04 MARIN Challenging Wind and Waves

7/28/2019 04 MARIN Challenging Wind and Waves

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WAVE LOADSMarine Structural Failures, September 2011

R.P.Dallinga, I.Drummen, MARIN


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Ship Design for extremes

J ohan de J ong


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3

SHIP DESIGN

SHIP DESIGNSHIP DESIGN

Building CostsBuilding Costs

PerformancePerformance

SafetySafety

ReturnCustomers

ReturnCustomers

Operational

Costs

Operational

Costs

(Hydrodyn.Characteristics)

Hull Form & GA

Climatology

Operational Scenario&

Behaviour Criteria

Operational Scenario&

Behaviour Criteria

Operator

Values

Design Space & Constraints

Stability

Structure


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Extreme?

Hydrodynamic Integrity (fit for purpose)

ingress of water/capsizing

Structural Integrity structural stress/buckling/sea fastening

System & Control Integrity

system malfunctioning/human performance

Human Safety physical tolerance/balance/mobility


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Safety

Hydrodynamic Integrity (fit for purpose)

ingress of water/capsizing

Structural Integrity structural stress/buckling/sea fastening

System & Control Integrity

system malfunctioning/human performance

Human Safety physical tolerance/balance/mobility


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Hydrodynamic Integrity Stability


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Hydrodynamic Integrity Ingress of Water


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Hydrodynamic Integrity State of the Art

Standards from Flag Authorities (classificat. Soc.)

intact and damaged ship

allows low GM (~30 cm)

IMO Open-Top Tests

Quantification (calculation tools): hydro-static evaluation intact ships

quasi-static evaluation of damaged cases

dynamic evaluation in research stage

Risks:

no tools for realistic risk evaluation (in waves) factual risk levels (and criteria) unknown


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IMO Goal Based Standards Proposal


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WAVE LOADSMarine Structural Failures, September 2011

MARIN


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A MapTime Frame

Static

Cyclic

Transient

Wind and Water Resistance

Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency

Forces from Appendages

Forces from Propulsor

Wave Drift Forces

Wind Gusting

Wave and Motion Ind. Pressures

Appendage Forces

Motion Induced Sloshing

Higher-Order Dynamic waveInduced Excitation

Green Seas ImpactsSlamming below the Fore Foot

Stern SlammingBow Flare Slamming

Motions & Structural Respon se

Forward Speed

Drift Angle

Course Deviations/Steering

Motions and Deflections

Springing

Decaying Vibrations

Speed Variations

Flutter induced Vibrations

Moonpool Resonance

Parametric Roll

Weight Distrib & Buoyancy

Weight Distrib./ Stability

Heel Angle

Sinkage & Trim

Hog-Sag in Calm Water

Resonant

Dynamic

Underlying Excitation

Hydrostatics

Steady Flow

Breaking Wave Impacts

Cavitation/Pressure Pulse

Fluctuating Flow Separation

Stability Variations

Waves

Wind

Motion Induced Inertia Forces

EngineResponse

Local and Global Vibrations


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A MapTime Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces






Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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13

A MapTime Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces






Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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14

A MapTime Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces






Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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Static Loads & Deflections

Time Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic P ressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces





Motions & Structural Response

Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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Static Loads and Deflections

Hydrostatics at zero-speed Hydrostatic pressure

Uneven distribution of buoyancy and weight

Wind and Steady Flow Drag forces

Friction, flow separation

Appendage drag

Lift forces (angle of attack) Rudder and hull lift during a turning circle

Dynamic pressure (Bernoulli) and relatedsteady wave system

Vertical forces leading to: Sinkage and trim (squat)

Increasing sag in calm water

Engine Propulsor thrust & torque


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Static Bending Moment

Bending moment Governed by longitudinal

distribution of buoyancy and weight

Buoyancy

Buoyancy

Weight

Weight

b=F/L

b=F/L

F

Shear Force

Bending Moment

-F/2

F/2

M=F.L/4

q

Homogeneous Buoyancy and Weight Distribution

In-homogeneous Buoyancy and Weight Distribution


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Dynamic Loads

Low-Frequency Oscillation frequencies below the wave encounter

frequency range

Related to manoevring, speed variations, wave

grouping and wind gusting Wave-Frequency

Oscillation frequencies corresponding with the waveencounter frequency

Driven by: Speed

Heading

Wave frequency

High-Frequency Oscillation frequencies corresponding with the

bending and torsion modes

Driven by: Occasional (transient) slamming

Repeated 1st or 2ndorder excitation

ln(|FFT|)

frequency

Wave-Frequency

2-Node Vibrations

3-Node Vibrations

Low-Frequency


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Sub-Frequency Loads & Deflections

Time Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces


Higher-Order Dynamic wave

Induced Excitation




Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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Sub(-wave) Frequency Loads & Deflections

Irregular Waves Variations in added resistance

due to wave grouping

Wind Wind gusting

Engine & Propulsion Thrust & torque variations due

to:

Speed variations

Course variations and steering Slow engine reaction on sudden

loss of torque due to propellerventilation


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Low Frequency Component in Speed and Propeller Thrust

Speed

Thrust

Time

Low-Frequency Component

Low-Freq

Wave-Freq

Frequency

SpectralDensityThrus

t


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Wave-Frequency Loads & Deflections

Time Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic P ressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces




Stern SlammingBow Flare S lamming


Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flo w





Waves

Wind


EngineResponse



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Wave-Frequency Loads Linear Components inSmooth Waves

Components Hull

External pressures

Structure

Motion related accelerations(including motion induced gravityforces)

Appendages

Fin and rudder lift and drag

Sloshing of (anti-roll) tanks Propeller

Variations in propeller entryvelocities due to waves motions


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Side Shell Pressures

Measured Pressure

Hydrostatic Pressure Variationassociated with

Relative Wave Elevation

Emerging Pressure Gauge

Measured

Pressure

[kPa]

Measured

Pressure

[kPa]

Hydrostatic Pressure Variation [kPa]


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Character Linear Vertical Bending Moment

High response not limited tohead seas

Long ships in typical stormconditions experience thehighest loads in waves fromthe bow-quarter

Forward speed:

magnifies the loads in waves

from forward directions reduces the loads in waves

from aftward directions

Short WavesLong Waves

Head

Beam

Stern

CrestTroughCrest

Character of the Transfer Function of Vertical BendingRectangular Barge in Regular Waves

Heading

Wave Frequency

/L=1

/L=1/2/L=1/3


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Relative Magnitude of Vertical and Transverse ForcesVertical and Transverse Bending Moment 18 knot Ferry in Irregular Waves of Unit Height

Vertical Bending Moment Transverse Bending Momentrms BM in kNm per m rms wave

Sternq.

Beam

Bowq.

Head

Following


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Character Torsional Moment

The magnitude is generally

relatively small

Because they are small, thecontribution of reaction forcesfrom fins and rudders is notnegligible

The loads are highest in short,oblique waves

Short WavesLong Waves

Head

Beam

Stern

CrestTroughCrest

Heading

Wave Frequency


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Linearity of Vertical Bending Moment

At the level of transferfunctions and rms values the

bending moments are quitelinear in character

Hog-sag a-symmetry haslittle effect on these quantities

Wave frequency [rad/s]

Measured in

irreg.waves

Calculated with

linear theory

Measured in

reg.waves

Hog-Sag A-symmetry


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Effects of Non-Linear Aspects in Bending Moments

Linear theory predictionsneed correction for:

mean value

weakly non-lineareffects

strongly non-lineareffects

HogSag

xa +xa - Negative Amplitude

10%

100%

1%

0

0.1%

Positive Amplitude

Linear Theoryw/o

Steady Flow Offset

Steady Flow Offset

Frequencyof Exceedance

(Rayleigh-Scale)

-2ln(F)

1: Correction for the mean value


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mean value



The weakly non-linearforces hardly affect thedynamic range

2: Correction for weakly

non-linear effects

HogSag

xa +xa -

10%

100%

1%

0.1%

Negative Amplitude Positive Amplitude

Linear Theoryw/o

Steady Flow Offset

Steady Flow Offset

WeaklyNo n-Lin .Effect

WeaklyNo n -Lin. Effect


(Rayleigh-Scale)

-2ln(F)

Dynamic Range


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mean value



Only the strongly non-linear contribution affectsthe dynamic range(=fatigue)

3: Correction for strongly

non-linear effects

HogSag

xa+

xa-

10%

100%

1%

0.1%


Linear Theoryw/o

Steady Flo w Offset

Steady Flow Offset


Weakly

No n-Lin .Effect

StronglyNon-Lin.Effect

StronglyNon-Lin.Effect


(Rayleigh-Scale)


(Rayleigh-Scale)

-2ln(F)

-2ln(F)

Dynamic Range


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Wave Frequency Component of Propeller Load Variations

Driver Varying angles of attack on

propeller blades due to

variations in flow velocity

Speed

Thrust

Time

Wave-Frequency Component


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Propeller Thrust VariationsEffect of wave-induced inflow variations

Contributions: Incident wave

Reflected wave

Ship motions andrelated radiatedwaves

WF thrust

variations are quitelinear in character

Transfer Funct ion Thrust on Wave Amplitude

0

50

100

150

200

250

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Wave Frequency [rad/s]

ThrustperunitWaveAmp[litude

[kN/m]

Ta/zeta a.

PRECAL

Transfer Funct ion Thrust on Wave Amplitude

0

10

20

30

40

50

60

70

80

90

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Wave Frequency [rad/s]

ThrustperunitWaveAmp[litude

[kN/m]

Ta/zeta a.

PRECAL

Speed: 7.6 knots dT/dVx 102.34 kN/m/sRevs 43 rpm dkT/dJ 0.41 -Heading 180 deg

Single-Screw Container Ship in Head Seas

Measured

Calculated


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Relative Magnitude Thrust VariationsContainer ship in head seas

Contributions rms Thrust 4.85 m Hs

0

50

100

150

200

250

300

0 200 400 600 800

rpm

rms[kN]

Tot

LF

WF

HF

Contributions rms Thrust 7.45 m Hs

0

50

100

150

200

250

300

0 200 400 600 800

rpm

rms[kN]

Tot

LF

WF

HF

WF

WF LF

LF

Thrust variations are substantialWF component dominates


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Fins and Rudders


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Fins and Rudders

Drivers Mechanical reaction on ship

behaviour

False angles of attack due tomotions and waves

Do not forget dynamic effects install (which magnify the loads)

Note Because the wave induced

torsional moment on the hullitself is not very large, the

contribution of fins and rudderscan be significant

Relation between fin lift and drag

in an unsteady angle of attack


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Sloshing & Anti-Roll Tanks

Controled U-Tank

Passive U-Tank

Free-Surface Flume Tank


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Sloshing & Anti-Roll Tanks


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Resonant Deflections

Time Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic P ressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces





Motions & Structural Respons e

Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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Super-Frequency Loads & Resonant Deflections

Definition External-excitation driven response at natural frequency of

structure

Driver First-order excitation

Linear forces at high encounter frequency

Higher-order, non-linear external excitation

Non-linear hull geometry

Steep waves

Proportional to damping

Response

Continuous resonant response (springing)


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Self Induced Deflections

Time Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces






Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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Self-Induced Response: Moonpool Response in Transit

Driver

Fluctuating leading

edge flow separation

Separation locks-inon natural frequency

Critical thresholddamping above whichthe structure does notrespond


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Parametric Roll

Conditions Adequate stability variations

(which are largest in head and

following seas) Wave height & period

Hull form

Tuning of GM variations withnatural roll period (factor 2)

Wave period

Speed

GM Sufficiently low roll damping

Speed

Appendages


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Strongly Non-Linear Impulsive Loads

Time Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces




Stern Slamming

Bow Flare Slamming


Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations

Flutter induced VibrationsMoonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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Green Seas

Drivers

Freeboard

Relative wave height Forward speed

Heading


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Green Seas Loading

Breaking Dam Impact

Water rises high above thedeck edge before collapsing

on the fore deck Symmetry in head seas

creates concentrate jet inaftwarddirection

Wave Crest Scoop

Wave crest runs more or

less undisturbed aft wardover the deck


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Bow flare impacts

Drivers

Angle between the face of thewave and the shell

Wave steepness Heading

Rake

Bow flare dead rise

Relative velocity

Forward speed

Trapping of air ?


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Bow flare impacts

Evolution of strongly non-linearlocal pressures

Spatial PressureDistribution

p1p2

p3

time

p1

p2p3

Total ReactionForce

FF

Spray

Pile-up

Spray-root

Rise-time

v

v/tan( )

0.6 0.8

10 0

20 0

30 0

Time [s]0.6 0.8

10 0

20 0

30 0

Time [s]

13

2

4

Panel

Panel PressureGauges

PressureFront3

4

1

2

P

ressu

re

[kP

a]


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Stern slamming

Drivers

Speed

Stern slamming disappears

at moderate speed Heading

Stern seas yield highestimpacts

Relative angle of impact

Dead rise of buttocks andframes

Wave slope

Trapping of air


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Slamming below the Fore Foot

Drivers

Draft

Relative velocity Ship speed

Transverse dead rise

Upward change inadded mass


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Breaking Waves


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Transient Propeller Ventilation Phenomenon

Transient thrust and torque variation

Recovery Sometimes slow dissipation of air-

pocket through the tip vortex

Consequences Transient load of propulsion train Engine speeding and subsequent

controller actions Loss of turbo-charger pressure Slow recovery of power

ThrustTorque

Time

Calm Water

Waves

Ventilation Event

Slow recoverySudden collapseof thrust and torque


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Character of Strongly Non-Linear Loads

Strongly non-linearforces show:

A negative exponentialdistribution

Implying:

A low mean (typical value

Disproportionally highextreme value

Weibull fit

0.01

0.10

1.00

0 5000 10000 15000 20000

Long. Force on breakwater [kN]

Prob.

ofexc.

[1/load

even


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Deformation and Stress

Time Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces




Stern Slamming

Bow Flare Slamming


Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations

Flutter induced VibrationsMoonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind


EngineResponse



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Whipping Multi-Purpose Ship in Head Seas

660 670 680 690 700 710 72010

987654321012345

6789

10

Vertical Accelerations at the Bow

Time [s]

V.Acc.[m/s2]

.

.


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Effect of Impulse Duration on Structural Response

A short pulse with aduration < Te/2

yields a relativelyhigh vibration

Longer pulsescontain moreimpulse but yield

a lower output

0 1 2 3 44

2

0

2

4

0

0.5

1

0 1 2 3 44

2

0

2

4

0

0.5

1

ExcursionVelocityExcitation

t/Te =1.0

t/Te =0.1


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Hull Girder Deformation Container Ship


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59

Distinction between Springing & Whipping

Springing: Continuous HFexcitation

Whipping: Isolatedtransient excitation

Green seas

Bow re-entry

Stern re-entry

Bow flare entry

Breaking waves

Sloshing

At a deflection level botheffects are hard todistinguish.

Because of the lowstructural dampingsubsequent impulsiveloads interact

Because designs that are

vulnerable to slamming arealso likely to showspringing


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Assessing the whipping response Adopted

procedure Definition

Identify rigid-body peakvalues

Find local maxima of the totalsignal in the vicinity of thesepeaks

Merits The total signal is a measure

for real life problems

Number of events = number of

wave encounters

x

x

aWF

aTOT

search range

primary signal

secondary signal


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Statistical Characteristics of the Whipping

Container ship, long test, BF 10, headseas, 16 knots

Rayleigh distribution fits theamplitudes of the rigid bodycomponent reasonably well

The increase due the flexuralcomponent can be approximated by anegative exponential distribution

Because structural damping is low,RB and HF extremes can simply beadded

0 2 4 6 8 101 10

3

0.01

0.1

1

WF measured

TOT measured

Sorted Increase of WF Response

Fitted Rayleigh Distrib. WF part

F vs sum sorted (azWF+azHF)

Neg Exp based on Mean

Joint Distribution

Amplitude [m/s2]

Freq.ofExceedance[-]

.Increase

Total

Rigid

1/2hr

3hrs


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Effect of Ship Design: Ferry Bow Alternatives

Effect Heading Extreme Bow Flare

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

90 105 120 135 150 165 180

Heading [deg]

4m7.6s 4m8.9s 5m8s 5m10s

Effect Heading Typical Bow Flare

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

90 105 120 135 150 165 180

Heading [deg]

4m7.6s 4m8.9s 4m11.6s

5m8s 5m10s 5m12s

Effect Heading Modest Bow Flare

0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

90 105 120 135 150 165 180

Heading [deg]

4m7.6s 4m8.9s 5m8s 5m10s

Bow Flare

Extreme Typical Modest


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Incidental Character of Slamming Events

Because of the incidental character the master finds ithard to anticipate

Avoidance requires extreme conservatism


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Fatigue Damage

Fatigue damage isgoverned by the stressrange

In fact, by its 3rd power!

Traditionally this range isestimated on basis of lineartheory (because the weaklynon-linear effects did notaffect the range anyway)

HogSag

xa+

xa-

10%

100%

1%

0.1%


Linear Theoryw/o

Steady Flow Offset

Steady Flow Offset


WeaklyNo n -Lin. Effect


(Rayleigh-Scale)

-2ln(F)

Dynamic Range


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Whyis the HF damage important

0 10 20 30 40 50 60 70 80 90 100-50

0

50WF

Time [s]

Stress[MPa]

0 10 20 30 40 50 60 70 80 90 100-50

0

50HF

Time [s]

Stress[MPa]

0 10 20 30 40 50 60 70 80 90 100-50

0

50WF +HF

Time [s]

Stress[MPa]

Damage = 0.35610-6

Damage = 0.00710-6

Damage = 1.10210-6

Damage = 1 failure


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Origin of wave induced vibrations

The global vibration of blunt ships is generally dominated byspringing

Whipping is the main source of wave-induced vibrations for slender

ships, such as containerships

It is expected that the trend of increasing dimensions will continuefor the coming years

The larger size of ships implies an increased flexibility, and a largernatural period of the two-node vertical vibration mode

As a result the importance of hydroelastic effects associated withwhipping and springing is increased


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Fatigue damage

Aalberts and Nieuwenhuijs (2006): 25%contribution for a small container vessel

Storhaug et al. (2003): 44% contribution on boarda 294m long iron ore carrier trading in the NorthAtlantic

Drummen et al. (2008): 40% contribution 281mlong containership


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A MapTime Frame

Static

Cyclic

Transient


Fluid Dynamic Lift

Dynamic Pressure

Steady Wave System

Sub-Frequency

Wave-Frequency



Wave Drift Forces

Wind Gusting


Appendage Forces






Forward Speed

Drift Angle



Springing

Decaying Vibrations

Speed Variations


Moonpool Resonance

Parametric Roll



Heel Angle

Sinkage & Trim


Resonant

Dynamic


Hydrostatics

Steady Flow





Waves

Wind

Motion Induced Inertia ForcesEngineResponse



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Application of the State of the Art

Design choices have an important effect Bow flare dead rise Stern shape

Ballasting options Structural stiffness and continuity Power & sustained speed in adverse weather

A quantitative balance of economy and risk is hampered by: Importance uncertainties in the operation of ships

The real effect of routing

Masters ability to recognize relevant conditions (re- and pro-active)

Lack of accurate design tools to account for the impulsiveloads and related structural response


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Thank you for your attention!

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04 MARIN Challenging Wind and Waves

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