Overview

The purpose of this technote is to address the engine compatibility modes and new calculation options that have been added to Bentley WaterCAD/WaterGEMS/Hammer V8i Select Series 2 (SS2). Additional information may be found in the Help menu of each program.

Background

The change in the Bentley products to include the upgraded EPANET engine was designed so that the user can turn it off and is even disabled (by default) for existing models. Only new models will have the new behavior turned on (by default). All changes to the user interface are fairly minor and are purely controlled at the calculation options level.

The new user interface includes 4 new calculation options added under the ‘Hydraulics’ section of the Calculation Options dialog. Each option will be covered in detail below.

Engine Compatibility Modes

The ‘Engine Compatibility’ Calculation option in V8i SS2 replaces the ‘Use EPANET Compatible Results?’ option, as seen in V8i SS1. In previous versions of WaterCAD/GEMS/Hammer (prior to V8i SS2), there was a ‘Use EPANET Compatible Results?’ option. When set to true, you were using EPANET 2.00.10. The software has been extended to include compatibility modes, which now includes the old behavior based on EPANET 2.00.10, as well as the revised engine changes in EPANET 2.00.12.

There are now 4 engine compatibility modes.  

WaterGEMS 2.00.12 – this engine is based on the EPANET 2.00.12 engine, including Bentley modifications. Choose this option to get all the latest engine improvements and fixes made by Bentley and an engine mode that is based upon EPANET 2.00.12.This is the default for new models. Meaning any new model created in WaterGEMS V8i SS2 will default to the ‘WaterGEMS 2.00.12’ engine compatibility option.

WaterGEMS 2.00.10 – this engine is based on the EPANET 2.00.10 engine, including Bentley modifications. Choose this option to maintain compatibility with previous versions of WaterGEMS (meaning V8i SS1 and earlier) where the computational engine is based upon EPANET 2.00.10. This is the default for upgraded (existing) models. Note: the ‘Use Linear Interpolation for Multi Point Pumps?’ option is FALSE by default in existing models as well. These default options are designed to make the transition smoother for users.

IF an existing model has ‘Enable EPANET Calculation Results?’ set to TRUE, then the ‘Use Linear Interpolation for Multi Point Pumps?’ option is hidden (as it will not apply).

EPANET 2.00.12 – models run using this engine have results that are compatible with EPANET 2.00.12. If choosing a version of the EPANET engine, any enhancements, calculation corrections, bug fixes, etc. made by Bentley will be disabled to match the specific EPANET version results. Imported EPANET models will default to the appropriate EPANET version.

EPANET 2.00.10 – models run using this engine have results that are compatible with EPANET 2.00.10.

Note: The following engine compatibility matrix is included in the WaterGEMS/WaterCAD/Hammer V8i Select Series 2 Help file (Modeling Capabilities>Calculation Options>Engine Compatibility Calculation Option).

Additional Calculation Options

If the user has selected either the WaterGEMS 2.00.12 or EPANET 2.00.12 versions, there are three additional calculation options now available. These options are the same for both the EPANET and WaterGEMS 2.00.12 engines.

Convergence Check Frequency – The Convergence Check Frequency option sets the number of solution trials that pass during the hydraulic balancing before the status of pumps, check valves, flow control valves (FCV) and pipes connected to tanks are once again updated. The default value is 2 (meaning that status checks are made every other trial). A value equal to the maximum number of trials would mean that status checks are made only after a system has converged. The frequency of status checks on pressure reducing (PRV) and pressure sustaining valves (PSV) is determined by the Damping Factor option.

Convergence Check Cutoff – The Convergence Check Cutoff option is the number of solution trials after which periodic status checks on pumps, check valves, flow control valves (FCV) and pipes connected to tanks are discontinued. Instead, a status check is made only after convergence is achieved. The default value is 10 (after 10 trials, instead of checking status every “convergence Check Frequency” trials, the status is only checked after convergence is achieved).

Damping Limit – The Damping Limit is the accuracy value at which solution damping and status checks on PRVs and PSVs should begin. Damping limits all flow changes to 60% of what they would otherwise be as future trials unfold. The default value is 0 (zero), which indicates that no damping should be used and that status checks on control valves are made at every iteration. Damping might be needed on networks that have trouble converging. A limit of 0.01 is suggested (relative to the default calculation hydraulic accuracy of 0.001).

Additional Post Calculation Warnings

Post Calculation warnings have been added to advise a user if they are using any features that are NOT supported by EPANET when they are running with one of the two EPANET compatibility settings. These are POST calculation and will not be displayed when validating a model (i.e. these calculation warnings are only displayed when computing a model.

See Also

Product TechNotes and FAQs

Haestad Methods Product Tech Notes And FAQs

[[General WaterGEMS V8 FAQ|General WaterGEMS V8 FAQ]]  

External Links

Water and Wastewater Forums

Bentley Technical Support KnowledgeBase

Bentley LEARN Server