CFFSUB

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"      
  />

Format

Fortran Calling Syntax

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

C/C++ Calling Syntax

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 Calling Syntax

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

MATLAB Calling Syntax

function vector = CFFSUB(id, time, par, npar, loci, locj, x, xdot, nforce, dflag, iflag)

Attributes

AREA: [double precision]; The area of the contact patch.
DFLAG: [logical]; A Boolean variable that MotionSolve sets to true when it needs partial derivatives. Otherwise, it is set to false.
ID: [integer]; Force_Contact element identifier.
IFLAG: [logical]; 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.
LOCI: [double precision]; 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.
LOCJ: [double precision]; 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.
NFORCE: [double precision]; The value of the normal force.
NPAR: [integer]; The number of entries in the PAR array.
PAR: [double precision]; An array that contains the constant arguments from the list provided in the user-defined statement.
TIME: [double precision]; The current simulation time.
X: [double precision]; 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.
XDOT: [double precision]; 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

RESULT: [double precision]; 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