Subroutine Type

Modeling

Definition

Used to calculate friction forces for the Force_Contact element.

Use

Implements a friction 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            = "Impact"

    stiffness           = "500."

    exponent            = "1.5"    

    damping             = "0.5"

    dmax                = "0.01"    

    cff_type            = "UserCFF"

    cff_param_string    = "USER(0.05,0.01,0.1,0.5)"

    cff_fnc_name        = "CFFSUB"

    cff_dll_name        = "NULL"    

 />

Calling Syntax

Fortran

SUBROUTINE CFFSUB (ID, TIME, PAR, NPAR, LOCI, LOCJ, X, XDOT, NFORCE, AREA, DFLAG, IFLAG, RESULTS)

C

void  STDCALL  CFFSUB (int *id, double *time, double *par, int *npar, double *loci, double *locj, double *x, double *xdot, double *nforce, int *dflag, int *iflag, double *result)

Python

def CFFSUB(id, time, par, npar, loci, locj, x, xdot, nforce, dflag, iflag):

    return result

MATLAB

function vector = CFFSUB(id, time, par, npar, loci, locj, x, xdot, nforce, 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.

[integer] ID

Force_Contact element identifier.

[logical] IFLAG

A Boolean variable that MotionSolve sets to true when it needs to know which functions CFFSUB depends on.  When the flag is set to false, 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] NFORCE

The value of the normal force.

[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.

[double precision] X

The contact deformation vector.

The first two elements contain deformation along the x- and y-axes of the I incident marker.  The third element contains the rotational deformation about z-axis of I incident marker.

[double precision] XDOT

The contact slip velocity vector.

The first two elements contain the slip velocity along the x- and y-axes of the I incident marker.  The third element contains the angular velocity about the z-axis of the I incident marker.

Output Values

[double precision] RESULT

The value of the friction force vector.

The first two elements contain the force along the x- and y-axes of the I incident marker.  The third element contains the torque about the z-axis of the I incident marker.

Example

def CFFSUB(id, time, par, npar, loci, locj, x, xdot, nforce, dflag, iflag):

    result = [0, 0, 0]

        mu_sta = float(par[0])

        mu_dyn = float(par[1])

        vs = float(par[2])

        vd = float(par[3])

        v = sqrt(xdot[0]*xdot[0]+xdot[1]*xdot[1])

        mu = 0.0

        if v>=vd:

            mu = mu_dyn

        elif v>vs:

            mu, errflg] = py_step(v, vs, mu_sta, vd, mu_dyn, 0)

        else:

            [mu, errflg] = py_step(v, -vs, -mu_sta, vs, mu_sta, 0)

                result[0] = -mu*(nforce)*xdot[0]/v

                result[1] = -mu*(nforce)*xdot[1]/v

        return result