Experimental modal analysis and motion amplification

Complex vibration problems are rarely solved by looking at a single measurement in isolation. When excessive movement is linked to the structural behaviour of an asset, understanding both how the structure naturally wants to move and how it is actually moving during operation can be key to identifying the root cause.

A recent project brought AVT Reliability’s Asset Integrity Division together with AVT Reliability Ireland engineers to carry out a specialist vibration investigation using Experimental Modal Analysis and Motion Amplification.

This combination of techniques provides engineers with two complementary views of structural behaviour, helping move an investigation beyond simply confirming that excessive vibration exists and towards understanding why it is happening.

Understanding natural frequencies with Experimental Modal Analysis

Every structure has natural frequencies at which it is more susceptible to vibration. If an operating frequency from machinery or another excitation source coincides with, or sits close to, one of these natural frequencies, resonance can occur and vibration levels can increase significantly.

Experimental Modal Analysis is used to identify these natural frequencies and the associated mode shapes of a structure.

During the recent investigation, an instrumented hammer was used to apply a controlled impact to the structure while its response was measured using a roving triaxial sensor at multiple locations. By analysing the relationship between the applied force and the measured response, engineers can build a detailed picture of the structure’s dynamic characteristics.

The result helps answer an important question: how does this structure naturally want to move?

AVT Reliability provides Experimental Modal Analysis as part of its wider Asset Integrity services, alongside techniques including Operational Deflection Shape analysis, Motion Amplification, Finite Element Analysis and structural vibration investigation.

Seeing vibration in operation with Motion Amplification

Modal testing provides insight into the inherent dynamic behaviour of a structure, but engineers also need to understand what is happening when the asset is operating under real loads and conditions.

This is where Motion Amplification provides another valuable layer of information.

Motion Amplification is a non-contact, video-based technique that captures subtle movement which may be difficult or impossible to see with the human eye. The recorded movement can then be amplified, allowing engineers to visualise vibration across machinery, structures and pipework while the equipment remains in operation.

By comparing this operational movement with the natural frequencies and mode shapes identified during modal testing, engineers can determine whether particular structural modes are being excited in service.

Why combine the two techniques?

Used together, Experimental Modal Analysis and Motion Amplification can provide a much stronger basis for root cause investigation.

Experimental Modal Analysis helps establish the dynamic characteristics of the structure. Motion Amplification shows the behaviour taking place under actual operating conditions. Combining the two can help engineers distinguish between symptoms and underlying structural causes, identify resonance or problematic movement patterns and develop corrective actions based on evidence rather than assumption.

This type of investigation can be particularly valuable where conventional vibration measurements have confirmed a problem but have not fully explained its source.

A practical example can be seen in AVT Reliability’s Modal Analysis for Resolving HVAC Fan Failures case study, where modal testing and operational analysis identified natural frequencies in a support structure close to the equipment operating range, helping explain repeated vibration-related failures.

Another example is the Water Industry Membrane Air Blower Fault Analysis case study, where vibration analysis and Motion Amplification were used to identify a structural fault that was contributing to excessive vibration.

From vibration problem to practical engineering solution

The purpose of advanced vibration investigation is not simply to produce more data. It is to provide the engineering understanding needed to decide what should happen next.

Once the behaviour of an asset and its supporting structure is understood, findings can be used to inform practical recommendations, structural modifications, further modelling or other corrective measures. Where required, techniques such as Operational Deflection Shape analysis and Finite Element Analysis can extend the investigation further.

For organisations experiencing complex vibration, resonance or structural issues, AVT Reliability combines specialist Asset Integrity expertise with wider condition monitoring and reliability engineering capabilities to investigate the problem from detection through to resolution.

With engineering teams supporting customers across the UK, Ireland and internationally, specialist expertise can be brought together around the needs of the asset and the site.

Local support. Specialist expertise. One AVT Reliability team.