ATA Engineering is the leading independent company for performing modal tests/modal surveys, which we have performed for more than 30 years. We pioneered the use of random excitation for modal testing and extended the method to include multishaker random testing and polyreference data processing. ATA continues to advance modal analysis with recent developments such as the Alias Free polyreference curve fitting technique and our patented Multi-sine sweep excitation method (U.S. Pat. No. 8,281,659). We have unsurpassed experience in modal testing of all types of mechanical systems, including aerospace and industrial systems. With over 900 accelerometers and twenty shakers, no modal survey is too large for ATA. The aerospace structures we have tested include aircraft, space launch vehicles, rocket motors, and satellites. Other modal tests we have performed include robotic figures, propeller blades, generator sets, fixtures, and countless others.
Our modal test team can setup, test, and provide results within a couple of days for most test articles. It is typical to provide our customers mode shapes, frequencies and damping values before the test article is released for instrumentation removal. This not only provides results quickly, but it also verifies that all goals of the test are accomplished before removing instrumentation.
End-to-End Modal Test Solutions
ATA can take responsibility for one or more phases of a typical modal survey from pretest analysis, to test planning, test execution, and model correlation/updating.
A typical modal test program starts with a structure that is currently being built or modified. A finite element model (FEM) is developed by either our customer or by ATA. Analytical results and optimization algorithms are used to determine the Test-Analysis Model (TAM), and the ideal set of measurement locations called the test Degrees of Freedom (DOF). This is where instrumentation will be applied and measurements will be recorded. Electro-dynamic shakers, impact hammers, or quick release (twang) mechanisms are used to apply an input to the structure. Accelerometers are used to measure the response. Frequency Response Functions (FRF) are then calculated and stored. The data quality is evaluated by analyzing signal to noise, reciprocity, coherence, spectral content of input force, FRF phase and the overall FRF appearance. After verifying quality data, the parameter estimation process begins.
Parameter estimation techniques, such as Alias-Free polyreference, are used to extract the modal parameters. These include the structures natural frequencies, damping estimates, and mode shapes. Mode Indicator Functions (MIF) and stability diagrams are generated to aid in determining the poles (natural frequencies) of the structure. Once the poles are selected, the residues are calculated and then the mode shape coefficients. The mode shape coefficients are then used to animate or display the mode shapes.
Modal Test Equipment
ATA Engineering owns a large inventory of modal accelerometers, data acquisition, electro-dynamic shakers, and impact hammers. All of our modal testing equipment is portable and is typically transported to the customer’s facility to perform on-site modal tests of large systems. In addition, ATA has a laboratory with a 6’ by 4.5’ steel T-slot table ideal for fixed base testing of small components and a larger 12’ by 12’ inertial mass that can be used to support larger structures.
We can provide a full modal solution, equipment rental, or expert consulting to help you perform your own test efficiently.