The equation of wave propagation in a circular chamber with mean flow is obtained. Computational solution based on finite element method is employed to determine the transmission loss of expansive chamber. The effect ...The equation of wave propagation in a circular chamber with mean flow is obtained. Computational solution based on finite element method is employed to determine the transmission loss of expansive chamber. The effect of the mean flow and geometry (length of expansion chamber and expansion ratio)on acoustic attenuation performance is discussed, the predicted values of transmission loss of expansion chamber without and with mean flow are compared with those reported in the literature and they agree well. The accuracy of the prediction of transmission loss implies that finite element approximations are applicable to a lot of practical applications.展开更多
A novel technique for reducing reverberation artifact in acoustic shadow imaging using nonlinear ultrasound interaction, called nonlinear acoustic shadow method, has been developed and experimentally studied. In this ...A novel technique for reducing reverberation artifact in acoustic shadow imaging using nonlinear ultrasound interaction, called nonlinear acoustic shadow method, has been developed and experimentally studied. In this technique, the conventional acoustic shadow method is modified by using the secondary wave generated by nonlinear interaction of two primary sound waves emitted from parametric array. Either conventional or nonlinear acoustic shadow imaging is carried out for aluminum square cylinder and the size of the shadow is compared. The result shows that the nonlinear acoustic shadow method reduces reverberation artifact inside the square cylinder and has better accuracy in the size measurement than conventional acoustic shadow method.展开更多
When acoustic method is used in leak detection for natural gas pipelines,the external interferences including operation of compressor and valve,pipeline knocking,etc.,should be distinguished with acoustic leakage sign...When acoustic method is used in leak detection for natural gas pipelines,the external interferences including operation of compressor and valve,pipeline knocking,etc.,should be distinguished with acoustic leakage signals to improve the accuracy and reduce false alarms.In this paper,the technologies of extracting characteristics of acoustic signals were summarized.The acoustic leakage signals and interfering signals were measured by experiments and the characteristics of time-domain,frequency-domain and time-frequency domain were extracted.The main characteristics of time-domain are mean value,root mean square value,kurtosis,skewness and correlation function,etc.The features in frequency domain were obtained by frequency spectrum analysis and power spectrum density,while time-frequency analysis was accomplished by short time Fourier transform.The results show that the external interferences can be removed effectively by the characteristics of time domain,frequency domain and time-frequency domain.It can be drawn that the acoustic leak detection method can be applied to natural gas pipelines and the characteristics can help reduce false alarms and missing alarms.展开更多
The conventional technique for positioning seafloor geophones in ocean bottom seismic exploration encounters several challenges,including the significant impact of outliers on positioning results,underutilization of h...The conventional technique for positioning seafloor geophones in ocean bottom seismic exploration encounters several challenges,including the significant impact of outliers on positioning results,underutilization of high-precision observations,and low efficiency in real-time data processing.These issues inevitably affect the quality of seismic exploration outcomes.To address these challenges and enhance the accuracy of geophone positioning,this paper proposes a rigorous real-time acoustic positioning method for geophones based on sequential adjustment and Baarda's outlier detection approach.The proposed method comprises three key steps:grouping the original acoustic observations,constructing the intra-group acoustic positioning model,and synthesizing the positioning results across the different groups.The validity and practicality of this approach are confirmed through a simulation experiment as well as the field experiment conducted in the Bohai Sea,China.The results demonstrate that the proposed method effectively eliminates outliers in the original observations and maximizes the utilization of high-quality observations.Compared to traditional acoustic positioning methods,it significantly reduces positioning errors from meters to decimeters,and in some cases can achieve centimeter-level precision.When the sound velocity profile in the operating sea area is measured,the method can attain the posterior standard deviation at the millimeter level and positioning errors within 10 cm.When the sound velocity profile is unknown,the method can achieve the posterior standard deviation at centimeter-level and positioning errors of approximately 20 cm.展开更多
Conventional element based methods for modeling acoustic problems are limited to low-frequency applications due to the huge computational efforts. For high-frequency applications, probabilistic techniques, such as sta...Conventional element based methods for modeling acoustic problems are limited to low-frequency applications due to the huge computational efforts. For high-frequency applications, probabilistic techniques, such as statistical energy analysis (SEA), are used. For mid-frequency range, currently no adequate and mature simulation methods exist. Recently, wave based method has been developed which is based on the indirect TREFFTZ approach and has shown to be able to tackle problems in the mid-frequency range. In contrast with the element based methods, no discretization is required. A sufficient, but not necessary, condition for convergence of this method is that the acoustic problem domain is convex. Non-convex domains have to be partitioned into a number of (convex) subdomains. At the interfaces between subdomains, specific coupling conditions have to be imposed. The considered two-dimensional coupled vibro-acoustic problem illustrates the beneficial convergence rate of the proposed wave based prediction technique with high accuracy. The results show the new technique can be applied up to much higher frequencies.展开更多
The distributed source boundary point method (DSBPM) is used as the spatial transform algorithm for realizing nearfield acoustic holography (NAH), the sensitivity of the reconstructed solution to the measurement e...The distributed source boundary point method (DSBPM) is used as the spatial transform algorithm for realizing nearfield acoustic holography (NAH), the sensitivity of the reconstructed solution to the measurement errors is analyzed, and the regularization method is proposed to stabilize the reconstruction process, control the influence of the measurement errors and get a better approximate solution. An oscillating sphere is investigated as a numerical example, the influence of the measurement errors on the reconstruction solution is demonstrated, and the feasibility and validity of the regularization method are validated. Key words: Acoustic holography Boundary point method Inverse problem Regularization展开更多
A comprehensive acoustic retrieval algorithm to investigate suspended sediment is presented with the combined validations of Acoustic Doppler Current Profiler(ADCP) and Optical Backscattering Sensor(OBS) monitorin...A comprehensive acoustic retrieval algorithm to investigate suspended sediment is presented with the combined validations of Acoustic Doppler Current Profiler(ADCP) and Optical Backscattering Sensor(OBS) monitoring along seven cross-channel sections in the high-turbidity North Passage of the Changjiang Estuary, China. The realistic water conditions, horizontal and vertical salinities, and grain size of the suspended sediment are considered in the retrieval algorithm. Relations between net volume scattering of sound attenuation(Sv) due to sediments and ADCP echo intensity(E) were obtained with reasonable accuracy after applying the linear regression method. In the river mouth, an intensive vertical stratification and horizontal inhomogeneity were found, with a higher concentration of sediment in the North Passage and a lower concentration in the North Channel and South Passage. Additionally, The North Passage is characterized by higher sediment concentration in the middle region and lower concentration in the entrance and outlet areas. The maximum sediment flux rate, occurred in the middle region, could reach 6.3×105 and 1.5×105 t/h during the spring and neap tide, respectively. Retrieved sediment fluxes in the middle region are significantly larger than that in the upstream and downstream region. This strong sediment imbalance along the main channel indicates potential secondary sediment supply from southern Jiuduansha Shoals.展开更多
This paper presents the basis of acoustic method used for temperature field measurement of seafloor hydrothermal vent and two techniques of the parabolic interpolation and the bending compensation of propagation paths...This paper presents the basis of acoustic method used for temperature field measurement of seafloor hydrothermal vent and two techniques of the parabolic interpolation and the bending compensation of propagation paths of acoustic signal are introduced. Experimental research is performed to exactly rebuild the temperature field around hot springs on the floor of Qiezishan Lake, Yunnan, China. The accuracy of the travel time estimation has been improved based on the aforementioned technique and method. At the same time, by comparison of the results of temperature field with different means, the max absolute error, the maximum relative error and the root mean square error are given. It shows that the technique and the method presented in the paper can be applied to the temperature field measurement detector around the seafloor hydrothermal vent. It also has a good accuracy.展开更多
To reduce computational costs, an improved form of the frequency domain boundary element method(BEM) is proposed for two-dimensional radiation and propagation acoustic problems in a subsonic uniform flow with arbitr...To reduce computational costs, an improved form of the frequency domain boundary element method(BEM) is proposed for two-dimensional radiation and propagation acoustic problems in a subsonic uniform flow with arbitrary orientation. The boundary integral equation(BIE) representation solves the two-dimensional convected Helmholtz equation(CHE) and its fundamental solution, which must satisfy a new Sommerfeld radiation condition(SRC) in the physical space. In order to facilitate conventional formulations, the variables of the advanced form are expressed only in terms of the acoustic pressure as well as its normal and tangential derivatives, and their multiplication operators are based on the convected Green's kernel and its modified derivative. The proposed approach significantly reduces the CPU times of classical computational codes for modeling acoustic domains with arbitrary mean flow. It is validated by a comparison with the analytical solutions for the sound radiation problems of monopole,dipole and quadrupole sources in the presence of a subsonic uniform flow with arbitrary orientation.展开更多
The effects of the temperature,salinity,and fluid type on the acoustic characteristics of turbulent flow around a circular cylinder were numerically investigated for the Reynolds numbers of 2.25×10^(4),4.5×1...The effects of the temperature,salinity,and fluid type on the acoustic characteristics of turbulent flow around a circular cylinder were numerically investigated for the Reynolds numbers of 2.25×10^(4),4.5×10^(4),and 9.0×10^(4).Various hybrid methodsReynolds-averaged Navier-Stokes(BANS)with the Ffowcs Williams and Hawkings(FWH)model,detached-eddy simulation(DES)with FWH,and large-eddy simulation with FWH-were used for the acoustic analyses,and their performances were evaluated by comparing the predicted results with the experimental data.The DES-FWH hybrid method was found to be suitable for the aero-and hydro-acoustic analysis.The hydro-acoustic measurements were performed in a silent circulation channel for the Reynolds number of 2.25×10^(4).The results showed that the fluid temperature caused an increase in the overall sound pressure levels(OASPLs)and the maximum sound pressure levels(SPL_(T))for the air medium;however,it caused a decrease for the water medium.The salinity had smaller effects on the OASPL and SPLT compared to the temperature.Moreover,the main peak frequency increased with the air temperature but decreased with the water temperature,and it was nearly constant with the change in the salinity ratio.The SPLT and OASPL for the water medium were quite higher than those for the air medium.展开更多
This paper presents the method named acoustic holography which can be used to identify noise sources. A new formula of holography reconstruction is obtained, based on the Kirchhoff integral formula. Some simulating te...This paper presents the method named acoustic holography which can be used to identify noise sources. A new formula of holography reconstruction is obtained, based on the Kirchhoff integral formula. Some simulating tests are carried out using the new formula. The comparison with other reconstruction formulas proves that the new formula is more effective. By using acoustic holography method, some interesting results about the noise of a vehicle are shown. The results proves that acoustic holography is an effective method for the identification of the complex noise sources.展开更多
The performance of conventional direction of arrival(DOA)method is greatly affected by the uncertainty of wave velocity in underwater environment.To solve this problem,an acoustic velocity-independent method is propos...The performance of conventional direction of arrival(DOA)method is greatly affected by the uncertainty of wave velocity in underwater environment.To solve this problem,an acoustic velocity-independent method is proposed to estimate the underwater DOA using two arbitrary intersecting uniform linear arrays in this study.By introducing the additional array compared to the conventional DOA methods,the proposed algorithm can make its performance independent of the acoustic velocity through the geometric relationship between those two arrays.The simulation results demonstrate that the proposed method is more accurate and robust than other methods in an unknown sound velocity.展开更多
Two coupled-mode methods, namely DGMCM (Direct-Global-Matrix Coupled- Mode Method) and CCMM (Consistent Coupled-Mode Method), are analyzed and compared. First, both of these two methods provide two-way solutions, ...Two coupled-mode methods, namely DGMCM (Direct-Global-Matrix Coupled- Mode Method) and CCMM (Consistent Coupled-Mode Method), are analyzed and compared. First, both of these two methods provide two-way solutions, and hence they are accurate models. Second, the series of local vertical modes in DGMCM converges as fast as that in CCMM, whereas DGMCM has a more tolerable requirement of the number of segments than CCMM. Third, these two models obtain the field solution by solving the coupled-mode system with different coefficient matrices, in which the computational effort for the required parameters is almost the same. Finally, DGMCM can handle some problems which are difficult for CCMM, such as in a waveguide with a rough bottom, a line source located right on top of a sloping bot- tom, or in the presence of multiple sources. In DGMCM, closed-form expressions for coupling matrices in a two-layer waveguide are given. In addition, the formulation for the line-source problem in plane geometry is derived to update CCMM.展开更多
To obtain a universal model solving the uncertain acoustic field in shallow water, a non-intrusive model coupled polynomial chaos expansion (PCE) method with Helmholtz equa- tion is established, in which the polynom...To obtain a universal model solving the uncertain acoustic field in shallow water, a non-intrusive model coupled polynomial chaos expansion (PCE) method with Helmholtz equa- tion is established, in which the polynomial coefficients are solved by probabilistic collocation method (PCM). For the cases of Pekeris waveguide which have uncertainties in depth of water column, in both sound speed profile and depth of water column, and for the case of thermocline with lower limit depth uncertain, probability density functions (PDF) of transmission loss (TL) are calculated. The results show that the proposed model is universal for the acoustic propa- gation codes with high computational efficiency and accuracy, and can be applied to study the uncertainty of acoustic propagation in the shallow water en^-ironment with multiple parameters uncertain.展开更多
The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propaga...The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normal- ized. It adopts fractional-decision feedback diversity equalizer (FDFDE) and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can im- prove communication system's ability in tracking the change of underwater acoustic channel, offset the impact of multipath and noise and improve the performance of communication system. The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate (BER) reduces 1.8%.展开更多
Doppler effect widely exists in the signal from the moving acoustic source. In order to solve such problems as frequency shift and frequency band expansion, a time domain cor- rection method is presented in this paper...Doppler effect widely exists in the signal from the moving acoustic source. In order to solve such problems as frequency shift and frequency band expansion, a time domain cor- rection method is presented in this paper. First, the discrete time vector for interpolation and the amplitude restoration formula is derived based on the moving relationship and the Morse acoustic theory, then the amplitude weights are corrected and the distortion signal is interpolated. Every point of the discrete signal is operated separately in time domain. Compared with the existing frequency domain methods, this method does not need to know the characteristic frequency beforehand and would not be influenced by the blending of the frequency band. Hence, this method can be employed to correct multiple frequency signals and it is also a simple and effective Doppler effect reduction method.展开更多
In the scenario of underwater acoustic sparse channel estimation with training sequences,grid points in the measuring matrix are caused by discretizing procedure.Estimated accuracy might not be guaranteed with the sta...In the scenario of underwater acoustic sparse channel estimation with training sequences,grid points in the measuring matrix are caused by discretizing procedure.Estimated accuracy might not be guaranteed with the state-of-the-art methods when multipath delays don't exactly locate on the grid points.In this paper,we construct a gridless measuring matrix for sparse channel estimation which contains an off-grid adjusting factor.The Relevance Vector Machine(RVM) algorithm is employed to estimate this factor.The numerical experiments for two different underwater channels are performed to testify the newly proposed method.The results demonstrate that this method outperforms conventional ones in terms of estimating error and bit error rate,especially when the grid gets coarser.展开更多
The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs (boundary element ...The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs (boundary element methods) for 3D acoustic problems based on constant elements are improved. To solve the problem of singular integrals, a Hadamard finite-part integral method is presented, which is a simplified combination of the methods proposed by Kirkup and Wolf. The problem of near-singular integrals is overcome by the simple method of polar transformation and the more complex method of PART (Projection and Angular & Radial Transformation). The effectiveness of these methods for solving the singular and near-singular problems is validated through comparing with the results computed by the analytical method and/or the commercial software LMS Virtual.Lab. In addition, the influence of the near-singular integral problem on the computational precisions is analyzed by computing the errors relative to the exact solution. The computational complexities of the conventional and fast multipole BEM are analyzed and compared through numerical computations. A large-scale acoustic scattering problem, whose degree of freedoms is about 340,000, is implemented successfully. The results show that, the near singularity is primarily introduced by the hyper-singular kernel, and has great influences on the precision of the solution. The precision of fast multipole BEM is the same as conventional BEM, but the computational complexities are much lower.展开更多
For accuracy and rapidity of audio event detection in the mass-data audio pro- cessing tasks, a generic method of rapidly recognizing audio event based on 2D-Haar acoustic super feature vector and AdaBoost is proposed...For accuracy and rapidity of audio event detection in the mass-data audio pro- cessing tasks, a generic method of rapidly recognizing audio event based on 2D-Haar acoustic super feature vector and AdaBoost is proposed. Firstly, it combines certain number of con- tinuous audio frames to be an "acoustic feature image", secondly, uses AdaBoost.MH or fast Random AdaBoost feature selection algorithm to select high representative 2D-Haar pattern combinations to construct super feature vectors; thirdly, analyzes the commonality and differ- ences between subcategories, then extracts common features and reduces different features to obtain a generic audio event template, which can support the accurate identification of multi- ple sub-classes and detect and locate the specific audio event from the audio stream accurately. Experimental results show that the use of 2D-Haar acoustic feature super vector can make recog- nition accuracy 5% higher than ones that MFCC, PLP, LPCC and other traditional acoustic features yielded, and can make tile training processing 7 20 times faster and the recognition processing 5-10 times faster, it can even achieve an average precision of 93.38%, an average recall of 95.03% under the optimal parameter configuration found by grid method. Above all, it can provide an accurate and fast mass-data processing method for audio event detection.展开更多
The safety of rail is very important for the development of high speed railway, and it is necessary to investigate the features of inner cracks in rail. In order to obtain the features of Acoustic Emission (AE) sour...The safety of rail is very important for the development of high speed railway, and it is necessary to investigate the features of inner cracks in rail. In order to obtain the features of Acoustic Emission (AE) sources of inner cracks in rail, AE sources with different types, depths and propagation distances are examined for crack in rail. The finite element method is utilized to model the rail with cracks and the results of experiment demonstrate the effectiveness of this model. Wavelet transform and Rayleigh-Lamb equations are utilized to extract the features of crack AE sources. The results illustrate that the intensity ratio among AE modes can identify the AE source types and the AE sources with different frequencies in rail. There are uniform AE mode features existing in the AE signals from AE sources in rail web, however AE signals from AE sources in rail head and rail base have the complex and unstable AE modes. Different AE source types have the different propagation features in rail. It is helpful to understand the rail cracks and detect the rail cracks based on the AE technique.展开更多
文摘The equation of wave propagation in a circular chamber with mean flow is obtained. Computational solution based on finite element method is employed to determine the transmission loss of expansive chamber. The effect of the mean flow and geometry (length of expansion chamber and expansion ratio)on acoustic attenuation performance is discussed, the predicted values of transmission loss of expansion chamber without and with mean flow are compared with those reported in the literature and they agree well. The accuracy of the prediction of transmission loss implies that finite element approximations are applicable to a lot of practical applications.
文摘A novel technique for reducing reverberation artifact in acoustic shadow imaging using nonlinear ultrasound interaction, called nonlinear acoustic shadow method, has been developed and experimentally studied. In this technique, the conventional acoustic shadow method is modified by using the secondary wave generated by nonlinear interaction of two primary sound waves emitted from parametric array. Either conventional or nonlinear acoustic shadow imaging is carried out for aluminum square cylinder and the size of the shadow is compared. The result shows that the nonlinear acoustic shadow method reduces reverberation artifact inside the square cylinder and has better accuracy in the size measurement than conventional acoustic shadow method.
基金funded by the National Science Foundation of China(51774313)Shandong Provincial Key R&D Program(2017GSF220007)National Key R&D Program of China(2016YFC0802104).
文摘When acoustic method is used in leak detection for natural gas pipelines,the external interferences including operation of compressor and valve,pipeline knocking,etc.,should be distinguished with acoustic leakage signals to improve the accuracy and reduce false alarms.In this paper,the technologies of extracting characteristics of acoustic signals were summarized.The acoustic leakage signals and interfering signals were measured by experiments and the characteristics of time-domain,frequency-domain and time-frequency domain were extracted.The main characteristics of time-domain are mean value,root mean square value,kurtosis,skewness and correlation function,etc.The features in frequency domain were obtained by frequency spectrum analysis and power spectrum density,while time-frequency analysis was accomplished by short time Fourier transform.The results show that the external interferences can be removed effectively by the characteristics of time domain,frequency domain and time-frequency domain.It can be drawn that the acoustic leak detection method can be applied to natural gas pipelines and the characteristics can help reduce false alarms and missing alarms.
基金supported by the National Key R&D Program of China(Grant No.:2016YFB0501703)Science and Technology Innovation Project(Grant No.:LSKJ202205102)Funded by Laoshan Laboratory.
文摘The conventional technique for positioning seafloor geophones in ocean bottom seismic exploration encounters several challenges,including the significant impact of outliers on positioning results,underutilization of high-precision observations,and low efficiency in real-time data processing.These issues inevitably affect the quality of seismic exploration outcomes.To address these challenges and enhance the accuracy of geophone positioning,this paper proposes a rigorous real-time acoustic positioning method for geophones based on sequential adjustment and Baarda's outlier detection approach.The proposed method comprises three key steps:grouping the original acoustic observations,constructing the intra-group acoustic positioning model,and synthesizing the positioning results across the different groups.The validity and practicality of this approach are confirmed through a simulation experiment as well as the field experiment conducted in the Bohai Sea,China.The results demonstrate that the proposed method effectively eliminates outliers in the original observations and maximizes the utilization of high-quality observations.Compared to traditional acoustic positioning methods,it significantly reduces positioning errors from meters to decimeters,and in some cases can achieve centimeter-level precision.When the sound velocity profile in the operating sea area is measured,the method can attain the posterior standard deviation at the millimeter level and positioning errors within 10 cm.When the sound velocity profile is unknown,the method can achieve the posterior standard deviation at centimeter-level and positioning errors of approximately 20 cm.
基金This project is supported by National Natural Science Foundation of China (No.10472035).
文摘Conventional element based methods for modeling acoustic problems are limited to low-frequency applications due to the huge computational efforts. For high-frequency applications, probabilistic techniques, such as statistical energy analysis (SEA), are used. For mid-frequency range, currently no adequate and mature simulation methods exist. Recently, wave based method has been developed which is based on the indirect TREFFTZ approach and has shown to be able to tackle problems in the mid-frequency range. In contrast with the element based methods, no discretization is required. A sufficient, but not necessary, condition for convergence of this method is that the acoustic problem domain is convex. Non-convex domains have to be partitioned into a number of (convex) subdomains. At the interfaces between subdomains, specific coupling conditions have to be imposed. The considered two-dimensional coupled vibro-acoustic problem illustrates the beneficial convergence rate of the proposed wave based prediction technique with high accuracy. The results show the new technique can be applied up to much higher frequencies.
基金This project is supported by National Natural Science Foundation of China(No.50275044)Research Fund for Doctoral Program of Ministry of Education of China(No.20020359005).
文摘The distributed source boundary point method (DSBPM) is used as the spatial transform algorithm for realizing nearfield acoustic holography (NAH), the sensitivity of the reconstructed solution to the measurement errors is analyzed, and the regularization method is proposed to stabilize the reconstruction process, control the influence of the measurement errors and get a better approximate solution. An oscillating sphere is investigated as a numerical example, the influence of the measurement errors on the reconstruction solution is demonstrated, and the feasibility and validity of the regularization method are validated. Key words: Acoustic holography Boundary point method Inverse problem Regularization
基金financially supported by the National Natural Science Foundation of China(Grant No.41306080)the Public Service Program of State Ocean Administration(Grant No.201205017-2)+1 种基金the Science and Technology Support Program of China(Grant No.2013BAB12B03-Z1)SKELC fund(Grant No.SKLEC-2011RCDW03)
文摘A comprehensive acoustic retrieval algorithm to investigate suspended sediment is presented with the combined validations of Acoustic Doppler Current Profiler(ADCP) and Optical Backscattering Sensor(OBS) monitoring along seven cross-channel sections in the high-turbidity North Passage of the Changjiang Estuary, China. The realistic water conditions, horizontal and vertical salinities, and grain size of the suspended sediment are considered in the retrieval algorithm. Relations between net volume scattering of sound attenuation(Sv) due to sediments and ADCP echo intensity(E) were obtained with reasonable accuracy after applying the linear regression method. In the river mouth, an intensive vertical stratification and horizontal inhomogeneity were found, with a higher concentration of sediment in the North Passage and a lower concentration in the North Channel and South Passage. Additionally, The North Passage is characterized by higher sediment concentration in the middle region and lower concentration in the entrance and outlet areas. The maximum sediment flux rate, occurred in the middle region, could reach 6.3×105 and 1.5×105 t/h during the spring and neap tide, respectively. Retrieved sediment fluxes in the middle region are significantly larger than that in the upstream and downstream region. This strong sediment imbalance along the main channel indicates potential secondary sediment supply from southern Jiuduansha Shoals.
基金supported by the National Science and Technology Support Program of China(Grant No.2012BAB09B02)Zhejiang Key Discipline of Marine Technology and Systems(Grant No.20120109)the National High Technology Research and Development Program of China(863Program,Grant No.2007AA09Z213)
文摘This paper presents the basis of acoustic method used for temperature field measurement of seafloor hydrothermal vent and two techniques of the parabolic interpolation and the bending compensation of propagation paths of acoustic signal are introduced. Experimental research is performed to exactly rebuild the temperature field around hot springs on the floor of Qiezishan Lake, Yunnan, China. The accuracy of the travel time estimation has been improved based on the aforementioned technique and method. At the same time, by comparison of the results of temperature field with different means, the max absolute error, the maximum relative error and the root mean square error are given. It shows that the technique and the method presented in the paper can be applied to the temperature field measurement detector around the seafloor hydrothermal vent. It also has a good accuracy.
基金supported by National Engineering School of Tunis (No.13039.1)
文摘To reduce computational costs, an improved form of the frequency domain boundary element method(BEM) is proposed for two-dimensional radiation and propagation acoustic problems in a subsonic uniform flow with arbitrary orientation. The boundary integral equation(BIE) representation solves the two-dimensional convected Helmholtz equation(CHE) and its fundamental solution, which must satisfy a new Sommerfeld radiation condition(SRC) in the physical space. In order to facilitate conventional formulations, the variables of the advanced form are expressed only in terms of the acoustic pressure as well as its normal and tangential derivatives, and their multiplication operators are based on the convected Green's kernel and its modified derivative. The proposed approach significantly reduces the CPU times of classical computational codes for modeling acoustic domains with arbitrary mean flow. It is validated by a comparison with the analytical solutions for the sound radiation problems of monopole,dipole and quadrupole sources in the presence of a subsonic uniform flow with arbitrary orientation.
文摘The effects of the temperature,salinity,and fluid type on the acoustic characteristics of turbulent flow around a circular cylinder were numerically investigated for the Reynolds numbers of 2.25×10^(4),4.5×10^(4),and 9.0×10^(4).Various hybrid methodsReynolds-averaged Navier-Stokes(BANS)with the Ffowcs Williams and Hawkings(FWH)model,detached-eddy simulation(DES)with FWH,and large-eddy simulation with FWH-were used for the acoustic analyses,and their performances were evaluated by comparing the predicted results with the experimental data.The DES-FWH hybrid method was found to be suitable for the aero-and hydro-acoustic analysis.The hydro-acoustic measurements were performed in a silent circulation channel for the Reynolds number of 2.25×10^(4).The results showed that the fluid temperature caused an increase in the overall sound pressure levels(OASPLs)and the maximum sound pressure levels(SPL_(T))for the air medium;however,it caused a decrease for the water medium.The salinity had smaller effects on the OASPL and SPLT compared to the temperature.Moreover,the main peak frequency increased with the air temperature but decreased with the water temperature,and it was nearly constant with the change in the salinity ratio.The SPLT and OASPL for the water medium were quite higher than those for the air medium.
基金This work wassupportedby the Natural Science Foundation of China(No.59775020).
文摘This paper presents the method named acoustic holography which can be used to identify noise sources. A new formula of holography reconstruction is obtained, based on the Kirchhoff integral formula. Some simulating tests are carried out using the new formula. The comparison with other reconstruction formulas proves that the new formula is more effective. By using acoustic holography method, some interesting results about the noise of a vehicle are shown. The results proves that acoustic holography is an effective method for the identification of the complex noise sources.
基金This work was supported by National Natural Science Foundation of China(No.61871191)Natural Science Foundation of Guangdong Province(Nos.2016A020222003 and 2017A030313368)Science and Technology Planning Project of Guangzhou(No.201804010209).
文摘The performance of conventional direction of arrival(DOA)method is greatly affected by the uncertainty of wave velocity in underwater environment.To solve this problem,an acoustic velocity-independent method is proposed to estimate the underwater DOA using two arbitrary intersecting uniform linear arrays in this study.By introducing the additional array compared to the conventional DOA methods,the proposed algorithm can make its performance independent of the acoustic velocity through the geometric relationship between those two arrays.The simulation results demonstrate that the proposed method is more accurate and robust than other methods in an unknown sound velocity.
基金supported by the National Natural Sciencc Foundation of China(11125420,11104312)
文摘Two coupled-mode methods, namely DGMCM (Direct-Global-Matrix Coupled- Mode Method) and CCMM (Consistent Coupled-Mode Method), are analyzed and compared. First, both of these two methods provide two-way solutions, and hence they are accurate models. Second, the series of local vertical modes in DGMCM converges as fast as that in CCMM, whereas DGMCM has a more tolerable requirement of the number of segments than CCMM. Third, these two models obtain the field solution by solving the coupled-mode system with different coefficient matrices, in which the computational effort for the required parameters is almost the same. Finally, DGMCM can handle some problems which are difficult for CCMM, such as in a waveguide with a rough bottom, a line source located right on top of a sloping bot- tom, or in the presence of multiple sources. In DGMCM, closed-form expressions for coupling matrices in a two-layer waveguide are given. In addition, the formulation for the line-source problem in plane geometry is derived to update CCMM.
文摘To obtain a universal model solving the uncertain acoustic field in shallow water, a non-intrusive model coupled polynomial chaos expansion (PCE) method with Helmholtz equa- tion is established, in which the polynomial coefficients are solved by probabilistic collocation method (PCM). For the cases of Pekeris waveguide which have uncertainties in depth of water column, in both sound speed profile and depth of water column, and for the case of thermocline with lower limit depth uncertain, probability density functions (PDF) of transmission loss (TL) are calculated. The results show that the proposed model is universal for the acoustic propa- gation codes with high computational efficiency and accuracy, and can be applied to study the uncertainty of acoustic propagation in the shallow water en^-ironment with multiple parameters uncertain.
基金supported by National Natural Science Foundation of China(61531018)
文摘The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normal- ized. It adopts fractional-decision feedback diversity equalizer (FDFDE) and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can im- prove communication system's ability in tracking the change of underwater acoustic channel, offset the impact of multipath and noise and improve the performance of communication system. The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate (BER) reduces 1.8%.
基金supported by the National Science Foundation of China(51075379)
文摘Doppler effect widely exists in the signal from the moving acoustic source. In order to solve such problems as frequency shift and frequency band expansion, a time domain cor- rection method is presented in this paper. First, the discrete time vector for interpolation and the amplitude restoration formula is derived based on the moving relationship and the Morse acoustic theory, then the amplitude weights are corrected and the distortion signal is interpolated. Every point of the discrete signal is operated separately in time domain. Compared with the existing frequency domain methods, this method does not need to know the characteristic frequency beforehand and would not be influenced by the blending of the frequency band. Hence, this method can be employed to correct multiple frequency signals and it is also a simple and effective Doppler effect reduction method.
基金supported by the National Natural Science Foundation of China(61431020)
文摘In the scenario of underwater acoustic sparse channel estimation with training sequences,grid points in the measuring matrix are caused by discretizing procedure.Estimated accuracy might not be guaranteed with the state-of-the-art methods when multipath delays don't exactly locate on the grid points.In this paper,we construct a gridless measuring matrix for sparse channel estimation which contains an off-grid adjusting factor.The Relevance Vector Machine(RVM) algorithm is employed to estimate this factor.The numerical experiments for two different underwater channels are performed to testify the newly proposed method.The results demonstrate that this method outperforms conventional ones in terms of estimating error and bit error rate,especially when the grid gets coarser.
基金supported by the National Natural Science Foundation of China(11304344,11404364)the Project of Hubei Provincial Department of Education(D20141803)+1 种基金the Natural Science Foundation of Hubei Province(2014CFB378)the Doctoral Scientific Research Foundation of Hubei University of Automotive Technology(BK201604)
文摘The numerical quadrature methods for dealing with the problems of singular and near-singular integrals caused by Burton-Miller method are proposed, by which the conventional and fast multipole BEMs (boundary element methods) for 3D acoustic problems based on constant elements are improved. To solve the problem of singular integrals, a Hadamard finite-part integral method is presented, which is a simplified combination of the methods proposed by Kirkup and Wolf. The problem of near-singular integrals is overcome by the simple method of polar transformation and the more complex method of PART (Projection and Angular & Radial Transformation). The effectiveness of these methods for solving the singular and near-singular problems is validated through comparing with the results computed by the analytical method and/or the commercial software LMS Virtual.Lab. In addition, the influence of the near-singular integral problem on the computational precisions is analyzed by computing the errors relative to the exact solution. The computational complexities of the conventional and fast multipole BEM are analyzed and compared through numerical computations. A large-scale acoustic scattering problem, whose degree of freedoms is about 340,000, is implemented successfully. The results show that, the near singularity is primarily introduced by the hyper-singular kernel, and has great influences on the precision of the solution. The precision of fast multipole BEM is the same as conventional BEM, but the computational complexities are much lower.
文摘For accuracy and rapidity of audio event detection in the mass-data audio pro- cessing tasks, a generic method of rapidly recognizing audio event based on 2D-Haar acoustic super feature vector and AdaBoost is proposed. Firstly, it combines certain number of con- tinuous audio frames to be an "acoustic feature image", secondly, uses AdaBoost.MH or fast Random AdaBoost feature selection algorithm to select high representative 2D-Haar pattern combinations to construct super feature vectors; thirdly, analyzes the commonality and differ- ences between subcategories, then extracts common features and reduces different features to obtain a generic audio event template, which can support the accurate identification of multi- ple sub-classes and detect and locate the specific audio event from the audio stream accurately. Experimental results show that the use of 2D-Haar acoustic feature super vector can make recog- nition accuracy 5% higher than ones that MFCC, PLP, LPCC and other traditional acoustic features yielded, and can make tile training processing 7 20 times faster and the recognition processing 5-10 times faster, it can even achieve an average precision of 93.38%, an average recall of 95.03% under the optimal parameter configuration found by grid method. Above all, it can provide an accurate and fast mass-data processing method for audio event detection.
基金supported by the China Scholarship Council,the National Natural Science Foundation of China(61171197,61201307,61371045)the Innovation Funds of Harbin Institute of Technology(Grant IDGA18102011)the Promotive Research Fund for Excellent Young and Middle-Aged Scientisits of Shandong Province(BS2010DX001)
文摘The safety of rail is very important for the development of high speed railway, and it is necessary to investigate the features of inner cracks in rail. In order to obtain the features of Acoustic Emission (AE) sources of inner cracks in rail, AE sources with different types, depths and propagation distances are examined for crack in rail. The finite element method is utilized to model the rail with cracks and the results of experiment demonstrate the effectiveness of this model. Wavelet transform and Rayleigh-Lamb equations are utilized to extract the features of crack AE sources. The results illustrate that the intensity ratio among AE modes can identify the AE source types and the AE sources with different frequencies in rail. There are uniform AE mode features existing in the AE signals from AE sources in rail web, however AE signals from AE sources in rail head and rail base have the complex and unstable AE modes. Different AE source types have the different propagation features in rail. It is helpful to understand the rail cracks and detect the rail cracks based on the AE technique.