灌木平茬机沙地通过性仿真研究

为研究灌木平茬机在科尔沁沙地的通过性能,基于ADAMS/ATV建立了其虚拟样机模型及符合沙地特性的平地、坡路、垂直障碍、凹坑、正弦路面等虚拟地形,进行了灌木平茬机在典型路面上行驶的仿真分析。结果表明,灌木平茬机能够平稳通过所建立的虚拟地形,在沙地上具有较好的通过性能,转向平稳。根据仿真结果确定灌木平茬机主动轮的最佳直径为280 mm、转向半径为0.75 m。     

How to characterize ‘good’ and ‘greening’ in the EU Common Agricultural Policy (CAP): the case of clay soils in the Netherlands

The change in the Common Agricultural Policy (CAP) of the European Union from product to producer support, including requirements for ‘good agricultural and environmental conditions’ and ‘greening’, is excellent. However, these requirements are now defined in rather general terms. Questions can be raised about suitable indicators, and there is a recognized need for effective management recommendations to support farmers in achieving the required ‘good’ conditions. These recommendations are bound to be quite different for different soils in different countries. A study of Dutch clay soils was based on a storyline describing current problems and management options for improvement, which were quantified using a soil–water–crop simulation model. Indicators were defined for agricultural conditions and suggestions made for the use of the model in a predictive mode to help farmers improve their soil management. Environmental conditions were judged by current environmental guidelines for water and air. When modelling, implicit assumptions that soils are homogeneous were shown to be unrealistic for these clay soils, requiring development of innovative methods and procedures, presenting a challenge for soil research.     

A review of the role of excess soil moisture conditions in constraining farm practices under Atlantic conditions

The Less Favoured Area (LFA) scheme is a major element of the EU Rural Development Policy, aimed at supporting farming in areas with natural handicaps or low soil productivity. It has been in place since 1975 and accounts for 14% of total Community funding. In 2003, the European Court of Auditors recommended that the socio‐economic criteria on which the current scheme is based be replaced by biophysical criteria. Reviews of the proposals suggest that in Atlantic climates of Northwest Europe, the new criteria do not delineate adequately areas where agricultural productivity is constrained by the biophysical environment and that such areas are instead demarcated by the occurrence of excess soil moisture conditions. In this paper, we review the impact of excess soil moisture conditions on the sustainability of farming systems and their role in constraining strategic and tactical farm management practices. In particular, we review the scientific evidence on the impact of excess soil moisture conditions on herbage growth, herbage utilization, farm operations and environmental sustainability. On the basis of this, we propose an additional biophysical criterion for the new delineation of LFAs, namely the length of time that soil water is in excess of field capacity (‘field capacity days’). While there is no clear threshold for field capacity days above which agricultural sustainability is acutely constrained, the evidence reviewed in this paper suggests that the sustainability of intensive livestock farming and tillage systems is particularly challenging in scenarios where the 80 percentile of field capacity days exceeds 220–230 days.     

滑转条件下星球车坡面通过性评估试验

星球车是执行深空探测任务的主要移动平台,针对星球表面崎岖地形地貌,开展滑转条件下星球车坡面沉陷研究,确保其安全通过性能具有重要意义。基于传统地面力学研究方法,以速度和坡度为试验因素,车轮滑转率和沉陷为试验指标,开展滑转条件下的缩比星球车坡面沉陷试验;分析了试验因素对各车轮滑转率影响,以及不同滑转率和速度条件下沉陷变化规律,建立了滑转率关于坡度的一元二次模型。结果表明,模型车前轮和中间轮的滑转率随速度和坡度变化趋势总体趋于一致,与后轮滑转率变化趋势明显不同。坡度为25°时,前轮和中间轮滑转率最大值达到92.3%,后轮相应的最大滑转率为61.8%。试验条件下,各车轮沉陷最大值分别为33.1 mm（前轮）、33.9 mm（中间轮）和13.6 mm（后轮）;当滑转率的范围为25%～60%时,前轮和中间轮沉陷增加的较为平缓,平均增加率为22.5%,对于后轮滑转率超过35%后,沉陷变化较小,波动范围为?1.3～1.8 mm;速度对各车轮沉陷的影响明显较滑转率的小,沉陷的相对变化率范围为?12.5%～10.7%。该研究可为低重力环境下星球车研制、坡面通过性评估提供参考。     

重塑黏土圆锥指数和抗剪强度的关系

为了定量评价轮式车辆在软黏土条件的附着、牵引及通过性能并建立软黏土的圆锥指数与抗剪强度关系,采用非标准普式击实法制备黏土试样,分别通过微型贯入试验与直剪试验得到重塑黏土的圆锥指数与抗剪强度,发现23%含水率是二者变化趋势的分界点,重塑土样的含水率低于该值时其圆锥指数与抗剪强度都随含水率呈二次多项式关系变化,而在高于该临界含水率时二者都随含水率呈线性关系变化。同样,在23%含水率以下圆锥指数与抗剪强度线性相关,而当含水率高于临界点后该线性关系消失。抛开含水率变化的影响,临界含水率以下的重塑样圆锥指数与抗剪强度关系仍然总体呈线性相关关系。     

丘陵山区自走式马铃薯联合收获机设计与通过性试验

针对丘陵山区马铃薯联合收获机短缺、履带底盘通过性较差等问题,设计了一款包括底盘行走装置、多级输送分离装置的自走式马铃薯收获机,开展了底盘通过性和机器收获性能理论分析。首先,对收获机底盘坡地行驶、越障性能进行理论分析,获得底盘通过性的临界参数;其次,对收获过程中马铃薯运动学进行分析,得到关键工作部件的相关参数。与此同时,运用RecurDyn仿真软件对整机进行多体动力学仿真分析,获得自走式马铃薯联合收获机适用于丘陵山区横向与纵向坡地及跨越壕沟与直壁的相关运动参数。仿真结果表明：纵向坡地行驶的最大爬坡角度为28°、横向坡地行驶的最大坡度角为20°、整机跨越垂直障碍的最大高度为150 mm、最大跨越壕沟宽度为300 mm。田间试验结果表明：收获作业时伤薯率为1.92%、破皮率为2.86%。收获机满足纵向坡度25°稳定行驶要求,跨越300 mm壕沟,翻越150 mm直壁,与仿真结果保持一致,验证了仿真的准确性,满足履带马铃薯收获机行驶通过性的设计要求。该研究可为丘陵山区根茎类履带式收获机的设计提供理论基础与参考。     

林火巡护与扑救车辆地形通过性仿真分析、实车试验

对国外引进的林火巡护与扑救车辆开展实际测绘,建立了车辆三维立体多体动力学模型,并对车辆的地形通过性进行仿真分析,对实际车辆进行地形通过性的实车试验验证,获取了该车在越野通过性方面的性能参数极值。     

履带式采伐机的通过性

研究履带式采伐机行走机构与地面的相互作用.建立履带三维实体模型,以三维实体模型的运动情况研究采伐机履带的通过性.建立通过性动力学分析模型,在产品的设计阶段进行采伐机履带的通过性虚拟试验,减少开发过程中试验和制造费用并提供求解方案.     

Seasonal dynamics in wheel load‐carrying capacity of a loam soil in the Swiss Plateau

Subsoil compaction is a major problem in modern agriculture caused by the intensification of agricultural production and the increase in weight of agricultural machinery. Compaction in the subsoil is highly persistent and leads to deterioration of soil functions. Wheel load‐carrying capacity (WLCC) is defined as the maximum wheel load for a specific tyre and inflation pressure that does not result in soil stress in excess of soil strength. The soil strength and hence WLCC is strongly influenced by soil matric potential (h). The aim of this study was to estimate the seasonal dynamics in WLCC based on in situ measurements of h, measurements of precompression stress at various h and simulations of soil stress. In this work, we concentrated on prevention of subsoil compaction. Calculations were made for different tyres (standard and low‐pressure top tyres) and for soil under different tillage and cropping systems (mouldboard ploughing, direct drilling, permanent grassland), and the computed WLCC was compared with real wheel loads to obtain the number of trafficable days (NTD) for various agricultural machines. Wheel load‐carrying capacity was higher for the top than the standard tyres, demonstrating the potential of tyre equipment in reducing compaction risks. The NTD varied between years and generally decreased with increasing wheel load of the machinery. The WLCC simulations presented here provide a useful and easily interpreted tool to guide the avoidance of soil compaction.     

Bodengefüge gegen Verdichtungen schützen – Lösungsansätze für den Schutz landwirtschaftlich genutzter Böden

Protecting soil structure against compaction—proposed solutions to safeguard agricultural soils To safeguard the ecological soil functions and the functions linked to human activities, measures against harmful changes to the soil are required, in line with the precautionary principle. The German Federal Soil Protection Act sets obligations for precaution in agricultural land use and, if harmful changes to the soil are foreseeable, measures for averting a danger. The results of a research project of the Federal Environmental Agency show that it is possible to describe an impairment of the soil structure, using methods of soil analysis. But this as a sole information would not qualify for the identification of harmful changes to the soil in the context of the Soil Protection Act, which requires an assessment of the severity of disruption of soil functions and the respective subject of protection. This would make additional soil investigations on site mandatory. Approaches in agricultural engineering and soil physics have introduced procedures to preserve the soil structure, in accordance with the precautionary principle. But these procedures have different goals and different ranges of application and hence offer partial solutions to safeguard against soil compaction. The assessment model of “trafficability by measuring the rut depth” provides information about the compaction status of the soil under applied conditions for farming gear, without providing detailed information about affected soil layers. The soil‐physical model of classifying soils into “risk classes for harmful soil compaction” focuses on the relationship between topsoil compaction and crop yields. The soil‐physical models “precompression stress” and “loading ratio” provide information for the assessment of subsoil compaction and a prognosis of a possible impairment of the soil structure at the water content of field capacity. It is necessary to validate the individual models with additional regional data about soil structure before a final assessment of the prognoses is made.