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1
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
2
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)
3
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)
4
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
6
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
7
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)
8
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
9
Measured mile
Leading marks («overettmerker»)
10
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
11
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
12
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
13
ISO 15016 correction flow chart
14
ISO 15016 correction method
• Compute resistance correction:
• Compute power correction:
• The propulsive efficiency is assumed to vary linearly with
the added resistance:
15
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
16
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!
17
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
18
Shaft measurements
Torque measurement Thrust measurem.
19
Optical torque sensor
20
Optical thrust and torque measurement
Required accuracy for thrust measurement is
25 naonometers!
Challenging, but possible, according to
supplier VAF Instruments
21
Bollard Pull
Tests
Good location Poor location
22
Bollard pull test
23
Bollard pull test
•2x460 kW
24
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
25
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
26
Zig-zag test
27
Test 2011: 20-20 zig zag
28
Turning circle
29
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
30
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
31
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
32
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
33
Wavex by Miros AS
34
Bow-mounted altimeter
• Measures relative wave motion
• Ship motions must also be measured
in order to calculate absolute wave
height
SM - 055
SM - 094
35
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
37
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
38
39
•Illustrations of Beufort wind (and wave) scale
•From: http://en.wikipedia.org/wiki/Beaufort_scale
40
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
41
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/
42
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
44
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
45
Kongsberg Seatex MRU 5+
46
Kongsberg Seapath 330
47
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:
48
Rolls-Royce Health and Monitoring
System - HEMOS
50
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
51
Propeller Cavitation
Observations
Seen from below Seen from the side
52
Cavitation observation techniques
1. generation borescope
2. generation borescope
Source: marin.nl
53
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
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