Numerical method for dynamics of multi-body systems with two-dimensional Coulomb dry friction and nonholonomic constraints

Based on the dynamical theory of multi-body systems with nonholonomic constraints and an algorithm for complementarity problems, a numerical method for the multi-body systems with two-dimensional Coulomb dry friction and nonholonomic constraints is presented. In particular, a wheeled multi-body system is considered. Here, the state transition of stick-slip between wheel and ground is transformed into a nonlinear complementarity problem （NCP）. An iterative algorithm for solving the NCP is then presented using an event-driven method. Dynamical equations of the multi-body system with holonomic and nonholonomic constraints are given using Routh equations and a con- straint stabilization method. Finally, an example is used to test the proposed numerical method. The results show some dynamical behaviors of the wheeled multi-body system and its constraint stabilization effects.

Intelligent Power Grid Load Transferring Based on Safe Action-Correction Reinforcement Learning

When a line failure occurs in a power grid, a load transfer is implemented to reconfigure the network by changingthe states of tie-switches and load demands. Computation speed is one of the major performance indicators inpower grid load transfer, as a fast load transfer model can greatly reduce the economic loss of post-fault powergrids. In this study, a reinforcement learning method is developed based on a deep deterministic policy gradient.The tedious training process of the reinforcement learning model can be conducted offline, so the model showssatisfactory performance in real-time operation, indicating that it is suitable for fast load transfer. Consideringthat the reinforcement learning model performs poorly in satisfying safety constraints, a safe action-correctionframework is proposed to modify the learning model. In the framework, the action of load shedding is correctedaccording to sensitivity analysis results under a small discrete increment so as to match the constraints of line flowlimits. The results of case studies indicate that the proposed method is practical for fast and safe power grid loadtransfer.

Freights loading optimization with balanced and unconcentrated loading constraints

The optimization of high density and concentrated-weight freights loading requires an even distribution of the freight's weight and unconcentrated loading on the floor of the car.Based on the characteristics of concentrated-weight category freights,an improvement method is put forward to build freight towers and a greedy-construction algorithm is utilized based on heuristic information for the initial layout.Then a feasibility analysis is performed to judge if the balanced and unconcentrated loading constrains are reached.Through introducing optimization or adjustment methods,an overall optimal solution can be obtained.Experiments are conducted using data generated from real cases showing the effectiveness of our approach: volume utility ratio of 90.4% and load capacity utility ratio of 86.7% which is comparably even to the packing of the general freights.

Topology optimization of shear wall structures under seismic loading

A topology optimization formulation is developed to find the stiffest structure with desirable material distribution subjected to seismic loads. Finite element models of the structures are generated and the optimality criteria method is modified using a simple penalty approach and introducing fictitious strain energy to simultaneously consider both material volume and displacement constraints. Different types of shear walls with/without opening are investigated. Additionally, the effects of shear wall-frame interaction for single and coupled shear walls are studied. Gravity and seismic loads are applied to the shear walls so that the definitions provide a practical approach for locating the critical parts of these structures. The results suggest new viewpoints for architectural and structural engineering for placement of openings.

Dynamic response characteristics of dry and watersaturated schist under impact loading

Many geological engineering hazards are closely related to the dynamic mechanical properties of rock materials.However,most existing studies on the dynamic mechanical properties of rock materials were conducted on the hard rocks such as sandstone,granite,limestone,and marble,whereas soft rocks,such as schist,are less studied.Therefore,in this study,a series of triaxial impact tests were conducted on dry and saturated schist by employing a modified triaxial split Hopkinson pressure bar system to reveal the coupling effects of water,strain rate,and triaxial confining pressure on the mechanical properties of schist.The results show that schist is a type of watersensitive rock and the stress-strain curve of saturated schist has apparent ductility.The effects of strain rate on dynamic strain,deformation modulus and peak stress were analyzed.The results also show that the dynamic peak stress is affected by the combined softening effect and viscous effect of water under impact loading.Finally,it was found that the failure mode of schist belongs to typical axial tensile failure under uniaxial impact tests,and shear failure is the main failure mode under triaxial impact tests.With the increase in confining pressure,the failure modes of schist change from tensile failure to shear failure.This research can provide useful parameters for geological engineering hazard prevention in mountain areas.

Topology Optimization with Aperiodic Load Fatigue Constraints Based on Bidirectional Evolutionary Structural Optimization

Because of descriptive nonlinearity and computational inefficiency,topology optimization with fatigue life under aperiodic loads has developed slowly.A fatigue constraint topology optimization method based on bidirectional evolutionary structural optimization(BESO)under an aperiodic load is proposed in this paper.In viewof the severe nonlinearity of fatigue damagewith respect to design variables,effective stress cycles are extracted through transient dynamic analysis.Based on the Miner cumulative damage theory and life requirements,a fatigue constraint is first quantified and then transformed into a stress problem.Then,a normalized termination criterion is proposed by approximatemaximum stress measured by global stress using a P-normaggregation function.Finally,optimization examples show that the proposed algorithm can not only meet the requirements of fatigue life but also obtain a reasonable configuration.

Load Balancing in WDM Optical Networks with and without Wavelength-Continuity Constraints

In practical optical networks, there is often the same number of wavelengths in a fiber. But if it is not carefully designed, there will be much difference in link load among different fibers, and unnecessary wavelengths will be needed. This paper investigated this load balancing issues to minimize the wavelength requirements. Both Integer Linear Programming (ILP) and heuristic algorithms were presented to solve such a problem in WDM optical networks with or without wavelength continuity constraints.

战术网络中基于资源负载均衡和服务优先级的业务调度策略

针对战术网络环境的多样化业务和网络异构性、高动态特性导致的网络负载易失衡的问题,提出了一种基于资源负载均衡和服务优先级的业务调度策略。通过所承载业务类型的优先级感知,基于通信网络当时可用资源等约束,将业务按需调度到战术通信网络的通信资源池,达到通信网络的自动负载均衡和资源可靠合理利用,提高业务服务质量,并保证高优先级业务可靠传输。通过仿真,验证了该策略算法可大大提高网络吞吐量和资源利用效率。

改进文化基因算法求解双资源约束柔性作业车间调度问题

针对具有机器和工人的双资源约束柔性作业车间调度问题,以最小化最大完工时间为目标构建调度模型,并设计一种改进文化基因算法对其进行求解。由于该调度问题需要同时考虑工序排序、机器选择及工人选择3个子问题,故采用三层序列编码。考虑传统解码方式存在收敛速度慢、收敛不完全的弊端,设计一种扩展型插入式主动解码方式,以提高算法的收敛速度;针对进化算法易陷入局部最优的缺陷,设计一种基于负载平衡的机器和工人再分配算子,增强算法的全局搜索能力,对种群中的优秀个体采用改进变邻域搜索以提高算法的局部寻优能力。最后,利用仿真算例及航空设备生产实例进行实验,验证所提算法求解双资源约束调度问题的有效性。

5G超密集网络绿色中继算法研究

文章针对轻载蜂窝网络中待转移移动台在切换中继接入点过程中存在的能耗管控问题,提出一种服务质量级的5G超密集网络绿色中继算法。该算法通过识别中继站及中继网络类型来制定基于信道差异化的绿色中继方案。所制定的方案有效地约束了设备到设备数据通信全信道、中继站以及移动台的能耗。同时引入载荷评估机制并通过最优速率接入函数从最优中继信道中再次筛选出更优中继方案,有效地规避了待转移移动台接入点切换后全网载荷失衡的风险。实验结果表明,绿色中继算法可在确保设备到设备数据通信服务质量的同时实现能耗最优管理。在覆盖范围越大、移动台越多的5G超密集网络中,算法能耗管理优势越加明显。

入水速度对冰孔约束下圆柱体倾斜入水过程的影响分析

针对极地环境下超空泡圆柱体入水问题,基于雷诺平均方程引入流体体积模型,结合重叠网格技术建立了冰孔约束下圆柱体入水数值仿真方法。在此基础上,开展不同入水速度下圆柱体穿越冰孔入水过程仿真,分析了圆柱体入水过程中的空泡演化与载荷特性。研究结果表明:冰孔约束限制了孔内水域的流动,进而改变了表面喷溅的状态及空泡壁的形态,以至延迟了空泡表面闭合时间。随着入水速度的增大,冰孔约束对空泡形态的限制作用基本一致,圆柱体头部出现了更大范围的高压区域,且呈现出非对称分布;冰孔约束增大了圆柱体入水冲击载荷,使得圆柱体水下速度加快衰减,并促使圆柱体偏转角度大于无冰工况。研究结果可为极地超空泡武器入水稳定性提供参考。

飞机载荷校准试验主动约束技术

在研究以往飞机载荷校准试验支持和约束方式的基础上,结合某型飞机结构特点,提出一种载荷校准主动约束方法。对主动约束方法和传统的起落架方法飞机载荷校准进行受力分析,建立了2种约束方法的理论模型;设计2种约束方法的机翼载荷校准对比试验,并提出主动约束载荷校准试验实施流程;结合某型飞机机翼载荷校准试验和飞行试验对主动约束方法进行了验证。结果表明:与传统的起落架约束方法相比,主动约束方法能有效解决有起落架布置的翼身整体结构机翼根部载荷测量难题,并将机翼载荷校准试验量级提高41%,机翼载荷模型误差可控制在3%以内。

基于希尔伯特变换的电网络约束关系研究

为了研究电压波动条件下的电网络约束关系,文章基于希尔伯特变换,构建了供电电压存在波动下线性时不变负载上电压、电流的解析信号模型,推导出了以解析信号表征线性时不变电网络的拓扑约束和元件约束关系,将相量法思想拓展至对供电电压波动下线性时不变电网络响应特性的分析与求解。仿真验证结果表明,供电电压存在波动条件下,文中所建立的基于希尔伯特变换的电网络约束关系,不仅物理意义清晰、表征简明,而且正确、好用。文章所建立的电网络约束关系,能够为供电电压波动条件下电网络中线性时不变负载上电压电流关系的建模、仿真分析与计算提供指导。

流式大数据平台下的弹性数据迁移能效优化策略

针对流式计算框架在最初设计时缺乏能效方面的考虑,导致其存在高能耗与低效率的问题,提出一种流式大数据平台下的弹性数据迁移节能优化策略。首先,建立负载预测模型与资源判定模型,并进一步设计负载预测算法,通过预测负载变化趋势确定节点资源占用,找到资源过载与过剩节点;其次,建立资源约束模型与最优数据迁移模型,由此提出最优数据迁移算法,以提高节点资源利用率为目的进行数据迁移;最后,建立能耗模型,计算集群进行数据迁移后节约的能耗。实验结果表明,数据迁移节能优化策略能够对集群内节点资源变化做出及时响应,并在提高节点资源利用率的基础上,有效提高集群数据处理的能效。

基于耦合约束解耦的虚拟电厂动态可行域求解方法

构建以新能源为主体的新型电力系统需深入挖掘需求侧灵活性资源的调度潜力,使其参与电网调度调节任务以提升电网平衡调节能力。灵活性资源的海量异构特性使其聚合可行域的求解计算复杂度提升、约束满足难度增大。该文基于顶点搜索法,建立计及分布式电源出力不确定性的虚拟电厂动态可行域求解模型,进而通过李雅普诺夫优化将求解模型内部耦合约束松弛解耦为虚拟队列稳定性问题,提出以顶点搜索与队列稳定为目标的数学模型,最终通过建立虚拟时间队列形成求解算法。所提算法通过耦合约束解耦以提高求解效率;通过满足调度能力约束以提升资源调度能力。算例结果表明,在日前与日内场景下,所提算法具备提升计算效率与约束满足能力等方面的优势。

基于高阶马尔可夫链的纯电重卡集群负荷预测

相比于普通电动汽车,纯电重卡具有更高的充电功率、更大的电池容量和更可观的调度潜力,同时受货物重量、物流特性及行驶路径等诸多因素影响,其充电负荷呈现更大的随机性,建立准确的纯电重卡集群负荷预测模型有利于掌握其充电规律,降低对电网的冲击。为此,提出了考虑物流特性基于高阶马尔科夫链的纯电重卡集群负荷预测方法。首先,在考虑软时间窗约束实现纯电重卡路径规划的基础上,通过分析纯电重卡行驶特性预测其开始充电时间,以获取各时刻纯电重卡充电数量;其次,对纯电重卡的荷电状态区间进行模糊双层离散化分区处理,将每个大区间进一步细分为n个小区间,提高预测精度;然后,在求取纯电重卡荷电状态多步转移概率基础上,采用高阶马尔可夫链建立集群负荷预测模型,实现更为精确的负荷预测;最后,采用某物流园区实际纯电重卡数据进行仿真验证,结果表明,所构建的负荷预测模型较准确地预测了纯电重卡集群功率,同时减小了普通马尔科夫链方法的预测误差。

带障碍物惩罚因子的多机器人路径规划

轻载环境中,复杂障碍物区域将引起机器人之间局部冲突加剧,进而导致路径求解效率下降,针对该问题,提出轻载环境下带障碍物惩罚因子的多机器人路径规划方法。在基于冲突搜索(conflict-based search,CBS)算法框架的下层单机规划过程中,通过对即将拓展机器人位置的周围障碍物分布类型进行判断,赋予与之对应的障碍物惩罚因子;对路径规划过程中的惩罚因子进行累加,作为单机规划的启发值对路径进行选取;结合CBS算法框架的上层冲突消解策略进行多机器人的路径规划与冲突协调。测试结果表明,在10%障碍物分布的轻载环境中,所提算法的求解时间约为CBS算法的81.38%~83.67%,二叉约束树(constraint tree,CT)拓展量为CBS算法的60.14%~71.66%。在Gazebo中仿真表明,所提方法可减小通过复杂障碍物区域的次数。

含小水电配电网重要负荷评估及其水光储优化配置方法

为保证含小水电配电网重要负荷的电能质量安全与稳定,发挥水光储系统互补作用,提出一种负荷重要程度评估方法和含小水电配电网重要负荷的水光储优化配置方法。首先,从用户角度出发,基于用电效益指标与用电体验指标2个维度建立负荷重要程度评估体系,采用G1熵权法量化用户节点的重要程度,确定重要负荷节点并将其作为光储接入备选节点,降低光储优化配置求解维度;其次,建立以水光储全寿命周期成本最小、电压偏差平方之和最小为目标的优化配置模型,引入规格化平面约束法求解两目标水光储优化配置问题,得到均匀的Pareto最优解集;然后,计算各解集综合偏移程度函数,得到最优折中解,作为优化配置最佳参考方案;最后,以改进的IEEE 33节点配电网为算例,证明所提的优化配置方法可以改善重要负荷的电压偏差,同时提高投资者的收益。

Bio-inspired Design and Inverse Kinematics Solution of an Omnidirectional Humanoid Robotic Arm with Geometric and Load Capacity Constraints

Inspired by the driving muscles of the human arm,a 4-Degree of Freedom(DOF)concentrated driving humanoid robotic arm is proposed based on a spatial double parallel four-bar mechanism.The four-bar mechanism design reduces the inertia of the elbow-driving unit and the torque by 76.65%and 57.81%,respectively.Mimicking the human pose regulation strategy that the human arm picks up a heavy object by adjusting its posture naturally without complicated control,the robotic arm features an integrated position-level closed-form inverse solution method considering both geometric and load capacity limitations.This method consists of a geometric constraint model incorporating the arm angle(φ)and the Global Configuration(GC)to avoid joint limits and singularities,and a load capacity model to constrain the feasible domain of the arm angle.Further,trajectory tracking simulations and experiments are conducted to validate the feasibility of the proposed inverse solution method.The simulated maximum output torque,maximum output power and total energy consumption of the robotic arm are reduced by up to 2.0%,13.3%,and 33.3%,respectively.The experimental results demonstrate that the robotic arm can bear heavy loads in a human-like posture,effectively reducing the maximum output torque and energy consumption of the robotic arm by 1.83%and 5.03%,respectively,while avoiding joints beyond geometric and load capacity limitations.The proposed design provides a high payload–weight ratio and an efficient pose control solution for robotic arms,which can potentially broaden the application spectrum of humanoid robots.

基于双人零和博弈的孤岛微电网有界L2增益负荷频率控制

针对含不确定建模误差和新能源接入的孤岛微电网,提出了一种结合有界L2增益基线控制和扰动补偿的综合负荷频率控制(LFC)方法。首先,推导了微电网的全驱模型,将建模误差和新能源的影响总结成一个综合扰动。为提高系统的鲁棒性,该综合扰动被定义成控制信号的对手玩家。进一步,关于扰动抑制的有界L2增益问题被等价成求解综合扰动和控制信号的零和博弈Nash均衡,由此推导出有界L2增益基线控制器。为改善频率的二次控制,设计了基于五阶广义积分观测器的扰动补偿控制,并在此基础上引入了一种针对发电速率约束(GRC)的新型抗发电速率约束(anti-GRC)措施。最后,搭建了16 MW的新能源-柴油混合微电网仿真模型,并在多种工况下对所提出的综合LFC方法进行测试,验证了其有效性。