SSPquadUP Element: Difference between revisions

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(Created page with '{{CommandManualMenu}} This command is used to construct a SSPquadUP element object. {| | style="background:yellow; color:black; width:800px" | '''element SSPquadUP $eleTag $iN...')
 
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|  style="width:150px" | '''$eleTag ''' || unique integer tag identifying element object
|  style="width:150px" | '''$eleTag ''' || unique integer tag identifying element object
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|  '''$iNode $jNode $kNode $lNode''' || the four nodes defining the element, input in counterclockwise order
|  '''$iNode $jNode $kNode $lNode''' || the four nodes defining the element, input in counterclockwise order (-ndm 2 -ndf 3)
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|-
|  '''$matTag''' || unique integer tag associated with previously-defined nDMaterial object
|  '''$matTag''' || unique integer tag associated with previously-defined nDMaterial object
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Equal-order interpolation is used for the displacement and pressure fields, thus, the SSPquadUP element does not inherently pass the ''inf-sup'' condition in the incompressible-impermeable limit.  A stabilizing parameter is employed to permit the use of equal-order interpolation for this element.  This parameter '''$alpha''' can be computed as
Equal-order interpolation is used for the displacement and pressure fields, thus, the SSPquadUP element does not inherently pass the ''inf-sup'' condition in the incompressible-impermeable limit.  A stabilizing parameter is employed to permit the use of equal-order interpolation for this element.  This parameter '''$alpha''' can be computed as


:::<math> \alpha = \alpha_0^{}\frac{\Delta t_{\mathrm{crit}}^2}{\rho}
alpha = 0.25*(h^2)/(den*c^2)
</math>
 
where '''h''' is the element size, '''c''' is the speed of elastic wave propagation in the solid phase, and '''den''' is the mass density of the solid phase.  The '''$alpha''' parameter should be a small number.
 


'''NOTES:'''
'''NOTES:'''

Revision as of 03:56, 18 November 2011



This command is used to construct a SSPquadUP element object.

element SSPquadUP $eleTag $iNode $jNode $kNode $lNode $matTag $thick $fBulk $fDen $k1 $k2 $void $alpha <$b1 $b2>


$eleTag unique integer tag identifying element object
$iNode $jNode $kNode $lNode the four nodes defining the element, input in counterclockwise order (-ndm 2 -ndf 3)
$matTag unique integer tag associated with previously-defined nDMaterial object
$thick thickness of the element in out-of-plane direction
$fBulk bulk modulus of the pore fluid
$fDen mass density of the pore fluid
$k1 $k2 permeability coefficients in horizontal and vertical directions, respectively
$void voids ratio
$alpha spatial pressure field stabilization parameter (see notes below for more information)
$b1 $b2 constant body forces in horizontal and vertical directions, respectively (optional, default = 0.0)



The SSPquadUP element is an extension of the SSPquad element for use in dynamic plane strain analysis of fluid saturated porous media. A mixed displacement-pressure (u-p) formulation is used, based upon the work of Biot as extended by Zienkiewicz and Shiomi (1984).

The physical stabilization necessary to allow for reduced integration incorporates an assumed strain field in which the volumetric dilation and the shear strain associated with the the hourglass modes are zero, resulting in an element which is free from volumetric and shear locking. The elimination of shear locking results in greater coarse mesh accuracy in bending dominated problems, and the elimination of volumetric locking improves accuracy in nearly-incompressible problems. Analysis times are generally faster than corresponding full integration elements.

Equal-order interpolation is used for the displacement and pressure fields, thus, the SSPquadUP element does not inherently pass the inf-sup condition in the incompressible-impermeable limit. A stabilizing parameter is employed to permit the use of equal-order interpolation for this element. This parameter $alpha can be computed as 

alpha = 0.25*(h^2)/(den*c^2)

where h is the element size, c is the speed of elastic wave propagation in the solid phase, and den is the mass density of the solid phase. The $alpha parameter should be a small number.


NOTES:

  1. Valid queries to the SSPquad element when creating an ElementalRecorder object correspond to those for the nDMaterial object assigned to the element (e.g., 'stress', 'strain'). Material response is recorded at the single integration point located in the center of the element.
  2. The SSPquad element was designed with intentions of duplicating the functionality of the Quad element. If an example is found where the SSPquad element cannot do something that works for the Quad element, please contact the developers listed below so the bug can be fixed.

EXAMPLES:

SSPquad element definition with element tag 1, nodes 1, 2, 3, and 4, material tag 1, plane strain conditions, unit thickness, horizontal body force of zero, and vertical body force of -10.0 

element SSPquad 1  1 2 3 4  1 "PlaneStrain" 1.0 0.0 -10.0

Elemental recorders for stress and strain when using the SSPquad element (note the difference from the Quad element) 

recorder Element -eleRange 1 $numElem -time -file stress.out  stress
recorder Element -eleRange 1 $numElem -time -file strain.out  strain


Code Developed by: Chris McGann, Pedro Arduino, & Peter Mackenzie-Helnwein, at the University of Washington

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