Sar-Drift: Drifting at sea, whence and whereto?

Transcription

1 Sar-Drift: Drifting at sea, whence and whereto? Michel Olagnon IFREMER Brest, France

2 With material from: Sar-Drift: Drifting at sea, whence and whereto? Øyvind Breivik Marc Pavec Art Allen José Perez Marrero Marc Le Boulluec Christophe Maisondieu Emmanuel Mansuy Bertrand Forest

3 Outline Problem and context. Uncertainties involved: - metocean - aerodynamics - hydrodynamics A few State-of-the-Art systems. Sar-Drift results: - Basin tests - Examples (Napoli) - Perspectives (field tests)

4 Problem Every day, objects are drifting at sea when we would want to have them back onshore or at least to know precisely where they are.

5 Problem Statistics of the use of MOTHY, French drift prediction system.

6 Problem Containers.

7 Problem Small crafts.

8 Problem Illegal immigrants.

9 Problem Person In Water (PIW)

10 Problem Self-locating marker buoys may not always drift as the object of interest, or may have failed to be deployed.

11 Objective To generate search areas for the Search and Rescue Services based on the best available wind and current information Challenge To paraphrase Einstein: Make search areas as small as possible, but not smaller

12 Search Maths POS = POD x POC POS: Probability of success (do we find what we are looking for?) POD: Probability of detection (the keen eyes of the rescuers) POC: Probability of containment (are we searching in the right place?), our business.

13 The Uncertainties Involved Where and when did the accident take place? Which object should we look for (life raft, person in water, )? What are the wind and wave conditions like in the area? What are the surface currents in the area? How does the object move when submitted to wind, waves and current?

14 Metocean Uncertainties Wind and wave conditions Meteorological forecast models are good in average, but often wrong on the precise timing of changes in speed and direction. Current Quick-varying and strong in tidal-dominated areas. Wind-dependence in addition to normal.

15 Metocean Uncertainties The directions to go: Improve the quality of forecast (nowcast) of sea state conditions, and provide associated confidence intervals. Solve the logistics problem of making that information readily available to those who need it. Be able to post-enhance forecast information from actual field observations.

16 Aero- & Hydro-dynamics Wind speed and object drift is approximately linearly related Different objects drift differently Undrogued life raft Life raft with drogue

17 Aero- & Hydro-dynamics Waves induce slowdrift on objects, and swell often coexists with the [locally generated] wind sea, so the use of a single mixed coefficient for wind and waves may not always be appropriate.

18 Empirical leeway data 63 classes of SAR objects have been compiled by the U.S. Coast Guard through extensive field campaigns and were generously made available to the project. GPS/ARGOS antennae 6 foot mannequin light Survival Suit Aanderaa Current Meter

19 Leeway divergence Objects do not drift exactly downwind!

20 Leeway divergence Objects drift at an angle to the wind (the leeway divergence angle) Symmetry allows stable drift left and right of downwind. This leads to a diverging search area as time progresses RWD = -135 o Leeway Drift Direction Wind to Wind Direction From L α = -25 o Wind to Lα = +25 o Wind to Wind Direction From Leeway Drift Direction RWD = +135 o

21 Drift models Several nations have developed drift models that enable to define search areas NORWAY: LEEWAY

22 Drift models USA: SAROPS

23 Drift models SWEDEN: BADIS

24 Drift models UK: SARIS

25 Drift models FRANCE: MOTHY

26 Drift models POLAND

27 Drift models All those models have in common a simple way to take into account uncertainties: run many cases perturbating the conditions in a rather empirical manner. Most of them rely on international collaboration for their inputs, as well for metocean forecasts as for drag coefficients. The main differences are more in their adaptation to local specifics (language, frequent objects, tidal currents, complex coastline, etc. ) than in their principles. In the Sar-Drift project, we want to improve the stochastic descriptions of metocean forecasts and drag coefficients and to have a system with the ability to accept and make full use of those improved descriptions.

28 Drag coefficients In the present version of most drift codes, waves are not present (or they are represented by an artifical increase in the wind drag coefficients). Need to get information from Ifremer basin tests

29 Coefficients for other objects Tank-Containers and Barrels Standard dimensions 20 x 8 x 8 6 (6.1m x 2.44m x 2.59m) Max. Gross 30.5 t Tare 4.2 t Max Payload 26.3 t Oil drums Diameter 0.6 m Height 1.21 m Volume 200 l (55 gal)

30 IFREMER wave tank in Brest Length: 50 m Width: 12,5 m Depth: 10 m and 20 m Wave maker : Regular and irregular waves Max. wave height (crest-to-trough): 50 cm. Range of Periods [0.8s 3.5 s].

31 Basin tests at Ifremer Tests carried out in September 2006 with 1/8 th models of 20 ft and 40 ft containers.

32 Basin tests at Ifremer Tests carried out in July/August 2007 with wind and with other models.

33 Basin tests at Ifremer First results on drift speed due to waves show computations are not too bad.

34 Basin tests at Ifremer Qualitative observations: In some conditions, fast drift, up to more than 2 knots real scale.

35 Basin tests at Ifremer Qualitative observations: Though head- and beam-orientations favoured, transverse lift does occur with waves only.

36 Basin tests at Ifremer First impressions: Waves and wind should be considered separately when possible for objects of the size of a container. Tests are very instructive.

37 Basin tests at Ifremer Preliminary conclusions: Need to improve the modeling of drag and drag uncertainties in the drift simulation software packages. Numerical hydrodynamic modeling can help develop the variety of the databases in addition to basin tests.

38 Complementary works : Trials with wind only at CSTB in Nantes

39 MSC NAPOLI

40 MSC NAPOLI

41 MSC NAPOLI Cookies Cookies and oil pellets arrived and started stranding on the North coast of Brittany on 25th of January. Could they come from the beached wreck?

42 MSC NAPOLI Cookies Most likely they came rather from losses during the towing operations!

43 NORNAVTRAINEST/Tactics & Doctrine PERSPECTIVES Field tests with Norwegian Coast Guards in the Fedje area NCV Aalesund Technical Details: Length: 63 M Width: 11,5 M Draft: 6,2 M Deplasement: 1357 T Oil equipment: Nofi 800S Transrec 250 Foxtail retrival system Oil recovery tank: 765m3 tank capacity Engine: Main: Wichmann 8V28B 2640 kw at 660 rpm Backup: 2 x Volvo Penta TAMD 163 A-A, 428 kw at 1800 pm Thrusters: Bow: Ulstein 90 TV, 420 Kw Aft: Ulstein 90 TV, 420 kw MOB-boats: -Sea Bear MKII 25 fot, 33 knop -Sea Rider 7 mtr, 2 x 75 Hk Yamaha, 36 knop Crew: Officers: 7 Conscripts 12 Civilians 3 Satcom with internet onboard Linecapasity:~215kb/s

44 NORNAVTRAINEST/Tactics & Doctrine The Area Experimentation Area Fedje Traffic Control Bergen Distance from base to AOP; ~42 nm Transit time; ~4 hrs Haakonsvern Naval Base

45 Perspectives Improve the modelling of drift Improve the inputs to drift programs Provide tools to optimize search operations

46 Perspectives We need to build on our strong points: International collaboration, with informal and formal exchanges. To this aim, we will set up a 3rd International SAR workshop in SeaTechWeek 2008 in Brest. Scientific quality. We want to raise interest in the scientific laboratories working in hydrodynamics and stochastics for the topic of search of drifting objects by publishing papers and offering PhD. scholarships. Media interest. We depend almost exclusively on public funding, and buzz-topics get much more chances to be funded.