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Understand Vibrations, Prevent Failures: With ZAset Vibration Client, you can monitor the vibration behavior of individual or multiple fans.
“Mechanical vibration” describes a time-varying motion of a mechanical system around a point of equilibrium or a state of rest, resulting from the interaction of mass (inertia) and restoring forces. This motion can be periodic or quasi-periodic.
Vibration is defined in ISO 2041:2018 as “mechanical oscillation of a body about a position of equilibrium.” In the practical context of mechanical and plant engineering, the term often refers to an undesirable, negatively assessed form of mechanical oscillation that can stress components, cause noise, or even impair the system’s operation.
The terms “vibration,” “mechanical oscillation,” and “oscillation" all describe the same fundamental physical principle: a time-varying motion or state change about an equilibrium position.
The difference lies primarily in their scope and typical field of application, and context rather than in the underlying physics:
The amplitude A quantifies the strength of a vibration and thus the maximum deflection of a system from its equilibrium position. It is of central importance in the assessment of vibration-induced stress and wear. The amplitude is directly related to the vibrational energy stored in the system. As the energy increases, so does the amplitude of the vibration.
The frequency f indicates how many oscillations occur per unit of time and is expressed in hertz (Hz). It is defined as the reciprocal of the period T. It is one of the key parameters in vibration analysis, since many technical causes generate characteristic frequencies.
As a general rule:
Mechanical vibrations can be classified according to various criteria. For understanding technical applications, the distinction based on the type of excitation, damping, and cause is particularly relevant.
In fan engineering, mechanical vibrations resulting from mechanical motion predominantly occur as forced, damped vibrations. Excitation typically arises from a combination of rotor-dynamic causes (e.g., imbalance) and flow-related factors (e.g., turbulence). The interaction of the excitation with the structural properties of the system determines the resulting vibration behavior.
The natural frequency is a system-specific physical quantity that describes the frequency at which a mechanical system oscillates freely after a single excitation. It is determined solely by the physical properties of a system, in particular its mass and stiffness. For a simple linear system, the natural frequency fe is given by the ratio of stiffness k to mass m:
As a general rule:
Real-world systems can have multiple natural frequencies simultaneously, which depend on their geometry and boundary conditions. Each of these natural frequencies is associated with a characteristic vibration pattern (mode).
This mode describes the spatial motion and deformation pattern of the system during vibration. Depending on the mode shape, deflections of varying magnitudes occur at different locations within the system. As a result, certain areas of a component may be subjected to particularly high stresses, while others remain virtually motionless.
Resonance is a physical phenomenon that occurs when the frequency of an external excitation approaches the natural frequency of a system:
fexitation ≈ fe
In this case, the energy supplied to the system is particularly efficient, which can cause the vibration amplitude to increase significantly.
In rotating machinery, the excitation frequencies are often directly related to the rotational speed. Critical speeds refer to those speed ranges in which resonance can occur. In these ranges, increased vibration amplitudes can occur, which can lead to increased wear, noise, or damage to components.
In fan technology, vibration behavior depends not only on the fan type, but also significantly on the installation configuration and operating conditions.
The factors described not only determine the magnitude of the vibrations that occur but also their mode of motion. In practice, these vibrations manifest as characteristic motion patterns known as modes.
When measuring vibrations, the displacement, vibration velocity, and vibration acceleration of a vibrating system are recorded in particular. These physical quantities enable a quantitative description of the vibration behavior.
For data acquisition, sensors are typically mounted at vibration-relevant locations, such as integrated 3-axis sensors in the engine electronics.
The analysis of vibration data is used to identify the causes of vibrations, evaluate operating conditions, and detect critical changes at an early stage. To this end, measurement data is analyzed and visualized using software.
Advanced software-based analysis systems enable the automated analysis of large amounts of data as well as the reproducible evaluation of complex vibration systems.
Continuous vibration monitoring enables the early detection of changes in operational behavior and forms the basis for condition-based maintenance (condition monitoring).
By the ongoing collection and analysis of vibration data, critical changes in operational behavior can be detected early, and potential damage can be predicted even before critical operating conditions arise.
In the case of fan arrays (fan walls), the vibration behavior must also be considered as an overall system. Compared to individually operated fans, the vibrations of multiple fans can influence one another.
These interactions arise in particular through shared support structures, housings, or flow-induced couplings. As a result, vibrations can be locally amplified, superimposed, or transmitted to other components.
If multiple fans are operated at similar but not exactly identical rotational speeds, beat phenomena may also occur. This results in periodic amplifications and attenuations of the vibration amplitudes.
Furthermore, the entire fan array has its own structural natural frequencies and modes. If these are excited simultaneously by multiple fans, increased dynamic loads can arise within the overall system.
Therefore, for analysis and monitoring, it is not only the evaluation of individual fans that is relevant, but also the dynamic behavior of the entire system. Advanced monitoring systems enable the synchronous acquisition and analysis of multiple fans within a single system.
To reduce critical vibrations, measures such as vibration isolators and the targeted avoidance of critical resonance ranges within the operating range are employed.
Automated Vibration Measurement & Vibration Analysis for Fans - With ZAset Vibration Client
In practice, vibration problems often do not occur in isolation but result from the interaction of several causes. Vibrations can be reduced through design, rotor dynamics, structural, or control measures.
The following selection of measures can help minimize vibration excitation, prevent resonance, and limit the transmission of vibrations to the surrounding environment:
