Effect of travel speed and vertical load on the subsoil force and displacement under a smooth steel roller

A smooth steel roller was tested in an indoor soil bin. Subsoil forces and displacements were measured at depths of 50, 100, 150, and 200 mm. Roller operating conditions included roller travel speed, the vertical load, and number of passes. Three travel speeds, 1, 3, and 5 km h^?1 and three vertical loads 20, 40, and 60 kN were tested. The draft needed to move the roller was also recorded. For multiple passes, subsoil forces were increased by 30% if vertical load increased by 50%; while the roller draft increased by 20%. For a single pass, no significant differences detected between the subsoil forces at speeds of 1 and 3 km h^?1; when the roller traveled at 5 km h^?1 with a vertical load of 60 kN, the subsoil force was approximately reduced by 30% compared to those at lower travel speeds. For both single and multiple passes, increasing travel speed did not significantly increase subsoil forces and displacement below 150-mm depth; however, the power required to drive the roller was significantly increased. Higher travel speed was more effective in creating larger subsoil displacement and subsoil forces within 100-mm from the soil surface. For similar effects below 100-mm, lower travel speed was found appropriate.     

Effect of trash board on moldboard plough performance at low speed and under two straw conditions

Draught requirement is an important parameter for tillage tool performances. This study investigated the influence of trash board on the performance of moldboard plough and the system optimization. Draught and vertical forces acting on the plough were measured with and without a trash board under two straw conditions, i.e. with only stubbles and with dense straw cover. Field soil moisture content was kept at 30%. The study also used the finite element method (FEM) to simulate stress distribution on the plough. Results showed that draught significantly increased without trash board under dense straw cover as compared with only stubbles. The trash board attachment reduced draught significantly. Similar trend was also true for vertical force. FEM results were found to be compatible with the experiment. The simulated maximum equivalent stress acting on the mouldboard plough was 279.43 MPa, while the material’s yield stress was 250 MPa. Attaching trash board with the moldboard plough is important where straw cover was dense.     

Measuring soil compaction and soil behavior under the tractor tire using strain transducer

Soil compaction can occur due to machine traffic and is an indicator of soil physical structure degradation. For this study 3 strain transducers with a maximum displacement of 5 cm were used to measure soil compaction under the rear tire of MF285 tractor. In first series of experiments, the effect of tractor traffic was investigated using displacement transducers and cylindrical cores. For the second series, only strain transducers were used to evaluate the effect of moisture levels of 11%, 16% and 22%, tractor velocities of 1, 3 and 5 km/h, and three depths of 20, 30 and 40 cm on soil compaction, and soil behavior during the compaction process was investigated. Results showed that no significant difference was found between the two methods of measuring the bulk density. The three main factors were significant on soil compaction at a probability level of 1%. The mutual binary effect of moisture and depth was significant at 1%, and the interaction of moisture, velocity, and depth were significant at 5%. The soil was compressed in the vertical direction and elongated in the lateral direction. In the longitudinal direction, the soil was initially compressed by the approaching tractor, then elongated, and ultimately compressed again.     

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

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 2–8 ms⁻¹ and at operational depths ranging from 0.1 to 0.3 m. 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.     

Razor clam-inspired burrowing in dry soil

RoboClam is a biomimetic burrowing robot that imitates the valve expansion/contraction digging pattern of the Atlantic razor clam, Ensis directus, to dig into submerged soil using an order of magnitude less energy than would be required to push into the soil with brute force. This paper examines whether it would theoretically be possible to use the same method to dig into dry soil. The stress state of the soil around the contracting robot was analyzed, and a target zero-stress state for dry soil digging was found. Then, the two possible modes of soil collapse were investigated and used to determine how quickly the robot would have to contract to achieve the target zero-stress state. It was found that for most dry soils, a RoboClam-like device would have to contract in 0.02 s, a speed slightly faster than the current robot is capable of, but still within the realm of possibility for a similar machine. These results suggest that the biomimetic approach successfully used by RoboClam to dig into submerged soil could feasibly be used to dig into dry soil as well.     

Development of a dynamometric vehicle to assess the drawbar performance of high-powered agricultural tractors

Agricultural tractors are machines originally designed to mechanize agricultural tasks, especially tillage and pulling. A large part of research activities have been interested in optimizing tractor efficiency, in particular in terms of emissions and energy. In this frame, the OECD Tractor Code 2 sets out a drawbar test in specific controlled conditions with the aim of evaluating the power of the tractor available at the drawbar. The principal measurement chain relies on dynamometric vehicles (DV) that are instrumented vehicles specifically engineered to develop horizontal force at the drawbar of agricultural tractors. The CREA Laboratory of Treviglio, Italy, engineered a new dynamometric vehicle to test tractors with up to 200 kW at the drawbar (245 kW at the engine flywheel) and a maximum of 118 kN drawbar force. The chosen basis is a FIAT 6605 N truck (TM 69 6 × 6) which has been transformed into a hydrostatic vehicle driven by a hydraulic system and an auxiliary gearbox. The maximum drawbar force was verified up to 122 kN. The drawbar power verification (200 kW) was successfully carried. The final verification confirmed that the project is valid for the investigation and optimization of the parameters regarding the traction efficiency of agricultural tractors.     

Differences in tractor performance parameters between single-wheel 4WD and dual-wheel 2WD driving systems

Vertical wheel load and tire pressure are both easily managed parameters which play a significant role in tillage operations for limiting slip which involves energy loss. This aspect to a great extent affects the fuel consumption and the time required for soil tillage. The main focus of this experiment was to determine the effect on the wheels’ slip, the fuel consumption and the field performance of a tractor running in a single-wheel 4WD driving system and in a dual-wheel 2WD driving system, due to the variations in air pressure of the tires as well as in the ballast mass. With no additional mass, the lowest fuel consumption was reached by a tractor with the least air pressure in the tires and running in a dual-wheel 2WD driving system. It was determined that for a stubble cultivation with a medium-power (82.3 kW) tractor running in a dual-wheel 2WD driving system, the hourly fuel consumption was by 1.15 L h⁻¹ (or 7.3%), the fuel consumption per hectare by 0.35 L ha⁻¹ (or 7.9%) and the field performance by 0.05 ha h⁻¹ (or 1.25%) lower compared to a single-wheel 4WD driving system, when driving wheels’ slip for both modes was the same, i.e., at 8–12%.     

Predictability of boreal forest soil bearing capacity by machine learning

In forest harvesting, terrain trafficability is the key parameter needed for route planning. Advance knowledge of the soil bearing capacity is crucial for heavy machinery operations. Especially peatland areas can cause severe problems for harvesting operations and can result in increased costs. In addition to avoiding potential damage to the soil, route planning must also take into consideration the root damage to the remaining trees. In this paper we study the predictability of boreal soil load bearing capacity by using remote sensing data and field measurement data. We conduct our research by using both linear and nonlinear methods of machine learning. With the best prediction method, ridge regression, the results are promising with a C-index value higher than 0.68 up to 200 m prediction range from the closest point with known bearing capacity, the baseline value being 0.5. The load bearing classification of the soil resulted in 76% accuracy up to 60 m by using a multilayer perceptron method. The results indicate that there is a potential for production applications and that there is a great need for automatic real-time sensoring in order to produce applicable predictions.     

Vertical stability of bubble chain: Multiscale approach

Linear stability is investigated of a uniform chain of equal spherical gas bubbles rising vertically in unbounded stagnant liquid at Reynolds number Re = 50–200 and bubble spacing s > 2.6 bubble radii. The equilibrium bubble positions are questioned for their stability with respect to small displacements in the vertical direction, parallel to the chain motion. The transverse displacements are not considered, and the chain is assumed to be laterally stable. The bubbles are subjected to three kinds of forces: buoyant, viscous, inviscid. The viscous and inviscid forces have both pairwise (local) and distant (nonlocal) components. The pairwise forces are expressed by the leading-order formulas known from the literature. The distant forces are expressed as a linear superposition of the pairwise forces taken over several farther neighbours. The stability problem is addressed on three different length scales corresponding to: discrete chain (microscale), continuous chain (mesoscale), bubbly chain flow (macroscale). The relevant governing equations are derived for each scale. The microscale equations are a set of ODE’s, the Newton force laws for the individual discrete bubbles. The mesoscale equation is a PDE for bubbles continuously distributed along a line, obtained by taking the continuum limit of the microscale equations. The macroscale equations are two PDEs, the mass and momentum conservation equations, for an ensemble of noninteracting mesoscale chains rising in parallel. This transparent two-step process (micro → meso → macro) is an alternative to the usual one-step averaging, in obtaining the macroscale equations from microscale information. Here, the scale-up methodology is demonstrated for 1D motion of bubbles, but it can be used for behaviour of 2D and 3D lattices of bubbles, drops, and solids.It is found that the uniform equilibrium spacing results from a balance between the attractive and repulsive forces. On all three length scales, the equilibrium is stabilized by the viscous drag force, and destabilized by the viscous shielding force (shielding instability). The inviscid forces are stability neutral and generate conservative oscillations and concentration waves. The stability region in the parameter plane s − Re is determined for each length scale. The stable region is relatively small on the microscale, larger on the mesoscale, and shrinks to zero on the macroscale where the bubbly chain flow is inherently unstable.The shielding instability is expected to occur typically in intermediate Re flows where the vertical bubble interactions dominate over the horizontal interactions. This new kind of instability is studied here in a great detail, likely for the first time. Its relation to the elasticity properties of bubbly suspension on different length scales is discussed too. The shielding force takes the form of a negative bulk modulus of elasticity of the bubbly mixture.     

Experimental study of extreme thrust on a tidal stream rotor due to turbulent flow and with opposing waves

Time-varying thrust has been measured on a rotor in shallow turbulent flow at laboratory scale. The onset flow has a turbulence intensity of 12% at mid depth and a longitudinal turbulence length scale of half the depth, about 5 times the vertical scale, typical of shallow flows. The rotor is designed to have thrust and power coefficient variations with tip speed ratio close to that of a full-scale turbine. Three extreme probability distributions give similar thrust exceedance values with the Type 1 Pareto in mid range which gives 1:100, 1:1000 and 1:10 000 exceedance thrust forces of 1.38, 1.5 and 1.59 times the mean value. With opposing waves superimposed the extreme thrust distribution has a very similar distribution to the turbulent flow only. Exceedance forces are predicted by superposition of a drag force with drag coefficient of 2.0 based on the wave particle velocity only and with an unchanged mean thrust coefficient of 0.89. These values are relevant for the design of support structures for marine turbines.     

Stress and fatigue life analyses of a five-piece rim and the proposed optimization with a two-piece rim

A five-piece rim and a two-piece bolt-connected rim were investigated to examine stress levels and fatigue lives on critical regions. The finite element models of the rim/tire assemblies were developed and validated through tire engineering data and previously validated modelling approaches. The rim/tire assemblies were simulated under two conditions, (1) application of a 23,100 kg static load followed by a 24.14 km/h travelling speed and an 82° wheel angle, and (2) application of a 26,900 kg static load followed by an 8.05 km/h travelling speed and an 82° wheel angle. The results revealed that travelling and steering speeds were the key factors in causing high stresses and bolt tension forces. Compared to the five-piece rim, the two-piece rim decreased the maximum stresses by over 30% for both loading conditions; consequently the fatigue lives were increased by over two orders of magnitude. The maximum bolt forces for the two-piece rim were estimated to be 195,680 N and 111,360 N separately.     

Soil disturbance and force mechanics of vibrating tillage tool

Experiments were conducted with vibrating tillage tools in a sandy loam soil. It was observed that during oscillating operation, initially draft increased slightly with an increase in forward speed but later it decreased. For the non-oscillating operation, draft increased continuously with increase in forward speed. The ratio of draft from oscillating to non-oscillating mode varied from 0.63 to 0.93. The total power required for oscillating operation was 41–45% more than the power required for non-oscillating operation. The soil surface was cracked due to tool motion showing the characteristics of lifting up of soil clods during the oscillating operation, whereas it showed the characteristics of soil flow during non-oscillating operation. The soil was pulverized more due to oscillating than non-oscillating operation. The reduction in dry bulk density of soil mass in the oscillating operation was about 70–270% more than that during the non-oscillating mode.     

Effects of various parameters on the attrition of bed material in a recirculating fluidized bed with a draft tube

We performed an experimental study to investigate the effects of various parameters on the attrition of bed material and its size distribution with increasing operation time in a recirculating fluidized bed (RCFB). The studied parameters included superficial velocity of fluidizing air, bed inventory, and spacing between the jet top and draft tube bottom (spacer height). The bed material was prepared from Indian Standard (IS) Grade I sand from sieves with a size range of 2.20–1.00 mm. Experiments were performed at ambient conditions, with the superficial air velocity ranging from 7.13–9.16 m/s, a bed inventory of 7–10 kg, spacing of 0.085 and 0.045 m between the jet top and draft tube bottom, and an operating time of 40 h. We investigated the influence of these parameters in terms of changes in the size distribution of particles, changes in the %-weight of particles of different size ranges, generation of particles with smaller diameters, the decrease of the downcomer bed height, variations in the coefficient of uniformity and coefficient of curvature, and material loss from entrainment of fines with increasing operation time. The mode of attrition was abrasion in all experiments. We found that with increasing operation time and other parameters (bed inventory, superficial air velocity, and spacer height) attrition of the bed material also increased. Generation and elutriation of fines were more pronounced at higher superficial air velocity, bed inventory, and spacer height.     

Discrete element method simulations of Mars Exploration Rover wheel performance

Mars Exploration Rovers (MERs) experienced mobility problems during traverses. Three-dimensional discrete element method (DEM) simulations of MER wheel mobility tests for wheel slips of i = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 0.99 were done to examine high wheel slip mobility to improve the ARTEMIS MER traverse planning tool. Simulations of wheel drawbar pull and sinkage MIT data for i ⩽ 0.5 were used to determine DEM particle packing density (0.62) and contact friction (0.8) to represent the simulant used in mobility tests. The DEM simulations are in good agreement with MIT data for i = 0.5 and 0.7, with reasonable but less agreement at lower wheel slip. Three mobility stages include low slip (i < 0.3) controlled by soil strength, intermediate slip (i ∼ 0.3–0.6) controlled by residual soil strength, and high slip (i > 0.6) controlled by residual soil strength and wheel sinkage depth. Equilibrium sinkage occurred for i < 0.9, but continuously increased for i = 0.99. Improved DEM simulation accuracy of low-slip mobility can be achieved using polyhedral particles, rather than tri-sphere particles, to represent soil. The DEM simulations of MER wheel mobility can improve ARTEMIS accuracy.     

The determination of plough draught—Part II the measurement and prediction of plough draught for two mouldboard shapes in three soil series

The draught of a 3-furrow reversible plough fitted with two types of bodies was measured at five separate test sites. Each site was ploughed on four different days to provide a range of soil moisture contents. The plough was operated at three different speeds in sequence for each type of body. The horizontal and vertical forces transmitted to the tractor were measured on a three-point linkage dynamometer. Tachogenerators monitored tractor wheel speed and fifth wheel ground speed. Cone index and soil specific weight were recorded at 30 mm intervals throughout the top-soil profile. Cone index at median plough depth was found to be a satisfactory measure of soil strength for the prediction of plough draught. Characterising specific plough draught by soil cone index, specific weight, moisture content, plough mouldboard tail angle and ploughing speed provided predicted values in closer agreement with measured draught compared with earlier equations. The sensitivity of cone index to soil moisture content supports the use of the cone penetrometer as a practical monitor of soil conditions in the field and as a management tool for judging the opportune times for agricultural tillage operations.     

Suitability of rubber track as traction device for power tillers

Suitability of using rubber tracks as traction device in power tillers replacing pneumatic tires was studied using an experimental setup consisting of a track test rig for mounting a 0.80 m × 0.1 m rubber track and a loading device for applying different drawbar pulls. Tests were conducted in the soil bin filled with lateritic sandy clay loam soil at an average soil water content of 9% dry basis by varying the cone index from 300 to 1000 kPa. Data on torque, pull and Travel Reduction Ratio (TRR) were acquired using sensors and data acquisition system for evaluating its performance. Maximum tractive efficiency of the track was found to be in the range of 77–83% corresponding to a TRR of 0.12–0.045. The Net Traction Ratio (NTR) at maximum tractive efficiency was found to be between 0.49 and 0.36.Using non-linear regression technique, a model for Gross Traction Ratio (GTR) was developed and it could predict the actual values with a maximum variation of 6% as compared to an average variation of 50% with Grisso’s model. Based on this model, tractive efficiency design curves were plotted to achieve optimum tractive performance of track for any given soil condition.     

Characteristic loading of light mouldboard ploughs at slow speeds

A study on four mouldboard ploughs, that are commonly used with animal traction in Kenya, was conducted. Draught, suction and torsion loads were measured and specific draught evaluated in field tests on four sites with typical agricultural soil conditions. Draught and suction are the horizontal and vertical components of the reaction to soil force, respectively, while torsion is the resisting moment about the plough shank. The objective was to quantify these parameters and to study their characteristics under variable conditions at operation, at speeds up to 1.12 m/s and tillage depths between 0 and 150 mm in an attempt to optimize the design, selection and utilization of mouldboard ploughs for animal traction in Kenya. It was found that depth of tillage is the most critical factor, and draught and suction increased significantly with depth while specific draught increased or decreased depending on the soil type. Draught and specific draught increased significantly with speed. The increase in suction with depth probably implies an increased stability in the ploughing operation, while its reduction with speed indicates a potential instability of plough control with varying speeds. Consequently, aiming for steady motion in the utilization of animal traction may aid in the optimization. It was also found that ploughs with a high specific draught (kN/m) are expected to experience higher torsional loads on the shanks. The characteristic draught, specific draught and suction loads of the ploughs were described by quadratic functions in speed and depth of tillage with coefficients of determination (R₂) ranging from 0.55 to 0.99. A significant difference in the coefficient of variation of draught loads in the three soil types probably implies that optimal duration for use of animal traction in tillage should be dependent on soil type.     

Dynamics of a powered disk in clay soil

Experiments were conducted with a single powered disk in a laboratory soil bin containing Bangkok clay soil with an average moisture content of 18% (db) and 1100 kPa cone index. The disk was 510 cm in diameter and 560 mm in radius of concavity. During the tests the disk angle was varied from 20° to 35°, ground speed from 1 to 3 km/h and rotational speed from 60 to 140 rpm. The working depth was kept constant at 12 cm. The vertical, horizontal and lateral reactions of the soil were measured by force transducers. The forward and rotational speeds were recorded. It was observed that disk angle, rotational speed and ground speed had significant effects on soil reactive forces and power requirement. With a small disk angle, low ground speed, and high rotational speed, the soil longitudinal reactive force was a pushing force and became a resistive one at larger disk angles and ground speeds. The soil transverse reactive force increased with an increase of rotational and ground speed but decreased with the increase of disk angle, whereas the vertical relative force increased only with the increase of ground speed but decreased with the increase of rotational speed and disk angle. It was found that the powered disk required the least power at a disk angle of 30° and rotational speed between 80 and 100 rpm. Increase in ground speed from 1 to 3 km/h increased the total power requirement by 31.8%. Upon driving the disk forward, the draft reduced considerably compared to that of the free-rolling disk. By driving the disk in the reverse direction, the draft reduced slightly. At a disk angle of 30°, rotational speed of 100 rpm, and ground speed of 3 km/h, the total power requirement of the forward-driven disk was 65% higher than that of the free-rolling disk. The predicted engine power of the forward-driven disk, however, was only 21% higher than that of the free-rolling one owing to the more efficient power transmission through the PTO, as opposed to the drawbar. The effects of reverse driving and free rolling of the disk were also studied.     

Force and pressure distribution under vibratory tillage tool

Experiments were conducted to study the force requirement and pressure distribution under vibratory tillage tools in a soil bin with a sandy loam soil. The tool was oscillated sinusoidally in the direction of soil bin travel. An octagonal ring transducer and pressure sensors were used to measure the forces and soil pressure on the blade. The tool was operated at oscillating frequency of 4.5–15.6 Hz and amplitude of 11–26 mm. The soil bin travel speed was varied from 0.05 to 0.224 m/s. The test results obtained showed both the horizontal force and the vertical force decreased with increase in oscillating frequency. The normal pressure on the blade surface varied considerably. The peak normal pressure was found to increase with increase in oscillating frequency, oscillating amplitude and soil bin travel speed. The change in average normal pressure with change in oscillating frequency and amplitude was also investigated.     

Estimation of a three-dimensional tyre footprint using dynamic soil–tyre contact pressures

A method for estimating the three-dimensional (3D) footprint of a 16.9R38 pneumatic tyre was developed. The method was based on measured values of contact pressure at the soil–tyre interface and wheel contact length determined from the contact pressures and the depths and widths of ruts formed in the soil. The 3D footprint was investigated in an area of the field where the pressure sensors of the tyre passed in a soft clay soil. The tyre was instrumented with six miniature pressure sensors, three on the lug face and the remaining three on the under-tread region between two lugs. The instrumented tyre was run at a constant forward speed of 0.27 m/s and 23% slip on a soft soil, 0.48 MPa cone index, 25.6% d.b. moisture content for four wheel load and tyre pressure combination treatments. The 3D footprint assessment derived from soil–tyre interface stress used in this research is a unique methodology, which could precisely relate the trend profile of the 3D footprint to the measured rut depth. The tyre–soil interface contact pressure distributions results showed that as inflation pressure increased the soil strength increased significantly near the centre of the tyre as a compaction increase sensed with the cone penetrometer.