Here's a site with lots of papers on modal analysis and operating deflection shape.
That site is a little tricky to navigate.
When you get to the homepage:
select "downloads" from the menu accross the top.
Then you'll ge a second menu below the first which includes "Application Notes" and "Technical Papers". If you select either of those you will see a list of papers but that is not the whole list. There will be a third menu below the first two that lists categories for the papers (or app notes).