Influence of soil and vehicle parameters on soil rut formation

Soil and vehicle parameters have significant effects on soil rut formation. A randomized design was used to investigate the effects of five treatments: soil texture, soil moisture, vehicle type, turning radius and velocity, on rut depth, rut width and rut index, which measure the degree of soil disturbance. This vehicle rutting study was conducted on four off-road military vehicles under two soil moisture conditions and two soil texture conditions at Fort Riley, Kansas. A GPS-based vehicle tracking system was used to track the vehicle dynamics, and rut measurements were taken manually. SAS 9.1 was used to investigate the effects of soil and vehicle parameters on rut formation. Results show that all the vehicle parameters (vehicle type, weight, velocity and turning radius) and soil parameters (soil texture and moisture) are statistically significant to affect rut formation.     

Environmental damage from tracked vehicle operation

Soil surface forces resulting from traffic tracked vehicles can cause environmental damage by decreasing plant development and increasing erosion. This paper investigates the soil surface disturbance from tracked vehicle operation. Sharp turns (lower turning radius) from M113 operation produce increased disturbed widths and more severe vegetation damage. The pad-load ratio for the M113 track shoe was determined at various loads. The soil rut produced from tracked vehicle operation was determined at various driving models (straight, smooth turn, sharp turn). The width and depth of track rut and height of soil piled increased when the tracked vehicle negotiated a sharp turn. The results of this study indicate for the soil conditions tested, the width of disturbance is dependent on the operating characteristics of the vehicle. A vehicle conducting sharp turns will disturb a larger width of soil than a vehicle travelling straight or conducting smooth turns.     

Rut depth, soil compaction and rolling resistance when using bogie tracks

There are few studies of rolling resistance for bogie tracks on forestry machines. The aim of this study was to compare the effects of wheels and two types of bogie tracks on rut formation, cone index, and vehicle rolling resistance on some typical forest soils in Sweden. In an experiment, two types of tracks were put on a trailer with a bogie with hydraulic extension on the pulling bar giving the trailer repeatable travelling speed. Loads of 0 and 9.9 Mg were used on the trailer. The main results of this study are: Compared to rather wide and soft tires, tracks on the bogie reduced rut depth by up to 40% and cone index in the ruts by about 10%, although the tracks increased the mass on the trailer by 10–12%. The relative rolling resistance coefficient was not higher for tracks than for wheels. Further studies should be conducted to show the effect of track tension on rolling resistance and flotation and of the effects of tracks on heavy vehicles on subsoil compaction.     

A methodology for quantitatively assessing vehicular rutting on terrains

This paper presents a quantitative method for assessing the environmental impact of terrain/vehicle interactions during tactical missions. Area wide mobility analyses were conducted using three standard US military tracked and wheeled vehicles over terrain regions representing both fine-grained and course-grained soils. The NATO reference mobility model, Version 2, was used to perform the on- and off-road mobility analysis. Vehicle and terrain characterizations along with different climate scenarios were used as input parameters to predict vehicle rut depth performance for the different vehicles and terrain conditions. The vehicles’ performance was statistically mapped over these terrain regions for percent area traveled and the resulting rut depth created by each vehicle. A selection of tactical scenarios for each vehicle was used to determine rut depth for a range of vehicle missions. A vehicle mission severity rating method, developed at the US Army Engineer Research and Development Center, was used to rate the selected missions and resulting rut depths.     

Rigid polyurethane foam testing for mine neutralization and vehicle traction performance

A rigid polyurethane foam (RPF) was dispensed on a test lane to determine if (1) a trafficability lane could be created that would neutralize vehicle and personnel mines and (2) the foam would increase vehicle traction in slippery soils. The RPF consisted of two liquids, 1,1-dichloro-1 -fluoroethane (known as urethane resin) and polymeric diphenylmethane diisocyanate (known as polymeric MDI). These two liquids were mixed in a commercial foam dispensing machine and dispensed at the test site. Two test areas were built to examine minefield neutralization and traction improvements separately. The minefield test lane consisted of a 7×17 m area, instrumented with pressure cells, M15 training mines, M1 tripwire devices and string tension sensors covered with approximately 0.6 m of 64.1 kg/m³ density RPF. Fifty passes each of an M88A2 and a HMMWV were made while engineers monitored changes in ground contact pressure. Trip wires were placed 5 cm above the ground in the lane and instrumented to measure tension placed on the devices by the expanding foam. Application of the RPF, at a depth of 0.6 m, appeared to neutralize most antitank mines examined in this program but triggered all the trip wire devices during the application. The foam also appeared to stand up well under vehicle traffic. The traction test lane consisted of two 5×35 m lanes. The lanes were created to test changes in traction in dry, wet, and foam-augmented wet soil. For these tests, 0.08 to 0.1 m of foam was dispensed into M88A2 and HMMWV ruts created during dry and wet drawbar-pull tests. Trafficability performance of the M88A2 decreased slightly with the application of the foam from an optimum drawbar pull coefficient of 0.21 after the simulated rainfall to 0.14 after application of the foam. Trafficability of the HMMWV showed moderate improvement from an optimum drawbar pull coefficient of 0.3 after the simulated rainfall to 0.5 after the application of the foam.     

Vehicle mobility on highly organic soils

Current political climates have generated a renewed interest in the northern regions of the world. These areas are known to have soft marshy peat, highly organic soils, and harsh winter climates. Current capabilities for vehicle mobility modeling on this terrain is limited and existing studies do not include contemporary military vehicles. This work presents mobility experiments of modern military vehicles at multiple field sites containing peat or highly organic soils that can be used to improve mobility modeling on these soils. Field experiments are being conducted during multiple seasons, including winter, spring, and summer. The vehicle traction, motion resistance, and hard surface rolling resistance of an instrumented High Mobility Multipurpose Wheeled Vehicle (HMMWV) and a Small Unit Support Vehicle (SUSV) were examined. The first is a common multi-purpose vehicle and the second is a vehicle designed to operate in these types of environments. This data set will provide the basis for model development and validation for vehicle mobility in highly organic soils.     

Prediction of impacts of wheeled vehicles on terrain

Traffic of off-road vehicles can disturb soil, decrease vegetation development, and increase soil erosion. Terrain impacts caused by wheeled off-road vehicles were studied in this paper. Models were developed to predict terrain impacts caused by wheeled vehicles in terms of disturbed width and impact severity. Disturbed width and impact severity are not only controlled by vehicle types and vehicle dimensions, but also influenced by soil conditions and vehicle dynamic properties (turning radius, velocity). Field tests of an eight-wheeled vehicle and a four-wheeled vehicle were conducted to test these models. Field data of terrain–vehicle interactions in different vehicle dynamic conditions were collected. Vehicle dynamic properties were derived from a global position system (GPS) based tracking system. The average prediction percentage error of the theoretical disturbed width model is less than 20%. The average absolute error between the predicted impact severity and the measured value is less than an impact severity value of 12%. These models can be used to predict terrain impacts caused by off-road wheeled vehicles.     

Effects of channel dimension,heat flux,and mass flux on flow boiling regimes in microchannels

Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to investigate the effects of channel size and mass flux (225–1420 kg/m²s) on microchannel flow boiling regimes by means of high-speed photography. Seven different silicon test pieces with parallel microchannels of widths ranging from 100 to 5850 μm, all with a depth of 400 μm, are considered. Flow visualizations are performed with a high-speed digital video camera while local measurements of the heat transfer coefficient are simultaneously obtained. The visualizations and the heat transfer data show that flow regimes in the microchannels of width 400 μm and larger are similar, with nucleate boiling being dominant in these channels over a wide range of heat flux. In contrast, flow regimes in the smaller microchannels are different and bubble nucleation at the walls is suppressed at a relatively low heat flux for these sizes. Two types of flow regime maps are developed and the effects of channel width on the flow regime transitions are discussed.     

Effects of two different forwarder steering and transmission drive systems on rut dimensions

Impact of two different forwarders, with similar carrying capacities but different transmission drive and steering systems, on rut formation was compared. El-forest F15 with three individual steerable axles without bogies, large wheels (?164 cm) and an electric hybrid transmission drive system, and a Valmet 860, with conventional transmission drive (?131 cm wheels, two bogies) were compared. The ruts from the El-forest with or without a load were generally deeper than those produced by the tracked Valmet when driving in a straight line on soft arable land. On an S-shaped or circular course the El-forest and Valmet produced the same rut depths after the first pass, but with an increasing number of passes, the Valmet made deeper ruts. On the intermediate forest land, after driving in a straight line, the El-forest generally produced shallower ruts than the non-tracked Valmet (tracks not used at this site). When driving on a circular course, this difference was also apparent when machines carried a load. The mean rut width created by the El-forest was significantly narrower than from the Valmet at both sites. A transmission drive system with axles and wheels that can be individually steered seems advantageous to reduce rut formation, especially if the wheels have reduced ground pressure on soft soils.     

Heat transfer characteristics in a sudden expansion pipe equipped with swirl generators

This investigation is aimed at studying the heat transfer characteristics and pressure drop for turbulent airflow in a sudden expansion pipe equipped with propeller type swirl generator or spiral spring with several pitch ratios. The investigation is performed for the Reynolds number ranging from 7500 to 18,500 under a uniform heat flux condition. The experiments are also undertaken for three locations for the propeller fan (N = 15 blades and blade angle of 65°) and three pitch ratios for the spiral spring (P/D = 10, 15 and 20). The influences of using the propeller rotating freely and inserted spiral spring on heat transfer enhancement and pressure drop are reported. In the experiments, the swirl generator and spiral spring are used to create a swirl in the tube flow. Mean and relative mean Nusselt numbers are determined and compared with those obtained from other similar cases. The experimental results indicate that the tube with the propeller inserts provides considerable improvement of the heat transfer rate over the plain tube around 1.69 times for X/H = 5. While for the tube with the spiral spring inserts, an improvement of the heat transfer rate over the plain tube around 1.37 times for P/d = 20. Thus, because of strong swirl or rotating flow, the propeller location and the spiral spring pitch become influential on the heat transfer enhancement. The increase in pressure drop using the propeller is found to be three times and for spiral spring 1.5 times over the plain tube. Correlations for mean Nusselt number, fan location and spiral spring pitch are provided.     

The effect of initial soil water content and vegetative cover on surface soil disturbance by tracked vehicles

A field trial was conducted to examine the effect of initial soil water content and vegetative cover on soil disturbance caused by tracked military vehicles. Disturbance was measured as depth of rut produced. Soil disturbance increased as the number of passes and turns increased, but especially after turning manoeuvres. Greater disturbance occurred on reduced vegetation plots and with increasing initial soil water content. Simple regression analysis was undertaken to determine which factor had the greatest influence on disturbance.     

Cross-country mobility on various snow conditions for validation of a virtual terrain

Realistic simulation of on- and off-road vehicle performance in all weather conditions is needed by the U.S. Army for virtual training of personnel on existing vehicles, and for new vehicle design. The virtual test site is a computer simulation representing an actual terrain defined as having spatially distributed terramechanics properties and terrain interaction with vehicles. We developed a virtual test site for Ethan Allen Firing Range (EAFR) in northern Vermont. The virtual test site for EAFR is composed of terramechanics properties including spatially distributed snow depth and density, soil type, drainage class, slope, and vegetation type. Snow depth and density were spatially distributed with regard to elevation, slope, and aspect using a surface energy balance approach. This paper evaluates whether the terramechanics representation of a virtual test site is improved by adding spatially distributed snow and soil properties, rather than using uniform properties. The evaluation was accomplished by conducting a cross-country vehicle performance analysis using the North Atlantic Treaty Organization (NATO) Reference Mobility Model (NRMM) to validate the new algorithms for realistic spatial distribution of snow properties. The results showed that the percentage of No-Go areas for uniform snow is lower than the distributed snow by 4% for the CIV (CRREL Instrumented Vehicle), 8% for the HMMWV (High Mobility Multipurpose Wheeled Vehicle), and 5% for the Stryker vehicle. For both light vehicles, approximately 12% of the No-Go areas are classified as such because of slopes 29%. These results imply that spatial distribution of snow properties provides realistic vehicle response as opposed to having the snow properties distributed uniformly throughout the entire terrain. This represents an improvement over previous versions of the terramechanics properties.     

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.     

Designing a forwarder operation considering tolerable soil disturbance and minimum total cost

A model is developed to minimize the sum of road construction plus forwarding costs with the constraint that rut depth caused by the forwarder cannot exceed a maximum depth during the anticipated season of operation. Road spacing, forwarder trail spacing, forwarder size, forwarder load capacity, and tire inflation pressures are used as decision variables in developing the transportation plan. The total cost was minimized using the optimum road spacing approach. The model identifies whether the cumulative rut depth caused by the forwarder exceeds the maximum allowable rut depth at the point of or prior to the spacing that minimizes the cost, and if so, the rut depth limits the road spacing. If the road spacing at the point of minimum cost is less than the road spacing at the maximum allowable rut depth, road spacing is not constrained by rut depth. This model will help logging managers to evaluate the trade-offs between specified decision variables and then to design an optimum forwarder operation with tolerable soil disturbance and minimum total cost. The solution procedure of the model is described and a computer program is used to apply this model using a numerical example.     

双尖槽干气密封特性对比研究

提出一种新型双尖槽端面密封,具体由两个开槽深度不同、径向长度相同的螺旋槽及1个圆弧槽组合而成. 建立了该双尖槽与燕尾螺旋槽端面密封的数学模型,并运用有限差分法进行了数值计算. 结果表明:在小间隙区域,双尖槽具有更大的开启力、泄漏量、刚度及刚漏比,且间隙越小,双尖槽较燕尾螺旋槽其端面的开启力、刚度及刚漏比差值越大;在间隙(h₀)小于3.0 μm区域,双尖槽开启力整体大于燕尾螺旋槽;在间隙小于6.0 μm区域,双尖槽气膜刚度整体大于燕尾螺旋槽;在间隙小于6.8 μm区域,双尖槽刚漏比整体大于燕尾螺旋槽;特别是在间隙为3.0~5.0 μm区域,双尖槽较10 μm和8 μm槽深燕尾螺旋槽刚度有显著增大,较5 μm槽深燕尾螺旋槽增幅也达到6%左右;在间隙约小于3.0 μm区域,双尖槽较燕尾螺旋槽的泄漏量值虽有所增大,但其值没超过泄漏量的设计值,密封基本性能指标合格. 故双尖槽在泄漏量不超标的情况下,具有更优的综合性能.      

Experimental investigation of vapor bubble growth during flow boiling in a microchannel

Experiments were conducted to analyze flow boiling characteristics of water in a single brass microchannel of 25 mm length, 201 μm width, and 266 μm depth. Different heat flux conditions were tested for each of two different mass flow rates over three different values of inlet fluid temperature. Temporal and spatial surface temperature profiles were analyzed to show the relative effect of axial heat conduction on temperature rise along the channel length and the effect of flow regime transition on local surface temperature oscillation. Vapor bubble growth rate increased with increasing wall superheat. The slower a bubble grew, the further it was carried downstream by the moving liquid. Bubble growth was suppressed for increased mass flux while the vapor bubble was less than the channel diameter. The pressure spike of an elongating vapor bubble was shown to suppress the growth of a neighboring bubble by more than 50% of its volume. An upstream progression of the Onset of Bubble Elongation (OBE) was observed that began at the channel exit and progressed upstream. The effects of conjugate heat transfer were observed when different flow regime transitions produced different rates of progression for the elongation sequence. Instability was observed at lower heat fluxes for this single channel experiment than for similar studies with multiple channels.     

考虑空化效应的螺旋槽机械密封液膜动力学特性研究

考虑液膜空化效应的影响，研究螺旋槽液体润滑机械密封的动力学特性. 基于液体润滑理论和小扰动法，建立了考虑液膜空化的密封微扰膜压控制方程，采用有限单元法对端面液膜三自由度微扰下的液膜刚度和阻尼系数进行了数值求解，分析了不同参数对液膜密封动力系数的影响. 螺旋槽深度在10 μm左右、槽坝比在0.75左右、槽宽比在0.4左右，螺旋角在9°左右时液膜具有最大的轴向和角向刚度系数. 螺旋槽深度在5 μm左右、槽宽比在0.6左右、螺旋角在20°左右时，两角向交叉阻尼绝对值最大. 初始偏角的存在使密封压力呈现非对称性，从而使两角向动力系数绝对值不再相等. 液膜轴向刚度k_zz在数量级上远大于其余液膜刚度值，液膜轴向阻尼d_zz、角向阻尼d_αα和d_ββ远大于液膜其余阻尼值且随着转速和间隙的增大而减小.      

Experimental studies of adiabatic flow boiling in fractal-like branching microchannels

Experimental results of adiabatic boiling of water flowing through a fractal-like branching microchannel network are presented and compared to numerical model simulations. The goal is to assess the ability of current pressure loss models applied to a bifurcating flow geometry. The fractal-like branching channel network is based on channel length and width ratios between adjacent branching levels of 2^−1/2. There are four branching sections for a total flow length of 18 mm, a channel height of 150 μm and a terminal channel width of 100 μm. The channels were Deep Reactive Ion Etched (DRIE) into a silicon disk. A Pyrex disk was anodically bonded to the silicon to form the channel top to allow visualization of the flow within the channels. The flow rates ranged from 100 to 225 g/min and the inlet subcooling levels varied from 0.5 to 6 °C. Pressure drop along the flow network and time averaged void fraction in each branching level were measured for each of the test conditions. The measured pressure drop ranged from 20 to 90 kPa, and the measured void fraction ranged from 0.3 to 0.9. The measured pressure drop results agree well with separated flow model predictions accounting for the varying flow geometry. The measured void fraction results followed the same trends as the model; however, the scatter in the experimental results is rather large.     

Prediction of track forces in skid-steering of military tracked vehicles

Track forces for outer and inner tracks have been calculated for a military tracked vehicle in a skid-steer situation. The present work is an attempt to improve the understanding of track force variation with turning radius. Furthermore, a reasonable estimate of transmission loads is required for the design of steering transmission for turning a tracked vehicle. This may also be obtained from the track forces. The understanding of track force variation with turning radius has been rather poor. In literature, the reason for lower track force at larger turning radius has been explained in terms of the deflection of the various suspension components like the track shoes, bushings, etc., which are associated with steer action. Deflection of the suspension components does not seem to be an adequate explanation for the variation of track forces with turning radius. In the present work, track forces have been obtained from the dynamics of the moving vehicle. The variation of tractive coefficient (coefficient of friction) due to lateral track slippage has also been considered. This is where the present work differs from the conventional track force estimation where a constant value of coefficient of lateral friction has been used. The estimation of tractive coefficient is made by using pull-slip equation found in literature. The explanation of decreasing track force with increasing radius is given in terms of variation of slip with speed and turning radius. It is found from the study that the concept of variation of coefficient of friction (tractive coefficient) is very important and probably a realistic one in the prediction of track forces. The results of the calculations compare reasonably well with the trends of test result plots obtained in the literature.     

Practical method of reducing turning motion resistance of tracked vehicles

A practical method of reducing the resistance of a tracked vehicle to turning or steering motion is discussed. The torque of the sprocket shaft for driving the crawler was measured and used to evaluate how the resistance varied compared with the existing method to turning. There are two ways of reducing the turning resistance by decreasing the contact area of track; one is to decrease the width of the braked track and the other is to shorten its contact length during turning or steering motion. The former is practically impossible to control, but the latter is comparatively easy to do, even under that condition. Applying this mechanism, the resistant force (evaluated by measuring the driving torque of the sprocket shaft) could be reduced about 20% when the contact length of the braked track was shortened to form a small pivot area at its center. It was also reduced more than 50% when the contact length of both tracks was shortened to a pivot during turning motion.