Simulation of soil-to-tool interaction using Discrete Element Method (DEM) and Multibody Dynamics (MBD) coupling

Multi-physics simulation of soil-to-tool interaction using a coupled Discrete Element Method (DEM) and Multibody dynamics (MBD) techniques can support the design of off-road equipment. Quantitative prediction of the soil reaction forces on the equipment is essential to provide a reliable simulation-based design. DEM is a computational method for simulating the dynamic behavior of granular materials. In the coupling interface, DEM gives a high fidelity prediction of the forces for soil-to-soil and soil-to-tool interaction, which can be used in the MBD simulation workflow. Two laboratory tests were used to capture the bulk material behavior: the angle of repose test for calibration of coefficients of static friction and rolling friction, and the cone penetrometer test to calibrate the soil shear modulus and normal and shear stiffnesses (related to the Hertz-Mindlin with bonding contact model). A simple pendulum test was developed to validate the DEM soil model in a soil-to-tool interaction application. The test was conducted in a soil bin filled loosely with loam soil at soil moisture content of 10% and initial soil bulk density of 1330 kg/m3. A cutting plate connected to the pendulum cut the soil at two levels of cutting depths (25 mm and 50 mm). The same application was simulated using the DEM simulation and DEM-MBD co-simulation. The horizontal and vertical soil cutting forces were compared between simulations and test. The magnitude of the maximum horizontal cutting forces for the experiment, DEM simulation, and DEM-MBD co-simulation were 73 N, 365 N, and 187 N, respectively for the 25 mm cutting depth and 108 N, 766 N, and 278 N, respectively for the 50 mm cutting depth. The DEM-MBD coupling improved the force prediction both for 25 mm and 50 mm cutting depths. It also closely predicted the trend in the increase in horizontal forces by cutting depth. The maximum horizontal soil cutting forces from experiment and DEM-MBD co-simulation increase by 48% and 49% by increasing the depth, respectively

Numerical modeling of soil flow and pressure distribution on a simple tillage tool using computational fluid dynamics

Soils, in general, undergo both elastic and plastic deformations upon loading. Strain dependant anisotropic elasto-plastic models are required for realistic modeling for soil-tool mechanics that will address issues like stress history and soil anisotropy. Although several such models have been proposed, the science of coupled poro-mechanical analysis of an unsaturated soil has not been fully addressed.Tillage tool modeling is primarily concerned with the analysis of soil deformation patterns and development of force prediction models for design optimization. Most of the models are based on quasi-static soil failure patterns that cause difficulty in accurately predicting soil-tool behaviour and soil forces for high speed operation. In recent years efforts have been made to improve the conventional analytical and experimental models by numerical approaches. Numerical simulations of soil-tool interactions using finite element modeling (FEM) and discrete element method (DEM) were mostly based on a solid mechanics approach. Due to limitations of constitutive relations, predictions of these numerical models have not been able to address tillage dynamics with high shear rates. The contribution of this research was to study the dynamics of soil-tool interaction using computational fluid dynamics (CFD) from the perspective of soil visco-plastic behavior.A motorised soil rheometer was developed for evaluating soil visco-plastic parameters for CFD simulations. The apparatus was used to determine soil yield stress and viscosity at different soil moisture and compaction levels.Three-dimensional CFD analyses were carried out using a commercial software CFX 4.4 to observe soil failure patterns around a tool and the pressure distribution on and around the tool. Duct flow as well as free-surface flow simulations of visco-plastic soil as a non-Newtonian Bingham material indicated soil deformation comprising of ‘plastic flow’ and ‘plug flow’ patterns. The soil failure front advancement demonstrated a critical speed range of 4 to 6.5 m s-1 where advancement of the failure front did not increase with speed. Soil pressure on the tool surface increased with the tool operating speed. Pressure distribution on the tool surface and draft requirement agreed well with the published literature based on experimental results and FEM analysis. The CFD approach, in its first attempt to tillage process, demonstrated its greater potential for dynamic modeling of soil-tool interaction

Using similitude theory and discrete element modeling to understand the effects of digging parameters on excavation performance for rubber tire loaders

The large sizes of mining equipment pose challenges for analysis using experiments or simulation. While scaled physical and simulation models can address this challenge, no previous work has explored how similitude theory and modeling can provide valid analysis of large equipment such as rubber tire loaders. The objective of this research was to apply similitude theory and discrete element modeling (DEM) to study the effect of different digging parameters on the penetration and the draft on the buckets of rubber tire loaders. The work sought to (1) test the hypothesis that the geometry of a rubber tire loader bucket and operating conditions significantly affects the resistive force (draft) and penetration; (2) test the hypothesis that different geometry orientations and operating conditions of a rubber tire loader bucket significantly affects draft and penetration; (3) apply DEM to scale models of rubber tire loader buckets to understand the effect of bucket geometry, orientations, and operating conditions on draft and penetration; and (4) evaluate the effectiveness of using discrete element models and similitude theory to predict draft and penetration. The results show that geometry, muckpile particle sizes, height above the floor, rake angle, speed, and motor power output are correlated to penetration and draft. This work has demonstrated that we can build valid DEM models for predicting at a larger scale. The chamfer angle of semi-spade bucket cutting blades significantly affects the draft on the buckets and 30° chamfer cut angle performs the best with the lowest peak resistive forces and energy consumption. The work finds that the forces observed during the rotation phase of the simulation are lower than the observed forces during penetration --Abstract, page iii

Effect of side-wings on draught: The case of Ethiopian Ard plough (maresha)

Ethiopian farmers have been using an ox-drawn breaking plough, known as ard plough – maresha, for thousands of years. Maresha is a pointed, steel-tipped tine attached to a draught pole at an adjustable shallow angle. It has narrow side-wings, attached to the left and right side of it, to push soil to either side without inverting. The aim of this paper is to explore the effect of side-wings on draught using a field soil bin test facility. To this end, a mobile and an in-situ soil bin test system, for online measurements of draught, was designed and developed. This research considered tool geometry (maresha plough with and without side-wings) and rake angle (shallow – 8°, medium deep – 15°, and deep – 24°, representing primary, secondary and tertiary tillage processes in Ethiopia, respectively). Maresha plough with side-wings has greater contact area, between the moving soil and tool, than its wingless counterpart. When the ploughshare surface and soil slide relative to one another, the draught expected to increase with contact area, as adhesion and friction resistance increases with area. However, experimental analysis indicated that the maresha with side-wings required less draught compared to maresha without side-wings (ρ < 0.001). This might be attributed to the effect of side-wings on crack propagation by a wedging effect to enhance and facilitate subsequent ploughing. This paper also dealt with the effect of rake angle on draught. Though the depth setup was getting smaller d1 < d2 < d3 for the successive tillage runs, analysis showed increment in draught force (ρ < 0.001) with rake angle. This might be attributed to higher soil compaction that comes with depth and downward force resulting from repeated use of maresha every season to the same depth for thousand years. Although more and rigorous studies should be undertaken considering soil, tool, and operational parameters to arrive at conclusive results, this paper gave some insights regarding effect of side-wings on maresha plough and rake angle on draught. This shows that there is still room for improvement of maresha plough geometry for minimum draught requirement and optimum soil manipulation

Finite element analysis of blade-formation interactions in excavation

The efficiency and costs of mining operations greatly depend on the efficient design and use of excavators. The performance of these capital-intensive excavators requires thorough understanding of the physical and design factors that affect the formation-cutting tool interaction process. The current body of knowledge, based on experimental and analytical methods, provides limited understanding of these factors, which limits the accurate design and performance of excavators. The soil constitutive equations used in most of the available finite element (FE) models also fail to adequately capture the elastic and plastic behaviors of soil formations. This research initiative uses FE techniques to model the soil-tool interaction phenomenon, with appropriate focus on the behavior of soils during excavation. This is a pioneering effort in developing FE model of the soil-dozer blade interaction using the modified Cam Clay elasto-plastic law. The model is validated with results from previous experimental and analytical methods. The results provided soil forces, a progressive developed failure zone, displacement fields and stress distribution along the tool surface. The sensitivity analysis of changes in blade angle on cutting force showed that, the cutting force increases with increasing blade angle. The cutting depth of the blade had a similar effect on blade cutting force. Increasing the depth of cut increases the required cutting force. Increasing the coefficient of friction at the soil blade interface increases the blade cutting force. Reducing the coefficient of friction at the soil blade interface from 0.3 to 0.05 reduces the cutting force by 22.3%. The percentage represents the maximum potential savings in blade cutting force. This research initiative advances the frontiers of soil-tool interactions, during excavations, to expand the limited knowledge in this critical area --Abstract, page iii

An investigation into jet assisted submarine cable burial ploughs

Fibre optic telecommunication cables laid across the seaoor are buried in shallow water depth (<2000m) for protection against hazards arising from commercial shing and shipping activity. The cables are buried in a trench created by a sea plough, often jet assisted and towed from a ship, or by a ROV with jet legs straddling the cable and uidising the soil around it. Recent trends in the industry require more versatile burial tools, so a sound understanding of their fundamental mechanics is required to enable their optimun design and performance. The aim of this research program was to study the mechanics of force reduction on jet assisted cable burial tools. The experimental program consisted of two stages, both conducted in controlled submerged conditions. The rst studied the effects of jet parameters, tool rake angle and pore pressure on tool force reduction. The second stage studied the action of a single horizontal buried jet on the surrounding soil, in which the rst series of experiments studied a static jet nozzle in sand and clay, and the second a dynamic jet nozzle. The flow rate or nozzle Velocity was varied in each respectively. The rst stage showed force reduction was caused by the reduced soil stress on the tool face in areas intersecting uidised sand. The larger the uidised area (FA), or the lower its intersection, the greater the force reduction. Evenly spaced nozzles gave greater FA coverage of the tool face. Interaction between jet and rake angle and force was complex, but upward angled jets and forward raked tools gave least force reduction. Results of the second stage showed cavity formation in sands characterised by shear erosion whereas in clay by pressure fracturing. The cavity size in sands was directly proportional to jet momentum ux and inversely proportional to tool Velocity. Mathematical models were developed from each stage, the rst to simulate tool force reduction created by the jets, given knowledge of the FA, and the second to simulate the FA created by a single jet. The second over predicted cavity length by a average of 7% over the range of tool velocities tested. The combined models over predicted tool force, and suggested reasons for the discrepancies are given. Further research is required to rene the model and provide a useful tool for the design and operation of jet assisted cable burial tools in saturated sands

Optimising conservation tillage systems for wheat and oilseed rape production.

The aims of the thesis are to determine the effect of different conservation tillage systems on the agronomic, environmental and economic performance of a wheat and oilseed rape rotation, and to understand the processes involved so that the systems can be improved. The field research examined five systems over three seasons (September 2013 to August 2016) in two fields (one clay and one clay loam) in Northamptonshire. The most disruptive tillage treatment was the Farm system comprising the use of a Sumo Trio when establishing oilseed rape, and the Sumo Trio and a Kuhn seed drill when establishing wheat. The least disruptive system was a Väderstad Seed Hawk or Rapid. The other three treatments were all one pass conservation tillage systems comprising a Claydon Hybrid Drill, a Mzuri Pro til 3, and a Sumo Deep Tillage Seeder (DTS). To understand the effect on draught and soil disturbance, specific components of the systems were tested under controlled conditions at Cranfield University’s soil bin facility. The shallow working Väderstad required the lowest draught and disturbed less soil than deep working treatments. A low aspect ratio (working depth/implement width) and rake angle reduced the draught. In the field immediately after tillage, the Farm system showed the greatest reduction in bulk density and penetration resistance at 0-50 mm and 150-200 mm, but this effect was not maintained during the season. The level of surface residue was lowest (15%) with the Farm system and greatest (75%) with the Väderstad. The shallow Väderstad led to the highest earthworm abundance in all years and both fields, proportions of water stable aggregates and microbial biomass carbon in third and first year respectively. In the clay field, blackgrass infestation doubled from 8.2% in 2013-14 to 16.0% in 2015-16; it was not a major problem in the clay loam field. Due to high variability, there was no significant effect (p>0.05) of tillage treatments on the yield of wheat and oilseed rape over the 3-year trial period in either field, except when delayed drilling of oilseed rape with the Sumo DTS in September 2015 which led to reduced yields. At a reduced significance level of p=0.15, higher yields observed for Väderstad and Mzuri in the clay soil were associated with higher levels of organic matter. The relative profitability of the five systems was primarily determined by the assumed yields and secondly by the cost of the systems. The predicted annual net margin for the five systems varied from £545 to £659 ha¯¹. The calculated cost of the five tillage systems (assuming working areas ranging from 370 to 1,100 ha) ranged from £11 to £31 ha¯¹ a¯¹, with the lowest cost achieved by the 6 m Claydon system. Assuming blackgrass weeds are not an issue, shallow low disturbance systems can result in low costs, improved soil biology and carbon storage, and sustainable high yields

Performance evaluation of a spring tine cultivator in a sandy loam soil

Selection and matching of appropriate tillage implements for a given farming operation are dependent on the data available on draft parameters for the particular tillage implement. Spring tine cultivator is one of the primary tillage implements commonly used by farmers in the study location. Performance information of spring tine cultivator is vital to enable the cost of tillage operation to be reduced. Field experiments were performed using spring tine cultivator and tractor at three tillage depths (10, 20 and 30 cm) and five tractor speeds (3.6, 5.4, 7.2, 9.0 and 10.8 km/hr) to determine the implement travel speed. The effects of tillage depth and implement travel speed on draft force, unit draft, vertical specific draft, horizontal specific draft and coefficient of pull were accessed. The results showed that increasing the tillage depth or implement travel speed increased the draft force, unit draft and vertical specific draft. The relationship between them is also linear. Increasing the tillage depth equally increase the horizontal specific draft and the coefficient of pull but increasing the implement speed reduce the horizontal specific draft and the coefficient of pull. Approximately 27.5 % of the draft force was focused towards cutting the soil and 72.5 % was spent in pulverization of the soil particles. The values of the vertical specific draft were much more than those of the horizontal specific draft for all the tillage depths and the implement travel speeds. The tillage depth had more influence on the draft, unit draft, specific draft and the coefficient of pull than the implement travel speed

Modelling of energy requirements by a narrow tillage tool

The amount of energy consumed during a tillage operation depends on three categories of parameters: (1) soil parameters (2) tool parameters and (3) operating parameters. Although many research works have been reported on the effects of those parameters on tillage energy, the exact number of affecting parameters and the contribution of each parameter in total energy requirement have not been specified. A study with the objectives of specifying energy consuming components and determining the amount of each component for a vertical narrow tool, particularly at high speeds of operation, was conducted in the soil bin facilities of the Department of Agricultural and Bioresource Engineering, University of Saskatchewan. Based on studies by Blumel (1986) and Kushwaha and Linke (1996), four main energy consuming components were assumed: (1) energy requirements associated with soil-tool interactions;(2) energy requirements associated with interactions between tilled and fixed soil masses;(3) energy requirements associated with soil deformation; and (4) energy requirements associated with the acceleration of the tilled soil. Energy requirement of a vertical narrow tool was calculated based on the draft requirement of the tool measured in the soil bin. The effects of three variables, moisture content, operating depth and forward speed, were studied at different levels: (1) moisture content at 14% and 20%; (2) depth at 40, 80, 120 and 160 mm; and (3) speed at 1, 8, 16 and 24 km h-1. Total energy requirement was divided into these four components based upon the procedure developed in the research. Regression equations for different energy components were developed based on experimental data of two replicates and then validated by extra soil bin experiments conducted at same soil and tool but different operational conditions. The set up of energy components data in the model development showed good correlation with the available experimental data for all four components. Coefficients of all regression equations showed a first order energy-moisture content relationship best applicable to those equations of energy components. For the acceleration component, energy-depth relationship at all speed levels resulted in an equation which included first and second orders of depth. In contrast, if only two higher levels of speed were used in the regression model, the relationship between acceleration energy and depth resulted in the second order of depth. When experimental data of acceleration energy at 8, 16, and 24 km h-1 speeds were used in the regression equation, the acceleration energy-speed relationship resulted in both linear and quadratic relationships. It was concluded that for the tool and soil conditions used in the experiments, 8 km h-1 speed resulted in only linear relationship. On the other hand, 16 and 24 km h-1 speeds resulted in a quadratic relationship. Therefore, for all 3 speeds used in experiments, both linear and quadratic relationships were obtained. Considering that the tool was operating at high speeds, this research is expected to contribute valuable experimental data to the researchers working in the field of soil dynamics

A multi sensor data fusion approach for creating variable depth tillage zones

Efficiency of tillage depends largely on the nature of the field, soil type, spatial distribution of soil properties, and the correct setting of the tillage implement. However, current tillage practice is often implemented without full understanding of machine design and capability leading to lowered efficiency and further potential damage to the soil structure. By modifying the physical properties of soil only where the tillage is needed for optimum crop growth, variable depth tillage (VDT) has been shown to reduce costs, labour, fuel consumption and energy requirements. To implement VDT it is necessary to determine and map soil physical properties, spatially and with depth through the soil profile. Up until now the measurement of soil compaction for VDT has been soil penetration resistance, expressed as Cone Index (CI). In this research a multi-sensor and data fusion approach was developed that allowed augmenting data collected with an electromagnetic sensor, a standard penetrometer, and conventional methods for the measurement of bulk density (BD) and moisture content (MC). Packing density values were recorded for eight soil layers of 0-5, 5-10, 10-15, 15-20, 20-25, 25-30 30-35 and 35-40 cm. From the results only 62% of the site required the deepest tillage at 38 cm, 16% required tillage at 33 cm and 22% required no tillage at all. The resultant maps of packing density were shown to be a useful tool to guide VDT operations. The results provided in this study indicate that the new multi0sensor and data fusion approach introduced is a useful approach to map layered soil compaction to guide VDT operations. The economic benefit analysis demonstrated fuel savings of 48% by implementing the proposed system. Further work is needed to implement the packing density map for VDT in larger numbers of field in order to generalise the approach