Biodynamic Modeling Techniques for Rotorcraft Comfort Evaluation

This work shows how different occupant biodynamic modeling techniques are integrated in a rotorcraft design environment and discusses the resulting differences in comfort assessment. Three modeling techniques, that are used for biodynamic characterization, are considered: lumped parameter, finite element and multibody dynamics. These models are identified for the same gender, age, weight and height, and then integrated into a virtual helicopter environment with a seat–cushion interface. A generic helicopter model is used to demonstrate the approach. For each of the three techniques, the vertical acceleration levels at the human–helicopter interface, as required by vibration regulations, and at the head are evaluated up to 30 Hz. At a first glance, it is observed that the lumped parameter is the easiest to implement in terms of model set-up. However, the use of lumped parameter models is limited to the population groups that they are identified from, and thus are not as flexible as the finite element and multibody ones in developing biodynamic models for individuals of an arbitrary population percentile. Furthermore, through numerical analysis, it is found that the differences are not very significant in terms of accelerations at the human–seat interface. Therefore, for comfort-related issues, the use of more complex models is not justified, unless complicated comfort assessments other than human interface accelerations are required. On the other hand, it is observed that the spine dynamics can play a significant role in estimating the acceleration of head; therefore, the sophisticated finite element and multibody dynamics models redeem their higher modeling cost and computation time when the head–neck health of occupants is considered.