Experimental Modal Analysis FRF

Experimental Modal Analysis FRF

At present, the designs made by the various engineering areas are characterized by being light, flexible and increasingly resistant.

These requirements often cause the new structures to be susceptible to unwanted vibrations; the information provided by Modal Analysis is necessary for a better understanding of the dynamic behavior of modern structures.

Modal Analysis is a method by which the dynamic properties of a real system are obtained: natural frequencies, modes of vibration and damping that, in turn, depend on rigidity, mass and edge conditions.

The Modal Analysis can be obtained experimentally, through the measurements of the Transfer Function (FRF), and numerically through the Finite Element Method (FEM).

The present article without using a rigorous mathematical treatment aims to introduce some concepts about how structures vibrate and how to determine their dynamic parameters.


In recent years, numerous articles have been published on the applications of modal analysis in the areas of engineering, science and technology. Despite the fact that most of the literature deals with issues related to aeronautical engineering, the automotive sector or particular cases of engineering, the growing increase in the applications of modal analysis in interdisciplinary fields should not be forgotten.

- With regard to automotive engineering, the safety and commercial aspects associated with the design of a vehicle have required greater knowledge of the dynamic properties of automobile structures; To this end, a great interest has been focused on the combination of experimental modal analysis and finite element analysis. By means of these techniques, designers have optimized, statically and dynamically, the components of automobiles, thus satisfying the demand for light vehicles and vehicles. high resistance

- The rapid development of the aeronautical and astronautical industries has challenged many engineering disciplines with diverse technological challenges. Optimizing the distribution of mass and rigidity in aircraft and spacecraft has been a challenge for designers who, supported by modal analysis, the finite element method and mathematical models, have managed to meet this challenge by guaranteeing the strictest requirements of structural integrity and dynamic behavior.

- The buildings, bridges, piping systems, racks, industrial structures and machines in general, are also made, in its design stage, a modal analysis; the objective of this is the optimization of material as well as the obtaining of natural frequencies, modes of vibration and damping. Many times the design of the aforementioned structures is not subjected to a dynamic analysis, which is why there is the possibility that the excitation frequency coincides with one of its natural frequencies, thus causing the phenomenon of resonance; before this problem it is necessary to carry out a modal analysis in order to quantify and analyze the dynamic parameters and thus to move away from the natural frequency of the excitation frequency, a detail that is achieved basically by strategically stiffening the structure in analysis.


- The modal analysis, in addition to determining the dynamic properties of a system: natural frequencies, vibration and damping modes; allows to transform a system of N degrees of freedom (GDL) into N systems of one degree of freedom (1 GDL).

- All structures and machines must pass, in their design stage, through a rigorous modal analysis study; knowing the dynamic properties can be optimized, without risk to the phenomenon of resonance, various components of machines and structures.

- To perform an experimental modal analysis it is necessary to have specialized analyzers and software. The analyzer as a minimum requirement has to have two channels, one for the impact hammer calibrated and the other for the accelerometer; In addition, the software has to be able to process, through the transfer function (FRF), both the response signal and the input signal and in this way with the real and imaginary part of the FRF, calculate the natural frequencies, the vibration modes and damping.

- One of the main functions of experimental modal analysis is the correction and validation of the results obtained by the Finite Element Method (FEM). Once the MEF model has been corrected and validated, it can be used to make various structural modifications as well as to predict faults.

- VIBRO TECHNOLOGY has qualified personnel as well as equipment, software and adequate tools to perform modal analysis studies on buildings, piping systems, racks, industrial structures and machines in general.