An alternative to modal analysis for material stiffness and damping identification from vibrating plates

This paper presents an alternative to modal analysis to extract stiffness and damping parameters from thin vibrating plates. Full-field slope measurements are performed through a deflectometry technique on a plate vibrating at a given frequency. Images are recorded in phase and at π/2 lag from the excitation. From this information, deflection fields are computed by integration and curvature fields are obtained by differentiation. This information is then input into the principle of virtual work to extract both stiffness and damping parameters. This procedure, known as the Virtual Fields Method, is detailed in the paper and the notion of special optimized virtual fields is extended to the present problem. Validation on simulated data is performed before moving to experimental data. One of the main advantages of this technique is that it is completely insensitive to the damping coming from the boundary conditions. This is illustrated experimentally on two tests where a viscoelastic layer and rubber washers are added in the experimental set up.     

Determining the tensile response of materials at high temperature using DIC and the Virtual Fields Method

An experimental approach based on Digital Image Correlation (DIC) is successfully applied to predict the uniaxial stress-strain response of 304 stainless steel specimens subjected to nominally uniform temperatures ranging from room temperature to 900 °C. A portable induction heating device equipped with custom made water-cooled copper coils is used to heat the specimen. The induction heater is used in conjunction with a conventional tensile frame to enable high temperature tension experiments. A stereovision camera system equipped with appropriate band pass filters is employed to facilitate the study of full-field deformation response of the material at elevated temperatures. Using the temperature and load histories along with the full-field strain data, a Virtual Fields Method (VFM) based approach is implemented to identify constitutive parameters governing the plastic deformation of the material at high temperature conditions. Results from these experiments confirm that the proposed method can be used to measure the full field deformation of materials subjected to thermo-mechanical loading.     

用虚量子理论研究重离子束—靶相互作用

本文将虚量了理论用于重离子束与靶相互作用过程中靶原子的Ｋ壳层电子的离子化以及入射重离子的Ｋ壳层电子的激发与离化，这一简单模型所提供的理论结果与实验符合得很好。     

On the interaction between ultrasound waves and bubble clouds in mono- and dual-frequency sonoreactors

Since the last decades, extensive work have been done on the numerical modeling of mono-frequency sonoreactors, we here consider the modeling of dual-frequency sonoreactors. We first present the basic features of the CAMUS code (CAvitating Medium under UltraSound), for mono-frequency excitation. Computation at low, medium and high frequency are presented. Extension of the numerical tool CAMUS is also presented: Caflisch equations are modified to take into account the dual-frequency excitation of the sound. We consider 28–56, 28–100 and 28–200 kHz sonoreactors. Fields of cavitation bubble emergence are quite different from the ones under mono-frequency. Study of spatio-temporal dynamics of cavitation bubbles in a 28–56 kHz sonoreactor is also considered. Taking into account the pressure field induced by the dual-frequency wave propagation, we compute the Bjerknes force applied on the cavitation bubble that is responsible for the bubble migration. A two phase flow approach allows to compute the bubble migration.     

A comparison of DIC and grid measurements for processing spalling tests with the VFM and an 80-kpixel ultra-high speed camera

During the last decades, the spalling technique has been more and more used to characterize the tensile strength of geomaterials at high-strain-rates. In 2012, a new processing technique was proposed by Pierron and Forquin [1] to measure the stress level and apparent Young’s modulus in a concrete sample by means of an ultra-high speed camera, a grid bonded onto the sample and the Virtual Fields Method. However the possible benefit to use the DIC (Digital Image Correlation) technique instead of the grid method has not been investigated. In the present work, spalling experiments were performed on two aluminum alloy samples with HPV1 (Shimadzu) ultra-high speed camera providing 1?Mfps maximum recording frequency and about 80?kpixel spatial resolution. A grid with 1?mm pitch was bonded onto the first sample whereas a speckle pattern was covering the second sample for DIC measurements. Both methods were evaluated in terms of displacement and acceleration measurements by comparing the experimental data to laser interferometer measurements. In addition, the stress and strain levels in a given cross-section were compared to the experimental data provided by a strain gage glued on each sample. The measurements allow discussing the benefit of each (grid and DIC) technique to obtain the stress-strain relationship in the case of using an 80-kpixel ultra-high speed camera.     

非圆化磨耗激励下高速列车转向架区域噪声边频带产生机理及影响

该文通过对车辆噪声和车轮非圆化磨耗开展跟踪测试和分析,发现存在车轮非圆化磨耗的列车在运行过程中,其转向架区域噪声窄带频谱上会出现了以非圆化磨耗激励频率为中心,以过轨枕频率为间隔等间距分布的噪声峰值(即噪声边频带).这使得车轮非圆化磨耗不仅会影响其激励频率处的列车轨道结构的振动和噪声,还会对其他频段的噪声产生重要影响.为...     

基于抖动测试的AFDX端到端延迟紧性修正

AFDX引入虚拟链路(Virtual Link)实现物理带宽资源的逻辑分隔。由于数据帧的异步到达和多路复用输出造成虚拟链路的时延抖动现象,并最终导致流量端到端延迟分析的不确定性。本文提出了一种基于抖动测试值的网络演算紧缩方法。通过分布式测试,获得虚拟链路在网络中的实际传输抖动,并以此为基础,建立了流量传输精确化模型,通过流量模型的逐级修正,使端到端延迟计算结果逐级精确化。通过将抖动实际值与理论分析结果相结合,提供了网络演算悲观度及其扩散影响度量的直观对比,提高了延迟计算的紧性。     

Prediction of Outdoor Noise Propagation Induced By Single-Phase Power Transformers

Outdoor power transformers are one of the most pervasive noise sources in power transmission and distribution systems. Accurate prediction of outdoor noise propagation plays a dominant role for the evaluation and control of noise relevant to the transformer stations. In this paper surface vibration tests are carried out on a scale model of a single-phase transformer tank wall at different excitation frequencies. The phase and amplitude of test data are found to be randomly distributed when the excitation frequency exceeds the seventh mode frequency, which allows the single-phase power transformer to be simplified as incoherent point sources. An outdoor-coherent model is subsequently developed and incorporated with the image source method to investigate noise propagation from single-phase power transformers, due to the occurrence of multiple reflections and diffractions in the propagation path of each point source. The proposed model is used to calculate the sound field of the power transformer group by exploiting the additional phase information. In comparison with the ISO9613 model and the boundary element method, it is found that the proposed coherent image source method leads to more accurate prediction results, and hence better performance for the prediction of the outdoor noise induced by single-phase power transformers.     

Penetration of Accelerated Multivalent Ions through a System of Parallel Thin Films

Fields of polarization that appear during the penetration of multiply charged ions through ultrathin nanomembranes are calculated by means of classical electrodynamics. The ponderomotive forces generated by these fields are able to press pores out of membranes. The dimensions of the penetrating ions’ wave packets determine the sizes of these pores. Calculations describe the experimental data on penetration through one film and through a system of four parallel films.     

菌紫质光致各向异性动力学的理论和实验

对菌紫质(Bacteriorhodopsin,BR)薄膜的光致各向异性特性进行了理论模拟.由随机取向的极性BR分子构成的聚合物薄膜在宏观上是各向同性的,但在线偏振光的作用下,BR分子对激发光的选择性吸收,导致不同异构体分子取向的不均匀分布,从而使BR薄膜在宏观上呈现出各向异性.利用BR光循环的二能级模型,得到了B态分子取向分布随时间的变化关系,推导出了BR薄膜光致各向异性动力学的数学表达式,模拟了不同激发光强下BR薄膜的光致各向异性动力学曲线,得到了和实验结果一致的计算结果.     

Comparison of moments and couple-generating forces near discontinuities in structural-acoustic systems

In modeling vibration isolators in structural-acoustic systems, the isolator's dynamic properties are often treated as acting only in the axial direction as moments are often neglected. Furthermore, the size, or scale, of the isolator is often neglected and the isolator is assumed to act at single points on the connected structures. Previous work has shown that concentrated moments can be particularly important when located near a fixed support or a structural discontinuity. This research extends that work to examine the importance of moment scale effects for a system containing a distributed structural discontinuity with its own scale. Moment scale effects are examined by determining the difference in radiated acoustic power for a simple system that is excited by a couple-generating distributed force and a concentrated moment. The distributed force produces a couple that is equivalent to the concentrated moment. As a result, only the scale is being examined. Particular interest occurs when the excitation is located near the structural discontinuity. Based on the cases studied here, moment scale is shown to be important at lower frequencies when the excitation is located near the edges of the discontinuity. At higher frequencies, any overlap of the excitation and discontinuity may warrant the need to consider moment scales.     

High quality non-blind image deconvolution using the Fields of Experts prior

In this paper, we propose a non-blind image deconvolution method under Bayesian probabilistic framework. A robust prior, i.e., the Fields of Experts (FoE) prior which is learned from natural images is adopted to regularize the latent image. To solve the resulted optimization problem, the Split Bregman algorithm is utilized. We use a data set to verify the effectiveness of the proposed approach. Experimental results show that the restored images are of higher quality than that of some state of the art algorithms.     

运载火箭飞行力学环境虚拟试验及可视化系统设计与实现

运载火箭的飞行力学环境随着飞行过程不断发生变化,而当前无论是基于实物试验还是基于数值分析,火箭的飞行力学环境分析大多针对特定飞行状态和工况而无法给出动态变化信息,因此开展了飞行力学环境虚拟试验及可视化技术研究。基于特征代理模型采用Fortran语言设计了场数据快速预测算法,在采样数值仿真的基础上实现了火箭在大气飞行过程中的动态气动力与气动热环境虚拟试验;采用C++开发了实时分站载荷算法,实现了火箭飞行期间的载荷环境虚拟试验。开发了与运载火箭飞行仿真配合的总线通信接口,并基于EnSight开发了分布式动态可视化系统,通过共享内存的进程间通信方式实现了飞行力学环境的动态显示。结果表明,该系统可以给出火箭飞行力学环境的全局和关注点信息的动态变化,为飞行力学环境精细化分析和直观可视化研究提供了手段。     

Direct observation of optical excitation transfer based on resonant optical near-field interaction

This article reports the direct observation of long-distance optical excitation transfer based on resonant optical near-field interactions in randomly distributed quantum dots (QDs). We fabricated optical excitation transfer paths based on randomly distributed QDs by using CdSe/ZnS core?Cshell QDs and succeeded for the first time in obtaining output signals resulting from a unidirectional optical excitation transfer length of 2.4???m. Furthermore, we demonstrate that the optical excitation transfer occurs via the resonant excited levels of the QDs with a comparative experiment using non-resonant QDs. This excitation-transfer mechanism allows for intersecting, non-interacting nano-optical wires.     

Controlled excitation of resonance self-oscillations in one-dimensional distributed systems

On the basis of the method of equivalent linearization combined with the method of moments, laws of self-oscillation excitation are obtained that provide the modes with maximum intensity of resonance (or quasi-resonance) oscillations in one-dimensional systems with distributed parameters. A restriction of a general type is imposed on the law of excitation. In the particular case of an integral quadratic restriction, the law of excitation leads to the generation of purely harmonic self-oscillations. The use of an extended (multiplicatively stabilizing) control provides the uniqueness and stability of the quasi-optimal mode of self-oscillation.     

A study on waviness induced vibration of ball bearings based on signal coherence theory

This paper focuses on the effects of waviness on vibration of ball bearings. An experimental analysis method is developed by adopting signal coherence theory of multiple-inputs/single-output (MISO) system. The inputs are waviness excitations of the inner and outer races, and the output is vibration response of the outer ring. Waviness excitation signals are first derived from the manufacturing deviations, and found to be strongly coherent in low frequency range. Virtual input signals are then introduced by the method of orthogonalization. In both cases of vibration acceleration and speed responses, the cumulated virtual input–output coherence function verifies that the first peak region of vibration spectrum is mainly induced by the waviness excitations. In order to distinguish the contributions of the inner and outer races, coherence functions of the virtual inputs with real inputs are calculated, and the results indicate that the outer race waviness contributes more to vibration than the inner race waviness does in the example. Further, a multi-body dynamic model is constructed and employed to frequency response analyses. It is discovered that the waviness induced spectral peak frequency is close to the natural frequency of bearing.     

The influence of the contact zone on the excitation of wheel/rail noise

Rolling noise is excited by surface roughness at the wheel/rail contact. The contact patch is known to attenuate the excitation at wavelengths that are short in comparison with its length. A distributed point-reacting spring (DPRS) model is used with measured roughness data to determine the contact filter effect, and this result is compared with analytical predictions. It is found that the analytical model gives an attenuation that is too large at short wavelengths but is usable for wavelengths down to somewhat smaller than the length of the contact patch. Additionally, variations in the detailed geometry of the profile can cause the contact point on the wheel and rail to oscillate laterally. This introduces an oscillating moment that can induce additional vibration and noise. The DPRS model and rolling noise prediction model are both extended and used together to allow an estimate of the contribution to the radiated noise. It is found that, while the direct roughness excitation is still more important, the moment excitation can be significant, particularly for conforming profiles.     

A new tool for the lamb-shift calculation

Zeitschrift für Physik C Particles and Fields - A summary is presented of analyses ofe + e ? annihilation data, some of which have been previously published and some of which are new....     

Autowaves in double-wire lines with the exponential-type nonlinear active element

The regimes corresponding to the appearance of localized excitation pulses in a nonlinear double-wire line with an exponential-type active element similar to that occurring in the distributed p-n junctions and nerve fibers are studied on the basis of exact solutions. It is shown that the line of this type is described by the nonlinear telegraph equation if there is a running inductance and by the one-dimensional nonlinear diffusion equation if it is absent. The main properties of the excitation waves and conditions for their appearance are examined.     

极点配置法弹性平板有源隔声系统优化

对混响声场中的弹性平板有源隔声系统进行优化。根据激励频率范围确定受控模态阶次,在模态空间中建立系统降阶方程,基于极点配置方法,采用分布式系统增加受控模态的阻尼,降低低频共振声传输。同时设计模态滤波器,为控制器提供所需的状态信息。为提高控制效能,本文对传感器和作动器布放位置进行优化,尝试不同极点配置方案,并对耦合控制与独立模态控制方法的隔声效果进行比较。仿真结果显示,极点配置法有源隔声可以有效降低共振声传输,优化布放和独立模态控制方式下,控制力明显降低。优化后的有源隔声系统效能有所提升。