The Effects of Vibrational Relaxation on Hypersonic Flow Past Blunt Bodies

SummaryThe analysis of Freeman is extended to the hypersonic flow of an inviscid, vibrationally relaxing gas past a bluff body. Expressions for the shock shape, streamline shapes and stand-off distance are derived; these expressions have been evaluated for a sphere for various values of an appropriate non-equilibrium parameter Λ.

An Investigation of the Effects of Incidence on the Flow Around a Square Section Cylinder

SummaryA study has been made of the changes that take place in the flow around a square section cylinder as the angle of incidence is increased from 0° to 45°. Measurements of the Strouhal number, S, and the vortex longitudinal spacing, a/d, are presented and used to estimate the vortex strength,, and vortex street spacing ratio, b/a.is found to vary between about 1.2 and 1.7 depending on incidence, and is given approximately by 0.52(1 - Cpb)/2πS, where Cpbis the mean base pressure coefficient. As the incidence is increased from 0°, S at first decreases slightly and then rises sharply to a maximum at 13.5° incidence, which is the incidence where reattachment of the shear layer, in some mean sense, is expected to commence. The spectra of pressure and velocity fluctuations were measured and subharmonic peaks were found in both spectra at 5° and 10° incidence. It is suggested that they may have been caused by an interaction between a vortex and a trailing edge corner. The degree of organisation of the vortex shedding process was estimated by calculating the sharpness factor, Q, of the spectral peaks at the vortex shedding frequency. In general Q fluctuated with changes in incidence. High values of Q occurred at angles of incidence where the rate of change of the mean base pressure coefficient with incidence is very small whereas low values occurred where the flow is changing to a different state.

A Model for Studying the Stress-Field around Simple Fractures in Human Patella

SummaryA mathematical model for estimating the stress-field in the vicinity of cracks in human patella has been studied. In conformity with experimental observations with regard to the mechanical properties of osseous tissues, elasticity and anisotropy of the patella have been paid due consideration. The present study being analytical, the problem is first formulated mathematically, and posed as a boundary value problem. Using Mellin transforms technique, the problem is reduced to solving a Fredholm integral equation which is treated numerically by employing Chebyshev quadrature formula. Numerical results are presented. It is suggested that the techniques used may also find application to engineering structures.

The Synthesis of an Active Flutter Suppression Law Based on an Energy Criterion

SummaryTheory and results are presented which show that it is questionable to base a flutter suppression law, synthesised in terms of an energy dissipation criterion, entirely on aerodynamic data. It is shown that aileron mass balance and aileron/jack impedance can adversely affect regions of stability which have been predicted using aerodynamic terms alone. Comments are also made which attempt to unify various cost functions which are used when either an energy dissipation or an energy dissipation and storage criterion is used in the formulation of flutter suppression laws.

Approximate Displacements of Exact Membrane Actions in a Shell Triangular Element

SummaryExact stress functions which satisfy the homogeneous differential equations of equilibrium for membrane actions are available from the static geometric analogue of previously derived exact displacements of inextensional bending. For finite element evaluation it is necessary to know the displacements (and rotations) caused by these membrane actions. A method of calculating approximate displacements is described which uses the principle of minimum potential energy. Results are given for specimen triangular elements with positive, zero and negative Gaussian curvatures. A listing is appended of a Fortran computer program which allows calculation of these approximate displacements, rotations and other physical quantities for other element shapes.