There are several types of forces that can be defined for analysis with AFT xStream:

• Point - Point forces are simply the difference in pressure between the fluid and ambient multiplied by the pipe area. This can be useful for places where the fluid is leaving the system, such as a relief valve or exit valve.

• Difference - Difference forces are defined as the unbalanced force between two nodes, or computation stations along two sequential pipes. An example of this is the pneumatic loading between two elbows along the length of a pipe. See Figure 1 below.

• Difference Exit - Similar to the difference force set in that two nodes are required. However, the user defined exit area will be used for calculating the force across the section. This is useful for modeling forces on something such as a nozzle.

• Difference (3+ Pipes) - The same as difference forces, but spans across more than two pipes. A pipe group must be defined that contains the pipes between the two locations. The Difference (3+ Pipes) force set type must still include only sequential pipes.

• Difference Exit (3+ Pipes) - The same as difference exit, but spans across more than two pipes, requiring a group.

Figure 1: Difference force type schematic. For Difference Exit, the area used at End Node is user defined