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How to eliminate spike flow at the inlet of the reservoir?

Hi,

I am trying to balance the flow going into a reservoir. However, there is a snapshot showing a spike which has made me very hard to see the tolerance. I realized the spike happened when the reservoir level reach to the highest level i set at the control or maximum level. Could anyone suggest what is the best way to set a control at the reservoir?

 

 

 

 

Parents
  • Azizah,

    In order to help you out I would need to see the model for this issue in order to give you an answer. There are two options for sharing your model files on BE Communities. If you would like the files to be visible to other members, compress the files into a zip file and upload them as an attachment using the ‘Advanced Reply editor’ before posting. If your data is confidential, you can follow the instructions in the link below to send it to us via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley.

    http://communities.bentley.com/content/bentleysecurefilesupload.aspx

    I'm assuming the spikes that you are referring to which you want to eliminate are at pipe P-06179, correct?

    Regards,
    Mark

    Mark

  • Hi Mark,

    I have uploaded the model on the secure upload site.

    Yes, I want to eliminate the spike at pipe P-06179 and P-07630 also. These two pipes are the inlet to two reservoirs (R-00017 and R-00003).

    If you still remember, the error notification " node is disconnected" when I used the negative demand is still appearing.

    Hope you could help me to solve this also. TQ for your help

    Regards,
    Azizah
  • Azizah,

    You have a control on pipe P-11050 that is controlled by the level in tank R-00014 which closes pipe P-11050 when the level in the tank gets to 6.52m. The problem is the tank is only 6.5m at the maximum, so your control never gets that high. Try setting that control to go off at 6.49 m and that should resolve your issue.

    Regards,
    Mark

    Mark

  • Azizah,

    If my above solution doesn't solve your issue please let me and please provide me with a detailed description using element labels where necessary to help me understand where I need to be looking to observe the problem you are seeing. In the model that you sent I've checked the areas that you referred to as the problem areas before and I am not seeing a problem there.

    Regards,
    Mark

    Mark

  • Hi Mark,

    Your solution is not solved my problem yet.

    This is about reservoir overflow. For my model, there are few reservoirs are overflow. Take example of tank label R-00014, the maximum level is 6m and the inflow is from borehole pump which is pump for 24hrs nonstop. If i set the control to go off at 5.9m, there would zero flow when level reach the max level which is in reality there are still have a flow into the reservoir. That is why the flow at the inlet  have a spike.

    For my model calibration to solve this i had introduced a dummy reservoir which is allowed the overflow and increased the max level and level to shut at control. That is why u doesn`t see the problem at the area i mentioned before. However, added the dummy reservoir  to solve this problem doesn`t looked practical. I just hope that u could provide other solution for this problem.

    Your help really appreciated.

    Azizah

  • Azizah,

    I'm a little confused as to what you have done in the model. Do you have a copy of the model that doesn't include all your dummy reservoirs in it? If so, can you please send that to me so I can have a look at the model that shows the issue you are seeing because right now in the current condition of the model I don't see a problem.

    Also, did you have those dummy reservoirs in the model before when I looked at it? I don't have the old model and don't recall if they were in the last version.

    Regards,
    Mark

    Mark

  • Azizah,

    I'm not sure if what I did was correct for how you have your model setup, but I tried to just delete all the reservoirs the you had the named "dummy". After I did that I think I saw the spikey opening and closing pattern problem you might have been referring to on pipes P-08299 and P-11333. It looks like it was the same problem as before too and has the same solution, if I'm seeing the problem you were referring to in your post above. I'm not really sure if I am though because the exact problem isn't 100% clear to me.  

    Based on what I have seen though from the location that you referenced in your screen capture above your problem is with the control labeled LC25268. The control reads: IF R-00014 Level >= 6.49 m THEN P-11050 Pipe Status = Closed  ELSE P-11050 Pipe Status = Open

    The problem with the control is that once the level of the tank drops below 6.49m then the pipe opens again. Just as with the last problem with the controls this type of setup will can cause sharp spikes flow because you're opening and closing the pipe rapidly until the flow out of the tank is great enough to drop the tank level fast enough and far enough below the point where the controls oscillate back and forth. What you'll need to do in order to fix this issue is make sure there is some kind of gap between the levels that cause the pipes to open and close. For example,  "IF R-00014 Level >= 6.49 m THEN P-11050 Pipe Status = Closed"  and then have a separate statement that reads, "IF R-00014 Level <= 3.0  m THEN P-11050 Pipe Status = Open". Keep in mind that these are just example levels and that you should use whatever levels these tanks operate at in the real systems for creating your controls.

    The other issue that you're running into is I don't think you are seeing all the little changes that are made in between your time steps because you have the "reporting time step" property in your calculation options set to report at a constant time step of 0.25 hours. When you're looking at the graphs this prevents you from seeing everything that occurs in between those 15 minute intervals. If you set the reporting time step to <All> that will allow you to see everything that is happening over the entire course of your simulation when you graph elements.

    If there are still saw-tooth pattern flow problems in your model after making these changes have a look at the controls related to the area in question and make sure there is some gap between whatever is controlling the elements. If there are still issues please let me know what you are seeing and where exactly you're seeing it, so I know exactly where to look in your model to observe the issue.

    Regards,

    Mark

    Mark

    Answer Verified By: Sushma Choure 

Reply
  • Azizah,

    I'm not sure if what I did was correct for how you have your model setup, but I tried to just delete all the reservoirs the you had the named "dummy". After I did that I think I saw the spikey opening and closing pattern problem you might have been referring to on pipes P-08299 and P-11333. It looks like it was the same problem as before too and has the same solution, if I'm seeing the problem you were referring to in your post above. I'm not really sure if I am though because the exact problem isn't 100% clear to me.  

    Based on what I have seen though from the location that you referenced in your screen capture above your problem is with the control labeled LC25268. The control reads: IF R-00014 Level >= 6.49 m THEN P-11050 Pipe Status = Closed  ELSE P-11050 Pipe Status = Open

    The problem with the control is that once the level of the tank drops below 6.49m then the pipe opens again. Just as with the last problem with the controls this type of setup will can cause sharp spikes flow because you're opening and closing the pipe rapidly until the flow out of the tank is great enough to drop the tank level fast enough and far enough below the point where the controls oscillate back and forth. What you'll need to do in order to fix this issue is make sure there is some kind of gap between the levels that cause the pipes to open and close. For example,  "IF R-00014 Level >= 6.49 m THEN P-11050 Pipe Status = Closed"  and then have a separate statement that reads, "IF R-00014 Level <= 3.0  m THEN P-11050 Pipe Status = Open". Keep in mind that these are just example levels and that you should use whatever levels these tanks operate at in the real systems for creating your controls.

    The other issue that you're running into is I don't think you are seeing all the little changes that are made in between your time steps because you have the "reporting time step" property in your calculation options set to report at a constant time step of 0.25 hours. When you're looking at the graphs this prevents you from seeing everything that occurs in between those 15 minute intervals. If you set the reporting time step to <All> that will allow you to see everything that is happening over the entire course of your simulation when you graph elements.

    If there are still saw-tooth pattern flow problems in your model after making these changes have a look at the controls related to the area in question and make sure there is some gap between whatever is controlling the elements. If there are still issues please let me know what you are seeing and where exactly you're seeing it, so I know exactly where to look in your model to observe the issue.

    Regards,

    Mark

    Mark

    Answer Verified By: Sushma Choure 

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