Product(s):	OpenRoads Designer
Version(s):	10.00.00.120+
Area:	Subsurface Utilities
Original Author:	Holly Herring, Bentley Technical Support Group

  

Understanding Scenarios and Alternatives

Global vs. Exceptional

Given that

• there are hundreds of properties involved in hydraulic design and calculations
• regulatory agencies often require analysis on multiple variations of constraints (such as multiple storm events)
• the engineering design process itself often requires evaluation of alternative solutions

having a logical and manageable system to manage and compare the variations and permutations in the hundreds of properties is essential to ensure optimum design.

StormCAD for OpenRoads groups similar properties into function-based groups called Alternatives. Calculations are performed on bundles of Alternatives called Scenarios.

Understanding Scenarios and Alternatives is essential in using StormCAD for OpenRoads effectively:

• Property - a property is any stored characteristic of a model element. Examples include:
  • a single numeric quantity such as a pipe’s Diameter, Length, and Roughness.
  • a Yes/No toggle such as Design Conduit?
  • A value from a list such as Design or Analysis for Calculation Type
• Alternative - an Alternative is a logically organized set of properties. Examples include:
  • The Physical Alternative groups physical data for the network's elements, such as elevations, sizes, and roughness coefficients.
  • The Design Alternative groups engineering criteria that will be applied during calculations such as velocity limits and criteria that may or may not be applied during calculations such as adjusting pipe diameters and inverts.
  • Rainfall Runoff Alternatives allow different storm events to be used in calculations.
• Scenario - a Scenario is a list of Alternatives used in a Calculation event. This "bundling" of Alternatives lets you easily generate system conditions that mix and match groups of data that have been previously defined. Note that Scenarios do not actually hold any attribute data—the referenced alternatives do.

Scenarios and Alternatives have the ability to "inherit" properties from other Scenarios and Alternatives. These Parent-Child relationships are a critical tool in easily managing variations from global properties.

 Scenarios

Scenarios let you calculate multiple "What If?" situations in a single project file. You can try several designs and compare the results, or analyze an existing system, using several different input alternatives, and compare the results.

A Scenario is a set of Alternatives and Calculation Options. A Scenario contains all the input data (in the form of Alternatives), calculation options, results, and notes associated with a set of calculations. Alternatives contain the actual model data. Calculation Options let you run different types of analyses.

Scenarios and Alternatives can be independent or based on a parent/child relationship, where a Child Scenario or alternative inherits data from the parent scenario or alternative. This can be useful in situations where a new scenario will use most of the model data from an existing scenario, with only minimal changes to an alternative.

Scenario Manager

The Scenario Manageris the primary interface for creating editing, and managing an unlimited number of Scenarios.

When creating a new project, Scenarios and Alternatives are copied from the Hydraulic Seed File.

There must be at least one scenario. Additional Alternatives and Scenarios are easily created to handle any design requirements. Examples include:

• Competing physical layouts may be managed by different Physical Alternatives.
• Different Storm Frequencies may be managed by different Rainfall Runoff Alternatives.

There are two types of Scenarios: Base Scenarios and Child Scenarios.

Base Scenarios contain all of your working data. When you start a new project, you begin with a default Base Scenario. As you enter data and calculate your model, you are working with this default Base Scenario and the alternatives it references.

When a Child Scenario is created, it inherits its data from its Parent. More precisely, its Alternatives and Calculation Options are links to the Alternatives and Calculations Options of its parent.

Scenario Properties

As stated above, scenarios are a compilation of alternatives and calculation options. Viewing, changing, and managing the different alternatives associated with a scenario is done through the Properties dialog.

To view the scenario properties, double-click on the scenario, or right-click on the scenario and choose Properties.

A list of the alternatives associated with the scenario will be displayed in the Properties dialog.

If you have created a new Base Scenario, all of the alternatives will default to the Base Alternatives.

If you created a Child Scenario, the scenario will initially inherit all of the alternatives from the parent scenario. In this case, you will see the "I" next to the name of the alternative. If you pick an alternative without the "I," then the Child Scenario will no longer inherit the changes in alternatives made in the parent scenario.

To change any alternative for a scenario, click the pulldown beside the scenario name and select the alternative.

If you have not yet created an alternative for the scenario, you can create a new alternative here as well, by selecting the "<New…>" item. You will be prompted to enter the name for the new alternative – after which the new alternative will be selected for the scenario, and listed in the Alternatives Manager.

Alternatives Manager

The Alternative Manager lets you create, view, and edit the alternatives that make up the project scenarios. The dialog box consists of a pane that displays folders for each of the alternative types which can be expanded to display all of the alternatives for that type and a toolbar.

As with Scenarios, there are two kinds of Alternatives: Base Alternatives and Child Alternatives. Base Alternatives contain local data for all elements in your system. Child Alternatives inherit data from Base Alternatives or even other Child Alternatives. The data within a Child Alternative consists of data inherited from its parent and the data altered specifically by you (local data).

Remember that all data inherited from the Base Alternative is changed when the Base Alternative changes. Only local data specific to a Child Alternative remain unchanged.

Editing Alternatives

To edit an alternative, expand the tree so that all of the alternatives for a given category are listed.

There are a number of ways to open an alternative. 

You can double-click on the alternative.

You can also highlight the alternative and select the Open icon.

Finally, you can right-click the alternative and select Open. This will open a new dialog.

Each alternative will have different properties. Any column that is shown as white is an editable field. Columns in yellow are not editable from the alternative, but in some cases may be editable from other places in the model, such as the FlexTables or Properties.

The first column in any alternative editor contains a series of check boxes, which indicate the records that have been changed in this alternative. If the box is checked, the record on that line has been modified and the data is local, or specific, to this alternative. If the box is not checked, it means that the record on that line is inherited from its higher-level parent alternative. Inherited records are dynamic. If the record is changed in the parent, the change is reflected in the child. The records on these rows reflect the corresponding values in the alternative's parent.

Note: changes made in the drawing pane, Properties, and Flextables will automatically make changes to the values in the active alternative.

Calculation Option:

The Calculation Options Manager lets you create, view, and edit the calculation options available for your scenarios. The dialog box consists of a pane that displays the calculation options created.

Note that the parent/child function is not used in for calculation options. New calculation options can be created by clicking the New icon.

To edit the calculation options, double-click on the one you want to edit. This will display the properties of the calculation options in the Properties dialog.

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