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1.
用声透射损失测气一水混相介质中的含气量   总被引:3,自引:0,他引:3       下载免费PDF全文
高永慧 《应用声学》1999,18(1):32-35
本文利用超声检测中的穿透法,用频率为0.5MHz、1MHz、1.25MHz、2MHz、2.5MHz的声波,测量了气-水混相介质听声速比值和声透射损失,结果表明,在气泡大小,分布一定的情况下,可能用声透射损失来确定混相介质中的含量量,但不宜用声速比值。  相似文献
2.
水听器线列阵近场声压测量误差实验研究   总被引:1,自引:0,他引:1       下载免费PDF全文
本文介绍了用于近场声压的测量水听器中阵元水听器测量声压的可靠性检验方法和实验结果,提出了元水听器测量球面波场中声传播衰减的曲线与现想球面波声场中场传播衰减的曲线对比的检验,要用球面声源声中心测量值对收发距离进行修正的方法,实验水池中对线列阵上十元水吸器在球形声源水池中进行了传播衰减曲线的测量分析,验证了基阵的弱散散射性能,表明线阵可用于距离小至1/7波长的极近场的扫描测量。  相似文献
3.
This paper presents a straightforward application of an indirect method based on a three-microphone impedance tube setup to determine the non-acoustic properties of a sound absorbing porous material. First, a three-microphone impedance tube technique is used to measure some acoustic properties of the material (i.e., sound absorption coefficient, sound transmission loss, effective density and effective bulk modulus) regarded here as an equivalent fluid. Second, an indirect characterization allows one to extract its non-acoustic properties (i.e., static airflow resistivity, tortuosity, viscous and thermal characteristic lengths) from the measured effective properties and the material open porosity. The procedure is applied to four different sound absorbing materials and results of the characterization are compared with existing direct and inverse methods. Predictions of the acoustic behavior using an equivalent fluid model and the found non-acoustic properties are in good agreement with impedance tube measurements.  相似文献
4.
In developing passive acoustic systems for detecting insect infestations in bulk-stored grain, it is advantageous to understand the transmission of sound in the grain between the insects and the sensors. In the work presented here grain is shown to be a strong acoustical absorber, the attenuation coefficient increasing roughly as the square root of the frequency. Tests with soft wheat immersed in three different gases: air, argon and carbon dioxide, support an earlier conclusion that sound is transmitted principally through the gas in the passageways between the grain kernels. The speed of sound and the attenuation coefficient were measured as a function of frequency for six different types of grain: hard and soft wheat, brown rice, soybeans, corn and sorghum. It was determined that sound is transmitted over longer distances in grains with a larger inter-kernel spacing, such as corn and soybeans. Grain depth, up to several meters, appears to have little effect on sound transmission.  相似文献
5.
Computational intelligence (CI) techniques offer powerful alternatives for investigating acoustical issues and providing acoustical solutions to problems. This paper presents information on two CI techniques by applying them to the sound transmission performance prediction and design of floor-ceiling constructions.First a simple neural network (NN) model for predicting the airborne sound transmission of typical floor-ceiling constructions is presented and explained in detail. This model is accessible to researchers with knowledge of neural network analysis (NNA) for further sophistication, specialisation or hybridisation. The model may also be used by architects and others with no knowledge of NNA and no access to any specialised neural network software. Evolutionary algorithms (EAs) were then applied to search the multidimensional space created by the neural network model in order to optimise the airborne sound transmission of floor-ceiling constructions within the range of design parameters utilised in buildings.  相似文献
6.
Although SEA is a suitable framework for predicting sound transmission through double walls it has been found that the standard method of computing the non- resonant coupling loss factor from a room to cavity underestimates the coupling. A revised model for computing this coupling loss factor is presented which gives much better agreement with measured data. This allows better predictions to be made of sound transmission through lightweight double walls.  相似文献
7.
高永慧 《应用声学》1999,18(1):32-35
本文利用超声检测中的穿透法,用频率为0.5 MHz、 1MHz、 1.25MHz、 2MHz、 2.5MHz的声波,测量了气一水混相介质中的声速比值和声透射损失。结果表明:在气泡大小、分布一定的情况下,可能用声透射损失来确定混相介质中的含气量,但不宜用声速比值.  相似文献
8.
This paper examines space averaging methods applied to structural level differences measured in lightweight building structures (two beam junction and single plate and beam junction). The methods studied include the averaging assuming a constant input force, the averaging based on a constant vibration level across the source element, and the arithmetic averaging of level differences. Tests indicate that a fairly steady input force can be easily produced when using an impulsive source such as a hammer; the constant input force method is then appropriate and can be used to space average level differences (the two beam structure showing a standard deviation of 0.1 dB from the averaging based on levels normalised to the force). On the other hand, acceleration levels can exhibit significant variations with position due to the low mode count and modal overlap of some lightweight elements such as timber beams. Variations in the vibration level across the source element can then be responsible for large inaccuracies in the level difference calculated from the constant level assumption, the two beams’ results showing errors greater than 5 dB at several 1/3 octave band frequencies. The latter averaging method is then inappropriate and should not be used.  相似文献
9.
An experimentally validated analytical model has been developed in order to investigate the effect on impact sound transmission at low frequencies of location of the impact, type of floor, edge conditions, floor and room dimensions, position of the receiver and room absorption. The model was developed in order to allow rapid repeated calculations necessary for a parametric survey, described in a companion paper. The analytical model uses natural mode analysis to predict the sound field generated in rectangular rooms by point sound sources and the point excitation of homogeneous rectangular plates with different edge conditions. A floor-room model of the sound field generated in a room by a vibrating floor also has been derived. Laboratory and in situ measurements confirm that the models can be used to estimate impact sound transmission at low frequencies. The approach applies to homogeneous simply supported base plates of uniform thickness with homogenous floating floors, which again were experimentally validated in the laboratory and in situ.  相似文献
10.
Multi-layer structures have issues with sound insulation at low and mid-frequencies due to mass-air-mass resonance. The purpose of this study is to investigate improvements to the sound insulation performance of multi-layer structures using a microperforated panel (MPP), which can absorb well over a wide frequency range. Although MPPs have been investigated over the last several decades, almost all studies have been conducted in terms of sound absorption. Herein the sound transmission loss of multi-layer structures with flexible MPPs of infinite extent is theoretically investigated. The calculation is based on the wave equation and the equation of panel vibration including the effect of perforation of the panel. Additionally to consider a more realistic sound insulation performance, the effect of the directional distribution of the incident energy in a reverberation chamber is taken into account. Experiments are conducted using an acoustic tube to validate the calculated results and the reverberation chamber method to verify the actual sound insulation characteristics. Both experiments agree well with the theoretically calculated perforation effects. Consequently, MMPs are confirmed to improve the deterioration of sound insulation performance due to mass-air-mass resonance of multi-layer structures.  相似文献
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