In this paper, an innovative design methodology is proposed to simultaneously optimize the size, layout, and number of stiffeners of a stiffened panel using a gradient-based optimizer. In the proposed method, CAD-based parameterization is used to parameterize the layout of the stiffeners. The location and orientation of each stiffener are controlled with only two layout variables. The geometric constraints to avoid overlapping and crossing of stiffeners are implicitly applied through the layout parameterization scheme, therefore no additional constraints on the grid point coordinates are required. Moreover, the CAD model is maintained throughout the optimization process, therefore the additional step of converting the optimal design back to CAD is eliminated. The layout changes are accommodated in the finite element mesh through the re-meshing technique. The number of stiffeners is controlled by allowing an optimizer to transform an existing stiffener into a ghost stiffener. Every stiffener is assigned a topology variable that can be optimized to a value of either 0 or 1 using a penalization constraint. In case the optimal value is 0 then the contribution of that stiffener in determining the mass and the stiffness of the panel is lost, and it is considered an inactive or ghost stiffener. The stiffener is considered fully active when the optimal value is 1. The sensitivities of grid point coordinates relative to layout variables are calculated analytically. The sensitivities of the structural responses relative to size, layout, and topology variables are achieved through Nastran. The effectiveness of the proposed methodology is evident from the obtained results.@en

An innovative design methodology is proposed for the simultaneous layout and sizing optimization of stiffened panels. A computer-aided design (CAD) modelling tool is used to generate the panel geometry and parameterize the stiffeners layout. The same geometric parameterization is used in the gradient-based optimization. Therefore no additional constraints are applied on grid points coordinates in order to conform with the geometric requirements. The proposed method also eliminates the extra step of converting the optimal design back to the CAD model. An effective parameterization scheme is used that defines the location and orientation of a stiffener with only two layout design variables. The sensitivities of the structural responses with respect to both layout and sizing design variables are computed through the semi-analytical method of Nastran. The proposed methodology is used to re-design a benchmark metallic stiffened panel from literature. The obtained results are used to demonstrate the effectiveness of the proposed method.

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Unlike metal structure, composite structures don’t give any clue till the fatal final collapse. The problem is more complicated when applied load on the structure is aeroelastic in nature. Under such loading, composite laminate experiences stresses. The first layer failure happens when stresses in the weakest ply exceed the allowable strength of the laminate. This initial layer-based failure changes overall material characteristics. It is important now to degrade the composite laminate characteristics for the subsequent failure prediction. The constitutive relations are required to be updated by the reduction in stiffness. The rest of the undamaged laminates continue to take the load till the updated strength is reached. In the present work, layer wise progressive failure analysis under aeroelastic loading has been performed by the inclusion of different failure criteria which allow for the identification of the location of the failure. ANSYS APDL environment has been used to model geometry of helicopter rotor. Under the loading conditions, stresses are calculated in the blade. Using stress tensor and failure criteria, failure location and modes have been predicted. It has been found that failure starts at higher speeds and failure starts from the root chord and tend towards the tip chord.

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