Hello Everyone,
I have a Channel of about 900m in length, in which the first 318m drops are given at every 40m of the channel about 1m drops as this can be seen in the profile of the channel to reduce the velocity at the remaining downstream of the channel about 582m(as shown in screenshot StormCad Solver). The cross-section of the channel varies with sizes(Side slopes, Width, Height) in different station intervals. Analysis was done with different solvers, this is done for better compatibility suitability for channels in which fixed flow is taken at the start as a base flow and in mid-interval addition of flow by urbanization taken due to lack of catchment area.
In comparison, when GVF-Rational (StormCAD) selection for analysis considering condition as backwater flow analysis as well as average velocity computation, the velocity is about approx 3m3/s for about start of the channel about 400m (Shown in the screenshot Cross Section Velocity (StormCad Solver)).
On other hand, while simulating on SWMM-Dynamic solver velocity shows negative velocity as shown in the screenshot CrossSection Velocity(SWMM Dynamic). Similarly when SWMM-Steady flow analysis is selected shows similar results computing with GVF-Rational as shown in the screenshot CrossSection Velocity (SWMM-Uniform) & Cross Section Velocity (StormCad Solver) expect places where drops are provided.
Profiles of the different computations of solvers are attached as screenshots.
Kindly, advise which solver to be used for the following data mentioned above. The main issue is to reduce the velocity in the channel with consideration of backwater flow.
https://drive.google.com/file/d/1sn9s1wP3iAraLVlgDUeOdSZZTMG5usxs/view?usp=share_link
Hello Azzemuddin,
For the GVF-Rational solver, you can find information on the different methods for calculating velocity here: Velocity Calculations and the Average Velocity Methods in SewerCAD and StormCAD.
With the Implicit or Explicit solvers, the velocity calculations will take into account other factors as part of the Saint-Venant equations used for these dynamic situations. I would recommend reviewing the Help documentation related to the Implicit and Explicit solvers.
With a negative velocity, it is possible you are looking at the results for the initial time step. The GVF-Rational solver is a peak flow calculation, where the Implicit and Explicit solvers would see the results change with time. You may want to either graph the velocity results or see if there is a Velocity (Maximum) field to look at.
Also related to the Implicit and Explicit solver, you would want to make sure the continuity error is relatively low. A higher continuity error would typically mean more unstable results. This link has information on troubleshooting unstable results in the Explicit solver: Troubleshooting unstable SewerGEMS and CivilStorm model results using the Explicit SWMM Solver.
For more information on the differences between the solvers, see the following link: Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM).
Regards,Scott
Hi Scott,
Thank you for sharing descriptive theory for the comparison of the explicit and implicit solver.
In my case study, it's a hilly area with steep slopes. In consideration to reduce the velocity downstream possible solutions of mild slope and drops are provided at every short interval in the upstream zone. Since I'm looking for a possible solver to get a solution as the flow is in a steady state, just like a peak flow.
As I think the best solver could be GVF-Rational with backwater analysis, but when I look results section for velocity it's not a huge difference when a drop of 1m is given. On the other way around I preferred the Explicit SWMM solver(uniform Flow), I found out that high velocities are found at the drops section. In comparison with the GVF solver, I don't see a difference in velocity.
Similarly, similar parameters were analyzed in HEC-RAS . The initial section velocities were similar to the result of the SEWERGEMS, but after the drop, the velocity increased and continued.
I hope you understand the situation for reducing the velocity, so need your advice to analyse such a situation in modelling.
Kindly, Suggest suitable solution for such a solution..
Regards
Azeemuddin Zeeshan
Hello Azeemuddin,
Did you try other velocity calculation methods? See the wiki provided earlier on this.
Regards,
Scott