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DYNAMIC POSITIONING CONFERENCE
October 14-15, 2014
POWER/THRUSTERS
DP Thrusters – Dynamic Loads and Mechanical Damages
Dr. Ir Jie Dang
MARIN
DP THRUSTER
DYNAMIC LOADS & MECHANICAL DAMAGES
Dr. Ir. Jie Dang
CONTENTS
• Introduction
• Test set-ups for hydrodynamic loads
• Test set-ups
• Load transducers
• Similarities and scaling
• Synchronized high-speed video recordings
• Test procedures
• Type of tests
• Data analysis
• Quasi-steady test technique
• Test results
• Ventilation loads
• Ice-thruster impact loads
• Concluding remarks
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INTRODUCTION
• More than 50 years of industry applications
• Diesel-electric drive
Classification statistics of mechanical damages
• Increase power and size
• Wide range applications
• Gear damages
• Surface pitting
• Sub-surface fatigue
• Tooth root damage
• ……
• Tooth Interior Fatigue Fracture (TIFF)
TIFF damage to a tooth of a bevel gear
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INTRODUCITON
• Lack of understanding, lack of workshop testing
• What the wind mill industry is doing:
NREL’s 2.5 MW Dynamometer Test Bed CURI’s 15MW RENK LABECO Test Systems
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INTRODUCTION
• What marine industry is catching up:
WPTC’s 2MW Thruster Test Centre in Helsinki
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TEST SET-UPS FOR HYDRODYNAMIC LOADS
• Typical thrusters for DP applications
• Generic pulling thruster with open propeller, electric motor
• Generic pushing thruster with ducted propeller, gear drive
generic pulling thruster with C4-70 propellers (2X6-C) generic pushing thruster with D4-70 in 19A (3X6-C)
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TEST SET-UPS FOR HYDRODYNAMIC LOADS
• The Depressurized Wave Basin (DWB) at MARIN
MARIN’s Depressurized Wave Basin (DWB) with wave generators
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TEST SET-UPS FOR HYDRODYNAMIC LOADS
• How to measure dynamic loads?
• Sensitivity of transducer response frequency
• Mass-spring-damper system
• Increase natural frequency of the system
• Increase the stiffness of transducers k
• Reduce mass on metric side - m
• Increase mass on non-metric side
mass-spring-damper system and its dynamic response
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TEST SET-UPS FOR HYDRODYNAMIC LOADS
• Six component transducers or frames
Unit Duct Shaft
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TEST SET-UPS FOR HYDRODYNAMIC LOADS
• Natural frequency of transducers
Unit Duct
Shaft
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TEST SET-UPS FOR HYDRODYNAMIC LOADS
• Scaling laws and similarities 𝜎𝜎𝑛𝑛 =
𝑝𝑝𝑎𝑎 + 𝜌𝜌𝑔𝑔ℎ − 𝑝𝑝𝑐𝑐
2
0.5𝜌𝜌𝐷𝐷 𝑛𝑛 2
=
𝑝𝑝𝑎𝑎 − 𝑝𝑝𝑐𝑐
2
0.5𝜌𝜌𝐷𝐷 𝑛𝑛 2
ℎ/𝑅𝑅
+ 2
𝐹𝐹𝑅𝑅𝑁𝑁
• Reynolds Number
• Froude law of ship
• Cavitation number of propeller 𝐷𝐷
𝐹𝐹𝑅𝑅𝑁𝑁 = � 𝑛𝑛
𝑔𝑔
𝜌𝜌𝑉𝑉 2 D 𝜌𝜌𝑛𝑛2 𝐷𝐷3
• Weber number 𝑊𝑊𝑒𝑒 =
𝛾𝛾
=
𝛾𝛾
• Air cushion effect
• Cauchy scaling for ice-propeller interactions
• Synchronized high-speed video recordings
Propeller Froude number effect
11
TEST PROCEDURES
• Type of tests – dynamic loads
• During extreme maneuvering
• During thruster-thruster interaction
• Ventilation
• Ice-thruster interaction
• Open water and also in behind conditions
12
TEST PROCEDURES
• Data analysis
• Coordinate systems
• Ship fixed O-XYZ
• Thruster fixed o-xyz
• Blade fixed o-xtr
• Non-dimensionalized
F ,T M ,Q
K F ,T = K M ,Q =
ρ n2 D 4 ρ n2 D5
• Fourier fitting
N
=K ∑ [ A sin(kδ ) + B
k =0
k k cos(kδ ) ]
The coordinate systems
13
TEST PROCEDURES
• Quasi-steady model tests The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.
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TEST RESULTS
• Ventilation inception – vortex induced
onset developing fully developed
An example of vortex induced ventilation in bollard pull condition, thruster with ducted propeller
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TEST RESULTS
• Ventilation inception – blade low pressure induced
onset fully developed retrieving finishing
An example of blade ventilation in waves, pulling thruster with open propeller
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TEST RESULTS
• Ventilation
inception
onset start duct L.E. ventilation blade ventilated
fully ventilated duct L.E. ventilation finishing finishing
17
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TEST RESULTS
• Alternate blade ventilation
An example of alternate blade ventilation on the propeller of a thruster with even-numbered blades
19
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TEST RESULTS
• Blade dynamic loads
Blade dynamic loads in 5 wave periods, open propeller P/D= 0.8, thruster steering angle 0 degrees, advance ratio 0,
shaft immersion 1.5R, cavitation number σn=2.0, wave amplitude 1R, period 2 seconds
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TEST RESULTS
• Shaft dynamic loads
Non-dimensionalized shaft loads in one wave period, propeller pitch ratio 0.8, thruster steering angle 0 degrees,
advance ratio 0.0, shaft immersion 1.5R, cavitation number σn=2.0, wave height 1R, wave period 2 seconds
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TEST RESULTS
• Ice-propeller impact loads
An example of propeller flow blocked (but not touched) by an ice floe, resulting in sudden increase in blade thrust FX
and torque MX, minor influence on blade spindle torque MZ, synchronized results
23
TEST RESULTS
• Ice-propeller impact loads
An example of ice impact on the suction side of a blade when the blade cuts into the ice, resulting in a strong
negative peak of thrust FX, torque MX and blade spindle torque MZ, synchronized results
24
TEST RESULTS
• Ice-propeller impact loads
An example of an ice floe being cut-off and extruded from the pressure side of a blade, resulting in a high positive
peak of blade thrust FX and torque MX, and fluctuations of blade spindle torque MZ, synchronized results
25
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CONCLUDING REMARKS
• Transducers with high accuracy and high response frequency
are essential.
• Test conditions and scaling laws are very important – DWB
• Quasi-steady test technique to reduce cost
• Dynamic loads are synchronized with high speed video
recordings – understanding the physics
Important for thruster designers, manufacturers, classification
societies, and also for the operators to prevent damages to
mechanical thrusters in service
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THANK YOU!
