John A. Tanner

ADVANCES AND TRENDS IN THE DEVELOPMENT OF COMPUTATIONAL MODELS FOR TIRES

Status and some recent developments of computational models for tires are summarized. Discussion focuses on a number of aspects of tire modeling and analysis including: tire materials and their characterization; evolution of tire models; characteristics of effective finite element models for analyzing tires; analysis needs for tires; and impact of the advances made in finite element technology, computational algorithms, and new computing systems on tire modeling and analysis. An initial set of benchmark problems has been proposed in concert with the U.S. tire industry. Extensive sets of experimental data will be collected for these problems and used for evaluating and validating different tire models. Also, the new Aircraft Landing Dynamics Facility (ALDF) at NASA Langley Research Center is described.

Analysis of aircraft tires via semianalytic finite elements

A computational procedure is presented for the geometrically nonlinear analysis of aircraft tires. The tire was modeled by using a two-dimensional laminated anisotropic shell theory with the effects of variation in material and geometric parameters included. The four key elements of the procedure are: (1) semianalytic finite elements in which the shell variables are represented by Fourier series in the circumferential direction and piecewise polynomials in the meridional direction; (2) a mixed formulation with the fundamental unknowns consisting of strain parameters, stress-resultant parameters, and generalized displacements; (3) multilevel operator splitting to effect successive simplifications, and to uncouple the equations associated with different Fourier harmonics; and (4) multilevel iterative procedures and reduction techniques to generate the response of the shell.

Aircraft Landing Dynamics Facility, A Unique Facility with New Capabilities

The Aircraft Landing Dynamics Facility (ALDF), formerly called the Landing Loads Track, is described. The paper gives a historical overview of the original NASA Langley Research Center Landing Loads Track and discusses the unique features of this national test facility. Comparisons are made between the original track characteristics and the new capabilities of the Aircraft Landing Dynamics Facility following the recently completed facility update. Details of the new propulsion and arresting gear systems are presented along with the novel features of the new high-speed carriage. The data acquisition system is described and the paper concludes with a review of future test programs.

Sensitivity of tire response to variations in material and geometric parameters

Abstract A computational procedure is presented for evaluating the analytic sensitivity derivatives of the tire response with respect to material and geometric parameters of the tire. The tire is modeled by using a two-dimensional laminated anisotropic shell theory with the effects of variation in material and geometric parameters included. The computational procedure is applied to the case of uniform inflation pressure on the space shuttle nose-gear tire when subjected to uniform inflation pressure. Numerical results are presented showing the sensitivity of the different response quantities to variations in the material characteristics of both the cord and the rubber.

Reduced basis technique for evaluating the sensitivity coefficients of the nonlinear tire response

An efficient reduced-basis technique is presented for calculating the sensitivity of nonlinear tire response to variations in the desin variables. The tire is discretized by using three-field mixed finite element models. The vector of structural response and its first- and second-order sensitivity coefficients (derivatives with respect to design variables) are each expressed as linear combinations of a small number of basis (or global approximation) vectors. The Bubnov-Galerkin technique is then used to approximate each of the finite element equations governing the response and the sensitivity coefficients, by a small number of algebraic equations in the amplitudes of these vectors

Review of NASA Antiskid Braking Research

NASA antiskid braking system research programs are reviewed. These programs include experimental studies of four antiskid systems on the Langley Landing Loads Track, flights tests with a DC-9 airplane, and computer simulation studies. Results from these research efforts include identification of factors contributing to degraded antiskid performance under adverse weather conditions, tire tread temperature measurements during antiskid braking on dry runway surfaces, and an assessment of the accuracy of various brake pressure-torque computer models. This information should lead to the development of better antiskid systems in the future.

Frictionless contact of aircraft tires

A computational procedure for the solution of frictionless contact problems of spacecraft tires was developed using a two-dimensional laminated anisotropic shell theory incorporating the effects of variations in material and geometric parameters, transverse shear deformation, and geometric nonlinearities to model the nose-gear tire of a space shuttle. Numerical results are presented for the case when the nose-gear tire is subjected to inflation pressure and pressed against a rigid pavement. The results are compared with experimental results obtained at NASA Langley, demonstrating a high accuracy of the model and the effectiveness of the computational procedure.

Analytical studies of the Space Shuttle orbiter nose-gear tire

A computational procedure is presented for evaluating the analytic sensitivity derivatives of the tire response with respect to material and geometrical properties of the tire. The tire is modeled by using a two-dimensional laminated anisotropic shell theory with the effects of variation in material and geometric parameters included. The computational procedure is applied to the case of the Space Shuttle orbiter nose-gear tire subjected to uniform inflation pressure. Numerical results are presented which show the sensitivity of the different tire response quantities to variations in the material characteristics of both the cord and rubber.

Experimental Research Supporting the National Tire Modeling Program

This paper presents the status of a dual-prong research effort by NASA experimentalists in support of the National Tire Modeling Program. Specifically, the first experimental thrust deals with tire responses in the form of heat build-up in a rolling tire; force distribution in the contact region of a statically loaded tire; and static tire mechanical properties, such as spring rate and damping characteristics. In addition, testing techniques have been demonstrated, such as the use of close-range photogrammetry for measuring tire deflection and the use of individual cord-load transducers imbedded in a tire carcass for determining the distribution of applied loads throughout the tire structure. Material characterization of viscoelastic materials is the second experimental thrust. In this regard, factors affecting modulus measurements have been studied, and test techniques for determining reliable, quantitative material properties are under development.

Nonlinear Analysis of Shells of Revolution via Semi-Analytic Finite Elements with Application to Tires

A computational procedure is presented for the geometrically nonlinear analysis of shells of revolution. The three key elements of the procedure are: 1) semianalytic three-field mixed finite element models in which the shell variables are represented by Fourier series in the circumferential direction and piecewise polynomials in the meridional direction; 2) multilevel operator splitting to uncouple the equations associated with different Fourier harmonics; and 3) multilevel iterative procedures and reduction technique to generate the response of the shell.