OUTLINE FOR CDB WATER HAMMER SOFTWARE INHOUSE TRAINING

1. Brief description of Water HammerWater hammer is produced when the liquid flowing in a pipe is suddenly decelerated to zero velocity by a fast closing valve, a pressure wave propagates upstream to the pipe inlet.

For an instantaneous flow stoppage of a truly incompressible fluid in an inelastic pipe, the pressure rise would be infinite. Finite compressibility of the fluid and elasticity of the pipe limit the pressure rise to a finite value.

The maximum pressure surge is obtained when the valve closes in less time than the period required for the pressure wave to travel from the valve to the pipe inlet and back, a total distance is 2L.

The pressure surge will be reduced when the time of flow stoppage exceeds the pipe period , due to cancellation between direct and reflected waves.

Successive reflections of the pressure wave between the pipe inlet and the closed valve result in alternating pressure increases and decreases, which are gradually attenuated by fluid friction and imperfect elasticity of the pipe. Periods of reduced pressure occur while the reflected pressure wave is traveling from inlet to valve. Degassing of the liquid may occur, as may vaporization if the pressure drops below the vapor pressure of the liquid. Gas and vapor bubbles decrease the wave velocity. Vaporization may lead to what is often called liquid column separation; subsequent collapse of the vapor pocket can result in pipe rupture.

Water hammer can be generated by:- closure of valve,- starting or stopping of pumps, - changing elevation of a reservoir, - waves on reservoir,

2. About CDBCDB is Saipem’s inhouse software develop by Remi Daures. It is used to simulate steady state and transient operations.

Validation :A report of validation was carried out in 2002. The conclusions are that the results are reliable as long as there is no vaporization. The treatment of cavitation has leads to overpressures which is more significant than actual.

Model :The network is modeled by means of nodes connecting of the branches or the equipment.Each branch is automatically divided into segments by the program, according to the step of time chosen by the user.

The boundary conditions are specified in flow or pressure by means of external regulators.

The elements that can be modeled are :- pump- valve- PSV- External regulator- Accumulator or reservoir- Regulator PID

3. UnitsThe following units are used:

- pressure : bar (can be modified by keyword “atm”)- flowrate : m3/hr- diameter : mm- length : km- time : second (can also use the notation h:m:s or m:s)

4. CDB outline:

a. General dataFrequently used keyword : tmx duration of simulation dtc step of time dti step of imposed time (replace dtc when it is wished that the step of

time being fixed dtp period of posting out listed of result

b. Fluid characteristicFrequently used keyword: prd name of product rho spec gravity vis viscosity (cSt) bmd bulk

modulus (MPa) vap vapor pressure

c. Equipment descriptionFrequently modeled equipment:

External RegulatorExternal regulator is used to specify a condition in a node. Only one condition need to specify in each external regulator xrg name of external regulator qmn minimum flow (m3/hr)

qmx maximum flow (m3/hr)pmn minimum pressure (bar)pmx maximum pressure (bar)

Pump: pum name of pump nfh shut off head (m) hea nominal head flo debit

Valves: vlv name of valve cvmx maximum valve coefficient crv valve curve

PSV: rlf name of valve coec coefficient of pressure loss dia orifice diameter

dpo delta p opening dpc delta p closing

Accumulator or reservoir:The difference between accumulator and reservoir is based on the coefficient polytropic (γ). The equipment is considered as a tank if γ = 0 while it is an accumulator if γ > 0.

The gas in accumulator follows the polytropic relation PVγ = constant. In the case of gas ideal, the value of exponent will be taken equalizes with γ = 1. If the process is adiabatic and reversible, γ = 1.4 and for isothermal and isentropic γ = 1.2

With the γ = 0, the pressure in the tank is considered constant.

acc name of accumulator kin inlet nozzle coefficient kou outlet nozzle coefficient dia diameter of orifice gam coefficient polytropic vol initial volume vmn minimum volume of gas vmx maximum volume of gas

PID Regulator: ctr name of regulator pro Kp der Td int Kl set C

followed by :- nod node number, if the point of measurement is a node (control of

pressure)- equ name of equipment, if the point of measurement is an equipment

(control of flow)- equ name of equipment par index of the variable, if the point of the

measurement is an equipment with a control of another variable except flow

- ctr name of regulator, if the point of measurement is the outlet of another regulator

d. NodeNode is used for specify the pipe segment and their elevation

nod identification number of node ele pipe elevation (m) lkp point kilometric (km) pre pressure (bar)

remarks :- the initial pressure of the node is optional- the definition of the nodes are not necessary when the lengths of each branch is specified in the line leg…. and the elevation of the node is 0- by default elevation of the node is same as the preceding node.- to specify some nodes which have same elevation, following notation can be applied:nod 1, 2, 3 ele 98ornod 1 ele 98 $nod 2 $nod 3

e. Network ConfigurationThe network is developed by various elements such as equipments and branches.

Branches :

leg name of branch or pipe segment nup upstream node number ndn downstream node number odi outside diameter wth wall thickness rou roughness ela pipe elasticity len length

If the branches or pipe segment has the same pipe property (outside diameter, wall thickness, roughness and elasticity) then following notification can be applied :

#d name of group of data odi outside diameter (mm) wth wall thickness (mm) rou roughness ela pipe elasticity (Mpa)

Example :#d PIPE1 odi 168.3 wth 3.40 rou 0.015 ela 207000

leg 10 nup 10 ndn 11 PIPE1 len 0.045leg 11 nup 11 ndn 12 PIPE1 len 0.033

Equipment : equ name of equipment nup upstream node number ndn downstream

node number equipment keyword (such as pum, vlv or acc) name of equipment as specified in equipment description

Example :equ P1101 nup 12 ndn 13 pum PUMP01

f. Scenario trs name of equipment tim time 1 val value 1 tim time 2 val value 2

val is one of the keywords specified below:

for pump:pup suction pressurepdn discharge pressureqmx flowratespd speed of the pump (%)num a number of pumps in series

for valve:pco percentage of valve openingqmx flowratepup upstream pressurepdn downstream pressure

for external regulator:qmn minimum flowrateqmx maximum flowratepmn minimum pressurepmx maximum pressure

for the group of data, following notations are equivalent :example for pump:

trs P1101 tim 0, 10, 50, 100 pco 100, 80, 20, 0

OR

#d PUMPSTOP tim 0 spd 100 tim 10 spd 10.97 tim 20 spd 5.8 \tim 28 spd 4.21 tim 34 spd 3.5 tim 100 spd 0

trs P1101 PUMPSTOP

g. Post process

Post process is the order to treat the result:

trend (equipment)The syntax is

trn file name equ name of equipment var equipment variable

List of equipment variable

PUM VLV RLF XRG ACC0 QV QV QV QV QV1 VOL VOL VOL VOL VOL2 P1 P1 P1 P1 P13 P2 P2 P2 Vi4 NB PCO LEV5 SPD Pi

trend (node)The syntax is:trn file name nod node number var node variable

copy the filesThe syntax is:cpy destination file file 1 + file 2 + file 3 + …..

h. GraphTo show the result in the graphic format, following annotation can be used :

cpy *.fig (name of file) *.txt (format of graph) + *.prn (the file which contain the result that will be transferred to the graphic format)

The list of command in the *.txt file is as follow:

TI title (optional)LX legend of X axisLY legend of Y ordinateX1 minimum axisX2 maximum axisDX delta XY1 minimum YY2 maximum YDY delta YLI style and thickness

5. Example