Akira Oida

Simulation of soil deformation and resistance at bar penetration by the Distinct Element Method

A mechanical model of soil is constructed using the Distinct Element Method (DEM) which makes it possible to analyze the discontinuous property of soil. To discuss the applicability of the soil model by the DEM, a bar penetration test was conducted and the result was compared with the simulation results. From the results of the behavior of elements, it could be said that the mechanical model by the DEM could well simulate the discontinuous behavior of soil and the parameters used in the simulation play important roles to make the soil model useful. As for the penetrating resistance, some problems which lie in the present DEM model are discussed and the key to solving these problems is indicated. Moreover, the method to determine the time interval used in the DEM simulations is mentioned in terms of the stability of the solution in the calculation.

Simulation of a soil loosening process by means of the modified distinct element method

Abstract We apply the Distinct Element Method (DEM) to analyze the dynamic behavior of soil. However, the conventional DEM model for calculation of contact forces between elements has some problems; for example, the movement of elements is too discrete to simulate real soil particle movement. Therefore, we modify the model to solve the difficulties. To investigate the validity of the modified model, we conduct an experiment in which soil is cut with a pendulum-typeblade, and simulate the soil loosening process with the modified DEM model. This paper presents details of the experimental apparatus and the comparison of soil behavior and energy absorption between the simulation and the experiment. Some characteristic phenomena of the experiment are reproduced in the simulation giving us confidence that the modified model is better than the conventional model for the simulation of soil behavior.

Electro-hydraulic tillage depth control system for rotary implements mounted on agricultural tractor Design and response experiments of control system

A tillage depth control system for rotary implements mounted on an agricultural tractor was designed and constructed to improve accuracy of tillage depth. The control system was composed of five main units: (1) a detecting unit to measure the tilting angle (position) of the lift arm, the pitching angle of the tractor and heights of sensors from ground surface, (2) a controlling unit, (3) a hydraulic unit to operate a three-point hitch linkage by a lift arm cylinder, (4) a three-point hitch linkage and rotary implements, and (5) a setting unit to put the reference tillage depth and a dead zone into the control circuit. The tillage depth was controlled by an on/off operation of a solenoid valve, of which time was proportional to the controlling time. Experiments to evaluate the response characteristics of the control system were conducted under various engine speeds, i.e. various flow rates of hydraulic oil, various tillage depths and some input frequencies. The results of the response experiments of the control system are discussed in this paper.

Non-contact sensors for distance measurement from ground surface

Abstract Optical and ultrasonic sensors were designed and fabricated for non-contact detection of ground height. Indoor and outdoor experiments were conducted to evaluate the detection performance of both sensors under the following test conditions: moisture content and type of soil; ambient temperature and sunlight intensity; configuration of the ground surface; distance of the sensor from the ground surface; and moving speed of the sensor. The type of soil, the sunlight intensity and the moving speed had little effect on the detection performance of both sensors. The optical sensor could detect the distance from the ground surface accurately in spite of irregularity of the ground surface configuration. High moisture content (40% D.B.) of the soil greatly affected the detection performance of the optical sensor due to the refraction of the light at the water film on the soil surface. On the other hand, the detection performance of the ultrasonic sensor was not affected by moisture content, but was largely influenced by temperature. The detection accuracy of the ultrasonic sensor on an irregular ground surface was greatly affected by the measuring distance due to its wide beam width.

Measurement of soil reaction forces on a single movable lug

Abstract In order to clarify characteristics of a new mechanism called a movable lug, a model of a single movable lug equipped with an L-shaped force transducer has been developed. The soil reaction forces (normal and tangential) on a flat single movable lug, a curved single movable lug and a fixed lug were measured on wet sandy loam soil in the laboratory soil bin test. These measured forces then were converted to lug pull and lift forces. The pull and lift forces obtained by the flat movable lug with 45° lug inclination angle and the curved movable lug were higher than those of the fixed lug. It was observed that the lift force of the fixed lug achieved its peak and dropped earlier than those of the movable lugs. However, the peaks of pull and lift forces of the flat and curved movable lugs were almost the same. The flat movable lug with 45° lug inclination angle generated a slightly higher peak of pull force than those with 30° and 60° lug inclination angles. However, the higher lug inclination angle produced, the lower peak of lift force. It was observed that the pull and lift forces increased as the sinkage increased. In contrast to the flat movable lug with 45° lug inclination angle, the curved movable lug produced greater lift force especially at high sinkage. The increase in lug slip from 5% to 25 and 50% caused an increase in the peaks of pull and lift forces. The soil moisture content affected the lug forces significantly.

Theoretical analysis of soil reaction on a lug of the movable lug cage wheel

Abstract The measurement of soil reaction forces on a lug of a movable lug cage wheel was carried out in a soil bin. To elucidate the experimental results, a theoretical analysis of soil reaction forces on the lug of the movable lug cage wheel was made by using an analysis of the lug trajectory and a modified theory in soil–vehicle mechanics. The existing theory was modified and adjusted by considering the actual lug trajectory and the soil trench made by the preceding lug. The results showed that the theoretical analysis gave a good representation of the reaction forces measured experimentally. The higher pull and lift forces of the movable lug cage wheel compared with those of the fixed lug wheel was supported by the theoretical analysis. Although the theoretical representation of soil reaction forces should be improved by further works, it is sufficiently accurate to estimate the performance of the movable lug cage wheels by the proposed theory.

The performance of cage wheels for small power tillers in agricultural soil

Abstract Five sizes of lug angle and four sizes of lug pitch were tested to determine the performance of open, flat-lugged wheels for a small power tiller operated on two different types of agricultural soils (sandy and clay loam). As a result, it was found that the maximum tractive efficiency and the maximum drawbar power of the wheels are significantly influenced by the lug angle, lug pitch, wheel slip and soil type.

The characteristics of soil reaction forces on a single movable lug

In order to understand clearly the characteristics of the soil reaction forces on a single movable lug, the resultant of measured soil reaction forces was determined and presented along with its position on the lug plate. The resultant of soil reaction forces acting on the movable lug increased gradually and reached the maximum value when the lug was on about its lowest position in the soil, then it decreased without offering any downward resistance to the lug till the lug left the soil. The maximum resultant force of the movable lug was higher than that of a fixed lug. The point of action of the resultant force on the movable lug shifted in a similar way in all test cases, that is, it moves to the center of the lug from the outer tip until it reaches the position where it becomes the maximum, then it moves to the outer tip till the lug leaves the soil. The inclination angle of the resultant force increased with the decrease of lug inclination angle. The bigger lug sinkage of the movable lug produced bigger soil reaction forces and shifted the point of action of the resultant force from the tip part to the central part of the lug. However, there was no significant effect of the lug sinkage on the direction of the resultant force. The increase in lug slippage from 25% to 50% brought bigger soil reaction forces on the movable lug, but did not influence the direction and point of action of the resultant force.

Dependency of observation parameters on soil dynamic parameters in unconfined impact compression tests

Abstract Unconfined impact compression tests were used to measure dynamic parameters of soil samples in the domains of stress wave propagation and dynamic deformation. The high-frequency equivalent Youngs modulus, which was determined by the reflection theory of one-dimensional elastic stress waves, increased exponentially with water content. The low-frequency equivalent Youngs modulus, which was defined as the initial gradient of a stress-strain curve, decreased exponentially with increasing water content. The high-frequency equivalent Youngs modulus was one to two orders of magnitude larger than the low-frequency one. Water content, height of soil samples and drop height affected the dynamic stress-strain relationships of the soil samples. The Maxwells viscoelastic fluid model described the stress-strain relationships well, and the values of the model parameters varied with water content and frequency.

Deformation of sand caused by tine implements

Abstract Soil failure mechanisms in sand caused by simple vertical tines were investigated. Based on surface soil movement, two failure mechanisms were observed: the sand either failed periodically or flowed steadily around the tine, depending on the width of the experimental tines. Wide tines caused periodic failures with cyclic reaction forces. Narrow tines acted like knives and caused a steady soil flow with a constant reaction force. The failure mechanisms of sand did not depend on the three moisture contents tested.