大跨度悬索桥颤振控制的研究状况与进展

当悬索桥主跨跨径超过2 000 m后, 气动稳定性已经成为悬索桥面临的最重要的安全问题,选择合适的装置避免桥梁在施工及运营阶段发生颤振势在必行.综述了国内外大跨度悬索桥颤振控制方法、措施及发展现状,系统介绍了大跨度悬索桥颤振控制的结构措施、耗能措施及气动措施的装置与应用,并讨论了各种措施的优缺点及其适用性.      

三河口碾压混凝土拱坝温控仿真研究

针对三河口碾压混凝土拱坝温度控制问题,综合考虑外界气温和混凝土热、力学性质随时间变化的影响,采用施工全过程仿真分析方法,动态模拟大坝碾压混凝土入仓温度、分层铺筑方式、通水冷却、后期养护等施工参数;分析了坝体温度场和温度应力场,提出了大坝温度、应力控制标准;根据计算结果及时进行温控方案的动态比较和调整,制定了具体的温控防裂要求和措施;在施工中对比实测监测数据。结果表明:坝体温度、应变的数值基本符合坝体温度控制的设计要求,证明温控措施有效。     

Low-dimensional intrinsic material functions for nonlinear viscoelasticity

Rheological material functions are used to form our conceptual understanding of a material response. For a nonlinear rheological response, the possible deformation protocols and material measures span a high-dimensional space. Here, we use asymptotic expansions to outline low-dimensional measures for describing leading-order nonlinear responses in large amplitude oscillatory shear (LAOS). This amplitude-intrinsic regime is sometimes called medium amplitude oscillatory shear (MAOS). These intrinsic nonlinear material functions are only a function of oscillatory frequency, and not amplitude. Such measures have been suggested in the past, but here, we clarify what measures exist and give physically meaningful interpretations. Both shear strain control (LAOStrain) and shear stress control (LAOStress) protocols are considered, and nomenclature is introduced to encode the physical interpretations. We report the first experimental measurement of all four intrinsic shear nonlinearities of LAOStrain. For the polymeric hydrogel (polyvinyl alcohol - Borax) we observe typical integer power function asymptotics. The magnitudes and signs of the intrinsic nonlinear fingerprints are used to conceptually model the mechanical response and to infer molecular and microscale features of the material.     

宁夏山区建设中的岩土工程问题

近年来 ,随着工业和旅游业的发展 ,在宁夏 ,特别是宁南低山黄土丘陵区及银川西侧的贺兰山区 ,一些不适于建筑的山坡、谷地 ,也成为建筑场地 ,随着也带来一系列与环境保护、岩土工程有密切关系的问题 ,如不慎重对待 ,妥善解决 ,必将产生十分严重的后果 ,阻碍山区建设的进一步发展。     

圆柱绕流的电磁控制

流体绕过非流线物体时，在物体尾部形成涡街，使其表面周期性变化的阻力和升力增加，从而导致物体振荡，产生噪音。本文通过实验和计算，研究圆柱绕流的电磁控制，阐述浸于弱电介质溶液中，表面包覆电磁激活板的圆柱，在电磁力作用下的流体控制原理，讨论电磁力的消涡、减阻和减振过程。     

A spread model of COVID-19 with some strict anti-epidemic measures

In the absence of specific drugs and vaccines, the best way to control the spread of COVID-19 is to adopt and diligently implement effective and strict anti-epidemic measures. In this paper, a mathematical spread model is proposed based on strict epidemic prevention measures and the known spreading characteristics of COVID-19. The equilibria (disease-free equilibrium and endemic equilibrium) and the basic regenerative number of the model are analyzed. In particular, we prove the asymptotic stability of the equilibria, including locally and globally asymptotic stability. In order to validate the effectiveness of this model, it is used to simulate the spread of COVID-19 in Hubei Province of China for a period of time. The model parameters are estimated by the real data related to COVID-19 in Hubei. To further verify the model effectiveness, it is employed to simulate the spread of COVID-19 in Hunan Province of China. The mean relative error serves to measure the effect of fitting and simulations. Simulation results show that the model can accurately describe the spread dynamics of COVID-19. Sensitivity analysis of the parameters is also done to provide the basis for formulating prevention and control measures. According to the sensitivity analysis and corresponding simulations, it is found that the most effective non-pharmaceutical intervention measures for controlling COVID-19 are to reduce the contact rate of the population and increase the quarantine rate of infected individuals.

     

液压换向阀的耦合水击振动特性研究

以某型舵机操纵液压换向阀为例,运用特征线法,对其由于自激振动以及启闭动作产生水击诱发非线性耦合振动现象的机理进行理论分析,获得换向阀水击振动的动态特性.通过实验验证,换向阀控制口水击压力幅值与计算结果偏差为2.87%,且压力变化趋势与计算结果基本一致.该结果可为掌握液压系统的振动特性、采取振动控制措施以及换向阀的设计和改进提供理论依据.     

A comparative study on the control of friction-driven oscillations by time-delayed feedback

We perform a detailed study of two linear time-delayed feedback laws for control of friction-driven oscillations. Our comparative study also includes two different mathematical models for the nonlinear dependence of frictional forces on sliding speed. Linear analysis gives stability boundaries in the plane of control parameters. The equilibrium loses stability via a Hopf bifurcation. Dynamics near the bifurcation is studied using the method of multiple scales (MMS). The bifurcation is supercritical for one frictional force model and subcritical for the other, pointing to complications in the true nature of the bifurcation for friction-driven oscillations. The MMS results match very well with numerical solutions. Our analysis suggests that one form of the control force outperforms the other by many reasonable measures of control effectiveness.     

黑龙江省矿区生态破坏与地质灾害及其防治

黑龙江省矿产分布情况和开发概况以及矿业开发在经济发展中占有重要地位 ;在矿业开发过程中引起的诸多生态破坏和地质灾害及其引起的危害 ,已引起高度重视 ;本文在综合论述黑龙江省矿区发展所带来各项利弊后提出了具体的防治对策。     

长江宜都河段茶店崩岸机理与防治研究

崩岸是长江汛期大堤最严重险情。 1998年长江特大洪水后期 ,宜都河段茶店岸坡崩岸直接威胁长江大堤安全。本文分析了长江宜都河段的环境地质条件 ,宜都河段河流地质作用的基本特征。系统研究了茶店崩岸的形成机制及稳定性分析 ,最后提出了岸坡崩岸防治措施。     

Nonlinear Oscillations of a Nonresonant Cable under In-Plane Excitation with a Longitudinal Control

The nonlinear oscillations of a controlled suspended elastic cable under in-plane excitation are considered. Active control realized by longitudinal displacement of one support is introduced in order to reduce the transverse in-plane and out-of-plane vibrations. Linear and quadratic enhanced velocity feedback control laws are chosen and their effects on the cable motion are investigated using a two degree-of-freedom model. Perturbation analysis is performed to determine the in-plane steady-state solutions and their stability under an out-of-plane disturbance. The analysis is extended to the bifurcated two-mode steady-state oscillations in the region of parametric excitation. The dependence of the control effectiveness on the system parameters is investigated in the case of the first symmetric mode and the range of oscillation amplitudes in which the proposed control ensures a dissipation of energy is determined. Although control based only on in-plane response quantities is effective in reducing oscillations with a prevailing in-plane component, addition of out-of-plane measures has to be considered when the motion is characterized by two comparable components.     

结构可靠度分析FORM迭代算法的混沌控制

利用混沌控制原理对FORM收敛失败进行控制. 理清了全局性和局部性两类混沌反馈 控制各种方法的内在联系，说明稳定转换法和自适应调节法属于全局混沌反馈控制 方法，自适应调节法可视为稳定转换法的特例. 参 数调节混合法不过是松弛牛顿法的另一种表达形式，它们都属于局部混沌反馈控制方法. 阐 明了混沌反馈控制表达式与工程力学收敛控制迭代算法的对应关系. 也揭示了这些迭代算法 收敛控制措施的功效和局限性. 提出了一个以稳定转换法为主联合松弛牛顿法的混 沌反馈控制方法，对可靠度分析FORM迭代算法实现了周期振荡、分岔和混沌控制.     

TEACHING OF OPTIMAL CONTROL 1)

最优控制课程是控制科学与工程学科研究生学位必修课,同时也是力学(特别是动力学与控制方向)学位课,是一门具有理论深度和广泛工程应用的基础课。本文围绕如何提高课程教学质量、培养学生学习兴趣和创新能力的问题,对最优控制课程的教改核心、教学目标、教学内容、教学材料和教学方法等展开讨论。部分教改措施(如研讨式教学和BOPPPS教学结构)已应用于课程实践且取得良好效果。     

Finite-dimensional approximation to global minimizers in functional spaces with R-convergence

A new concept of convergence (R-convergence) of a sequence of measures is applied to characterize global minimizers in a functional space as a sequence of approximate solutions in finite-dimensional spaces. A deviation integral approach is used to find such solutions. For a constrained problem, a penalized deviation integral algorithm is proposed to convert it to unconstrained ones. A numerical example on an optimal control problem with non-convex state constraints is given to show the effectiveness of the algorithm.     

爆炸箔起爆器小尺寸飞片速度测试

设计了一套爆炸箔起爆装置,通过精确控制桥箔-飞片-加速腔三者的定位,在飞片表面镀一定厚度的铝膜（铝膜的质量与飞片的质量相比可忽略）,合理选择VISAR探头的工作距离和与干涉腔延迟时间相关的条纹常数,屏蔽测试系统以及加设滤光片等,利用VISAR测试技术有效解决了小尺寸飞片速度的测试问题。给出了两种尺寸0.7 mm0.025 mm和0.5 mm0.025 mm飞片的速度测试结果。结果表明,采取新的措施后,获得了信噪比好、能正确反映爆炸箔起爆器驱动飞片物理过程的信号和飞片速度历史。     

南阳膨胀土的宏观结构与路堑边坡病害治理

南阳盆地是我国膨胀土主要分布地区之一,在宁(南京)—西(西安)铁路施工工程地质调查中,发现南阳地区上第三系中新统湖相沉积膨胀土中发育的构造裂隙、中更新统冲洪积膨胀土中发育的卸荷裂隙和全新统湖沼相膨胀土中发育的收缩裂隙控制了路堑边坡病害的形式、规模和破坏特征。施工过程中采取了针对性措施治理边坡病害,取得了明显的工程效果。     

水布垭马崖高边坡岩体地下开挖三维数值模拟研究

清江水布垭水电站是清江上游拟建的一个特大型水电工程,马崖高边坡位于水布垭峡谷出口右侧,总体地质结构具上硬下软特征,电站导流洞及尾水洞将从马崖高陡边坡坡脚穿出,地下开挖主要在软岩层中。应用FINAL及ROCKY程序对水布垭马崖高陡边坡岩体地下开挖进行数值模拟,研究了边坡岩体内进行地下洞室开挖后边坡力学状态的改变及洞室岩体（含岩柱）的稳定性,基于削坡是水布垭马崖高陡边坡的重要整治措施之一,研究中进行了各种分步开挖工况下的削坡有效性定量研究,重要工况还同时进行了VI度地震作用下的动力作用分析。     

Fuzzy logic based automatic slip control system for agricultural tractors

In this study, a fuzzy-based automatic slip control system was developed for agricultural tractors. The developed system continuously measures the amount of slip that occurs during the tillage activities and automatically changes the operation depth of tillage equipment according to the amount of increase in the slip value. The amount of slip occurring on the driving wheels was applied as a separate input to the designed fuzzy control system (FCS) and at the fuzzy rule base, it was decided how much the depth of tillage would be reduced. The system was mounted on an agricultural tractor and trials were carried out in actual field conditions. The results of the tillage trials performed with the developed FCS were compared separately with the results of the tillage trials performed with an operator control (OC) without using any automatic control system. As a result of the trials, compared to the operator control, it was determined that in the tillage activities carried out with FCS, there were 42% decreases in slip values, 30% decreases in draft force values, 44% decreases in fuel consumption values and 5% increases in field work performance values. It was also observed that there were 10% changes in tillage depth.     

Dynamics and control of COVID-19 pandemic with nonlinear incidence rates

World Health Organization (WHO) has declared COVID-19 a pandemic on March 11, 2020. As of May 23, 2020, according to WHO, there are 213 countries, areas or territories with COVID-19 positive cases. To effectively address this situation, it is imperative to have a clear understanding of the COVID-19 transmission dynamics and to concoct efficient control measures to mitigate/contain the spread. In this work, the COVID-19 dynamics is modelled using susceptible–exposed–infectious–removed model with a nonlinear incidence rate. In order to control the transmission, the coefficient of nonlinear incidence function is adopted as the Governmental control input. To adequately understand the COVID-19 dynamics, bifurcation analysis is performed and the effect of varying reproduction number on the COVID-19 transmission is studied. The inadequacy of an open-loop approach in controlling the disease spread is validated via numerical simulations and a robust closed-loop control methodology using sliding mode control is also presented. The proposed SMC strategy could bring the basic reproduction number closer to 1 from an initial value of 2.5, thus limiting the exposed and infected individuals to a controllable threshold value. The model and the proposed control strategy are then compared with real-time data in order to verify its efficacy.

     

黑龙江省的界河坍塌地质灾害及其防治对策

界河坍塌是黑龙江省特殊的、主要的地质灾害,也是当前亟待解决的问题。本文总结了黑龙江省的两条主要界河—黑龙江和乌苏里江的塌岸状况;说明了界河坍塌的分布规律;论证了界河坍塌的形态类型;探讨了界河坍塌的形成机制;分析了界河坍塌的原因;最后提出了防止界河坍塌的一系列对策。