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Colorado State University

1. Siefken, Seth. Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs.

Degree: MS(M.S.), Civil and Environmental Engineering, 2019, Colorado State University

Rock vanes (also known as stream barbs) and bendway weirs are two types of transverse rock structures used to modify the flow field in river bends. This study examines the effectiveness of the two types of structures at reducing velocity along the outer bank of river bends to protect the bank from erosion. A numerical model using the commercially available FLOW-3D software was used to evaluate the effect of various rock vane and bendway weir configurations on the flow field through two river bends typical of the Middle Rio Grande. The model was calibrated and validated using data from a previous physical model study of rock vanes. 33 different rock vane configurations were tested in the numerical model to evaluate the effect of altering planform angle, crest slope, projected length, and structure spacing. In addition, 14 different bendway weir configurations were tested to provide a comparison of the relative performance of bendway weirs and rock vanes. The numerical modeling results indicate that rock vanes are more effective at reducing the velocity along the outer bank of a bend than bendway weirs. Modelling showed that the completely submerged crest of bendway weirs allows a substantial amount of flow to pass over the crest, limiting their effectiveness in reducing velocity along the bank. In contrast, rock vanes, with a sloped crest intersecting the waterline at the design flow rate, directed more flow around the tip of the structure rather than over the crest and were much more effective at reducing velocity along the bank. Based on the modeling results, it is recommended that bendway weirs not be installed for the purpose of erosion protection along riverbanks. The reduction in velocity along the bank produced by the various rock vane configurations varied considerably with the geometry of the configuration. Based on the results, the following conclusions are made regarding rock vane geometry: (1) Rock vanes should be installed at a planform angle between 45° and 90° to the river bank. (2) There exists an optimal projected length of rock vane, which lies in the neighborhood of 1/5 to 1/3 of the channel top-width. (3) Rock vanes with a 10% crest slope perform well, although decreasing the crest slope will decrease the velocity along the outer bank and vice versa. (4) Decreasing the spacing of rock vanes decreases the velocity along the outer bank, up to a limit. A design equation was developed to predict the velocity reduction along the bank of a river bend produced by a given configuration of rock vanes, based on the geometry of the rock vanes and the river channel. The equation provided good predictions for the range of configurations tested, having a coefficient of determination r2 = 0.83 and predicting the velocity reduction along the outer bank to within 15 percentage points for all of the tested configurations. Advisors/Committee Members: Ettema, Robert (advisor), Thornton, Christopher (committee member), McGrath, Daniel (committee member).

Subjects/Keywords: bendway weirs; erosion protection; stream barbs; computational fluid dynamics; bank stabilization; rock vanes

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Siefken, S. (2019). Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs. (Masters Thesis). Colorado State University. Retrieved from http://hdl.handle.net/10217/197259

Chicago Manual of Style (16th Edition):

Siefken, Seth. “Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs.” 2019. Masters Thesis, Colorado State University. Accessed April 16, 2021. http://hdl.handle.net/10217/197259.

MLA Handbook (7th Edition):

Siefken, Seth. “Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs.” 2019. Web. 16 Apr 2021.

Vancouver:

Siefken S. Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs. [Internet] [Masters thesis]. Colorado State University; 2019. [cited 2021 Apr 16]. Available from: http://hdl.handle.net/10217/197259.

Council of Science Editors:

Siefken S. Computational fluid dynamics models of Rio Grande bends fitted with rock vanes or bendway weirs. [Masters Thesis]. Colorado State University; 2019. Available from: http://hdl.handle.net/10217/197259

2. Kashyap, Shalini. A 3-D Numerical Study of Flow, Coherent Structures and Mechanisms Leading to Scour in a High Curvature 135° Channel Bend with and Without Submerged Groynes .

Degree: 2012, University of Ottawa

This thesis focused on investigating flow, coherent structures, and mechanisms leading to scour around a series of three submerged groynes in a high curvature (radius of curvature (R)/channel width (B)=1.5) channel bend using a Large Eddy Simulation Numerical (LES) model. Flow was investigated during both an initial and a later stage of scour. The results showed that the groynes appeared effective in keeping the main core of high streamwise velocity away from the outer bank wall in the region where they were installed, although high potential still existed for local scour around the groynes. During the initial stage of scour, horseshoe vortices (HVs) showed the greatest propensity to induce scour immediately upstream of the groyne tips. During the later stage of scour, the HV in front of the first upstream groyne (G1) induced very high mean pressure fluctuations on the outer bank wall. Scour was also of very great concern around the tip of G1 due to severe mean bed pressure fluctuations. Downstream of the groyne field, the presence of a counter-rotating outer bank cell was capable of endangering the stability of the outer bank. The second focus of this thesis was to investigate flow in a 135° channel bend using both Reynolds Averaged Navier Stokes (RANS) and LES numerical models. The RANS study examined the effects of curvature ratio (R/B), and aspect ratio (B/H, where H is the inlet flow depth), on secondary circulation strength, and bed shear stresses. The study revealed that a decrease in R/B was associated with an increase in secondary circulation strength and peak bed shear stress. A change in B/H also substantially affected cross stream circulation strength. The LES study was conducted in a 135° (R/B = 1.5) bend flume with a fixed bed corresponding to near equilibrium scour conditions, and the results were compared to a similar high curvature 193° bend numerical study. Inner bank vortices and shear layers were present in both cases although their characteristics were substantially different. Distributions of boundary friction velocities, and turbulence were also quite different for each case.

Subjects/Keywords: river erosion; submerged groynes; stream barbs; bend erosion; Large Eddy Simulation; Reynolds Averaged Navier Stokes Model; coherent structures; numerical modeling; bed hardening technique

…152 7.4.2. Streamwise Velocity Distribution and Cross-Stream Circulation Strength… …u/U) contours and 2-D streamlines are shown in frames a, b, e and f. Cross-stream… …R1C1.5H20DB. a) Bed shear stress magnitude, τM/0, and b) cross-stream bed shear stress… …stress magnitude, τM/0, and b) cross-stream bed shear stress divided by bed shear stress… …stress magnitude, τM/0, and b) cross-stream bed shear stress divided by bed shear stress… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Kashyap, S. (2012). A 3-D Numerical Study of Flow, Coherent Structures and Mechanisms Leading to Scour in a High Curvature 135° Channel Bend with and Without Submerged Groynes . (Thesis). University of Ottawa. Retrieved from http://hdl.handle.net/10393/23323

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Kashyap, Shalini. “A 3-D Numerical Study of Flow, Coherent Structures and Mechanisms Leading to Scour in a High Curvature 135° Channel Bend with and Without Submerged Groynes .” 2012. Thesis, University of Ottawa. Accessed April 16, 2021. http://hdl.handle.net/10393/23323.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Kashyap, Shalini. “A 3-D Numerical Study of Flow, Coherent Structures and Mechanisms Leading to Scour in a High Curvature 135° Channel Bend with and Without Submerged Groynes .” 2012. Web. 16 Apr 2021.

Vancouver:

Kashyap S. A 3-D Numerical Study of Flow, Coherent Structures and Mechanisms Leading to Scour in a High Curvature 135° Channel Bend with and Without Submerged Groynes . [Internet] [Thesis]. University of Ottawa; 2012. [cited 2021 Apr 16]. Available from: http://hdl.handle.net/10393/23323.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Kashyap S. A 3-D Numerical Study of Flow, Coherent Structures and Mechanisms Leading to Scour in a High Curvature 135° Channel Bend with and Without Submerged Groynes . [Thesis]. University of Ottawa; 2012. Available from: http://hdl.handle.net/10393/23323

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.