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Modal Testing and Analysis

Saeed Ziaei-Rad

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Introduction What is modal testing?The experimental study of structural dynamics.

Experimental studies are useful for: Determining the nature and extent of vibration

response. Verifying theoretical models. Measurements of material properties under dynamic

loading such as damping capacity, friction and fatigue endurance.

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Types of Tests Vibration forces or response are measured during

operation of machine or structure. Measurement under more controlled conditions and

therefore more accurate results.

Modal Testing: The process involved in testing components or structures with the objective of obtaining a mathematical description of their dynamic or vibration behavior.

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Historical Developments1947 Kennedy & PancuDescribing the accurate determination of natural frequency and

damping level in aircraft structures.1963 Bishop & GladwellExplaining the theory of resonance testing.1969 SalterNon-analytical approach to the interpretation of measured data.1970 Major advances in trancducers, electronics and digital analyzer.1980Many papers and advances in this period.

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Books1- D. J. Ewins, 2000, Modal testing theory and practice,

2nd edition, Research Studies Press Ltd.2- N. Maia, J. Silva, J. He, N. Lieven, R. Lin, G. Skingle,

W. To, A. Urgueira, 1997, Theoretical and experimental modal analysis, Research Studies Press Ltd.

3- W. Heylen, S. Lammens, P. Sas, 1998, Modal analysis theory and testing, KUL, Belgium.

4- H. Natke, 1992, Fundamentals and advances in the engineering sciences, Friedr. Vieweg and Sons.

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Books (Cont.)5- Z. Fu, 1995, Vibration modal analysis and parameter

identification, Mechanical Industry Publishing Co., People’s Republic of China

6- K.G. McConnell, 1995, Vibration testing theory and practice, John Wiley & Sons.

7- Dynamic Testing Agency (DTA), 1993, Handbook on modal testing.

8- DTA, 2000, Primer on best practice in dynamic testing.

Books (Cont.) ،نالـيز مودال

نوشته جيمين هي و ژي فانگ فو، ترجمه سعيد ضيايــي راد و ا

1384مهدي صالحي، انتشارات دانش پژوهان برين،

الت دوار، سعيد كاربرد ارتعاشات در پايش وضعيت و عيب يابي ماشين ا

1386ضيايــي راد، سعيد نوريان، انتشارات دانش پژوهان برين،

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Conferences

International Modal Analysis Conference (IMAC), 1982-2009

International Seminar on Modal Analysis (ISMA), bi-annual, 1975-2009, KUL, Leuven, Belgium

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Journals

The international journal of analytical and experimental modal analysis, Society of experimental mechanics, USA

Journal of mechanical systems and signal processing (MSSP), Academic press, UK

Journal of vibration and control, Sage science press Journal of sound and vibration

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Applications of Modal Testing Measurements of a structure vibration properties in

order to compare them with corresponding data produced by a FE or other theoretical models.

Adjust or correct the theoretical mode to bring modal properties close into line with measurements.

Using a modal test to produce a mathematical model of a component which may be used for structural assembly (substructuring)

Effects of modifications to the original structure. Force determination.

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Test Procedure

1- Measure a set of mobilities or FRFs.

2- Analyze these FRFs using appropriate curve-fitting procedure

3-Combine the results of curve-fitting to construct the required model.

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Test LevelsLevel 0 - Estimation of natural frequencies and

damping factors.

Level 1 - Estimation of natural frequencies and damping factors. Mode shapes defined qualitatively.

Level 2 - Measurements of all modal parameters and un-normalized mode shapes.

Level 3 - Measurements of all modal parameters and normalized mode shapes. Full quality check performed and model usable for model validation.

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Test Levels (Cont.)

Level 4 - Measurements of all modal parameters and residual effects for out-of-range modes. Full quality check performed. The model usable for all response-based applications including modification, coupling and response prediction.

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Models Spatial ModelMass, Stiffness and damping matrices

Modal ModelNatural Frequencies, Modal damping and mode shapes

Response ModelFrequency response functions, FRFs (X/F)

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Route to Vibration analysis

Spatial ModelM, K, D

Modal ModelNF, MD, MS

Response Model

FRFs (X/F)

Theoretical Route

Response Model

Modal Model

Spatial Model

Experimental route