logo

Open channel flow characteristics (pdf)

   

Added on  2021-04-21

5 Pages1247 Words85 Views
OPEN CHANNEL FLOW CHARACTERISTICS INTRODUCTION The scenario In this case, I consider the following given scenario where a trapezoidal channel is considered such that it gets watered by a river and meanders through to the downstream. Along the channel, there are physical characteristics such as roughness of the bed and its slopes. The channel seems to be clean in the upstream section but it gets rough as it approaches its downstream end hence Manning’s equation of surface roughness is considered. Additionally, due to the bends along thechannel, the profile (which is to be determined) will be affected and that will have to be accommodated. Meanwhile, the roughness results from the vegetative growth more prevalent at the downstream end. Otherwise, the other sections of the river are all free of vegetation. Notably,for the given scenario, the following shall be undertaken: (A)Deriving a program in excel to calculate gradually-varied flow profiles along this canal for a steady flow rate of 14.5 m3 /s at the downstream control. (B)Determining the profile that would occur for each of the three downstream hydraulic control conditions that are under consideration for this canal: (1) A free over fall into a drain at the downstream end of the canal reach(2) Free flow over a rectangular sharp-crested weir at the downstream end of the canal reach, having a crest length of 7 m and a crest elevation at 1.5 m above the canal bed ("Sharp Crested Iir 2")(3)Free flow under a 3.5-m-wide vertical sluice gate with the gate set at 0.95 m above the canal bed at the downstream end of the canal reach Furthermore, in consideration of the cross-section for a given length of the channel, the profile will be broken down into those sections hence the following is considered: (1)The 20-m spacing between cross sections for the first 500 m upstream from the downstream control(2) 50-m spacing for the next 1000 m upstream, and (3)100-m spacing for the last 4500 m upstream. Therefore, from the above-given scenario, I present the following as the requirements: (1) Step by step procedure used in arriving at the final results. Hence the following output parameters are provided in the program: y, A, R, u, H, Sf, and Fr (Jfccivilengineer No “page”). (2)A plot of the profiles for the three cases. (3)A comparison of the three computed profiles (4)Discussion of the results and explanation for the same

Notably, the aim of the above-given case is to establish flow profiles for all the given case conditions by considering normal depth only Yn()CALCULATION Procedure DescriptionFirstly, I assume the flow is constant along the channel hence the following governing equation (based on energy and mass conservation) to describe the various profiles given the conditions(Defina, and Bixio No “page”): The following equations will come in handy for the given parameters: (i)H= Z+Y+αU2/2g(ii)Sf= n2U2/R4/3(iii)OHe= Cb(αU2/2g)(iv)H’ = H+average Sf+0’He(v)Fr= Q/A2g(vi)U= qX where X is the distance between cross section i and i+1(vii)A= by +my21st Condition: Consider the rectangular weir But first, I must establish an iterative formula for determining the normal depth and this is given as (best on specific energy): Y= (nQ/bs0.5)3/5x(1+2h/b)2/5...(i)Hence substituting appropriately I end up with this iterative formula : Yn= y0(1+2yo/b)2/5.....(ii)Equation (ii) will therefore be used in generating the various values of yWith an increment of h= (2.7987-1.8128)= 0.9859/90=0.0109542nd Condition: Consider the free overfall Where the flow is assumed critical hence Fr= 1.0And the parameters are determined accordingly

End of preview

Want to access all the pages? Upload your documents or become a member.

Related Documents
3-D Floodway Design Methodology Presentation
|18
|1105
|245