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.     

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.     

Effect of tine rake angle and aspect ratio on soil failure patterns in dry loam soil

Studies were conducted in a laboratory glass-sided soil bin with dry compact loam soil (c = 0.02 kPa, Φ = 20° and cone index 210 kPa) with the specific objective of observing the effect of flat tine rake angle and aspect ratio on soil failure patterns. The tine was moved in the soil in a quasi-static condition and soil failure patterns were observed through a glass window. Tine rake angles of 50°, 90° and 130° were used while aspect ratio effects were studied by varying both width and depth of the tine. Individual effects of width and depth were investigated by maintaining a constant aspect ratio of 2.0 but varying width and depth. Results obtained indicated that soil failure patterns are affected by tine design parameters. Soil failure patterns were observed to be of progressive shear type in all cases. For 50° rake angle tines, the patterns consisted of inclined shear lines starting from the tine tip and gradually moving upwards towards the horizontal soil surface, intersecting it at an average failure angle of 32°. In the case of 90° rake angle tines, the inclined shear surface was at a distance from the tine tip whereas, for 130° rake angle tines, prismatic-shaped stationary soil wedges were formed adjacent to the tine. Failure angles for the 90° and 130° rake angle tines were almost the same as those for 50° rake angle tines. The results of this study also indicated that aspect ratio alone cannot account for changes in soil failure patterns, their corresponding soil reactions, forward rupture or surcharge profiles. The effects are mainly due to the individual changes in width and depth. There were no distinct zones as described in the passive soil pressure theory. Soil failures were in regular cycles resulting in corresponding variations in the soil reactions on the tines.     

Comparison of the tractive performance of a tractor driving wheel during its first and second passes in the same track

The tractive performance of a conventional 13.6–38 tractor driving wheel tyre was measured in 19 different fields using the NIAE Single Wheel Tester. In each field the performance was measured on the undisturbed ground and again in the rut formed by a previous run with the same tyre. The second run simulated the operation of the rear wheels on a four-wheel drive tractor.The performance during the second pass was generally better than during the first pass. On average, the coefficient of traction increased by 7%, rolling resistance reduced by 11% and maximum tractive efficiency increased by 5%. The improvement increased as ground conditions deteriorated but was never large enough to fully explain the differences in performance between two and four-wheel drive tractors previously measured. It is suggested, therefore, that these differences may be primarily due to the greater ease with which power, weight, implement size and working speed can be matched with four-wheel drive tractors.     

Draftability of a 8.95 kW walking tractor on tilled land

A 8.95-kW walking tractor was evaluated for draft and drawbar power on tilled land. Empirical equations were developed to correlate the relationship between draft and wheel slip, drawbar power and wheel slip and drawbar power and fuel consumption. The values of draft, drawbar power and specific fuel consumption were calculated at 25% wheel slip. The results indicated that the values of draft on tilled land with pneumatic wheels at engine speed of 2000 rpm were 803 and 773 N in second low and third low gears, respectively. The respective draft values at engine speed of 1500 rpm were 748 and 735 N in second low and third low gears under slightly loose soil conditions. Mounting of a 40-kg wheel ballast increased the value of draft to 901 and 921 N at an engine speed of 2000 rpm and 872 and 888 N at an engine speed of 1500 rpm in second low and third low gears. Replacement of pneumatic wheels by steel wheels further increased the draft readings to 1034 and 999 N at an engine speed of 2000 rpm and 913 and 935 N at engine speed of 1500 rpm in second low and third low gears, respectively, indicating significant increase in drawbar power both at 2000 and 1500 rpm in second low and third low gears with the use of steel wheels. The specific fuel consumption decreased by about 28% and 27% at engine speed of 2000 rpm and about 17% and 21% at engine speed of 1500 rpm in second low and third low gear with the use of steel wheels over pneumatic wheels without wheel ballast. The specific fuel consumption decreased by about 4% and 14% at engine speed of 2000 rpm and 7% and 23% at engine speed of 1500 rpm in second low and third low gears, respectively, with the use of steel wheels over pneumatic wheels with 40 kg wheel ballast.     

Performance of coated floats in different soils

Experiments were conducted in a laboratory soil bin to evaluate the performance of coated floats in different soils. Two coating materials were studied, namely enamel and Teflon, and three soil types, namely clay, loam and sandy soil were used for testing. The forces required to overcome the drag of the floats and pull them over the soil surface were measured. The normal loads were varied to 25, 44 and 64 N. The effect of moisture content (db) was evaluated by varying the soil moisture from 21.2 to 62.4% for clay soil, 16.6 to 36.1% for loam soil and 0.7 to 13.8% for sandy soil. All tests were conducted at a constant speed of 0.20 m/s. The performance of the enamel coated float was superior to Teflon and uncoated floats in all soil conditions. In clay and loam soils, the drag force increased initially until the soil moisture content reached the plastic limit. The drag forces showed a decreasing trend once soil moisture exceeded the plastic limit. In sandy soil, the drag force increased with increase in moisture content. The overall reductions for the enamel coated float compared to uncoated float were from 4 to 64% in clay soil, 16 to 46% in loam soil and 26 to 45% in sandy soil. Besides this superior performance, the enamel coated float compared to the other floats showed excellent resistance to wear due to abrasion and superior scouring.     

Prediction of soil structures produced by tillage

A statistical method for describing the distribution of aggregates and voids within tilled soil is used as the basis for a prediction technique. Transforms of aggregate-void and void-void transition probabilities are used in such a way that factors can be defined which describe how the soil structure differs under a range of circumstances. A standard structure is defined for a given soil as that which is produced at the 5 cm depth by one pass of a set of tines working at 10 cm depth when tillage is done at a speed of 1.4 m/s in soil at a water content equal to the plastic limit and which has previously grown a cereal crop. Factors are defined which describe deviations from this standard structure as a function of depth in the tilled layer, implement type, previous use of the soil, number of implement passes, water content at time of tillage, and subsequent compaction of thettilled layer. Application of the inverse transform then enables estimates of the distributions of aggregates and voids in the tilled layer to be predicted for required, specified conditions.     

Reverse-rotational rotary tiller for reduced power requirement in deep tillage

In this paper details of rotary tillage regarding the movement of tilled soil are presented. A noticeable reduction of tillage power requirement was achieved during rotary tillage. The soil movement depended upon the direction of rotation and the ratio of tilling depth (H) to blade radius (R). With the differences in the soil movement, four kinds of rotary tilling patterns were determined. Increase in operating power generally resulted when a large amount of tilled soil was re-tilled in the zone of blade rotation. Improvement of backward throwing of the soil was required for power reduction, especially in deep tillage. A backward throwing model of soil by the blade was developed on the basis of trochoidal motion of the blade and sliding motion of the soil over a scoop-surface on the horizontal portion of the blade. The throwing model estimated the conditions for avoiding re-tillage, such as direction of rotation and shape of scoop-surface. The throwing model was applied to the design of the shape of the scoop-surface which enabled maximum backward throwing of the soil sufficient to avoid re-tilling. At tilling depths greater than 300 mm, reverse rotation with the new shaped blades brought about a tillage power reduction by about a half compared to forward or reverse rotation with conventional blades.     

Prediction of soil structures produced by tillagePrédiction des structures du sol produites par labourageVoraussage der durch bodenbearbeitung erzeugten bodenstrukturen

A statistical method for describing the distribution of aggregates and voids within tilled soil is used as the basis for a prediction technique. Transforms of aggregate-void and void-void transition probabilities are used in such a way that factors can be defined which describe how the soil structure differs under a range of circumstances. A standard structure is defined for a given soil as that which is produced at the 5 cm depth by one pass of a set of tines working at 10 cm depth when tillage is done at a speed of 1.4 m/s in soil at a water content equal to the plastic limit and which has previously grown a cereal crop. Factors are defined which describe deviations from this standard structure as a function of depth in the tilled layer, implement type, previous use of the soil, number of implement passes, water content at time of tillage, and subsequent compaction of thettilled layer. Application of the inverse transform then enables estimates of the distributions of aggregates and voids in the tilled layer to be predicted for required, specified conditions.     

一种高灵敏度石英微机械陀螺敏感器件

针对石英晶体各向异性的特点,设计了一种驱动梁为双"W"截面形状的石英音叉微机械陀螺,通过在驱动梁表面凹槽两端设置深凹槽,有效提高了凹槽侧壁的陡直性,进而提高了驱动梁内部电场的激励效率和陀螺灵敏度。采用有限元仿真的方法,分析了不同截面形状的驱动梁压电激励力的相对大小,优化设计了陀螺芯片结构参数。依据陀螺芯片的结构,设计了合理的工艺方案并在3英寸石英圆片上制作出了三种驱动梁截面形状的陀螺器件,测试结果表明,相对于矩形驱动梁截面的陀螺芯片,双"W"形驱动梁截面的陀螺芯片的灵敏度提高约60%。     

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.     

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.     

Evaluation of a 6.71 kW power tiller for draft and drawbar power on tar roads

A 6.71 kW power tiller was evaluated for draft and drawbar power on tar roads. The effect of mounting 40 kg of wheel ballast was also studied. Polynomial regression analysis was used to establish the relationship between draft and wheel slip, drawbar power and wheel slip, drawbar power and fuel consumption, and drawbar power and specific fuel consumption. The results of the study showed draft values of 2107, 2110 and 2110 N in second low, third low and first high gears at an engine speed of 150o rpm with a 15% wheel slip. The respective draft values at engine speed of 2000 rpm with a 15% wheel slip were 2172, 2189 and 2212 N. With the mounting of 40kg wheel ballast there was an increase in draft of 217, 207 and 291 N at 1500 rpm, and 328, 306 and 344 N at 2000 rpm of the engine with a 15% wheel slip in second low, third low and first high gears, respectively. The increase in drawbar power with 40 kg ballast was 10.88%, 7.83% and 20.13% at 1500 rpm and 18.89%, 16.56% and 14.88% at 2000 rpm of engine over the drawbar power available with zero ballast. The fuel consumption with the use of wheel ballast was slightly more than the fuel consumption without any ballast.     

刚性钝头弹体正冲击GH4169间隔靶的消耗功分析

在380～680 m/s的弹体初速范围内,开展了直径8 mm钨球正冲击GH4169间隔靶实验,测得弹体初速、余速及靶板形貌,明显看出第1层板挠度较小,主要表现为剪切破坏,并产生了杯状挤凿块,第3层板挠度较大,主要表现为拉伸破坏。提出了间隔靶消耗功计算公式,结合剪切冲塞模型和建立的挤凿块速度模型计算了刚性钝头弹体冲击间隔靶中各层板的消耗功。结果表明,第2～3层板的单位面密度消耗功远高于相同面密度的第1层板,这与各层板的变形和失效形式密切相关。消耗功分析可用于定量描述间隔靶中各层板的抗侵彻性能。     

Influence of the axle load, tyre size and configuration on the compaction of a freshly tilled clayey soil

Enhancement of the potential root growth volume is the main objective of farmers when they establish a conventional tillage system. Therefore, the main function of primary tillage is to increase soil’s structural macroporosity. In spite of this, during secondary tillage operations on these freshly tilled soils, the traffic on seedbeds causes significant increases in soil compaction. The aim of this paper was to quantify soil compaction induced by tractor traffic on a recently tilled non consolidated soil, to match ballast and tyre size on the tractors used during secondary tillage. The work was performed in the South of the Rolling Pampa region, Argentina. Secondary tillage traffic was simulated by one pass of a conventional 2WD tractor, using four configurations of bias-ply rear tyres: 18.4×34, 23.1×30, 18.4×38 and 18.4×38 duals, two ballast conditions were used in each configuration. Soil bulk density and cone index in a 0 to 600 mm profile were measured before and after traffic. Topsoil compaction increased as did ground pressure. Subsoil compaction increased as total axle load increased and was independent from ground pressure. At heavy conditions, topsoil levels always showed higher cone index values. From 150 to 450 mm depth, the same tendency was found, but with smaller increases in the cone index parameter, 22 to 48%, averaging 35%. Finally, at the deepest layer considered, 600 mm, differential increases due to the axle load are great enough as to be considered similar to those found in the upper horizon, 36 to 64%, averaging 55%. On the other hand, bulk density tended to be less responsive than cone index to the traffic treatments. Topsoil compaction can be reduced by matching conventional bias-ply tyres with an optimized axle weight.     

Third‐order Cartesian overset mesh adaptation method for solving steady compressible flows

A third‐order mesh generation and adaptation method is presented for solving the steady compressible Euler equations. For interior points, a third‐order scheme is used on Cartesian and curvilinear meshes. Concerning the mesh adaptation, the method of Meakin is also extended to third order. The accuracy of the new overset mesh adaptation method is demonstrated by a grid convergence study for 2‐D inviscid model problems and results are compared with a second‐order method. Finally, the method is applied to the computation of an inviscid 3‐D flow around a hovering blade of the ONERA 7A helicopter rotor exhibiting an improvement in the wake capture. With a 7 million point mesh, the tip vortex can be followed for more than three rotor revolutions with the third‐order method. The CPU time needed for this calculation is only 3% higher than with a conventional second‐order method. Copyright © 2007 John Wiley & Sons, Ltd.     

离子束增强沉积氮化钛膜改善硬质合金刀具抗切削损伤性能的研究

通过切削对比试验，考察了分别用离子束增强沉积法和离子镀法镀覆ＴｉＮ膜的硬质合金刀具和无镀层的同种硬质合金刀具的抗切削损伤性能．结果表明，在给定的试验条件下，有离子束增强沉积ＴｉＮ膜硬质合金刀具的切削距离远比无镀层刀具的长，也比有离子镀ＴｉＮ膜刀具的长，其前面和后面的损伤都很小．这是离子束增强沉积过程中各种参数可以分别调节，膜层质量易于控制，能够形成致密度高且与基体结合力强的硬质薄膜的结果．刀具切削损伤的原因主要有磨损和脆性损伤，这都与刀具材料同被切削金属产生的粘着有关     

双模态振幅调制原子力显微术对比度反转研究

双模态振幅调制原子力显微术广泛应用于微纳米力学成像,然而成像过程中可能存在的对比度反转问题会造成成像结果的难以理解和解释。将有限差分法和同相正交法相结合,采用数值方法研究了不同力常数探针、样品组分力学性能以及成像参数设置对双模态振幅调制原子力显微术二阶模态振幅和相位对比度反转的影响。研究结果显示,对于硬探针,不同粘度系数组分上二阶模态振幅和相位对比度随弹性模量增加无反转产生。探针在不同弹性模量组分上二阶模态振幅对比度随粘度系数增加会产生反转,而二阶模态相位对比度则无反转产生。对于软探针,组分弹性模量或粘度系数增加会造成相互作用区转变,使探针响应产生跳变。软探针在组分弹性模量较高时二阶模态相位对不同粘度系数的对比度以及在粘度系数较小时对不同弹性模量组分的对比度均较硬探针更低。两种探针在不同弹性模量组分上二阶模态振幅对比度随着二阶模态自由振幅的增加会发生反转,而不同粘度系数下的对比度则未出现反转。此外,二阶模态自由振幅越小,则二阶模态相位对不同弹性模量或粘度系数组分的对比度越高。二阶模态振幅或相位对比度在不同相互作用区可能会发生反转,成像时应使相互作用区处于排斥区,可提高对比度。     

Effects of tine rake angle and aspect ratio on soil reactions in dry loam soil

Study was conducted in a laboratory glass-sided soil bin with dry compact loam soil with 5.2% (d.b.) moisture content. The specific objective of this study was to determine the effects of flat rigid tine rake angle (forward angle between tine face and horizontal soil surface) and aspect ratio (tine width/tine depth) on soil reactions. The tine was moved in the soil in a quasi-static condition and soil reactions were recorded using L-shaped force transducers. Corresponding soil failure patterns were observed through a glass window. Tine rake angles of 50°, 90° and 130° were used. The effects of aspect ratio were studied by varying both width and depth of the tines. Individual effects of width and depth were investigated by maintaining a constant aspect ratio of 2.0 but varying width and depth. Observations indicated that soil reactions are affected by tine design parameters. For all tine rake angles and aspect ratios, soil reactions were observed to be cyclic in nature and could be matched well with corresponding soil failure patterns. The horizontal and vertical soil reactions were in phase. Investigations into the individual effects of tine width and depth revealed that the aspect ratio alone cannot account for changes in soil reactions. The effects are mainly due to the individual changes in width and depth.     

Scattering of elastic waves from symmetric inhomogeneities at low frequencies

The problem of the scattering of elastic waves is treated in the low-frequency regime by a systematic expansion in powers of the frequency in the spatial domain of the scatterer. The zeroth and first degree scattering amplitudes vanish if the scatterer is localized in all directions. The second degree scattering amplitude corresponds to the so called Rayleigh regime in which the quasi-static result of Gubernatis et al. is valid. In general, the third and higher degree scattering amplitudes are nonvanishing. However, in the case where the scatterer has inversion symmetry about the origin, it is shown that the third degree scattering amplitude vanishes identically for all incident and scattered directions and for all polarizations. This result implies that the frequency derivative of the phase shift approaches zero at least quadratically as the frequency goes to zero. In other words, at sufficiently low frequencies the effective scattering center of a scatterer with inversion symmetry is its geometrical center. The use of this result in the processing of experimental scattering data is discussed.