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ALDENSolving Flow Problems Since 1894
Better Spillway Designs Through Computational Modeling
Alden Webinar Series
April 30, 2009
For audio, please dial 1 (866) 809-5996, participant code 6504656
ALDENSolving Flow Problems Since 1894
Housekeeping
• Questions and Audio
• Availability of slides and recording
• Q&A period
For audio, please dial 1 (866) 809-5996, participant code 6504656
ALDENSolving Flow Problems Since 1894
Agenda
• Spillway Safety– Mario Finnis, MWH Americas
• ANSYS Fluid Mechanics Tools– Marc Horner, ANSYS, Inc.
• FLOW-3D in the Design of Hydraulic Structures– David Souders, Flow Science, Inc.
• Using CFD for Spillway Analysis– Dan Gessler, Alden
For audio, please dial 1 (866) 809-5996, participant code 6504656
ALDENSolving Flow Problems Since 1894
MWH is committed to helping create a
sustainable future for this planet.
MWH: The Wet Infrastructure Leader
Business
Solutions
Consulting
Energy and
HydropowerEnvironmental
Management
Dams and
Water
Resources
Water
Treatment and
Distribution
Wastewater
Collection and
Treatment
Industrial and
Hazardous
Waste
Environmental,
Health and
Safety
Pollution
Control
•Complete business solutions in
Water, Energy and the
Environment.
•Over 7,000 people in 197
offices in 38 countries.
•Building Better World by
providing innovative, resource-
effective solutions to municipal,
government, utility, industrial,
and private clients worldwide
www.mwhglobal.com ; [email protected]; Tel: 312-831-3230
ALDENSolving Flow Problems Since 1894
Spillway SafetyOne Part of an Effective Dam Safety Program
•Design and Analysis• Spillway Adequacy
• Stability/Stress Analysis
• Seismic Design
• Foundation Analysis
•Inspection and Evaluation
•Performance Monitoring
•Maintenance
•Preparedness•Emergency Action Plans
•Public Safety Plans
ALDENSolving Flow Problems Since 1894
NATIONAL DAM SAFETY PROGRAMPublic Law 92-367NOTABLE U.S. DAM FAILURES
Year Name Location Deaths Damages
1972 BuffaloCreek
West Virginia 125 $400 million
1972 Canyon Lake South Dakota 139 $60 million
1976 Teton Idaho 11 $1,000 million
1977 Laurel Run Pennsylvania 40 $5 million
2005 Taum Sauk Missouri 0 $180 million settlement
Laurel Run
Taum Sauk
ALDENSolving Flow Problems Since 1894
Modes of Failure
• Overtopping (34%)
• Foundations (30%)
• Seepage and Piping (28%)
• Other (8%)
– Earthquakes
– Cracking
– Sliding
ALDENSolving Flow Problems Since 1894
An Issue for Years to Come
• More than 94,000 dams in the U.S.
• Over 50 Dam Failures per Year With Total Loss of Life in Thousands
• Most Failures Occur at Dams Under 75 Feet in Height
• Estimated Costs of Failures Exceed $1 Billion US Each Year Globally
• Over the next 20 years, 85% of dams in the U.S. will turn 50 years old
ALDENSolving Flow Problems Since 1894
Relevant Regulations
• Numerous Regulatory Agencies
– Corps of Engineers
– Bureau of Reclamation
– Tennessee Valley Authority
– Federal Energy Regulatory Commission
– Federal Emergency Management Agency
– State Dam Safety Agencies
ALDENSolving Flow Problems Since 1894
Spillway Adequacy
• Components of Spillway Adequacy need to be addressed:
– Spillway Design Flood Criteria
– Calculation of Design Flood (PMF) Hydrograph
– Routing of Flood Hydrograph
ALDENSolving Flow Problems Since 1894
• Early Days -•Before 1900 – Estimates of Past Peak Discharge on Stream x Multiple (e.g. 2)•Prior to 1940 – Regional Flood Equations (e.g. Creager). Start of Statistical Analysis (100-year Flood, or 10,000-yr flood (Institution of Civil Engineers)•Phase I Program by U.S. Army Corps of Engineers (1977 to 1981) based on Recommended Guidelines for Safety Inspection of Dams, ER-1110-2-106 c.1979). Empirical method using size and hazard classification.
•Recent/Current – PMP based, PMF or Selection Using Inflow Design Flood •Evolving toward Risk Based – First suggested in earnest in 1973 by ASCE Committee
History of Spillway Design Flood Criteria
ALDENSolving Flow Problems Since 1894
Changes in Spillway Design Flood• Urbanization and Development
• Downstream Development Changes Hazard Classification or Changes IDF
• Changes in Watershed
increases runoff
• Additional Data Changes Flood
Frequency Analysis
(100 yr or 10,000 yr return)
ALDENSolving Flow Problems Since 1894
Changes in Spillway Design Flood
• Changes in Calculating PMP • 1956 - HMR 33• 1978 - HMR 51• 1982 - HMR 52• 1980 - HMR 53• 1986 - HMR 56• 1993 - HUG/EPRI (MI/WI)
• Future: More Intense,Extreme Events?(Global Warming?)
ALDENSolving Flow Problems Since 1894
Spillway Remediation
– New Auxiliary Spillways
– Expanded Spillways
– Raise Dam Crest/Reservoir Rim
– Operational Changes (drawdown)
– Lower Spillway Crests
– Overtopping Protection (RCC, Articulated Blocks)
ALDENSolving Flow Problems Since 1894
Why CFD Modeling• Computer power and software have reduced cost and increased
speed, allowing programs to solve difficult problems that previously would have required physical models.
• Build ‘virtual prototypes’ and apply real world physics to predict behavior
• Develop deeper insight to test a system that is normally too costly or time consuming through physical models
• Predict behavior under different ‘what if’ conditions.
• Design better and faster.
ALDENSolving Flow Problems Since 1894
CFD Modelling
ALDENSolving Flow Problems Since 1894
ANSYS CFD Solutions forSpillway Modeling
Marc Horner, Ph.D.
Lead Technical Services Engineer
ANSYS, Inc.
ALDENSolving Flow Problems Since 1894
ANSYS in the Environmental and Hydro-Electric Industries
spillways(courtesy Ingeciber)
draft tubes(courtesy Alden)
(courtesy Alden and MWH Americas)vortex rope phenomenon
(courtesy GE Energy)
turbines
ALDENSolving Flow Problems Since 1894
Outline• About ANSYS, Inc.
• Overview of computational modeling for spillways
– Set-up and solution process
– Free surface modeling
– Post-processing
• Conclude
ANSYS, Inc.
• World’s leading provider of
engineering simulation software
and services
• More than 13,000 customers
• More than 200,000 commercial
seats
© 2007 ANSYS, Inc. All rights reserved. 20 ANSYS, Inc. Proprietary
• Single-minded focus on simulation
• Financially strong and stable
• Nearly 40 years of experience
• Annual investment in R&D
greater than most CAE
companies’ revenues
ALDENSolving Flow Problems Since 1894
Fluids
FLUENT
ANSYS CFX
ANSYS Icepak
ANSYS Airpak
FloWizard
More…
Fluids
ANSYS Icepak
ANSYS Airpak
FloWizard
More…
Fluids
Depth and Breadth of Products
Conduction
Convection
Radiation
Phase Change
Mass Transport
More…
ThermalTe
ch
nic
al D
ep
th
Steady-State, Transient, Harmonic & Modal
Linear & Nonlinear
Technical Breadth
Quasi static (Low Freq)
Full Wave (High Freq)
Eddy current
Transient with motion
Circuit Coupling
More…
ElectromagneticsStructural
Large Displacements
Finite Strain
Contact
Multibody Dynamics
Random Vibration
Implicit & Explicit
More…
Tet/Prism
Hex/Hex Core
Structured
Unstructured
Multi-zone
Body-fitted Cartesian
Patch Independent
More…
Meshing
ICEM/CFD
AI*Environment
GAMBIT
TGridCFX-Mesh
Meshing
DesignModeler
TurboGrid
Structural
ANSYS Mechanical
ANSYS Professional
ANSYS Structural
ANSYS Rigid Dynamics
ANSYS DesignSpace
ANSYS Autodyn
ANSYS LS-DYNA
More…
Ansoft HFSS
Ansoft Maxwell
ANSYS Emag
Ansoft Designer/Nexxim
Ansoft Siwave
More…
Electromagnetics
ANSYS TAS
…as well as the
Structural and Fluids
products
Thermal
FLUENT
ANSYS CFX
ALDENSolving Flow Problems Since 1894
• Analysis begins with a mathematical model of a physical problem.
– Conservation of mass, momentum, and energy must be satisfied throughout the region of interest.
– Engineering assumptions are made to simulate the real process
– Modeling requires material properties and appropriate boundary and initial conditions for the problem.
Spillway geometry
The CFD Process - Geometry
(courtesy Ingeciber)
ALDENSolving Flow Problems Since 1894
• The domain is broken up into a collection of cells, called the grid or mesh.
• CFD then utilizes numerical methods (called discretization) to develop algebraic equations that approximate the governing differential equations of fluid mechanics in the domain to be studied.
• The system of algebraic equations is solved numerically for the flow field variables in each computational cell.
Meshing
ALDENSolving Flow Problems Since 1894
The Volume of Fluid Model• A spillway model requires the presence of a free surface,
representing the air-water interface.• The Volume of Fluid (VOF) model is one such approach for
accurately tracking the interface between immiscible liquids.
t = 0.1 s t = 0.4 st = 0.3 st = 0.2 s t = 0.5 s
ALDENSolving Flow Problems Since 1894
• The final solution is then post-processed to extract quantities of interest,
e.g. speed, pressure, fluid elevation, streamlines, etc.
Post-processing
ALDENSolving Flow Problems Since 1894
Post-processing (cont’d)• The final solution is then post-processed to extract quantities of interest,
e.g. speed, pressure, fluid elevation, streamlines, etc.
ALDENSolving Flow Problems Since 1894
Post-processing (cont’d)• The final solution is then post-processed to extract quantities of interest,
e.g. speed, pressure, fluid elevation, streamlines, etc.
ALDENSolving Flow Problems Since 1894
Post-processing (cont’d)• The final solution is then post-processed to extract quantities of interest,
e.g. speed, pressure, fluid elevation, streamlines, etc.
ALDENSolving Flow Problems Since 1894
Closing Remarks
• ANSYS offers a comprehensive and accurate suite of CFD (and even mechanical and electromagnetic) modeling solutions.
• These solutions are widely used in the environmental and hydro-electric industries to model flows with free surfaces, rotating machinery, etc.
• ANSYS has expertise and a focus on the needs of these industries.
THANK YOU!For further information, contact: [email protected]
ALDENSolving Flow Problems Since 1894
Utilizing FLOW-3D in the Design of Hydraulic Structures
• What is CFD• How Hydraulics Structures
can be Optimized• Time and Accuracy
• Meshing• Free Surface Modeling
• Advanced Models• General Moving Object• Multi-physics
• Post Processing
ALDENSolving Flow Problems Since 1894
What is Computational Fluid Dynamics (CFD)
• Predict behavior of a real processes
• Numerically solve equations governing the physics
• CFD provides a virtual laboratory to test ideas
• Ultimate Goal: make better products, faster, cheaper
ALDENSolving Flow Problems Since 1894
Question: How can we
represent a complex
geometry such as this in a
rectangular grid?
FLOW-3D’s Numerical Approach
ALDENSolving Flow Problems Since 1894
How Can Hydraulic Structures be Optimized
Fish passages• Analyze critical components in the design of
hydraulic structures• Capture complex flow characteristics • Obtain velocity information, making it possible to
make changes to the fish ladder’s design• Visualize the distribution of flow, water surface
elevations and velocities in the ladder
Dam and Spillway safety and Performance• Simulate multitude of configurations to best
determine flow of spillways, stilling basins and energy dissipaters
• Determine flow rates at Probable Maximum Flood conditions
• Find regions of cavitation and pressure loading on gates.
ALDENSolving Flow Problems Since 1894
Meshing
• Import geometry
• Overlay mesh blocks
• Preprocessor does the rest
ALDENSolving Flow Problems Since 1894
• Fractional Area / Volume Ratios
• Integrated into conservation equations
• Advantages
– Easy mesh generation
– Independent geometry specification
Quantities stored:
• Area fractions at cell faces
• Volume fraction for each cell
• Heat Transfer Area
z
CwA
y
CvA
x
CuA
t
C
Vz
Cw
y
Cv
x
Cu
t
Czyx
f
1
• Integrated into conservation equations
VF open volume
volume of cell
AF open area
cell edge area
Conference Name EDIT in View>Slide Master / Insert > Header & Footer / Apply All
Realistic Geometry using FAVOR™
ALDENSolving Flow Problems Since 1894
Free Surface Modeling with TruVOF
What is a “free surface”?
• liquid/gas interface;
- pressure gradients and shear forces in gas are negligible;
- usually applicable when density ratio is large, e.g. ~ 1000:1 as for
water and air;
Modeling approach:
- gas flow is ignored;
- gas only applies a normal force and is, therefore, replaced with a
pressure boundary condition at liquid free surface.
ALDENSolving Flow Problems Since 1894
Validation of TruVOFTM
Numeric versus experimental data for water overflow.
Quantity Exp. Cal.
Pool depth, h1/H 0.41 0.4
Outflow depth, h2/H 0.094 0.092
Pool length, L/H 1.0 1.0
Nappe angle, a 57 52
Energy loss, (E1-E2)/E1 0.29 0.284
Data: N. Rajaratnam and M.R. Chamani, J. Hydraulic Res. 33, p.373, (1995)
•a
•E1•E1
•H•h2•h1
•L
•a
Overflow Test
•E1
ALDENSolving Flow Problems Since 1894
General Moving Object
ALDENSolving Flow Problems Since 1894
Extensive Physical ModelsFluid Dynamics
• Free-surface flows
• Sediment scour
• Air entrainment with bulking effects
• Flow rate boundaries
• Wave boundaries
• Density variation
• Phase change
• Particles – mass and marker
Solid-Mechanics
• Fluid/solid coupling
• Solid/solid collisions
Wave BoundariesSediment Scour Air Entrainment
ALDENSolving Flow Problems Since 1894
Data Output Focused on Hydraulics
• Filling time
• Residence time
• Fluid elevation
• Fluid depth
• Distance traveled by Fluid
• Vorticity
ALDENSolving Flow Problems Since 1894
Thank You
To schedule a demo of the FLOW-3Dsoftware interface and its capabilities please contact:
David [email protected]
Phone: (505) 982–0088Web: www.flow3d.com
ALDENSolving Flow Problems Since 1894
About Alden
• Oldest operating hydraulics lab in US
– 5 Areas of specialization, including hydraulics
• Calibration
• Environmental Services
• Air and Gas Flow Modeling
• Field Services
• Hydraulics
ALDENSolving Flow Problems Since 1894
About Alden
• Hydraulics
– Dams and Spillways
• Physical Modeling
• Numeric Modeling
ALDENSolving Flow Problems Since 1894
Numeric Modeling of Spillways
• New Structures
– Likely validated with physical model
• Existing Structures
– Changes in the design basis flow
– Changes to the structure
– Forensic (structure did not perform as expected)
– Validate with prototype data or physical model
ALDENSolving Flow Problems Since 1894
Why Use Numeric Models
• Typically less expensive than physical
• Screening tool to reduce physical runs
• Requires less time to complete than physical
• Consider more alternatives than physical
• Velocity and shear stress in stilling basin
• Aspects of flow field that are hard to evaluate with physical models
ALDENSolving Flow Problems Since 1894
Results
• Stage vs discharge rating curve
• Pressure distributions (cavitation index)
• 3D Velocity field
• Standing waves
• Air entrainment characteristics
• Hydraulic jumps
ALDENSolving Flow Problems Since 1894
Need for Validation
• Typ. CFD compares favorable to physical data
• Hydraulic jump location hard to predict
• Stilling basin flows are very turbulent
• Time dependent aspects of problem
• High hazard structures
ALDENSolving Flow Problems Since 1894
Example 1
• Canton Dam
– Used CFD to test various approach channel layouts
– Final design was tested in physical model
– Saved cost by reducing number of modifications to physical model
ALDENSolving Flow Problems Since 1894
ALDENSolving Flow Problems Since 1894
ALDENSolving Flow Problems Since 1894
ALDENSolving Flow Problems Since 1894
Example 2
• Flip Bucket Simulation
– Used CFD to evaluate spillway performance at flows greater than design event
– Validated with results from pre construction physical model study
– Saved cost by eliminating need for physical model
– Approach and results were accepted by FERC
ALDENSolving Flow Problems Since 1894
Velocity (ft/s)
80
60
40
20
0
Velocity (ft/s)
80
60
40
20
0
ALDENSolving Flow Problems Since 1894
ALDENSolving Flow Problems Since 18945/4/2009 54
Elev. 685 ft
Elev. 662 ft
Elev. 685 ft
Elev. 662 ft
ALDENSolving Flow Problems Since 1894
Stage Discharge Rating Curves
Smith Mountain Dam
794
796
798
800
802
804
806
808
810
812
814
0 10 20 30 40 50 60
Discharge Capacity of 2 Spillways (cfs x 1e4)
Re
serv
oir
Wa
ter
Le
ve
l (f
t)
Laboratory Results
CFD Results
Lab Results corrected for scaling
Corrected curve plus 5 percent
Note:The spillway rating curve on sheet G-165374, based on model test results 5/20/1960 was estimated by Alden
Research Laboratory to under predict the discharge by approximately 3% for a given pool elevation.
Stage vs Discharge Rating Curves
Discharge Through 2 Spillways (x 1000 cfs)
Reserv
oir W
ate
r Level (f
t)
10 20 30 40 50 600
794
814
796
798
800
802
804
806
808
810
812
ALDENSolving Flow Problems Since 1894
Example 3
• Effect of flows greater than design flows
– Validated CFD against Design of Small Dams
– Compute pressure on spillway surface for off design flow
– Demonstrate with readily validated standard ogee spillway
– Can be applied to non standard designs
ALDENSolving Flow Problems Since 1894
Ogee Spillway
ALDENSolving Flow Problems Since 1894
Example 3
• Discharge computed by (Design of Small Dams)
• Design flow is 124 cfs/ft
• CFD computed flow is 123 cfs/ft
• Within 1%
ALDENSolving Flow Problems Since 1894
Example 3
• How does pressure distribution vary with flow
Pressure tap
ALDENSolving Flow Problems Since 1894
Example 3
-20
-15
-10
-5
0
5
10
15
20
60 80 100 120 140 160
Pre
ssu
re (
ft o
f w
ater
)
Flow (cfs/ft)
Pressure as a Function of Discharge
Design Flow
Slightly positive pressure
at design flow
ALDENSolving Flow Problems Since 1894
Example 3
• This example shows what we can do with CFD using an easily validated model.
• For non standard designs, CFD becomes a major resource if flow or physical properties of a structure are changed.
• Can also evaluate free board considerations.
ALDENSolving Flow Problems Since 1894
Summary
• Showed three examples of how we use CFD in spillway applications
• There are additional uses of CFD that have not been presented
• Important to consider validation
ALDENSolving Flow Problems Since 1894
Webinar Summary
• Spillway Safety– Mario Finnis, MWH Americas
• ANSYS Fluid Mechanics Tools– Marc Horner, ANSYS, Inc.
• FLOW-3D – David Souders, Flow Science, Inc.
• Using CFD for Spillway Analysis– Dan Gessler, Alden
ALDENSolving Flow Problems Since 1894
QuestionsPlease use the Q&A tab in
LiveMeeting
Mario Finnis: [email protected]
Marc Horner: [email protected]
David Souders: [email protected]
Dan Gessler: [email protected]