High-fidelity Multidisciplinary Sensitivity Analysis and Design Optimization for Rotorcraft Applications

A multidisciplinary sensitivity analysis of rotorcraft simulations involving tightly coupled high-fidelity computational fluid dynamics and comprehensive analysis solvers is presented and evaluated. A sensitivity-enabled fluid dynamics solver and a nonlinear flexible multibody dynamics solver are coupled to predict aerodynamic loads and structural responses of helicopter rotor blades. A discretely consistent adjoint-based sensitivity analysis available in the fluid dynamics solver provides sensitivities arising from unsteady turbulent flows and unstructured dynamic overset meshes, while a complex-variable approach is used to compute structural sensitivities with respect to aerodynamic loads. The multidisciplinary sensitivity analysis is conducted through integrating the sensitivity components from each discipline of the coupled system. Accuracy of the coupled system is validated by conducting simulations for a benchmark rotorcraft model and comparing solutions with established analyses and experimental data. Sensitivities of lift computed by the multidisciplinary sensitivity analysis are verified by comparison with the sensitivities obtained by complex-variable simulations. Finally the multidisciplinary sensitivity analysis is applied to a constrained gradient-based design optimization for a HART-II rotorcraft configuration

High-Fidelity Multidisciplinary Design Optimization Methodology with Application to Rotor Blades

A multidisciplinary design optimization procedure has been developed and applied to rotorcraft simulations involving tightly-coupled, high-fidelity computational fluid dynamics and comprehensive analysis. A discretely-consistent, adjoint-based sensitivity analysis available in the fluid dynamics solver provides sensitivities arising from unsteady turbulent flows on unstructured, dynamic, overset meshes, while a complex-variable approach is used to compute structural sensitivities with respect to aerodynamic loads. The multidisciplinary sensitivity analysis is conducted through integrating the sensitivity components from each discipline of the coupled system. Accuracy of the coupled system for high-fidelity rotorcraft analysis is verified; simulation results exhibit good agreement with established solutions. A constrained gradient-based design optimization for a HART-II rotorcraft configuration is demonstrated. The computational cost for individual components of the multidisciplinary sensitivity analysis is assessed and improved

Innovative strategies for rotary-wing coupled aeroelastic simulations

Issued as final reportUnited States. National Aeronautics and Space Administratio

Acoustic emission bearing fault diagnostics system

Issued as final repor

On the compatibility equations in geometrically exact beam finite element

peer reviewedThis paper discusses the compatibility equations which relate the velocity field and the strain field in geometrically exact beam theory. The analysis is carried out in the context of intrinsic equations, namely the dynamic equilibrium equations are formulated in terms of velocity and strain only. In addition to the well established objectivity and path-independence requirements of the spatial discretization, these compatibility equations show that a consistent spatial interpolation of the velocity field should depend on the curvature of the beam, including initial curvature and curvature from the deformation, and it is shown that this consistency is connected to the ability of the element to represent rigid body motion velocity. A two node interpolation scheme is studied and it appears that, as the element gets smaller under mesh refinement, the effect of this dependency reduces, leading eventually to the classical linear shape functions

A motion formalism approach to modal reduction for flexible multibody system applications

peer reviewedMultibody systems are often modeled as interconnected multibody and modal components: multibody components, such as rigid bodies, beams, plates, and kinematic joints, are treated via multibody techniques whereas the modal components are handled via a modal reduction approach based on the small strain assumption. In this work, the problem is formulated within the framework of the motion formalism. The kinematic description involves simple, straightforward frame transformations and leads naturally to consistent deformation measures. Derivatives are expressed in local frames, which results in the remarkable property that the tangent matrices are independent of the position and orientation of the modal component with respect to an inertia frame. This implies a reduced level of geometric non-linearity as compared to standard description. In particular, geometrically non-linear problems can be solved with the tangent matrices of the reference configuration, without re-evaluation and re-factorization. Copyright © 2018 ASM

Dynamic Analysis of Bearingless Tail-rotor Blades Based on Nonlinear Shell Models

The unique structural features of helicopter bearingless rotors call for the development of design and modeling methodologies for laminated composite flex-structures. Indeed, the flex-structure should be flexible enough to replace the flap, lead-lag, and feathering bearings, while maintaining high strength and stiffness in the axial direction. Laminated composite materials are a material of choice for such an application. Chordwise deformations, transitional zones between different cross sections and localized compressive stresses are all likely to be present in the flex-structure, rendering the validity of a beam model questionable. In this article a nonlinear anisotropic shallow shell model is developed that accommodates transverse shearing deformations, and arbitrarily large displacements and rotations, but strains are assumed to remain small. The displacement-based shell model has six degrees of freedom at each node and allows for an automatic compatibility of the shell and beam models. The model is validated by comparing its predictions with several benchmark problems. A four-bladed composite bearingless tail rotor system is analyzed in detail using the shell model and compared with the predictions of a beam model. Significant differences are observed between the two models, especially in the torsional behavior

A Lie group approach for the formulation of beam and shell refined theories used in flexible multibody systems

peer reviewe