TransientAnalysisInitialCondition

Non Zero Initial DIsplacements and Imposed Velocity

In the class of "non zero initial displacements" falls the condition by which you have loaded structure in an equilibrium condition whose balanced situation is more or less suddenly broken at time t=0. According to the following facts

• time 0.0 cannot set
• velocity is calculated from a difference formula referring to the previous step (hence time=0.0)
• by default the variation between one step and the next is assumed linear (RAMPED)

The calculated velocity with only one step is always different from zero, so it is necessary to:

1. use more then one step in the form of substeps or more then one static step
2. Stepped chenge between steps

The second is required because the "ramping" variation will make the displacements values, needed by the difference formula, different leading to non-zero velocity. The following example code considers for example an hanged (stressesd) structure suddenly released

/solu
ANTYPE,TRANS
TRNOPT,FULL
NLGEOM,ON
OUTRES,ALL,ALL
!
D,1,ALL
ACEL,0.,0.,9.81
!
!      Uncomment to test effect of applied FORCE EQUAL to GRAVITY
!
F,    1,FZ,0.81053E+06
TIMINT,OFF
TIME,0.001
solve
TIME,0.0002
D,ALL,UZ,%_FIX%
solve
NSUBST,10
TIMINT,ON
DDELE, ALL,UZ,     ,    ,FORCE
TIME,0.0003

-- RobertoBernetti - 02 Aug 2013