Effect of process parameters on microstructure and properties of AM50A magnesium alloy parts formed by double control forming

Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting （DC） due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength （YS）, ultimate tensile strength （UTS） and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 ＆#176;C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 ＆#176;C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.

CONTROLLABILITY CANONICAL FORM FOR NONLINEAR CONTROL SYSTEMS

General nonlinear control systems are studied in this paper with the goal to transform them into the so-called controllability canonteal form via state transformation only. The conditions of transformability are given for both single input and multiple input cases. Besides, by an algebraic approach the procedure for constructing the state transformation is established. This paper is formulated in the framework of calculus rather than differential geometry approach.

FE simulation and process analysis on forming of aluminum alloy multi-layer cylinder parts with flow control forming

The aluminum alloy parts used in airbag of car were studied with flow control forming(FCF) method, which was a good way to low forming force and better mechanical properties. The key technology of FCF was the design of control chamber to divide metal flow. So, the design method of FCF was analyzed and two type of control chamber were put forward. According to divisional principle, calculation model of forming force and approximate formula were given. Then forming process of aluminum alloy multi-layer cylinder parts was simulated. The effect of friction factor, die radius and punch velocity on metal flow and forming force was obtained. Finally, the experiment was preformed under the direction of theory and finite element(FE) simulation results. And the qualified parts were manufactured. The simulation data and experimental results show that the forming sequence of inner wall and outer wall, and then the force step, can be controlled by adjusting the process parameters. And the FCF technology proposed has very important application value in precision forging.

NEW NORMAL FORMS FOR NONLINEAR SYSTEMS (Ⅱ)——CONTROLLABLE FORM

This paper proposes a sort of new normal forms consisting of observer form and controllable form for nonlinear systems. The conditions for transforming to these normal forms are given, respectively. These normal forms are used to treat the problems of observer design and linearization. The first part of this paper deals with the observer form, and the second the controllable form.

CONTROLLED HOT FORMING OF RETAINING RING OF GENERATOR

The relevant results of thermodynamics simulation test, recrystallization study and FEM numercal simulation are described. A method is also introduced that the controlled hot forming is carried out by adopting the program of expansion-extrusion compound forming.

Release Characteristics of Different N Forms in an Uncoated Slow/Controlled Release Compound Fertilizer

This study examined the release characteristics of different N forms in an uncoated slow/controlled-release compound fertilizer （UCRF） and the N uptake and N-use efficiency by rice plants. Water dissolution, soil leaching, and pot experiments were employed. The dynamics of N release from the UCRF could be quantitatively described by three equations： the first-order kinetics equation [N1=N0 （1-e^-kt）], Elovich equation （N1=a ＋ blnt）, and parabola equation （N1=a ＋ bt^0.5）, with the best fitting by the first-order kinetics equation for different N （r= 0.9569^＊＊-0.9999^＊＊）. The release potentials （No values estimated by the first-order kinetics equation） of different N in the UCRF decreased in the order of total N 〉 DON 〉 urea-N 〉 NH4^＋-N 〉 NO3^-N in water, and total N 〉 NH4^＋-N 〉 DON 〉 urea-N 〉 NO3^--N in soil, respectively, being in accordance with cumulative amounts of N release. The constants of N release rate （k values and b values） for different N forms were in decreasing order of total N 〉 DON 〉 NH4^＋-N 〉 NO3^--N in water, whereas the k values were urea- N 〉DON 〉 NH4^＋-N 〉 total N 〉 NO3^--N, and the b values were total N 〉 NH4^＋-N 〉 DON 〉 NO3^--N 〉 urea-N in soil. Compared with a common compound fertilizer, the N-use efficiency, N-agronomy efficiency, and N-physiological efficiency of the UCRF were increased by 11.4%, 8.32 kg kg^-1, and 5.17 kg kg^-1, respectively. The ratios of different N to total N in the UCRF showed significant correlation with N uptake by rice plants. The findings showed that the first-order kinetics equation [Nt=N0 （l-e^kt）] could be used to describe the release characteristics of different N forms in the fertilizer. The UCRF containing different N forms was more effective in facilitating N uptake by rice compared with the common compound fertilizer containing single urea-N form.

构网型技术:演进历程、功能定位与应用展望

为支撑新能源高效利用和电力保供,构网型技术在电力系统不同应用场景中已获得初步探索实践。为促进构网型技术的规模化应用,文中探讨了构网型技术在新型电力系统中的功能定位和应用发展方向。通过梳理构网型技术的演进历程,以及国内外现有的标准和规范,分析了构网型技术发展的内在驱动需求,明晰了不同形态电网场景下构网型技术的功能定位;最后,从静、动、暂态的稳定性分析等维度,剖析了构网型技术当前面临的挑战,并对其大规模应用所需解决的问题进行了展望。

Humanoid Based Intelligence Control Strategy of Plastic Cement Die Press Work-Piece Forming Process for Polymer Plastics

The plastic cement belongs to a sort of polymer material, the chemical composition is very complex, and the plastic cement work-piece is generally manufactured by die press forming. Aimed at being difficult to control in parameters of forming process, the paper explored the humanoid based intelligence control strategy. In the paper, it made the anatomy in control puzzle resulted in uncertainty such as chemical component of plastic cement etc., summarized up the characteristic of cybernetics in forming process, researched on the humanoid based intelligence control strategy, and constructed the control algorithm of forming process in plastic cement work-piece. Taking the process experiment of temperature and pressure control as an example, it validated the good dynamic and static control quality through simulation of control algorithm constructed in this paper. The experimental results show that the control algorithm explored in this paper is reasonably available.

Noether-Form Invariance of Nonholonomic Controllable Mechanical Systems in Phase Space

In this paper,we study the Noether-form invariance of nonholonomic mechanical controllable systems inphase space.Equations of motion of the controllable mechanical systems in phase space are presented.The definitionand the criterion for this system are presented.A new conserved quantity and the Noether conserved quantity deducedfrom the Noether-form invariance are obtained.An example is given to illustrate the application of the results.

Teaching Form Reform of "Prevention and Control of Poultry and Poultry Diseases" Course in Higher Vocational Colleges

[ Objective] To meet the needs of ＂Prevention and Control of Poultry and Poultry Diseases＂ course in higher vocational colleges in new period. [Method] In order to introduce theoretical knowledge, enhance practical ability and train quality, teaching content, teaching methods and practical teaching of the course were explored according to trends of academic development and personnel training. [ Result] The reform of teaching form improved the teaching effect, mobilized the learning enthusiasm and initiative of students, and enhanced their ability to solve practical prob- lems. [ Conclusion] The teaching form of ＂Prevention and Control of Poultry and Poultry Diseases＂ course has been successfully reformed.

透明空腔复合滤棒成型纸恒张力控制系统设计

在滤棒成型过程中,包裹基棒的成型纸的张力稳定性对滤棒中基棒间距的稳定性具有较大影响。为提高透明空腔复合滤棒产品质量,对成型纸的输送进行恒张力控制。针对透明成型纸的材质特殊性,设计了透明空腔复合滤棒卷制成型过程中成型纸恒张力控制系统,采用闭环伺服控制原理,解决了透明成型纸在滤棒卷制过程中,因张力波动大导致的滤棒质量问题。测试结果表明,透明成型纸在10N的拉力作用下长度方向变形率为0.5%,对于120mm滤棒,在急速升速过程中,最大张力波动值0.21N所引起的长度方向变形为0.012mm,对于滤棒±0.8mm的误差许可范围基本没有影响。在生产透明空腔复合滤棒的YL22滤棒成型机组上的生产应用结果显示,成型纸恒张力控制系统实现了成型纸的恒张力控制,提高了基棒定位准确性,消除了因张力引起的滤棒空腔尺寸的波动,提高了产品质量,满足滤棒稳定生产要求。

SCR低氧铜连铸坯凝固组织异常现象研究

SCR连铸连轧生产线中,五轮式连铸机将高温铜液凝固成型,为后续铜杆的轧制过程提供铸坯,铸坯的质量影响着最终轧制出的铜杆产品的品质,但是该产线铸造过程中生产出的铸坯普遍存在凝固组织异常的现象,本文针对SCR连铸铜杆坯凝固组织的晶粒粗大、等轴晶过多、结晶线弯曲及偏移等异常现象,基于现有生产经验及经典金属凝固成型理论,对铸坯凝固组织的形成机理和铸坯凝固组织异常的形成机制进行分析,重点讨论了连铸过程中浇铸温度、浇铸速度、铸轮表面涂炭厚度、冷却水喷嘴堵塞、铸轮裂纹及车修、铸轮结垢等因素对凝固组织的影响,并给出了凝固组织异常的调控方案,为实际生产中工艺标准的合理制定提供了参考。

构网型单元异常下的孤岛交直流混合微电网群分布式协同控制策略

当构网型单元处于限功率运行与故障等工况下,传统孤岛交直流混合微电网群分布式协同控制方法易造成交流子微网母线电压与频率失去支撑,进而导致系统失稳.为解决上述问题,本文提出了一种面向构网型单元限功率运行与故障工况的孤岛交直流混合微电网群分布式协同控制策略.当子微网构网型单元处于限功率运行或故障工况时,首先,在构网型单元异常子微网变换器控制层,构网型单元将输出功率钳位于最大值或退出运行,跟网型单元通过与互联变换器进行二次协同控制,实现功率的合理分配;其次,在网间互联变换器控制层,与构网型单元异常子微网相连的互联变换器转为构网型控制模式,为构网型单元异常子微网提供母线电压与频率支撑,其余互联变换器按照正常子微网自身剩余容量分担构网型单元异常子微网所需的支撑功率.多工况下的仿真结果表明,当负荷连续增加,构网型单元处于限功率运行工况时,所提分布式协同控制策略可通过网间互联变换器的变模式运行,实现构网型单元异常子微网交流母线电压与频率的快速恢复、跟网型单元输出功率的精准分配;当构网型单元处于故障工况时,所提分布式协同控制策略可以有效解决构网型单元异常子微网因交流母线电压与频率失去支撑导致的失稳问题.

十二烷基硫酸钠与氨基酸双模板调控碳酸钙形貌的研究

球形碳酸钙因其高的比表面积、低的密度、优异的介孔性、优良的分散性和平滑性,在涂料、造纸、黏合剂、塑料、油墨、化妆品、药物的负载与缓释等方面有着广阔的应用前景。采用简单的复分解法,以氢氧化钙和碳酸钠为反应原料,十二烷基硫酸钠(SDS)、谷氨酸、脯氨酸和精氨酸为晶型控制剂,调控制备了多形貌的碳酸钙(CaCO_(3)),并用扫描电镜、X射线衍射仪等检测方法对产物进行表征分析。研究表明:SDS调控下,CaCO_(3)形貌主要为椭圆形;氨基酸调控下,CaCO_(3)形貌主要为不规则块状;在SDS与氨基酸双模板条件下,随着氨基酸从碱性到中性再到酸性,制得的CaCO_(3)形貌从不规则棒状逐渐缩短变为椭圆形,最后形成规整球形结构。考察了反应温度、诱导剂用量、反应时间和pH等工艺参数对碳酸钙粒子晶型和形貌的影响,提出了双模板作用的反应原理。结果表明,在反应温度为20℃、SDS浓度为0.1mol/L、谷氨酸质量浓度为40g/L、反应时间为2h、pH为12.3时,可制得微米级、规整光滑的方解石球形CaCO_(3),可为球形碳酸钙的工业化生产提供借鉴。

柔直构网新能源送端系统故障响应特性计算方法

故障等值建模是系统级响应特性计算的基础。然而,现有研究较少涉及构网型换流器的故障等值建模。传统针对跟网型电力电子设备接入交流电网的短路电流计算方法,在柔直构网系统中容易出现结果失稳发散的问题。因此,文中考虑构网型柔直换流器的电压-频率构网控制策略、主动降压策略以及跟网型新能源的低压穿越控制策略,建立了不同类型电力电子设备的故障等值模型。基于此,考虑不同电力电子设备电压源、电流源等值模型的频繁切换,提出了一种适用于柔直构网新能源送端系统的全网链式迭代故障响应特性计算方法,实现了短路电流计算的快速可靠收敛。基于PSCAD/EMTDC仿真平台,搭建了柔直构网新能源送端系统仿真模型,以进行多种故障类型和影响因素的大量仿真测试,充分验证了所提计算方法的可行性、精确性和优越性。

基于Normal Form方法的电机系统分岔控制

研究了无刷直流电机系统等效非线性数学模型,分析了系统的Hopf分岔行为,并设计了washout滤波器,对系统产生的分岔行为进行控制。引入直接Normal Form(规范型)计算方法,求出系统的Hopf分岔规范式。通过规范式系数讨论控制参数的选择原则以及对Hopf分岔类型及极限环幅值的影响。理论和仿真结果表明:在施加控制器之前,系统发生亚临界Hopf分岔,极限环不稳定,系统进入混沌状态;在施加控制器之后,当受控系统规范式系数实部小于零时,系统发生超临界Hopf分岔,原系统不稳定极限环被控制为稳定极限环,从而抑制了混沌的产生,保证了电机运行性能的稳定性。

孤岛下基于虚拟振荡器控制的构网型并联逆变器电压控制策略

现有基于虚拟振荡器控制的构网型并联逆变器由于控制参数耦合,存在母线电压谐波含量高、受负载影响波动大的问题,降低了孤岛模式下的供电质量。因此,针对电压建立阶段和电压维持阶段的不同需求,通过优化虚拟振荡器参数提出了谐波抑制方法。基于逆变器输出特性,提出了调压方法。结合参数滚动优化方法将谐波抑制和调压关联,形成电压控制策略。此外,建立了基于虚拟振荡器控制的并联逆变器系统带阻感性负载的小信号状态空间模型。结果表明,在所提电压控制策略下,并联系统的母线电压总谐波畸变率能降低至1.13%,负载切换时母线电压能快速恢复稳定,在轻载、额定和重载3种工况下,系统状态矩阵的主导特征值均位于左半复平面内,系统是渐近稳定的。

算法支配下新业态从业者的生存之困与化解方法

目前,以数字算法为核心技术支撑的平台企业已成为我国吸纳各类新业态从业者的重要载体。研究显示,新业态从业者不仅在劳动收入、劳动时间、劳动强度、劳动安全等方面不同程度地受制于平台企业的“算法控制”,而且由于后者常常有意凭借算法技术优势模糊劳动雇佣关系,从业者普遍面临着合同签约率低、社会保障覆盖低、工伤保险认定和劳动维权难等一系列问题。与此同时,受“算法支配”的生存处境也对从业者的自我感知、情绪稳定性、社会心态等造成了不同程度的负面影响,从而引发了许多不容忽视的社会安全隐患。有效化解新业态从业者的生存之困,需要政府、平台企业、从业者三方共同努力,从加强制度保障、技术优化、提高从业群体组织化水平等方面入手,积极营造一个更公平、更包容、更可持续的平台经济发展环境。

基于Normal Form方法的UPFC多个功能控制器间交互影响分析

统一潮流控制器(UPFC)的重要特点之一就是它具有的多控制功能,包括潮流控制、电压控制和稳定性控制等等。然而时域仿真研究表明统一潮流控制器的多个控制器之间可能存在着较强的交互影响。本文研究了规范型(Normal Form)方法用于分析UPFC控制器间的交互影响问题的可能性,并引入一非线性交互指标定量地指示出控制器间的交互强弱程度。所提方法应用到新英格兰10机39节点系统,并通过时域仿真验证了所提规范型理论分析方法的有效性。

跟网型和构网型新能源并网控制阻抗对比与振荡机理分析

“双碳”战略下,以电力电子变换器为并网接口的风电、光伏等新能源发展迅速。跟网型(grid-following,GFL)和构网型(grid-forming,GFM)作为电力电子变换器的两种控制方式,其并网宽频振荡问题引起了广泛关注。现有研究基于阻抗模型和Nyquist稳定判据对比GFM和GFL阻抗特性差异与振荡风险。由于GFM和GFL具有多控制回路,且二者在不同频段阻抗特性差异来源和主导因素仍未明确,特别是同步环节在其中的角色和作用亟需深入研究。此外,GFM并网实现GFL并网宽频振荡抑制的作用机理仍有待分析。该文首先对GFL和GFM不同频段阻抗特性进行对比,定量分析同步环节在阻抗特性中的角色和作用,揭示了决定二者不同频段阻抗特性差异的主导因素;然后,建立GFL和GFM并网的三端口稳定性判据,分析GFM并网实现GFL并网宽频振荡抑制的作用机理;最后,基于控制硬件在环仿真平台,开展GFL和GFM并网实验,验证该文分析的正确性。