Introduction
Vibration analysis is an important and popular discipline within mechanical engineering and engineering mechanics. It typically involves predicting vibration in new equipment, or analyzing the vibration that occurs in existing machinery. Vibration analysis is a learned skill that becomes easier with experience. While there is much credence given to classroom study, there is much to be gained from actually predicting and measuring vibratory motion. The process of vibration analysis can occur in all types of products, from airplanes and missiles to microelectronics and mini-structures. In a theoretical sense, vibration analysis is the study of deformable structures vibrating about a neutral position of equilibrium. The main tasks in vibration analysis include modal analysis, FEA, random vibration, and sine vibration. Today’s modern engineering tools and software advancements make the practice of vibration analysis a much more accurate process than in years past.

Machinery Vibration Analysis
Analyzing the vibration that occurs in existing machinery is an important aspect of condition monitoring. It is a predictive maintenance technique that is used to determine when failure of a machine is likely to occur. This allows the plant engineering staff to schedule maintenance and downtime when it is least likely to affect the overall operational scenario of the equipment being monitored. This process typically involves measuring the vibratory frequencies and amplitudes that occur over time, while the equipment is operating. Analyzing trends in the vibratory behavior of rotating machinery can predict problems with misaligned shafts, worn bearings, or rotating parts that are out of balance. Suspect parts can then be replaced before more costly equipment failures and resulting downtime occur.

Modal Analysis
Modal analysis is the most important aspect of vibration analysis. If algebra is the study of X, then vibration is the study of resonance. Modal analysis is the process of predicting a structure’s natural (resonant) frequencies (eigenvalues) and corresponding mode shapes (eigenvectors). Modal analysis characterizes a structure’s response to dynamic or vibratory excitation. Any structure will respond to dynamic excitation at a specific number of ‘natural frequencies’, and their corresponding deformation shapes. Modal analysis assumes that the structure vibrates in the absence of damping. Each natural frequency and mode shape is called a mode. Even though modal analysis can (in theory) predict an infinite number of modes, the corresponding dynamic response and stresses will occur at a much smaller number, usually three to six.

Once modal analysis is completed, the analyst can proceed to determining the effects of various dynamic excitations, such as sine or random vibration. The resulting displacements and stresses can now be predicted and assessed. In important consideration in modal analysis is the fact that the mode shapes are only shapes, not deflections. These results can be used, however, for comparisons of movement within the same mode. Typically, mode shapes are normalized so that the maximum movement is one. However, the addition of damping and a vibration input to a mode shape makes it a deflection shape.

Superimposing a structure’s modes is an effective way to characterize its dynamic response. This allows the analyst to perform analysis in the time domain, as well as the frequency domain. Time domain dynamic analysis is necessary for performing transient dynamic response. In summary, modal analysis is the most important step in performing vibration analysis.

FEA Vibration Analysis
Finite Element Analysis (FEA) is a popular and important method used in vibration analysis. Advances in FEA technology allow the analyst to solve more complex vibration problems and make more accurate predictions of vibratory response. Today’s popular FE programs (such as ANSYS) provide solutions for modal analysis, harmonic and random vibration response, and transient dynamic behavior. Most of today’s FE programs allow the analyst to import solid models from CAD programs to begin the process of analyzing a specific structure. As with any vibration analysis, the process begins with modal analysis. The FE mesh for this process does not necessarily have to be as refined as one that would be used to predict dynamic stresses. However, there must be enough nodal density to accurately describe the critical modes (natural frequencies) and their associated mode shapes. Also, a coarse mesh will overestimate the stiffness, and the calculated natural frequencies will be artificially high.

Introduction
Condition monitoring is the practice of monitoring parameters that determine the operating condition of machinery. This process predicts impending equipment failure by noting significant changes in machinery behavior. Condition monitoring is a significant component of predictive maintenance, where scheduled maintenance can be used to prevent equipment failure, before it occurs. The prediction of the time of failure is a cost-effective means of maintaining rotating machinery and stationary machinery, such as boilers and heat exchangers.
Vibration Monitoring in Rotating Machinery
Monitoring vibration in rotating machinery is an important aspect of condition monitoring. The vibration signatures in rotating machinery can be complex, so specialized training and experience is necessary to interpret the data. Today’s technology, however, automatically provides the analyst with the necessary parameters to allow assessment of equipment vibratory behavior. Analyzing vibration data is typically a matter of interpreting the frequency content and amplitude of the vibration signal. The vibratory frequencies typically can be interpreted in lieu of mechanical component performance. These components include rolling element bearings and out-of-balance or misaligned shafts.
Analyzing the Vibration Frequency Content
Vibration frequencies and amplitudes usually tell a story. For example, frequencies that correspond to the equipment’s rotational speed usually indicate an imbalance that can be corrected by rebalancing the machine. Rolling element bearings usually exhibit increasing vibratory amplitudes at specific frequencies. These frequencies usually indicate a bearing that is wearing out. When this occurs, the bearing can be replaced, before total equipment failure occurs. This type of maintenance activity is very cost-effective, as the cost of machinery down time can be very large.
Analyzing the Vibration Amplitude
Today’s vibration data collectors utilize a Fast Fourier Transform (FFT) to convert the time domain vibration signal into a frequency domain signal. Utilizing the frequency content (spectral analysis) is only one method of interpreting machinery vibration data. Depending on the equipment type, a maintenance analyst may also use the time domain data, historical trends, the shape of the vibration signal, and the phase relationships between various amplitudes.
Measuring Vibration with Handheld Data Collectors
Advances in technology and computer software now allow the technician to take measurements using handheld data collectors. This greatly simplifies the data collection process, and can allow for data analysis on site. Larger equipment may still require a dedicated vibration monitoring system, but many equipment types can be analyzed using handheld data collectors. Using either method of data collection, the diagnostic tools are generally the same.

Introduction
Vibration measurements have been used to reliably diagnose performance problems in machinery and related mechanical products. A vibration data collector can be used effectively to measure and analyze the machinery vibration content in gearboxes, engines, turbines, fans, compressors, pumps and bearings. Ideally, a machine will have little or no vibration, indicating that the rotating components are appropriately balanced, aligned, and well maintained. Quick analysis and assessment of the vibration content can lead to fault diagnosis and prognosis of a machine’s ability to continue running. When compared to historical vibration data, vibration measurements can be used to pinpoint mechanical defects such as unbalance, misalignment, resonance, and part loosening.

Collecting Vibration Data
During vibration condition monitoring, the data from the rotating machinery is collected, stored, interpreted, and then compared with historical vibration measurements. Depending on the machine, the vibration data may be gathered using two different techniques. Vibration measurements on larger machines are taken using permanently attached transducers (accelerometers). For smaller machines (with hard-to-reach locations), vibration data is taken using handheld data collectors with portable transducers. The data is then stored and analyzed to determine the machine’s mechanical condition.

Analyzing Vibration Data
Vibration measurements can be expressed in terms of displacement, velocity, acceleration, and high frequency content (for bearing condition detection). Most data collectors use FFT (Fast Fourier Transform) to convert the data from the time domain to the frequency domain. Vibration data collectors have a built-in PC interface that allows transfer of the measurements to a PC for data management. Analysis software displays spectrum, trend, waterfall plots, and waveform for advanced analysis. To assess a machine, the vibration data is compared with historical profiles from the same machine.

Vibration Data Collector Features
Quick, accurate diagnosis of machine vibration conditions, including bearing vibration
Simplifies the task and increases the speed of collecting vibration monitoring data
Incorporates the latest software for vibration data analysis and performance prediction
Combines basic analysis functions and rotating machinery balancing capabilities
Lightweight, compact portable vibration data collectors are easy to use
Used with a portable computer, such as a laptop or notebook
Multiple channel models are available
Usually do not require any special training

Vibration Analysis Introduction
Vibration analysis training is a necessary process for engineers and technicians who desire to understand the vibration that exists in structures and machines. There are two types of vibration analysis tasks that are regularly done today. The first involves predicting the mechanical vibration that will exist in new products. The second involves evaluating the vibration that occurs in rotating machinery such as motors, pumps, and compressors. Advances in technology have greatly enhanced the vibration analysis process for both new and existing products. It is important for professionals in the vibration industries to keep up with the state-of-the-art in vibration analysis techniques.

Vibration Analysis Basics
Whether you are predicting the vibratory response of a new product, or you are analyzing the vibration that occurs in an existing product, vibration analysis is the study of resonance. Resonance occurs at specific frequencies (natural frequencies), where the vibration of the product is increased. Called modal analysis, this process is crucial to understanding the vibration behavior of any product. Once the fundamentals of vibration analysis are learned, vibration analysis training can proceed to more complicated topics, such as finite element analysis.

Finite Element Analysis
Finite element analysis (FEA) is normally used for vibration analysis of new product designs. This method allows the analyst to consider real-world structures that cannot be analyzed with elementary vibration analysis training. Using FEA for vibration analysis involves dividing the structure into a number of elements, and then performing a modal analysis. Using a defined vibration excitation (random vibration, for instance), FEA software is then used to predict the vibratory stresses in the structure. Vibration in existing machinery is analyzed with vibration analysis equipment and integrated software.

Machinery Vibration Measurement
Vibration analysis training is necessary for analyzing and evaluating the mechanical vibration that occurs in rotating machinery, such as motors, pumps, and bearings. Today’s vibration measurement equipment utilizes software that simplifies the analysis of machinery vibration performance. Multiple vibration data parameters are assessed to predict machinery operation. Called vibration condition monitoring, this procedure involves processing large quantities of data to determine if unscheduled maintenance is necessary, or if shutdown is required.

Introduction
Vibration analysis software is an essential tool for professionals who are analyzing the vibratory behavior of structures and machines. There are two types of vibration analysis investigations that are commonly done today. The first involves analyzing the mechanical vibration of new products that are being designed or tested. The second involves analyzing the vibration that exists in rotating machinery such as compressors, turbines, and motors. Advances in computing power and software have greatly enhanced the vibration analysis process for both new and existing products. The most common software package for analyzing new products is finite element analysis software. Vibration in existing machinery is analyzed with integrated software that enhances the vibration analysis equipment.

Vibration Analysis Using Finite Element Analysis Software
Finite element analysis (FEA) software is routinely used for vibration analysis of structures and new products. This method allows the analyst to consider the complicated structures that cannot be analyzed with elementary structural analysis software. Using FEA for vibration analysis involves dividing the structure into a number of elements, and then using the software to calculate the product’s natural frequencies and mode shapes. Using a defined vibration excitation (random vibration, for instance), FEA software is then used to predict the vibratory response (displacements and stresses) of the structure being analyzed. This process can then be repeated until the product is structurally optimized.

Vibration Analysis Software for Evaluating Machinery Vibration
Vibration analysis software is an essential tool for analyzing and evaluating the mechanical vibration that occurs in rotating machinery. In the past, diagnosis of equipment problems using vibration analysis was mostly dependent on the ability of the maintenance technician or the plant engineer. However, today’s vibration analysis equipment utilizes software that has greatly enhanced the analysis of vibration measurements and the prediction of equipment performance. Vibration condition monitoring involves transmitting large quantities of data from a transducer to a separate data collector for subsequent processing and analysis. The software is then used in analysis of multiple machine vibration parameters to assess operating performance. Maintenance personnel then use the data to determine if unscheduled maintenance is necessary, or if shutdown is required..

Summary
Vibration analysis software can be used effectively to analyze new products, or to evaluate the vibration that occurs in rotating machinery. Finite element analysis software allows engineers to optimize new product designs by predicting the vibration scenarios that would occur during operation. Using vibration analysis software for assessing machinery vibration is a cost-effective method to minimize down time and maximize equipment utilization.