scholarly journals Temperature and Circulation Dynamics in a Small and Shallow Lake: Effects of Weak Stratification and Littoral Submerged Macrophytes

Water ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 128 ◽  
Author(s):  
Péter Torma ◽  
Chin Wu
Keyword(s):  
Velocity Profile ◽  
Shallow Lake ◽  
Littoral Zone ◽  
Submerged Macrophytes ◽  
Layer Structure ◽  
Maximum Velocity ◽  
Mean Flow ◽  
Circulation Patterns ◽  
Weak Stratification ◽  
Circulation Dynamics

In this paper, the effects of littoral submerged macrophytes on weak stratification conditions in a small and shallow lake are investigated. Diverse submerged macrophytes occupying a large portion of the littoral zone act as resistance to water motions and affect lake hydrodynamics. Strong solar radiation and mild wind forcing typically occurring during the summer season result in weak stratification characterized by a diurnal cycle with a temperature differential of 1–3 °C. Temperature and circulation dynamics of a small and shallow lake are depicted by extensive field measurements and a three-dimensional non-hydrostatic model with a generic length scale (GLS) approach for the turbulence closure and drag forces induced by macrophytes. Results show that the effects of macrophytes on velocity profiles are apparent. In the pelagic area, the circulation patterns with and without macrophytes are similar. The velocity profile is generally characterized by a two-layer structure with the maximum velocity at both the water surface and the mid-depth. In contrast, inside the littoral zone, the mean flow is retarded by macrophytes and the velocity profile is changed to only one maximum velocity at the surface with a steeper decrease until 2.0 m depth and another slight decrease to the lake bottom. From the whole lake perspective, littoral macrophytes dampen the horizontal water temperature difference between the upwind side and download side of the lake. Macrophytes promote a stronger temperature stratification by retarding mean flows and reducing vertical mixing. Overall, this study shows that the temperature structures and circulation patterns under weak stratification conditions in a small and shallow lake are strongly affected by littoral vegetation.

Doppler Profiler and Radar Observations of Boundary Layer Variability during the Landfall of Tropical Storm Gabrielle

2006 ◽  
Vol 63 (1) ◽  
pp. 234-251 ◽  
Author(s):  
Kevin R. Knupp ◽  
Justin Walters ◽  
Michael Biggerstaff
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Layer Structure ◽  
Flow Direction ◽  
Surface Flow ◽  
Tropical Storm ◽  
Mean Flow ◽  
Boundary Layer Structure ◽  
Stratiform Precipitation ◽  
Wind Profiles

Abstract Detailed observations of boundary layer structure were acquired on 14 September 2001, prior to and during the landfall of Tropical Storm Gabrielle. The Mobile Integrated Profiling System (MIPS) and the Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) were collocated at the western Florida coastline near Venice, very close to the wind center at landfall. Prior to landfall, the boundary layer was rendered weakly stable by a long period of evaporational cooling and mesoscale downdrafts within extensive stratiform precipitation that started 18 h before landfall. The cool air mass was expansive, with an area within the 23°C surface isotherm of about 50 000 km2. East-northeasterly surface flow transported this cool air off the west coast of Florida, toward the convergent warm core of the Gabrielle, and promoted the development of shallow warm and cold fronts that were prominent during the landfall phase. Airflow properties of the boundary layer around the coastal zone are examined using the MIPS and SMART-R data. Wind profiles exhibited considerable temporal variability throughout the period of observations. The stable offshore flow within stratiform precipitation exhibited a modest jet that descended from about 600 to 300 m within the 20-km zone centered on the coastline. In contrast, the onshore flow on the western side of the wind center produced a more turbulent boundary layer that exhibited a well-defined top varying between 400 and 1000 m MSL. The horizontal variability of each boundary layer is examined using high-resolution Doppler radar scans at locations up to 15 km on either side of the coastline, along the mean flow direction of the boundary layer. These analyses reveal that transitions in boundary layer structure for both the stable and unstable regimes were most substantial within 5 km of the coastline.

scholarly journals Determining strength training needs using the force-velocity profile of elite female handball and volleyball players

2020 ◽  
pp. 174795412096404
Author(s):  
Leonidas Petridis ◽  
Gergely Pálinkás ◽  
Zsófia Tróznai ◽  
Bettina Béres ◽  
Katinka Utczás
Keyword(s):  
Velocity Profile ◽  
Strength Training ◽  
Body Mass ◽  
Female Athletes ◽  
Vertical Jump ◽  
Body Height ◽  
Maximum Velocity ◽  
Total Force ◽  
Volleyball Players ◽  
Force Velocity

The aim of this study was to assess the vertical jump performance and the force-velocity profile of elite female handball and volleyball players. Forty-one female athletes were measured, 28 handball players (age: 24.0 ± 3.6 years, body height: 1.75 ± 0.05 m, body mass: 69.0 ± 7.3 kg) and 13 volleyball players (age: 24.1 ± 5.2 years, body height: 1.83 ± 0.07 m and body mass: 74.9 ± 7.9 kg). All players performed unloaded and loaded countermovement jumps (CMJ) on a force platform. The theoretical maximal force ( F0), the theoretical maximum velocity ( v0), the theoretical maximal power ( Pmax), the slope of the F-v relationship ( Sfv) and the force-velocity imbalance ( FVimb) were calculated. Mean value of vertical jump height was 0.33 ± 0.03m, with no difference between handball and volleyball players. Mean values of F0, v0, Pmax, Sfv and FVimb for all players were 31.2 ± 2.6 N/kg, 3.10 ± 0.50 m·s−1, 24.2 ± 3.2 w/kg, -10.32 ± 2.09 Ns/m/kg and 28.1 ± 13.3% respectively. Two players had a low magnitude velocity-deficit, whereas most of the players exhibited a low to high force-deficit. A strong correlation was found between the ratio of measured to optimal F-v slope with the change in the proportion of net force to total force during unloaded and loaded conditions. The findings suggest that it would be beneficial for these athletes to first decrease their force deficit through mainly maximal strength training before implementing training to further maximize power output. Establishment of the F-v profile could be a useful diagnostic tool for coaches to optimize strength training and to design training intervention based on the individual need of each athlete.

scholarly journals Influence of Rigid Emerged Vegetation in a Channel Bend on Bed Topography and Flow Velocity Field: Laboratory Experiments

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 118 ◽  
Author(s):  
Hossein Hamidifar ◽  
Alireza Keshavarzi ◽  
Paweł M. Rowiński
Keyword(s):  
Laboratory Experiments ◽  
Flow Characteristics ◽  
Maximum Velocity ◽  
Flow Conditions ◽  
Mean Flow ◽  
Bed Topography ◽  
Channel Bend ◽  
Bed Erosion ◽  
Flow Hydraulics ◽  
The Mean

Trees have been used extensively by river managers for improving the river environment and ecology. The link between flow hydraulics, bed topography, habitat availability, and organic matters is influenced by vegetation. In this study, the effect of trees on the mean flow, bed topography, and bed shear stress were tested under different flow conditions. It was found that each configuration of trees produced particular flow characteristics and bed topography patterns. The SR (single row of trees) model appeared to deflect the maximum velocity downstream of the bend apex toward the inner bank, while leading the velocity to be more uniformly distributed throughout the bend. The entrainment of sediment particles occurred toward the area with higher values of turbulent kinetic energy (TKE). The results showed that both SR and DR (double rows of trees) models are effective in relieving bed erosion in sharp ingoing bends. The volume of the scoured bed was reduced up to 70.4% for tests with trees. This study shows the effectiveness of the SR model in reducing the maximum erosion depth.

Maximum Velocity Decay in a Submerged Laminar Jet Issuing from a ‘Long Tube

1983 ◽  
Vol 7 (1) ◽  
pp. 41-43 ◽  
Author(s):  
M. Arulraja ◽  
G.W. Rankin ◽  
K. Sridhar
Keyword(s):  
Velocity Profile ◽  
Maximum Velocity ◽  
Momentum Equation ◽  
Experimental Fact ◽  
Laminar Jet ◽  
Developing Region ◽  
Other Information ◽  
Velocity Decay ◽  
Matching Schemes ◽  
Jet Axis

Decay of the maximum velocity of an incompressible, axisymmetric, submerged, laminar free jel is related to the second derivative of the velocity profile at the centre line by using the momentum equation along the jet axis with boundary layer approximations. Using this decay relation and the experimental fact that the velocity profile near the jet axis remains parabolic it is shown that maximum velocity decay is linear in the developing region. The length of the developing region and the location of the virtual origin are obtained by matching the maximum velocity variations at the boundary between the developing and fully developed regions. These values are compared with the results of conventional jet matching schemes and with other information available in the literature.

Mean Flow Measurements Near the Plane of an Open Rotor Operating with an Inlet Velocity Gradient

1981 ◽  
Vol 103 (2) ◽  
pp. 445-450
Author(s):  
M. L. Billet
Keyword(s):  
Flow Field ◽  
Velocity Profile ◽  
Velocity Gradient ◽  
Vortex Motion ◽  
Field Measurements ◽  
Velocity Data ◽  
Mean Flow ◽  
Flow Measurements ◽  
Inlet Velocity ◽  
Open Rotor

As part of a study on the structure of a trailing vortex, laser doppler anemometer (LDA) measurements were made of the flow field near an open rotor having an inlet velocity gradient. The measurements were made in the 1.22 m dia water tunnel of the Applied Research Laboratory at The Pennsylvania State University. Velocity data were obtained for rotor inlet and outlet flow fields for several different inlet velocity gradients. Velocity data were also obtained downstream of the rotor plane that shows the vortex structure. Flow field measurements show the development of the downstream vortex motion. Small variations in the inlet velocity gradient near the rotor wall caused large differences in the structure of the trailing vortex. In addition, a measured downstream velocity profile is compared with a calculated velocity profile.

The structure of a shear layer bounding a separation region. Part 2. Effects of free-stream turbulence

1988 ◽  
Vol 192 ◽  
pp. 577-595 ◽  
Author(s):  
I. P. Castro ◽  
A. Haque
Keyword(s):  
Shear Layer ◽  
Free Stream ◽  
Layer Structure ◽  
Low Frequency ◽  
Flow Region ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Turbulence Data ◽  
Upstream Flow

Detailed measurements throughout the separated region behind a flat plate placed normal to a turbulent stream are reported. A long, central, downstream splitter plate prevented vortex shedding and led to a relatively extensive reversed flow region. Mean flow and turbulence data are compared with results obtained in the (nominal) absence of free-stream turbulence, and attention is concentrated on the changes in the shear-layer structure resulting from the different nature of the upstream flow.Many aspects of the results confirm those obtained recently by other workers. Free-stream turbulence enhances shear-layer entrainment rates, reduces the distance to reattachment and modifies the relatively low-frequency ‘flapping’ motion of the shear layer. In addition, however, extensive use of pulsed wire anemometry has allowed detailed measurements of the turbulence structure throughout the flow and it is shown that this is also modified significantly by the stream turbulence.

Application of the CNOP Method in the Shallow Lake Ecosystem

2014 ◽  
Vol 1010-1012 ◽  
pp. 658-661 ◽  
Author(s):  
Qian Qian Qi ◽  
Bo Wang
Keyword(s):  
Ecological Restoration ◽  
Shallow Lake ◽  
Submerged Macrophytes ◽  
Finite Amplitude ◽  
Water Transparency ◽  
Lake Ecosystem ◽  
Initial Condition ◽  
Turbid Water ◽  
Variable Model

It is serious on the degradation of the shallow lake ecosystem at present, while the recovery of the macrophytes vegetations and the increase in water transparency have been the main contents of the ecological restoration. Using a two-variable model, we discuss the instability and sensitivity of the ecosystem to the finite-amplitude perturbations related to the initial condition with CNOP-I method. Results show that the linearly stable clear (turbid) water states can be nonlinearly unstable with the finite-amplitude perturbations. The results also demonstrate that the facilitation interactions between the submerged macrophytes and the water transparency are the main trigger for a shift from the turbid to the clear state.

Turbulent planar wakes under pressure gradient conditions

2017 ◽  
Vol 830 ◽  
Author(s):  
Sina Shamsoddin ◽  
Fernando Porté-Agel
Keyword(s):  
Pressure Gradient ◽  
Maximum Velocity ◽  
Wind Farms ◽  
Parameter Tuning ◽  
Momentum Equation ◽  
Mean Flow ◽  
Self Similarity ◽  
High Lift ◽  
Velocity Deficit ◽  
The Mean

Accurate prediction of the spatial evolution of turbulent wake flows under pressure gradient conditions is required in some engineering applications such as the design of high-lift devices and wind farms over topography. In this paper, we aim to develop an analytical model to predict the evolution of a turbulent planar wake under an arbitrary pressure gradient condition. The model is based on the cross-stream integration of the streamwise momentum equation and uses the self-similarity of the mean flow. We have also made an experimentally supported assumption that the ratio of the maximum velocity deficit to the wake width is independent of the imposed pressure gradient. The asymptotic response of the wake to the pressure gradient is also investigated. After its derivation, the model is successfully validated against experimental data by comparing the evolution of the wake width and maximum velocity deficit. The inputs of the model are the imposed pressure gradient and the wake width under zero pressure gradient. The model does not require any parameter tuning and is deemed to be practical, computationally fast, accurate enough, and therefore useful for the scientific and engineering communities.

South Baltic rip currents detected by a field survey

Baltica ◽  
2020 ◽  
Vol 33 (1) ◽  
pp. 11-20
Author(s):  
Rafał Ostrowski ◽  
Jan Schönhofer ◽  
Magdalena Stella ◽  
Alexey Grave ◽  
Aleksander Babakov ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Maximum Velocity ◽  
Experimental Investigations ◽  
Rip Currents ◽  
The South ◽  
Storm Waves ◽  
Circulation Patterns ◽  
Wave Conditions ◽  
Deep Water Wave ◽  
Russian Research

The paper presents results of experimental investigations of currents in the nearshore region of the south Baltic Sea. The analysis is based on the field data collected near Lubiatowo (Poland) using the measuring equipment which was simultaneously operated both by the Polish and Russian research teams. The venture was aimed at detection of rip currents that are rare and insufficiently explored phenomena in the south Baltic coastal zone. The data include wind velocity and direction, deep-water wave buoy records and currents surveyed by means of drifters. The measurements were carried out in the area whose hydrodynamics, lithodynamics and morphodynamics are typical of the south Baltic sandy coast. It appears that the nearshore water flows are mostly represented by longshore wave-driven currents with mean velocities of 0.22–0.53 m/s, and the maximum velocity of 1.32 m/s. Water circulation patterns resembling rip currents with velocities of up to 0.34 m/s were identified only on one day, when specific wave conditions occurred at the study site. Contrary to strong longshore currents generated by storm waves, rip currents occur under mild or moderate wave conditions, when many beach users are willing to swim in nearshore waters. The present findings can therefore be useful for the improvement of swimmers’ safety in the south Baltic Sea regions.

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