98 results about "Acoustic wave equation" patented technology

A method of prestack reverse-time migration of seismic data that yields significant gains in computer storage and memory bandwidth efficiency is disclosed. The values only of the source wave incident on the boundaries of a simulation domain are saved, rather than all of the values of the wavefield throughout the entire simulation domain. This data allows an accurate and robust approximation of the forward propagated source wave for all finite-difference approximation orders of the acoustic wave equation. The method reduces the amount of data storage required by an order of magnitude and overcomes the present challenge of requiring special large memory hardware while allowing for the implementation of 3D prestack reverse-time migration on off-the-shelf platforms.

The invention provides a high-precision spatial and temporal arbitrary multiple variable grid finite difference forward modeling method, which comprises the steps of: step 1, establishing a forward modeling speed model of an underground medium; step 2, subjecting the forward modeling speed model to two-dimensional grid discretization, and subjecting an acoustic wave field in the forward modeling speed model to two-dimensional grid discretization, wherein the acoustic wave field is located on grid nodes; step 3, subjecting a perfectly matched layer boundary condition to grid discretization; and step 4, conducting time-domain finite difference forward modeling simulation through an acoustic wave equation, wherein time sampling step lengths are variable step lengths at grids of different sizes. The high-precision spatial and temporal arbitrary multiple variable grid finite difference forward modeling method can effectively suppress forward modeling frequency dispersion, significantly increases signal-to-noise ratio, and greatly improves precision and efficiency of forward modeling simulation.

The present invention relates to a seismic wave full waveform inversion method based on a least square gradient update speed model, comprising the following steps: 1) obtaining a sound wave equation of a seismic wave field in time domain; 2) constructing an initial speed model, setting a speed model update iteration number N and an allowed minimum error value epsilon; 3) constructing observation wave field data and calculating a wave field error vector of the wave field data; 4) constructing an object function; 5) calculating the object function to obtain a standard equation of seismic wave full waveform inversion; 6) introducing a speed model update gradient direction g<k> and an update amount step length alpha; 7) solving the speed model update gradient direction g<k> by using a least square method; 8) performing interpolation calculation for the update amount step length alpha; and 9) updating the speed model, wherein m<k>=m<k-1>+alpha*g<k>; when |alpha*g<k>| < epsilon or the update number of the speed model reaches the speed model update iteration number N, ending the update of the speed model; otherwise, entering into the step 3). The seismic wave full waveform inversion method of the present invention can quickly achieve update of the speed model, and can be widely applied in seismic wave full waveform inversion.

A frequency domain optimization mixture staggered grid finite difference forward modeling method comprises the following steps: 1) providing a time-domain two-dimension sound wave equation; 2) eliminating artificial boundary reflection and obtaining a time-domain two-dimension sound wave equation with a perfectly-matched layer boundary condition; 3) performing Fourier transform on time variables at the two sides of the equation and obtaining a frequency-domain sound wave equation; 4) carrying out finite difference discretization on the frequency-domain sound wave equation with the perfectly-matched layer boundary condition based on a conventional staggered grid and obtaining a finite difference discretization format; 5) carrying out finite difference discretization on the frequency-domain sound wave equation with the perfectly-matched layer boundary condition based on a rotation staggered grid and obtaining a finite difference discretization format; 6) performing optimization mixing on the conventional staggered grid and the rotation staggered grid, grid difference item being weighted average of the grid difference item in the two grid systems, and quality acceleration item being weighted average of a center point and eight points around the center point; and 7) under the criterion of the minimum phase velocity error, calculating an optimized coefficient. The weighting coefficient enables frequency dispersion error due to the finite difference discretization to be the smallest, and the precision of the frequency-domain forward modeling is greatly improved.

The invention discloses a multi GPU calculation based reverse time migration imaging method of a 3D TTI medium. According to the method, a stable second-order coupling equation set serves as a calculation model, finite SV wave components are given to enhance the wave field spreading stability, an anisotropy parameter matching method is used to suppress interference of pseudo-transverse waves, uniform anisotropy boundaries corresponding to a random speed boundary and other parameters are introduced, storage of large amount of wave field data and frequency disk reading and writing are avoided, and a GPU-based CUDA platform is used to realize high-performance parallel calculation. According to the invention, a second-order coupling quasi-acoustic equipment in the TTI medium is solved in a difference method on the basis of multi-GPU parallel calculation technology, wave field spreading is stable, pseudo-transverse waves are suppressed effectively, application of the random boundary reduces wave field storage and disk reading and writing, a multi-asynchronous-flow high parallel strategy of multi GPU calculation is used, the calculation efficiency is improved obviously, and the imaging method meets requirements for industrialization of anisotropy reverse time migration.

The invention relates to a method for processing seismic exploration data in the process of controlling full acoustic wave equation inversion. The method comprises the following steps: acquiring seismic data of a theoretical model to obtain a depth-domain bulk modulus and density initial model; simulating a seismic wave field in an acoustic medium by a pseudo-spectral method; calculating the difference of analog data of the theoretical model and the initial model; giving that delta is equal to 1.0 e-6; calculating error energy E; when E is less than or equal to delta, stopping inversion and outputting the inversion result; if E is more than delta, continuing the following steps; calculating residual error data; calculating the conjugated modification quantity of the bulk modulus and density model; calculating the modified step length to obtain the gradient; modifying the initial model; using the modified model data as a new initial model; carrying out automatic control on the inversion process to make the acoustic wave equation inversion stable, rapid and convergent and improve the inversion convergence speed by nearly five times than a routine method.

The invention discloses a frequency-domain higher-order sound wave equation forward modeling method based on directional derivative, belongs to the technical field of seismic exploration, and aims at providing a frequency domain two-dimensional scalar sound wave equation forward modeling simulation method with the higher simulation precision. The method comprises the steps: building a fourth-order 17-point finite difference equation comprising a plurality of weighting coefficients according to a frequency domain scalar sound wave equation through the directional derivative; carrying out the normalized phase velocity frequency dispersion analysis, and solving an optimal weighting coefficient through an optimization algorithm; constructing a finite difference equation with the absorbing boundary condition; carrying out the seismic wave field data simulation through the fourth-order 17-point finite difference equation, and obtaining a seismic wave forward modeling record. The method can inhibit the frequency dispersion to the greatest extent, improves the simulation precision of the seismic wave field data, and also can adapt to a condition that the longitudinal and lateral grid sizes are not equal. The method is mainly used in the technical field of seismic exploration, and provides basic data and technological support for the simulation and analysis of a seismic wave field, the seismic inversion imaging, and geologic modeling.

The invention relates to a travel-time table and angle table acquisition method for anisotropic medium angle domain Kirchhoff prestack depth migration and an imaging method thereof. The acquisition method comprises steps: according to an anisotropic medium acoustic wave equation, an eikonal equation in the anisotropic medium is deduced, ray equations for anisotropic medium acoustic approximation are deduced and solved through the eikonal equation, ray paths, travel time and propagation direction information under the anisotropic medium acoustic approximation meaning are thus acquired, Angle domain ray tracing is carried out, and a travel-time table and an emergence angle table are built. The method of the invention has the advantages that the ray equations for the anisotropic medium can be approximatively deduced based on an acoustic law; the reliable travel-time table and the reliable angle table can be provided for Kirchhoff prestack depth migration; and thus, angle domain imaging can be realized accurately.

The invention discloses a true amplitude migration imaging method, in particular, an onshore double/multi-detector total sound wave equation true amplitude pre-stack depth migration method. The method includes the following steps that: a plurality of detection layers are arranged on a ground surface or below the ground surface; seismic signal data are acquired; the partial derivatives of wave fields at the ground surface relative to depth are calculated; wave field continuation is performed a detection point wave field and a shot point wave field; and cross-correlation correlation imaging principles or reflection coefficient imaging principles are utilized to image the continued detection point wave field and shot point wave field. With the method of the invention adopted, a defect that an existing seismic data acquisition system can only record the values of wave fields at the ground surface and cannot accurately solve an acoustic wave equation at the depth domain can be eliminated; an acoustic wave equation can be utilized to accurately solve seismic wave field information; reliable subsurface structure and lithological information can be provided for subsequent geological interpretation personnel; the confidence level of geological interpretation and seismic inversion analysis can be improved; migration imaging can be performed on various kinds of wave fields; and the true amplitude migration of the lithological changes of subsurface structures can be reflected.

The invention relates to a least square reverse time migration gradient precondition method based on a direct wave field, belongs to the field of seismic migration imaging. The method comprises the steps that: a seismic record is obtained by adopting the sound wave equation finite difference linearization forward modeling technology based on a background speed model and a reflection coefficient model in each iteration process of least squares reverse time migration, then timing 'approximate direct' wave field energy with shot point seismic source wavelets as disturbance and reverse 'approximate direct' wave field energy with the above seismic record obtained by linearization forward modeling as disturbance are obtained by simulation by using the non-reflection acoustic wave equation finitedifference forward modeling technology, and finally, the timing 'approximate direct' wave field energy and the reverse 'approximate direct' wave field energy are applied to perform precondition processing on the gradient. Model experiment results show that the defect of inaccurate wave field energy in a conventional gradient precondition method based on seismic wave energy can be effectively overcome, the precision of the gradient precondition is improved, so that the imaging effect of least square reverse time migration is remarkably improved.

The invention relates to a two-dimensional liquid-liquid phononic crystal topology optimization method, which comprises the following steps of dividing a phononic crystal primitive cell into an N*N square pixel structure; developing a plane wave expansion method program for quickly calculating a two-dimensional liquid-liquid pixel phononic crystal energy band laid by any material according to an acoustic wave equation satisfied by a two-dimensional liquid-liquid phononic crystal dispersion relationship, and calculating a band gap; and finally, searching the optimal material layout of the two-dimensional liquid-liquid phononic crystal primitive cell according to the requirements on the band gap by utilizing a genetic optimization algorithm. The process comprises the following steps of inputting a parameter to be solved, and initializing; calculating individual fitness; sequentially performing the genetic operations of selection, crossover and mutation to generate the next generation of genus group, so that the genus group evolutes forwards; and checking whether the genus group meets a stop condition. Through the topology optimization method, the designability of phononic crystals is enhanced, and the novel phononic crystal structure with optimal band gap characteristics is obtained; and meanwhile, the calculating time is reduced, and the calculating efficiency is improved, so that the designed phononic crystal has the best technical and economic performances.

The invention relates to an implementation method for a mixed absorbing boundary condition applied to a variable density acoustic wave equation. The implementation method comprises the steps of dividing a whole simulation region into an internal region and a boundary region, calculating the wave field value of a sound wave of each absorbing boundary layer by using the variable density acoustic wave equation and a variable density AWWE (Arbitrary Wide-angle wave equation) respectively, and performing linear weighting on the two calculation results to obtain the wave field value of the sound wave of each absorbing boundary layer. On the basis of realizing a single variable density AWWE absorbing boundary layer and in 2D (2 dimensional) and 3D (3 dimensional) space coordinate systems, the wave field value of the sound wave of each absorbing boundary layer is calculated by respectively adopting a combination mode of processing edges of the variable density AWWE and processing angles of a modified 15-degree one-way wave equation, and a combination mode of processing faces of the variable density AWWE, the processing edges of the modified 15-degree one-way wave equation and the processing angles of a 5-degree one-way wave equation, and the mixed absorbing boundary condition of the variable density AWWE is realized. The implementation method can be widely applied to the numerical simulation of constant density and variable density acoustic wave equations.

The invention relates to a finite difference calculation method based on the quasi-spatial domain acoustic wave equation and belongs to the field of seismic exploration. The main idea of the method isto transform a conventional acoustic wave equation into a quasi-spatial domain acoustic wave equation so that the equally spaced 'distance' grid length steps in the spatial domain is transformed intonon-equally spaced 'propagation time' length steps. Thus, a user can accurately calculate the 'propagation time' on both sides of a velocity interface based on a strictly defined velocity model. Then, the equation of a 2N-order (N is a positive integer) precision finite difference expression for its perfectly matched layer boundary condition is given based on this. Accordingly, the finite difference wavefield extension of seismic waves in the process of reverse time migration can be realized. The method can well solve the problem of the shape distortion of the velocity interface in the reverse-time migration profile of a conventional acoustic wave equation. In addition, the wave field extension based on the quasi-spatial domain acoustic wave equation can significantly weaken the interfacepseudo-scattering and the inter-layer reflection wave so as to further improves the quality of offset imaging.

The invention discloses a time high-order precision staggered mesh finite difference method for variable density acoustic wave equations, comprising: designing a new difference template; using the newdifference template to perform staggered mesh finite difference numerical dispersing on the variable density acoustic wave equations; deducing a frequency dispersion relationship of the variable density acoustic wave equations under the new difference template; using Taylor series expansion or an optimal method to solve a new finite difference coefficient; introducing the new difference coefficient into corresponding discrete equations so as to perform numerical simulation on the variable density acoustic wave equations; analyzing precision and stability of the novel difference method. The time high-order precision staggered mesh finite difference method for variable density acoustic wave equations has the advantages that precise temporal (2M) order and time 10-order simulation precisionare provided, calculating efficiency can be improved by extending time step length; zero distortion of waveform in remote simulation can be better guaranteed.

The embodiment of the present application provides a method and device for eliminating numerical dispersion in a finite difference forward process. The method comprises a step of carrying out Fourier transform on a preset acoustic wave equation and second-order finite difference numerical dispersion processing of a time domain, and obtaining frequency dispersion relation data and a numerical dispersion equation, a step of carrying out Fourier transform on the numerical dispersion equation, obtaining numerical dispersion relation data, and determining a frequency mapping relation according to the dispersion relation data and the numerical dispersion relation data, a step of carrying out Fourier transform on the seismic forward simulation record of finite difference forward to be corrected, and obtaining a frequency domain seismic forward simulation record, and a step of using the frequency domain seismic forward simulation record to carry out numerical frequency dispersion correction, obtaining a corrected frequency domain seismic forward simulation record, and carrying out Fourier inverse transform on the corrected frequency domain seismic forward simulation record, and obtaining a seismic forward simulation record with elimination of the difference numerical dispersion. By using the technical scheme provided by the embodiment of the present application, the accuracy and resolution of wave field simulation are improved.

The invention relates to an acoustic anisotropic reverse-time migration mixing method. A reverse-time migration imaging process is divided into the following steps: 1, setting an observation system and a seismic source location when no seismic data is input to obtain seismic data in anisotropic media, and solving an anisotropic acoustic wave equation by a mixed pseudo-spectral method and an finitedifference method, wherein during application of the finite difference method, high-order rotating staggered grids are adopted to ensure the calculation accuracy and stability, and only one fast Fourier transform is needed at each time step; and 2, applying an improved excitation amplitude imaging condition according to the input seismic data to perform inverse-time migration imaging. The forwardseismic transmission process and the reverse seismic record transmission process are carried out based on the above algorithm, and then reverse-time migration imaging is carried out. The need for computational memory is reduced in a wide range of computational areas. The calculation efficiency of reverse-time migration is improved, seismic acoustic recording is simulated in a large scale of complex anisotropic media, and reverse-time migration imaging is performed.

Provided is an underwater sound projector response time reversal focusing measuring method, comprising the steps of: 1) collecting probing signals; 2) generating time reversal transmitting signals; 3) measuring current and voltage signals; 4) calculating sending response; and 5) correcting sending response. The method is based on an acoustic wave equation time reversal invariance principle, and realizes standard hydrophone receiving signal spatial and temporal focusing through an underwater sound reciprocity principle, thereby restraining reverberation in measuring projector response within a limited space, and solving difficulties in measuring projector response time under limited space strong reverberation.

The invention relates to an attenuation compensation reverse time migration realization method based on a constant Q viscous sound wave equation. The method comprises the following steps: a decouplingconstant Q viscous sound wave equation which takes Taylor series expansion as a strategy to process a variable fractional order problem is taken as a forward model to carry out forward and reverse continuation of a wave field; according to an absorption attenuation mechanism of sound waves in a viscoelastic medium, from an angle of indirect compensation, a ratio of a pure frequency dispersion sound wave field to a viscous sound wave field is used to represent a compensation operator, and the compensation operator is embedded into an excitation amplitude imaging condition so as to acquire an absolute stable compensation imaging condition. A new imaging condition is used to realize stable attenuation compensation reverse time migration of the viscous sound waves. The method is popularized to three dimensions on the basis of a two-dimensional constant Q viscous sound wave equation so as to realize three-dimensional constant Q viscous sound wave equation reverse time migration under the stable compensation excitation amplitude imaging condition. The method can be widely applied to forward modeling, reverse time migration and attenuation compensation reverse time migration of the viscous sound waves in the two-dimensional/three-dimensional viscoelastic medium.

The invention discloses a full-waveform inversion method based on dynamic random seismic source coding. The invention discloses a dynamic random seismic source coding new strategy, belongs to the field of geophysics, and provides a dynamic random seismic source coding new strategy by randomly selecting four aspects of amplitude, phase, polarity and shot point position of a seismic source, which comprises the following main steps of: randomly selecting actual shots and time coding sequence convolution, and synthesizing a super shot profile; calculating a super shot residual error, a gradient direction and an optimal step length; inversion iteration is carried out, and target parameters are updated; and judging whether an inversion termination condition is met or not. Crosstalk noise betweenshots is avoided, and the inversion efficiency is greatly improved on the premise that the inversion precision is not affected. The new dynamic random seismic source coding strategy is introduced into the solution of the L-BFGS algorithm of the variable density acoustic wave equation full waveform inversion, the crosstalk influence of the medium density and the acoustic wave speed during the synchronous inversion is effectively reduced, and the full waveform inversion speed is improved.

The invention discloses a combined absorbing boundary condition applied to sound wave finite difference numerical simulation, and belongs to the field of seismic exploration numerical simulation. The combined absorbing boundary condition applied to the sound wave finite difference numerical simulation specifically comprises the following steps of: when sound wave equation numerical simulation is performed based on a 2N-order (N>0) accuracy staggered-mesh finite difference scheme, at first, setting L (L>N) perfectly matched layers (PML) at an artificial truncated boundary, and absorbing boundary reflected waves from a central wave field by using a PML boundary condition; and then, for N layers of boundaries outside the PML, by using an Higdon three-order absorbing boundary condition, absorbing outer boundary reflexes of the PML. According to the method provided by the present invention, by fully utilizing the advantages of both the PML boundary condition and the Higdon three-order absorbing boundary condition are fully utilized, the boundary reflexes of inner layers and outer layers of artificial boundaries can be effectively absorbed, thereby achieving high-accuracy finite difference numerical simulation.

The invention discloses a staggered mesh forward modeling method based on time-space domain optimization. According to the method, a plane wave general solution of a first order pressure intensity-speed partial differential equation set is solved, a pressure intensity field and polarization speed field analysis expression of a first order sound wave equation is acquired, a traditional space staggering grid difference format is combined with a precise time recursion format to acquire a precise staggering time recursion format, and least square iteration solution is lastly employed to acquire a high precision staggering grid difference operator for forward modeling. The method is advantaged in that value frequency dispersion is improved to a certain degree, phase velocity precision is improved, and the substantial effect can be realized under high-order conditions.

The invention discloses a car interior sound field visualization method applied to active noise control over a car engine. The car interior sound field visualization method comprises the steps that (1) car interior sound pressure values under car engine vibration noise are tested; and (2) sound field modal coefficient recognition and sound field distribution visualization are conducted, specifically, a, time domain signals of sound pressure values of test point positions are converted into frequency domain signals; b, sound pressure values of all the positions are calculated through a modal expansion equation; c, modal parameters are recognized according to the sound pressure values obtained in the step a; d, the sound pressure values of all the positions of a sound field are calculated; and e, the calculated sound pressure values are subjected to cloud picture displaying. According to the car interior sound field visualization method applied to active noise control over the car engine, through the time domain signals tested in sound field distribution and a modal expansion formula obtained by an acoustic wave equation, car interior sound field visualization can be realized under the engine vibration noise, and reference can be provided for optimizing the active noise control effect and error microphone arrangement.

The invention relates to an L-BFGS initial matrix solving method applied to least square reverse time migration, which belongs to the field of seismic exploration migration imaging. The method comprises the following steps of: in each iteration process of least square reverse time migration, based on a background speed model and a reflection coefficient model, taking shot point seismic source wavelets as disturbance, adopting a second-order scalar acoustic wave equation finite difference linearization forward modeling technology to obtain a timing wave field and a seismic record, and calculating a shot point one-way illumination compensation factor based on the timing wave field, performing reverse time continuation by taking the seismic record as disturbance to obtain a reverse time wavefield, obtaining a detection point one-way illumination compensation factor, and finally obtaining a shot-detection two-way illumination compensation factor. On the basis, the compensation factor is introduced into an L-BFGS algorithm as an initial approximate matrix of a Hessian inverse matrix, and an L-BFGS initial matrix solving method applied to least square reverse time migration is developed. According to the method, the least square reverse time migration imaging precision can be effectively improved, and the convergence speed is increased.