Increase In Pressure Gradient Research Articles

Stability of Tollmien-Schlichting modes in magnetohydrodynamic boundary layer flow in porous medium: energy budget analysis

Abstract Linear temporal and spatial stability analyses of the magnetohydrodynamic boundary layer flow over a wedge embedded in a porous medium have been carried out to analyze the effects of pressure gradient, Hartmann and Darcy numbers. Firstly, we determine the base state velocity profiles by imposing suitable similarity transformations on governing boundary layer equations and then find linear perturbed equations involving Reynolds number and disturbance wavenumber using Fourier modes. The Chebyshev spectral collocation method which provides insight into the complete structure of the eigenspectrum is used. The effect of Hartmann and Darcy numbers on the boundary layer is to stabilize the flow for all adverse pressure gradient parameters while only unstable modes are noticed in the absence of these effects. The noticed unstable modes are always part of the wall mode for which the phase speeds are found to approach zero. The eigenspectrum for all involved parameters has a balloon-like structure with the appearance of wall mode instability. The critical Reynolds number is found to be increasing for increasing pressure gradient, Hartmann and Darcy numbers. For an adverse pressure gradient, the energy budget shows that the energy production due to Reynolds stress dominates the viscous dissipation which results in destabilization of the flow, while the kinetic energy due to magnetic field and porous medium plays a role in stabilizing the flow. The physical dynamics behind these interesting modes are discussed.

Quantitative in silico analysis for patient-specific annuloplasty in bicuspid aortic valve regurgitation

Bicuspid aortic valve (BAV) patients are more predisposed to aortic regurgitation. Annuloplasty is a crucial therapeutic intervention, however, determining its ideal size remains a clinical challenge. This study aims to quantify the effects of varying annuloplasty sizes on treating BAV regurgitation, providing optimal size range for effective treatment while avoiding complications. Annuloplasty was simulated on a patient-specific BAV model using 19–27 mm diameter Hegar dilators to reduce the basal ring and elastic ring sutures to constrain it. Finite element simulation was performed to simulate BAV motion, followed by computational fluid dynamics simulation to obtain hemodynamic parameters at peak systole. Results show that as the basal ring size decreased, the leaflet coaptation area increased, accompanied by a reduction in maximum principal stress at the coaptation zone. However, the reduction in annuloplasty size significantly elevated the peak systolic flow velocity within the sinus, particularly near the basal ring, leading to a higher wall shear stress in the adjacent region. Moreover, an excessively small basal ring diameter induced a sharp increase in transvalvular pressure gradient. These findings suggest that the small-sized annuloplasty enhances BAV function and durability, whereas excessive ring reduction may aggravate mechanical burden on the aortic root, potentially resulting in long-term complications such as tissue damage and stenosis. Thus, these factors establish critical upper and lower limits for optimal annuloplasty sizing.

Entropy generation and heat transfer in Time-Fractional mixed convection of nanofluids in Darcy-Forchheimer porous channel

This study investigates the role of time-fractional derivatives in the entropy analysis of mixed convection in a reacting nanofluid within a vertical permeable channel saturated with a Darcy-Forchheimer porous medium. This is crucial for enhancing heat and mass transfer, incorporating memory effects, and addressing delayed responses in various engineering applications. Key phenomena such as thermophoresis, porous medium permeability, buoyancy forces, chemical reactions, viscous dissipation, Brownian motion, and velocity slip are considered. The study presents an advanced computational methodology that integrates the Euler wavelets collocation method with an implicit difference scheme to discretize the system of time-fractional partial differential equations. This advanced numerical framework is thoroughly validated, ensuring high accuracy in capturing the complex interactions between fluids and solids. The study reveals that a 20% increase in the Eckert number leads to a 15% rise in entropy generation, signifying greater energy dissipation within the system. Likewise, higher Reynolds numbers contribute to increased entropy generation, emphasizing the flow’s dissipative nature. On the other hand, a 10% increase in pressure gradient and Forchheimer parameters results in a 12% reduction in entropy generation, demonstrating their ability to control the system’s irreversibility. These findings pave the way for more optimized and energy-efficient designs in engineering systems involving porous media.

Intensification of an Autumn Tropical Cyclone by Offshore Wind Farms in the Northern South China Sea

AbstractThe rapid development of the wind industry is accompanied by increasing environmental impacts. Currently, there is a lack of research on the impacts of offshore wind farm (OWF) on tropical cyclone (TC) intensity, including the mechanisms involved. This research is carried out by using a coupled and an uncoupled numerical model to investigate the impact of OWF on an autumn TC in the northeastern South China Sea. The results show that the wind speed deficit caused by OWF leads to an increase in surface pressure on the inflow side. This causes the surface pressure in the TC periphery to increase by advection, even if the TC is some distance away from the OWF. The increase in pressure gradient from the periphery to the TC center enhances the TC secondary circulation, thereby intensifying the TC. When the TC enters the OWF, the above mechanisms weaken and the ocean dominates the TC intensification. This is because the reduction in wind speed caused by the OWF results in a weaker sea surface current velocity, which weakens the flow of upstream cold water into the OWF, warming the sea surface temperature (SST) within the OWF. This implies that the horizontal gradient of the local SST is an important factor to be considered in the development of OWF. Sensitivity experiments indicate that OWF can also intensify other types of TC, and that higher cut‐out wind speeds lead to stronger intensification effects. These results also provide a new perspective on TC intensity forecasts.

Edemoascitis decompensation. Is it always liver cirrhosis?

Abstract Portal hypertension (PH) is a clinical syndrome characterized by an increase in the portal hepatic venous pressure gradient (HVPG), defined as the gradient between the portal vein and the inferior vena cava. When there is clinically significant PH, it is usually associated with clinical events such as the development of esophagogastric varices (EGV), oedemoascitic decompensation, encephalopathy... these being more frequent in the case of PH due to liver cirrhosis. In all etiologies of PH there is an increase in resistance to portal blood flow, followed by an increase in said flow. Depending on the location of the increased resistance, it will be classified as prehepatic, intrahepatic or posthepatic PH. Posthepatic portal hypertension occurs when there is a deterioration in hepatic venous outflow, increasing resistance at this level. We present the case of a patient where a striking portal dilation led to the diagnosis of posthepatic PH.

Microscopic Remaining Oil Classification Method and Utilization Based on Kinetic Mechanism

In reality, the remaining oil in the ultra-high water cut period is highly dispersed, so a thorough investigation is required to understand the microscopic remaining oil. This will directly influence the technological direction and allow for countermeasures such as enhanced oil recovery (EOR). Therefore, this study aims to investigate the state, classification method and utilization mechanism of the microscopic remaining oil in the late period of the ultra-high water cut. To achieve this, the classification of microscopic remaining oil based on mechanical mechanism was developed using displacement CT scan and micro-scale flow simulation methods. Three carefully selected mechanical characterization parameters were used: oil–water connectivity, oil–mass specific surface and oil–water area ratio. These give five types of microscopic remaining oil, which are as follows: A (capillary and viscous oil cluster type), B (capillary and viscous oil drop type), C (viscous oil film type), D (capillary force control throat type), and E (viscous control blind end type). The state of the microscopic remaining oil in classified oil reservoirs was defined after high-expansion water erosion. Based on micro-flow simulation and analysis of different forces during the displacement process, the main microscopic remaining oil recognized is in class-I, class-II and class-III reservoirs. Within the Eastern sandstone oilfields in China, the ultra-high water-cut stage is a good indicator that the class-I oil layer is dominated by capillary and viscous oil drop types distributed in large connected holes. The class-II oil layer has capillary and viscous force-controlled clusters distributed in small and medium pores with high connectivity. In the case of the class-III oil layer, it enjoys the support of capillary force control throats that are mainly distributed in small holes with high connectivity. Integrating mechanisms of different types of micro-remaining oil indicates that, enhancing utilization conditions requires increasing pressure gradient and shear force while reducing capillary resistance. An effective way to improve the remaining oil utilization is to increase the pressure gradient and change the flow direction during the water-drive development process. Hence, this forms a theoretical basis and a guide for the potential exploitation of remaining oil. Likewise, it provides a strategy for optimizing enhanced oil recovery in the ultra-high water-cut stage of mid-high permeability oil reservoirs worldwide.

Flow stability and permeability in a nonrandom porous medium analog

The estimation of the permeability of porous media to fluids is of fundamental importance in fields as diverse as oil and gas industry, agriculture, hydrology, and medicine. Despite more than 150 years since the publication of Darcy's linear law for flow in porous media, several questions remain regarding the range of validity of this law, the constancy of the permeability coefficient, and how to define the transition from Darcy flow to other flow regimes. This study is a numerical investigation of the permeability and flow stability in a nonrandom quasi-tridimensional porous medium analog. The effect of increasing pressure gradient on the velocity field and on the estimation of Darcy and Darcy–Forchheimer coefficients is investigated for three different obstacles radius. The transition from Darcy flow to nonlinear behavior is associated with the formation of jets in the outlet of the porous medium and development of flow instabilities. Different representations of the Reynolds number proved adequate to detect deviation from the linear law. The instantaneous permeability calculated at each pressure gradient was sensitive to flow velocity, in agreement with previous studies stating that permeability cannot be conceptualized as a constant for real flows.

Possible influence of the large-scale environment on extreme waves over the Yellow Sea in boreal spring

The Yellow Sea (YS) is exposed to various weather systems, such as typhoons, monsoon activities, and extratropical cyclones, which can pose a major threat to the adjacent coastal regions through the development of energetic oceanic surface waves. Unusually severe surface wave events in the YS occur with considerable frequency during the boreal spring (March-April-May), but have received less attention compared to winter and summer. This study focuses on the characteristics of spring extreme wave height (EWH) events in the YS during 1979-2022, based on observational and long-term reanalysis datasets. Our analysis shows that extreme waves, i.e. daily maximum heights in the top 5% of all spring days, take about 12 h to build up to the peaks, while they decay more slowly after the peaks. During the extreme events, the Siberian High is found to extend anomalously eastward compared to spring climatology. Such an anomalous extension contributes to the increase of the sea level pressure gradient and the intensification of the surface wind speed in the YS. Meanwhile, in the range of 6 ∼ 24 h following the peaks of the EWH events in the YS, swells induced by strong northerly winds begin to have an impact in the YS. These swells contribute to maintaining higher wave energy levels in the YS for longer after the atmospheric source has been removed. We further explore the large-scale environmental conditions that could provide the predictability of extreme waves in the basin developed by these findings. This study presents implications for assessing the risks associated with extreme waves in coastal regions and for improving coastal management strategies in the YS.

Failure of Surgical Aortic Valve Prostheses: An Analysis of Heart Team Decisions and Postoperative Outcomes.

Objectives: To analyze Heart Team decisions and outcomes following failure of surgical aortic valve replacement (SAVR) prostheses. Methods: Patients undergoing re-operations following index SAVR (Redo-SAVR) and those undergoing valve-in-valve transcatheter aortic valve replacement (ViV-TAVR) following SAVR were included in this study. Patients who underwent index SAVR and/or Redo-SAVR for endocarditis were excluded. Data are presented as medians and 25th-75th percentiles, or absolute numbers and percentages. Outcomes were analyzed in accordance to the VARC-3 criteria. Results: Between 01/2015 and 03/2021, 53 patients underwent Redo-SAVR, 103 patients ViV-TAVR. Mean EuroSCORE II was 5.7% (3.5-8.5) in the Redo-SAVR group and 9.2% (5.4-13.6) in the ViV group. In the Redo-SAVR group, 12 patients received aortic root enlargement (22.6%). Length of hospital and ICU stay was longer in the Redo-SAVR group (p < 0.001; p < 0.001), PGmax and PGmean were lower in the Redo-SAVR group as compared to the ViV-TAVR group (18 mmHg (10-30) vs. 26 mmHg (19-38), p < 0.001) (9 mmHg (6-15) vs. 15 mmHg (9-21), p < 0.001). A higher rate of paravalvular leakage was seen in the ViV-TAVR group (p = 0.013). VARC-3 Early Safety were comparable between the two populations (p = 0.343). Survival at 1 year and 5 years was 82% and 36% in the ViV-TAVR cohort and 84% and 77% in the Redo-SAVR cohort. The variables were patient age (OR 1.061; [95% CI 1.020-1.104], p = 0.004), coronary heart disease (OR 2.648; [95% CI 1.160-6.048], p = 0.021), and chronic renal insufficiency (OR 2.711; [95% CI 1.160-6.048], p = 0.021) showed a significant correlation to ViV-TAVR. Conclusions: Heart Team decisions are crucial in the treatment of patients with degenerated aortic bioprostheses and lead to a low mortality in both treatment paths thanks to patient-specific therapy planning. ViV-TAVR offers a treatment for elderly or intermediate-risk profile patients with comparable short-term mortality. However, this therapy is associated with increased pressure gradients and a high prevalence of paravalvular leakage. Redo-SAVR enables the surgical treatment of concomitant cardiac pathologies and allows anticipation for later VIV-TAVR by implanting the largest possible valve prostheses.

Study on the Evolution Law of Temperature, Pressure, and Productivity near the Well for Gas Hydrate Exploitation by Depressurization

In this paper, a one-dimensional model of gas–water two-phase productivity for hydrate depressurization is established, which takes into account permeability variation and gas–water two-phase flow. By solving the coupled algebraic equations of dissociation front position, equilibrium temperature, and pressure in an iterative scheme, the movement law of the hydrate dissociation front and the evolution process of temperature and pressure near the well were obtained, and the effects of bottom hole pressure, reservoir temperature, and hydrate saturation on productivity were analyzed. The results show that the hydrate reservoir is divided into a decomposed zone and an undecomposed zone by the dissociation front, and the temperature and pressure gradients of the former are greater than those of the latter. Reducing bottom hole pressure, increasing reservoir temperature, and increasing hydrate saturation all lead to an increase in temperature and pressure gradient in the decomposed zone. Methane gas production is a sensitive function of bottom hole pressure, reservoir temperature, and hydrate saturation. The lower the bottom hole pressure, the higher the reservoir temperature, the lower the hydrate saturation (within a certain range), and the higher the gas production rate. The trend of the water production curve is the same as that of gas, but the value is 3–4 orders of magnitude smaller, which may be due to the large difference in the viscosity of gas and water, and the gas seepage speed is much larger than that of water.

Propagation Characteristics of Initial Compression Wave Induced by 400 km/h High-Speed Trains Passing through Very Long Tunnels

When high-speed trains enter tunnels, an initial compression wave is generated. As the compression wave propagates at the local speed of sound to the tunnel exit, it radiates into the surrounding environment, forming micro-pressure waves (MPWs). MPWs create sonic booms, resulting in significant environmental issues. The magnitude of the micro-pressure waves is directly proportional to the pressure gradient of the compression wave at the tunnel exit. The nonlinear effects of the initial compression wave during propagation lead to a significant increase in pressure gradient. Therefore, the propagation characteristics of the initial compression wave during the tunnel are the crucial factor affecting the amplitude of MPWs. Based on the one-dimensional compressible unsteady non-isentropic flow model and the improved generalized Riemann variable characteristic method, this paper researched the propagation and evolution characteristics of an initial compression wave generated when 400 km/h high-speed trains enter tunnels with three portal shapes: (no tunnel entrance hood (no hood), an oblique, enlarged tunnel entrance hood (type A), an enlarged equal-section non-uniform opening hole tunnel entrance hood (type B)). The results show that when the initial compression wave propagates inside very long tunnels, the pressure gradient of the compression wave exhibits a trend of initially increasing and then decreasing with the increase in propagation distance. When the pressure gradient of the compression wave reaches its maximum value, the corresponding propagation distance is the steepening critical distance. For no tunnel entrance hoods, type A tunnel entrance hoods, and type B tunnel entrance hoods, the steepening critical distances are 5 km, 6 km, and 16 km, respectively. The steepening critical distance shortens with increasing train speed. Steady friction and unsteady friction effects mainly affect the pressure amplitude and pressure gradient during compression wave propagation, respectively. At lower ambient temperatures, the nonlinear effects in compression wave propagation are significantly enhanced. The mitigation effects of type A tunnel entrance hoods and type B tunnel entrance hoods on pressure gradient reduction are mainly concentrated within 4 km and 12 km, respectively. It is necessary to determine the optimal matching relationship between the tunnel entrance hood and tunnel length based on the characteristics of compression wave propagation to ensure their mitigating performance is maximized.

Analysis of electromagnetic and radiative heat source on tangential hyperbolic fluid under Arrhenius kinetic with convective cooling

The global threat of environmental degradation from harmful waste discharge is evident, leading to unusual diseases and natural disasters. Some of these toxic emissions result from human activities, such as the incomplete combustion of hydrocarbons. As such, this study aims to explore the analysis of electromagnetic and radiative heat sources on tangential hyperbolic fluid under Arrhenius kinetic with convective cooling. The transformed momentum and heat equations are solved using a rigorous computational approach called the Galerkin integration approximation with weighted residual method. This computational methodology ensures the reliability and accuracy of the results. Various graphs illustrate the results, showing parametric sensitivity profiles for the velocity, temperature, skin friction, thermal gradient, Bejan, and entropy generation. As noticed from the outcomes, electric field loading increases heat dispersion by about 3.25 % as heat source terms are enhanced. Increasing magnetic field, radiation, and electric field loading parameters strengthened thermodynamic equilibrium and minimized entropy generation. The tangential hyperbolic combustion process is 6.11 % increased with rising Brinkman number and electric field loading terms. The flow rate and temperature field are increased to the peak along the middle of the channel for increasing pressure gradient.

Experimental study on radial suction flow and its effect in water vortex unit

A water vortex unit is a non-contact adsorption unit that utilizes water as a flowing medium. Negative pressure is generated on the adsorbed surface through the high-velocity rotation of the fluid, resulting in suction force. In comparison to the air vortex unit, the water vortex unit exhibits a substantial increase in suction force and has the capability to deliver greater power. However, the presence of the central bubble in the water vortex unit weakens the suction force. To address the impact of the central bubble, a suction hole was introduced on the vortex unit to remove them. Experimental results indicate that solely removing the central bubble has almost no effect on the radial pressure gradients in the gap flow path and chamber center of the water vortex unit. However, in the cylindrical neighborhood, the radial pressure gradient increases, leading to a certain degree of improvement in suction force. Further increasing the suction flow rate induces inward radial flow within the vortex chamber. This flow field further enhances the suction force. To analyze the reasons for this pressure distribution, we indirectly obtained the radial velocity distribution by examining the relationship between the pressure gradient and tangential velocity. The results of the tangential velocity distribution indicate that the radially inward suction flow significantly increases the rotational velocity of the fluid in the chamber center, enhancing the centrifugal inertial effect. This further reduces the negative pressure, resulting in a significant improvement in the suction of the vortex unit.

#1397 Predictive factors for bioprosthetic valve stenosis and prognostic factors for survival following TAVR in hemodialysis patients with severe AS

Abstract Background and Aims Transcatheter aortic valve replacement (TAVR) is a promising option for the treatment of severe aortic valve stenosis (AS) in patients undergoing hemodialysis. Although the incidence of bioprosthetic valve deterioration (SVD) after TAVR has been reported to be lower than after surgical aortic valve replacement (SAVR), hemodialysis itself is still associated with a high risk of SVD. Until now, the factors that determine the prognosis of TAVR in hemodialysis patients were unknown. We previously reported that preoperative hypomagnesemia was correlated with an increase in postoperative mean aortic valve pressure gradient (MPG), an index of bioprosthetic valve stenosis as one of the indicators of SVD, in hemodialysis patients (Ren Fail. 2022 Dec;44(1):1083-1089). However, the study had a limited sample size of 24 cases, which raised concerns about statistical power. Therefore, we re-evaluate predictors of SVD and life expectancy in a larger number of post-TAVR hemodialysis patients. Methods From April 2012 to November 2021, all 100 hemodialysis patients treated with TAVR at Osaka University Hospital were included in the analysis. Pre- and post-operative demographic and laboratory data were analyzed by linear mixed-effects model and cox proportional hazards model. Results During the follow-up period (maximum 7 years), 4 out of 100 patients required re-TAVR (valve-in-valve) due to valve stenosis. The MPG increased over time with the lower preoperative serum Mg concentration (linear mixed-effects mode; +1.40 mmHg/year per 1mg/dl lower in Mg, p=0.006). However, serum calcium, phosphate, and intact PTH levels had no significant effect on the increase in MPG. In addition, a higher preoperative left ventricular ejection fraction (LVEF) was associated with a lower risk of death in a multivariate Cox proportional hazards model (hazard ratio [HR] 0.97 per 1% increase in LVEF; P=0.02). Conclusions Consistent with our previous report, preoperative hypomagnesemia was associated with increased MPG after TAVR. In addition, preoperative low cardiac function (LVEF&amp;lt;40%) may be a risk factor for postoperative mortality in dialysis patients. This was a single-center observational study, and the number of patients was still small, so our data may not be necessarily applicable to every patient. Further research is needed to identify a prognostic predictor of SVD and mortality, that will lead to the prevention of adverse outcomes in hemodialysis patients.

Heat and concentration analysis of two-layered muco-ciliary third grade fluid flow in human airways

Understanding the mechanisms involved in the movement and clearance of mucus within the human airways is important from a physiological perspective. A mathematical model of muco-ciliary two-layered fluid flow in a finite two-dimensional channel is proposed. Due to the presence of both the airway ciliary layer (ACL) and the periciliary liquid layer (PCL) in airways epithelial cells, the two-layered model is adopted. The third grade fluid models is used to characterize the viscoelastic nature of mucus secreted in the airways. The mathematical modeling of two-layer flow problem is simplified by using long wavelength and small Reynolds number approximation. A formulated set of partial differential equations (PDEs) is solved for series-form solutions of velocity, temperature, concentration, and pressure gradient by using the Adomian decomposition method (ADM). The analysis delineated that with an increase in pressure gradient at airways entrance ξ the velocity and temperature increases while concentration decreases. Deborah numbers impact ACL and PCL velocities differently, with De(A) influencing flow direction and De(P) causing fluid to flow faster in the forward direction. It also emphasizes the significance of the rate of thermal diffusion, viscous dissipation, and relaxation time. The results showed that the suggested two-layered muco-ciliary model provides a better description of mucus transport in the human airways. The pressure gradient at the airways entrance has a significant impact on mucus transport through the airways.

Long-Term Outcomes With Expanded Polytetrafluoroethylene Valved Conduits in Pediatric Patients

BackgroundThe expanded polytetrafluoroethylene (ePTFE) valved conduit (VC) has been reported for pulmonary valve replacement (PVR). The purpose of this study was to review long-term outcomes of our trileaflet ePTFE VC. MethodsThis multicenter study was performed with institutional review board approval from each institution. Our VC is fashioned from commercially available ePTFE tube grafts (for the conduit) and 0.1-mm-thick ePTFE membrane (for the trileaflet material). The patients were followed up in our clinic. Valve function was assessed by echocardiography in the operating room and at follow-up clinic visits after implantation. ResultsFifty-five patients received ePTFE VC between 2012 and 2023 (16-28 mm in diameter). Patients’ age at the time of implantation ranged from 6 months to 20 years (median, 7.5 years). Clinical follow-up ranged from 4 days to 10.1 years (average, 3.6 years). There were no hospital deaths. There were 2 non–valve-related late deaths. There have been no cases of endocarditis. Two patients required balloon dilation for the distal pulmonary artery stenosis, and 1 patient required residual ventricular septal defect closure. Five patients have received transcatheter PVR (TPVR) because of increased pressure gradient across the VC. Freedom from TPVR at 10 years was 90%. No valves required explantation or surgical replacement. ConclusionsCompared with historical data for other PVR options, our ePTFE VC shows excellent long-term performance and, when required, provides an easily accessible “landing zone” for TPVR. Our technique is easily learned, is reproducible, and can be a valuable option for surgeons performing PVR in pediatric patients.

Evaluation and clinical significance of contrast-enhanced ultrasound on changes in liver blood flow perfusion after TIPS surgery.

To investigate the clinical value of contrast-enhanced ultrasound in the prediction of hepatic encephalopathy (HE) in patients with hepatitis B cirrhosis after intrahepatic portal-systemic shunt via jugular vein. In this retrospective study, we collected data from 75 patients with hepatitis B, cirrhosis, and portal hypertension who underwent jugular intrahepatic portosystemic shunt from February 2019 to February 2022. The diagnostic instrument used was the TOSHIBA Aplio500 color Doppler ultrasound with contrast-enhanced ultrasound capabilities. The trial group comprised 20 patients with HE within 3 months postsurgery, while the control group (CG) included 55 patients without HE within the same postoperative period. All patients underwent various examinations before and within 48 hours after surgery, including observation of liver and spleen size and stent position, as well as assessment of blood flow direction in portal and hepatic veins. Subsequently, contrast-enhanced ultrasound was employed to examine and observe perfusion changes of contrast agents in hepatic veins, hepatic arteries, and portal veins (PV). Changes in PV pressure gradient, intrahepatic, and stent blood flow perfusion (BFP) were explored in both postoperative trials and CGs. The trial group exhibited higher BFP volume, PV pressure gradient difference, and percentage decrease compared to the CG. A weak positive correlation was observed between blood flow within the liver stent and PV pressure gradient difference, as well as the percentage decrease in PV pressure gradient. The correlation coefficient between blood flowing perfusion volume within the stent and the difference in PV pressure gradient was R = 0.415 (P = .000). The correlating coefficient between BFP amount within the stent and the percentage decrease in PV pressure gradient was R = 0.261 (P = .027). The area under the receiver operating characteristic curve for stent perfusion volume, difference in PV pressure gradient, and percentage decrease in PV pressure gradient was 0.691, 0.759, and 0.742, respectively. An increase in PV pressure gradient accelerates blood flow within the stent, predisposing to HE. Changes in hepatic BFP following transjugular intrahepatic portosystemic shunt can effectively predict the occurrence of HE, demonstrating significant clinical relevance.

Fractal study on the nonlinear seepage mechanism during low-permeability coal water injection

In the initial stage of coal seam water injection, due to the high density and low permeability of coal bodies, an obvious startup pressure gradient is observed in relation to water seepage; this phenomenon leads to low-velocity nonlinear seepage. In this paper, we study the nonlinear seepage law and the main influencing parameters of the water injection process. First, based on the startup pressure gradient, the nonlinear seepage equation, and the fractal theory, we formulated a nonlinear seepage model of coal seam water injection that considered the fractal characteristics of a complex coal structure. Subsequently, we carried out coal seam water injection and gas radial seepage experiments under a high overburden pressure, obtaining the startup pressure gradient according to the seepage characteristics and the changes of dynamic parameters. Then, the dynamic parameters of water injection, the structural parameters of the coal samples, the physical parameters, and the fractal dimension were substituted into the theoretical model to obtain the theoretically calculated value. Finally, through comparative analysis of theoretical and experimental startup pressure gradient calculation results, it is found that with the increase in the overburden pressure, the permeability of coal and the connectivity effect are reduced, while the fracture tortuosity and the startup pressure gradient increase. Moreover, coal seam permeability does not seem to be the single decisive factor for the nonlinear startup pressure gradient.

Evaluation of Recovery of Tight Sandstone Gas Reservoirs Based on a Seepage Steady-State Model

As an important indicator for measuring the effectiveness and level of oil and gas field development, recovery rate has always been a focus in the research of oil and gas fields. Reservoirs of tight sandstone gas formations have significant characteristics of low porosity, high permeability, and high water content, which leads to greater difficulty in their development and makes it challenging to evaluate the recovery rate. Newtonian mechanics, as an important component of the mechanical system, is an innovative application of classical mechanics in the field of seepage mechanics when applied to the two-phase flow of gas and water. Firstly, starting from the perspective of mechanics analysis, we derive a steady-state model for gas–water two-phase infiltration and obtain the productivity equation based on this model. Then, according to the steady-state model, we establish a method to calculate the effective control radius of gas reservoirs under different production conditions and reservoir physical properties. Finally, using Matlab 2018a programming based on the productivity equation, we calculate the gas recovery under different conditions during constant pressure drop production and constant production rate production. The results indicate that the effective control radius of the reservoir decreases with an increase in the economic ultimate daily gas production, increases with an increase in production pressure difference, slightly decreases with an increase in startup pressure gradient, and correspondingly increases with an increase in microtube radius and quantity. Regardless of whether it is production with a fixed pressure drop or production with a fixed production rate, the gas recovery decreases as the production pressure drop and bottomhole abandonment pressure increase, but it increases as the proportion of the single-well control radius increases. In production with a fixed pressure drop, the gas recovery remains consistent across different reservoir quality indices. However, in production with a fixed production rate, the gas recovery initially increases rapidly and then gradually slows down as the reservoir quality index increases, and there is an obvious critical permeability (0.1 mD). The research findings are based on the mechanical analysis of porous media, delving into the laws governing fluid flow during infiltration. The derived infiltration model can be used to calculate the effective control radius and evaluate recovery rates, providing practical guidance for reservoir development.

Effects of implantation height on the performance of a redo transcatheter aortic valve replacement using a balloon-expandable valve

ObjectiveThe use of the transcatheter aortic valve in low-risk patients might lead to a second intervention due to the deterioration of the first 1. Understanding the implantation height is key to an effective redo transcatheter aortic valve replacement treatment. MethodsThe effects of implantation height on the performance of a balloon-expandable valve within a self-expandable valve were assessed using hemodynamic testing and particle image velocimetry. The hemodynamic performances, leaflet kinematics, and turbulent shear stresses were measured and compared. ResultsWhen a second balloon-expandable valve was positioned at varying heights relative to the first self-expandable valve, the leaflet motion of the first valve transitioned from free opening and closing to overhanging, and eventually to being entirely pinned to the stent, forming a neo-skirt. When the leaflets of the self-expandable valve could move freely, a decrease in regurgitation fraction was observed, but with an increased pressure gradient across the valve. Flow visualization indicated that the overhanging leaflets disrupted the flow, generating a higher level of turbulence. ConclusionsThis study suggests that the overhanging leaflets should be avoided, whereas the other 2 scenarios should be carefully evaluated based on an individual patient's anatomy and the cause of failure of the first valve.