A Journal of Applied Mechanics and Mathematics by DrD, # 28
© Machinery Dynamics Research, 2016
Analytical Design -- Part III
In Parts I and II of this series, we began looking into the design analysis for an emergency steam cut-off valve for a nuclear power plant. Part I simply posed the problem, and Part II got into the detailed kinematic analysis of the four bar linkage that is to control the motion of the plug as it shuts off the steam flow. We would like to move on to the dynamic simulation of the motion to get an idea about the time required to close and ultimately to a force analysis so that the links can be appropriately sized. Before that can be done, it is necessary to spend some effort on the design of the plug itself so that the dynamic properties of the plug (mass, mass moment of inertia) can be estimated.
In the stress analysis of the plug, I am at somewhat of a disadvantage with respect to most of you. I know that many of you have access to Finite Element programs which enable you to do a fairly complete and correct stress analysis. Because I am no longer connected with a university or an industry that would give me that access, I have do not have access to FEA. Thus the analysis that I will present here is somewhat crude, rather approximate, and not recommended where better methods are available. You may choose to look at this as somewhat of a "historical approach" to the stress analysis, the way it would have been done before the arrival of FEA. The model that I will present is overly simplified, but it is the best that I can provide for this series.
The maximum temperature and pressure for the steam system are given as P = 1000 psi, T = 1000 deg F or equivalently, P = 68.95 bar, T = 538 deg C. These are the targets specified for the plug design.