Smooth Shear Research Articles

Flow visualization study to improve hemocompatibility of a centrifugal blood pump.

A correlation study was conducted among quantitative flow visualization analysis, computational fluid dynamic analysis, and hemolysis tests regarding the flow in a centrifugal blood pump to prevent hemolysis. Particular attention was paid to the effect of the impeller/casing gap widths on the flow in the volute and in the outlet. Flow vector maps were obtained for 250% scaled-up models with various geometries, using an argon ion laser light sheet, a high speed video camera, and particle tracking velocimetry. In terms of the results, in the small radial gap model, high shear occurred near the inside wall of the outlet and stagnation near the outside wall of the outlet whereas the standard model maintained smooth flow and low shear. The small radial gap model showed a lower head and greater hemolysis than the standard model. This head decrease could be partly restored by relocating the outlet position; however, the hemolysis level hardly decreased. From these results, it was found that the small radial gap itself is important. It was also confirmed by detailed flow visualization and simple laminar shear analysis near the wall that the small radial gap caused a wider high shear layer (110-120 microm) than the standard model (approximately 80 microm). In the small radial gap model, the high shear layer in the outlet (approximately 50 microm) is much narrower than that in the volute. Flow visualization together with the aid of computational fluid dynamic analysis would be useful to eliminate the causes of hemolysis.

Rheo-optical Behaviors and Stability of a Silica Particle Suspension Coated with Silane Coupling Agents

The rheo-optical behaviors and suspension stability of silica particles coated with silane coupling agents were investigated experimentally. Mono-dispersed silica particles were synthesized by the sol–gel method and the particles were coated with silane coupling agents such as vinyltriethoxy silane (VTES) and γ-methacryloxypropyl triethoxy silane (MPTES). Although all the suspensions of identical particle volume fraction exhibited similar rheological behaviors at high shear rates, only the stabilized suspensions coated with either VTES or MPTES displayed smooth shear thinning rather than abrupt change in the shear viscosity, as is typical of suspensions with no surface treatment. The present study showed that the MPTES coating was very effective in enhancing the phase stability compared to the VTES coating. The flow-induced dichroism for the MPTES-coated suspensions did not experience sign change, while those of the non-stabilized suspensions changed sign as the shear rate was increased. The VTES-coated suspensions underwent a transition from a stable to an unstable state as the particle volume fraction increased. Specifically, the rheological behaviors of the VTES-coated suspensions of particle volume fraction 0.35 were similar to those of the MPTES-coated suspensions. When the volume fraction exceeded 0.45, however, the effect of VTES coating diminished. Finally, the stress-optical rule proposed by Bender and Wagner was adopted to model the stabilized suspensions considered here. The present results indicated that the stress-optical coefficient could be predicted successfully by the proposed stress-optical rule if the contribution from the hydrodynamic interaction is considered separately from the thermodynamic contribution.

Safety factor profile shape and the ideal magnetohydrodynamic stability of n = 1 internal modes

The ideal magnetohydrodynamic (MHD) stability of n = 1 internal modes in an axisymmetric toroidal configuration is investigated for plasma equilibria with rather general profiles of the safety factor q using an analytical approach (Bussac et al 1975 35 1638). We find that instability strongly depends on the q radial profile and that, characteristically, it occurs for values of the relevant poloidal beta parameter in the range of 0.1 to 0.2. These values are considerably lower than the often quoted value , obtained for a parabolic q-profile in the limit . In general, q-profiles with a large central zone of low magnetic shear and an outer zone of high magnetic shear have worse stability properties than profiles with a smooth shear variation across the whole plasma column. Effects due to shaping of the plasma boundary are also considered. Ellipticity is destabilizing, while triangularity is stabilizing. The overall effect of shaping depends on the value of the magnetic shear inside the q = 1 surface, and low values are required for the beneficial effect of triangularity to prevail over that of ellipticity.

Linear Mechanism of Wave Emergence from Vortices in Smooth Shear Flows

A new linear mechanism of wave abrupt emergence from vortices in smooth shear flows is found. The phenomenon is closely related to non-normality of linear dynamics of disturbances in shear flows and is best interpreted in the framework of a nonmodal approach---by tracing of linear dynamics of spatial Fourier harmonics of vortex in time. Found phenomenon, demonstrated in the Letter for the simplest example of unbounded, compressible, plane Couette flow, should be important for numerous engineering applications and should be realized in various terrestrial and astrophysical shear flows.

THE EFFECT OF REGULAR AND IRREGULAR SHEAR LIPS ON FATIGUE CRACK GROWTH IN Al 2024

Abstract— Multiple underloads and overloads with constant ΔK were carried out on centre‐cracked tension specimens. It was found that when shear lips develop, underloads or overloads affect the crack growth rate da/dN and the subsequent retardation. The appearance of the shear lip fracture surfaces depends on the frequency. At higher frequencies a greater number of rough shear lip fracture surfaces will develop, while at lower frequencies there is a tendency towards smooth shear lips. The amount of crack closure differs in each case. It was found that the type of shear lip, rough or smooth, can be related to the effect on da/dN during and after underloads. The effect of rough and smooth shear lip growth was investigated in constant ΔK tests, performing these tests with and without crack closure.

Three‐dimensional magnetic reconnection without null points: 1. Basic theory of magnetic flipping

In two or three dimensions, magnetic reconnection may occur at neutral points and is accompanied by the transport of magnetic field lines across separatrices, the field lines (or flux surfaces in three dimensions) at which the mapping of field lines is discontinuous. Here we show that reconnection may also occur in three dimensions in the absence of neutral points at so‐called “quasi‐separatrix layers,” where there is a steep gradient in field line linkage. Reconnection is a global property, and so, in order to determine where it can occur, the first step is to enclose the volume being considered by a boundary (such as a spherical surface). Then the mapping of field lines from one part of the boundary to another is determined, and quasi‐separatrix layers may be identified as regions where the gradient of the mapping or its inverse is very much larger than normal. The most effective measure of the presence of such layers is the norm of the displacement gradient tensor; their qualitative location is robust and insensitive to the particular surface that is chosen. Reconnection itself occurs when there is a breakdown of ideal MHD and a change of connectivity of plasma elements, where the field line velocity becomes larger than the plasma velocity, so that the field lines slip through the plasma. This breakdown can occur in the quasi‐separatrix layers with an electric field component parallel to the magnetic field. In three dimensions the electric field E (and therefore the field line velocity v⊥) depends partly on the imposed values of E (or v⊥) at the boundary and partly on the gradients of the inverse mapping function. We show that the inverse mapping determines the location of the narrow layers where the breakdown of ideal MHD can occur, while the imposed boundary values of v⊥ determine mainly the detailed flow pattern inside the layers. Thus, in general, E (and therefore v⊥) becomes much larger than its boundary values at locations where the gradients of the inverse mapping function are large. An example is given of a sheared X field, where a slow smooth continuous shear flow imposed on the boundary across one quasi‐separatrix produces a flipping of magnetic field lines as they slip rapidly through the plasma in the other quasi‐separatrix layer. It results in a strong plasma jetting localized in, and parallel to, the separatrix layers.

The analyses of the three-dimensional stress structure near the crack tip of mode I CT specimens in elastic-plastic state (II)—The analyses of the stress structure

Based on [1], the stress structures of the smooth region and shear lip of the specimens have been investigated in the paper. The characteristics of the stress structure in the smooth region have been found that the variable z can separated out; the stresses in the midsection can be obtained by the plane strain FEM results or HRR structure modified by the stress triaxiality. The effects of load level and thickness on the stress structure can be reflected by the distribution of CTOD along the thickness direction. The obtained expressions of the stresses are very simple and visualized. The analyses of the stress structure in the shear lip show that the stresses can be obtained by different methods of interpolation to a certain precise degree.

Probability distribution of forces and pressures on a square cylinder

Wind tunnel experiments on a three-dimensional square cylinder model revealed that, except perhaps on the frontal face, the probability distribution of pressures, forces or overturning moments are not normal (gaussian). In fact, on points where the effect of the Karman vortices is pronounced the probability distribution of pressures shows a significant skewness to the left and kurtosis (peakdeness). This means that the negative pressure peaks are more intense than the positive pressure peaks and the crest factor is considerably larger than 3.0 or 4.0.The present paper discusses this subject and shows results regarding smooth or turbulent shear flow. Besides probability distribution curves, parameters such as mean value, rms value, crest factor, and skewness and kurtosis coefficients (for pressures on several points, for forces on individual faces, and for global forces) are also presented.

Erratum

Table 3 in the report "Latitudinal and longitudinal oscillations of cloud features on Neptune" by Lawrence A. Sromovsky (1 Nov., p. 684) contained errors. In column 4, the two values for inferred shear should have been -0.8 and -13.8 m/(s-deg), respectively. The corresponding text in column 1 on page 686 should have read, "the advection model is quantitatively upheld for the DS2 motions, but not for the short-period component of the GDS motions. They both agree on phase lags, although the GDS is not in good quantitative agreement on amplitudes. Relative to a smooth shear profile obtained from a simple polynomial fit to the observed wind speeds as a function of latitude (11), the shear derived from the advective model amplitude ratio is almost the same for DS2, but a ninth as large for the GDS."

Erratum: Latitudinal and Longitudinal Oscillations of Cloud Features on Neptune

Table 3 in the report "Latitudinal and longitudinal oscillations of cloud features on Neptune" by Lawrence A. Sromovsky (1 Nov., p. 684) contained errors. In column 4, the two values for inferred shear should have been –0.8 and –13.8 m/(s-deg), respectively. The corresponding text in column 1 on page 686 should have read, "the advection model is quantitatively upheld for the DS2 motions, but not for the short-period component of the GDS motions. They both agree on phase lags, although the GDS is not in good quantitative agreement on amplitudes. Relative to a smooth shear profile obtained from a simple polynomial fit to the observed wind speeds as a function of latitude ( 11 ), the shear derived from the advective model amplitude ratio is almost the same for DS2, but a ninth as large for the GDS."

An Evidence of Melting along Adiabatic Shear Band in High-Speed Shearing Process.

Commercial quarter-hard pure aluminum (Al-1/4H) sheets of 10 mm thickness are tested. A circular disk is sheared from a circular specimen concentrically. Clearance between punch and die is 1 and 0.5%. Two testing machines are used, one of which is aided by a drop hammer for high punch speed (10 m/s) and the other, driven by hydraulic pressure for low punch speed (0.1 mm/s). At high-speed shearing, not only the occurrence of the adiabatic shear band (ASB) but also melting along it is clearly demonstrated by measuring the micro-Vicker's hardness distribution over the sheared-off surface, by optical microscopy of the sheared section, which shows a thin layer with a different microstructure from the adjacent smooth shear flow region, by the mirrorlike appearance of the sheared-off surface, and above all, by a theoretical analysis of the shearing process.

Smooth HDPE-clay liner interface shear strengths: compaction effects. Technical note : J Geotech Engng Div ASCE V117, N4, April 1991, P686–693

Smooth HDPE-clay liner interface shear strengths: compaction effects. Technical note : J Geotech Engng Div ASCE V117, N4, April 1991, P686–693

RETARDATION IN FATIGUE CRACK GROWTH IN Al‐2024 AFTER BLOCKS OF UNDERLOADING

AbstractIn contrast with overloads, small numbers of underloads lead to acceleration in crack growth rate after application of the underloads. Larger numbers of underloads, however, give rise to retardation effects comparable with the effects of overloads. The retardation effects are attributed to the development of shear lips. Irregular shear lips show a greater effect than regular (smooth) shear lips. Increasing numbers of underloads give rise to greater retardation. For high numbers of underloads at high ΔKeff there is even an increase in the total life of the fatigue specimen with respect to the situation without underloads. High numbers of underload at high ΔKeff cause crack arrest at one side of the centre‐cracked tension specimen. The non‐growing side is often in single shear, the growing side always in double shear.

Smooth HDPE‐Clay Liner Interface Shear Strengths: Compaction Effects

This paper provides two complete sets of shear strength data for smooth HDPE-compacted clay liner interfaces with two significantly different clay liner materials. Data are presented for interface shear strength behavior under as-compacted conditions, and also for conditions representing unconsolidated, undrained shear after sustained presoaking under light surcharges. Samples are tested over a broad range of compaction conditions, and the resulting data show that as compacted HDPE-clay liner interface shear strengths can change by a factor of two or more as a result of relatively minor variations in as-compacted dry density and water content. Moreover, the controlled range of specified field compaction conditions usually employed for waste repository compacted clay liners (in order to optimize ductility and to achieve the low permeabilities mandated by law) appears to encompass the range of compaction conditions over which these significant changes in interface shear strength behavior can occur. In addition, the data peresented show clearly the potentially important impact of wetting of compacted clay liner materials on smooth HDPE-clay liner interface shear strengths.

Global existence of smooth shearing motions of nonlinear viscoelastic fluid

Global existence of smooth shearing motions of nonlinear viscoelastic fluid

Multilayer sheet coextrusion: Analysis and design

AbstractA numerical simulation of multilayer coextrusion flows has been undertaken for polymer melts used in producing multilayered plastic sheets. Viscosity data and other material properties are used for typical melts and adhesives applied in coextrusion. Industrial designs have been employed for feedblock geometry and multimanifold vane flat dies. The analysis is based on the lubrication approximation theory (LAT), which treats the flow locally as fully developed. A Newton‐Raphson iterative scheme is employed to solve the equations for a pressure‐driven flow of N number of layers (N ⩽ 11). For a given total flow rate and flow rate ratios (or correspondingly total sheet thickness and individual layer thicknesses), the solution provides the interface locations and individual pressure drops that each extruder has to supply. The shear stresses at the channel walls are checked as a criterion for proper design. The die design or melt combinations are altered to produce smooth shear stresses with no humps or discontinuities at the points of confluence. A Adiabatic temperature rises are also computed based on the pressure drops in the system. Such an analysis provides a quick qualitative as well as quantitative insight into the proper design and melt combinations for multilayer sheet coextrusion.

Wind tunnel experiments on the effects of turbulence on the aerodynamic behaviour of bridge road decks

Experimental results are presented for several different road deck systems including a truss system, a plate girder, and two box sections. The measurements have been made with a variety of test techniques including a full model in smooth and turbulent shear flow, taut strip models in smooth and turbulent flow and sectional models in smooth flow and grid generated turbulence. Comparisons are made between behaviour in the different flows and between two dimensional and three dimensional response.

Finite deformation solution of a dynamic problem of combined compressive and shear loading for an elastic-plastic half-space

A self-similar problem involving combined compressive and shear loading of a non work-hardening elastic-plastic half-space is solved, for large deformations, within the framework proposed earlier by J.R. W illis (1969). The thermodynamic system, which was left open in the general framework, is taken to be that proposed recently by G.W. S wan and C.K. T hornhill (1974). Results are presented for oblique loading of a block of low carbon steel. For an imposed normal velocity of the order of 1,100 m s −1, a smooth shear wave behind the shock that is formed is possible only for small transverse velocities, perhaps no greater than 14 m s −1, depending upon the value assumed for the yield stress. Larger transverse velocities would give rise to a thin layer of intense shear near the surface of the block, whose study would require allowance for both work-hardening and temperature-dependent yield stress.

Observations of the vertical structure of internal waves

Velocity profiles in the open ocean reveal variations in the current structure throughout the water column. Superimposed on a smooth low-frequency shear profile are many layers of large time-variable shear. Repeated profiles at one location show that the time-dependent structure is dominated by rotary currents of diurnal-inertial period. Coherence calculated between profiles lagged in time indicates downward energy propagation. The kinetic energy of these internal waves varies with depth in a manner similar to that of the Brunt-Vaisala frequency, but over a brief series of profiles there can be localized zones which are more energetic than might be expected. Based on velocity shear measured over 10-dbar intervals and a time mean Brunt-Vaisala profile, Richardson numbers between ½ and 4 are observed over much of the water column. Simultaneous profiles are most similar at a separation of 100 m, gradually becoming more different for larger separations of up to 10 km.