MSC.Nastran : RESVEC

RESVEC - Controls the Calculation of Residual Vectors

Using the RESVEC parameter in MSC.Nastran controls to calculation of Residual Vectors.

RESVEC has the following parameters : INRLOD, APPLOD, RVLOD, DAMPLOD

Following are the explanation of these parameters :

INRLOD    Controls calculation of residual vectors based on inertia relief.

APPLOD    Controls calculation of residual vectors based on applied loads.

ADJLOD    Controls calculation of residual vectors based on adjoint load vectors (SOL 200 only)

RVDOF    Controls calculation of residual vectors based on RVDOFi entries

DAMPLOD    Controls calculation of residual vectors based on viscous damping.

Q1.) Does INRLOD always produces 6x (3 transl & 3 rotational) additional inertia relief shapes?
R1) Yes, for a fixed interface structure.


Q2.) What is the different (apart from 'bulk' definition) between RVDOF and APPLOD residual vectors ? Do not both use an unit load for estimation ?
R2) The RVDOF create a load vector at each dof ( i.e. 10 RVDOF = 10 load vectors = 10 displaced shapes). Whereas the APPLOD creates a load vector for each LOAD = (i.e. LOAD = 55 is one load vector and thus only one residual vector. This load could be a combination of FORCEs/MOMENTs/GRAV/PLOADs/etc.)

Q3.) Does APPLOD produces always in maximum 6 additional rigid body shapes for each inertia loads ? e.g. 3 loads -> 3 x 6 DOFs = max. 18 x inertia relief shapes ; is this also true for RVDOF ? From my experience RVDOF's produces only one additional shape per RVDOF entry !
R3) Total Residual Vectors =
APPLOD (i.e. subcases with LOAD=)
+ RVDOF (i.e. one load vector for each RVDOF)
+ INRLOD (i.e. inertia relief modes)
and if discrete dampers are present, one vector for each damper so that a representation of the mode associated with damping energy is retained in the modal space.

Here is an explanation on how the RESVEC vector works :

Under 'typical' circumstances with a fixed interface structure, RESVEC first calculates BASE VECTORS (i.e. static displacements)

The APPLOD and RVDOF force a static analysis that creates displacement vectors that are the same as a SOL 101 analysis.
No inertia relief involved. (Base Vectors = number static subcases plus total number of RVDOF)

INRLOD can be thought of as applying a gravity/rforce to the structure and solving statically.
(Base Vectors = 6 vectors)

DAMPLOD can be thought of as a RVDOF applied at discrete dampers.
(Base Vectors = number of discrete dampers (i.e. cdamp))

The base vectors from the APPLOD/RVDOF/INRLOD/DAMPLOD are then compared to the normal mode vectors and linear combinations of the normal modes are removed from the static displacement vectors so that we don't count the same effect more than once. The residual vectors are 'higher order' modes because the lower order content is removed when the linear combinations of the normal modes are removed. These mode are also orthonormalized w.r.t. the mass matrix. (i.e. {Phi}^T [M] {Phi} = [I] )