几种声扩散结构的模型试验研究

室内声场的扩散程度是影响房间音质的重要因素。本文讨论实现声扩散的各种结构的声学特性,并就此进行模型试验。文中着重比较了M.R.Schroeder提出的QR序列(二次剩余序列)扩散板与常用的规则形扩散体的散射性能。试验结果表明,QR扩散板明显优于规则形的扩散体。首先,QR扩散板的散射图案十分均匀;其次,它的作用频带较宽;再者,它对于任意方向的入射声都有较好的散射作用。此外,它可以产生反射声序列。因此,这种扩散板对于录音室、音乐厅等建筑的声学设计具有良好的应用价值。     

水下三弹性柱壳耦合声散射特性研究

为研究3个并排无限长弹性圆柱壳受垂直于柱轴方向的平面声波作用的声散射特性,采用Fourier级数展开法建立了圆柱壳声散射数学物理模型,考虑了三圆柱壳弹性振动声辐射和刚性声散射,建立了3个壳体辐射声场和刚性散射声场的耦合作用关系,比对了等效散射强度的刚性散射分量与弹性散射分量,并分析了三壳体等效散射强度特性。计算结果表明:当ka_2>40,在频率f=3000 Hz以上频段,弹性分量对等效散射强度变化趋势的贡献可以忽略。当ka_2>30,在频率f=2400 Hz以上频段,弹性散射分量对等效散射强度影响不超过3 dB;三壳与单壳的等效散射强度在0°入射角方位相当,其它方位三壳体等效散射强度明显大于单壳体。本文的理论公式可推广到任意数量阻抗柱的声透射和声反射问题。     

三弹性圆柱壳体多重耦合声辐射计算方法

为研究多圆柱壳组合结构的声辐射特性,采用模态叠加法建立了3个并排无限长弹性圆柱壳的振动声散射耦合物理模型,充分考虑了三圆柱壳的表面振动与散射声场的耦合,其中散射声场可分解为各圆柱壳刚性散射声场和弹性辐射声场的叠加,数学上将各壳间的声场耦合关系通过柱函数加法公式描述。利用该物理模型,分析了多重散射对稳态声场求解结果的影响,比较了三圆柱壳耦合系统与单个圆柱壳系统的辐射声场指向性、声压级及辐射声功率级的差异及其产生机理,结果表明:结构弹性耦合声辐射不仅在低频对总声场有显著影响,在高频范围也不可忽略;另外,针对本文设定参数的组合圆柱壳,在150 Hz以上频段,两旁圆柱壳对中间圆柱壳在正横方位产生了声辐射遮蔽效应,垂直方位则体现声泄漏作用。本文建立的方法可推广到三维空间任意多壳结构的声振耦合建模。     

海洋波导中刚性球及旋转椭球前向散射场时频特征的畸变

利用波导中目标声散射理论的简正波方法,数值模拟了自由空间和浅海均匀波导中刚性球、旋转椭球的散射场,分析了波导中刚性体前向散射时频特征的畸变规律。仿真结果表明:波导中刚性体的前向散射时域波形与频谱特征受波导制约;目标散射场的固有特征受波导色散特征的调制,时频谱上呈现出由于色散的简正波间的耦合而导致各简正波能量条纹界限模糊的现象。时频特征的畸变程度与组成散射共振系统的波导、目标的尺度以及散射体布放深度有关,随波导底质透声能力和深度增加、散射体散射强度(信混比)增强而减弱。     

水下弹性球体对Bessel波束散射的计算及分析

以弹性球体为例,分析Bessel波束入射到水下物体时的声散射。将水下弹性球体声散射场的分波序列计算公式加以推广,应用于Bessel波束入射的情况。借鉴平面波散射的模式,通过几何分析指出了Bessel波束入射下镜反射波和Franz波干涉所形成的反向散射形函数上的峰一峰间隔与波束特征参数β的关系,并首次给出了峰峰间隔的预报公式。同时,采用共振散射理论对每阶分波的弹性散射单独分析,深入研究了β对纯弹性共振的影响,发现通过选取特定的β可以使相应阶分波的弹性散射贡献被消除,从而使在反向散射中对应频率及其附近处的共振得到显著的抑制。     

采用球面波叠加法还原自由声场的方法

为解决非自由声场中近场声全息重建时,干扰声在目标声源表面产生的散射影响,提出一种基于球面波叠加法的自由场还原技术。该技术首先采用基于球面波叠加法的声场分离技术获得向内和向外传播的声场,然后以目标声源的表面导纳作为边界条件,实现目标声源辐射声和散射声的分离,从而获得等效于自由声场的测量条件。该技术为准确实现非自由声场中的噪声源识别创造了条件。文中首先详细描述了该技术的基本原理,并提出一种最优球面波展开项数选取方法,最后通过数值仿真说明了该技术的有效性。结果表明:在频率较低时,散射声影响较小,采用声场分离技术和自由场还原技术效果相当;但随着频率升高,散射声影响逐步增强,必须采用自由场还原技术才能准确获得目标声源辐射声。     

基于声源定位技术的建筑立面声反射研究

建筑立面对场地的声环境存在不可忽视的影响。以往的研究都是基于国际标准或者计算机模拟,不能直观地展示建筑立面上不同部位对入射声的几何反射和扩散反射效应。本文通过现场实测的方式,运用声学照相机,对建筑立面如何影响周围场地声环境的全过程展开可视化研究。结果表明,由于台阶、雨篷檐口等建筑构件在空间位置上处于立面之前,会发生声扩散反射现象。台阶的声扩散反射性能在315~630 Hz频段最强,雨篷檐口的声扩散反射性能在100~1k Hz频段最强。建筑立面上声扩散反射强信号区域为雨篷内部空间和立面中轴线。雨篷内的声反射强信号区域面积随着声源距离的增加而逐渐变大。在中轴线上,来自建筑立面的扩散反射声信号的声压级随着立面高度的增加而有所衰减,这种衰减趋势随声源距建筑立面的距离越远越明显。     

水泥-粉煤灰-黏土复合浆材的注浆试验研究

通过室内模型注浆试验,研究水泥-粉煤灰-黏土复合浆材扩散半径与注浆后结石体单轴饱和抗压强度受注浆压力、浆液水灰比、注浆时间等单因素和多因素耦合影响规律及其之间的数学模型.试验结果表明:对浆液的扩散半径影响显著性的顺序依次为注浆压力、浆液水灰比与注浆时间;对注浆后结石体抗压强度影响显著性的顺序依次为浆液水灰比、注浆压力与注浆时间,其中水灰比为负向影响。     

汉传佛寺大雄宝殿内空间要素与声源指向对声场的影响

为了探讨汉传佛教大雄宝殿内空间要素与声源指向对声场的影响机制,首先通过实测和计算机声学模拟,确定古建筑室内材料的声学参数和软件的参数设置,然后建立并分析佛寺大雄宝殿的计算机声场模型。研究结果表明,佛殿内的空间要素中,佛像可以起到声扩散体的作用,特别是设置在侧墙位置的次要佛像能够显著影响声场的混响时间及STI值,佛殿内设置的各类装饰织物能够起到吸声体作用,对声场影响主要体现在混响时间RT30和EDT上,声源的指向性主要影响EDT和C80值。     

混合弹性颗粒体系声衰减数值模拟

采用概率统计方法——蒙特卡罗方法,建立一种预测液固两相体系中混合弹性球形颗粒声衰减的理论模型。在单颗粒声散射和吸收的基础上,将连续超声波抽象离散化为大量独立的声子,追踪声散射过程,通过统计接收器探测声子数最终确定声衰减系数。采用数值方法对单一球形颗粒的液固两相体系中声衰减进行预测和比较,确定了该方法的可行性后将该方法推广到混合颗粒体系中,对玻璃微珠/铁粉构成的混合颗粒及多分散混合颗粒体系进行数值研究。结果表明:在体积浓度低于10%时,蒙特卡罗法预测得玻璃微珠或铁粉颗粒声衰减和ECAH,Lloyd和Berry,Waterman等建立的模型结果吻合。对于混合颗粒构成的两相体系,算例中,随着体积浓度增大到10%,声衰减系数随混合颗粒数目比的变化呈现出了非线性的变化,同时颗粒物性也会影响不同组分颗粒对声衰减的贡献,算例中铁粉颗粒比玻璃微珠对声衰减的影响更大。     

Numerical investigation of the swirling air diffuser: Parametric study and optimization

During the recent decade, high induction diffusers have become more appealing in applications which require relatively high ventilation airflow rates, such as clean rooms. In this research, the effect of geometric parameters on the performance of a specific type of swirling air diffuser is investigated numerically. The results show that although the diffuser slots geometry, namely their angle and aspect ratio, is impressive on the diffuser performance, it is not as important as the swirling blade angle and the performance is almost constant in a wide range of slots specifications. The results also demonstrate that the diffuser performance and the resultant indoor airflow distribution highly depends on the blades angle and their sensitivity is surprisingly significant when the angle is between 30° and 35°. It is also worth mentioning that the optimum angle of 32° is almost independent of the diffuser airflow rate. Finally, the diffuser jet indexes, namely jet decay coefficient and entrainment ratio, are evaluated for the optimum diffuser and are compared with other common types of diffusers. This research and its results are useful in gaining a better understanding of the swirling diffuser airflow and the effect of diffuser geometry features on its performance.     

Experimentelle und numerische Untersuchungen eines komplexen Luftdurchlasses

Numerical and experimental investigations of a complex diffuser. Experiments and numerical simulations (CFD) are conducted for the evaluation of the supply air flow through a complex air diffuser. For the numerical calculations the diffuser is incorporated and presented in detail in the simulation resolving the flow field inside the diffuser. Velocity measurements are performed in the occupied region as well as in the near‐zone of the diffuser. The analyzed diffuser shows a complex flow pattern with transient flow structures in the induced room air. The calculated velocities und the velocity distribution in the near‐zone of the diffuser agree rather well with measurements. The applied standard two equation turbulence model is not able to resolve the detached vortices revealed in the experiments. Furthermore, the modelling approach of the perforated plate by a source term in the momentum equation seems to be not sufficient.     

CFD modelling of an industrial air diffuser—predicting velocity and temperature in the near zone

This article describes experimental and modelling results from CFD simulation of an air diffuser for industrial spaces. The main objective of this paper is to validate a manufacturer model of the diffuser. In the air diffuser, the low velocity part is placed on top of a multi-cone diffuser in order to increase airflow rates and maximize the cooling capacity of a single diffuser unit. This kind of configuration should ensure appropriate performance of industrial air diffusers, which is discussed briefly at the end of the article. The paper illustrates the importance of a simulation model jointly with the manufacturer's product model and the grid layout near the ventilation device to achieve accurate results. Parameters for diffuser modelling were adapted from literature and manufacturer's product data. Correct specification of diffuser geometry and numerical boundary conditions for CFD simulations are critical for prediction. The standard k–ε model was chosen to model turbulence because it represents the best-known model utilized and validated for air diffuser performance. CFD simulations were compared systematically with data from laboratory measurements; air velocity was measured by ultrasonic sensors. Results show that CFD simulation with a standard k–ε model accurately predicts non-isothermal airflow around the diffuser. Additionally, smoke tests revealed that the flow around the diffuser is not completely symmetrical as predicted by CFD. The cause of the observed asymmetry was not identified. This was the main reason why some simulation results deviate from the measured values.     

声学材料研究的进展与展望

简述了我国现代声学材料的现状和存在的问题，介绍了声学材料的研究范围和发展史，提出声学材料将向环保型和安全型，复合型和多功能型的方向发展，表现出声学材料在现代建筑设计中的重要作用。     

A model for an under floor air distribution system

We present a simplified model of an underfloor air distribution (UFAD) system consisting of a single source of heat and a single cooling diffuser in a ventilated space. Laboratory experiments were carried out to simulate the flow and a model for the flow in this space is proposed. The model is based on plume theory for the heat source and a fountain model for the diffuser flow, and predicts a steady-state two-layer stratification in the room. The governing parameters are shown to be the buoyancy flux of the heat source, and the volume and momentum fluxes of the cooling diffuser. The results suggest ways to optimize UFAD design and operation.     

试论厅堂音质的主观评价

厅堂音质的评价是建筑声学与音乐声学共同关心的课题．从质量、数量和空间等三个方面论述了厅堂音质一些常见的主观评价指标，提出了避免由一些明显的建筑方面问题引起的声学缺陷．     

Sensitivity of the predicted convective heat transfer in a cooled room to the computational fluid dynamics simulation approach

Computational fluid dynamics (CFD) plays an increasingly important role in the design, analysis and optimization of engineering systems. However, CFD does not necessarily provide reliable results. The most crucial numerical solution error is caused by inadequate grid resolution, and the key modelling error sources in CFD in ventilated indoor environments are turbulence modelling and diffuser modelling. Many researchers already proposed guidelines, but they based their analyses on local variables. In response, underlying study intended to verify the impact of the CFD simulation approach on the convective heat flux, an integral quantity. The authors tested several grids, Reynolds averaged Navier–Stokes turbulence models and diffuser models for three convection regimes in a cooled room. The diffuser modelling had a much larger impact than the grid and the turbulence modelling, as long as the jet dominated the airflow. So, CFD users, who want to model forced/mixed convection airflow indoors, certainly need to pay attention to the diffuser modelling.     

Development of a shrouded wind turbine with a flanged diffuser

We have developed a wind turbine system that consists of a diffuser shroud with a broad-ring flange at the exit periphery and a wind turbine inside it. The flanged-diffuser shroud plays a role of a device for collecting and accelerating the approaching wind. Emphasis is placed on positioning the flange at the exit of a diffuser shroud. Namely, the flange generates a low-pressure region in the exit neighborhood of the diffuser by vortex formation and draws more mass flow to the wind turbine inside the diffuser shroud. To obtain a higher power output of the shrouded wind turbine, we have examined the optimal form of the flanged diffuser, such as the diffuser open angle, flange height, hub ratio, centerbody length, inlet shroud shape and so on. As a result, a shrouded wind turbine equipped with a flanged diffuser has been developed, and demonstrated power augmentation for a given turbine diameter and wind speed by a factor of about 4-5 compared to a standard (bare) wind turbine. In a field experiment using a prototype wind turbine with a flanged diffuser shroud, the output performance was as expected and equalled that of the wind tunnel experiment.     

Comparison of Displacement and Mixing Diffusers

In order to cumpare the peformance of different supply diffuers of ventilation air, the airflow passern, temperature stratifiation and contaminant dispersion in a furnitured office ventilated by three kinds of air diffuer were numerically investigated. The air diffuers studied in this paper are a quarter-cylinder displacement diffuer on the floor and mixing diffuers (linear and vortex diffuers) on the ceiling. The heat sources in the of-fice are considered to be 50% convective and 50% radiative. The k-? two-equatwn model of turbulence is employed to predict the turbulent diffusion. The results show that the displacement diffuser provides a rather uniform flow field with low velocify in most areas, and the vertical temperature difference from floor to ceiling is as high as 6 K. With the linear diffuser, the air velociry is high, and the temperature is uniform both horizontally and vertically. The air velocity generated by the vortex diffuser is moderate. The distributions of the temperature and the contaminant are rather uniform.     

Virtual reconstruction of indoor acoustics in cathedrals: The case of the Cathedral of Granada

Virtual acoustics provides a highly useful tool for the investigation into the influence that spatial transformations may exert on indoor acoustics of cathedrals, which are remarkable spaces due to their heritage value, complexity and multifunctional character. The spatial organization of cathedrals is primarily governed by the location of the choir, which represents the main musical expression. Following various reforms, certain European cathedrals undertook a relocation of the choir stalls from their original position. The Cathedral of Granada is a highly significant case. Since its original construction, three major changes have occurred due to the relocation of the choir. In this article, simulation of indoor acoustics is employed to recover the soundfield in each of these three configurations. An extensive analysis compares the results of the main acoustic parameters in each of the virtual reconstruction models. Consequently, acoustic models are created and then calibrated based on a campaign of onsite measurements.