【摘要】：近年來,隨著瞬變電磁技術(shù)的不斷發(fā)展,瞬變電磁儀器的不斷進步,我們可以采集到越來越精確可靠的瞬變電磁野外數(shù)據(jù)。然而我們隊瞬變電磁法的研究仍不深入,沒能很好地發(fā)揮作用。目前瞬變電磁反演,主要以一維為主,二維三維反演仍不成熟。為了更加深入地研究瞬變電磁法,我們對時間域有限差分三維瞬變電磁正演進行深入研究,但是常規(guī)地CPU上的計算耗時太長,模型太大的話計算時間長到無法忍受。隨著近些年GPU并行計算的深入發(fā)展,形成了包括CUDA、OpenGL、OpenAcc 等一大批 GPU 并行技術(shù)。但是由于 CUDA、OpenGL等傳統(tǒng)的并行技術(shù)要與硬件結(jié)構(gòu)高度結(jié)合,因而程序編寫難度較大,并且對于已經(jīng)寫好的程序移植性較差,所以技術(shù)普及應(yīng)用受到限制。而OpenAcc技術(shù)解決了傳統(tǒng)并行技術(shù)在這些方面難題,并取得了較大的進步。本文利用新型的GPU并行編程技術(shù)OpenAcc對時域有限差分三維瞬變電磁正演算法進行改進,極大縮短了三維正演的計算時間,增大了計算效率,并針對其進行了如下研究:首先,應(yīng)用Yee (1966)提出的交錯網(wǎng)格方案和Wang Hohmann (1993)提出的DuFort-Frankel方案對均勻網(wǎng)格剖分下的麥克斯韋方程組的FDTD離散形式進行推倒,并采用軟源直接注入的方式施加激勵源,推導得到有源媒質(zhì)中的MaxWell有限差分方程組。對GPU并行技術(shù)的發(fā)展與優(yōu)勢進行簡要介紹,重點介紹了 OpenAcc并行技術(shù)的執(zhí)行模式與優(yōu)勢,應(yīng)用實際實例證明OpenAcc并行技術(shù)相較于傳統(tǒng)CUDA技術(shù)的優(yōu)勢以及選取其作為本文研究工具的原因;其次,對FDTD三維正演算法進行分析,找出程序最耗時的部分,應(yīng)用OpenAcc并行技術(shù)對其進行并行化處理。并應(yīng)用經(jīng)典的均勻半空間模型、層狀模型以及三維異常體模型對并行程序的準確性進行驗證;最后,對并行程序的加速性能進行評價,通過試驗,并行程序的最大加速比可以達到20x左右。通過大量的模型試驗得到在本文所用的計算環(huán)境下并行程序的計算上限,分析網(wǎng)格剖分方式對并行程序加速性能的影響,尋找最適合的模型剖分方法。最后在更加實際的有覆蓋的地質(zhì)模型、復雜的地質(zhì)模型進行計算,驗證了并行程序在絕大多數(shù)地質(zhì)模型下準確性極高,加速性性能也達到滿意效果。
[Abstract]:In recent years, with the continuous development of transient electromagnetic technology and the continuous progress of transient electromagnetic instruments, we can collect more and more accurate and reliable transient electromagnetic field data. However, the study of transient electromagnetic method in our team is still not thorough and has not worked well. At present, transient electromagnetic inversion is mainly one-dimensional, two-dimensional inversion is still immature. In order to study the transient electromagnetic method more deeply, we study the 3-D transient electromagnetic forward modeling in finite difference time domain, but the computation time on the conventional CPU is too long, and if the model is too large, the calculation time is too long to bear. With the development of GPU parallel computing in recent years, a large number of GPU parallel technologies have been formed, such as CUDAN OpenGL OpenAcc and so on. However, because the traditional parallel technology such as CUDA-OpenGL is highly integrated with the hardware structure, it is difficult to program writing, and the portability of the written program is poor, so the popularization and application of the technology is limited. OpenAcc technology solves these problems in traditional parallel technology and has made great progress. In this paper, a new GPU parallel programming technique, OpenAcc, is used to improve the 3-D transient electromagnetic forward algorithm of finite-difference time-domain, which greatly shortens the computing time and increases the computational efficiency. Using the staggered grid scheme proposed by Yee (1966) and the DuFort-Frankel scheme proposed by Wang Hohmann (1993), the FDTD discrete form of Maxwell equations under uniform mesh division is pushed down, and the excitation source is applied by direct injection of soft source. The MaxWell finite difference equations in active media are derived. The development and advantages of GPU parallel technology are briefly introduced, and the execution mode and advantages of OpenAcc parallel technology are emphatically introduced. A practical example is used to prove the advantage of OpenAcc parallel technology compared with traditional CUDA technology and the reason why it is chosen as the research tool in this paper. Secondly, the 3D forward algorithm of FDTD is analyzed to find out the most time-consuming part of the program. OpenAcc parallel technology is applied to parallelize it. The accuracy of the parallel program is verified by the classical uniform half-space model, layered model and 3D abnormal volume model. Finally, the acceleration performance of the parallel program is evaluated and tested. The maximum speedup of parallel programs can reach about 20x. Through a large number of model tests, the upper limit of parallel programs is obtained in the computing environment used in this paper. The effect of grid generation on the acceleration performance of parallel programs is analyzed, and the most suitable model generation method is found. Finally, in the more practical overlay geological model and the complex geological model, it is verified that the parallel program is highly accurate under most geological models, and the speedup performance is satisfactory.
【學位授予單位】：中國地質(zhì)大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P631.325

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