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OLGA User Group Meeting
OLGA Support Tips & Tricks
Johan Henriksson
Aberdeen, November 10th 2010
OLGA support
• Send to [email protected]
• Support Center – access to FAQ, track your support requests
• Requesting user feedback on support
• Check www.sptgroup.com for new minor releases
Feedback from earlier UGMs
Tips & Tricks
1. What is the main difference between OLGA 6 and OLGA 5 ?
2. What hardware is recommended to achieve maximum
performance with OLGA ?
3. Is OLGA compatible with Windows 7 ?
4. Can OLGA simulate Water Hammer effects ?
5. Why does not always the 2nd order numerical scheme give
more accurate results?
6. Why is AXIALHEAT not included in OLGA 6?
What is the main difference between
OLGA 6 and OLGA 5 ?
What is NOT different in
OLGA 6 compared to OLGA 5 ?
OLGA 6 and OLGA 5 : same concept
• fundamental modeling concept is the same
– Flow model
– Numerical methods for conservation equations
• Graphical User Interface (GUI) is the same
• Comparisons from cases in OVIP data base and from the
SPT functional test repository show that:
OLGA 5 and OLGA 6 will in general give very similar results
both for steady-state and transient simulations
Conservation equations in OLGA 6
• three momentum equations (gas, oil, water)
– effect when individual momentum of oil and water are
important (heavy slugging in risers)
• an interfacial level gradient term between oil and water
– give higher water content in gas condensate pipelines for low
flow rates
• better consistency between steady state pre-processor and
dynamic solution
– interfacial level gradients included in pre-processor
• 2nd order scheme for mass equations
– optional
OLGA 6 has a new node model
• Internal nodes have a finite volume
– use same physical and numerical models as sections
– more general than split/merge => easier to model closed loops
• No momentum transfer across nodes
– higher pressure drop for cases with high velocity
Process equipment in OLGA 6
• Controllers are signal network components
– Coupled in the controller signal network
• Separator is a flow network component
– Similar to multi-train separator in OLGA 5
The OLGA 6 code is parallelized
• developed for multi core platforms, and may give
significant performance boost when run on such systems
• Most benefit for
– large cases with few nodes, long pipelines and a relative
small amount of process equipment
What hardware is recommended to achieve
maximum performance with OLGA ?
Effect of several cores and CPU’s
Tested using 2 Quad core Intel CPUs with Hyperthreading
(2 threads per core)
Speedup is case dependent
0
0.2
0.4
0.6
0.8
1
1.2
1 2 3 4 4+4 2*(4+4)
No
rma
lize
d w
all
clo
ck
tim
e
Cores+Hyperthreading
Oil field Gas-condensate
Running 2 CPUs on
same machine
Running 2 threads on
each core
(Hyperthreading)
What CPU to buy?
• Speedup is dependent on e.g.
– Size of problem
– Dominating flow regime
– Modules used
• True multicores give good speedup
• Good effect of Hyperthreading (Intel)
• Effect of multi-CPU for larger problems
• AMD and Intel Quad core give good speedup
• Expects good performance on new 6 and 8 cores CPUs
14
Is OLGA compatible with Windows 7 ?
Windows 7 compatibility
• Yes, with some known exceptions
• OLGA is not supported on
– PCs with Windows 7 + integrated Intel graphic card and
integrated Intel driver
• Following issues happen more often on Windows 7
– ‘Copy as picture’ of the network view to clipboard fails
– Input report does not include image of the network view
Can OLGA simulate Water Hammer effects?
Water Hammer simulations in OLGA
• Hammer effects occur in liquid systems with fast transients
– Injection systems
• Maximum hammer pressure :
P = Pressure (Pa)
c = Wave propagation velocity (speed of sound) (m/s)
v = Fluid flowing velocity (m/s)
ρ = Density (kg/m3)
• Maximum hammer pressure achieved if valve closure time is shorter than system response time:
L = pipeline length
ll vcP max
c
Ltr
2
19
Water Hammer simulations in OLGA
• Fluid packing
contributes to
pressure increase
• Small spatial
discretization
gives better
resolution of
pressure wave
4 km long pipeline with flowing water
20
Water Hammer simulations in OLGA
• Elastic walls
• more correct
volume change &
speed of sound
4 km long pipeline with flowing water
21
Theoretical comparisons
• Instantaneous closing valve, Joukowski equation:
• For slower occurring changes the following relationship is
used to estimate the surge pressure:
Comparison between OLGA,
Joukowski equation and
slow-close-equation
0
5
10
15
20
25
30
35
40
45
50
0 10 20 30 40 50
Ha
mm
er
pre
ssu
re (
bar)
Valve closing time (s)
OLGA
Slow close
Joukowski
Water Hammer simulations in OLGA
• Advice for simulation hammers in OLGA
– Spatial discretization is important
– Use DTCONTROL : SOUND_CFL = ON
small fixed time steps (dt = 2Ls/c)
– Account for elastic walls with ELASTIC = ON
• CONCLUSION
– OLGA can simulate water hammer effects
Why does not always the 2nd order numerical
scheme give more accurate results?
2nd Order Scheme for Mass Equations
• It should be used for cases with holdup or concentration
gradients e.g.
– Start-up
– Rate change
– Slugging
– Injection of inhibitors
• 2nd order scheme is not recommended for simulations where
instabilities are observed
• enhances the numerical oscillations
Why is AXIALHEAT not included in OLGA 6?
AXIALHEAT
• Not implemented in OLGA 6 yet because
– Model in OLGA 5 is sensitive to pipeline geometry
– Should only be used for vertical risers
– No field data is available
• May be included in later versions depending on feedback
from users
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be dynamic