Research On Airborne Transient Electromagnetic Multi-granular Parallel Acceleration Forward Algorithm

China has a vast land,a vast territory,and abundant resources,but most of the resources are in swamps,mountains,deserts,and other complex terrain conditions,and the environment is relatively harsh.Due to the harsh environment in these areas,the traditional ground electromagnetic method exploration Great difficulty.Even in the area where the environment is relatively friendly and the terrain conditions are relatively flat,the traditional ground electromagnetic method is relatively inefficient,making it difficult to carry out large-scale rapid exploration.Since the middle of the last century,the aerospace electromagnetic method was born,and in the decades since its inception,it has been widely used in geological exploration,mineral resource exploration,and groundwater survey.The time domain aviation electromagnetic method is a fast and efficient detection method.The excitation source and the receiving device of the method are both mounted on a flying platform such as a drone,and can complete transmission and reception in the air.The operation method of this method can adapt to areas where exploration work is difficult under complex terrain conditions.By receiving the secondary field generated after the primary field is turned off and analyzing its response characteristics,geological exploration can be performed.At present,although the time-domain aeronautical electromagnetic method is developing rapidly,the existing time-domain three-dimensional aeronautical electromagnetic finite element algorithm has low calculation efficiency and cannot meet people's calculation requirements for numerical simulation of complex geoelectric models.This problem greatly limits the Development and promotion of methods.In recent years,parallel acceleration technology has been widely used in the field of geophysics to solve the problem of slow forward calculation and low efficiency.Based on previous research,this paper mainly introduces the multi-granularity parallel acceleration technology based on MPI + OpenMP into the time domain aviation electromagnetic 3D forward modeling.MPI can be compatible with multiple languages and is mostly used for large cluster servers to achieve large-scale coarse-grained cross-process parallelism.The 3D time domain aviation electromagnetic forward modeling method in this paper uses local grid technology in order to reduce the amount of grid computing while ensuring that For calculation accuracy,a model is split into multiple local meshes.MPI can distribute the multiple local meshes generated in different processes to perform calculations at the same time,thereby reducing the calculation time.OpenMP belongs to the instruction-level fine-grained parallel acceleration method.By enabling multithreading to perform computing tasks,it can use any number of cores of a machine(process)to perform calculations.When the maximum number of cores that a machine(process)has,The utilization of CPU resources reaches the maximum(100%),which can be used for forward processes that require a large number of iterations,such as compressing large sparse matrices into non-zero matrices,calculating the governing equation coefficient matrices,and calculating interpolation basis functions.Based on previous research,this paper based on MPI + OpenMP multi-granularity parallel acceleration technology to achieve parallelization of 3D aerospace electromagnetic forward modeling in time domain.The same model was numerically simulated using serial algorithm,parallel algorithm and finite volume method,which verified the validity and correctness of the parallelization of 3D time-domain aviation electromagnetic forward modeling,and analyzed the acceleration capabilities of MPI and OpenMP respectively.With different numbers of cores and processes enabled,the acceleration ratio of OpenMP and MPI shows that the acceleration effect is positively related to the hardware conditions.Through forward calculation of a typical geoelectric model and analysis of its electromagnetic response characteristics,it was found that Bz has a better detection ability for low-resistance anomalies than d Bz / dt,and also confirmed the parallel processing The three-dimensional time-domain aviation electromagnetic forward modeling method greatly improves the calculation speed of the forward modeling,and The highest acceleration ratio up to 10 times.The MPI + OpenMP parallel forward algorithm developed in this paper provides the possibility for time-domain aeronautical electromagnetic 3D inversion,and also helps the problem of large 3D forward modeling of complex models and long calculation time.