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Transcript of Full Scale Measurements Sea trials - IV - · PDF fileFull Scale Measurements –Sea trials...
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Full Scale Measurements – Sea trials
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
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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)
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Delivery Sea trials (Contractual trials)
• 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)
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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
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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
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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)
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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
•Steady Approach
> Min. 10 minutes
•Steady Approach
> Min. 10 minutes
Waves
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Measured mile
Leading marks («overettmerker»)
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Trial Conditions – max acceptable
• 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
– If or correction is required
– Tests shall not be performed in waters whereor
• Current
– 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
1 3 2.25 100PPH L
1 3 1.5 100PPH L
3 Mh B T 22.75 Sh V g
2 Mh B T 22 Sh V g
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Trial Conditions – Contractual
• Sea state
– No waves
– In practice: Beufort 1 (Wave height 0.1 m)
• Wind
– No wind
– In practice: Beufort 2 (Wind speed ≤ 6 knots)
• Water depth h
– Deep,
– In practice: and
• Current
– No current
– No practical limit for when corrections are made. Use of double runs
means that corrections are always included
3 Mh B T 22.75 Sh V g
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Correction of trial results
• 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
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ISO 15016 correction flow chart
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ISO 15016 correction method
• Compute resistance correction:
• Compute power correction:
• The propulsive efficiency is assumed to vary linearly with
the added resistance:
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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
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Speed measurement
• “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!
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Measurement of shaft power
• 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
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Shaft measurements
Torque measurement Thrust measurem.
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Optical torque sensor
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Optical thrust and torque measurement
Required accuracy for thrust measurement is
25 naonometers!
Challenging, but possible, according to
supplier VAF Instruments
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Bollard Pull
Tests
Good location Poor location
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Bollard pull test
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Bollard pull test
•2x460 kW
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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
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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
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Zig-zag test
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Test 2011: 20-20 zig zag
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Turning circle
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Testing of position-keeping ability and
thruster performance at zero speed
• 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
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Measurements – environmental conditions
• 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
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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
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Wave buoys
• 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
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Wavex by Miros AS
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Bow-mounted altimeter
• Measures relative wave motion
• Ship motions must also be measured
in order to calculate absolute wave
height
SM - 055
SM - 094
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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
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Beufort wind scale with related sea conditionsSea Description term Wind sp. [knots] Wave height [m] Sea
Beufort state Wind Wave min max Probable Max Description
0 0 Calm Calm 0 1 0 0 calm; like a mirror
1 0 Light air Ripples 1 3 0.1 0.1 Ripples with appearance of scales:no foam crests
2 1 Light breeze Small wavelets 3 6 0.2 0.3 Small wavelets; crests of glassy appearance, not breaking
3 2 Gentle breeze Large wavelets 6 10 0.6 1 Large wavelets; crests begin to break; scattered whitecaps
4 3 Moderate breeze Small waves 10 16 1 1.5 Small waves, becoming longer numerous whitecaps
5 4 Fresh breeze Moderate waves 16 21 2 2.5 Moderate waves, taking longer form; many whitecaps; some spray
6 5 Strong breeze Large waves 21 27 3 4 Larger waves forming; whitecaps everywhere; more spray
7 6 Near gale Large waves 27 33 4 5.5 Sea heaps up; white foam from breaking waves begins to be blown in streaks
8 7 Gale Moderately high waves 33 40 6 7.5 Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks
9 8 Strong gale High waves 40 47 7 10 High waves; sea begins to roll; dense streaks of foam; spray may reduce visibility
10 9 Storm Very high waves 47 55 9 12.5 Very high waves with overhanging crests; sea takes white appearance as foam is blown in very dense streaks; rolling is heavy and visibility is reduced
11 9 Violent storm Exceptionally high waves 55 63 11.5 16 Exceptionally high waves; sea covered with white foam patches; visibility still more reduced
12 9 Hurricane Exceptionally high waves 63 71 14 16 Air filled with foam; sea completely white with driving spray; visibility greatly reduced
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
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Hindcast data
• 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/fou-
hi/norkyst800m-1h/catalog.html
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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
http://www.ecmwf.int/
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Ocean current
• 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
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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
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Kongsberg Seatex MRU 5+
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Kongsberg Seapath 330
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Measurement of forces:
Hull Monitoring
• Strain gauges most
common sensor
• Short and long gauges
• Cabling exposed to
damage, gauges work
loose
• Sensors based on fiber-
optics - polarimetric and
bragg-grating suggested as
alternative
Hull Monitoring System:
Strain gauge in protective casing:
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Rolls-Royce Health and Monitoring
System - HEMOS
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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
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Propeller Cavitation
Observations
Seen from below Seen from the side
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Cavitation observation techniques
1. generation borescope
2. generation borescope
Source: marin.nl
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Sample picture from full scale propeller cavitation observation
Summary:
•Types of tests
•How to perform and correct speed trials
•Wave monitoring
•Measurement
•Observations
•Motion measurement
•Hull monitoring
•Propeller cavitation observations