inertial fog and acoustic aiding references for dynamic positioning applications
DESCRIPTION
By Yann Casamajou technical. product line manager Ixblue With DP-PHINS, iXBlue has expanded the functionality of its industry-leading PHINS inertial navigation system (INS). The new DP-PHINS is designed to interface with any third-party acoustic positioning equipment to provide INS-enhanced acoustic data input to marine dynamic positioning (DP) systems. Additionally DP-PHINS can also take data from a range of other sensors, some not normally associated with DP, such as Doppler velocity logs (DVL), for use in maintaining vessel position. Using DP-PHINS with INS produces positioning data that is smoother, more accurate and is updated at a higher rate. Consequently, station-keeping performance is significantly improved, vessels use less fuel, and wear and tear on the DP system components is reduced. The system has been fully qualified at sea with industry leaders operating in West Africa O&G development field.TRANSCRIPT
PHINS for DP Applications
Yann CASAMAJOUEuroport 2013
2Agenda
Introduction to INS
DP-PHINS : bringing INS benefits to DP
Augmented USBL Performances
LUSBL Performances
Robustness to Outages
Conclusion
3What's in an INS?
What is an Inertial Navigation System (INS)?An instrument (electronic + sensors) which is using its initial state (position) and internal motion sensors (gyroscopes + accelerometers) to measure and calculate its subsequent positions in space with high accuracy, stability and update rate
PHINS PHINS 6000 ROVINS
4What's in an INS?
3 “FOG” gyrometersmonitor rotation and speed in X, Y & Z axis
3 accelerometersmeasure acceleration (>> speed >> motion) in 3 axis
Powerful electronic / firmware packagePHINS “knows” in real time its motion in space . Firmware (Kalman filter) calculates its position in real time + heading, pitch, roll, heave, etc…
All integratedsmall, lean, powerful!(PHINS 6000 example)
5INS Introduction
What makes an INS good.. or not? Internal sensors (gyroscopes & accelerometers) are never perfect,
bias and scale factors accumulate over time Navigation is mostly about Gyroscopes
Gross figures: Accelerometers errors are not heavily involved in the position drift –
4m – Schuller period Gyroscope are heavily involved in the drift – 400 m
Conclusions A good INS requires good gyro’s IXBLUE manufactures FOG (Fiber Optic Gyroscope) and controls the
whole process A range of FOG’s (FOG90, FOG120, FOG180…) for a range of INS
6INS Introduction
The best sensors are still not perfect, accumulating small errors vs. time makes the system drift on the long term
External sensors (aiding) are required to bound drift within acceptable limits.PHINS & ROVINS includes interfaces for most common external sensors
GPS DVL (Doppler Velocity Log) Pressure sensor Acoustic positioning references (USBL, LBL) …and all IXBLUE products!
IXBLUE INS are fully integrated Inertial Positioning solutions designed for ease of installation & operation, flexible enough to fit most requirements, with no specialist engineer to install / operate.
7Benefits of data fusion: Robustness to signal losses
GPS positioning with masking
8Benefits of data fusion: outages
GPS + INS positioning with masking
9Benefits of data fusion: accuracy
Data Fusion Use various and different technologies to measure the same parameter Blend (fuse all this data (Kalman filter) in order to correlate it and obtain a
better result A simple example GPS + INS (PHINS or GAPS typical use case)
0
0,5
1
1,5
2
2,5
3
0 20 40 60 80 100
time t (s)
po
sit
ion
ac
cu
rac
y (
m)
PHINS pure inertial drif t (0.0002 x t^2m)
Averaging of DGPS data (3 / sqrt(t)m)
PHINS+DGPS
10Benefits of data fusion: accuracy (USBL case)
Acoustic positioning can be poor, low update rate, or out of range. INS + USBL combination / data fusion provides continuous high quality positioning:
Survey @2500m depth: INS accuracy is much better than USBL’s one (noise rejection)
11Agenda
Introduction to INS
DP-PHINS : bringing INS benefits to DP
Augmented USBL Performances
LUSBL Performances
Robustness to Outages
Conclusion
12DP-PHINS, Why raising expectations?
Augmented GNSS is an accurate and generally reliable positioning solution.
For DP in deep water, the main issue is the lack of other performing positioning systems.
What to do in water that is too deep for useful acoustics? After a certain depth acoustics become too noisy, too deep for taut
wire, no other structures for relative based systems.
Too many vessels relying on single PME – GNSS
DP PHINS is the simplest way to raise positioning performances on a vessel
13
DP-PHINS What is it?
Missing link between PHINS and USBL PME
Goals of the system :
DP-PHINS cabinet extends PHINS capabilities to :
Context: Offshore works and installation jobsDeep sea (>1000m)Necessity to pursue operations without any reliable GPSSevere daily scintillation phenomena (Africa, Brazil...)
Use PHINS fusion algorithms to enhance raw USBL positioning
Improve USBL performances to make it usable for DP during GPS scintillation
use raw acoustic detections from any USBL for positioningprovide positioning telegram to DP Desk
14DP-PHINS What is it?
Time Signals
Time and Position For Initialisation Only
Time stamped beacon positions (in vessel reference frame)
Processed Positions
Enhanced Position
Acoustic Positions
USBL system
...
DGPSGNSS
DP desk
DP-PHINS
15DP- PHINS, Features
PHINS Natural Features: Native fusion of a wide range of sensors (GPS, DVL...) Strong noise rejection Sparse-array capability
DP-PHINS cabinet additional improvements: Relative to Global co-ordinate transforms Unlimited number of beacon Sparse array LBL Flexible Expandable
Future Sensors Taut Wire Fan Beam Radascan Etc. Etc.
16Agenda
Introduction to INS
DP-PHINS : bringing INS benefits to DP
Augmented USBL Performances
LUSBL Performances
Robustness to Outages
Conclusion
17DP- PHINS Performances: Augmented USBL, case 1
USBL raw dataPHINS + USBL, SD livePHINS + DGPS
Nov2012: 1300m depth operations
Single vessel, 2 cases:
DP with manoeuvring operations1x standard omnidirectional transducer, tonal codesDP with static vessel position1x directional transducer improved USBL accuracy
Accuracy Gain
x3.3
x2.65
Accuracy (%slant range)
0.055%
0.035%
Test CASE USBL SD (1DRMS,DGPS ref)
DP-PHINS SD (1DRMS,DGPS ref)
Dynamic, omni 2.34m 0.71m
Static, directional 1.22m 0.46m
DP-PHINS raises USBL PME to submetric performances on
performing vessels
18DP- PHINS Performances: Augmented USBL, case 2
Less performing USBL
Kongsberg CAT, 1360m depthStandard tonal transpondersDP performances in dynamic test
Error Type USBL vs GPS accuracy
PHINS vs GPS accuracy
max 86,79m 7,94m
1DRMS 6,21m 2,64m
Accuracy GAIN (GPS ref)
x10,93
x2,35
% Slant range
0.57%
0.19%
DP-PHINS raises poor DP-USBL to acceptable levels of performances in most fields
19Agenda
Introduction to INS
DP-PHINS : bringing INS benefits to DP
Augmented USBL Performances
LUSBL Performances
Robustness to Outages
Conclusion
20DP-PHINS, LUSBL performances
In May this year iXBlue commissioned DP-PHINS onboard Subsea7 vessel Simar Esperanca.
Augmented-USBL brings x2 to x3 improvement over raw USBL, operating in over 1,350m on acoustics
LUSBL makes it even better Most of the USBL error is on the angle
measurements Range measurements are always consistent Extract ranges out of USBL data string and
generate Pseudo LBL data Simply add a beacon... And take the full benefit
of DP-PHINS ! DP-PHINS operating in 1364m (4475ft)
21DP-PHINS, LUSBL performances
Measured ranges extracted computed from HiPAP USBL Data
Slant range standard deviation on CW signals: <30cm 1DRMS
B14
B15
Vessel
2 beacons used during this testB14, 312m northB15, 285m south
LUSBL achievements in such a situation: Optimum precision on latitude No improvement on longitude
22
DP-PHINS, LUSBL performances
Performance improvement on latitude:
1DRMS Standard deviation on latitude
At 1360m depth, LUSBL is 15.9x better than basic USBL5.1x better than augmented-USBL
... With same beacons, same vessel, pole and USBL transceiver !
23Agenda
Introduction to INS
DP-PHINS : bringing INS benefits to DP
Augmented USBL Performances
LUSBL Performances
Robustness to Outages
Conclusion
24DP-PHINS: what if the positioning source fails ?
INS Station keeping on GPS
25DP-PHINS: what if the positioning source fails ?
1mn outage
26DP-PHINS: what if the positioning source fails ?
2mn outage
27DP-PHINS: what if the positioning source fails ?
3mn outage
28DP-PHINS: what if the positioning source fails ?
4mn outage
29DP-PHINS: what if the positioning source fails ?
5mn outage
30DP-PHINS: what if the positioning source fails ?
6mn outage
31DP-PHINS: what if the positioning source fails ?
7mn outage
32DP-PHINS: what if the positioning source fails ?
8mn outage
33DP-PHINS: what if the positioning source fails ?
9mn outage
34
11m in 10 minutes
DP-PHINS: what if the positioning source fails ?
10mn outage
35
38m in 20 minutes
DP-PHINS: what if the positioning source fails ?
20mn outage
36DP-PHINS: what if the positioning source fails ?
INS will drift quickly if the acoustics fail. 3m in 2 min, 20m in 5 min. 0.6Nmi in an hour
When using INS with a single aiding sensor, a single failure will take out your INS also.
INS is most effective with multiple aiding sensors.
INS SHOULD be used with multiple aiding sensors
37DP-PHINS: what if the positioning source fails ?
INS free inertial specification is based on time. The more time, the greater the drift. Adding a DVL to DP-PHINS is an option to contain this drift DVL aided INS specification is based on distance travelled. If you don’t move the error
can’t grow as much.
PHINS-DVL performance is still good at low update rate compatible with deep water Problem: DVL is only available in water depths up to around 1,000m
DVL Update
Rate
Error, %
travelled
distance
Drift speed
m/h
1S 0.03% 0.18
2S 0.13% 0.82
3S 0.26% 1.67
4S 0.27% 1.77
6S 0.32% 2.08
8s 0.30% 1.98
38Agenda
Introduction to INS
DP-PHINS : bringing INS benefits to DP
Augmented USBL Performances
LUSBL Performances
Robustness to Outages
Conclusion
39Conclusion: DP-PHINS as a PME
INS is a proven technology on Land, Under water, in Space, why not in DP?
INS has a long track record, Modern FOG based systems bring extreme robustness and reliability.
INS can produce heading and attitude data as well as positioning. INS Should not be aided just by GPS for DP applications.
DP-PHINS can make your acoustics as good as high accuracy GPS. The biggest benefits can be obtained by combining aiding sensors. With the addition of DVL, PHINS can even be considered a stand
alone PME for a significant period of time.
40Conclusion: Why moving to DP-PHINS ?
Intrinsic improvement of USBL due to PHINS IMU performances Augmented-USBL: x2 to x3 better than USBL with single USBL beacon Augmented-LUSBL: up to 16x times better with additional beacons
Sequential use of beacons for LUSBL ➯ battery savings of field transponders
Extended acceptable water depth for DP ➯ extended DP class Continued operation in case GPS outage ➯ recurring financial gain Easy refit of vessels with existing USBL
➯ unchanged USBL, pole… DP-PHINS can be installed anywhere on board
Fuel saving thanks to DP-PHINS output position smoothness Positioning system open to any additional sensor (DVL, deep water CVL…)
41
Thanks for your attention
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