基于深度自编码器的大型龙门加工中心热误差建模方法

为提高热误差模型的预测能力,提出一种基于深度学习方法的数控机床热误差建模方法。利用模糊聚类法和灰色关联度分析法选取温度变量的热敏感点,采用深度自编码器（Stacked automatic encoder, SAE）网络从选出的输入样本中提取特征,构建特征集,然后使用遗传优化算法（Genetic optimization algorithm, GA）对BP神经网络参数进行寻优,从而提出一种基于SAE-GA-BP的数控机床热误差建模方法。以某大型龙门五面加工中心为实验对象,研究并选择了加工中心加工过程中的主要误差源——主轴热误差进行补偿,对主轴热误差深度学习模型和多元回归模型进行了分析对比。结果表明,在预测精度方面所提出的建模方法优于传统多元回归模型,从而验证了该建模方法的可行性和有效性。     

A simulation-based analysis of productivity and soil carbon in response to time-controlled rotational grazing in the West African Sahel region

In the Sahel region of West Africa, the traditional organization of the population and the grazing land avoided overexploitation of pastures. Since independence in the 1960s, grazing lands have been opened to all without specific guidance, and the vulnerability of the pastures to degradation has increased. Rotational grazing is postulated as a possible solution to provide higher pasture productivity, higher animal loads per unit land, and perhaps improved soil carbon storage. The objective of this study was to conduct a simulation-based assessment of the impact of rotational grazing management on pasture biomass production, grazing efficiency, animal grazing requirement satisfaction, and soil carbon storage in the Madiama Commune, Mali. The results showed that grazing intensity is the primary factor influencing the productivity of annual pastures and their capacity to provide for animal grazing requirements. Rotating the animals in paddocks is a positive practice for pasture protection that showed advantage as the grazing pressure increased. Increasing the size of the reserve biomass not available for grazing, which triggers the decision of taking the animals off the field, provided better pasture protection but reduced animal grazing requirements satisfaction. In terms of soil carbon storage, all management scenarios led to reduction of soil carbon at the end of the 50-year simulation periods, ranging between 4% and 5% of the initial storage. The differences in reduction as a function of grazing intensity were of no practical significance in these soils with very low organic matter content, mostly resistant to decomposition.     

基于UG的排气消声器模块开发及应用

由于在消声器声学性能仿真计算中,需要对消声器不断重复建模,为了简化建模过程,在分析消声器结构特征的基础上,提取了消声器实体建模的设计变量,并使用UGOpenAH编程实现了抗性消声器建模的程序开发。另外,系统地介绍了基于UG平台CAD二次开发的主要方法。     

高压共轨柴油机电控喷油器的仿真

高压共轨电控喷油器是共轨系统的核心部件,改善高压共轨电控喷油系统性能是提高柴油机整体性能和降低排放的有效手段之一.为此,介绍了共轨喷油器的基本结构和工作原理,并运用仿真软件对喷油器的电磁阀和喷油器体进行模块化建模.通过模型仿真分析结果,探讨喷油器主要结构参数对共轨喷油系统的影响,为高压共轨喷油器的设计和研发提供有效的依据.     

车辆传动系统虚拟样机建模与验证

为实现在设计阶段对车辆传动系统性能进行预测,以目前广泛应用的液力机械传动系统的组成和工作原理为基础,提出了可闭锁式液力变矩器和换挡离合器两个关键部件级,以及整个系统级虚拟样机建模方法,并进一步分析建立了相对应的数学模型。以起步工况试验的动力输入特性和操纵方式作为模型的输入条件对其进行了验证。通过仿真与试验测试结果对比,表明所建立的模型正确、合理并具有较高的精度。     

三维离散元法边界建模软件设计

针对目前离散元法边界建模中存在的问题,基于UG软件二次开发,结合VC++平台、MFC函数库和Access数据库,设计了三维离散元法边界建模软件,实现了与UG软件和三维离散元法分析软件的集成.以型孔轮式排种器为例,通过排种器的CAD设计、排种器工作过程的三维离散元法仿真分析以及与试验的对比,证明了边界建模软件的可行性和有...     

水稻钵苗纵向送秧装置的设计与试验

为满足水稻钵苗移栽机送秧装置精准稳定的送秧要求,设计一种新型纵向送秧装置。此装置采用链轮驱动,通过弹簧钢丝拨动钵盘实现纵向送秧,提高纵向送秧的精度和稳定性。分析新型纵向送秧驱动机构的工作原理,建立秧箱链轮机构的运动学模型,并通过Matlab软件优化出一组设计参数。设计并研制纵向送秧装置试验台,进行纵向送秧精度测试试验以及取苗试验。试验结果表明:纵向送秧的偏差量在±2 mm范围内,且多次试验没有产生累积偏差,符合设计要求;试验台的最低取苗成功率为91.37%,新型纵向送秧装置送秧效果良好,结构设计可行。     

基于数值模拟的红枣片不同干燥方式热质传递仿真与试验

为揭示并对比红枣片热风干燥、红外热风干燥及红外真空脉动干燥中的传热传质及干燥动力学特性,并填补关于果蔬红外真空脉动干燥数值模型的研究空白。该研究使用菲克扩散定律、安托因方程及比尔朗伯定律等控制方程分别建立了针对3种干燥方式的红枣片三维热质传递耦合数值模型,并利用试验数据对模型的可靠性进行验证。该研究基于枣片的实际几何尺寸进行建模并利用COMSOL求解。结果表明：1）与热风干燥相比,红外热风与红外真空脉动干燥分别缩短了46.43%和41.07%的干燥时间,且仿真结果与实测值吻合较好;2）温度场模拟图显示红外辐射可有效对红枣片内部进行加热,干燥20 min时红外热风和红外真空干燥的物料中心温度较热风干燥分别提高了11.33%和5.59%;3）模拟数据显示红外真空脉动干燥中的压力变化对干燥动力学产生了明显影响,其中含水率和干燥速率随压力脉动分别呈现阶梯状和峰状分布,并且干燥速率对压力变化的敏感性随着物料含水率的下降而下降;4）将测得的红枣片品质及质构特性与仿真数据进行综合对比,给出了关于分段组合干燥研究方向的见解,并对果蔬干燥数值模型的发展方向进行展望。该研究建立并验证了红枣片3种干燥方式下...     

DESIGNING DIVERSIFIED CROPPING SYSTEMS IN CHINA: THEORY,APPROACHES AND IMPLEMENTATION

•Agricultural green transformation of China requires restructuring of cropping systems.•Ecosystem services enhanced by crop diversification is key to sustainable agriculture.•Crop diversification improve ecosystem services at field, farm and landscape scales.•Cropping system design should meet regional characteristics and socio-economic demand.Intensive agriculture in China over recent decades has successfully realized food security but at the expense of negative environmental impacts. Achieving green transformation of agriculture in China requires fundamental restructuring of cropping systems. This paper presents a theoretical framework of theory, approaches and implementation of crop diversification schemes in China. Initially, crop diversification schemes require identifying multiple objectives by simultaneously considering natural resources, limiting factors/constraints, and social and economic demands of different stakeholders. Then, it is necessary to optimize existing and/or design novel cropping systems based upon farming practices and ecological principles, and to strengthen targeted ecosystem services to achieve the identified objectives. Next, the resulting diversified cropping systems need to be evaluated and examined by employing experimental and modeling approaches. Finally, a strategic plan, as presented in this paper, is needed for implementing an optimized crop diversification in China based upon regional characteristics with the concurrent objectives of safe, nutritious food production and environmental protection. The North China Plain is used as an example to illustrate the strategic plan to optimize and design diversified cropping systems. The implementation of crop diversification in China will set an example for other countries undergoing agricultural transition, and contribute to global sustainable development.     

玉米三维重构及可视化系统的设计与实现

重构出植物的三维形态是数字植物研究的基础。介绍了玉米三维重构及可视化系统的整体结构、数学基础及实现过程。系统由器官几何造型模块、生长模型模块、可视化控制模块、数据库和人机交互界面组成。其中，玉米叶片、茎节、雄穗、雌穗和根系的三维形态是由基于器官形态结构主要特征而构建的参数化的几何模型来描述的。模型参数具有较明确的生物学意义，均可由品种特征或生长模型生成；系统运行时，根据玉米品种特征和玉米生长模型生成植株的拓扑结构参数和器官几何模型参数，通过人机交互操作来确定行株距等农艺措施参数，进而结合VC++和openGL在计算机上重构出玉米器官、个体和群体的三维形态，具有较好地真实感。系统界面友好、使用方便，易于交互，为农学研究者提供了新的手段。