Introduction

Currently, vibration analysis in industrial assets is highly relevant to ensure the safe and efficient operation of equipment and structures, and is also extremely important to protect workers' health and provide a quality end product. This analysis aims to promote availability and safety for operation, since an asset in operation generates vibrations that, if not treated properly, can drastically reduce the useful life of the structure or even cause a collapse due to frequency coupling.

In this context, these vibration data are commonly used in conjunction with structural analysis by the finite element method (FEM), which simulates the behavior of equipment and structures when subjected to acceleration and vibration. Vibration measurements are used to calibrate the computational model, establishing a comparison between theoretical and experimental data in order to validate the model developed.

This article will present two successful cases, each using a different methodology for collecting and analyzing vibrations: accelerometry and the motion amplification camera.

Accelerometry

Methodology

In general, accelerometry instrumentation is widely used in industrial assets for measuring and monitoring vibrations. As the name suggests, the method uses an accelerometer, which is a device sensitive to acceleration that converts mechanical vibration into an electrical signal proportional to the acceleration. One such sensor can be seen in Figure 1 below.

Figure 1: Accelerometer model - SOURCE: Kot Collection.

These sensors are attached to the surfaces of the assets to be monitored, and their positioning is extremely important in order to capture the vibrations of interest. After installation, vibrations are recorded over time, so that data can be collected either at specific intervals or continuously.

Next, the electrical signals generated by the accelerometers are processed by specific software, enabling the extraction of relevant vibration data such as frequency, amplitude, and waveform. This data is then interpreted, at which point possible vibration patterns and non-conformities with applicable standards are evaluated, which may be indicative of problems such as misalignment, imbalance, or even looseness in components and structures.

Succes story

In one of its recent projects, Kot Engenharia vibration measurements in a metal structure building that is part of a mining plant. This type of asset usually consists of various pieces of equipment whose operation results in dynamic loads, the magnitude, direction, and position of which may vary over time. As a result, the asset's responses in terms of displacement, velocity, and acceleration may also vary, making the measurement and collection of vibration data extremely important for assessing the structural condition of the building.

In this study, the client had reported excessive vibrations in the building's structure. This prompted a request to carry out vibration measurements on the building, followed by a structural analysis and, if necessary, proposed changes to remedy the excessive vibrations in the structure.

First, measurements were taken with accelerometers at certain points of interest in the structure, with the aim of assessing vibration levels in beams, columns, and equipment bases. Figure 2 below shows one of these sensors after installation.

Figure 2: Accelerometer installed - SOURCE: Kot Collection.

The measurements collected cross-sectional, vertical and longitudinal data, in which speeds higher than those permitted by the standard for long-term vibrations in industrial buildings were identified. This data was used to calibrate the computer model, which was then used to analyze the structure of the asset and propose improvements to adjust vibration levels. Gif 1 shows one of the natural vibration modes investigated in the modal analysis and Gif 2 shows the variation in speed over time in one of the axes.

Gif 1: Natural vibration modes - SOURCE: Kot Collection.

Gif 2: Speed variation over time - SOURCE: Kot Collection.

For this reason, it was possible to identify that the main vibrations in the structure were coming from a specific piece of equipment. Reinforcements were then proposed which, after further structural analysis, indicated a significant improvement in the vibration levels of the structure.

Motion amplification camera

Methodology

One of the methodologies recently developed for collecting and processing vibration data is image processing, a method associated with the use of a high-speed camera responsible for generating video recordings that measure the actual displacement of the structure. These recordings are processed in specific software, resulting in waveforms and vibration spectra from the amplified videos.

In addition, one of the main benefits of this methodology is the simultaneous measurement at several points, with the only requirement being that these points are framed in the same image to be captured. Furthermore, the camera also eliminates the need to stop equipment to install sensors, so that measurements can be taken at a safe distance from the asset being evaluated.

In this sense, this method is capable of performing high-precision measurements, using a system composed of high-resolution and high-speed cameras, lighting systems, lenses, and computers with specific software. The software in question transforms the pixels of the image into "sensors," and these points are then analyzed to obtain the vibration spectrum and waveform. Figure 3 below shows a Kot professional using the equipment in question to collect vibration data.

Figure 3: Vibration measurement with a motion amplification camera - SOURCE: Kot Collection.

Success of success

In one of the applications of this methodology, one of our clients requested the collection of vibrations in an industrial building that had undergone some modifications. After the installation of these new structures, the building began to show excessive vibrations, which is why an assessment of the structural condition of the asset under these conditions was requested, with the proposal of improvements to bring the vibration levels into line with those permitted by the standard, if necessary.

Therefore, the use of a motion amplification camera was proposed to meet the client's needs. One of the recordings collected during the field measurements can be viewed below in GIF 3.

Gif 3: Images collected by the camera - SOURCE: Kot Collection.

Next, after the vibration measurements, the collected data were used to calibrate the computational model, which was then used to perform the structural analysis using the finite element method (FEM). This assessment identified that the excitation loads on the building were below the maximum dynamic loads specified in the design. Next, a comparison was made between the displacements in the axes for the actual condition, measured in the field with the camera, and for the theoretical condition, and the model was validated based on the proximity of these values, as can be seen below in Figure 4.

Figure 4: Displacement on one of the axes - SOURCE: Kot Collection.

After calibration, it was found that the vibration frequency of the structure was very close to the operating frequency of a specific piece of equipment located in the building. This was due to the proximity of the equipment's frequency to the building's first natural frequencies. After the study, structural non-conformities were identified at certain points in the structure, and reinforcements were proposed to bring the vibrations into line with the admissible levels recommended by the applicable standards.

Conclusion

Following the two cases presented, it is clear that the methodologies for carrying out vibration measurements and analysis are increasingly present in day-to-day industry, and are very relevant for assessing the levels of vibration acting on equipment, components and structures, and their possible implications.

In addition, prior knowledge of these methodologies is essential in order to define the best course of action for each situation. With the assessment of technical experts, this information is used to make decisions, defining improvements and modifications to be implemented for greater reliability, safety and operational efficiency.

Kot has a large team of qualified professionals to assess, select, and apply the methodologies and solutions best suited to your business and assets. Consult our team for more information!

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