Classical Modal Analysis

Modal analysis is vital to understanding and optimising the inherent dynamic behaviour of structures, leading to lighter, stronger and safer constructions, less fuel/power consumptions, higher comfort, and better performance.

In modal analysis a mathematical model of a structure’s dynamic behaviour is obtained. The mathematical model consists of a set of mode shapes each with an associated natural frequency and modal damping. These modal parameters provide a complete description of the structure’s dynamic behaviour.

Experimental Modal Analysis is based on determining the modal parameters by testing, unlike Analytical Modal Analysis, where the modal parameters are derived from Finite Element Models (FEMs). There are two ways of doing Experimental Modal Analysis: Classical Modal Analysis and Operational Modal Analysis . In Classical Modal Analysis frequency response functions (or impulse response functions) are calculated from measured input forces and output responses of a structure. In Operational Modal Analysis only the output responses are measured. The ambient and operating forces are used as unmeasured input.

Classical Modal Analysis is used in a vast range of applications including:

• Ensuring that resonances are away from excitation frequencies
• Prediction of the dynamic behaviour of components and assembled structures
• Optimisation of the structure’s dynamic properties (mass, stiffness, damping)
• Prediction of the forces from measured responses
• Prediction of the responses due to complex excitation
• Prediction of the effect of structural modifications
• Inclusion of damping in Finite Element Models
• Updating of Finite Element Models
• Damage detection and assessment

Classical Modal Analysis ranges from simple mobility tests with impact hammers to multi-shaker testing of large and complex structures with hundreds of response accelerometers. Brüel & Kjær’s modal solution are expandable and can grow with your requirements.

Structural Dynamic Test Consultants

Modal Test Consultant (MTC) Type 7753 and Operating Deflection Shapes Test Consultant (ODS TC) Type 7765 are PULSE applications developed to simplify and dramatically reduce the time required to perform structural dynamic measurements. Together they are referred to as Structural Dynamic Test Consultants. MTC supports both Classical Modal Analysis and Operational Modal Analysis. 

The Structural Dynamic Test Consultants utilise the PULSE multi-analysis platform. They are graphically driven and easily controlled, linking the measurement directly to the on-screen test object geometry. These features, together with highly effective tools for setup, measurement and validation, make testing fast and reliable. ODS results can be animated directly in ODS TC and FRFs directly in MTC. The data generated (time, spectra, geometry and DOF information) can then be used directly by your chosen post-processing package, such as I-deas^® Test or ME'scopeVES^tm (both available through Brüel & Kjær)  

	Modal Test Consultant is graphically driven, linking the measurement directly to the on-screen test object geometry. The user is safely guided through the specific tasks required for the test
	Points, lines, surfaces or basic shapes can be edited and combined to rapidly build up the test object geometry. Complex geometry objects can be imported from CAD software in UFF or DXF format
	Modal Test Consultant incorporates timesaving tools for maximum data reliability and shorter test time. One example is the automatic double-hit detection and rejection tool
	PULSE seamlessly handles multiple exciter testing (MIMO analysis providing accurate, precise and reliable FRF data sets for the modal parameter extraction process
	FRFs can be animated directly in the MTC. In a post-processing package like ME’scopeVES™ the modal parameter can be extracted and the mode shapes animated with photo realism
	ME’scopeVES™ exhibits several tools for improved confidence in the modal parameter extraction process including Mode Indicator Functions, Stabilisation Diagram, Complexity Plot, MAC and COMAC

Hammer Guide