mark Bodie

Journal of Terramechanics, Volume 104, 2022, Pages 25-29, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.08.003.(https://www.sciencedirect.com/science/article/pii/S0022489822000568)

Abstract: Determining trafficability of winter surfaces is a critical capability for Army operations in cold regions. Over the years, a substantial amount of research has been conducted to characterize different winter surfaces (and different vehicles, tires, and tracks on these surfaces) for this purpose. Trafficability model for snow and ice have been implemented in numerous tools currently in use by the Army including the NATO Reference Mobility Model (NRMM), GeoWATCH, and other stand-alone implementations. However, these models are generally based on empirical testing of vehicles driving through snow of shallow to moderate depth and do not adequately capture additional compressive and inertial plowing forces as well as friction drag forces resulting from deep snow being pushed forward by the vehicle bumper, nose, compression caused by the undercarriage, or undercarriage components catching the snow (e.g. suspension arms). In this paper we propose a generalizable snow plowing model for estimating the force required for a vehicle to travel through deep snow. The results of the model compare well to empirical measurements of the force required for a mid-weight all-terrain tactical vehicle to move through different depths of deep snow (over the bumper) and at different ride height settings.

Keywords: Mobility modeling; Trafficability; Off-road; Military vehicles; Snow

An adapted Burckhardt tire model for off-road vehicle applications

David Vieira, Rodolfo Orjuela, Matthias Spisser, Michel Basset

Journal of Terramechanics, Volume 104, 2022, Pages 15-24, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.08.001.(https://www.sciencedirect.com/science/article/pii/S0022489822000544)

Abstract: Off-road vehicle mobility is a real challenge in many areas such as agriculture, military, or construction machinery. The introduction of autonomous vehicles in these fields requires more advanced control algorithms. Furthermore, the deformable nature of the terrain has a significant impact on vehicle behavior. In this context, a lot of research has been conducted to describe the wheel-ground interaction phenomena. Among the most significant factors, traction force, lateral force, and wheel sinkage are crucial aspects in the study of vehicle mobility. One of the most used approaches is based on the Bekker-Wong description. However, due to the mathematical complexity of this model, this approach is rather intended for vehicle simulation. Since the design of control laws requires less complex models, this paper proposes a method based on a road tire model structure adapted to deformable surfaces. This modification is based on the original Burckhardt tire model with a modified structure and estimated parameters. Furthermore, the parameter identification is performed by simulating a realistic virtual test bench allowing the data collection for the parameter estimation process. Finally, the obtained results show the applicability of the proposed method through a new tire model called the Adapted Burchardt Tire Model (ABTM).

Keywords: Off-road; Wheeled vehicle; Soft Soils; Control-oriented tire model; Tire parameter estimation; Adapted Burckhardt Tire Model (ABTM)

A unified equation for predicting gross traction for wheels on clay over a range of braked, towed, and powered operations

George L. Mason, Farshid Vahedifard, Tyler J. Caster, Jody D. Priddy

Journal of Terramechanics, Volume 104, 2022, Pages 1-13, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.08.002.(https://www.sciencedirect.com/science/article/pii/S0022489822000556)

Abstract: A characteristic curve is presented for predicting gross traction of a wheel over a range of powered, towed, and braked modes on clay soils for slip ranging from positive 100% powered slip to negative 100% skid slip. The characteristic curve is a unified approach that relates the ratio of the contact pressure of the wheel to soil strength and predicts the gross traction coefficient over a continuous range of slip. The unified equation is defined by five inflection points: maximum/minimum traction, traction at zero slip, max change in traction with slip, and a shape factor coefficient. The inflection points aim to simplify the calibration of gross traction, slip, soil strength, and contact pressure by using functions adaptable to machine learning. The unified equation is comparable to historic traction equations but is unique in its ability to predict asymmetric braking and powered gross traction. The unified equation is supported and substantiated via error analysis by utilizing the Database Records for Off-road Vehicle Environments (DROVE) – a database constructed around the archived laboratory and field tests for wheels and tracks operating on different soils. The accuracy of the proposed model is assessed and compared to other conventional equations such as the Brixius equation and Maclaurin’s extension of the Pacejka equation for off-road traction.

Keywords: Off-road mobility; Clays; Gross Traction; Powered, braked, and towed modes; Vehicle Terrain Interface (VTI) model; Database Records for Off-road Vehicle Environments (DROVE)

Evaluation of in-situ relationships between variable soil moisture and soil strength using a plot-scale experimental design

Brad D. Sion, Sally A. Shoop, Eric V. McDonald

Journal of Terramechanics, Volume 103, 2022, Pages 33-51, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.07.002.(https://www.sciencedirect.com/science/article/pii/S0022489822000453)

Abstract: Off-road vehicle trafficability depends on mechanical soil properties and terrain characteristics that reflect the soil forming environment. Empirical laboratory data show how soil moisture influences soil strength; however, such relationships are mostly devoid of in-situ soil conditions. This study presents results from field experiments conducted at four research sites in the western and midwestern United States to examine the effects of increased soil moisture on in-situ soil strength. Plot-scale grids were used to apply water to the soil surface at regular 24-hour intervals. Soil samples were collected at three depth intervals prior to each of five water application/infiltration periods to compare field-based soil moisture with soil strength measurements. Systematic increases in saturation levels were observed that correspond with reduction of compressive strength, cohesive strength, and penetration resistance. These results exhibit regional differences in the responses of dynamic soil properties that can be explained using soil taxonomic information and differences in the state factors of soil development. Our results provide an expanded dataset to improve the development of relationships between soil type and soil strength to impact next generation mobility models, and enable remote evaluation of vehicle trafficability under soil moisture conditions based on knowledge of regional geomorphic and pedogenetic characteristics.

Keywords: Soil strength; Vehicle mobility; Soil moisture; Soil cohesion; California bearing ratio

Experimental safety analysis of transplanting device of the cam-type semi-automatic vegetable transplanter, Journal of Terramechanics

Markumningsih Sri, Seok-Joon Hwang, Ju-Seok Nam

Volume 103, 2022, Pages 19-32, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.07.001.(https://www.sciencedirect.com/science/article/pii/S0022489822000441)

Abstract: A transplanting device is a part of a vegetable transplanter that performs a key role and receives a large load during the transplanting work. The load characteristics affect the static and dynamic safety of the transplanting device. The aim of this research was to experimentally investigate the load and safety of the transplanting device of the cam-type semi-automatic vegetable transplanter commonly used in Korea. A strain-based load measurement system was constructed using 15 strain gauges attached to selected measurement spots on the transplanting device. Field tests were conducted at 4 levels of engine speed and 12 levels of planting distance. Measured strain data were converted into stress values to analyse the static safety factor and fatigue life of the transplanting device. The results showed that the stress acting on the transplanting device tended to increase with the increase in the engine speed or the decrease in the planting distance. The static safety factors of the transplanting device under various working conditions were greater than 1.0 for all the measurement spots. The minimum fatigue life was 66,416 h at the upper side of the hopper which is sufficient lifetime, considering 25.5 h of annual usage time in Korea.

Keywords: Fatigue life; Rain-flow counting method; Static safety factor; Transplanting device; Vegetable transplanter

Prediction and optimizing the multiple responses of the overall energy efficiency (OEE) of a tractor-implement system using response surface methodology

Mohammad Askari, Yousef Abbaspour-Gilandeh, Ebrahim Taghinezhad, Rashad Hegazy, Mahmoud Okasha

Journal of Terramechanics, Volume 103, 2022, Pages 11-17, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.06.003.(https://www.sciencedirect.com/science/article/pii/S002248982200043X)

Abstract: The aim of this paper was to predict and optimize the overall energy efficiency (OEE) of a tractor-implement system in semi-deep tillage via response surface methodology (RSM) approach. The OEE was affected by two tillage tines (i.e., subsoiler and paraplow), four forward speeds (i.e., 1.8, 2.3, 2.9 and 3.5 km/h), three operating depths (i.e., 30, 40 and 50 cm) and vertical load imposed on tractor rear wheels at two levels (i.e., 225 kg and no-weight). All tests were replicated four times, forming 192 data points. Field test results revealed all variables were influential on the OEE except vertical load. An increment of speed and depth increased OEE. The RSM approach displayed 3D views with higher accuracy for the OEE change due to changing tine, speed, depth and vertical load relative to regression prediction models. Another feature of the RSM approach was the output graphs with many small pixels. Accordingly, input variables changes and their influences on the OEE are more locational and visible. Moreover, the RSM model accurately predicted the OEE as 35.216% with the desirability of 0.843 at the optimum state as paraplow tine, 30 cm depth, 2.07 km/h forward speed, and 0.01 kg vertical load.

Keywords: Response surface methodology; Draft; Fuel consumption; Energy efficiency; Tines; Subsoiling

Piecewise model of track sinkage based on underwater cohesive soil

Jiaxiong Wu, Boshen Liu, Yanhua Shen, Zhipeng Feng, Qian Jiao

Journal of Terramechanics, Volume 103, 2022, Pages 1-10, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.06.002.(https://www.sciencedirect.com/science/article/pii/S0022489822000428)

Abstract: The soil resistance force prediction model plays a vital role in estimating trafficability of unmanned tracked vehicles on unknown terrain, especially for river floor soil, a kind of soft soil with high saturation. In order to obtain characteristics of soft soil, a soil test platform was built which track segment sinkage, and shear tests can be performed in river floor soil. Comprehensive analysis of mechanics of track-soil interaction, a new pressure-sinkage empirical model is proposed for soft soil. This piecewise empirical model with two functions relies on two sets of independent parameters to describe the stratification of the underwater soil, including loose layer and dense layer. To evaluate the accuracy of the piecewise empirical model, an underwater tracked vehicle driven by two brushless DC motors was designed and an underwater travel test platform was built, which the vehicle can be operating in the river floor soil. The main external forces enacting on the vehicle, including environmental loads caused by the river floor soil and water, were analyzed in the process of vehicle running at a constant speed, and a soil resistance force prediction model was deduced with the proposed piecewise empirical model. The current of two brushless DC motors is used to estimate the external loads and validate the piecewise empirical model. Test results indicate that the soil resistance force prediction model was effective and feasible.

Keywords: Soft soil; Pressure-sinkage; Piecewise model; Motion resistance prediction; Underwater tracked vehicle

Vibration characteristics analysis and suspension parameter optimization of tractor/implement system with front axle suspension under ploughing operation condition

Jinming Zhang, Haoping Yao, Lizhong Chen, Enlai Zheng, Yue Zhu, Jinlin Xue

Journal of Terramechanics, Volume 102, 2022, Pages 49-64, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.05.001.(https://www.sciencedirect.com/science/article/pii/S0022489822000325)

Abstract: To improve the riding comfort and driving safety of the tractor system, it’s necessary to build a vibration model of wheeled tractor/implement system to analyze its corresponding vibration characteristics. A discrete element model of plough-soil coupling system was developed in this work to obtain the tillage resistance and its effectiveness is verified through experiment. Then, the vibration model of wheeled tractor/implement system with front axle suspension under ploughing condition was constructed and the corresponding vibration characteristics of the tractor system under road transportation, farmland transportation and plough operation conditions were simulated. It’s demonstrated that the simulated vibration responses agree well with the measured data and the validity of the proposed model is proved. The simulation results show that the natural frequency of the tractor system almost remains constant under the three working conditions above and the natural frequencies of vertical vibration for front axle, cabin, driver seat and implement are 2.09 Hz, 2.84 Hz, 2.84 Hz and 2.09 Hz, respectively. The existence of front axle suspension will deteriorate the ride comfort of driver but improve the handing stability obviously. The farmland road roughness and tillage resistance can reduce the vibration responses of the wheeled tractor/implement system with front axle suspension significantly. With the increase of tillage speed or depth, the vibration responses of the tractor system rise tremendously. When the tillage speed or depth is constant, the largest vertical vibration acceleration exists on the front axle. In addition, the multi-objective optimization of stiffness and damping parameters for the front axle suspension is implemented through particle swarm algorithm and the optimal stiffness and damping are recommended to be 60 kNm−1 and 8.919 kNsm−1, respectively.

Keywords: Tractor; Implement; Soil; Discrete element; Vibration acceleration; Particle swarm algorithm; Multi-objective optimization

Effect of surface roughness on tyre characteristics

Carl Becker, Schalk Els

Journal of Terramechanics, Volume 102, 2022, Pages 27-48, ISSN 0022-4898

https://doi.org/10.1016/j.jterra.2022.04.003.(https://www.sciencedirect.com/science/article/pii/S0022489822000301)

Abstract: Tyre characterisation is not a trivial or inexpensive exercise thus it is important to obtain representative measurements during tyre characterisation tests. Different test methods exist and vary from laboratory tests to outdoor tests on different surfaces. Each of the test surfaces have different surface roughness and will result in different tyre characteristics. This study compares friction coefficient measurements on dry non-deformable surfaces for laboratory test surfaces and outdoor test tracks on the same agricultural tyre with large lugs at two inflation pressures and three tread wear conditions. The influence of surface roughness on friction coefficient is investigated. The macrotexture and microtexture of multiple surfaces are measured and compared. The importance of measuring the microtexture of the outdoor test surface is noted. Static/Non-rolling tyre tests in a laboratory are compared to Static/Non-rolling tyre tests as well as Dynamic/Rolling tyres tests at an outdoor test facility. Excellent correlation is found between the Static vs. Dynamic and laboratory vs. outdoor tests results when the laboratory tests are conducted on a surface representing the outdoor surface.

Keywords: Agricultural tyre; Tyre wear; Friction coefficient; Tyre test; Surface roughness; Microtexture; Macrotexture