One of SewerCAD’s many powerful and versatile project tools is Scenario Management. Scenarios allow you to calculate multiple "What If?" situations in a single project file. You may wish to try several designs and compare the results, or analyze an existing system using several different loading possibilities and compare the resulting profiles. A scenario consists of a group of alternatives, which are groups of actual model data. Both scenarios and alternatives are based on a parent/child relationship where child scenarios and alternatives inherit data from the parent scenarios and alternatives.
In this lesson we will use Scenario Management to set up the scenarios needed to test four "What If?" situations for the purpose of analyzing a new sanitary sewer system design. At the end of the lesson, we will compare all of the results using the Scenario Comparison tool.
If, at any time during this lesson the program asks, "Do you wish to reset all calculated results to N/A?" click NO.
Part 1 - Opening the Project File
For this lesson we will use the system designed in Lesson 2. Click the Open Existing File button in the Welcome dialog, or select File / Open from the pull-down menus to bring up the Open Project File dialog. Open the project you saved from Lesson 2, or find lesson3.swr (lesson3.dwg in the AutoCAD version) in the SWRC / Lesson directory.
In Lesson 2 we designed the gravity portion of this system using the automatic design tool. In this lesson, we will use scenario management to model different force main designs.
Part 2 - Creating Alternatives
First, we need to set up the required data sets (alternatives). An alternative is a group of data describing a specific part of the model. There are eleven alternatives: Physical Properties, Sanitary (Dry Weather) Loading, Infiltration and Inflow Loading, Known Flow Loading, Structure Headlosses, Boundary Conditions, Design Constraints, Initial Settings, Operational, Cost, and User Data. In this example, we need to set up a different physical alternative for each design trial we want to evaluate. Each physical alternative will contain different pressure pipe data.
Select Analysis / Scenarios from the pull-down menu to load the Scenario Manager. Click the Alternatives button on the left side of the Scenario Manager, and select the Physical Properties tab. In SewerCAD, we create families of alternatives. There are parent alternatives (base alternatives) and there are child alternatives. A child alternative inherits data from its parent. You can, however, override data inherited from the parent, making it local to the child.
Currently, there is only one Physical Alternative listed. The Base-Physical alternative contains the properties for the current undersized force mains. We would like to add a child of the Base-Physical alternative so we can inherit most of the data but change only the properties that we want to modify. Click the Add Child button and enter a descriptive name such as "Larger Pressure Pipes" for the new alternative and click OK.
The Physical Properties Alternative Editor for the new alternative will appear, and contains the data that was inherited from the parent alternative. Select the Pressure Pipes tab at the top of the dialog. Notice the legend at the bottom describing the check boxes. It indicates, all of our data is inherited. If you change any piece of data, the check box will automatically become checked because that record is now local to this alternative and not inherited from the parent.
Set up this design trial by making the changes shown in the Pipe Alternative Data table below. Click Close to exit the Physical Properties Alternative Editor and return to the Alternatives Manager.
Pipe Alternative Data
Change From: To:
Diameter (mm) Diameter (mm)
FM-1 200 300
FM-2 200 300
FM-3 200 300
Next, we will add another physical alternative for another design trial. Highlight the Base-Physical alternative and click the Add Child button. Enter a descriptive name for the new alternative, such as "Smaller Pump." Click OK to enter the Physical Properties Alternative Editor.
Select the Pump tab. For this trial, we will leave the existing system the same but with a different size pump. To change the pump curve, click the cell in the Pump Type column, and set it to Standard (3 point). Click the ellipsis (…) button to edit the pump curve. Change this design alternative by adding the data shown in the Pump Alternative Data table below and click OK. Click Close to exit the Physical Properties Alternative Editor and return to the Alternatives Manager.
Pump Alternative Data
Change From: To:
Head (m) Discharge (m3/min) Head (m) Discharge (m3/min) Shutoff 22.67 0 20 0 Design 17 24 15 19 Max Operating 0 48 0 38
Last, we will add a Physical alternative that combines the first two design trials in the same alternative for a third design trial. Highlight the "Larger Pressure Pipes" alternative and click the Add Child button. Enter a name for the new alternative, such as "Larger FM-3." Click OK to enter the Physical Properties Alternative Editor.
Select the Pressure Pipe tab. This alternative has inherited the new pressure pipe data that we entered in the "Larger Pressure Pipes" alternative. Change the diameter of FM-3 from 300 mm to 400 mm. Click Close to exit the Physical Properties Alternative editor and return to the Alternatives Manager.
You now have four Physical Properties alternatives. The base alternative contains the existing system’s data, while the other three contain several changes for different design trials. However, the rest of the data is the same.
Click Close to exit the Alternatives Manager and return to the Scenario Manager. We must now create the scenarios that will contain the Physical Properties alternatives we just created.
Part 3 - Editing Base Scenarios
You are now in the Scenario Manager. There is always a default Base scenario that is comprised of the eleven base alternatives, currently listed in the right pane. The left pane of the Scenario Manager contains a list of the scenarios. Only the Base is available initially, because we have not created any new scenarios. Alternatives are the building blocks of a scenario. A scenario is a group of the eleven alternatives and all of the calculation information needed to solve a model.
For our example, if we wish to analyze the three different design trials for the force main portion of our system, we must create a new scenario for each of the Physical Properties alternatives we created. The first step in this process is to rename the Base scenario to a more appropriate name and set the correct calculation options. Select Base Scenario, click the Scenario Management button, and select Rename from the pull-down menu. The scenario name in the left pane will become editable. Type a descriptive name for the scenario, such as "Existing System" and press Enter. Next, click the Scenario Management button and select Edit from the pull-down menu. Select the Calculation tab. Uncheck the Design check box in the Steady State section of the dialog. Click Close.
Part 4 - Creating Child Scenarios
The last step in setting up our scenarios is to create child scenarios. The new child scenarios will contain the Physical Properties alternatives created earlier. Highlight the base scenario entitled "Existing System" and click the Scenario Management button. Select Add / Child Scenario from the pull-down menu. You will be prompted for a scenario name. Again, the name should be descriptive, such as "Design Trial #1." Click OK.
Scenarios work in families just like alternatives, except scenarios do not inherit data directly. A scenario is a group of alternatives, so a child scenario will inherit the parent’s alternatives. To change the new scenario you need to change one or more of the alternatives.
Our new child scenario initially consists of the same alternatives as its parent scenario. We want to set the Physical Properties alternative to the first alternative we created, "Larger Pressure Pipes." Click the check box next to Physical Properties to make that alternative local to this scenario. Then, from the list box, select Larger Pressure Pipes. Click Close.
Next, make sure the base scenario entitled "Existing System" is selected and click Scenario Management / Add / Child Scenario. Enter "Design Trial #2" into the field and click OK.
Again click the check box next to Physical Properties and select Smaller Pump from the list box. Click Close when you are done.
To make a third child scenario, highlight the base scenario again and click Scenario Management / Add/Child Scenario. Enter the scenario name "Design Trial #3" into the field and click OK. Change the Physical Properties list box to Larger FM-3. Click Close.
Now we have four scenarios. The base scenario is our existing system. Each child scenario contains a different physical alternative. The first design trial resizes the pressure pipes, the second design trial resizes the pump, and the third design trial considers a different combination of pipe sizes. Now we need to calculate them.
Part 5 - Calculate and Compare
We are going to calculate all of the scenarios at the same time using the Batch Run tool. Click the Batch Run button on the left side of the Scenario Manager. Click Select / All, or select the check box next to each scenario, and click the Batch button. Click Yes at the prompt to run the batch for four scenarios. When it has finished computing, click OK.
You can see the results for each scenario by selecting it in the scenario list. Click the Results tab to see the selected scenario’s results. We can see that each scenario is different, but what exactly is different about them? We will use the Scenario Comparison tool to find out.
Click the Scenario Comparison button to start the Annotation Comparison Wizard. Select the Existing System scenario in the first list box and the Design Trial #1 scenario in the second list box, then click Next.
We will compare the results for pressure junctions and pressure pipes, so click the check box next to the Pressure Junction and Pressure Pipe and click Next.
Select Pressure from the first list box under the Attributes column for pressure junction annotation. You can edit the actual label in the Mask column. Click Next. Select Velocity from the first list box under the Attributes column for pressure pipe annotations and click Next. Verify that the annotation is correct and click Finished.
A plan view of the system with annotation displaying the difference between the two scenarios will appear. The difference between the two is found by subtracting Scenario 1 from Scenario 2. For example, say Scenario 1 has a total sanitary load of 4,000,000 l/d at a wet well, and Scenario 2, which represents a future scenario, has a total sanitary load of 4,500,000 l/d at the same wet well. Comparing total sanitary loads for Scenario 1 and Scenario 2 would result in annotation stating a difference of 500,000 l/d.
You can select different combinations of the four scenarios from the two list boxes and click the Update button to view the differences between the two. Or, click the Auto Update check box and the differences will automatically update every time you change the combination of scenarios in the list boxes. If you would like to learn more about the various results presentation methods available in SewerCAD, see Lesson 4.
Close the dialogs and save this project before proceeding to Lesson 4.