Time integration and Initialize DOF values.

[mubeen]

Hi FEAP team,
I need help regarding initialization of DOF values (initial displacements) in my user element subroutine.
This user defined element has 3 displacement components per node, as well as other (density like) scalar variables as DOF. The element residual and stiffness matrix equations involve first time derivative of that scalar variables. Since there is no second time derivative and hence no "mass" matrix is involved, therefore I have programmed the entire system of equations after time discretization using Backward Euler scheme with a fixed time increment (time increment as input from user via TINPUT).
After this simple time integration and getting rid of first time derivative, it seems the system has become quasi-static, as I am calculating total stiffness K'_T = c1*K + c2*C, and there is no damping matrix C generated for FEAP (instead I am returning K'_T to s matrix in element routine).
The problem is to initialize the values of extra DOF (those density like variables). Since this is not transient problem anymore, I am not sure if

Code: [Select]

BATCh
INITial DISPlacement
END
1  1 0. 0. 0. 2.5 2.5 2.5 1.5 1.5 1.5 2.0 2.0 2.0 2.5 2.5 2.5 1.5 1.5 1.5
27 1 0. 0. 0. 2.5 2.5 2.5 1.5 1.5 1.5 2.0 2.0 2.0 2.5 2.5 2.5 1.5 1.5 1.5
will work in this case. Is there any other way to initialize these extra DOF values in FEAP?
I have tried with above INITial DISPlacement but FEAP crashed and I couldn't find any clue from the trivial debugger (I have compiled FEAP with Release configuration).

Second problem is that: in some cases, the number of DOF can be up to 15. In that case the number of data values at EBOUN and INITial DISPlacement cards will be more than 16. The version 8.3 Programmer Manual of FEAP (section 2.1 page 11) states that the TINPUT/PINPUT allow 16 individual values per one input record. Is this limit also for every/all lines in FEAP input file (or only those which are meant to be processed by TINPUT/PINPUT)? If yes, then is there any way to pass values of  15 or more DOF values for boundary and initial displacements?

Kindly pardon if the question seems silly, but I have spent quite long time trying to find answers to  these questions.

Thanks.

[Prof. R.L. Taylor]

In general, if there are more than 16 items on a line the remaining terms are placed on a second line

There could still be places where this has not been corrected so try the steps and report any that do not work.

the INIT DISP should set initial conditions for any dof -- again you are using a large number of dof/node so be careful that the input module can handle them -- there are dimensions internal that limit the maxium no dofs/node to something -- it should be > 20 though

[mubeen]

Dear Prof. Taylor,

I am very thankful for the reply.  I am using FEAP 8.2 .
The initialization works using

Code: [Select]

INITIal DISPlacement card.


However, when specifying more than 16 values on a single line (or split on two lines),

Code: [Select]

BATCH
INITIAL DISPLACEMENTS
END
1  1  0. 0. 0. 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0
 3.0
27 0  0. 0. 0. 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0
 3.0

FEAP crashes with error (in Log file):

Code: [Select]

  --------------------------------- START OF FEAP LOG ----------------------------------
  INPUT FILE NAME: ielmt11                                                                                                                         
  MESH INPUT RECORDS
  ------------------
     parameter                     
     MATERIAL        1             
     COORDINATES                   
     ELEMENTS                       
     FORCES                         
     EBOUNDARY                     
     END                           
 *ERROR* ENDCLR: End of file encountered in TINPUT
         Unit Number =  12
     0     0    0  0.000E+00  0.00E+00  0.00E+00            0.00E+00                0.01
 Total     0    0
  ---------------------------------- END OF FEAP LOG -----------------------------------

and in DOF assignments in Output file are:

Code: [Select]

     Material  Number   1 for User Element Type 11

     Degree of Freedom Assignments    Local    Global
                                     Number    Number
                                        1         0
                                        2         0
                                        3         0
                                        4         0
                                        5         0
                                        6         0
                                        7         0
                                        8         0
                                        9         0
                                       10         0
                                       11         0
                                       12         0
                                       13         0
                                       14    210840
                                       15    130420
                                                                         

I couldn't find the way to specify initial values of so many DOFs.
I will be very thankful for the guidance to resolve this problem.

I have attached the input file for this problem.