Minimum Pressure Values Research Articles

Global experience on irrigation management under different scenarios

Abstract This study aims to assess global experience on agricultural water management under different scenarios. The results showed that trend of permanent crops to cultivated area, human development index (HDI), irrigation water requirement, and percent of total cultivated area drained is increasing and trend of rural population to total population, total economically active population in agriculture to total economically active population, value added to gross domestic production (GDP) by agriculture, and the difference between national rainfall index (NRI) and irrigation water requirement is decreasing. The estimating of area equipped for irrigation in 2035 and 2060 were studied acc. to the three scenarios: I - the values of the main indices would be changed by the same slope of the past half of century, II and III - the slopes would be decreased by 30% and 50% respectively. The minimum and maximum values of pressure on renewable water resources by irrigation, are related to the third and first scenarios by 2035 (6.1%) and 2060 (9.2%), respectively.

Investigation of Turbulence for Wind Flow over a Surface Mounted Cube using Wall Y+ Approach

Objective: To find the best mesh based on wall y+ approach and to model turbulence flow numerically over a surface mounted cube so that appropriate mesh can be selected and thereby the best grid configuration can be found. Methods: The study uses three mesh configuration based on wall y plus to capture the turbulence and its complex characteristic for moderate high Reynolds number. The study depends on Reynolds number 40,000 which is based on height of the cube and bulk velocity and the numerical and analysis results are compared with the recognised published work on the flow past ground mounted prismatic body placed in a fully developed turbulent channel flow. The turbulence model used in this work is large eddy simulation incorporating Smagorinsky scheme. The investigation of near wall treatments is done for maximum wall y+≈5 covering the viscous sub layer, maximum y+≈23 the buffer region and maximum y+≈40 resolving the log-law region.OpenFoam platform under Linux OS is used for the study. Findings: After completion of three numerical simulations based on three grids various results in terms of fluid parameters are discussed such as drag and lift, velocity profile, pressure profile, Q criteria etc. It has been found that the drag force varies from 1.13 to 1.38 and lift coefficients varies from 0.8 to 1.0. Strouhal number varies from 0.45 to 2.17. Maximum and minimum pressure values are also been found and is discussed in the result & discussion section of this paper. Application: The method described in the present study is very helpful in finding the best suitable grid for CFD analysis. As it is very well known fact that, if the grid is not good enough for any CFD study, the result of the simulation will be wayward. Finding the best grid or mesh is a time consuming process and also involves high cost. This method can minimize the cost and also saves lots of computational time.

Flow Characteristics of Large Hydropower Bifurcation Under Structure Rounding Optimization

The reinforced concrete bifurcation in hydropower station is consistently under high internal water pressure, and its diameter is usually larger than common duct junctions. To diminish or to decrease the heavy plastic zone and stress concentration, structure rounding is commonly used on bifurcation. This will bring some changes to the flow characteristic of bifurcation, and it is an interesting attempt to figure out the influence of structure rounding optimization. The realizable k–e model was employed in computational fluid dynamics numerical simulation. The water pressure distribution was compared quantitatively at several certain sections. Furthermore, uneven pressure is analyzed by relative standard deviation. Hydraulic characteristics are discussed as well, including flow pattern, excavation volume and head loss in different working conditions. The results indicate that the pressure of the pipe wall is uneven, and the maximum and minimum pressure value has a differential of 0.3–1.2 % compared to the relative static water pressure. The pressure unevenness will increase after structure rounding, and it has a positive correlation with structure rounding radius. At the same time, it is more reasonable for structure rounding in the obtuse angle region than that in the acute angle region, on account of well-distributed flow conditions and better economic benefit.

A comparative study of the carbon dioxide and nitrogen minimum miscibility pressure determinations for an Iranian light oil sample

ABSTRACTMiscible gas injection is an approved profitable process that could significantly enhance oil recovery from different types of reservoirs while the major factor affecting its efficiency would be the minimum miscibility pressure (MMP) value. A recent experimental technique, known as vanishing interfacial tension (VIT), can estimate the MMP for gas–oil mixtures by measuring interfacial tension values and extrapolating them to zero at a sequence of pressures. Compositional simulation models are also useful in MMP determination by tuning an equation of state to compute the realistic phase behavior of reservoir fluid. In this paper, the capability and quality of MMP prediction via different methods such as laboratory slim tube tests, VIT technique, compositional simulation, and various empirical correlations were examined using a light oil sample taken from an Iranian carbonate reservoir, employing two pure gases of CO2 and N2 as the injectants. The accuracy and validation of the mentioned methods were then confirmed successfully by obtaining negligible overall absolute deviation percentages (AD%) compared with the conducted slim tube tests results.

Experimental investigation of the innovative foaming device using gas as the sole power for firefighting

Foam is used as an efficient means of firefighting. The innovative foaming device using gas as the sole power is designed to replace the previous foam generating system using two or three power sources, and appropriate size of the new foaming device can be made to control dust and fire in households or companies based on the actual need. The results of the experimental investigation on the new device in three cases are as follows: in the first case, the minimum working pressure is 0.4 MPa and the working flow range is: 8.0858 m3/h ≤ qa ≤ 48.45 m3/h and qL ≤ 0.4532 m3/h. In the second case, the maximum working time of the new foaming device is 109 s and the minimum working pressure of the storage tank II is 0.26 Mpa. In the third case, the maximum working time of the new device is 205 s and the minimum working pressure values of the storage tanks I and II are 0.26 Mpa and 0.3 Mpa respectively. The fire extinguishing experiment is explained in this article, and the results show that the foam generated by the new foaming device is more effective and efficient than the ABC powder fire extinguisher. © 2016 American Institute of Chemical Engineers Process Saf Prog 36: 150–157, 2017

Study on the Aerodynamic Characteristics of Tunnel and Metro Station with PSD During High-speed Train Passing Tunnel

A numerical simulation on the 3D compressible viscous unsteady flow field induced by a high-speed subway train, while it’s passing by the platform screen door of subway station, is presented in the paper. The research on transient pressure in tunnel due to changes of positions of platform screen door is proceeded in order to design platform screen doors for underground stations of Dong-guan to Huizhou inter-city rail traffic. Result shows that the platform is subjected to aerodynamic compression and tension cycle loads all the time. And compression load is larger than tension load. The maximum and minimum pressure values in absolute terms got from measuring points of the whole station decrease gradually along the direction train going ,no matter whether the platform screen door is fixed or not. The absolute values of maximum and minimum pressure of piston wind generated at platform screen door are decreasing while the spacing between platform screen door and platform becomes wider. The pressure value of air at exit is larger than that of air at entrance. As for a high-speed subway station, it is a practicable way to set air shafts at entrance and exit of station to mitigate pressure of air in station and tunnel. The pressure value of air could have a 10 to 15 percent reduction if there is an air shaft. Besides, the platform screen door can be installed in half tall of PSD.

Characteristics of quasi-liquid metal layer in the cumulative jet and barrier contact zone

According to the known experimental data on explosive metal processing, as well as the theoretical and experimental studies on the sintered metal powders, we estimated the minimum pressure and temperature values at which this layer and its thickness are formed. The study used a hypothetical model of forming a quasi-liquid metal layer between the leader of the cumulative jet, and a barrier at the time of its destruction.

Determination of Gas-oil Interfacial Tension

Reliable knowledge of minimum miscibility pressure plays a vital parameter in the design and implementation of any miscible gas injection process and gas-oil interfacial tension extremely impacts on minimum miscibility pressure values. In this article two Iranian oil fields were investigated. Gas-oil interfacial tension technique relies on the measurements of gas/oil interfacial tension by pendant drop at several pressures and reservoir temperature for the first field and results were compared with generated values by the Parachor method. Then at different pressures and constant temperature (115°F) condition in the second field interfacial tension values have been evaluated for different oil-gas molar ratios.

Encapsulated Water Hammer: Theoretical/Experimental Study

Water hammer phenomenon involves the transformation of kinetic energy in pressure energy, this transformation occurs as the fluid conditions change inside the pipe in quite a short time. Industry requires to affront frequent flow interruptions in pipe systems due to the closing of valves or stopping of pumping equipment. This phenomenon can initiate serious damages like destruction of the pipe system involving leakage of the working fluid to the environment. If the system operates in a fragile environment, as in cold regions, concern about the consequences of leakage increases due to the variation of physical properties of fluid as well as the pipe material as a function of the temperature. Water hammer effects can be controlled focusing efforts on reducing the pressure increment that takes place once the phenomenon is presented. Some methods try to reduce the time of closure or the rate of change before the closure using special valves, others install additional elements to absorb the pressure surge and dissipate energy, others install relief valves to release the pressure, and others try to split the problem is smaller sections by installing check valves with dashpot or non-return valves. Splitting the pipeline into shorter sections is often used to help preventing the pipeline length of water falling back after a pump stops. In this paper the numerical results of maximum and minimum pressure values at both ends of a closed section are compared to experimental data. The numerical results follow the experimental trends.

Subject-Specific Fully-Coupled and One-Way Fluid-Structure Interaction Models for Modeling of Carotid Atherosclerotic Plaques in Humans.

BackgroundHemodynamics play an important role in the development and progression of carotid atherosclerosis, and may be important in the assessment of plaque vulnerability. The aim of this study was to develop a system to assess the hemodynamics of carotid atherosclerotic plaques using subject-specific fluid-structure interaction (FSI) models based on magnetic resonance imaging (MRI).Material/MethodsModels of carotid bifurcations (n=86 with plaques from 52 patients, n=14 normal carotids from 12 participants) were obtained at the Department of Radiology, Beijing Tian Tan Hospital between 2010 and 2013. The maximum von Mises stress, minimum pressure, and flow velocity values were assessed at the most stenotic site in patients, or at the carotid bifurcations in healthy volunteers. Results of one-way FSI were compared with fully-coupled FSI for the plaques of 19 randomly selected models.ResultsThe maximum von Mises stress and the minimum pressure and velocity were significantly increased in the stenosis group compared with controls based on one-way FSI (all P<0.05). The maximum von Mises stress and the minimum pressure were significantly higher and the velocity was significantly lower based on fully coupled FSI compared with on-way FSI (all P<0.05). Although there were differences in numerical values, both methods were equivalent. The maximum von Mises stress of vulnerable plaques was significantly higher than stable plaques (P<0.001). The maximum von Mises stress of the group with fibrous cap defect was significantly higher than the group without fibrous cap defect (P=0.001).ConclusionsThe hemodynamics of atherosclerotic plaques can be assessed noninvasively using subject-specific models of FSI based on MRI.

Evaluation of the different sleep-disordered breathing patterns of the compressed tracheal sound

ObjectiveSuitability of the compressed tracheal sound signal for screening different sleep-disordered breathing patterns was evaluated. The previous results suggest that the plain pattern in the compressed sound signal represents mostly normal, unobstructed breathing, the thick pattern consists of periodic apneas/hypopneas and during the thin pattern, flow limitation in the nasal cannula signal is abundant. MethodsTwenty-seven patients underwent a polysomnography with a tracheal sound and oesophageal pressure monitoring. The tracheal sound data was compressed and scored visually into three different breathing patterns. The percentage of oesophageal pressure values under −8cm H2O, the minimum pressure value and the average duration of the breathing cycles were extracted from 10-min episodes of those plain, thick and thin patterns. In addition, the spectral contents of the tracheal sound during the different breathing patterns were evaluated. ResultsThe percentage of time when the oesophageal pressure negativity increased was highest during the thin pattern and lowest during the plain pattern. In addition, the thin pattern presented most high frequency components in the 1001–2000Hz frequency band of the tracheal sound. ConclusionsThe results confirmed our previous findings that both the thick and thin patterns seem to consist of obstructed breathing, whereas during the plain pattern the breathing is normal, unobstructed. SignificanceMost screening methods for sleep-disordered breathing reveal only periodic apneas/hypopneas, but with the compressed sound signal the sustained partial obstruction can be estimated as well.

A clinically applicable stochastic approach for noninvasive estimation of aortic stiffness using computed tomography data.

The degeneration of the vascular wall tissue induces a change of the arterial stiffness, i.e., the capability of the vessel to distend under the pulsatile hemodynamic load. In the literature, the aortic stiffness is usually computed following a simple deterministic approach, in which only the maximum and the minimum values of arterial diameter and blood pressure over the cardiac cycle are considered. In this paper, we propose a stochastic approach to assess the stiffness, and its spatial variation, of a given aortic region exploiting patient-specific geometrical data derived from computed tomography angiography (CTA). In particular, the arterial stiffness is computed linking the aortic kinematic information derived from CTA with pressure waveforms, generated using a lumped parameter model of the arterial circulation. The proposed method is able to include the uncertainty of the input variables as well as to use the entire diameter and blood pressure waveforms over the cardiac cycle rather than only their maximum and minimum values. Although the efficiency and accuracy of the proposed method are tested on a single patient-specific case, the proposed approach is powerful and already possesses the ability to evaluate regional changes of stiffness in human aorta using noninvasive data. The final objective of our paper is to support the adoption of techniques such as CTA as a standard tool for diagnosis and treatment planning of aortic diseases.

A Study Of Correlation Between Central Corneal Thickness And Intra Ocular Pressure Measurement Using Goldmann Applanation Tonometer And Rebound Tonometer

Introduction: The purpose of this study was to note the influence of central corneal thickness on the intraocular pressure measurementand to compare rebound tonometer and Goldmannapplanation tonometerduring the recent 2 years in Ophthalmology OPD of JSS Hospital. Objectives:  To compare rebound tonometer and Goldmannapplanation tonometer  Influence of central corneal thickness on the intraocular pressure measurement Methodology:A total of 409 patients inclusive of normal controls, proven glaucoma cases and glaucoma suspects were evaluated prospectively, from October 2010 to June 2012. They were studied for their presentation, clinical features and intraocular pressure readings and central corneal thickness were measured. Results: A total of 797 eyes were included in the study. 199 eyes were examined under glaucoma group, out of which 33 patients had closed angle glaucoma and 166 had open angle glaucoma. Majority of the patients in the study population were males in both control and glaucoma group (54.03%). In the glaucoma group consisting of proven glaucoma cases and glaucoma suspects majority had open angle (83.41%). More number of participants belonged to the age group of 40-50 years (45%). The highest mean GAT, RBT and CCT values were obtained for the age group between 61-70 years. The minimum intraocular pressure value obtained using rebound tonometer was 9 mm Hg and maximum value was 56 mm Hg in the entire study group. The minimum intraocular pressure value obtained using Goldmannapplanation tonometer was 8 mm Hg and maximum value was 50 mm Hg in the entire study group. The minimum value for central corneal thickness was 443µm and maximum value was 675µm for the entire study group. For the entire study group intraocular pressure values obtained by rebound tonometer(14.81±2.81mm Hg in normal group and 20.55±8.74mm Hg In glaucoma group) was more than Goldmannapplanation tonometer (14.47±2.98mm hg and 19.88±8.74mm Hg). For central corneal thickness ≤ 530µm, Rebound tonometer values were more than Goldmannapplanation tonometer values in both control and control group. The mean difference was 0.4± 3.9mm Hg and 0.3 mm Hg which was not statistically significant (p values- 0.74, 0.792). For central corneal thickness ≥ 531µm, Rebound tonometer values were less than Goldmannapplanation tonometer values in both control and control group. The mean difference was 0.0811mm Hg and0.96 mm Hg which was not statistically significant (p values- 0.811,0.93). At higher corneal thickness, Goldmannapplanation tonometer gave higher values than rebound tonometer but the difference was not statistically significant. As the central corneal thickness increased the intraocular pressure value recorded by both the tonometers increased. Conclusion:Central corneal thickness can influence the intraocular pressure recordings of both rebound tonometer and Goldmannapplanation tonometer and thicker corneas yield higher intraocular pressure values. Therefore correction for central corneal thickness will provide a more accurate IOP reading and aid in the proper management of glaucoma cases. The Rebound tonometer gave higher readings in comparison to Goldmannapplanation tonometer in thinner corneas and lesser readings in thicker corneas. There was no statistically significant difference between the two tonometers and they showed good correlation in relation to the central corneal thickness.

Investigation of pressure variations over stepped spillways using smooth particle hydrodynamics

In this paper the smoothed particle hydrodynamics, (SPH), technique is used to investigate the pressure distribution on steps located in the non-aerated flow region of a stepped spillway for different discharges typical of skimming flow conditions. The open source code 2D SPHysics has been employed after being validated against the laboratory model studies of flow over broad crested weirs and flow over stepped spillways. The numerical results, in terms of the water surface and velocity profiles at different sections, are in good agreement with the corresponding experimental results. The code is then applied to determine the pressure distribution on the vertical and horizontal step faces. Also, the aspects of the pressure pattern are described and the positions/magnitudes of the maximum and minimum pressure values are presented.

An exact analytical solution of the Reynolds equation for the finite journal bearing lubrication

The Reynolds equation for the pressure distribution of the lubricant in a journal bearing with finite length is solved analytically. Using the method of separation of variables in an additive and a multiplicative form, a set of particular solutions of the Reynolds equation is added in the general solution of the homogenous Reynolds equation thus a closed form expression for the definition of the lubricant pressure is presented. The Reynolds equation is split into four linear ordinary differential equations of second order with non-constant coefficients and together with the boundary conditions they form four Sturm–Liouville problems with the three of them to have direct forms of solution and one of them to be confronted using the method of power series. The mathematical procedure is presented up to the point that the application of the boundaries for the pressure distribution yields the final definition of the solution with the calculation of the constants. The current work gives in detail the mathematical path with the help of which the analytical solution is derived, and ends with the pressure evaluation and a comparison with past numerical solutions and an approximate analytical solution for a finite bearing. The resultant pressure distribution presents slight differences compared to this of the numerical solution and the approximate analytical solution in the values of maximum and minimum pressure but also in the domain of lower values of pressure.

The Numerical Analysis of Radial Thrust and Axial Thrust in the Screw Centrifugal Pump

The solid-liquid two-phase unsteady flow in the screw centrifugal pump is simulated during one revolution by using CFD software. The pressure fluctuations at the volute outlet, the distribution of radial thrust and axial thrust in the screw centrifugal pump during one revolution are given in the paper. The results show that the minimum pressure value at the volute outlet occurs when the maximum impeller radius just turned the tongue of volute, and maximum value occurs when the maximum impeller radius just turned between the section VI and VII the radial thrust on the impeller is assumed the circumference distribution approximately during one revolution. As the solid volume fraction increases, the radial thrust increases gradually. The direction of radial thrust is inverse against the maximum value of pressure in the pump outlet; the maximum radius position has much influence on the changes of axial thrust, the axial thrust maximum value occurs when the maximum impeller radius just turned the tongue of volute, and minimum value occurs when the maximum impeller radius is away from the tongue of volute.

Influence of tunnel length on the pressure wave generated by high-speed trains passing each other

The prediction of the pressure wave amplitude produced when two trains pass each other in the tunnel is important to the train design for airtightness and tunnel conditions in China. In this paper, the key factors of this problem were firstly studied based on theoretical analysis. The equation of the worst tunnel length for the global maximum and minimum pressure values was derived. Then, the influence of tunnel length on global minimum pressure and the critical region in which the global minimum pressure varies rapidly were investigated. Finally, a numerical method based on two-dimensional Navier-Stokes equations was established. Typical conditions of two trains passing-by in tunnels of different lengths were simulated. The theoretical and computational results agree with each other closely.

Clinical practices, complications, and mortality in neurological patients with acute severe hypertension: The Studying the Treatment of Acute hyperTension registry

To determine the demographic and clinical features, hospital complications, and predictors of 90-day mortality in neurologic patients with acute severe hypertension. Studying the Treatment of Acute hyperTension (STAT) was a multicenter (n=25) observational registry of adult critical care patients with severe hypertension treated with intravenous therapy. Emergency department or intensive care unit. A qualifying blood pressure measurement>180 mm Hg systolic or >110 mm Hg diastolic (>140/90 mm Hg for subarachnoid hemorrhage) was required for inclusion in the STAT registry. Patients with a primary neurologic admission diagnosis were included in the present analysis. All patients were treated with at least one parenteral (bolus or continuous infusion) antihypertensive agent. Of 1,566 patients included in the STAT registry, 432 (28%) had a primary neurologic diagnosis. The most common diagnoses were subarachnoid hemorrhage (38%), intracerebral hemorrhage (31%), and acute ischemic stroke (18%). The most common initial drug was labetalol (48%), followed by nicardipine (15%), hydralazine (15%), and sodium nitroprusside (13%). Mortality at 90 days was substantially higher in neurologic than in non-neurologic patients (24% vs. 6%, p<.0001). Median initial blood pressure was 183/95 mm Hg and did not differ between survivors and nonsurvivors. In a multivariable analysis, neurologic patients who died experienced lower minimal blood pressure values (median 103/45 vs. 118/55 mm Hg, p<.0001) and were less likely to experience recurrent hypertension requiring intravenous treatment (29% vs. 51%, p=.0001) than those who survived. Mortality was also associated with an increased frequency of neurologic deterioration (32% vs. 10%, p<.0001). Neurologic emergencies account for approximately 30% of hospitalized patients with severe acute hypertension, and the majority of those who die. Mortality in hypertensive neurologic patients is associated with lower minimum blood pressure values, less rebound hypertension, and a higher frequency of neurologic deterioration. Excessive blood pressure reduction may contribute to poor outcome after severe brain injury.

ICONE19-43215 NUMERICAL RESEARCH ON THE THERMAL HYDRAULICS OF THE COOLANT IN A PEBBLE BED REACTOR CORE BY CFD

The water cooled pebble bed reactor with the pebble diameter from 2-10 mm has both the characteristics of high temperature gas-cooled pebble bed reactor and the traditional light water one. In the conceptual design of high temperature gas-cooled reactor and supercritical water-cooled reactor, pebble bed reactor has attracted much interest because of its outstanding advantages in the safety and fuel cycle. As far as china is concerned, it is worth researching and designing the water cooled pebble bed reactor, and the formers' researches were focused on the water cooled reactor. So it is great important to investigate the thermal-hydraulic characteristics of coolant in a pebble bed reactor core. The 3-D physical and geometrical models of the water cooled pebble bed reactor were built using the commercial software Pro/E and CFX, in which the thermal-hydraulic characteristics of the reactor core were studied. The velocity and temperature fields and pressure distribution of the coolant as well as the distribution of internal temperature of the fuel are obtained and analyzed in the case of diameter of 3mm and diameter of 6mm, and its effects on the core safety are also analyzed. The results indicate that the tendency of the same parameter values under different diameters are nearly identical, and it is larger with the diameter of 6mm, contrary, the flow disturbance with the diameter of 6mm is weaker than that of 3mm. The two maximum temperature of the pebble were found at the gap area. The maximum velocities of the first layer pebbles were found at the gap area, thereafter the maximum velocity was found between the gap areas. The pressure gradually reduces from bottom to top and the minimum values of pressure were generated at the gap area.

Measurement and modeling of pulsatile flow in microchannel

An experimental study of pulsatile flow in microchannel is reported in this paper. Such a study is important because time-varying flows are frequently encountered in microdevices. The hydraulic diameter of the microchannel is 144 μm and deionized water is the working fluid. The pressure drop across the microchannel as a function of time is recorded, from which the average and r.m.s. pressure drops are obtained. The experiments have been performed in the quasi-steady flow regime for a wide range of flow rate, frequency of pulsations, and duty cycle. The results suggest that the pressure with pulsations lies between the minimum and maximum steady state pressure values. The average pressure drop with pulsation is approximately linear with respect to the flow rate. The theoretical expression for pressure has also been derived wherever possible and the experimental data is found to lie below the corresponding theoretical values. The difference with respect to the theoretical value increases with an increase in frequency and a decrease in flow rate, with a maximum difference of 32.7%. This is attributed to the small size of the microchannel. An increase in frequency of square waveform leads to a larger reduction in pressure drop as compared to rectangular waveform, irrespective of the duty cycle. The results can be interpreted with the help of a first-order model proposed here; the model results are found to compare well against the experimental results. A correlation for friction factor in terms of the other non-dimensional governing parameters is also proposed. Experimental study of mass-driven pulsatile flow in microchannel is being conducted for the first time at these scales and the results are of both fundamental and practical importance.