Reservoir Discharge Controlled Using a Deadband

This GoldSim model demonstrates dynamic reservoir discharge control using a Controller element configured with the Deadband method. It simulates an ON/OFF outflow system where a fixed discharge rate is activated or deactivated based on the reservoir's storage volume relative to defined upper and lower boundaries. The Controller element monitors the reservoir volume (the process variable) and turns the discharge ON when the volume hits the upper boundary (Top) and OFF when it drops to the lower boundary (Bottom), incorporating hysteresis to prevent rapid cycling.

By utilizing the dedicated Controller element, this model accurately represents systems like pump operations or simple gate controls that exhibit hysteretic behavior. The deadband (the range between the Top and Bottom boundaries) ensures the outflow doesn't rapidly oscillate around a single target. This approach is valuable for simulating discrete operational rules and provides a robust alternative to simpler conditional logic or older methods using Status elements, especially leveraging GoldSim's ability to precisely detect when state variables cross threshold boundaries.

This model uses GoldSim's Controller element to manage reservoir discharge with a deadband logic, replacing older methods that might have used Status and Selector elements. Key components include:

• Pool ("Reservoir"): Represents the reservoir. Its volume typically serves as the process variable monitored by the controller.
• Controller1 The core logic element, configured as an Outflow Controller using the Deadband method. It monitors the Reservoir volume and determines the ON/OFF state of the discharge.
• Outflow_Capacity: Defines the fixed discharge rate (e.g., pump capacity or fixed gate release) applied when the controller state is ON.
• Deadband and Target: Defines the Top and Bottom boundaries for the Controller's deadband logic. The Controller allows defining these via "Target and Thickness" or "Top and Bottom" methods.
• Depth_Volume_Table: Used to convert between elevations and corresponding volumes and vice versa for defining the deadband boundaries in volume units, which is generally recommended when volume is the process variable.
• Discharge_Rate: Represents the actual outflow from the Reservoir Pool.
• Inflow/Evaporation: Placeholders representing other gains and losses to the reservoir.

Why Use a Deadband Controller?

Employing GoldSim's dedicated Deadband Controller element offers specific advantages for modeling ON/OFF control systems:

• Built-in Hysteresis: The element is explicitly designed to model systems with different ON and OFF thresholds, accurately capturing hysteretic behavior without requiring complex custom logic involving multiple elements like Status and Selectors.
• Prevents Oscillation: The deadband functionality effectively prevents rapid cycling ("chattering") of controlled equipment (like pumps or gates) that might occur with simple single-threshold logic, leading to more realistic and computationally stable simulations.
• Accurate Threshold Detection: When monitoring a state variable (like Pool volume), GoldSim's simulation engine can insert unscheduled updates (internal timesteps) precisely when boundaries are crossed, ensuring accurate switching behavior regardless of the specified reporting timestep length.
• Common Control Strategy: Directly represents a common real-world control strategy found in various applications involving upper and lower operational limits.

This method is ideal for simulating discrete (ON/OFF) controls with inherent hysteresis, such as pump management based on sump levels, simple gate operations triggered by water levels, or basic thermostatic controls.

Example Simulation Results

Below is an example time history chart showing the simulated reservoir water level relative to the operational deadband (defined by the Top and Bottom volume boundaries, which correspond to specific elevations). It also shows the resulting inflow and the ON/OFF behavior of the reservoir discharge as dictated by the Deadband Controller logic.

 Figure 2: Example time history results showing water level oscillating within the deadband range, inflow, and the resulting stepped ON/OFF discharge pattern from the Controller.