Comparing some Methods and Preconditioners for Hydropower Plant Flow Simulations Luiz M. Carvalho 1 , Wagner Fortes 1 , and Luc Giraud 2 1 Group of Environmental Studies of Hydropower Reservoirs (GESAR), Rio de Janeiro State University, R. Fonseca Teles, 121, 20550-013, Rio de Janeiro, RJ, Brazil [luizmc,wfortes]@gmail.com 2 ENSEEIHT-IRIT ,Toulouse, France giraud@n7.fr Abstract. We describe some features of a three-dimensional numerical simula- tor currently under development for studying water physico-chemical properties during the flooding of hydroelectric plants reservoirs. The work is sponsored by the Brazilian Electric Energy National Agency (ANEEL) and conducted with Furnas Centrais El´ etricas S. A., the leading Brazilian power utility company. An overview of the simulator requirements is given. The mathematical model, the software modules, and engineering solutions are briefly discussed, including the finite element based transport module. We compare methods, iterative methods and preconditioners used to solve the sparse linear systems which arise from the discretization of three-dimensional partial differential equations. 1 Introduction Is flooding of soils, consecutive to the creation of water reservoirs, a significant an- thropic source of greenhouse gases (GHG) emissions? In a mid and long term per- spective, can hydroelectrical energy be considered a clean energy? The answers of the scientific and industrial communities to these questions are not conclusive [1], [2]. In order to participate in this discussion, a group of researchers have been developing a nu- merical simulator for studying water physico-chemical properties during the flooding of hydroelectric plants reservoirs [3, 4]. In the near future, this simulator will be able to analyze the production, stocking, consumption, transport, and emission of carbon diox- ide (CO 2 ) and methane (CH 4 ) in reservoirs. The simulator comprises a Graphical User Interface (GUI) using OpenGL, and a Shell Interpreter. Geographical data in various formats are fed to the Terrain module, that generates the level sets and prepares the site geometry for the next module, Phyto. Drainage and phyto-physionomy data are added by Phyto and handed over to the Mesh module which generates the grid for the transport simulator. The prototype was developed with Matlab and is currently being rewritten in C++. The Transport module comprises the core of the simulator and uses a mixed finite element scheme. The simulator is based on a nonlinear system of partial differential equations, the Navier-Stokes equation and scalar transport [5,6], presented bellow in a nondimensional form: