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Meakin, Robert L.

Publications and source records attributed to Meakin, Robert L..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

An Interface for Specifying Rigid-Body Motions for CFD Applications

An interface for specifying rigid-body motions for CFD applications is presented. This interface provides a means of describing a component hierarchy in a geometric configuration, as well as the motion (prescribed or six-degree-of-freedom) associated with any component. The interface consists of a general set of datatypes, along with rules for their interaction, and is designed to be flexible in order to evolve as future needs dictate. The specification is currently implemented with an XML file format which is portable across platforms and applications. The motion specification is capable of describing general rigid body motions, and eliminates the need to write and compile new code within the application software for each dynamic configuration, allowing client software to automate dynamic simulations. The interface is integrated with a GUI tool which allows rigid body motions to be prescribed and verified interactively, promoting access to non-expert users. Illustrative examples, as well as the raw XML source of the file specifications, are included.

Murman, Scott M.↗
NASA NTRS2003

A General Simulation Method for Multiple Bodies in Proximate Flight

Methods of unsteady aerodynamic simulation for an arbitrary number of independent bodies flying in close proximity are considered. A novel method to efficiently detect collision contact points is described. A method to compute body trajectories in response to aerodynamic loads, applied loads, and inter-body collisions is also given. The physical correctness of the methods are verified by comparison to a set of analytic solutions. The methods, combined with a Navier-Stokes solver, are used to demonstrate the possibility of predicting the unsteady aerodynamics and flight trajectories of moving bodies that involve rigid-body collisions.

Meakin, Robert L.↗
NASA NTRS2003

An Aerodynamic Analysis of a Spinning Missile with Dithering Canards

A generic spinning missile with dithering canards is used to demonstrate the utility of an overset structured grid approach for simulating the aerodynamics of rolling airframe missile systems. The approach is used to generate a modest aerodynamic database for the generic missile. The database is populated with solutions to the Euler and Navier-Stokes equations. It is used to evaluate grid resolution requirements for accurate prediction of instantaneous missile loads and the relative aerodynamic significance of angle-of-attack, canard pitching sequence, viscous effects, and roll-rate effects. A novel analytical method for inter- and extrapolation of database results is also given.

Meakin, Robert L.↗
NASA NTRS2001

CHSSI Software for Geometrically Complex Unsteady Aerodynamic Applications

A comprehensive package of scalable overset grid CFD software is reviewed. The software facilitates accurate simulation of complete aircraft aerodynamics, including viscous effects, unsteadiness, and relative motion between component parts. The software significantly lowers the manpower and computer costs normally associated with such efforts. The software is discussed in terms of current capabilities and planned future enhancements.

Chan, William M.↗
NASA NTRS2001

Flowfield And Download Measurements And Computation of a Tiltrotor Aircraft In Hover

A multipart study of the V-22 hover flowfield was conducted. Testing involved a 0.15-scale semispan model with multiple independent force balance systems. The velocity flowfield surrounding the airframe was measured using a robotic positioning system and anemometer. Both time averaged and cycle-averaged results are reported. It is shown that the fuselage download in hover can be significantly reduced using a small download reduction device. Measurements indicate that the success of the device is attributed to the substantial elimination of tiltrotor fountain flow. As part of.the study, an unsteady CFD prediction is time-averaged, and shown to have excellent agreement in predicting the baseline configuration fountain flow. Some discrepancies at the outboard edge of the rotor are discussed. An &&sessment of an advanced tip shape rotor comp"'Ietes the study. Derived from a nonrotating study, the advanced tip shape rotor was developed and tested on the Bell 0.15 scale semi-span V-22 model. The tip shape was intended to diffuse the tip vortex and reduce BVI noise. Rotor wake vorticity is extracted from the measured velocity dam to show that the advanced tip shape produces a tip vortex that is only slightly more diffuse than the baseline tip blade. The results indicate that nonrotating tests may overpredict the amount of tip vortex diffusion achieved by tip shape design in a rotating environment.

Brand, Albert G.↗
NASA NTRS1997

On Efficient Parallel Implementation of Moving Body Overset Grid Methods

An investigation into the parallel performance of moving-body overset grid methods will be presented. Parallel versions of the OVERFLOW flow solver, DCF3D domain connectivity software, and SIXDO six-degree-of-freedom routine are coupled with an automatic load balance routine and tested for 3D Navier-Stokes calculations on the IBM SP2. The primary source of parallel inefficiency in moving and problems are the domain connectivity costs with DCF 3D. Although this algorithm constitutes a relatively low fraction of the total solution cost (e.g. 10-20%) in calculations on serial machines, the consequently cause a significant degradation in the overall parallel performance. The paper will highlight some approaches for improving the scalability of DCF3D. The paper will present results of a proposed new load balancing scheme that seeks more equal distribution of the inter-grid boundary points in order to more evenly load balance the donor search costs associated with DCF3D. Some preliminary results will also be given from a new solution-adaption algorithm coupled with OVERFLOW which incorporates overset cartesian grids with various levels of refinement. The measured parallel performance from a descending delta-wing configuration and a generic store-separation from a wing/pylon case will be presented.

Wissink, Andrew M.↗
NASA NTRS1996

Global Flowfield About the V-22 Tiltrotor Aircraft

This final report includes five publications that resulted from the studies of the global flowfield about the V-22 Tiltrotor Aircraft. The first of the five is 'The Chimera Method of Simulation for Unsteady Three-Dimensional Viscous Flow', as presented in 'Computational Fluid Dynamics Review 1995.' The remaining papers, all presented at AIAA conferences, are 'Unsteady Simulation of the Viscous Flow About a V-22 Rotor and Wing in Hover', 'An Efficient Means of Adaptive Refinement Within Systems of Overset Grids', 'On the Spatial and Temporal Accuracy of Overset Grid Methods for MOving Body Problems', and 'Moving Body Overset Grid Methods for Complete Aircraft Tiltrotor Simulations.'

Meakin, Robert L.↗
NASA NTRS1996

The Chimera Method of Simulation for Unsteady Three-Dimensional Viscous Flow

The Chimera overset grid method is reviewed and discussed in the context of a method of solution and analysis of unsteady three-dimensional viscous flows. The state of maturity of the various pieces of support software required to use the approach is discussed. A variety of recent applications of the method is presented. Current limitations of the approach are defined.

Meakin, Robert L.↗
NASA NTRS1996

Unsteady Simulation of the Viscous Flow About a V-22 Rotor and Wing in Hover

Results of an unsteady thin-layer Navier-Stokes simulation of a 0.658-scale V-22 rotor and wing configuration in hover are presented. All geometric components of the flapped-wing and rotor test rig, including rotor blades, are accurately modeled. Rotor motion and rotor/airframe interference effects are simulated directly using moving body overset grid methods. Tiltrotor hover aerodynamics are visualized via unsteady particle trace images. Wing download predictive ability is demonstrated. Simulation results are compared with experimental data.

Meakin, Robert L.↗
NASA NTRS1996

An Efficient Means of Adaptive Refinement Within Systems of Overset Grids

An efficient means of adaptive refinement within systems of overset grids is presented. Problem domains are segregated into near-body and off-body fields. Near-body fields are discretized via overlapping body-fitted grids that extend only a short distance from body surfaces. Off-body fields are discretized via systems of overlapping uniform Cartesian grids of varying levels of refinement. a novel off-body grid generation and management scheme provides the mechanism for carrying out adaptive refinement of off-body flow dynamics and solid body motion. The scheme allows for very efficient use of memory resources, and flow solvers and domain connectivity routines that can exploit the structure inherent to uniform Cartesian grids.

Meakin, Robert L.↗
NASA NTRS1996

On the Spatial and Temporal Accuracy of Overset Grid Methods for Moving Body Problems

A study of numerical attributes peculiar to an overset grid approach to unsteady aerodynamics prediction is presented. Attention is focused on the effect of spatial error associated with interpolation of intergrid boundary conditions and temporal error associated with explicit update of intergrid boundary points on overall solution accuracy. A set of numerical experiments are used to verify whether or not the use of simple interpolation for intergrid boundary conditions degrades the formal accuracy of a conventional second-order flow solver, and to quantify the error associated with explicit updating of intergrid boundary points. Test conditions correspond to the transonic regime. The validity of the numerical results presented here are established by comparison with existing numerical results of documented accuracy, and by direct comparison with experimental results.

Meakin, Robert L.↗
NASA NTRS1995

On automating domain connectivity for overset grids

An alternative method for domain connectivity among systems of overset grids is presented. Reference uniform Cartesian systems of points are used to achieve highly efficient domain connectivity, and form the basis for a future fully automated system. The Cartesian systems are used to approximate body surfaces and to map the computational space of component grids. By exploiting the characteristics of Cartesian systems, Chimera type hole-cutting and identification of donor elements for intergrid boundary points can be carried out very efficiently. The method is tested for a range of geometrically complex multiple-body overset grid systems. A dynamic hole expansion/contraction algorithm is also implemented to obtain optimum domain connectivity; however, it is tested only for geometry of generic shapes.

Chiu, Ing-Tsau↗
NASA NTRS1995

Global flowfield about the V-22 Tiltrotor Aircraft

The Chimera overset grid method is reviewed and discussed in the context of a method of solution and analysis of unsteady three-dimensional viscous flows. The state of maturity of the various pieces of support software required to use the approach is discussed. A variety of recent applications of the method is presented. Current limitations of the approach are identified.

Meakin, Robert L.↗
NASA NTRS1993

Domain connectivity among systems of overset grids

This progress report describes research performed to achieve algorithmic improvements in the use of overset grids for the computation of unsteady flowfields about geometrically complex and moving component configurations. A hole-map computational method is detailed that reduces computational demand and corresponding demand on human resources. Results indicate that the method is both efficient and flexible for use in complex simulation cases. Tests were performed on shuttle orbiter/external tank, wing/store, and V-22 tilt-rotor configurations. The number of simulated points and the corresponding time on a SGI 4D-210 workstation are presented.

Meakin, Robert L.↗
NASA NTRS1993

Dynamic overset grid communication on distributed memory parallel processors

A parallel distributed memory implementation of intergrid communication for dynamic overset grids is presented. Included are discussions of various options considered during development. Results are presented comparing an Intel iPSC/860 to a single processor Cray Y-MP. Results for grids in relative motion show the iPSC/860 implementation to be faster than the Cray implementation.

Barszcz, Eric↗
NASA NTRS1993

Moving body overset grid methods for complete aircraft tiltrotor simulations

A hypothetical, but realistic, set of flight conditions for the V-22 aircraft is established to facilitate rigorous testing of a new domain connectivity algorithm, and to carry out an overset grid proof-of-concept tiltrotor simulation. Relative motion and interference effects between the V-22 airframe and rotor-blades are directly simulated within the context of an unsteady, thin-layer Navier-Stokes computation. The domain connectivity algorithm is verified to perform at rates equal to or greater than those realized previously for store-separation-like applications. The feasibility of carrying out unsteady Navier-Stokes analyses of rotorcraft problems is demonstrated.

Meakin, Robert L.↗
NASA NTRS1993

GDCF - An interactive approach to domain connectivity among systems of overset grids

The graphical domain connectivity function (GDCF) graphical interface, which was designed to address the need to simplify hole cutter shape selection and positioning in order to exploit the computational savings obtainable through the domain connectivity function (DCF) is described. GDCF was used to prepare data for the V22 tilt-rotor geometry, and data input time was decreased by an order of magnitude. The combined use of GDCF and DCF to satisfy domain connectivity requirements for systems of overset grids is found to minimize both human and computational resources.

Mccann, Karen M.↗