Structural Dynamic Response Reconstruction in the Time Domain

Abstract

To assist in the development of mechanical structures which are subjected to dynamic loads, structural dynamic testing, using a test rig loaded by servo-hydraulic actuators to reproduce operational measured responses in the laboratory, may form an essential element of the development process. The input loads acting on the structure under operational conditions can in most cases not be measured directly, and instead the structural dynamic responses to these loads are recorded. The input forcing functions then need to be determined to effect a simulation of the operational conditions. With this work, a time domain based testing system has been developed to enable the reproduction of service-acquired dynamic responses on any actual full scale structure in the laboratory, taking into account the full multiple axis dynamics of the system. The system is able to determine the input forcing functions in such a way that, when applied to the teststructure, an accurate reproduction of the in-service measured responses are reproduced on the computer controlled laboratory test rig. The test structure is instrumented with suitable transducers which are used to record the structural dynamic response under operational conditions. The test structure is thereafter installed in a servo-hydraulic actuator test rig in the laboratory. The test rig is excited with synthetic random inputs while simultaneously recording the responses to these inputs. Using the experimental input-output data, a dynamic model of the test system is found by using parametric dynamic system identification techniques. By using the service aquired vibration responses together with the dynamic model, the system inputs may be determined. A series of iterations around this first approximation finally provides a high degree of accuracy in the simulation. To prove the integrity of the developed system, it has been applied to a number of case studies using a variety of different engineering structures, and very accurate results were achieved.