Abstract:In order to improve the performance of the draft tube in hydraulic turbine, a multi-objective optimization method for the draft tube is developed by combining the design of experiment (DOE), the radial basis function (RBF) and the non-dominated sorting genetic algorithm (NSGA-II) in this paper. The geometrical design variables of the median section in the draft tube and the cross section in its exit diffuser are considered as design parameters in this optimization, which objective function is to maximize the pressure recovery factor (Cp) and minimize the energy loss coefficient (ζ). The limited numbers of design matrix required for the shape optimization of the draft tube is generated by optimal Latin hypercube (OLH) method of the DOE technique, of which performances are evaluated through computational fluid dynamic (CFD) numerical simulation. For reducing of the computational consumption, the approximate model is used based on the RBF. The Pareto optimal solutions are finally performed using the NSGA-II for obtaining the best geometrical parameters of the draft tube. The optimization result of the draft tube shows a marked performance improvement over the original, which verifies the theoretical validity and feasibility of the proposed method in this paper.

A modeling method is presented for grinding of the designated geometrical parameters of twist drill in a Biglide parallel machine, which has the more effective and economic potentialities for grinding of drill point. The grinding kinematics trajectory and condition are analyzed based on the structure of the Biglide parallel machine. Moreover, the mathematical model of twist drill flank are derived and used to develop the parametric models of twist drill based on the grinding parameters of the Biglide parallel machine. The optimal grinding parameters are obtained for the custom-oriented twist drill using genetic algorithm. The grinding experiment results using the optimal grinding parameters agree well with the designated geometrical parameters of twist drill and show a marked improvement in grinding precision of the drill point in the Biglide parallel machine, depending on the customers' demands.