Greater Suction Research Articles

Modeling the Salinity Effect on the Water Retention Curve of Geosynthetic Clay Liner (GCL) on the Drying Path.

The water retention curve (WRC) of a geosynthetic clay liner (GCL) is influenced by the presence of exchangeable cations in the leachate during changes in water content in a landfill construction. This research aims to investigate the impact of salinity on the WRC of GCL. To measure the WRC of GCL under different sodium chloride (NaCl) concentrations on the drying path, a chilled-mirror dew-point device capable of controlling the GCL's volume was employed. Additionally, the dry state microstructure of the GCL was examined using electron microscopy. The test outcomes indicate that GCL hydrated with higher salinity has greater suction at the same water content during drying. This influence can be attributed to changes in salinity and the precipitation of NaCl crystals within the bentonite when water evaporates, which in turn affects the bentonite's microstructure and leads to increased matric suction. By introducing the Fredlund and Xing model and parameter relationship, it is possible to predict the WRC of GCL under salinity effects after measuring the WRC under different salinity conditions on the drying path.

Flow development over inclined flat plates in ground effect and relation to aerodynamic loads

The aerodynamics of finite-span inclined flat plates in ground effect is experimentally investigated at a chord-based Reynolds number of 50 000 for aspect ratios of 1 and 2. The minimum ground height is varied between 0.1 and 1.0 chord lengths, and lift and drag forces are measured using a force balance for angles of attack between −90° and 90°. Planar, two- and three-component particle image velocimetry is used to perform streamwise and cross-plane measurements at the midspan and one chord length downstream of the trailing edge, respectively. Ground effect is significant at ground clearances below 0.5 chord lengths, most notably near the stall angle, where it leads to significant changes to flow development. At sufficiently low free flight pre-stall angles, the increase in edge velocity at low gap ratios caused greater suction, generating higher lift with a minimal increase in drag for both orientations. Closer to the free flight stall angle, a decrease in aerodynamic loading is observed for negative orientations due to earlier onset of stall with a decreasing gap ratio. The exception was the higher aspect ratio plate at negative orientations, where the loading was largely invariant to changes in gap ratio for all angles tested. At positive orientations, the increase in average static pressure along the pressure surface in ground proximity led to an overall increase in loading prior to deep-stall conditions for both aspect ratios. The ground effect was minimal at post-stall angles of attack. The results may be used to guide the design of photovoltaic supports at relevant latitudes.

Wind-Induced Interference of a Rectangular-Section Building on the Dome-Roof

There are no specific regulations regarding the interference effects that an adjacent building can place on the wind load distribution of a dome roof structure. Furthermore, the influence between an adjacent rectangular-section building and the dome roof structure on the wind-induced interference is not well understood yet. Thus, in this paper, computational fluid dynamics (CFD) is used to simulate the mean wind pressure of the dome roof structure after interference by a rectangular-section building facing the dome. The accuracy of numerical results is verified through a wind tunnel test. The effects of different building heights or widths as well as distances between the interference building and the dome on the interference are analyzed. Different wind directions in intervals of 15∘are examined in the analysis to identify the worst wind direction. The results reveal that the passage effect caused by the interference is the main reason for the increase of suction on the roof, and the height ratio has the greatest influence on the passage effect. The region of the roof nearest to the interference building experiences the greatest suction considering all wind directions, and the side regions of the roof are relatively safe in most cases. The results of this paper can provide a reference for engineers tasked with wind-resistant design of long-span dome structures.

Unsteady magnetohydrodynamic couple stress fluid flow from a shrinking porous sheet: Variational iteration method study

AbstractMotivated by magnetic polymer manufacturing applications, the present research article examines theoretically the hydromagnetic boundary layer flow of an electrically conducting non‐Newtonian couple stress fluid due to a transient shrinking (contracting) porous sheet. The conservation partial differential equations for mass and momentum are rendered into a fifth‐order nonlinear ordinary differential equation via similarity transformations with associated boundary conditions. A semi‐analytical/numerical scheme employing Lagrangian multipliers and known as the variational iteration method (VIM) is implemented to solve the ordinary differential boundary value problem. Validation of the solutions is conducted by benchmarking against earlier Newtonian studies and very good agreement is achieved. A detailed assessment of the impact of couple stress (rheological), unsteadiness, magnetic body force parameter, and wall transpiration (suction/injection) parameter on flow characteristics is conducted with the aid of graphs. A significant deceleration in the flow is computed with increasing injection (acceleration is caused with greater suction) and acceleration is induced with higher unsteadiness parameter values. Increasing magnetic field (higher magnetic number) generates flow acceleration, rather than the customary deceleration, due to the shrinking sheet dynamics. A stronger couple stress effect manifests in strong retardation in the boundary layer flow and an increase in momentum (hydrodynamic|) boundary layer thickness. VIM demonstrates excellent convergence and accuracy and shows significant promise in studying further magnetic polymer fabrication flow problems.

MHD stagnation point flow of nanofluid over a curved stretching/shrinking surface subject to the influence of Joule heating and convective condition

The existing article explores the attributes of convection and Joule heating across a magnetohydrodynamics two-dimensional stagnation point flow of a nano liquid depending on the permeable curved stretching/shrinking surface and mass suction. Applying the non-dimensional variables, the basic model of partial differential equations (PDEs) is converted to the dimensionless ordinary differential equations (ODEs), which are solved through the bvp4c method (bult-in function in MATLAB). Multiple graphical results have been examined to observe the effect of diverse flow parameters against temperature, friction drag, velocity and heat transfer. From these results, it has been determined that the temperature profile escalates with the escalation of Hartmann, Eckert and Biot number, nanoparticles concentration and curvature parameter, although the velocity of fluid reduces with escalating values of nanoparticle concentration parameter, curvature parameter, and Hartmann number. It is equally important to indicate that the friction drag reduces with large curvature and rises with greater suction however the rate of heat transfer declines with least value of Eckert number and improves with strong suction, Hartmann, and Biot number.

An In Vitro Study Measuring the Effects of Circumferential and Near-Circumferential Closed Incisional Negative Pressure Wound Therapy Dressings.

BackgroundNegative pressure wound therapy (NPWT) and closed incisional negative pressure wound therapy (ciNPWT) have been shown to promote the healing of acute and chronic wounds. Despite the growth in their usage, the mechanism by which they promote healing is not fully understood. Several studies have shown that NPWT results in a combination of microdeformation and macrodeformation, which may promote wound recovery. The macrodeformation forces have raised concerns about circumferential NPWT compressing the extremity and decreasing perfusion distal to the NPWT. The literature on circumferential NPWT is mixed, with some studies showing increased perfusion, while others have shown decreased perfusion. We hypothesized that a near-circumferential ciNPWT dressing applied over intact skin would provide a “lift-off” force rather than a compressive force. We also theorized that as the sponge contracts under negative pressure while in a near-circumferential setting, the dressing will pull on the surrounding skin and tissue, leading to a decrease in the pressure of the extremity. This could potentially translate to improved venous and lymphatic return, increasing perfusion to the tissue beneath the sponge as well as distal to the sponge.MethodsThis study consisted of three separate experiments. The first experiment measured the width and length of a ciNPWT dressing at various negative pressures. The second experiment utilized an in vitro model consisting of an elastic ball and tubing to examine the effects that circumferential and near-circumferential ciNPWT dressings may have on extremity pressure. Varying lengths of ciNPWT dressings were applied to the ball, ranging from 25% circumferential to 100% circumferential. The pressure within the ball was monitored as varying lengths of circumferential dressings were applied at various negative pressures. The third experiment utilized the same model as the second experiment but with a 66% circumferential dressing and various baseline ball pressures to see how extremity pressure may impact the ability of the ciNPWT dressing to alter extremity pressure.ResultsThe first experiment demonstrated that a ciNPWT dressing decreased in length and width in a linear fashion as negative pressure was applied. The second experiment revealed that both fully circumferential and near-circumferential dressings resulted in a decrease in the pressure of the elastic ball at lower levels of suction. The greatest decrease in ball pressure was noted with the 66% near-circumferential dressing. With greater suction, however, the pressure within the ball was noted to increase above baseline. The third experiment illustrated that as the baseline pressure of a ball was increased, the dressing had less of an ability to change the pressure of the ball.ConclusionsThese results suggest that near-circumferential and circumferential ciNPWT systems may decrease the pressure of an extremity at certain negative pressures and that compression may be less likely to occur when used on a higher-pressure extremity.

Design and analysis of an electrical magnetic holding device

Electromagnets are widely used as driving devices in industry. In this article, we describe various designs and methods of analysis for a built-in coil electromagnetic holding device based on three main design characteristics: volume, applied voltage, and suction force. Our aim is to achieve greater suction force or Gaussian value without changing the external dimensions of the frame, by varying the magnetic pole surface area, the thickness of the iron frame, and/or the electromagnetic material. We verify the design with the simulation software ANSYS Maxwell, which uses a commercial finite element method, to find the best design parameters to maximize the suction force or Gaussian value. The experimental results confirm the results of our simulation studies and demonstrate that simulations can achieve substantial reductions in cost and time over traditional trial-and-error methods. Furthermore, the experimental results indicate that electromagnetic products with bigger pole surface areas provide more suction force than electromagnetic products with smaller pole surface areas only when the applied voltage is less than 9 V. Above 9 V, smaller pole surface areas definitely result in bigger suction force.

Oral and nonoral sensorimotor interventions facilitate suck–swallow–respiration functions and their coordination in preterm infants

BackgroundPreterm infants are at high risk of encountering oral feeding difficulties. Early sensorimotor interventions may improve oral feeding skills in preterm infants. AimTo further explore the effects of an oral (O), tactile/kinesthetic (T/K), and combined (O+T/K) sensorimotor intervention on preterm infants' nutritive sucking, swallowing and their coordination with respiration. Study designSeventy-five infants (29 [0.3, standard error of mean, SEM] weeks gestation, 49 males/26 females) were randomly assigned to an O group involving sensorimotor input to the oral structures; a T/K group involving sensorimotor input to the trunk and limbs; a combined (O+T/K) group; and a control group. Outcome measuresStage of sucking, suction and expression amplitudes (mmHg), suck–swallow ratio, stability of suck–swallow interval, and swallow–respiration patterns. ResultsThe O group had significantly more advanced sucking stages, and greater suction and expression amplitudes than controls [p≤0.035, effect size (ES) >0.6]. The suck–swallow ratio and stability of suck–swallow intervals did not significantly differ among groups (p≥0.181, ES≤0.3). The three interventions led to fewer swallows bracketed by prolonged respiratory pauses compared to controls (pause–swallow–pause, p≤0.044, ES≥0.7). The T/K and combined (O+T/K) groups had greater occurrence of swallows bracketed by expiration than the control and O groups (expiration–swallow–expiration, p≤0.039, ES≥0.3). ConclusionThe O intervention enhanced specific components of nutritive sucking. All three interventions resulted in improved swallow–respiration coordination. Sensorimotor interventions have distributed beneficial effects that go beyond the specific target of input.

Morphological Change in the Tessellated Darter (Etheostoma olmstedi) Following the Introduction of the Banded Darter (E. zonale) to the Susquehanna River Drainage

Abstract The strong connection between ecology and morphology in fishes predicts that ecologically relevant morphological features will change in concert with changes in habitat use and feeding ecology even over relatively short timescales following species introduction. Here, this hypothesis is tested by examining the trophic morphology of specimens of the native Tessellated Darter, Etheostoma olmstedi, collected at Catatonk Creek, Candor, Tioga Co., NY, USA, between 1961 and 2002. The collections of E. olmstedi bracket a 1980 range expansion by the non-native Banded Darter, E. zonale. Examination of the E. olmstedi specimens revealed that the length of the buccal cavity relative to body size increased following the invasion of Catatonk Creek by E. zonale. An increase in buccal cavity length (BCL) is expected to result in higher suction feeding performance measured as volumetric flow rate of water through the mouth. Such an increase in BCL may enable E. olmstedi to exert greater suction forces on prey an...

Effect of vortex formation on powder sinkability for reconstituting milk powders in water to high solids content in a stirred-tank

Vortex formation in a stirred-tank improves the sinkability of powders in liquids and consequently allows the mixing of powders in liquids to form higher solids content dispersions and solutions. This work investigates the effect of vortex formation on the sinkability of milk powders in water, and how vortex depth, impeller position and solution viscosity influences sinkability and impeller power requirement. When adding milk powder into solution, there was a surprising sudden improvement in powder sinkability at higher solution viscosities. At higher viscosity, more power is required by the impeller to form the vortex, and this provides much greater suction in the vortex, which may explain the rapid powder sink-rates obtained. In addition, impeller position below the liquid surface has a major influence on sink-rate and impeller power requirement at higher viscosities. An impeller position close to the bottom of the desired depth of the vortex greatly reduces the power required to maintain this vortex and sink the powder. Sinking of powder into a liquid should not limit the dispersion or solubilization of powder provided the impeller has sufficient power input to maintain the vortex providing the suction to sink the powder. It should be possible to sink powder up until a % powder addition is attained at which the dispersion or solution has become so viscous that it behaves more like a solid than a liquid.

Characterization of a Fiberglass Geotextile for Unsaturated In-Plane Water Transport

Abstract The methods and results of the characterization of a woven, multifilament fiberglass geotextile are described in this paper. The moisture characteristic curve was measured with capillary rise and hanging column methods for both wetting and drying paths. In-plane flow was first measured with a simple siphon test, followed by measurement of the unsaturated transmissivity using a constant suction permeameter. The fiberglass geotextile became transmissive during wetting at a suction of 100 mm, and remained transmissive during drying to a suction of 600 mm. A lateral drainage test with the fiberglass geotextile indicated that the geotextile accepted and laterally drained water infiltrating through a soil layer under suctions in excess of 600 mm. The fiberglass geotextile is shown to contain more water and is more transmissive at greater suctions compared to other geotextiles, and has considerable capacity to drain water under suction.

A model of roof-top surface pressures produced by conical vortices : Evaluation and implications

The greatest suction on the cladding of flat roof low-rise buildings is known to occur beneath the conical vortices that form along the roof edges for cornering winds. In a companion paper, a model of the vortex flow mechanism has been developed which can be used to connect the surface pressure beneath the vortex to adjacent flow conditions. The flow model is experimentally validated in this paper using simultaneous velocity and surface pressure measurement on a 1 : 50 model of the Texas Tech University experimental building in a wind tunnel simulated atmospheric boundary layer. Flow visualization gives further insight into the nature of peak suction events. The flow model is shown to account for the increase in suction towards the roof corner as well as the presence of the highest suction at wind angles of 60°. It includes a parameter describing vortex suction strength, which is shown to be related to the nature of the reattachment, and also suggests how different components of upstream turbulence could influence the surface pressure.

A model of roof-top surface pressures produced by conical vortices : Model development

The objective of this study is to understand the flow above the front edge of low-rise building roofs. The greatest suction on the building is known to occur at this location as a result of the formation of conical vortices in the separated flow zone. It is expected that the relationship between this suction and upstream flow conditions can be better understood through the analysis of the vortex flow mechanism. Experimental measurements were used, along with predictions from numerical simulations of delta wing vortex flows, to develop a model of the pressure field within and beneath the conical vortex. The model accounts for the change in vortex suction with wind angle, and includes a parameter indicating the strength of the vortex. The model can be applied to both mean and time dependent surface pressures, and is validated in a companion paper.

Flow visualization of conical vortices on flat roofs with simultaneous surface pressure measurement

Wind tunnel and full-scale pressure studies of flow over low-rise buildings have repeatedly shown that on the roof, the largest mean and peak suction values are observed for taps beneath the conical “delta-wing type” corner vortices that occur for oblique winds. To better understand the flow mechanism which produces these negative pressure coefficients, a flow visualization study of conical vortex behaviour was performed in the wind tunnels of Colorado State University (CSU) and at full scale at Texas Tech University (TTU). The mean position and size of the vortices as a function of wind direction is presented. Pressures were also simultaneously measured beneath the vortex visualization plane in the wind tunnel for the worst case wind directions. These pressure profiles were correlated with the digitally enhanced images of the vortex flow. The greatest suction was found to follow directly beneath the moving vortex core. For smooth flow, the magnitude of the suction beneath the core was seen to vary inversely with the vortex size, but no relationship between vortex size and suction could be seen for turbulent flow.

Geochemical and Physical Controls on Vadose Zone Hydrology of Holocene Carbonate Sands, Grand Bahama Island

This paper explores the relationship between vadose zone hydrology and geochemical changes in mixed mineralogy carbonate sands from a Bahamian coastal dune of Holocene age. Cores were taken from two sites: at site A, a shallow humic Entisol is developed beneath open scrub vegetation, while at site B a deeper, more organic-rich Inceptisol has formed beneath a mature hardwood coppice. X-ray diffraction analysis reveals significant contrasts in mineralogy both within and between the two sites, with partial stabilization of high-Mg calcite and aragonite, to low-Mg calcite. Stabilization is greater at site B, and is accompanied by a significant increase in total porosity. Diagenetic changes in pore-size distribution have implications for residence times of percolating water, as determined using measurements of moisture retention characteristics using pressure plate apparatus, and hydrological models of unsaturated zone moisture flux. The diagenetically more mature sands from site B have a 50–100 per cent higher moisture retention, although unsaturated hydraulic conductivity is also higher, particularly at greater suctions. The increase in water retention is likely to enhance further rates of mineral-controlled reactions, while development of an organic-rich soil also enhances the geochemical drive for dissolution. Carbonate diagenesis thus appears to be strongly linked to vadose zone hydrology, and the interactions identified here have important consequences for the nature and long-term rates of mineral stabilization. © 1997 by John Wiley & Sons, Ltd.

Chloride displacement by water in layered soil columns

The displacement of a surface slug of chloride as affected by rates of water application (v) and redistribution time in two-layered combinations of loamy sand, sandy loam, and silt loam soils was studied in 10 cm I.D., 95 cm long plexiglass columns. The salt moved deeper with a given amount of water in coarse-over-fine than in the fine-over-coarse sequence of layering. This is attributed to the low water retention of the coarse top layer and more complete and rapid redistribution of water due to greater suction in the lower fine layer. The chloride peak, after redistribution, coincided with the wetting front in the coarse-over-fine, but lagged behind it in fine-over-coarse profiles. However, the solute front coincided with the wetting front in all cases. Immediately following infiltration, salt was displaced deeper with v = 0.1 cm h-1 than with 1.0 cm h-1 (or ponding) in all combinations. But when infiltration plus redistribution times were matched for the two rates, v = 1.0 cm h-1 (or ponding) was more efficient than v = 0.1 cm h-1 in a coarse-over-fine profile, except in loamy sand-over-silt loam. In fine-over-coarse profiles both rates displaced the solute to comparable depths. The findings have implications in reducing leaching losses of nutrients.

Movement of water through soil as influenced by osmotic pressure and temperature gradients

The equation used to describe steady-state water flow through a soil in response to hydraulic pressure (or suction in unsaturated soil), osmotic pressure, and temperature gradients is Jv = Lvv grad P + LvD grad ? - Lvq grad T. Published research results indicate that Lvq is relatively independent of suction when suctions are greater than about 0.06 bar, becomes quite small when suctions are lower than 0.06 bar, and increases in a predictable manner as the average temperature increases. A value of 3.0 × 10-3 cm2deg-1hr-1 is suggested for Lvq for estimates of water flow in response to temperature gradients. LvD can be considered to be zero for suctions less than about 0.25 bar except under conditions of very high clay content. The value of LvD is not likely to be greater than 10 per cent of Lvv (3 per cent is suggested for approximate calculations) at suctions between 0.25 and 1 bar. LvD would more nearly equal Lvv at greater suctions, but no data are available on this relationship at higher suctions. The suggested values of Lvq and LvD are based on relatively few data and are to be considered as approximate. Additional data are required for more specific values for these coefficients.

Sap Pressure in Vascular Plants

A method is described which permits measurement of sap pressure in the xylem of vascular plants. As long predicted, sap pressures during transpiration are normally negative, ranging from -4 or -5 atmospheres in a damp forest to -80 atmospheres in the desert. Mangroves and other halophytes maintain at all times a sap pressure of -35 to -60 atmospheres. Mistletoes have greater suction than their hosts, usually by 10 to 20 atmospheres. Diurnal cycles of 10 to 20 atmospheres are common. In tall conifers there is a hydrostatic pressure gradient that closely corresponds to the height and seems surprisingly little influenced by the intensity of transpiration. Sap extruded from the xylem by gas pressure on the leaves is practically pure water. At zero turgor this procedure gives a linear relation between the intracellular concentration and the tension of the xylem.

Constant‐Velocity Aerofoils

FOR aerofoils intended for use at high speeds, it is evident that the maximum lift on the back, consistent with a given maximum intensity of suction, will be attained when the suction, and hence the velocity, over the back is uniform; in other words, for a given mean lift on the back, the greatest suction will be a minimum, and so will the greatest velocity. On the hypothesis that compressibility stalling and compressibility effects generally depend on the amount of the greatest velocity at any point, such an aerofoil will have the ideal shape for high speed work. Interest, therefore, attaches to the theoretical solutions which are possible giving the form of an aerofoil having this property, particularly in view of the success of the theory in predicting velocity and pressure distributions for the ordinary range of aerofoils. When the thickness is finite somewhat involved problems in conformal representation require to be solved, although there is no fundamental difficulty in working out the solution. For thin aerofoils of small camber, such as those considered by Glauert in his classical theory, the problem is much simpler and it is known that the results of this theory are actually applicable to aerofoils such as are used in practice. Glauert himself considered only the case of infinitesimal thickness; this gives one solution of the problem here considered. Others are obtained by extending the theory to thicknesses of the same order as the camber, the order of approximation remaining the same. A particular case which will be treated here is that of an aerofoil having a flat face, i.e., camber equal to half the thickness.