No abstract

From the beginning of the early 1960s helicopter seats underwent a deep evolution. They play a key role in survivability during emergency landings. The rotorcraft structure must be, in fact, designed to give to each occupant every reasonable chance of avoiding severe injury in crash landings. To reach this result several improvements in the design of crashworthy seats with special emphasis on the energy absorption systems were introduced during development of rotorcrafts. This paper, based on previous experiments on carbon foam modelling under high strain rate evolution, will show their potential application for an energy absorption system based on a constant load response. This solution would allow easy manufacturing, lightweight structures, as well as possible further development into variable load energy absorbers. These latter represent a further evolution providing better performances for occupants of different weights beyond certification requirements. The investigation has been developed in two phases: first a typical engineering test was computed on carbon foam-based damper finite element model; second, this was followed by an hybrid FEM multi-body modelling of seats certification procedure using previous results as lumped element. Finally, a comparison with the state of the art constant load energy absorption system was performed. The carbon foam-based system showed good performance compared with an ideal fixed load energy absorber (FLEA). The results demonstrated that this kind of material could offer a new solution to limit the load transmitted to the occupants of a helicopter seat during emergency landing and suggested to investigate for further development and experimental testing.

The paper proposes a novel approach to identify the feasible region for a constrained optimisation problem. In engineering applications the search for the feasible region turns out to be extremely useful in the understanding of the problem as the feasible region defines the portion of the domain where design parameters can be ranged to fulfil the constraints imposed on performances, manufacturing and regulations. The search for the feasible region is not a trivial task as non-convex, irregular and disjointed shapes can be found. The algorithm presented in this paper moves from the above considerations and proposes a recursive feasible-infeasible segment bisection algorithm combined with Support Vector Machine (SVM) techniques to reduce the overall computational effort. The method is discussed and then illustrated by means of three simple analytical test cases in the first part of the paper. A real-world application is finally presented: the search for the survivability L. Lanzi zone of a crashworthy helicopter seat under different crash conditions. A finite element model, including an anthropomorphic dummy, is adopted to simulate impacts that are characterised by different deceleration pulses and the proposed algorithm is used to investigate the influence of pulse shape on impact survivability.