Research On Optimization Design Theory And Methods Of Flywheel For Energy Storage

Today, with the environment and energy problems growing, techniques for energy saving and environment protectiing become the hotspots and frontiers in current researches. Energy storage technology is an important way to utilize the energy efficiently, and is paid more attention to by energy sectors and industrial circles. Flywheel is proved to be an ideal form of energy storage on account of its high energy density, high power density, high efficiency, long lifetime, low environmental impact, etc. It is finding increasing use in aerospace, vehicles and power system. A high-speed rotating flywheel is a key component in the flywheel energy storage system. So the design of the flywheel is very crucial and important, which will directly determine the energy storage ability of the flywheel system. Based on assimilating current research findings, factors that affect energy storage performances of the flywheel are fully researched in this paper. Approaches and measures for improving energy storage ability of isotropic material, composite and founctionally graded material (FGM) flywheels are proposed and modified respectively. Works in this paper further round out the optimization design theory and methods for high-speed flywheels for energy storage, and provide important theory basses and effective approaches for designing and manufacturing a reliable and cost-effective flywheel for energy storage.In this paper, shape optimization of the isotropic material flywheel is researched. To overcome the shortcomings that the calculation efficiency of the ordinary method is low in the flywheel shape optimization, effects of rotating speed on the optimal shapes of the flywheel are analyzed, and brief analytic expressions of the flywheel optimal shapes are directly gained adopting the optimal control theory by dividing the rotating speed into low, medium and high speed intervals. Through comparing the optimal shapes of the isotropic solid and hollow flywheels at low, medium and high speed respectively, change rules of the optimal shapes with the rotating speed are revealed. Based on the research results above, a low cost, low speed metal flywheel is designed to use as the power traction device for automobile crash test system in this paper. At last, a microbus front crash test is conducted by this new power traction device using merely a30kW motor and validates the availability of applying the energy storage flywheel to the automobile crash test system. After analyzing the problems and flaws in the previous evolutionary structural topology method, the previous bi-directional evolutional structural optimization (BESO) method based on von Mises stress is improved by introducing a new material interpolation model and a new performance convergence index in this paper. For the implementation of the modified BESO method, a combination of finite element software Abaqus with programming language Matlab is used. Adopting this modified BESO method, the topology optimization of the flywheel is further researched in this paper, and the optimized flywheels with rational structures and clear profiles are found. At last, variation characteristics of the flywheel optimal topology are analyzed and summarized as the structure volume and rotationally period are changing.For the press-fit multi-rim composite flywheel, the possible material failures that except radial crack drawn by the centrifugal force, too high interference press may crush the composite and too low interference press may separate the outer rims while the flywheel is rotating are pointed out and analyzed in this paper. And then, using the two-stage Augmented Lagrange Particle Swarm Optimization (TS-ALPSO) algorithm proposed in this paper, which can solve nonlinear optimization problems with constraints and has global convergence and higher computational efficiency, cost optimization of the multi-rim hybrid composite flywheel is researched. For a certain material price, the influences of material sequence, rims number and interferences on the energy storage performance of flywheel are discussed. At last, as the prices of materials change continuously, variation rules of radius of each rim, interferences and rotating speed are revealed and summarized for the composite flywheel when its stored energy per unit cost is maximized.For the functionally graded material flywheel, firstly, a modified plane stress theory is presented by extending the2D PS theory in order to make up for the shortcomings that with thickness of the flywheel increasing, the plane stress(PS) solution becomes inaccurate. Then, a3D modified plane stress (MPS) solution of the functionally graded material flywheel is derived. Secondly, based on the piecewise cubic shape-preserving interpolation method, an adaptive shape-preserving (ASP) interpolation method is proposed to solve the problem that in the shape optimization, the locations and number of the control points are difficult to determine. Using this interpolation method, the accuracy of shape optimization is improved significantly. At last, using the sequential quadratic programming (SQP) optimization method based on the ASP interpolation method, shape and material distribution of FGM flywheel is optimized simultaneously. Both of the shape and material optimization produces a really better flywheel in which the stress is more even and the material is made better use of. Through analyzing the optimization results, influences of the shape and material properties on the energy storage performance of FGM flywheel are summarized.