Energy decay for a class of nonlinear wave equations with a critical potential type of damping

The Cauchy problem for the nonlinear wave equation with a critical potential type of damping coefficient（1＋│x│）-1 and a nonlinearity │u│p-1u is studied.The total energy decay estimates of the global solutions are obtained by using multiplier techniques to establish identity ddtE（t）＋F（t）=0 and skillfully selecting f（t）,g（t）,h（t）when the initial data have a compact support.Using the similar method,the Cauchy problem for the nonlinear wave equation with a critical potential type of damping coefficient（1＋│x│＋t）-1 and a nonlinearity │u│p-1u is studied,similar solutions are obtained when the initial data have a compact support.

Critical Initial Amplitude of Langmuir Wave Damping

By one-dimensional Vlasov-Poisson simulation, the critical initial state marking the transition between the Landau scenario, in which the electric fields definitively damped to zero and the O＇NEIL scenario, in which the Landau damping is stopped after a certain damping stage, is studied. It is found that the critical initial amplitude e＊ can only exist when the product of the wave number （k~） and the electron thermal velocity （vth） is moderate, that is, 0.2 〈 k^vth 〈 0.7. Otherwise, no critical initial amplitude is found. The value c＊ increases with the increase in km for a fixed Vth, and also increases with the increase in Vth for a fixed kin. When kmVth is fixed, the value s＊ also changes with the wave number and the electron thermal velocity, even though the damping rate and the oscillation frequency are the same in this case.

Asymptotic Solutions for the Fifth Order Critically Damped Nonlinear Systems in the Case for Small Equal Eigenvalues

This article examines a fifth order critically damped nonlinearsystem in the case of small equal eigenvalues and tries to find out an asymptotic solution. This paper suggests that the solutions obtained by the perturbation techniques based on modified Krylov-Bogoliubov-Mitropoloskii (KBM) method is consistent with the numerical solutions obtained by the fourth order Runge-Kutta method.

ENHANCEMENT OF DAMPING PERFORMANCE OF POLYMERS BY FUNCTIONAL SMALL MOLECULES

The addition effects of organic small molecular substances N,N'-dicyclohexyl-benzothiazyl-2-sulfenamide (DZ) and 3,9-bis{1,1-dimethyl-2[beta-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80) on the dynamic mechanical properties of chlorinated polyethylene (CPE), chlorinated polypropylene (CPP), acrylate rubber (ACM) and their blends were investigated. In the case of compatible systems such as CPE/DZ and ACM/AO-80, the height of the loss tangent (tandelta) peak of a matrix polymer (CPE or ACM) increases, and its peak position shifts to a higher temperature with the addition of DZ or AO-80. By contrast, for incompatible CPE/AO-80, a novel transition appeared above the glass transition temperature of CPE. This additional transition was assigned to dissociation of the intermolecular hydrogen bond between the alpha-hydrogen of CPE and the hydroxyl groups of AO-80 within the AO-80-rich domain. This will provide a new concept for developing damping material. However, the minimum value between two tandelta peaks is lower. It was found that the temperature dependence of tandelta could be improved by adding chlorinated paraffin (CP) or ACM to CPE/AO-80. In addition, another ternary system of ACM/CPP with more AO-80 was found to be a very good self-adhesive damping material because of the appearance of a novel transition due to an interfacial layer of ACM/CPP.

A NOVEL SECOND-ORDER TRANSITION IN ORGANIC HYBRIDS CONSISTING OF POLYMERS AND SMALL MOLECULES

A novel transition appeared above thc glass transition temperature of chlorinated polyethylene (CPE) for binaryblends of CPE and additives such as organic small molecules or oligomers. This transition was assigned to the dissociation ofintermolecular hydrogen bonds between the polymer ard additive within the edditive rich phase. Of particular interest is thata novel pyramid crystal was observed in the annealed CPE/hindered phenol blends. Another intriguing observation is thatthese polymer/small molecule blends organized by intermolecular hydrogen bonding have several potential properties, suchas shape-memorization, self-restoration, self-adhesiveness and super damping.

The Extended Non-Elementary Amplitude Functions as Solutions to the Damped Pendulum Equation, the Van der Pol Equation, the Damped Duffing Equation, the Lienard Equation and the Lorenz Equations

In this paper, we define some non-elementary amplitude functions that are giving solutions to some well-known second-order nonlinear ODEs and the Lorenz equations, but not the chaos case. We are giving the solutions a name, a symbol and putting them into a group of functions and into the context of other functions. These solutions are equal to the amplitude, or upper limit of integration in a non-elementary integral that can be arbitrary. In order to define solutions to some short second-order nonlinear ODEs, we will make an extension to the general amplitude function. The only disadvantage is that the first derivative to these solutions contains an integral that disappear at the second derivation. We will also do a second extension: the two-integral amplitude function. With this extension we have the solution to a system of ODEs having a very strange behavior. Using the extended amplitude functions, we can define solutions to many short second-order nonlinear ODEs.

均匀流场下平单轴光伏支架扭转气动失稳特征试验研究

由于发电量明显高于固定式光伏系统,平单轴光伏发电系统近些年得到了广泛的应用。平单轴光伏支架由于扭转刚度较低,在大风天气下容易出现扭转气动失稳现象,从而造成支架结构破坏。为了进一步深入了解该振动的发生条件和机理,本研究通过节段模型测振风洞试验研究结构自振频率、倾角、阻尼等参数对扭转气动失稳的影响,分析了气动阻尼和气动刚度随着风速和倾角的变化规律。研究表明,平单轴光伏支架的扭转气动失稳表现出较强的气动耦合效应,气动阻尼和气动刚度是影响平单轴光伏支架气动失稳的重要参数,对风速和倾角的变化较为敏感,该失稳现象具备自激振动的特点;扭转刚度的提高在某些倾角下可以有效地限制振幅,同时可提高结构在各倾角的临界风速;扭转气动失稳的倾角范围为-15°~20°,0°倾角附近临界风速较高,若采用小倾角进行保护时,建议将大风保护角度设为0°。

全风向下平单轴光伏支架风致扭转气动失稳试验研究

针对平单轴光伏支架风致扭转气动失稳问题,采用全气弹模型,在风洞中复现了光伏支架的扭转气动失稳现象。通过对扭转响应和临界风速的分析,明确了平单轴光伏支架的风致振动特性。结果表明:光伏支架在-45°~45°的倾角范围内都可能发生扭转气动失稳,光伏组件水平放置时临界风速较高;小倾角下阻尼对临界风速影响较小,大倾角下增加阻尼可以提高临界风速;随着来流与光伏支架法线方向夹角(风向角)的增大,临界风速逐渐增加;斜风向下光伏支架尾流端部振动比迎风端部更剧烈。

单轴压缩试验法向临界阻尼比对岩石宏观参数的影响研究

为研究法向临界阻尼比对岩石的宏观参数的影响,基于单轴压缩试验,采用PFC^(2D)数值模拟软件,通过前期标定,完成试样模型的建立,并通过改变法向临界阻尼比,研究其对峰值强度、弹性模量、泊松比、试样能量损耗的影响,同时观察试样破坏形态的改变。结果表明,法向临界阻尼比对峰值强度、泊松比影响较大,对弹性模量影响较小,随着法向临界阻尼比的增大,试样的能量损耗和破坏形态都有先减少后增大的趋势。

电子产品振动响应检查研究

介绍了电子产品振动响应检查目的、方法和注意事项等要点。重点梳理了国内外5个标准中振动响应检查的要求、频率容差要求、检查的试验条件,阐述了振动响应检查结果判定的理论依据,结合振动响应检查实例详细描述振动响应检查方法、判定以及结果运用。

高速内置式永磁电动机转子系统的模态特性

针对含多组件的高速内置式永磁同步电动机转子结构等效弹性模量准确获取难度大,忽略轴承支承阻尼引起的模态分析误差大的问题,提出一种基于悬臂梁模型的等效弹性模量解析法,采用复数里卡蒂传递矩阵法建立考虑支承阻尼的转子系统动力学模型,分析了轴承支承特性和等效弹性模量对模态特性的影响,并进行了仿真和试验验证。结果表明:增加轴承刚度将增大转子系统的刚性临界转速并降低系统稳定裕度,增加轴承阻尼将减小刚性临界转速并增大系统稳定性;当转子系统阻尼比增加到0.4左右时,锥动刚性模态消失;等效弹性模量主要影响转子系统的弯曲模态,而对刚性模态几乎无影响。

运中汤治疗危重症患者脾虚浊毒型急性胃肠功能障碍临床研究

目的 探讨运中汤治疗危重症患者胃肠功能障碍(脾虚浊毒型)的临床疗效。方法 选取危重症合并胃肠功能障碍(脾虚浊毒型)患者80例,按照随机数字表法分为2组。对照组(40例)予西医基础治疗,观察组(40例)在对照组治疗基础上加用运中汤加减治疗。比较2组患者疾病治疗效果及胃肠功能恢复情况,评价其临床疗效。结果 观察组治疗后的临床疗效较对照组明显提高;腹内压、ICU治疗时间、APACHE-II评分、机械通气时间、血乳酸、胃泌素较对照组明显下降,胃蛋白酶较对照组升高,差异有统计学意义(P<0.05)。结论 运用运中汤可改善危重症合并胃肠功能障碍患者的胃肠功能,改善患者预后,为危重症患者胃肠功能障碍的治疗提供了新的思路及可行性。

基于变步长精细积分法的电磁暂态仿真计算方法

随着大规模新能源的并网以及新型电力电子器件的应用,电力系统数字仿真的复杂性不断提高,电磁暂态特性也变得日趋复杂。电力电子系统在进行电磁暂态仿真时,会遇到很多不连续现象和状态突变现象。在计算时,变步长精细积分多步法可以通过对步长的调节,使每一段步长达到要求的计算精度。为克服在不连续情况下由状态变量突变引起的数值波动,进一步优化电磁瞬态模拟,拟利用基于Adams线性多步法的精细积分法,并通过误差估计实现对非均匀项的自适应逼近。在MATLAB/Simulink仿真平台利用理论分析法进行数值模拟,结果表明,所提算法可以有效地提高电磁暂态计算效率和计算精度。该方法弥补了实际应用中传统的临界阻尼调整算法“忽略”不连续问题这一漏洞。

Existence of Multiple Equilibrium Points in Global Attractor for the Strongly Damped Wave Equations

The aim of this paper is to study the long-term behavior of strongly damped wave equations with a Lyapunov function. Using the theory established by estimating the Z2 index of some sets and the idea of invariant sets of semi-flow,the properties of the global attractor for strongly damped wave equation are discussed. The existence of multiple equilibrium points in global attractor for strongly damped wave equations with critical growth of nonlinearity is obtained. And under some additional condition, the infinite dimension of the attractor is proven.

小阻尼模态颤振临界风速的简明判定方法

在低速颤振试验中,小阻尼型颤振模型发生等幅振动的起始风速通常较低,也没有明显的颤振发散现象,采用目测或基于常规模态参数识别的“阻尼法”判定颤振临界风速具有一定的不确定性。针对此问题,根据小阻尼模态颤振试验与抖振试验具有相似的振动现象,提出一种与确定抖振边界类似的“振幅拐点法”来判定颤振临界风速。该方法以振动幅值的均方根值为基础,绘制归一化振动均方根值随风速的变化曲线,以曲线首个拐点对应的风速值为颤振临界风速。将该方法应用于某小阻尼模态颤振试验的发动机挂架变参数据处理,并将处理结果与数值计算结果、阻尼法处理的试验结果进行了对比,结果表明:振幅拐点法与数值计算、阻尼法处理得到的结果规律一致,振幅拐点法得到的结果更接近计算结果,具有简明可靠、稳定性好、适用性强的特点。

柔性接地补偿电流离散域矢量控制策略研究

柔性接地通过电力电子变流器补偿单相接地故障电流的有功和谐波分量,实现对故障电流的全补偿,从而有利于接地点电弧的快速熄灭,因此柔性接地在配电网具有重要的应用前景。针对柔性接地有功与谐波电流控制,通过建立电力电子变流器的离散模型,直接考虑数字控制的一拍延时,设计了离散矢量电流控制器,在静止坐标系实现了对交流信号的无静差调节。针对所提电流控制器,通过离散域根轨迹分析,提出了临界阻尼参数设计方法,优化暂态响应避免了过补偿。仿真结果验证了所提控制器与设计方法的有效性。

一种用于小型电控越野机器人的克里斯蒂悬挂特性研究

针对小型电控越野机器人的应用需求,采用一种克里斯蒂悬挂形式的机械结构,结合力学模型与非线性规划来求解悬挂中几何结构参数最优解,利用动态微分方程分析悬挂弹簧处的时间与位移调节过程,解决悬挂系统的特性参数选取问题。根据与动态响应仿真结果的对比,选取临界阻尼进行悬挂弹簧系统的参数调整,得到相应的弹簧刚度系数与黏性阻尼系数,实现悬挂系统特性参数的优化。

协作机器人辅助的空间展开机构桁架铰链微重力装配

针对大型空间展开机构桁架铰链装配中重力卸载过程复杂、需手工反复调整、装配精度一致性差的难题,提出一种采用协作机器人辅助的桁架铰链微重力装配方法。首先提出协作机器人辅助的微重力装系统架构和工艺流程;然后利用视觉引导结合四元数有界偏差关节路径规划法,实现桁架铰链的快速自动抓取;构建基于D-H法的机器人运动学模型,并利用牛顿—拉夫森迭代法在线补偿位姿误差,提高机器人在桁架铰链装配中的绝对定位精度;最后构建桁架铰链的重力卸载等效模型,并利用基于内环位置控制的机器人阻抗控制方法,实现桁架铰链的自动平稳重力卸载。实验表明,该方法的位姿精度满足桁架铰链装配要求,并可使桁架铰链以临界阻尼形式进行平稳重力卸载,为大型空间展开机构关键组件高精度装配和重力卸载提供理论依据和技术支持。

缝纫机旋梭轴转子动力学特性研究

针对缝纫机旋梭轴系高速运行不稳定的问题,计算了旋梭轴系的转子动力学,分析了失稳的原因,对旋梭轴系稳定性进行了理论分析,对旋梭轴转子动力学特性进行了仿真研究。首先,根据缝纫机转子瞬时位置及其受力情况,推导出了转子动力学方程,建立了旋梭轴系动力学分析模型;然后,在ANSYS Workbench软件中对刚性支承下旋梭轴系进行了转子动力学仿真分析,通过模态分析和不平衡响应分析,找到了旋梭轴系在工作转速内失稳的原因;最后,研究了旋梭轴径、支承位置、支承刚度、阻尼系数、轴向预紧力对旋梭轴系稳定性的影响,确定了满足使用工况的旋梭轴系结构和支承刚度范围。研究结果表明:缝纫机工作转速内有1个临界转速,影响了旋梭轴系的稳定性;增大轴径对提升临界转速的效果不明显;增加一个支承点,轴承刚度高于1 000 N/mm,轴套支承刚度高于100 N/mm,阻尼系数小于0.1,轴向预紧力小于100 N;旋梭轴系在工作转速内可以稳定运行。

Controllability results for damped second-order impulsive neutral integrodifferential systems with nonlocal conditions

In this paper, we establish a set of sufficient conditions for the controllability of damped second-order impulsive neutral integrodifferential systems with nonlocal initial conditions in Banach spaces. The approach used is the Sadovskii fixed point theorem combined with a noncompact condition on the cosine family of operators. An example is oresented to illustrate the result.