Study Of Acoustic Source Localization Techniques Based On TDOA

The safety of structural health has been emphasized.The generation of acoustic emission(AE)source(the impact of foreign objects,the generation of cracks,and the failure of substrates,etc.)indicates that the structural health is threatened.Such acoustic events could cause the degraded performance even hidden dangers especially for large engineering structures(bridges,buildings,roads,large equipment,etc.),which are susceptible to being impacted by foreign objects,or are aging and in maintenance.Accurate prediction of acoustic source localization(ASL)can effectively reduce even avoid injuries caused by structural health damage.The AE technology which is sensitive to active defects has the advantage of rapid overall inspection of large structures.It has an indispensable position in the field of non-destructive testing.The ASL is an important part of AE detection.Locating the damage in structures by obtaining responses through sensors is a key part of structural health monitoring.Two-dimensional(2D)plate-like structures and three-dimensional(3D)structures have been the research focus in domestic and abroad because of their wide application.Rapid ASL can quickly predict the damage location and contribute to the repair of structural damage.In recent years,some new materials have been widely used in our daily life.However,due to the anisotropy or heterogeneity of the materials,the difficulty of AE detection increases and the related research lacks.This paper focuses on the importance and difficulties in the ASL and proposes the solutions.The main work and innovations are as follows:(1)In this paper,the ASL methods are studied based on new triangulation time difference technique.Time difference of arriving(TDOA)technique locates acoustic sources through time and space information from the ultrasonic sensor,which is a common and high-precision localization technique.Traditional ASLtechnique has the disadvantages of large number of sensors needed,large required space,the limitation due to the material anisotropy,and the complicated nonlinear equations need to be solved.These greatly restrict the development of ASL technology.To solve these problems,two localization methods with simple structure,small number of sensors and spacing are proposed.The methods include the Z-type and square-type sensor cluster location methods,which are based on the triangulation time difference technique of L-type sensor cluster.The methods can be applied to both isotropic and anisotropic materials without solving nonlinear equations.They can also quickly locate the AE source in 2D plane structure.The methods facilitate the in-depth application of the AE source location method in the field of 2D structure nondestructive testing.A 2D ASL experiment system is built to verify the localization method.At the same time,the finite element model of isotropic 2D structure is established to carry out the numerical simulation of ASL source location and verify the location method.(2)Based on the uniform 2D plane structure,the localization of AE source is studied for the idealized layered 2D heterogeneous structure.Considering the influence of heterogeneous interface formed by different media on the acoustic path in non-uniform structure,the ASL method is proposed for the 2D heterogeneous structure using the refraction law.The AE source is located by the time difference information,the position and geometry information of the structure received by sensors.For the inhomogeneous structure with known material properties,AE source can be located by at least six ultrasonic sensors.For the heterogeneous structure with unknown material properties,a group of sensor clusters are set up in each layer of different media.Through the time difference information and spatial information received by the sensors,the acoustic velocity in each layer of media is calculated and the acoustic source is located.The new technology considering the refraction can accurately locate the AE source in the 2D heterogeneous structure.It greatly improves the application scope and accuracy of the ASL method,and provides a theoretical reference for the ASL technology of complex structure.The 2D heterogeneous structure AE source positioning platform is built,and the 2D heterogeneous structureformed by different saturation rocks is used for experimental verification.At the same time,the more complex three-layer 2D heterogeneous structure is simulated by finite element method to verify the new technology.Compared with the traditional average velocity location method,the accuracy of the new method is proved.(3)The ASL method is studied for 3D structure.The 3D ASL method is difficult because of many parameters.At present,most of the localization methods need to solve complex nonlinear equations,which seriously depends on the algorithm and greatly limits the efficiency of localization.Based on the new trigonometric time difference method,this paper proposes a method of rectangular tetrahedron sensor cluster to locate the AE source in 3D structure by determining the direction of the acoustic source through four sensor clusters with equal spacing.This method does not need to solve the nonlinear equation,do not need to know the material characteristics in advance,and is not limited by the material anisotropy.A small number of sensors are used to locate the acoustic emission source quickly and accurately.Meanwhile,a small number of sensors are used to locate the AE source quickly and accurately.With the experimental verification,3D finite element simulation is established.This study provides a new perspective for 3D source localization.(4)Based on the ASL method for 3D structure,the 3D heterogeneous structure is studied.The 3D heterogeneous structure composed of multi-layer media are widely used.Some localization methods using fast path or minimum energy path rely heavily on tedious calculation or grid division,which greatly slows down the localization speed.In this paper,based on the rectangular tetrahedral sensor cluster,considering the refraction phenomenon when the acoustic wave passes through the heterogeneous interface,a novel fast ASL method for 3D heterogeneous structure is proposed.The new method does not need to know the velocity distribution in advance,and is not affected by the anisotropy of the material.A few sensors are used to realize the fast linear solution.When the position of the heterogeneous interface is known,the time difference is used to locate the position of the AE source.The two-layer and three-layer 3D heterogeneous models are validated by finite element simulation.The research results provide an important and universal reference for optimizing locationspeed and improving location efficiency.In this paper,the ASL method as a nondestructive testing is studied,which has the advantages of fewer sensors,fast linear calculation and no need to know the velocity distribution in advance.The ASL method would have a valuable theoretical reference for other fields.