【摘要】：近年來,瞬變電磁儀的研制取得了巨大突破,使得我們能夠采集到高精度的野外數(shù)據(jù),但是目前我們對瞬變電磁法的理論研究還不夠深入,資料處理、反演解釋水平不高,不能很好發(fā)揮瞬變電磁法的優(yōu)勢。尤其在反演方面,一維反演仍然是最常用的手段,二維、三維反演依然處于起步階段,使得我們無法將瞬變電磁法應(yīng)用于地下復(fù)雜的三維地質(zhì)構(gòu)造的研究中去。為了更好地發(fā)展三維反演技術(shù),就必須充分了解瞬變場在地下三維復(fù)雜介質(zhì)中的響應(yīng)特性,為此,本文針對回線源瞬變電磁法的時域有限差分(FDTD)三維數(shù)值模擬進(jìn)行了如下研究：首先采用YEE(1966)交錯網(wǎng)格方案和Wang Hohmann(1993)提出的改進(jìn)的DuFort-Frankel方案對均勻網(wǎng)格剖分下Maxwell方程的FDTD離散形式進(jìn)行了推導(dǎo)。激勵源采用軟源直接注入的方式施加,即源所在網(wǎng)格,需要在無源媒質(zhì)的Maxwell方程組右端項中加入源電流密度,將其修改為有源情況下的方程。這種以軟源直接注入來施加激勵源的方式克服了Wang Hohmann以均勻半空間解析解作為初始時刻電磁場值的局限性,可以模擬無法計算解析解的任意復(fù)雜三維模型的瞬變電磁響應(yīng)。其次本文還研究了邊界條件的設(shè)置、穩(wěn)定性條件及數(shù)值色散等問題。并給出了適用于多種回線源裝置(中心回線、重疊回線、大定回線源),任意激勵源激發(fā)的瞬變電磁法三維有限差分?jǐn)?shù)值模擬程序。分別計算了均勻半空間瞬變場解析解、水平層狀模型數(shù)字濾波解,并將它們和本文給出的FDTD解進(jìn)行了對比分析。結(jié)果表明,均勻半空間解析解、水平層狀模型數(shù)字濾波解與FDTD解的整體相對誤差均在可以接受的范圍內(nèi),平均相對誤差達(dá)到4%以內(nèi)。之后針對一系列復(fù)雜三維模型的瞬變電磁響應(yīng)進(jìn)行了數(shù)值模擬,最終通過快速反演證明本文給出的三維FDTD解精度高、結(jié)果穩(wěn)定,能適應(yīng)三維復(fù)雜介質(zhì)的數(shù)值模擬。最后以本文得出的瞬變電磁理論為基礎(chǔ),對山西朔州安家?guī)X露天煤礦的實際野外瞬變電磁勘探數(shù)據(jù)進(jìn)行了處理,繪制了各測線視電阻率擬斷面圖,并利用現(xiàn)有的一維反演軟件IX1D進(jìn)行了反演解釋,最終推斷得到了地下三維空間下的煤層采空區(qū)賦存狀態(tài),并且結(jié)果得到了實際地質(zhì)資料的驗證。
[Abstract]:In recent years, the development of transient electromagnetic instrument has made a great breakthrough, so that we can collect high-precision field data, but at present our theoretical research on transient electromagnetic method is not deep enough, the data processing, the level of inverse interpretation is not high. The advantage of transient electromagnetic method can not be brought into play well. Especially in inversion, one-dimensional inversion is still the most commonly used means, two-dimensional, three-dimensional inversion is still in its infancy, which makes it impossible for us to apply the transient electromagnetic method to the study of the complex underground three-dimensional geological structure. In order to better develop 3D inversion technology, it is necessary to fully understand the response characteristics of transient field in underground 3D complex medium. In this paper, the finite-difference time-domain (FDTD) three-dimensional numerical simulation of loop source transient electromagnetic method is studied as follows: firstly, the improved DuFort-Frankel scheme proposed by YEE (1966) staggered grid scheme and Wang Hohmann (1993 is used to simulate uniformity. In this paper, the FDTD discrete form of the Maxwell equation is derived. The excitation source is directly injected into the soft source, that is, the source is in the grid, and the source current density is added to the right end of the Maxwell equation system of the passive medium, and the source current density is modified to the equation in the active case. This method overcomes the limitation of Wang Hohmann using uniform half-space analytical solution as the initial time electromagnetic field value, and can simulate the transient electromagnetic response of any complex three-dimensional model which cannot be calculated by analytical solution. Secondly, the setting of boundary conditions, stability conditions and numerical dispersion are also studied. A three-dimensional finite difference numerical simulation program of transient electromagnetic method for multiple loop source devices (center loop, overlapping loop, large definite loop source) and arbitrary excitation source is also given in this paper. The analytical solutions of the transient field in homogeneous half-space and the digital filtering solutions of the horizontal layered model are calculated and compared with the FDTD solutions given in this paper. The results show that the global relative errors of the analytical solution of the homogeneous half-space, the digital filtering solution of the horizontal layered model and the FDTD solution are all within acceptable range, and the average relative error is less than 4%. Then the transient electromagnetic response of a series of complex three-dimensional models is numerically simulated. Finally, it is proved by fast inversion that the three-dimensional FDTD solution presented in this paper has high accuracy, stable results and can adapt to the numerical simulation of three-dimensional complex medium. Finally, on the basis of the transient electromagnetic theory obtained in this paper, the actual field transient electromagnetic survey data of Anjialing opencast coal mine in Shuozhou, Shanxi Province are processed, and the quasi-sectional diagrams of the apparent resistance rates of each line are drawn. The existing one-dimensional inversion software IX1D is used to carry out the inversion interpretation. Finally, the occurrence state of coal seam goaf in underground three-dimensional space is inferred, and the results are verified by the actual geological data.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P631.325

【參考文獻(xiàn)】

相關(guān)期刊論文 前1條

1 張玉良;馬安麗;;瞬變電磁法在基巖找水中的應(yīng)用[J];地下水;2010年04期

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本文編號：2464447