CONTACTPOST

Use

This subroutine can be used to extract rigid or flexible body contact results from a MotionSolve simulation which can then be used to generate an output file or process the results programmatically.

<Force_Contact
    id                  = "303001"
    ...
    cpost_dll_name      = "my_contact_post_sub"
    cpost_param_string  = "USER(1000) "
    cpost_fnc_name      = "CONTACTPOST"
/>

Format

Fortran Calling Syntax

SUBROUTINE CONTACTPOST (ID, I_GRA_ID, J_GRA_ID, TIME, PAR, NPAR, IFLAG, ENDFLG)

C/C++ Calling Syntax

void STDCALL CONTACTPOST (int *id, int *i_gra_id, int *j_gra_id, double *time, double *par, int *npar, int *iflag, int *endflg)

Python Calling Syntax

def CONTACTPOST(id, i_gra_id, j_gra_id, time, par, npar, iflag, endflg):

Attributes

ID: [integer]; The ID of the contact force modeling element (Force_Contact in XML) for which the results are desired.; This argument is automatically populated and passed in by MotionSolve.
I_GRA_ID: [integer]; The ID of the I body's graphic representation. If the body is flexible, this attribute is ignored.; This argument is automatically populated and passed in by MotionSolve.
J_GRA_ID: [integer]; The ID of the J body's graphic representation. If the body is flexible, this attribute is ignored.; This argument is automatically populated and passed in by MotionSolve.
TIME: [double]; The current simulation time.; This argument is automatically populated and passed in by MotionSolve.
PAR: [double]; An array that contains the constant arguments from the list provided in the user-defined statement.; This argument is defined by the user in the model.
NPAR: [integer]; The number of entries in the PAR array.; This argument is automatically populated and passed in by MotionSolve based on the size of the PAR array.
IFLAG: [integer]; The initialization flag. 3
ENDFLG: [integer]; The end flag. 3

Example

The following example retrieves the penetration depth and total force at each time step for a simulation that models body contact:

<Force_Contact
     id                  = "303001"
     label               = "Contact 0"
     num_i_graphics      = "1"
     i_graphics_id       = "90001"
     num_j_graphics      = "1"
     j_graphics_id       = "90000"
     cnf_type            = "Impact"
     stiffness           = "1000."
     exponent            = "1.2"
     damping             = "1."
     dmax                = "0.01"
     cff_type            = "Coulomb_Off"
     cpost_dll_name      = "my_contact_post_sub"
     cpost_param_string  = "USER()"
     cpost_fnc_name      = "CONTACTPOST"
/>

The contents of CONTACTPOST in my_contact_post_sub are:

void STDCALL CONTACTPOST (int*id,int*i_gra_id,int*j_gra_id,double*time,double*par,int*npar,int*iflag,int*endflg)
{
/*
Input argument
----------------------------------------------------------
  id    Identifier of calling CONTACT statement
  i_gra_id Identifier of calling I_GRAPHIC 
  j_gra_id Identifier of calling J_GRAPHIC
  time  Time of contact
  par   Array containing passed parameters 
  npar  Number of passed parameters 
*/
    int nof_contacts;
    bool errflg;

    c_get_ncontacts(*id, *i_gra_id, *j_gra_id, &nof_contacts, &errflg);
    intipar[4] = {30102020, 0, 0, 0};
    double states[6];
    int nstates;
    int ierr;

    c_sysary("tdisp", ipar, 1, states, &nstates, &ierr);
    printf(" I gra %d - J gra %d  time : %f  nof %d \n", *i_gra_id, *j_gra_id, *time, nof_contacts);
    for (inti=0; i<nof_contacts; i++) 
    {
        double pd;
        double f[3];
        int n_results;
        c_get_contact_post(*id, *i_gra_id, *j_gra_id, "PD", i, &pd, &n_results, &errflg);
        c_get_contact_post(*id, *i_gra_id, *j_gra_id, "TOTAL_FORCE", i, f, &n_results, &errflg);
        printf(" %d PD = %f, F=[%f %f %f] z = %f \n", i, pd, f[0], f[1], f[2], states[2]);     
    }
}

Comments

The CONTACTPOST subroutine is called by MotionSolve whenever contact occurs between the bodies defined in the corresponding contact force model element. Note, this subroutine is not called when there is no contact between the rigid bodies.
Further, if the I and/or J bodies defined in the contact statement refer to more than one graphic of a rigid body, the CONTACTPOST is called for each combination of the I graphic (I_GRA_ID) and/or the J graphic (J_GRA_ID).
From within the CONTACTPOST subroutine, you may call the access functions GET_NCONTACTS and GET_CONTACT_POST to obtain additional information about the contact states during the simulation. Please see the documentation for syntax and usage of these access functions.
The CONTACTPOST is called by MotionSolve with IFLAG set to 1 at the beginning of each simulate. At the end of each simulate, CONTACTPOST is called with ENDFLG set to 1. This allows you to correctly open/close files and do memory allocation/de-allocation properly. If you would like to save data in between multiple simulates, you may use the utility functions SAVPAR and RELPAR to do so.
The CONTACTPOST subroutine enables you to obtain information about the rigid body contact states during a MotionSolve simulation that are not otherwise available by using standard MotionSolve expressions. This data can then be written in any format you desire for downstream CAE processes like exporting to an FE/fatigue solver.