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Facial distributed loading
Distributed loading is triggered by the *DLOAD
card. Facial distributed loads are entered as pressure loads on the
element faces, which are for that purpose numbered according to
Figures 60, 61 and 62.
Figure 60:
Face numbering for hexahedral elements
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Figure 61:
Face numbering for tetrahedral elements
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Figure 62:
Face numbering for wedge elements
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Thus, for hexahedral elements the faces are numbered as follows:
- Face 1: 1-2-3-4
- Face 2: 5-8-7-6
- Face 3: 1-5-6-2
- Face 4: 2-6-7-3
- Face 5: 3-7-8-4
- Face 6: 4-8-5-1
for tetrahedral elements:
- Face 1: 1-2-3
- Face 2: 1-4-2
- Face 3: 2-4-3
- Face 4: 3-4-1
for wedge elements:
- Face 1: 1-2-3
- Face 2: 4-5-6
- Face 3: 1-2-5-4
- Face 4: 2-3-6-5
- Face 5: 3-1-4-6
for quadrilateral plane stress, plane strain and axisymmetric elements:
- Face 1: 1-2
- Face 2: 2-3
- Face 3: 3-4
- Face 4: 4-1
for triangular plane stress, plane strain and axisymmetric elements:
- Face 1: 1-2
- Face 2: 2-3
- Face 3: 3-1
for beam elements:
- Face 1: pressure in 1-direction
- Face 2: pressure in 2-direction
For shell elements no face number is needed since there is only one kind of loading:
pressure in the direction of the normal on the shell.
Applying a pressure to a face for which a pressure was specified in a
previous step replaces this pressure. The parameter OP=NEW on the
*DLOAD card removes all previous distributed loads. It only takes
effect for the first *DLOAD card in a step. A buckling step always removes all previous loads.
In a large deformation analysis the pressure is applied to the deformed face of the element. Thus, if you pull a rod with a constant pressure, the total force will decrease due to the decrease of the cross-sectional area of the rod. This effect may or may not be intended. If not, the pressure can be replaced by nodal forces. Figures 63 and 64 show the equivalent forces for a unit pressure applied to a face of a C3D20(R) and C3D10 element. Notice that the force is zero (C3D10) or has the opposite sign (C3D20(R)) for quadractic elements. For the linear C3D8(R) elements, the force takes the value 1/4 in each node of the face.
Figure 63:
Equivalent nodal forces for a face of a C3D20(R) element
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Figure 64:
Equivalent nodal forces for a face of a C3D10 element
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Next: Centrifugal distributed loading
Up: Loading
Previous: Point loads
Contents
guido dhondt
2007-02-18