I have run a modal analysis with the consistent mass matrix using the mass matrix offest with 5% and add modal masses with 5% and an anallysis with noe eccssentriseties. how come the offset mass matrix results are so different??
Adding to nodes -that's clear, masses are added \ moved from nodes to other nodes
Offseting mass matrix - whole mass matrix is shifted; by "kind of" rigid links it is linked with previous state and additionally small "rotation" of this matrix (masses) may appear because of "rigid links" so it is less phisical approach than shifting by adding masses to nodes.