Конечно-разностная миграция в трехмерном варианте с распараллеливанием процесса вычислений

Переход сейсморазведки на трехмерные или площадные системы наблюдений ведет к значительному увеличению объема зарегистрированных волновых полей, которые необходимо обработать в кратчайшие сроки. При этом необходимо учитывать постоянно возрастающие требования к детальности результата и сложность строения изучаемой площади. В то же время, несмотря на быстрый прогресс в области развития вычислительной техники, появляется проблема недостаточности ресурсов для обработки трехмерных сейсмических наблюдений на отдельно взятом компьютере. Поэтому задача программной реализации существующих процедур обработки с привлечением кластера становится чрезвычайно актуальной в современной сейсморазведке. Рассмотрены разработанные алгоритм и программная реализация трехмерной конечно-разностной миграции после суммы с распараллеливанием процесса вычислений.Перехід сейсморозвідки на тривимірні або площові системи спостережень приводить до значного збільшення обсягу зареєстрованих хвильових полів, які необхідно обробити у найкоротші терміни. При цьому потрібно враховувати постійно зростаючі вимоги до детальності результату і складність будови досліджуваної площі. Водночас, незважаючи на швидкий прогрес у сфері розвитку обчислювальної техніки, з’являється проблема недостатності ресурсів для обробки тривимірних сейсмічних спостережень на окремо взятому комп’ютері. Тому задача програмної реалізації існуючих процедур обробки із залученням кластера стає надзвичайно актуальною в сучасній сейсморозвідці. Розглянуто розроблені алгоритм і програмну реалізацію тривимірної скінченнорізницевої міграції після суми з розпаралелюванням процесу обчислень.The purpose of the paper is to develop a three-dimensional post stack finite-difference migration with parallelization of computing process to process 3D seismic observations on a separate computer, taking into account the ever-increasing requirements for detailed results and the complexity of the structure of the study area. The effectiveness of the developed version of the post stack finite-difference migration is proved with practical examples, in particular, for the structure of medium complicated by the presence of the salt body. Design/methodology/approach. Algorithm of a three-dimensional post stack migration is based on reverse full-wave field continuation in the medium that is carried out by solving the differential wave equation using a finite difference method. In this case the differential wave equation is approximated by the difference one in the four-dimensional space-time grid. In this approach, the coordinate system is converted according to the seismic wave propagation from the depths to the surface, ensuring optimal finite-difference wave field continuation. Parallelization of computations process is on time slices which are defined with a queue. The calculation of the previous slice is stored in the intermediate memory cube. In parallelizing we used library pthread, which is present in all modern versions of the Linux system and allows you to control the execution of the task in the separation calculations on several processors. The software was developed according to the proposed algorithm of a three-dimensional post stack finite-difference migration with parallelization of the computing process for processing. Findings. The developed three-dimensional post stack full-wave finite-difference migration with parallelization of computing process for processing has been tested in a model and real mode. The obtained results confirm the applicability of the developed method of migration in studding the geological environment of deep structure with different degrees of complexity. To demonstrate the effectiveness of this method we compared the results obtained with those obtained using standard software migration system ProMAX and the developed program with parallelization of computing process on the cluster, developed at the Institute of Geophysics. The comparison of the results allows us to emphasize a general similarity of the results and the difference in some of the particular parts of the image (larger extension of reflecting horizons in the direction of the salt body as a result of applying the proposed variant of post stack full-wave finite-difference migration), which may be attributed to a more accurate migration transformation in the developed program. Practical value/implications. The developed version of a three-dimensional post stack full-wave finite-difference migration with parallelization of computing process allows on to carry out high-quality processing of large volumes of spatial seismic data in a short time, which depend on the number of processors in the cluster. The results of the testing of developed programs as in model and real data areal seismic survey, prove accuracy and efficiency even in the structure of the medium complicated by the presence of salt body, which is important for oil and gas companies, exploration activities

Fast and High Accurate Algorithm and Its Implementation for Acoustic waves and Elastic Waves in Reverse Time Migration

逆时偏移技术（Reversetimemigration，RTM）主要应用于解决地震成像问题，是现行偏移方法中最精确的一种。逆时偏移成像的优势在于其成像过程是基于数值方法求解双程波动方程，不仅没有角度限制，还充分考虑了回转波、棱柱波、多次反射等复杂传播路径，因此能够在高倾角、速度变化剧烈的复杂地下结构中得到高质量的图像。逆时偏移成像质量优于基于射线理论的Kirchhoff偏移或基于单程波动方程的其他偏移方法，然而求解双程波动方程计算量大、计算需要的存储资源多，导致逆时偏移成像计算成本较高，这在一定程度上限制了其在工业应用中的推广。 缓解计算瓶颈可以从两个方面入手：一方面使用快速、高精度算法求解...Reverse time migration (RTM) is a high-efficiency tools for seismic imaging. RTM has been considered to be one of the most accurate seismic pre-stack depth migration methods, especially for imaging geologically complex structures. RTM calculates the two-way wave equations numerically. It has no angle limit, and has considered complex propagating paths, such as turning, prismatic and multiple refle...学位：理学博士院系专业：物理科学与技术学院_无线电物理学号：1982011015405

Parallel Seismic Ray Tracing

Seismic ray tracing is a common method for understanding and modeling seismic wave propagation. The wavefront construction (WFC) method handles wavefronts instead of individual rays, thereby providing a mechanism to control ray density on the wavefront. In this thesis we present the design and implementation of a parallel wavefront construction algorithm (pWFC) for seismic ray tracing. The proposed parallel algo- rithm is developed using the stapl library for parallel C++ code.We present the idea of modeling ray tubes with an additional ray in the center to facilitate parallelism. The parallel wavefront construction algorithm is applied to wide range of models such as simple synthetic models that enable us to study various aspects of the method while others are intended to be representative of basic geological features such as salt domes. We also present a theoretical model to understand the performance of the pWFC algorithm. We evaluate the performance of the proposed parallel wavefront construction algorithm on an IBM Power 5 cluster. We study the effect of using different mesh types, varying the position of source and their number etc. The method is shown to provide good scalable performance for different models. Load balancing is also shown to be the major factor hindering the performance of the algorithm. We provide two load balancing algorithms to solve the load imbalance problem. These algorithms will be developed as an extension of the current work

Green Wave : A Semi Custom Hardware Architecture for Reverse Time Migration

Over the course of the last few decades the scientific community greatly benefited from steady advances in compute performance. Until the early 2000's this performance improvement was achieved through rising clock rates. This enabled plug-n-play performance improvements for all codes. In 2005 the stagnation of CPU clock rates drove the computing hardware manufactures to attain future performance through explicit parallelism. Now the HPC community faces a new, even bigger challenge. So far performance gains were achieved through replication of general-purpose cores and nodes. Unfortunately, rising cluster sizes resulted in skyrocketing energy costs - a paradigm change in HPC architecture design is inevitable. In combination with the increasing costs of data movement, the HPC community started exploring alternatives like GPUs and large arrays of simple, low-power cores (e.g. BlueGene) to offer the better performance per Watt and greatest scalability. As in general science, the seismic community faces large-scale, complex computational challenges that can only be limited solved with available compute capabilities. Such challenges include the physically correct modeling of subsurface rock layers. This thesis analyzes the requirements and performance of isotropic (ISO), vertical transverse isotropic (VTI) and tilted transverse isotropic (TTI) wave propagation kernels as they appear in the Reverse Time Migration (RTM) imaging method. It finds that even with leading-edge, commercial off-the-shelf hardware, large-scale survey sizes cannot be imaged within reasonable time and power constraints. This thesis uses a novel architecture design method leveraging a hardware/software co-design approach, adopted from the mobile- and embedded market, for HPC. The methodology tailors an architecture design to a class of applications without loss of generality like in full custom designs. This approach was first applied in the Green Flash project, which proved that the co-design approach has the potential for high energy efficiency gains. This thesis presents the novel Green Wave architecture that is derived from the Green Flash project. Rather than focusing on climate codes, like Green Flash, Green Wave chooses RTM wave propagation kernels as its target application. Thus, the goal of the application-driven, co-design Green Wave approach, is to enable full programmability while allowing greater computational efficiency than general-purpose processors or GPUs by offering custom extensions to the processor's ISA and correctly sizing software-managed memories and an efficient on-chip network interconnect. The lowest level building blocks of the Green Wave design are pre-verified IP components. This minimizes the amount of custom logic in the design, which in turn reduces verification costs and design uncertainty. In this thesis three Green Wave architecture designs derived from ISO, VTI and TTI kernel analysis are introduced. Further, a programming model is proposed capable of hiding all communication latencies. With production-strength, cycle-accurate hardware simulators Green Wave's performance is benchmarked and its performance compared to leading on-market systems from Intel, AMD and NVidia. Based on a large-scale example survey, the results show that Green Wave has the potential of an energy efficiency improvement of 5x compared to x86 and 1.4x-4x to GPU-based clusters for ISO, VTI and TTI kernels

Full-Waveform Inversion with Scaled-Sobolev Preconditioning Applied to Vibroseis Field Data

I present an application of a high-resolution subsurface imaging technique known as “full-waveform inversion” (FWI) to a vibroseis seismic dataset from eastern Ohio, USA. The data were collected over a crooked line with rough topography, 3.5 km maximum offsets, and no significant frequency content below 12 Hz. These parameters present challenges to obtaining quality images from FWI. The use of a preconditioner–the ‘scaled-Sobolev preconditioner’ (SSP - Zuberi and Pratt, 2017)–on the gradient of the misfit functional was key to obtaining low wavenumbers without discarding high wavenumbers. The results represent the first successful application of FWI with the SSP to a field dataset, with a high-resolution image that generally matches the trends of the Big Injun sand and Berea sandstone layers at the survey location. The novel FWI results confirm the absence of small scale structure (including the lack of visible faults) in the first 0.66 km

C-Coll: Introducing Error-bounded Lossy Compression into MPI Collectives

With the ever-increasing computing power of supercomputers and the growing scale of scientific applications, the efficiency of MPI collective communications turns out to be a critical bottleneck in large-scale distributed and parallel processing. Large message size in MPI collectives is a particularly big concern because it may significantly delay the overall parallel performance. To address this issue, prior research simply applies the off-the-shelf fix-rate lossy compressors in the MPI collectives, leading to suboptimal performance, limited generalizability, and unbounded errors. In this paper, we propose a novel solution, called C-Coll, which leverages error-bounded lossy compression to significantly reduce the message size, resulting in a substantial reduction in communication cost. The key contributions are three-fold. (1) We develop two general, optimized lossy-compression-based frameworks for both types of MPI collectives (collective data movement as well as collective computation), based on their particular characteristics. Our framework not only reduces communication cost but also preserves data accuracy. (2) We customize an optimized version based on SZx, an ultra-fast error-bounded lossy compressor, which can meet the specific needs of collective communication. (3) We integrate C-Coll into multiple collectives, such as MPI_Allreduce, MPI_Scatter, and MPI_Bcast, and perform a comprehensive evaluation based on real-world scientific datasets. Experiments show that our solution outperforms the original MPI collectives as well as multiple baselines and related efforts by 3.5-9.7X.Comment: 12 pages, 15 figures, 5 tables, submitted to SC '2

Memristors for the Curious Outsiders

We present both an overview and a perspective of recent experimental advances and proposed new approaches to performing computation using memristors. A memristor is a 2-terminal passive component with a dynamic resistance depending on an internal parameter. We provide an brief historical introduction, as well as an overview over the physical mechanism that lead to memristive behavior. This review is meant to guide nonpractitioners in the field of memristive circuits and their connection to machine learning and neural computation.Comment: Perpective paper for MDPI Technologies; 43 page