Brick u-p Element
This command is used to construct an BrickUP element object. A BrickUP element is an 8-node hexahedral linear isoparametric element. Each node has 4 degrees-of-freedom (DOF): DOFs 1 to 3 for solid displacement (u) and DOF 4 for fluid pressure (p). This element is implemented for simulating dynamic response of solid-fluid fully coupled material, based on Biot's theory of porous medium.
The arguments for the construction of this element are:
| element brickUP $eleTag $Node1 $Node2 $Node3 $Node4 $Node5 $Node6 $Node7 $Node8 $matTag $bulk $fmass $PermX $PermY $PermZ <$bX=0 $bY=0 $bZ=0> |
| $eleTag | unique element object tag |
| $Node1 .. $Node 8 | Eight element node (previously defined) numbered as shown in figure below. |
| $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 |
| $PermX | Permeability coefficient in X direction |
| $PermY | Permeability coefficient in Y direction |
| $PermZ | Permeability coefficient in Z direction |
| $bX, $bX $bZ | Optional gravity acceleration components in X, Y and Z directions respectively (defaults are 0.0) |
NOTE:
This element requires 4 degrees-of-freedom (ndf=4), the 4th degree-of-freedom being pore pressure. The Pore pressure can be recorded at an element node using OpenSees Node Recorder:
recorder Node <-file $fileName> <-time> <-node ($nod1 $nod2 …)> -dof 4 vel
The valid queries to a BrickUP element when creating an ElementRecorder are 'force', and 'material matNum matArg1 matArg2 ...', where matNum represents the material object at the corresponding integration point.
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 |
EXAMPLE:
Please visit http://cyclic.ucsd.edu/opensees for examples.
REFERENCES:
Code Developed by: Zhaohui Yang, UC San Diego