Full Scale Measurements Sea trials 1 Experimental Methods in Marine Hydrodynamics Lecture in week 45 Contents: Types of tests How to perform and correct speed trials Wave monitoring Measurement Observations Motion measurement Hull monitoring Propeller cavitation observations Performance monitoring Covers Chapter 11 in the Lecture Notes
Dedicated sea trials are conducted under the following circumstances: Delivery of newbuildings (Contractual Trials) Speed-power (compliance with contracted performance) Bollard Pull test (tugs and offshore vessels compliance with contracted performance) Maneuvering (compliance with IMO criteria) Sea keeping (only high speed craft) If a special problem has arisen, for instance: Propeller noise and/or erosion Steering problems Excessive fuel consumption For research purposes (quite rare due to high costs) 2
Delivery Sea trials (Contractual trials) 3 Ship building contracts contain specific requirements for speed-power performance Failure to meet requirements means fees to be paid and ultimately that the ship owner has the right to refuse to accept the ship For tugs and offshore vessels, there will be requirements for bollard pull as well There might be requirements also for maneuvering trials : Emergency stop test Turning circles Zig-zag tests High speed craft requirements also for seakeeping tests IMO: 2000 HSC Code (IMO 185E)
Applicable standards ISO 19019:2005 Sea-going vessels and marine technology -- Instructions for planning, carrying out and reporting sea trials ISO 15016:2015(E) Guidelines for the assessment of speed and power performance by analysis of speed trial data Replaced previous version in 2015. Significant differences! ITTC Recommended procedure 7.5-04-01-01.1 Preparation and Conduct of Speed/Power Trials ITTC Recommended procedure 7.5-04-01-01.2 Analysis of Speed/Power Trials Data IMO: 2000 HSC Code (IMO 185E) Requirements for testing of high speed craft 4
5 http://ittc.info
IMO HSC testing requirements Stopping Normal stop from max speed to zero Emergency stop Crash stop Cruise performance in two sea states Normal conditions Worst intended conditions Measurements of accelerations, speed, relative wave heading Failure tests Check that the ship, crew and passengers are not at risk if for instance the steering fails 6
Organization of Delivery Trials The Shipbuilder is responsible Trial Leader From the shipbuilder Responsible for the execution of all phases of the trial Ship masters There is one ship master hired by the shipbuilder who is in charge of handling the ship There is usually one or more ship masters hired by the shipowner who is going to take over the ship Measurements are performed by shipbuilder or by third party (like Marintek or Maskindynamikk) 7
Execution of speed trials Always run back and forth at same engine setting Run back and forth at the same track Perform runs at different speeds (at least three) If possible, orient the track with and against the wave direction > Min. 10 minutes Steady Approach Steady Approach > Min. 10 minutes 8 Waves
Leading marks («overettmerker») Measured mile 9
Trial Conditions max acceptable 10 Sea state When wave spectrum is measured: When wave height is visually observed: Wind Beufort 6 (20 knots) (for ships with L>100 m) Beufort 5 (for ships with L 100 m) Water depth h 2 If h 3 B TM or h 2.75V S g correction is required Tests shall not be performed in waters where h 2 B T 2 M or h V g Current 2 S H13 2.25 L PP 100 H13 1.5 L PP 100 In cases of current time history deviating from the assumed parabolic/sinusoidal trend and the change of the current speed within the timespan of one Double Run is more than 0,5 knots, tests shall not be carried out
Trial Conditions Contractual Sea state Wind No waves In practice: Beufort 1 (Wave height 0.1 m) No wind In practice: Beufort 2 (Wind speed 6 knots) Water depth h Deep, In practice: and Current No current h 3 B TM 2 h 2.75V S g No practical limit for when corrections are made. Use of double runs means that corrections are always included 11
Correction of trial results 12 When trial conditions are not fulfilled corrections must be made Typical corrections: Draught interpolation in model test results on two draughts Wind calculation of wind resistance using empirical drag coef. or results from wind tunnel tests Shallow water empirical formulas Waves calculation of added wave resistance and speed loss Standards for how corrections shall be performed: ISO 15016 Guidelines for the assessment of speed and power ITTC Recommended procedure 7.5-04-01-01.2 Analysis of Speed/Power Trials Data STAWAVE by Marin Comes with a free software package for performing the analysis
13 ISO 15016 correction flow chart
ISO 15016 correction method Compute resistance correction: Compute power correction: The propulsive efficiency is assumed to vary linearly with the added resistance: 14
IMO Energy Efficiency Design Index - EEDI Increases the need for standardized trial and correction procedures The speed at 75% MCR in calm water must be accurately determined Now longer just a matter for yard and ship owner Shall be approved by classification society 15
Speed measurement 16 Speed over ground and Speed through water Timing a measured mile the old-fashioned way, only applicable to dedicated speed trials Gives speed over ground GPS The obvious choice, always used Gives speed over ground Speed log Device to measure speed through water Always installed on ships Doppler log is most common on large ships Measures speed at about 10 m below bottom, close to bow The accuracy is questionable!
Measurement of shaft power 17 Strain gauges glued directly to the shaft Calibration factor must be calculated, so shaft dimensions and material properties must be known exactly Tachometer to measure shaft speed Commercial power meters Made for permanent installation The best, but most expensive alternative Poor, but cheap alternatives are fuel rack measurements (measurement of fuel consumption, combined with supplier data for fuel quality) measurement of cylinder pressure (used on large, slow speed engines) For diesel-electric drive-trains, the frequency converter ( drive ) will usually be able to output information about power supplied to the electric motor
Shaft measurements 18 Torque measurement Thrust measurem.
19 Optical torque sensor
Optical thrust and torque measurement Required accuracy for thrust measurement is 25 naonometers! Challenging, but possible, according to supplier VAF Instruments 20
Bollard Pull Tests 21 Good location Poor location
22 Bollard pull test
Bollard pull test 2x460 kw 23
Maneuvering trials Trial types and execution same as in model scale Measurements: (D)GPS position measurement Gyro compass course Rate of turn (if possible) Rudder angle Propeller revs 24
Types of Ship Maneuvers IMO standard maneuvers: Zig-zag tests 10º/ 10º to both sides 20º/ 20º to both sides Turning circle test 35º rudder angle Full astern stopping test Additional maneuvers: Spiral test Reverse spiral test Pull-out maneuver normally added at the end of a turning test 25
26 Zig-zag test
27 Test 2011: 20-20 zig zag
28 Turning circle
Testing of position-keeping ability and thruster performance at zero speed 29 Important for vessels that have requirements to Dynamic Positioning (DP) performance No standard tests or commonly recognised procedures There is a need for development of standardized tests and analysis procedures for this purpose A way to characterise thruster performance at zero speed: Run the thrusters in different combinations (one by one, and in specific combination) for a short time Measure the acceleration of the ship in the horizontal plane Compute the impulse required to create the acceleration Compare the effective impulse with the impulse provided by the thruster(s) to arrive at a kind of efficiency
Measurements environmental conditions 30 Water depth Echo sounder (ship instrument) or nautical charts Water quality Temperature: Cooling water intake temperature can be used Density: From nautical charts or density measurements Wind Velocity and direction from anemometer A separate, calibrated instrument is preferable Watch out for influence of superstructure on the measurement Current Nautical charts and tables the difference in speed between double runs a 360º turning test at low speed The difference between log speed and GPS speed often, one doesn t trust the speed log sufficiently for this purpose
Wave measurements Visual observation and estimation Estimates by yard representative, ship-owner representative, and possibly a neutral third party are compared and averaged Mobile wave buoy Accurate (but only at a single point) Recovery of the buoy is difficult (risk of loosing it) Fixed weather station Good solution if one is nearby Wave radar (Wavex) Bow-mounted altimeter Wave information without measurement: Hindcast data 31
Wave buoys 32 Fugro Oceanor Wavescan Directional wave spectrum Wind Current Water temperature and salinity Must be moored; large, heavy, costly Smaller, spherical buoys Drifting or moored Simple buoys measure wave height only by use of an accelerometer Advanced buoys can measure the directional wave spectrum through use of the Doppler shift of the GPS signals Usually measures position for a drifting buoy this can be used as an estimate of current Can be brought along for a full scale test
33 Wavex by Miros AS
Bow-mounted altimeter SM - 094 Measures relative wave motion Ship motions must also be measured in order to calculate absolute wave height SM - 055 34
Using the ship as wave buoy Measurement of ship motions and accelerations Knowledge of ship motion transfer functions can be used to find the wave spectrum from the measured ship motion power spectrum Current research topic Can hardly work for short waves, since then the ship doesn t move Problematic when heading, speed or other operational parameters change 35
37 Beufort wind scale with related sea conditions Sea Description term Wind sp. [knots] Wave height [m] S Beufort state Wind Wave min max Probable Max D 0 0 Calm Calm 0 1 0 0 c 1 0 Light air Ripples 1 3 0.1 0.1 R 2 1 Light breeze Small wavelets 3 6 0.2 0.3 S 3 2 Gentle breeze Large wavelets 6 10 0.6 1 L 4 3 Moderate breeze Small waves 10 16 1 1.5 S 5 4 Fresh breeze Moderate waves 16 21 2 2.5 M 6 5 Strong breeze Large waves 21 27 3 4 L 7 6 Near gale Large waves 27 33 4 5.5 S 8 7 Gale Moderately high waves 33 40 6 7.5 M 9 8 Strong gale High waves 40 47 7 10 H 10 9 Storm Very high waves 47 55 9 12.5 V 11 9 Violent storm Exceptionally high waves 55 63 11.5 16 E 12 9 Hurricane Exceptionally high waves 63 71 14 16 A 13 9 Hurricane Exceptionally high waves 71 80 >14 >16 14 9 Hurricane Exceptionally high waves 80 89 >14 >16 15 9 Hurricane Exceptionally high waves 89 99 >14 >16
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Illustrations of Beufort wind (and wave) scale From: http://en.wikipedia.org/wiki/beaufort_scale 39
Hindcast data 40 Information about wave and wind condition in the past Data collected by meteorological institutes From wave buoys, weather stations, satellites, observations Many different sources European Centre for Medium-Range Weather Forecasts ECMWF National Oceanic and Atmospheric Administration www.noaa.gov is the main source Many different applications are using their open data From hindcast data you can get information about sea state and wind in your area You can of course not get wave elevation time series! Localized information for the Norwegian coast: Norkyst 800 http://thredds.met.no/thredds/catalog/fouhi/norkyst800m-1h/catalog.html
http://www.ecmwf.int/ European Centre for Medium-Range Weather Forecasts An independent intergovernmental organisation founded in 1975 and supported by 34 states Produces global numerical weather forecasts for users worldwide Offers hindcast data for wind and waves freely available for download Data in GRIB file format requires a suitable routine for reading and interpreting 41
Ocean current 42 Important to correct speed-power related measurements for the effect of current Dedicated speed trials aim at cancelling the effect of current by using double runs For ship monitoring (monitoring performance during normal operation) this is not an option Direct measurement possible by using buoys Not a practical solution for ship monitoring! If accurate speed-through-water measurement on the ship was available, problem would be solved, but it isn t! Hindcast data available from OSCAR Ocean Surface Current Analyses Real-time http://www.esr.org/oscar_index.html The Norkyst 800 model gives current forecast and hindcast
Measurement of motions Accelerations: Conventional accelerometers Angles: Gyros, compass, accelerometers Rate gyro to measure rate of change of angles Inertial Measurement Units (IMU) Consists of a number of accelerometers built into one compact unit Gives out accelerations, velocities and motions at any point Konsberg Seatex MRU is a good example of a commercial IMU Kongsberg Seapath Combination of DGPS and IMU for accurate position measurement 44
45 Kongsberg Seatex MRU 5+
46 Kongsberg Seapath 330
Measurement of forces: Hull Monitoring Hull Monitoring System: Strain gauges most common sensor Short and long gauges Cabling exposed to damage, gauges work loose Sensors based on fiberoptics - polarimetric and bragg-grating suggested as alternative Strain gauge in protective casing: 47
Rolls-Royce Health and Monitoring System - HEMOS 48
Performance monitoring Typical merchant ship application: To monitor the development of speed and fuel consumption over time, in order to detect need for maintenance Challenges: Monitoring and correcting for environmental conditions Waves, wind, water temperature Accurate measurement of shaft power and speed through water Measuring and correcting for loading condition Data processing Setting-up and running automatic data transmission Many other types of performance monitoring coming up Ref. Rolls-Royce HeMOS system 50
Propeller Cavitation Observations 51 Seen from below Seen from the side
Cavitation observation techniques 2. generation borescope 52 Source: marin.nl 1. generation borescope
Sample picture from full scale propeller cavitation observation 53 Summary: Types of tests How to perform and correct speed trials Wave monitoring Measurement Observations Motion measurement Hull monitoring Propeller cavitation observations