The XTS Module for AFT Fathom adds the dimension of time to your piping and ducting system modeling. While some systems have a 'steady-state' nature to their operation, a closed loop cooling system under constant load, for example, other systems are inherently more 'transient' in the operating nature, such as a transfer system where varying tank levels cause significant hydrostatic head differences over time.

With XTS, you no longer have to approximate time varying system operation with multiple steady-state cases, you can directly model these situations with time varying parameters such as tank liquid level and the resulting effect on the system calculated by AFT Fathom. In addition, the XTS Module let's you define a wide variety of operating transients, such pump operation change, valve position and control valve setpoints. These may be defined as function of time and, importantly, event based transients; e.g. valve closure based on tank liquid level.

Tank Modeling in XTS

Three types of tanks may be modeled with XTS -

• Infinite reservoir - liquid level does not change with time, such as pump from or to a lake
• Finite open tank - liquid level changes in accordance with volume changes and tank geometry, with tank vented to atmospher (or other specified pressure above the liquid)
• Finite closed tank - liquid level changes in accordance with volume changes and tank geometry, volume above tank is trapped gas so that pressure changes in accordance with the gas volume and properties

Finite tanks may be defined with a constant cross sectional area, such as a vertical cylindrical tank, or a cross sectional area varying with height, a horizontal cylinder tank, for example. Finite tanks may be specified with an initially known liquid height and surface pressure or with either liquid height or surface pressure as an unknown, in which case XTS will determine the balance liquid height or surface pressure for the first time step.

Modeling Operating Transients in XTS

Operating transients that may be defined in XTS include -

• Pump speed, on/off
• Tank surface pressure
• Valve K or Cv (position)
• Control Valve setpoint
• Spray discharge nozzle resistance
• Assigned pressure junction pressure/head
• Assigned flow junction flow

Transients can be defined to begin at a specified time or based on an event occuring within the system, such as a pressure ,flow or velocity in a pipe, liquid level in a tank, pump speed, valve open percentage, pressure drop across a junction or pipe, or the differential pressure between two pipes or junctions.

Further, event transients can be single event (occurs once), cyclic event (e.g. a valve that opens and closes indefinately based on changing liquid level in a tank) or a sequential event (e.g. a valve the will open and close based on tank liquid level, but only cycle once).

Transient Output

XTS offers a wide range of text based and graphical output to clearly illustrate time varying parameters.

Text based transient output is displayed in the Output for both a selected time period and for all time periods in the simulation. A slider along the bottom of the Output window to set the output to any time step. The current time is displayed along with the pipe, junction and summary report output for the current time. Transient tabs in the pipe and junction output and the summary reports display output for all times in the simulation by object (pipe, junction, pump, etc.).

Graph Results plots parameters vs time and includes a unique animation feature that dynamically displays time vary parameters along a selected flow path.