Introduction

Structural vibration analysis studies the motion of machines, frames, foundations, buildings, piping and more. At M&B, we use the ME’scope software package for doing both Operating Deflection Shape (ODS) & Experimental Modal Analysis (EMA).

Background

All objects will move if shaken with enough force. The input forces can come from nearby machines, or from wind, water or product flow. Nearby traffic, railways and construction can also cause vibration. When these inputs match with a structure’s resonance, high vibration can result. As an example, we have tested many fan & blower frames. Some of theses were poorly designed, with a focus on low cost, and lacked the strength needed to restrain machine forces. This leads to higher vibration & lower reliability.

Modelling

To begin an analysis we will create a 3D model of the machine in ME’scope. Next, we measure the machine vibration at many points, and then import the data to the model. After pairing the data and points on the model, we can create animated mode shapes to visualize the vibration. We can then identify where changes are needed to help control or reduce the vibration.

ODS Analysis

For rotating machines, our first step is an ODS study that is done with the machine running. We gather phase-tagged data from the structure, and couple it within the 3D model.This creates the FRFs to animate the model, and shows the machine response at operating speed. By using slow-motion ODS videos, we can study the overall machine motion, and define how parts move relative to each other. Points with high vibration, flexure, looseness, or with no vibration, are all easily found using the animated models.

EMA Studies

To get more insight from rotating machines, or from static structures and piping, we then use EMA studies. For EMA, we use measured inputs across a range of frequencies, to excite a structure. The input sources can include force (modal) hammers & shakers. By varying the input frequency, we find a structure’s response across the desired range of frequencies. Curve fitting & parameter estimation can also be used to get better clarity around closely coupled resonances.

Like ODS, once we identify the mode shapes, we can correlate them to likely vibration sources, and then design changes to reduce or control the vibration.

Reporting

To help everyone better understand the data, we create digital movies of each important mode shape. The files use an MP4 format and are easy to share with management & staff. And, they can be used in documents & slide shows, helping show the problems clearly.

If you have a structural vibration issue, give us a call, we can help – contact us.

• Compressors
• Boiler & Process Fans
• Cooling tower fans
• Vertical & Horizontal Pumps
• Reciprocating Engines
• Gearboxes
• Pulverizers & Ball Mills