体积速度匹配分布源边界点法的特解源位置优化方法研究

在分布源边界点法中,选择特解源及特解源位置对声场计算的精度具有很大的影响。为减小声场计算的误差,提出了一种确定特解源位置的优化方法。在该方法中,采用三极子作为特解源,以1%体积速度相对误差对结构声辐射计算的上限频率进行预测,然后在计算上限频率范围内通过体积速度匹配搜索,得到体积速度相对误差最小意义下的特解源优化位置,在该优化位置处构造声压与表面体积速度之间的传递矩阵来计算声场,以减小计算误差。数值仿真结果表明:在求取的计算上限频率范围内,特解源处于优化位置时,计算误差得以显著减小。当振速测量存在一定误差时,采用该方法仍可将计算误差控制在5%以内。     

体积速度匹配分布源边界点法的特解源位置优化方法研究

在分布源边界点法中,选择特解源及特解源位置对声场计算的精度具有很大的影响。为减小声场计算的误差,提出了一种确定特解源位置的优化方法。在该方法中,采用三极子作为特解源,以1%体积速度相对误差对结构声辐射计算的上限频率进行预测,然后在计算上限频率范围内通过体积速度匹配搜索,得到体积速度相对误差最小意义下的特解源优化位置,在该优化位置处构造声压与表面体积速度之间的传递矩阵来计算声场,以减小计算误差。数值仿真结果表明:在求取的计算上限频率范围内,特解源处于优化位置时,计算误差得以显著减小。当振速测量存在一定误差时,采用该方法仍可将计算误差控制在5%以内。     

基于分布源边界点法的局部近场声全息技术

为了克服基于分布源边界点法的近场声全息技术在小全息孔径条件下造成的重建误差问题,提出了基于分布源边界点法的局部近场声全息技术.该技术运用分布源边界点法,采用测得的较小全息面上的声压数据来外推较大全息面上的声压数据,然后用外推的数据进行全息重建.仿真和实验结果验证了采用该技术在小全息孔径条件下进行声源局部重建的有效性.     

Extension of the distributed point source method for ultrasonic field modeling

The distributed point source method (DPSM) was recently proposed for ultrasonic field modeling and other applications. This method uses distributed point sources, placed slightly behind transducer surface, to model the ultrasound field. The acoustic strength of each point source is obtained through matrix inversion that requires the number of target points on the transducer surface to be equal to the number of point sources. In this work, DPSM was extended and further developed to overcome the limitations of the original method and provide a solid mathematical explanation of the physical principle behind the method. With the extension, the acoustic strength of the point sources was calculated as the solution to the least squares minimization problem instead of using direct matrix inversion. As numerical examples, the ultrasound fields of circular and rectangular transducers were calculated using the extended and original DPSMs which were then systematically compared with the results calculated using the theoretical solution and the exact spatial impulse response method. The numerical results showed the extended method can model ultrasonic fields accurately without the scaling step required by the original method. The extended method has potential applications in ultrasonic field modeling, tissue characterization, nondestructive testing, and ultrasound system optimization.     

半自由声场的全息重建和预测技术研究

在半自由声场中,实际测量声压为直达声压和反射声压的叠加,而声压为标量,很难直接将其中直达声压成分分离出来,因而不能简单地用常规的方法来直接进行声源重建和声场预测。在充分地考虑到反射声压的情况下,建立了半自由声场环境下反射面为刚性和非刚性时的声场全息重建和预测理论模型,并通过实例验证了此模型的可行性和正确性。结果表明:此方法有效地解决了半自由声场中进行声场全息重建和预测时所存在的声压反射问题,从而扩充了声全息重建和预测技术的应用范围;采用分布源边界点法作为全息变换算法,提高了声全息重建和预测的速度、精度和稳定性。     

分布源边界点法及其在振动体声辐射计算中的应用

讨论了一种新型的计算振动体声辐射的方法──分布源边界点法.通过诸多算例,对分布源边界点法的计算精度、计算稳定性、适用范围和克服外部声辐射在特征频率处解的非唯一问题的可行性等进行了评价。     

Numerical simulation of electromagnetic acoustic transducers using distributed point source method

In spite of many advances in analytical and numerical modeling techniques for solving different engineering problems, an efficient solution technique for wave propagation modeling of an electromagnetic acoustic transducer (EMAT) system is still missing. Distributed point source method (DPSM) is a newly developed semi-analytical technique developed since 2000 by Placko and Kundu (2007) [12] that is very powerful and straightforward for solving various engineering problems, including acoustic and electromagnetic modeling problems. In this study DPSM has been employed to model the Lorentz type EMAT with a meander line and flat spiral type coil. The problem of wave propagation has been solved and eddy currents and Lorentz forces have been calculated. The displacement field has been obtained as well. While modeling the Lorentz force the effect of dynamic magnetic field has been considered that most current analyses ignore. Results from this analysis have been compared with the finite element method (FEM) based predictions. It should be noted that with the current state of knowledge this problem can be solved only by FEM.     

A point source solution for unidirectional flow of a viscoelastic fluid

A Fourier point source solution modelling the effect of an impulse on a viscoelastic fluid of second-grade is investigated. By examining the second-moment of a Fourier point source solution we show that for Dt1, where D=ν/ for ν the kinematic viscosity, a viscoelastic parameter and t the time; the fluid undergoes superdiffusion indicating the dominance of the fluids viscoelastic properties. For Dt1 the fluid undergoes classical diffusion indicating that the viscous properties of the fluid are dominating.     

A boundary piecewise constant level set method for boundary control of eigenvalue optimization problems

This paper investigates optimization of the least eigenvalue of ?Δ with the constraint of one-dimension Hausdorff measure of Dirichlet boundary. We propose the boundary piecewise constant level set (BPCLS) method based on the regularity technique to combine two types of boundary conditions into a single Robin boundary condition. We derive the first variation of the least eigenvalue w.r.t. the BPCLS function and propose a penalty BPCLS algorithm and an augmented Lagrangian BPCLS algorithm. Numerical results are reported for experiments on ellipse and L-shape domains.     

Design of a grating by a joint optimization method for a phase-shifting point diffraction interferometer

A grating is an important element of a phase-shifting point diffraction interferometer, and the grating constant and duty cycle have a great impact on the interferometer, so the design of a grating becomes significant. In order to measure the projection objective with a numerical aperture of 0.2, we present a joint optimization method of a pinhole and grating based on scalar diffraction and the finite difference time domain method. The grating constant and the film thickness are selected, and the duty cycle of the grating is optimized. The results show that in the grating processing the material chromium is adopted, the thickness is 200 nm, and the grating constant is 15 μm. When the duty cycle is 55%, the interference fringe contrast is the greatest. The feasibility of the design result is further verified by experiment.     

Artificial boundary conditions for the numerical solution of the Euler equations by the discontinuous galerkin method

We present artificial boundary conditions for the numerical simulation of compressible flows using high-order accurate discretizations with the discontinuous Galerkin (DG) finite element method. The construction of the proposed boundary conditions is based on characteristic analysis and applied for boundaries with arbitrary shape and orientation. Numerical experiments demonstrate that the proposed boundary treatment enables to convect out of the computational domain complex flow features with little distortion. In addition, it is shown that small-amplitude acoustic disturbances could be convected out of the computational domain, with no significant deterioration of the overall accuracy of the method. Furthermore, it was found that application of the proposed boundary treatment for viscous flow over a cylinder yields superior performance compared to simple extrapolation methods.     

Validation of the blocked force method for various boundary conditions for automotive source characterization

Vibro-acoustic source characterization is an essential task in vehicle development to enable prediction of receiver response. For structure-borne noise, the interface forces in multiple degrees of freedom due to internal loads are often quantified for root cause analyses in a single system assembly, as in transfer path analysis (TPA). However, for a reliable prognosis of the acoustic performance of a known component such as a motor or pump, a receiver-independent source characterization is required, and the method of acquiring blocked forces from in-situ measurements has been shown to be a preferred technique for such purposes. The benefits of the method are the characterization of the intrinsic properties of the source and the possibilities of measuring the component attached to receivers with varying dynamic properties.     

旋转运动点声源近场声学频域解

本文在任意运动点源声辐射频域解基础上，得到旋转运动声源近场声学的一个近似解。如果旋转半径相对于场声波是紧致的，此解就可以表示为在远场解基础上叠加三项近场修正项。根据此解，本文得到适合于近场的自由空间Ｇｒｅｅｎ函数，由此讨论了声源旋转导致的声场方向性特征，研究了声源位置及源频率以及旋转频率等对近场声学结构的影响。     

Equalization of acoustic source using multi-pole sources and source strength estimation using inverse method

Sound measured at various points around the environment can be evaluated by a series of multi-pole sources and their acoustic strength can be acquired. In this numerical study, a method, called the inverse method, was examined to achieve this goal. A variety of arrangements of different sources were considered and the acoustic strength of these sources was acquired. Through the application of the mismatch criterion, good conformity was observed between these sound models and the original sound. Furthermore, with regard to results, sound was generated via different source arrangements which showed acceptable agreement with the original sound. Finally, an arrangement named ‘sources vertical arrangement’ was selected as the best approach.     

Near field acoustic solution of a rotating point source in frequency domain

I.IntroductionAerodyntalcnoiseofturbomaChinrynotoalythectstheenvironmentbutalsosometimesresultsinstructuredamage.Aeroacoustics,asaintewhsciPlineofacousticsandaerodynamics,isattractingmorandmoreatteDtionandresearch.TherearetwoimportalltcontentsonthenoiseproducingmechAnsmsinaeroacousticproblem.OneisaboutthesourcesofnoiseinturbomachinryGenetallytherearethreetyPesofsources:thickness,forceandturbulencestress,correspondingrespectivelyTomonopole,dipoleandquadruplesourcesThelatertwokindsofsourcesh…     

基于能量分布的红外像点定位分析方法

在红外探测器的应用中,常用统计分析、算例验证等方法研究目标成像精确定位问题。鉴于上述方法难以充分阐释物理意义与揭示普遍规律,提出基于能量分布及成像特征的分析方法,针对红外探测目标成像精确定位问题,利用能量分布和数字图像中成像规律,研究像点定位及精度分析。研究了红外目标成像和数字图像特点,建立了定位模型和方法流程;分析了定位误差影响因素,实现了定位结果精度评定;最后结合典型应用实例,进行了计算验证。该方法与已有方法相比,分析过程更直观,获取了红外像点定位分析的理论依据,并给出了定位结果的精度水平:通常红外成像应用中,精度优于1/6像元;在成像较大时,精度可达1/10像元以上。该研究结论对红外探测应用中目标准确定位具有重要意义。     

Extension of the spectral volume method to high-order boundary representation

In this paper, the spectral volume method is extended to the two-dimensional Euler equations with curved boundaries. It is well-known that high-order methods can achieve higher accuracy on coarser meshes than low-order methods. In order to realize the advantage of the high-order spectral volume method over the low order finite volume method, it is critical that solid wall boundaries be represented with high-order polynomials compatible with the order of the interpolation for the state variables. Otherwise, numerical errors generated by the low-order boundary representation may overwhelm any potential accuracy gains offered by high-order methods. Therefore, more general types of spectral volumes (or elements) with curved edges are used near solid walls to approximate the boundaries with high fidelity. The importance of this high-order boundary representation is demonstrated with several well-know inviscid flow test cases, and through comparisons with a second-order finite volume method.     

Registration efficiency of electrons for point sources and of delta-electrons in volume of fast ion tracks in solids

Registration of fast electron flux in solid state detector was studied. We considered spatial distributions over detector volume of three values - probability of local responses, dissipated energy and number of moving electrons. We made a definition of a registration efficiency for dissipated energy dose and for electron flux. They were calculated and compared for three cases in nuclear emulsion type-R2: plane and axial sources for a set of angles of electron emitting, and a track of fastio as a source of δ-electrons.     

透射边界条件在点声源海底地震波数值计算中的应用

航行舰船在海底岩土层中引起的弹性波被称为舰船地震波,主要由舰船低频辐射噪声引起,可用于识别舰船目标。本文采用大型有限元软件ANSYS中的流固耦合计算模块,结合多次透射公式(MTF)人工边界条件,对较为简单的水平分层海洋环境下低频点声源海底地震波进行了数值计算,并为了分析数值计算方法的精度,将数值计算结果与波数积分方法结果进行了比较。频率较低时两种方法的声传播损失曲线符合较好,频率较高时结果存在一定差别;两种计算方法所得声传播频率特性曲线的形式有所不同,但曲线总体变化趋势基本一致;而海底表面竖直位移、水平位移、竖直加速度和水平加速度的频率特性曲线基本符合。由此认为,基于多次透射公式人工边界,采用大型有限元软件ANSYS中的流固耦合模块,对较复杂环境下低频点声源海底地震波问题进行数值计算是基本可行的。