Since the first competent surge analysis and simulation techniques were developed in the 1950's, repeated research work has shown that the wavespeed in a piped fluid changes with pressure and that these variations must be included into any simulation/surge program. A typical variation is shown on the graph.
Some surge programs only allow the wavespeed to be varied at the start of a simulation, yet as the previous graph shows the wavespeed also varies during the simulation. Our program automatically models the variations in wavespeed during the simulation and we have some good validations to show that the techniques used are accurate (see the Rising Main case study for just one such example).
Occasionally we hear an old and incorrect argument that fixing the wavespeed guarantees a worst case (or highest waterhammer pressures). The graph below compares a variable wavespeed simulation with one in which the wavespeed is fixed at the start - the higher pressures are generated by the variable wavespeed approach and it is these that match the site data.
Wavespeed is defined an discussed in our glossary.
