InitialStateAnalysisWrapper

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This command is used to construct an InitialStateAnalysisWrapper nDMaterial object.

nDMaterial InitialStateAnalysisWrapper $matTag $nDMatTag $nDim

$eleTag	unique integer tag identifying nDMaterial object
$nDMatTag	the tag of the associated nDMaterial object
$nDim	number of dimensions (2 for 2D, 3 for 3D)

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The InitialStateAnalysisWrapper nDMaterial allows for the use of the InitialStateAnalysis command for setting initial conditions. The InitialStateAnalysisWrapper can be used with any nDMaterial. This material wrapper allows for the development of an initial stress field while maintaining the original geometry of the problem. An example analysis is provided below to demonstrate the use of this material wrapper object.

NOTES:

1. There are no valid recorder queries for the InitialStateAnalysisWrapper.
2. The InitialStateAnalysis off command removes all previously defined recorders. Two sets of recorders are needed if the results before and after this command are desired. See the example below for more.
3. The InitialStateAnalysisWrapper material is somewhat tricky to use in dynamic analysis. Sometimes setting the displacement to zero appears to be interpreted as an initial displacement in subsequent steps, resulting in undesirable vibrations.

EXAMPLES:

InitialStateAnalysisWrapper definition with material tag 1, and associated nDMaterial tag 2 for a 2D analysis

nDMaterial InitialStateAnalysisWrapper 1  2 2

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

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EXAMPLE ANALYSIS:

The example input file below demonstrates an how the InitialStateAnalysis command can be used with the InitialStateAnalysisWrapper to generate a gravitational state of stress in a single element. As shown below, the use of the InitialStateAnalysis command necessitates the use of two sets of recorders, one to record results during the initial state analysis, and one for all subsequent steps. It is not required to record results during the initial state analysis, but the example below includes this data to demonstrate the effect of the InitialStateAnalysis command. At the end of the analysis, there should be non-zero stress and strain in the element with zero displacement.

wipe

model BasicBuilder -ndm 3 -ndf 3

# create the nodes
node 1	1.0	0.0	0.0
node 2	1.0	1.0	0.0
node 3 	0.0	1.0	0.0	
node 4	0.0	0.0	0.0
node 5	1.0	0.0	1.0
node 6 	1.0	1.0	1.0
node 7 	0.0	1.0	1.0
node 8 	0.0	0.0	1.0

# boundary conditions
fix 1 	1 1 1
fix 2 	1 1 1
fix 3	1 1 1
fix 4 	1 1 1
fix 5	1 1 0
fix 6 	1 1 0
fix 7	1 1 0
fix 8 	1 1 0

# define main material obeject
nDMaterial ElasticIsotropic 1 25000 0.35

# define material wrapper
nDMaterial InitialStateAnalysisWrapper 2 1 3

# create the element (NOTE: the material tag associated with this element is that of the wrapper)
element SSPbrick 1  1 2 3 4 5 6 7 8  2  0.0 0.0 -17.0   

# create the pre-gravity recorders
set step 0.1

recorder Node -time -file Gdisp.out -dT $step -nodeRange 5 8 -dof 1 2 3 disp
recorder Element -ele 1 -time -file Gstress.out  -dT $step stress
recorder Element -ele 1 -time -file Gstrain.out  -dT $step  strain

# create the gravity analysis
integrator LoadControl 0.5
numberer RCM
system SparseGeneral
constraints Transformation
test NormDispIncr 1e-5 40 1
algorithm Newton
analysis Static

# turn on the initial state analysis feature
InitialStateAnalysis on

# analyze four steps
analyze 4

# turn off the initial state analysis feature
InitialStateAnalysis off

# create post-gravity recorders
recorder Node -time -file disp.out -dT $step -nodeRange 5 8 -dof 1 2 3 disp
recorder Element -ele 1 -time -file stress.out  -dT $step  stress
recorder Element -ele 1 -time -file strain.out  -dT $step  strain

# analyze for three steps, should have non-zero stress and strain with zero displacement
analyze 3

wipe