Minimum Induced Drag Theorems for Nonplanar Systems and Closed Wings
Springer optimization and its applications, 2016
An analytical formulation for the induced drag minimization of generic single-wing non-planar sys... more An analytical formulation for the induced drag minimization of generic single-wing non-planar systems, biwings, and closed systems is presented. The method is based on a variational approach, which leads to the Euler–Lagrange integral equations in the unknown circulation distributions. The relationship between quasi-closed C-wings, biwings, and closed systems is discussed and several induced drag theorems/properties are introduced. It is shown that under optimal conditions these systems present the same minimum induced drag and the circulation can be obtained from a fundamental one by just adding a constant. The shape of the optimal aerodynamic load on the Box Wing is showed to change with the distance between the wings; differently that what assumed in previous works, it is not the superposition of a constant and an elliptical function.
Variable Angle Tow (VAT) composites remove the constraint of having straight fibers, typical of t... more Variable Angle Tow (VAT) composites remove the constraint of having straight fibers, typical of traditional composite structures. This dramatically increases the design space and allows a more effective tailoring of the material properties to minimize the weight and increase structural performance. To provide an accurate prediction of the displacement and stress fields in an efficient computational framework, a multi-theory architecture based on the Generalized Unified Formulation (GUF) is proposed. In particular, Equivalent Single Layer, Zig-Zag, and Layer Wise theories with different orders of expansions for the different variables are generated with a theory-invariant mathematical model. This feature allows the user to tailor the computational accuracy and cost to the needs of the case under investigation and is inherently well suited for optimization and reliability problems. For the in-plane discretization, a fourth-order triangular shell element presenting 15 nodes is adopted. The interlaminar displacement continuity is imposed in the finite element assembling in the thickness direction of the layer stiffness matrices, whereas the inter-element displacement compatibility is enforced with the penalty method. This approach allows one to use independent GUF discretization for any desired direction within each element, providing significant versatility (accuracy vs computational time) in the structural modeling. A transverse stress recovery procedure taking into account the variability of the structural properties due to the fibers' curvilinear paths is also presented. Results are compared with the literature and a commercial software (NX NASTRAN) featuring 3D finite elements.
The Generalized Unified Formulation (GUF) is a multi-theory and a multi-fidelity architecture for... more The Generalized Unified Formulation (GUF) is a multi-theory and a multi-fidelity architecture for the generation of an infinite class of Advanced Shear Deformation Theories or Zig Zag theories or Layerwise theories with any order of expansion for the different primary variables. This work will present, an extension of GUF to address problems in which every single variable can have either an Equivalent Single Layer or a Layer-Wise description.
Minimum Induced Drag Conditions for Winglets: the Best Winglet Design Concept
AIAA Scitech 2019 Forum, 2019
Minimum Induced Drag Conditions for Truss-Braced Wings
AIAA Journal, 2018
Traditional monoplane aircraft have been used for many decades. A promising improvement is repres... more Traditional monoplane aircraft have been used for many decades. A promising improvement is represented by truss-braced wing configurations because studies have shown potential advantages in terms o...
There is currently a large interest towards unconventional aircraft configurations. According to ... more There is currently a large interest towards unconventional aircraft configurations. According to many experts, only revolutionary concepts can meet the demand of a sustainable aviation. Within this scenario, studies and investigations on innovative aircraft layouts have been flourished: Blended Wing Body, Joined Wings and Box Wings are relevant examples of configurations departing from the traditional monoplane. Joined Wings are characterized by strong geometric nonlinear effects, whose complexity is enhanced by the over-constrained layout and the intrinsic relevant bending-torsion coupling. Thus, the application of standard linear analysis tools of routine use in the aerospace industry is neither acceptable nor practical: the preliminary design phase needs a large number of simulations that have to be computationally fast and at the same time preserve an acceptable level of accuracy/fidelity. For this reason, reduced order models are particularly relevant for the design of these systems. However, several reduced order methods applied in the past to Joined Wings did not provide satisfactory accuracy and reliability. The poor performance is mainly due to the very early onset of nonlinear effects, even at very moderate deflections. This work provides an assessment, and an algorithm enhancement when needed, of several existing techniques aimed to build an effective reduction basis for model order reduction. In particular, Vibration Modes, Modal Derivatives, Ritz Vectors, Static Modes, Trial Solutions and Corrections Vectors are critically examined when applied to a representative JW configuration. The results indicate that Ritz Vectors and Modal Derivatives provide excellent accuracy of the reduced solution when compared with the full order solution. Specifically, a drastic increase in the performance of the reduced order model is noticed when ab-initio information regarding Modal Derivatives are included. This highlights and confirms the relevance of nonlinearities even at the early deformation stages. Hence, taking into account nonlinearities since the early design phases seems to be an unavoidable necessity for Joined Wings. As a consequence, efficient and reliable reduced order modeling might play an essential role in the design of such innovative configurations.
Diamond Wings, Strut-and Truss-Braced Wings, Box Wings, and PrandtlPlane, the so-called "Join-edW... more Diamond Wings, Strut-and Truss-Braced Wings, Box Wings, and PrandtlPlane, the so-called "Join-edWings", represent a dramatic departure from traditional configurations. Joined Wings are characterized by a structurally overconstrained layout which significantly increases the design space with multiple load paths and numerous solutions not available in classical wing systems. A tight link between the different disciplines (aerodynamics, flight mechanics, aeroelasticity, etc.) makes a Multidisciplinary Design and Optimization approach a necessity from the early design stages. Researchers showed potential in terms of aerodynamic efficiency, reduction of emissions and superior performances, strongly supporting the technical advantages of Joined Wings. This review will present these studies, with particular focus on the United States joined-wing SensorCraft, Strut-and Truss-Braced Wings, Box Wings and PrandtlPlane.
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Papers by Luciano Demasi