Hello,

is it possible to calculate water hammer?
and do I use the dynamic or the static analyze for it?

greetz

rick

Whether you use dynamic or static is situational, i.e. how quickly the water momentum is changed. If slowly, static with a dynamic multiplier (typically 2) is fine. If quickly, you're better served with a dynamic analysis.

The most conservative approach is to calculate surge pressure and multiply it by cross sectional area. This is usually unrealistic, however.

Instead, reduce it to a physics problem. You have a mass of fluid. You must stop this fluid. Calculate the average force required to do so in the time frame that you have. If it makes sense, multiply this average force by a factor if the mechanism is non-linear.

E.G. if your mechanism is a gate valve that closes at a linear rate, the maximum instantaneous change in cross sectional area is at the center, which is 27% higher than average, if I recall correctly.

You can calculate water hammer using dynamic approach as shown in CAESAR II Applications Guide. There's a section called "Dynamic Analysis of Water Hammer Loads (HAMMER)". The "Notes for Analyzing Water Hammer Loads" section is a good read too.

I think first you may want to find out if you really have to do it. I've had a client who confused water hammer with liquid slug. I've also had a case where I was asked to analyze for water hammer due to valve closure. Then I found that the valve in question could not possibly close fast enough to cause the pressure surge.