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一种计算随机变量函数均值和标准差的方法 总被引:2,自引:0,他引:2
在工程实践中常常需要对随机变量函数的均值和标准差进行计算。对于这种问题,通常采用的是Monte Carlo方法、Taylor级数展开法、Taguchi法及其改进方法、Rosenbluthe法及其改进方法等。其中最有效的是Monte Carlo方法,但其计算效率低。为此,提出利用数论方法产生分布均匀的数论网格点,以此伪随机数代表由Monte Carlo方法产生的随机数计算随机变量函数的均值及标准差。计算实例表明,这种利用伪随机数的方法不但克服了Rosenbluthe改进方法在处理高阶函数时计算结果偏离实际值的缺点,而且与Monte Carlo方法相比,提高了计算效率。 相似文献
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针对随机结构在随机过程激励下的动态响应问题,利用Karhunen-Loève分解方法将随机激励过程分解为以Gauss-Legendre积分节点为时间点的一系列时域确定性函数与独立随机变量相组合的形式,同时结合基于Gauss-Legendre积分公式的精细时程积分方法,求得各时域确定性函数下的时域响应.运用点估计法,计算随机结构系统在确定性时域激励下响应的统计矩.考虑随机过程的随机性与结构随机性相互独立的特性,得到随机结构参数和随机激励复合随机作用下响应的统计矩,并利用可靠性分析的四阶矩方法计算了随机结构在随机激励下的动态瞬时可靠度.与Monte Carlo模拟方法的对比可以验证所提出方法的精确性.对动态瞬时可靠度的分析可以获得振动系统在瞬态受载过程中的薄弱时刻,通过改进结构设计能够避免系统在薄弱时刻的失效,为振动系统的瞬态可靠性评估提供了理论基础. 相似文献
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考虑输入转矩和负载转矩的随机波动量,以及随机啮合误差,建立了单级直齿轮传动系统的弯-扭耦合动力学模型,经数值求解,得到了作用于轮齿的动应力。将工作周期内的动应力作用过程视为随机过程,并用该随机过程中最大应力的概率模型等效随机过程的作用,得到了应力的概率分布模型。使用Monte Carlo法得到了许用应力的概率分布模型。基于应力-强度干涉理论建立了考虑齿根弯曲疲劳失效和齿面接触疲劳失效相关性的齿轮传动系统动态可靠性模型。研究发现啮合误差越大,系统的可靠性越低。 相似文献
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建立了HSK主轴-刀柄结合部的有限元模型(FEM),利用弹性理论和黏性阻尼理论辨识结合部内各位置的刚度和阻尼参数。提出将HSK主轴-刀柄系统分为HSK主轴、主轴-刀柄结合部和刀柄三部分:HSK主轴与刀柄简化为多段Timoshenko梁,并使用响应耦合法来计算其频响函数;主轴-刀柄结合部简化为多点弹簧-阻尼模型,采用多点响应耦合法来计算其频响函数;将各个部件的频响函数进行刚性耦合,进而获得基于结合部的HSK主轴-刀柄系统频响函数。分别假定HSK主轴-刀柄结合部为刚性连接、5点弹性连接和7点弹性连接,计算其频响函数,并与实验结果相比较得到相应的结论。 相似文献
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六维加速度传感器因其系统的复杂性,对其动态特性的研究较少。针对所研究的并联式六维加速度传感器(以下简称并联惯性传感器),建立基于Kane方法的动力学模型,对并联惯性传感器的动态特性进行理论分析,通过传感器理论模型的结构简化和忽略系统阻尼的影响,建立动力学模型的解析解方程,推导传感器的固有频率和振型,与有限元法仿真环境下得到的试验数据进行比对,验证所建立动力学模型的准确性。在传感器工作频率带宽内,采用一定频率的加速度荷载进行标定试验,试验结果表明线加速度测量精度为1.3%。 相似文献
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Neumann展开Monte Carlo随机无网格点插值法 总被引:1,自引:0,他引:1
用Neumann展开Monte Carlo随机无网格点插值法(NMC-SMPIM)进行随机结构分析。在随机无网格点插值法(stochastic meshless point interpolation method,SMPIM)中,所求解问题的域由分布的节点表示;并且利用具有Delta函数性质的多项式进行节点插值,为此,很容易类似有限元法一样处理本质边界条件。同时利用Neumann展开法,建立随机结构分析的Neumann展开Monte Carlo随机无网格点插值法。数值实例表明,Neumann展开Monte Carlo随机无网格点插值法适用于材料变异系数大和要求精度高的随机结构分析。 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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《Mechanical Systems and Signal Processing》2014,42(1-2):115-128
In this paper, we newly propose a fast computation method for the nonlinear transient responses including coupling between nonlinear springs and sound proof structures having porous materials using FEM. In this method, we extend our numerical method named as Modal Strain and Kinetic Method (i.e. MSKE method proposed previously by Yamaguchi who is one of the authors) from linear damping analysis to nonlinear dynamic analysis. We assume that the restoring force of the spring has cubic nonlinearity and linear hysteresis damping. To calculate damping properties for soundproof structures including elastic body, viscoelastic body and porous body, displacement vectors as common unknown variable are solved under coupled condition. The damped sound fields in the porous materials are defined by complex effective density and complex bulk modulus. The discrete equations in physical coordinate for this system are transformed into nonlinear ordinary coupled differential equations using normal coordinates corresponding to linear natural modes. Further, using MSKE method, modal damping can be derived approximately under coupled conditions between hysteresis damping of viscoelastic materials, damping of the springs and damping due to flow resistance in porous materials. The modal damping is used for the nonlinear differential equation to compute nonlinear transient responses.Moreover, using the proposed method, we demonstrate new vibration phenomena including nonlinear coupling between nonlinear springs and soundproof structures by use of a simplified model. As a typical numerical example of the soundproof structure, we adopt double walls with a porous material. The double walls are supported by nonlinear concentrated springs. We clarify influences of amplitude of the impact force on nonlinear transient responses. We focused on the vibration modes, which magnify the amplitudes of the double walls. In these modes, the internal air of the porous material played a role of a pneumatic spring. Under a very large impact force as a severe condition, there exist the complicated nonlinear couplings between these modes and the super harmonic components of the rigid modes of the whole structure with large deformations in the nonlinear springs. 相似文献
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For evaluation of measurement uncertainty for conducted emission measurements, we propose a new model which uses mixed distribution. Namely, evaluation of probability density function (PDF) for the measurand has been done using a Monte Carlo method and a modified least-squares method. As the Monte Carlo method required numerical calculation of approximate PDF values, pseudorandom number generator (PRNG) was developed for these requirements. For illustration, this work presents mixed distributions of two normal distributions, normal and rectangular distributions, and normal and also triangular distributions in case of conducted emission measurements. The results obtained by the Monte Carlo method and the modified least-squares method are compared to the corresponding results when applying the standard Guide to the Expression of Uncertainty in Measurement (GUM) procedure. 相似文献
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基于MATLAB综合的数值分析、矩阵计算和图形功能,对含液压挺杆气门机构的运动过程进行仿真。对于其常见的动力学模型———“多自由度集中质量-弹簧-阻尼模型”,按照牛顿第二定律及MATLAB仿真所规定的输入条件、步骤,导出适于MATLAB编程环境的数学模型,并据此编写模型的数值仿真计算程序,经过对气门机构关键参数———气门加速度计算结果与实测结果的比较,计算程序切实可行;此类模型的仿真方法及过程亦在文中作了介绍。 相似文献
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设计了一种用于四轮独立转向独立驱动电动轿车的独立悬架,该悬架采用双横臂、螺旋弹簧结构,悬架连接带轮毂电机的大质量电动车轮。对悬架系统进行简化,建立了悬架二自由度振动模型,采用均方根值分析方法,计算出振动系统的频率响应函数及振动响应的均方根值(包括车身加速度均方根值、车轮相对动载荷均方根值及悬架动挠度均方根值),基于悬架参数对电动车辆垂向性能的研究,提出了新型悬架弹簧刚度和减振器阻尼系数的设计方法,结合仿真及实验验证了设计方法的合理性。 相似文献
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Uncertainty modeling and predicting the probability of stability and performance in the manufacture of dynamic systems 总被引:2,自引:0,他引:2
Roger Fales 《ISA transactions》2010,49(4):528-534
In this work, a method for determining the reliability of dynamic systems is discussed. Using statistical information on system parameters, the goal is to determine the probability of a dynamic system achieving or not achieving frequency domain performance specifications such as low frequency tracking error, and bandwidth. An example system is considered with closed loop control. A performance specification is given and converted into a performance weight transfer function. The example system is found to have a 20% chance of not achieving the given performance specification. An example of a realistic higher order system model of an electro hydraulic valve with spring feedback and position measurement feedback is also considered. The spring rate and viscous friction are considered as random variables with normal distributions. It was found that nearly 6% of valve systems would not achieve the given frequency domain performance requirement. Uncertainty modeling is also considered. An uncertainty model for the hydraulic valve systems is presented with the same uncertain parameters as in the previous example. However, the uncertainty model was designed such that only 95% of plants would be covered by the uncertainty model. This uncertainty model was applied to the valve control system example in a robust performance test. 相似文献
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Most references on hydropneumatic suspension analysis regard it as harden Duffing spring and take the white noise as the system input, which is quite different from real physical model. It will introdu... 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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Eun-Ho Choi Jae-Bong Ryoo Jin-Rae Cho O.-Kaung Lim 《Journal of Mechanical Science and Technology》2010,24(1):323-330
At the concept design stage of an armored vehicle, most design effects focus on firing accuracy, mobility and physical properties
of the vehicle which are directly related to the firing power. This paper addresses an optimal design of the suspension unit
of a four-wheeled armored vehicle to maximize the mobility performance after firing, which is characterized by the stabilizing
time and the vertical acceleration of the driver’s seat after firing. For the numerical analysis and design, a half-car dynamic
model consisting of four degrees and four design variables, spring and damping coefficients of suspension and tire is constructed.
The response surface functions (RSFs) of both the stabilizing time and vertical acceleration are approximated through the
dynamic analysis of the four-degree half-car model. The objective function is defined by a weighted linear combination of
the stabilizing time and the vertical acceleration, and the resulting optimization of the vehicle mobility is carried out
by the PLBA algorithm. To support the validity of the proposed optimization procedure, illustrative numerical experiments
are also performed. 相似文献
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应用拉格朗日方程,建立轮椅车转向轮系统非线性动力学微分方程,运用ODE方法进行求解,并对此动力学模型线性化,进行稳定性分析;建立转向轮系统摆振试验台,对动力学模型进行实验验证,最后,应用基因遗传算法对转向轮系统参数进行优化设计,采用替换阻尼轴承的方法主动防范摆振。 相似文献