Random vibration of hysteretic systems under Poisson white noise excitations

Hysteresis widely exists in civil structures,and dissipates the mechanical energy of systems.Research on the random vibration of hysteretic systems,however,is still insufficient,particularly when the excitation is non-Gaussian.In this paper,the radial basis function(RBF)neural network(RBF-NN)method is adopted as a numerical method to investigate the random vibration of the Bouc-Wen hysteretic system under the Poisson white noise excitations.The solution to the reduced generalized Fokker-PlanckKolmogorov(GFPK)equation is expressed in terms of the RBF-NNs with the Gaussian activation functions,whose weights are determined by minimizing the loss function of the reduced GFPK equation residual and constraint associated with the normalization condition.A steel fiber reinforced ceramsite concrete(SFRCC)column loaded by the Poisson white noise is studied as an example to illustrate the solution process.The effects of several important parameters of both the system and the excitation on the stochastic response are evaluated,and the obtained results are compared with those obtained by the Monte Carlo simulations(MCSs).The numerical results show that the RBF-NN method can accurately predict the stationary response with a considerable high computational efficiency.

EXACT SOLUTIONS FOR STATIONARY RESPONSES OF SEVERAL CLASSES OF NONLINEAR SYSTEMS TO PARAMETRIC AND/OR EXTERNAL WHITE NOISE EXCITATIONS

The exact solutions for stationary responses of one class of the second order and three classes of higher order nonlinear systems to parametric and/or external while noise excitations are constructed by using Fokkcr-Planck-Kolmogorov et/ualion approach. The conditions for the existence and uniqueness and the behavior of the solutions are discussed. All the systems under consideration are characterized by the dependence ofnonconservative fqrces on the first integrals of the corresponding conservative systems and arc catted generalized-energy-dependent f G.E.D.) systems. It is shown taht for each of the four classes of G.E.D. nonlinear stochastic systems there is a family of non-G.E.D. systems which are equivalent to the G.E.D. system in the sense of having identical stationary solution. The way to find the equivalent stochastic systems for a given G.E.D. system is indicated and. as an example, the equivalent stochastic systems for the second order G.E. D. nonlinear stochastic system are given. It is pointed out and illustrated with example that the exact stationary solutions for many non-G.E.D. nonlinear stochastic systems may he found by searching the equivalent G.E.D. systems.

Noise color influence on escape times in nonlinear oscillators-experimental and numerical results

The interplay between noise and nonlinearites can lead to escape dynamics.Associated nonlinear phe-nomena have been observed in various applications ranging from climatology to biology and engineering.For reasons of computational ease,in most studies,Gaussian white noise is used.However,this noise model is not physical due to the associated infinite energy content.Here,the authors present extensive experimental investigations and numerical simulations conducted to examine the impact of noise color on escape times in nonlinear oscillators.With a careful parameterization of the numerical simulations,the authors are able to make quantitative comparisons with experimental results.Through the experi-ments and simulations,it is illustrated that the noise color can drastically influence escape times and escape probability.

ON THE TWO BIFURCATIONS OF A WHITE-NOISE EXCITED HOPF BIFURCATION SYSTEM

The present work is concerned with the behavior of the second bifurcation of a Hopf bifurcation system excited by white-noise. It is found that the intervention of noises induces a drift of the bifurcation point along with the subtantial change in bifurcation type.

ON THE MAXIMAL LYAPUNOV EXPONENT FOR A REAL NOISE PARAMETRICALLY EXCITED CO-DIMENSION TWO BIFURCATION SYSTEM (Ⅱ)

For a co_dimension two bifurcation system on a three_dimensional central manifold, which is parametrically excited by a real noise, a rather general model is obtained by assuming that the real noise is an output of a linear filter system_a zeromean stationary Gaussian diffusion process which satisfies detailed balance condition. By means of the asymptotic analysis approach given by L. Arnold and the expression of the eigenvalue spectrum of Fokker_Planck operator, the asymptotic expansions of invariant measure and maximal Lyapunov exponent for the relevant system are obtained.

ON THE MAXIMAL LYAPUNOV EXPONENT FOR A REAL NOISE PARAMETRICALLY EXCITED CO_DIMENSION TWO BIFURCATION SYSTEM (Ⅰ)

For a real noise parametrically excited co_dimension two bifurcation system on a three_dimensional central manifold, a model of enhanced generality is developed in the present paper by assuming the real noise to be an output of a linear filter system, namely,a zero_mean stationary Gaussian diffusion process that satisfies the detailed balance condition. On such basis, asymptotic expansions of invariant measure and maximal Lyapunov exponent for the relevant system are established by use of Arnold asymptotic analysis approach in parallel with the eigenvalue spectrum of Fokker_Planck operator.

Identification of Modal Parameters with Linear Structure under Non-stationary Ambient Excitation

Empirical mode decomposition (EMD) is proposed to identify linear structure under non-stationary excitation,and non-white noise coefficient is introduced under the assumption of random signals consisting of white noise and non-white noise signals. The cross-correlation function of response signal is decomposed into mode functions and residue by EMD method. The identification technique of the modal parameters of single freedom degree is applied to each mode function to obtain natural frequencies, damping ratios and mode shapes. The results of identification of the five-degree freedom linear system demonstrate that the proposed method is effective in identifying the parameters of linear structures under non-stationary ambient excitation.

A kind of noise-induced transition to noisy chaos in stochastically perturbed dynamical system

We investigate a kind of noise-induced transition to noisy chaos in dynamical systems. Due to similar phenomenological structures of stable hyperbolic attractors excited by various physical realizations from a given stationary random process, a specific Poincar6 map is established for stochastically perturbed quasi-Hamiltonian system. Based on this kind of map, various point sets in the Poincar6＇s cross-section and dynamical transitions can be analyzed. Results from the customary Duffing oscillator show that, the point sets in the Poincare＇s global cross-section will be highly compressed in one direction, and extend slowly along the deterministic period-doubling bifurcation trail in another direction when the strength of the harmonic excitation is fixed while the strength of the stochastic excitation is slowly increased. This kind of transition is called the noise-induced point-overspreading route to noisy chaos.

MINIMIZING EXCITATION LIGHT LEAKAGE AND MAXIMIZING MEASUREMENT SENSITIVITY FOR MOLECULAR IMAGING WITH NEAR-INFRARED FLUORESCENCE

Near-infraredfluorescence(NIRF)imaging involves the separation of weakfluorescence signals from backscattered excitation light.The measurement sensitivity of current NIRF imaging systems is limited by the excitation light leakage through rejectionfilters.In this contribution,the authors demonstrate that the excitation light leakage can be suppressed upon using appropriatefilter combination and permutations.The excitation light leakage and measurement sensitivity were assessed and compared in this study by computing the transmission ratios of excitation to emission light collected and the signal-to-noise ratios in well-controlled phantom studies with differentfilter combinations and permutations.Using appropriatefilter combinations and permutations,we observe as much as two orders of magnitude reduction in the transmission ratio and higher signal-to-noise ratio.

Impact of field strength and RF excitation on abdominal diffusion-weighted magnetic resonance imaging

AIM:To retrospectively and prospectively compare diffusion-weighted(DW)images in the abdomen in a1.5T system and 3.0T systems with and without twochannel functionality for B1shimming.METHODS:DW images of the abdomen were obtained on 1.5T and 3.0T(with and without two-channel functionality for B1shimming)scanners on 150 patients(retrospective study population)and 10 volunteers(prospective study population).Eight regions were selected for clinical significance or artifact susceptibility(at higher field strengths).Objective grading quantified signal-to-noise ratio(SNR),and subjective evaluation qualified image quality,ghosting artifacts,anddiagnostic value.Statistical significance was calculated usingχ2tests(categorical variables)and independent two-sided t tests or Mann-Whitney U tests(continuous variables).RESULTS:The 3.0T using dual-source parallel transmit(dpTX 3.0T)provided the significantly highest SNRs in nearly all regions.In regions susceptible to artifacts at higher field strengths(left lobe of liver,head of pancreas),the SNR was better or similar to the 1.5T system.Subjectively,both dpTX 3.0T and 1.5T systems provided higher image quality,diagnostic value,and less ghosting artifact(P【0.01,most values)compared to the 3.0T system without dual-source parallel transmit(non-dpTX 3.0T).CONCLUSION:The dpTX 3.0T scanner provided the highest SNR.Its image quality,lack of ghosting,and diagnostic value were equal to or outperformed most currently used systems.

无轴泵喷叶片流激共振产生机理及其抑制

针对无轴泵喷异常高频梳状线谱噪声,本文研究了梳状线谱的产生原因及其噪声抑制特点。基于推进器实测噪声谱、振动谱梳状特征,初步定位梳状线谱与泵喷叶轮密切相关;进一步采用单向流固耦合分析方法,验证了无轴泵喷高频线谱来源于流激引起的叶轮面内2弯模态共振,并提出了一种在叶轮过流通道增设环筋以提高叶片支撑刚度的方案。流固耦合仿真及实测结果表明:带有环筋加强的泵喷叶轮对流激振动与噪声有明显抑制作用,梳状线谱噪声降幅达25.2~30.2 dB,且未向其他频段转移。

具有组分梯度的HgCdTe探测器在激光测量中的潜在应用

该文将组分梯度引入HgCdTe探测器结构设计中,提出了一种可以降低PN结附近热激发载流子浓度的方法。建立暗电流机制模型,分析高温下暗电流成份,分析结果表明,降低热激发载流子浓度对结区的影响是提高器件工作温度的关键。利用组分梯度在PN结附近构建不同的电场,不同电场下样品暗电流和噪声电流随温度的变化曲线表明,构建的电场越强,降低结区附近热激发载流子浓度的效果越明显。通过数据分析,提出构建103 V/cm量级的组分梯度内建电场可抑制热激发载流子向结区的扩散运动,有效地降低结区附近热激发载流子浓度。

基于IAAKF算法的结构激励识别与响应重构

针对传统卡尔曼滤波(Kalman filter,KF)算法实际应用于响应重构时,需要已知结构外部激励并预设先验恒定噪声方差的问题,提出了一种基于IAAKF(innovation-based adaptive augmented Kalman filter)算法的结构激励识别与响应重构方法。首先,基于增广状态空间模型将外部激励向量与状态向量联合构成增广状态向量,并根据增广新息统计特性实时自适应地调整卡尔曼滤波增益和状态估计误差协方差矩阵;其次,仅借助加速度传感器根据模态法来识别锤击激励,并且重构出加速度、速度、位移以及应变响应等数据;最后,对起重机桁架和简支梁分别进行数值模拟和试验分析。结果表明,所提方法能够有效地自适应调整噪声方差和识别结构外部激励,从而实现结构响应重构。

齿轮箱内部激励下振动噪声仿真研究

目的研究齿轮箱体在内部激励下的传动稳定性和振动噪声的产生、传播和辐射规律。方法考虑时变刚度、误差激励等因素对齿轮系统的影响,利用集中参数法建立齿轮传动纯扭转动力学模型。结合MATLAB数值计算,从动态啮合力入手,分析振动噪声在内部动态激励作用下的时域和频域特征。建立齿轮箱体有限元模型,进行模态分析和频率响应分析。以动力学分析结果为边界条件,分别利用声学无限元法和无反射边界法进行齿轮箱振动噪声仿真。结果获得了2000Hz内的固有频率、振型和频率响应曲线,结合振动峰值频率,对齿轮箱的振动情况进行了预测。得到了齿轮箱在无界声场中的辐射声功率级曲线、场点声压级曲线、声指向性和声压级云图,并对声学无限元法和无反射边界法的计算结果进行了对比,得到了二者的最佳适用条件。结论齿轮箱内部动态激励具有明显的周期性和冲击性,齿轮传动过程中含有较多的啮合频率和二倍频成分。齿轮箱上下表面为薄壁结构,振动比较明显,是各阶振型发生振动的主要部位。箱体在低阶模态下为单一振型,在高阶模态下出现多种振型耦合的现象。无限元法计算时间较长,但在近场分析时精度较高,适用于近场声学问题分析。无反射边界相比于无限元法耗费更少的计算时间,远场分析的精度更高,适用于高频、远场声学问题分析。

变截面压电悬臂梁能量采集器在高斯白噪声激励下的稳态统计特性研究

环境振动是一种非周期、随机的宽频激励,研究振动能量采集器在环境振动下的能量采集特性具有重要意义。本文采用改进随机平均法,求解了变截面压电梁在高斯白噪声激励下的等效振幅、位移、速度的稳态概率密度函数,位移与速度的联合概率密度函数以及稳态均方输出电压,随后研究了变截面压电梁的能量采集效能。结果表明:负载电阻一定时,截面系数β>0时的变截面压电梁相比β=0时的等截面压电梁有更好的稳态均方输出电压;截面系数β>0时,随着电阻电容乘积的倒数的增加,变截面压电梁的均方电压均呈现逐渐减小的趋势,当电阻电容乘积的倒数值一定时,β值越大,均方电压也越高;随着噪声强度的增加,变截面压电梁的均方电压均呈现逐渐增大的趋势,当噪声强度一定时,β值越大,均方电压也越高。本文研究结果可为变截面压电悬臂梁能量采集系统的设计及应用提供理论依据。

励磁电流对TMPS-HESM振动噪声影响的仿真分析

为了研究励磁电流对切向聚磁型并联结构混合励磁电机(TMPS-HESM)振动噪声的影响,根据TMPS-HESM切向聚磁特点,建立电机等效磁路模型和Maxwell有限元仿真模型,在不同励磁电流条件下仿真分析了与电机振动噪声有关的转矩脉动、气隙磁密和电磁力等电磁性能。利用ANSYS Workbench仿真平台搭建了电磁振动噪声耦合仿真模型,计算了不同励磁电流条件下电机的振动响应与噪声变化。结果表明:励磁电流对混合励磁电机转矩脉动影响较小,对电机径向电磁力谐波(8,2f1)、(16,4f1)、(0,12f1)分量影响较大,是造成电机振动噪声的主要原因,其中(0,12f1)分量虽然与其它分量不是一个数量级,但仍会恶化电机振动噪声。

动车组车内噪声OTPA分析研究

分析工作模式下的传递路径分析的原理和方法,利用激励点和目标点的响应分析,得到各激励源对响应点的贡献量,并在动车组中进行试验及数据分析验证。动车组转向架区域的牵引电机、齿轮箱、轴箱,设备舱区域的牵引电机、牵引风机、牵引变压器,以及车体表面的气动噪声为主要激励源,用客室端部噪声点作为目标响应点,较准确地计算出动车组激励源的噪声贡献量。该研究可为动车组的结构优化和减振降噪提供数据支撑。

基于量子行为粒子群算法的舱室噪声监测点优化布置

针对舱室噪声在线监测及声场预报问题,本文提出了一种基于量子行为粒子群算法的舱室内部声监测点优化布置方法。根据研究频段范围确定所需声腔模态阶数,计算全部备选监测点位置处各阶声腔模态的声场分布,采用模态置信矩阵作为目标函数,基于量子行为粒子群算法对监测点位置进行优化,获得优化布置方案。从声腔模态采样的正交性及内外声场响应的角度与其他测点布置方案进行了性能比较。研究表明:本文方法优化得到的测点布置方案采集声腔模态信息更全面,可有效提升舱室内声场的重建精度和基于舱室内声场监测的水下辐射噪声预报精度。

强噪声与非周期脉冲激励下单稳系统的随机共振及应用

随机共振是噪声背景下非线性系统对微弱特征信号的最优响应,能够对微弱特征信号进行增强。偏置单稳态系统相较于传统的双稳态系统,对非周期脉冲激励具有良好的共振特性。然而,非线性系统的参数影响系统的最优输出,对不同的非周期脉冲激励,系统难以自适应调节。针对上述问题,该研究强噪声与非周期脉冲激励下偏置单稳态自适应随机共振。首先,基于优化算法实现不同非周期脉冲激励下的自适应随机共振。然后,以强噪声背景下钢丝绳漏磁检测信号为应用对象,经偏置单稳态系统自适应随机共振输出后,以峰峰值作为损伤特征演化评价指标,评估不同微弱损伤特征间的差异。同时,应用偏置单稳态自适应随机共振法和自适应移位平均法对强噪声背景下钢丝绳漏磁信号进行对比分析,以峰峰值增益和信噪比增益为指标,结果表明偏置单稳态自适应随机共振法效果优于自适应移位平均法。最后,讨论了噪声强度对单稳态自适应随机共振的影响,发现偏置单稳态自适应随机共振具有较强的抗噪能力。

次级源和误差传感器布放对带弹性障板的充液直管声振复合有源控制的影响

针对充液管路系统噪声有源控制问题,研究了次级源和误差传感器布放对带弹性障板的充液直管管路系统有源消声与有源消振复合控制效果的影响。基于声固耦合方法建立了带弹性障板的充液直管管路系统的有限元模型,在声激励下对比了次级声源布放对系统有源消声性能的影响,并在组合激励下分析了次级力源、次级声源和误差传感器布放对系统复合有源控制的影响。结果表明,非对称分布的次级声源容易激起管壁振动,进而带动障板振动,导致有源消声效果不佳;采用对称分布的次级声源可使低频段的降噪量提高10 dB以上。复合有源控制可进一步提升全频段的控制效果。通过增加振动误差传感器数量,可使绝大多数频点的降噪量提高1∼20 dB不等。此外,在管壁上布放的两圈次级力源的间距小于管壁振动波长的1/4,且都不位于管壁振动节点附近时控制效果更好。