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FourNodeQuadUP is a four-node plane-strain element using bilinear isoparametric formulation. This element is implemented for simulating dynamic response of solid-fluid fully coupled material, based on Biot's theory of porous medium. Each element node has 3 degrees-of-freedom (DOF): DOF 1 and 2 for solid displacement (u) and DOF 3 for fluid pressure (p).
element quadUP $eleTag $iNode $jNode $kNode $lNode $thick $type $matTag $bulk $fmass $hPerm $vPerm <$b1 $b2 $t>
$eleTag |
unique element object tag |
$iNode, $jNode, $kNode, $lNode |
Four element node (previously defined) numbers in counter-clockwise order around the element |
$thick |
Element thickness |
$type |
The string "PlaneStrain" |
$matTag |
Tag of an NDMaterial object (previously defined) of which the element is composed |
$bulk |
Combined undrained bulk modulus Bc relating changes in pore pressure and volumetric strain, may be approximated by:
where Bf is the bulk modulus of fluid phase (2.2x106 kPa for water), and n the initial porosity. |
$fmass |
Fluid mass density |
$hPerm |
Permeability coefficient in horizontal direction |
$vPerm |
Permeability coefficient in vertical direction |
$b1, $b2 |
Optional body forces in horizontal and vertical directions respectively (defaults are 0.0) |
$t |
Optional uniform element normal traction, positive in tension (default is 0.0) |
TYPICAL RANGE OF PERMEABILITY COEFFICIENT (m/s)
Gravel |
Sand |
Silty Sand |
Silt |
Clay |
>1.0x10-3 |
1.0x10-5 ~ 1.0x10-3 |
1.0x10-7 ~ 1.0x10-5 |
1.0x10-9 ~ 1.0x10-7 |
<1.0x10-9 |
OUTPUT INTERFACE:
Pore pressure can be recorded at an element node using OpenSees Node Recorder:
recorder Node <-file $fileName> <-time> <-node ($node1 $node2 ...)> -dof 3 vel
Note: dof 3 is for pore pressure output.
The valid queries to a quadUP element when creating an ElementRecorder are 'force', 'stiffness', or 'material matNum matArg1 matArg2 ...', where matNum represents the material object at the corresponding integration point.
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