Research On Parameters Inversion Of Water Quality Model Based On Niche Ant Colony Algorithm

With the development of social economy, it’s really the time to takemeasures to resolve the water pollution problem which has become more andmore serious. Water quality model plays an important role in the environmentprediction and pollution control of water resources. By being given the correctwater quality model, we can obtain more accurate information that including theconcentration of pollutants and its changing. Therefore, water quality modelplays more and more significant role in the prediction of future water quality anddeveloping countermeasures to control water pollution. The parameters inversionof model is the most important part. Because that can determine the applicationof the model is successful or not. In the inversion of river water quality, theobjective function usually presents a highly nonlinear. Traditional solutions, suchas Newton method, gradient method and the simplex method, have thedisadvantage of over-dependent on the initial value. Generally we can onlyobtain the local optimal value near the initial value. That is not the globaloptimum.As a relatively new member of optimization algorithm, ant colony algorithm(ACA) is a global optimization method. Parallel computation mechanism isadopted in this algorithm. Ant colony algorithm has strong robustness. And thatis easy to combine with other methods in optimization. But it has the obviousdisadvantage of long searching time, and is easy to fall into local optimums(ie,‘premature’ phenomenon). As for the disadvantage above of traditional antcolony algorithm, a lot of scholars have proposed many methods to improve it.Based on previous research foundation, the adopted algorithm in this thesis isniche ant colony algorithm based on the principle of fitness sharing (NACA),that is obtained by applying the fitness sharing principle to the combination ofniche method and ant colony algorithm.This thesis mainly focuses on the application of algorithm. Firstly, weapplied the improved niche ant colony algorithm (ie, NACA) to the typicalmulti-modal function optimization problem, and comparing the obtained resultswith the results found by basic ant colony algorithm, which proved theeffectiveness and superiority of the algorithm adopted by this thesis. Then basedon the one-dimensional and two-dimensional water quality model, both of themhave analytical solution, we researched on the parameters inversion of them. Theobtained results have indicated this method with a very high precision and computational efficiency and easy realized by computer.Taking into account the basic form of generally more applicable waterquality model is the convection diffusion equation, and most of them have noanalytical solution. By applying finite element method, we can obtain thenumerical solution to construct the objective function of the algorithm. Taking aspecific convection diffusion equation as an example. From the result of theparameter inversion based on the example equation, we can see although theprogram runs a little longer, which needs to be improved. While the inversionprecision is so high that almost fully consistent with the true value. The highprecision of the inversion results proved the feasibility of the algorithm.Therefore, the algorithm we adopted in this thesis has actual significance in theparameter inversion of water quality model, and that is expected to be widelyused.