扬声器低频谐波失真的数值分析

扬声器作为一种非线性振动系统，在低频段仅考虑力学恢复力非线性可用经典的Duffing方程来描述；同时考虑恢复力和磁场非线性可用广义的Duffing方程来表征。Yoshinisa研究了仅含恢复力非线性扬声器低频非线性现象中的低频谐波失真现象，但对恢复力和磁场非线性同时存在的扬声器低频谐波失真问题未作研究。西方利用Matlab软件求解扬声器非线性振动系统的广义Duffing方程的数值解，又利用Spectra Plus频谱分析软件得到扬声器低频谐波失真与频率的关系曲线，通过分析低频谐波失真与频率的关系曲线，并着重讨论磁场的非线性对扬声器低频谐波失真的影响，得出一些有价值的结论。     

Predicting residual distortion of aluminum alloy stiffened sheet after friction stir welding by numerical simulation

Friction stir welding (FSW) has been widely applied in aluminum alloy manufacturing with its advantages of low residual stress and small deformation. But some FSW cases indicated that the residual distortion was still significant if a large size sheet be welded. In order to reduce the residual distortion of large aluminum alloy sheet after FSW, a general method adopted in this paper was that some stiffeners were designed on the sheet before it be welded. The process of FS-welded structure (sheet with stiffeners) was numerically simulated by finite element analysis (FEA) method. Based on the numerical simulation, the residual distortion of the structure was predicted and the effect of stiffeners was investigated. First, a three-dimensional FEA model was developed to analyze the welding process on a sheet, and the simulation results were verified by FSW experiments. Then, the verified model was applied on structure to compute residual distortion. The prediction displayed that the distortion pattern of structure was convex in longitudinal direction and concave in transversal direction after FSW. In simulation results, the distortion shape of structure was similar to that of sheet, but the distortion value of structure was much smaller. The comparison of simulation results showed that the residual plastic strain generated by FSW on the sheet and the structure was nearly the same, so the part of distortion which was reduced by stiffeners was the distortion induced by buckling.     

Measurement of harmonic losses in transformers supplyingnonsinusoidal load currents

The spread of the load control techniques based on power electronics is causing the increase of harmonic losses in power distribution systems. A digital method for the evaluation of these losses in power transformers, which only requires measurements taken at the transformer output terminals, is discussed. The accuracy of the method, along with the performance of a virtual-instrumentation-based instrument implementing it, is also discussed. The results of some experimental work are reported     

Wavelength response of harmonic distortion in AC-bias recording

Wavelength response of harmonic distortion in ac-bias recording is analyzed. The wavelength response is affected in both the record and playback processes. In the record process tape nonlinearity and magnetization phase shift, which is dependent on signal-field intensity, are taken into account. In the playback process, tape thickness, tape-to-head spacing, gap length, etc. axe taken into account. An approximate expression for the third-harmonic distortion is derived. The experimental data show quantitative agreement with theory.     

Numerical simulation of welding distortion in thin plates

A three-dimensional model based on the finite-element method is developed to simulate the temperature field and stress distribution in the welding and heat-affected zones during fusion welding of thin plates. The governing equations are solved using the SYSWELD program commercial code. The model’s predictions are tested and verified against the experiments. Angular distortion and longitudinal bending are measured, the results are compared with those obtained from the mathematical model, and a relatively good agreement between them is found. The verified model is used to evaluate the effects of various parameters on the temperature and stress distributions in the welding and heat-affected zones of a thin austenitic stainless steel plate.     

Predicting the total fatigue life in metals

When a metal specimen is subjected to cyclic loading, a large number of initiated cracks will initiate in its volume. The specimen forms a sample of initial cracks: the larger specimen, the larger is the sample. In previous work of the author it was shown that the fatigue limit can be predicted by estimating the largest expectable crack depth with the help of statistics of extremes. In this paper it is shown that the fatigue crack initiation time above the fatigue limit can be predicted in an analogous manner. Instead of estimating the largest crack size with the distribution of maxima, prediction of the shortest expectable initiation time is obtained using the distribution of minima. Good agreement with extensive set of experimental data was obtained.The presented method offers a new way for estimating the total fatigue life of a component. When estimates of the crack initiation life and the critical crack size are obtained, the stable crack growth can be computed using Paris law. The estimate of the total fatigue life is obtained as the sum of initiation and crack growth lives. A method for constructing design curves for finding the crack initiation life for any material is presented.     

基于数字图像相关法的薄板焊接变形研究

针对薄板焊接结构的大变形研究,目前采用数值模拟方法计算量大且误差较大,传统的应变片等测量手段无法实现焊缝处的在线密集测量。该文提出基于数字图像相关法的非接触检测方法对大型Q235薄板进行平板堆焊变形测量,重点研究热输入对薄板面内面外变形规律的影响。实验结果表明:基于数字图像相关技术的焊接变形测量方法能够在线、动态、全场获取薄板变形数据;随着热输入的增大,薄板的Z向面外变形及横向/纵向的面内变形也越大;冷却结束后,在焊缝处及热影响区内,薄板的纵向应变较小,而横向应变较大。热输入影响下的薄板焊接变形规律为揭示薄板焊接变形机理提供可靠的依据,为焊接结构件提供准确的制造数据。     

Predicting the effect of various ISA penetration grades on pedestrian safety by simulation

Intelligent speed adaption (ISA) is one type of vehicle-based intelligent transportation systems (ITS), which warns and regulates driving speed according to the speed limits of the roads. Early field studies showed that ISA could reduce general mean speed levels and their variances in different road environments. This paper studies the effects of various ISA penetration grades on pedestrian safety in a single lane road. A microscopic traffic simulation tool, TPMA, was further developed and used to implement different ISA penetration grades. Momentary spot speed and traffic flow data are first logged in the traffic simulation for later prediction of pedestrian safety. Then a hypothetical vehicle–pedestrian collision model is extended from early researches in order to estimate two safety indicators: probability of collision, and risk of death. Finally, Monte Carlo method is applied iteratively to compute those safety indices. The computational result shows that raising ISA penetration in traffic flow will reduce both the probability of mid-block collision between vehicle and pedestrian and the risk of death in the collision accidents. Furthermore, the decrease of the risk of death will be more prominent than that of the collision probability according to this method.     

Motion generation and virtual simulation in a digital environment

The growing complexity in product design and manufacturing processes has made virtual prototyping an important new approach that enhances products and process development. Considering the ergonomic issues evident in product lifecycles, digital human modelling (DHM) is adopted for virtual simulation and proactive evaluation. A motion generation from semantics (MGS) system is proposed in this research. The MGS system features include virtual prototyping, natural language instruction, a method time measurement (MTM) translator and motion generator. The system was implemented using product lifecycle management (PLM) software and validated in an automotive manufacturing company. The practice of intuitively generating manual operations and conducting virtual simulations enables the system planners to quickly respond to manufacturing process changes and recursively improve the tooling and process design flexibility and efficiency.     

微机和数字信号处理器模拟室内脉冲响应的音质仿真

音质仿真是模拟某一厅的听音效果，给人一种如身临其境的感受，本文用微机和数字信号处理器（ＴＭＳ３２０Ｃ２５Ｅ型）组成一个室内音质仿真系统，将试听声信号－预先在消声室内录制的“干”语声或标准语音磁带，输入进该系统，并让声信号模拟室内的脉冲响应，作时间延迟和大小衰减变化，即模拟直达声和随扣众多的反射声，最后送入耳机发声，使人感受到仿佛在实际厅堂中听音，全部过程采用微机控制并且做到了实时仿真。     

Predicting availability functions in time-dependent complex systems with SAEDES simulation algorithms

In this paper, we propose the use of discrete-event simulation (DES) as an efficient methodology to obtain estimates of both survival and availability functions in time-dependent real systems—such as telecommunication networks or distributed computer systems. We discuss the use of DES in reliability and availability studies, not only as an alternative to the use of analytical and probabilistic methods, but also as a complementary way to: (i) achieve a better understanding of the system internal behavior and (ii) find out the relevance of each component under reliability/availability considerations. Specifically, this paper describes a general methodology and two DES algorithms, called SAEDES, which can be used to analyze a wide range of time-dependent complex systems, including those presenting multiple states, dependencies among failure/repair times or non-perfect maintenance policies. These algorithms can provide valuable information, specially during the design stages, where different scenarios can be compared in order to select a system design offering adequate reliability and availability levels. Two case studies are discussed, using a C/C++ implementation of the SAEDES algorithms, to show some potential applications of our approach.     

Control of ion distortion in field asymmetric waveform ion mobility spectrometry via variation of dispersion field and gas temperature

Field asymmetric waveform ion mobility spectrometry (FAIMS) has emerged as an analytical tool of broad utility, especially in conjunction with mass spectrometry. Of particular promise is the use of FAIMS and 2-D ion mobility methods that combine FAIMS with conventional IMS to resolve and characterize protein and other macromolecular conformers. However, FAIMS operation requires a strong electric field, and ions are inevitably heated by energetic collisions with buffer gas molecules. This may induce ion isomerization or dissociation, which distort the separation properties of FAIMS (and subsequent stages) or reduce instrumental sensitivity. As FAIMS employs a periodic waveform, whether those processes are controlled by ion temperature at maximum or average field intensity has been debated. Here we address this issue by measuring the unfolding of compact ubiquitin ion geometries as a function of waveform amplitude (dispersion field, E(D)) and gas temperature, T. The field heating is quantified by matching the dependences of structural transitions on E(D) and T: increasing E(D) from 12 to 16 or from 16 to 20 kV/cm is equivalent to heating the (N2) gas by approximately 15-25 degrees C. The magnitude of field heating for any E(D) can be estimated using the two-temperature theory, and raising E(D) by 4 kV/cm augments heating by approximately 15-30 degrees C for maximum and approximately 4-8 degrees C for average field in the FAIMS cycle. Hence, isomerization of ions in FAIMS appears to be determined by the excitation at waveform peaks.     

An advanced digital filter for one-dimensional spectroscopic data: minimizing distortion in band shapes and band intensities

A wide variety of digital filters exist for processing one-dimensional (1D) signals; however, the application of some filters results in pronounced systematic distortions in band shapes and band intensities. In the present contribution, filtering is achieved by optimization in which a general objective function is constructed that possesses a number of desirable qualities, such as (1) smoothness of the resulting spectrum as well as (2) statistical constraints on the residual. Since the residual is explicitly used in the optimization, one can control systematic distortions and therefore avoid over-filtering. In tests using a variety of synthetic as well as real 1D spectroscopic data, the filter adequately preserves both band shapes and band intensities. In addition, the filter appears to accommodate homoscedastic, heteroscedastic, and frequency-dependent noise. Examples of its application and usefulness to powder X-ray diffraction (PXRD), Raman, and Fourier transform infrared (FT-IR) emission data are provided. Tests with synthetic data indicate that considerable noise reduction can be achieved in many applications. Finally, an iterative form of the filter is presented. This iterative form further minimizes distortions in band shapes and band intensities when very high levels of denoising are desired. The present filtering approach is an alternative to existing filters, particular when the quality of the residual is important to the user.     

On evaluation of the green functions for harmonic line loads in a viscoelastic half space

Comparison of different quadratures for evaluation of the improper wavenumber integrals which arise in evaluation of the Green functions for a viscoelastic half space and harmonic line loadings is investigated. The model is assumed to be of the plane strain type. Extensive testing of the numerical accuracy for various quadratures is performed. A measure of numerical efficiency of the quadratures is proposed and compared for different integration formulae. It was determined that among the procedures tested the Clenshaw-Curtis quadrature offers the most efficient way of evaluating the wavenumber integrals numerically.     

Transmission line model for simulation of guided-wave defect signals in piping

A simple transmission line model for analytically simulating the guided-wave signal reflected from a volumetric defect of arbitrary shape in piping is described. In the model, the guided-wave interaction with a defect is treated as the one-dimensional problem of plane wave reflection from a boundary of multilayered media of different acoustic impedances in a transmission line. Results of simulation show good qualitative agreement with experimentally measured signals.     

Signal distortion induced by Fresnel reflection in open-loop fiber-optic gyroscopes

The signal distortion that is due to Fresnel reflection in open-loop fiber-optic gyroscopes was theoretically analyzed to determine the relationship between the reflection ratio and the scale factor error of the gyroscopes. The analysis showed that the in-phase component of each Fourier harmonic of the gyroscope signal deviates from the true sinusoidal function, a quadrature-phase component appears, and the pi/2 rotation rates of harmonic components disagree. We evaluated the degree of scale factor degradation by defining the harmonic distortion ratio, which can be used as a measure for the reflectional quality of the gyroscopic optical system. The theory was verified by the response of an experimental gyroscope. The Fresnel reflection was eliminated by optical and electrical means, and the signal distortion of the experimental gyroscope was suppressed.     

Numerical simulation of the oscillation line width in synchronous multi-element Josephson structures

A method of simulating the dynamics of systems with Josephson junctions with allowance for thermal fluctuations is developed using the PSCAN program package followed by calculation of the Josephson oscillation spectrum using an autoregression method. An investigation is made of the synchronous Josephson oscillation line width in several types of Josephson structures. Pis’ma Zh. Tekh. Fiz. 24, 52–59 (August 12, 1998)     

非主轴宽带辐射噪声测量线列阵的性能仿真

对采用线列阵系统的水下大型结构的辐射噪声测量原理进行了讨论,分析了测量的要素,对非主轴方向上的目标辐射噪声测量进行了建模,给出了非主轴方向的宽带波束形成方法。通过计算机仿真,得到了主波束宽度、阵元数和阵增益之间的关系,并对计算机仿真结果进行了比较,该结果对浅海条件下的线列阵水下大型结构辐射噪声测量具有一定的指导意义。