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随机杆系结构的概率优化设计 总被引:3,自引:2,他引:3
对随机参数结构在随机载荷作用下的结构分析、可靠性分析和优化设计等问题进行研究。以衍架结构为对象进行结构分析,分别或同时考虑结构材料的物理参数、构件的几何尺寸和作用载荷幅值等的随机性。应用代数综合法对结构响应(位移、应力)随机变量的数字特征计算表达式进行推导。在结构可靠性分析的基础上,构建以杆件截面积为设计变量,使结构重量极小化为目标函数,同时具有应力和位移可靠性约束的优化设计数学模型。对模型中的可靠性约束进行等价显示化处理;对结构响应进行基于可靠性的灵敏度分析,导出结构响应可靠性约束的灵敏度计算公式。通过算例验证了文中提出的基于概率的结构分析和优化设计模型与方法的合理性与可行性。 相似文献
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研究了具有随机物理参数和几何参数的桁架结构在随机振动激励下的动力响应问题.从结构在随机振动激励下其振动响应在频率域上的表达式出发,利用求解随机变量函数矩的方法和求解随机变量数字特征的代数综合法,导出了桁架结构的位移响应均方值和应力响应均方值的均值、方差和变异系数的计算表达式.通过算例分析了结构物理参数和几何参数的随机性对桁架结构在随机振动激励下动力响应随机性的影响,得出了若干有用的结论,为随机桁架结构的动力设计奠定了基础. 相似文献
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平稳随机激励下线性随机结构动力响应分析 总被引:1,自引:0,他引:1
对于外载是平稳随机激励的线性随机结构分析问题,在随机变量函数矩点估计和虚拟激励法的基础上,建立随机响应均方值特征参数的矩估计算法.应用虚拟激励法将随机载荷转化为确定性简谐载荷,计算确定性结构在平稳随机激励下响应的均方值,采用点估计方法分析平稳响应均方值的均值和方差,并计算响应均方值的变异系数,通过两个算例考察结构参数的随机性对结构响应均方值的影响.由于基于随机变量函数矩的点估计和虚拟激励法具有较高的效率和精度,因而所提方法具有一定的工程意义. 相似文献
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随机参数弹性连杆在平稳随机激励下的动力可靠性分析 总被引:2,自引:0,他引:2
研究随机参数弹性连杆机构在平稳随机激励下的动力响应分析。利用拓广的随机因子法,从求解系统固有频率的瑞利商公式出发,得出物理参数和几何参数均为随机变量的弹性连杆时变固有频率的均值和方差。从动力平稳随机响应在频域上的表达式出发,利用求解随机变量函数的矩法和数字特征的代数综合法,计算出随机参数弹性连杆机构在平稳随机激励下弹性位移和速度的均方值的均值、方差表达式,由动力可靠度的公式导出其动力可靠度的均值和方差的计算公式。通过算例,分析机构物理参数和几何尺寸的随机性对机构动力可靠度随机性的影响。 相似文献
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In this paper, a method to obtain the sensitivity of eigenvalues and the random responses of the structure with uncertain
parameters is proposed. The concept of the proposed method is that the perturbed equation of each uncertain substructure is
obtained using the finite element method, and the perturbed equation of the overall structure is obtained using the mode synthesis
method. By this way, the reduced order perturbed equation of the uncertain system can be obtained. And the response of the
uncertain system is obtained using probability method. As a numerical example, a simple piping system is considered as an
example structure. The damping and spring constants of the support are considered as the uncertain parameters. Then the variations
of the eigenvalues, the correlation function and the power spectral density function of the responses are calculated. As a
result, the proposed method is considered to be useful technique to analyze the sensitivities of eigenvalues and random response
against random excitation in terms of the accuracy and the calculation time. 相似文献
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提出了一种随机模型修正方法以确定结构不确定性参数的概率统计特性,使得模型修正的应用更符合工程实际。将随机模型修正过程分解为一组确定性修正过程,利用蒙特卡罗仿真得到的响应样本并结合响应面模型的快速运算特性,构造优化反演过程来求得各个样本所对应的一组参数值,进而基于大量样本统计得到参数的均值和方差。所提出方法经过一组试验钢板的验证,准确求得了钢板厚度和材料参数的均值和方差,说明了方法的可行性和可靠性。 相似文献
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为了有效评价测量响应中不确定性对结构参量识别结果的影响,提出一种基于λ概率密度函数(Probability distribution function,PDF)和一次二阶矩的不确定性计算反求方法。采用二次衍生λ-PDF对待识不确定性参量的PDF进行建模。内层通过对参量呈λ-PDF的功能函数采用一次二阶矩法进行正问题求解,得到计算响应的概率分布;外层通过最小化测量响应与计算响应之间的概率分布特征量将不确定性反问题转化为确定性的最优化问题,并用隔代映射遗传算法识别未知参量 的参数。本方法不仅有效地实现了结构未知参量PDF的估计,而且与传统基于抽样的统计方法相比,计算效率较高。数值算例和工程应用验证了本方法的可行性和有效性。 相似文献
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Randomness exists in engineering Tolerance, assemble-error, environment temperature and wear make the parameters of a mechanical system uncertain So the behavior or response of the mechanical system is uncertain In this paper, the uncertain parameters are treated as random variables So if the probability distribution of a random parameter is known, the simulation of mechanical multibody dynamics can be made by Monte-Carlo method Thus multibody dynamics simulation results can be obtained in statistics A new concept called functional reliability is put forward in this paper, which can be defined as the probability of the dynamic parameters (such as position, orientation, velocity, acceleration etc) of the key parts of a mechanical multibody system belong to their tolerance values A flexible mechanical arm with random parameters is studied in this paper The length, width, thickness and density of the flexible arm are treated as random variables and Gaussian distribution is used with given mean and variance Computer code is developed based on the dynamic model and Monte-Carlo method to simulate the dynamic behavior of the flexible arm At the same time the end effector’s locating reliability is calculated with cncular tolerance area The theory and method presented in this paper are applicable on the dynamics modeling of general multibody systems 相似文献
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Bao-Guo Liu 《Journal of Mechanical Science and Technology》2012,26(1):1-10
A general method for investigating the eigenvalue problems of a rotor system with uncertain parameters is presented in this
paper. The recurrence perturbation formulas based on the Riccati transfer matrix method are derived and used for calculating
the first- and secondorder perturbations of eigenvalues and their respective eigenvectors for the rotor system with uncertain
parameters. In addition, these formulas can be used for investigating the independent, and repeated, as well as the complex
eigenvalue problems. The general method is called the Riccati perturbation transfer matrix method (Riccati-PTMM). The formulas
for calculating the mean value, variance, and covariance of the eigenvalues and eigenvectors of the rotor system with random
parameters are also given. Riccati-PTMM is used for calculating the random eigenvalues of a simply supported Timoshenko beam
and a test rotor supported by two oil bearings. The results show that the method is accurate and efficient. 相似文献
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A general class of linear time-invariant systems with time delays is studied. A number of methodologies have been suggested to assess the stability in the parametric domain of time delay or coefficient. This study offers an exact, structured and robust methodology to determine the stability regions of uncertain parameters in both time-delay space and coefficient space. The Rekasius transformation is used as a connection between time-delay space and coefficient space. An explicit analytical expression in terms of the system parameters which reveals the stability regions(pockets) in the domain of time delay and coefficient is presented. The method starts with the determination of all possible values of uncertain parameters which result in purely imaginary characteristic roots. In addition, some special stability boundaries are also discussed. After generating stability boundaries in parametric space, the two-step determination procedure is proposed to determine the actual stability regions. Such an approach can be used to determine the stability regions of any uncertain parameters of any retarded time-delay system. A complete example case study is also provided. 相似文献
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Dynamic displacement and acceleration responses of cars with uncertain parameters under random road input excitations are
investigated by using a quarter-car model. Based on the theory of random vibration, the vehicle’s random displacement and
acceleration responses are developed in time domain and frequency domain. The sprung mass, unsprung mass, suspension damping,
suspension and tire stiffness are considered as random variables. The mean value, standard deviation and variation coefficient
of the vehicle’s natural frequencies and mode shapes are obtained by using the Monte-Carlo simulation method. The computational
expressions for the numerical characteristics of the root mean square value of vehicle’s random displacement and acceleration
responses in the frequency domain are developed by means of the random variable’s functional moment method and algebra synthesis
method. The influences of the uncertainty of the vehicle’s parameters on the vehicle’s random responses are investigated in
detail using a practical example, and some useful conclusions are obtained. 相似文献
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挖掘机器人伺服系统存在高度非线性、参数不确定和未建模动态等诸多不利因素,提出了一种结合径向基函数(RBF)神经网络的非线性滑模控制器,以提高控制精度和鲁棒性。首先,建立了单联伺服系统的数学模型;其次,采用RBF神经网络对系统的不利因素进行逼近,提出积分滑模面进一步减小稳态误差,同时减少对伺服系统参数的依赖,在此基础上,设计了基于RBF神经网络的滑模控制器(SMC-RBF),利用Lyapunov理论证明了系统的渐近稳定性;最后,通过不同的参考信号和整平实验验证了控制器的优越性。仿真结果表明,SMC-RBF控制器响应快,跟踪精度高且鲁棒性强,与PID控制器相比正弦轨迹跟踪精度提高了46%。整平实验结果表明,铲斗末端轨迹跟踪精度提高了52%。 相似文献