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H Y D R A U L I C T R A N S I E N T M O D E L I N G
A C A S E S T U DY F O R A T E X A S WAT E R C O N V E YA N C E S YS T E M
• Presented By Ryan Haller• Water Engineer at Arcadis
• February 5, 2019
OVERVIEW
Transient Fundamentals
Case Study
Model Setup
Transient Results
Final Recommendations
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TRANSIENT CONDITIONS
• Rapid change in system pressures/velocities
• Deviation from normal system conditions
• Impact depends on duration
– Transient events
– Surge events
TRANSIENT CAUSES
• Rare/Emergency Conditions Causes– Power Failure – Pump Trip
– Pipe Break
• Normal Operating Conditions Causes– Pump Startup
– Pump Shutdown
– Valve Slamming Shut
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TRANSIENT MODELING FUNDAMENTALS
• Modeling movement of energy
• Valve movements and pump operation generate transient energy
• Frictional loss dissipates transient energy
• Surge modeling – Identify extreme pressures
– Evaluate surge protection
TRANSIENT THEORIES
Wave Speed Characteristic Length
JoukowskyEquation
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TRANSIENT THEORIES
Simple Calculation of Transient Wave Speed:• Wave Speed aka “celerity”
– 𝒂 𝑬𝒗𝝆
𝟏𝑫𝑬𝒗𝒆𝑬
𝝋
– a = pressure wave speed (ft./s)
– Ev = Young’s modulus – pipe (psi)
– E = bulk modulus – liquid (psi)
– Ρ = liquid density
– D/e = dimension ratio
– Ψ = pipe support index (anchored, joints, etc.)
TRANSIENT THEORIES
Calculation of Characteristic Time:• Characteristic Time
– Time required for a pulse to travel from the source to the downstream boundary and back to the source
• 𝑻𝒄 𝟐𝑳
𝒂
– Tc = characteristic time (s)
– L = longest length of pipe (ft.)
– a = pressure wave speed (ft./s)
• What does rapid change in flow/pressure mean?
– A transient event occurs faster than characteristic time
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TRANSIENT THEORIESSimple Calculation of Transient Impact:
• Joukowsky/Allievi Equation
• ∆𝑯 𝒂
𝒈∆𝐕
– H = pressure head (ft.)
– a = pressure wave speed (ft./s)
– g = gravitational constant (32.2 ft./s2)
– V = velocity (ft./s)
– Ratio a/g ranges from about 30 to 120
– If ∆H = 100 ∆V, stopping 1 ft./s causes an upsurge of 100 ft. (43 psi) !
– What is your pipe pressure rating??
TRANSIENT MODELING SOFTWARE• Various modeling software to predict
hydraulic transientsHAMMER WANDA
KYPipeSurge InfoSurge
• Capabilities– Preventative
– Reflective
– Surge Protection
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C A S E S T U D Y
TEXAS WATER CONVEYANCE SYSTEM
• Two pump stations service 200 MGD to residential and commercial areas
• Source of water is five clearwells
• Flow is sent to four pressure zones
• Proposed Project:– New Pump Station
– New interconnect
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SETTING UP THE MODEL• New pump station
further South
• Utilizes existing Pump Station wet well
• New interconnect increases flow capacity
4
1
23
PS2
PS1
Clearwells
1
2
3
4
New
SCENARIO DEVELOPMENT
Power Failure Maximum Flow
Establish Baseline & Proposed Conditions
Assess Surge Protection
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SCENARIOS
• Power failure assessed
• Max flow conditions
• Four residential/ commercial supply zones
75 MGD
140 MGD
100 MGD
Current Conditions
75 MGD
180 MGD
100 MGD
ProposedConditions
75 MGD
180 MGD
100 MGD
Surge Protection
T R A N S I E N T S C E N A R I O
R E S U LT S
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CURRENT CONDITIONS: POWER FAILURE AT PUMP STATION
Pump SuctionPump DischargeMinimum Pressures
Maximum Pressures
Initial Pressures
Vapor Pressure
PROPOSED CONDITIONS: POWER FAILURE AT PUMP STATION
Minimum Pressures
Maximum Pressures
Initial Pressures
Vapor Pressure
Pump Suction Pump Discharge
Minimum Pressures
Initial Pressures
Vapor Pressure
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PROPOSED CONDITIONS: POWER FAILURE THROUGH INTERCONNECT
Clearwells
Pressure Zone 3
Minimum Pressures
Maximum Pressures
Initial Pressures
Vapor Pressure
KEY FINDINGS
DISTANCE FROM WATER
SOURCE
FLOW PATH
PS2 FLOW IS BENEFICIAL
INTERCONNECT CAPABILITIES
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RECOMMENDATIONS TO EVALUATE• Type of surge device depends on
pressure conditions• Minimum pressures – add energy to
the system– Combination Air Valves
– Surge Tanks
– Hydropneumatics Tanks
– Bypass Lines
• Maximum pressures – relieve energy from the system
– Surge Relief Valves
– Air Relief Valves
– Reduced Pressure Zone Valves
• Optimize surge device location
Stand Pipe
Combination Air Valve
Surge Tank
Air Relief Valve
FINAL RECOMMENDATIONS
• What: Two 24-inch Surge Anticipator Valves
• Where: On the discharge header, routing back to the pump suction – Between pumps 1 & 2 and 3 & 4
• Why: Replace energy lost
Mitigates all scenarios
Best implementation
Cost effective
Discharge Header
Suction Header
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R E S U LT S W I T H A D D E D
S U R G E P R O T E C T I O N
PROPOSED CONDITIONS:POWER FAILURE AT PUMP STATION WITH SAV
Minimum Pressures
Pump SuctionPump DischargeMinimum Pressures
Maximum Pressures
Initial Pressures
Vapor Pressure
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PROPOSED CONDITIONS: POWER FAILURE THROUGH INTERCONNECT WITH SAV
Clearwells
Pressure Zone 3
Minimum Pressures
Maximum Pressures
Initial Pressures
Vapor Pressure
CONCLUSION
Prevent/
OptimizeReflective
Surge Protection
Cost Effective
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Q U E S T I O N S &
C O M M E N T ST H A N K YO U !
