Performance evaluation of an animal drawn puddling implements under controlled soil-bin conditions

Trials were conducted to evaluate the performance of three commonly used puddling implements, i.e. animal drawn rotary puddler (I₁), 3-tine tiller (I₂) and local plough (I₃) under controlled soil bin conditions for different numbers of passes of each implement. The performance of the rotary puddler was found to be better when operated more than twice under the controlled conditions in terms of quality and quantity of puddling. It was found that the rotary puddler gave a higher puddling index and required less energy to puddle the soil. The rotary puddler provided good “puddle” with a puddling index of 50% after two passes whereas, the other two implements required more than five passes for the same quality of puddling or puddling index in sandy clay loam soil     

Effect of different size and orientation of rectangular rotary blades on quality of puddling

The effect of different combinations of size and orientation of rectangular blades of a wet land puddler, on puddling index, force requirement and performance index was investigated under controlled conditions in a soil-bin from the study. It was observed with the blade size of 15-cm width × 8.5-cm depth and a blade angle of 30° with respect to shaft gave better performance than other combinations in terms of minimum puddling index, minimum horizontal force, vertical force, specific energy and maximum performance index. The values are, respectively, 67.95%, 105.12 N, 33.85 N, and 9.71 kJ/m³ and 6.69. The above-mentioned parameters of the blade were found to be very close to the predicted values obtain through MREG computer programme for optimization of size and orientation of puddler blades.     

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.     

On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve

In comparison with direct measurements of unsaturated hydraulic conductivity, the methods of calculations from the moisture retention curve are attractive for their fast and simple use and low cost. These are the main reasons for their increasing use, mainly in spatial variability studies. On the other hand, it is known that their applicability is limited. The possibility of the use of the retention curve to indirectly determine hydraulic conductivities is analyzed as follows. The theoretical derivation of the relationK(h) – (h) is briefly discussed with regards to potential sources of inaccuracy. The sensitivity of the algorithm forK(h) calculation is studied as a response to possible inaccuracies in the retention curve determination. Conclusions about the usability of calculated hydraulic conductivities are drawn.     

Percolation approach to the problem of hydraulic conductivity in porous media

While percolation theory has been studied extensively in the field of physics, and the literature devoted to the subject is vast, little use of its results has been made to date in the field of hydrology. In the present study, we carry out Monte Carlo computer simulations on a percolating model representative of a porous medium. The model considers intersecting conducting permeable spheres (or circles, in two dimensions), which are randomly distributed in space. Three cases are considered: (1) All intersections have the same hydraulic conductivity, (2) The individual hydraulic conductivities are drawn from a lognormal distribution, and (3) The hydraulic conductivities are determined by the degree of overlap of the intersecting spheres. It is found that the critical behaviour of the hydraulic conductivity of the system,K, follows a power-law dependence defined byK (N/N _c–1)^x, whereN is the total number of spheres in the domain,N _c is the critical number of spheres for the onset of percolation, andx is an exponent which depends on the dimensionality and the case. All three cases yield a value ofx1.2±0.1 in the two-dimensional system, whilex1.9±0.1 is found in the three-dimensional system for only the first two cases. In the third case,x2.3±0.1. These results are in agreement with the most recent predictions of the theory of percolation in the continuum. We can thus see, that percolation theory provides useful predictions as to the structural parameters which determine hydrological transport processes.     

A new method for calculating hysteretic <Emphasis Type="Italic">K</Emphasis>(<Emphasis Type="Italic">S</Emphasis>) relationship

A new method for calculating the hysteretic relationship between hydraulic conductivity (K) and suction (S) is proposed. This method uses the experimental (K–S) data of the main wetting and drying branches and predicts satisfactorily the scanning drying and wetting curves. The proposed method is applicable to those porous media where the hysteretic Θ–S relationship complies with the independent domain concept.     

Effective hydraulic conductivities in unsaturated heterogeneous media by Monte Carlo simulation

When modeling flow and transport through unsaturated heterogeneous geological deposits, it may be neither computationally nor technically feasible to account for the actual heterogeneity in the simulations. One would fall short in terms of technical feasibility because there is simply no way that the entire spatial domain could be characterized (e.g., you cannot measure hydraulic conductivity at every location at a site). With respect to computational feasibility, the non-linear nature of the Richards equation (which is used to model the flow process) makes simulation of most sites extremely computationally intensive. The computational roadblock is being dismantled as computer hardware advances, but our inability to precisely characterize geological heterogeneity is expected to remain with us for a very long time. To address this problem, the analyst typically uses average or effective properties to model flow and transport behavior through heterogeneous media. In this paper, a variety of approaches for developing effective unsaturated flow properties are assessed. Computational results have been obtained which give the hydraulic conductivity ratios (K _parallel/K _nomal) for highly nonisotropic layered materials. These results are compared with analytical models. Good agreement was obtained for all soil saturation levels except for extremely dry conditions.This work was performed at Sandia National Laboratories, which is operated for the U.S. Department of Energy under contract number DE-AC04-76DP00789.     

Accuracy of the Renormalization Method for Computing Effective Conductivities of Heterogeneous Media

The accuracy of the renormalization method for upscaling two-dimensional hydraulic conductivity fields is investigated, using two canonical 2 × 2 blocks: a checkerboard geometry and a geometry in which three of the cells have conductivity K ₁ and the other has conductivity K ₂. The predictions of the renormalization algorithm are compared to the arithmetic, harmonic and geometric means, as well as to theoretical predictions and finite element calculations. For the latter geometry renormalization works well over the entire range of the conductivity ratio K ₂/K ₁, but for the checkerboard geometry the error becomes unbounded as the conductivity ratio grows.     

Characteristic loading of light mouldboard ploughs at slow speeds

A study on four mouldboard ploughs, that are commonly used with animal traction in Kenya, was conducted. Draught, suction and torsion loads were measured and specific draught evaluated in field tests on four sites with typical agricultural soil conditions. Draught and suction are the horizontal and vertical components of the reaction to soil force, respectively, while torsion is the resisting moment about the plough shank. The objective was to quantify these parameters and to study their characteristics under variable conditions at operation, at speeds up to 1.12 m/s and tillage depths between 0 and 150 mm in an attempt to optimize the design, selection and utilization of mouldboard ploughs for animal traction in Kenya. It was found that depth of tillage is the most critical factor, and draught and suction increased significantly with depth while specific draught increased or decreased depending on the soil type. Draught and specific draught increased significantly with speed. The increase in suction with depth probably implies an increased stability in the ploughing operation, while its reduction with speed indicates a potential instability of plough control with varying speeds. Consequently, aiming for steady motion in the utilization of animal traction may aid in the optimization. It was also found that ploughs with a high specific draught (kN/m) are expected to experience higher torsional loads on the shanks. The characteristic draught, specific draught and suction loads of the ploughs were described by quadratic functions in speed and depth of tillage with coefficients of determination (R₂) ranging from 0.55 to 0.99. A significant difference in the coefficient of variation of draught loads in the three soil types probably implies that optimal duration for use of animal traction in tillage should be dependent on soil type.     

Soil compaction and over-winter changes to tracked-vehicle ruts, Yakima Training Center, Washington

We monitored two experimental areas at the Yakima Training Center (YTC) in central Washington to measure changes to M1A2 Abrams (M1) tank-rut surface geometry and in- and out-of-rut saturated hydraulic conductivity (K_fs), soil penetration resistance (SPR) and soil bulk density (BD). Profile-meter data show that rut cross-sectional profiles smoothed significantly and that turning ruts did so more than straight ruts. Rut edges were zones of erosion and sidewall bases were zones of deposition. K_fs values were similar in and out of ruts formed on soil with 0–5% moisture by volume, but were lower in ruts formed on soil with about 15% water. Mean SPR was similar in and out of ruts from 0- to 5-cm depth, increased to 2 MPa outside ruts and 4 MPa inside ruts at 10- to 15-cm depth, and decreased by 10–38% outside ruts and by 39–48% inside ruts at the 30-cm depth. Soil BD was similar in and out of ruts from 0- to 2.5-cm depth, and below 2.5 cm, it was generally higher in ruts formed on moist soil with highest values between 10- and 20-cm depth. Conversely, BD in ruts formed on dry soil was similar to out-of-rut BD at all depths. This information is important for determining impacts of tank ruts on water infiltration and soil erosion and for modifying the Revised Universal Soil Loss Equation (RUSLE) and the Water Erosion Prediction Project (WEPP) models to more accurately predict soil losses on army training lands.     

砂-膨润土混合屏障材料渗透性影响因素研究

建立了一个新的结构-尾流振子耦合模型. 流场近尾迹动力学特征被模化为非线性阻尼 振子,采用van der Pol方程描述. 以控制体中结构与近尾迹流体间受力互为反作 用关系来实现流固耦合. 采用该模型进行了二维结构涡激振动计算,得到了合理的 振幅随来流流速的变化规律和共振幅值,并正确地预计了共振振幅值$A_{\max}^\ast$ 随着质量阻尼参数$\left( {m^\ast + C_A } \right)\zeta $的变化规律,给出了预测$A_{\max }^\ast $值的拟合公式. 采用该模型计算了三维柔性结构在均匀来流和简谐波形来流作用下的VIV 响应. 结构在均匀来流作用下振动呈现由驻波向行波的变化过程, 并最后稳定为行波振动形态. 在简谐波形来流作用下,结构呈现混合振动形态,幅值随时间呈周期变化.     

Changes in physical properties of two dry soils during tracked vehicle passage

Soil strength, surface micro-relief, bulk density and saturated hydraulic conductivity were measured for two soil types (Dd 1.13 and Uc 2.12) at Shoalwater Bay, Queensland, before and after the passage of a tracked vehicle. Such impact of a vehicle resulted in a decrease in the strength of the surface soil, an increase in bulk density, a decrease in saturated hydraulic conductivity and the formation of ruts. The degree of change depended on soil type, the number of vehicular passes and whether the vehicle was travelling in a straight line or turning.     

Overwinter changes to near-surface bulk density, penetration resistance and infiltration rates in compacted soil

Previous studies at Yakima Training Center (YTC), in Washington State, suggest freeze-thaw (FT) cycles can ameliorate soil compacted by tracked military vehicles [J. Terramechanics 38 (2001) 133]. However, we know little about the short-term effects of soil freezing over a single winter. We measured bulk density (BD), soil penetration resistance (SPR), and steady-state runoff rates in soil newly tracked by an Abrams tank and in uncompacted soil, before and after a single winter at YTC. We similarly measured BD, SPR and saturated hydraulic conductivity (k_fs) in simulated tank tracks at another site near Lind Washington. Average BD was significantly greater in tank ruts at YTC and in simulated tracks at the Lind site than in uncompacted soil soon after tracking and did not change significantly during the winter of 1997–1998. Measurements of SPR were strongly influenced by soil moisture. When soil was moist or tracks were newly formed, SPR was significantly higher in tank ruts than in uncompacted soil from the surface to a depth of about 10–15 cm. The greatest average SPR in compacted soil was observed between 4 and 6 cm depth. We observed less difference in SPR between tank ruts and uncompacted soil near-surface at YTC as the time after trafficking increased. We observed highest SPR ratios (compacted rut:undisturbed) in fresh tracks near the surface, with lower ratios associated with increasing track age or soil depth, indicating that some recovery had occurred at YTC near-surface. However, we did not observe a similar over-winter change in SPR profiles at the Lind site. Rainfall simulator data from YTC showed higher steady-state runoff rates in tank ruts than over uncompacted soil both before and after winter. However, more time was required to reach steady-state flow in tank ruts and the proportion of runoff was slightly lower in May 1998 than in August 1997. At the Lind site, k_fs was lower in newly compacted soil than in one-year old compacted soil or uncompacted soil. Our data suggest that indices of water infiltration such as steady-state runoff rates or k_fs, are more sensitive indicators of soil recovery after compaction than are BD or SPR.     

Percolation Cluster Statistics and Conductivity Semi-Variograms

Cluster statistics of percolation theory have been shown to generate expressions for the distribution of hydraulic conductivity values in accord with field studies. Percolation theory yields directly the smallest possible generalized resistance value, R _c, for which a continuous path through an infinite heterogeneous system can avoid all larger resistances. R _c, defines an infinite system hydraulic conductivity. Cluster statistics generate the number of clusters of resistors of a given size with a given R, for which a continuous path through the cluster can avoid resistances larger than R. The probability that a volume of size x ³ falls on a particular cluster gives the probability that volume has a characteristic resistance, R. Determining the semi-variogram of the hydraulic conductivity is now elementary; it is necessary only to determine whether translation h of the center of the volume x ³ removes it from the cluster in question. If the cluster is larger than (x+h)³, then, on the average, the same cluster resistance R will control K. Otherwise, the value of K at x+h will be uncorrelated with its value at x. The condition is then expressed as an integral related to the one, which gives the distribution of K. Then an integral over the derived distribution of K gives the variogram. Results obtained are that the variogram should be similar to either the exponential or Gaussian forms typically in use, if K is a power law function of random variables (as in Poiseuilles Law), or more closely related to the spherical approximation if K is an exponential function of random variables.     

Measuring the thermal conducitivity of uranin

A convenient experimental method for measuring the thermal conductivity of uranin (fluorecein sodium, C₂₀H₁₀O₅Na₂) is described. Two similar blocks of uranin, produced from a strong uranin/water solution, were exposed to one-dimensional steady-state conduction. It was found that, for a mean bulk temperature ranging from ambient up to 55°C, the uranin has a constant thermal conductivity of 0.43 W/mK. Above these temperatures, the material begins to soften and the thermal conductivity is seen to decrease     

变形对非饱和土渗透系数影响规律模拟研究

对有、无缝合复合材料层合板的拉伸疲劳性能进行了试验研究,考察了0^\circ 缝合对复合材料光滑板拉伸疲劳损伤扩展规律的影响. 通过有限元素法分析了有、无缝合复 合材料层合板的应力状态分布情况,对缝合复合材料层合板的拉伸疲劳损伤及其扩展机理进 行了分析. 研究表明,缝合改变了复合材料层合板拉伸疲劳损伤起始与扩展的机理,针脚 附近的面内正应力\sigma_{x}与层间剪应力的集中对层合板拉伸疲劳损伤的 发生与扩展有着重要的作用,自由边界处的层间集中应力对缝合板的疲劳性能也有影响. 自 由边界处的层间集中应力是导致无缝合层合板疲劳损伤及其扩展的主要原因.     

Effects of Bubbles on the Hydraulic Conductivity of Porous Materials – Theoretical Results

In a porous material, both the pressure drop across a bubble and its speed are nonlinear functions of the fluid velocity. Nonlinear dynamics of bubbles in turn affect the macroscopic hydraulic conductivity, and thus the fluid velocity. We treat a porous medium as a network of tubes and combine critical path analysis with pore-scale results to predict the effects of bubble dynamics on the macroscopic hydraulic conductivity and bubble density. Critical path analysis uses percolation theory to find the dominant (approximately) one-dimensional flow paths. We find that in steady state, along percolating pathways, bubble density decreases with increasing fluid velocity, and bubble density is thus smallest in the smallest (critical) tubes. We find that the hydraulic conductivity increases monotonically with increasing capillary number up to Ca 10^–2, but may decrease for larger capillary numbers due to the relative decrease of bubble density in the critical pores. We also identify processes that can provide a positive feedback between bubble density and fluid flow along the critical paths. The feedback amplifies statistical fluctuations in the density of bubbles, producing fluctuations in the hydraulic conductivity.     

Experimental measurement of thermophysical properties of oxide-water nano-fluids down to ice-point

This paper presents the measurement of the thermal conductivity and the dynamic viscosity of Al₂O₃-water (1-4% particle volume fraction) and TiO₂-water (1-6% particle volume fraction) nano-fluids carried out at atmospheric pressure in the temperature range from 1 to 40 °C, which is particularly interesting for the application of nano-fluids as thermal medium in refrigeration and air-conditioning.The thermal conductivity measurement was performed by using a Transient Hot Disk TPS 2500S apparatus instrumented with a 7577 probe (2.001 mm in radius) having a maximum uncertainty (k = 2) lower than ±5.0% of the reading. The dynamic viscosity measurement and the rheological analysis were carried out by a rotating disc type rheometer Haake Mars II instrumented with a single cone probe (60 mm in diameter and 1° angle) having a maximum uncertainty (k = 2) lower than ±5.0% of the reading.The thermal conductivity measurements of the tested nano-fluids show a great sensitivity to particle volume fraction and temperature and a weak sensitivity to cluster average size: TiO₂-water and Al₂O₃-water nano-fluids show a thermal conductivity enhancement (with reference to pure water) from −2 to 16% and from −2 to 23% respectively.TiO₂-water and Al₂O₃-water nano-fluids exhibit a Newtonian behaviour in all the investigated ranges of temperature and nano-particle volume fraction. The relative viscosity shows a great sensitivity to particle volume fraction and cluster average size and no sensitivity to temperature: TiO₂-water and Al₂O₃-water nano-fluids show a dynamic viscosity increase with respect to pure water from 17 to 210% and from 15 to 150% respectively.Al₂O₃-water nano-fluid seems to be more promising as thermal medium than TiO₂-water nano-fluid, particularly at low thermal level (between ambient temperature and ice point) where TiO₂-water is not suitable showing worse performance than pure water.Present experimental measurements were compared both with available measurements carried out by different researchers and computational models for thermophysical properties of suspensions.     

锂盐添加剂对润滑油摩擦学性能和导电性的影响

采用MFT-R4000型往复摩擦磨损试验机测试四氟硼酸锂(Li BF4),双三氟甲烷基磺酰亚胺锂(Li NTf2)和六氟磷酸锂(Li PF6)这3种锂盐作为润滑油添加剂时对基础油的摩擦学性能的影响,利用OLS4000型三维形貌测量仪测量钢块的磨损体积,并利用扫描电子显微镜(SEM)观察钢块磨痕的表面形貌.采用DDSJ-308A型电导率测定仪测量不同锂盐含量下,润滑油的盐度和电导率的变化情况,阐述锂盐含量和润滑油电导率之间存在的关系.研究结果表明:锂盐能够降低润滑油的摩擦系数,增强其抗磨性,具有良好的摩擦学性能;同时锂盐的加入使基础油的导电性得到很大提高.