Investigation of mechanical properties of water-based friction modifier for railway applicationsRecherches des propriétés mécaniques du modificateur frottement dans une forme de l'émulsion d'eau applique dans les chemins de fer

This Note outlines the investigation of the water-based friction modifier used in railway technology. This investigation involves measurements made using a novel measuring stand, a new modelling of the modifier and the identification of its parameters using measured results. The proposed model of the modifier is composed of a dry friction slider, a dash-pot and a spring. The investigation contributes to a deeper understanding of the modifier's performance. To cite this article: J. Piotrowski, C. R. Mecanique 332 (2004).     

Confidence Judgments for Discriminations in Nonlinear Psychophysics

Psychophysical tasks requiring stimulus discrimination frequently report underconfidence; subjects think they are doing less accurately at discrimination or identification than is the case, measured in terms of probabilities of correct performance. An investigation to see if underconfidence is predictable from the intrinsic nonlinearities of the psychophysics, without assuming that confidence itself is a subjective analogue of a frequentist probability of correct identification, is explored using the algebra of cascaded nonlinear psychophysics previously developed.     

Simultaneous identification of stiffness and damping properties of isotropic materials from forced vibrating platesIdentification simultanée de rigidités et d'amortissements de matériaux isotropes à partir de plaques en vibrations forcées

This paper presents a novel methodology for the identification of damping of isotropic plates. It relies on forced inertial excitation of a clamped plate and full-field curvature measurements using a suitable optical technique. Using the Virtual Fields Method, it is shown that the damping parameter is easily related to the curvature field, even on a non-resonant plate. This paper opens a totally new field of investigation for damping identification. To cite this article: A. Giraudeau, F. Pierron, C. R. Mecanique 331 (2003).     

Experiments on crack identification in cantilever beams

In this paper we present an experimental investigation of the identification of crack location and size. By providing the first three natural frequencies through vibration measurements, curves of crack equivalent stiffness versus crack location are plotted, and the intersection of the three curves predicts the crack location and size. In the experiments, the cracked specimens were made using a wire-cut electrical discharge machine, and the cantilever beams were excited next to the free end by means of an impulse force hammer. In order to obtain the accurate natural frequencies from the transient signal measured, the method of zoom fast Fourier transform is adopted to improve frequency resolution. From experimental results, it is observed that the identification errors of crack location and size are less than 2% and 4%, respectively. The effectiveness of crack identification through vibration measurements is verified.     

Identification of material parameters for inelastic constitutive models: statistical analysis and design of experiments

In this paper we introduce stochastic methods to describe the influence of scattering test data on the identification of material parameters. We employ the viscoplastic constitutive model of Chan, Bodner, and Lindholm in its uniaxial form. The available test data result from three types of experiments performed at 600 °C on AINSI SS316 stainless steel, namely creep tests, constant strain rate tension tests with intermediate relaxation, and cyclic tension–compression tests. Each test has been performed with 12 specimens at different strain rates and stress rates respectively. However, for a serious statistical evaluation a larger number of experiments is required. In order to increase the number of tests we introduce stochastic simulations based on time series analysis which generate artificial data with the same stochastic behaviour as the experimental data. The method of stochastic simulation presents a widely accepted technique in engineering which does not add complexity to the process of parameter identification, but allows an investigation of the confidence in the fits of the material parameters. To keep the computation time for the identification of the material parameters as low as possible, very efficient numerical methods have to be implemented. The methods applied here for integration and nonlinear optimization are briefly introduced. The optimization strategy contains stochastic elements. Furthermore, we apply the method of statistical design of experiments to derive which combination of tests yields the most important information for an effective identification of material parameters.     

基于模态参数灵敏度的损伤方程组求解正则化方法研究

基于模态参数的结构损伤识别方法是振动损伤识别领域中应用最为广泛的方法.利用模态参数灵敏度构建结构损伤方程组,对其进行求解可以识别结构损伤位置和程度.由于实际工程中模态参数不完备性和噪声的影响,结构损伤方程易出现病态问题,直接求解可能产生错误的结果.为了解决这一问题,可以引入正则化方法进行求解.然而,各类正则化方法的基本...     

A comparative study on parameter identification of fluid viscous dampers with different models

Fluid viscous dampers are extensively adopted as efficient and cheap energy dissipation devices in structural seismic protection. If we consider the usefulness of these passive control devices, the exact recognition of their mechanical behavior is of outstanding importance to provide a reliable support to design a very efficient protection strategy. In scientific and technical applications, many different constitutive models have been proposed and adopted till now to represent fluid viscous dampers, with different levels of complexity and accuracy. This paper focuses on parameter identification of fluid viscous dampers, comparing different existing literature models, with the aim to recognize the ability of these models to match experimental loops under different test specimens. The identification scheme is developed evaluating the experimental and the analytical values of the forces experienced by the device under investigation. The experimental force is recorded during the dynamic test, while the analytical one is obtained by applying a displacement time history to the candidate mechanical law. The identification procedure furnishes the device mechanical parameters by minimizing a suitable objective function, which represents a measure of the difference between the analytical and experimental forces. To solve the optimization problem, the particle swarm optimization is adopted, and the results obtained under various test conditions are shown. Some considerations about the agreement of different models with experimental data are furnished, and the sensitivity of identified parameters of analyzed models against the frequency excitation is evaluated and discussed.     

连续体结构动力拓扑优化中局部模态处理的新方法

采用固体各向同性材料惩罚模型（solid isotropic material with penalization, SIMP） 进行动力拓朴优化通常在优化过程中会出现虚假的局部振动模态,为消除这种虚假模态产生的不利影响,提出了移频与虚假模态识别相结合的通用方法. 研究中考虑以材料体积为约束、结构基频最大化为目标的优化模型,并采用节点设计变量描述设计域内材料分布. 基于虚假模态的特性,首先在特征值分析中应用移频方法排除特征值接近于零的低阶虚假模态,然后再依据虚假模态识别准则判定并剔除其他可能存在的虚假模态,从而可以高效可靠地确定结构真实的固有振动模态. 数值算例表明,提出的方法可以有效地消除动力拓扑优化中虚假模态可能产生的不利影响,并保证优化解的可靠性.      

Stability of limit cycles in autonomous nonlinear systems

Periodical solutions or limit cycles (LC) comprise a significant family among the response types of nonlinear autonomous systems. Their identification and stability assessment is of a great importance during the analysis of an unknown system. A new analytical/iterative method of LC identification and portrait investigation was presented recently. The current study proposes a novel technique for their stability assessment. This strategy facilitates the distinction of stable and unstable LCs, thereby allowing the definition of attractive and repulsive response fields. A narrow toroidal domain is constructed around the LC, which is arithmetized by an orthogonal system that is positioned by tangential and normal vectors to the LC. The stability of the LC is investigated using the transformed differential system of the normal components of the response, which are functions of the coordinate along the LC trajectory. Exponential LC stability criteria are also proposed, which are based on the first degree of the perturbation procedure. Theoretical considerations are illustrated using single and two degree of freedom systems including demonstrations with specific systems. The strengths, future steps, and shortcomings of this method are evaluated.     

The Proper Orthogonal Decomposition, wavelets and modal approaches to the dynamics of coherent structures

We present brief précis of three related investigations. Fuller accounts can be found elsewhere. The investigations bear on the identification and prediction of coherent structures in turbulent shear flows. A second unifying thread is the Proper Orthogonal Decomposition (POD), or Karhunen-Loève expansion, which appears in all three investigations described. The first investigation demonstrates a close connection between the coherent structures obtained using linear stochastic estimation, and those obtained from the POD. Linear stochastic estimation is often used for the identification of coherent structures. The second investigation explores the use (in homogeneous directions) of wavelets instead of Fourier modes, in the construction of dynamical models; the particular problem considered here is the Kuramoto-Sivashinsky equation. The POD eigenfunctions, of course, reduce to Fourier modes in homogeneous situations, and either can be shown to converge optimally fast; we address the question of how rapidly (by comparison) a wavelet representation converges, and how the wavelet-wavelet interactions can be handled to construct a simple model. The third investigation deals with the prediction of POD eigenfunctions in a turbulent shear flow. We show that energy-method stability theory, combined with an anisotropic eddy viscosity, and erosion of the mean velocity profile by the growing eigenfunctions, produces eigenfunctions very close to those of the POD, and the same eigenvalue spectrum at low wavenumbers.Prepared for presentation at International Union of Theoretical and Applied Mechanics Symposium Eddy Structure Identification in Free Turbulent Shear Flows, Poitiers, France, 12–14 October 1992. Supported in part by: the U.S. Air Force Office of Scientific Research, The U.S. Office of Naval Research (Mechanics Branch and Physical Oceanography Program), and the U.S. National Science Foundation (program in Physical Oceanography).     

Experimental Observation of Chaotic Motion in a Rotor with Rubbing

This paper presents an application for chaotic motion identification in a measured signal obtained in an experiment. The method of state space reconstruction with delay co-ordinates with the dynamic evolution described by a map is used. Poincaré diagrams, correlation dimensions and Lyapunov exponents are obtained as tools for deciding about the existence of chaotic behaviour. The method is applied to measurements of the lateral displacement of a vertical rotor experiencing rubbing and in some signals chaos is observed. The work concludes that the possibility of chaotic motion is well determined with the observation of Poincaré diagrams and computation of Lyapunov exponents. Correlation dimensions computations, strongly influenced by noise, are not convenient tools for investigation of chaotic behaviour in signals generated by mechanical systems.     

大庆地区湿陷性黑土研究

大庆南部地区分布着一种颜色发黑、结构松散、成分复杂、对水极度敏感的工程性质极差的地质材料 ,它兼有湿陷性土、有机质土、碱土和分散土等诸多特殊土的劣质特性。通过野外调查、原位测试和室内各种试验研究 ,对这种黑土的野外特性、成分结构、物理力学性质、承载力和湿陷特性、地层年代等进行了较系统的阐述和分析 ,并通过综合比较 ,将其定名为湿陷性黑土.     

Input-output reduced-order modeling of unsteady flow over an airfoil at a high angle of attack based on dynamic mode decomposition with control

Due to the damage caused by stall flutter, the investigation and modeling of the flow over a wind turbine airfoil at high angles of attack are essential. Dynamic mode decomposition (DMD) and dynamic mode decomposition with control (DMDc) are used to analyze unsteady flow and identify the intrinsic dynamics. The DMDc algorithm is found to have an identification problem when the spatial dimension of the training data is larger than the number of snapshots. IDMDc, a variant algorithm based on reduced dimension data, is introduced to identify the precise intrinsic dynamics. DMD, DMDc and IDMDc are all used to decompose the data for unsteady flow over the S809 airfoil that are obtained by numerical simulations. The DMD results show that the dominant feature of a static airfoil is the adjacent shedding vortices in the wake. For an oscillating airfoil, the DMDc results may fail to consider the effect of the input and have an identification problem. IDMDc can alleviate this problem. The dominant IDMDc modes show that the intrinsic flow for the oscillating case is similar to the unsteady flow over the static airfoil. Moreover, the input–output model identified by IDMDc can give better predictions for different oscillating cases than the identified DMDc model.     

Identification,characterization and evolution of non-local quasi-Lagrangian structures in turbulence

The recent progress on non-local Lagrangian and quasi-Lagrangian structures in turbulence is reviewed. The quasi-Lagrangian structures, e.g., vortex surfaces in vis-cous flow, gas-liquid interfaces in multi-phase flow, and flame fronts in premixed combustion, can show essential Lagrangian following properties, but they are able to have topological changes in the temporal evolution. In addition, they can represent or influence the turbulent flow field. The challenges for the investigation of the non-local structures include their identification, characterization, and evolution. The improving understanding of the quasi-Lagrangian struc-tures is expected to be helpful to elucidate crucial dynamics and develop structure-based predictive models in turbulence.     

A boundary-field integral equation for analysis of cavity acoustic spectrum

The acoustic spectrum of cavities can be identified using integral equation formulations. Because of the transcendental dependence on frequency of the Green function, difficulties arise in calculating acoustic frequencies and modes of vibration when the Kirchhoff–Helmholtz boundary-integral operator is applied. This trouble is circumvented by the present, nonstandard, integral formulation that, by using the fundamental solution of the Laplace operator, allows the identification of acoustic spectra of cavities through solution of a standard eigenvalue problem. This formulation is compared both with that based on the Kirchhoff–Helmholtz operator and with an alternative integral approach introduced in the past that, akin to the one used here, analyzes cavity acoustics in terms of an eigenvalue problem. The numerical investigation deals both with a simple box-shaped cavity and with cavities related to applications of aeronautical interest.     

基于应力波传播机理的混凝土无损检测研究综述

混凝土结构在基础设施中应用广泛,但环境与荷载导致材料和结构的老化损伤问题,势必影响材料性能及耐久性和结构完整性及安全性.构建有效的混凝土材料性能评估和结构损伤识别体系是当前研究热点.现有研究因对应力波传播机理不深入理解、损伤定位定量模型理想化、损伤形式简化等问题仍存在局限性.因此,开发普适全面、稳定可靠的无损检测系统,对在建或既有混凝土结构服役状况进行长期、实时跟踪,具有重要学术意义和工程应用价值.本文结合混凝土无损检测领域的国内外研究现状及进展,从智能压电材料振动机理研究、混凝土无损检测方法发展、基于应力波的无损检测研究进展这三个逻辑层面,即按照研究手段到研究方法再到具体研究方案的顺序,循序渐进地对混凝土材料性能评估和结构损伤识别的研究进行了成果总结和方法提炼;基于此进一步概述了该领域所存在的瓶颈问题、研究重难点,最后提出了针对这些局限性的混凝土无损检测研究展望.     

Model of a fracture as an emitter of elastic vibrations

During the past two decades a new method has begun to be intensively developed for the investigation of fracture processes which is based on recording the mechanical vibrations generated by the defects of a medium [1]. The new method's problems include: extraction of a useful signal from the extraneous noises, identification of the type of defect, determination of its characteristic dimensions, and an estimate of the danger of the situation which has developed. The solution of the problems indicated has great meaning in such practical applications as nondestructive quality control and the engineering diagnostics of materials and manufactured goods. Therefore, the investigation of the spectrum of the signals produced by the formation of macroscopic fractures, such as the terminal and, consequently, most dangerous phase of fracture, is of great interest. The kinematical characteristics of a fracture as an emitter of elastic vibrations are formulated in this paper. The spatial and time spectra of the dynamical motions caused by the appearance of a growing fracture in a thin plate are discussed. Relationships are derived between the spectral characteristics of propagating disturbances and the parameters of the fracture.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 160–166, March–April, 1976.The author thanks L. I. Slepyan for valuable discussion and attention to this research.     

Nonlinear Frequency Response of Nonisothermal Adsorption Systems

A general method for the investigation of adsorption kinetics of nonlinear,nonisothermal systems, based on frequency response analysis, ispresented. It is based on the definition of higher-order frequency response functions (FRFs) on the adsorber and on the particle level. FRFs on the adsorber level can be estimated from experimentally measuredadsorber FR and used to calculate FRFs on the particle level,which can be further used for model identification, by comparison withtheoretical particle FRFs. The general procedure for calculation of particle FRFs from those of adsorber is given. Also, the generalprocedure for theoretical derivation of particle FRFs is given andillustrated with an example of nonisothermal adsorption governed bymicropore diffusion and film resistance heat transfer, as well as theprocedure for calculating unmeasured adsorber FRFs, which isillustrated with an example of a batch adsorber with volume modulation.