Force Definitions Panel

AFT xStream includes the ability to calculate transient pneumatic forces, which occur when a transient pressure wave passes through a portion of the system.

Note: As AFT xStream is only a pneumatic solver, only pneumatic forces are accounted for. AFT xStream is not a pipe stress analyzer and as such does not have the ability to directly model piping supports or similar objects. Pneumatic force files can be generated for import into software designed for force analysis.

Defining Force Sets from Analysis Setup

In order to process force data, the locations where the forces are to be calculated must be defined. Force Sets can be defined from the Force Definitions panel of the Forces group in Analysis Setup.

Note: Force calculation accuracy in AFT xStream is dependent not only on accurately defining the Force Sets, but can also be highly dependent on the Sectioning and Fluid panel settings. This is discussed further in the Pipe Forces from Turbine Shutdown Example.

• New - Add a new force set to the table.

• Duplicate - Copy an existing force set.

• Delete/Delete All - Remove the selected force set / remove all force sets.

• Swap Nodes - The calculation will be the same, but the sign of the force will be reversed. This may be important for proper interpretation of results or for exporting data to other applications.

• Import from CSV - If force sets are defined in another application or by hand they can easily be imported with a comma separated value file. Click the Import from CSV button for an explanation on the required format.

• Generate Force Names - Automatically changes the names for the selected force sets to "upstream junction name - downstream junction name" using the names from the connected junctions on the workspace.

• Point Force Ambient Pressure - If using a Point force set, the ambient pressure is required to calculate the force balance. This defaults to the Environmental Properties panel value, but can be changed here.

Each individual force set has a number of required parameters:

• Force Type - There are several force set types available. They are described in detail in Force Set Types.

• Force Set Name - A unique name for the force set.

• Start Pipe - Where the first node is located.

• Start Location - Force Sets in xStream must have their endpoints at either the inlet or outlet of a pipe.

• End Pipe - The second node (for Difference force types). Note that the selection must be valid for the specified force type. See Force Set Types.

• End Location - Force Sets in xStream must have their endpoints at either the inlet or outlet of a pipe.

• Exit Area - For Exit force types, an exit area is required.

• Force Unit Vector Coordinates - Define unit vectors for your linear pipe to give the resulting forces a three-dimensional direction. xStream is still only a one-dimensional fluid modeling software, and specifying a unit vector will not change the force calculations. However, by defining the XYZ vector for a given force set, that data can be brought into other software for further analysis using the Export Force Data tool. These unit vectors should be defined based on the coordinate system in the force stress analyzing software that the force sets will be exported to.

Defining Force Sets from the Workspace

Force Sets for individual pipes can be defined directly from the Workspace by right-clicking on a selected pipe. Choose the Create Force Set With Selected Pipe... option to launch the Create Force Set window, shown below in Figure 2. If multiple pipes are selected, an individual Difference Force Set will be created for each pipe applying the specified settings for each.

Each force has several required and optional parameters:

• Pipe Name - If the pipe has a name entered other than 'Pipe', the user can choose whether to include that pipe name or not in the Force Set name.

• Force Set Name - Users can add a name for the Force Set to better organize and manage Force Sets in the model.

• Force Unit Vectors or Length - Define unit vectors for your linear pipe to give the resulting forces a three-dimensional direction. xStream is still only a one-dimensional fluid modeling software, and specifying a unit vector will not change the force calculations. However, by defining the XYZ vector for a given force set, that data can be brought into other software for further analysis using the Export Force Data tool. These unit vectors should be defined based on the coordinate system in the force stress analyzing software that the force sets will be exported to.

• Show Analysis Setup Force Definitions after Creation - If checked the user will be brought to the Force Definitions panel of the Analysis Setup window to view all Force Set information defined for that scenario.