动力总成液压悬置系统固有属性的拉普拉斯域分析方法

针对液压悬置随激振频率呈非线性变化的动刚度特性,采用了一种拉普拉斯域分析方法计算动力总成液压悬置系统的固有属性。首先,建立液压悬置的集中参数线性流体模型,分析悬置在低频段和高频段的稳态动刚度特性,而得到悬置的宽频动刚度表达式。接着建立悬置系统在曲轴坐标系下的振动模型,在拉普拉斯域内直接应用液压悬置的动刚度表达式推导系统固有属性的分析方法。最后采用这一新方法计算了某液压悬置系统的固有属性。结果显示,液压悬置系统具有复特征值和复模态向量。复特征值同时包含系统的固有频率和阻尼比信息;根据阻尼比、复模态向量的幅值等信息可对模态类型作出判断;结合复模态向量的相位信息可确定模态的具体形状。

基于时域加权的拉普拉斯—频率域弹性波全波形反演

弹性波全波形反演是强非线性问题,极易因为对初始模型精度或记录的低频成分的强烈依赖性而陷入局部极小,导致反演失败。为此,建立了一种基于时域加权的拉普拉斯—频率域弹性波全波形反演方法。首先在结合了两种域各自优势的时间—频率域弹性波全波形反演基础上,通过引入拉普拉斯衰减因子降低了全波形反演对于低频成分的依赖性,形成了兼具三种域优势的时间—拉普拉斯—频率域弹性波全波形反演方法,并且通过时域加权记录这一灵活多变的形式消除了拉普拉斯衰减因子所带来的负面影响。模型试算结果表明,在缺失低频成分的情况下,该方法能够得到较精确的反演结果,对初始模型的依赖性较低。

指数型阻尼模型复模态更新及阻尼矩阵识别

提出了在模态测试的基础上识别得到指数型非粘滞阻尼系统中阻尼系数矩阵的方法.通过求解一个带约束最优化问题,得到满足系统特征方程的最优修正阻尼系数矩阵.考虑了实际模态测试中得到的模态参数的非完备性,可以利用有限的低阶模态,较为准确地识别出系统的阻尼系数矩阵,但随着系统的非粘滞阻尼特性逐渐增强时,想要精确识别出阻尼系数矩阵所需要的模态数目会逐渐增加.同时,进一步考虑到模态测试中复模态的虚部受噪声影响较大,提出了阻尼矩阵识别过程中对复模态虚部进行更新的方法,使之满足指数型阻尼系统特征方程,且利用上述方法得到的复模态虚部,能较为精确地识别出阻尼系数矩阵.由于目前对松弛因子识别的研究较少,在模态更新方法的基础上提出了不依赖于复模态虚部的松弛因子识别公式,并通过数值算例,验证了指数型非粘滞阻尼模型的阻尼识别方法及复模态更新方法的适用性和有效性,及松弛因子识别的准确性.最后通过悬臂梁的振动测试进行模态参数识别,并讨论了指数阻尼模型的适用性和合理性.

A Semi-Analytical Approach to Green＇s Functions for Problems in Multiply-Connected Regions on a Spherical Surface

This work aims at potential fields generated by point sources in conductive perforated fragments of spherical shells. Such fields are interpreted as profiles of Green＇s functions of relevant boundary-value problems stated in multiply-connected regions for Laplace equation written in geographical coordinates. Those are efficiently computed by a modification of the method of functional equations, with closed analytical forms preliminary obtained for Green＇s functions for the corresponding simply-connected regions.

The existence and concentration of weak solutions to a class of p-Laplacian type problems in unbounded domains

In this paper,we study the existence and concentration of weak solutions to the p-Laplacian type elliptic problem-εp△pu+V(z)|u|p-2u-f(u)=0 in Ω,u=0 on ■Ω,u>0 in Ω,N>p>2,where Ω is a domain in RN,possibly unbounded,with empty or smooth boundary,εis a small positive parameter,f∈C1(R+,R)is of subcritical and V:RN→R is a locally Hlder continuous function which is bounded from below,away from zero,such that infΛV<min ■ΛV for some open bounded subset Λ of Ω.We prove that there is anε0>0 such that for anyε∈(0,ε0],the above mentioned problem possesses a weak solution uεwith exponential decay.Moreover,uεconcentrates around a minimum point of the potential V inΛ.Our result generalizes a similar result by del Pino and Felmer(1996)for semilinear elliptic equations to the p-Laplacian type problem.

Leak detection in pipelines by exclusively frequency domain method

A further development of exclusively inverse frequency domain method for leak detection in pipelines is presented and validated.The location and leakage can be determined by analyzing the difference of transient water head response between the simulated and measured data in frequency domain.The transient signals are generated by portion sharp closure of a valve from the small constant opening and it needs only a few meters of water.The discrete boundary conditions and observation data are both transformed in frequency domain by Laplace transform.Example in numerical simulation is studied for demonstration of this approach.The application of the method to an experimental pipeline confirms the analysis and illustrates successful detection of the single pipeline leak.The precalibration approach is presented to minimize the effect of data and model error and it splits the method into two parts.One uses data from a known state to fit the parameters of the model and the other uses data from the current state for the fitting of leak parameters using the now calibrated model.Some important practical parameters such as wave speed,friction in steady and unsteady state and the adaptability of the method are discussed.It was found that the nonlinearity errors associated with valve boundary condition could be prevented by consideration of the induced flow perturbation curve shape.

Regional gravity field modeling based on rectangular harmonic analysis

Regional gravity field modeling with high-precision and high-resolution is one of the most important scientific objectives in geodesy, and can provide fundamental information for geophysics, geodynamics, seismology, and mineral exploration. Rectangular harmonic analysis （RHA） is proposed for regional gravity field modeling in this paper. By solving the Laplace＇s equation of gravitational potential in local Cartesian coordinate system, the rectangular harmonic expansions of disturbing potential, gravity anomaly, gravity disturbance, geoid undulation and deflection of the vertical are derived, and so are the formula for signal degree variance and error degree variance of the rectangular harmonic coefficients （RHC）. We also present the mathematical model and detailed algorithm for the solution of RHC using RHA from gravity observations. In order to reduce the edge effects caused by periodic continuation in RHA, we propose the strategy of extending the size of computation domain. The RHA-based modeling method is validated by conducting numerical experiments based on simulated ground and airborne gravity data that are generated from geopotential model EGM2008 and contaminated by Gauss white noise with standard deviation of 2 mGal. The accuracy of the 2.5＇×2.5＇ geoid undulations computed from ground and airborne gravity data is 1 and 1.4 cm, respectively. The standard error of the gravity disturbances that downward continued from the flight height of 4 km to the geoid is only 3.1 reGal. Numerical results confirm that RHA is able to provide a reliable and accurate regional gravity field model, which may be a new option for the representation of the fine structure of regional gravity field.