Optimization of Blade Geometry of Savonius Hydrokinetic Turbine Based onGenetic Algorithm

Savonius hydrokinetic turbine is a kind of turbine set which is suitable for low-velocity conditions.Unlike conventional turbines,Savonius turbines employ S-shaped blades and have simple internal structures.Therefore,there is a large space for optimizing the blade geometry.In this study,computational fluid dynamics(CFD)numerical simulation and genetic algorithm(GA)were used for the optimal design.The optimization strategies and methods were determined by comparing the results calculated by CFD with the experimental results.The weighted objective function was constructed with the maximum power coefficient Cp and the high-power coefficient range R under multiple working conditions.GA helps to find the optimal individual of the objective function.Compared the optimal scheme with the initial scheme,the overlap ratioβincreased from 0.2 to 0.202,and the clearance ratioεincreased from 0 to 0.179,the blade circumferential angleγincreased from 0°to 27°,the blade shape extended more towards the spindle.The overall power of Savonius turbines was maintained at a high level over 22%,R also increased from 0.73 to 1.02.In comparison with the initial scheme,the energy loss of the optimal scheme at high blade tip speed is greatly reduced,and this reduction is closely related to the optimization of blade geometry.As R becomes larger,Savonius turbines can adapt to the overall working conditions and meet the needs of its work in low flow rate conditions.The results of this paper can be used as a reference for the hydrodynamic optimization of Savonius turbine runners.

Resistive switching and artificial synaptic performances of memristor based on low-dimensional bismuth halide perovskites

Zero-dimensional(0D)-Cs_(3)Bi_(2)I_(9),two-dimensional(2D)-Cs_(3)Bi_(2)Br_(9),and one-dimensional(1D)-Cs3Bi2Cl9 perovskite films have been successfully grown on indium tin oxide(ITO)glass substrates,which were used to fabricate memristors with the structure of Al/Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)/ITO glass.The current three types of memristors exhibited bipolar resistive switching behaviors.Both the endurance and retention time tests clearly demonstrated the excellent stability of present devices.Especially,the ON/OFF ratio of the 0D-Cs_(3)Bi_(2)I_(9)device is close to 104 at the reading voltage of 0.1 V,which is nearly 100 and 1000 times larger than those of the 1D-Cs3Bi2Cl9 device and the 2D-Cs_(3)Bi_(2)Br_(9)device,respectively.The activation energy of halide vacancies in the Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)films was calculated using the density functional theory by considering a minimum migration path,demonstrating the dimensionality of the Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)film affected the formation and rupture of conductive filaments.Moreover,the short-term plasticity and long-term plasticity of biological synapse were simulated by evaluating the conductance responses of Al/Cs_(3)Bi_(2)X_(9)(X=I,Br,and Cl)/ITO devices under various voltage pulses in detail.The duration time of long-term plasticity in all the present devices can last for up to 250 s.The 0D-Cs_(3)Bi_(2)I_(9)device showed both the highest spikeduration-dependent plasticity and paired-pulse facilitation indexes compared to the other two devices.Additionally,the 0DCs_(3)Bi_(2)I_(9)device successfully established the associative learning behavior by simulating the Pavlov’s dog experiment.

Electrically manipulating magnetization reversal via energy band engineering

Realization of a magnetization reversal by an external electric field is vital for developing ultra-low-power spintronic devices.In this report,starting from energy band engineering,a general design principle is proposed for achieving electrical manipulation of a nonvolatile 180°magnetization reversal.A half semiconductor(HSC)and a bipolar magnetic semiconductor(BMS)are selected as the model of magnetic layers,whose conduction-band minimum and valence-band maximum are in the same and opposite spin states,respectively.Based on the analysis of virtual hopping and tight-binding models,the interlayer coupling of HSC/insulator/BMS devices is successfully tuned between ferromagnetic and antiferromagnetic interactions by varying electric field directions.Moreover,the interlayer coupling nearly disappears after removing the electric field,proving the nonvolatile magnetization reversal.Using first-principles calculations,the feasibility of present design strategy is further confirmed by a representative device with the structure of CrBr3/h-BN/2H-VSe_(2).This design guideline and physical phenomena may open an avenue to explore magnetoelectric coupling mechanisms and develop next-generation spintronic devices.