Dear Editor,This letter concentrates on distributed event-triggered formation control problems with finite-time convergence in an arbitrarily dimensional Euclidean space.A new unified approach of finite-time event-tri...Dear Editor,This letter concentrates on distributed event-triggered formation control problems with finite-time convergence in an arbitrarily dimensional Euclidean space.A new unified approach of finite-time event-triggered formation control is proposed by steering all agents to a sliding manifold(the affine image)to achieve general formations,like affine,rigid or translational formation.It only requires to design an extra steering law driving at least d+1 leaders from an affine image to a rigid or translational image,where d is the dimension of the space.The event-triggered function is designed in a distributed and discontinuous manner based only on local information to reduce the communication and calculation resources by aperiodic sampling.In the proposed event-triggered formation law,zeno-free behavior is ensured.展开更多
Surface/underwater target classification is a key topic in marine information research.However,the complex underwater environment,coupled with the diversity of target types and their variable characteristics,presents ...Surface/underwater target classification is a key topic in marine information research.However,the complex underwater environment,coupled with the diversity of target types and their variable characteristics,presents significant challenges for classifier design.For shallow-water waveguides with a negative thermocline,a residual neural network(ResNet)model based on the sound field elevation structure is constructed.This model demonstrates robust classification performance even when facing low signal-to-noise ratios and environmental mismatches.Meanwhile,to address the reduced generalization ability caused by limited labeled acoustic data,an improved ResNet model based on unsupervised domain adaptation(“proposed UDA-ResNet”)is further constructed.This model incorporates data on simulated elevation structures of the sound field to augment the training process.Adversarial training is employed to extract domain-invariant features from simulated and trial data.These strategies help reduce the negative impact caused by domain differences.Experimental results demonstrate that the proposed method shows strong surface/underwater target classification ability under limited sample sizes,thus confirming its feasibility and effectiveness.展开更多
According to the features of the wideband underwater acoustic signals,an algorithm for the wideband ambiguity function is put forward based on Mellin transform.The wideband acoustic signal processing using the fast Me...According to the features of the wideband underwater acoustic signals,an algorithm for the wideband ambiguity function is put forward based on Mellin transform.The wideband acoustic signal processing using the fast Mellin transform is also explored.The theoretical analysis and simulation results show that the algorithm has not only high computation efficiency but also good concentration in wideband ambiguity domain.It suits for the wideband underwater acoustic signal processing.展开更多
An algorithm of broadband minimum variance distortionless response(MVDR) based on the frequency energy normalization is proposed.First,every narrowband frequency component of the broadband signal is normalized by the ...An algorithm of broadband minimum variance distortionless response(MVDR) based on the frequency energy normalization is proposed.First,every narrowband frequency component of the broadband signal is normalized by the total narrowband energy of all array elements,and the narrowband power is calculated by MVDR.Finally,final spatial energy spectrum can be obtained by averaging or summing all results of every narrowband frequency bin.Any prior-information about the noise or the signal is unnecessary for the proposed method in this paper.The processing gain of the proposed method compared to the conventional broadband MVDR can be obtained as long as the amplitude fluctuation of the array noise frequency spectrum is severer than that of the target signal.The validity of the method is validated by the optimal signal detection theory.Simulation and real data are used to validate the performance of the method.Analysis results show that about 4 dB processing gain compared to the general broadband MVDR can be reached by the proposed method.展开更多
The study was to investigate thrombolysis in vitro with ultrasound, and to discuss effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold under different ultrasound intensity ...The study was to investigate thrombolysis in vitro with ultrasound, and to discuss effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold under different ultrasound intensity and exposure time. The structure of erythrocyte in thrombus was evaluated under light microscope. The relationship between the structure of erythrocyte in thrombus and ultrasound intensity and exposure time was obtained. The results showed that ultrasound eliminated the thrombus. According to the change of the structure of erythrocyte in thrombus and ultrasound intensity and exposure time, the effects of thrombolysis with ultrasound could be divided into three kinds of areas: the A, B, C area. The area A was the safe area, the area B was the relatively safe area, and the area C was the irreversible damage area. The study suggested that ultrasound intensity and exposure time had significant impact on the structure of erythrocyte. Stronger ultrasound intensity or longer exposure time could cause erythrocytes irreversible damage. It could accelerate thrombolysis and shorten the exposure time that the ultrasound intensity was little bit increased. The study of effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold were important for practical applications.展开更多
Based on Schaaff＇s collision factor theory （CFT） in liquids, the equations for nonlinear ultrasonic parameters in both organic liquid and binary organic liquid mixtures are deduced. The nonlinear ultrasonic paramet...Based on Schaaff＇s collision factor theory （CFT） in liquids, the equations for nonlinear ultrasonic parameters in both organic liquid and binary organic liquid mixtures are deduced. The nonlinear ultrasonic parameters, including pressure coefficient, temperature coefficients of ultrasonic velocity, and nonlinear acoustic parameter B/A in both organic liquid and binary organic liquid mixtures, are evaluated for comparison with the measured results and data from other sources. The equations show that the coefficient of ultrasonic velocity and nonlinear acoustic parameter B/A are closely related to molecular interactions. These nonlinear ultrasonic parameters reflect some information of internal structure and outside status of the medium or mixtures. From the exponent of repulsive forces of the molecules, several thermodynamic parameters, pressure and temperature of the medium, the nonlinear ultrasonic parameters and ultrasonic nature of the medium can be evaluated. When evaluating and studying nonlinear acoustic parameter B/A of binary organic liquid mixtures, there is no need to know the nonlinear acoustic parameter B/A of the components. Obviously, the equation reveals the connection between the nonlinear ultrasonic nature and internal structure and outside status of the mixtures more directly and distinctly than traditional mixture law for B/A, e.g. Apfel＇s and Sehgal＇s laws for liquid binary mixtures.展开更多
Cam-lobe radial-piston hydraulic motors are widely used as rotation driving units for various marine machinery owing to their ultrahigh output torque(more than 100 kN m).A multi-row cam roller bearing(MCRB)is the key ...Cam-lobe radial-piston hydraulic motors are widely used as rotation driving units for various marine machinery owing to their ultrahigh output torque(more than 100 kN m).A multi-row cam roller bearing(MCRB)is the key component that directly determines the fatigue life of a cam-lobe radial-piston hydraulic motor.However,compact geometry and complex loads render MCRB susceptible to fatigue failure,highlighting the need for an optimized MCRB to achieve longer fatigue life and higher reliability.Therefore,this study proposes an innovative geometry optimization method for an MCRB to improve its fatigue life.In this method,a quasi-static model was developed to calculate the load distribution,with the fatigue life of the MCRB calculated using both basic dynamic loading and load distribution.Subsequently,a genetic algorithm was used to obtain the optimized geometry parameters,which significantly improved the fatigue life of the MCRB.Finally,a loading test was conducted on a hydraulic motor installed with both the initial and optimized MCRB to validate the effectiveness of the proposed optimization method.This study provides a theoretical guideline for optimizing the design of MCRB,thereby increasing the fatigue life of hydraulic motors.展开更多
The ultrasonic pulse signal resonance features in layered carbon fiber reinforced plastic（CFRP） within voids were researched. The frequency domain model of acoustic wave propagation in multilayered medium was establ...The ultrasonic pulse signal resonance features in layered carbon fiber reinforced plastic（CFRP） within voids were researched. The frequency domain model of acoustic wave propagation in multilayered medium was established. Then the reflection coefficient of multilayered CFRP within voids was numerically calculated. The results are as follows. When the CFRP laminate is tested by ultrasonic whose center frequency is close to the CFRP inherent resonant frequency, the ultrasonic may generate resonance phenomenon in CFRP. If CFRP contains evenly distributed voids, the frequency of resonant signal and its amplitude all decrease with the increase of porosity. For the thick section CFRP within local concentrated voids, the local concentrated voids near testing surface will cause signal frequency reduction and the decrease of its amplitude. But the voids which exist in layers far away from testing surface almost have no influence on signal resonance. The ultrasonic pulse echo testing was conducted for thick section CFRP specimen. The analysis results of testing signals were in accordance with the results of the numerical calculation, showing that the reflection coefficient frequency response model can effectively explain the ultrasonic resonance phenomenon in layered CFRP within voids.展开更多
An ultrasound method of sterilizing aspergillus flavus and fusarium is proposed and demonstrated.The dependence of sterilizing effect on ultrasonic intensity,frequency,and treatment time is experimentally investigated...An ultrasound method of sterilizing aspergillus flavus and fusarium is proposed and demonstrated.The dependence of sterilizing effect on ultrasonic intensity,frequency,and treatment time is experimentally investigated.The density of surviving spores decreases first with increasing ultrasonic frequency and then increases with the further increase of the frequency,that is to say,there exists the optimum frequency 26 kHz at which the killing rate is near 100%.The killing rate seems proportional to the intensity and the time.展开更多
Genetic algorithm (GA) based on wavelet transform threshold shrinkage (WTS) and translation-invariant threshold shrinkage (TIS) is introduced into the method of noise reduction, where parameters used in WTS and TIS, s...Genetic algorithm (GA) based on wavelet transform threshold shrinkage (WTS) and translation-invariant threshold shrinkage (TIS) is introduced into the method of noise reduction, where parameters used in WTS and TIS, such as wavelet function, decomposition levels, hard or soft threshold and threshold can be selected automatically. This paper ends by comparing two noise reduction methods on the basis of their denoising performances, computation time, etc. The effectiveness of these methods in-troduced in this paper is validated by the results of analysis of the simulated and real signals.展开更多
Donnell’s thin shell theory and basic equations based on the wave propagation method discussed in detail here, is used to investigate the natural frequencies of thin finite length circular cylindrical shells under va...Donnell’s thin shell theory and basic equations based on the wave propagation method discussed in detail here, is used to investigate the natural frequencies of thin finite length circular cylindrical shells under various boundary conditions. Mode shapes are drawn to explain the circumferential mode number n and axial mode number m, and the natural frequencies are cal-culated numerically and compared with those of FEM (finite element method) to confirm the reliability of the analytical solution. The effects of relevant parameters on natural frequencies are discussed thoroughly. It is shown that for long thin shells the method is simple, accurate and effective.展开更多
Models based on a parabolic equation(PE)can accurately predict sound propagation problems in range-dependent ocean waveguides.Consequently,this method has developed rapidly in recent years.Compared with normal mode th...Models based on a parabolic equation(PE)can accurately predict sound propagation problems in range-dependent ocean waveguides.Consequently,this method has developed rapidly in recent years.Compared with normal mode theory,PE focuses on numerical calculation,which is difficult to use in the mode domain analysis of sound propagation,such as the calculation of mode phase velocity and group velocity.To broaden the capability of PE models in analyzing the underwater sound field,a wave mode calculation method based on PE is proposed in this study.Step-split Pade PE recursive matrix equations are combined to obtain a propagation matrix.Then,the eigenvalue decomposition technique is applied to the matrix to extract sound mode eigenvalues and eigenfunctions.Numerical experiments on some typical waveguides are performed to test the accuracy and flexibility of the new method.Discussions on different orders of Padéapproximant demonstrate angle limitations in PE and the missing root problem is also discussed to prove the advantage of the new method.The PE mode method can be expanded in the future to solve smooth wave modes in ocean waveguides,including fluctuating boundaries and sound speed profiles.展开更多
Terfenol is an ideal choice for medium to high power low frequency sonar.It can offer the transducer designer higher strain,higher power density,but the designer must be aware of the eddy current.To enhance efficiency...Terfenol is an ideal choice for medium to high power low frequency sonar.It can offer the transducer designer higher strain,higher power density,but the designer must be aware of the eddy current.To enhance efficiency of the barrel-stave transducer powered by a Terfenol rod,radial slots rather than laminations were used to control eddy currents in the Terfenol drive rod,and the effectiveness and the number of these slots were studied experimentally and calculated by finite element modeling.Based on the characteristic of vortex path,a new simple geometrical method to calculate the number of the radial slots of a Terfenol rod at the operating frequency is put forward in this paper.Moreover,the calculated results are in good agreement with those of using the finite element method(FEM)for the slotted Terfenol rod given by the literature.The method will save much cost to design Terfenol rod transducers.展开更多
An optical fiber hydrophone based on equivalent phase shift fiber Bragg grating （EPS-FBG） with temperature compensation package provides an improvement of sensitivity in underwater acoustic measurement at wide frequ...An optical fiber hydrophone based on equivalent phase shift fiber Bragg grating （EPS-FBG） with temperature compensation package provides an improvement of sensitivity in underwater acoustic measurement at wide frequency range, from 2.SkHz to 12kHz. The acoustic pressure is transduced into elastic vibration of a circle metal disk, resulting in an intensity modulation of the reflected light wave back from fiber Bragg grating （FBG）. Experiment shows that the 500 EPS-FBG hydrophone has a minimum detectable acoustic pressure of about at 5 kHz and achieves about 18-dB improvement of acoustic pressure sensitivity compared with a regular apodized FBG hydrophone.展开更多
Based on Jacobson’s molecular free length theory in liquids and the relationship between the ultrasonic velocity and the molecular free length in organic liquids, the equation of the acoustic nonlinearity parameter i...Based on Jacobson’s molecular free length theory in liquids and the relationship between the ultrasonic velocity and the molecular free length in organic liquids, the equation of the acoustic nonlinearity parameter in organic liquid binary mixtures is derived. The calculated values from the equation are in good agreement both with those from Apfel’s and from Sehgal’s mixture laws.展开更多
This paper proposes an optimized simulated annealing(SA) algorithm for thinning and weighting large planar arrays in 3D underwater sonar imaging systems.The optimized algorithm has been developed for use in designing ...This paper proposes an optimized simulated annealing(SA) algorithm for thinning and weighting large planar arrays in 3D underwater sonar imaging systems.The optimized algorithm has been developed for use in designing a 2D planar array(a rectangular grid with a circular boundary) with a fixed side-lobe peak and a fixed current taper ratio under a narrow-band excitation.Four extensions of the SA algorithm and the procedure for the optimized SA algorithm are described.Two examples of planar arrays are used to assess the efficiency of the optimized method.The proposed method achieves a similar beam pattern performance with fewer active transducers and faster convergence ability than previous SA algorithms.展开更多
A truncated broadband parametric array with a primary frequency of 500 kHz and difference frequency range of 1 kHz to 30 kHz was designed as a sound source of the underwater acoustic material measurement system.By ana...A truncated broadband parametric array with a primary frequency of 500 kHz and difference frequency range of 1 kHz to 30 kHz was designed as a sound source of the underwater acoustic material measurement system.By analyzing the theoretical calculation and actual measurement results in array directivity of the truncated broadband parametric source at typical frequencies,we observed that the curves of the two results were basically consistent,which proved that the calculation model was correct.Application of bell-shaped short-duration pulse to achieve broadband measurement for characteristics of underwater acoustic materials was beneficial to reduce the effects of diffraction from the panel edges.The measurement system was established for measuring the sound pressure reflection coefficients,sound pressure transmission coefficients and absorption coefficients of the large panel sample in the pressure vessel.The size of this tank isφ4 m×12 m,the maximum hydrostatic pressure is 4.5 MPa,and the corresponding measuring frequency range is from 1 kHz to 30 kHz.The measured curves had a good agreement with theoretical curves,which verified that the parametric source measurement method was feasible.Then,the sound absorption properties of the rubber plate sample were measured under different hydrostatic pressures.The studying results could show that the parametric source measurement method had the potential application in the limited space water,such as the pressure vessel.展开更多
With Laser Reflective Tomography（LRT）,the near fields of ultrasonic transducers were measured and analyzed.The principle of LRT measurement of ultrasonic field distribution was introduced and an experimental system ...With Laser Reflective Tomography（LRT）,the near fields of ultrasonic transducers were measured and analyzed.The principle of LRT measurement of ultrasonic field distribution was introduced and an experimental system was set up.Acoustic pressure of a multiple element piston transducer was measured by using of a laser vibrometer.Its distribution in amplitude and phase was obtained.The acoustic pressure in the same region was measured with a needle hydrophone to validate the LRT method.Furthermore,through reconstruction of acoustic fields,it indicated that LRT method is suitable for predicting the distribution on transducers＇surface and conditions of active elements.展开更多
Time reversal processing （TRP） might be regarded as matched field processing with known environmental knowledge. However, the performance of TRP is degraded in an uncertain environment. A technique based on the Maxi...Time reversal processing （TRP） might be regarded as matched field processing with known environmental knowledge. However, the performance of TRP is degraded in an uncertain environment. A technique based on the Maximin criterion is pro- posed for enhancing the robustness of TRP in a waveguide with uncertain water depth. The relationship between the water depth and the focal spot translation is examined based on the waveguide-invariant theory. Then the time reversal transmissiou scheme with the Maximin criterion is performed to maximize the minimum transmission power on a target of interest. At the receiving end, coherent summation operation is carried out over the received data by a reception focusing bank. If it is neces- sary to enhance the target echo further, the iterative time reversal can be considered where the target echo corresponding to the first time reversal transmission is regarded as a secondary source. Numerical simulations and experimental results of the target localization in a waveguide tank have verified the effectiveness of robust TRP.展开更多
The radial vibration characteristic of an annular ultrasonic concentrator with multi- slits is studied. Based on the electro-mechanical analogy and by introducing an area ratio coef- ficient, the radial vibrational eq...The radial vibration characteristic of an annular ultrasonic concentrator with multi- slits is studied. Based on the electro-mechanical analogy and by introducing an area ratio coef- ficient, the radial vibrational equivalent circuit and the frequency equation of the concentrator are derived. The radial displacement amplitude magnification factor of it is obtained. By nu- merical calculating, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator at the first and second resonance and its radius ratio are investigated. Also, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator and the length, the angle and the number of the silts are analyzed. It is illustrated that a maximum of displacement ampli- tude magnification factor of the concentrator appears with the increase of the radius ratio, and the amplitude magnification factor increase as the length, the angle and the number of the silts increase, while the radial resonance frequency of the concentrator decreases as the length, the angle and the number of the silts increase. The theoretical resonance frequencies are in good agreement with that of the FEM simulations and measurement.展开更多
基金supported by the National Natural Science Foundation of China(62173118).
文摘Dear Editor,This letter concentrates on distributed event-triggered formation control problems with finite-time convergence in an arbitrarily dimensional Euclidean space.A new unified approach of finite-time event-triggered formation control is proposed by steering all agents to a sliding manifold(the affine image)to achieve general formations,like affine,rigid or translational formation.It only requires to design an extra steering law driving at least d+1 leaders from an affine image to a rigid or translational image,where d is the dimension of the space.The event-triggered function is designed in a distributed and discontinuous manner based only on local information to reduce the communication and calculation resources by aperiodic sampling.In the proposed event-triggered formation law,zeno-free behavior is ensured.
基金supported by the National Natural Science Foundation of China(Grant Nos.62471024 and 62301183)the Open Research Fund of Hanjiang Laboratory(KF2024001).
文摘Surface/underwater target classification is a key topic in marine information research.However,the complex underwater environment,coupled with the diversity of target types and their variable characteristics,presents significant challenges for classifier design.For shallow-water waveguides with a negative thermocline,a residual neural network(ResNet)model based on the sound field elevation structure is constructed.This model demonstrates robust classification performance even when facing low signal-to-noise ratios and environmental mismatches.Meanwhile,to address the reduced generalization ability caused by limited labeled acoustic data,an improved ResNet model based on unsupervised domain adaptation(“proposed UDA-ResNet”)is further constructed.This model incorporates data on simulated elevation structures of the sound field to augment the training process.Adversarial training is employed to extract domain-invariant features from simulated and trial data.These strategies help reduce the negative impact caused by domain differences.Experimental results demonstrate that the proposed method shows strong surface/underwater target classification ability under limited sample sizes,thus confirming its feasibility and effectiveness.
基金Sponsored by National Nature Science Foundation of China(10474079)
文摘According to the features of the wideband underwater acoustic signals,an algorithm for the wideband ambiguity function is put forward based on Mellin transform.The wideband acoustic signal processing using the fast Mellin transform is also explored.The theoretical analysis and simulation results show that the algorithm has not only high computation efficiency but also good concentration in wideband ambiguity domain.It suits for the wideband underwater acoustic signal processing.
基金Sponsored by New Century Excellent Talent Support Project (NCET-04-0545)
文摘An algorithm of broadband minimum variance distortionless response(MVDR) based on the frequency energy normalization is proposed.First,every narrowband frequency component of the broadband signal is normalized by the total narrowband energy of all array elements,and the narrowband power is calculated by MVDR.Finally,final spatial energy spectrum can be obtained by averaging or summing all results of every narrowband frequency bin.Any prior-information about the noise or the signal is unnecessary for the proposed method in this paper.The processing gain of the proposed method compared to the conventional broadband MVDR can be obtained as long as the amplitude fluctuation of the array noise frequency spectrum is severer than that of the target signal.The validity of the method is validated by the optimal signal detection theory.Simulation and real data are used to validate the performance of the method.Analysis results show that about 4 dB processing gain compared to the general broadband MVDR can be reached by the proposed method.
基金The work was supported by the National Natural Science Foundation of China ( No.10074043) and the Natural ScienceFoundation of Shaanxi Province (No.2003A05) .
文摘The study was to investigate thrombolysis in vitro with ultrasound, and to discuss effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold under different ultrasound intensity and exposure time. The structure of erythrocyte in thrombus was evaluated under light microscope. The relationship between the structure of erythrocyte in thrombus and ultrasound intensity and exposure time was obtained. The results showed that ultrasound eliminated the thrombus. According to the change of the structure of erythrocyte in thrombus and ultrasound intensity and exposure time, the effects of thrombolysis with ultrasound could be divided into three kinds of areas: the A, B, C area. The area A was the safe area, the area B was the relatively safe area, and the area C was the irreversible damage area. The study suggested that ultrasound intensity and exposure time had significant impact on the structure of erythrocyte. Stronger ultrasound intensity or longer exposure time could cause erythrocytes irreversible damage. It could accelerate thrombolysis and shorten the exposure time that the ultrasound intensity was little bit increased. The study of effects of thrombolysis with ultrasound on the structure of erythrocyte and its safety threshold were important for practical applications.
文摘Based on Schaaff＇s collision factor theory （CFT） in liquids, the equations for nonlinear ultrasonic parameters in both organic liquid and binary organic liquid mixtures are deduced. The nonlinear ultrasonic parameters, including pressure coefficient, temperature coefficients of ultrasonic velocity, and nonlinear acoustic parameter B/A in both organic liquid and binary organic liquid mixtures, are evaluated for comparison with the measured results and data from other sources. The equations show that the coefficient of ultrasonic velocity and nonlinear acoustic parameter B/A are closely related to molecular interactions. These nonlinear ultrasonic parameters reflect some information of internal structure and outside status of the medium or mixtures. From the exponent of repulsive forces of the molecules, several thermodynamic parameters, pressure and temperature of the medium, the nonlinear ultrasonic parameters and ultrasonic nature of the medium can be evaluated. When evaluating and studying nonlinear acoustic parameter B/A of binary organic liquid mixtures, there is no need to know the nonlinear acoustic parameter B/A of the components. Obviously, the equation reveals the connection between the nonlinear ultrasonic nature and internal structure and outside status of the mixtures more directly and distinctly than traditional mixture law for B/A, e.g. Apfel＇s and Sehgal＇s laws for liquid binary mixtures.
基金Supported by National Key R&D Program of China(Grant No.2021YFB3400501).
文摘Cam-lobe radial-piston hydraulic motors are widely used as rotation driving units for various marine machinery owing to their ultrahigh output torque(more than 100 kN m).A multi-row cam roller bearing(MCRB)is the key component that directly determines the fatigue life of a cam-lobe radial-piston hydraulic motor.However,compact geometry and complex loads render MCRB susceptible to fatigue failure,highlighting the need for an optimized MCRB to achieve longer fatigue life and higher reliability.Therefore,this study proposes an innovative geometry optimization method for an MCRB to improve its fatigue life.In this method,a quasi-static model was developed to calculate the load distribution,with the fatigue life of the MCRB calculated using both basic dynamic loading and load distribution.Subsequently,a genetic algorithm was used to obtain the optimized geometry parameters,which significantly improved the fatigue life of the MCRB.Finally,a loading test was conducted on a hydraulic motor installed with both the initial and optimized MCRB to validate the effectiveness of the proposed optimization method.This study provides a theoretical guideline for optimizing the design of MCRB,thereby increasing the fatigue life of hydraulic motors.
基金Funded by the National Natural Science Foundation of China(Nos.5161101582 and 51575541)Zhejiang Provincial Natural Science Foundation of China(No.LY15E050012)Zhejiang Provincial Public Projects on Industrial Technology(No.2015C31052)
文摘The ultrasonic pulse signal resonance features in layered carbon fiber reinforced plastic（CFRP） within voids were researched. The frequency domain model of acoustic wave propagation in multilayered medium was established. Then the reflection coefficient of multilayered CFRP within voids was numerically calculated. The results are as follows. When the CFRP laminate is tested by ultrasonic whose center frequency is close to the CFRP inherent resonant frequency, the ultrasonic may generate resonance phenomenon in CFRP. If CFRP contains evenly distributed voids, the frequency of resonant signal and its amplitude all decrease with the increase of porosity. For the thick section CFRP within local concentrated voids, the local concentrated voids near testing surface will cause signal frequency reduction and the decrease of its amplitude. But the voids which exist in layers far away from testing surface almost have no influence on signal resonance. The ultrasonic pulse echo testing was conducted for thick section CFRP specimen. The analysis results of testing signals were in accordance with the results of the numerical calculation, showing that the reflection coefficient frequency response model can effectively explain the ultrasonic resonance phenomenon in layered CFRP within voids.
基金Supported by the National Natural Science Foundation of China under Grant No.19674035。
文摘An ultrasound method of sterilizing aspergillus flavus and fusarium is proposed and demonstrated.The dependence of sterilizing effect on ultrasonic intensity,frequency,and treatment time is experimentally investigated.The density of surviving spores decreases first with increasing ultrasonic frequency and then increases with the further increase of the frequency,that is to say,there exists the optimum frequency 26 kHz at which the killing rate is near 100%.The killing rate seems proportional to the intensity and the time.
基金Project (No. 51446020203JW0401) supported by the State KeyLaboratory of Oceanic Acoustics Foundation, China
文摘Genetic algorithm (GA) based on wavelet transform threshold shrinkage (WTS) and translation-invariant threshold shrinkage (TIS) is introduced into the method of noise reduction, where parameters used in WTS and TIS, such as wavelet function, decomposition levels, hard or soft threshold and threshold can be selected automatically. This paper ends by comparing two noise reduction methods on the basis of their denoising performances, computation time, etc. The effectiveness of these methods in-troduced in this paper is validated by the results of analysis of the simulated and real signals.
文摘Donnell’s thin shell theory and basic equations based on the wave propagation method discussed in detail here, is used to investigate the natural frequencies of thin finite length circular cylindrical shells under various boundary conditions. Mode shapes are drawn to explain the circumferential mode number n and axial mode number m, and the natural frequencies are cal-culated numerically and compared with those of FEM (finite element method) to confirm the reliability of the analytical solution. The effects of relevant parameters on natural frequencies are discussed thoroughly. It is shown that for long thin shells the method is simple, accurate and effective.
基金Project supported by Young Elite Scientist Sponsorship Program by CAST(Grant No.YESS20200330).
文摘Models based on a parabolic equation(PE)can accurately predict sound propagation problems in range-dependent ocean waveguides.Consequently,this method has developed rapidly in recent years.Compared with normal mode theory,PE focuses on numerical calculation,which is difficult to use in the mode domain analysis of sound propagation,such as the calculation of mode phase velocity and group velocity.To broaden the capability of PE models in analyzing the underwater sound field,a wave mode calculation method based on PE is proposed in this study.Step-split Pade PE recursive matrix equations are combined to obtain a propagation matrix.Then,the eigenvalue decomposition technique is applied to the matrix to extract sound mode eigenvalues and eigenfunctions.Numerical experiments on some typical waveguides are performed to test the accuracy and flexibility of the new method.Discussions on different orders of Padéapproximant demonstrate angle limitations in PE and the missing root problem is also discussed to prove the advantage of the new method.The PE mode method can be expanded in the future to solve smooth wave modes in ocean waveguides,including fluctuating boundaries and sound speed profiles.
文摘Terfenol is an ideal choice for medium to high power low frequency sonar.It can offer the transducer designer higher strain,higher power density,but the designer must be aware of the eddy current.To enhance efficiency of the barrel-stave transducer powered by a Terfenol rod,radial slots rather than laminations were used to control eddy currents in the Terfenol drive rod,and the effectiveness and the number of these slots were studied experimentally and calculated by finite element modeling.Based on the characteristic of vortex path,a new simple geometrical method to calculate the number of the radial slots of a Terfenol rod at the operating frequency is put forward in this paper.Moreover,the calculated results are in good agreement with those of using the finite element method(FEM)for the slotted Terfenol rod given by the literature.The method will save much cost to design Terfenol rod transducers.
文摘An optical fiber hydrophone based on equivalent phase shift fiber Bragg grating （EPS-FBG） with temperature compensation package provides an improvement of sensitivity in underwater acoustic measurement at wide frequency range, from 2.SkHz to 12kHz. The acoustic pressure is transduced into elastic vibration of a circle metal disk, resulting in an intensity modulation of the reflected light wave back from fiber Bragg grating （FBG）. Experiment shows that the 500 EPS-FBG hydrophone has a minimum detectable acoustic pressure of about at 5 kHz and achieves about 18-dB improvement of acoustic pressure sensitivity compared with a regular apodized FBG hydrophone.
文摘Based on Jacobson’s molecular free length theory in liquids and the relationship between the ultrasonic velocity and the molecular free length in organic liquids, the equation of the acoustic nonlinearity parameter in organic liquid binary mixtures is derived. The calculated values from the equation are in good agreement both with those from Apfel’s and from Sehgal’s mixture laws.
基金Project (No.2006AA09Z109) supported by the National High-Tech Research and Development Program (863) of China
文摘This paper proposes an optimized simulated annealing(SA) algorithm for thinning and weighting large planar arrays in 3D underwater sonar imaging systems.The optimized algorithm has been developed for use in designing a 2D planar array(a rectangular grid with a circular boundary) with a fixed side-lobe peak and a fixed current taper ratio under a narrow-band excitation.Four extensions of the SA algorithm and the procedure for the optimized SA algorithm are described.Two examples of planar arrays are used to assess the efficiency of the optimized method.The proposed method achieves a similar beam pattern performance with fewer active transducers and faster convergence ability than previous SA algorithms.
文摘A truncated broadband parametric array with a primary frequency of 500 kHz and difference frequency range of 1 kHz to 30 kHz was designed as a sound source of the underwater acoustic material measurement system.By analyzing the theoretical calculation and actual measurement results in array directivity of the truncated broadband parametric source at typical frequencies,we observed that the curves of the two results were basically consistent,which proved that the calculation model was correct.Application of bell-shaped short-duration pulse to achieve broadband measurement for characteristics of underwater acoustic materials was beneficial to reduce the effects of diffraction from the panel edges.The measurement system was established for measuring the sound pressure reflection coefficients,sound pressure transmission coefficients and absorption coefficients of the large panel sample in the pressure vessel.The size of this tank isφ4 m×12 m,the maximum hydrostatic pressure is 4.5 MPa,and the corresponding measuring frequency range is from 1 kHz to 30 kHz.The measured curves had a good agreement with theoretical curves,which verified that the parametric source measurement method was feasible.Then,the sound absorption properties of the rubber plate sample were measured under different hydrostatic pressures.The studying results could show that the parametric source measurement method had the potential application in the limited space water,such as the pressure vessel.
文摘With Laser Reflective Tomography（LRT）,the near fields of ultrasonic transducers were measured and analyzed.The principle of LRT measurement of ultrasonic field distribution was introduced and an experimental system was set up.Acoustic pressure of a multiple element piston transducer was measured by using of a laser vibrometer.Its distribution in amplitude and phase was obtained.The acoustic pressure in the same region was measured with a needle hydrophone to validate the LRT method.Furthermore,through reconstruction of acoustic fields,it indicated that LRT method is suitable for predicting the distribution on transducers＇surface and conditions of active elements.
基金supported by the National Natural Science Foundation of China(Grant Nos.60872066 and 61171148)the National High-Tech R&D Program of China(Grant No.2009AA093601-3)
文摘Time reversal processing （TRP） might be regarded as matched field processing with known environmental knowledge. However, the performance of TRP is degraded in an uncertain environment. A technique based on the Maximin criterion is pro- posed for enhancing the robustness of TRP in a waveguide with uncertain water depth. The relationship between the water depth and the focal spot translation is examined based on the waveguide-invariant theory. Then the time reversal transmissiou scheme with the Maximin criterion is performed to maximize the minimum transmission power on a target of interest. At the receiving end, coherent summation operation is carried out over the received data by a reception focusing bank. If it is neces- sary to enhance the target echo further, the iterative time reversal can be considered where the target echo corresponding to the first time reversal transmission is regarded as a secondary source. Numerical simulations and experimental results of the target localization in a waveguide tank have verified the effectiveness of robust TRP.
基金supported by the Natural Science Foundation of China Under Grant(11274279,11074222)the College Scholar Professional Development Program of Zhejiang Province Under Grant(FX2013017)
文摘The radial vibration characteristic of an annular ultrasonic concentrator with multi- slits is studied. Based on the electro-mechanical analogy and by introducing an area ratio coef- ficient, the radial vibrational equivalent circuit and the frequency equation of the concentrator are derived. The radial displacement amplitude magnification factor of it is obtained. By nu- merical calculating, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator at the first and second resonance and its radius ratio are investigated. Also, the relationship between the radial displacement amplitude magnification factor, the resonance frequency of the concentrator and the length, the angle and the number of the silts are analyzed. It is illustrated that a maximum of displacement ampli- tude magnification factor of the concentrator appears with the increase of the radius ratio, and the amplitude magnification factor increase as the length, the angle and the number of the silts increase, while the radial resonance frequency of the concentrator decreases as the length, the angle and the number of the silts increase. The theoretical resonance frequencies are in good agreement with that of the FEM simulations and measurement.
