Intelligent Fault Diagnosis and Remaining Useful Life Prediction of Rotating Machinery

Yaguo Lei

• Publisher: Butterworth-Heinemann
• Year: 2016
• Print ISBN:
  9780128115343
• eBook ISBN:
  9780128115350
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Intelligent Fault Diagnosis and Remaining Useful Life Prediction of Rotating Machinery provides a comprehensive introduction of intelligent fault diagnosis and RUL prediction based on the current achievements of the author's research group. The main contents include multi-domain signal processing and feature extraction, intelligent diagnosis models, clustering algorithms, hybrid intelligent diagnosis strategies, and RUL prediction approaches, etc. This book presents fundamental theories and advanced methods of identifying the occurrence, locations, and degrees of faults, and also includes information on how to predict the RUL of rotating machinery. Besides experimental demonstrations, many application cases are presented and illustrated to test the methods mentioned in the book. This valuable reference provides an essential guide on machinery fault diagnosis that helps readers understand basic concepts and fundamental theories. Academic researchers with mechanical engineering or computer science backgrounds, and engineers or practitioners who are in charge of machine safety, operation, and maintenance will find this book very useful. - Provides a detailed background and roadmap of intelligent diagnosis and RUL prediction of rotating machinery, involving fault mechanisms, vibration characteristics, health indicators, and diagnosis and prognostics - Presents basic theories, advanced methods, and the latest contributions in the field of intelligent fault diagnosis and RUL prediction - Includes numerous application cases, and the methods, algorithms, and models introduced in the book are demonstrated by industrial experiences

1

Introduction and background

Abstract

This chapter gives an overall introduction and background of this book. It starts by introducing the importance of rotating machinery in industrial applications. Then, some commonly used components of rotating machinery are briefly introduced. From the analysis of some reports it is concluded that, the health management of rotating machinery is significant for reducing the operation and maintenance costs. It further introduces the development of the maintenance strategies and the strategy of prognostics and health management is overviewed, which includes five major processes, that is, data acquisition, signal processing, diagnostics, prognostics, and maintenance decision. By the end of the chapter, the organization of the rest of the book is introduced, which aims to offer a guideline for readers.

Keywords

rotating machinery

maintenance strategy

predictive maintenance

prognostics and health management

diagnostics

prognostics

1.1. Introduction

Rotating machinery is commonly used in mechanical systems and plays an important role in industrial applications (Lei et al., 2013). It generally operates under tough working environment and is therefore frequently subject to faults. Any fault of the rotating machinery possibly causes a breakdown of the entire mechanical system, which may reduce the reliability, security, and availability of the machinery. With the rapid development of science and technology, rotating machinery in modern industry is growing larger and more precise. The structure of rotating machinery is becoming more complex. As a result, its potential faults become more difficult to be detected. Therefore, how to maintain the normal operation of rotating machinery has attracted considerable attention in recent years.

There are various kinds of rotating machinery in various industry fields, such as the aeroengine in the field of aerospace, the gas turbine and wind turbine in the field of energy, and the automobile transmission in the field of traffic. Even though the rotating machinery is diversified, it generally includes some common essential rotating parts, such as rotors, rolling element bearings, and gears.

A rotor is defined as a rotating part of a machine that is generally supported by bearings. They are the indispensable components in rotating machinery. With the increasing requirement of reliability and precision of rotating machinery, rotors become more flexible and operate under tight clearances and harsh environment. Under such circumstances, one incipient fault possibly causes severe damages in other components and results in failures of the entire machine. For example, a little unbalance of a rotor might cause rub or serious impact between the rotating parts and the stationary parts under a high-speed condition. Severe thermal and mechanical stresses might lead to a fatigue crack in the rotors. The common fault types of rotors include mass unbalance, bent, misalignment, rub, resonance, and so on.

A rolling element bearing is a component that carries loads by placing rolling elements (such as balls or rollers) between two races. The relative motion of the rings causes the rolling elements to roll with little rolling resistance and little sliding. The rolling element bearing is developed from an ancient transportation strategy where sets of logs are laid on the ground with a large stone block on the top. As the stone is pulled, the logs roll along the ground with little sliding friction. A rolling element bearing generally includes three components: an outer race, an inner race, and several rolling elements. Rolling elements, such as balls or rollers, are able to reduce the friction forces between the contacting elements. A rolling element bearing is generally used to connect a shaft and a much larger hole with rollers tightly filling the space between the shaft and hole. As the shaft turns, each roller acts as the logs in the above example. Since the special position and function, rolling element bearings generally suffer from various attacks, such as improper mounting, mishandling, poor lubrication, entry of foreign matter, and abnormal heat generation. All of these may cause different types of faults on rolling element bearings. The common fault types include flaking, spalling, peeling, abrasion, scoring, corrosion, pitting, crack, material failure, and so on.

A gear is a rotating machine part having cut teeth, which meshes with another toothed part to transmit torque. Two or more gears working in a sequence (train) are called a gear train or, in many cases, a transmission. Such gear arrangements are able to produce a mechanical advantage through a gear ratio. Geared devices can change the speed, torque, and direction of a power source. Although, the most common situation is that a gear meshes with another gear. A gear meshes with a nonrotating toothed part, called a rack, thereby producing translation instead of rotation. The gears in a transmission are similar to the wheels in a crossed belt pulley system. An advantage of gears is that the teeth of a gear can prevent slippage. When two gears mesh, and one gear is bigger than the other, a mechanical advantage is produced, with the rotational speeds and the torques of the two gears differing in an inverse relationship. On account of the characteristics of the gears, they are widely used to transmit torque and rotation in mechanical systems.

Rotating machinery plays an important role in the industry applications because of its specific functions for mechanical systems. However, due to the specific function requirement, rotating machinery generally operates under tough working environment. Consequently, it always has a higher fault rate compared with other components, and most maintenance costs are directly or indirectly caused by the fault of rotating machinery. Here, we take the wind turbine system, for example, and give some reports about its fault rates and maintenance costs.

The worldwide wind markets have been dramatically developed in recent years because of its economic advantages and environmental protection compared with other sources of electricity. According to the half-year report in 2014 published by the World Wind Energy Association (WWEA) (The World Wind Energy Association, 2014), the total installed capability of the worldwide wind turbine presents a stable increasing trend from 2011 to 2014 as shown in Fig. 1.1. The worldwide wind turbine capacity reached 336,327 MW by the end of June 2014. The total worldwide installed wind turbine capacity by mid-2014 has generated around 4% of the world’s electricity demand.

Figure 1.1 Total installed capacity of the worldwide wind turbine.

A major issue with the wind turbine system is the relatively high costs of operation and maintenance (OM). Wind turbines are hard-to-access structures, and they are often located in remote areas. These factors increase the OM costs for wind turbine systems. In addition, poor reliability directly reduces the availability of wind power due to the turbine downtime. For a turbine with over 20 years of operating life, the OM costs are estimated to be 10–15% of the total income for a wind farm, and the OM costs for offshore wind turbine are estimated to be 20–25% of the total income (Lu et al., 2009). The main fault types of the wind turbine are shown in Fig. 1.2, including imbalance, wear, fatigue, and impending cracks in rotor blades, bearings, shafts, the gearbox, the generator, the yaw, and the pitch angle mechanism. A study result for the causes of failures of wind turbines is shown in Fig. 1.3. It is seen that, the gearbox and generator are responsible for 17% of failures and 30% of the maintenance costs, which are clearly leading candidates for the causes of failures. Even in the wind turbine generators, most faults are still caused by the rotating machinery. For induction machines, about 40% failures are related to bearings, 38% to the stator and 10% to the rotor (Hyers et al., 2006).

Figure 1.2 Overview of the main faults of wind turbines.

Figure 1.3 Statistic results for the causes of failure of wind turbines.

It is concluded from the above reports that the fault of rotating machinery is the main cause of the failure of wind turbines. This trend is similar in many other mechanical systems. So the health management of rotating machinery is significant for reducing the OM costs of mechanical systems. Analysis of maintenance costs has shown that a repair made after failure always wastes lots of costs compared with the same maintenance when the failure has not occurred. A survey carried out by major organizations has revealed that with an investment of 10,000 – 20,000 dollars in health management, one can save up to 500,000 dollars annually (Saranga and Knezevic, 2001). Thus, it is apparent that an appropriate health management strategy is essential to sustain the inherent reliability of mechanical systems and reduce...

Table of contents

• Cover
• Title page
• Table of Contents
• Copyright
• Preface
• About the Author
• 1: Introduction and background
• 2: Signal processing and feature extraction
• 3: Individual intelligent method-based fault diagnosis
• 4: Clustering algorithm–based fault diagnosis
• 5: Hybrid intelligent fault diagnosis methods
• 6: Remaining useful life prediction
• Glossary
• Index