INTERACTION AND COMPATIBILITY BETWEEN PROPULSIVE PLANT AND ENGINE ROOM / DOUBLE BOTTOM STEELWORK.

INTERACTION AND COMPATIBILITY BETWEEN PROPULSIVE PLANT AND ENGINE ROOM /

DOUBLE BOTTOM STEELWORK

SOME CONSIDERATIONS ABOUT SHIP DESIGN

• Combination of optimised structure and increased installed power

- this is possible due to computer power and extensive Finite Element calculations

- high ship performance

- better profitability in operating the ship

- steel weight is optimised

- cost of the ship is optimised

• Problem of compatibility between propulsive plant and hull is raised

UNDERSTANDING INTERACTION BETWEEN MACHINERY AND HULL

• How machinery and hull interact ?

- reactions on bearings (static and dynamic interactions)

- influence of operation conditions (loading conditions, r.p.m.)

• Compatibility between machinery and hull- bad compatibility damages, vibrations

- good compatibility (static and dynamic) is absolutely necessary

GOOD COMPATIBILITY BETWEENMACHINERY AND HULL

• Correct design of propulsive plant- proper position of bearings- good design of engine room and double bottom steelwork

• Optimum distribution of bearing reactions- for significant loading conditions- for normal operation conditions (rpm, temperature values of main engine and sea water, sea-swell)

• Alignment conditions - must be pre-calculated- all significant effects must be anticipated

SPECIFICITIES

• What happens if aft part is very flexible ?

- large structural deformations in engine room between full load and ballast conditions

- large structural deformations in engine room due to wave loads

• What happens in case of high output power ? - line shafting is very stiff (small length and big diameter)

- mean values (quasi-static) and fluctuation values (dynamic) of propeller forces and moments are high (or very high)

SOME SPECIFICITIES OF BIG SHIPS(VLCC’s, Big Container Ships,…)

• Low rpm diesel engine

- main engine and crankshaft stiffness are relevant parameters due to specific

architecture of main engine

• Direct coupling between line shafting and crankshaft

ADDITIONAL IMPORTANT PARAMETERS

• Anti-friction material behaviour

- white metal, Railko, ...

• Oil film thickness / stiffness - depends of alignment conditions

- depends of rpm (propeller forces and moments)• Thermal effects

- cold conditions (alignment operations)

- hot conditions (ship operation conditions)• Sea-swell effects

OBTAINING GOOD COMPATIBILITYBETWEEN MACHINERY AND HULL

• Our experience• Calculations

- effects of all relevant parameters must be included in the calculations

• Measurements - access to specific parameters to be used as input

data in the calculations

- correlation with calculated values

- validation of calculation models


Our experienceRecommendations for line shafting design


Our experienceAlignment conditions

• Rational alignment– infinite bearing stiffness

• Elastic alignment– elastic supports (bearing

material, hull structure)– influence of oil film– influence of propeller

forces and moments

Pressure distributionon bearings

Flexibility

-anti friction-steel-work

-bossing

Line shafting model for elastic alignment calculations


Elastic Alignment

• Influence of oil film– pressure distribution– reaction distribution– oil film thickness– oil film stiffness (used as

input data for calculations of lateral vibrations of line shafting or for global vibration analysis)

Variation of contact

Squeezing of white metal

Distribution of local reactions

Maximum pressure on white metal

Contact distribution between tail-shaft journal and white metal of aft bush of stern tube

simple slope boringdouble slope boring


Elastic Alignment

Pressure distribution in aft bush as a functionof alignment conditions

alignment condition 2



Influence of propeller forces and moments on contact conditions between shaft and bearings

ForcesMoments


Rational Alignment (basic)


Rational Alignment (practical operations)


Our experienceShip A Alignment conditions





Aft bush

Forward bush

OBTAINING GOOD COMPATIBILITYBETWEEN MACHINERY AND HULLOur experience SHIP B Alignment conditions

OBTAINING GOOD COMPATIBILITY BETWEEN MACHINERY AND HULLOur experience SHIP C Alignment conditions

+0.22

+0.43

-5.85

+0.50

0.0-0.43

+0.14

-2.80

-5.55

-3.84

+1.80

2.00

-2.00

-4.00

-6.00

-8.00

-10.00

-12.00

Ballast hotLoaded hot

Docking cold

Launching cold

+0.84

-1.35 -1.61

-0.72

-3.30

-3.84

-3.84

-3.30

-3.63

-3.50

+0.40

OBTAINING GOOD COMPATIBILITYBETWEEN MACHINERY AND HULLOur experience SHIP D Alignment conditions

OBTAINING GOOD COMPATIBILITYBETWEEN MACHINERY AND HULLOur experience SHIP D Alignment conditions










PRELIMINARY STUDIES SOPHISTICATED STUDIES

RATIONALALIGNMENT

DYNAMIC STUDIESLATERAL VIBRATIONS

& WHIRLING

ELASTICALIGNMENT

DYNAMIC STUDIESLATERAL VIBRATIONS

WHIRLINGNumber of supports in

AFT BUSH2 2 Up to 10 Up to 10

STIFFNESS OF ANTIFRICTION MATERIAL

Estimation Estimation CalculatedCalculated for elastic

alignment

OIL FILM STIFFNESS Estimation Estimation CalculatedCalculated for elastic

alignment

CLEARANCE EFFECTSEstimated or given

by SupplierEstimated or given by

SupplierEstimated or given by

SupplierEstimated or given by

SupplierEFFECT of STERN

STRUCTURE STIFFNESSEstimation Estimation

Calculated (FEMcalculations)

Calculated (FEMcalculations)

PROPELLER FORCESNot taken into

accountNot taken into account Included Included

ADDED MASS of WATER Not taken into account IncludedHULL GIRDER

DEFORMATION (loadingconditions)

EstimationIncluded (FEMcalculations)


Calculations Methodology

• Finite Element Model n° 1 (Hull + main engine)

- pre/post processing: I-DEAS

- solver: MSC / NASTRAN

- calculations of hull flexibility in way of bearings

- calculations of relative deformations of engine room

steelwork between ballast and full load conditions

- calculations of steel work deformations on waves


Calculations Finite Element Model

Finite Element Model n°2 (line shafting and crankshaft)



• Finite Element Model n° 2

- calculations of line-shafting / crankshaft stiffness in way of bearings

- calculation of shaft gravity loads


Calculations Methodology• Solving the global problem

- specific Bureau Veritas Group in-house developed software- effects of all relevant parameters are included:

propeller forces and momentshull deformations and flexibilitymain engine / crankshaft stiffnessoil film effectsanti-friction material behaviourclearancesrpm, temperature...



• Output / deliverables

- reactions on bearings

- line shafting deformations

- oil film stiffness to be used as input data in

vibration calculations


Calculations Vibration behaviour assessmentAnalysis of excitations

• Propeller – propeller forces and moments– hull surface forces

• Main engine – free forces and moments– lateral moments


Calculations Vibration behaviour assessment

• Calculation of natural

frequencies and mode

forms

• Calculation of response in forced vibrations for determination of vibration level (values of excitations - forces, moments, pressures - are needed)

D

ispl

acem

ent,

Vel

ocit

y, A

ccel

erat

ion

Adverse commentsprobable

Adverse commentsnot probable

REVOLUTION (rpm)


Calculations Vibration behaviour assessment








OBTAINING GOOD COMPATIBILITY BETWEEN MACHINERY AND HULL

Measuring sets

Sensor

SENSORS

RecorderAmplifierconditionner

Analyser

Analyser

On Site orLaboratory

• Spot investigations

• Full investigations


Measurements Equipment installation on propulsive plant Location of Measuring Points

(Propulsive plant)

T

M5 M6

Mf1 Mf2 Mf3Mf4

M1

M7

M2

M3

M4

Non Contact transducer

D1

D2

D3

D4

Cylinder position1 2 3 4 5 6 7

Girder cyl. 3/4

J1 J8...to...


Measurements Equipment installation on ship structure

TV

LVVV

VV

LVTV

Location of Measuring Points

(Accelerometers)

S3

S4

S5

S1

S6

S7S8

S2

M6

M1

M2

M5

M3

M4


Measurements Structural deformations

Transducer support

Influence of quasi static phenomenaon actual position of supports:

•loading conditions•sea swell•mean thrust

Measuring points

Reference linepiano wire

ExperimentsOBTAINING GOOD COMPATIBILITY BETWEEN MACHINERY AND HULL

Engine VibrationsCoupling Side Vertical

0

5

10

15

20

25

0 25

50

75

100

125

150

175

200

Frequency (Hz)

Velo

city

(m

m/s)

O scil lo g ra m

- 0 .0 7 5

- 0 .0 5

- 0 .0 2 5

0

0 .0 2 5

0 .0 5

0 .0 7 5

0 1 2 3 4t i m e ( s )

MeasurementMeasurement Data Data Processing Processing

Evolution vs RPM

0

2

4

6

0 50 100 150 200

RPMorder 4 order 8

Deck 5 - CL fr.0

From time domain ...

WATERFALLS

TRACKING TIME HISTORY(Trends)

TIME EVOLUTION

-5

5

15

25

0 10 20 30 40 50 60 70

Record Number

Velo

city (m

m/s

)

N=1 N=2 N=3.5N=4 N=7.5 N=8.5

Coupling Side (Transverse)

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

Evolution of Shaft positionduring RPM increasing

30

30

45

55

65

70

75

85

shaftshaft clearance clearance

SPECTRUM

ORBIT

SPACE VARIATIONS

MODAL ANALYSIS

-0.02

-0.01

0

0.01

0.02

-0.02 -0.01 0 0.01 0.02


M e a s u re m e n t D a ta P ro c e s s in g 1

G EN ER A T O R

0

2

4

6

8

1 0

0 2 5 5 0 7 5 1 0 0Fr e q u e n c y (H e r tz )

Ve

loc

ity

am

pli

tud

em

m/s

RM

S

V e r tic a l Tra n s v e rs e

C O U P LIN G S ID E

VI BRAT I ON SPECT RUM

Id e n tific a tio n o f m a in v ib ra tio n c o m p o n e n ts :

o f th e m a c h in e its e lf

o f o th e r n e x t m a c h in e s

T im e e v o lu tio n (tre n d s )

C o m p a ris o n o f a m p litu d e s w ith s ta n d a rd s

T IM E EV O L UT IO N

0

1 0

2 0

3 0

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0

Re c o r d Nu m b e r

Velo

city

am

plitu

dem

m/s

RM

S

N=8 .5

T ra n s fo rm a tio n th ro u g h F F T :

fro m tim e s ig n a l to fre q u e n c yd o m a in


WATERFALLS & TRACKING

Giving a General view of of the dynamic behaviour

(machine or structure)

Critical RPM (tracking procedure)

Superposition of instantaneous spectra

N0=8

N0=4

f=12.5 Hz(from generators)

2 DataMeasurement Processing

Waterfall

TrackingN0=8

N0=4

N0=4 N0=6 N0=7

2 nd V

V3

nd V

V4

nd V

V N0=8

RP

M

74

40

Water Falls detailsOBTAINING GOOD COMPATIBILITY BETWEEN MACHINERY AND HULL


Measurement Data Processing 3

ORBITS & TRAJECTORIES

Comparison with clearances (bearing)

Risk of contact or hammering

Composition in time domain of 2 motions

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

Evolution of Shaft positionduring RPM increasing

30

30

45

55

65

70

75

85

-2.00E-02

-1.00E-02

0.00E+00

1.00E-02

2.00E-02

-2.00E-02 -1.00E-02 0.00E+00 1.00E-02 2.00E-02


Measurements Shaft motions

Vertical Motion

Transverse Motion


Measurements Main Engine Crankshaft Orbits

s

0 .0 0 .5 1 .0 1 .5 2 .0 2 .5 3 .0 3 .5 4 .0 4 .5 5 .0

Delta 1 Delta 2 Delta 5 Delta 6 Delta 9 Delta 10 MF1

RPM

1,00

0 ,75

0 ,50

0 ,25

0 ,00

-0 ,25

-0 ,50

-0 ,75

-1 ,001 ,00

0 ,75

0 ,50

0 ,25

0 ,00

-0 ,25

-0 ,50

-0 ,75

-1 ,00

V

1,000,500,00-0,50-1,00

CAP #5 M/E Fw

V

1,00

0,50

0,00

-0,50

-1,00

M/E crankshaft bearing


Measurement Data Processing 4

MODAL ANALYSIS

Dynamic mode shapes

Indication on areas with high stress levels

Information on supporting structure

Definition of reinforcements

point by point measurements at constant RPM

amplitude & phasis

ExperimentsExcitation tests generally during outfitting works

• Harmonic exciter• Hammering tests

• Natural frequencies, mode shapes

• Coupling effects• Local resonance

(proposition of reinforcements)


Torsion meterTorque bridge

Measurements of torsion Vibrations• at free end•directly on the shaft•Critical RPM•Stresses in the shaft


Torsion vibrations of shaft and engine

Torque bridge

Measurements of Output on shaft

•directly on the shaft (strain gages)

•together with torsion measurements


Power and Torque Measurements

Gage bridge for bending measurements

Measurements of bending moments on the shaft line by stress gages

Static alignmentdynamic alignmentInfluence of external parameters


Shaft Bending Moments Measurements

CONCLUSION

• Good interaction between propulsive plant and hull is essential

- to avoid anti friction material damages

- to build vibration-free propulsion plants and ships

• Target : Optimum distribution of bearing reactions for any operating condition- scientific detailed analysis including all relevant

parameters (if possible at early design stage)

- experiments will be helpful for ships in service

CONCLUSION • Potential consequences of bad interaction

between propulsive plant and hull

- may be disastrous- are out of proportion in comparison to the costs of the studies

• Types of assistance- review of documents- calculations and/or experiments

• Numerous references

- for different types of ships- for ships classed in various Classification Societies

INTERACTION AND COMPATIBILITY BETWEEN PROPULSIVE PLANT AND ENGINE ROOM /

DOUBLE BOTTOM STEELWORK

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INTERACTION AND COMPATIBILITY BETWEEN PROPULSIVE PLANT AND ENGINE ROOM / DOUBLE BOTTOM STEELWORK.

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