# Articles: Vibration Analysis

by Ron Brook

## A Look into Pulse Theory And Why the Walls of Jericho Fell

An excerpt from the book Vibration Spectrum Analysis by Steve Goldman P.E.

This author has spent many years lecturing to different groups of people who were interested in spectrum analysis for problems ranging from detailed physical tests of cavitation phenomena to philosophical questions about why the walls of Jericho Fell. Often, a very simple explanation involving pulse theory has sufficed to explain some of the observed phenomena. This excerpt is designed to give the reader food for thought rather than quantitative answers.

## A Tough Diagnosis - The Saga of the Never Ending Problem

by Greg Davison

You are often told that there is never just one problem with a machine. My very first vibration class taught me that a phase and magnitude vector was a combination of all the vibration from all of the forces acting upon the machine. Likewise, a spectrum also contains all of the frequencies from all of the forces acting upon a machine. So, it is never just imbalance, or just misalignment. It is always some combination of many forcing frequencies. This is precisely why wall charts and cookie cutter solutions do not always work. What follows is a story of multiple problems of mythical proportions.

A Variety of Tools Needed to Locate Problems
by Daniel T. Ambre, P.E.

This article is a vibration case history using Operating Deflection Shape (ODS), Experimental Modal Analysis (EMA) and Finite Element Analysis (FEA) tools and computer animation techniques to solve difficult rotating machinery problems.

## An Introduction to Time Waveform Analysis

In recent years there has been a resurgence in the use of time waveform analysis techniques. Condition monitoring personnel have now come to realize some of the limitations of the FFT process. Since many find the time waveform analysis process difficult and confusing the technique is rarely used to its full potential. The key to the successful utilization of time waveform data is knowing when to use it. This paper examines the limitations of the FFT process and identifies specific applications where enhancing FFT information with time waveform analysis is appropriate.

The paper also details in practical terms how to set up, acquire and manipulate time waveform data. Having discussed the acquisition of the data the paper continues to discuss the interpretation of the data including the time-frequency relationship, symmetry, and pattern recognition of common faults.

## Analysis of Fan Excessive Vibration Using Operating Deflection Shape Analysis - Case Study

Ken Singleton and Bob Bracher

An unspared process fan had exhibited high vibration levels for several months. A request was received to investigate the root cause of the high vibration. The vibration data indicated high levels of fan bearing housing vibration primarily in the axial direction. Plant operations had concerns about the reliability of the fan since it was unspared and the plant was operating at capacity. An outage was not scheduled for several months.

## Balancing a Generator at a Hydro Electric Plant

Just two years after installation of a new turbine-generating unit at the 93-MW Thompson Falls hydro project, PPL Montana LLC noticed increasing vibration values on the generator guide bearing. After several unsuccessful attempts to correct the problem, plant personnel adjusted the clearance on the guide bearings. Since that work was completed, the unit has operated within acceptable vibration values.

## Belt Faults

Belt drives can cause many strange looking spectra. To analyze and troubleshoot belt drives it is imperative to have a high resolution analyzer. I use one with 3200 lines of FFT. To those still using 400 lines that might seem like overkill. This paper, though, will show the necessity of high resolution when troubleshooting many vibration problems.

## Book Review: Case Histories in Vibration Analysis and Metal Fatigue For the Practicing Engineer

Of course, we could have made good use of such a book decades ago. Granted, we have since had access to several good vibration texts by authors with notable academic credentials. Some of these books were based on good course notes and then neatly expounded theories of obvious importance. However, while some of these texts moved on to combine theory and practice, they often fell short of satisfying the true needs of industrial audiences. In clear contrast, Case Histories in Vibration Analysis and Metal Fatigue For the Practicing Engineer by Dr. Anthony Sofronas easily manages to meet these important needs and criteria.

## Detecting Bearing Faults

By Jason Tranter

This article is the first in a series of four. In this article we will provide an overview of how vibration analysis can be used to detect bearing faults. We will only consider the typical failure mode where a spall develops in the bearing and the fault slowly worsens until the bearing ultimately fails. In the next article we will explore how techniques such as enveloping, PeakVue, Shock Pulse, time waveform, and spectrum analysis can be used to detect bearing wear. In future articles we will explore additional fault conditions (cocked bearing, EDM, skidding and other conditions), and in the final article we will examine what the vibration analyst can do to extend the life of the bearing through acceptance testing, correction of unbalance and other conditions, and root cause failure analysis.

## Detecting Bearing Faults -  Part 4

by Jason Tranter

This is the final part of the series on dealing with rolling element bearing defects. In previous articles, we looked at how vibration analysis can be used to detect a range of faults conditions, including lubrication problems; wear, spalls, cracks and other defects; and problems that relate to poor installation practices. In this article, we will discuss how the vibration analyst (and others within the maintenance and operations group) can minimize the number and severity of bearing faults. This is arguably the most important of the four articles.

## Detecting Bearing Faults - Part 3

by Jason Tranter

In the two previous articles (Dec/Jan 2011, Apr/May 2011), the focus has been on how the vibration changes when a "typical" bearing fault develops. We have explored spectrum analysis, time waveform analysis, and a raft of high frequency detection techniques. But there are a number of fault conditions related to rolling element bearings that will not necessarily change the vibration patterns in the ways described thus far. Thus, in this article we will explore fault conditions that relate to poor installation (cocked on the shaft or on in the housing), current flow through the bearing (EDM damage), skidding, and slipping.

## Detecting Bearing Faults Part 2

This article is the second in a series of four. The first article provided a summary of how the vibration patterns change as the bearing fails. After very briefly recapping the basics, this article will discuss the detection and analysis tools that can be used to determine the nature and severity of the bearing fault: ultrasound, Shock Pulse, PeakVue, enveloping, and spectrum and time waveform analysis.

## Diagnosing Tiny Bubbles

### Vibration Signatures of Cavitation in a Centrifugal Pump

by Dr. Lin Liu & Dr. Suri Ganeriwala

Cavitation is a major source of problems in centrifugal pumps.  If it is not detected early enough, it can even destroy a pump.  Vibration analysis is often used to determine the cavitation, but its vibration signature is still elusive.

## Flake Breaker Vibration Analysis Case Study

by Ronald Blay, Lead Analyst, Allied Reliability - Cargill Oil Seed, Fayetteville, NC

This is a Flake Breaker Vibration Analysis Case Study at the Cargill Salt Division Watkins Glen plant

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