Stochastic analysis of steady seepage underneath a water-retaining wall through highly anisotropic porous media

2015 ◽  
Vol 778 ◽  
pp. 253-272 ◽  
Author(s):  
G. Severino ◽  
S. De Bartolo
Keyword(s):  
Spatial Variability ◽  
Retaining Wall ◽  
Mean Flow ◽  
Integral Scale ◽  
Anisotropic Porous Media ◽  
Correlation Integral ◽  
Porous Formation ◽  
The Mean ◽  
Steady Seepage ◽  
The Impact

Steady seepage is determined by a head drop upstream/downstream of a water-retaining wall. Due to its erratic variations, hydraulic log-conductivity $Y=\ln K$ is modelled as a stationary random space function (RSF). We deal with a highly anisotropic porous formation, i.e. an axisymmetric medium where the horizontal correlation integral scale of $Y$ is much larger than the vertical one. The goal of computing the resulting flow field within a stochastic framework is complicated by non-uniformity of the mean flow. Simple (closed-form) expressions for the correlation functions of the flow variables as well as the mean head are derived. We use these results to quantify the impact of spatial variability of $Y$ upon the probability that the exit volumetric flow rate downstream of the wall is greater than that obtained by regarding the formation as homogeneous (with constant hydraulic conductivity). In particular, we show that the spatial variability of $Y$ may lead to predictions (and consequently to design choices) which significantly differ from those achieved by regarding the porous formation as homogeneous.

scholarly journals A numerical study on the impact of nonlinear interactions on the amplitude of the migrating semidiurnal tide

2006 ◽  
Vol 24 (12) ◽  
pp. 3241-3256 ◽  
Author(s):  
C. M. Huang ◽  
S. D. Zhang ◽  
F. Yi
Keyword(s):  
Numerical Study ◽  
Steady Solution ◽  
Nonlinear Interactions ◽  
Semidiurnal Tide ◽  
Mean Flow ◽  
Structure Variation ◽  
Amplitude Difference ◽  
The Mean ◽  
The Impact ◽  
Mlt Region

Abstract. To quantitatively study the effects of nonlinear interactions on tide structure, a nonlinear numerical tidal model is developed, and the reliability and convergence of the adopted algorithm and coding are checked by numerical experiments. Under the same conditions as those employed by the GSWM-00 (Global Scale Wave Model 2000), our model provides the nonlinear quasi-steady solution of the migrating semidiurnal tide, which differs from the GSWM-00 result (the linear steady solution) in the MLT region, especially above 100 km. Additionally, their amplitude difference displays a remarkable month-to-month variation, and its significant magnitudes occur during the month with strong semidiurnal tide. A quantitative analysis suggests that the main cause for the amplitude difference is that the initial migrating 12-h tide will interact with the mean flow as well as the nonlinearity-excited 6-h tide, and subsequently yield a new 12-h tidal part. Furthermore, our simulations also show that the mean flow/tidal interaction will significantly alter the background wind and temperature fields. The large magnitudes of the tidal amplitude difference and the background alteration indicate that the nonlinear processes involved in tidal propagations should be comprehensively considered in the description of global atmospheric dynamics in the MLT region. The comparisons among our simulations, the GSWMs and some observations of tides suggest that the nonlinearity-induced tidal structure variation could be a possible mechanism to account for some discrepancies between the GSWMs and the observations.

Reconstruction of GRACE Total Water Storage Through Automated Machine Learning

2020 ◽  
Author(s):  
Alex Sun ◽  
Bridget Scanlon ◽  
Himanshu Save ◽  
Ashraf Rateb
Keyword(s):  
Machine Learning ◽  
Spatial Variability ◽  
Large Scale ◽  
Water Storage ◽  
Total Water ◽  
New Paradigm ◽  
Satellite Mission ◽  
Automated Machine Learning ◽  
The Mean ◽  
The Impact

<p>The GRACE satellite mission and its follow-on, GRACE-FO, have provided unprecedented opportunities to quantify the impact of climate extremes and human activities on total water storage at large scales. The approximately one-year data gap between the two GRACE missions needs to be filled to maintain data continuity and maximize mission benefits. There is strong interest in using machine learning (ML) algorithms to reconstruct GRACE-like data to fill this gap. So far, most studies attempted to train and select a single ML algorithm to work for global basins. However, hydrometeorological predictors may exhibit strong spatial variability which, in turn, may affect the performance of ML models. Existing studies have already shown that no single algorithm consistently outperformed others over all global basins. In this study, we applied an automated machine learning (AutoML) workflow to perform GRACE data reconstruction. AutoML represents a new paradigm for optimal model structure selection, hyperparameter tuning, and model ensemble stacking, addressing some of the most challenging issues related to ML applications. We demonstrated the AutoML workflow over the conterminous U.S. (CONUS) using six types of ML algorithms and multiple groups of meteorological and climatic variables as predictors. Results indicate that the AutoML-assisted gap filling achieved satisfactory performance over the CONUS. For the testing period (2014/06–2017/06), the mean gridwise Nash-Sutcliffe efficiency is around 0.85, the mean correlation coefficient is around 0.95, and the mean normalized root-mean square error is about 0.09. Trained models maintain good performance when extrapolating to the mission gap and to GRACE-FO periods (after 2017/06). Results further suggest that no single algorithm provides the best predictive performance over the entire CONUS, stressing the importance of using an end-to-end workflow to train, optimize, and combine multiple machine learning models to deliver robust performance, especially when building large-scale hydrological prediction systems and when predictor importance exhibits strong spatial variability.</p>

scholarly journals Turbulence and Scale Measurements in a Square Channel with Transverse Square Ribs

1996 ◽  
Vol 2 (3) ◽  
pp. 209-218 ◽  
Author(s):  
Richard B. Rivir ◽  
Mingking K. Chyu ◽  
Paul K. Maciejewski
Keyword(s):  
Turbulence Intensity ◽  
Turbulent Shear ◽  
Mean Flow ◽  
Integral Scale ◽  
Square Channel ◽  
Turbulent Shear Layer ◽  
The Third ◽  
Mainstream Flow ◽  
The Mean ◽  
Flow Turbulence

Hot-wire measurements of the mean flow, turbulence characteristics, and integral scale in a square channel roughened with transverse ribs mounted on two opposing sidewalls are presented for three rib configurations: single rib, in-line multiple ribs, and staggered multiple ribs. Test conditions for multiple ribs use p/H = 10, H/D 0.17, andRe⁡D23,000. Measured results highlight the spatial distribution and evolution of turbulence intensity and integral scale from the flow entrance of the first period to the developed regime near the exit of the third period. The highly turbulent, shear layer initiated near the trailing upper-edge of a rib elevates the turbulence level in the mainstream of the channel. The magnitude of turbulence intensity in the channel core rises from 0.7% in the approaching flow to about 20–25% near the exit of the third period. The integral scale dominating the mainstream flow increases from approximately one-half the rib-height, 0.5H, in the approaching flow to 1.5-2.5H behind the first rib and further downstream.

Investigating the Impact of Reemerging Sea Surface Temperature Anomalies on the Winter Atmospheric Circulation over the North Atlantic

2007 ◽  
Vol 20 (14) ◽  
pp. 3510-3526 ◽  
Author(s):  
Christophe Cassou ◽  
Clara Deser ◽  
Michael A. Alexander
Keyword(s):  
Mixed Layer ◽  
North Atlantic ◽  
Mean Flow ◽  
Thermal Anomalies ◽  
Temperature Anomalies ◽  
The North ◽  
The Mean ◽  
The North Atlantic ◽  
The Impact ◽  
Control Integration

Abstract Extratropical SSTs can be influenced by the “reemergence mechanism,” whereby thermal anomalies in the deep winter mixed layer persist at depth through summer and are then reentrained into the mixed layer in the following winter. The impact of reemergence in the North Atlantic Ocean (NAO) upon the climate system is investigated using an atmospheric general circulation model coupled to a mixed layer ocean/thermodynamic sea ice model. The dominant pattern of thermal anomalies below the mixed layer in summer in a 150-yr control integration is associated with the North Atlantic SST tripole forced by the NAO in the previous winter as indicated by singular value decomposition (SVD). To isolate the reemerging signal, two additional 60-member ensemble experiments were conducted in which temperature anomalies below 40 m obtained from the SVD analysis are added to or subtracted from the control integration. The reemerging signal, given by the mean difference between the two 60-member ensembles, causes the SST anomaly tripole to recur, beginning in fall, amplifying through January, and persisting through the following spring. The atmospheric response to these SST anomalies resembles the circulation that created them the previous winter but with reduced amplitude (10–20 m at 500 mb per °C), modestly enhancing the winter-to-winter persistence of the NAO. Changes in the transient eddies and their interactions with the mean flow contribute to the large-scale equivalent barotropic response throughout the troposphere. The latter can also be attributed to the change in occurrence of intrinsic weather regimes.

scholarly journals EFFECTS OF ACTUATOR IMPACT ON THE NONLINEAR DYNAMICS OF A VALVELESS PUMPING SYSTEM

2011 ◽  
Vol 11 (03) ◽  
pp. 591-624 ◽  
Author(s):  
TIAN-SHIANG YANG ◽  
CHI-CHUNG WANG
Keyword(s):  
Fluid Transport ◽  
Numerical Solutions ◽  
Lumped Parameter Model ◽  
Momentum Balance ◽  
Parameter Study ◽  
Driving Frequency ◽  
Mean Flow ◽  
Valveless Pumping ◽  
The Mean ◽  
The Impact

Valveless pumping assists in fluid transport in various biomedical and engineering systems. Here we focus on one factor that has often been overlooked in previous studies of valveless pumping, namely the impact that a compression actuator exerts upon the pliant part of the system when they collide. In particular, a fluid-filled closed-loop system is considered, which consists of two distensible reservoirs connected by two rigid tubes, with one of the reservoirs compressed by an actuator at a prescribed frequency. A lumped-parameter model with constant coefficients accounting for mass and momentum balance in the system is constructed. Based on such a model, a mean flow in the fluid loop can only be produced by system asymmetry and the nonlinear effects associated with actuator impact. Through asymptotic and numerical solutions of the model, a systematic parameter study is carried out, thereby revealing the rich and complex system dynamics that strongly depends upon the driving frequency of the actuator and other geometrical and material properties of the system. The driving frequency dependence of the mean flowrate in the fluid loop and that of the mean reservoir pressures also are examined for a number of representative cases.

scholarly journals On the impact of swirl on the growth of coherent structures

2014 ◽  
Vol 741 ◽  
pp. 156-199 ◽  
Author(s):  
K. Oberleithner ◽  
C. O. Paschereit ◽  
I. Wygnanski
Keyword(s):  
Stability Analysis ◽  
Coherent Structures ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Shear Mode ◽  
Mean Flow ◽  
Swirling Jet ◽  
The Mean ◽  
The Impact ◽  
Helical Mode

AbstractSpatial linear stability analysis is applied to the mean flow of a turbulent swirling jet at swirl intensities below the onset of vortex breakdown. The aim of this work is to predict the dominant coherent flow structure, their driving instabilities and how they are affected by swirl. At the nozzle exit, the swirling jet promotes shear instabilities and, less unstable, centrifugal instabilities. The latter stabilize shortly downstream of the nozzle, contributing very little to the formation of coherent structures. The shear mode remains unstable throughout generating coherent structures that scale with the axial shear-layer thickness. The most amplified mode in the nearfield is a co-winding double-helical mode rotating slowly in counter-direction to the swirl. This gives rise to the formation of slowly rotating and stationary large-scale coherent structures, which explains the asymmetries in the mean flows often encountered in swirling jet experiments. The co-winding single-helical mode at high rotation rate dominates the farfield of the swirling jet in replacement of the co- and counter-winding bending modes dominating the non-swirling jet. Moreover, swirl is found to significantly affect the streamwise phase velocity of the helical modes rendering this flow as highly dispersive and insensitive to intermodal interactions, which explains the absence of vortex pairing observed in previous investigations. The stability analysis is validated through hot-wire measurements of the flow excited at a single helical mode and of the flow perturbed by a time- and space-discrete pulse. The experimental results confirm the predicted mode selection and corresponding streamwise growth rates and phase velocities.

scholarly journals In Vitro Red Blood Cell Segregation in Sickle Cell Anemia

2021 ◽  
Vol 9 ◽  
Author(s):  
Viviana Clavería ◽  
Philippe Connes ◽  
Luca Lanotte ◽  
Céline Renoux ◽  
Philippe Joly ◽  
...  
Keyword(s):  
Red Blood Cells ◽  
Flow Velocity ◽  
Sickle Cell ◽  
Sickle Cell Anemia ◽  
Blood Cells ◽  
Vascular Wall ◽  
Mean Flow ◽  
The Mean ◽  
The Impact ◽  
Mean Flow Velocity

Red blood cells in sickle cell anemia (sRBC) are more heterogeneous in their physical properties than healthy red blood cells, spanning adhesiveness, rigidity, density, size, and shape. sRBC with increased adhesiveness to the vascular wall would trigger vaso-occlusive like complications, a hallmark of sickle cell anemia. We investigated whether segregation occurs among sRBC flowing in micron-sized channels and tested the impact of aggregation on segregation. Two populations of sRBC of different densities were separated, labeled, and mixed again. The mixed suspension was flowed within glass capillary tubes at different pressure-drops, hematocrit, and suspending media that promoted or not cell aggregation. Observations were made at a fixed channel position. The mean flow velocity was obtained by using the cells as tracking particles, and the cell depleted layer (CDL) by measuring the distance from the cell core border to the channel wall. The labeled sRBC were identified by stopping the flow and scanning the cells within the channel section. The tube hematocrit was estimated from the number of fluorescence cells identified in the field of view. In non-aggregating media, our results showed a heterogeneous distribution of sRBC according to their density: low-density sRBC population remained closer to the center of the channel, while the densest cells segregated towards the walls. There was no impact of the mean flow velocity and little impact of hematocrit. This segregation heterogeneity could influence the ability of sRBC to adhere to the vascular wall and slow down blood flow. However, promoting aggregation inhibited segregation while CDL thickness was enhanced by aggregation, highlighting a potential protective role against vaso-occlusion in patients with sickle cell anemia.

The Effect of Land Taper Angle on Trailing Edge Slot Film Cooling

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Julia Ling ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Concentration Distribution ◽  
Turbine Blades ◽  
Mean Flow ◽  
Trailing Edge ◽  
Taper Angle ◽  
Flow Features ◽  
The Mean ◽  
Slot Film Cooling ◽  
The Impact

Trailing edge slot film cooling is a widely used method of protecting the thin trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations which can be broadly classified as either “tapered” or “straight.” This paper examines the effect of the land taper angle on the mixing of the coolant flow with the main flow by comparing three configurations: a case with straight lands, a previously reported case with slightly tapered lands, and a case with strongly tapered lands. In each case, the slot width and the land width at the plane of the slot exit are kept constant. For each configuration, the mean volumetric coolant concentration distribution and three-component velocity field were measured using magnetic resonance imaging (MRI) techniques. It is shown that the land taper angle has a strong effect on the mean flow features and coolant surface effectiveness. Furthermore, the impact of the lands configuration on the flow field and concentration distribution is seen not just in the cutback region, but also in the wake of the blade.

scholarly journals The Impact of the State of the Troposphere on the Response to Stratospheric Heating in a Simplified GCM

2010 ◽  
Vol 23 (23) ◽  
pp. 6166-6185 ◽  
Author(s):  
Isla R. Simpson ◽  
Michael Blackburn ◽  
Joanna D. Haigh ◽  
Sarah N. Sparrow
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Lower Latitude ◽  
Mean Flow ◽  
Magnitude Response ◽  
Stratospheric Temperature ◽  
The Mean ◽  
Climate Forcings ◽  
The Impact ◽  
Jet Structure

Abstract Previous studies have made use of simplified general circulation models (sGCMs) to investigate the atmospheric response to various forcings. In particular, several studies have investigated the tropospheric response to changes in stratospheric temperature. This is potentially relevant for many climate forcings. Here the impact of changing the tropospheric climatology on the modeled response to perturbations in stratospheric temperature is investigated by the introduction of topography into the model and altering the tropospheric jet structure. The results highlight the need for very long integrations so as to determine accurately the magnitude of response. It is found that introducing topography into the model and thus removing the zonally symmetric nature of the model’s boundary conditions reduces the magnitude of response to stratospheric heating. However, this reduction is of comparable size to the variability in the magnitude of response between different ensemble members of the same 5000-day experiment. Investigations into the impact of varying tropospheric jet structure reveal a trend with lower-latitude/narrower jets having a much larger magnitude response to stratospheric heating than higher-latitude/wider jets. The jet structures that respond more strongly to stratospheric heating also exhibit longer time scale variability in their control run simulations, consistent with the idea that a feedback between the eddies and the mean flow is both responsible for the persistence of the control run variability and important in producing the tropospheric response to stratospheric temperature perturbations.

scholarly journals Effect of Reynolds number and inflow parameters on mean and turbulent flow over complex topography

2016 ◽  
Vol 1 (2) ◽  
pp. 237-254 ◽  
Author(s):  
Ryan Kilpatrick ◽  
Horia Hangan ◽  
Kamran Siddiqui ◽  
Dan Parvu ◽  
Julia Lange ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Wind Shear ◽  
Large Scale ◽  
Flow Behaviour ◽  
Complex Topography ◽  
Mean Flow ◽  
Effective Roughness ◽  
The Mean ◽  
The Impact

Abstract. A characterization of mean and turbulent flow behaviour over complex topography was conducted using a large-scale (1 : 25) model in the WindEEE Dome at Western University. The specific topographic feature considered was the Bolund Hill escarpment facing westerly winds. A total of eight unique inflow conditions were tested in order to isolate the impact of key parameters such as Reynolds number, inflow shear profile, and effective roughness, on flow behaviour over the escarpment. The results show that the mean flow behaviour was generally not affected by the Reynolds number; however, a slight increase in speed-up over the escarpment was observed for cases with lower inflow roughness. The shape of the inflow wind shear profile also had a minor impact on the mean flow near the escarpment. More significant effects were observed in the turbulent flow behaviour, where the turbulent kinetic energy (TKE) over the escarpment was found be a strong function of inflow roughness and a weak function of the Reynolds number. The local change in the inflow wind shear was found to have the most significant influence on the TKE magnitude, which more closely approximated the full-scale TKE data, a result which had not been previously observed in wind tunnel modelling of this topography.

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