The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new meth...The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new method for estimating ultrasonic attenuation using a spectral ratio based on an S transform(SR-ST)is presented to improve the stability and accuracy of Q estimation.The variable window of ST is used to solve the time window problem.We add two window factors to the Gaussian window function in the ST.The window factors can adjust the scale of the Gaussian window function to the ultrasonic signal,which reduces the calculation error attributed to the conventional Gaussian window function.Meanwhile,the frequency bandwidth selection rules for the linear regression of the amplitude ratio are given to further improve stability and accuracy.First,the feasibility and influencing factors of the SR-ST method are studied through numerical testing and standard sample experiments.Second,artificial samples with different Q values are used to study the adaptability and stability of the SR-ST method.Finally,a further comparison between the new method and the conventional spectral ratio method(SR)is conducted using rock field samples,again addressing stability and accuracy.The experimental results show that this method will yield an error of approximately 36%using the conventional Gaussian window function.This problem can be solved by adding the time window factors to the Gaussian window function.The frequency bandwidth selection rules and mean slope value of the amplitude ratio used in the SR-ST method can ensure that the maximum error of different Q values estimation(Q>15)is less than 10%.展开更多
The multi-dimensional time-domain computational fluid dynamics(CFD) approach is extended to calculate the acoustic attenuation performance of water-filled piping silencers. Transmission loss predictions from the time-...The multi-dimensional time-domain computational fluid dynamics(CFD) approach is extended to calculate the acoustic attenuation performance of water-filled piping silencers. Transmission loss predictions from the time-domain CFD approach and the frequency-domain finite element method(FEM) agree well with each other for the dual expansion chamber silencer, straight-through and cross-flow perforated tube silencers without flow. Then, the time-domain CFD approach is used to investigate the effect of flow on the acoustic attenuation characteristics of perforated tube silencers. The numerical predictions demonstrate that the mean flow increases the transmission loss, especially at higher frequencies, and shifts the transmission loss curve to lower frequencies.展开更多
In this paper, the authors propose a new approach to image compression based on the principle of Set Partitioning in Hierarchical Tree algorithm （SPIHT）. Our approach, the modified SPIHT （MSPIHT）, distributes entr...In this paper, the authors propose a new approach to image compression based on the principle of Set Partitioning in Hierarchical Tree algorithm （SPIHT）. Our approach, the modified SPIHT （MSPIHT）, distributes entropy differently than SPIHT and also optimizes the coding. This approach can produce results that are a significant improvement on the Peak Signal-to-Noise Ratio （PSNR） and compression ratio obtained by SPIHT algorithm, without affecting the computing time. These results are also comparable with those obtained using the Embedded Zerotree Wavelet （EZW） and Joint Photographic Experts Group 2000 （JPG2） algorithms.展开更多
We report two models of the lateral displacement of acoustic-wave scattering on a fluid-solid interface that reveal an acoustic analog of the Goos-Hainchen effect in optics. This acoustic analog is called the acoustic...We report two models of the lateral displacement of acoustic-wave scattering on a fluid-solid interface that reveal an acoustic analog of the Goos-Hainchen effect in optics. This acoustic analog is called the acoustic Goos-Hainchen effect. Using newly proposed models, we made numerical calculations for the system ofa water-Perspex interface. Specifically, in the post-critical-angle region, we observed a lateral displacement （and transition time） of the reflected P-wave with respect to the incident P-wave. The first arrival of the acoustic signal from the interface is found to be a reflected P-wave rather than the sliding-refraction P-wave usually described in traditional acoustic-logging sliding P-wave theory. For both proposed models, the effective propagation speed of the reflected P-wave along the interface depends on not only the physical properties of the interracial media but also the incident angle. These observations are intriguing and warrant further investigation.展开更多
基金supported by the Special Fund of the Institute of Geophysics,China Earthquake Administration(Nos.DQJB19B02 and DQJB17T04)
文摘The quality factor(or Q value)is an important parameter for characterizing the inelastic properties of rock.Achieving a Q value estimation with high accuracy and stability is still challenging.In this study,a new method for estimating ultrasonic attenuation using a spectral ratio based on an S transform(SR-ST)is presented to improve the stability and accuracy of Q estimation.The variable window of ST is used to solve the time window problem.We add two window factors to the Gaussian window function in the ST.The window factors can adjust the scale of the Gaussian window function to the ultrasonic signal,which reduces the calculation error attributed to the conventional Gaussian window function.Meanwhile,the frequency bandwidth selection rules for the linear regression of the amplitude ratio are given to further improve stability and accuracy.First,the feasibility and influencing factors of the SR-ST method are studied through numerical testing and standard sample experiments.Second,artificial samples with different Q values are used to study the adaptability and stability of the SR-ST method.Finally,a further comparison between the new method and the conventional spectral ratio method(SR)is conducted using rock field samples,again addressing stability and accuracy.The experimental results show that this method will yield an error of approximately 36%using the conventional Gaussian window function.This problem can be solved by adding the time window factors to the Gaussian window function.The frequency bandwidth selection rules and mean slope value of the amplitude ratio used in the SR-ST method can ensure that the maximum error of different Q values estimation(Q>15)is less than 10%.
基金Project(11174065)supported by the National Natural Science Foundation of China
文摘The multi-dimensional time-domain computational fluid dynamics(CFD) approach is extended to calculate the acoustic attenuation performance of water-filled piping silencers. Transmission loss predictions from the time-domain CFD approach and the frequency-domain finite element method(FEM) agree well with each other for the dual expansion chamber silencer, straight-through and cross-flow perforated tube silencers without flow. Then, the time-domain CFD approach is used to investigate the effect of flow on the acoustic attenuation characteristics of perforated tube silencers. The numerical predictions demonstrate that the mean flow increases the transmission loss, especially at higher frequencies, and shifts the transmission loss curve to lower frequencies.
文摘In this paper, the authors propose a new approach to image compression based on the principle of Set Partitioning in Hierarchical Tree algorithm （SPIHT）. Our approach, the modified SPIHT （MSPIHT）, distributes entropy differently than SPIHT and also optimizes the coding. This approach can produce results that are a significant improvement on the Peak Signal-to-Noise Ratio （PSNR） and compression ratio obtained by SPIHT algorithm, without affecting the computing time. These results are also comparable with those obtained using the Embedded Zerotree Wavelet （EZW） and Joint Photographic Experts Group 2000 （JPG2） algorithms.
基金the Xi’an University of Posts and Telecommunicationsthe Physical Sciences Division at the University of Chicagothe Scientific Research Program(Grant No.15JK1685)of the Shaanxi Provincial Education Department
文摘We report two models of the lateral displacement of acoustic-wave scattering on a fluid-solid interface that reveal an acoustic analog of the Goos-Hainchen effect in optics. This acoustic analog is called the acoustic Goos-Hainchen effect. Using newly proposed models, we made numerical calculations for the system ofa water-Perspex interface. Specifically, in the post-critical-angle region, we observed a lateral displacement （and transition time） of the reflected P-wave with respect to the incident P-wave. The first arrival of the acoustic signal from the interface is found to be a reflected P-wave rather than the sliding-refraction P-wave usually described in traditional acoustic-logging sliding P-wave theory. For both proposed models, the effective propagation speed of the reflected P-wave along the interface depends on not only the physical properties of the interracial media but also the incident angle. These observations are intriguing and warrant further investigation.
