基于性能驱动的船载稳定平台尺度参数优化设计

为提升船载稳定平台的运动学性能,针对■并联机构的尺度参数优化问题,以机构的工作空间体积和全域力传递率为综合评价指标,采用小生境遗传算法优化得到稳定平台的最佳几何构形。具体地,采用数值法与解析法相结合的方式判断支链长度、关节转角、奇异位形等约束条件的生效情况,求解出并联稳定平台的工作空间;基于力雅可比矩阵逆矩阵的最小奇异值定义机构的局部力传递性能,以工作空间内局部力传递率的平均值作为全域力传递性能评价指标;以工作空间体积和全域力传递率的加权和为优化目标,采用小生境自适应遗传算法完成优化求解,获得最优尺度参数。与初始构形的性能对比分析表明,优化构形在力传递性能方面有35%的提升,具有更好的综合运动学性能。制作试验样机并完成相关实验,验证了所提尺度参数优化方法的有效性。最后探讨了多目标优化过程中不同的权重系数取值对优化结果的作用规律,发现选用均衡的权重可获得更佳的综合性能。     

极弱电网下直驱风电并网变流器小信号建模及稳定性运行策略分析

极弱电网下,直驱风电并网变流器各控制环路动态交互、满功率运行会改变并网点电压,导致不能稳定运行。对此,建立了考虑控制延时环节的全阶状态空间小信号模型,并采用特征值分析方法分析系统稳定性。研究表明系统稳定性随电网强度降低呈非线性变化,存在不连续稳定区间,且控制延时对不同振荡模式的阻尼比影响也呈非线性,部分阻尼比变大,部分阻尼比变小;同时,得到了参与电压、电流和锁相环之间交互作用的主导状态/控制变量,其参与度随电网强度减弱而加剧,进一步分析了各控制器参数对系统稳定性的影响规律,拉开控制带宽,避免频带交叠,将有助于提高系统稳定性;通过对比分析直驱风电系统在定交流电压控制和电压下垂控制下的适用性,发现定交流电压控制更适合极弱电网工况。通过MATLAB/Simulink仿真验证了理论分析的正确性。     

一款具有稳定扫描波束分辨率的宽视角相控阵天线北大核心CSCD

基于自适应稀疏阵的结构,提出了一种具有宽视角与稳定扫描波束分辨率性能的相控阵天线。阵列单元是可以在相同谐振频率下实现TM;和TM;两种模式共同工作的单激励圆环贴片天线,其具有140°的半功率波束宽度,这种宽波束辐射效果能够较好地拓展相控阵天线的扫描范围。基于此单元构建了一个35元线阵,对其波束扫描分析发现在限定增益波动小于2 dB的条件下阵列扫描范围可以达到-70°~+70°,但主瓣波束宽度随着扫描角度的增加而增大。为解决这个问题,引入了自适应稀疏阵的概念,并采用基于互耦补偿矩阵的迭代快速傅里叶变换(Iterative Fast Fourier Transform,IFFT)技术进行自适应稀疏阵的优化设计。结果表明,所提出的基于自适应稀疏阵结构的35单元相控阵天线在-60°~+60°扫描范围内增益波动始终小于1.5 dB,波束宽度波动小于1°,且峰值旁瓣电平基本保持在-20 dB以下。相较于均匀周期阵列,所提出的自适应稀疏相控阵天线能够在实现低旁瓣宽视角扫描的同时,有效提高天线在宽角度范围内扫描波束分辨率的稳定性。     

Analysis of retailers’ coalition stability for supply chain based on LCS and stable set

To attain the general form of stable coalition structure, this paper addressed the problem of retailers’ coalition stability in a two-stage supply chain consisting of one supplier and multiple retailers. A profit gain function was established via introducing market gain coefficient and coalition cost coefficient for different coalition structures. Based on the function, the profit of each retailer in all kinds of coalition structures was analysed, and the general feature of a stable coalition structure was attained by the largest consistent set method and the stable set method. Furthermore, some insights were obtained. For example, stable coalition structures are equidistributed or approximate equidistributed; with supplier’s cost increasing, the size of the retailers’ coalition increases. Finally, the above conclusions are verified by numerical simulation. The results of this paper provide a reference for retailers’ coalition in a supply chain, such as automobile or Information Technology supply chain.     

Polyethylene Glycol–CaCl2 Coordination Compounds as a Novel Form‐Stable Phase Change Material with Excellent Thermophysical Properties

Polyethylene glycols (PEGs) have been extensively studied as phase change materials (PCMs). To overcome the problem of liquid leakage, the authors firstly report a novel form‐stable phase change material (FSPCM) using coordination compound. The structure, morphology, thermal property, and thermal stability of the self‐prepared samples are determined. The obtained results confirm the existence of coordination bonds between PEG and Ca²⁺ species, and no liquid leakage is observed for the synthesized PEG–CaCl₂ composites at temperatures as high as 120 °C. The PEG8000–CaCl₂ (1:2) FSPCM exhibits a relatively large latent heat of 147.7 J g^?1, corresponding to 87.8% of that of pure PEG. From the dynamical viewpoint, the activation energy of crystallization process is increased by only 5.2% for the PEG8000–CaCl₂ composite due to the formation of coordination bonds; however, the activation energy is reduced by 18.3% during melting process. After adding 3 wt% conductive carbon black, the heat storage performance of the PEG phase change material can be optimized. The PEG‐CaCl₂ composite would be a promising material for thermal energy storage applications and can be used in various engineering fields.

     

时变时滞NCS控制器的改进设计

建立时滞差分不等式,得到网络化控制系统(NCS)的指数稳定判据,基于该判据设计NCS状态反馈控制器。该设计以线性矩阵不等式(LMI)形式给出,不包含任何自由矩阵,通过Matlab中的LMI工具箱进行求解。数值仿真结果表明,该设计具有计算量小、求解方便、保守性弱的特点。     

模糊合作博弈及其广义核心解的应用研究

为了解决模糊合作博弈传统核心解在资源分配问题中的应用局限,提出了对模糊合作博弈(N,v)中总收益值v(e~N)进行保留,不将全部总收益值分配给所有参与者,进而实现资源再分配或再发展的方案,进一步适应模糊合作博弈核心解的应用需求.首先定义了广义转归、广义核心,广义稳定集等解的概念,然后指出了其含义,在此基础上描述了模糊合作博弈模型.最后以定理证明了各广义核心解之间的关系,说明通过相应系数的调整即可提供合理的分配方案,表明了推广后的模糊合作博弈核心解具有更高的理论及应用价值.