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DYNAMIC POSITIONING CONFERENCEOctober 15-16 2013October 15-16, 2013

SENSORS SESSION II

Ten Years of Experience from Acoustic Aided Inertial

Are B. Willumsen

Kongsberg

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10 Years of Experience from Acoustic Aided Inertial Are B. Willumsen, Product Manager HAIN, Kongsberg Maritime

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Inertial Navigation System (INS) • Inertial measurements

• +Accelerations – accelerometers • +Angular rates – gyroscopes • = Inertial Measurement Unit (IMU)

• Integration – Orientation – Velocity – Position (integrate twice)

• Independent – Of external systems – Of vehicle dynamics

• Integration without correction inherently instable

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• Hydroacoustic Aided Inertial Navigation – HAIN Subsea – HAIN Reference

• HUGIN Navigation System • 2003

– First HAIN Reference trial on Seaway Osprey – First commercial use of HAIN Subsea

• 2013 – 50+ HAIN Reference sold

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(Pictures in courtesy of respective owners)

System integrity • INS never independent of aid.

– Never use both as references simultaneously.

• Unaided increasingly inaccurate. – Safety measure: exclude inertial

position if unaided 3-5 mins. • DP receive acoustics if INS fails. • INS must be GNSS independent.

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HAIN APOS/ HiPAP

Transceiver

DP Inertial position

Acoustic position

Inertial position

Acoustic position

Acoustic principles

17-Oct-13 WORLD CLASS – through people, technology and dedication / 5 /

Acoustic principals and inertial • SSBL

– High standard deviation – Almost never drift – Rapidly varying errors

• LBL – Often slow rate – Low standard deviation – Occasional drift/ – Slowly varying errors

• AINS – w/ SSBL or LBL – Less drift – Increased accuracy – Added integrity – Slowly varying errors

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DP weighting

• DP weighting is a quadratic function of standard deviation. – 2 meters standard deviation gives only 1/4 weight.

• DP weighting is a linear function of update rate. – 2 seconds update period gives only 1/2 weight.

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Inertial Measurement Unit (IMU)

• Accelerometers are fairly cheap • Gyroscopes are more costly

• FOG – Fiber Optic Gyro

– Solid state may yield lower MTBF – OK Performance

• MEMS – Microelectromechanical systems – Cannot gyrocompass – yet – Cheaper

• RLG – Ring Laser Gyro – Hearable noise – Best performance

/ 8 / 17-Oct-13

(Pictures in courtesy of respective owners)

Installation

• Anywhere on vessel – RLG noise annoying – Stable temperature and humidity is good – Cannot factory align

• Mounting – Coarsely aligned with Vehicle axes – UPS – Connection to ships acoustics

• Lever arm accuracy of 0.2 meters sufficient – 150+ m – OK

• 2-4 hours IMU alignment • FMEA and performance testing

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Problems • IMUs are export restricted • INS errors

– Carries high DP weight – Drifts off and stays off

• HAIN Reference – Few problems and service – Little crew attention

• IMU – To spec or broken down

• Acoustics – Outliers and noise – Non-white errors

• Problems leads to improvement in both acoustics and INS

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2D trajectory in meters, pMBM

HPR400OutliersHAIN

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Conclusions

• Acoustic aided INS is well proven as DP Reference – 7+ years of HAIN – 50+ HAIN units

• INS will work on – any acoustics – any vessel (without tuning)

• INS is easy to use • Technical problems are few • It improves

– update rate – precision (accuracy) – integrity

• Increased DP weighting

/ 11 / 17-Oct-13

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