use of ABAQUS Explicit - importance of *bulk viscosity

Hello there!

 I am fairly new to ABAQUS but I have been trying to model several experimental set-ups on cold-formed steel beams. I intend to obtain both the elastic buckling critical modes (*buckle analysis), as well as the load parameter corresponding to failure, which i first modelled through a NLGEOM analysis (*STEP, NLGEOM, INC=xxx/*STATIC, RIKS).

 I have realized that using ABAQUS/Standard and applying distributed loads, often leads to poor results. Thus, I have decided to move to a quasi-static model (ABAQUS/explicit) where displacement is applied instead of force, through the *boundary , amplitude command. In this context,I have found some trouble answering the following doubts:

(i) given the fact that the amplitude definitions are not available on a *buckle analysis, how do I get the load parameter for each buckling mode (eigen values)? Should I apply force instead for the first-order buckling analysis?

(ii) i have moved from the riks analysis to use the *Dynamic, Explicit instruction, which allows me to apply a time dependent displacement function (thus more accurately modeling the actual experiment). How important is the *Bulk Viscosity instruction, and how should I define its parameters?

Thanks in advance to any answers!

PN