Numerical/Experimental Validation of Thin-Walled Composite Box Beam Optimal Design

Thin-walled composite box beam structural configuration is representative of a specific high aspect ratio wing structure. The optimal design procedure and lay-up definition including appropriate coupling necessary for aerospace applications has been identified by means of “ad hoc” analytical formulation and by application of commercial code. The overall equivalent bending, torsional and coupled stiffness are derived and the accuracy of the simplified beam model is demonstrated by the application of Altair Optistruct. A simple case of a coupled cantilevered beam with load at one end is introduced to demonstrate that stiffness and torsion angle distribution does not always correspond to the trends that one would intuitively expect. The maximum of torsional stiffness is not obtained with fibers arranged at 45° and, at the maximum torsional stiffness, there is no minimum rotation angle. This observation becomes essential in any design process of composite structures where the constraints impose structural couplings. Furthermore, the presented theory is also extended to cases in which it is necessary to include composite/stiffened hybrid configurations. Good agreement has been found between the theoretical simplified beam model and numerical analysis. Finally, the selected composite configuration was compared to an experimental test case. The numerical and experimental validation is presented and discussed. A good correlation was found confirming the validity of the overall optimization for the optimal lay-up selection and structural configuration.

Multi-objective optimal design of composite box beam using hybrid adaptive harmony search with dynamically reconfigurable harmony memory

In the design of helicopter rotor blades, the composite materials are being popularly used, as they are lighter in weight with high specific strength and modulus apart from superior fatigue characteristics. As the performance of the composite materials can be tailored with the optimized layup sequence, the robust optimization algorithms, which cater to this, become necessary. We propose an approach for multi-objective optimization of composite box beam by considering the cross-sectional dimensions and the discrete ply angles as design variables. We present a new improved version of the basic harmony search optimization algorithm by building the features like adaptivity, hybrid search with a customized local search, and multiple sub harmonies with dynamic interaction among them. These features greatly improve both intensification and diversification capabilities of the proposed algorithm. Numerical studies carried out on a box beam clearly reflects the superiority of the proposed approach in providing wider as well as improved design configuration while handling multiple objectives of box-beam design. Finally, we have used a set of performance metrics to demonstrate the effectiveness of the proposed algorithm by comparing with other very recent stochastic algorithms.