scholarly journals EFFECTS OF OPPOSING CURRENT ON WAVE TRANSFORMATION ON SLOPING SEA BED

1984 ◽  
Vol 1 (19) ◽  
pp. 77 ◽  
Author(s):  
Shigeki Sakai ◽  
Kiroshi Saeki
Keyword(s):  
Free Surface ◽  
Energy Flux ◽  
Wave Transformation ◽  
Stokes Wave ◽  
Unit Width ◽  
Bernoulli’S Equation ◽  
Sea Bed ◽  
Dimensionless Unit ◽  
Change In The Mean ◽  
The Mean

The transformation and the breaking of waves affected by an opposing current on the sloping sea bed were discussed. It was found that the characteristics of wave transformation before breaking point can be determined by the deep water wave steepness and the dimensionless unit width discharge. Concerning the wave decaying due to breaking, the characteristics of the change in the wave height depend only on the slope of the sea bed. Fourth order solutions of Stokes wave on a uniform current were calculated based on the first and second definition of the wave celerity, respectively. The theoretical solutions for wave transformation by the energy flux method were presented. Comparisons between the theoretical solutions and the experimental results gave the criteria of the applicability of our solutions corresponding to the dimensionless unit width discharge. In the calculation of energy flux, it was pointed out that the change in the mean level of the free surface should be taken into account. It was made clear that the change in the mean level of the free surface can be evaluated by Bernoulli's equation, and the energy flux in which the change in the mean level of the free surface was taken into account was proposed. The criteria of breaking corresponding to the dimensionless unit width discharge were clarified, experimentally.

scholarly journals IRREGULAR WAVE TRANSFORMATION AFFECTED BY OPPOSING CURRENTS

1986 ◽  
Vol 1 (20) ◽  
pp. 53
Author(s):  
Shigeki Sakai ◽  
Kouestu Hiyamizu ◽  
Hiroshi Saeki
Keyword(s):  
Wave Height ◽  
Present Model ◽  
Surf Zone ◽  
Transformation Model ◽  
Irregular Waves ◽  
Wave Transformation ◽  
Irregular Wave ◽  
Sea Bed ◽  
Dimensionless Unit ◽  
Deep Water Wave

Transformation of irregular waves affected by opposing currents on a sloping sea bed was discussed, experimentally and theoretically. It was found that representative values of wave height, such as a significant wave height, are larger before breaking and the wave height decaying occurs more promptly in a surf zone as opposing currents become dominant, and that characteristics of a irregular wave transformation are determined by the dimensionless unit width discharge q* and the deep water wave steepness. This means that the effects of opposing currents on irregular wave transformation are qualitatively identical to that on the regular waves. A transformation model of irregular waves affected by opposing currents was presented. In the model, formulations for a regular wave transformation, in which the effects of opposing currents were taken into account, were applied to individual waves defined by zero-down" cross-method from irregular wave profiles. Comparisons between experimental results and the prediction by the model showed that the present model gives a good explanation for wave height distributions and the experimental finding that the surf zone is moved offshore by opposing currents.

Seven years follow-up of corneal cross-linking (CXL) in pediatric patients: Evaluation of treated and untreated eye

2021 ◽  
pp. 112067212110206
Author(s):  
Iliya Simantov ◽  
Lior Or ◽  
Inbal Gazit ◽  
Biana Dubinsky-Pertzov ◽  
David Zadok ◽  
...  
Keyword(s):  
Visual Acuity ◽  
Pediatric Patients ◽  
Pediatric Population ◽  
Corneal Thickness ◽  
Cross Linking ◽  
Uncorrected Distance Visual Acuity ◽  
Mild Reduction ◽  
Change In The Mean ◽  
The Mean

Background: Retrospective cohort study evaluating long term keratoconus progression amongst cross-linking (CXL) treated pediatric patients in the treated and the fellow untreated eyes. Methods: Data on 60 eyes of 30 patients, 18 years old or younger, who underwent CXL in at least one eye was collected and analyzed. Follow-up measurements taken from the treated and untreated eye up to 7 years after CXL treatment, were compared to baseline measurements. Parameters included uncorrected distance visual acuity (UCDVA), best-corrected spectacle visual acuity (BCSVA), manifest refraction, pachymetry, corneal tomography, and topography. Results: Mean age of patients was 16 ± 2.1 years. For the treated eyes, during follow-up period mean UCDVA had improved (from 0.78 ± 0.22 at baseline to 0.58 ± 0.26 logMAR at 7 years; p = 0.13), as well as mean BCSVA (from 0.23 ± 0.107 at baseline to 0.172 ± 0.05 logMAR at 7 years; p = 0.37). The mean average keratometry showed a significant flattening (from 49.95 ± 4.04 to 47.94 ± 3.3 diopters (D); p < 0.001), However there was no change in the mean maximal keratometry. The mean minimal corneal thickness (MCT) showed a significant mild reduction of 26 µm ( p = 0.006). Although statistically insignificant, the mean manifest cylinder was also reduced to 2D ( p = 0.15). During the follow-up period, eight untreated eyes (26.6%) deteriorated and underwent CXL, while only one treated eye (3.33%) required an additional CXL. Conclusion: CXL is a safe and efficient procedure in halting keratoconus progression in the pediatric population, the fellow eye needs to be carefully monitored but only a 25% of the patients will require CXL in that eye during a period of 7 years.

scholarly journals Personality development from 12 to 18 years of age: changes in mean levels and structure of traits

2004 ◽  
Vol 18 (6) ◽  
pp. 445-462 ◽  
Author(s):  
Jüri Allik ◽  
Kaia Laidra ◽  
Anu Realo ◽  
Helle Pullmann
Keyword(s):  
Personality Traits ◽  
Personality Development ◽  
The Self ◽  
Age Changes ◽  
Cross Sectional ◽  
Adult Personality ◽  
12Th Grade ◽  
Self Reports ◽  
Change In The Mean ◽  
The Mean

The Estonian NEO‐FFI was administered to 2650 Estonian adolescents (1420 girls and 1230 boys) aged from 12 to 18 years and attending 6th, 8th, 10th, or 12th grade at secondary schools all over Estonia. Although the mean levels of personality traits of Estonian adolescents were quite similar to the respective scores of Estonian adults, there was a developmental gap in Agreeableness and Conscientiousness. Three of the five personality dispositions demonstrated a modest cross‐sectional change in the mean level of the trait scores: the level of Openness increased and the levels of Agreeableness and Conscientiousness decreased between 12 and 18 years of age. Although the five‐factor structure of personality was already recognizable in the sample of 12‐year‐old children, it demonstrated only an approximate congruence with the adult structure, suggesting that not all children of that age have developed abilities required for observing one's own personality dispositions and for giving reliable self‐reports on the basis of these observations. The self‐reported personality trait structure matures and becomes sufficiently differentiated around age 14–15 and grows to be practically indistinguishable from adult personality by the age of 16. Personality of adolescents becomes more differentiated with age: along with the growth of mental capacities the correlations among the personality traits and intelligence become smaller. Copyright © 2004 John Wiley & Sons, Ltd.

Analysis of Turbulence in the Tip Region of a Waterjet Pump Rotor

2010 ◽  
Author(s):  
Huixuan Wu ◽  
Rinaldo L. Miorini ◽  
Joseph Katz
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Multiple Scales ◽  
Tip Clearance ◽  
Mean Flow ◽  
Production Characteristic ◽  
Pump Rotor ◽  
The Mean ◽  
Turbulence Production ◽  
Waterjet Pump

A series of high resolution planar particle image velocimetry measurements performed in a waterjet pump rotor reveal the inner structure of the tip leakage vortex (TLV) which dominates the entire flow field in the tip region. Turbulence generated by interactions among the TLV, the shear layer that develops as the backward leakage flow emerges from the tip clearance as a “wall jet”, the passage flow, and the endwall is highly inhomogeneous and anisotropic. We examine this turbulence in both RANS and LES modelling contexts. Spatially non-uniform distributions of Reynolds stress components are explained in terms of the local mean strain field and associated turbulence production. Characteristic length scales are also inferred from spectral analysis. Spatial filtering of instantaneous data enables the calculation of subgrid scale (SGS) stresses, along with the SGS energy flux (dissipation). The data show that the SGS energy flux differs from the turbulence production rate both in trends and magnitude. The latter is dominated by energy flux from the mean flow to the large scale turbulence, which is resolved in LES, whereas the former is dominated by energy flux from the mean flow to the SGS turbulence. The SGS dissipation rate is also used for calculating the static and dynamic Smagorinsky coefficients, the latter involving filtering at multiple scales; both vary substantially in the tip region, and neither is equal to values obtained in isotropic turbulence.

scholarly journals Analysis of hydrological changes and flood increase in Niamey based on the PERSIANN-CDR satellite rainfall estimate and hydrological simulations over the 1983–2013 period

2015 ◽  
Vol 370 ◽  
pp. 117-123 ◽  
Author(s):  
C. Casse ◽  
M. Gosset
Keyword(s):  
Land Use Changes ◽  
Marked Change ◽  
Extreme Rainfall ◽  
Rapid Flow ◽  
Change In The Mean ◽  
The Mean ◽  
Satellite Rainfall ◽  
The City ◽  
Satellite Rainfall Estimate

Abstract. A dramatic increase in the frequency and intensity of floods due to the Niger River in the city of Niamey (Niger) has been observed in the last decade. Previous studies highlighted the role of the land use changes on the flood increase since 1970s. In the last decade, observations have raised the issue of a possible increase in extreme rainfall in the Sahel, which may have caused the recent and extreme floods in Niamey in 2010, 2012 and 2013. The study focuses on the 125 000 km2 basin between Ansongo and Niamey. This is the drainage area of the monsoon rainfall that leads to the rapid flow rise occurring between June and October. To understand the possible role of rainfall in flood intensification, satellite rainfall estimate is attractive in a region where the operational gauge network is sparse. This paper analyses the evolution of the Niger hydrograph in Niamey based on discharge observations, hydrological modelling and the satellite product PERSIANN-CDR, over the 1983–2013 period. PERSIANN-CDR is first compared with four other rainfall products. The salient features of the observed changes, i.e. a marked change in the mean decadal hydrograph, is well mimicked by the simulations, implying that rainfall is the first driver to the observed changes. The increase of flooded years over the period is also well reproduced but with some uncertainties in the exact number of flood days per year.

scholarly journals Assessment of CFD turbulence models for free surface flow simulation and 1-D modelling for water level calculations over a broad-crested weir floodway

Water SA ◽  
2019 ◽  
Vol 45 (3 July) ◽  
Author(s):  
Ahmed M Helmi
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Water Level ◽  
Dimensional Analysis ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Cfd Simulations ◽  
One Dimensional ◽  
The Mean ◽  
The One

Floodways, where a road embankment is permitted to be overtopped by flood water, are usually designed as broad-crested weirs. Determination of the water level above the floodway is crucial and related to road safety. Hydraulic performance of floodways can be assessed numerically using 1-D modelling or 3-D simulation using computational fluid dynamics (CFD) packages. Turbulence modelling is one of the key elements in CFD simulations. A wide variety of turbulence models are utilized in CFD packages; in order to identify the most relevant turbulence model for the case in question, 96 3-D CFD simulations were conducted using Flow-3D package, for 24 broad-crested weir configurations selected based on experimental data from a previous study. Four turbulence models (one-equation, k-ε, RNG k-ε, and k-ω) ere examined for each configuration. The volume of fluid (VOF) algorithm was adopted for free water surface determination. In addition, 24 1-D simulations using HEC-RAS-1-D were conducted for comparison with CFD results and experimental data. Validation of the simulated water free surface profiles versus the experimental measurements was carried out by the evaluation of the mean absolute error, the mean relative error percentage, and the root mean square error. It was concluded that the minimum error in simulating the full upstream to downstream free surface profile is achieved by using one-equation turbulence model with mixing length equal to 7% of the smallest domain dimension. Nevertheless, for the broad-crested weir upstream section, no significant difference in accuracy was found between all turbulence models and the one-dimensional analysis results, due to the low turbulence intensity at this part. For engineering design purposes, in which the water level is the main concern at the location of the flood way, the one-dimensional analysis has sufficient accuracy to determine the water level.

scholarly journals Diurnal Dynamics of the Umov Kinetic Energy Density Vector in the Atmospheric Boundary Layer from Minisodar Measurements

Atmosphere ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1347
Author(s):  
Alexander Potekaev ◽  
Nikolay Krasnenko ◽  
Liudmila Shamanaeva
Keyword(s):  
Energy Density ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Flux ◽  
Wind Effect ◽  
Kinetic Energy Density ◽  
Near Surface ◽  
Density Vector ◽  
The Mean ◽  
Umov Vector

The diurnal hourly dynamics of the kinetic energy flux density vector, called the Umov vector, and the mean and turbulent components of the kinetic energy are estimated from minisodar measurements of wind vector components and their variances in the lower 200-meter layer of the atmosphere. During a 24-hour period of continuous minisodar observations, it was established that the mean kinetic energy density dominated in the surface atmospheric layer at altitudes below ~50 m. At altitudes from 50 to 100 m, the relative contributions of the mean and turbulent wind kinetic energy densities depended on the time of the day and the sounding altitude. At altitudes below 100 m, the contribution of the turbulent kinetic energy component is small, and the ratio of the turbulent to mean wind kinetic energy components was in the range 0.01–10. At altitudes above 100 m, the turbulent kinetic energy density sharply increased, and the ratio reached its maximum equal to 100–1000 at altitudes of 150–200 m. A particular importance of the direction and magnitude of the wind effect, that is, of the direction and magnitude of the Umov vector at different altitudes was established. The diurnal behavior of the Umov vector depended both on the time of the day and the sounding altitude. Three layers were clearly distinguished: a near-surface layer at altitudes of 5–15 m, an intermediate layer at altitudes from 15 m to 150 m, and the layer of enhanced turbulence above. The feasibility is illustrated of detecting times and altitudes of maximal and minimal wing kinetic energy flux densities, that is, time periods and altitude ranges most and least favorable for flights of unmanned aerial vehicles. The proposed novel method of determining the spatiotemporal dynamics of the Umov vector from minisodar measurements can also be used to estimate the effect of wind on high-rise buildings and the energy potential of wind turbines.

A study about the linearity of trends between extreme and mean temperatures in Argentina

2021 ◽  
Author(s):  
Solange Suli ◽  
Matilde Rusticucci ◽  
Soledad Collazo
Keyword(s):  
Linear Regression ◽  
Linear Relationship ◽  
Statistical Significance ◽  
Coefficient Of Determination ◽  
Maximum Temperature ◽  
Mean Temperature ◽  
Change In The Mean ◽  
The Mean ◽  
Student’S T ◽  
Cold Extremes

&lt;p&gt;Small variations in the mean state of the atmosphere can cause large changes in the frequency of extreme events. In order to deepen and extend previous results in time, in this work we analyzed the linear relationship between extreme and mean temperature (&amp;#932;) on a climate change scale in Argentina. Two monthly extreme indices, cold nights (TN10) and warm days (TX90), were calculated based on the quality-controlled daily minimum and maximum temperature data provided by the Argentine National Meteorological Service from 58 conventional weather stations located over Argentina in the 1977&amp;#8211;2017 period. Subsequently, we evaluated the relationship between the linear trends of extremes and mean temperature on a seasonal basis (JFM, AMJ, JAS, and OND). Student's T-test was performed to analyze their statistical significance at 5%. Firstly, positive (negative) and significant linear regressions were found between TX90 (TN10) trends and mean temperature trends for the four studied seasons. Therefore, an increase in the &amp;#932;-trend maintains a linear relationship with significant increase (decrease) of warm days (cold nights). Moreover, we found that JFM was the one with the highest coefficient of determination (0.602 for hot extremes and 0.511 for cold extremes), implying that 60.2% (51.1%) of the TX90 (TN10) trend could be explained as a function of the &amp;#932;-trend by a linear regression. In addition, in the JFM (OND) quarter, the TX90 index increased by 7.02 (6.02) % of days each with a 1 &amp;#186;C increase in the mean temperature. Likewise, the TN10 index decreased by 4.94 (and 4.99) % of days from a 1&amp;#186;C increase in the mean temperature for the JFM (AMJ) quarter. Finally, it is worthwhile to highlight the uneven behavior between hot and cold extremes and the mean temperature. Specifically, it was observed that the slopes of the linear regression calculated for the TX90 index and &amp;#932;&amp;#160;presented a higher absolute value than those registered for the TN10 index and &amp;#932;. Therefore, a change in the mean temperature affects hot extremes to a greater extent than cold ones in Argentina.&lt;/p&gt;

Nonlinear Aspects of Subcritical Shallow-Water Flow Past Two-Dimensional Obstructions

1978 ◽  
Vol 22 (04) ◽  
pp. 203-211
Author(s):  
Nils Salvesen ◽  
C. von Kerczek
Keyword(s):  
Free Surface ◽  
Shallow Water ◽  
Flow Problem ◽  
Free Stream ◽  
The Body ◽  
Two Dimensional ◽  
Third Order ◽  
Submerged Body ◽  
The Mean ◽  
The Waves

Some nonlinear aspects of the two-dimensional problem of a submerged body moving with constant speed in otherwise undisturbed water of uniform depth are considered. It is shown that a theory of Benjamin which predicts a uniform rise of the free surface ahead of the body and the lowering of the mean level of the waves behind it agrees well with experimental data. The local steady-flow problem is solved by a numerical method which satisfies the exact free-surface conditions. Third-order perturbation formulas for the downstream free waves are also presented. It is found that in sufficiently shallow water, the wavelength increases with increasing disturbance strength for fixed values of the free-stream-Froude number. This is opposite to the deepwater case where the wavelength decreases with increasing disturbance strength.

Sign in / Sign up

Export Citation Format

Share Document