基于流固耦合的分动器齿轮两相流动数值模拟与试验

针对分动器齿轮啮合传动中,润滑油运动过程缺乏研究和油压油速等相关参数不确定的问题,应用数值模拟与试验相结合的方法进行了详细的分析。建立分动器齿轮流场三维模型,基于流固耦合理论,应用Fluent UDF命令设定齿轮动网格运动,建立VOF两相流模型进行数值模拟,结果表明:0～0.5T(小齿轮以400 r/min速度旋转一周耗时为1T)时刻,从动大齿轮旋转带油对啮合区润滑起主要作用、速度流线在啮合区附近出现明显的漩涡现象、啮合齿面间压力值相对较大、两相流模型的改变对齿轮带油润滑效果有较大影响;应用高速摄影技术,对透明分动器壳体内流场流动情况进行观察试验,其油面波动与数值模拟结果作对比,最大误差为12.2%,误差较小,表明试验与数值模拟的分析结果相吻合。研究成果为下一步改善分动器齿轮润滑方面的工作提供参考。     

球面圆弧锥齿轮接触点轨迹方程

为了提高农业机械等领域的中央传动系统中齿轮的承载能力,减小中央传动的总体尺寸,降低机构的离地间隙,研究了一类理想状态下的球面圆弧锥齿轮。该文根据圆弧锥齿轮的啮合原理、坐标转换以及球面三角几何的方法,确定了球面圆弧锥齿轮接触点轨迹方程和齿轮副圆弧齿廓齿面方程,进一步完善了球面圆弧锥齿轮的设计理论,并根据研究出的方程,进行了齿轮的三维造型,为正确的设计和加工大端面呈理想球面且螺旋齿形端面为圆弧齿廓的球面圆弧螺旋锥齿轮提供了理论基础,也为后续的球面圆弧锥齿轮的参数化设计和数字化加工提供了研究基础。     

涂层强化齿轮传动抗胶合机理分析与试验

为提高农机装备传动齿轮于润滑条件恶劣、变速、重载工况下的抗胶合承载性能，该研究将表面涂层强化技术应用于啮合齿面。首先，基于齿轮啮合原理、摩擦学、热力学等理论，建立涂层与齿轮接触特性、胶合承载能力关系数学模型，分析不同膜基弹性模量比下系统应力场的分布特点，阐明齿面摩擦系数对油膜厚度、瞬时接触温度的影响规律，为择取齿面抗胶合涂层提供理论参考。由此进一步对标准钢球表面分别沉积含钨ta-C和a-C:H碳膜，通过四球法评价涂层材料摩擦学性能，并在FZG（Forschungsstelle für Zahnräder und Getriebesysteme）传动试验台上对两种涂层齿轮进行耐胶合试验。结果表明：与无涂层齿轮相比，碳膜摩擦副跑合性更好，其中a-C:H涂层的sp² C-C键含量高于ta-C，具有更低的摩擦系数（0.055～0.058）；ta-C涂层齿轮抗胶合承载能力提高了2个FZG载荷级，a-C:H涂层齿轮至少提升了4个载荷级；ta-C齿面展现为涂层剥落后的磨粒磨损和黏着磨损；且无涂层齿面与ta-C齿面均显示出热胶合与微点蚀损伤竞争性关系，并兼存齿面塑性变形；而a-C:H涂层主要表现为常规性疲劳磨损，在齿轮上适用性较佳。研究结果可为涂层强化技术在高性能农机装备齿轮乃至服役工况苛刻的其他传动系统应用奠定基础。     

力平衡型多输入齿轮马达的转矩特性分析与试验

针对传统齿轮马达径向力不平衡、只能输出一种转矩和转矩脉动较高的问题,提出了力平衡型多输入齿轮马达。该马达在一个壳体内有内、外两种马达,可通过不同的连接方式实现4种定转矩和定转速的输出。通过对马达的输出转矩进行理论计算和试验,分析了马达在4种工作方式下的瞬时转矩及转矩脉动,结果表明,单个马达工作时的转矩脉动与啮合齿轮的齿数有关。多个马达同时工作时的转矩脉动与齿轮啮合点的位置及脉动周期有关,当3个内马达共同工作,内、外马达共同工作,内、外马达差动工作时,在内、外马达脉动周期相同的前提下,可调节啮合点的位置,分别使3个小齿轮的轮齿啮合位置相差1/3,内、外马达轮齿啮合位置相差1/2,内、外马达轮齿啮合位置相同,通过瞬时转矩的叠加,使输出合转矩的脉动最小。试验结果表明,在调节齿轮啮合点的位置后,相同工作方式下的转矩脉动程度明显减少,该研究为多输入马达的进一步研究提供了参考。     

基于低速困油模型的外啮合齿轮泵高速困油特性分析

为了更好地预测高速下外啮合齿轮泵的困油程度,以及高速离心作用对困油的影响。在现有研究成果的基础上,简述了困油压力仿真的静、动态模型。利用龙格-库塔法的迭代运算,获得高速下困油压力和齿轮副振动在一个困油周期内的动态仿真结果,且就困油压力与泵齿轮副动力学特性的耦合性进行了分析。结果表明,高速下泵的困油压力比较严重;困油压力越大,齿轮副的振动越剧烈;高速离心作用对困油压力的缓解效果明显;齿侧间隙和卸荷槽的共同作用能使困油压力大幅降低;高速下应尽量通过卸荷槽结构的创新设计来降低困油压力和减缓振动。该研究为下一步高速下外啮合齿轮泵的开发提供理论指导。     

少齿差星轮型减速器的弹性静力学分析

针对目前少齿差星轮型减速器在机械应用中行星轴承易烧毁的现象,对其进行力学分析以寻求解决的途径。综合考虑内啮合齿轮副、行星轴承的变形以及各轴的扭转变形,构造少齿差星轮型减速器的变形协调条件,并采用子结构法建立该类传动系统的弹性静力学模型。通过求解系统的弹性静力学方程,获得系统各环节的受力,并给出了一个运动周期内两相机构的齿轮啮合力、行星轴承力和各曲轴扭矩的变化规律。弹性静力学仿真表明,少齿差星轮型减速器两相机构各环节的受力均呈周期性变化,且二者的变化规律基本相同,仅存在180?相位差。两相机构中齿轮副的啮合较为平稳,其啮合力在一个运动周期内仅存在微小波动;但行星轴承的载荷状况较为恶劣,其中星轮轴行星轴承的载荷波动较大,而输入轴行星轴承的载荷幅值较大,这恰与星轮型减速器应用中行星轴承易烧蚀的现象相吻合。该研究可为少齿差星轮型减速器的强度设计和结构优化提供准确的力学依据。     

新月形内齿轮泵内部泄漏与黏性摩擦损失模型构建

为了准确表征新月形内齿轮泵的内部流动特性,该研究根据静压支撑油膜理论及牛顿摩擦定理构建了该型齿轮泵内部泄漏数学模型及黏性摩擦损失数学模型,依据齿轮泵结构特点以及实际流动特征建立了基于两相流及动网格技术的CFD仿真模型,模拟分析了齿轮泵内部含气油液的流动特性,并与理论计算结果进行对比,最后进行试验验证。结果表明：在1/3周期内的瞬时体积流量与瞬时输入功率曲线均呈现连续周期性变化,两条曲线都有4个脉动;由于理论分析无法全面考虑油液实际流动过程而导致总泄漏量的理论值与仿真值相差60.11%,总黏性摩擦功率损失的理论值与仿真值相差66.66%;静态区域中流线相互平行,质点流动呈现层流状态,而在运动区域中却呈现完全湍流形态;压差流沿着新月形隔板内外两侧壁面以超过12 m/s的速度逆时针运动,而剪切流沿着外齿轮及内齿圈外壁同样以超过12 m/s的速度顺时针运动,在完全密封的齿间出现不同尺度的旋涡,旋涡中心的液体脱落现象使得其中的流体速度为0。在啮合齿面油膜的密封作用下,间隙最小处出现断流,啮合区的最大泄漏量为0.16 L/min;试验与仿真的容积效率相差1.34%,偏差率为1.37%;试验与仿真总效率相差1.40%,偏差率为1.74%。该研究获得了新月形内齿轮泵流动特性精确数学模型,验证了数值计算模型的适用性及仿真结果的准确性,可为完善齿轮泵设计理论与内流场特征分析提供参考。     

基于网络集成的弧齿锥齿轮数字化闭环制造技术

为突破弧齿锥齿轮数字化闭环制造过程信息继承性与集成性低的局限,实现弧齿锥齿轮齿面数字化闭环过程的集成运行和齿面制造信息的集成管理,该文提出了一种弧齿锥齿轮的网络化闭环制造模型,建立了网络化闭环制造的运行机制,采用基于TCP/IP(transmission control protocol/internet protocol,传输控制/网络通讯协定)的分布式集成控制模式构建网络化闭环制造模型的通信网络,利用Web服务应用集成方法建立闭环制造过程信息集成机制,并通过设计开发闭环制造集成系统实现网络化闭环制造信息的集成统一管理。应用结果表明:该模型及其实现技术可行实用,实现了齿面制造过程的数字化和集成化运行,使齿轮副的齿面精度和啮合性能都得到明显提高。以该文的准双曲面齿轮副滚动检测试验为例,辐射噪声降低约7%,振动加速度幅值降低约15%。该研究为弧齿锥齿轮的网络化和集成化制造提供参考。     

错排齿轮式排肥器优化与试验

为提升双齿轮式排肥器的排肥均匀性，该研究基于原始结构参数对直齿排肥齿轮进行改进，设计错排齿轮式排肥器。在参数化建模和确定轮齿容肥体积的基础上，结合理论分析确定了排肥器的理论排肥量。利用EDEM对排肥过程进行仿真，通过单因素试验分析错排齿轮片数、排肥轮间隙对排肥均匀性的影响，选用L₉(3⁴)正交表进行正交仿真试验。试验结果表明：试验因素对试验指标影响的主次顺序为错排齿轮片数、排肥轮间隙，当错排齿轮片数为3片、排肥轮间隙为5 mm时，排肥均匀性变异系数为4.69%。采用台架试验对双齿轮和错排齿轮式排肥器进行对比试验，结果表明：转速60 r/min时错排齿轮式排肥器的排肥流量变异系数为4.74%，与理论值基本吻合，且比双齿轮排肥器变异系数减小10.68%。基于实测排肥器转速-流量曲线设计电控排肥控制器并进行台架试验，施肥精度偏差为3.1%，优化后的排肥器排肥均匀性良好，且可实现精控排肥。研究结果可为精控排肥器的设计及优化提供参考。     

困油现象对泵齿轮副综合刚度的影响分析

为了对外啮合齿轮泵齿轮副的动力学模型进行综合刚度的计算,从泵齿轮副的侧隙位置和啮合位置的交替变化,以及体积弹性模量的定义,建立了包括接触刚度与困油刚度在内的泵齿轮副综合刚度的计算模型,进行了一个困油周期内实例的仿真计算.研究结果表明泵齿轮副在综合刚度方面与常规齿轮副有所不同,困油刚度是影响综合刚度的最主要因素之一,得出...     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.