Mass Matrix

The consistant mass matrix for plane and axisymmetric curved shells is computed by performing a volume integration over the element domain, as follows

$\displaystyle {\bf M}$	=	$\displaystyle \int_\Omega \rho \; {\bf A}^T {\bf A}\; d\Omega$	(71)
$\displaystyle {\bf A}$	=	$\displaystyle \left[ {\bf A}_1 \; {\bf A}_2 \; \cdots \right]$	(72)
$\displaystyle {\bf A}_i$	=	$\displaystyle \left[ {\bf N}_i \; {\bf Z}_i \right]$	(73)
$\displaystyle {\bf N}_i$	=	$\displaystyle \left[ \begin{array}{cc} N_i & 0\\ 0 & N_i \end{array} \right]$	(74)
$\displaystyle {\bf Z}_i$	=	$\displaystyle \eta N_i \frac{t_i}{2} {\bf R}_i$	(75)