scholarly journals Applying of depth-averaged hydrodynamic modeling with different methods of turbulence closure for flow near channel groyne. Part I – hydrodynamic background

2018 ◽  
Vol 23 ◽  
pp. 00009
Author(s):  
Ryszard Ewertowski
Keyword(s):  
Eddy Viscosity ◽  
Rectangular Channel ◽  
Simulation Models ◽  
Shear Stresses ◽  
Research Activity ◽  
Simulation Experiments ◽  
Hydrodynamic Simulation ◽  
Training Structures ◽  
Averaged Model ◽  
Bed Shear Stresses

Training structures in flow stream play an important role in shaping flow and bed properties. Planning to introduce such training elements like groins or dikes into the river stream one need to know consequences they may introduce into flow field and bed shear stresses. These consequences can be investigated by laboratory experiments on hydraulic models or by numerical modelling using hydrodynamic simulation models. In the paper the second possibility is exploited by applying two-dimensional depth-averaged model for straight rectangular channel with a groyne. This paper contains the first part of the research results and it describes hydrodynamic background of the flow phenomenon, concentrating on hydrodynamic equations for depth-averaged flow, types of eddy viscosity method used and kind of boundary conditions applied. Based on the hydrodynamic descriptions, different simulation experiments have been conducted for the flow problem and the whole analysis of simulation results for flow in channel near groyne is contained in the second part of the research activity (Part II = Analysis of simulation).

scholarly journals Applying of depth-averaged hydrodynamic modeling with different methods of turbulence closure for flow near channel groyne. Part II – Analysis of simulation

2018 ◽  
Vol 23 ◽  
pp. 00010
Author(s):  
Ryszard Ewertowski
Keyword(s):  
Eddy Viscosity ◽  
Rectangular Channel ◽  
Point Of View ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Hydrodynamic Models ◽  
Training Structures ◽  
Flow Phenomena ◽  
Training Structure ◽  
Averaged Model

Training structures in flow stream play an important role in shaping flow and bed properties. To investigate consequences of introducing training elements like groins or dikes into the river stream one can successfully use numerical modelling. This paper is the second part of the research concentrated on utilizing some hydrodynamic models for resolving the problem. In the first part some hydrodynamic background has been described and here the analysis of applying two-dimensional depth-averaged model for straight rectangular channel with a groyne is discussed. Three models of eddy viscosity were applied to investigate their influence on results of simulation and to attempt choosing the most suitable method of modelling the flow phenomena around the groin. Results of simulation in steady flow conditions show that from the hydrodynamic point of view the more profitable method of turbulence description is the mixed-length or even the parabolic method instead of the broadly suggested k-e model. They allow producing the most reliable vortexes in the shear layer of flow behind the training structure end well preserve the mass balance contrary to the results obtained with k-e model of eddy viscosity.

scholarly journals MEASUREMENT AND MODELING OF SOLITARY WAVE INDUCED BED SHEAR STRESS OVER A ROUGH BED

2012 ◽  
Vol 1 (33) ◽  
pp. 21 ◽  
Author(s):  
Jaya Kumar Seelam ◽  
Tom E Baldock
Keyword(s):  
Shear Stress ◽  
Eddy Viscosity ◽  
Breaking Waves ◽  
Shear Stresses ◽  
Bed Shear Stress ◽  
Eddy Viscosity Model ◽  
Friction Factors ◽  
Convolution Model ◽  
Rough Bed ◽  
Bed Shear Stresses

Bed shear stresses generated by solitary waves were measured using a shear cell apparatus over a rough bed in laminar and transitional flow regimes (~7600 < Re < ~60200). Modeling of bed shear stress was carried out using analytical models employing convolution integration methods forced with the free stream velocity and three eddy viscosity models. The measured wave height to water depth (h/d) ratio varied between 0.13 and 0.65; maximum near- bed velocity varied between 0.16 and 0.47 m/s and the maximum total shear stress (sum of form drag and bed shear) varied between 0.565 and 3.29 Pa. Wave friction factors estimated from the bed shear stresses at the maximum bed shear stress using both maximum and instantaneous velocities showed that there is an increase in friction factors estimated using instantaneous velocities, for non-breaking waves. Maximum positive total stress was approximately 2.2 times larger than maximum negative total stress for non-breaking waves. Modeled and measured positive total stresses are well correlated using the convolution model with an eddy viscosity model analogous to steady flow conditions (nu_t=0.45u* z1; where nu_t is eddy viscosity, u* is shear velocity and z1 is the elevation parameter related to relative roughness). The bed shear stress leads the free stream fluid velocity by approximately 30° for non-breaking waves and by 48° for breaking waves, which is under-predicted by 27% by the convolution model with above mentioned eddy viscosity model.

scholarly journals Assessing Machine Learning versus a Mathematical Model to Estimate the Transverse Shear Stress Distribution in a Rectangular Channel

Mathematics ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 596
Author(s):  
Babak Lashkar-Ara ◽  
Niloofar Kalantari ◽  
Zohreh Sheikh Khozani ◽  
Amir Mosavi
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Fuzzy Inference ◽  
Rectangular Channel ◽  
Tsallis Entropy ◽  
Shear Stress Distribution ◽  
Data Series ◽  
Shear Stresses ◽  
Inference System ◽  
Aspect Ratios

One of the most important subjects of hydraulic engineering is the reliable estimation of the transverse distribution in the rectangular channel of bed and wall shear stresses. This study makes use of the Tsallis entropy, genetic programming (GP) and adaptive neuro-fuzzy inference system (ANFIS) methods to assess the shear stress distribution (SSD) in the rectangular channel. To evaluate the results of the Tsallis entropy, GP and ANFIS models, laboratory observations were used in which shear stress was measured using an optimized Preston tube. This is then used to measure the SSD in various aspect ratios in the rectangular channel. To investigate the shear stress percentage, 10 data series with a total of 112 different data for were used. The results of the sensitivity analysis show that the most influential parameter for the SSD in smooth rectangular channel is the dimensionless parameter B/H, Where the transverse coordinate is B, and the flow depth is H. With the parameters (b/B), (B/H) for the bed and (z/H), (B/H) for the wall as inputs, the modeling of the GP was better than the other one. Based on the analysis, it can be concluded that the use of GP and ANFIS algorithms is more effective in estimating shear stress in smooth rectangular channels than the Tsallis entropy-based equations.

Interaction between a spatially growing turbulent boundary layer and embedded streamwise vortices

1996 ◽  
Vol 326 ◽  
pp. 151-179 ◽  
Author(s):  
Junhui Liu ◽  
Ugo Piomelli ◽  
Philippe R. Spalart
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Vortex Core ◽  
Eddy Viscosity ◽  
Shear Stresses ◽  
Streamwise Vortices ◽  
Mean Velocity ◽  
Production Term

The interaction between a zero-pressure-gradient turbulent boundary layer and a pair of strong, common-flow-down, streamwise vortices with a sizeable velocity deficit is studied by large-eddy simulation. The subgrid-scale stresses are modelled by a localized dynamic eddy-viscosity model. The results agree well with experimental data. The vortices drastically distort the boundary layer, and produce large spanwise variations of the skin friction. The Reynolds stresses are highly three-dimensional. High levels of kinetic energy are found both in the upwash region and in the vortex core. The two secondary shear stresses are significant in the vortex region, with magnitudes comparable to the primary one. Turbulent transport from the immediate upwash region is partly responsible for the high levels of turbulent kinetic energy in the vortex core; its effect on the primary stress 〈u′v′〉 is less significant. The mean velocity gradients play an important role in the generation of 〈u′v′〉 in all regions, while they are negligible in the generation of turbulent kinetic energy in the vortex core. The pressure-strain correlations are generally of opposite sign to the production terms except in the vortex core, where they have the same sign as the production term in the budget of 〈u′v′〉. The results highlight the limitations of the eddy-viscosity assumption (in a Reynolds-averaged context) for flows of this type, as well as the excessive diffusion predicted by typical turbulence models.

scholarly journals Paleotsunami Inundation of a Beach Ridge Plain: Cobble Ridge Overtopping and Interridge Valley Flooding in Seaside, Oregon, USA

2010 ◽  
Vol 2010 ◽  
pp. 1-22 ◽  
Author(s):  
Curt D. Peterson ◽  
Harry M. Jol ◽  
Tom Horning ◽  
Kenneth M. Cruikshank
Keyword(s):  
Shear Stresses ◽  
Before Present ◽  
Beach Ridge ◽  
Beach Ridges ◽  
Cobble Beach ◽  
Bed Shear Stresses ◽  
Beach Plain

The Seaside beach ridge plain was inundated by six paleotsunamis during the last ~2500 years. Large runups (adjusted >10 m in height) overtopped seawardmost cobble beach ridges (7 m elevation) at ~1.3 and ~2.6 ka before present. Smaller paleotsunami (6–8 m in height) likely entered the beach plain interior (4-5 m elevation) through the paleo-Necanicum bay mouth. The AD 1700 Cascadia paleotsunami had a modest runup (6-7 m height), yet it locally inundated to 1.5 km landward distance. Bed shear stresses (100–3,300 dyne cm−2) are estimated for paleotsunami surges (0.5–2 m depths) that flowed down slopes (0.002–0.017 gradient) on the landward side of the cobble beach ridges. Critical entrainment shear stresses of 1,130–1,260 dyne cm−2 were needed to dislodge the largest clasts (26–32 cm diameter) in paleotsunami coulees that were cut (100–200 m width) into the landward side of the cobble ridges.

scholarly journals Investigation of bed shear stresses subject to external turbulence

2003 ◽  
Vol 24 (6) ◽  
pp. 816-824 ◽  
Author(s):  
Nian-Sheng Cheng ◽  
B.Mutlu Sumer ◽  
Jørgen Fredsøe
Keyword(s):  
Shear Stresses ◽  
External Turbulence ◽  
Bed Shear Stresses

Simulation Modeling and Theoretical Analysis in Sociology

1995 ◽  
Vol 38 (4) ◽  
pp. 457-462 ◽  
Author(s):  
Robert A. Hanneman
Keyword(s):  
Mathematical Modeling ◽  
Simulation Modeling ◽  
Simulation Analysis ◽  
Full Range ◽  
Simulation Models ◽  
Special Issue ◽  
Simulation Experiments ◽  
Scientific Disciplines ◽  
Causal Laws ◽  
Over Time

The use of computer simulation experiments as a tool for working with theories is not as widespread in sociology as it is in most scientific disciplines. This brief article explains how modeling is a distinctive activity from either “theory” or “empirical analysis” but how it informs both and connects them. Simulation models are artificial objects created to translate theoretical generalizations into specific scenarios involving states (variables and/or actors) and rates (the dynamic causal laws hypothesized to generate change over time in the states). Simulation models are analyzed to understand the full range of implications of theoretical statements as they apply to producing historical realizations under particular circumstances. Simulation analysis operates by a method of experimentation, unlike mathematical modeling and statistical modeling. The strengths and limitations of these three approaches to studying models are discussed, and suggested to be complementary rather than competitive with each other. Last, this article briefly points out some of the unique features of the exemplars that compose the remainder of this special issue of Sociological Perspectives.

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