Constant Suction Research Articles

MHD flow of chemically reacting Casson fluid through a moving plate in non-Darcian porous medium with second-order slip velocity

The MHD flow of optically thick, incompressible, chemically reacting Casson fluid through a moving vertical plate exposed in a non-Darcian porous medium with second-order slip velocity is studied in this work. The plate is under a constant suction velocity. A consistently strong magnetic field is anticipated to be applied normally to the plate. This study includes the effects of Joule heating, viscous dissipation, Soret number and heat source. The MATLAB-bvp4c method is employed for solving the associated governing equations. The flow velocity rises with the growth of porosity parameter, solutal Grashof number, thermal Grashof number and Soret number but it decreases with the inertia parameter, chemical reaction parameter and magnetic parameter. The effect of Soret number raises the skin friction.

The Study of the Process of Supplying Seeds of Row Crops Using a Vacuum Seed-Placing Unit

Introduction. The performance of precision seeders depends on many factors, including the functionality of their dosing systems, the modernization of which is possible only on the basis of patterns, which allows forecasting the indicators of single seed placing into a furrow.Aim of the Study. The study is aimed at analyzing the influence of the diameter of the suction holes of seed-placing units and the rarefaction created in them on the characteristics of placing seeds of the main row crops.Materials and Methods. The results of the study were obtained based on a series of experiments on sowing corn and sunflower seeds using an MS-8 seeder, the operation principle of which can be considered typical for vacuum seed-placing units.Results. There have been obtained empirical dependences of the particular features of zero and group placing seeds of such row crops as corn and sunflower on the area of the suction holes and the rarefaction in the vacuum chamber.Discussion and Conclusion. The quantitative estimates obtained may differ for seeds of the same crop, but having different technological properties. The general factor is that the frequency of missing seeds is proportional to the suction force magnitude in the working plane of the metering element, regardless of its area. At the same time, the probability of double seed placing depends on the area of the metering ports with a constant suction force, a decrease in their diameter leads to a decrease in the frequency of double seed placing. The data obtained allow considering joint variations in the magnitude of the rarefaction in the vacuum chamber and the diameter of the suction holes as effective tools for improving the seed placing quality.

Empirical formulas for dynamic effective suction head in the modified green-ampt model

The Green-Ampt model, which is a widely used infiltration model, assumes a constant effective suction head during infiltration; however, the capillary pressure is dynamic and related to the saturation rate. One factor affecting the dynamic suction head is the dynamic contact angle, which is parameterized using different formulas. Previous studies applied a power-law formula to parameterize the effective suction head, which substantially improved the ability to describe the velocity-dependent suction head. However, other dynamic contact angle formulas have not been tested. In this study, we performed a series of 1-D downward infiltration experiments with 60-cm sand columns and constructed modified Green-Ampt models (MGAMs) based on four formulas of dynamic contact angle (power-law, Jiang’s law, Hoffman’s law, and Cox-Voinov law) and a linear approximation. These modified Green-Ampt models were named MGAM-PW, MGAM-Jiang, MGAM-Hoff, MGAM-CV, and MGAM-LN. After parameter optimization, all modified Green-Ampt models resulted in similar root-mean-square errors, which were lower than those of the classical Green-Ampt model. The modified Green-Ampt models yielded similar values for the equilibrium suction head, which were larger than those of the classical Green-Ampt model. Among the modified Green-Ampt models, MGAM-CV has an intrinsic limitation in the range of parameter values. MGAM-Hoff typically requires more fitting parameters than do the other methods. MGAM-LN can be solved more efficiently than other modified Green-Ampt models because of its analytical solution and small number of fitting parameters. We demonstrated that the data length and slight time delay of the measurement affected optimization of the equilibrium suction head. Moreover, the relationship between the capillary pressure and saturation rate based on MGAM-PW was similar to the findings in the literature.

Analytical and experimental evaluation of two-layered unsaturated sand bearing capacity

Pavement design methods based on principles of unsaturated soil mechanics take into account high soil shear strength due to matric suction resulting in more economical design especially in long roads. In this study, the bearing capacity of two-layer unsaturated sand was investigated using both analytical and experimental methods. At first, using the limit equilibrium method an analytical formula was proposed to determine the bearing capacity of two-layer unsaturated sand in which linear suction profile was considered in soil layers. It should be considered that the constant matric suction distribution assumed by the previous researchers does not show the real profile of matric suction within the soil, sometimes resulting in miscalculated unsaturated bearing capacity. Also, the bearing capacity of two-layer unsaturated poorly graded sand was investigated experimentally in different suctions by a special unsaturated chamber apparatus (UCA) designed for this purpose. The results show more than double increase of unsaturated soil bearing capacity with Sr = 25% compared to saturated soil. The formation of failure wedges in all experiments was investigated by image processing. An acceptable agreement was obtained between the theoretical and experimental bearing capacity results.

Stability of plane Couette flow with constant wall transpiration

Plane Couette flow with constant wall transpiration, i.e., constant blowing from below and constant suction from above, is a solution of the Navier-Stokes equations in terms of exponentials. It is characterized by two Reynolds numbers Re and ReV, where Re parametrizes the moving wall and ReV describes the influence of the transpiration. For this flow the modified Orr-Sommerfeld equation admits one of the very few exact solutions in terms of hypergeometric functions. Based on this, we solve the stability problem, though for the main part focus on temporal stability. For small wall-transpiration rates up to ReV≃6.71, the flow remains unconditionally stable, analogous to the classical Couette flow for arbitrary Reynolds numbers Re. By further increasing ReV an instability sets in and a minimum critical Reynolds number of Re=668350.491 is reached at ReV=9.799. Hence, around this point, the destabilizing effect of blowing outweighs the stabilizing effect of suction. By further increasing the transpiration rate beyond this point, the corresponding critical Reynolds number Re increases again and continues to grow. This limiting case is accompanied by the development of a strong boundary-layer-like velocity profile near the upper wall and the flow transitions to the asymptotic suction boundary layer (ASBL). Thus, the present analysis comprises the whole range from classical Couette flows extended by transpiration to the ASBL, which is known to have a strongly stabilizing effect. Published by the American Physical Society 2024

Effect of volumetric deformation on saturation of unsaturated soils under constant suction

The soil–water retention curve (SWRC) represents a fundamental relationship in the study of unsaturated soils, where volumetric deformation plays a crucial role in shaping the water retention characteristics by impacting the pore size distribution. This study conducted a thermodynamic analysis to derive a relationship between the effective stress parameter and the water retention properties of unsaturated soils. Consequently, a streamlined formula was introduced to forecast the impact of volumetric deformation on saturation at constant suction. This formula, incorporating a singular parameter from the effective stress parameters equations, can be seamlessly integrated with any prevailing SWRC model to characterize the influence of volume deformation on the SWRC. The effectiveness of the proposed model was corroborated through seven sets of experimental data spanning various soils, affirming its capability to precisely describe the water retention behavior of deformable soils under deformation.

The Utility of Prevena Negative Pressure Wound Therapy on Groin Incisions for Critical Limb-Threatening Ischemia: A Single Institution Experience.

Incisional negative pressure wound therapy (iNPWT) is an adjunctive treatment that uses constant negative pressure suction to facilitate healing. The utility of this treatment modality on vascular operations for critical limb-threatening ischemia (CLTI) has yet to be elucidated. This study compares the incidence of postoperative wound complications between the Prevena Incision Management System, a type of iNPWT, and standard wound dressings for vascular patients who also underwent plastic surgery closure of groin incisions for CLTI. We performed a retrospective cohort study of 40 patients with CLTI who underwent 53 open vascular surgeries with subsequent sartorius muscle flap closure. Patient demographics, intraoperative details, and wound complications were measured from 2015 to 2018 at the University of California San Francisco. Two cohorts were generated based on the modality of postoperative wound management and compared on wound healing outcomes. Of the 53 groin incisions, 29 were managed with standard dressings, and 24 received iNPWT. Patient demographics, comorbidities, and operative characteristics were similar between the 2 groups. Patients who received iNPWT had a significantly lower rate of infection (8.33% vs 31.0%, P = 0.04) and dehiscence (0% vs 41.3%, P < 0.01). Furthermore, the iNPWT group had a significantly lower rate of reoperation (0% vs 17.2%, P = 0.03) for wound complications within 30 days compared with the control group and a moderately reduced rate of readmission (4.17% vs 20.7%, P = 0.08). Rates of infection, reoperation, and dehiscence were significantly reduced in patients whose groin incisions were managed with iNPWT compared with standard wound care. Readmission rates were also decreased, but this difference was not statistically significant. Our results suggest that implementing iNPWT for the management of groin incisions, particularly in patients undergoing vascular operations for CLTI, may significantly improve clinical outcomes.

Elastoplastic solution for cylindrical cavity contraction in unsaturated soils

This paper develops an elastoplastic solution for cylindrical cavity contraction in unsaturated soils under constant suction conditions. The elastoplastic cavity contraction problem is formulated into a set of first-order ordinary differential equations by introducing a new auxiliary variable, which is solved as an initial value problem. The new solution is validated by comparison with numerical simulation results. Finally, parametric studies show that, as soil suction increases, the internal support pressure decreases faster with cavity contraction, the unloading-induced plastic zone becomes narrower, and the changes in effective stresses are smaller for a given tunnel convergence.

Laboratory Investigation of the Unsaturated Shear Strength Characteristics of Sand–Clay Mixtures

Sandy‐clay mixtures are commonly used in civil engineering projects, such as transportation and water resources, due to their unique construction properties. While the macromechanical characteristics of these mixtures under saturated conditions are well understood, their behavior in unsaturated states is still not fully elucidated. This study aims to investigate the mechanical behavior of sand–clay mixtures under unsaturated conditions by examining the influence of varying sand content and matric suction on their shear strength. The research includes unsaturated shear strength tests and nuclear magnetic resonance (NMR) experiments to analyze the pore characteristics within the mixtures at different sand content levels. The correlation between changes in pore structure and shear strength is systematically analyzed. The unsaturated shear strength of the mixtures is predicted using the Fredlund shear strength formula and compared with the measured values. The results indicate that the unsaturated shear strength of the mixture decreases as the sand content increases but stabilizes once the sand content reaches 20%. Below 20% sand content, the changes in micropore distribution are not significant with increasing sand content. However, beyond 20% sand content, there is a noticeable increase in the ratio of large pores and a decrease in the proportion of small pores. The sand content of 20% represents a critical threshold for the strength and porosity variations in the mixture. Under constant matric suction, the unsaturated shear strength of the mixture improves with the increase in sand content. However, the predictive accuracy of the Fredlund shear strength formula gradually diminishes as the sand content increases.

Exploratory Research on Comparing Breast Pumps: Using Data to Objectively Evaluate Pump Qualities

Objective:By understanding the terminology, functionality, and metrics that matter in breast pumps, both lactation professionals and pump users will be able to better identify, compare, and effectively use breast pumps for efficient milk removal.Methods:A device was created (breast pump vacuum monitoring system) that monitors and logs pressure data with respect to time and generates a pressure/time graph for a visual representation of breast pump performance in addition to providing max/min pressures, average pressure, and periodic cycle time estimations.Results:This exploratory testing showed that breast pumps varied widely in their abilities to maintain effective vacuum suction during simultaneous pumping. Maximum suction data points often refer to single-sided pumping. Cycles per minute (CPM) vary widely as well across breast pumps but can be categorized into two main ranges of 10–70 CPM (expression) and 60–120 CPM (stimulation). We found four major categories of suction patterns in our testing: standard pull and release, microvibration, constant suction, and combination patterns. A combination of these metrics makes up an individual pump’s unique programming.Conclusions:Breast pumps are a complex combination of vacuum strength, cycle speeds, and suction pattern, all of which must be optimized appropriately to function effectively. The lack of available important metrics on individual breast pumps, along with an incomplete understanding of the data presented in popular pump marketing, provides a difficult scenario for evaluating and comparing breast pumps.

Cavity expansions in two silty tailings with high degrees of saturation and a comparison to CPT results

Tailings, being mixtures of water and soil-sized particles, and sometimes air, are waste products generated by mining. They are stored on sites, often contained by embankments, forming what are known as tailings storage facilities (TSFs). Assessments of the state and strength of tailings inside a TSF may involve in situ tests, especially the cone penetration test (CPT) and occasionally the pressuremeter test (PMT). Cavity expansion theory may assist the interpretation of these tests. The coexistence of air and water in the pore space means the tailings is unsaturated and gives rise to a suction. The suction, and the extent to which air and/or water can drain through the pores, affects the cavity expansion results as well as CPT and PMT results. The cavity expansion problem is solved here considering four possible drainage conditions, constant suction, constant water mass, constant contribution of suction to the effective stress, and a constant air and water mass (closed system). It is reasoned that solutions for a closed system are relevant to the interpretations of CPTs and PMTs when < 15 % of the tailings volume is occupied by air, and that the constant effective stress condition (which is a close approximation to a constant water mass condition) is relevant when larger air volumes are present. By considering CPT data it is observed that linear proportionalities exist between effective cone penetration resistances and cavity wall pressures. The cavity expansion results are then converted to equivalent CPT results and used to construct charts which relate the normalised cone penetration resistance to the initial state parameter. The charts have use for unsaturated conditions and a variety of air volume fractions, as well as saturated conditions when the cone penetration rate is slow enough so drained conditions prevail or fast enough so that undrained conditions prevail.

A hydromechanical material model for compacted bentonite

This paper presents a new hydromechanical model, developed with the intention to be used for predicting the mechanical evolution of compacted bentonite components in repositories for spent nuclear fuel. The model is based on a thermodynamic relation for the chemical potential of the clay water, and uses empirical functions which are parametrized and calibrated with data on water retention properties at free swelling conditions, swelling pressure, and shear strength; the latter two are central for defining technical requirements for the bentonite buffer components. This results in a model which at its core incorporates all these properties, as well as the hysteresis behaviour. The validity of the model was investigated by analysing nine experimental test conditions, using COMSOL Multiphysics®, with a single set of parameter values. Model results were compared with experimental data for both saturated conditions (free swelling retention test; oedometer tests and triaxial compression tests) and for unsaturated conditions (swelling pressure build-up; swelling or shrinkage at constant load; compression at constant water or constant suction and unconfined compression tests). These comparisons gave a broad demonstration of the predictive capabilities of the model. Some limitation of the model regarding the representation of shrinkage, the shear strength at lower water contents, and the path dependence can nevertheless be noted.

The function of relaxation and retardation phenomena on time-dependent natural convective and oscillatory flowing of dissipative Oldroyd-B fluid via an infinite vertical plate with fixed suction

Constant suction phenomenon has been executed in free convective Oldroyd-B material in an oscillatory flow mode over infinite vertical porous plate. For heat transfer, this study includes the influence of heat dissipation. The resulting governing equations are transferred into a set of dimensionless form of coupled-ordinary differential equations with appropriate non-dimensional variables. MAPLE code is developed for the regular perturbation method and executed to solve the set of non-dimensional couple-ordinary derivative equations. The impact of different embedded parameters on the mean, fluctuating, transient velocities and temperatures on the Oldroyd-B fluid have been discussed and depicted in graphical forms. The influence of some physical terms on the plate mean friction and plate heat mean gradient are computed and demonstrated in a tabular form. The attained results show that as an increase in relaxation time, greater amplitude of temperature fluctuations is observed. Remarkable enhancement is observed in all the parameters (Grashof, Prandtl and Eckert numbers) for transient temperature profiles.

P62: A Unique case of Transcatheter aortic valve replacement dislodgement in the presence of a durable left ventricular assist device

Background: Transcatheter aortic valve replacement [TAVR] for severe pure aortic insufficiency [AI] in the presence of a durable left ventricular assist device [LVAD] is fraught with challenges. We report an interesting case of TAVR valve dislodgement by the LVAD that was treated with redeployment of another TAVR valve, and redo surgery for extraction of the intraventricular TAVR valve. Methods and Results: A 46-year-old man presented to our unit in cardiogenic shock [CS] and severe pulmonary hypertension [PH] of 72/45mmHg. He underwent placement of an Impella 5.5 [Abiomed, Danvers, MA] as a bridging strategy to treat his CS and PH while transplant candidacy was being assessed. However, he remained pulmonary hypertensive with a trans-pulmonary gradient 26mmHg and pulmonary vascular resistance 5.3 wood units, despite 14 days of impella 5.5 therapy combined with aggressive management with milrinone 0.25 mcg/kg/min and bumetanide infusion 1mg/hr. He therefore underwent implantation of heart mate 3 [HM3] LVAD [Abbott Laboratories, Chicago, IL] by a limited left thoracotomy in the 5th intercostal space and upper ‘inverse-T’ hemi-sternotomy into the fourth intercostal space. His postoperative course was complicated by requirement for 31mm percutaneous Protek Duo [LivaNova, London, UK] Right VAD [RVAD] for 32 days, and gastrointestinal bleeding requiring cessation of heparin therapy, which prompted formation of thrombus in the left coronary cusp of the aortic valve. Organization of this thrombus and consequent retraction of the left coronary leaflet led to severe AI and consequent CS, requiring inotropic support and discussion on optimal management strategy. He underwent TAVR with a 29mm Edwards Sapien 3 valve [Edwards Lifesciences, Irvine, CA] with 20% over-sizing, which got dislodged and migrated into the LV. Another 29mm Edwards Sapien 3 TAVR valve was successfully deployed. The patient was then placed on cardiopulmonary bypass via the femoral vessels, and the left thoracotomy was reopened. The LVAD was temporarily stopped, and the latch mechanism on the HM3 was opened. The HM3 was removed from the sewing cuff, and the TAVR valve was ‘fished-out’ from the cavity of the LV. The HM3 was reinserted and restarted after thorough de-airing through the outflow graft. The incisions were closed in a standard manner and the patient was discharged home on the 20th postoperative day. Conclusions: TAVR for severe AI in the presence of a durable LVAD is fraught with challenges due to the constant suction action of the LVAD, and the absence of calcium in the native annulus to anchor the prosthesis. Our case highlights the feasibility of extricating a dislodged TAVR valve through simple redo-surgery. With this approach, we managed to avoid a more conventional redo procedure involving administration of cardioplegia for a surgical AVR or for extricating the prosthesis, with its inherent risk of right ventricular failure requiring RVAD. Figure showing dislodged TAVR on the left and redeployment on the right

EFFECT OF INTERNAL HEAT AND VARIABLE ELECTRICAL CONDUCTIVITY ON CONVECTIVE MHD FLOW ALONG A VERTICAL ISOTHERMAL PLATE

The study investigates convective MHD flow of incompressible fluid of low Prandtl number along a vertical non-conducting plate in porous medium at constant temperature where fluid is sucked through a vertical plate with a constant suction velocity under the action of small internal volumetric heat generation and transverse magnetic field applied externally. The electrical conductivity of the fluid is considered to be temperature dependent variable. Incorporating the Boussinesqs approximation for the boundary layer flow and considering the action of local specific dissipation of mechanical energy due to permeability of the medium, numerical values of various flow parameters such as velocity, temperature, skin-friction, heat transfer etc. are calculated numerically, analysed graphically and conclusions are drawn.

A hydro-mechanical constitutive model for unsaturated soils over a wide saturation range

A hydro-mechanical constitutive model for unsaturated soils is proposed to describe the hydraulic and mechanical behaviour over a wide saturation range. Bishop’s effective stress and the effective degree of saturation are taken as the basic constitutive variables. A simple and novel loading-collapse yield curve is constructed to capture the variation of the yield stress with the hydraulic state over a wide saturation range. A non-orthogonal plastic flow rule is adopted to obtain the direction of the plastic strain increment. A simple water retention model is developed to describe the hydraulic behaviour of unsaturated soils. The proposed constitutive relation is presented through the calculation of the total strain increment and the calculation of the increment of the effective degree of saturation. All material parameters can be determined through conventional laboratory tests. The performance of the proposed model is illustrated through numerical examples of three classical stress paths, i.e., the isotropic compression path with constant suction, the wetting path with constant net stress, and the triaxial shearing path with constant suction and mean net stress. The capability of the proposed model to capture the hydraulic and mechanical behaviour of unsaturated soils is validated by simulating the test results from the literature.

A soil freezing-thawing model based on thermodynamics

The freezing-thawing behavior of soil plays a crucial role in frozen soil engineering. In this study, a soil freezing-thawing model is proposed from the perspective of statistical thermodynamics. First, the phase equilibrium relation for pore ice-water interface is deducted by applying statistical thermodynamics and the theoretical relationship is defined between the freezing temperature (i.e., the temperature at the ice-water interface) and the potential energy (i.e., total suction) of pore-water. This relation reveals that the matric suction of pore-water solely depends on the negative temperature at the pore ice-water interface for a given soil with constant osmotic suction and air pressure. Further, using the aforementioned relation and regarding the ice content of soil as an unknown variable, the thermo-hydraulic field in the soil freezing-thawing process can be solved by the mass and heat conversation. The governing equations related to this model are proposed in detail. Finally, to enhance the applicability of the proposed model, simplified forms in three typical conditions are provided, including the freezing process of saturated soil in artificial ground freezing technique, the capillary water migration coupled with freezing process of unsaturated soil in subgrade engineering and the vapor migration coupled with freezing process of semidry coarse soil under airport runways. Overall, the proposed model can be applied to various conditions and to other types of porous media (such as rock or concrete) that undergo freezing-thawing processes.

Computational Irreversibility Analysis in Transient Flow of a Non-Newtonian Fluid through a Channel with Porous Walls

A second law analysis is explored to investigate the irreversibility properties in a transient, porous channel flow of a viscous, incompressible, and non-Newtonian fluid. The non-Newtonian fluid model is of a Generalized Newtonian Fluid type with no elastic properties but with shear-thinning viscosity. Additionally, given that the flow is non-isothermal, the viscosity is therefore expectedly also assumed to be temperature dependent. The porous channel is subjected to constant suction and injection of fluid through the walls. Computational solutions for the underlying fluid dynamical equations, based on robust finite difference numerical techniques, are developed and implemented in time and space. We demonstrate the effects of the embedded fluid flow and heat transfer parameters on the fluid velocity and temperature profiles. We also explore the competing effects of heat transfer irreversibility versus fluid friction irreversibility. The major observations are that, in the flow regions where the maximum velocity obtains, heat transfer irreversibility significantly dominates over the otherwise insignificant fluid friction irreversibility. It is also observed that, in those flow regions away from the region of maximum velocity, the opposite scenario obtains, and hence fluid friction irreversibility significantly dominates over heat transfer irreversibility. Along the channel walls, fluid friction irreversibility notably dominates over heat transfer irreversibility. The possibility that certain parameter choices may lead to reverse scenario is not discounted.

Modelling unsaturated silty tailings and the conditions required for static liquefaction

The potential for static liquefaction of tailings is a major focus in the design and operation of tailings storage facilities. This research models the behaviour of unsaturated tailings, with a variety of degrees of saturation, addressing the propensity for static liquefaction during monotonic loading. Unsaturated triaxial tests, including constant suction conditions and constant water–air mass conditions, were performed. A bounding surface plasticity model was used to simulate the results. The constant mass condition is relevant to undrained closed-system loading, which may prevail during fast deformation after the tailings becomes unstable, when the air and water in the pore space remain locked inside the tailings. Boyle's law and hydraulic hysteresis were accounted for to model the changes of pore air and water pressures, and suction, with the change in tailings volume. Good agreement was achieved between test results and model simulations. Additional simulations to mimic rising water tables under constant total stress states in the field, situations that may trigger instabilities, are also shown. Results are added to charts which relate peak and post-liquefaction strengths, as well as collapse lines, to measures of initial state, for unsaturated conditions, which may be of use in practice.

The effect of hydro-mechanical coupling on the onset and orientation of localisation bands in partially saturated soils

Constant suction triaxial tests on partially saturated soils demonstrate the dependence of the onset and orientation of localisation bands upon different mechanical loading and saturation conditions, in addition to the material properties of soils. This effect of hydro-mechanical coupling, via the combination of effective stress and suction, on the onset and inclination of the shear bands is investigated in this paper using a model with a single yield surface dependent on both stress and suction. The cross-coupling terms in the asymmetric tangent stiffness allow the model to capture the coupled effects of suction and effective stress on the behaviour upon yielding and hence facilitate the bifurcation analysis for the onset and orientation of localisation bands in various loading and hydraulic states. The model parameters are determined with its experimental bifurcation characteristics, showing the sensitiveness of conditions that favour bifurcation under the effect of hydro-mechanical coupling and dilation.