Power spectral density analysis of draft and torque fluctuations of a PTO powered disk tiller

Experiments were conducted in a typical Bangkok clay soil with a PTO driven disk tiller to collect the draft force and torque variation data. Tests were conducted at different forward speeds of 0.29, 0.59, 0.86, 1.08 and 1.37 m/s and at 28° and 33° disk gang angle settings. Average soil moisture content was 26% and average cone index of the test soil was 1870 kPa during all the tests. The draft force was measured by a three point linkage dynamometer. The PTO torque was measured by a slip ring type torque transducer. Tests were also conducted in the unpowered mode. Fast Fourier transform (FFT) and power spectral density (PSD) analysis techniques were used to analyse the draft force and torque variations in a time domain. The results indicated that the dominant frequencies of the draft force variations were within the range of 2.5–5.5 cycles/m of forward travel. The wave length was longer at a higher disk gang angle setting. The dominant frequency component of the torque variations varied from 3.3 to 4.3 cycles/revolution of the disk. In the unpowered mode the dominant frequencies of the draft signals had less magnitude than those of the powered mode for the same operating conditions at both disk gang angle settings of the powered disk.     

Prediction of clay soil compaction

Field measurements were made of soil density and moisture patterns under different vehicle tire paths with varying external pressures and number of passes. In addition, laboratory index tests were performed to determine the compaction behaviour of the same soil. Using these results, a prediction equation of dry density in terms of applied pressure and moisture content was obtained for the clay soil. A previously developed equation for sandy soil was modified for the complete range of moisture contents encountered. Estimation of shear strength for the clay soil was made using plastic and liquid limits.     

Pulverization characteristics of clay soil

Soil pulverization and failures during chip formation using rotating simple wedge-shaped blades for microsite preparation were analyzed to determine soil cutting characteristics. Equations were developed for soil bite size and blade projected area, and a new term was proposed relating the power requirement for rotating the pulverizer blade to the power required for penetrating the soil profile. The results of this study indicated that the rotational power requirements, in general, increased with increases in rotational and downward speeds, and the penetration power was slightly affected by the rotational speeds and was very small in comparison with the rotational power. The soil bite size appeared to play a great role in identifying the power requirements of a pulverizer blade. A substantial increase in rotational power requirement at the same rotational speeds was required due to increases in bite sizes; this increase might be due to the increases in soil-blade friction forces. During soil pulverization, chip dimensions were affected by the operational speeds, soil strength, blade geometry, and number of pulverizer blades. The pulverizer shaft diameter has little influence on the total power requirements but definitely affects the soil packing sequence of the planting cycle when the soil pulverizer for microsite preparation is incorporated into the planting head. An example illustrating the use of the data presented in this study is included to assist in the selection and sizing of a soil pulverizer's power unit.     

Dynamics of viscoelastoplastic soil under a moving wheel

A rate-dependent inelastic behavior or viscoelastoplastic behavior of soil subjected to dynamic loading of a moving rigid wheel is studied herein. A rational approach to this seemingly complex problem is treated in the context of continuum mechanics. Together with the concept of critical state soil mechanics for inelastic behavior we incorporate the so-called internal state variables for viscous effects. It is assumed that the free energy functional containing inelastic behavior may not be smooth for its entire domain of time histories. Rather, we assume a form of discretized free energy as a function of elastic strains, plastic strains, and internal or hidden variables of incremental quantity considered to be valid only for a small time interval or a fraction of loading increments. The finite element method is used to derive governing equations of motion. Exhaustive numerical examples are presented to demonstrate effectiveness of the present method.     

Dynamics of digging in wet soil

Numerous animals live in, and locomote through, subsea soils. To move in a medium dominated by frictional interactions, many of these animals have adopted unique burrowing strategies. This paper presents a burrowing model inspired by the Atlantic razor clam (Ensis directus), which uses deformations of its body to cyclically loosen and re-pack the surrounding soil in order to locally manipulate burrowing drag. The model reveals how an anisotropic body - composed of a cylinder and sphere varying sinusoidally in size and relative displacement - achieves unidirectional motion through a medium with variable frictional properties. This net displacement is attained even though the body kinematics are reciprocal and inertia of both the model organism and the surrounding medium are negligible. Our results indicate that body aspect ratio has a strong effect on burrowing velocity and efficiency, with a well-defined maximum for given kinematics and soil material properties.     

The reference shrinkage curve of clay soil

The objective of this work is to develop and validate a model that predicts the reference soil shrinkage curve, that is one without crack volume contribution, as a necessary preliminary step in future estimation of soil crack volume from soil shrinkage data. Current soil shrinkage models are based on the approximation of soil shrinkage data by some a priori taken mathematical expressions and justified by the fitting of their parameters to the data. However, the crack volume entering the data is not single valued and depends on shrinkage conditions. Unlike that the reference shrinkage curve is single valued. For soils with sufficiently high clay content when there are no large pores (lacunar pores) inside the intra-aggregate clay, the reference shrinkage curve is derived from the assumption of the rigid superficial (interface) layer of aggregates with changed pore-size range and distribution compared with the intra-aggregate matrix. This consideration is based on accounting for contributions of the interface aggregate layer and intra-aggregate matrix to the soil volume and water content during shrinkage. The reference shrinkage curve is predicted by eight fundamental physical immediately measured parameters of (i) the intra-aggregate matrix (including clay content); (ii) the aggregate structure; and (iii) the mean silt-sand grain size or mean interface layer thickness. The model was validated using the data for eight soils. In addition to the major potential application for estimating a soil crack volume, the model explains differences between the observed shrinkage curves of soil and pure clay, and it can have other numerous applications.     

Modes of wet clay soil behaviour under a single cage wheel lug

This paper presents the results of studies on the effect of sinkage and slip of a single cage wheel lug on the deformation of wet clay soil. It was observed that the deformation pattern was strongly influenced by lug sinkage and slip. Soil wedge formation on the lug was also found to be a function of sinkage and slip. Four different deformation patterns were identified during this investigation. It seems unlikely that these can be predicted without a more exact knowledge of stress-strain relationships in soils.     

Computing the aeroelastic disk vibrations in a hard disk drive

The turbulent flow of air caused by the spinning of a single disk inside a typical hard disk drive casing is calculated using large eddy simulation (LES). The pressure acting on the disk is recorded as a function of time and is used to compute the vibrations of the spinning disk using a self-developed hybrid-spectral finite-difference code. This unidirectional fluid–structure interaction problem is computed for two commonly occurring cases: a disk actuated on one side only (Case 1) and a disk actuated on both sides (Case 2). The pressure loading on the disk is characterized in terms of its mean, root-mean-square (r.m.s.) and its spectral content. The mean pressure acting on the disk is asymmetrical in the case where the disk is actuated on one side only, leading to a mean deformation of the disk to one side. The r.m.s. vibrations of Case 2 are higher than those for Case 1 and their spectral distributions are almost identical. Large pressure fluctuations of the flow are found in the wake of the actuator arm and near the region where the shroud expands to accomodate the actuator. The spectral content of the excitation force due to the pressure is mainly in the low kHz frequency range, while higher frequencies are seen at the disk edge. This typically results in the excitation of the first 3–4 modes of the disk; however, (asymmetric) Case 1 displays the excitation of higher modes compared with (symmetric) Case 2.     

Effect of rotation direction of a rotary tiller on draft and power requirements in a Bangkok clay soil

Experiments were conducted in a Bangkok clay soil to evaluate the performance of a rotary tiller equipped with reverse or conventional blades. The conventional rotary tiller was equipped with C-type blades whereas the reverse-rotary tiller had new types of blades. Tests were conducted on wet land as well as in dry land. Tests were conducted at tractor forward speeds of 1.0, 1.5 and 2.0 km/h. A power-take-off (PTO) power consumed was calculated from the PTO torque and speed. The results indicated that the PTO power consumption was less for the reverse-rotary tiller compared to the conventional tiller for all passes and forward speeds. For both rotary tillers, power consumption decreased as the number of passes increased, whereas power consumption increased when the forward speed was increased. At all forward speeds, the power consumption was the highest during the first pass and lowest during the third pass. The maximum difference of PTO power requirement was after the first pass at 1.0 km/h forward speed. The reverse-rotary tiller consumed about 34% less PTO power under this condition.     

A numerical mapping of energy gains in a powered Swing-By maneuver

The present paper studies the effects of a powered Swing-By maneuver, considering the particular and important situations where there are energy gains for the spacecraft. The objective is to map the energy variations obtained from this maneuver as a function of the three parameters that identify the pure gravity Swing-By with a fixed mass ratio (angle of approach, periapsis distance and velocity at periapsis) and the three parameters that define the impulsive maneuver (direction, magnitude and the point where the impulse is applied). The mathematical model used here is the version of the restricted three-body problem that includes the Lemaître regularization, to increase the accuracy of the numerical integrations. It is developed and implemented by an algorithm that obtains the energy variation of the spacecraft with respect to the largest primary of the system in a maneuver where the impulse is applied inside the sphere of influence of the secondary body, during the passage of the spacecraft. The point of application of the impulse is a free parameter, as well as the direction of the impulse. The results make a complete map of the possibilities, including the maximum gains of energy, but also showing alternatives that can be used considering particularities of the mission.     

Temperature distribution in a thin rotating disk

The problem of heat conduction in a thin rotating disk with heat input at a fixed point is considered. The disk is cooled by forced convection from its lateral surfaces. By defining a complex temperature, the temperature throughout the disk is presented as a series of Bessel functions of complex argument. Results are given for a range of rotational speeds.Nomenclature R radial coordinate - angular coordinate - a radius of disk - b thickness of disk - T temperature - T ambient temperature - rotational speed of disk - q heat flux into disk - k thermal conductivity of disk - density of disk - c specific heat of disk - h coefficient of convective heat transfer - r dimensionless radial coordinate, R/a - T* characteristic temperature, q ₀ a/ k - t dimensionless temperature, (T–T )/T* - C ₁, C ₂ dimensionless parameters defined in (3)     

Mode identification of a rotating disk

A modal testing method permitting identification of the natural frequencies, the number of nodal diameters and wave motions in a rotating disk is presented in this paper. This method is applicable at arbitrary rotation speed without requiring a priori information about the vibration modes of the stationary disk. The influence of disk rotation speed on the prediction of mode shapes with this method is shown, and experimental predictions of modal parameters are presented for both axisymmetric and asymmetric disks.     

Dynamics of Sutterby fluid flow due to a spinning stretching disk with non-Fourier/Fick heat and mass flux models

The magnetohydrodynamic Sutterby fluid flow instigated by a spinning stretchable disk is modeled in this study. The Stefan blowing and heat and mass flux aspects are incorporated in the thermal phenomenon. The conventional models for heat and mass flux, i.e., Fourier and Fick models, are modified using the Cattaneo-Christov(CC)model for the more accurate modeling of the process. The boundary layer equations that govern this problem are solved using the apt similarity variables. The subsequent system of equations is tackled by the Runge-Kutta-Fehlberg(RKF) scheme. The graphical visualizations of the results are discussed with the physical significance. The rates of mass and heat transmission are evaluated for the augmentation in the pertinent parameters. The Stefan blowing leads to more species diffusion which in turn increases the concentration field of the fluid. The external magnetism is observed to decrease the velocity field. Also,more thermal relaxation leads to a lower thermal field which is due to the increased time required to transfer the heat among fluid particles. The heat transport is enhanced by the stretching of the rotating disk.     

Thermal deformation of a bimetallic disk

Institute of Computational Technology, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russia). Translated from Prikladnaya Mekhanika, Vol. 29, No. 8, pp. 61–68, August, 1993.     

Developed cavitation behind a disk in a vertical tube

The theoretical and experimental investigation of developed cavities in a vertical flow shows [1–3] that the size and shape of the cavities depend in this case to a greater extent on the Froude number than for horizontal flow. Experiments in a longitudinal gravity field are usually made under conditions of a confined flow, which requires analysis of the influence of this circumstance on their results. Such an analysis has been made for horizontal flow confined by walls in both an approximate [4–6] and an exact [7–10] formulation; the problems have been solved for both two- and three-dimensional flows. In the present paper we solve in a nonlinear formulation the axisymmetric cavitation problem of determining the influence of the restriction of flow in a vertical circular tube on a developed cavity. The obtained results describe well the cavities realized under experimental conditions even when there is an appreciable deviation of the shape of the tube section from a circle.