Reengineering of the aircraft structural life prediction process to fully exploit advances in very high performance digital computing is proposed. The proposed process utilizes an ultrahigh fidelity model of individual aircraft by tail number, a Digital Twin, to integrate computation of structural deflections and temperatures in response to flight conditions, with resulting local damage and material state evolution. A conceptual model of how the Digital Twin can be used for predicting the life of aircraft structure and assuring its structural integrity is presented. The technical challenges to developing and deploying a Digital Twin are discussed in detail.

/pdf/reengineering-aircraft-structural-life-prediction-using-a-285ed7pvc8.pdf

Reengineering Aircraft Structural Life Prediction Using a Digital Twin

Full-scale unsteady RANS CFD simulations of ship behaviour and performance in head seas due to slow steaming

Ship motions using single-phase level set with dynamic overset grids

Grid generation for overset grids on complex geometry can be divided into four main steps: geometry processing, surface grid generation, volume grid generation and domain connectivity. For each of these steps, the procedures currently practiced by experienced users are described. Typical problems encountered are also highlighted and discussed. Most of the guidelines are derived from experience on a variety of problems including space launch and return vehicles, subsonic transports with propulsion and high lift devices, supersonic vehicles, rotorcraft vehicles, and turbomachinery.

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Best Practices in Overset Grid Generation

SUGGAR: A General Capability for Moving Body Overset Grid Assembly

This paper describes a computational fluid dynamic method used for modelling changes in aircraft geometry due to icing. While an aircraft undergoes icing, the accumulated ice results in a geometric alteration of the aerodynamic surfaces. In computational simulations for icing, it is necessary that the corresponding geometric change is taken into consideration. The method used, herein, for the representation of the geometric change due to icing is a non-cut cell Immersed Boundary Method (IBM). Computational cells that are in a body fitted grid of a clean aerodynamic geometry that are inside a predicted ice formation are identified. An IBM is then used to change these cells from being active computational cells to having properties of viscous solid bodies. This method has been implemented in the NASA developed node centered, finite volume computational fluid dynamics code, FUN3D. The presented capability is tested for two-dimensional airfoils including a clean airfoil, an iced airfoil, and an airfoil in harmonic pitching motion about its quarter chord. For these simulations velocity contours, pressure distributions, coefficients of lift, coefficients of drag, and coefficients of pitching moment about the airfoil's quarter chord are computed and used for comparison against experimental results, a higher order panel method code with viscous effects, XFOIL, and the results from FUN3D's original solution process. The results of the IBM simulations show that the accuracy of the IBM compares satisfactorily with the experimental results, XFOIL results, and the results from FUN3D's original solution process.

/pdf/a-non-cut-cell-immersed-boundary-method-for-use-in-icing-2qdjhqf9bc.pdf

A Non-Cut Cell Immersed Boundary Method for Use in Icing Simulations

Coupled multibody dynamics and computational fluid dynamics approach for amphibious vehicles in the surf zone

Computational simulation of flows involving bodies in relative motion is a challenging problem, which requires the capability of relocating the grid associated with moving bodies as well as the formulation of grid speed terms in the flux evaluation of the governing equations. An overset grid framework enables the computational fluid dynamics (CFD) flow solver to model this class of problems. However, implementing this technology into an existing CFD code can be very tedious and time consuming due to the need for laborious book-keeping as well as proper data interpolation between different layers of grids. This paper describes an overset grid approach to alleviate these problems and enhance the capability of flow solvers to handle problems involving bodies in relative motion. A library approach has been developed and adopted to handle the bookkeeping of the overlapping grids among different layers and the transfer of information across them. To have a wide applicability, this library approach should be able to support structured, unstructured, and generalized grid topologies. This approach makes it easier to incorporate the overset capability into legacy CFD solvers. In the present study, a set of developed overset grid libraries (SUGGAR and DiRTLib) was implemented into a density-based generalized grid flow solver and a pressure-based structured grid flow solver as demonstration. This implementation of the overset capability has been validated with static and moving grids and is presented in the paper.

A Library Based Overset Capability Development for Density- and Pressure- Based Flow Solvers

An efficient solver for the incompressible vorticity transport equations on adaptive Cartesian grids is coupled to an unstructured spectral volume solver for the conservative form of the compressible Euler equations using overset grid assembly and interpolation provided by SUGGAR and DiRTlib, respectively. Vortical flow structures originate at solid surfaces in near-body regions employing the Euler solver and are transported into the wake region that employs an Eulerian Vorticity Transport (EVT) solver. The excessive numerical dissipation common to most grid-based Navier-Stokes solvers is avoided in the wake region by solving the fluid dynamic equations in vorticity conservation form. In addition, the adaptive Cartesian mesh utilized in the wake region allows for efficient transport and preservation of vortical structures by means of localized adaptive mesh refinement and coarsening. Two different approaches for evaluating the EVT velocity field, one involving a fast summation technique based on the Cartesian Treecode method, and the other utilizing a multigrid Poisson approach, are presented and compared. The implementation of both the solution algorithm and overset coupling methodology is described in detail, and results for several different test cases are presented which demonstrate the effectiveness of the hybrid EVT-Euler simulation capability for accurately transporting vortical structures between a near-body compressible Euler solver and an off-body EVT solver.

http://enu.kz/repository/2010/AIAA-2010-4751.pdf

A coupled overset vorticity transport and compressible Euler solver for vortex-dominated flows

Unstructured mesh h-re nement replaces an existing element with a set of smaller child elements to improve the local resolution. A template can be used to create the child elements from the original nodes of the parent element and any new nodes that are introduced at edge, face, or element centers. Homogeneous re nement results when all the edges of the element are split and the child elements are typically of the same type as the parent. A transition re nement element is required to interface the homogeneously re ned element with the surrounding unre ned elements. The number of possible transition re nement templates is very large and typically only a fraction of the possible templates are implemented. The present e ort automates the process of generating the transition element templates through the use of metaprogramming: one program will generate the templates and write out software to be compiled into the actual mesh re nement code. The current approach is described in detail and demonstrated on three di erent test cases. The rst is re nement of all elements within a bounding box as might be used to improve local solution accuracy. The second case is re nement to eliminate orphans in an overset mesh system when the overlap between the meshes is insu cient to provide quality interpolation sources. The nal test case combines re nement to eliminate orphans with re nement to improve local solution accuracy. The current procedure generates over 900 unique templates that expands to over 12,000 possible combinations of transition re nement templates.

Ralph W. Noack

Papers

A Non-Cut Cell Immersed Boundary Method for Use in Icing Simulations

Coupled multibody dynamics and computational fluid dynamics approach for amphibious vehicles in the surf zone

A Library Based Overset Capability Development for Density- and Pressure- Based Flow Solvers

A coupled overset vorticity transport and compressible Euler solver for vortex-dominated flows

Unstructured Mixed Element Mesh Renement Using Templates Generated by Metaprogramming