新型液压打桩锤的系统仿真研究

对一种新型液压打桩锤的打桩过程进行了运动学及动力学分析,并在此基础上提出了桩锤在各个打击过程的数学模型.最后对各阶段进行了仿真及分析,仿真研究对改进和优化打桩锤的各个设计参数具有指导意义.     

3-RSR并联机器人动力学研究

该文利用雅可比矩阵建立了3-RSR并联机器人动平台惯性力、惯性力矩和重力到驱动关节的映射关系，在合理的假设基础上，运用牛顿欧拉动力学方程得到了比较精确的动力学模型。再用拉格朗日方程建立动力学模型并和前者比较，在同样假设情况下，给出数值实例，两个模型的计算结果完全一致。牛顿欧拉法比拉格朗日法减少了大量的计算，但动力学模型仍保持3-RSR并联机器人的动力学特征，用牛顿欧拉方程建立的模型作为驱动力矩控制设计的基础是可行的。     

车辆动力学稳定性系统变结构滑模控制研究

探讨了转弯车辆行驶在极限运动工况下时，依靠施加各车轮不同纵向制动力从而产生辅助横摆力矩来提高车辆动力学稳定性的基本原理，推导了两自由度车辆横向动力学方程，提出了车辆侧滑速度的3种实时估计方案（积分法，代数法和Luenberger观察器法），视实际车辆前后轮胎侧偏刚度为有界不确定性参数，为跟踪线性两自由度理想车辆模型的稳态输出响应，设计了车辆动力学稳定性变结构控制策略，通过仿真验证了该方案可行性。     

基于计算流体动力学解析的液压锥阀噪声评价

结合试验结果和计算流体动力学的解析结果，研究液压锥阀的噪声评价方法。对Oshima和Ichikawa试验所用的液压锥阀进行计算流体动力学解析，得到流入和流出两种工况下，对应不同的锥面夹角时阀座上的压力分布和速度分布。
对压力和速度进行积分加权分析，结合前人试验所得液压锥阀噪声特性，找到一种基于压力分布和漩涡脱离回流的液压锥阀噪声特性评价方法。应用该方法对实际液压锥阀进行噪声评价，评价结果与试验结果一致，证明了该方法的可行性。     

整机结构动力学特性边界元法解析

研究了考虑结合部特性的机床结构动力学特性的系统建模解析方法。将整机结构用梁元件、弹簧元件和集中质量元件来等效,并将结合部特性引入到整机模型中,基于边界元法建立了整机结构的动力学方程,快速地求得了整机结构相应的动力学特性。数值算例与实验结果表明,上述方法不但节约了计算量,而且具有很高的精度,可有效地解决各种复杂系统结构的动力学建模解析问题。上述方法对于提高机床结构的理论计算和设计水平具有十分重要的意义。     

头/盘界面对润滑剂转移行为及分布的影响

为进一步提高磁头飞行的稳定性,增加硬盘存储容量,采用分子动力学方法研究磁头磁盘接触条件下盘片上类金刚石薄膜(DLC)层粗糙度、DLC表层官能团比例及单个润滑剂分子中羟基数对润滑剂转移行为及润滑剂在盘片表面分布的影响.研究结果表明:降低DLC层粗糙度,增加DLC表层官能团比例都将降低磁头磁盘间的润滑剂转移量;当磁盘表面存在物理吸附态的润滑剂分子时,增加单个润滑剂分子中的羟基数也可降低润滑剂转移量;但降低DLC层粗糙度或同时增加DLC表层官能团的比例和单个润滑剂中羟基数会增加润滑剂在盘片表面堆积的高度,进而降低磁头飞行稳定性.综合考虑润滑剂转移量和润滑剂在磁盘表面堆积厚度对磁头飞行稳定性的影响,DLC层粗糙度应降低至约0.07 nm,DLC表层官能团比例增至约80%,单个润滑剂分子中的羟基数量应少于8个.     

The interplay of electronic structure,molecular orientation and charge transport in organic semiconductors: Poly(thiophene) and poly(bithiophene)

Ultrathin films of poly(thiophene) (PT) and poly(bithiophene) (PBT) were prepared by electrochemical route using ionic liquid (BFEE) as medium and electrolyte. Distinct morphologies and electrical properties were observed in these materials. To evaluate its response in photovoltaics, these films were used as active layer in bilayer geometry solar cells with the electron acceptor molecule C₆₀. The best performance was observed for PT films. In order to probe the differences in molecular dynamics and structural order, ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core–hole clock method at the sulfur K absorption edge. Electron delocalization times for the different polymeric films were derived as a function of the excitation energy. Photoabsorption measurements were conducted and molecular orientation derived. These results corroborated with the morphology found for these films and thus the performance of PT and PBT in the devices, and with the proposed conduction mechanism.     

Uncertainty analysis and evaluation of a complex,multi-specific weed dynamics model with diverse and incomplete data sets

Weed dynamics models are needed to test prospective cropping systems but are rarely evaluated with independent data (“validated”). Here, we evaluated the FlorSys model which quantifies the effects of cropping systems and pedoclimate on multispecific weed dynamics with a daily time step. We adapted existing validation methodologies and uncertainty analyses to account for multi-specific, multi-annual and diverse outputs, focusing on missing input data, incomplete and imprecise weed time series. Field data ranged from entirely monitored cropping system trials to annual snapshots recorded on farm fields by the French Biovigilance-Flore network. FlorSys satisfactorily predicted weed seed bank, plant densities and crop yields, at daily and multi-annual scales, at well monitored sites. It overestimated plant biomass and underestimated total flora density. Missing processes (photoperiod dependency in flowering, crop:weed competition for nitrogen) and inadequately predicted scenarios (weed dynamics in untilled fields, floras with summer-emerging species) were identified. Guidelines for model use were proposed.     

A Stokesian dynamics approach for simulation of magnetic particle suspensions

The dynamic behaviour of μm-scale ferromagnetic particles in suspension is of interest for various mineral beneficiation processes. It is, however, difficult to experimentally study such processes at the particle-level. In these instances it can be advantageous to resort to suitable particle simulation methods.Stokesian dynamics is a mesh-free numerical technique developed for suspensions of nm to mm size particles. The method inherently considers hydrodynamic interactions, but additional interaction models can be included depending on the system under investigation. We here present a Stokesian dynamics (SD) implementation, which allows for simulation of the motion of suspended magnetic particles in presence of an external magnetic field. The magnetic interaction model includes particle-field interactions as well as pairwise interactions between magnetised particles.Simulations are compared with experiments using a laboratory-scale flow cell. The method is shown to be realistic for studying ferromagnetic suspensions in mineral processing applications, and can be useful in understanding and predicting the efficiency of mineral separation processes.