Using multiscenario to vary wind conditions for a dispersion modelling project

The following section provides a walk through of a multiscenario project setup to define variations of a dispersion scenario. The intention is to demonstrate the capability of the multiscenario function to easily create simulations with different wind directions and speeds without the need to manually edit cs files or manually create new scenarios in CASD.

The dispersion scenario consists of a single ammonia jet release a vessel at an onshore refinery. The release scenario is based on a 50mm diameter leak and a pressure of 10 barg.

Creating a multiscenario project

1. Firstly, an existing dispersion scenario opened in CASD to be used as the base scenario. A multiscenario project is then created via: File -> New project.

2. Within the New Project dialog pop-out the project name is set (Ammonia Dispersion Project) and the Input Directory, Scenario and Output Directory fields are all left as defaults.

3. After clicking OK, the project should switch to the multiscenario layout as below.

Note: since the project was created whilst a scenario was open in CASD, the input directory and scenario should already relate to the current scenario by default. By leaving Output Directory as default, a folder called output will be created within the working scenario directory.

Varying wind speeds

1. Add a node for wind conditions: by selecting the right-most node in Graph View, right-click -> Add -> Wind (shown below).

2. Delete Wind direction properties: the new added node has both wind speed and direction keys added to the properties by default. Select the node in Graph View and then in Node Properties expand wind properties and delete Wind direction.

3. Clone the wind speed node: right-click on the wind0 -> Clone -> number of clones: 1

4. Rename the nodes: to identify scenarios by selecting the node and modifying the Name field in Node Properties. Change these names to WindSpeed2 and WindSpeed5.

5. Input wind speeds: select the nodes in Graph View and enter wind speeds 2m/s and 5m/s in Node Properties.

Varying wind directions

1. Add a connector: in Graph View, select the nodes then Right-click -> Add -> Connector.

2. Create a wind node: right-click on the connector -> Add -> Wind

3. Delete wind speed properties: select the node and then in Node Properties, select Wind speed -> Delete.

4. Clone the wind direction node: add 7 clones of this node and change the names to WindDir0, WindDir45, WindDir90, WindDir135, WindDir180, WindDir225, WindDir270, WindDir315.

5. Input wind directions: Select all WindDir nodes in the Graph View and change wind direction in the Node Properties window.

Save the project and export scenarios

1. Save the project: via File -> Save. The project is then saved as a thf file.

2. Export all scenarios: select Export all scenarios in the Table View.

Note 1

When exporting scenarios, it is good to keep track of the information in the Output Window. If any errors occur it should be reported here. Output Window can be enabled by right-click on the toolbar and enable ‘Output Window’.

Note 2

To export only one scenario, select the scenario path in the Graph View and Export Scenarios. You can also select specific scenario in the Table View (with Show only scenarios option selected). The corresponding path in the Graph View will be highlighted.

Note 3

Porosities can be calculated upon export. This option can be accessed in the Multi Scenario tab within Preferences. Here, the calculator will look for scenarios with identical geometries and grids and link the porosity calculation for quicker results.

Running the simulations

Simulations exported by the multiscenario tool do not need to be handled any differently in RunManager.

1. Simply navigate to the output folder when adding a directory and run the simulations as normal.

Walk through video