ME'scopeVES Application Note #11 - Using a Tuned Absorber to Suppress Vibration

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App Note #11

www.vibetech.com

2/25/2014

ME’scope Application Note #11 Using a Tuned Absorber to Suppress Vibration INTRODUCTION NOTE: The steps in this Application Note can be duplicated using any Package that includes the VES-5000 SDM option.

plitude resonance is replaced by two resonances on either side of it. More importantly, the vibration level at the troublesome resonant frequency is greatly reduced because of the suppression of the resonance at that frequency.

Tuned Absorbers are used in many industrial applications to suppress the level of troublesome resonant vibration. A Tuned Absorber is modeled as a mass attached to the problem structure with a spring & damper, as shown in Figure 1. Constructing a physical Tuned Absorber that behaves as a mass-spring-damper system is a separate challenge. Nevertheless, ME’scope is useful for examining the effects of different absorber parameters and locations before fabricating an actual absorber. The key idea behind the use of the Tuned Absorber is that the mass and spring stiffness are chosen so that the Tuned Absorber vibrates at the same frequency as the troublesome resonance. Also, the Tuned Absorber is attached to the structure at an anti-node (high amplitude point) of the troublesome resonance, so the absorber will absorb the vibration energy instead of the resonance. The best way to examine the effect of a Tuned Absorber is to compare FRFs at an active point on the structure before and after the absorber has been attached to it.

Figure 2. Driving Point FRFs Overlaid. How It Works Adding a Tuned Absorber to a structure involves solving a sub-structuring problem. To solve this problem, three parts are needed; 

The mode shapes of the unmodified structure.

The rigid body mode shape of the Tuned Absorber mass.

The spring & damper required to attach the Tuned Absorber to the structure.

Use of the Tuned Absorber will be illustrated by attaching an absorber to an SDOF system. The accuracy of the results of adding the Tuned Absorber will be checked in two different ways; 

Comparing the modes of the SDOF model with the Tuned Absorber attached with the modes of a 2-DOF model.

Comparing the modal frequencies with those calculated from an analytical handbook formula.

By comparing with the modes of a 2-DOF model, and analytical frequencies from a handbook. Figure 1. Tuned Absorber & SDOF Model.

CONSTRUCTING THE SDOF MODEL

Figure 2 shows the typical effect of a Tuned Absorber on a structure. After the absorber is applied, a single high am-

In this example, an SDOF (mass-spring-damper) model will be created, and its single flexible body mode of vibration

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