Andersen, Ingrid Marie Vincent

Nielsen, Ulrik Dam

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Downloaded from orbit.dtu.dk on: Dec 20, 2017Sea state estimation from an advancing ship - The wave buoy analogyPresentation at Skibsteknisk SelskabNielsen, Ulrik Dam; Andersen, Ingrid Marie VincentPublication date:2012Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Nielsen, U. D., & Andersen, I. M. V. (2012). Sea state estimation from an advancing ship - The wave buoyanalogy: Presentation at Skibsteknisk Selskab DTU Mechanical Engineering. [Sound/Visual production (digital)].Operational Decision Support and Performance Monitoring, København, Denmark, 05/03/2012Sea State Estimation from an Advancing Ship –The wave buoy analogyUlrik Dam Nielsen and Ingrid Marie Vincent AndersenTechnical University of DenmarkPresentation at Skibsteknisk SelskabMarch 5th , 2012, Ingeniørhuset Kalvebod BryggeContent•  Introduction ‐ Field of interest (guidance and decision support systems)•  Means to obtain sea state parameters • The wave buoy analogy – Wave estimation using measured ship responses• Results Numerical simulations and full scale data –       ‐  • Summary/conclusionsE i f h i i l f f d ffi i hiIntroductionst mates o  t e on‐s te wave spectrum are essent a   or sa e an  e c ent s p operations at sea: Operational guidance and decision support systems(e.g. risk of parametric roll and large wave‐induced accelerations; evaluation offatigue damage accumulation, etc.) Vessel performance and monitoring Basically, we would like to look into the future....Performance model:NowHow to look into the future?The future?? The future??•  For a ship advancing with constant speed and at a constant wave heading, future (risk) events can be derived on the basis of trend analysis (i.e. statistics) of the past recorded signals. (Assuming a stationary sea!)•  However, to include the effect of changing operational parameters (speed, course, etc.),information about the on‐site sea state is required!• Means to estimate sea states: wave rider buoys, wave radars, satellite measurements, wave buoy analogy.Means and problems for wave estimation• For decision support systems the sea state parameters are needed on acontinuous basis (i.e. on a 10‐20 minutes basis) and at the exact position ofthe moving vessel.• Due to their fixed position, the information from wave rider buoys is difficult to use (in particular on open oceanwhere the information is scarce)        .• Satellite measurements offer a paramounttool for the statistical description and treat‐ment of ocean waves and sea states. However, presently satellite measurements cannot beused in the context of DSS. (Further develop‐ments are needed.)Means and problems for wave... contd.• Wave radar systems work on a continuous basisand at the exact position of the vessel. Several studies report good and reliable estimation of seastates, but reports on the opposite also exist.Systems are somewhat expensive and require careful calibration.• What about a ship; is it not similar to a wave buoy???Content•  Introduction ‐ Field of interest (guidance and decision support systems)•  Means to obtain sea state parameters • The wave buoy analogy – Wave estimation using measured ship responses• Results – Numerical simulations and full‐scale data• Summary/conclusionsWave buoy analogyEstimation of wave spectra based on measured ship responses(measurements by a number of sensors)The principle of the wave buoy analogy1)  Measurements: from measuredship responses response spectra1)  ,   are measured.2)  Calculations: by combination of awave spectrum and linear transfer functions of the responses, re‐sponse spectra are calculated.2)   • Assumptions: stationary ship responses, linear relationship between wave excitations and ship responses (linear transfer functions)• Representations by parametric and non‐parametric modelling Studies by e g          .      . . Tannuri et al. (2003), Aschehoug (2003), Waals et al. (2002), Iseki and Terada (2002), Nielsen (2006, 2008).Which type of responses should be considered?• Global ship responses, including the complex‐valued transfer function.(acceleration(s), roll, wave induced VBM amidships, ...)• A set of three responses is simultaneously considered.           This has shown to be the best compromise.• At least one response must exhibit port/star‐board asymmetry in its corresponding     transfer function (e.g. sway and roll).• Responses of different sensitivity in the frequency range.Important issues to keep in mind...• For severe sea states (non‐linearity between excitations and responses), esti‐mations are likely to be less reliable.• Frequency insensitivity (the ship needs to respond to the waves). Consider responses with different frequency sensitivity.Rhigh‐freq. excitationstransfer functionwave energyesponsespectrumwave freq. wave freq.Governing equation(s)Measured Calculated UnknownContent•  Introduction ‐ Field of interest (guidance and decision support systems)•  Means to obtain sea state parameters • The wave buoy analogy – Wave estimation using measured ship responses• Results – Numerical simulations and full‐scale data• Summary/conclusionsResults ‐ Overview1) A study based on only numerical simulations.‐ LNG carrier‐ responses: {heave, pitch, roll}(Nielsen, 2008a, 2010)2) Analysis of full‐scale motion measurements ‐ container ship‐ eight data sets, A, B, ..., H. Duration of 15 minutes.‐ responses: {heave, pitch, roll}‐ measurements recorded during operation.‐ comparison with wave radar (WAVEX)(Nielsen 2006 2008b),  , 3) Analysis of full‐scale motion measurements from sea strial‐ research vessel (DRDC Atlantic)‐ comparisons with buoy data(Nielsen, 2011, 2012)Numerical simulations of time series (1) Time series data where the underlying wave parameters are precisely known  . LNG carrier. RAOscalculated by 3D panel code( )WasimNumerical simulations of time series (2)Uni-modal sea statesHeading 135 deg Heading 135 deg + 45 degMixed sea (wind + swell) .  .   .Heading 45 deg. Heading 90 deg. + 45 deg.Full‐scale measurements from container ship (1)FEABCDGH‐ eight data sets, A, B, ..., H. ‐ responses: heave, pitch, roll.‐ measurements recorded during operation.http://maps.google.com/maps‐ comparison with wave radar (WAVEX)‐ RAOs calculated by WasimFull‐scale measurements from container ship (2)Full‐scale measurements from sea trial (1) Responses: roll rate, roll angle, pitch rate, pitch angle, horizontal acc. and vertical acc. (all recorded at bridge). Ship motions calculated by DRDC (SHIPMO7) using(L = 71.6 m, B = 12.8 m, T = 4.8 m, Cb = 0.51)       2D strip theory Sea state monitored continuously by three wave rider buoys (MEDS C44137 and two drifting Triaxys buoys) 16 sets of trials, all with identical “relative” run patternsFull‐scale measurements from sea trial (2)WBA: Results by wave    buoy analogy.DRDC: Results obtained as the weighted average value of three floating wave rider buoys.Content•  Introduction ‐ Field of interest (guidance and decision support systems)• Means to obtain sea state parameters              • The wave buoy analogy – Wave estimation using measured ship responses• Results – Numerical simulations and full‐scale data• Summary/conclusionsConcluding remarks• Several means and methods (e.g. wave ride buoys, satellite meas., wave radars) exist to estimate wave parameters.• In DSS wave parameters are needed continuously and at actual position of the  ,                        vessel. (Exclusion of some means...)• By use of the wave buoy analogy the ship is itself considered as a wave buoyand, hence, wave estimations can be based on measured ship responses.•  Comparisons based on numerical simulations show good agreement.•  Comparisons based on full‐scale data show reasonable agreement with estimatesfrom wave radar and wave rider buoy measurements.h h f f l ll ff h•  T e p enomenon o   i tering wi  a ect t e wave estimations.•  Which combination of responses is – under given conditions – the best?And, can this combination be chosen automatically? What about uncer‐tainties in RAOs and sea state estimation? Ungoing work as a Ph.D. project (IMVA).Thank you – Questions?

Sea state estimation from an advancing ship - The wave buoy analogy:Presentation at Skibsteknisk Selskab

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Sea state estimation from an advancing ship - The wave buoy analogy:Presentation at Skibsteknisk Selskab

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