Ground Vibration Test – GVT
Ground Vibration Testing (GVT) is a specific type of modal test that is performed for aircrafts. The GVT is a very important step in the design process of the aircraft and it is a part of the certification process.
The test procedure is basically the same as a regular modal test. The first step is to create similar boundary conditions as encountered in flight. Usually, the aircraft (or spacecraft) is suspended on air glides or the tires of the aircraft are deflated slightly. Suspending the aircraft with bungee cords can also be applied for smaller aircrafts.
The next step is instrumentation. Several accelerometers (uniaxial or traxial) are placed on the aircraft in order to have a complete insight on the dynamic character. The excitation of the aircraft is performed by 3-5 vibration exciters usually located at the tips of the wings, tail and if necessary other locations.
The aircraft is vibrated with burst random or step sine signal several times for transfer function generation. The modal testing finishes when the Frequency Response Functions (FRF) of the aircraft are measured.
Structural system identification consists of finding transfer function of the system which is established by finding the modal parameters of the structure such as, natural frequencies, damping, modal vectors and residues. Several commercial tools are available in the market that can extract the modal parameters from FRFs.
The modal parameters of the aircraft can be used for modal updating process of the aircraft and flight flutter assessment.
