The Blunderbuss effect is described in the Introduction to Dynamics e-Learning course.
Torsional modes can look strange in the post-processor view due to a spurious graphics effect. I labeled this the ‘blunderbuss effect’ many years ago.
This module describes this effect further with animations of torsional modes
The lesson within the module shows a video of the effect. Data descriptions and download links are also included in the lessons.
You may navigate around in whichever way you find most useful.
Please enjoy the module!