某汽车空调单体音调噪声的烦恼度评价研究

针对汽车空调工作时产生的音调噪声会使驾乘人员产生烦恼感,对某汽车空调单体的音调噪声烦恼度模型进行研究。首先采用模拟噪声的方法解决实际噪声样本不足的问题,然后通过主客观评价和相关性分析,建立了汽车空调单体音调噪声的烦恼度模型。研究表明:汽车空调单体的音调噪声烦恼度主要受音噪比和响度的影响;通过该模型能够准确预测汽车空调单体音调噪声对人耳造成的烦恼度数值。

Ultrasonic frogs call at a higher pitch in noisier ambiance

The ultrasonic communication in Concave-eared torrent flogs Odorrana tormota is believed to be an adaptation to avoid masking by the intense low-frequency noise of the rushing stream in their habitat. The acoustic adaptation hypothesis for ultrasonic origin predicts that some organisms subjecting to persistent acoustic interference from broadband, low-frequency en- vironmental noise, might shift their signal frequency upward into frequency bands with lower noise energy. In other words, low-frequency environmental noise might cause upward shifts of species＇ vocalization frequencies making their signals more conspicuous. Presently, it is unclear whether male O. tormota adjust their signal features in response to a change in the ambient noise level. We tested the prediction of the acoustic adaptation hypothesis by recording the vocalizations of male O. tormota in- habiting two streams with different background noise levels in Huangshan in central China and comparing their call features in- cluding the fundamental frequency （F0）. Results showed that the spectrotemporal characteristics of the vocal signals of males in the two habitats were indifferent, except the duration of the call harmonic segments and three parameters related to the call fun- damental frequency （F0）. In terms of the F0, the pooled and individual frog data showed that flogs inhabiting the noisier habitat tended to emit calls having higher F0. The higher F0 increases the signal-to-noise ratio, thus benefiting the detection of vocaliza- tion. Thus, similar to several anuran species, concave-eared torrent frogs also display noise-dependent adjustment of vocal pitch in their vocalizations for making them more audible

Jet Screech Reduction with Perforated Flat Reflector

In the present experimental study, investigations have been carded out to evaluate the performance of the new control technique of jet screech with different perforated flat reflectors. Mainly two types of porous flat reflectors had been used in the experiment. One reflector （reflector-V） designed for placing the reflector surface vertical to the jet axis, when, another type of reflector （reflector-H） designed for placing the reflecting surface horizontal to the jet axis. In both cases the reflectors had been placed at the nozzle （base tube with uniform cross-sectional area） exit. The diameter of the reflector-V was 15D when the diameter of the reflector-H was 10D. The porous area of the reflector-V was 6D and 4.5D for reflector-H where D indicated the diameter of the nozzle exit. The placement of the reflector at the exit of the nozzle reduces the sound pressure at the nozzle exit. Thus the muted sound can not excite the unstable disturbance at the nozzle exit and the loop of the feedback mechanism disappeared, finally, the generation of jet screech be cancelled. The suction space located at the back side of the porous surface of the reflector-V improves the efficiency of the screech control technique. However, in the case of reflector-H, the receptivity process of feedback loop had been controlled by reducing the disturbances at the effective shock fronts as well as at the nozzle exit. The performance of the proposed method was verified with a flat reflector concept and good performance in jet screech suppression has been confirmed in the case of porous reflector.

Mechanism of Tonal Noise Generation from Circular Cylinder with Spiral Fin

The pitch of the spiral finned tube influences seriously to the acoustic resonance in the heat exchanger.In this research,the flow characteristics in relating to the aeolian tone from the finned cylinder are studied by the numerical simulation.It is observed that the tonal noise generated from the finned tube at two pitch spaces.The ratio of the fin pitch to the cylinder diameter is changed at 0.11 and 0.27.The tone level increases and the frequency decreases with the pitch shorter.The separation flow from the cylinder generates the span-wise vortices,Karman vortices,and the separation flow from the fin generates the stream-wise vortices.When the fin pitch ratio is small,the stream-wise vortices line up to span-wise and become weak rapidly.Only the Karman vortices are remained and integrate in span.So the Karman vortex became large.This causes the low frequency and the large aeolian tone.