3.1.1 Mass Density

To determine weight load and to setup mass matrices in dynamic and transient analysis, DIANA needs the mass density $\rho$ .

    (syntax)

DENSIT

rho is the mass density $\rho$ . ( $\rho$ $\geq$ 0 )For all regular structural elements $\rho$ is the mass density per unit volume. For regular structural interface elements $\rho$ is the mass density per unit area. For fluid-structure interface elements $\rho$ is the density of the fluid $\rho_{{\mathrm{f}}}^{}$ .

Correction for dead weight.

For plane strain, axisymmetric and solid elements DIANA accepts a so-called reduced mass density $\rho_{{\mathrm{red}}}^{}$ according to the syntax below.

    (syntax)

DENSIT

rho is the full mass density $\rho$ ( $\rho$ $\geq$ 0 )applied for the element mass matrices. If you only specify the full density then DIANA will apply this for the dead weight as well. [ $\rho_{{\mathrm{red}}}^{}$ = $\rho$ ]

DENSRE

rhored is the reduced mass density $\rho_{{\mathrm{red}}}^{}$ applied for the dead weight. If you only specify the reduced density, then DIANA will apply this for the mass matrices as well. [ $\rho$ = $\rho_{{\mathrm{red}}}^{}$ ]

DIANA will use $\rho_{{\mathrm{red}}}^{}$ instead of the full $\rho$ , to calculate the dead weight of the model. However, the full $\rho$ will still be used to set up the element mass matrices, i.e., the reduced mass density does not affect the dynamic behavior of the model. A typical application of the reduced mass density is the correction for buoyancy of the weight of a submerged porous medium like soil.