Holt Ashley

Bio: Holt Ashley is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Mach number & Aeroelasticity. The author has an hindex of 7, co-authored 10 publications receiving 906 citations.

Piston Theory-A New Aerodynamic Tool for the Aeroelastician

Abstract: Representative applications are described which illustrate the extent to which simplifications in the solutions of high-speed unsteady aeroelastic problems can be achieved through the use of certain aerodynamic techniques known collectively as "piston theory." Based on a physical model originally proposed by Hayes and Lighthill, piston theor}^ for airfoils and finite wings has been systematically developed by Landahl, utilizing expansions in powers of the thickness ratio 8 and the inverse of the flight Mach Number M. When contributions of orders 8/M and 8/M are negligible, the theory predicts a point-function relationship between the local pressure on the surface of a wing and the normal component of fluid velocity produced by the wing's motion. The computation of generalized forces in aeroelastic equations, such as the flutter determinant, is then always reduced to elementary integrations of the assumed modes of motion.

Observations on the dynamic behavior of large flexible bodies in orbit.

Abstract: 9 Warren, W R and Diaconis, N S, "Air arc simulation of hypersonic environments," ARS Progress in Astronautics and Rocketry: Hypersonic Flow Research, edited by F R Riddell (Academic Press Inc, New York, 1962), Vol 7, pp 663-700; also General Electric Co, GE MSD TIS R62SD25 (April 1962) 10 Eschenroader, A W, Boyer, D W, and Hall, J G, "Exact solutions for non-equilibrium expansions of air with coupled chemical reactions," Cornell Aeronautical Labs, Rept AF-1413A-l, Air Force Office of Scientific Research 622 (May 1961) 11 Boison, J C and Curtiss, H A, "An experimental investigation of blunt body stagnation point velocity gradient," ARS J 29,130-135(1959) 12 Scala, S M and Baulknight, C W, "Transport and thermodynamic properties in a hypersonic laminar boundary layer, Part 2, Applications," ARS J 30, 329-336 (1960)

New directions in lifting surface theory

Abstract: speed of sound, dimensionless aspect ratio of planar lifting surface wing semichord, ft chordwise dimension of area element in supersonic and transonic theory local wing chord, ft reference chordlength, ft 2L/PxU*S = lift coefficient coefficient of pitching moment (p — ?>oo)/(pooM/2) = pressure coefficient depth of x-y plane below free liquid surface, ft or dimensionless depth below free surface, referred to I U/(gl) = Froude number gravitational constant, ft/sec height of wing midspan above ground plane, ft; also downward bending or heaving displacement, ft reference value of bending displacement at wingtip ( —1) /2 = complex unit wk/U or tal/U = reduced frequency kbi/b = reduced frequency based on areaelement size kernel function of subsonic integral equation reference length, ft upward normal force or force per unit span acting on lifting surface chordwise and spanwise coordinates of "receiving" area element, dimensionless flight Mach number static pressure distance between points, dimensionless {(x £) + (1 M)[(j/ T?) + (z 2o(i?))]) /2 = elliptical distance curvilinear coordinates measured spanwise along and normal to surface, dimensionless E S/STIP = normalized s projected cylindrical lifting surface area, ft or dimensionless; also spanwise distance on cantilever wing, measured in semispans. time coordinate, sec fluid velocity components, dimensionless flight speed, f ps velocity component normal to S, dimensionless function describing wake surface rectangular Cartesian coordinates, dimensionless, see Fig. 1 height of S above x-y plane, dimensionless displacement of wing above its projected surface, dimensionless angle of attack measured from zero lift : (M — 1) = cotangent of Mach angle discontinuous jump in a quantity, passing from lower to upper surface of wing

Applications of the Theory of Free Molecule Flow to Aeronautics

Abstract: The breakdown of certain assumptions of conventional aerodynamics in the case of highly rarefied gas is shown to call for the use of the theory of free molecule flow in studying forces on bodies moving above 120-150 km. in the earth's atmosphere. A tentative standard table of atmospheric properties from 120-220 km. is computed. The parameter M oo, ratio of flight speed to most probable speed of air molecules, becomes useful in comparing free molecule flows. Techniques are developed for finding analytically or numerically the lift and drag coefficients of any object, based on two extreme opposite assumptions concerning the nature of reflection of molecules from surfaces. These methods are employed to find coefficients of a number of simple bodies. The drag of missiles is demonstrated to be negligibly small above 120 km. except at extremely high speeds. The possibility of aerodynamically sustained flight is discussed.

Dynamics of multibody systems

Abstract: 1. Introduction 2. Reference kinematics 3. Analytical techniques 4. Mechanics of deformable bodies 5. Floating frame of reference formulation 6. Finite element formulation 7. Large deformation problem Appendix: Linear algebra References Index.

Flexible Multibody Dynamics: Review of Past and Recent Developments

Abstract: In this paper, a review of past and recent developments in the dynamics of flexible multibody systems is presented. The objective is to review some of the basic approaches used in the computer aided kinematic and dynamic analysis of flexible mechanical systems, and to identify future directions in this research area. Among the formulations reviewed in this paper are the floating frame of reference formulation, the finite element incremental methods, large rotation vector formulations, the finite segment method, and the linear theory of elastodynamics. Linearization of the flexible multibody equations that results from the use of the incremental finite element formulations is discussed. Because of space limitations, it is impossible to list all the contributions made in this important area. The reader, however, can find more references by consulting the list of articles and books cited at the end of the paper. Furthermore, the numerical procedures used for solving the differential and algebraic equations of flexible multibody systems are not discussed in this paper since these procedures are similar to the techniques used in rigid body dynamics. More details about these numerical procedures as well as the roots and perspectives of multibody system dynamics are discussed in a companion review by Schiehlen [79]. Future research areas in flexible multibody dynamics are identified as establishing the relationship between different formulations, contact and impact dynamics, control-structure interaction, use of modal identification and experimental methods in flexible multibody simulations, application of flexible multibody techniques to computer graphics, numerical issues, and large deformation problem. Establishing the relationship between different flexible multibody formulations is an important issue since there is a need to clearly define the assumptions and approximations underlying each formulation. This will allow us to establish guidelines and criteria that define the limitations of each approach used in flexible multibody dynamics. This task can now be accomplished by using the “absolute nodal coordinate formulation” which was recently introduced for the large deformation analysis of flexible multibody systems.