Ejemplo n.º 1
0
def test_kT():
    mns = [[4, 4], [4, 5], [4, 6], [5, 5], [5, 6], [6, 6],
           [8, 9], [9, 8]]
    for m, n in mns:
        for model in ['plate_clt_donnell_bardell',
                      'cpanel_clt_donnell_bardell']:
            p = Panel()
            p.model = model
            p.w1tx = 0
            p.u1tx = 1
            p.u1ty = 1
            p.u2ty = 1
            p.a = 2.
            p.b = 0.5
            p.r = 10
            p.stack = [0, 90, -45, +45]
            p.plyt = 1e-3*0.125
            p.laminaprop = (142.5e9, 8.7e9, 0.28, 5.1e9, 5.1e9, 5.1e9)
            p.m = m
            p.n = n
            p.nx = m
            p.ny = n

            P = 1000.
            npts = 5
            p.forces_inc = []
            for y in np.linspace(0, p.b, npts):
                p.forces_inc.append([0., y, P/(npts-1.), 0, 0])
            p.forces_inc[0][2] /= 2.
            p.forces_inc[-1][2] /= 2.

            k0 = p.calc_k0(silent=True)
            kT = p.calc_kT(c=np.zeros(p.get_size()), silent=True)

            error = np.abs(kT-k0).sum()

            assert error < 1.e-7
Ejemplo n.º 2
0
def test_kT():
    mns = [[4, 4], [4, 5], [4, 6], [5, 5], [5, 6], [6, 6], [8, 9], [9, 8]]
    for m, n in mns:
        for model in [
                'plate_clt_donnell_bardell', 'cpanel_clt_donnell_bardell'
        ]:
            p = Panel()
            p.model = model
            p.w1tx = 0
            p.u1tx = 1
            p.u1ty = 1
            p.u2ty = 1
            p.a = 2.
            p.b = 0.5
            p.r = 10
            p.stack = [0, 90, -45, +45]
            p.plyt = 1e-3 * 0.125
            p.laminaprop = (142.5e9, 8.7e9, 0.28, 5.1e9, 5.1e9, 5.1e9)
            p.m = m
            p.n = n
            p.nx = m
            p.ny = n

            P = 1000.
            npts = 5
            p.forces_inc = []
            for y in np.linspace(0, p.b, npts):
                p.forces_inc.append([0., y, P / (npts - 1.), 0, 0])
            p.forces_inc[0][2] /= 2.
            p.forces_inc[-1][2] /= 2.

            k0 = p.calc_k0(silent=True)
            kT = p.calc_kT(c=np.zeros(p.get_size()), silent=True)

            error = np.abs(kT - k0).sum()

            assert error < 1.e-7
Ejemplo n.º 3
0
class TStiff2D(object):
    r"""T Stiffener using 2D Formulation for the Base and Flange

    T-type of stiffener model using a 2D formulation for the flange and a
    2D formulation for the base::


                 || --> flange       |
                 ||                  |-> stiffener
               ======  --> base      |
      =========================  --> panels
         Panel1      Panel2

    The difference between this model and :class:'.BladeStiff2D' is that here
    the stiffener's base has independent field variables allowing the
    simulation of skin-stiffener debounding effects.

    Each stiffener has a constant `y_s` coordinate.

    """
    def __init__(self,
                 bay,
                 mu,
                 panel1,
                 panel2,
                 ys,
                 bb,
                 bf,
                 bstack,
                 bplyts,
                 blaminaprops,
                 fstack,
                 fplyts,
                 flaminaprops,
                 model='tstiff2d_clt_donnell_bardell',
                 mb=15,
                 nb=12,
                 mf=15,
                 nf=12):

        print(
            '\n\nWARNING - TStiff2D no longer recommended!\n'
            '          There is a numerically unstable way to compute the\n'
            '          connection between the skin and stiffener\'s base, it is\n'
            '          recommended to use panel.assembly instead.\n'
            '          Module panel.assembly allows stable ways to perform\n'
            '          connection among panels, and avoids using sliced\n'
            '          integration intervals that were causing trouble in\n'
            '          TStiff2D\n\n')

        self.bay = bay
        self.panel1 = panel1
        self.panel2 = panel2
        self.model = model

        if bstack is None:
            raise ValueError('Base laminate must be defined!')
        self.ys = ys
        y1 = ys - bb / 2.
        y2 = ys + bb / 2.
        self.base = Panel(a=bay.a,
                          b=bb,
                          r=bay.r,
                          alphadeg=bay.alphadeg,
                          stack=bstack,
                          plyts=bplyts,
                          laminaprops=blaminaprops,
                          mu=mu,
                          m=mb,
                          n=nb,
                          offset=0.,
                          u1tx=1,
                          u1rx=0,
                          u2tx=1,
                          u2rx=0,
                          v1tx=1,
                          v1rx=0,
                          v2tx=1,
                          v2rx=0,
                          w1tx=1,
                          w1rx=1,
                          w2tx=1,
                          w2rx=1,
                          u1ty=1,
                          u1ry=0,
                          u2ty=1,
                          u2ry=0,
                          v1ty=1,
                          v1ry=0,
                          v2ty=1,
                          v2ry=0,
                          w1ty=1,
                          w1ry=1,
                          w2ty=1,
                          w2ry=1,
                          y1=y1,
                          y2=y2)
        self.base._rebuild()

        if fstack is None:
            raise ValueError('Flange laminate must be defined!')
        self.flange = Panel(a=bay.a,
                            b=bf,
                            model='plate_clt_donnell_bardell',
                            stack=fstack,
                            plyts=fplyts,
                            laminaprops=flaminaprops,
                            mu=mu,
                            m=mf,
                            n=nf,
                            offset=0.,
                            u1tx=0,
                            u1rx=0,
                            u2tx=0,
                            u2rx=0,
                            v1tx=0,
                            v1rx=0,
                            v2tx=0,
                            v2rx=0,
                            w1tx=0,
                            w1rx=1,
                            w2tx=0,
                            w2rx=1,
                            u1ty=1,
                            u1ry=0,
                            u2ty=1,
                            u2ry=0,
                            v1ty=1,
                            v1ry=0,
                            v2ty=1,
                            v2ry=0,
                            w1ty=1,
                            w1ry=1,
                            w2ty=1,
                            w2ry=1)
        self.flange._rebuild()

        self.eta_conn_base = 0.
        self.eta_conn_flange = -1.

        self.k0 = None
        self.kM = None
        self.kG0 = None

        self._rebuild()

    def _rebuild(self):
        assert self.panel1.model == self.panel2.model
        assert self.panel1.r == self.panel2.r
        assert self.panel1.alphadeg == self.panel2.alphadeg
        a = None
        b = None
        if self.panel1 is not None:
            a = self.panel1.a
            b = self.panel1.b
        elif self.panel2 is not None:
            a = self.panel2.a
            b = self.panel2.b
        if a is not None and b is not None:
            if a / b > 10.:
                if self.base.m <= 15 and self.flange.m <= 15:
                    raise RuntimeError(
                        'For a/b > 10. use base.m and flange.m > 15')
                else:
                    warn(
                        'For a/b > 10. be sure to check convergence for base.m and flange.m'
                    )

        self.flange.lam = laminate.read_stack(
            self.flange.stack,
            plyts=self.flange.plyts,
            laminaprops=self.flange.laminaprops)
        #NOTE below offset is not needed since it is already considered in the
        #     connectivity matrices, using dpb
        h = 0.5 * sum(self.panel1.plyts) + 0.5 * sum(self.panel2.plyts)
        hb = sum(self.base.plyts)
        self.dpb = h / 2. + hb / 2.
        self.base.lam = laminate.read_stack(self.base.stack,
                                            plyts=self.base.plyts,
                                            laminaprops=self.base.laminaprops,
                                            offset=0.)

    def calc_k0(self, size=None, row0=0, col0=0, silent=False, finalize=True):
        """Calculate the linear constitutive stiffness matrix
        """
        self._rebuild()
        msg('Calculating k0... ', level=2, silent=silent)

        # NOTE
        #     row0 and col0 define where the stiffener's base matrix starts
        #     rowf and colf define where the stiffener's flange matrix starts
        rowf = row0 + self.base.get_size()
        colf = col0 + self.base.get_size()

        k0 = 0.
        k0 += self.base.calc_k0(size=size,
                                row0=row0,
                                col0=col0,
                                silent=True,
                                finalize=False)
        k0 += self.flange.calc_k0(size=size,
                                  row0=rowf,
                                  col0=colf,
                                  silent=True,
                                  finalize=False)

        # connectivity panel-base
        conn = stiffmDB.db[self.model]['connections']

        ktpb, krpb = calc_kt_kr(self.panel1, self.base, 'bot-top')
        ktpb = min(1.e7, ktpb)

        #TODO remove from Cython the capability to run with debonding defect
        y1 = self.ys - self.base.b / 2.
        y2 = self.ys + self.base.b / 2.
        bay = self.bay

        k0 += conn.fkCppy1y2(y1, y2, ktpb, bay.a, bay.b, self.dpb, bay.m,
                             bay.n, bay.u1tx, bay.u1rx, bay.u2tx, bay.u2rx,
                             bay.v1tx, bay.v1rx, bay.v2tx, bay.v2rx, bay.w1tx,
                             bay.w1rx, bay.w2tx, bay.w2rx, bay.u1ty, bay.u1ry,
                             bay.u2ty, bay.u2ry, bay.v1ty, bay.v1ry, bay.v2ty,
                             bay.v2ry, bay.w1ty, bay.w1ry, bay.w2ty, bay.w2ry,
                             size, 0, 0)

        k0 += conn.fkCpby1y2(
            y1, y2, ktpb, bay.a, bay.b, self.dpb, bay.m, bay.n, self.base.m,
            self.base.n, bay.u1tx, bay.u1rx, bay.u2tx, bay.u2rx, bay.v1tx,
            bay.v1rx, bay.v2tx, bay.v2rx, bay.w1tx, bay.w1rx, bay.w2tx,
            bay.w2rx, bay.u1ty, bay.u1ry, bay.u2ty, bay.u2ry, bay.v1ty,
            bay.v1ry, bay.v2ty, bay.v2ry, bay.w1ty, bay.w1ry, bay.w2ty,
            bay.w2ry, self.base.u1tx, self.base.u1rx, self.base.u2tx,
            self.base.u2rx, self.base.v1tx, self.base.v1rx, self.base.v2tx,
            self.base.v2rx, self.base.w1tx, self.base.w1rx, self.base.w2tx,
            self.base.w2rx, self.base.u1ty, self.base.u1ry, self.base.u2ty,
            self.base.u2ry, self.base.v1ty, self.base.v1ry, self.base.v2ty,
            self.base.v2ry, self.base.w1ty, self.base.w1ry, self.base.w2ty,
            self.base.w2ry, size, 0, col0)

        k0 += conn.fkCbbpby1y2(y1, y2, ktpb, bay.a, bay.b, self.base.m,
                               self.base.n, self.base.u1tx, self.base.u1rx,
                               self.base.u2tx, self.base.u2rx, self.base.v1tx,
                               self.base.v1rx, self.base.v2tx, self.base.v2rx,
                               self.base.w1tx, self.base.w1rx, self.base.w2tx,
                               self.base.w2rx, self.base.u1ty, self.base.u1ry,
                               self.base.u2ty, self.base.u2ry, self.base.v1ty,
                               self.base.v1ry, self.base.v2ty, self.base.v2ry,
                               self.base.w1ty, self.base.w1ry, self.base.w2ty,
                               self.base.w2ry, size, row0, col0)

        # connectivity base-flange
        ktbf, krbf = calc_kt_kr(self.base, self.flange, 'ycte')
        ycte1 = (self.eta_conn_base + 1) / 2. * self.base.b
        ycte2 = (self.eta_conn_flange + 1) / 2. * self.flange.b
        k0 += fkCBFycte11(ktbf, krbf, self.base, ycte1, size, row0, col0)
        k0 += fkCBFycte12(ktbf, krbf, self.base, self.flange, ycte1, ycte2,
                          size, row0, colf)
        k0 += fkCBFycte22(ktbf, krbf, self.base, self.flange, ycte2, size,
                          rowf, colf)

        if finalize:
            k0 = finalize_symmetric_matrix(k0)
        self.k0 = k0

        #NOTE forcing Python garbage collector to clean the memory
        #     it DOES make a difference! There is a memory leak not
        #     identified, probably in the csr_matrix process
        gc.collect()

        msg('finished!', level=2, silent=silent)

    def calc_kG0(self,
                 size=None,
                 row0=0,
                 col0=0,
                 silent=False,
                 finalize=True,
                 c=None,
                 NLgeom=False):
        """Calculate the linear geometric stiffness matrix

        See :meth:`.Panel.calc_k0` for details on each parameter.

        """
        self._rebuild()
        if c is None:
            msg('Calculating kG0... ', level=2, silent=silent)
        else:
            msg('Calculating kG... ', level=2, silent=silent)

        # NOTE:
        # - row0 and col0 define where the stiffener's base matrix starts
        # - rowf and colf define where the stiffener's flange matrix starts

        rowf = row0 + self.base.get_size()
        colf = col0 + self.base.get_size()

        kG0 = 0.
        kG0 += self.base.calc_kG0(c=c,
                                  size=size,
                                  row0=row0,
                                  col0=col0,
                                  silent=True,
                                  finalize=False,
                                  NLgeom=NLgeom)
        kG0 += self.flange.calc_kG0(c=c,
                                    size=size,
                                    row0=rowf,
                                    col0=colf,
                                    silent=True,
                                    finalize=False,
                                    NLgeom=NLgeom)

        if finalize:
            kG0 = finalize_symmetric_matrix(kG0)
        self.kG0 = kG0

        #NOTE forcing Python garbage collector to clean the memory
        #     it DOES make a difference! There is a memory leak not
        #     identified, probably in the csr_matrix process
        gc.collect()

        msg('finished!', level=2, silent=silent)

    def calc_kM(self, size=None, row0=0, col0=0, silent=False, finalize=True):
        """Calculate the mass matrix
        """
        self._rebuild()
        msg('Calculating kM... ', level=2, silent=silent)

        rowf = row0 + self.base.get_size()
        colf = col0 + self.base.get_size()

        kM = 0.
        kM += self.base.calc_kM(size=size,
                                row0=row0,
                                col0=col0,
                                silent=True,
                                finalize=False)
        kM += self.flange.calc_kM(size=size,
                                  row0=rowf,
                                  col0=colf,
                                  silent=True,
                                  finalize=False)

        if finalize:
            kM = finalize_symmetric_matrix(kM)
        self.kM = kM

        #NOTE forcing Python garbage collector to clean the memory
        #     it DOES make a difference! There is a memory leak not
        #     identified, probably in the csr_matrix process
        gc.collect()

        msg('finished!', level=2, silent=silent)
Ejemplo n.º 4
0
class TStiff2D(object):
    r"""T Stiffener using 2D Formulation for the Base and Flange

    T-type of stiffener model using a 2D formulation for the flange and a
    2D formulation for the base::


                 || --> flange       |
                 ||                  |-> stiffener
               ======  --> base      |
      =========================  --> panels
         Panel1      Panel2

    The difference between this model and :class:'.BladeStiff2D' is that here
    the stiffener's base has independent field variables allowing the
    simulation of skin-stiffener debounding effects.

    Each stiffener has a constant `y_s` coordinate.

    """
    def __init__(self, bay, mu, panel1, panel2, ys, bb, bf, bstack, bplyts,
            blaminaprops, fstack, fplyts, flaminaprops,
            model='tstiff2d_clt_donnell_bardell', mb=15, nb=12, mf=15, nf=12):

        print('\n\nWARNING - TStiff2D no longer recommended!\n'
              '          There is a numerically unstable way to compute the\n'
              '          connection between the skin and stiffener\'s base, it is\n'
              '          recommended to use panel.assembly instead.\n'
              '          Module panel.assembly allows stable ways to perform\n'
              '          connection among panels, and avoids using sliced\n'
              '          integration intervals that were causing trouble in\n'
              '          TStiff2D\n\n')

        self.bay = bay
        self.panel1 = panel1
        self.panel2 = panel2
        self.model = model

        if bstack is None:
            raise ValueError('Base laminate must be defined!')
        self.ys = ys
        y1 = ys - bb/2.
        y2 = ys + bb/2.
        self.base = Panel(a=bay.a, b=bb, r=bay.r, alphadeg=bay.alphadeg,
                stack=bstack, plyts=bplyts, laminaprops=blaminaprops,
                mu=mu, m=mb, n=nb, offset=0.,
                u1tx=1, u1rx=0, u2tx=1, u2rx=0,
                v1tx=1, v1rx=0, v2tx=1, v2rx=0,
                w1tx=1, w1rx=1, w2tx=1, w2rx=1,
                u1ty=1, u1ry=0, u2ty=1, u2ry=0,
                v1ty=1, v1ry=0, v2ty=1, v2ry=0,
                w1ty=1, w1ry=1, w2ty=1, w2ry=1,
                y1=y1, y2=y2)
        self.base._rebuild()

        if fstack is None:
            raise ValueError('Flange laminate must be defined!')
        self.flange = Panel(a=bay.a, b=bf, model='plate_clt_donnell_bardell',
                stack=fstack, plyts=fplyts, laminaprops=flaminaprops,
                mu=mu, m=mf, n=nf, offset=0.,
                u1tx=0, u1rx=0, u2tx=0, u2rx=0,
                v1tx=0, v1rx=0, v2tx=0, v2rx=0,
                w1tx=0, w1rx=1, w2tx=0, w2rx=1,
                u1ty=1, u1ry=0, u2ty=1, u2ry=0,
                v1ty=1, v1ry=0, v2ty=1, v2ry=0,
                w1ty=1, w1ry=1, w2ty=1, w2ry=1)
        self.flange._rebuild()

        self.eta_conn_base = 0.
        self.eta_conn_flange = -1.

        self.k0 = None
        self.kM = None
        self.kG0 = None

        self._rebuild()


    def _rebuild(self):
        assert self.panel1.model == self.panel2.model
        assert self.panel1.r == self.panel2.r
        assert self.panel1.alphadeg == self.panel2.alphadeg
        a = None
        b = None
        if self.panel1 is not None:
            a = self.panel1.a
            b = self.panel1.b
        elif self.panel2 is not None:
            a = self.panel2.a
            b = self.panel2.b
        if a is not None and b is not None:
            if a / b > 10.:
                if self.base.m <= 15 and self.flange.m <= 15:
                    raise RuntimeError('For a/b > 10. use base.m and flange.m > 15')
                else:
                    warn('For a/b > 10. be sure to check convergence for base.m and flange.m')

        self.flange.lam = laminate.read_stack(self.flange.stack,
                plyts=self.flange.plyts, laminaprops=self.flange.laminaprops)
        #NOTE below offset is not needed since it is already considered in the
        #     connectivity matrices, using dpb
        h = 0.5*sum(self.panel1.plyts) + 0.5*sum(self.panel2.plyts)
        hb = sum(self.base.plyts)
        self.dpb = h/2. + hb/2.
        self.base.lam = laminate.read_stack(self.base.stack,
                plyts=self.base.plyts, laminaprops=self.base.laminaprops,
                offset=0.)


    def calc_k0(self, size=None, row0=0, col0=0, silent=False, finalize=True):
        """Calculate the linear constitutive stiffness matrix
        """
        self._rebuild()
        msg('Calculating k0... ', level=2, silent=silent)

        # NOTE
        #     row0 and col0 define where the stiffener's base matrix starts
        #     rowf and colf define where the stiffener's flange matrix starts
        rowf = row0 + self.base.get_size()
        colf = col0 + self.base.get_size()

        k0 = 0.
        k0 += self.base.calc_k0(size=size, row0=row0, col0=col0, silent=True, finalize=False)
        k0 += self.flange.calc_k0(size=size, row0=rowf, col0=colf, silent=True, finalize=False)

        # connectivity panel-base
        conn = stiffmDB.db[self.model]['connections']

        ktpb, krpb = calc_kt_kr(self.panel1, self.base, 'bot-top')
        ktpb = min(1.e7, ktpb)


        #TODO remove from Cython the capability to run with debonding defect
        y1 = self.ys - self.base.b/2.
        y2 = self.ys + self.base.b/2.
        bay = self.bay

        k0 += conn.fkCppy1y2(y1, y2,
                             ktpb, bay.a, bay.b, self.dpb, bay.m, bay.n,
                             bay.u1tx, bay.u1rx, bay.u2tx, bay.u2rx,
                             bay.v1tx, bay.v1rx, bay.v2tx, bay.v2rx,
                             bay.w1tx, bay.w1rx, bay.w2tx, bay.w2rx,
                             bay.u1ty, bay.u1ry, bay.u2ty, bay.u2ry,
                             bay.v1ty, bay.v1ry, bay.v2ty, bay.v2ry,
                             bay.w1ty, bay.w1ry, bay.w2ty, bay.w2ry,
                             size, 0, 0)

        k0 += conn.fkCpby1y2(y1, y2,
                             ktpb, bay.a, bay.b, self.dpb,
                             bay.m, bay.n, self.base.m, self.base.n,
                             bay.u1tx, bay.u1rx, bay.u2tx, bay.u2rx,
                             bay.v1tx, bay.v1rx, bay.v2tx, bay.v2rx,
                             bay.w1tx, bay.w1rx, bay.w2tx, bay.w2rx,
                             bay.u1ty, bay.u1ry, bay.u2ty, bay.u2ry,
                             bay.v1ty, bay.v1ry, bay.v2ty, bay.v2ry,
                             bay.w1ty, bay.w1ry, bay.w2ty, bay.w2ry,
                             self.base.u1tx, self.base.u1rx, self.base.u2tx, self.base.u2rx,
                             self.base.v1tx, self.base.v1rx, self.base.v2tx, self.base.v2rx,
                             self.base.w1tx, self.base.w1rx, self.base.w2tx, self.base.w2rx,
                             self.base.u1ty, self.base.u1ry, self.base.u2ty, self.base.u2ry,
                             self.base.v1ty, self.base.v1ry, self.base.v2ty, self.base.v2ry,
                             self.base.w1ty, self.base.w1ry, self.base.w2ty, self.base.w2ry,
                             size, 0, col0)

        k0 += conn.fkCbbpby1y2(y1, y2,
                           ktpb, bay.a, bay.b, self.base.m, self.base.n,
                           self.base.u1tx, self.base.u1rx, self.base.u2tx, self.base.u2rx,
                           self.base.v1tx, self.base.v1rx, self.base.v2tx, self.base.v2rx,
                           self.base.w1tx, self.base.w1rx, self.base.w2tx, self.base.w2rx,
                           self.base.u1ty, self.base.u1ry, self.base.u2ty, self.base.u2ry,
                           self.base.v1ty, self.base.v1ry, self.base.v2ty, self.base.v2ry,
                           self.base.w1ty, self.base.w1ry, self.base.w2ty, self.base.w2ry,
                           size, row0, col0)

        # connectivity base-flange
        ktbf, krbf = calc_kt_kr(self.base, self.flange, 'ycte')
        ycte1 = (self.eta_conn_base + 1)/2. * self.base.b
        ycte2 = (self.eta_conn_flange + 1)/2. * self.flange.b
        k0 += fkCBFycte11(ktbf, krbf, self.base, ycte1, size, row0, col0)
        k0 += fkCBFycte12(ktbf, krbf, self.base, self.flange, ycte1, ycte2, size, row0, colf)
        k0 += fkCBFycte22(ktbf, krbf, self.base, self.flange, ycte2, size, rowf, colf)

        if finalize:
            k0 = finalize_symmetric_matrix(k0)
        self.k0 = k0

        #NOTE forcing Python garbage collector to clean the memory
        #     it DOES make a difference! There is a memory leak not
        #     identified, probably in the csr_matrix process
        gc.collect()

        msg('finished!', level=2, silent=silent)


    def calc_kG0(self, size=None, row0=0, col0=0, silent=False, finalize=True,
            c=None, NLgeom=False):
        """Calculate the linear geometric stiffness matrix

        See :meth:`.Panel.calc_k0` for details on each parameter.

        """
        self._rebuild()
        if c is None:
            msg('Calculating kG0... ', level=2, silent=silent)
        else:
            msg('Calculating kG... ', level=2, silent=silent)

        # NOTE:
        # - row0 and col0 define where the stiffener's base matrix starts
        # - rowf and colf define where the stiffener's flange matrix starts

        rowf = row0 + self.base.get_size()
        colf = col0 + self.base.get_size()

        kG0 = 0.
        kG0 += self.base.calc_kG0(c=c, size=size, row0=row0, col0=col0, silent=True,
                finalize=False, NLgeom=NLgeom)
        kG0 += self.flange.calc_kG0(c=c, size=size, row0=rowf, col0=colf,
                silent=True, finalize=False, NLgeom=NLgeom)

        if finalize:
            kG0 = finalize_symmetric_matrix(kG0)
        self.kG0 = kG0

        #NOTE forcing Python garbage collector to clean the memory
        #     it DOES make a difference! There is a memory leak not
        #     identified, probably in the csr_matrix process
        gc.collect()

        msg('finished!', level=2, silent=silent)


    def calc_kM(self, size=None, row0=0, col0=0, silent=False, finalize=True):
        """Calculate the mass matrix
        """
        self._rebuild()
        msg('Calculating kM... ', level=2, silent=silent)

        rowf = row0 + self.base.get_size()
        colf = col0 + self.base.get_size()

        kM = 0.
        kM += self.base.calc_kM(size=size, row0=row0, col0=col0, silent=True,
                finalize=False)
        kM += self.flange.calc_kM(size=size, row0=rowf, col0=colf, silent=True,
                finalize=False)

        if finalize:
            kM = finalize_symmetric_matrix(kM)
        self.kM = kM

        #NOTE forcing Python garbage collector to clean the memory
        #     it DOES make a difference! There is a memory leak not
        #     identified, probably in the csr_matrix process
        gc.collect()

        msg('finished!', level=2, silent=silent)