Using Manual Excitation for Large Displacement on a Highly Damped System

Abstract

Small-scale, quickly executed modal surveys can yield an incredible amount of useful information. Electrodynamic shakers and especially impact hammers have been the excitation methods of choice for these tests because of their ease of use. However, large low-frequency structures with highly damped modes are difficult to excite due to exciter stroke limitations or inability to apply long duration pulse inputs. Hydraulic actuation allows large displacements at low frequencies, but it is expensive and challenging to install in a short amount of time. Similarly, while step-relaxation techniques allow large force and displacement inputs, setup, using a reaction structure, and execution is complicated by the need to reset the system multiple times. In order to overcome some of these drawbacks, ATA developed a modal handle to apply a manual excitation while measuring the input levels of the excitation force. This paper presents results of using this modal handle to perform a modal survey on a test article to evaluate the effect of different dampers and damper configurations on the test article primary torsion mode. This inexpensive and efficient excitation method proved to be successful in quickly completing over eighty test configurations needed to down select to a final damper configuration.