EGL and HGL Jump Error in Autodesk SSA

[tonykhoury]

Can someone please help ? I am having the same problem and i have spent a week and i cant solve it. 
Please see the attached files. 

[MattAndersonPE]

Tony -

EGL should always be above the HGL by definition.  [Velocity^2/2G]

Remember that at each structure that you see the EGL jumps, you have added flow, either by pipe or by subbasin, and that each jump, you see a significant increase in the downstream pipes velocity.  To remove the jumps, you have to make the velocities of the system closer from pipe to pipe.

A simple solution might be to increase your outlet size, which in turn will reduce your velocity.   The small outlet that is nearly submerged leave very little capacity for flow with the fixed outlet tailwater.

If you need quicker assistance, please open a subscription support request where they can provide assistence.

[tonykhoury]

Matt, 
Thank you for your response. Can you please me if there is a way to export numerical values of the EGL line ? 

I see that you are an Autodesk employee, - did anyone validate the software ? Can you please send me the files ? 

Can you please elaborate on "If you need quicker assistance, please open a subscription support request where they can provide assistence. "
How can i do it ?

Also, 
Does Autodesk have techinical support outside this forum for SSA  ( That's ok if it is paid - the forum it is great but sometimes i need a quiker assistance and if it is from Autodesk employees that will be great) ?


Thank you so much for your help.  

[MattAndersonPE]

Tony- 

Autodesk provides techincal support outside of this forum.  Typically, a user will follow the subscription support link found here.

http://knowledge.autodesk.com/search-result/caas/sfdcarticles/sfdcarticles/How-to-request-Technical-...

Watch the velocity of your pipes.  As you step down the network in your image, you step up in velocity.  From about 1.5 fps, to 5 fps to 11 fps at the end of the network.

Each jump in maximum velocity will necessitate a jump in the EGL. 

To remove the EGL jumps, make sure the system matches velocities.

[tonykhoury]

Matt,
Thank you again.
One last question, i do understand that the new pipe coming into the MH is adding Velocity to the system. Please see the attached files, i cut two profiles going into NODE 2.  Link1 and Link2 both going into NODE 2 and they both introduce water to the MH. 
However, the maximum velocity in Link 1 is 7.25ft/s, which is equivalent to 0.82 Ft of head, and look about right looking at the profile plot 1.JPG. Also, Link2 max velocity is 4.34 ft/s, which is equivalent of 0.3  Ft of head, and it seems about right looking at the profile plot 2.JPG.  

If i add the head from link 1 to link 2 i get about 1.22 ft of Head, but looking at the jump in Figure 2, the jump is about 1.8 ft. 

1. Where is the 0.5 ft of extra head is coming from ? 

2. The way the EGL is showing the jump, shouldn't the line before the jump be slopped in the opposite direction ? water flows always from high energy point to lower energy point. 


Tony, 

[MattAndersonPE]

Tony -

The downstream pipe's max velocity is 11.43 fps.   Pipe 10 controls this jump in the EGL.

SSA does not calculate the velocity of water within junction, nor does it perform peak flow step backwater calculations.  The image shows a downstream pipe with a significant velocity requirement needed to push the water from the junction into the outlet pipe.   To reduce this jump, enlarge the downstream pipe, or remove the static tailwater condition.

[MattAndersonPE]

Tony -

Forgive me for not responding to the 2nd point.

The Energy Grade line in a steady state step backwater analysis or peak flow situation will flow from high to low. 

SSA utilizes the St. Venant equations, balances both mass and momentum of the water over time, to arrive at a depth of water in the pipe and an average velocity of the pipe.    The flow into and out of those junctions is unsteady, and the velocity is computed as an average within the pipe.