Pressure Accumulation Research Articles

Effect of cyclic shear stress ratio on cyclic behavior of clay under multidirectional shear loading

In offshore engineering, soft clay foundations supporting infrastructure are subjected to significant multidirectional cyclic shear stresses due to earthquake or storm loads. To explore the undrained multidirectional cyclic behavior of foundation clays under critical loading conditions, a series of tests were conducted using a variable-direction dynamic cyclic shear system. By controlling the amplitude ratio (η) of two mutually perpendicular shear stresses in the horizontal plane, both unidirectional and multidirectional cyclic shear stress paths were achieved. The shear strength, stiffness, and pore water pressure are presented and discussed by considering the effects of η and cyclic stress ratio (CSR). The results suggest that the increase of CSR and η accelerates the cyclic failure, stiffness degradation, and pore water pressure accumulation of the clay specimens. An η-independent cyclic strength curve is established by normalizing the CSR to 0.755 η . Although η hardly affects the shear modulus in the x direction (G x) during the first cycle and at failure, it affects the parameter (χ) governing the shape of the stiffness degradation curve. Additionally, a model is proposed for predicting the evolution of normalized residual pore water pressure with respect to the number of cycles, wherein the parameter d remains unaffected by CSR and η.

Joint analysis of macroscopic response and microfabric evolution of coral sand during earthquake-induced liquefaction

This study addresses the microfabric evolution of coral sand during earthquake-induced liquefaction using the joint tests of macroscopic shaking table and microscopic X-ray computed tomography. Based on the non-destructive scanning and image reconstruction in three-dimensional, the change in the grain–pore structure of sands under earthquakes is discussed. Furthermore, the special microstructural evolution of coral sand is studied by the contrast tests with Fujian sand. The results show that the coordination number of coral sand is larger than that of Fujian sand after liquefaction, which is consistent with that the reduction in acceleration of coral sand is smaller than that of the Fujian sand, and the coral sand foundation still has a larger shear strength due to the smaller excess pore pressure accumulation. Moreover, the contact index of Fujian sand and Reigate sand fluctuates in a similar range with the change of void ratio and coordination number compared with coral sand. This is due to the fact that the Fujian sand and Reigate sand are both general terrigenous sands (quartz sand), while coral sand has irregular particle shapes and larger surface friction caused by marine biogenesis. The test results deepen the understanding of the liquefaction mechanism of coral sand.

Cerebral microvascular markers of intracranial pressure in acute and subacute porcine hydrocephalus model

Hydrocephalus affects 1.1% of infants, resulting in abnormal accumulation of cerebrospinal fluid and elevated intracranial pressure (ICP). Elevated ICP can occur prior to detectable morphological changes using computed tomography, resulting in delayed diagnosis and treatment. To improve early diagnosis, we propose vascular imaging using ultrasound localization microscopy (ULM) and ultrafast Doppler to measure cerebral blood flow changes due to acute to subacute elevations in ICP. We performed a pre-clinical study on a neonatal porcine model with 30 min, 8 h, 12 h, and 24 h ICP elevations while performing brain ultrasound measurements in hourly intervals. Ultrafast plane-wave ultrasound imaging was implemented using the Verasonics Vantage-256 and GE IC59D curved array probe at 400Hz frame rate. Lumason contrast agent was infused into each animal, providing tracers for ULM and enhancing the ultrafast Doppler imaging. Based on preliminary analysis, ultrafast Doppler showed reduced total cerebral blood volume after acute ICP elevation. ULM showed highly correlated parabolic reductions in cortical microcirculation with increasing ICP. Drastic reductions in cerebral microcirculation but less so in microcirculation accompanied microdialysis evidence of brain ischemia. Additionally, there were spatiotemporal changes in cerebral microvascular flow with varying ICP durations that warrant additional investigations using ultrafast ultrasound imaging.

Suppressing Methods of the Pressure Fluctuation in Open Jet Wind Tunnels

Due to the distinctive structure of the test section, the open jet wind tunnel generates low-frequency pressure fluctuations (LFFs) within the range of typical wind speeds. These fluctuations significantly compromise the quality of the flow field in the test section. The evolution of the flow structure and vortex is analysed through the improved delayed detached eddy simulations (IDDES). The LFFs and the control mechanism in the open jet wind tunnel of Jilin University are then studied. The interaction between the large-scale vortex shedding at the nozzle exit and the collector forms the edge feedback, which is the main reason for the pressure fluctuation. According to the feedback mechanism, the LFFs are suppressed using the throat gap and by improving the collector shapes. The results show that the increase of the throat gap length at the collector can significantly alleviate the pressure accumulation inside the collector. The change of the collector shapes can control the impact area and time of the incoming flow, or produce permanent vortex structure to affect the impact shape of the vortex and the flow field at the collector, which allows to control the LFFs. This study lays a solid foundation for further comprehension of the aerodynamic characteristics of the open jet wind tunnels.

REVIEW AND CRITICAL ANALYSIS OF THE CURRENT STATE AND WAYS TO IMPROVE REGULATED POWER SUPPLIES AND AUTOMATIC CONTROL SYSTEMS FOR ELECTRIC CENTRIFUGAL PUMPING UNITS IN INTERMITTENT OPERATION OF OIL WELLS

Link for citation: Kladiev S.N. Review and critical analysis of the current state and ways to improve regulated power supplies and automatic control systems for electric centrifugal pumping units in intermittent operation of oil wells. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 203-215. In Rus. Relevance. At present efforts are being made to convert low- and medium-flow oil wells to cyclical or short-term operation in order to reduce the excess pumping capacity that resulted from the reduction of well flow that is caused by reduced reservoir pressure during long-lasting exploitation of the deposit. The need for such a conversion requires justification for the use of more complex configurations of regulated power supply sources and automatic control systems of centrifugal pump units electric drives in automated process control systems. The local low-level automatic control systems for a mechanized electric drive method for lifting an oil-containing liquid from the well to the surface, namely the installation of variable-speed AC electric drives consist of ground-based devices and special submersible equipment. The ground-based devices are control stations with AC voltage and frequency converters with built-in telemetry units, external sine filter, step-up transformer. The special submersible equipment includes asynchronous induction electric motor, power cable, submersible telemetry unit, process sensors, centrifugal pump. The power supply of such a unit is provided from the external electric three-phase network of 6 kV through a reducing transformer substation of 6/0,4 kV. In the continuous mode of operation of oil pumping plants the electric pumps and other equipment, operate in quasi-static modes. Unregulated electric drive, as well as the open-loop controlled electric drive does not allow for smooth acceleration to the nominal performance of pumping equipment for pumping oil out of well in difficult conditions and its smooth regulation when reducing the well flow because of reducing oil flow to the slaughter. Therefore, the main way of smoothly reducing the excess performance of the submersible centrifugal pump is the periodic activation mode, which includes pumping the oil mixture out of the well and stop – for its accumulation and recovery of formation pressure. The introduction of cyclical technology shows that it is impossible to use the open-loop system of regulated electric drive everywhere, where acceptable quality indicators of transition comparable with the quality of closed-loop control systems are objectively unattainable. Due to the fact that the amount of pressure at the well intake created by a centrifugal pump, necessary to lift the well fluid to the surface, depends on the square of the rotation speed of the pump working stages, the operating pump productivity range Qmin... Qmax (m3/day) is obtained by varying the motor stator winding voltage (80…100) % from the nominal voltage value by using AC voltage controller with a phase control mode. If the stator voltage value is less than 80 % of Unom then the well fluid is not lifted to the surface and does not flow out of wellhead equipment. Therefore, when a frequency converter with Unom/fnom=const is used, the supply voltage and frequency of the motor should be varied in the same range. The price for using cyclic operation is a decrease in the reliability of submersible pumps. It is necessary to use special designs of submersible electric motors, improve power supply systems and synthesize closed-loop control systems of automatic control of electric drive of submersible pump. The purpose of the study is the review and critical analysis of the current state and ways to improve regulated power supplies and automatic control systems for electric centrifugal pumping units in intermittent operation of oil wells. Object: systems of power supply and automatic control of centrifugal pump units in intermittent operation of oil well, telemetry systems, energy-efficient submersible motors and centrifugal pump designs. Methods: methods of the theory of the automatic control system for developing the concept of operation of low flow of wells, analysis and synthesis of open and closed loop control systems of electric submersible centrifugal pumping units. Results. The paper introduces the scientific problem of development, implementation, models and methods of identification of technological processes, complexes and integrated control systems of oil extraction by electric drive method, taking into account the influence of a long submerged cable, low flow of wells and difficult operating conditions. The author proposed scientifically based technical solutions in the form of a structure of a power channel of an electromechanical system with a frequency-regulated induction motor, long submersible cable and indirect method of measuring state variable from ground-based measurements at load changes and measurement channel characteristics.

Thermal decrepitation of Pilbara (PB) lump ore: Characteristic, mechanism, and inhibitory strategy

Nowadays, more natural lump ores are directly used in blast furnace (BF) smelting to cut down costs and pollution issues. However, the decrepitation of lump ores at high-temperature deteriorates the permeability of BF operation. In this work, thermal decrepitation behavior of the PB lump ore was studied based on the international standard (ISO 8371). Effects of temperature, duration, lump size, the type and content of moisture on thermal decrepitation of PB lumps were investigated. The significant roles of heating temperature and crystalline water in lump ore were identified, while the critical decrepitation condition was determined. Decrepitation mechanism can be clarified as vapor pressure accumulation caused by crystalline water decomposition via TG-DSC, mercury porosimeter and SEM-EDS analysis. Inhibition method was developed from aspects of crystalline water decomposition and vapor diffusion to reduce the pressure accumulation. The decrepitation index (DI-6.3) of PB lump ore can be cut down from 17.5% to 0.4% effectively.

Numerical simulation of pore pressure development beneath suction anchor under undrained condition during uplift

Suction anchors are increasingly used in the deep-sea anchoring infrastructure, and the accurate evaluation of the uplift behavior is of great importance. In this paper, the development of pore pressure under the suction anchor lid during the undrained pullout process was investigated. The numerical model based on the solid-fluid two-phase theory and by updated Lagrangian method was employed. Laboratory experimental studies with three different aspect ratios were carried out to verify the effectiveness and accuracy of numerical method. Parametric studies were performed to analyze the effect of key soil properties on the accumulation of pore pressure. The results show that the numerical method in terms of capturing the failure pattern and simulating pore pressure evolution was significantly efficient. The development of excess pore pressure increased faster at the beginning, followed by a slower increase and then tended to level off. The maximum excess pore pressure appeared just beneath the suction anchor, and decreased with the increasing soil depth. Parametric analysis showed that a greater negative pore pressure needed a larger shear modulus, MCC swelling index and critical stress ratio, or a smaller porosity, permeability and MCC compression index. The softening coefficient had little effect on the pore pressure generation.

Investigation of the effects of cyclic lateral load characteristics on monopiles in saturated sandy soils using hypoplastic material model

AbstractOffshore wind turbines play a critical role as a renewable energy source and are experiencing continuous growth in usage. Both the design and implementation phases of constructing these structures present difficulties. It is crucial to ensure these structures are built to resist such conditions, assuring their durability, as they are exposed to lateral external influences such as wind and wave loads. This study investigated how monopile foundations behave in saturated sandy soil under cyclic loading. Pore water pressure accumulations in saturated sandy soil, monopile head lateral displacements, and vertical settlements around the monopile are investigated using the hypoplastic material model and two‐phase element with the ANSYS finite element program. Analyses conducted in this study demonstrated that lateral cyclic loads could cause excessive pore water pressure accumulations around the monopile, leading to displacements in the monopile head and soil settlements around it, highlighting the importance of carefully considering loading characteristics during the design process to provide the security and longevity of offshore wind turbines.

Discovery of novel isopropanolamine inhibitors against MoTPS1 as potential fungicides with unique mechanisms

The resistance and ecotoxicity of fungicides seriously restrict our ability to effectively control Magnaporthe oryzae. Discovering fungicidal agents based on novel targets, including MoTPS1, could efficiently address this situation. Here, we identified a hit VS-10 containing an isopropanolamine fragment as a novel MoTPS1 inhibitor through virtual screening, and forty-four analogs were synthesized by optimizing the structure of VS-10. Utilizing our newly established ion-pair chromatography (IPC) and leaf inoculation methods, we found that compared to VS-10, its analog j11 exhibited substantially greater inhibitory activity against both MoTPS1 and the pathogenicity of M. oryzae. Molecular simulations clarified that the electrostatic interactions between the bridging moiety of isopropanolamine and residue Glu396 of contributed significantly to the binding of j11 and MoTPS1. We preliminarily revealed the unique fungicidal mechanism of j11, which mainly impeded the infection of M. oryzae by decreasing sporulation, killing a small portion of conidia and interfering with the accumulation of turgor pressure in appressoria. Thus, in this study, a novel fungicide candidate with a unique mechanism targeting MoTPS1 was screened and discovered.

Numerical investigation of solute migration and release from sediments driven by wave-induced accumulation of pore water pressure

Sediments with poor drainage conditions are prone to build-up of excess pore water pressure when exposed to dynamic wave loading. This results in accumulated seepage flow that may have a significant impact on migration of solutes in marine sediments. In this study, the complex interplay between solute transport and wave-induced seepage process is investigated through a pioneering approach that combines and synchronously solves the two-dimensional advection-dispersion equation governing nonreactive solute transport with the governing equations for wave-induced oscillatory and residual pore pressures. The simulated results have demonstrated that the accumulated seepage flow significantly contributes to the advective and dispersive fluxes of solute, where the advection leads to movement of the solute layer and the hydrodynamic dispersion primarily enlarges the thickness of solute layer. The distribution of residual pore water pressure along depth exhibits two patterns that are primarily influenced by the thickness of the seabed. When the seabed is thinner than 0.3 times the wavelength, the residual pore pressure increases monotonically with depth (Pattern I). In this situation, the solute always migrates upwards to the seabed surface. Otherwise, Pattern II depicts the distribution of residual pore pressure, where the peak value of residual pore pressure attains at a certain depth and may advance downwards with wave action time. In this case, the direction of solute migration in regions shallower than a certain depth (e.g., 0.6 times the thickness of sediment) may alternate over time but the solute can eventually be transported upwards to seabed surface. The parametric study shows that when the seabed thickness is 0.2–0.3 times the wavelength, accumulated seepage flow has less effect on solute migration, whereas decreasing relative density and shear modulus, as well as increasing soil permeability can enhance the effect of accumulated pore water pressure on solute migration.

The effect of flexible obstacles with different thicknesses on explosion propagation of premixed methane-air in a confined duct

The effect of flexible obstacles with varying thicknesses on the explosion characteristics of combustible gas in a simulated confined duct (cross section 80 mm × 80 mm, length 3 m) was experimentally investigated, aiming to reduce the huge losses caused by gas explosion accidents in the process industries and mining industries. In this paper, plant fiber membranes with an opening area of 0 and thicknesses of 0.105 mm, 0.210 mm, 0.315 mm, 0.420 mm, 0.525 mm, and 0.630 mm were selected as flexible obstacles. The thickness of the flexible obstacle determines the strength of its compressive resistance. The characteristics of overpressure and flame during methane explosions are analyzed and conclusions are drawn. Results indicate that several shock wave reflection processes occur before the diaphragm ruptures, resulting in turbulent flames. In addition, the explosion wave generated numerous shock reflections during the rupture process of the diaphragm, which was gradually discharged downstream of the pipe by ejection as the pressure wave accumulated in front of the diaphragm. It should be noted that the thickness of the flexible obstacle determines the pressure accumulation in front of the membrane. Generally, the thinner the flexible obstacle, the less intense the turbulent flame is induced by the flexible obstacle, decreasing the contact area between the unignited gas downstream of the pipeline and the turbulent flame area. In conclusion, with an increase in the thickness of the flexible barrier, it exhibits a mechanism of initially suppressing and subsequently enhancing the impact on methane explosions. The increase of the thickness of the flexible obstacle motivates the flame propagation speed, which leads to an increase of turbulence intensity and explosion intensity.

Development of evening sleep homeostatic pressure in early adolescent boys

The physiological processes governing sleep regulation show maturational changes during adolescent development. To date, data are available to specify when delays in circadian timing occur; however, no longitudinal data exist to characterize the maturation of the accumulation of sleep pressure across the evening. The aim of this longitudinal study was to test whether this change in evening sleep propensity can be identified during early adolescence. Twenty pre-pubescent boys’ (Mage = 10.3, SD = 0.4 years) evening sleep homeostats were assessed using a series of sleep latency tests every hour (7:30 p.m. to 3:30 a.m.) at 6-month intervals across four waves. While results revealed shorter sleep onset latencies with increasing wakefulness (p < .001), this effect was not moderated by study wave (p = .79). Evening sleep propensity thus appears to remain stable in boys during early adolescence. Future studies should expand upon these findings by using larger samples of girls as well as boys across an extended age range during the teenage years.

Loading rate influence on high-cyclic loading of clays

Experimental observations reported in the literature, based on cyclic triaxial and cyclic simple shear tests, show that the loading frequency influences the excess pore pressure and strain accumulation for fine-grained soils under undrained conditions. A high-cycle accumulation (HCA) model for clay was introduced by Wichtmann (2016) and Staubach et al. (2022) to quantify the strain/pore pressure accumulation as a function of the number of applied cycles, amplitude, void ratio, stress ratio, OCR and loading frequency. This article explores the convenience of including the loading frequency factor in the HCA clay model based on the interpretation of a series of cyclic undrained triaxial tests performed on three different clay materials, namely Dorfner kaolin, Lower Rhine clay and Onsøy clay. Analysis of results shows that for those specific three clay materials, the normalization of the pore pressure accumulation rate u̇acc with the amplitude function fampl purifies the data from the influence of loading frequency and thus no explicit frequency function ff is required.

ПАРАДИГМА ФІНАНСУВАННЯ ВИДАТКІВ ДЕРЖАВНОГО БЮДЖЕТУ УКРАЇНИ В УМОВАХ ВОЄННОЇ ТА ПІСЛЯВОЄННОЇ СОЦІАЛЬНО ОРІЄНТОВАНОЇ РИНКОВОЇ ЕКОНОМІКИ

The article highlights the problem of financing state budget expenditures in the conditions of the war and post-war market economy, which, for objective reasons, has a significant social burden. The study found that the new paradigm of public financing in the conditions of the war and postwar social-oriented market economy should solve three key tasks: to sufficient finance the defense sector of Ukraine, modernization of the army of Ukraine; to ensure the systematic growth of the main macroeconomic indicators, in particular, the inflow of new foreign investments and, as a result, and, as a result, guarantee an adequate and fair social security system for vulnerable segments of the population and certain social categories of citizens, including those participating in hostilities. The main macroeconomic indicators and indicators of the State Budget of Ukraine in 2018-2023 were studied, and the thesis of significant social pressure on the country’s budget was confirmed. The authours tracked changes in the structure of budget expenditures in 2018-2023 in various key sectors of the economy, in particular, a significant increase in expenditures from the State budget for the defense sector, which was caused by the war. In this regard, an attemt was made to analyse the best practices of foreign countries that faced the situation of limited budgetary funds, crisis tendencies in the economy, accumulation of social pressure and escalation of the military conflict. In particular, the experience of Israel, Turkey and China was analysed. Based on the analysis of the experience of other countries, the authours proposed a model of public-private partnership in the development and support of the post-war socially oriented economy of Ukraine. The model identifies the key participants and the relationship between them on issues of interaction in filling the main budget items, financing key investment-intensive sectors of the economy. The state investment platform «Advantage Ukraine» identifies the following investment-intensive sectors: logistics and infrastructure of 30 projects; defense-industrial complex from 10 projects; energy from 50 projects; agro-industrial complex from 300 projects; pharmaceuticals of 30 projects and others. Therefore, we can conclude that the state and the government are already moving in the outlined direction of public-private partnership, which actually makes the proposed model relevant. As a result of applying the proposed model of public-private partnership, its economic effect was determined, which boils down to the systemic macroeconomic growth of Ukraine, the scaling of investment projects, the development of science in Ukraine, and the overcoming of socio-economic contradictions in the development of Ukraine.

An experimental study on the moisture migration characteristics of liquefiable iron ore

Cargo liquefaction is still the biggest causes of casualties during its sea transportation. To understand the liquefaction mechanism deeply, research of moisture migration characteristics of liquefiable cargo is the priority. Closer to the actual transportation conditions of iron ore, unsaturated undrained, saturated undrained and saturated drained experiments were all carried out. Effects of ship motion accelerations, frequencies and sample densities were also taken into account. Results indicate that the largest drainage happens in the first ten minutes when drained, and accounts for 75.3% of the total volume. The external loads have a little promotion for the drainage. The pore water pressure dissipates quickly and its value goes below zero. When undrained, the water would migrates upward and the middle part have a relative higher water content. The pore water pressure accumulates and increases quickly in the first 50–100 s, and also the middle part has the largest increase of pore water pressure. A larger motion acceleration could enhance the accumulation of the pore water pressure and the water migration. There are critical motion frequencies, under which the accumulation of the pore water pressure and the water migration become obvious. For the sample with a higher density, the accumulation of the pore water pressure and the ability of water migration are all bounded. This study could be provided as an useful reference to reveal the liquefaction mechanism.

Robust omniphobic ceramic hollow fibre membrane with leaf-like copper oxide hierarchical structure by membrane distillation

Omniphobic membranes have recently shown promising performance in water desalination using MD due to their ability to repel all liquid drop types and keep the membrane surface dry. This study successfully modified the surface of robust hydrophilic mullite-stainless steel hollow fibre membranes (M-SS HFMs) to omniphobic properties. The omniphobic layer was achieved through surface grafting with copper oxide (CuO) rough layer by a hydrothermal technique at different hydrothermal reaction times of 1, 2, 3, 4 and 5 h, followed by fluorination step using 1H,1H,2H,2H-perfluorode-cyltriethoxysilane (C8, 97 %). Next, the omniphobic membranes were characterized in terms of membrane morphology, roughness, mechanical strength, pore size/distribution, liquid entry pressure, contact angle and fouling accumulation. The prepared omniphobic M-SS HFMs were also tested through the DCMD system at 80 °C using a feed solution containing 35 g/L of NaCl and 10 mg/L of humic acid as a foulant agent. The results indicated that M-SS HFMs subjected to a 4 h hydrothermal reaction time, resulting in a leaf-like surface structure, exhibited superior characteristics compared to other omniphobic HFMs reported in the literature that used titania (SiO2), zinc oxide (ZnO), and cobalt (Co3O4) as roughing material. These superior features included higher roughness of 0.798 μm, liquid entry pressure of 5.40 bar, and enhanced liquid repellence and contact angles towards DI water of 167°, olive oil of 152°, and ethanol of 145°. Additionally, the M-SS HFMs at 4 h hydrothermal demonstrated remarkable performance in terms of rejection performance (99.99 %) and vapour flux stability of about 29 kg/m2.h in DCMD operations, surpassing the performance of omniphobic HFMs fabricated using mullite-ball clay, mullite-kaolinite, and alumina (Al2O3). Notably, no fouling/wetting on the membrane surface and elements leaching was observed throughout the MD operation. These findings highlight the potential of this omniphobic HFM for seawater desalination using DCMD systems, even in the presence of organic contaminants.

Influence of the opening pressure of explosion‐venting surface on methane deflagration characteristics in municipal sewage confined spaces

AbstractThis study investigates the influence of the opening pressure of the explosion‐venting surface (EVS) of a vertical branch pipeline on the deflagration characteristics of methane at different concentrations. The results indicate that the increase in the opening pressure of the EVS promotes the accumulation of deflagration pressure in the horizontal pipeline, whereas the venting effect in the vertical branch pipeline attenuates the peak value of the deflagration pressure. The vertical branch pipeline has both “promoting” and “inhibiting” effects on the flame propagation speed in the horizontal pipeline. With an increase in the methane concentration and opening pressure of the EVS, the promoting effect gradually plays a dominant role, resulting in an increase in the flame propagation speed. In actual industrial production and daily life, in order to avoid explosion hazards, it is essential to install EVSs or reduce their opening pressure in a confined space.

Liquid–vapor phase transition process during underwater electrical wire explosion

The liquid–vapor two-phase region has attracted the attention of various fundamental studies and applications. To explore the liquid–vapor two-phase region, underwater electrical wire explosion (UEWE) is a useful tool. In this work, we observe two different mechanisms of the liquid–vapor transition in UEWE: volume vaporization and spinodal decomposition. The main factors through which the mechanisms occur are the heating power and pressure accumulation in the system during UEWE. From the electrical properties and shadowgraph images, the phase transition process of the exploding wire is analyzed. The effects of possible instabilities during the liquid–vapor phase transition are also discussed. We expect that the thermodynamic properties of the liquid–vapor two-phase region can be explored using the UEWE technique based on the understanding of the phase transition process.

CARD20: Investigating the Impact of Ventriculoatrial Shunts on Venous Hydrodynamics: A Computational Fluid Dynamics Analysis

Ventriculoatrial (VA) shunts are a common treatment option for patients suffering from hydrocephalus and requiring cerebrospinal fluid (CSF) drainage. However, the impact of this treatment on cardiac hydrodynamics has yet to be fully understood. To shed light on this issue, the present study employs computational fluid dynamics (CFD) simulations to evaluate the effects of VA catheters on venous hydrodynamics in hydrocephalus patients. The study focuses on five models of different sections of veins, including the Internal Jugular Vein (IJV), Right and Left Brachiocephalic Veins (RBV-LBV), and the Superior Vena Cava (SVC). The vein geometry was reconstructed from neck CT scans of a patient with mild hydrocephaly without a catheter. Blood flow simulations were performed using pressure-based transient laminar models solved with the Ansys Fluent Navier-Stokes solver. The analysis was conducted on two healthy cases with and without catheters, and three hydrocephalus cases with catheters, considering mild, moderate, and severe hypertension. The results show that pressure accumulation near the IJV bulb was observed in all cases, with maximum pressure in the severe hypertension case. A pressure of 3,050 Pa was reached over the catheter insertion site. The healthy case without the shunt showed velocities of up to 0.8 m/s, while in the severe hypertension case, velocities were less than 0.2 m/s in similar regions for the IJV, RBV, and LBV. Healthy streamlines showed some vortices throughout the IJV, which seemed to be minimized by the presence of the catheter in the other models. In conclusion, this study provides valuable information regarding the hydrodynamic alterations seen in patients with VA shunts. The observed pressure accumulation and decreased velocity can be associated with potential adverse effects such as thrombotic formation. These findings can be used to guide future treatment options and warrant further long-term study. The use of CFD simulations offers a non-invasive and efficient method to study the effects of VA shunts on cardiac hydrodynamics and can provide a deeper understanding of the complex interplay between cerebrospinal fluid drainage and venous hydrodynamics.

Experimental investigation on cyclic behavior of geogrid-reinforced coral sand from the South China Sea

The present study provides insight into the cyclic behavior of unreinforced and geogrid-reinforced coral sand. To achieve these goals, stress-controlled undrained cyclic triaxial tests were conducted on medium-dense coral sand with and without geogrid reinforcements. The influence of geogrid reinforcement, cyclic stress ratios, and confining pressure on the deformation, pore pressure, liquefaction resistance, stiffness degradation, and particle breakage characteristics of saturated coral sand was investigated. The results indicated that coral sand reinforced with geogrid increased the liquefaction resistance and decreased the rate of pore pressure accumulation. The effectiveness of the geogrid inclusion on coral sand’s liquefaction resistance was found to be more pronounced under large effective confining pressure and a smaller cyclic stress ratio. Increasing the effective confining pressure increases the liquefaction resistance for both unreinforced and geogrid-reinforced coral sand, whereas increasing the cyclic stress ratios decreases the liquefaction resistance of the unreinforced and reinforced coral sand. The particle breakage was observed to be increased with increasing the effective confining pressure and cyclic stress ratio, and the breakage was more in the reinforced coral sand than the unreinforced coral sand.