Numerical Filling Simulation of Injection Molding Using Three-Dimensional Model

1 Introduction During injection moulding, the rheological response of polymer melts is generally non-Newtonian and nonisothermal with the position of the moving flow front. Because of these inherent factors, it is difficult to analyze the filling process. Therefore, simplifications usually are used. For example, in middle-plane technique and dual domain technique [1], because the most injection molded parts have the characteristic of being thin but generally of complex shape, the Hele-Shaw …     

Wcomet直接还原法渣铁分离影响因素研究

研究还原温度、渣相配料碱度和渣中CaF2、K2O、P2O5、S、FeO的含量等因素对2CaO·SiO2形成及其相变的影响规律。结果表明,在快速升温条件下,温度高于1300℃后2CaO·SiO2才大量生成;CaF2、S和FeO对2CaO·SiO2相变不产生影响,但K2O和P2O5对2CaO·SiO2相变具有明显抑制作用;渣相二元碱度R〈1．8时渣的自然粉化效果明显变差。     

大数据环境下MES作业计划与调度能力云服务化研究

云制造技术给制造企业带来机遇的同时,也为其制造执行系统MES的设计与实现带来了新的挑战。为了解决单件小批MES中作业计划与调度优化问题,首先设计了一个从作业计划静态制定,到作业执行情况实时监控与主动感知,再到异常事件智能响应,最后到作业调度动态调节的闭环体系结构。接着针对异常信息实时获取与异常事件发现、异常事件智能化处理以及作业计划与调度优化算法计算能力服务化三个子问题,依次进行了问题分析并给出了技术解决方案。最后,以哈尔滨电机厂为案例对象,综合利用IEC/ISO 62264标准、大数据分析与挖掘方法以及由虚拟化、服务化和SOA等组成的云计算技术实现了单件小批MES作业计划与调度综合优化系统,验证了上述理论与方法的有效性。     

基于反步法的直流电机鲁棒速度跟踪控制

为实现具有电枢反应非线性和参数不确定性的直流电机速度跟踪控制,采用自适应反步法,设计了鲁棒自适应速度跟踪控制器.首先推导了电机的非线性动态模型并考虑了电机转动惯量及负载转矩的不确定性,然后经非线性变换并利用线性参考模型导出了系统的误差动态方程,基于自适应反步法设计了鲁棒速度跟踪控制器,最后时其稳定性进行了分析证明.     

Static and dynamic postural loadings during computer work in females: Sitting on an office chair versus sitting on an exercise ball

Seated computer work results in prolonged static loading, which has been associated with the development of musculoskeletal disorders. A popular alternative to sitting on an office chair while performing computer work is to sit on an exercise ball. Sitting on an exercise ball might affect static and dynamic aspects of working posture. We monitored posture, muscle activation and spinal shrinkage in 10 females performing a 1-h typing task, while sitting on an office chair with armrests and while sitting on an exercise ball. Sitting on an exercise ball resulted in 33% more trunk motion and in 66% more variation in lumbar EMG. Both of these findings can be considered to be an advantage for the exercise ball. However, the fifth percentile and average lumbar EMG were also higher when sitting on an exercise ball, with 38% and 78%, respectively. In addition, more spinal shrinkage occurred when sitting on an exercise ball than when sitting on an office chair. Arm flexion was reduced, but trapezius activation was unaffected when sitting on an exercise ball. It is concluded that the advantages with respect to physical loading of sitting on an exercise ball may not outweigh the disadvantages.     

水文模型参数的灵敏度分析

利用RSA和Sobol’两种全局灵敏度分析方法,对新安江模型中的主要产汇流参数进行了灵敏度分析,分析中采用Latin超立方采样方法,设定了模型参数的合理取值范围。参数灵敏度分析结果表明,两种方法得到的结果比较一致,流域蓄水容量是最敏感的参数,其次为汇流参数。灵敏度分析为水文模型有效的参数率定提供了技术支持。     

糯扎渡水电站溢洪道抗冲耐磨混凝土拌和工艺及质量控制

通过对抗冲耐磨混凝土原材料、拌和工艺等方面的质量控制管理,糯扎渡水电站溢洪道工程抗冲耐磨混凝土拌和物工作性能、混凝土强度、耐久性、抗冲耐磨强度均满足设计规范要求,为保证糯扎渡工程高流速溢洪道工程质量奠定了基础。     

Stepwise and Pulse Transient Methods of Thermophysical Parameters Measurement

Stepwise transient and pulse transient methods are experimental techniques for measuring the thermal diffusivity and conductivity of solid materials. Theoretical models and experimental apparatus are presented, and the influence of the heat source capacity and the heat transfer coefficient is investigated using the experiment simulation. The specimens from low-density polyethylene (LDPE) and polymethylmethacrylate (PMMA) were measured by both methods. Coefficients of variation were better than 0.9 % for LDPE and 2.8 % for PMMA measurements. The time dependence of the temperature response to the input heat flux showed a small drop, which was caused by thermoelastic wave generated by thermal expansions of the heat source.     

快时变环境下 OFDM系统中的信道估计

在OFDM系统中,怎样对快时变信道进行较为准确的估计是一个具有挑战性的课题。该文在利用信道基扩展模型的基础上,提出了一种适合于快时变环境下OFDM系统的信道估计方法,并且依据使估计的均方误差最小的准则,推导了相应最优的导频序列,包括最优的导频取值和最优的导频分布。可以证明,最优的导频序列是由一些相邻的等间隔等能量的子序列构成,每个子序列的导频之间满足一定的相位关系。仿真结果表明了所提估计算法在快时变环境下的有效性和采用所推导的最优导频序列进行估计的优越性。