A novel approach for increasing test efficiency and realism in multi-axial vibration control testing

Vibration control tests are typically performed on shakers in order to replicate the in-service dynamic response of structures. The methodologies for performing vibration control tests are constantly evolving thank to the enormous advances of the available control technologies. The avant-garde test facilities have the capability to address simultaneous multi-axial vibration testing by exploiting Multi-Input Multi-Output (MIMO) control techniques. Over recent years, numerous publications point out the advantages in replicating the in-service conditions by using MIMO control strategies, satisfying the will of the environmental research community to turn multi-axis vibration control testing into the main reference procedure. This work presents a test campaign carried out on a high performance motorbike engine. In particular, the device under test (DUT) is the entire exhaust system connected to the head of the engine. A three-axial electrodynamic shaker table is used for replicating the acceleration time histories previously acquired during field-testing. The test results clearly highlight the importance of reproducing in the laboratory the operational boundary conditions. Differences between test and in-field conditions produce mechanical impedance mismatches that alter the dynamic behaviour of the DUT during the control test. The purpose of the work is to define a MIMO control methodology that makes the test conditions closer to the in-field ones, thus improving the test result reliability. As a consequence, it is possible to directly assess the dynamic response (experimentally retrieved) of the exhaust system after introducing design modifications to some components.