Twenty Eight Node Brick u-p Element
Twenty_Eight_Node_BrickUP is a 20-node hexahedral isoparametric element.
The eight corner nodes have 4 degrees-of-freedom (DOF) each: DOFs 1 to 3 for solid displacement (u) and DOF 4 for fluid pressure (p). The other nodes have 3 DOFs each for solid displacement. This element is implemented for simulating dynamic response of solid-fluid fully coupled material, based on Biot's theory of porous medium.
Please click here for examples.
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 Twenty_Eight_Node_BrickUP 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 20_8_BrickUP $eleTag $Node1 … $Node20 $matTag $bulk $fmass $PermX $PermY $PermZ <$bX=0 $bY=0 $bZ=0>|
|$eleTag||A positive integer uniquely identifying the element among all elements|
|$Node1,… $Node20||20 element node (previously defined) numbers (see figure above for order of numbering).|
|$matTag||Tag of an NDMaterial object (previously defined) of which the element is composed|
|$bulk||Combined undrained bulk modulus Bc relating changes in pore pressure and volumetric strain, may be approximated by:
Bc ≈ Bf/n
where Bf is the bulk modulus of fluid phase (2.2x106 kPa (or 3.191x105 psi) for water), and n the initial porosity.
|$fmass||Fluid mass density|
|$permX, $permY, $permZ||Permeability coefficients in x, y, and z directions respectively.|
|$bX, $bY, $bZ||Optional gravity acceleration components in x, y, and z directions directions respectively (defaults are 0.0)|
Code Developed by: UC San Diego (Dr. Zhaohui Yang):
UC San Diego Soil Model:
- Element Command
- NDMaterial Command
- UC San Diego soil models (Linear/Nonlinear, dry/drained/undrained soil response under general 2D/3D static/cyclic loading conditions (please visit UCSD for examples)
- UC San Diego Saturated Undrained soil
- Related References