With improvement in innovative manufacturing technologies, e.g. automated tow-placement, it is now possible to fabricate any complex shaped structural design for practical applications. This innovative manufacturing technology allows for the fabrication of curvilinearly stiffened pressure vessels and pipes. Compared to straight stiffeners, curvilinear stiffeners have been shown to have better structural performance and weight savings under certain loading conditions. In this paper, an optimization framework for optimal structural design for curvi-linearly stiffened composite pressure vessels and pipes is presented. Non-Uniform Rational B-Spline (NURBS) curves are utilized to define curvilinear stiffeners over the surface of the pipe. An integrated tool using Python, NURBS-based Rhinoceros 3D, MSC.PATRAN and MSC.NASTRAN is implemented for performing topology optimization of curvilinearly stiffened cylindrical shells. Rhinoceros 3D is used for creating the geometry, which later can be exported to MSC.PATRAN for finite element model generation. Finally, MSC.NASTRAN is used to perform structural analysis. A hybrid optimization technique, consisting of Particle Swarm Optimization (PSO) and Gradient Based Optimization (GBO), is used for finding the optimized locations of stiffeners, optimal geometric dimensions for stiffener cross-sections and the optimal layer thickness for the composite skin. Optimization studies show that stiffener placement influences the buckling mode of the structure. Furthermore, the structural weight can be decreased by optimizing the stiffener’s cross-section and skin thickness. In this paper, a cylindrical pipe stiffened by orthogonal and curvilinear stiffeners under internal pressure and bending load is studied. It is shown that curvilinear stiffeners lead to a potential 8% weight saving in the composite laminated skin as compared to the case of using straight stiffeners.

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