應用FreeFEM++模擬污染場址水流及污染傳輸特性

十年來數值模式的發展日新月異，已廣泛應用到許多領域中，有限元素方法是一個功能強大的數值方法，它可以靈活處理許多複雜的問題。但有限元素法的解法非常複雜，且繁瑣的操作過程容易使得每個元素產生計算上的錯誤。為了克服這個困難，本研究應用高階計算偏微分方程的軟件FreeFEM++（Free Finite Element ++），使用者能夠專注於物理控制方程的變分推導，並快速的建立數值模式。另外一項好處是FreeFEM++是免費的，而且使用者有不斷增加的趨勢本研究模擬場址位於高雄市大寮區，範圍為2,300平方米，主要污染物為三氯乙烯（TCE）。本研究分別建立地下水流和移流延散兩個模式，模式考慮了污染物的吸脫附和自然衰減的影響。由於研究場址過去有豐富的觀測與整治數據，因此可以利用整治結果與模擬結果交互驗證，並藉此推估能將污染物有效整治的有效方法。運用地質統計中的一般克力金方法重建場址區域的水文參數分布，如水力傳導係數、分配係數（Kd）和初始濃度分布。將參數加入模式中，與現地觀測數據做率定修正，建立本場污染傳輸模式。分析結果顯示區域的流場大致為西向東，在井中放污染團之後，污染團濃度分布與觀測結果近似，污染團由西向東移動，證實本研究所開發的FreeFEM++地下水流與污染傳輸模式可適切反應污染場址內，污染團之移動機制。2009年到2010年的觀測井資料顯示場址內細部流場會隨著季節有些微變化，影響污染物的移動。未來將進行不同位置點的抽水整治模擬，比較不同位置點的現地污染物傳輸行為，作為未來該場址後續整治的參考。

關鍵字

FreeFEM++ ；三氯乙烯；污染傳輸模式；地質統計

並列摘要

In the past several decades there have been considerable advances in numerical simulations, and these have been widely applied in many fields. The finite element method is a powerful numerical scheme, due to its flexibility with regard to many complex, practical applications. However, initiating a full set of the scheme involves many routinely tedious data operations with regard to each element, and this can be an error-prone process. To overcome this difficulty, FreeFEM++ (Free Finite Element ++), a high level computational language for partial differential equations, was developed to customize these basic elementwise operations, allowing users to focus on the variational form of the physical governing equation, and thus enabling researchers or engineers to design specific numerical schemes. The additional benefits include the fact that FreeFEM++ is a public domain framework, and the number of users has been increasing in recent years. In the present study we applied FreeFEM++ to a contaminant transport problem. Contamination of groundwater due to heavy metals and organic compounds is one important environmental protection issue that has received considerable attention in recent years. It is important to choose an appropriate remediation method to achieve the most effective results at the lowest possible cost. For this reasons it is important to correctly estimate the physics of contamination transport in the underground environment, and simulations can be performed to better understand the groundwater and contamination hydrology and make predictions with regard to remediating treatments of the contaminated sites. The contaminated site in the present study is in Kaohsiung City, and is about 2,300 m^2 in size and was identified to be polluted with trichloroethylene (TCE) in 2001. The model of contaminant transport included two main parts: the Darcy’s groundwater flow and the advection-dispersion model. The effects of contaminant adsorption-desorption and natural attenuation were included. The remediation efforts at the contamination site began in 2001, in an attempt to confine the concentration of TCE and other contaminants at a controlled level. Therefore, a large set of observations and remediation data have been gathered, and we developed the present model based on the available data. The in-situ data were incorporated into the model by using kriging methods. The in-situ geo-statistical data included the initial concentration distribution of TCE, hydraulic conductivity and partition coefficients (Kd). For parameters that were not measured in the field, this study used the values obtained from laboratory experiments or from the literature. The simulation results show that the groundwater mainly flowed from west to east. The concentration of the contaminated plume between 2009 and 2010 was simulated, and the results agreed with the field observations. Seasonal variations of the contaminant concentration were observed. The effects of pollutant pumping will be simulated in future works, and its effectiveness with regard to remediation will also be investigated.

並列關鍵字

FreeFEM++ ； TCE ； contaminant transport ； kriging

國際替代計量

應用FreeFEM++模擬污染場址水流及污染傳輸特性

全文下載

主題瀏覽