模式偏置波前传感器理论模拟及实验验证

将模式偏置法与全息多重存储法波前传感器原理联系起来,通过研究模式偏置波前传感器的输出响应特性,间接得到全息模式波前传感器的运行规律.对模式偏置波前传感器进行理论分析与总结,并建立简化模型,针对若干阶Zernike像差,通过数值模拟对理论结果进行验证.模拟结果显示:传感器输出信号与各种类型待测像差系数有不同的变化关系,这...     

模式偏置波前传感器理论模拟及实验验证

将模式偏置法与全息多重存储法波前传感器原理联系起来,通过研究模式偏置波前传感器的输出响应特性,间接得到全息模式波前传感器的运行规律。对模式偏置波前传感器进行理论分析与总结,并建立简化模型,针对若干阶Zernike像差,通过数值模拟对理论结果进行验证。模拟结果显示：传感器输出信号与各种类型待测像差系数有不同的变化关系,这与理论分析结果吻合。以散焦模式像差为例,利用两个相位型空间光调制器动态加载模式像差,分别在入射光波中引入待测像差和偏置像差,探测焦平面光斑强度变化。实验结果表明：以峰值光强作为焦平面光强分布的信息提取方式,进而得到正负偏置光斑的光强差和归一化光强差,这比在小孔光阑上进行积分更简单有效。     

SIM--simultaneous inverse filtering and matching of a glottal flow model for acoustic speech signals

A new method "simultaneous inverse filtering and model matching" (SIM) is proposed that allows one to calculate voice source measures without any user interaction. It is based on the discrete all-pole modeling (DAP) technique for inverse filtering (IF), which is modified to include a model of the glottal flow as integral part [LF model, Fant et al., STL-QPSR (Stockholm) 4/1985, 1-13 (1986)]. As the correct LF parameters are initially unknown, they are estimated in an iterative procedure using multi-dimensional optimization techniques that are initialized according to the results of an exhaustive search. The error criteria applied reflect how well the IF is performed after the spectral contribution of the glottal flow has been removed. The resulting optimal LF parameter constellation serves as the basis to calculate 11 voice source measures. The performance was evaluated using synthesized signals and recordings of natural utterances. For the synthesized signals, the accuracy to reproduce the original parameters was high (correlations exceeding 0.88) for measures where the starting point of the glottal cycle did not enter explicitly. Errors were smaller compared to conventional estimation methods where the measures were estimated from the IF signal. The analysis of natural utterances indicates that problems still exist with regard to robustness, but that under advantageous conditions the open quotient, the speed quotient, the closing quotient, the parabolic spectral parameter, and the negative peak amplitude of the glottal flow derivative can indeed be determined automatically by the SIM method.     

Comparing turbulence models for flow through a rigid glottal model

Flow through a rigid model of the human vocal tract featuring a divergent glottis was numerically modeled using the Reynolds-averaged Navier-Stokes approach. A number of different turbulence models, available in a widely used commercial computational fluid dynamics code, were tested to determine their ability to capture various flow features recently observed in laboratory experiments and large eddy simulation studies. The study reveals that results from unsteady simulations employing the k-omega shear stress transport model were in much better agreement with previous measurements and predictions with regard to the ability to predict glottal jet skewing due to the Coanda effect and the intraglottal pressure distribution or related skin friction coefficient, than either steady or unsteady simulations using the Spalart-Allmaras model or any other two-equation turbulence model investigated in this study.     

Efficient kinetic schemes for steady and unsteady flow simulations on unstructured meshes

This paper presents efficient second-order kinetic schemes on unstructured meshes for both compressible unsteady and incompressible steady flows. For compressible unsteady flows, a time-dependent gas distribution function with a discontinuous particle velocity space at a cell interface is constructed and used for the evaluations of both numerical fluxes and conservative flow variables. As a result, a compact scheme on the unstructured meshes is developed. For incompressible steady flows, a continuous second-order gas-kinetic BGK type scheme is presented, for which the time-dependent gas distribution function with a continuous particle velocity is used on unstructured meshes. The efficiency of the schemes lies in the fact that the slopes of the flow variables inside each cell can be constructed using values of the flow variables within that cell only without involving neighboring cells. Therefore, even with the stencil of a first-order scheme, a high resolution method is constructed. Numerical examples are presented which are compared with the benchmark solutions and the experimental measurements.     

Numerical simulation of turbulence transition and sound radiation for flow through a rigid glottal model

Large eddy simulation (LES)-based computational aeroacoustics techniques were applied to a static model of the human glottis, idealized here as a planar channel with an orifice, to study flow-acoustic interactions related to speech. Rigid models of both converging and diverging glottal passages, each featuring a 20 deg included angle and a minimal glottal diameter of 0.04 cm, with an imposed transglottal pressure of 15 cm H2O, were studied. The Favre-filtered compressible Navier-Stokes equations were integrated for this low-Mach-number flow using an additive semi-implicit Runge-Kutta method and a high-order compact finite-difference scheme with characteristic-based nonreflecting boundary conditions and a multiblock approach. Flow asymmetries related to the Coanda effect and transition to turbulence, as well as the far-field sound, were captured. Acoustic-analogy-based far-field sound predictions were compared with direct simulations and showed that dipole sources, arising from unsteady flow forces exerted on the glottal walls, are primarily responsible for the tonal sound observed in the divergent glottis case.     

超声速转子叶片非定常引射器流场特性数值模拟

采用计算流体力学方法,结合适当的边界条件,对超声速转子叶片非定常引射器进行了模拟。从结果可以看出:此类引射器内流态复杂,主气流出口斜激波干扰现象明显,叶片设计参数对引射器性能影响很大。叶片尾部的膨胀波有效诱导了被引射气流,在短距离内增强了气流混合,湍流效应对引射器性能的影响较小;叶片可维持自旋转,提升叶片转速可增强引射效率。最后,对引射器内的流动机理进行了探讨。     

Parameterization of the glottal area, glottal flow, and vocal fold contact area

A new set of parameters is described for analysis and synthesis of glottal area, vocal fold contact area, and glottal volume flow. Parameters are all nondimensionalized and consist of an abduction quotient, a shape quotient, a phase quotient, and a load quotient in addition to fundamental frequency and vibrational amplitude. The parameters show promise in interpretation of electroglottographic, photoglottographic, and inverse filtered volume velocity waveforms in terms of the glottal configuration. Some comparisons between modeled and measured glottographic waveforms are made.     

超声速转子叶片非定常引射器流场特性数值模拟

采用计算流体力学方法,结合适当的边界条件,对超声速转子叶片非定常引射器进行了模拟。从结果可以看出:此类引射器内流态复杂,主气流出口斜激波干扰现象明显,叶片设计参数对引射器性能影响很大。叶片尾部的膨胀波有效诱导了被引射气流,在短距离内增强了气流混合,湍流效应对引射器性能的影响较小;叶片可维持自旋转,提升叶片转速可增强引射效率。最后,对引射器内的流动机理进行了探讨。     

长周期光纤光栅的理论分析及实验验证

采用简化的三层光纤模型,从模式理论和耦合模理论出发,分析了长周期光纤光栅的耦合特性及功率透射谱,给出了长周期光栅的主要特性参数。利用计算机建模,采用Matlab软件对实用的SMF 28单模光纤加以特定的光栅折射率调制参数进行数值计算,并采用振幅掩模法刻写长周期光纤光栅进行实验验证,计算结果与实验结果相吻合。     

Uncertainty-based experimental validation of nonlinear reduced order models

This paper presents the first results of a combined experimental–computational investigation focused on the validation of reduced order models of geometrically nonlinear structures in the presence of uncertainty. The validation approach considered here is based on the premise that the model is valid if the experimental results can be considered as random sample responses of the stochastic system of which the reduced order model is the mean. For the situation considered here, the power spectra of the experiments should lie within the 2nd and 98th percentiles of the response (forming the uncertainty band) of the stochastic model. Nominally clamped–clamped beams are considered to demonstrate the entire process. The construction of two mean reduced order models and their stochastic counterparts are first performed. Then, the validation effort is carried out by comparing experimentally obtained power spectra and their corresponding computational uncertainty bands. This process leads, for both reduced order models, to a very good representation of the important upper envelope (98th percentile) of the experimental data but a less good fit of the lower envelope (2nd percentile).     

3D simulation and visualization of unsteady wake flow behind a cylinder

In this paper we focus on 3D simulation of unsteady wake flow behind a circular cylinder. We show that in addition to accurate formulations and sufficiently-refined meshes, efficient computing methods are essential components of an effective simulation strategy. We use the Multi-Domain Method (MDM) we developed recently in computation of two cases. At Reynolds number 300, we demonstrate how the MDM enables us to use highly-refined meshes to capture wake patterns which we otherwise cannot fully represent. At Reynolds number 140, we show that with the MDM we can extend our computations sufficiently downstream, and with sufficient accuracy, to successfully capture the second phase of the Karman vortex street, which has been observed in laboratory experiments, and which has double the spacing between the vortices compared to the first phase.     

Theoretical analysis and experimental validation of radial cascaded composite ultrasonic transducer

A radial cascaded composite ultrasonic transducer is analyzed.The transducer consists of three short metal tubes and two radially polarized piezoelectric ceramic short tubes arranged alternately along the radial direction.The short metal tubes and the piezoelectric ceramic short tubes are connected in parallel electrically and in series mechanically,which can multiply the input sound power and sound intensity.Based on the theory of plane stress,the electro-mechanical equivalent circuit of radial vibration of the transducer is derived firstly.The resonance/anti-resonance frequency equation and the expression of the effective electromechanical coupling coefficient are obtained.Excellent electromechanical characteristics are determined by changing the radial geometric dimensions.Two prototypes of the transducers are designed and manufactured to support the analytical theory.It is concluded that the theoretical resonance/anti-resonance frequencies are consistent with the numerical and experimental results.When R_2 is at certain values,both the anti-resonance frequency and effective electromechanical coupling coefficient corresponding to the second mode have maximal values.The radial cascaded composite ultrasonic transducer is expected to be used in the fields of ultrasonic water treatment and underwater acoustics.     

A theoretical study on the unsteady aerothermodynamics for attached flow models

The principle of the unsteady aerothermodynamics was theoretically investigated for the attached flow. Firstly, two simplified models with analytic solutions to the N-S equations were selected for the research, namely the compressible unsteady flows on the infinite flat plate with both time-varying wall velocity and time-varying wall temperature boundary conditions. The unsteady temperature field and the unsteady wall heat flux (heat flow) were analytically solved for the second model. Then, the interaction characteristic of the unsteady temperature field and the unsteady velocity field in the simplified models and the effects of the interaction on the transient wall heat transfer were studied by these two analytic solutions. The unsteady heat flux, which is governed by the energy equation, is directly related to the unsteady compression work and viscous dissipation which originates from the velocity field governed by the momentum equation. The main parameters and their roles in how the unsteady velocity field affects the unsteady heat flux were discussed for the simplified models. Lastly, the similarity criteria of the unsteady aerothermodynamics were derived based on the compressible boundary layer equations. Along with the Strouhal number Stu, the unsteadiness criterion of the velocity field, StT number, the unsteadiness criterion of the temperature field was proposed for the first time. Different from the traditional method used in unsteady aerodynamics which measures the flow unsteadiness only by the Stu number, present results show that the flow unsteadiness in unsteady aerothermodynamics should be comprehensively estimated by comparing the relative magnitudes of the temperature field unsteadiness criterion StT number with the coefficients of other terms in the dimensionless energy equation.     

Conservative numerical simulation of multi-component transport in two-dimensional unsteady shallow water flow

An explicit finite volume model to simulate two-dimensional shallow water flow with multi-component transport is presented. The governing system of coupled conservation laws demands numerical techniques to avoid unrealistic values of the transported scalars that cannot be avoided by decreasing the size of the time step. The presence of non conservative products such as bed slope and friction terms, and other source terms like diffusion and reaction, can make necessary the reduction of the time step given by the Courant number. A suitable flux difference redistribution that prevents instability and ensures conservation at all times is used to deal with the non-conservative terms and becomes necessary in cases of transient boundaries over dry bed. The resulting method belongs to the category of well-balanced Roe schemes and is able to handle steady cases with flow in motion. Test cases with exact solution, including transient boundaries, bed slope, friction, and reaction terms are used to validate the numerical scheme. Laboratory experiments are used to validate the techniques when dealing with complex systems as the κ–?$\kappa ''–''?$ model. The results of the proposed numerical schemes are compared with the ones obtained when using uncoupled formulations.     

Identification of source velocities on 3D structures in non-anechoic environments: Theoretical background and experimental validation of the inverse patch transfer functions method

In noise control, identification of the source velocity field remains a major problem open to investigation. Consequently, methods such as nearfield acoustical holography (NAH), principal source projection, the inverse frequency response function and hybrid NAH have been developed. However, these methods require free field conditions that are often difficult to achieve in practice. This article presents an alternative method known as inverse patch transfer functions, designed to identify source velocities and developed in the framework of the European SILENCE project. This method is based on the definition of a virtual cavity, the double measurement of the pressure and particle velocity fields on the aperture surfaces of this volume, divided into elementary areas called patches and the inversion of impedances matrices, numerically computed from a modal basis obtained by FEM. Theoretically, the method is applicable to sources with complex 3D geometries and measurements can be carried out in a non-anechoic environment even in the presence of other stationary sources outside the virtual cavity. In the present paper, the theoretical background of the iPTF method is described and the results (numerical and experimental) for a source with simple geometry (two baffled pistons driven in antiphase) are presented and discussed.     

A stabilized MLPG method for steady state incompressible fluid flow simulation

In this paper, the meshless local Petrov–Galerkin (MLPG) method is extended to solve the incompressible fluid flow problems. The streamline upwind Petrov–Galerkin (SUPG) method is applied to overcome oscillations in convection-dominated problems, and the pressure-stabilizing Petrov–Galerkin (PSPG) method is applied to satisfy the so-called Babuška–Brezzi condition. The same stabilization parameter τ(τ_SUPG = τ_PSPG) is used in the present method. The circle domain of support, linear basis, and fourth-order spline weight function are applied to compute the shape function, and Bubnov–Galerkin method is applied to discretize the PDEs. The lid-driven cavity flow, backward facing step flow and natural convection in the square cavity are applied to validate the accuracy and feasibility of the present method. The results show that the stability of the present method is very good and convergent solutions can be obtained at high Reynolds number. The results of the present method are in good agreement with the classical results. It also seems that the present method (which is a truly meshless) is very promising in dealing with the convection- dominated problems.     

Theoretical and experimental validation of UTD applied to electromagetic-wave scattering by circular cylinders

The scattering of obliquely incident electromagnetic waves by a perfectly conducting circular cylinder is analyzed. In this paper the accuracy of a high-frequency asymptotic model based on the Uniform Theory of Diffraction (UTD) is investigated by comparing UTD simulations with results obtained from the exact eigenfunction solution for plane-wave incidence.UTD results are also compared with results from experiments carried out at 50 GHz, for various cylinder radii and for different linear wave polarizations. Excellent agreement between the measurement results and the theoretical ones is obtained.