better spillway designs through computational modeling · pdf filebetter spillway designs...

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

http://www.mwhglobal.com/

http://www.ansys.com/default.asp

http://www.flow3d.com/


Housekeeping

• Questions and Audio

• Availability of slides and recording

• Q&A period







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







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mailto:[email protected]


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





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





Modes of Failure

• Overtopping (34%)

• Foundations (30%)

• Seepage and Piping (28%)

• Other (8%)

– Earthquakes

– Cracking

– Sliding





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





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





Spillway Adequacy

• Components of Spillway Adequacy need to be addressed:

– Spillway Design Flood Criteria

– Calculation of Design Flood (PMF) Hydrograph

– Routing of Flood Hydrograph





• 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





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)





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?)





Spillway Remediation

– New Auxiliary Spillways

– Expanded Spillways

– Raise Dam Crest/Reservoir Rim

– Operational Changes (drawdown)

– Lower Spillway Crests

– Overtopping Protection (RCC, Articulated Blocks)





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.





CFD Modelling





ANSYS CFD Solutions forSpillway Modeling

Marc Horner, Ph.D.

[email protected]

Lead Technical Services Engineer

ANSYS, Inc.





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






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


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






• 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)






• 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






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






• The final solution is then post-processed to extract quantities of interest,

e.g. speed, pressure, fluid elevation, streamlines, etc.

Post-processing






Post-processing (cont’d)• The final solution is then post-processed to extract quantities of interest,

e.g. speed, pressure, fluid elevation, streamlines, etc.






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]






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






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






Question: How can we

represent a complex

geometry such as this in a

rectangular grid?

FLOW-3D’s Numerical Approach






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.






Meshing

• Import geometry

• Overlay mesh blocks

• Preprocessor does the rest






• 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™






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.






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






General Moving Object






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






Data Output Focused on Hydraulics

• Filling time

• Residence time

• Fluid elevation

• Fluid depth

• Distance traveled by Fluid

• Vorticity






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






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






About Alden

• Hydraulics

– Dams and Spillways

• Physical Modeling

• Numeric Modeling






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






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






Results

• Stage vs discharge rating curve

• Pressure distributions (cavitation index)

• 3D Velocity field

• Standing waves

• Air entrainment characteristics

• Hydraulic jumps






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






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






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






Velocity (ft/s)

80

60

40

20

0

Velocity (ft/s)

80

60

40

20

0






ALDENSolving Flow Problems Since 18945/4/2009 54

Elev. 685 ft

Elev. 662 ft

Elev. 685 ft

Elev. 662 ft









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






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






Ogee Spillway






Example 3

• Discharge computed by (Design of Small Dams)

• Design flow is 124 cfs/ft

• CFD computed flow is 123 cfs/ft

• Within 1%






Example 3

• How does pressure distribution vary with flow

Pressure tap






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






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.






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






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






QuestionsPlease use the Q&A tab in

LiveMeeting

Mario Finnis: [email protected]

Marc Horner: [email protected]

David Souders: [email protected]

Dan Gessler: [email protected]










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