Presentation on theme: "Current Research Experimental and numerical modeling of flow in a levee breach Experiments and simulation of sandbag motion at a levee breach Measurement."— Presentation transcript:
Current Research Experimental and numerical modeling of flow in a levee breach Experiments and simulation of sandbag motion at a levee breach Measurement and simulation of dam break flows Experimental study of erosion due to levee overtopping
Graduate students: S. Yusuf, M. Elkholy, C. Riahi-Nezhad, L. Larocque, J. Feliciano, L. Alva-Solari
Experimental and numerical modeling of flow in a levee breach
Objectives To obtain detailed 3-D flow field from measurements in a model levee breach To measure flow field around submerged structures To simulate complex 3-D flow field in a levee breach and a flooded urban area using the VOF model
Breach Dimensions 465 ft 200 ft 45 ft S W N E Source: IPET Report 2, https://ipet.wes.army.milhttps://ipet.wes.army.mil
Flow Model Scale 1:50 Aerial View of the Physical Model
Sampling rate (HZ) …………………..……. 0.1 to 50 Sampling Volume (CC) ………………..…. 0.09 Dist. To sampling volume (cm) ……….. 5 Resolution (cm/s) ….………………………. 0.01 Prog. Velocity range (cm/s) ………..….. 3, 10, 30, 100, 250 Accuracy ………………………………………… 1% of measured velocity, 0.25 cm/s Maximum depth (m) ………………………. 60 ADV Source: http://www.sontek.com/download/brochure/adv.pdf Velocity measured using 16 MHZ SonTek MicroADV
UVP An Ultrasonic Velocity Profiler (UVP) transducer transmits a short emission of ultrasound, which travels along the measurement axis. When the ultrasonic pulse hits a small particle in the liquid, part of it scatters on the particle and echoes back. Figure 1: This diagram explains the process of data collection by the UVP. The UVP is placed at an angle and reflection of the particles and from the bottom creates a velocity profile.
Breach Geometry in Gambit 2.4.6 Inlet (Blue) Outlet (Red) Houses (solid Blocks) Arrows shows the direction of flow
Mathematical Model General Ansys Fluent 6.3.26 used for modeling of levee breach flows Solver: Pressure based Multiphase model: VOF (Implicit scheme) Turbulence model: k-epsilon Grid specification Boundary layer : meshed at the bottom of the channel Grid: hexahedral with size = 2 cm
Ongoing and Future Research Flow measurements around model buildings using UVP Comparison of computed and measured velocity distributions Characterization of turbulence over irregular topography Inclusion of erosion and deposition of channel bottom and sides
Methods for the closure of 17 th Street Levee Breach
Tracking Sand Bag Motion in a Levee Breach using DPTV Technique
Developing a visual technique for tracking the motion of the sand bags and plotting their trajectories. Determining the three-dimensional velocity components of the sand bags. Formulating relationships between the sand bag size and shape and flow parameters. Determining optimum sand bag size, and more efficient procedures for levee closure.
Trials for breach closure Source: http://www.usace.army.mil/katrina-images/NO-A-09-04-05_0072.jpg
Recording device SpecificationGRAS-03K2M/C Maximum resolution640(H) x 480(v) Pixel size 7.4 m x 7.4 m Maximum Frame rate200 Fps Shutter speed0.02 ms to 10s Transfer rate100 Mbit/s Area covered at distance of 1.0 m 370 x 270 mm 2 Angle of view221627
The Model Sand bags Plan view Elevation 14.525.436.354.4108.8 21.826.329.633.942.8 4,0007,00010,00015,00030,000 Weight (gm) Equivalent Dia. (mm) Equivalent prototype weight (Ib) 1:50
3-D Stereoscopic System Image Plane Lens Plane Water surface Camera-axis 2 f d z x dz dx o a a1o1o2a2 x1x1 x2x2 x1x1 x2x2 S Camera-axis 1
Centroiding Testing of extraction of sandbag in stationary flow After Extraction
x x x U/S Levee D/S Levee Bed Elevation Contour Map for the Katrina Model Ditch x x Canal 9.70 – 16.1 16.1 – 19.1 19.1 – 22.3 22.3 – 25.7 cm Datum: Top of the U/S levee 12345
Trajectories of 10,000 Ib sandbag at different locations (Plan view) 1 2 4 3 5
Trajectories of 10,000 Ib sandbag (vertical direction) Time (sec) Location (3) Time (sec) Location (1)
Ongoing and Future Research Understanding the general mechanics of sand bag motion. Formulating relationships between the sand bag size and shape and flow parameters. Determining the optimum size of sand bags and procedures for levee breach closure.
Experimental and Numerical Investigations of Dam-Break Flows
To measure the instantaneous velocity over time for a dam break experiment. using an Ultrasonic Velocity Profiler (UVP) To conduct LES simulation of a dam break wave. To compare the measured and simulated flow field Figure: Experimental dam break set up. Notice the left hand side of the dam is filled with water up to 25 cm.
Flume: 7.67 m long, 25 cm deep, 18 cm wide, and 3.5% slope. UVP placed at 45 deg. (schematics shown below). UVP start measuring velocity as dam is lifted Experimental Set up UVP Probe UVP probe facing upward to determine water level over time UVP Probe UVP probe facing downward to find the velocity profile at the bottom of a dam break wave Experiment 1 Experiment 2
A numerical grid with two separate volumes (water and air) was generated using Gambit, a grid generating program. The numerical simulation was conducted using FLUENT. Large Eddy Simulation (LES) and Volume of fluid (VOF) models were used. Numerical Set-up The grid used in the numerical simulation. The blue grid indicates the water and the other portion is the air at the initial location. Volume: WATER Volume: AIR
Experimental Results The UVP continuously measures the velocity over time and generates a velocity profile at a specified time step. Multiple trials were conducted to compare the repeatability of the experiment. This graph shows the velocity profile measured using a UVP. The two lines represent two separate trials of the experiment. T=1.0s
Comparison A comparison between the numerical simulation and the experiment velocity profile on the upstream side of the dam break
Additional measurements throughout the model Experimental measurements of flow field including erosion and deposition following dam failure. Simulation of flow field following dam failure including erosion and deposition of bottom material Ongoing and Future Research
Objectives To understand and identify the parameters that govern the erosion and headcut formation during the overtopping of a levee. To conduct laboratory experiments overtopping small-scale dikes in a flume. To collect and evaluate the data and improve/modify breach models.
Dike and Flume Dimensions DIKE DIMENSIONS Height0.22 m Top0.09 m Side slope2H:1V FLUME DIMENSIONS Length6.5 m Width0.46 m Height0.26 m
MaterialD50 Specific Gravity LLPL Sand 30400 μm2.69 --- Kaolin0.6 μm2.5981.1%33.6% Silt 10622 μm2.65 --- Silt 25049 μm2.65 --- Material
Compaction DATA Weight of the roll 20.5 Kg Soil Layer Thickness 0.05 m No Passes per Layer 10, 15, 18 Compaction obtained 80% to 95% of γ d
Instrumentation DescriptionQuantity Water level gauge downstream01 Water level gauge upstream01 Video cameras04 UVP sensor for velocity measurement (being implemented) 04 Data acquisition (being implemented)01 Weir01 Timer01
Instrumentation UVP Sensor Upstream UVP Sensor Downstream Top Video Camera Front Video Camera Video Camera Data Acquisition
Levee Breach Experiments 1, 2 & 3 1 2 3 EROSION ON THE DOWN STREAM FACE OF THE DIKE HEADCUT UNDERMINING RESERVOIR FLOW MAIN ELEMENTS OF THE PROCESS: - SOIL PROPERTIES - GEOMETRY - FLOW CHARACTERISTICS
Headcut Experiment 4 FRONT VIEW TOP VIEW 0.02 m 1.5H:1V HEADCUT GEOMETRY
Ongoing and Future Work a.Systematically vary non-dimensional numbers involving soil properties, levee geometry and flow properties in experiments. b.Understand and evaluate the scale effect. c.Focus on the effect of cohesion on the breach process. d.Conduct experiments at larger scales.