G'day Team,
Can someone please tell me how to change the MSX units for the pre-defined term 'D' from feet to meters?
The MSX Manual states that Diameter can either be in Feet or Meters, however no-where does it say how to change it or what the unit selection is based on.
I have the Area units set to M2, which I thought would have set the MSX to use meters for D, however it's still using feet.
Context:
I'm back after 4 years trying to solve the problem of modelling wall decay in MSX. It had fallen off my priority list before I was able to get it to work last time but here I am again.
I intend to model two wall decay theories, EXPBIO (referenced in this previous query) ( RE: How to include Mass Transfer Coefficient into MSX ) and first order. The first order method still needs to be done in MSX to incorporate bulk decay modelling.Yashodhan provided a great answer to the EXPBIO query outlining how the STEP function can be used to select between different equations here: Adding custom parameters and equations with Multi Species Extension (MSX) . However please note that he states that the equations used in that example are indicative only, they don't combine wall decay with bulk decay correctly.
P.S.
If anyone can also explain how the 'Wall Species' in WaterCAD MSX works it would be greatly appreciated. I ran a test model where I simply set the wall species RATE to 1 (e.g. RATE W 1) and the results make no sense to me whatsoever.
Thank you,
Ryan Catling
Hello Ryan,
For the units issue, we are checking with our development team for input.
For the wall species question, are you able to provide a copy of the sample model you mentioned. This would help to better understand what is happening.
Regards,
Scott
Uploaded (confidential) "BDS.wtgpkg"
If anyone else comes across this problem a workaround you can use to substitute for D is to replace it with 1/(250*AV). This will work when you have Area units set to M2 and your equation requires diameter in meters.i.e. D (m) = 1/(250*Av) when Av is in m^2/L
Answer Verified By: Ryan Catling
Thanks for the information. We received the model and will look into this to provide some feedback soon.
Based on what the developers are seeing in SewerGEMS, the diameter units will need to be in feet. In MSX, an INP file is used and the units (feet or meters) is based on the the type of units being used in the INP file itself. However, the MSX module within WaterGEMS does not use the INP file. All calculations within WaterGEMS is done in US units. If a model uses SI units, internally they are converted to US units when running the model. For this reason, pipe diameter units will be expressed in Feet. If you workaround works, that should work as well.
For the wall species results, this appears to be working as expected. The developers tested with a wall specifies of 1, which would mean that the there is a constant linear growth. Note that wall species only applies to pipes, and not tanks. Though the wall species is defined in the [TANKS] section, the wall species is not used. This is mentioned in the MSX manual.
In the model, you are using the following global initial conditions (i.e., 0 for all pipes).
[QUALITY]GLOBAL W 0
With the other input, the pipe values start at 0, then grow linearly (rate = 1). Tank values start at 0 and stay at 0 because wall species don’t apply to tanks. I will be updating the MSX wiki article with this information.