• aircraft
• ground vibration test

The realization of this project has required, first of all, a study of the theoretical basis of the modal testing and particularly of the approximate criteria used in the experimental modal analysis. A precise knowledge of the physical meaning of the modal characteristics is essential to properly describe the vibrational behaviour of a structure, starting from experimental observations.
Moreover an important part of this work consists in the acquisition of the mathematical tools necessary to evaluate the quality of the measures (i.e. mode isolation).
A full description of these tools and of their practical applications will be reported in the chapter dedicated to the final analysis, where it will be shown how these tools can be used to improve and validate the measures.
The second part of this project consists in the performance of experiments and collection of data during the ground vibration tests on a Morane-Sauliner (Paris) airplane located in the ONERA laboratory of Modane. In this way it has been possible to master the techniques and the methodologies used at ONERA to undertake the experimental modal analysis and, at the same time, to construct an experimental data base for testing the program MFGUI (Modal Filtering Graphical User Interface) developed for the final analysis of data.
A deep knowledge of all the mathematical concepts and of instrumental tools used in the experimental tests has been a necessary prerequisite to develop the MFGUI program. In fact this program has the goal to identify the natural frequencies of the analyzed structure processing the data (according to proper criteria described in the following chapters) selected during the acquisition phase.
The technical requirements for this program consist in the realization of a graphical environment realized with the MATLAB 6.5 language running on PCs. The goal is to offer to the engineers, during and after the vibration tests, a graphical user friendly and multi-functionality tool for the processing and the visualization of the data sets (numerical data correlated to a given geometry) for the modal analysis. This environment has to recall other programs all integrated in MATLAB.
The different motivations of the choice of the MATLAB language are:
• the good knowledge of this software in the DDSS department,
• it is a clear and not compiled language, sufficiently fast for several applications,
• the easy way of reading and writing the data files,
• the possibility of later evaluations,
• the existence of tools, for the data analysis, that can be modified and consequently integrated as subroutines of the main program.
The graphical user interface has to allow:
• the loading and saving of files as Microsoft “Windows Explorer” does,
• the accessibility to MATLAB tools for the data analysis,
• a graphical interface for the visualization and comparison of the data,
• the realization of a function able to store the modification history in order to realize the “undo” and “redo” options,
• the creation of a contextual menu and a bar menu to facilitate the accessibility to the available tools and the basic classical functions,
• the creation of tools able to detect measurement errors.
Some of the programs integrated in the graphical interface already existed so they have been modified, instead some others tools have been developed ex-novo.