scholarly journals CFD NUMERICAL ANALYSIS OF A PROPOSED CHANGE IN THE CHANNEL GEOMETRY DOWNSTREAM OF A REVERSED TAINTER GATE

2015 ◽  
Vol 14 (1) ◽  
pp. 71
Author(s):  
M. D. Corte ◽  
R. C. Oliveski ◽  
M. G. Marques ◽  
M. Dai Pra
Keyword(s):  
Shape Change ◽  
Pressure Fluctuations ◽  
Control Flow ◽  
Navigation Systems ◽  
Straight Section ◽  
Channel Geometry ◽  
High Speeds ◽  
Negative Pressures ◽  
Geometric Changes ◽  
Cfd Numerical Analysis

Reversed Tainter gates are often used to control flow in the filling and emptying locks navigation systems of high fall. High speeds and pressure fluctuations may occur in the flow downstream of these gates, the flow cavitation may occur, damaging the structure. One way proposed to mitigate this problem is through geometric changes in the channel downstream of the gate. In this study was analyzed using CFD the effect of an expansion in the roof and the base of the conduit, followed by a straight section and a subsequent contraction until returning to the original geometry. It was observed that the pressure at the base of the conduit increases with the modification, however peaks of positive and negative pressures occur due to the shape change of the geometry of the corners not be smooth. The size of recirculation downstream of the gate increases with the geometrical alteration, increasing the distance required for pressure recovery.

scholarly journals Predictive Modeling the Free Hydraulic Jumps Pressure through Advanced Statistical Methods

2020 ◽  
Author(s):  
Seyed Nasrollah Mousavi ◽  
Renato Steinke Júnior ◽  
Eder Daniel Teixeira ◽  
Daniele Bocchiola ◽  
Narjes Nabipour ◽  
...  
Keyword(s):  
Pressure Fluctuations ◽  
Maximum Pressure ◽  
Hydraulic Jumps ◽  
Third Order ◽  
Stilling Basin ◽  
Laboratory Flume ◽  
Order Polynomial ◽  
Characteristic Points ◽  
Negative Pressures ◽  
Cumulative Curves

Pressure fluctuations beneath hydraulic jumps downstream of Ogee spillways potentially damage stilling basin beds. This paper deals with the extreme pressures underneath free hydraulic jumps along a smooth stilling basin. The experiments were conducted in a laboratory flume. From the probability distribution of measured instantaneous pressures, the pressures with different non-exceedance probabilities (P*a%) could be determined. It was verified that the maximum pressure fluctuations, as well as the negative pressures, are located at the positions closest to the spillway toe. The minimum pressure fluctuations are located at the downstream of hydraulic jumps. It was possible to assess the cumulative curves of P*a% related to the characteristic points along the basin, and different Froude numbers. To benchmark, the results, the dimensionless forms of mean pressures, standard deviations, and pressures with different non-exceedance probabilities were assessed. It was found that an existing methodology can be used to interpret the present data, and pressure distribution in similar conditions, by using a new third-order polynomial relationship for the standard deviation (σ*X) with the determination coefficient (R2) equal to 0.717. It was verified that the new optimized adjustment gives more accurate results for the estimation of the maximum extreme pressures than the minimum extreme pressures.

A two-dimensional numerical analysis of a circular-arc gear pump operating at high pressures and high speeds

2015 ◽  
Vol 231 (3) ◽  
pp. 432-443 ◽  
Author(s):  
Yang Zhou ◽  
Shuanghui Hao ◽  
Minghui Hao
Keyword(s):  
Critical Points ◽  
High Pressures ◽  
Pressure Fluctuations ◽  
Gear Pump ◽  
Circular Arc ◽  
Outlet Pressure ◽  
High Speeds ◽  
Outlet Flow ◽  
The Mathematical Model ◽  
Variation Tendency

This paper examines the flow field of a circular-arc gear pump operating at high pressures and high speeds by the commercial finite-volume-based code Fluent. The performance of circular-arc gear pump operating at high pressures and high speeds have been discussed. The mathematical model of the tooth profile is established. The pressures including gears mesh, outlet pressures, and outlet flow rate are studied under different rated outlet pressures and rotational speeds. There are dynamic pressures at clearance between chamber and tip circle of gear. Moreover, parts of radial leakages are prevented by dynamic pressures. The outlet pressures almost remain constant. However, there are strong pressure fluctuations in gears mesh under the high pressures and high speeds. The pressures are several times higher than the rated outlet pressure when the circular-arc gear pump operates at 10,000 r/min and 12,000 r/min. Gear meshing pressure fluctuations increase with the increase in rotational speeds. However, gear meshing pressure fluctuations decrease with the increase of outlet rate pressures. There are rotational speeds and outlet rate pressure critical points for gear meshing pressures, and the variation tendency of gear meshing pressures changes dramatically when it exceeds the critical points. Hence, the research results provide base model for circular-arc gear pump operating at high pressures and high speeds.

Plasticity of the actin cytoskeleton in response to extracellular matrix nanostructure and dimensionality

2014 ◽  
Vol 42 (5) ◽  
pp. 1356-1366 ◽  
Author(s):  
Josefine Starke ◽  
Bernhard Wehrle-Haller ◽  
Peter Friedl
Keyword(s):  
Extracellular Matrix ◽  
Actin Cytoskeleton ◽  
Shape Change ◽  
Leading Edge ◽  
High Speeds ◽  
Efficient Induction ◽  
Important Input ◽  
Single Force ◽  
And Migration

Mobile cells discriminate and adapt to mechanosensory input from extracellular matrix (ECM) topographies to undergo actin-based polarization, shape change and migration. We tested ‘cell-intrinsic’ and adaptive components of actin-based cell migration in response to widely used in vitro collagen-based substrates, including a continuous 2D surface, discontinuous fibril-based surfaces (2.5D) and fibril-based 3D geometries. Migrating B16F1 mouse melanoma cells expressing GFP–actin developed striking diversity and adaptation of cytoskeletal organization and migration efficacy in response to collagen organization. 2D geometry enabled keratinocyte-like cell spreading and lamellipod-driven motility, with barrier-free movement averaging the directional vectors from one or several leading edges. 3D fibrillar collagen imposed spindle-shaped polarity with a single cylindrical actin-rich leading edge and terminal filopod-like protrusions generating a single force vector. As a mixed phenotype, 2.5D environments prompted a broad but fractalized leading lamella, with multiple terminal filopod-like protrusions engaged with collagen fibrils to generate an average directional vector from multiple, often divergent, interactions. The migratory population reached >90% of the cells with high speeds for 2D, but only 10–30% of the cells and a 3-fold lower speed range for 2.5D and 3D substrates, suggesting substrate continuity as a major determinant of efficient induction and maintenance of migration. These findings implicate substrate geometry as an important input for plasticity and adaptation of the actin cytoskeleton to cope with varying ECM topography and highlight striking preference of moving cells for 2D continuous-shaped over more complex-shaped discontinuous 2.5 and 3D substrate geometries.

scholarly journals On-The-Fly Ambiguity Resolution Based on Double-Differential Square Observation

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2495 ◽  
Author(s):  
Tengfei Wang ◽  
Zheng Yao ◽  
Mingquan Lu
Keyword(s):  
Ambiguity Resolution ◽  
Carrier Phase ◽  
Base Stations ◽  
Navigation Systems ◽  
Phase Measurements ◽  
Positioning Systems ◽  
Key Factor ◽  
Fixed Solution ◽  
Geometric Changes ◽  
Global Navigation Systems

Global navigation systems provide worldwide positioning, navigation and navigation services. However, in some challenging environments, especially when the satellite is blocked, the performance of GNSS is seriously degraded or even unavailable. Ground based positioning systems, including pseudolites and Locata, have shown their potentials in centimeter-level positioning accuracy using carrier phase measurements. Ambiguity resolution (AR) is a key issue for such high precision positioning. Current methods for the ground based systems need code measurements for initialization and/or approximating linearization. If the code measurements show relatively large errors, current methods might suffer from convergence difficulties in ground based positioning. In this paper, the concept of double-differential square observation (DDS) is proposed, and an on-the-fly ambiguity resolution (OTF-AR) method is developed for ground based navigation systems using two-way measurements. An important advantage of the proposed method is that only the carrier phase measurements are used, and code measurements are not necessary. The clock error is canceled out by two-way measurements between the rover and the base stations. The squared observations are then differenced between different rover positions and different base stations, and a linear model is then obtained. The floating integer values are easy to compute via this model, and there is no need to do approximate linearization. In this procedure, the rover’s approximate coordinates are also directly obtained from the carrier measurements, therefore code measurements are not necessary. As an OTF-AR method, the proposed method relies on geometric changes caused by the rover’s motion. As shown by the simulations, the geometric diversity of observations is the key factor for the AR success rate. Moreover, the fine floating solutions given by our method also have a fairly good accuracy, which is valuable when fixed solutions are not reliable. A real experiment is conducted to validate the proposed method. The results show that the fixed solution could achieve centimeter-level accuracy.

Investigation on Flow Characteristics of Pump-Turbine Runners With Large Blade Lean

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Baoshan Zhu ◽  
Lei Tan ◽  
Xuhe Wang ◽  
Zhe Ma
Keyword(s):  
High Pressure ◽  
High Efficiency ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Control Flow ◽  
Pump Turbine ◽  
Good Efficiency ◽  
Operating Modes ◽  
Partial Load

Frequent changes in the operating modes pose significant challenges in the development of a pump-turbine with high efficiency and stability. In this paper, two pump-turbine runners, one with a large positive blade lean and the other with a large negative lean, are investigated numerically and experimentally. These two runners are designed by using the optimum stacking condition at the high pressure edge (HPE). The experimental and the numerical results show that both runners have good efficiency performances, and pressure fluctuations for the runner with a negative blade lean are much lower than those for the runner with a positive blade lean. The internal flow field analyses clarify the effects of the blade lean on the pressure distribution around the runner blades. In the turbine mode at partial load, the negative blade lean can control flow separation in the high pressure side of the runner and then reduce the pressure fluctuations in the vaneless space.

Blood flow distribution within the airway wall

2002 ◽  
Vol 92 (5) ◽  
pp. 1964-1969 ◽  
Author(s):  
Elizabeth M. Wagner ◽  
Robert H. Brown
Keyword(s):  
Blood Flow ◽  
Smooth Muscle ◽  
Airway Resistance ◽  
Flow Distribution ◽  
Control Flow ◽  
Blood Flow Distribution ◽  
Airway Wall ◽  
Fluorescent Microspheres ◽  
Geometric Changes ◽  
And Control

Altered perfusion of the bronchial mucosal plexus relative to the adventitial plexus may contribute to geometric changes in the airway wall and lumen. We studied bronchial perfusion distribution in sheep by using fluorescent microspheres at baseline and during intrabronchial artery challenge with methacholine chloride (MCh; n = 7). Additionally, we measured airway resistance (Raw) during MCh with control or increased perfusion ( n = 9). Raw with MCh was significantly greater for high than control flow. Microspheres in histological sections lodged predominantly in the mucosa (60%), and this was not altered by MCh. However, more microspheres lodged in airways >1-mm in diameter during MCh and increased perfusion than MCh and control flow. In airways ≤1 mm in diameter, fewer microspheres lodged during control than increased flow. If the number of microspheres represents regional agonist access to airway smooth muscle, then the differences observed in Raw can be explained by the distribution of agonist. During challenge, there was greater MCh delivery to larger airways during increased flow and less delivery to smaller airways during control flow. The results demonstrate the effects of axial perfusion distribution on Raw.

Nonlinear Acoustic Sources in Squeezed Car Tyre Cavities

2000 ◽  
Vol 31 (4) ◽  
pp. 9-19 ◽  
Author(s):  
M. J. Gagen
Keyword(s):  
Wave Equation ◽  
Acoustic Wave ◽  
Pressure Fluctuations ◽  
Nonlinear Effects ◽  
Pressure Gradients ◽  
Acoustic Wave Equation ◽  
Ambient Conditions ◽  
High Speeds ◽  
Acoustic Sources ◽  
Ground Impact

At high speeds, the grooves cut into car tire treads can be rapidly squeezed and suffer volume losses of around 10%. This decrease in groove volume can occur much faster than air can evacuate from the squeezed groove as ground impact causes the groove walls to move with velocities of order 1m/s, and with accelerations of 103m/s2 over time scales of about 1ms. The resulting volume loss without any accompanying evacuation of air leads to significant increases in pressure and density in the groove. The pressure fluctuations can exceed 10% of ambient conditions which makes the usual approximations underlying use of the acoustic wave equation invalid. The acoustic wave equation can only be used when pressure fluctuations and pressure gradients are small. When substantial pressure fluctuations exist or when shock waves are present the usual acoustic wave equation cannot be used and a fuller treatment is required. This paper presents preliminary analytical and numerical investigations of the various nonlinear effects which might create novel acoustic sources from squeezed cavities in car tires.

Cross-Ventilation of Underground Railway Tunnels

1979 ◽  
Vol 101 (1) ◽  
pp. 128-134
Author(s):  
A. E. Vardy
Keyword(s):  
Drag Force ◽  
Aerodynamic Drag ◽  
Pressure Fluctuations ◽  
Rapid Transit ◽  
Transit Systems ◽  
Low Speed ◽  
High Speeds ◽  
Large Pressure ◽  
Underground Railway ◽  
Small Holes

The aerodynamic merits and demerits of cross-ventilating adjacent tunnels in underground rapid transit systems are discussed. Three types of cross-ventilation are considered, namely (a) numerous small holes in the dividing wall between the tracks in a cut-and-cover tunnel, (b) a curtailed dividing wall and (c) passages linking separately bored tunnels. It is shown that considerable reductions in the air velocities expected on station platforms will result if the end regions of the tunnels are well cross-ventilated. Additionally, useful reductions in the aerodynamic drag force on trains can be expected if cross-ventilation is provided along the whole length of the tunnel. However, this is recommended only for low speed systems because interaction between passing trains will cause large pressure fluctuations at high speeds.

Spray Outputs from a Variable-Rate Sprayer Manipulated with PWM Solenoid Valves

2018 ◽  
Vol 34 (3) ◽  
pp. 527-534
Author(s):  
Joao Eduardo Silva ◽  
Heping Zhu ◽  
João Paulo Arantes Rodrigues da Cunha
Keyword(s):  
Flow Rate ◽  
Duty Cycle ◽  
Pressure Fluctuations ◽  
Control Flow ◽  
Operating Pressure ◽  
Regression Equations ◽  
Variable Rate ◽  
Total Flow ◽  
Total Flow Rate ◽  
Flow Rates

Abstract. Pressure fluctuations from air-assisted orchard sprayers can cause nozzles to discharge inaccurate flow rates during variable-rate spray applications. Variations in total flow rate discharged from 40 nozzles, each coupled with a pulse-width-modulated (PWM) solenoid valve, were determined for a variable-rate air-assisted sprayer. Variables for the total flow rate measurements were number of active nozzles ranging from 1 to 40 and PWM duty cycle ranging from 10% to 100%. Experiments were conducted under conditions with and without operating pressure adjustments. Under the no-pressure-adjustment condition, the operating pressure in the spray line was not adjusted for compensation when either the number of active nozzles or PWM duty cycle was changed. Under the pressure-adjustment condition, the operating pressure was adjusted to retain at 242 kPa. The total flow rate increased as duty cycle and/or number of active nozzles increased under both pressure conditions. However, the operating pressure in the spray line dropped considerably as either the number of active nozzles or duty cycle increased under the no-pressure-adjustment condition, resulting in significant lower total flow rates compared to the pressure-adjustment condition. The differences in total flow rates between the two pressure conditions increased as duty cycle and number of active nozzles increased. To improve future intelligent sprayer accuracy, two-variable regression equations were established to predict and control total flow rates with different duty cycles and numbers of active nozzles operated simultaneously. Keywords: Flow control, Flow rate, Hydraulic nozzle, Pesticide, Precision sprayer.

Role of spectrin in membrane fusion and in shape change of human erythrocyte ghost

1978 ◽  
Vol 36 (2) ◽  
pp. 328-329
Author(s):  
Hideo Hayashi ◽  
Yoshikazu Hirai ◽  
John T. Penniston
Keyword(s):  
Conformational Changes ◽  
Human Erythrocyte ◽  
Shape Change ◽  
Membrane Surface ◽  
Slight Modification ◽  
Active Role ◽  
Main Role ◽  
Bank Blood ◽  
Human Erythrocyte Ghost

Spectrin is a membrane associated protein most of which properties have been tentatively elucidated. A main role of the protein has been assumed to give a supporting structure to inside of the membrane. As reported previously, however, the isolated spectrin molecule underwent self assemble to form such as fibrous, meshwork, dispersed or aggregated arrangements depending upon the buffer suspended and was suggested to play an active role in the membrane conformational changes. In this study, the role of spectrin and actin was examined in terms of the molecular arrangements on the erythrocyte membrane surface with correlation to the functional states of the ghosts.Human erythrocyte ghosts were prepared from either freshly drawn or stocked bank blood by the method of Dodge et al with a slight modification as described before. Anti-spectrin antibody was raised against rabbit by injection of purified spectrin and partially purified.

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