Editing Flywheel (section)

== Design ==

A [[rimmed flywheel]] has a [[Rim (wheel)|rim]], a hub, and [[spoke]]s.<ref>Flywheel Rotor And Containment Technology Development, FY83. Livermore, Calif: Lawrence Livermore National Laboratory, 1983. pp. 1–2</ref> Calculation of the flywheel's moment of inertia can be more easily analysed by applying various simplifications. One method is to assume the spokes, shaft and hub have zero moments of inertia, and the flywheel's moment of inertia is from the rim alone. Another is to [[Lumped-element model|lump]] moments of inertia of spokes, hub and shaft into the rim. These may be estimated as a percentage of the flywheel's moment of inertia, with the majority from the rim, so that <math>I_\mathrm{rim}=KI_\mathrm{flywheel}</math>. For example, if the moments of inertia of hub, spokes and shaft are deemed negligible, and the rim's thickness is very small compared to its mean radius (<math>R</math>), the radius of rotation of the rim is equal to its mean radius and thus <math display="inline">I_\mathrm{rim}=M_\mathrm{rim}R^2</math>.{{Citation needed|date=May 2022}}

A [[shaftless flywheel]] eliminates the annulus holes, shaft or hub. It has higher energy density than conventional design<ref>{{Cite journal|last1=Li|first1=Xiaojun|last2=Anvari|first2=Bahar|last3=Palazzolo|first3=Alan|last4=Wang|first4=Zhiyang|last5=Toliyat|first5=Hamid|date=2018-08-14|title=A Utility Scale Flywheel Energy Storage System with a Shaftless, Hubless, High Strength Steel Rotor|url=https://www.researchgate.net/publication/321059437|journal=IEEE Transactions on Industrial Electronics|volume=65|issue=8|pages=6667–6675|doi=10.1109/TIE.2017.2772205|s2cid=4557504}}</ref> but requires a specialized magnetic bearing and control system.<ref>{{Cite journal|last1=Li|first1=Xiaojun|last2=Palazzolo|first2=Alan|date=2018-05-07|title=Multi-Input–Multi-Output Control of a Utility-Scale, Shaftless Energy Storage Flywheel With a Five-Degrees-of-Freedom Combination Magnetic Bearing|journal=Journal of Dynamic Systems, Measurement, and Control|volume=140|issue=10|pages=101008|doi=10.1115/1.4039857|issn=0022-0434}}</ref> The specific energy of a flywheel is determined by<math display="inline">\frac{E}{M} = K \frac{\sigma}{\rho} </math>, in which <math>K </math> is the shape factor, <math>\sigma </math> the material's tensile strength and <math>\rho </math> the density.{{Citation needed|date=May 2022}} While a typical flywheel has a shape factor of 0.3, the shaftless flywheel has a shape factor close to 0.6, out of a theoretical limit of about 1.<ref>{{Citation|last=Genta|first=G.|chapter=Application of flywheel energy storage systems|date=1985|pages=27–46|publisher=Elsevier|isbn=9780408013963|doi=10.1016/b978-0-408-01396-3.50007-2|title=Kinetic Energy Storage}}</ref>

A [[superflywheel]] consists of a solid core (hub) and multiple thin layers of high-strength flexible materials (such as special steels, carbon fiber composites, glass fiber, or graphene) wound around it.<ref>{{Cite web|title=Technology {{!}} KEST {{!}} Kinetic Energy Storage|url=https://www.kest.energy/tech?lang=en|access-date=2020-07-29|website=KEST Energy|language=en|archive-date=2020-07-27|archive-url=https://web.archive.org/web/20200727075859/https://www.kest.energy/tech?lang=en|url-status=dead}}</ref> Compared to conventional flywheels, superflywheels can store more energy and are safer to operate.<ref>{{Cite book|last=Genta|first=G.|url=https://books.google.com/books?id=LKXpAgAAQBAJ|title=Kinetic Energy Storage: Theory and Practice of Advanced Flywheel Systems|date=2014-04-24|publisher=Butterworth-Heinemann|isbn=978-1-4831-0159-0|language=en}}</ref> In case of failure, a superflywheel does not explode or burst into large shards like a regular flywheel, but instead splits into layers. The separated layers then slow a superflywheel down by sliding against the inner walls of the enclosure, thus preventing any further destruction. Although the exact value of energy density of a superflywheel would depend on the material used, it could theoretically be as high as 1200 Wh (4.4 MJ) per kg of mass for graphene superflywheels.{{Citation needed|date=May 2022}} The first superflywheel was patented in 1964 by the Soviet-Russian scientist [[Nurbei Guilia]].<ref>{{Cite book |last1=Egorova |first1=Olga |url=https://books.google.com/books?id=tpreDwAAQBAJ&q=gulia+patent+superflywheel&pg=PA117 |title=Proceedings of the 2020 USCToMM Symposium on Mechanical Systems and Robotics |last2=Barbashov |first2=Nikolay |date=2020-04-20 |publisher=Springer Nature |isbn=978-3-030-43929-3 |pages=117–118 |language=en}}</ref><ref>{{Cite patent|title=Маховик|gdate=1964-05-15|url=https://patents.google.com/patent/SU1048196A1/ru}}</ref>