How to appy initial acceleration to a node ?

[oscar]

I am applying a dynamic load to nodes 3 and 4 as follows :

set force1 "Series -dt 0.005 -filePath LOAD1.txt -factor 0.5";

pattern Plain 2 $force1 {

load 3 1 0
load 4 1 0

}

[b]I also want to add an initial acceleration to nodes 3 and 4. How is this possible? [/b]

I guess this should be a bit different than the imposed motion assignment. Because I only want to apply an initial acceleration not a history.

I know there is an option for the uniform excitation for which we can specify an initial velocity.

Also note that nodes 3 and 4 are free they arent fixed. (These are the nodes of a 2-D quad element and they are constrained to each other in both vertical and horizontal actually).

Thanks

[fmk]

you can add another load pattern with the accelerations in it and remove it after 1 step.

[oscar]

Frank,

How can I remove it after 1step?

Thanks

[oscar]

Let me ask the question again.

Im applying a dynamic force history to a node. Dynamic force history is a sine function and it is a function of velocity. As force history starts from zero ( velocity starts from 0), initial acceleration and displacement shouldnt be zero. How can I solve this problem?

Thanks

[fmk]

to remove a load pattern after 1 step do the following:

[code]
analyze 1
remove loadPattern $loadPatternTag
analyze [expr $numIter -1]
[/code]

if you are just doing a sine wave input motion, here:
[url]
http://opensees.berkeley.edu/wiki/index ... aveExample
[/url]

[oscar]

Frank,
Lets say I want to assign an initial acceleration of 0.981 m/s2 to node 4.
In acc.txt file there is 0.981 value as only 1 row without anything else.
====================
pattern MultipleSupport 100 {
set accSeries "Series -dt 0.0005 -filePath acc.txt -factor 1.0";
groundMotion 500 Plain -accel $accSeries
imposedMotion 4 1 500
};
constraints Transformation;
test NormDispIncr 1.E-12 2500
algorithm ModifiedNewton
numberer RCM
system ProfileSPD
rayleigh 0.1047198 0 0.0005305 0
integrator Newmark 0.5 0.25
analysis Transient
analyze 1 0.0005
remove loadPattern 100
analyze 0 0.0005
=============================

Is this what you mean? It didn't work so far .
Thanks

[fmk]

you need 2 rows .. the first row corresponds to time 0.0, the second row would correspond to time $dt .. assuing you are using an implicit integration scheme the time is set to $dt and loads for $dt calculated.