Hi Bill,
It looks like you're referring to the pipe wave speed calculator tool. The "pipeline support" field in that calculator determines the value of the Ψ coefficient in the equation for wave speed, shown in the Help documentation under the "Celerity and Pipe Elasticity" topic. As seen in this topic, the following values are used:
- Pipe is anchored throughout against axial movement: Ψ = 1 - µ2, where µ is Poisson's ratio - Pipe is equipped with functioning expansion joints throughout: Ψ = 1 - µ/2 - Pipe is supported only at one end and allowed to undergo stress and strain both laterally and longitudinally: Ψ = 5/4 - µ (ASCE, 1975)
I do not personally know the answers to your questions (maybe another contributor could comment), but I would suggest picking the closest representation to your pipeline. If it's a "gray area" where you're not sure if the system falls under one of these categories, I would recommend a sensitivity analysis (try multiple methods and compare the results).
Regards,
Jesse
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
I would recommend reading about this further in a good textbook (e.g. Fluid Transient in Pipeline Systems by A.R.D. Thorley).
My 2c is that underground pipes are usually restrained against axial movement by thrust blocks at major changes in direction, so I would tend to use the "Pipe is anchored throughout against axial movement" equation.
In Thorley's book he actually says that since none of these idealized cases will ever be fully realized in practice, and since the influence of this factor on the calculated wavespeed will generally be small compared to the influence of uncertainties in the estimation of other parameters (material elastic modulus, fluid density and bulk modulus), the restraint factor is often just set to 1.
Mal Sharkey
Bentley