Noise Measurement Conical Vector Array Formation And Constant Beamwidth

Submarines as a large underwater mobile platform,which can perform all kinds of complex tasks underwater because of its high attack and concealment,are recognized strategic weapons.The radiated noise measurement as an effective means to evaluate submarine underwater noise performance is an important way to measure the acoustic stealth performance of the submarines.Recently,with the continuous development of the submarine vibration and noise reduction technology,the radiated noise level of the submarine is gradually reduced,even close to the background noise of the marine.This brings a severe test to the underwater radiated noise measurement technology.Early measurement methods based on the single pressure sensor and the linear array measurement system cannot meet the requirements of the radiated noise measurement.Consequently,how to realize the accurate measurement and analysis of the radiated noise from submarines is an urgent problem to be solved.Volume sensor arrays can further improve the directivity gain of the sensor system compared to the linear and planer arrays because they can simultaneously achieve the beampattern with narrow beamwidth in both the azimuthal and elevation plane.Consequently,the volume array has been gradually applied in the radiated noise measurement in recent years.At present,the radiated noise measurement based on the volume array mostly adopts uniform cylindrical arrays,however,whether measurement methods in array element or modal domain,the ability of cylindrical arrays in the broadband noise measurement is limited.In the radiated noise measurement procedure,the volume array only needs to ensure the constant beamwidth beampattern with the high spatial gain,but also meet the specified beamwidth within the measurement required broadband.In addition,in the measurement of the low-frequency radiated noise,the array aperture of the volume array is bound to be large to ensure the high directivity gain and the required constant beamwidth,however,the larger aperture array makes it difficult to arrange and recover the array.Consequently,how to realize the low-frequency broadband radiated noise measurement without changing the size of the measurement array is another urgent problem to be solved.Focusing on the above-mentioned issues,this paper studies the constant beamwidth beamforming methods for the vector bi-cone array and the low-frequency expanded constant beamwidth beamforming.The main contents include the following aspects:1.This paper proposes constant beamwidth beamforming methods based on the vector volume array.Firstly,the vector bi-cone array model in the array element domain is constructed,and the vector hydrophone is introduced to construct the vector biconical array,which improves the ability to suppress noise for the measurement array.Using the constant beamwidth beamforming technology,the frequency weighting coefficients of different subarrays are calculated to realize the constant beamwidth beamforming of the bi-cone array,which solves the problem of the required constant beamwidth beampattern in the measurement of the broadband radiated noise.To narrow the beamwidth of the beampattern in the elevation plane and improve the directivity gain of the bi-cone measurement array,a constant beamwidth beamforming method of the bi-cone array in the modal domain is then proposed.The layer number of the circular arrays is increased in the elevation plane and the bi-cone array model in the modal domain is constructed.The bi-cone array is first transformed into a virtual plane array in the modal domain.Then,the virtual plane array is divided into high-and low-frequency subarrays and further are used to obtain constant beamwidth beampattern by the frequency weight coefficients,which solves the problem of low directivity gain of the bi-cone array in the elevation plane.To further improve the measurement performance of constant beamwidth beamforming of the bi-cone measurement array,an optimized constant beamwidth beamforming method of the bi-cone array is proposed.This method derives the optimal array element positions by the continuous array beam equation and calculates the beam weighting coefficients,which solves the high-frequency aliasing problem of subarrays in modal transformation,and further improves the directivity gain.Finally,the beamforming performance of the constant beamwidth beamforming of the different bi-cone arrays is analyzed to verify the effectiveness by carrying out the computer simulations.2.‘Compound ear’ constant-beamwidth low-frequency-expansion beamforming methods are proposed.The paper firstly studies the response characteristics of the hearing system of the Ormia fly and construct the bionic hearing system model and the associated motion equation.Based on this,the complex-ear beamforming matrices for the linear and circular arrays are derived and then achieves the complex ear beamforming with narrower beamwidth and lower sidelobes.To solve the problem of the low-frequency broadband radiated noise measurement without changing the size of the measurement array,a compound ear constant beamwidth lowfrequency-expansion beamforming method is proposed.By combining the characteristics of the bi-cone array in the element and modal domain,this method constructs the complex ear matrices for the horizontal and vertical direction arrays of the bi-cone array to narrow the beamwidth of the low-frequency beampattern.Then,the constant beamwidth beampatterns with narrow beamwidth and low sidelobes are achieved by introducing the frequency weighted coefficients of the constant beamwidth beamforming technology.Besides,this paper studies the relationship of the beamwidth of the complex ear constant beamwidth beamforming and the complex ear parameters,and then gives the variation curves of the beamwidth and the complex ear parameters.The proposed methods not only improve the directivity gain of low-frequency broadband constant beamwidth and the measurement ability of the measurement array in the lower-frequency broadband radiated noise,but also can obtain the required beamwidth of the constant beamwidth beamforming for the actual radiated noise measurement according to the selected parameters.Simulation results show that compared with the traditional methods,the complex ear constant beamwidth low-frequency-extension beamforming method widens the low-frequency radiated noise measurement frequency band without changing the size of the measurement array,and the complex ear vector bi-cone array has lower sidelobes,higher directivity gain and higher low-frequency noise measurement performance than the complex ear pressure bi-cone array.3.Experimental research on the constant beamwidth beamforming methods for the vector bi-cone array and the low-frequency expanded constant beamwidth beamforming are carried out.This paper designs the vector combined array and bi-cone microphone array.Then,according to the content of this paper,the experimental tests,which include the constant beamwidth beamforming of the vector combined array and bi-cone microphone array,the complex ear beamforming of the linear and circular arrays,and the complex ear constant beamwidth beamforming of bi-cone arrays,are carried out.Experimental results are essentially consistent with the simulations,and verify the effectiveness and feasibility of the proposed algorithms,which provide a certain experimental basis and guidance for the engineering application of the submarine radiated noise measurement in the free field environment.