高动态特性步进电机驱动器系统设计(英文)

针对步进电机在快速加、减速及制动过程中容易出现的失步、过冲等现象,提出基于混合续流的功率器件优化导通驱动方式,能够最大程度减小在加、减速与制动过程中反电势对步进电机动态特性的影响,同时快速跟随细分电流给定波形。在此优化导通方式的基础上设计了一种具有高动态特性的全数字化步进电机驱动器,解决了步进电机在快速启停与加减速过程中出现的过冲和失步现象。实验结果表明,设计的驱动器具有很高的动态特性,符合设计要求。

Simulation of Start-Up Process of Turbofan Engine Based on Full-State Characteristics of Fan

Difficulties in obtaining component characteristics in the sub-idle state of rotor constrain the simulation capabilities of ground and windmill start-up processes for turbofan engines.This paper proposes a backbone feature method based on conventional characteristics parameters to derive the full-state characteristics of fan.The application of the fan’s full-state characteristics in component-level model of turbofan engine enables zero-speed iterative simulation for ground start-up process and windmill simulation for windmill start-up process,thereby improving the simulation capability of sub-idle state during turbofan engine start-up.

高多普勒扩频通信快速捕获技术研究

目前,超高速运动目标(如某些飞行器)的运动速度往往达到或超过20倍音速,当使用较高的通信频率时,高动态特性将引入较大的Doppler频移,通信信号的捕获跟踪变得异常困难。针对大的Doppler频移,重点研究了基于FFT的时域(伪码)并行捕获法、FLL环辅助PLL环的载波跟踪方法,提出了一整套信号接收方案。理论分析和仿真结果表明,提出的算法可以在0.2 s内完成较大多普勒频率及变化率的高动态扩频信号的捕获和同步。

数控磨床采用高性能直线电机进给的试验与研究

介绍了数控磨床采用高性能直线电机进给的试验与研究过程。重点分析了直线电机的应用情况及需要考虑的配套项目。根据直线电机在MK1432/H万能外圆磨床上的应用。验证了采用直线电机比采用传统的丝杆进给机构的性能指标和动态特性有了很大的改善。研究结果表明,数控万能螺纹磨床采用了高性能直线电机进给功能部件后,重复定位精度可达1μm。这项成果已应用于非圆工件磨削随动机构的驱动系统,可为其他数控磨床实现高精度进给提供参考。

一种基于OLSR的无人机网络适用路由算法

无人机自组网的高动态特性以及节点能量高度受限的特点,使得传统路由协议难以适用于无人机网络。针对该问题,在OLSR协议的基础上提出一种无人机网络适用路由(UAV-OLSR)算法。依据链路变化情况实现无人机集群状态感知,综合考虑节点能量、节点位置等因素进行节点质量评估。采用多径思想并通过特定的路径度量准则选择较优路径进行数据转发。仿真结果表明,与OLSR和AODV协议相比,UAV-OLSR具有更低的数据包平均传输延迟、更高的数据包投递率以及更好的能量均衡效果,可以延长无人机网络的生存时间。

Effect of specimen size on energy dissipation characteristics of red sandstone under high strain rate

In this experiment, red sandstone specimens, having slenderness ratios of 0.5, 0.7, 0.9 and 1.1 respectively, were subjected to blow tests using a Split Hopkinson Pressure Bar(SHPB) system at a pressure of 0.4 atmospheres. In this paper, we have analyzed the effect of slenderness ratio on the mechanical properties and energy dissipation characteristics of red sandstone under high strain rates. The processes of compaction, elastic deformation and stress softening deformation of specimens contract with an increase in slenderness ratio, whilst the nonlinear deformation process extends correspondingly. In addition, degrees of damage of specimens reduced gradually and the type of destruction showed a transformation trend from stretching failure towards shear failure when the slenderness ratio increased. A model of dynamic damage evolution in red sandstone was established and the parameters of the constitutive model at different ratios of length to diameter were determined. By comparison with the experimental curve, the accuracy of the model, which could reflect the stress–strain dynamic characteristics of red sandstone, was verified. From the view of energy dissipation, an increase in slenderness ratio of a specimen decreased the proportion of energy dissipation and caused a gradual fall in the capability of energy dissipation during the specimen failure process. To some extent, the study indicated the effects of slenderness ratios on the mechanical properties and energy dissipation characteristics of red sandstone under the high strain rate, which provides valuable references to related engineering designs and academic researches.

Research on Crustal Flow and Its Dynamic Characteristics in Sichuan and Its Adjacent Area

Using the broadband seismic data of the regional stations in the Sichuan Digital Seismic Network and the mobile seismic stations in this region,the receiver function inversion method was adopted to study the characteristics of crustal flow and dynamic effects in Sichuan and adjacent areas. The results show that: Velocity in the crust and upper mantle of the Sichuan basin is significantly higher than that beneath the eastern margin of the Qinghai-Tibetan plateau. The velocity v_S is from 3. 6 to 3. 8km / s in the crust and4. 5- 4. 8km / s in the upper mantle beneath the basin,and there is no low-velocity layer in the crust. The lithology shows a hard block. The v_S velocity in the eastern margin of the Qinghai-Tibetan plateau is lower,with average v_Sof 3. 0- 3. 4km / s in the mid crust and4. 0- 4. 5km / s in the upper mantle. Low-velocity layers are distributed widely in the crust,most of which are in the mid crust at a depth of 20km- 40 km,and there are also a few low-velocity layers appearing in the upper crust at depths of 10km- 20 km and the lower crust at depths of 40km- 60 km. Affected by the northward pushing of the Indian plate,the eastward movement of the eastern margin of the Qinghai-Tibetan plateau is blocked by the hard Sichuan basin,producing a southward and southeastward component.Such movement process is produced by the complicated forces acting in this area. Just under the action of these forces, the eastern margin of the Qinghai-Tibetan plateau becomes a region with complicated geology and intensive earthquake activity. Obstructed by the hard Sichuan basin,the low-velocity crustal flow is delaminated and split into two or three upward and downward tributaries. The upward flow intruded into the upper crust,causing uplift of the earths urface,forming mountain crests; the downward flow intruded into the lower crust and upper mantle,resulting in thickening of the crust and depression of the Moho. The crustal flow in the eastern margin of the Qinghai-Tibetan plateau is mainly distributed along the active faults. The crustal flow flows out from the Qiangtang block in the middle part of the eastern margin of the Qinghai-Tibetan plateau,the mainstream flows along the NW-SE trending Xianshuihe fault zone,then turns NS and flows to the south along the Anninghe and Xiaojiang faults. There is another crustal flow in the north of the study area,flowing in the NE and E-W directions to the Longmenshan faults.

Study on the dynamic characteristics of flow over building cluster at high Reynolds number by large eddy simulation

In this paper,the dynamic characteristics of building clusters are simulated by large eddy simulation at high Reynolds number for both homogeneous and heterogeneous building clusters.To save the computational cost a channel-like flow model is applied to the urban canopy with free slip condition at the upper boundary.The results show that the domain height is an important parameter for correct evaluation of the dynamic characteristics.The domain height must be greater than 8h(h is the average building height)in order to obtain correct roughness height while displacement height and roughness sublayer are less sensitive to the domain height.The Reynolds number effects on the dynamic characteristics and flow patterns are investigated.The turbulence intensity is stronger inside building cluster at high Reynolds number while turbulence intensity is almost unchanged with Reynolds number above the building cluster.Roughness height increases monotonously with Reynolds number by 20%from Re*=103 to Re*=105 but displacement height is almost unchanged.Within the canopy layer of heterogeneous building clusters,flow structures vary between buildings and turbulence is more active at high Reynolds number.