Kinetic Energy Storage

Theory and Practice of Advanced Flywheel Systems

G. Genta

• Publisher: Butterworth-Heinemann
• Year: 2014
• Print ISBN: 9780408013963
• eBook ISBN: 9781483101590
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Kinetic Energy Storage: Theory and Practice of Advanced Flywheel Systems focuses on the use of flywheel systems in storing energy. The book first gives an introduction to the use of flywheels, including prehistory to the Roman civilization, Christian era to the industrial revolution, and middle of the 19th century to 1960. The text then examines the application of flywheel energy storage systems. Basic parameters and definitions, advantages and disadvantages, economic considerations, road vehicle applications, and applications for fixed machines are considered. The book also evaluates the flywheel, including materials, radial bar and filament flywheel, composite material disc flywheel, rotor stress analysis, and flywheel testing. The text also discusses housing and vacuum systems and flywheel suspension and transmission systems. Aerodynamic drag on wheels, burst containment, types of bearings, rotor dynamics, dampers, and types of transmissions are described. The text is a vital source of information for readers wanting to explore the composition and functions of flywheels.

1

Historical background

Publisher Summary

This chapter presents a background of ancient mechanics, which was dominated by the idea that a body could be maintained in motion only if a suitable force was applied to it. Aristotle thought that the velocity of a body was proportional to the force applied. For ancient philosophers, translatory and rotary motions were different phenomena, and often the explanations offered for one were not applied to the other. The failure of ancient thought to recognize the basic principles of motion did not, however, hamper the development of devices that exploit the inertia of bodies. Inertia of translation was exploited far earlier and to a larger extent than rotary as it is far easier to move an object on a more or less straight line than to spin it. The first object that made use of rotary inertia was the spindle whorl. Spinning, that is, drawing fibers and twisting them to form threads, was started by rolling the fibers between the palms of the hands or the hand and another part of the body.

1.1 Philosophers and flywheels

Ancient Mechanics^* was dominated by the idea that a body could be maintained in motion only if a suitable force was applied to it. Aristotle thought that the velocity of a body was proportional to the force applied.

Some major difficulties arose from this idea, particularly when the motion of projectiles or the free falling of bodies had to be explained. The ideas on these subjects were quite confused and contradictory explanations were often propounded by the same author. As an example, it was necessary to assume the existence of a prime mover which sustained the motions of celestial and earthly bodies.

Aristotle, in his fourth book of Physica, explains the motion of projectiles by assuming that the air, rushing behind the projectile in order to fill the empty space left by its motion, exerts a continuous push.

The problems, however, remained unsolved and even in the 6th century AD the grammarian Johannes Philoponus in his comment to the Physica of Aristotle was able to offer an equally spurious counter-proposal that in being thrown, a certain undefined ‘force’ is transferred to the projectile, which was able to sustain its motion for some time.

For ancient philosophers, translatory and rotary motion were different phenomena, and often the explanations offered for one were not applied to the other.

The two theories attributing the causes of motion to the medium and in the object itself remained for centuries, sometimes battling with each other and sometimes with attempts to integrate them in a single theory.

Ibu Sina (Avicenna, 1037), in his comments on Aristotle, states that this ‘inclination’ (in Arabic, ‘mail’) transferred to the projectile in being thrown would last indefinitely were it not for the drag of the medium in which motion takes place.

The same opinion was put forward by Jean Buridan, the famous rector of the University of Paris in the 14th century, in his theory of impetus. He suggests that there is no need to think that God continues to move the celestial bodies as it is simpler to assume that He gave them the required impetus when they were created, there being no resistance to motion in the perfect celestial world.

He takes as an example of motion, which can be explained only with his theory, the flywheel, or the ‘rotula sive lignea sive plumbea turnatilis’, which maintains its velocity for a long time without changing its position in space. He also affirmed that the impetus is proportional to mass and speed and says that the difficulty found in slowing a heavy grinding stone is due to mass and speed of rotation.

Buridan seems to think that rotational and translational ‘impetus’ are essentially the same thing. Other philosophers held the opposite opinion (e.g. Henry of Assia, who worked in Paris between 1360 and 1380). About the fact that only external resistance slows down a body, others thought that the impetus could not last for ever even in the absence of forces which resist motion. Of this opinion was Oresme, another famous disciple of Buridan.

G. B. Benedetti (1585) states that a wheel cannot continue its rotation indefinitely even in the absence of friction as, normally, the impetus would make the parts which compose it move in a straight line (i.e. tangentially). The constraint which compels them to follow a circle has the effect of diminishing their impetus. He uses this tendency of the parts of the wheel to move in a straight line to explain the stability of a top or other rotating body.

It is interesting that, while ancient science failed to explain inertial motion, it was well aware of centrifugal stressing of rotating bodies and realized the danger of the bursting of rotating objects such as grinding wheels.

Copernicus opposes the opinion of Tolomeo that if the earth were to rotate it would burst, by observing that the sky moves faster, being of greater diameter and would more likely burst if the circular motion were imparted to it. A very interesting discussion on the stability of the sky can be found in Copernicus. He says that it is absurd to think that the sky does not collapse because it rotates as this equilibrium would be unstable and it would either collapse or grow infinitely. The fact that things are unable to remain whole if they rotate too rapidly is assumed from experimental evidence. Only when the law of inertia was proposed by Galileo and modern mechanics was started by Galileo and Newton could the way in which inertial devices work be explained in a satisfactory way.

1.2 From prehistory to the Roman civilization

The failure of ancient thought to recognize the basic principles of motion did not, however, hamper the development of devices which exploit the inertia of bodies. It must be remembered that in the ancient world, science, i.e. philosophy and technology, were far more separated than in modern times and, besides this, inertial devices were already well established thousands of years before attempts were made to explain rotary motion.

Inertia of translation was exploited far earlier and to a larger extent than rotary, as it is far easier to move an object on a more or less straight line than to spin it.

The principle of the hammer is so easily grasped that simple tools such as sticks are used even by lower animals. Some examples are reported in the well-known History of Technology edited by C. Singer, E. J. Holmyard and A. R. Hall.

It was, however, only with the evolution of man that the use of simple tools became common, but hundreds of thousands of years were to elapse before rotary inertia could play a role in human life. The first tool using rotary motion was probably the drill, in its two main applications, boring and lighting fires. But the hand drill, like its immediate successors, the strap drill and the bow drill, which are still widely used by some primitive peoples, did not need the addition of a flywheel to work properly.

The first object which made use of rotary inertia is the spindle whorl. Spinning, i.e. drawing fibres and twisting them to form threads, was started by rolling the fibres between the palms of the hands or the hand and another part of the body. Eventually the use of a stick to wind the thread was established and the spindle evolved from it. If the spindle was rotated directly by hands or rolled on the thigh there was no need to increase its inertia. A third method of spinning, however, evolved in which the spindle was suspended by the thread itself. A length of fibres would be drawn, twisted slightly and fastened to the spindle. The latter was then rotated by hand and dropped while the fibres were regularly paid out. The spindle maintains its rotation under its own inertia and therefore utilizes a flywheel effect.

If the spindle is simply a stick of wood, the flywheel, namely the whorl, can be a small piece of wood, stone, pottery, metal, glass, or bone, with a central hole. More modern forms of integral spindles appeared later.

A spinning whorl found in the excavation of Pan Po prehistoric site near Xian is shown in Figure 1.1(a). It is difficu...

Table of contents

• Cover image
• Title page
• Table of Contents
• To Franca and Alessandro
• Copyright
• Preface
• Symbols
• Chapter 1: Historical background
• Chapter 2: Application of flywheel energy storage systems
• Chapter 3: The flywheel
• Chapter 4: The housing and vacuum system
• Chapter 5: Flywheel suspension systems
• Chapter 6: Transmission systems
• Chapter 7: A look to the future
• Bibliography
• Appendices: Computer programs
• Appendix 1: Program HYPER
• Appendix 2: Program MADIS
• Appendix 3: Program RIMDIS
• Appendix 4: Program NONMAN
• Appendix 5: Program SPOKES
• Appendix 6: Program SUBDIS
• Appendix 7: Program ORTDIS
• Appendix 8: Program DYNROT
• Index