Modal analysis (EMA) / Operational deformation (ODS)
The vibratory behavior of industrial structures depends directly on their dynamic characteristics. When mechanical or acoustic excitation coincides with one of a system’s natural frequencies, resonance phenomena can occur, leading to vibration amplification, material fatigue and the risk of failure.
Modal analysis and the study of operational deformations enable us to understand these mechanisms and objectify the actual operation of structures. SIM Engineering supports manufacturers in identifying eigenmodes, analyzing vibratory movements and preventing resonance-related risks.
Stakes involved in the dynamic behavior of structures
Industrial structures such as machine frames, racks, skids, piping, walkways and mechanical supports are subject to a wide range of dynamic stresses. These excitations can come from rotating machines, process pulsations, fluid flows or the external environment.
When the dynamic response is not controlled, excessive deformation, cracking or failure can occur. Vibration engineering aims to precisely characterize these behaviors in order to secure the design and operation of installations.
Meshing and structure instrumentation
SIM Engineering’s modal studies begin with the definition of a representative mesh of the structure. This mesh is used to select the measurement points required for an accurate description of vibratory movements.
Instrumentation is carried out using accelerometers positioned in the relevant directions, ensuring that displacements are taken into account along all three axes. This step determines the quality of the results and the relevance of subsequent analyses.
Experimental modal analysis (EMA)
Experimental modal analysis aims to determine the intrinsic dynamic characteristics of a structure. It is based on the measurement of the vibratory response to controlled excitation.
The excitation force is applied by means of an instrumented impact hammer, enabling precise measurement of the force injected. The dynamic response is simultaneously recorded by accelerometers arranged on the defined mesh.
The tests are carried out on a stationary machine or on an isolated structure, in order to eliminate external excitations and characterize only the system’s own dynamic properties.
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Identification of eigenmodes
The data acquired during the EMA tests can be used to identify natural frequencies, modal shapes and damping coefficients. These parameters constitute the dynamic signature of the structure.
The analysis highlights the modes likely to be excited during operation, and helps anticipate the risk of resonance when process excitation frequencies approach the eigenmodes identified.
Operational distortion (ODS)
The operational deformation completes the modal analysis by describing the actual behavior of the structure under operating conditions. Unlike EMA, ODS is carried out on a machine in service, under natural excitation.
Accelerations are measured over the entire mesh, with synchronized acquisition enabling instantaneous vibratory movements to be restored. This approach provides a direct view of the actual deformations observed during normal operation.Analysis of actual operating movements
The ODS study identifies areas of high dynamic stress, displacement amplitudes and the modes actually excited. It highlights interactions between the structure and surrounding mechanical or acoustic excitations.
This analysis is particularly useful for understanding vibrations observed on site, and for linking measured phenomena to frequencies derived from vibration monitoring or pulsation measurements.
EMA and ODS complement each other
The combination of experimental modal analysis and operational deformation provides a comprehensive approach to vibration behavior. EMA provides theoretical dynamic properties, while ODS reveals actual behavior under load.
By comparing these two analyses, we can precisely identify the mechanisms at the root of excessive vibration, and effectively guide corrective action.
Results and recommendations
The results of modal studies are used to define appropriate technical solutions, such as modifying stiffness, adding reinforcements, modifying weights, shifting natural frequencies or optimizing operating conditions.
These recommendations are designed to achieve a lasting reduction in vibration amplitudes and limit resonance phenomena, while preserving plant functionality.
Vibration engineering for reliability
Modal analysis and the study of operational deformations are essential tools for a detailed understanding of the dynamic behavior of industrial structures. By combining precision instrumentation, advanced dynamic analysis and field expertise, SIM Engineering supports its customers in securing their equipment.
This approach makes it possible to prevent mechanical failures, optimize the service life of structures and make vibration management part of a sustainable industrial performance approach.
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