We propose the design of anisotropic metamaterials with cascading meta-atoms.Each meta-atom array behaves as an impedance-tuned interface and dramatically modifies the complex reflection and transmission coefficients....We propose the design of anisotropic metamaterials with cascading meta-atoms.Each meta-atom array behaves as an impedance-tuned interface and dramatically modifies the complex reflection and transmission coefficients.By engineering the frequency-dependent impedances,the reflection phase difference along the two axes of anisotropic metamaterials approximates to a constant in a wide range.We numerically demonstrate the proposed anisotropic metamaterials can accomplish achromatic polarization transformation from 0.5 THz to 3.1 THz.The polarization conversion ratio is higher than 80%,which exhibits excellent agreements with the theoretical calculation.Such design is scalable to other bands and can provide helpful guidance in broadband devices design.展开更多
We have successfully ported an arbitrary highorder discontinuous Galerkin method for solving the threedimensional isotropic elastic wave equation on unstructured tetrahedral meshes to multiple Graphic Processing Units...We have successfully ported an arbitrary highorder discontinuous Galerkin method for solving the threedimensional isotropic elastic wave equation on unstructured tetrahedral meshes to multiple Graphic Processing Units （GPUs） using the Compute Unified Device Architecture （CUDA） of NVIDIA and Message Passing Interface （MPI） and obtained a speedup factor of about 28.3 for the single-precision version of our codes and a speedup factor of about 14.9 for the double-precision version. The GPU used in the comparisons is NVIDIA Tesla C2070 Fermi, and the CPU used is Intel Xeon W5660. To effectively overlap inter-process communication with computation, we separate the elements on each subdomain into inner and outer elements and complete the computation on outer elements and fill the MPI buffer first. While the MPI messages travel across the network, the GPU performs computation on inner elements, and all other calculations that do not use information of outer elements from neighboring subdomains. A significant portion of the speedup also comes from a customized matrix-matrix multiplication kernel, which is used extensively throughout our program. Preliminary performance analysis on our parallel GPU codes shows favorable strong and weak scalabilities.展开更多
Synthetic seismograms generated by solving the seismic wave equation using numerical methods are being widely used in seismology. For fully three-dimensional seismic structure models, the generation of these synthetic...Synthetic seismograms generated by solving the seismic wave equation using numerical methods are being widely used in seismology. For fully three-dimensional seismic structure models, the generation of these synthetic seismograms may require large amount of computing resources. Conventional high-performance computer clusters may not provide a cost-effective solution to this type of applications. The newly emerging cloud-computing platform provides an alternative solution. In this paper, we describe our implementation of a synthetic seismogram generator based on the reciprocity principle using the Windows Azure cloud application framework. Our preliminary experiment shows that our cloud-based synthetic seismogram generator provides a costeffective and numerically efficient approach for computing synthetic seismograms based on the reciprocity principle.展开更多
Abstract Recent advances in commodity high-performance computing technology have dramatically reduced the computational cost for solving the seismic wave equation in complex earth structure models. As a consequence, w...Abstract Recent advances in commodity high-performance computing technology have dramatically reduced the computational cost for solving the seismic wave equation in complex earth structure models. As a consequence, wave-equation-based seismic tomography techniques are being actively developed and gradually adopted in routine subsurface seismic imaging practices. Wave-equation travel-time tomography is a seismic tomography technique that inverts cross-correlation travel-time misfits using fullwave Frechet kernels computed by solving the wave equation. This technique can be implemented very efficiently using the adjoint method, in which the misfits are back-propagated from the receivers （i.e., seismometers） to produce the adjoint wave-field and the interaction between the adjoint wave-field and the forward wave-field from the seismic source gives the gradient of the objective function. Once the gradient is available, a gradient-based optimization algorithm can then be adopted to produce an optimal earth structure model that minimizes the objective function. This methodology is conceptually straightforward, but its implementation in practical situations is highly complex, error-prone and computationally demanding. In this study, we demonstrate the feasibility of automating wave-equation travel-time tomography based on the adjoint method using Kepler, an open-source software package for designing, managing and executing scientific workflows. The workflow technology allows us to abstract away much of the complexity involved in the implementation in a manner that is both robust and scalable. Our automated adjoint wave-equation travel-time tomography package has been successfully applied on a real active-source seismic dataset.展开更多
基金supported in part by National Science Foundation(NSF)
文摘We propose the design of anisotropic metamaterials with cascading meta-atoms.Each meta-atom array behaves as an impedance-tuned interface and dramatically modifies the complex reflection and transmission coefficients.By engineering the frequency-dependent impedances,the reflection phase difference along the two axes of anisotropic metamaterials approximates to a constant in a wide range.We numerically demonstrate the proposed anisotropic metamaterials can accomplish achromatic polarization transformation from 0.5 THz to 3.1 THz.The polarization conversion ratio is higher than 80%,which exhibits excellent agreements with the theoretical calculation.Such design is scalable to other bands and can provide helpful guidance in broadband devices design.
基金supported by the School of Energy Resources at the University of WyomingThe GPU hardware used in this study was purchased using the NSF Grant EAR-0930040
文摘We have successfully ported an arbitrary highorder discontinuous Galerkin method for solving the threedimensional isotropic elastic wave equation on unstructured tetrahedral meshes to multiple Graphic Processing Units （GPUs） using the Compute Unified Device Architecture （CUDA） of NVIDIA and Message Passing Interface （MPI） and obtained a speedup factor of about 28.3 for the single-precision version of our codes and a speedup factor of about 14.9 for the double-precision version. The GPU used in the comparisons is NVIDIA Tesla C2070 Fermi, and the CPU used is Intel Xeon W5660. To effectively overlap inter-process communication with computation, we separate the elements on each subdomain into inner and outer elements and complete the computation on outer elements and fill the MPI buffer first. While the MPI messages travel across the network, the GPU performs computation on inner elements, and all other calculations that do not use information of outer elements from neighboring subdomains. A significant portion of the speedup also comes from a customized matrix-matrix multiplication kernel, which is used extensively throughout our program. Preliminary performance analysis on our parallel GPU codes shows favorable strong and weak scalabilities.
文摘Synthetic seismograms generated by solving the seismic wave equation using numerical methods are being widely used in seismology. For fully three-dimensional seismic structure models, the generation of these synthetic seismograms may require large amount of computing resources. Conventional high-performance computer clusters may not provide a cost-effective solution to this type of applications. The newly emerging cloud-computing platform provides an alternative solution. In this paper, we describe our implementation of a synthetic seismogram generator based on the reciprocity principle using the Windows Azure cloud application framework. Our preliminary experiment shows that our cloud-based synthetic seismogram generator provides a costeffective and numerically efficient approach for computing synthetic seismograms based on the reciprocity principle.
文摘Abstract Recent advances in commodity high-performance computing technology have dramatically reduced the computational cost for solving the seismic wave equation in complex earth structure models. As a consequence, wave-equation-based seismic tomography techniques are being actively developed and gradually adopted in routine subsurface seismic imaging practices. Wave-equation travel-time tomography is a seismic tomography technique that inverts cross-correlation travel-time misfits using fullwave Frechet kernels computed by solving the wave equation. This technique can be implemented very efficiently using the adjoint method, in which the misfits are back-propagated from the receivers （i.e., seismometers） to produce the adjoint wave-field and the interaction between the adjoint wave-field and the forward wave-field from the seismic source gives the gradient of the objective function. Once the gradient is available, a gradient-based optimization algorithm can then be adopted to produce an optimal earth structure model that minimizes the objective function. This methodology is conceptually straightforward, but its implementation in practical situations is highly complex, error-prone and computationally demanding. In this study, we demonstrate the feasibility of automating wave-equation travel-time tomography based on the adjoint method using Kepler, an open-source software package for designing, managing and executing scientific workflows. The workflow technology allows us to abstract away much of the complexity involved in the implementation in a manner that is both robust and scalable. Our automated adjoint wave-equation travel-time tomography package has been successfully applied on a real active-source seismic dataset.
