63 research outputs found
Effects of cooling and internal wave motions on gas transfer coefficients in a boreal lake
Peer reviewe
Observation and Parameterization of Bottom Shear Stress and Sediment Resuspension in a Large Shallow Lake
Abstract Parameterizations for bottom shear stress are required to predict sediment resuspension from field observations and within numerical models that do not resolve flow within the viscous sublayer. This study assessed three observationâbased bottom shear stress (Ïb) parameterizations, including (a) the sum of surface wave stress and mean current (quadratic) stress (Ïb=Ïw+Ïc ); (b) the logâlaw (Ïb = ÏL); and (c) the turbulent kinetic energy (Ïb = ÏTKE); using 2 years of observations from a large shallow lake. For this system, the parameterization Ïb = Ïw + Ïc was sufficient to qualitatively predict resuspension, since bottom currents and surface wave orbitals were the two major processes found to resuspend bottom sediments. However, the ÏL and ÏTKE parameterizations also captured the development of a nepheloid layer within the hypolimnion associated with highâfrequency internal waves. Reynoldsâaveraged NavierâStokes (RANS) equation models parameterize Ïb as the summation of modeled currentâinduced bottom stress (Ïc,m) and modeled surface waveâinduced bottom stress (Ïw,m). The performance of different parameterizations for Ïw,m and Ïc,m in RANS models was assessed against the observations. The optimal parameterizations yielded rootâmeanâsquare errors of 0.031 and 0.025 Pa, respectively, when Ïw,m, and Ïc,m were set using a constant canonical drag coefficient. A RANSâbased ÏL parameterization was developed; however, the gridâaveraged modeled dissipation did not always match local observations, leading to O(10) errors in prediction of bottom stress. Turbulenceâbased parameterizations should be further developed for application to flows with mean shearâfree boundary turbulence
A parametric study of the generation and degeneration of wind-forced long internal waves in narrow lakes
Quantifying the effect of wind on internal wave resonance in Lake Villarrica, Chile
ArtĂculo de publicaciĂłn ISILake Villarrica, located in south central Chile, has amaximum depth of 167mand
amaximum fetch of about 20 km.The lake is monomictic, with a seasonal thermocline located
at a depth of approximately 20 m. Field data show the presence of basin-scale internal waves
that are forced by daily winds and affected by Coriolis acceleration. A modal linear and nonlinear
analysis of internal waves has been used, assuming a two-layer system. The numerical
simulations show good agreement with the internal wave field observations. The obtained
modes were used to study the energy dissipation within the system, which is necessary to
control the amplitude growth. Field data and numerical simulations identify (1) the occurrence
of a horizontal mode 1 Kelvin wave, with a period of about a day that coincides with the
frequency of daily winds, suggesting that this mode of the Kelvin waves is in a resonant state
(subject to damping and controlled by frictional effects in the field) and (2) the presence of
higher-frequency internal waves, which are excited by non-linear interactions between basinscale
internal waves. The non-linear simulation indicates that only 10% of the dissipation
rate of the Kelvin wave is because of bottom friction, while the rest 90% represents the
energy that is radiated from the Kelvin wave to other modes. Also, this study shows that
modes with periods between 5 and 8 h are excited by non-linear interactions between the
fundamental Kelvin wave and horizontal Poincaré-type waves. A laboratory study of the
resonant interaction between a periodic forcing and the internal wave field response has also
been performed, confirming the resonance for the horizontal mode 1 Kelvin wave.The authors acknowledge support of the Civil Engineering Department, Universidad de
Chile, FONDECYT Project 1080617 and the Civil Engineering Department, University of Dundee. The first
author acknowledges financial support from Department of Graduate and Postgraduate Degree, Universidad
de Chile
Numerical studies on the degeneration of internal waves induced by an initial tilted pycnocline
Multi scenario simulation analysis of environmental carrying capacity in western region based on fusion support vector machine regression prediction algorithm
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