How Many Modes to Include? (Modal Truncation) — Lesson 3

In linear dynamics, the mode-superposition method provides a very efficient method of determining the response of a system. Since this method uses linear combination of modes for calculating the response of a structure over a range of frequencies, an adequate number of modes needs to be carefully extracted. This video lesson will discuss the significance of modal truncation, and we will also discuss some guidelines and tools on how to extract enough modes. We have a short lecture followed by a workshop example to demonstrate the importance of modal truncation using Ansys Mechanical.

Alternate video link.

Video Highlights

01:12 — Generalized coordinates or modal methods

02:05 — Extracting an optimal number of modes

03:22 — Guideline 1: Appropriate frequency range

04:10 — Guideline 2: Ratio of effective mass to total mass

05:20 — Guideline 3: Understanding actual modes

07:20 — Improving accuracy with fewer modes

08:18 — Walkthrough Example — Clamp

Simulation Files

Download the accompanying archived project file used in the video lesson here. The student version of Ansys simulation software can be downloaded for free here.