A successful case history of exploring for concealed structure using the high-resolution EM method in the investigation of the West-East Gas Pipeline Project＇s B Tunnel is presented in this paper. The high frequency ...A successful case history of exploring for concealed structure using the high-resolution EM method in the investigation of the West-East Gas Pipeline Project＇s B Tunnel is presented in this paper. The high frequency electromagnetic image system named STRATAGEM EH4, operating at frequencies ranging from 90KHz to 1Hz, was used for data acquisition. The orthogonal components of the electromagnetic field were measured during the field acquisition and the relevant electromagnetic attributes of the object body were extracted from the electromagnetic data. Hybrid sources, consisting of natural and full tensor-controlled sources, were utilized to produce high-quality electromagnetic field data. B Tunnel lies in the western part of Hubei province, at depths of less than 200m. The geologic setting of B tunnel is very complex. Following an initial geologic investigation, an outcrop considered to be a bedrock interface by investigators, collapsed during tunneling operations. A second investigation applied high-resolution EM and seismic refraction methods to reveal a more complex geologic structure along the tunnel route. The predicted rock classes and fault were encountered during the subsequent tunneling operations.展开更多
Torsional guided waves have been widely utilized to inspect the surface corrosion in pipelines due to their simple displacement behaviors and the ability of longrange transmission.Especially,the torsional mode T(0,1),...Torsional guided waves have been widely utilized to inspect the surface corrosion in pipelines due to their simple displacement behaviors and the ability of longrange transmission.Especially,the torsional mode T(0,1),which is the first order of torsional guided waves,plays the irreplaceable position and role,mainly because of its non-dispersion characteristic property.However,one of the most pressing challenges faced in modern quality inspection is to detect the surface defects in pipelines with a high level of accuracy.Taking into account this situation,a quantitative reconstruction method using the torsional guided wave T(0,1)is proposed in this paper.The methodology for defect reconstruction consists of three steps.First,the reflection coefficients of the guided wave T(0,1)scattered by different sizes of axisymmetric defects are calculated using the developed hybrid finite element method(HFEM).Then,applying the boundary integral equation(BIE)and Born approximation,the Fourier transform of the surface defect profile can be analytically derived as the correlative product of reflection coefficients of the torsional guided wave T(0,1)and the fundamental solution of the intact pipeline in the frequency domain.Finally,reconstruction of defects is precisely performed by the inverse Fourier transform of the product in the frequency domain.Numerical experiments show that the proposed approach is suitable for the detection of surface defects with arbitrary shapes.Meanwhile,the effects of the depth and width of surface defects on the accuracy of defect reconstruction are investigated.It is noted that the reconstructive error is less than 10%,providing that the defect depth is no more than one half of the pipe thickness.展开更多
In this paper, HFEM is proposed to investigate the circular arch problem. Optimal error estimates are derived, some superconvergence results are established, and an asymptotic exactness posteriori error estimator is p...In this paper, HFEM is proposed to investigate the circular arch problem. Optimal error estimates are derived, some superconvergence results are established, and an asymptotic exactness posteriori error estimator is presented. In contrast with the classical displacement variational method, the optimal convergence rate for displacement is uniform to the small parameter. In contrast with classical mixed finite element methods, our results are free of the strict restriction on h(the mesh size) which is preserved by all the previous papers. Furtheremore we introduce an asymptotic exactness posteriori error estimator based on a global superconvergence result which is discovered in this kind of problem for the first time.展开更多
基金The work is sponsored by National Natural Science Foundation of China (No. 40074036).
文摘A successful case history of exploring for concealed structure using the high-resolution EM method in the investigation of the West-East Gas Pipeline Project＇s B Tunnel is presented in this paper. The high frequency electromagnetic image system named STRATAGEM EH4, operating at frequencies ranging from 90KHz to 1Hz, was used for data acquisition. The orthogonal components of the electromagnetic field were measured during the field acquisition and the relevant electromagnetic attributes of the object body were extracted from the electromagnetic data. Hybrid sources, consisting of natural and full tensor-controlled sources, were utilized to produce high-quality electromagnetic field data. B Tunnel lies in the western part of Hubei province, at depths of less than 200m. The geologic setting of B tunnel is very complex. Following an initial geologic investigation, an outcrop considered to be a bedrock interface by investigators, collapsed during tunneling operations. A second investigation applied high-resolution EM and seismic refraction methods to reveal a more complex geologic structure along the tunnel route. The predicted rock classes and fault were encountered during the subsequent tunneling operations.
基金Project supported by the National Natural Science Foundation of China(Nos.11502108 and 1611530686)the State Key Laboratory of Mechanics and Control of Mechanical Structures at Nanjing University of Aeronautics and Astronautics(NUAA)(No.MCMS-E-0520K02)and the Key Laboratory of Impact and Safety Engineering,Ministry of Education,Ningbo University(No.CJ201904)。
文摘Torsional guided waves have been widely utilized to inspect the surface corrosion in pipelines due to their simple displacement behaviors and the ability of longrange transmission.Especially,the torsional mode T(0,1),which is the first order of torsional guided waves,plays the irreplaceable position and role,mainly because of its non-dispersion characteristic property.However,one of the most pressing challenges faced in modern quality inspection is to detect the surface defects in pipelines with a high level of accuracy.Taking into account this situation,a quantitative reconstruction method using the torsional guided wave T(0,1)is proposed in this paper.The methodology for defect reconstruction consists of three steps.First,the reflection coefficients of the guided wave T(0,1)scattered by different sizes of axisymmetric defects are calculated using the developed hybrid finite element method(HFEM).Then,applying the boundary integral equation(BIE)and Born approximation,the Fourier transform of the surface defect profile can be analytically derived as the correlative product of reflection coefficients of the torsional guided wave T(0,1)and the fundamental solution of the intact pipeline in the frequency domain.Finally,reconstruction of defects is precisely performed by the inverse Fourier transform of the product in the frequency domain.Numerical experiments show that the proposed approach is suitable for the detection of surface defects with arbitrary shapes.Meanwhile,the effects of the depth and width of surface defects on the accuracy of defect reconstruction are investigated.It is noted that the reconstructive error is less than 10%,providing that the defect depth is no more than one half of the pipe thickness.
文摘In this paper, HFEM is proposed to investigate the circular arch problem. Optimal error estimates are derived, some superconvergence results are established, and an asymptotic exactness posteriori error estimator is presented. In contrast with the classical displacement variational method, the optimal convergence rate for displacement is uniform to the small parameter. In contrast with classical mixed finite element methods, our results are free of the strict restriction on h(the mesh size) which is preserved by all the previous papers. Furtheremore we introduce an asymptotic exactness posteriori error estimator based on a global superconvergence result which is discovered in this kind of problem for the first time.
