Scenario and Alternative Management

 

 

 

 

 

 

 

 

 

 

OverviewThe purpose of this technote is to briefly discuss the scenario management in the Bentley Hydraulics and Hydrology products. There are also Quick Start Lessons related to Scenario Management. These can be found by opening the product and going to Help > Quick Start Lessons.

 

BackgroundScenario Management is one of many project tools available in Bentley Hydraulics and Hydrology products. Scenarios allow the user to calculate multiple "What If?" situations in a single project file. The user 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. Alternatives contain the actual model data. Calculation Options allows the user to run different types of analyses. The available items and properties listed for Alternatives and Calculation Options will vary from product to product.

     Applies To    

  Product(s):WaterGEMS, WaterCAD, HAMMER, SewerCAD, StormCAD, SewerGEMS, CivilStorm, Pondpack

  Version(s):V8i or V8 XM  Environment: N/A  Area: N/A  Subarea: N/A

 Original Author:

Scott Kampa, Bentley Technical Support Group

   

Scenarios and alternatives are 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.

As noted above, different products will have different available Alternatives. For simplicity, the screenshots below will show the alternatives list for WaterGEMS. The general steps involved will be the same across all products.

 

Scenarios: 

A Scenario contains all the input data (in the form of Alternatives), calculation options, results, and notes associated with a set of calculations. Scenarios let you set up an unlimited number of "What If?" situations for your model and allow you to modify, compute, and review your system under different conditions.

This section will describe how to create new Scenarios, how to switch between existing scenarios, how to calculate a batch run, and how to compare results from different scenarios.

Scenario Manager

The Scenario Manager allows you to create, edit, and manage an unlimited number of scenarios. When opening a new project, there will be one default scenario, called “Base”. If you want to model different conditions in a system, whether it is modeling peak demands versus average demands or the current system layout versus a proposed future system layout, you can create additional scenarios that reference the alternatives needed to perform and recall the results of each of your calculations.

The Scenario Manager can be opened by going to Analysis > Scenarios. You can also click the Scenario icon listed above the drawing pane.

Creating New Scenarios 

There are two methods to create a new scenario. First, you can select the New icon in the upper right and choose either Base or Child Scenario. As stated above, child scenarios will inherit data from the parent scenario.

Second, you can right-click on any scenario listed in the Scenario Manager, select New, and choose either Base or Child Scenario.

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.

Child Scenarios inherit data from a base scenario or other child scenarios. Child scenarios allow you to freely change data for one or more elements in your system. Child scenarios can reflect some or all of the values contained in their parent. This is a very powerful tool, giving you the ability to make changes in a parent scenario that will trickle down through child scenarios, while also giving you the ability to override values for some or all of the elements in child scenarios.

Changing the Current Scenario 

Once you have multiple scenarios, you will want to switch between them to view the properties and results in a given scenario. There are a few different ways of doing this. First, you can select the Make Current icon in the Scenario Manager. This will make the highlighted Scenario the active scenario.

Second, you can right-click on any scenario and select Make Current.

Third, there is a way of changing the current scenario outside of the Scenario Manager. In the main page, there is a pulldown menu listing the name of the current scenario. By clicking in this box, you will see a list of the available scenarios. Choosing a scenario from the list will set that scenario as current.

Note: If the pulldown is not available, it can be added. Right-click on the space around the other icons and select the Scenarios item. This will add the pulldown, as well as icon to open the Scenario Manager, Alternatives Manager, and Calculation Options Manager.

Batch Run 

You can compute your scenarios one at a time by making a scenario current and then computing the model. You can also compute more than one scenario consecutively by doing a Batch Run. As with many functions in Scenario Management, there are multiple ways of doing this. First, you can select the small triangle beside the Compute icon, then select Batch Run.

Second, you can right-click on any scenario, then select Compute, then Batch Run.

Either method will result in a new dialogue listing all available scenarios. Click the box beside the scenarios you wish to compute and then select Batch. Each selected scenario will then compute.

Note: Once multiple scenarios are computed, either manually or with a batch run, it is possible to compare results either by switch between scenarios (see “Changing the Current Scenario” above) or by graphing given elements in the model.

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. In order to view the scenario properties, double-click on the scenario. Alternatively, you can right-click on the scenario and choose Properties.

Displayed in the Properties dialog will be a list of the alternatives associated with the scenario. If you have created a new scenario, you will likely wish to change to an alternative that reflects the properties of the scenario. 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. 

When you create a child scenario, by default it inherits the selection/configuration of alternatives of the parent scenario. In which 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. Select the item “New”. You will be prompted to enter the name for the new alternative. After entering the name, the new alternative will be selected for the scenario.

Note: The new alternative will now be listed in the Alternatives Manager.

Alternatives:

Alternatives Manager 

The Alternative Manager allows you to 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.

The Alternative Manager can be opened by going to Analysis > Alternatives. You can also click the Alternatives icon listed above the drawing pane.

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.

Steps to create new alternatives are the same as the steps to create new scenarios. See the section “Creating New Scenarios” above.

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 window.

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.

Information on the individual alternatives available in the different hydraulics and hydrology software can be found by searching the Help menu for the product.

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

Calculation Options 

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

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

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

Properties contained in the calculation options will differ between different hydraulics and hydrology software. Information on what properties are available can be found by searching the Help menu for the product.

Scenario Comparison 

The scenario comparison tool is a new feature in the V8i builds of the products. It enables you to compare input values between any two scenarios to identify differences quickly. While users of older versions have previously had the capability to open a child scenario or alternative and compare it with its parent, this tool extends that capability in that you can compare any two scenarios or alternatives (not necessarily parent-child) and very easily detect differences.

The scenario comparison tool can be accessed by choosing Tools > Scenario Comparison or by selecting the Scenario Comparison button from the toolbar. If the button is not visible, it can be added using the "Add or Remove Buttons" drop down from the Tools toolbar.

Upon first opening the scenario comparison tool, a dialog opens which gives an overview of the steps involved in using the tool. Pick the New button (leftmost).

This opens a dialog which allows you to select which two scenarios will be compared.

The scenario manager button next to each selection gives you the ability to see the tree view of scenarios. Chose Okay to begin the scenario comparison process. What is initially displayed is a list of alternatives and calculation options. Those with identical properties are displayed with a yellow background. Those with different properties are displayed with a pink background. The background color can be changed from pink to any other color by selecting the sixth button from the left and then selecting the desired color.

The screenshot below shows that the Demand alternative is different between the scenarios. There is a second tab for Calculation Options which shows if the calculation options are different between scenarios.

To obtain more detailed information on differences, highlight one of the alternatives and select the green Compute icon at the top of pane (fourth button).

This initially returns a summary of the comparison which indicates the time when the comparison was run, which scenarios were involved, and the number of elements and attributes for which there were differences.

By picking "Differences" in the left pane for the alternative of interest, you can view the differences between alternatives. In this display, only the elements and properties that are different are shown with a pink background. In the example below, sixteen junctions have different demands between the two alternatives. Separate tables are generated for each element type.

Using the buttons on top of the right pane, when Differences is selected, you can create a selection set of the elements with differences or highlight those elements in the drawing. This is very useful for finding elements with differences in a large model.