Hello Ryan,
When the valve closes, the flow is basically zero. However, the presence of a reservoir (which has a constant hydraulic grade during the transient simulation) may cause small flows in the pipe after the valve is closed. These small flows would normally cause friction head loss, which would eventually attenuate the pressure wave (you may need to run the simulation for a while). So, it is not the reservoir itself that causes the attenuation but instead the small movement of water that occurs in and out of it as the pressure wave bounces back and forth.
So, you'll need to make sure that the headloss for your pipe is appropriate. If for some reason there is no headloss through your pipe, or the flows are very close to zero, then no attenuation will occur. This can be observed in the "sample1.wtg" file that ships with HAMMER, located in the "Samples" subfolder - the pipe in this model has no headloss, so attenuation doesn't occur. If you reduce the stop hgl of that pipe and re-run, the wave will be attenuated due to friction.
The other factor on this topic is the transient friction method, which you can set in the transient calculation options. This changes how the friction factors are applied.
I hope this helps. If not, or if you have any further questions about HAMMER, please submit a service ticket to technical support with your model files.
Regards,
Jesse
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.