高超声速热线/热膜风速仪研究综述及分析

针对高超声速流场测量对热线/热膜风速仪的需求,对近年来国内外热线/热膜风速仪研制现状进行了归纳.重点从探头制备、控制电路设计及探头校准三个方面,阐述了热线/热膜测试系统应用于高超声速流场测量必须解决的关键问题及各种方案的特点;分析了探头材料、构型及控制电路模式对高超声速流场中热线/热膜测试系统性能的影响,并对热线/热膜探头校准的几种方法进行了对比,总结出可供发展我国自主知识产权高超声速热线/热膜技术的意见.     

桥梁移动荷载识别的不适定性及其试验研究

对桥梁移动荷载识别方程不适定问题进行研究，提出采用预处理共轭梯度法（PCGM）求解超定方程组，通过选择不同的预优矩阵，改善和解决超定方程组的欠秩和病态问题。为验证基于PCGM方法的现场实用性，设计制作了车桥试验模型，通过试验采集到的桥梁弯矩响应数据识别桥面移动荷载。比较桥梁模态数、预处理共轭梯度法迭代次数、桥面粗糙度、车辆重量以及测点选择对识别结果精度的影响后，研究结果表明：基于PCGM方法能够很好地识别车辆荷载，收敛较快且能较好改善荷载识别方程的不适定性。     

Flow diagnostics in a vortex furnace by particle image velocimetry

The internal aerodynamics of a model vortex furnace for a steam generator with a horizontal axis of flow rotation and distributed input of fuel-air mixture jets has been studied. Average characteristics of the flow velocity field in various cross sections have been determined using a digital tracer imaging (particle image velocimetry) technique. Results are compared to data obtained by the method of laser Doppler anemometry.     

The near-neutral atmospheric surface layer: turbulence and non-stationarity

The neutrally stable atmospheric surface layer is used as a physical model of a very high Reynolds number, canonical turbulent boundary layer. Challenges and limitations with this model are addressed in detail, including the inherent thermal stratification, surface roughness and non-stationarity of the atmosphere. Concurrent hot-wire and sonic anemometry data acquired in Utah's western desert provide insight to Reynolds number trends in the axial velocity statistics and spectra.     

On augmented Lagrangian algorithms for thermomechanical contact problems with friction

The detailed discretization of contact zones with contact stiffness based on real physical characteristics of contact surfaces can produce stiffness terms which induce ill-conditioning of the global stiffness matrix. Moreover the consistent treatment of frictional behaviour generates non-symmetric tangent stiffness matrices due to the non-associativity of the slip phase. Other non-symmetries are due to the coupling terms and to the dependencies on various parameters that can be involved. To overcome these difficulties almost consistent techniques based on two-step algorithms have been proposed in the past. Here an augmentation technique is proposed which takes into account micro-mechanical effects, and permits the symmetrization of the tangent stiffness during frictional slip phase.     

去噪正则化模型修正方法在桥梁损伤识别中的应用

以传统基于灵敏度分析的有限元模型修正方法为基础,提出一种结合小波去噪过程的正则化模型修正损伤识别方法.为改进模型修正方法损伤识别效果,一方面利用有损结构模态与模态噪声的波形在时频域内的差异,以结构有限元模型为基准,对实测模态差进行小波去噪处理,并利用修正后的模态构造目标函数;一方面采用正则化方法改善反问题求解的非适定性.由于从输入数据和求解过程两方面同时改善了结构损伤识别反问题的求解,因此可以有效抑制实测模态参数中噪声的影响,正确识别结构损伤.以连续梁桥模型为例的损伤识别数值模拟表明,所提出方法在保持识别算法鲁棒性、抑制噪声的同时,可有效提高桥梁结构损伤的识别精度.     

Efficient, numerically robust characterisation of a large, double-loop antenna array

Arrays of circular, double-loops are treated via a semi-analytical technique, on the basis of a Method of Moments formulation. A Pocklington-type integral equation for the current is derived and discretised via a suitable set of basis functions. The matrix corresponding to the pertinent linear system is found to consist of circulant blocks. The system is therefore analytically solvable, and hence, potential ill-conditioning, encountered in large geometry cases, cannot possibly introduce any numerical instabilities to the calculations. Introduction of a delta gap source as excitation facilitates very efficient computation of the current and input admittance. The algorithm exploits almost exclusively elementary functions and yields results in terms of a set of rapidly convergent series, applicable to extremely large loops. Data for such loops are presented for the first time in literature. The method is expected to lead in the future to very efficient designs of multi-loop arrays.     

基于矩量法的移动荷载识别

从桥梁响应识别桥面移动荷载往往出现逆问题的病态（不适定性）等共性问题。本文基于移动荷载识别理论，借助矩量法求解积分方程理论并采用整域基函数——正交勒让德多项式表达桥面移动荷载，提出了一种移动荷载识别的时域改进算法。两轴车辆多种组合工况下的常载和时变荷载数值仿真研究表明：与时域法比较，改进时域法识别桥面移动荷载时，其识别精度高、抗噪能力强，识别结果不适定性有显著改善。     

Eliminating high-order scattering effects in optical microbubble sizing

Measurements of bubble size and velocity in multiphase flows are important in much research and many industrial applications. It has been found that high-order refractions have great impact on microbubble sizing by use of phase-Doppler anemometry (PDA). The problem has been investigated, and a model of phase-size correlation, which also takes high-order refractions into consideration, is introduced to improve the accuracy of bubble sizing. Hence the model relaxes the assumption of a single-scattering mechanism in a conventional PDA system. The results of simulation based on this new model are compared with those based on a single-scattering-mechanism approach or a first-order approach. An optimization method for accurately sizing air bubbles in water has been suggested.     

New advances in the forced response computation of periodic structures using the wave finite element (WFE) method

The wave finite element (WFE) method is investigated to describe the harmonic forced response of one-dimensional periodic structures like those composed of complex substructures and encountered in engineering applications. The dynamic behavior of these periodic structures is analyzed over wide frequency bands where complex spatial dynamics, inside the substructures, are likely to occur. Within the WFE framework, the dynamic behavior of periodic structures is described in terms of numerical wave modes. Their computation follows from the consideration of the finite element model of a substructure that involves a large number of internal degrees of freedom. Some rules of thumb of the WFE method are highlighted and discussed to circumvent numerical issues like ill-conditioning and instabilities. It is shown for instance that an exact analytic relation needs to be considered to enforce the coherence between positive-going and negative-going wave modes. Besides, a strategy is proposed to interpolate the frequency response functions of periodic structures at a reduced number of discrete frequencies. This strategy is proposed to tackle the problem of large CPU times involved when the wave modes are to be computed many times. An error indicator is formulated which provides a good estimation of the level of accuracy of the interpolated solutions at intermediate points. Adaptive refinement is carried out to ensure that this error indicator remains below a certain tolerance threshold. Numerical experiments highlight the relevance of the proposed approaches.     

周边固支的矩形板的动力耦合热弹性问题分析

本文研究的是周边固支的矩形板上表面受均匀分布热流冲击的动力耦合热弹性问题，在热冲击过程中，板的周边温度场保持稳定，下表面绝热。采用算子法将热传导方程由三维降为二维问题，以和二维的热弹性动力方程相协调，二方程相互耦合，故用带补充项的双重富里叶级数消去对坐标的微分项，再用拉普拉斯变换消去方程中对时间的微分项，然后尝试用加权最佳逼近法作数值拉普拉斯逆变换，给出问题在原象空间的解。为防止误差的扩大，本文利用正交齐异分解法求解方程，并对计算结果中动力项和耦合项的影响作出分析。     

A new model for non-Gaussian random excitations

Very often one is called upon to model time series data which are clearly non-Gaussian, but which retain some aspects of a Gaussian process. In the present paper, a novel methodology which helps in modelling such data is presented. The method is essentially to express the process as a series with finite number of terms, wherein the first term is a Gaussian process with zero mean and unit standard deviation. Non-Gaussian higher order correction terms are added to this such that each succeeding term is orthogonal or uncorrelated with all the previous terms. The unknown coefficients in the series representation can be expressed in terms of the estimated moments of the data. Further the autocorrelation or PSD of the data can be exactly reproduced by the non-Gaussian model. The use of the proposed model is illustrated by considering the unevenness data of railway tracks. Application to response of systems under non-Gaussian excitation is also briefly discussed.     

A probabilistic framework for detecting and identifying anomalies

This paper develops a probabilistic framework to detect and identify anomalies such as damage in structures. The framework is developed by introducing new terms and definitions with their corresponding mathematical formulation. An advantage of the new framework is that ill-conditioning in the identification problem is avoided and that a clear relation between measurements and modeling is established. Special results are then obtained in the form of bounds that allow for computationally efficient applications. An example application is then presented. The application is to detect and identify part-through cracks in a plate from surface strain measurements. In this application problem, the role of strain gauge size and measurement errors are considered and discussed.     

Method of phase-Doppler anemometry free from the measurement-volume effect

A novel method is developed to improve the accuracy of particle sizing in laser phase-Doppler anemometry (PDA). In this method the vector sum of refractive and reflective rays is taken into consideration in describing a dual-mechanism-scattering model caused by a nonuniformly illuminated PDA measurement volume. The constraint of the single-mechanism-scattering model in the conventional PDA is removed. As a result the error caused by the measurement-volume effect, which consists of a Gaussian-beam defect and a slit effect, can be eliminated. This new method can be easily implemented with minimal modification of the conventional PDA system. The results of simulation based on the generalized Lorenz-Mie theory show that the new method can provide a PDA system free from the measurement-volume effect.     

Parameter Estimation Employing a Dual-Channel Sine-Wave Model Under a Gaussian Assumption

The CramÉr–Rao bound (CRB) is a lower bound on the error variance of any estimator. For a Gaussian scenario, the CRB is derived for a seven-parameter, dual-channel sine-wave model, which is a model relevant to applications such as impedance measurements and the estimation of particle size and velocity by laser anemometry. Four different parameterizations were considered: the common quadrature/in-phase and amplitude–phase models and two relative amplitude–phase models. The CRB indicated the achievable error variance of an unbiased estimator as a function of the signal-to-noise ratio (SNR), the number of samples, and noise power. A nonlinear least squares fit of the signal model to the collected data was employed. The problem at hand is separable and can be solved by a 1-D search followed by a linear least squares fit of the remaining parameters. The performance of the method was investigated with the aid of a simulation study, and the outcome was compared with that of the corresponding CRB and with a recently proposed seven-parameter fit. For high SNRs, the performance of the proposed method is close to optimal with an error variance close to the predictions made by the CRB.      

Regularized broadband filter method for spectral responsivitymeasurements

A regularized formulation of the broadband filter method is presented for measuring the spectral responsivity of photodetectors. Same a priori knowledge of the spectral responsivity to be measured is exploited in the framework of the standard broadband filter method. Partial information on the spectral behavior coming from theory, experience and/or catalog data allows one to overcome the ill-conditioning intrinsic to the original formulation of the problem. Simulated and experimental tests on actual photodetectors show the capabilities of this method. In particular, it acts successfully with V(λ)-corrected detectors     

The method of fundamental solutions for fracture mechanics—Reissner's plate application

The application of the method of fundamental solutions (MFS), a mesh-free technique, to solve cracked Reissner's plates is discussed in this work. Here, the numerical Green's function (NGF) previously developed by the authors is used as the fundamental solution required by the method. Stress intensity factors or the related force intensity factors are obtained using the generalized crack openings at a single point near the tip, computed through a summation of the fundamental generalized openings at that point weighted by their influence factors. Despite the ill-conditioning of the equations system, which may require appropriate handling to solve (such as the singular value decomposition method), examples show good results for problems with embedded cracks. The method can be a good option to evaluate stress intensity factors of given problems due to its simple and intuitive implementation.     

Ill-Conditioned equations in kinematics and dynamics of machines

During mechanical system kinematic and dynamic analysis, linear and non-linear algebraic equations must be solved. Algebraic equations are often ill-conditioned, due either to physical singularities or large numerical errors, in which case solutions may have large errors or analysis methods may fail. Causes of ill-conditioned problems are studied and illustrated with examples. Ill-conditioned matrices and matrix condition numbers are discussed and an efficient and reliable indicator of ill-conditioned matrices is suggested. In constrained kinematic and dynamic analysis, equations are solved repetitively, so symbolic factorization is used. The ill-conditioning problem due to symbolic factorization is discussed and methods of detecting ill-conditioning are suggested. Three examples are studied to demonstrate the effectiveness and use of condition numbers and ill-conditioned system detection methods.     

Application of a sensorial response model to the design of an oral liquid pharmaceutical dosage form

In this paper, we discuss the application of a compartmental model to study the sensorial response, in terms of taste intensity versus time, in an oral solution for pharmaceutical use. The numerical model was developed from sensorial response curves obtained by a panel of three trained individuals. Parameter identification was carried out by means of a least-squares procedure that obtained the linear coefficients in the model by solving an exact linear least-squares problem conditional on the values of the nonlinear parameters for each iteration. Thus, nonlinear estimation was done in terms of the first-order kinetic parameters only, and ill-conditioning of the Hessian matrix present in these models was solved. Results of modeling for a set of formulations were used to determine the effects of various ingredients (sweeteners and an essence) on a baseline unflavored formulation of acetaminophen in a mixture of cosolvents. The first moment of the area under the curve of taste intensity versus time was found to be the best global indicator of taste for the purpose of product design. It was found that a mixture of sweeteners and an essence was the most efficient way of masking the bitter taste of this active ingredient.