基于CEL模型的搅拌摩擦焊接7055铝合金仿真模拟

基于耦合的欧拉—拉格朗日(CEL)模型,建立了高可靠性、高精度的搅拌摩擦焊7055铝合金热力耦合计算模型,开展了焊接工艺参数对7055铝合金焊接接头温度、等效应变以及缺陷预测结果的影响规律的研究,并分析和讨论了搅拌摩擦焊试验验证模拟结果的可靠性.7055铝合金搅拌摩擦焊CEL模型预测结果表明,温度和等效塑性应变与转速呈正比,与焊接速度呈反比,这主要与焊接工艺参数影响轴肩与7055铝合金的摩擦生热及材料的流动,使焊接温度和等效塑性应变值发生变化有关.当焊接速度在60-300 mm/min、转速在300-1200 r/min范围内,焊接温度均低于7055铝合金熔点,当焊接速度增加到300 mm/min时,由于产热不足,温度和等效塑性应变均降低,此时在焊接接头处容易产生孔洞缺陷.7055铝合金搅拌摩擦焊试验结果表明,当转速为600 r/min、焊接速度为180 mm/min时,7055铝合金接头组织致密,接头抗拉强度达到489 MPa,断后伸长率为4.0%.当焊接速度提高至300 mm/min时,接头抗拉强度为411 MPa,断后伸长率仅为1.0%.这与产热不足导致接头处结合较差有关,与模拟结果一致.

基于无源控制的无速度传感器异步电机调速控制

建立其交流异步电机的欧拉—拉格朗日数学模型,再以无源控制理论实现电机调速控制。为了转速反馈的准确性,加入了转速估算环节。充分利用被控系统已有的结构,直接比较给定的电磁转矩和估算的电磁转矩,运用PI闭环控制构造出转速信号。在Simulink中搭建仿真模型进行实验,仿真结果表明:此控制方法对交流异步电机速度控制具有较好的静/动态性能和抗干扰性。

多电平铁路功率调节器的无源控制方法

为了治理铁路系统的电能质量问题,研究了一种多电平铁路功率调节器(MRPC),其采用多电平级联型H桥链,只需要通过一个隔离变压器与牵引供电臂连接。若采用同相供电方式,MRPC可直接与牵引供电臂连接,不再需要隔离变压器。根据MRPC的拓扑结构推出了其等效电路图,并对其进行了数学建模。在此基础上,通过Park(αβ/dq)变换建立了dq坐标系下的欧拉—拉格朗日(EL)模型,分析了系统的无源性,提出了一种无源性控制方法,并设计了无源控制器。仿真和实验结果表明,该控制方法能提高MRPC对控制参数扰动的鲁棒性,改善牵引网电能质量。

Introduction and evaluation of a novel hybrid brattice for improved dust control in underground mining faces: A computational study

A proper control and management of dust dispersion is essential to ensure safe and productive underground working environment. Brattice installation to direct the flow from main shaft to the mining face was found to be the most effective method to disperse dust particle away from the mining face. However,it limits the movement and disturbs the flexibility of the mining fleets and operators at the tunnel. This study proposes a hybrid brattice system- a combination of a physical brattice together with suitable and flexible directed and located air curtains- to mitigate dust dispersion from the mining face and reduce dust concentration to a safe level for the working operators. A validated three-dimensional computational fluid dynamic model utilizing Eulerian–Lagrangian approach is employed to track the dispersion of dust particle. Several possible hybrid brattice scenarios are evaluated with the objective to improve dust management in underground mine. The results suggest that implementation of hybrid brattice is beneficial for the mining operation: up to three times lower dust concentration is achieved as compared to that of the physical brattice without air curtain.

Retrospect and Perspective of Micro-mixing Studies in Stirred Tanks

Mixing problems are most likely encountered and sometimes can be severe in scaling-up projects. Micro-mixing is an important aspect for fast or quasi-instantaneous reactions. Poor micro-mixing might produce more undesired by-products, leading to higher purification costs. This paper gives an extensive review and analysis of micro-mixing studies in single- and multi phase stirred tanks. The relevant experiment techniques, micro-mixing models and nurherical approaches are critically reviewed and analyzed with remarks and perspectives. The reported studies on two-phase micro-mixing experiments and on the impact of the presence of the dispersed phases on turbulence have been limited to a narrow range of conditions. More importantly, disparities widely exist among different reports. Both Lagrangian and Eulerian models are based on oversimplified assumptions, which may lead to uncertainties or even unrealistic results. A heuristic model, which is from the perspective of CFD （computational fluid dynamics） and can cover the whole spectrum of scales and also focus on every subrocess, is desired in the future.