Why are there so many extra element types listed for WaterGEMS and WaterCAD, such as surge tank, rupture disk, periodic head-flow?
These elements were added in version 08.09.400.34 to support the our transient simulation product, Bentley HAMMER. Models developed in WaterGEMS or WaterCAD can be directly opened in HAMMER. So, the user can lay out their transient related elements in their WaterGEMS/CAD hydraulic model, open the model in HAMMER and be ready to perform a transient simulation. The user can then re-open that model back in WaterGEMS if they'd like, without losing information on the transient elements. The following is a list of transient elements and how they are handled during a WaterGEMS or WaterCAD steady state or EPS simulation:
•Periodic Head/Flow - Element using Head: A reservoir with the HGL determined from the sinusoidal wave properties, or from the head pattern. Only the initial (time zero) HGL is applied so that the steady state analysis will correspond to the transient initial conditions.
•Periodic Head/Flow - Element using Flow: A junction with demand determined from the sinusoidal wave properties, or from the flow pattern. Only the initial (time zero) flow is applied so that the steady state analysis will correspond to the transient initial conditions.
•Air Valve: If the "Treat Air Valve as Junction" property is set to True the Air Valve is loaded as a junction with no demand. If the "Treat Air Valve as Junction" property is set to False, the air valve is loaded such that it opens the system to atmosphere. This is most commonly used to simulate high points in pumped sewer systems, so the default behavior is to treat the air valve as a junction. See this TechNote for details.
•Hydropneumatic Tank: A hydropneumatic tank is loaded as a normal tank with the properties of the tank being dictated by the tank calculation model that is used. This means that it either follows the gas law or the constant area equivalent method to calculate a change in inflow and outflow. For example, if you set the tank to use the gas law, the tank HGL rises and falls according to the PV = nrt formula.
•Surge Valve: Junction with no Demand.
•Check Valve: Short Pipe with a Check Valve in line with the direction of flow.
•Rupture Disk: Junction with no demand.
•Discharge to Atmosphere: For the Orifice and Valve types this element is loaded as a junction with emitter coefficient determined by the flow and pressure drop properties. If either of these properties are invalid (<= 0) then no emitter coefficient is loaded. Furthermore, for the valve type if the valve is initially closed, no emitter coefficient is loaded. For the rating curve type this element is loaded as a reservoir connected to a GPV with rating curve used as the GPV headloss curve.
•Valve with linear area change: GPV with a headloss curve based on the valve's discharge coefficient.
•Turbine: GPV using the turbine's headloss curve.
•Orifice between pipes: GPV with a headloss curve calculated from the nominal head/flow loss using the orifice equation.
•Surge Tank: Without a check valve, this element is loaded as a tank. With a check valve this element is loaded as a Junction.
How are surge tanks and hydropneumatic (hydro) tanks used in WaterGEMS and WaterCAD models?