You are currently reviewing an older revision of this page.
This technote explains how to configure a Multi-species analysis (MSX) which is an advanced Water Quality Modeling extension.
Using a constituent analysis, a user can track a single constituent through a water distribution system, provided the constituent behaves according to one of the kinetic models (e.g. first order decay). However, some constituents (E.g. Multi-source chlorine decay) cannot be modeled this way because they are involved in significant multi-species reactions or their kinetics do not fit one of the existing models. To handle these cases, WaterGEMS and WaterCAD provides Multi-species Analysis, based on the EPANET-MSX model with a WaterGEMS or WaterCAD user interface. This is available in V8i SELECTseries 5 and greater.
Multi-species analysis allows for consideration of multiple interacting species in the bulk flow and on the pipe walls.
It can be accessed from Components > Water quality > Multi Species analysis setups (or Components>Multi Species analysis setups. for V8i)
To perform a multi-species analysis,
The time step for calculations that is used in the multi-species analysis is the one which is defined in the OPTIONS section of the Multi Species analysis setup. If it is not defined in the options of Multi Species analysis, then the default water quality time step is used which is 1/10th of the hydraulic time step.
NOTE : For detailed information on Multi Species analysis and Multi Species analysis model configuration, please navigate to the related topic in the in-program Help documentation.
Reference : More information about Multi Species analysis can be found in the EPA MSX manual.
EPANET Multi-Species Extension Software and User’s Manual
General Troubleshooting
If the multi species analysis fails to compute, try computing in a small test model for debugging purposes (to determine what is causing the failure).
For the actual model, ensure that the basic EPS is in good shape
Issue 1 - When computing, the following user notification is returned.
"Could not solve reaction equilibrium expressions"
If the model has a negative demand applied at a junction upstream of a tank try one of the following
Issue 2 - The model is slow to compute.
If there are adjacent tanks, that are hydraulically close, try combining them into a single equivalent composite tank.
See: Rapid flow oscillation between hydraulically close tanks
Mixing Chlorine and Chloramines
Understanding the Water Quality Time Step
Modeling DBP Formation - Water Quality Analysis
Rapid flow oscillation between hydraulically close tanks
Forum: Multi Species Analysis