双声源驱动热声系统的理论声场重构与实验验证

搭建了一套双声源驱动热声热机实验系统,该系统包括双扬声器、谐振管、置于谐振管内的回热器和换热器等元件。利用双声源法,可实现对谐振管及回热器边界声场的任意调制,包括调节幅值(调幅)、调节相位(调相)和调节频率(调频)。在给定双声源条件下,采用双传感器法对该系统谐振管中的声场参数(包括声压、质点速度、当地声阻抗等)分布进行理论声场重构,并通过实验分析,证实了该方法在等径谐振管内非声压腹点和节点处的适用性和准确性,而在声压腹点和节点处(附近)的误差最大达到12.4%。同时,对谐振管内的声场进行了行波驻波分解,得到了谐振管中行驻波成分比例。     

空气声源激发的浅海声场的理论研究

研究了将空气中声速分布建模为Epstein分布,水层和海底均为均匀分布的三层介质模型的条件下,空气中点源激发的水下声场。既推导得到了声压场的形式解,通过数值分析,表明空气中点源激发浅水波导,在水层中形成的波导简正波具有实数本征值,可以远距离传播,称其为"水波"。空气层中的Epstein波导简正波在水层中为非均匀波,传播速度取决于空气中声速,称其为"水面波",并指出空气中声源运动产生的水面波多普勒频移大于水波多普勒频移。     

旋转点声源声场的数值仿真计算

旋转声源辐射声场的计算是利用点源模型预测风扇离散噪声的关键所在,对叶片式机械气动噪声的研究具有重要参考价值.提供了在任意边界条件下计算旋转点声源辐射卢场的数值仿真计算方法.将连续的旋转声源离散化,处理为分布于旋转轨迹上的有限个固定点声源.利用离散化处理后的声源,通过边界元法分别计算旋转单极子和旋转点力源的辐射声场.在自由空间内的计算结果与理论解进行了对比验证,得到较为理想的结果:另外进行了有限长圆管内旋转点声源辐射声场的数值计算,由此对不同长度圆管的结果进行对比,分析了管道长度对声场分布以及指向性的影响规律.     

二维声场的边界元分析

本文将边界元法应用于二维声场分析,给出了以第二类汉克尔函数为基本解的数值计算公式,比较了处理奇异积分的三种不同方法。通过对三种不同边界条件的管道声场和脉动圆柱的辐射声场的计算并与精确解比较,表明了方法是正确而有效的。     

舰船声场的近程分布式声源模型

根据舰船声场的近程分布式声源特性,采用三轴声强测量法建立了模型,提出了提高其精度的方法.     

半消声室中离地升高声源的声场特性

按照ＩＳＯ３７４５规定，鉴定半消声室时，声中心贴在地面上（ｈ＝０），这时如果半消声室符合要求，则不呈现声场的复杂性，但半消声室的实际使用情况是，置于其中的大型机器设备，其声中心离地面均有一定高度ｈ（往往大于０．２ｍ乃至１．０ｍ），这时就出现直达声和反射声（主要是地面反射声）的较复杂的选加声场，这个声场与ｈ＝０的声场有很大不同。１．纯音声场的特性若是纯音声源，则在室内形成完全干涉声场，利用镜像法，我们计算了在不同直线路径上的干涉声场，并且在中科院声学所的半消声室内作了相应实验。若无反射声，则声场为…     

声强向量法对声源定向的理论和实验研究

文章应用的双传声器声强探头CM－202和与之配套的传声器,自行设计了1个声强探头支撑架,使之可以把声强探头转动到空间微卡儿坐标系的3个互相垂直的方向,并且它们的几何中心保持不变,这样就可以测量平衡声场中1点的声强矢量的3个分量,由此就能对声源进行定向,在半消声室中应用这套实验装置对声源进行了定向研究,并探讨了各种误差因素与定向精度的关系。     

热声回热器内声场数值模拟研究

对热声系统板叠及其附近流域进行了声场、流场特性的数值模拟研究。通过不同计算方法的对比,网格独立性验证等确定了误差最小的二维可压缩湍流模型。模拟结果分析了典型工况下热声回热器内部的压流分布特点,观察了板叠末端涡结构的周期性,并且对比了不同周期下涡结构的变化。结果表明,在压力场达到稳定后,由于流场的粘性,使得回热器内速度场的稳定具有滞后性,两者的稳定并不同步。     

室内指向性声源的声场数值模拟

为了利用计算机对室内指向性声源的声场进行模拟,文中将声线跟踪法,虚源法和Monte Carlo法相结合,编制了一种场场数值模拟仿真程序,该程序能模拟有（或无）指向性声源在室内给定点的声压级等参数值,还能计算出该点的脉冲响应函数,作为例子,分别利用该法和声压叠加法研究了点源和偶极子声源的指向性。     

基于精确数值积分的点声源反射声场模型研究

点声源辐射条件下的反射声场计算是一经典的Sommerfeld积分问题.在以往的研究中,含有表面波项的解由于其简便性和易计算性在室外声传播和大面积吸声材料的在体吸声测量中得到了较为广泛的应用,但对其在不同入射角度以及针对不同性质的材料(如局部响应或非局部响应材料)时带来的模型有效性问题较少提及.通过利用数值积分方法精确计算Sommerfeld积分,对两种不同性质的声学材料在不同入射角度下的辐射声场进行了研究,并和解析模型进行了对比,认为随着入射角度的降低和材料流阻的增加(即表现为局部响应性质),含有表面波项的解析解可以较好地表达辐射声场.     

回热器声阻抗特性的直接测量法─—传递函数法

报告了一种直接测量回热器声阻抗特性的传递函数法。将实验管内的声波分解成入射波和反射波，通过两个不同位置上的传感器所测得的压力波之比，以及两个位置上反射波与入射波声压之间的简单传递函数关系，确定实验段入出口处的复反射因子，再由复反射因子确定实验段入出口处的压力波动和流量波动，从而得到实验段的阻抗特性。同时报告了理论分析和实验测量得到的简单管道阻抗特性的对比。结果表明，这种直接测量方法是可靠的。     

Non‐reflecting boundary conditions for acoustic propagation in ducts with acoustic treatment and mean flow

We consider a time‐harmonic acoustic scattering problem in a 2D infinite waveguide with walls covered with an absorbing material, in the presence of a mean flow assumed uniform far from the source. To make this problem suitable for a finite element analysis, the infinite domain is truncated. This paper concerns the derivation of a non‐reflecting boundary condition on the artificial boundary by means of a Dirichlet‐to‐Neumann (DtN) map based on a modal decomposition. Compared with the hard‐walled guide case, several difficulties are raised by the presence of both the liner and the mean flow. In particular, acoustic modes are no longer orthogonal and behave asymptotically like the modes of a soft‐walled guide. However, an accurate approximation of the DtN map can be derived using some bi‐orthogonality relations, valid asymptotically for high‐order modes. Numerical validations show the efficiency of the method. The influence of the liner with or without mean flow is illustrated. Copyright © 2011 John Wiley & Sons, Ltd.     

A new boundary element method for resonance of an acoustic enclosure

Abstract

This paper presents a new boundary element formulation in which the eigenvalue appears outside the integral operator, which distinguishes it from the Helmholtz integral equation. Thus, the formation of global matrices need only be assembled once. Since the kernel of the operator used in the new formulation is real‐valued, all calculations can be carried out in a much simpler way in the real domain. The complex acoustic pressure amplitude is considered herein to deivate by a certain amount from a harmonic function. It is an important contribution that an exact relation between the deviator and the complex acoustic pressure amplitude is constructed locally and thus no more approximations are introduced except conventional boundary discretizations. Several examples are given to illustrate the feasibility of an accurate, effective prediction of resonance.     

边界条件对多孔材料声学参数测试的影响研究

多孔材料声学特征参数测试前需要采用机械切割方法和样品容器匹配,然而切割后的材料边缘不能完全和样品容器匹配,因此采用加环的方式进行处理。以三聚氰胺泡沫为例,通过控制测试材料的边界条件,测试材料的流阻率,在软件中选用合适的声学模型计算得出该材料的声学特征参数。最后将阻抗管测试得到的吸声系数与AMDesigner仿真得到的吸声系数进行比较。结果显示,加两个环后仿真得到的值与测试值吻合效果较好,加一个环在低频区吻合效果较好,而直接将切割得到的材料进行测试效果最差。该研究可以为今后的声学材料测试研究提供指导。     

Inverse problem of fracture mechanics for a circular disc under mixed boundary conditions

Solution method for the problem of prevention of early brittle fracture of a circular disc with mixed boundary conditions was proposed. Theoretical analysis on determination of normal displacement of points on the boundary of a circular disc weakened by arbitrarily allocated rectilinear cracks was carried out. A closed system of algebraic equations permitting to provide minimization of fracture parameters (stress intensity factors) subject to geometrical and mechanical characteristics of a disc was constructed. Minimization of the stress intensity factors in a circular disc was carried out. They found normal displacement of points on the boundary of the circular disc increases carrying capacity of the disc.     

随机振动结构声辐射的统计边界点法分析

文章利用作者提出的统计边界点法,对随机振动结构声辐射的计算进行了研究。文中详细地介绍了统计边界点法,并以随机振动球为例,计算了其在表面振速功率谱密度函数分布已知情况下的随机声场,并与解析解以及统计边界元法的计算结果进行了比较。结果表明：该方法与统计边界元法相比,在边界剖分相同的情况下,能够在相当宽的振动频率范围内,给出更加满意的计算结果。     

驻波热声制冷机分层回热器的特性研究

针对驻波制冷机回热器的7种分层方式进行研究,并通过DeltaEC计算驻波制冷机的声场分布、热流分布和相位差分布、最低制冷温度,以及制冷量与COP的特性规律。计算结果表明:随着制冷温度的降低,通过回热器的分层相应增大回热器的孔隙率,有利于改善流动损失,有效降低制冷温度,提高制冷效率。回热器的分层可以为热声制冷机性能的优化提供一种有效的手段。     

Transmitting boundary conditions for 1D peridynamics

The peridynamic theory reformulates the equations of continuum mechanics in terms of integro‐differential equations instead of partial differential equations. It is not straightforward to apply the available artificial boundary conditions for continua to peridynamic modeling. We therefore develop peridynamic transmitting boundary conditions (PTBCs) for 1D wave propagation. Differently from the previous method where the matching boundary condition is constructed for only one boundary material point, the PTBCs are established by considering the interaction and exchange of information between a group of boundary material points and another group of inner material points. The motion of the boundary material points is recursively constructed in terms of their locations and is determined through matching the peridynamic dispersion relation. The effectiveness of the PTBCs is examined by reflection analyses, numerical tests, and numerical convergent conditions. Furthermore, two‐way interfacial conditions are proposed. The PTBCs are then applied to simulations of wave propagation in a bar with a defect, a composite bar with interfaces, and a domain with a seismic source. All the analyses and applications demonstrate that the PTBCs can effectively remove undesired numerical reflections at artificial boundaries. The methodology may be applied to modeling of wave propagation by other nonlocal theories. Copyright © 2016 John Wiley & Sons, Ltd.     

An efficient indirect boundary element technique for multi‐frequency acoustic analysis

An efficient indirect boundary element solution procedure for the analysis of multi‐frequency acoustic problems is developed by incorporating techniques that improve the efficiency of the integration and matrix solution phases of the computing process. The integration phase is made efficient by computing the system matrices at few predetermined key frequencies only and then evaluating the matrices at other intermediate frequencies by quadratic interpolation. The matrix solution process is made efficient by iterating the solutions using the factored form of the key frequency matrices. The effectiveness of the present development is confirmed by solving a number of example problems. Copyright © 1999 John Wiley & Sons, Ltd.