Minoru Yamazaki

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.

Soil compaction by multiple passes of a rigid wheel relevant for optimization of traffic

Abstract Agricultural field operations of various levels of mechanization are heavily dependent on wheel tractors as a source of traction power. It is common practice to use the same tractor for different operational requirements. Hence the soil with different load bearing capacity is exposed to repeated compressive stress of the same magnitude. This results in the formation of a dense layer within the soil mass which is poor in hydraulic conductivity, aeration, and unfavorable for the growth of plants. It creates a cyclic effect of change in soil strength and increases in power requirements together with decreases in productivity year after year. This paper presents an experimental study of soil compaction as a result of multiple loading by the running device. It is valuable for present farming systems in determining the combined effects of load and number of passes so as to utilize the field power effectively with minimum compaction effect. In this work soil compaction was studied in the laboratory using soil bin facilities. An analysis was made based on investigations on experimental results of surface and sub-surface deformation, specific volume and compaction index (coefficient) which characterize soil compaction phenomena. The results showed that the number of passes and the load as independent variables significantly affected the compaction capacity of the soil. According to the experimental results, the first three passes of a loaded wheel are critical and the intensity of soil compaction within a depth of 120 mm is serious.

Numerical simulation of a 4WD-4WS tractor turning in a rice field

Abstract For the steady-state circular turning of a 4WD–4WS (4 wheel driven–4 wheel steered) tractor in a rice field, a numerical simulation was achieved. Equations of motion of this tractor were developed in a vehicle fixed x–y coordinate system. By comparing the calculated and measured results of acting forces on the tractor tires, this simulation was evaluated. Then, the characteristic parameters of the turning vehicle, which are the side slip angle and the yaw angular velocity of the vehicle center of gravity, were simulated in several combinations of the steering wheel angle and the forward speed. Also the same simulation applied to a 4WD–2WS tractor which had the same body as the 4WD–4WS tractor. The simulated results showed a clear difference of turnability between 4WS and 2WS. ©

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 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.

Characteristics of soil reactions of an open lugged wheel under paddy soil conditions

In the past, experimental studies on an open lugged wheel-soil interaction were conducted under predetermined constant slip and sinkage given mechanically. In practice, the soil reactions and motion of an open lugged wheel are determined by interaction between the soil-lug contact, and the soil under some load. For this study therefore, an experimental device giving freedom of movement in the vertical direction to a lugged wheel and self-propelled mechanism, was constructed. The slip and sinkage and soil reactions obtained in this experiment were considered to represent the actual phenomena of soil-lug interaction. Dynamic behaviour of the lugged wheel has already been reported [1]. Furthermore, the characteristics of soil reactions of the lugged wheel induced by lugs moving into the soil were measured and discussed.

Dynamic behaviour of an open lugged wheel under paddy soil conditions

Abstract Many experimental studies of open lugged wheel-soil interaction have been conducted, mainly based on the condition of constant slip and sinkage. As a result the reaction force to lugs seemed to be equal to the soil cutting resistance to a metal surface. However, analyses based on such methods do not appear to represent the actual behaviour of lugged wheel-soil interaction, especially when the lugs are spaced widely. The actual motion the wheel axle. In this study, an experimental device for a model lugged wheel was constructed to investigate the characteristics of the interaction between a lugged wheel and soil. Experiments were conducted under several test conditions of soil including paddy soil with a hard pan. The result of both theoretical and experimental data indicated that slip and sinkage of a lugged wheel showed a fluctuation with rotation angle of which the period is equal to the angular lug spacing. In each test soil condition used, the motion of the lugged wheel and the reaction forces acting on each lug from the soil for a free sinking wheel were different from that of the condition of constant slip and sinkage. It was found that the results obtained from this study could clarify the actual behaviour of lugged wheel-soil interaction.