Subroutine Type

Modeling

Definition

Used to calculate normal forces for the Force_Contact element.

Use

Implements a custom normal force for contact.

<Force_Contact

    id                  = "301001"

    num_i_graphics      = "1"

    i_graphics_id       = "90000"

    num_j_graphics      = "1"

    j_graphics_id       = "90001"

    cnf_type            = "UserCNF"

    cnf_param_string    = "USER(500.,1.5,0.5,0.01)"

    cnf_fnc_name        = "CNFSUB"

    cnf_dll_name        = "NULL"

    cff_type            = "Coulomb_On"

    mu_static           = "0.05"

    mu_dynamic          = "0.01"

    stiction_trans_vel  = "0.1"

    friction_trans_vel  = "0.5"

 />

Calling Syntax

Fortran

SUBROUTINE CNFSUB (ID, TIME, PAR, NPAR, LOCI, NI, LOCJ, NJ, GAP, GAPDOT, GAPDOTDOT, AREA, DFLAG, IFLAG, RESULTS)

C

void STDCALL CNFSUB (int *id, double *time, double *par, int *npar, double *loci, double *ni, double *locj, double *nj, double *gap, double *gapdot, double *gapdotdot, int *dflag, int *iflag, double *result)

Python

def CNFSUB(id, time, par, npar, loci, ni, locj, nj, gap, gapdot, gapdotdot, dflag, iflag):

    return result

MATLAB

function vector = CNFSUB(id, time, par, npar, loci, ni, locj, nj, gap, gapdot, gapdotdot, dflag, iflag)

Input Arguments

[double precision] AREA

The area of the contact patch.

[logical] DFLAG

A Boolean variable that MotionSolve sets to true when it needs partial derivatives.  Otherwise, it is set to false.

[double precision] GAP

The gap between I_GRAPHICS_ID and J_GRAPHICS_ID.  If GAP is positive or zero, there is no contact or penetration.

[double precision] GAPDOT

The first time derivative of GAP.

[double precision] GAPDOTDOT

The second time derivative of GAP.

[integer] ID

Force_Contact element identifier.

[logical] IFLAG

A Boolean variable that MotionSolve sets to true when it needs to know on which functions CNFSUB depends.  When the flag is set to false, then the values of the user-defined expressions are computed.

[double precision] LOCI

An array that contains the position vector of the contact point on I_GRAPHICS_ID with respect to the origin of the I_GRAPHICS_ID reference marker, resolved in the I_GRAPHICS_ID reference marker coordinate system.

[double precision] LOCJ

An array that contains the position vector of the contact point on J_GRAPHICS_ID with respect to the origin of the J_GRAPHICS_ID reference marker, resolved in the J_GRAPHICS_ID reference marker coordinate system.

[double precision] NI

An array that contains the surface normal vector at the contact point on I_GRAPHICS_ID, resolved in the I_GRAPHICS_ID reference marker coordinate system.

[double precision] NJ

An array that contains the surface normal vector at the contact point on J_GRAPHICS_ID, resolved in the J_GRAPHICS_ID reference marker coordinate system.

[integer] NPAR

The number of entries in the PAR array.

[double precision] PAR

An array that contains the constant arguments from the list provided in the user-defined statement.

[double precision] TIME

The current simulation time.

Output Values

[double precision] RESULT

The value of the normal force.

Example

def CNFSUB(id, time, par, npar, loci, ni, locj, nj, gap, gapdot, gapdotdot, dflag, iflag):

    stiffness = par[0]

    exponent = par[1]

    damping = par[2]

    dmax = par[3]

    spring_force = stiffness*pow(fabs(gap),exponent)

    [tmp,errflg] = py_step(gap,-dmax,damping,0.0,0.0,0)

    damping_force = -tmp*gapdot

        result = 3*[0]    

        result[0] = spring_force+damping_force

        if result[0]<0.0:

            result[0] = 0.0

    return result