Non-smooth dynamic modeling and simulation of an unmannedbicycle on a curved pavement

The non-smooth dynamic model of an unmanned bicycle is established to study the contact-separate and stick-slip non-smooth phenomena between wheels and the ground.According to the Carvallo-Whipple configuration,the unmanned bicycle is reduced to four rigid bodies,namely,rear wheel,rear frame,front fork,and front wheel,which are connected by perfect revolute joints.The interaction between each wheel and the ground is simplified as the normal contact force and the friction force at the contact point,and these forces are described by the Hunt-Crossley contact force model and the Lu Gre friction force model,respectively.According to the characteristics of flat and curved pavements,calculation methods for contact forces and their generalized forces are presented.The dynamics of the system is modeled by the Lagrange equations of the first kind,a numerical solution algorithm of the dynamic equations is presented,and the Baumgarte stabilization method is used to restrict the drift of the constraints.The correctness of the dynamic model and the numerical algorithm is verified in comparison with the previous studies.The feasibility of the proposed model is demonstrated by simulations under different motion states.

An adaptive large neighborhood search for the multi-point dynamic aggregation problem

The multi-point dynamic aggregation(MPDA)problem is a challenging real-world problem.In the MPDA problem,the demands of tasks keep changing with their inherent incremental rates,while a heterogeneous robot fleet is required to travel between these tasks to change the time-varying state of each task.The robots are allowed to collaborate on the same task or work separately until all tasks are completed.It is challenging to generate an effective task execution plan due to the tight coupling between robots abilities and tasks'incremental rates,and the complexity of robot collaboration.For effectiveness consideration,we use the variable length encoding to avoid redundancy in the solution space.We creatively use the adaptive large neighborhood search(ALNS)framework to solve the MPDA problem.In the proposed algorithm,high-quality initial solutions are generated through multiple problem-specific solution construction heuristics.These heuristics are also used to fix the broken solution in the novel integrated decoding-construction repair process of the ALNS framework.The results of statistical analysis by the Wilcoxon rank-sum test demonstrate that the proposed ALNS can obtain better task execution plans than some state-of-the-art algorithms in most MPDA instances.

基于LuGre摩擦模型补偿的动态电液测力建模与实验研究

为提高电液测力系统在动态下测量其负载的精度,采用Lu Gre摩擦模型描述动态测力时摩擦力非线性特征,搭建了基于比例阀压力控制的动态电液测力系统,对其在不同油液压力、速度下的摩擦力进行测量,依据实验数据及动、静态参数辨识模型辨识得到动、静态参数,进一步研究油液压力及移动速度对Lu Gre模型中各个参数的影响,得到关于油液压力及移动速度的Lu Gre摩擦模型,之后对油液推力实时补偿,得到基于Lu Gre摩擦模型补偿的动态电液测力精度。实验结果表明,动态电液测力状态下库仑摩擦力、最大静摩擦力及动态参数随油液压力的增大而变大,粘性摩擦系数和Stribeck速度随油液压力的增大而降低;基于Lu Gre摩擦补偿的动态电液测力系统测量精度可达0.45%。

GRE-over-IPsec vPN工程设计及实现——基于合肥百大集团网络的VPN应用

人类社会已经进入21世纪，计算机信息网络已深入到世界的各个角落，地域、国家、政府、企业甚至家庭。计算机网络的飞速发展给人来带来了诸多便利，而然其潜在的网络信息安全威胁也弥漫在各个领域。探讨的VPN技术则是建立在GRE over IPSec技术之上，并通过合肥百大集团的网络拓扑对其进行设计与仿真。GREoverIPSecVPN技术是通过GRE与IPSec相结合，而形成的一种安全性更好VPN技术，其主要借用IPSec的安全加密和GRE支持多播的优点，从而使得VPN网络更加安全。该项技术的主要工作原理：将一个完整的组播、广播数据包或非IP数据包封装在一个单播数据包（IPSEC）里，以处理如OSPF的组播或RIP的广播数据流，以完成在IPSec隧道里通信实体之间的动态路由学习。

Fast T_(1)mapping MRI in preclinical and clinical settings using subspace-constrained joint-domain reconstructions

This work aims to develop fast T_(1)mapping methods for preclinical and clinical scanners based on subspace-constrained reconstructions.Two sequences are explored for rapid T_(1)characterizations:1)Interleaved spatiotemporal encoding incorporating variable repetition times.2)Inversion recovery gradient echo with random sampling of the phaseencoding(PE)dimension.For both sequences,the subspace reconstruction of the signal recovery was applied,to jointly reconstruct the down-sampled images while characterizing the T_(1)relaxation.In vivo scans on human brains and abdomens confirmed the efficiency of the proposed methods,including compatibility with breath-holding.In addition,Scans on animals with abdominal tumors and dynamic contrast-enhanced T_(1)mapping on kidneys support the applicability of the proposed methods also in preclinical settings.

穿越动态NAT的IPv6 over IPv4隧道方案

文章提出了在跨越IPv4骨干网络进行IPv6用户接入时,实现穿越IPv4网络动态NAT节点隧道的解决方案,探讨了多层隧道嵌套及封装的技术原理及其应用特点,为IPv4向IPv6的网络过渡过程提供了一种在现有网络架构下平稳过渡的技术实现方案。文章提出的隧道嵌套技术已在中国南方电网CNGI驻地网实施过程中成功实现。

四电机伺服系统有限时间动态面控制

针对含有非线性齿隙和LuGre摩擦的四电机同步驱动伺服系统,在反步法的基础上结合动态面控制技术和有限时间控制技术设计基于观测器的有限时间动态面控制方法。在反步设计过程中,设计了鲁棒控制项抑制非线性齿隙的影响;构造了非线性观测器来估计摩擦力矩并在反步法中实现摩擦补偿;采用动态面控制技术解决了反步法存在的“计算爆炸”问题,并建立了补偿机制用于减小跟踪误差;采用有限时间控制技术加快了系统响应速度,进一步减小了跟踪误差。最后运用李雅普诺夫理论分析了闭环系统的稳定性,仿真结果验证了所提方法的有效性。

IPSec双中心动态多点VPN网络的设计与实现

高校在进行多校区一体化管理的时候,往往会因为过多的公网传输而使数据面临极大的安全威胁.针对这个问题,选择采用IPSec VPN来实现校区间的隧道加密传输,并结合学校实际提出了双中心站点动态多点VPN的设计方案,增加了网络冗余,提高了网络安全.

Optimal two-impulse space interception with multiple constraints

We consider optimal two-impulse space interception problems with multiple constraints.The multiple constraints are imposed on the terminal position of a space interceptor,impulse and impact instants,and the component-wise magnitudes of velocity impulses.These optimization problems are formulated as multi-point boundary value problems and solved by the calculus of variations.Slackness variable methods are used to convert all inequality constraints into equality constraints so that the Lagrange multiplier method can be used.A new dynamic slackness variable method is presented.As a result,an indirect optimization method is developed.Subsequently,our method is used to solve the two-impulse space interception problems of free-flight ballistic missiles.A number of conclusions for local optimal solutions have been drawn based on highly accurate numerical solutions.Specifically,by numerical examples,we show that when time and velocity impulse constraints are imposed,optimal two-impulse solutions may occur;if two-impulse instants are free,then a two-impulse space interception problem with velocity impulse constraints may degenerate to a one-impulse case.