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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). Please visit http://cyclic.ucsd.edu/opensees for examples.
OUTPUT INTERFACE:
Pore pressure can be recorded at an element node using OpenSees Node Recorder:
recorder Node <-file $fileName> <-time> <-node ($nod1 $nod2 …)> -dof 3 vel
See OpenSees command manual (McKenna and Fenves 2001) for nodal displacement, velocity, or acceleration recorders.
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.
element quadUP $eleTag $iNode $jNode $kNode $lNode $thick $matTag $bulk $fmass $hPerm $vPerm <$b1=0 $b2=0 $t=0>
$eleTag |
A positive integer uniquely identifying the element among all elements |
$iNode, $jNode, $kNode, $lNode |
Four element node (previously defined) numbers in counter-clockwise order around the element |
$thick |
Element thickness |
$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 gravity acceleration components 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 (cm/s)
Gravel |
Sand |
Silty Sand |
Silt |
Clay |
>1.0x10-1 |
1.0x10-3 ~ 1.0x10-1 |
1.0x10-5 ~ 1.0x10-3 |
1.0x10-7 ~ 1.0x10-5 |
<1.0x10-7 |
