How to Specify Nonlinear Supports in Piping Systems
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Piping systems often include nonlinear effects such as directional stops, one-way motion and friction.
In the PipePak piping design and analysis system, such nonlinear restraints are modeled by using the
following kinds of supports:
- limit stops, which allow a piping system to move a certain amount in either direction before
the support becomes active.
- one-way supports, which act in either a positive or negative direction only.
- guides, which restrain pipe movement in the plane perpendicular to the pipe direction.
- inclined supports, which are generalized translational restraints.
Nonlinear restraints can be specified in the "Extra Data" field of
the PipePlus spreadsheet by using the "Support" option. The
"Support Selection" pop-up screen will appear with a pull-down menu of
options for the available supports (see Figure 1.)
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Figure 1: Selecting a support. |
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Upon selecting a support, the associated support definition screen will
appear. For example, Figure 2 shows the "One Way Restraint Definition"
screen.
When defining nonlinear supports, you might want to consider expansion load
cases, which include the effect of thermal expansion on the piping system. To
model expansion load cases, you can choose to base nonlinear supports on either the operating case
(dead weight + pressure + thermal) or solely on the thermal load case. This option is controlled by
the ExpGapInd keyword in the PipePlus configuration file (pipeplus.cnf).
The pipeplus.cnf file, which is located in your ALGOR directory, can be edited with any text editor.
Alternatively, you can use the PipePak interface to specify the ExpGapInd analysis option.
From the Windows desktop, use the
"Start:Programs:Algor Software:PipePak Piping Design & Analysis"
command sequence to access the PipePak interface.
As shown in Figure 3, click on the "Configuration" button to change the PipePlus
configuration settings.
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| Figure 2: The "One Way Restraint Definition" screen. |
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Figure 3: Using the PipePak interface to access the "PipePlus Configuration"
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The "PipePlus Configuration" screen will appear. On the "Loads/Supports" tab,
you can activate the option
"Set the gap status for expansion load cases to be independent from other load
cases" (see Figure 4). Activating this option
on the "PipePlus Configuration" screen causes the ExpGapInd setting to be activated in the
pipeplus.cnf file.
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Figure 4: Setting the option for expansion load cases. |
Note: If you do not activate this option for a piping system model
with nonlinear supports, then, during analysis, a message will appear
asking if you want to use the ExpGapInd option. If you choose "Yes", then the ExpGapInd setting
will be used for only the current analysis run; it will not be activated in the pipeplus.cnf file for
subsequent runs.
For more information about nonlinear supports in piping systems, see the PipePak User's Guide.
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