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Transient Analysis and Design Considerations for Hydraulic Pipelines Jonathan Funk, EIT
May 29, 2015
2Transient Analysis
• Develop an intuitive understanding of water hammer and transient response
• Present a case study where transient analysis mattered
• NOT Teach the science of wave formation and propagation
(too many formulas)
Objectives
May 29, 2015
3Transient Analysis
Water Hammer (noun)
The concussion and accompanying
noise that result when a volume of
water moving in a pipe suddenly
stops or loses momentum.
Transient Response (noun)
The response of a system to a
change from equilibrium.
Definitions
Source: water hammer. (n.d.). Dictionary.com Unabridged. Retrieved May 19, 2015, from Dictionary.com website: http://dictionary.reference.com/browse/water hammer
May 29, 2015
4Transient Response
Everyone’s Favorite Analogy
Energy Absorption
Flow >
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5Transient Analysis
• Decelerating flow increases pressure
• Pressure spikes can travel and oscillate throughout a pipeline
• Design for transient pressures! (not just “Steady State”)
• Prevent or absorb pressure spikes
Overview So Far
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6Transient AnalysisCase Study – Skookum Creek Power Project
May 29, 2015
7
March 11, 2011
8
March 11, 2011
9Skookum Creek Power Project
• Located near Squamish, BC
• 6.4 km FRP & Steel pipeline
• 1.8 – 2.2 m diameter
• 340m elevation change
• 9,900 L/s design flow
• Rated Capacity: ~25 MW
May 29, 2015
10Skookum Creek Power Project
Hydraulic Scenarios
• Power Generation = Flow x Pressure = $ (Steady State)
• Normal shut-down – No long-term damage (Transient)
• Emergency shut-down – No short-term damage (Transient)
• Needle Valve Failure – Survivability (Transient)
May 29, 2015
11Transient Analysis
∆� � ��
�∆�
where
∆P = change in head (m) (pressure rise)
a = wave speed (m/s) (“communication” speed)
g = acceleration of gravity (m/s2)
∆V = change in velocity (m/s)
Pressure Rise
Gate valve
Reservoir
Flow >
Hydraulic Grade Line (Steady State)∆P
∆P
∆P
(negative pressure)
Max HGL Envelope
Min HGL Envelope
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12Transient Analysis
Negative Pressure & Cavitation
At standard temperature and
pressures, cavitation starts
at -10m HGL (-14 psi)
-14 psi
Siphon
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13Skookum Creek Power Project
Design Limitations
• Topography
• Hydrology & Wetlands
• Old Growth Management Areas (protected)
• Site Access (de-activated forest service roads)
• Geotechnical Conditions
• Max/Min Elevations
• Hydraulics!
May 29, 2015
14Skookum Creek Power Project
Steady State Analysis
• More headloss = less pressure = less power generation
• Design flow and pipeline deterioration
• Siphon! Hard to release air. Closer to Cavitation.
• Remote site considerations
Recommendation: Eliminate Siphon
May 29, 2015
15Normal Operations (12 minute shut-down)
Outcomes
• Nothing to worry about
• Ongoing, successful operation
May 29, 2015
16Emergency Shut-down
Surge Tower
Initial Outcomes
• Negative Pressures (enough for cavitation)
• Initial ‘Emergency Period’ too short
• Additional protection required
• Recommendation: Add a Surge Tower
Negative Pressure
Max Transient HGL
Min Transient HGL
May 29, 2015
17Emergency Shut-down (90 seconds)
Surge Tower
Final Outcomes
• Determined 90 second threshold for emergency shut-down
• Addition of surge tower (doubles as air release)
• Successfully completed project, potential problems prevented
May 29, 2015
18Transient Analysis
• ∆P ∝∝∝∝ ∆V (“is proportional to”)
• Design for pressure spikes (not just steady state)
• -14 psi = Cavitation (please avoid)
• Change flows as slow as you can manage
• Transient Analysis is understanding and mitigating these phenomenon
Overview
May 29, 2015
19Transient Analysis
• Valve Operation (Fast AND Slow)
• Pump Start-up / Pump Shut-down
• Power Failure
Common Sources of Water Hammer
Mitigation
• Perform a transient analysis
• Slow down your flow changes (prevention!)
• Pressure relief / vacuum break
• Combination air release / vacuum valves
• Surge tanks
Transient Analysis and Design Considerations for Hydraulic Pipelines Jonathan Funk, EIT
Special thanks to:Adrian Gygax (Gygax Engineering Associates) Peter Zell (Run of River Power)Ted Steele (KWL)Steve Mills (KWL)