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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 !