Modeling the effect of liquid movement on the center of gravity calculation of agricultural vehicles

Farzaneh Khorsandi, Paul D. Ayers, Robert S. Freeland, Xinyan Wang
Journal of Terramechanics, Volume 75, 2018, Pages 37-48, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.09.005.

Abstract: Due to a high center of gravity (CG) location, agricultural vehicles are more vulnerable to overturns. The CG location can be calculated using the lifting axle method of ISO 16231-2:2015. But, as a vehicle is lifted, its liquid payloads are not entirely contained. The liquids will shift both in position and form, affecting the CG height calculation. A mathematical model was developed to predict the effect of liquid movement on the CG height calculation of a tilted vehicle. The model was validated using an agricultural utility tractor and a prototype. The developed model was applied to calculate the CG location considering the effect of the liquid shift. Results showed tilting produced a higher calculated center of gravity due to liquid movement, but by increasing the tilting angle, the calculated CG height decreased. The effect of the liquid shift on CG height measurement for the wagon with 16.0% liquid mass was 14.8% and for the tractor with 1.2% liquid mass was 0.41%. The model error was less than 1.3% for all tests. Considering the effect of the liquid shift in CG height calculation, the error in CG height calculation decreased from 11.9% to 2.6% for the wagon.

Keywords: Center of gravity; Stability; ISO 16231-2:2015; Liquid shift; Tractor; Overturn; Safety

Development of a dynamic simulation model of a towed seeding implement

Ian W.P. Paulson, Allan T. Dolovich, Scott D. Noble
Journal of Terramechanics, Volume 75, 2018, Pages 25-35, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.10.006.

Abstract: As the size of western Canadian farms increase and the productivity demands on seeding equipment rise, improvement in the depth consistency performance of seeding implements at higher seeding speeds is a future focus of equipment designers. The objective of this work was to develop a dynamic simulation tool for predicting the motion of a hoe-opener style seeding implement with independent row units. The model was developed using simple low-order models available in the literature to compute the forces generated at soil-tire and soil-tool interfaces. By maintaining low computational cost, early-stage parameter sensitivity and design trade-off studies can assess the risk of a given design change. The amplitude of the power spectral density (PSD) of simulated row unit motion was typically lower with sharper peaks than measured results up to 3.3 m/s; these differences were due to both input amplitude differences, and the sensitivity of the model itself. Frequency agreement of major measured and simulated PSD peaks was acceptable considering the model simplifications. Row unit motion was dominated by two phenomena – a strong periodic input in the terrain surface, and feedback between the hoe-opener and packer wheel of the row unit.

Keywords: Vehicle dynamics; Soil-tire interaction; Soil-tool interaction; Vibration; Seeding depth

The Hohenheim Tyre Model: A validated approach for the simulation of high volume tyres – Part II: Validation

Paul Witzel
Journal of Terramechanics, Volume 75, 2018, Pages 15-24, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.09.004.

Abstract: 
This publication series describes the development of the Hohenheim Tyre Model – an approach that considers the properties of high volume, agricultural tyres. The research project was conducted in accordance with the V-Model, which proposes a standardised development methodology for mechatronic systems. The previous publication described amongst others the model structure and parameterisation. This paper elucidates the validation, which is an essential part of the V-Model. Validation received special attention and is divided into three parts. First, three-dimensional tyre behaviour on level surfaces was investigated. Within the second step, single tyre behaviour is validated during obstacle passages. Similar obstacles were then used in the final step that shows up the correlation between measured and simulated whole vehicle behaviour. Throughout the validation avery high level of accuracy is achieved.

Keywords: Tyre model; Handling; Comfort analysis; Multi-body simulation

The Hohenheim Tyre Model: A validated approach for the simulation of high volume tyres – Part I: Model structure and parameterisation

Paul Witzel
Journal of Terramechanics, Volume 75, 2018, Pages 3-14, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.07.002.

Abstract: 
The applied tyre model influences significantly the accuracy of vehicle simulations. This is especially the case for farm machinery that is equipped with high volume tyres and mostly suspended on one axle only. In order to account for the special properties of these tyres – such as the nonlinearities that come along with high deflections – a new tyre model was developed at the University of Hohenheim. During the development phase the main requirements to fulfil were short computation times, an easy to apply parameterisation process and a high model quality. In order to attain these goals an all new multi-spoke tyre model was developed. Various adaptations were made to the model structure in order to achieve a real-time factor of 0.6. All eighteen parameters have a physical meaning and can be determined with two in-house tyre test stands. Validation comprises aspects relevant to both handling and ride quality and will be addressed in part two of this publication series.

Keywords: Tyre model; Handling; Comfort analysis; Multi-body simulation

Terrain classification using ToF sensors for the enhancement of agricultural machinery traversability

Francisco Yandun Narváez, Eduard Gregorio, Alexandre Escolà, Joan R. Rosell-Polo, Miguel Torres-Torriti, Fernando Auat Cheein
In Journal of Terramechanics, Volume 76, 2018, Pages 1-13, ISSN 0022-4898
https://doi.org/10.1016/j.jterra.2017.10.005.

Abstract:

Ground properties influence various aspects of mobile machinery navigation including localization, mobility status or task execution. Excessive slipping, skidding or trapping situations can compromise the vehicle itself or other elements in the workspace. Thus, detecting the soil surface characteristics is an important issue for performing different activities in an efficient, safe and satisfactory manner. In agricultural applications, this point is specially important since activities such as seeding, fertilizing, or ploughing are carried on within off-road landscapes which contain a diversity of terrains that modify the navigation behaviour of the vehicle. Thus, the machinery requires a cognitive capability to understand the surrounding terrain type or its characteristics in order to take the proper guidance or control actions. This work is focused on the soil surface classification by implementing a visual system capable to distinguish between five usual types of off-road terrains. Computer vision and machine learning techniques are applied to characterize the texture and color of images acquired with a Microsoft Kinect V2 sensor. In a first stage, development tests showed that only infra-red and RGB streams are useful to obtain satisfactory accuracy rates (above 90%). The second stage included field trials with the sensor mounted on a mobile robot driving through various agricultural landscapes. These scenarios did not present illumination restrictions nor ideal driving roads; hence, conditions can resemble real agricultural operations. In such circumstances, the proposed approach showed robustness and reliability, obtaining an average of 85.20% of successful classifications when tested along 17 trials within agricultural landscapes.

Keywords: Agricultural robotics; Terrain classification; Pattern recognition
 

2D FE–DEM analysis of contact stress and tractive performance of a tire driven on dry sand

Kenta Nishiyama, Hiroshi Nakashima, Hiroshi Shimizu, Juro Miyasaka, Katsuaki Ohdoi

Journal of Terramechanics, Volume 74, 2017, Pages 25-33, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.09.003.

Abstract:
Normal and tangential stresses acting over a contact interface of a tire driven on dry sand were investigated to expand the applicability of our model incorporating 2D FE–DEM with proportional–integral–derivative (PID) control. A simple averaging method for contact reaction was introduced: computational segments were defined over the lower half part of the tire circumference that translates without rotation with the tire; then the contact stresses were calculated segment by segment. For the analysis, it was assumed that the tire was in rigid contact mode and that it would travel on the model sand terrain in stationary condition. The integration of normal and tangential contact stresses with respect to the angle of rotation was then applied to calculate the vertical contact load, gross tractive effort, net traction, and running resistance of the tire by parametric (or semi-empirical) analysis. The result of tractive performance obtained through the parametric analysis was found to be similar to the result of tractive performance obtained directly using FE–DEM analysis. A forward shift of the consistent angle of rotation for maximum normal contact stress and that for maximum tangential contact stress with the increase of slip from 22% was also observed in the FE–DEM result.

Keywords: Soil–wheel system; Normal contact stress; Tangential contact stress; Traction performance; DEM; FEM
 

Influence of atmosphere on lunar rover performance analysis based on soil parameter identification

Masataku Sutoh, Sachiko Wakabayashi, Takeshi Hoshino

Journal of Terramechanics, Volume 74, December 2017, Pages 13-24, ISSN 0022-4898, https://doi.org/10.1016/j.jterra.2017.08.001.
http://www.sciencedirect.com/science/article/pii/S0022489817300812
Abstract: Abstract  

This paper outlines an analysis of the traveling performance of a lunar rover. The analysis is in the form of numerical simulations and it uses soil properties, identified in vacuum, and mechanics of wheel-based travel. The wheel-to-ground contact model and soil parameters are determined first so they could be used in the numerical simulation. A soil test device is introduced and the soil parameters are identified from plate-pressing and shear tests. Finally, numerical simulations are conducted using the parameters identified and their results are discussed along with those of the traveling tests conducted in vacuum. The soil tests indicated that the wheel sinkage into the ground can increase in vacuum and that the shear stress acting beneath the wheel in vacuum is almost the same as that in the atmosphere. Because of these trends, the simulations and traveling tests showed that the traveling performance of the wheel can decrease in vacuum. Although it has been widely considered that the vacuum environments enhance the traveling performance of the wheel, this study confirmed that it is not always the case.

Keywords: Lunar exploration; Rover; Traveling performance; Vacuum; Soil parameter identification

Creating 3D models of tractor tire footprints using close-range digital photogrammetry

Amaneh E. Kenarsari, Stanley J. Vitton, John E. Beard,

Journal of Terramechanics, Volume 74, 2017, Pages 1-11, ISSN 0022-4898, http://dx.doi.org/10.1016/j.jterra.2017.06.001.
http://www.sciencedirect.com/science/article/pii/S0022489817301519

Abstract: Close-range digital photogrammetry is utilized to construct the 3D models of an agricultural tire footprint. These models were then analyzed to obtain the tire footprint depth, area and volume. The procedure of using the photogrammetry technique for developing 3D models of a tire footprint on soil as well as an assessment of the accuracy of the 3D models are discussed in this paper. Testing was conducted using a tractor tire in a large soil bin in a lab to generate a single tire footprint along with a rolling tire test to simulate a longer tire rut. Our experiments showed that the close-range digital photogrammetry provides an efficient and accurate method to assess the depth and volume of the tire footprint in soil.
Keywords: Photogrammetry; Tire footprint; 3D models; Large scale laboratory tests
 

Modeling of share/soil interaction of a horizontally reversible plow using computational fluid dynamics

Lin Zhu, Jia-Ru Ge, Xi Cheng, Shuang-Shuang Peng, Yin-Yin Qi, Shi-Wu Zhang, De-Quan Zhu

Journal of Terramechanics, Volume 72, 2017, Pages 1-8, ISSN 0022-4898

http://dx.doi.org/10.1016/j.jterra.2017.02.004.
http://www.sciencedirect.com/science/article/pii/S0022489817300393
Abstract: The horizontally reversible plow (HRP) is currently widely used instead of the regular mold-board plow due to its high operational performance. Soil pressure during HRP tillage generally has adverse effects on the plow surface, especially on either the plowshare or the plow-breast. This effect eventually shortens the tool’s service life. For this reason, this investigation used a three-dimensional (3D) computational fluid dynamics (CFD) approach to characterize the share/soil interaction and thus assess the effects of different tillage conditions on the interaction. To achieve this goal, a 3D model of the plowshare was first constructed in the commercial software SolidWorks, and soil from Xinjiang, China, was selected and subsequently characterized as a Bingham material based on rheological behaviors. Finally, 3D CFD predictions were performed using the control volume method in the commercial ANSYS code Fluent 14.0 in which the pressure distributions and patterns over the share surface were addressed under different tillage speeds in the range of 2–8ms−1 and at operational depths ranging from 0.1 to 0.3m. The results show that the maximum pressure appeared at the share-point zone of the plowshare and that the increase in soil pressure was accompanied by either higher tool speed or greater operational depth. The calculated results qualitatively agreed with the preliminary experimental evidence at the same settings according to scanning electron microscopy (SEM). Once again, the CFD-based dynamic analysis in this study is demonstrated to offer great potential for the in-depth study of soil-tool interactions by simulating realistic soil matter.
Keywords: Soil-share interaction; Computational fluid dynamics (CFD); Tillage speed; Operational depth; Horizontally reversible plow (HRP)