Measurement of the thickness of a fluid layer by light absorption

A method to measure the thickness of a fluid layer and thus the depth of the interface between two layers has been developed. It uses light absorption by dye and quantitative analysis of video images. Its main advantages are that it is not intrusive and that the places and times for which measurements are made can be chosen after the experiment and so be optimally related to particular phenomena.     

Accuracy of thermocouples in radiant-heat testing

Results of an investigation of the accuracy of iron-constantan thermocouples in measuring transient surface temperatures produced by radiant heating on metallic specimens are given. The criterion of thermocouple accuracy was derived from the theory of heat conduction. The thermocouples were tested on metallic specimens of different thicknesses at varying heating rates. Comparison of these results with analytical criteria permitted quantitative determination of thermocouple errors.     

Acoustics and dynamics of coaxial interacting vortex rings

Using a contour dynamics method for inviscid axisymmetric flow we examine the effects of core deformation on the dynamics and acoustic signatures of coaxial interacting vortex rings. Both “passage” and “collision” (head-on) interactions are studied for initially identical vortices. Good correspondence with experiments is obtained. A simple model which retains only the elliptic degree of freedom in the core shape is used to explain some of the calculated features.     

An LDV system for turbulence length scale measurements

An LDV system for making spatial correlation measurements of velocity fluctuations in turbulent nonreacting and reacting flows is presented. The LDV system is the dual beam type and consists of an elongated probe volume and a two-point optical fiber detector. Results are presented of the integral length scale measured in a nonreacting grid generated turbulent flow.A version of this paper was presented at the ASME Winter Annual Meeting of 1984 and printed in AMD, Vol. 66     

Problems of powder flow in tabletting processes

Summary The flow of non-compacted granules in the tablet machine hopper is discussed with relevance to the unit dose of drug, which is required to be dispensed. The various factors used to describe powder flow such as angle of repose, interparticulate cohesion and friction, flow through apertures, bulk density and die fillability are considered. The effects of humidity and of addition of fines or lubricants and the use of commercially available apparatus for induced die feeding are included.During compression powder flows to form a dense compact. Theories of this densification and the effects of entrapped air and die wall friction during the compression and ejection of the tablets are examined.An attempt is made to correlate non-uniformity in the final tablet with problems of powder flow.Paper presented at a meeting of the British Society of Rheology, University of Nottingham, April 6–8, 1965.     

On the nullification of stress-concentration factors by stress equalization

During a recent design study involving a critically stressed “tongue-and-groove” type compression joint of dissimilar materials, a novel technique was conceived for nullifying the effects of an otherwise high local stress-concentration factor. In principle, the nominal stresses in the tongue-and-groove portions of the joint are forced to be uniform. For idealizedfit conditions, the stress concentration in the fillet under this stress-equalized condition is theorized to approach unity (1.00). In the present paper, experimental verification is provided.     

A variational principle for a class of layered media

A variational principle is stated which describes the isothermal flow of a class of ideal incompressible materials, of which the ideal non-Newtonian liquid and the rigid-plastic von Mises solid are special cases. The principle is extended to multi-layered media separated by a prescribed interface. An inverse method is outlined for the determination of the common surface between two materials for flows parallel to a given plane.     

An actuator-disc model for the prediction of abrupt stall in an axial compressor rotor

The representation of loss in a cascade by the appearance of blockage has been extended to deal with blade rows by the use of a source distribution to represent this blockage, and in the case of the actuator disc approximation, the presence of sources is confined to an axi-symmetric dìstribution over the actuator disc. It is found that if a typical dependence of loss (and consequently diffusion ratio) upon incidence for each section of an axial compressor rotor is represented in this manner, the influence of blockage on the axial velocity distribution may be found using the potential equation combined with the usual actuator disc approximation. Study of the behaviour of the controlling ordinary differential equation for the axial velocity ahead of the disc reveals that as the flow is reduced, the equation contains a singularity within the range of radius and a meaningful solution does not exist. This result is interpreted as the limit to continuous operation and reasonable agreement between this predicted limit and the appearance of abrupt stall (experimentally) is found.     

Response of circular clamped plates to square-wave stress pulses

An account is given of an experimental investigation of the reeponse of clamped circular mild-steel plates of various thicknesses subjected to rectangular stress pulses over a small circular region. The stress pulses were transmitted to the plates through a 1/2-in.-diam shock bar and the strain-time responses of the plates were measured. The stress-wave interactions between the bar and the plates were measured for a number of thicknesses and the effect of the applied stress on the extent of the plastic deformation was determined. It was found that the elastic response was accurately predicted by the theory of Sneddon and the plastic response behaved according to a simple modification of this theory. The interaction between the stress pulse and plates of various thickness was theoretically predicted and found to be in excellent agreement with experimental measurements. The final plate deflections were theoretically predicted using a rigid viscoplastic theory and was in substantial agreement with the data. From this theory, the data were analyzed to determine the visco-plastic constant or relaxation time of the material. It is proposed that this testing arrangement is a suitable and convenient method for determining dynamic yield properties under biaxial-loading conditions.