Pipe Cross Section
In the Pipe Cross Section node, you specify the geometric properties of the pipe’s cross section. In addition, some stress evaluation properties can be defined.
For 3D models, a default Section Orientation subnode is added, in which you specify the orientation of the principal axes of the section. You can add any number of Section Orientation subnodes if the same section appears with different spatial orientations in the structure.
Pipe Shape
The default is Not Set. Select Circular, Square, Rectangular, or User defined. Then go to the relevant section below to continue defining the section
For User defined go to Wall Cross Section Properties and Stress Evaluation Properties to continue defining the cross section.
Circular
Enter values or expressions for the following.
Piping standards may require stresses to be evaluated using a reduced thickness to account for possible corrosion or erosion effects on the pipe’s wall. The thickness changes can occur on both the inner and the outer side of the wall. In the section Thickness reduction for stress evaluation enter values or expressions for the thickness reduction on the inner or outer sides:
For both sides the default value is 0[%]*pipem.t_nom, where the variable pipem.t_nom is the nominal wall thickness given by do and di. The reduced inner and outer diameters are then defined as
Note that the reduced wall thickness only has an effect on the stress evaluation. That is, the flexibility of the piping system is still computed using nominal thicknesses. Internally, COMSOL Multiphysics creates separate variables for stiffness properties such as the cross-section area or the 2nd moment of inertia. All stress measures that can be evaluated in postprocessing are computed using the reduced wall diameters.
Square
Enter values or expressions for the following:
Rectangular
Enter values or expressions for the following:
Wall Cross Section Properties
This section is only available if User defined is selected as the Cross-Section Definition.
The following table lists the basic section properties (some apply in 3D only). Enter values for these properties in the associated fields. The default values correspond to a circular cross section with a diameter of 0.1 m:
m2
Izz
m4
ez
Iyy
m4
ey
m4
For 3D models, the orientation of the cross section is given in Section Orientation. If the beam’s cross section is a square or circle (solid or tube), the area moments of inertia are the same independent of direction, so the beam is totally symmetric and the orientation of the principal axes of the cross section is not a problem unless you are interested in looking at results defined using the local coordinate system. Such results are bending moments, shear forces, local displacements and rotations.
Fluid Cross Section Properties
Enter the Fluid cross section area, Af. This is the same as the internal cross section of the pipe.
Stress Evaluation Properties
This section is only available if User defined is selected as the Cross-Section Definition.
Select the Bending stress evaluation pointsFrom section heights (the default) or From specified points.
Stress evaluation using only section heights is meaningful only when the cross section is symmetric.
The max shear stress factor determines the ratio between the peak and the average shear stress over the cross section as described by Equation 12-1 and Equation 12-2.
From Section Heights
For From section heights enter values in each field for the following parameters as needed for the space dimension:
hy
μy
Wt
m3
μz
γm
From Specified Points
For From specified points enter values in the Evaluation points in local system table as needed for the space dimension. Then enter the following parameters in the applicable fields.
μy
Wt
m3
μz
Location in User Interface
Context Menus
Ribbon
Physics tab with Pipe Mechanics selected: