合成双射流对下游声压级影响试验

在Ma=0.4的来流条件下, 利用安装在主翼后缘处的合成双射流激励器对襟翼上的流动进行控制, 在风洞中开展了合成双射流对下游声压级影响的研究. 基于脉动压力测量结果, 结合油流显示试验, 得到了合成双射流对下游不同流动状态区域声压级影响的一些结论. 对于附着流, 在其峰值频率附近激励会明显提高其声压级; 对于受旋涡主导的流动, 恰当的合成双射流控制可以降低声压级, 激励频率较为关键. 在俯仰运动过程中, 对于附着流, 激励提高了声压级, 但不改变其迟滞特性; 对于受旋涡主导的流动, 激励对声压级的影响与攻角有关, 能够减弱其迟滞特性, 但激励强度对迟滞特性的影响较小, 减小声压级的最佳激励与运动历程有关.      

未知耦合腔体积活塞发声器声压级的检测

本文简要介绍了活塞发声器的工作原理及其声压级的测量原理，着重分析了未知耦合腔体积活塞发声器的有效体积与声压级的测量方法。     

烟火药和压缩氮气声源水下声辐射特征对比研究

为研究烟火药水下燃烧声辐射机理,采用烟火药和压缩氮气喷射声源对比的方法,利用水声测试系统,通过实验研究不同体积流量下两种声源装置的声辐射规律。结果表明,烟火药水下燃烧声源与压缩氮气声源的声辐射特征相似,辐射频率主要集中在0～1000 Hz内,峰值频率均位于100 Hz附近,总声压级、峰值声压级均随着气体流量增加而增强。当气体流量从60 ml/s增加到84 ml/s时,烟火药峰值声压级由155 d B增加到163 d B,0～1000 Hz内总声压级由159 d B增加到165 d B;当喷气流量从70 ml/s增加到141 ml/s时,压缩氮气源峰值声压级由136 d B增加到139 d B,0～1000 Hz内总声压级由144 d B增加到147 d B。当气体流量相近时,烟火药相比压缩氮气声压级相差显著,其声压级均高于同频率下压缩氮气源,两者的峰值声压级分别为157 d B、139 d B,0～1000 Hz内总声压级分别为160 d B、147 d B。     

利用智能手机显示声音的频谱并探究声压级与距离的关系

利用智能手机中的Phyphox软件设计了2个声学实验,即声音的频谱显示和验证声压级与距离的关系,详述了在声音的频谱显示实验中如何直观显示声音的3要素,在探究声压级与距离关系的实验中如何测量不同距离的声压级,然后将实验数据拟合成图线,验证理论公式.     

凹腔非定常特性的数值模拟

采用基于Menter SST两方程湍流模型的DES方法,数值模拟开式凹腔在跨声速条件下的非定常流动特性.计算凹腔底部和后壁面上的点的声压级频谱以及总声压级,证明在第二噪声模态上的声压级最大.     

航天飞行器实验室的高声强噪声产生能力

加拿大NAE空气动力装备、结构和材料实验室设置了总声压级为157dB的航天飞行器混响室,总声压级为167dB的行波管和总声压级为150—155dB的高声强小型混响室,它们的噪声谱可以用不同截止频率喇叭和噪声发声器组合来进行控制,这是根据1980年要求对加拿大航天飞行器的质量鉴定需具有低频分量的高声强噪声环境而改建的。气源为300Psig,50001~3。     

超声空化状态对苯酚降解的影晌

给出不同空化状态下超声波降解苯酚溶液的实验结果,比较了相应的声压级频谱和合成声强。研究了苯酚溶液的浓度、二阶铁盐、超声辐照时间对苯酚降解率的影响,讨论了不同空化状态下的声压级频谱特征。     

声波作用下铜球传热特性实验*

针对频率为500 Hz～3000 Hz和声压级为110 d B～133 d B的声场作用对铜球在空气中自然冷却的传热特性的影响,通过热电偶测温的方法,分析铜球温度梯度的分布与声场声压级、频率以及铜球直径的关系。结果表面,当频率f一定时,随着声压级的增加,铜球的传热效果得到明显增强,对于直径为5 mm的铜球,在133 d B声场中传热系数最大增加了25%。当声压级一定时,在频率范围中存在某一频率,此时铜球的传热系数最大,此特殊频率随着声压级的增大而增大。当铜球的直径为5 mm时,可以在低频段观测到声流效应的影响,而当铜球的直径为10 mm、15mm时,很难在低频段辨别出声流效应的影响。所得结论为声波应用于电站锅炉中,强化煤颗粒燃烧提供了依据。     

超声空化状态对苯酚降解的影响

给出不同空化状态下超声波降解苯酚溶液的实验结果,比较了相应的声压级频谱和合成声强。研究了苯酚溶液的浓度,二阶铁盐,超声辐射时间对苯酚降解率的影响,讨论了不同空化状态下的声压级频谱特征。     

环境噪声对儿童短时记忆力和注意力的影响

通过实验室研究探讨了不同噪声源在不同声压级条件下对儿童短时记忆力和注意力的影响。在每一个实验中都选取了30名710岁的儿童作为被试,在他们完成相应认知任务的同时,用耳机随机播放3565 dBA的交通噪声、白噪声和空调噪声,考察各种噪声条件对被试认知成绩和主观烦恼度的影响。研究结果表明,噪声对儿童的影响主要体现在主观烦恼度的变化上,不同的噪声条件并没有引起作业成绩的显著差异。影响儿童主观烦恼度的主要因素是声压级,随着声压级的增大,儿童的烦恼度会增加,当声压级在4550 dBA时,儿童对噪声开始产生烦恼感,当声压级在6065 dBA时,儿童对噪声产生了较显著的烦恼感。声压级对儿童烦恼度的影响没有随着噪声源的改变而改变。在相同的噪声条件下,短时记忆力实验中儿童的主观烦恼度都高于注意力实验,说明随着认知过程复杂程度的增加,噪声引起的烦恼度会相应增加。      

水声声强测量分析系统及其在水下噪声鉴别中的应用

本文将空气中能形成测量分析系统的声强测量技术引入到水介质中，建立了一套水声声强测量分析系统，讨论了此套水声声强测量分析系统的硬，软件组成及特征，实验验证了本系统的可靠性，利用此声强分析系统对水下双噪声源的近场作了平面扫描测量，可以定位和鉴别这两个噪声源。     

Estimated subglottal pressure in six professionalcountry singers

Estimates of subglottal pressure in six professional male country singerswere obtained during the /p/ occlusion while the subjects spoke, sang a country tune, and sang the tune of the United States national anthem. The subglottal pressure values, which were very similar in both the speech-like and singing-mode syllables, usually measured below 45 cm of water column, but they ranged as high as 59 cm. The sound pressure level in singing was also measured and was lower than that discovered in classically trained singers at high subglottal pressures.     

一种强指向性基阵的设计及声场计算

提出了一种新的基阵:将90个小圆环分布于半径不同的5个同心圆周上,对每个小圆环采用了抛物型的振速加权。通过改变阵元尺寸、间距等参数研究了声场特征的变化。计算结果表明,该基阵模型具有非常高的指向性和抑制旁瓣的能力。通过优化阵元组合方式和参数,可获得最佳的声压分布效果。     

应用于热声系统的声学倒相变压器

给出了一种声学调相变压结构,并理论上讨论了该结构的调相变压机理。结果表明:在一定的几何条件下,该结构能够实现不受负载影响的声压放大功能,并输出声压倒相;将该结构应用于热声热机驱动热声制冷机或脉冲管制冷机的耦合,可以取得更好的效果。     

Estimation of increases in noise levels due to installation of transverse rumble strips on urban roads

Increases in noise due to the installation of transverse rumble strips were investigated, by first measuring noise due single vehicles crossing a pilot test field with and without a rumble strip. After that, a procedure was proposed and carried out to estimate increases in noise due to the traffic of vehicles, based on the measurements previously mentioned. This procedure was checked against expressions from the literature that estimate traffic noise as well as measurements in three arterial urban roads without rumble strips installed. Its accuracy was compatible with the ones obtained by applying the literature expressions, the errors lying below 3 dB(A). Then, by taking the aforementioned roads as case studies, estimations were carried out for the increases that would occur in noise levels if rumble strips were installed on them, leading to values between 6 and 7 dB(A). Although such values are dependent on the configuration of the rumble strip employed, the proposed procedure presents generality and could be applied to estimate increases in traffic noise due to installation of rumble strips, by departing from measurements of noise due to single vehicles obtained for a given rumble strip configuration.     

Ultrasound pressure distributions generated by high frequency transducers in large reactors

The performance of an ultrasound reactor chamber relies on the sound pressure level achieved throughout the system. The active volume of a high frequency ultrasound chamber can be determined by the sound pressure penetration and distribution provided by the transducers. This work evaluated the sound pressure levels and uniformity achieved in water by selected commercial scale high frequency plate transducers without and with reflector plates. Sound pressure produced by ultrasonic plate transducers vertically operating at frequencies of 400 kHz (120 W) and 2 MHz (128 W) was characterized with hydrophones in a 2 m long chamber and their effective operating distance across the chamber’s vertical cross section was determined. The 2 MHz transducer produced the highest pressure amplitude near the transducer surface, with a sharp decline of approximately 40% of the sound pressure occurring in the range between 55 and 155 mm from the transducer. The placement of a reflector plate 500 mm from the surface of the transducer was shown to improve the sound pressure uniformity of 2 MHz ultrasound. Ultrasound at 400 kHz was found to penetrate the fluid up to 2 m without significant losses. Furthermore, 400 kHz ultrasound generated a more uniform sound pressure distribution regardless of the presence or absence of a reflector plate. The choice of the transducer distance to the opposite reactor wall therefore depends on the transducer plate frequency selected. Based on pressure measurements in water, large scale 400 kHz reactor designs can consider larger transducer distance to opposite wall and larger active cross-section, and therefore can reach higher volumes than when using 2 MHz transducer plates.     

Determination of the sound power levels emitted by various vehicles using a novel testing method

This paper presents a new and efficient method to determine sound power levels (PWLs). PWLs, generally used for modeling outdoor sound simulations, are obtained from sounds that are emitted by various types of vehicles and cause road traffic noise. Other models, such as HARMONOISE and the ASJ Model, are also based on PWLs. However, a more efficient method is required for determining PWLs from sound pressure levels (SPLs) that typically are measured by field testing and evaluating the influence of different vehicles and road surfaces. The statistical pass-by (SPB) of ISO 11819-1 is used for SPL measurements; however, numerous SPBs must be carried out to reduce measurement uncertainty as well as to satisfy requirements related to meteorological conditions and background noise. In order to alleviate this problem and to make the determination of PWLS more efficient, a testing approach is presented that uses both the novel close proximity (NCPX) method and the pass-by method to determine PWLs.     

Field measurement of airborne sound insulation between rooms with non-diffuse sound fields at low frequencies

Procedures for the field measurement of airborne sound insulation between rooms with diffuse fields are described in International Standard ISO 140-4. However, many dwellings contain rooms with volumes less than 50 m³, where low frequency measurements are less reliable; hence there is a need for a measurement procedure to improve the reliability of field measurements in rooms with non-diffuse fields. Procedures are proposed for sound pressure level and reverberation time measurements for the 50, 63 and 80 Hz third octave bands. The sound pressure level measurement combines corner microphone positions with positions in the central region of each room. This provides a good estimate of the room average sound pressure level with significantly improved repeatability.