Reducing the radiated noise of a gearbox is a difficult problem in aviation,navigation,machinery,and other fields.Structural improvement is the main means of noise reduction for a gearbox,and it is realized primarily ...Reducing the radiated noise of a gearbox is a difficult problem in aviation,navigation,machinery,and other fields.Structural improvement is the main means of noise reduction for a gearbox,and it is realized primarily through contribution analysis and structure optimization.However,these approaches have certain limitations.In this study,a low-noise design method for a gearbox that combines the two approaches is proposed,and experimental verification is performed.First,a finite element/boundary element model is established using a single-stage herringbone gearbox.Considering the vibration excitation of the gear system,the radiation noise of a single-stage gearbox is predicted based on the modal acoustic transfer vector(MATV)method.Subsequently,the maximum field point of the radiated noise is determined,and the acoustic transfer vector(ATV)analysis and modal acoustic contribution(MAC)analysis are conducted to determine the region that contributes significantly to the radiated noise of the field point.The optimization region is selected through the panel acoustic contribution(PAC)analysis.Next,to reduce the normal speed in the optimization region,topology optimization is performed.According to the topology optimization results,four different noise reduction structures are added to the gearbox,and the low-noise optimization models are established respectively.Finally,by measuring the radiated noise of the gearbox before and after optimization under a given working condition,the validity of the radiated noise prediction method and the low-noise optimization design method are verified by comparing the simulation and experimental data.A comparison of the four optimization models proves that the noise reduction effect can be achieved only by adding a noise reduction structure to the center of the density nephogram.展开更多
A combined method of wave superposition and finite element is proposed to solve the radiation noise of targets in shallow sea.Taking the sound propagation of spherical sound source in shallow sea as an example,the rad...A combined method of wave superposition and finite element is proposed to solve the radiation noise of targets in shallow sea.Taking the sound propagation of spherical sound source in shallow sea as an example,the radiation sound field of the spherical sound source is equivalent to the linear superposition of the radiation sound field of several internal point sound sources,and then the radiated noise induced by spherical sound source can be predicted quickly.The accuracy and efficiency of the method are verified by comparing with the numerical results of finite element method,and the rapid prediction of underwater radiated noise of cylindrical shell is carried out based on the method.The results show that compared with the finite element method,the relative error of the calculation results under different simulation conditions does not exceed 0.1%,and the calculation time is about 1/10 of the finite element method,so this method can be used to solve the radiated noise of shallow underwater targets.展开更多
The underwater acoustic field influenced by a selected ocean internal wavewas computed using the Parabolic Equation (PE) method and split-step difference algorithm in thispaper. Acoustic field is formed by sound sourc...The underwater acoustic field influenced by a selected ocean internal wavewas computed using the Parabolic Equation (PE) method and split-step difference algorithm in thispaper. Acoustic field is formed by sound source with different frequency covering the range ofradiation noise of ships and submarines. Owing to the adoption of complex variables, sparse matrix,Gaussian source and analysis on the grid size, numerical results are achieved smoothly. The resultsshow that internal wave''s influence on underwater sound can''t be neglected, especially for highersound frequency. So it'' s necessary to take internal wave into account in identifying radiationnoise of ships and submarines, namely for sound intensity, transmission loss and spectra shape.展开更多
The active control of structural sound radiation in an acoustic enclosure is studied by using distributed point force actuators as the secondary control force, and the control mechanisms for the radiated noise in the ...The active control of structural sound radiation in an acoustic enclosure is studied by using distributed point force actuators as the secondary control force, and the control mechanisms for the radiated noise in the cavity are analyzed. A rectangular enclosure involving two simply supported flexible plates is created for this investigation. The characteristics of the primary and secondary sound field and the structural-acoustic coupled system are analyzed, and the optimal control objective for reducing the sound pressure level （SPL） in the cavity is derived. The response of the SPL in the cavity is analyzed and compared when the secondary point force actuators with different locations and parameters are applied to the two flexible plates. The results indicate that the noise in the cavity can be better controlled when some point force actuators are applied to two flexible plates for cooperative control rather than the point force actuators being only applied to the excited flexible plate.展开更多
Electric contact discharge is subject closely related to digital information transmission, and integrity of digital signals for realizing high reliablility transmission. This kind of problem is a part of EMC (electrom...Electric contact discharge is subject closely related to digital information transmission, and integrity of digital signals for realizing high reliablility transmission. This kind of problem is a part of EMC (electromagnetic compatibility). From such a viewpoint, contact noise problems will be mentioned which disturb and degrade digital signals. The induction noise and radiation noise from discharge, electrostatic discharge (ESD), and connector related fundamental subject will be mentioned.展开更多
The double-peak characteristic of underwater radiated noise in the near field on top of the target submarine was analyzed in depth on the basis of submarine test data on the sea. The contribution of three major noise ...The double-peak characteristic of underwater radiated noise in the near field on top of the target submarine was analyzed in depth on the basis of submarine test data on the sea. The contribution of three major noise sources to the radiated noise of a submarine were compared and analyzed, and emphasis was put on the original source, production mechanism, and their correlative characteristics. On the basis of analysis on underwater tracking and pass through characteristics of the target submarine, the double-peak phenomenon was reasonably interpreted. Furthermore, the correctness of the theoretical interpretation was verified adequately in real submarine tests. The double-peak phenomenon indicates that the space distributing character on submarine radiated noise are both asymmetrical with time and space, whereas that is provided with directivity. Studying the double-peak phenomenon in depth has important reference value and meaning in engineering practice for understanding the underwater radiated noise field of submarines.展开更多
The flow-induced noise is simulated with a hybrid method.Firstly,a steady-state background flow field is given by solving Reynolds averaged Navier-Stokes(RANS)equations with finite volume(FV)method on structured grid....The flow-induced noise is simulated with a hybrid method.Firstly,a steady-state background flow field is given by solving Reynolds averaged Navier-Stokes(RANS)equations with finite volume(FV)method on structured grid.Then the linearized Euler equations(LEE)can be constructed based on the resulted background flow field,where the source term on the right hand side is computed using stochastic noise generation and radiation(SNGR)method.Finally,the unsteady acoustic field is obtained through solving LEE using high-order discontinuous Galerkin(DG)method on unstructured grid,where the parallel computing based on mesh partitioning and a″Quadrature-Free Implementation″method for high-order DG are employed to accelerate the computation.In order to demonstrate the sound propagation in detail,a visualization method for high-order schemes is also developed here.Moreover,in order to test the validation and the accuracy,a 3D cavity test in comparison with the experimental data is displayed first in this paper,then a 3D high-lift wing is also simulated to demonstrate its capability for very complex geometries.展开更多
Shipping traffic is one of the largest contributors to anthropogenic noise in the ocean. Noise generated by merchant ships elevates natural occurring ambient noise level by 20-30 dB in many areas of the world＇s ocean...Shipping traffic is one of the largest contributors to anthropogenic noise in the ocean. Noise generated by merchant ships elevates natural occurring ambient noise level by 20-30 dB in many areas of the world＇s ocean. In order to model the contributions of the noise generated by merchant ships to underwater ambient noise level correctly, a database that consists of the source levels as a function of frequency for different types of ships is essential. This paper describes the conceptual design, with an emphasis on the characteristics of shipping noise as sound sources, of a marine noise database. It was developed for providing necessary parameters for underwater ambient noise modelling. The parameters relevant to shipping noise modelling are organized in two catalogues： （l） source-receiver geometry related parameters, namely the coordinates of the ships at a given time period, as well as the sizes/types of the ships from which the noise source depths may be derived, and （2） acoustically relevant parameters, i.e., the acoustic SLs （source levels） at given frequencies. An example is presented here to demonstrate the efficacy of this database. The study area is a 117 × 55 km2 region off the coast of La Spezia, Italy, in the Mediterranean Sea.展开更多
A rare Type I-like noise storm was observed with the solar radio spectrometers (1.0-2.0 GHz and 2.60-3.8 GHz) at National Astronomical Observatories of China (NAOC) on September 23, 1998. We concentrate on checking th...A rare Type I-like noise storm was observed with the solar radio spectrometers (1.0-2.0 GHz and 2.60-3.8 GHz) at National Astronomical Observatories of China (NAOC) on September 23, 1998. We concentrate on checking the Type I-like noise storm occurred in the decay phase of a Type Ⅳ radio burst. This noise storm consists of many Type I bursts and isolated Type Ⅲ or Type Ⅲ pair bursts. It has a bandwidth of ≤0.5 GHz. The duration of each Type I burst is of the order of 100-300 ms. The total duration is greater than 11 minutes. The circular polarization degree of the components of Type Ⅰ and associated Type Ⅲ bursts are about 40%-100% and almost 100%, respectively, which is greater than that of the background continuum (nearly the precision of our instrument). This short decimetric Type Ⅰ-like storm may be another kind or the extension of the kind of metric Type Ⅰ storm, and may possess the duality of metric and decimetric radio emission. It may be in favor of an earlier emission mechanism of the fundamental plasma radiation due to the coalescence of Langmuir waves with low-frequency waves.展开更多
This paper discusses the basic categories of noise in detecting high frequency gravitational waves in the microwave band （-0.1-10GHz）, which contain shot noise from the laser and the thermal radiation photons, therm...This paper discusses the basic categories of noise in detecting high frequency gravitational waves in the microwave band （-0.1-10GHz）, which contain shot noise from the laser and the thermal radiation photons, thermal noise from statistical fluctuation of the thermal photons and fluctuation of the temperature, radiation press noise on the fractal membrane, the noise caused by the scattering of the Gaussian Beam （GB） in the detecting tube and noise in the microwave radiometers. The analysis shows that a reasonable signal-to-noise ratio may be achieved for a detecting device with the fixed power of GB （105 W）, only when the temperature of the environment is no more than T=I K, and the optimal length of the microwave radiometers is about 0.3 m.展开更多
The requirement of low radiated noise is increasing for underwater propulsors as the noise significantly affecting the comfort and quietness of ships,submarines,and vessels.To broaden the view of noise characteristics...The requirement of low radiated noise is increasing for underwater propulsors as the noise significantly affecting the comfort and quietness of ships,submarines,and vessels.To broaden the view of noise characteristics of pump-jet propulsors(PJPs),this paper considers the radiated noise of a pre-swirl stator PJP with the effects of the advance coefficient and rotor rotational speed.Radiated noise is obtained by the“hybrid method”approach,which combines a hydrodynamic solver with a hydroacoustic solver.The turbulence flow is obtained through improved delayed detached eddy simulation(IDDES),which show good agreement with the experiment,including the performance and flow field.The solver precision,permeable surface size,and sampling frequency notably affect the noise calculation.The spectra of thrust fluctuation and radiated noise are characterized by the tonal phenomenon around the blade passing frequency and its harmonics.The spectrum of radiated noise and overall sound pressure level(OSPL)are considerably affected by both the advance coefficient and the rotor rotational speed.Overall,the numerical results and analysis given in this paper should be partly helpful in deepening the understanding of the radiated noise characteristics of PJPs.展开更多
This study investigates the underwater radiated noise(URN)of a manned submersible support mother ship.To this end,a detailed finite element model of the hull and outflow field is established,and the vibration wet mode...This study investigates the underwater radiated noise(URN)of a manned submersible support mother ship.To this end,a detailed finite element model of the hull and outflow field is established,and the vibration wet mode of the scientific research ship is calculated.A combination of finite element and boundary element methods is used to analyze the spectral features of ship low-frequency URN.The URN source is comprehensively analyzed,the vibration energy is considered the basic parameter to describe the vibration,and the medium-and high-frequency URN of the ship are calculated using the statistical energy analysis.To obtain the full frequency-band URN of the ship,the risk position of exceeding the standard is determined,and the contribution of each main noise source in the ship to the URN is analyzed.The URN level of the ship is comprehensively measured in the free navigation state.The accuracy of the URN control evaluation model,and the method of the ship are verified.The data support for the ship to apply for the classification society certificate provides a scheme reference for the URN control of other scientific research ship in the future.展开更多
The natural flow cooling strategy is commonly employed in modern high-speed vessels and nuclear-powered submarines. These vessels rely on the energy generated by their own speed to drive the cooling system and supply ...The natural flow cooling strategy is commonly employed in modern high-speed vessels and nuclear-powered submarines. These vessels rely on the energy generated by their own speed to drive the cooling system and supply cooling water to the condenser. The circulating pump, which operates without a motor drive under natural flow conditions, is a large resistance component in the cooling system. However, it is also the primary noise source, significantly impacting the vessel’s safe operation and acoustic stealth performance. This study investigates the induced noise characteristics of a multi-stage pump under natural flow conditions by experiment, computational fluid dynamics (CFD), and acoustic finite element method. The analysis encompasses the distribution of the flow field, variations in acoustic power, spectral features of flow-induced noise, and directivity of external field radiation noise under different natural flow conditions. The results show that the acoustic power distribution is correlated with the flow field. When the impeller is stuck, the noise sources primarily concentrate in the flow separation area at the blade’s leading edge, the interface area between the impeller and the guide vane, and the flow shock area inside the guide vane. Conversely, when the impeller rotates passively, the blade wake area has a higher acoustic power. The flow noise spectrum under natural flow conditions mainly exhibits broadband and discrete characteristics. Additionally, the pump structure influences the external field radiation noise, and its directivity varies with different flow rates and characteristic frequencies. This study provides valuable insights into optimal design to reduce the noise of the circulating pump in the vessel’s natural flow cooling system. It is essential for ensuring the safe operation and acoustic stealth performance of high-speed vessels and nuclear-powered submarines.展开更多
In an atrocious ocean environment,the lateral propulsion hole could potentially be partly out of water and capture an air cavity.Bubbles would form when the captured air cavity escapes underwater and they may affect t...In an atrocious ocean environment,the lateral propulsion hole could potentially be partly out of water and capture an air cavity.Bubbles would form when the captured air cavity escapes underwater and they may affect the performance of the sonar.The common commercial computational fluid dynamics software CFX was adopted to calculate the ambient flow field around the lateral propulsion hole generated by a moving vessel.The oscillation of the spherical bubble was based on the Rayleigh-Plesset equation and its migration was modeled using the momentum equation.The radiated noise of the oscillating bubble was also studied.The aim is that the results from this paper would provide some insight into corresponding fluid and acoustic study.展开更多
To improve the ability of detecting underwater targets under strong wideband interference environment,an efficient method of line spectrum extraction is proposed,which fully utilizes the feature of the target spectrum...To improve the ability of detecting underwater targets under strong wideband interference environment,an efficient method of line spectrum extraction is proposed,which fully utilizes the feature of the target spectrum that the high intense and stable line spectrum is superimposed on the wide continuous spectrum.This method modifies the traditional beam forming algorithm by calculating and fusing the beam forming results at multi-frequency band and multi-azimuth interval,showing an excellent way to extract the line spectrum when the interference and the target are not in the same azimuth interval simultaneously.Statistical efficiency of the estimated azimuth variance and corresponding power of the line spectrum band depends on the line spectra ratio(LSR)of the line spectrum.The change laws of the output signal to noise ratio(SNR)with the LSR,the input SNR,the integration time and the filtering bandwidth of different algorithms bring the selection principle of the critical LSR.As the basis,the detection gain of wideband energy integration and the narrowband line spectrum algorithm are theoretically analyzed.The simulation detection gain demonstrates a good match with the theoretical model.The application conditions of all methods are verified by the receiver operating characteristic(ROC)curve and experimental data from Qiandao Lake.In fact,combining the two methods for target detection reduces the missed detection rate.The proposed post-processing method in2-dimension with the Kalman filter in the time dimension and the background equalization algorithm in the azimuth dimension makes use of the strong correlation between adjacent frames,could further remove background fluctuation and improve the display effect.展开更多
Aerodynamic characteristics, the noise characteristics in the course of intermittence exhaust are investigated and the expressions for sound pressure level of the noise generated by single-pole source and quadrupole s...Aerodynamic characteristics, the noise characteristics in the course of intermittence exhaust are investigated and the expressions for sound pressure level of the noise generated by single-pole source and quadrupole source in the intermittence exhaust noise are established. The effects of all parameters in pneumatic system on the noise are also comprehensively studied.展开更多
On the basis of the theory of the propeller sheet cavitation noise radiation, this paper proposes a method for inversion of ship propeller noise radiation for the non-uniform wake field behind a ship. The Markovian es...On the basis of the theory of the propeller sheet cavitation noise radiation, this paper proposes a method for inversion of ship propeller noise radiation for the non-uniform wake field behind a ship. The Markovian estimation of the wake field parameters defined in the paper is obtained, and the existence and uniqueness of the solution of the inverse problem is discussed.展开更多
Radiation-induced 1/f noise degradation in the LM117 bipolar linear voltage regulator is studied. Based on the radiation-induced degradation mechanism of the output voltage, it is suggested that the band-gap reference...Radiation-induced 1/f noise degradation in the LM117 bipolar linear voltage regulator is studied. Based on the radiation-induced degradation mechanism of the output voltage, it is suggested that the band-gap reference subcircuit is the critical component which leads to the 1/f noise degradation of the LM117. The radiation makes the base surface current of the bipolar junction transistors of the band-gap reference subcircuit increase, which leads to an increase in the output 1/f noise of the LM117. Compared to the output voltage, the 1/f noise parameter is more sensitive, it may be used to evaluate the radiation resistance capability of LM117.展开更多
A unified theory for calculating the noise radiation of an infinite elastic plate excited by the turbulent boundary layer pressure fluctuations is presented . Using the wave number frequency transfer function to desri...A unified theory for calculating the noise radiation of an infinite elastic plate excited by the turbulent boundary layer pressure fluctuations is presented . Using the wave number frequency transfer function to desribe the whole system , consisting of the plate and the liquid loading, a general expression of the cross spectrum was derived. It is an integral in the complex wave number plane and leads to a sum of the residues at the poles of two types. One pole introduced by the convective ridge of the pressure fluctuations yields a direct transfer component , which is an evanescent wave in liquid because the pole lies in the high wave number region . The other poles introduced by the transfer function of structure produce the radiation field components with the resonance modes of a liquid loaded plate. The pole positions and their residues can be computed approximately by use of the Resonance Scattering Theory . For the case of hydrodynamic noise, where the range of the frequency-thickness product of interest is relatively low , the symmetric zero-order mode dominates the noise radiation.展开更多
The tip vortex cavitation（TVC） noise of marine propellers is of interest due to the environmental impacts from commercial ships as well as for the survivability of naval ships. Due to complicated flow and noise fiel...The tip vortex cavitation（TVC） noise of marine propellers is of interest due to the environmental impacts from commercial ships as well as for the survivability of naval ships. Due to complicated flow and noise field around a marine propeller, a theoretical approach to the estimation of TVC noise is practically unrealizable. Thus, estimation of prototype TVC noise level is realized through extrapolation of the model TVC noise level measured in a cavitation tunnel. In this study, for the prediction of prototype TVC noise level from a model test, a novel scaling law reflecting the physical basis of TVC is derived from the Rayleigh-Plesset equation, the Rankine vortex model, the lifting surface theory, and other physical assumptions. Model and prototype noise data were provided by Samsung Heavy Industries（SHI） for verification. In applying the novel scaling law, similitude of the spectra of nuclei is applied to assume the same nuclei distribution in the tip vortex line of the model and the prototype. It was found that the prototype TVC noise level predicted by the novel scaling law has better agreement with the prototype TVC noise measurement than the prototype TVC noise level predicted by the modified ITTC noise estimation rule.展开更多
基金National Key R&D Program of China(Grant No.2018YFB2001501)Key Program of National Natural Science Foundation of China(Grant No.51535009).
文摘Reducing the radiated noise of a gearbox is a difficult problem in aviation,navigation,machinery,and other fields.Structural improvement is the main means of noise reduction for a gearbox,and it is realized primarily through contribution analysis and structure optimization.However,these approaches have certain limitations.In this study,a low-noise design method for a gearbox that combines the two approaches is proposed,and experimental verification is performed.First,a finite element/boundary element model is established using a single-stage herringbone gearbox.Considering the vibration excitation of the gear system,the radiation noise of a single-stage gearbox is predicted based on the modal acoustic transfer vector(MATV)method.Subsequently,the maximum field point of the radiated noise is determined,and the acoustic transfer vector(ATV)analysis and modal acoustic contribution(MAC)analysis are conducted to determine the region that contributes significantly to the radiated noise of the field point.The optimization region is selected through the panel acoustic contribution(PAC)analysis.Next,to reduce the normal speed in the optimization region,topology optimization is performed.According to the topology optimization results,four different noise reduction structures are added to the gearbox,and the low-noise optimization models are established respectively.Finally,by measuring the radiated noise of the gearbox before and after optimization under a given working condition,the validity of the radiated noise prediction method and the low-noise optimization design method are verified by comparing the simulation and experimental data.A comparison of the four optimization models proves that the noise reduction effect can be achieved only by adding a noise reduction structure to the center of the density nephogram.
基金Foundation item:This study was financially supported by the National Natural Science Foundation of China(Grant No.52101351)。
文摘A combined method of wave superposition and finite element is proposed to solve the radiation noise of targets in shallow sea.Taking the sound propagation of spherical sound source in shallow sea as an example,the radiation sound field of the spherical sound source is equivalent to the linear superposition of the radiation sound field of several internal point sound sources,and then the radiated noise induced by spherical sound source can be predicted quickly.The accuracy and efficiency of the method are verified by comparing with the numerical results of finite element method,and the rapid prediction of underwater radiated noise of cylindrical shell is carried out based on the method.The results show that compared with the finite element method,the relative error of the calculation results under different simulation conditions does not exceed 0.1%,and the calculation time is about 1/10 of the finite element method,so this method can be used to solve the radiated noise of shallow underwater targets.
文摘The underwater acoustic field influenced by a selected ocean internal wavewas computed using the Parabolic Equation (PE) method and split-step difference algorithm in thispaper. Acoustic field is formed by sound source with different frequency covering the range ofradiation noise of ships and submarines. Owing to the adoption of complex variables, sparse matrix,Gaussian source and analysis on the grid size, numerical results are achieved smoothly. The resultsshow that internal wave''s influence on underwater sound can''t be neglected, especially for highersound frequency. So it'' s necessary to take internal wave into account in identifying radiationnoise of ships and submarines, namely for sound intensity, transmission loss and spectra shape.
基金The National Natural Science Foundation of China(No.50975047)
文摘The active control of structural sound radiation in an acoustic enclosure is studied by using distributed point force actuators as the secondary control force, and the control mechanisms for the radiated noise in the cavity are analyzed. A rectangular enclosure involving two simply supported flexible plates is created for this investigation. The characteristics of the primary and secondary sound field and the structural-acoustic coupled system are analyzed, and the optimal control objective for reducing the sound pressure level （SPL） in the cavity is derived. The response of the SPL in the cavity is analyzed and compared when the secondary point force actuators with different locations and parameters are applied to the two flexible plates. The results indicate that the noise in the cavity can be better controlled when some point force actuators are applied to two flexible plates for cooperative control rather than the point force actuators being only applied to the excited flexible plate.
文摘Electric contact discharge is subject closely related to digital information transmission, and integrity of digital signals for realizing high reliablility transmission. This kind of problem is a part of EMC (electromagnetic compatibility). From such a viewpoint, contact noise problems will be mentioned which disturb and degrade digital signals. The induction noise and radiation noise from discharge, electrostatic discharge (ESD), and connector related fundamental subject will be mentioned.
基金Supported by the Navy Equipment Advanced Research Project under Grant No. 40113070203
文摘The double-peak characteristic of underwater radiated noise in the near field on top of the target submarine was analyzed in depth on the basis of submarine test data on the sea. The contribution of three major noise sources to the radiated noise of a submarine were compared and analyzed, and emphasis was put on the original source, production mechanism, and their correlative characteristics. On the basis of analysis on underwater tracking and pass through characteristics of the target submarine, the double-peak phenomenon was reasonably interpreted. Furthermore, the correctness of the theoretical interpretation was verified adequately in real submarine tests. The double-peak phenomenon indicates that the space distributing character on submarine radiated noise are both asymmetrical with time and space, whereas that is provided with directivity. Studying the double-peak phenomenon in depth has important reference value and meaning in engineering practice for understanding the underwater radiated noise field of submarines.
基金Supported by the Aeronautical Science Foundation of China(20101552018)the National Natural Science Foundation of China(11272152)
文摘The flow-induced noise is simulated with a hybrid method.Firstly,a steady-state background flow field is given by solving Reynolds averaged Navier-Stokes(RANS)equations with finite volume(FV)method on structured grid.Then the linearized Euler equations(LEE)can be constructed based on the resulted background flow field,where the source term on the right hand side is computed using stochastic noise generation and radiation(SNGR)method.Finally,the unsteady acoustic field is obtained through solving LEE using high-order discontinuous Galerkin(DG)method on unstructured grid,where the parallel computing based on mesh partitioning and a″Quadrature-Free Implementation″method for high-order DG are employed to accelerate the computation.In order to demonstrate the sound propagation in detail,a visualization method for high-order schemes is also developed here.Moreover,in order to test the validation and the accuracy,a 3D cavity test in comparison with the experimental data is displayed first in this paper,then a 3D high-lift wing is also simulated to demonstrate its capability for very complex geometries.
文摘Shipping traffic is one of the largest contributors to anthropogenic noise in the ocean. Noise generated by merchant ships elevates natural occurring ambient noise level by 20-30 dB in many areas of the world＇s ocean. In order to model the contributions of the noise generated by merchant ships to underwater ambient noise level correctly, a database that consists of the source levels as a function of frequency for different types of ships is essential. This paper describes the conceptual design, with an emphasis on the characteristics of shipping noise as sound sources, of a marine noise database. It was developed for providing necessary parameters for underwater ambient noise modelling. The parameters relevant to shipping noise modelling are organized in two catalogues： （l） source-receiver geometry related parameters, namely the coordinates of the ships at a given time period, as well as the sizes/types of the ships from which the noise source depths may be derived, and （2） acoustically relevant parameters, i.e., the acoustic SLs （source levels） at given frequencies. An example is presented here to demonstrate the efficacy of this database. The study area is a 117 × 55 km2 region off the coast of La Spezia, Italy, in the Mediterranean Sea.
文摘A rare Type I-like noise storm was observed with the solar radio spectrometers (1.0-2.0 GHz and 2.60-3.8 GHz) at National Astronomical Observatories of China (NAOC) on September 23, 1998. We concentrate on checking the Type I-like noise storm occurred in the decay phase of a Type Ⅳ radio burst. This noise storm consists of many Type I bursts and isolated Type Ⅲ or Type Ⅲ pair bursts. It has a bandwidth of ≤0.5 GHz. The duration of each Type I burst is of the order of 100-300 ms. The total duration is greater than 11 minutes. The circular polarization degree of the components of Type Ⅰ and associated Type Ⅲ bursts are about 40%-100% and almost 100%, respectively, which is greater than that of the background continuum (nearly the precision of our instrument). This short decimetric Type Ⅰ-like storm may be another kind or the extension of the kind of metric Type Ⅰ storm, and may possess the duality of metric and decimetric radio emission. It may be in favor of an earlier emission mechanism of the fundamental plasma radiation due to the coalescence of Langmuir waves with low-frequency waves.
基金supported by the National Basic Research Program of China (Grant No 2003CB716300)the National Natural Science Foundation of China (Grant No 10575140)CAEP Foundation (Grant Nos 2008 T0401 and 2008 T0402)
文摘This paper discusses the basic categories of noise in detecting high frequency gravitational waves in the microwave band （-0.1-10GHz）, which contain shot noise from the laser and the thermal radiation photons, thermal noise from statistical fluctuation of the thermal photons and fluctuation of the temperature, radiation press noise on the fractal membrane, the noise caused by the scattering of the Gaussian Beam （GB） in the detecting tube and noise in the microwave radiometers. The analysis shows that a reasonable signal-to-noise ratio may be achieved for a detecting device with the fixed power of GB （105 W）, only when the temperature of the environment is no more than T=I K, and the optimal length of the microwave radiometers is about 0.3 m.
基金The National Natural Science Foundation of China(Grant No.51979226).
文摘The requirement of low radiated noise is increasing for underwater propulsors as the noise significantly affecting the comfort and quietness of ships,submarines,and vessels.To broaden the view of noise characteristics of pump-jet propulsors(PJPs),this paper considers the radiated noise of a pre-swirl stator PJP with the effects of the advance coefficient and rotor rotational speed.Radiated noise is obtained by the“hybrid method”approach,which combines a hydrodynamic solver with a hydroacoustic solver.The turbulence flow is obtained through improved delayed detached eddy simulation(IDDES),which show good agreement with the experiment,including the performance and flow field.The solver precision,permeable surface size,and sampling frequency notably affect the noise calculation.The spectra of thrust fluctuation and radiated noise are characterized by the tonal phenomenon around the blade passing frequency and its harmonics.The spectrum of radiated noise and overall sound pressure level(OSPL)are considerably affected by both the advance coefficient and the rotor rotational speed.Overall,the numerical results and analysis given in this paper should be partly helpful in deepening the understanding of the radiated noise characteristics of PJPs.
基金The National Key R&D Plan(Grant No.2016YFC03000704)National Key R&D Plan(Grant No.2018YFC03009202).
文摘This study investigates the underwater radiated noise(URN)of a manned submersible support mother ship.To this end,a detailed finite element model of the hull and outflow field is established,and the vibration wet mode of the scientific research ship is calculated.A combination of finite element and boundary element methods is used to analyze the spectral features of ship low-frequency URN.The URN source is comprehensively analyzed,the vibration energy is considered the basic parameter to describe the vibration,and the medium-and high-frequency URN of the ship are calculated using the statistical energy analysis.To obtain the full frequency-band URN of the ship,the risk position of exceeding the standard is determined,and the contribution of each main noise source in the ship to the URN is analyzed.The URN level of the ship is comprehensively measured in the free navigation state.The accuracy of the URN control evaluation model,and the method of the ship are verified.The data support for the ship to apply for the classification society certificate provides a scheme reference for the URN control of other scientific research ship in the future.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52279087,51879122).
文摘The natural flow cooling strategy is commonly employed in modern high-speed vessels and nuclear-powered submarines. These vessels rely on the energy generated by their own speed to drive the cooling system and supply cooling water to the condenser. The circulating pump, which operates without a motor drive under natural flow conditions, is a large resistance component in the cooling system. However, it is also the primary noise source, significantly impacting the vessel’s safe operation and acoustic stealth performance. This study investigates the induced noise characteristics of a multi-stage pump under natural flow conditions by experiment, computational fluid dynamics (CFD), and acoustic finite element method. The analysis encompasses the distribution of the flow field, variations in acoustic power, spectral features of flow-induced noise, and directivity of external field radiation noise under different natural flow conditions. The results show that the acoustic power distribution is correlated with the flow field. When the impeller is stuck, the noise sources primarily concentrate in the flow separation area at the blade’s leading edge, the interface area between the impeller and the guide vane, and the flow shock area inside the guide vane. Conversely, when the impeller rotates passively, the blade wake area has a higher acoustic power. The flow noise spectrum under natural flow conditions mainly exhibits broadband and discrete characteristics. Additionally, the pump structure influences the external field radiation noise, and its directivity varies with different flow rates and characteristic frequencies. This study provides valuable insights into optimal design to reduce the noise of the circulating pump in the vessel’s natural flow cooling system. It is essential for ensuring the safe operation and acoustic stealth performance of high-speed vessels and nuclear-powered submarines.
基金Supported by the National Science Foundation of China （11002038）Key Project of National Natural Science Funds （50939002）+2 种基金National Defense Foundation Scientific Project （B2420110011）the National Science Foundation for Young Scientists of China （51009035）Natural Science Funds of Heilongjiang Province （E201047,A200901）
文摘In an atrocious ocean environment,the lateral propulsion hole could potentially be partly out of water and capture an air cavity.Bubbles would form when the captured air cavity escapes underwater and they may affect the performance of the sonar.The common commercial computational fluid dynamics software CFX was adopted to calculate the ambient flow field around the lateral propulsion hole generated by a moving vessel.The oscillation of the spherical bubble was based on the Rayleigh-Plesset equation and its migration was modeled using the momentum equation.The radiated noise of the oscillating bubble was also studied.The aim is that the results from this paper would provide some insight into corresponding fluid and acoustic study.
基金supported by the National Natural Science Foundation of China(51875535)the Natural Science Foundation for Young Scientists of Shanxi Province(201701D221017,201901D211242)。
文摘To improve the ability of detecting underwater targets under strong wideband interference environment,an efficient method of line spectrum extraction is proposed,which fully utilizes the feature of the target spectrum that the high intense and stable line spectrum is superimposed on the wide continuous spectrum.This method modifies the traditional beam forming algorithm by calculating and fusing the beam forming results at multi-frequency band and multi-azimuth interval,showing an excellent way to extract the line spectrum when the interference and the target are not in the same azimuth interval simultaneously.Statistical efficiency of the estimated azimuth variance and corresponding power of the line spectrum band depends on the line spectra ratio(LSR)of the line spectrum.The change laws of the output signal to noise ratio(SNR)with the LSR,the input SNR,the integration time and the filtering bandwidth of different algorithms bring the selection principle of the critical LSR.As the basis,the detection gain of wideband energy integration and the narrowband line spectrum algorithm are theoretically analyzed.The simulation detection gain demonstrates a good match with the theoretical model.The application conditions of all methods are verified by the receiver operating characteristic(ROC)curve and experimental data from Qiandao Lake.In fact,combining the two methods for target detection reduces the missed detection rate.The proposed post-processing method in2-dimension with the Kalman filter in the time dimension and the background equalization algorithm in the azimuth dimension makes use of the strong correlation between adjacent frames,could further remove background fluctuation and improve the display effect.
基金Special Fund for the Whole Nation Excellent Doctorate Thesis of the Colleges and University of China.
文摘Aerodynamic characteristics, the noise characteristics in the course of intermittence exhaust are investigated and the expressions for sound pressure level of the noise generated by single-pole source and quadrupole source in the intermittence exhaust noise are established. The effects of all parameters in pneumatic system on the noise are also comprehensively studied.
文摘On the basis of the theory of the propeller sheet cavitation noise radiation, this paper proposes a method for inversion of ship propeller noise radiation for the non-uniform wake field behind a ship. The Markovian estimation of the wake field parameters defined in the paper is obtained, and the existence and uniqueness of the solution of the inverse problem is discussed.
基金Project supported by the National Natural Science Foundation of China(Nos.61076101,61204092)
文摘Radiation-induced 1/f noise degradation in the LM117 bipolar linear voltage regulator is studied. Based on the radiation-induced degradation mechanism of the output voltage, it is suggested that the band-gap reference subcircuit is the critical component which leads to the 1/f noise degradation of the LM117. The radiation makes the base surface current of the bipolar junction transistors of the band-gap reference subcircuit increase, which leads to an increase in the output 1/f noise of the LM117. Compared to the output voltage, the 1/f noise parameter is more sensitive, it may be used to evaluate the radiation resistance capability of LM117.
文摘A unified theory for calculating the noise radiation of an infinite elastic plate excited by the turbulent boundary layer pressure fluctuations is presented . Using the wave number frequency transfer function to desribe the whole system , consisting of the plate and the liquid loading, a general expression of the cross spectrum was derived. It is an integral in the complex wave number plane and leads to a sum of the residues at the poles of two types. One pole introduced by the convective ridge of the pressure fluctuations yields a direct transfer component , which is an evanescent wave in liquid because the pole lies in the high wave number region . The other poles introduced by the transfer function of structure produce the radiation field components with the resonance modes of a liquid loaded plate. The pole positions and their residues can be computed approximately by use of the Resonance Scattering Theory . For the case of hydrodynamic noise, where the range of the frequency-thickness product of interest is relatively low , the symmetric zero-order mode dominates the noise radiation.
文摘The tip vortex cavitation（TVC） noise of marine propellers is of interest due to the environmental impacts from commercial ships as well as for the survivability of naval ships. Due to complicated flow and noise field around a marine propeller, a theoretical approach to the estimation of TVC noise is practically unrealizable. Thus, estimation of prototype TVC noise level is realized through extrapolation of the model TVC noise level measured in a cavitation tunnel. In this study, for the prediction of prototype TVC noise level from a model test, a novel scaling law reflecting the physical basis of TVC is derived from the Rayleigh-Plesset equation, the Rankine vortex model, the lifting surface theory, and other physical assumptions. Model and prototype noise data were provided by Samsung Heavy Industries（SHI） for verification. In applying the novel scaling law, similitude of the spectra of nuclei is applied to assume the same nuclei distribution in the tip vortex line of the model and the prototype. It was found that the prototype TVC noise level predicted by the novel scaling law has better agreement with the prototype TVC noise measurement than the prototype TVC noise level predicted by the modified ITTC noise estimation rule.
