Size and Topological Optimization for Crashworthiness Design of Helicopter Subfloor

This work deals with the development of an optimization procedure under crashworthiness requirements applied to a typical helicopter subfloor made of aluminum alloy. The difficulties due to the non-linear design space and the nonlinear structural behavior are overcome by developing an optimization procedure based on decomposition approach. To evaluate the response of each subsystem during the optimization, global approximation strategies, based on neural networks, are used. Size variables (dimensions, thickness, and number of rivets) and topological variables (position of the elements) are considered in order to maximize the global crashworthiness performances. The mass specific energy absorbed by the subfloor is chosen as objective function and acceleration constraints are considered so to remain inside the human tolerance limits. Genetic algorithms are then used to find the optimal feasible configuration. The constrained optimization problem is transformed into an unconstrained maximization problem by means of penalty functions. The optimization allowed to increase the crush force efficiency of 12% and to decrease the subfloor mass of 4%. A significant CPU time saving was also obtained by replacing the finite element analyses with response surfaces.