Good Day,
I am using Watergems V8i to model a water supply network. It is a large network with numerous Tanks supplying each other along a bulk line as well as providing water to a stand pipe network.
I know the system works and have confidence in the fact that the tanks are large enough however. When creating an EPS with a 48 hour pattern using only 50% of the demands I keep getting errors regarding disconnected demand nodes detected and unbalanced network. I am purely using an additional tank to provide the input for the top reservoir but when I decrease the Volume in this new tank the whole network freaks out for no reason. The tanks are all at least 90% full and demands are low.
Anyone with any help for me. I am at a loss.
Regards
Lloyd Wallace
Lloyd,
It sounds like your tanks are becoming empty at some point during the EPS, which triggers the built-in altitude valve to close the adjacent pipe. If all tanks are closed, the demands will be disconnected. A good way to visualize this is to go to Edit > Select by Element > Tanks, then right click > Graph and choose "percent full" as the attribute. If they are becoming empty around the time when you see these problems, you should check your controls that I presume you have in place to prevent this from happening. Also check your base demands, pattern multipliers, tank input fields and units used.
If you need further help, please send your model to technical support.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Jesse,
I identified that that is indeed the problem. I would like to know the reason for an ocsillating result within the modelling process. I have supplemented the top tank with a reservoir to supply endless water. When however I try use an FCV to control the amount of water flowing to the tank I get ocsillations in the supply curve from zero to full in very, very short time steps.
What is the reason for this?
Ilifa Engineers
I'm not quite sure what you mean by oscillations or supply curve. Is the network unbalanced? Do you have controls in place in the real system to prevent tanks from becoming empty? Perhaps you have hydraulically close tanks? WaterGEMS will simply balance energy for each steady state that makes up the EPS simulation, so the following forum thread may pertain:
http://communities.bentley.com/products/hydraulics___hydrology/f/5925/p/26590/61409.aspx
If this doesn't help, I'll need to understand your system and what you're trying to model a bit better to be able to answer. I would suggest sending the model to technical support with any specific question you might have.
Thank you for the help thus far. I would like to know why water would be flowing through the system when there is no demand present. As I said I am using an EPS and for the first 5 hours there is no demand. Why then is water flowing out from my top tank to the other 2 tanks. Must I place conditions on the tanks to counter this?
Thanks
Water can still flow without a demand. WaterGEMS will route flow through the system in order to balance energy, based on demands and boundary conditions. In your case, if the tank water surface elevations differ, then there must be flow between them, to cause a head loss equal to that difference. So, water will flow from the tank at a higher elevation to the tank at a lower elevation, to induce such a loss with friction.
If you're expecting the tank elevations to be in 'equilibrium' and not have flow between them, please see the thread I mentioned in my last post (you may need to combine hydraulically close tanks).