Theoretical Overview of Surge Analyses

7/24/2019 Theoretical Overview of Surge Analyses

1/14

THEORETICAL OVERVIEWTHEORETICAL OVERVIEW

OF SURGE ANALYSESOF SURGE ANALYSES

3 December 2001

University of Pretoria

Prof SJ van Vuuren

Tel: +27 012 420 2438Website:

http://www.up.ac.za/academic/civil/divisions/water.html

Layout of PresentationLayout of Presentation

Introduction

Basic theory of transient flows Rigid Column Theory

Elastic Theory

Influence of pipeline support on wave celerity

Propagation of transient waves

Theory for non-instantaneous disturbances

Calculation of transient pressures

Causes of transient flows

Fluid transient risk assessment procedure(TRAP)

Surge protection options

Computer-aided transient analysis


2/14

IntroductionIntroduction

What is surge?Variation in pressures that are generated

by a change in the operational status

How are surge waves

created?Foreseen operational changesUnforeseen operational changes

Layout changes

Basic theory of transient flowBasic theory of transient flow

RIGID COLUMN THEORY

dt

dv

g

LH =

ELASTIC THEORY (RIGID PI PE)

0cVP =

)/(

)/(

)/(

)/(

0

3

2

smvelocityflowV

mkgwaterofmassunit

smpiperigidaforceleritywaveC

mNnfluctuatiopressureP

=

=

==

Where:


3/14


ELASTIC THEORY (RIGID PIPE)(Continued)

+

=

t

D

D

Kcc

1

1'

Where:

)(

)(

)/(

)/(mod

)/('

*2

*2

mpipeofthicknesswallt

mpipeofdiameterD

mmNmaterialpipeofelasticityE

mmNwaterofulusbulkK

smpipeelasticanforceleritywavec

===

=

=

*Values of K and E are shown in Annexure 1


SUPPORT OF THE PIPEL INE

PROPAGATION OF TRANSIENT WAVES

Case 1: Anchored at upstream end

21

=C

Case 2: Anchored throughout against longitudinal movement

2

11 =C


4/14

Transient flow theory for nonTransient flow theory for non--

REQUIREMENTS

elasticity

effect of losses

non-instantaneous valve movement

PARTIAL DIFFERENTIAL FORMULAE

instantaneous disturbancesinstantaneous disturbances

0sin2

=+

++

x

u

g

c

t

Hu

x

Hu

02

=++

dt

du

D

uu

x

Hg

Visualizing the movementVisualizing the movement


5/14



Surgemov1.mov

Surgemov2.mov


6/14

Calculation of transientCalculation of transient

arithmetic

graphic

characteristics

algebraic

implicit

linear

wave-plan

other

pressurespressures

Causes of transient flowsCauses of transient flows

Pump start-up

Pump trip

Variation in demand

Unintentional changes in operationalposition of control valves


7/14

Fluid Transient RiskFluid Transient Risk

Checklist of fault conditions

TRAP

Assessment Procedure (TRAP)Assessment Procedure (TRAP)


The route of the pipeline is changed?

The demand on the system is increased?

The basic design data is unreliable by x % (e.g. heads,

flows, component operating characteristics, materials

specifications, fluid properties and quality, etc.)?

Changes are made to the system design?

Assessment Procedure (TRAP)Assessment Procedure (TRAP)Checklist of fault conditions

Design/Installation


8/14


The power fails to the motors driving the pumps?

The pump delivery valve is closed in t seconds?

One pump trips but others keep running?

An operator opens/shuts valve y too quickly?

The demand on the system is increased?


Normal operation


A pump is re-started within t seconds of being tripped?

A control or emergency shut-down valve is shut rapidly?

An operator opens/shuts valve y too quickly?


Hazardous operation


9/14


Component x malfunctions (e.g. an automatic control

valve, pressure relief valve, vacuum breaker, etc.)?

The surge suppression strategy/control devices

malfunction?


System malfunction

Fluid Transient RiskFluid Transient RiskAssessment Procedure (TRAP)Assessment Procedure (TRAP)

All the operational

variances should be

identified

List all the possible causes that can change

the steady state situation and distinguish

between: internal and external factors that

can result in transients (Use Annexure 2).

The bottom line: What can go wrong,

where, how, and why? How will the flowbe influenced?

3

Quantify the operational

scenarios

Define the operating regimes and the

operational limits of the system.

2

Obtain the characteristics

of the system

Describe the system which normally

consists of pumping stations, pipelines,

control equipment, demand centres, etc.Define the operating regimes and the

operational limits of the system.

1

ObjectiveDescriptionAction


10/14


Cost effective controlReview options for a control and

transient suppressions strategy

6

Ultimate solution for possible

future system application

Consider the influence of future

extensions or alterations to the system

7

First indication of the

magnitude of the transient

pressures

Determine the celerity, pipeline period,

pump rundown time, valve operation

and the Joukowskys head for all the

situations listed in 3

5

The difference between the

residual pressures and

permissible internal pressures

will indicate the ability of the

system to handle higher

pressures.

Draw a longitudinal section and

determine the hydraulic grade lines

(both for static and dynamic conditions).

4



Successful

implementation

Devise test programme for commissioning

procedures

10

Ensure long term

efficiency

Finalize the design, and prepare operational

constraints and guidelines in accordance

with the validated control and suppression

strategy

9

Optimal surge analysisPrepare specifications for detailed computer

analysisRefine the control measures

8



11/14

Surge protection optionsSurge protection options

Pump start-up

Pump trip


Surge tank Air valve Reflux valve


12/14

Surge protection optionsSurge protection optionsWhere is the transient

event initiated?

Upstream end An intermediate point Downstream end

Pressure

rises first

Pressure

drops first

Pressure

rises first

Pressure

drops first

Air vessel /accumulator

Check valve

Relief

system

Surge shaft

Could secondary devices elsewhere in the system be of benefit ?

e.g. Air valves, Feed tanks, surge shafts, etc.


By-pass

Check valve

Vacuum

breaker


Reliefsystem

Surge shaft


Feed tank

Surge shaft

Vacuum

breaker

Can a By-

pass device

help ?

No No

Select and/or Design

Yes

Select and/or Design


Summary of Water Hammer Protection

Normally used in conjunction

with some other method of

protection. Water column

separation possible

In-line reflux valve

Pipeline profile should be

convex downwards. Water

column separation likely

Automatic release valve

Some water may also be

drawn through the pump

Pump bypass reflux valve

Approximate onlyInertia of pump

RemarksRequired range of

variables

Method of protection (in

approximate order of

increasing cost)

01.02

0

2

>wALH

MN

10

0 >>gH

cV

10 >gh

cV

10

0


13/14


Summary of Water Hammer Protection


near hydraulic grade line tolimit the height of tank

(practical)

Limited heightSurge tanks

H = pressure head at tank,


convex upwardsDischarge tanks

Pipeline profile preferably

convex downwards

Air vessel

RemarksRequired range of

variables

Method of protection (in

approximate order of

increasing cost)

10 >gh

cV

10

0

Theoretical Overview of Surge Analyses

Documents

Transcript of Theoretical Overview of Surge Analyses