MARINTEK

NTNU

Experimental studies of springing and

whipping of container vessels

Ole Andreas Hermundstad

MARINTEK

CeSOS Highlights and AMOS Visions Conference

27-29th May 2013 in Trondheim

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Outline

Background and motivation

Description of containership models and instrumentation

Test program and sample results

Conclusions

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Background and motivation

Wave impact in the bow may give large

high-frequency hull girder vibrations

(whipping).

This occurs in rough seas and adds to the

wave-frequency loads

Hence, the loads under such impacts will

generally be the most severe wave loads

experienced by the ship.

Whipping will also contribute to fatigue

3

-20

-15

-10

-5

0

5

10

15

Pitch [

deg],

Rel. w

ave [

m],

V

BM

/50 [

kN

m]

450440430420410400

time [s]

120

100

80

60

40

20

0

Pre

ssure

[kP

a]

Pitch Rel. wave elev. VBM amidships

Press. lower panel Press. upper panel

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Background and motivation (II)

If the frequency of the wave

loads coincide with one of the

natural frequencies of the hull

girder, resonant vibrations

(springing) will occur.

This will contribute to fatigue

4

Wave elevation

Bending moment

Power

spectrum Resonance

(springing)

Ordinary

wave loads

Frekvens (Hz)

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Background and motivation (III) Ultra Large Containerships (ULCS)

Larger ships → Larger natural periods in bending and torsion

Larger ships generally go faster → More high-frequency wave loads

Larger bow flare → More nonlinear wave loads

Little experience with large (>9000 TEU) containerships in N. Atlantic / N. Pacific. Classification rule formulae uncertain.

→ Need for model tests with realistic designs

JIP 2008-2010: DNV, CeSOS, MARINTEK, BV and Hyundai (HHI)

Objective: Perform model tests with two large containerships in realistic conditions to provide data for further analysis: How important is springing and whipping wrt. fatigue and extreme loading?

Which sea-states contribute the most?

How well do available numerical methods predict the loads and responses?

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Two large containerships

8600 TEU 13000 TEU

Lpp [m] 323 350

B [m] 45 48

Design draught [m] 13 14.5

Displacement [ton] 128000 170000

2-node bending freq. [Hz] 0.48 0.48

Torsional freq. [Hz] - 0.39

Damping ratio [%] 0.9-1.0 0.9-1.0

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Design of models

Criteria:

Realistic natural frequencies in the 2-node vertical mode

and in torsion

Measure 6 DOF forces and moments at 3 locations

Low damping

Speeds up to 27 knots

Significant wave heights up to 11.5 m

To be tested in head and oblique seas

To be towed

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Ship model concepts

Fully elastic

Backbone

Hinged

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Fully elastic models

The hull itself is made flexible

Realistic deformation pattern

Expensive to produce

Difficult to adjust flexibility

Forces and moment measurements require extensive

strain gauge instrumentation and calibration

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Elastic backbone models

Flexibility modelled with an

elastic backbone

Hull is segmented

Responses measured at the

backbone (strain gauges)

Difficult to adjust stiffness after

production

10

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Segmented models

Flexibility is only in the ”hinges”

Relatively easy to manufacture

”Hinges” can be made with adjustable

stiffness -> Model can be calibrated to give the correct

vibration frequencies in the lowest modes

Forces and moments measured close to the hinges

New challenge: Include torsional flexibility

11

1560 1560 10201350

B

B

C

C

D

D

E

E

320

A

A

top view

longitudinal at centre line

Construction Drawing

Canmar Spirit (1:45)

topview and longitudinal at CL

Ingo Drummen

340

200 1000

MS

horizontal at 267 mm above base line

propeller

motor

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Segmented containership models

4 segments.

3 flexible connections

Forces and moments are measured close to the flexible

connections.

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Requirements to the flexible connections

Minimum damping

Flexible in vertical bending and torsion

Adjustable stiffness

Low complexity, robust

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Design of frame and connection details

Verified using finite element analysis

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Flexible connection

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Instrumentation

6 DOF motion measurements (optical system)

Accelerometers (x,y,z-directions)

Wave probes (conductive and acoustic types)

Slamming panels

Pressure gauges

Force/moment transducers close to the

flexible connections

Measure towing speed and towing forces

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Slamming panels in the flare

Sampled at 4800 Hz

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Accelerometers

Located fore, aft

and amidships

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Wave probes

Some fixed to

the model

Some fixed to

the carriage

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Optical motion measurement system

Pressure gauge

Slamming panel

Wave probes

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Pressure gauge for green water events

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Test set-up

Towed model

Towing connection

at the aft segment

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Decay tests

To measure eigenperiods and damping

Forward speed tests in calm water

To measure steady forces and moments

Forward speed tests in regular waves

For comparison with numerical predictions

Forward speed tests in irregular waves

Focus on realistic conditions

In head seas: 16 sea-states (4 Tp and 4 Hs values) + 2 extreme

In oblique seas (13000TEU only): 9 longcrested + 9 shortcrested

Speed is adjusted to obtain a realistic speed in each sea-state

Test duration: At least 30 min in each sea-state. Up to 3 hours for

selected extreme conditions.

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13000TEU model in head seas

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13000TEU model in oblique seas

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26

0 200 400 600 800 1000 1200 1400 1600 1800-4

-2

0

2

4x 10

7Project 8600TEU Run 4161

Comparison of low pass f iltered VSF at Cut3 ( < 0.35Hz )

VS

F (

N)

Time(s)

0 200 400 600 800 1000 1200 1400 1600 1800-4

-2

0

2

4x 10

7Comparison of high pass f iltered VSF at Cut3 ( > 0.35Hz )

VS

F (

N)

Time(s)

0 200 400 600 800 1000 1200 1400 1600 1800-6

-4

-2

0

2

4x 10

7Comparison of total VSF at Cut3

Time(s)

VS

F (

N)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.80

5

10

15x 10

14Comparison of Calculated and Measured Power Density Spectrum of Total VSF

Frequency (Hz)

Sp

ectr

um

of

VS

F (

N2S

)

Calculation

Measurement

8600 TEU

VSF

V=24 knots

Hs=5.5m,

Tp=10.5s

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References with analysis of measured data –

Focus on fatigue and extreme hull girder loads

Storhaug et al. Consequence of whipping and springing

on fatigue for a 8600TEU container vessel in different

trades based on model tests. PRADS 2010.

Storhaug et al. Consequence of whipping and springing

on fatigue and extreme loading for a 13000TEU container

vessel based on model tests. PRADS 2010.

Storhaug et al. Effect of whipping on fatigue and extreme

loading of a 13000TEU container vessel in bow quartering

seas based on model tests. OMAE 2011.

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Wu et al. Comparative Study of Springing and Whipping

Effects in Ultra Large Container Ships, ITTC Workshop on

Seakeeping 2010.

Suji Zhu, Investigation of Wave-Induced Nonlinear Load

Effects in Open Ships considering Hull Girder Vibrations in

Bending and Torsion, Ph.D. thesis CeSOS, NTNU 2012.

References where measured data is used for

validation of numerical tools

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Conclusions

Most of the fatigue damage comes from high-frequency hull girder

vibrations, caused by whipping and springing

Changing the ship's course is from head seas to bow quartering seas

is not effective to reduce fatigue

Wave energy spreading does not reduce fatigue significantly

Extreme VBM was higher in oblique seas than in head seas, and well

above the IACS rule values.

Whipping was found to give a significant contribution to the extreme

vertical, torsional and horizontal bending moments.

Current numerical tools do not completely capture all mechanisms that

produce the whipping and springing loads.

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References Storhaug G., Choi, B-K, Moan, T. and Hermundstad, O.A. 2010. Consequence of

whipping and springing on fatigue for a 8600TEU container vessel in different trades

based on model tests. Proc. PRADS 2010.

Storhaug G., Malenica, S., Choi, B-K, Zhu, S. and Hermundstad, O.A. 2010.

Consequence of whipping and springing on fatigue and extreme loading for a

13000TEU container vessel based on model tests. Proc. PRADS 2010.

Storhaug G., Derbanne, Q., Choi, B-K, Moan, T. and Hermundstad, O.A. 2011. Effect of

whipping on fatigue and extreme loading of a 13000TEU container vessel in bow

quartering seas based on model tests. Proc. OMAE 2011.

Wu, M-K, Hermundstad, O.A. and Zhu, S. Comparative Study of Springing and

Whipping Effects in Ultra Large Container Ships, Proc. ITTC Workshop on Seakeeping

2010.

Zhu, S., Hermundstad, O.A. Iijima, K. and Moan T. 2010, Wave-induced Load Effects of

a Backbone Model under Oblique Seas in a Towing Tank. Proc. PRADS 2010.

Suji Zhu, Investigation of Wave-Induced Nonlinear Load Effects in Open Ships

considering Hull Girder Vibrations in Bending and Torsion, Ph.D. thesis CeSOS, NTNU

2012.