Optimum design of linear tuned mass dampers for structures with nonlinear behaviour

This paper investigates the optimum design of tuned mass dampers (TMDs) for the seismic protection of inelastic structures. A single linear TMD is treated and is assumed to be applied to a single nonlinear degree of freedom system, described by the Bouc–Wen hysteretic model. The seismic load is modelled by a stationary filtered stochastic process to consider its intrinsic stochastic nature. The optimization problem is set by taking into consideration three different possible objective functions (OFs): the maximum of the peak structural displacement standard deviation, the average hysteretic dissipated energy of a protected building with reference to an unprotected one, and a functional damage that considers the two indexes previously described. Different numerical examples and parametric analysis are shown to confront the three optimization criteria and to determine the best tuning frequency and damping ratio of the TMDs to be used in the structure. Results confirm that the application of a TMD system reduces the amount of the hysteretic dissipated energy, which is a direct measure of damage in the structure, and so it is beneficial for the protection of buildings that develop a nonlinear behaviour under severe dynamic loadings.     

Velocity profile effects in Coriolis mass flowmeters: Recent findings and open questions

The aim of this paper is to discuss velocity profile effects in Coriolis flowmeters and to review related research work. The measurements made by Coriolis flowmeters are dependent upon the steady flow velocity distribution within them whenever certain features of the fluid vibrational fields are not uniform inside the measuring tube. This dependence is confirmed by simulation results on two straight tube configurations, one operating in a beam-type mode and the other in a shell-type mode. Findings to date and open questions regarding velocity profile effects in Coriolis flowmeters are discussed for both fully developed and disturbed inlet flow conditions.     

Effect of streamwise and preferential diffusion on cylindrical Burke-Schumann flames

Effect of streamwise and preferential diffusion on cylindrical Burke-Schumann flame has been analyzed using perturbation method and Green’s function technique. Results show that for large Peclet number, streamwise diffusion has little effect, while for small Pe, it is balanced with radial diffusion such that a finite minimum flame height exists. Preferential diffusion induces flame temperature variation along the flame surface and the results agree qualitatively with existing experimental data. It also shows that the symmetry in flame temperature variation by the sign of (Le-1) in two dimensional case does not hold in cylindrical flames due to focusing and defocusing effects of mass and thermal diffusion by the radial curvature of flame.     

采用线性求角的旋变轴角解码与激磁系统

设计了一种基于单片DSP的旋变轴角解码与激磁系统并进行了实验验证.由于轴角解码中反正切运算需要很大运算量或很多数据空间存储查表值,甚至需要外扩存储芯片,因此,提出一种反正切运算补偿成分区间的线性运算求角方法.同时,在保证测角精度的基础上降低旋变激磁的电压幅值,从而实现了旋变轴角解码与激磁系统的高集成度与低功耗.实验结果显示:测角精度可达0.013°,框架电机速率精度达到0.000 4°/s.体积、质量、功耗与原激磁电源模块JD20-D15C36MK和轴角解码模块19XSZ2413相比均减少80%以上,很好地满足了航天应用小体积、轻质量和低功耗的要求.     

Scheduling problems with the nonlinear effects of learning and deterioration

In this paper, we present both nonlinear job deterioration and nonlinear learning which exist simultaneously. Job deterioration and learning co-exist in many realistic scheduling situations. By the effects of learning and deterioration, we mean that the processing time of a job is defined by the increasing function of its execution start time and position in the sequence. The following objectives are considered: single-machine makespan and sum of completion times (square) and the maximum lateness. For the single-machine case, we derive polynomial time optimal solutions. For the case of an m-machine permutation flowshop, we present polynomial time optimal solutions for some special cases of the problems to minimize makespan and total completion time.     

An investigation on effects of traveling mass with variable velocity on nonlinear dynamic response of an inclined Timoshenko beam with different boundary conditions

In this paper, the nonlinear dynamic response of an inclined Timoshenko beam with different boundary conditions subjected to a traveling mass with variable velocity is investigated. The nonlinear coupled partial differential equations of motion for the bending rotation of cross-section, longitudinal and transverse displacements are derived using Hamilton’s principle. These nonlinear coupled PDEs are solved by applying Galerkin’s method to obtain dynamic response of the beam under the act of a moving mass. The appropriate parametric studies by taking into account the effects of the magnitude of the traveling mass, the velocity of the traveling mass with a constant acceleration/deceleration and effect of different beam’s boundary conditions are carried out. The beams’ large deflection has been captured by including the stretching effect of its mid-surface. It was seen that the existence of quadratic-cubic nonlinear terms in the governing coupled PDEs of motion renders hardening/stiffening behavior on the dynamic responses of the beam when traversed by a moving mass. In addition, the obtained nonlinear results are compared with those from the linear analysis.     

基于线性求角的旋变轴角解码与激磁系统研究

控制力矩陀螺(CMG)是空间站等大型航天器姿态控制的关键执行机构,旋转变压器（旋变）是CMG框架伺服系统的常用测角部件,由于大多数旋变激磁模块和轴角解码模块不满足航天应用小体积、轻重量和低功耗的要求,本文提出一种基于单片DSP的旋变轴角解码与激磁系统设计方法并进行了实验验证。轴角解码中反正切运算需要很大运算量或很多数据空间存储查表值,甚至需要外扩存储芯片,因此本文提出一种线性求角方法,其思想是把反正切运算补偿成分区间的线性运算;同时在保证测角精度的基础上降低旋变激磁的电压幅值,从而实现了整个伺服系统的高集成度与低功耗。实验结果显示：体积、重量、功耗与原激磁电源模块JD20-D15C36MK和轴角解码模块19XSZ2413相比均减少80%以上,测角精度可达0.011º,框架电机运转平稳。     

Computer-controlled susceptometer for investigating the linear and nonlinear dielectric response

A fully automatized alternating current (ac) susceptometer is constructed for simultaneous measurements of the phase resolved complex linear and complex nonlinear ac susceptibilities of lossy and dispersive dielectric materials. This relatively simple setup allows measurements over a wide range of experimental variables, such as ac amplitudes up to 40 V, frequencies from 10(-2) to 10(3) Hz, and temperatures from 100 to 600 K utilizing only current/voltage and analog/digital converters and a personal computer. In contrast with the commonly used analysis of the charge accumulated on a standard capacitor in series with the sample our method is based on the analysis of the current flowing directly through the sample. Absence of any capacitive voltage dividers in the measurement circuit eliminates uncontrolled phase shifts. This is why the instrument provides high quality, nonlinear susceptibility data and in particular appears as a very convenient tool for discrimination between continuous and discontinuous phase transitions when determining the sign of the real part of the third order dielectric susceptibility.     

Simultaneous observation of acoustic resonance phenomena at both surfaces of a plate coated with thin layers

Acoustic resonance phenomena at the front and back surfaces of a plate coated with thin layers were successfully observed in the amplitude spectrum of the back surface echo. The amplitude ratio of spectra with and without layers takes its maximum and minimum values at the resonant frequencies of the front and back coatings and both frequencies can clearly be distinguished from each other. As an application, the thicknesses of the front and back coatings on a steel plate were measured simultaneously using their resonant frequencies, thus verifying the validity of the principle.     

Application of PIV measurement techniques to study the characteristics of flame–acoustic wave interactions

The present paper introduce the development of the experimental setup and measurement methodologies to study the structure of acoustic wave and the interaction between the acoustic fields and flame flow inside a square tube by using a time-resolved Particle Image Velocimetry (PIV). The design of signal synchronisation system, the selection of seeding particles, the test of seeding methods and the statistical analysis of the PIV data were introduced. The titanium dioxide (TiO₂) was selected as the seeding particle for the PIV. The accuracy of synchronisation system was checked by a simple experiment. A time-resolved PIV results showed that the acoustic velocity difference was less than 2.8% at specific phase angle over 1000 excitation cycles at an excitation frequency of 385 Hz. For the case of hot flame gas, the largest difference is 4.4% over 100 excitation cycles at an excitation frequency of 10 Hz. Results proves that the present experimental system has high reliability to measure and analyse the characteristics of flame–acoustic interactions.     

Online monitoring method of hydrate agglomeration in natural gas pipelines based on acoustic active excitation

Natural gas hydrate, which forms and agglomerates under the condition of low temperature and high pressure, can easily affect production or even lead to serious accidents. In order to prevent hydrate agglomeration in a pipeline, the industries generally add seriously excess inhibitor with experience, which causes serious environmental pollution and huge costs. However, due to the uncontrollable production and environmental conditions, hydrate plugging in a pipeline still occurs. According to the issues above, the method, for hydrate agglomeration online monitoring in a natural gas pipeline based on acoustic active excitation, has been presented in this paper. The method is to monitor and locate the hydrate agglomeration in a pipeline in order to take measures in time. Both the modeling and the experimental results show that the method can monitor and locate the hydrate agglomeration online at different locations with good accuracy.     

An experimental and mathematical study on the effects of ignition energy and system on the flame kernel development

A constant volume combustion chamber is used to investigate the flame kernel development of gasoline air mixtures under various ignition systems, ignition energies and spark plugs. Three kinds of ignition systems are designed and assembled, and the ignition energy is controlled by the variation of the dwell time. Several kinds of spark plugs are also tested. The velocity of flame propagation is measured by a laser deflection method, and the combustion pressure is analyzed by the heat release rate and the mass fraction burnt. The results represent that as the ignition energy is increased by enlarging either dwell time or spark plug gap, the heat release rate and the mass fraction burnt are increased. The electrodes materials and shapes influence the flame kernel development by changing he transfer efficiency of electrical energy to chemical energy. The diameter of electrodes also influences the heat release rate and the burnt mass fraction.     

伺服系统线性特性和非线性摩擦的解耦辨识方法研究

针对伺服进给机构包含线性结构和非线性摩擦特性的特点,提出一种将线性模型和非线性摩擦特性进行分步解耦辨识的方法.首先分别确定伺服系统的线性模型和非线性模型,将伺服系统结构模型转化为线性模型加非线性摩擦反馈的结构.为了消除非线性摩擦力对线性模型的影响,采用2路同向非过零速信号对系统激励,利用2组系统输入和输出信号的差值作为线性参数的辨识数据对线性参数进行估计.获得线性模型后进一步利用系统稳态输出实现对非线性Coulomb摩擦幅值特性的估计.系统仿真和实验都证明了该辨识方法对提高伺服系统的辨识精度及控制器设计的有效性和可靠性.     

The effects of spherical aberration on multiphoton fluorescence excitation microscopy

Multiphoton fluorescence excitation microscopy is almost invariably conducted with samples whose refractive index differ from that of the objective immersion medium, conditions that cause spherical aberration. Due to the quadratic nature of multiphoton fluorescence excitation, spherical aberration is expected to profoundly affect the depth dependence of fluorescence excitation. In order to determine the effect of refractive index mismatch in multiphoton fluorescence excitation microscopy, we measured signal attenuation, photobleaching rates and resolution degradation with depth in homogeneous samples with minimal light scattering and absorption over a range of refractive indices. These studies demonstrate that signal levels and resolution both rapidly decline with depth into refractive index mismatched samples. Analyses of photobleaching rates indicate that the preponderance of signal attenuation with depth results from decreased rates of fluorescence excitation, even in a system with a descanned emission collection pathway. Similar results were obtained in analyses of fluorescence microspheres embedded in rat kidney tissue, demonstrating that spherical aberration is an important limiting factor in multiphoton fluorescence excitation microscopy of biological samples.     

Effects of a one-way clutch on the nonlinear dynamic behavior of spur gear pairs under periodic excitation

Nonlinear behavior analysis was used to verify whether a one-way clutch is effective for reducing the torsional vibration of a paired spur gear system under periodic excitation. The dynamic responses were studied over a wide frequency range by speed sweeping to check the nonlinear behavior using numerical integration. The gear system with a one-way clutch showed typical nonlinear behavior. The oscillating component of the dynamic transmission error was reduced over the entire frequency range compared to a system without a one-way clutch. The one-way clutch also eliminated unsteady continuous jump phenomena over multiple solution bands, and prevented double-side contact, even with very small backlash. Installing a one-way clutch on both sides of the gear system was more effective at mitigating the negative effects of external periodic excitation and various parameter changes than a conventional gear system without a one-way clutch.     

Effect of the hereditary kernel on the solution of linear and nonlinear dynamic problems of hereditary deformable systems

A differential dependence between stresses and deformations is shown to be equivalent, even in the most general case, to integral dependences with regular hereditary kernels that have a serious disadvantage. Numerical results are presented that were obtained by solving dynamic problems of hereditary deformable systems using exponential and weakly singular hereditary kernels.     

Identification of the nonlinear excitation force acting on a bowed string using the dynamical responses at remote locations

For achieving realistic numerical simulations of bowed string instruments, based on physical modeling, a good understanding of the actual friction interaction phenomena is of great importance. Most work published in the field including our own has assumed that bow/string frictional forces behave according to the classical Coulomb stick-slip model, with an empirical velocity-dependent sliding friction coefficient. Indeed, the basic self-excited string motions (such as the Helmholtz regime) are well captured using such friction model. However, recent work has shown that the tribological behavior of the bow/string rosin interface is rather complex, therefore the basic velocity-dependent Coulomb model may be an over-simplistic representation of the friction force. More specifically, it was suggested that a more accurate model of the interaction force can be achieved by coupling the system dynamical equations with a thermal model which encapsulates the complex interface phenomena. In spite of the interesting work performed by Askenfelt [32], a direct measurement of the actual dynamical friction forces without disturbing the string motion is quite difficult. Therefore, in this work we develop a modal-based identification technique making use of inverse methods and optimization techniques, which enables the identification of the interface force, as well as the string self-excited motion, from the dynamical reactions measured at the string end supports. The method gives convincing results using simulated data originated from nonlinear computations of a bowed string. Furthermore, in cases where the force identifications are very sensitive to errors in the transfer function modal parameters, we suggest a method to improve the modal frequencies used for the identifications. Preliminary experimental results obtained using a basic bowing device, by which the string is excited with the stick of the bow, are then presented. Our identifications, from the two dynamical string reactions, are consistent as attested by the comparison of the two available versions of the string dynamical motion and of the friction force. Furthermore, the method seems adequate to investigate the interface force for the bowed string.     

直线型Sagnac光纤干涉仪声传感器及其去噪方法研究

光纤声传感器可广泛应用于能源和安防等重要领域,但其噪声复杂进而影响测量精度和稳定性,针对此问题,基于直线型光纤Sagnac干涉仪声传感系统,提出了一种改进小波阈值去噪方法,在此基础上,结合信号特征还设计了一种综合滤波方案,以提高系统语音探测质量。以实测语音信号为例,所提算法能将信号Allan方差值减小到824×10-14,而类间距判据值增大为691,有效改善了语音信号的质量。所提方法可广泛应用于声音传感领域,且对于光纤干涉仪声传感系统后期声源定位的准确性也具有重要意义。     

拉杆式压弯聚焦镜组件线性与接触非线性方法的比较

在压弯聚焦镜的工程分析中,采用接触非线性分析方法分析某些关键部位可提高分析精度,比以往只用线性分析得出的结果更接近实际情况。针对用线性分析方法分析所研究的对象求解误差较大,本文分析了系统产生非线性的主要因素。对某压弯聚焦镜组件进行了有限元建模,采用接触非线性分析方法对拉杆被拉弯时聚焦镜的响应进行了分析。对比非线性分析和检测结果可知,当压弯的矢高相等时,检测结果和非线性分析的斜率和半径误差在0.4μrad和5km范围内,基本满足要求。对比线性分析、非线性分析的结果和实验数据表明:采用非线性分析的结果更接近实际情况,完全可在误差允许的范围内模拟压弯机构的实际压弯情况。