Design of a Flywheel

Introduction

A flywheel is an inertial energy-storage device. It absorbs mechanical energy and serves as a reservoir, storing energy during the period when the supply of energy is more than the requirement and releases it during the period when the requirement of energy is more than the supply.

Functions and Operation

The main function of a fly wheel is to smooth en out variations in the speed of a shaft caused by torque fluctuations. Flywheel absorbs mechanical energy by increasing its angular velocity and delivers the stored energy by decreasing its velocity

Design Approach

There are two stages to the design of a flywheel.
First, the amount of energy required for the desired degree of smoothing must be found and the (mass) moment of inertia needed to absorb that energy determined.
Then flywheel geometry must be defined that caters the required moment of inertia in a reasonably sized package and is safe against failure at the designed speeds of operation.

Design Parameters 

•  Speed Fluctuation - This gives the range of speed
• Coefficient of speed fluctuation - This gives a dimension-less ratio which is a normalized form obtained by dividing range by average

Geometry of Flywheel
The geometry of a flywheel may be as simple as a cylindrical disc of solid material, or may be of spoked construction like conventional wheels with a hub and rim connected by spokes or arms Small fly wheels are solid discs of hollow circular cross section. As the energy requirements and size of the flywheel increases the geometry changes to disc of central hub and peripheral rim connected by webs and to hollow wheels with multiple arms.

The latter arrangement is a more efficient of material especially for large flywheels, as it concentrates the bulk of its mass in the rim which is at the largest radius. Mass at largest radius contributes much more since the mass moment of inertia is proportional to mr2.

Stresses in Flywheel
Flywheel being a rotating disc, centrifugal stresses acts upon its distributed mass and attempts to pull it apart. Its effect is similar to those caused by an internally pressurized cylinder.
Analogous to a thick cylinder under internal pressure the tangential and radial stress in a solid disc flywheel as a function of its radius r is given by:

The point of most interest is the inside radius where the stress is a maximum. What causes failure in a flywheel is typically the tangential stress at that point from where fracture originated and upon fracture fragments can explode resulting extremely dangerous consequences, Since the forces causing the stresses are a function of the rotational speed also, instead of checking for stresses, the maximum speed at which the stresses reach the critical value can be determined and safe operating speed can be calculated or specified based on a safety factor.

The promotion of ergonomics in industrially developing countries

The promotion of ergonomics in industrially developing countries

Personal experience of author in Industrially Developing Countries (IDC) is presented in this paper. Some key differences between IDC and Industrially Advanced Countries (IAC) are given.

Relevance to Industry

The IAC approach to implementing ergonomics research and development projects for commercially competitive or legislative reasons may not be appropriate to IDCs.

Introduction

The application of ergonomics in industrially developing countries (IDCs) could bring about major benefits to productivity and health is not widely shared outside the ergonomics community.

There are some fundamental differences between IDCs and IACs which are as follows:

 

Indigenous Ergonomics

India is the IDC with the greatest level of ergonomics activity.

Where India may differ from other countries is the proportionately greater attention paid to ergonomics in the rural sector, particularly to agricultural production for both commercial and smallholder farming.

Singleton in 1970 recommended that ergonomics should address health and productivity rather than consumerism and job satisfaction. Author is still contending on this recommendation.

Other relatively advanced IDCs also have professional bodies to represent the subject and its practitioners, and these organisations may also help serve the ergonomics needs of other IDCs in their regions. Issues cutting across aspects of working in IDCs are manual handling, transport and occupational health and safety, in general.

Jeyeratnam in 1992 contends that in IDCs occupational health services should be provided as a function of primary health care, whereas in IACs, occupational health lies within the remit of those responsible for the control of occupational injury and disease.

ExogenousErgonomics

IACs contribution in the development or application of ergonomics in IDCs seems to be relatively rare. Ergonomics, as such, is rarely requested because it is not sufficiently understood in the IDC (i.e. by the ‘‘customer’’ in demand-led projects) and senior managers in the funding agencies in IACs do not specify ergonomics, by name, although they may espouse the principles and welcome the benefits that ergonomics can bring.

Even international agencies, such as the ILO and the WHO, which undoubtedly sanction and promote ergonomics principles rarely use the term ‘‘ergonomics’’. There are, of course some exceptions, particularly in the ILO, which employs ergonomists, but it is surprising that ergonomics is not more prevalent in the culture and image of the ILO.

The five capitals, collectively known as livelihood assets, are natural, physical, human, social and financial. By focusing on the use and development of the human capital, ergonomics and ergonomists should find an entry point to playing a more prominent in development projects and programmes.

Conclusion

The principles of ergonomics and its potential to deliver benefits have been accepted and practised in a small number of Development and Technology Transfer Programmes but not enough decision-makers are conversant with the breadth and depth of ergonomics, and the profession is not well recognised by name. The opportunities for ergonomics to mapon to the livelihoods approach and play a more prominent role in Development Aid Programmes, particularly through participatory processes, just be fully identified and taken up with aid agencies. Otherwise, the profession will remain undervalued as one of the means of alleviating third world poverty.

Ergonomists must actively contribute to the debate on whether occupational health and associated ergonomics issues in IDCs should be considered within primary health care or elsewhere (e.g. Ministry of Health, Ministry of Labour or private sector organisations).