ALPHAD
ALPHAD,
VALUE,
Auto-adjust, Energy Ratio
Defines the mass matrix multiplier for damping.
VALUEMass matrix multiplier for damping. This also serves as the intial multiplier if
Auto-adjustis used.Auto-adjustSet this field to
Autoto enable the software to automatically vary the mass matrix multiplier for damping to aid in convergence (adaptive mass proportional damping). . When this field is set toAuto, the value in field 2 serves as the initial multiplier with a default of 1000. See the Notes section for details.Energy RatioProvide a maximum damping energy to potential energy ratio that the software will try to maintain while auto-adjusting the damping multiplier. This field is only valid if automatic adjustment is activated. Defaults to 0.01.
Notes
This command defines the mass matrix multiplier 
used to form the viscous damping matrix 
, where 
is the mass matrix.
Values of 
can also be input as a material property (MP,ALPD or
TB,SDAMP,,,,ALPD). If ALPD in either form is included, the ALPD value is added
to the ALPHAD value as appropriate. (See Material Damping in the Material Reference and Damping Matrices in the Theory Reference.)
Damping is not used in static (ANTYPE,STATIC) or buckling
(ANTYPE,BUCKLE) analyses.
Use auto-adjustment of mass matrix multiplier for damping to help with convergence in difficult to converge non-linear problems that use the quasi-static (TINTP,QUASI) or static to transient (SOLOPTION,STOT) methods to aid in convergence. Adaptive mass proportional damping is expected to benefit problems that involve:
local buckling
under or unconstrained models
contacts where contact might be getting lost during the solution
At the beginning of every substep, the damping is adjusted to be high enough to provide some stability but low enough that damping energy is a small fraction of the potential energy of the system. This ensures an accurate solution.
The initial value specified in the command is used to determine an upper and lower value for the damping while adjusting. Adjustment is based on the damping and potential energy ratio of the system. If you specify a damping to potential energy ratio, that ratio is only used as a guide during the automatic adjustment. The ratio is not strictly enforced.
This command is also valid in PREP7.