CW V.134 Programme:BSc (Hons) Engineering (Civil) Top UpUnit Code/Title6HX509 Civil Engineering HydraulicsUnit Credits/ levelCredits 20 QCF LEVEL: 6Tutor:V.OkeInternal VerifierA.Janbey Academic year2020/2021IndividualGroupAssessmentNumberRetake Issue date: May 2020Submission deadline: TBAThe aim of this assignment is to demonstrate the students’ ability to produce a technical engineeringreport investigating steady fluid flow phenomena in open channels, using both laboratory experimentsand computer simulations. As such, the assignment comprises two components: Part A. It is concerned with laboratory investigation of two methods of measuring open channelflow and hydraulic jumps.o A.1. Crump weir [25 marks]o A.2. Broad crested weir [10 marks] Part B. It involves a computer model of gradually varied flow in an open channel (M2 backwaterprofile). [15 marks]Part AThis part investigates the phenomenon of rapidly varied steady flow in an open channel. This will bebased on a laboratory experiment comparing the measurement of flow using a crump weir with thatusing a broad crested weir, and will also investigate hydraulic jumps occurring downstream from thetwo weirs, and matching the experimental results obtained from those from theory. Estimates will also bemade of the loss of specific energy of the flow over the two weirs. The experimental procedures andrequired analyses are outlined below:A.1. Crump Weir[Total marks: 25]Experimental Procedure.1. Verify that the hydraulic bench unit (water tank and pump) has enough water and is connected tothe H23 flume water intake.2. Measure the channel dimensions (width and depth), and ensure that the slope (So) of the flume iscero (So=0%),INTERNAL VERIFICATIONAssignment Brief TemplateFORM D1CW V.1353. Install the crump weir at about 800mm downstream from the point at which the water leaves thestilling filter.4. Turn on the pump of the hydraulic bench, and adjust the flow to its maximum by opening thevalve. The water should not overflow from the channel.5. Obtain the depth of the flow at the following locations by using the depth gauge provided. Thedepth is the result of the difference of two readings: bottom bed and water surface.a. Some 100mm upstream of the weir (y1)b. At the lowest depth at the bottom of the weir (y2)c. Just before the jump (y3)d. After the jump where the water is in tranquil flow (y4)6. Estimate the length of the jump (L), i.e. the distance between y3 and y4.7. By using the Pitot tube measure the velocity head (if possible) at the same four locations,comment on any difficulties experienced.8. Measure the flow rate by using the volume gauges built into the hydraulic bench, and the stopwatch provided. It is suggested to record the time that takes to deliver 5 litres of water.Please note that the tank starts filling when the plug (rubber ball) is blocking the outlet.In order to reduce the uncertainty and improve the results, measure the flow rate at least 3 timesand obtain an average.Calculate the mean flow in m3s-19. Decrease the flow rate by closing slightly the valve and repeat the procedure from point 5. Verifythat the depth upstream of the weir decreases at least 5 mm. And repeat this procedure at least 5times more, every time with a different discharge.Calculation Procedurea- For the very first value of volumetric flow rate (?), calculate the critical depth (??) and critical energy(??).[2 marks]b- Using that value of volumetric flow rate per unit width (?), evaluate the specific energy for a range oftheoretical depths up to a maximum of 200 mm. Plot these values in a dimensionless form: ( ???) versus( ???). On the same curve, plot the values of the ?1 and ?2 calculated from the measured ?1 and ?2indimensionless form, for the same discharge. Explain how the graph has been generated and investigate the phenomenon of rapidlyvaried steady flow in an open channel along with the characteristics of a free hydraulicjump.[2 marks] Briefly list the equipment used.[1 mark ]CW V.136 Experimental set up.[1 mark ] Tabulated results.[2 marks] Raw measurement[in appendix] Fully annotated plots and description of it.[2 marks]c- Now using the whole 5 experimental results; calculate the ratio ?4/?3, and the Froude number (??)just before the jump in each case. Using this calculated??, calculate the theoretical value of ?4/?3. Plot?4/?3 against ?? for both experimental and theoretical results. For fully annotated plots anddescription of it, including equation for Froude number.[4 marks]d- Discuss your results, assessing their validity and reliability, comment on the accuracy and draw therelevant conclusions.[2marks] How valid the equations.[2 marks] What were the assumptions for the equations when derived, what human and lab errors werepresent, accuracy of instruments used etc.[2 marks] Draw conclusions.[2 marks] For wider implications.[1 mark]e- For each case, calculate the flow force across the gate, the head loss across the jump.[2 marks]A.2. Broad Crested WeirRepeat the procedures outlined in A.1 using the broad crested weir in the same position as the crumpweir was.[Total marks: 10]a. Calculate the loss of specific energy across each weir and through each hydraulic jump.[3 marks]b. Calculate the Drag Coefficient of the weir[3 marks]c. In your conclusion compare the performance of the two weirs as measuring systems for the flow inopen channels and discuss this with reference to published work on each weir.[2 marks]d. Suggest which weir would be used if you needed an accurate measure of irrigation water deliveredto an area or a large agricultural businessCW V.137[1 mark]e. Comment on the use of hydraulic jumps to reduce the energy in open channel flows.[1 mark]Part B. Gradually Varied Flow SimulationThis part requires you to produce a “simple computer model” (using EXCEL) to establish water levelprofiles in a proposed channel (delivery canal to a reservoir, terminating with a free outfall) using thedirect step method.[Total marks: 15]The channel, rectangular in cross-section, with a width b=0.050m, is required to carry a minimumdischarge (Q) of 0.001 m3/s. The channel has a bed slope,?0 = 0.0010, constructed at a minimumelevation of 1.0m above Ordnance Datum (OD) at the downstream end of the channel. The channel willbe lined with neat a cement surface, having a Manning’s friction factor, ? = 0.011.If the critical depth (ycr) is assumed at the outfall (x=0), obtain the minimum length that the channelneeds upstream to attain the normal depth (yn). Use the direct step method to determine the water levelprofile along the channel(backwater curve), assuming gradually varied flow. It is recommended to useΔy=0.001m.Plot this profile to scale. You will need to illustrate two calculations steps in your report, and then use aspreadsheet (e.g. MS Excel) to obtain the full flow profile.???? =?0 – ??1 – ?? ^2 ?????? = ?0 – ????=?2?2?4 3??? ?? =?√?ℎGVF Direct Step Method1. Identify the condition of the flow2. Identify the type of transition and subsequently the corresponding profile3. Identify the control depth, and determine if the calculations go upstream or downstream fromcontrol section, setting that point as chainage x=04. Assume a depth increment (Δy).5. Determine the geometrical characteristics of two consecutives cross sections (control depth andthe control depth with the increment): hydraulic area (A), wetted perimeter (P) and hydraulicradius (R)6. Determine the velocity (V2/2g) and the total energy head (E) of the section.7. Determine the friction slope (Sf): ?? = ?2?2?4 38. Calculate the energy head increment (ΔE) between consecutives sections.9. Find the mean friction slope value: ?? ???? = (?? ? + ?? ?+1)/210. Find the horizontal increment (Δx) from ????= ?0 – ?? ????11. Accumulate Δx as ? = ∑? ?=1 ???12. Determine the bed and water surface levels:CW V.138Bed level = OD + ? ?0Water surface level = Bed level + ?13. Repeat the process from step 5, until Sf mean=0 or until it changes its signalFill the table below with the results obtained from the procedure suggested above.h A=b*h P=b+2h R=A/P R^(4/3) V=Q/A v^2/2g E=h+y^2/2g Fr ΔE Sf = v^2 n^2 / R^1.33 Sfmean=(Sf i + Sf i+1)/2 S0 -Sf mean Δx x = Σ (Δx) BED Level Water Surface Levela) Description of how the spreadsheet was constructed[3 marks]b) Show two calculation steps[2 marks]c) The actual spreadsheet of the rectangular channel[4 marks]d) Plot the variation of the water surface and bed level with respect to the length, starting at theoutfall (x=0)[3 marks]e) Final answer on length[3 marks]END OF BRIEFCW V.139
