Pipe Model

Size

The size section of the Pipe Model tab specifies the pipe geometry.

• Pipe Material

• User Specified - If selected, the geometry of the pipe must be directly specified.

• Library Material - Many common pipe materials are included in the standard Pipe Material Library. These and any other accessible library materials can be selected. When a library material is selected, the parameters defining the geometry cannot be modified.

• Size - Select from a list of defined nominal sizes for the selected Pipe Material. Only available for library materials.

• Type - Select from a list of defined types (classes/schedules) for the selected Pipe Material. Only available for library materials.

• ID Reduction (Scaling) - Reduction in hydraulic diameter due to scaling can be accounted for by entering a percent reduction in this field. Zero represents no reduction.

Length

The Length is defined as the distance between the two connecting junctions. This length has no relationship to the visual length of the pipe drawn on the Workspace.

Model As Zero-length Connector can be checked to turn the pipe into a lossless connection between two junctions, such as for two components that are directly welded together. Zero-Length Connectors (ZLCs) are denoted by a red C icon next to the pipe name on the Workspace. Intermediate branching flow is not allowed between two ZLCs, and they can only be used in up to two sequential pipes.

ZLCs are hidden by default in the Model Data and Output. Generally the output for ZLCs is not of interest because they will have the same inlet and outlet properties.

You can enable ZLCs to be shown in the Model Data by opening the Model Data Control, going to the Show Selected Pipes/Junctions tab, and selecting the Show Zero-Length Connectors checkbox under the list of pipes. The same checkbox is present in the Output Control on the Show Pipes/Jcts tab. You will then need to click on the pipe numbers in the list to make them visible in the Model Data or Output, or you can use the All button to select all pipes in the model.

Due to the nature of the solution method for ZLCs, there are several configurations that are not allowed to be used. See below for a list of restricted options:

• Junctions that can only be connected to one zero-length connector

  • Reservoir with Infinite Reservoir tank model and no loss factors defined on the Pipe Depth & Loss Coefficients tab

  • Assigned Pressure

  • Tee/Wye with simple loss model

  • Spray Discharge

  • Branch with Flow Source/Sink defined on Optional tab and no loss factors on the Pipe Depth & Loss Coefficients tab

• Junctions not allowed to be connected to zero-length connectors

  • Reservoir with Finite Open tank model

  • Check Valve with Force Balance valve model

  • Gas Accumulator

  • Surge Tank

  • Air Valve

  • Liquid Accumulator

  • Weir

  • Turbine

  • Tee/Wye with detailed loss model

  • Branch with loss factors on the Pipe Depth & Loss Coefficients tab

  • Reservoir with loss factors on the Pipe Depth & Loss Coefficients tab

  • Pumps with Four Quadrant Curve

  • Relief Valve with Internal or Inline Exit valve model

  • Volume Balance

Wavespeed

The wavespeed is the speed at which transient events propagate through the pipe. Typical values for the wavespeed are 2000-5000 ft/sec (700-1600 m/sec). This parameter depends on the liquid acoustic velocity and the pipe material and support.

There are two options to determine a wavespeed for the pipe:

• User Specified Wavespeed - If this option is selected the wall thickness, modulus of elasticity, poisson ratio, and pipe support fields will no longer be used and will be grayed out so that the user can enter their own wavespeed.

• Calculated Wavespeed - This option will use information from the Fluid panel, the Pipe Material Library, and the chosen Pipe Support model to estimate the wavespeed for the user.

The Pipe Support selection is made from the provided drop down list to obtain the constant c1. This constant is required for pipes in which the wavespeed is calculated. AFT Impulse provides nine common pipe support types from Wylie, et. al, 1993Wylie, E.B., V.L. Streeter & L. Suo, Fluid Transients in Systems, Prentice Hall, Englewood Hills, New Jersey, 1993..

• Thin-Walled - Piping in which the wall is relatively thin with respect to diameter so that D/e > 25, where D is diameter and e is thickness. Three types are available:

• Thin-Walled Anchored Upstream - Pipe anchored at its upstream end only.

• Thin-Walled Anchored Throughout - Pipe anchored throughout against axial movement.

• Thin-Walled With Expansion Joints - Pipe anchored with expansion joints throughout.

• Thick-Walled - Piping in which the wall is relatively thick with respect to diameter so that D/e < 25, where D is diameter and e is thickness. Three types are available:

• Thick-Walled Anchored Upstream - Pipe anchored at its upstream end only.

• Thick-Walled Anchored Throughout - Pipe anchored throughout against axial movement.

• Thick-Walled With Expansion Joints - Pipe anchored with expansion joints throughout.

• Circular Tunnel (unlined) - Models a conduit through solid rock or concrete.

• Circular Tunnel (lined) - Accounts for increase in wavespeed due to a steel liner in contact with a solid rock or concrete tunnel. An additional input for the Rock Modulus of Rigidity is required for this model.

• Buried Pipe - Accounts for wavespeed in a buried pipeline. An additional input for the Soil Modulus of Rigidity is required for this model.

Friction Model

Multiple friction data sets can be compiled for each library pipe material. These different data sets are then made available in the Data Set drop down list. For AFT standard materials, the friction data set is generally "Standard."

The Friction Model can be modified for any individual pipe, and the default friction model can be set in Parameter Options. The Friction Model for a library material can be modified by selecting the User Specified radio button in Data Set, and must be directly specified for User Specified materials.

Theses models apply to Newtonian viscosity models. If a non-Newtonian model is selected in the Viscosity Model panel, the below friction models may not be used.

• Absolute roughness (default) - Absolute average roughness height. Values of pipe roughness can be found in many pipe handbooks or from manufacturer's data.

• Relative roughness - Relative roughness is the absolute roughness divided by the pipe diameter.

• Hydraulically smooth - Hydraulically smooth implies that roughness is negligible. This is not the same as frictionless.

• Hazen-Williams - A method using an empirical factor to relate flow and pressure drop, common in water distribution.

• Explicit Friction Factor - friction factor for the pipe, you can enter the value explicitly.

• Resistance - You can specify a pipe resistance in terms of head loss and volumetric flow rate. The pipe head loss will then be as follows: dH = RQ².

• Frictionless - For troubleshooting purposes, it is occasionally useful to model a pipe as having no friction. There are limitations to where such a pipe can be located in your model.

• MIT Equation - A model appropriate for crude oil.

• Miller Turbulent - A model appropriate for light hydrocarbons.

For detailed information on how these Friction Models are defined, see Pressure Drop in Pipes - Detailed Discussion.