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Simulation Objects
Inflow Stage Table Look Up Method
The “Inflow Stage Table Look Up” method was added to the Reach object. This method uses inflow to determine the stage. It was added to avoid some of the issues that occur when a reach re-dispatches and uses the existing “Stage Table Look Up” method. A full description of both methods is Stage in Objects and Methods.
Also, for both of these methods, negative values in the stage tables are no longer necessary. If the flow is less than the value on the stage table, the smallest value is used.
Reach Seepage Routing method
A new method, “One Timestep Seepage Lag” was added to the reach “Seepage Routing” category. This method lags the computed Seepage by one timestep. This method was added for use with the “Stage Table Lookup” stage calculation and “Head Based Seepage” calculation to provide an explicit solution on the reach. For more information, please see One Timestep Seepage Lag in Objects and Methods.
Also, Seepage can now be input or set by a rule for any of the seepage methods.
Variable Time Lag Routing
Outflow was removed as a required unknown for dispatch conditions. This makes it more consistent with other dispatch methods.
Spill Capacity Fractions:
New functionality was added to the reservoir objects to allow better modeling of Spill. For each type of spill—Regulated, Unregulated, and Bypass—Capacity fraction slots were added to represent the fraction of the spillway that is available. For example, the Bypass Capacity Fraction is used to specify the percentage of the Bypass works that is available. See the spill methods Spill in Objects and Methods (for the level power reservoir).
Regulated Spill Overflow
A new category, “Regulated Spill Overflow”, and method “Closed Gate Overflow” were added to represent uncontrolled flow that spills over a regulated spill structure that is closed for maintenance or other reasons. See Regulated Spill Overflow in Objects and Methods for more information (on the level power reservoir).
Spill slots linked to Expression Slots
A change was made to the spill methods to check if Bypass or Regulated Spill are linked to an expression slot. If they are linked and they have a valid value, they are treated as known values and are not re-computed. Note, the expression slots should be configured to evaluate at the beginning of the current timestep to make this linking approach work correctly.
Slope Power Reservoir: Editing of Column labels on select slots
Changes were made to allow user editing of Slot Column labels for the following two slots on the Slope Power Reservoir:
• Partition Flow Parameters
• Partition BW Elevation
Power Reservoirs - Unit Power Methods
A new power method, Unit Power, was added to better model power production at the individual unit level. This method uses a three dimensional table that contains the columns Operating Head, Turbine Release, and Power for each unit in the plant. For more information, see Unit Power Table in Objects and Methods.
Also, as part of the Unit Power Method, the following categories and methods were added. They are all dependent on having the Unit Power Method Selected:
• Startup category and Unit Lumped Cost method: Used to compute the cost of starting or stopping one or more units. For more information, see Unit Lumped Cost Method in Objects and Methods.
• Head Loss category and Shared Penstock Head Loss method: Used to compute additional head loss that occurs when individual units share a penstock. Shared Penstock Head Loss method in Objects and Methods
• Cavitation category and Unit Head and Tailwater Based Regions method: Used to check if a unit is operating in a cavitation region. Unit Head and Tailwater Based Regions in Objects and Methods
• Avoidance Zones category and Unit Head Based Avoidance Zones method: Used to check if a unit is operating in an avoidance region. Unit Head Based Avoidance Zones in Objects and Methods
• Frequency Regulation category and Unit Frequency Regulation method: Used to model frequency regulation (Note , not implemented fully). Unit Frequency Regulation in Objects and Methods
U Flag
The U flag has been added for use with the new Unit Power method. The flag is set on Energy or Turbine Release and causes the slot to be considered an Input, but no value is required. The flag indicates that the unit level values (Unit Turbine Release or Unit Energy) will be specified. It can be set on the Slot dialog, through the SCT, or using a Rule.
Thermal Object
Economic Valuation Categories
The ThermalReplacementValueCategory has been removed and replaced by the following categories:
• Linear Economic Value - Linear Economic Value in Objects and Methods - This is a new approach to valuation. It is a simplified version of the existing Block evaluation where only a single block is used.
• Thermal Unit Replacement Value - Thermal Unit Replacement Value in Objects and Methods
Each category contains a default, no-action method and a method that does that type of evaluation. Thus, both optimization and simulation may have up to three independent evaluations: Linear, Block, or Thermal Unit Replacement. Accordingly, each type of evaluation has its own slots which are typically the existing slots with either Linear, Block, or Thermal added to the beginning of the name.
For each method, the inclusion and ordering of power sources are now in a table. The tables may differ for different evaluations. Previously the ordering was specified by selection of specifically named methods.
The following slots have been removed, but their functionality has been replaced with new slots specific to the economic evaluation methods:
• Avoided Operating Cost
• Net Avoided Operating Cost
• Conventional Replacement Value
• Pump Replacement Value
• Allocated Replacement Value
• Marginal Operating Costs
• Previous Marginal Operating Costs
• Total Values
Also, the Thermal Cost slot is no longer used. It used to be needed to facilitate the optimization formulation. The Block Hydro Capacity Slot has been eliminated because it is not used in the new optimization controller.
Additional information on converting a thermal object to this new approach can be found Modeling a Thermal Object in Optimization.
Regulation Category
On the Thermal object Regulation category, the name of the method Regulation was changed to Two Sided Regulation. For more information on this method, see Regulation in Objects and Methods.
System Startup Cost
On the Thermal object, a slot System Startup Cost was added as a general slot.
USACE - SWD Functionality
A number of performance related changes were made to speed up U.S. Army Corp of Engineers - Southwest Division (USACE-SWD) models. These include:
• No dispatching beyond forecast period
• No setting of values beyond forecast period in the Reach step response routing
• Caching of routing vectors in the Computational Subbasin, and
• Implementing a custom top/down dispatching order in situations where slots are being set on a number of objects across the network.
These changes were made explicitly for USACE models and should not adversely affect other models. The described behavior only occurs when there is a Computational Subbasin with Operating Level Balancing method selected in the Flood Control category and there is a Forecast Period slot.
In addition, a specific document was developed that describes all of the functionality used in USACE-SWD models. It can be found Conceptual Overview in USACE‑SWD Modeling Techniques.
Revised: 08/02/2021