Fluid effects and response in transverse impact on liquid-filled tubes

Two long tubes each of aluminum and polymethyl methacrylate, with two different wall thicknesses, were subjected to transverse impact by two different steel spheres when in an empty or a fluid-filled condition. Water and a high-density electric capacitor liquid were emplaced in the interior, usually under stationary, but occasionally under streaming, conditions. Input-force history and response of the system at two gage stations involving single axial and hoop, as well as coupled symmetric and antisymmetric strain histories, were recorded from the response of strain gages, while fluid pressures were measured by means of small tourmaline crystals suspended at the tube center line. The effect of parameter variation in input and system material and geometry on these quantities was studied. The measured signal speed and frequency of the breathing mode of the system were compared with corresponding analytical predictions.     

On the optimal distribution of the flow rate of gas blown through the side walls of the channel of a de plasmotron (plasma generator)

It is well known that the blowing of cold gas through the side walls of the channel of a dc plasmotron (plasma generator) with longitudinal blowing over the arc leads to an increase in the useful power of the plasmotron [1]. The increase is due to the increase in the combustion voltage of the arc and also the decrease in the heat fluxes to the wall of the channel. The present paper solves the problem of the optimal distribution of the flow rate of gas blown through the side walls into the channel of a dc plasmotron of arbitrary shape F(x). The flow in the main channel and in the ducts in the side walls is described by the quasi-one-dimensional gas-dynamic equations investigated qualitatively in [2] and verified experimentally in [3].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 120–124, May–June, 1981.     

A moving-load controlled-displacement fracture-toughness testing machine

In conventional fracture-toughness testing, the line of application of the loads remains fixed with respect to specimen geometry. In this testing machine, the load moves with the advancing crack front, and displacement is used as the controlled variable to propagate and arrest a crack. The energy-release rate at the onset of crack propagation and, hence, the plane-strain fracture toughnessK _Ic can be measured directly without compliance calibration or stress-intensity evaluation. The specimen is in the form of a flat plat 25 by 50 cm which is simple to machine and provides about 30 values ofK _Ic. The versatility of the machine is demonstrated by making a statistical analysis ofK _Ic for 7075-T6 Al by showing the effect of plate thickness on the fracture toughnessK _c using a tapered specimen, and by evaluatingK _c in 7075 Al as a function of aging temperature in a thermal-gradient-treated specimen.     

Some experiments on the effect of isolated protuberances on flow through tubes

At various locations in the arterial system, plaques, or small relatively isolated protuberances, can develop on the inner wall of the vessel and project into the lumen. A number of investigators have suggested that the development and growth of these protuberances is related to the flow in the vicinity of the protuberance. In this study, the conditions under which the flow separates from an isolated protuberance located in a cylindrical tube were investigated. The critical Reynolds number at which separation first takes place for a given protuberance was determined. A series of tests was performed for steady flow of a Newtonian fluid through a rigid tube in which protuberances of various sizes were inserted. The results of the tests show the effect of the protuberance height and shape on the separation characteristics. In general, the results indicate that separation takes place at relatively small values of the Reynolds number; values that commonly occur in the arterial system, so that this phenomenon may be important in the study of the “coupling” between blood flow and arterial lesions.     

Graphite combustion in a chemical-equilibrium boundary layer

The mechanism of graphite decomposition in a dissociated air stream in the presence of heterogeneous reactions on the surface and nonequilibrium evaporation for the case of a frozen boundary layer is studied in [1, 2]. Examples of the calculation of graphite decomposition in an oxygen stream with equilibrium [3] and nonequilibrium [4] chemical reactions in the boundary layer are presented in [3, 4]. The effect of the chemical reactions in the boundary layer on the rate of mass transfer and on the surface temperature with variation of the external flow parameters (p, T_e) remains unexplained. The present paper is devoted to a study of the mechanism of graphite ablation over a wide range of temperatures and pressures with air flow about the body in the case of an equilibrium boundary layer. The effect of the individual components on the heat and mass transfer processes is investigated.In conclusion, the author wishes to thank N. A. Anfimov for this constant interest and valuable advice, and also I. S. Epifanovskii for fruitful discussion of the results.     

Small strain and moderate rotation

Kinematical assumptions leading to the approximate theory of small strain accompanied by moderate rotations are discussed with reference to a three-dimensional continuous body. In particular, the relationship with Korn's inequality is examined. It is found that for bounded bodies the coincidence of small strain and moderate rotation on subsets of non-zero volume measure is not possible. Two explicit examples are presented to illustrate this point.     

On the structure of a turbulent spot in a heated laminar boundary layer

An artificially generated turbulent spot was investigated experimentally in a heated boundary layer using a rake of mini-thermocouples. Simultaneous temperature traces were used to determine the spot's leading and trailing edge characteristics. The measurements on the centerline of the plate at a constant velocity and variable streamwise positions provided a Re _x range of 2.45–12.6 x 10⁵. At one axial station the free stream velocity was varied and off-axis measurements were obtained.The shape of the interface between the spot and the surrounding laminar flow was described by conventional and conditional histograms. The length of the spot's leading edge (i.e. the overhang) increased linearly with the downstream distance. Off-axis, the length of the overhang decreased slightly towards the wing tips but became larger with respect to the spot's streamwise extent. The trailing edge changed less significantly in the downstream direction.It was shown that when two spots are generated such that the leading edge of the upstream spot is in the calmed region of the downstream spot, the celerity of the upstream spot is decreased and the spots ultimately merge.     

A CFD comparative study of bubble break-up models in a turbulent multiphase jet

In this paper several bubble break-up models are compared. They have been implemented in the CFX-4.4 fluid dynamic commercial code, which uses the population balance equations for describing liquid/gas multi-phase flows. The models have been assessed against published experimental data, obtained for air bubble break-up within a turbulent water jet. The model of Martínez-Bazán, based on purely kinematics arguments, has shown better agreement with the experimental data. The capabilities of using these models coupled to a CFD code for multiphase flow prediction in industrial applications have been demonstrated.     

A discrete 3D model for bridge aerodynamics and aeroelasticity: nonlinearities and linearizations

A framework for the numerical analysis of bridges under wind excitation is outlined. It is based on structural finite element scheme and cross-sectional wind load models. Two aspects are investigated: (1) how considering the mean steady configuration in the aerodynamic stability calculation; and (2) the effects of load nonlinearities on structural response. A quasi-steady load model is adopted, which is able to deal with the considered problems by using experimental data easily available in the practice. By means of numerical examples, it is pointed out (1) that both the modifications in structural tangential stiffness and in the aerodynamic coefficients due to the mean steady deformation may affect the aeroelastic stability threshold and (2) that load linearization may produce an underestimation of the structural response.     

Morphology development of a PS/PMMA polymer blend during flow in dies

The morphology development in dilute and semi-concentrated blends (2 and 15 wt% disperse phase) of viscoelastic polymers is studied during flow in dies. In the entrance region the droplets deform into fibrils. In the die itself some of the fibrils can break up depending on their shear history and hence on their radial position. The morphology at the exit of the die is investigated by quenching the extrudate and visualizing the structure via scanning electron microscopy (SEM). For fibrils moving along the die axis, the theory of Tomotika for break-up of a fibril in a quiescent matrix describes the observations satisfactorily. Fibrils flowing off center undergo a shearing flow in the die, which could have an effect on the growth of the Rayleigh disturbances that cause break-up. It is observed that during flow break-up still occurs via Rayleigh instabilities. As a first approximation the theory of Tomotika also predicts the break-up of fibrils flowing off center, if the viscosity at the relevant shear rate is used.