A Flying V aircraft is a tailless, V-shaped flying wing with two cylindrical pressurized cabins placed in the wing leading edge and two over-the-wing engines. Elevons provide longitudinal and lateral control while two tip-mounted vertical tails double as winglets. The goal of the presented study is to estimate the lift-to-drag ratio of this configuration at the cruise condition: M = 0.85, h = 13, 000m, and CL = 0.26. A vortex-lattice method is used to rapidly investigate the feasible design space, whereas an Euler solver on an unstructured grid is adopted for a more accurate wave and vortex-induced drag estimation. The profile drag is computed by an empirical method. The NASA Common Research Model is adopted as a benchmark with an estimated lift-to-drag ratio of 18.9. The three-dimensional geometry of the Flying V is generated according to a multi-level parametrization: the planform shape is parametrized with 10 variables, five wing sections are identified and described by a total of 43 parameters, while the winglet planform is defined by 3 additional variables. After a multi-fidelity design space exploration, two design approaches are investigated: a dual-step optimization, where planform and airfoil variables are subsequently varied, and a single-step optimization, where planform and airfoil variables are varied simultaneously. The highest lift-to-drag ratio is attained with the single-step optimized configuration and amounts to 23.7. It is therefore concluded that the Flying V Aircraft can have a 25% higher lift-to-drag ratio than the reference aircraft.

This paper presents an evolutionary structural topology optimization method for design of completely submerged buoyant modules with design-dependent fluid pressure loading. This type of structure is used to support offshore rig installation and pipeline transportation in all water depths. The proposed optimization method seeks to identify the buoy design that has the highest stiffness, allowing it to withstand deepwater pressure, uses the least material and has a minimum prescribed buoyancy. Laplace's equation is used to simulate an underwater fluid pressure, and a polymer buoyancy module is considered to be linearly elastic. Both domains are solved with the finite element method. Using an extended bi-directional evolutionary structural optimization (BESO) method, the design-dependent pressure loads are modeled in a straightforward manner without any need for pressure surface parametrization. A new buoyancy inequality constraint sets a minimum required buoyancy effect, measured by the joint volume of the structure and its interior voids. Solid elements with low strain energy are iteratively removed from the initial design domain until a certain prescribed volume fraction. A test case is described to validate the optimization problem, and a buoy design problem is used to explore the features of the proposed method.

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