Abstract
A multi-objective optimization strategy to find optimal designs of composite multi-rim flywheel rotors is presented. Flywheel energy storage systems have been expanding into applications such as rail and automotive transportation, where the construction volume is limited. Common flywheel rotor optimization approaches for these applications are single-objective, aiming to increase the stored energy or stored energy density. The proposed multi-objective optimization offers more information for decision-makers optimizing three objectives separately: stored energy, cost and productivity. A novel approach to model the manufacturing of multi-rim composite rotors facilitates the consideration of manufacturing cost and time within the optimization. An analytical stress calculation for multi-rim rotors is used, which also takes interference fits and residual stresses into account. Constrained by a failure prediction based on the Maximum Strength, Maximum Strain and Tsai-Wu criterion, the discrete and nonlinear optimization was solved. A hybrid optimization strategy is presented that combines a genetic algorithm with a local improvement executed by a sequential quadratic program. The problem was solved for two rotor geometries used for light rail transit applications showing similar design results as in industry.
Highlights
Leading countries in renewable energy such as Sweden or Germany rely on energy storage systems
Small rotors made of lightweight materials such as fiber-reinforced polymer composites having a mass in the order of a few tens kilograms can typically be found in mobility applications such as hybrid and electric vehicles, including energy recovery systems for some race cars
To tailor the model to the assembly methods used in the case studies considered as part of this article, press fitting was included in the present investigation
Summary
Leading countries in renewable energy such as Sweden or Germany rely on energy storage systems. Small rotors made of lightweight materials such as fiber-reinforced polymer composites having a mass in the order of a few tens kilograms can typically be found in mobility applications such as hybrid and electric vehicles, including energy recovery systems for some race cars. Steel FESS rotors with mass in the order of tens of metric tons exist as stationary systems for the short-term energy supply for very high peak-power applications [7]. One of the first analytical methods to calculate the rotor stresses was published in [9] This model considered interference between adjacent rims caused by press fits. Numerical models using the finite element method can determine results with greater accuracy especially for complex geometries These methods cause higher computation time, which is a significant disadvantage for optimization problems. Irrespective of the modeling approach, the design space for multi-rim rotors is significant and the challenge for optimization strategies is finding optimal design parameters, such as the number of rims, the rim thicknesses, the size of interference fits and the material selection, and providing guidance to the designer by elucidating suitable designs within the design space
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