TorsionalVibration Presentation

Date : 27th March 2007

Torsional Vibration

1Contents

1. General Vibrations

2. Principle of Torsional Vibration

3. Necessary Data for Torsional Vibration Calculation

4. Calculation of Torsional Vibration

5. Optimization of Torsional Vibration

6. Calculation Plan of Shaft Vibration

7. Comparison between Calculation and Measurement

8. Summary

21.1 Shafting vibration1) Torsional vibration 2) Axial vibration3) Whirling vibration

1.2 Engine vibration1) H mode (Transverse Direction)2) X mode (Transverse Direction)3) L mode (Longitudinal Direction)

1. General Vibrations

Fig 1. Shafting arrangement

Fig 3. Anti-vibration solutionFig 2. Engine vibration mode

32. Principle of Torsional Vibration

2.1 Excitation1) Engine Cylinder pressure Rotating and reciprocating masses

2) Propeller Torque variation

2.2 Criteria1) Continuous limit2) Transient limit

Fig 5. Propeller excitation Fig 6. Cyclic gas force

Fig 4. Admissible limit(1 and 2)


3.1 Engine Data

M.O.I

M.O.I/Stiffness

M.O.I/Stiffness

Specification

4

3

2

Turning wheel

TV damper or Tuning wheel

Mass elastic data

Crank throw1

PurposeDataNo.

These data are provided by Engine maker


Fig 7. Mass elastic data for Main engine


3.2 Data for Propulsion Shaft and Propeller

Stress limitTensile strength of propeller and intermediate shafts4

Operating speedPosition of acceptable barred speed range3

Technical data

Technical data

Technical data

M.O.I

Dimension

Shafting arrangement

8

7

6

5

2

Expanded area ratio

Pitch ratio

Number of blades

Polar moment of inertia in air & in water

Propeller & intermediate shaft drawing

Shafting arrangement drawing1

PurposeDataNo.

Data for propulsion shaft and propeller should be supplied from shipyard


4.1 Torsional Stress

Fig 8. Torsional stress of crankshaft Fig 9. Torsional stress of Intermediate shaft

Torsional stresses of intermediate or propeller shafts exceed the continuous limit Barred Speed Range should be applied by shipyard

Barred Speed Range


4.2 Torsional Torque & Acceleration

Fig 10. Torsional torque at flange Fig 11. Torsional acceleration at chain wheel

Torsional torque at flange between crankshaft and intermediate shaft Torsional acceleration at chain wheel

Barred Speed Range


5.1 Tuning Wheel or Heavy Turning Wheel

Stress : Slightly changeable Natural frequency : Shift to low frequency Installation : Tuning wheel (free end side)

Fig 13. Torsional stress w/o Tuning wheel Fig 14. Torsional stress w/ Tuning wheel

38rpm 32rpm 38rpm

Fig 12. Installation of Tuning/Turning wheel

Tuning wheel

Turing wheel

Aftside

10


5.2 Torsional Vibration Damper (TV damper)

Stress : Reduction Natural frequency : Slightly changeable or split Installation : Free end side Type : Viscous type, Spring type

Fig 15. Torsional stress with TV damper

11


5.3 Increase Material Strength

Stress : Constant Natural frequency : Constant Vibration limit : Increase of intermediate or propeller shafts

ex) UTS 500N/mm2 600N/mm2

Fig 16. Torsional stress in original material Fig 17. Torsional stress in improved material

Increaselimit

12


5.4 Increase Shaft Diameter

Stress : Reduction at MCR Natural frequency : Shift to above MCR Usage : Intermediate and propeller shafts are very short

Fig 18. Torsional stress in original shaft Fig 19. Torsional stress in increasing diameter

Increase resonance

MCR

MCR

13

6. Calculation Plan of Shaft Vibration

Installation of engineon vessel

Deliveryof engine

Shaft alignmentcalculation

Receptionof data for S/A calculation

D +5~8 months

D-DayD -7 months

D -8 months

Receptionof data for T/V calculation

D -15 months

D -14 months

T/V calculation &TV dampers orderConsidering leadtime

Lead time from engine assembly Spring damper : 12months Viscous damper : 10months Tuning wheel : 5months

14


Fig 20. Angular amplitude in free end side

Fig 21. Torsional stress in intermediate shaft Fig 22. Torsional stress in propellerl shaft

99.5%38.5rpm38.8rpm7th order

RemarkMeas.Calc.resonance

103.5%38.9N/mm237.4N/mm27th order

RemarkMeas.Calc.resonance

7.1 Natural frequency

7.2 Torsional stress in intermediate shaft

15


7.3 Measurement Variation1) The vibration measurement itself may have the fluctuation2) Five(5) measurement results for sister vessels Measured values: approximately 95% ~ 120% of calculation at critical speed Major background for measurement fluctuation The varied engine load by sea status

Temperature of sea water Influence on propeller damping

by water density3) The actual stress and torque

will be reduced by minimum 20~30% owing to quick passage on barred speed range.

Calculation Measured

Barred range

Expected

Fig 23. Torsional amplitude at crankshaft

16

8. Summary

1. Input data for calculation1) Engine : Mass elastic data, Turning wheel , Tuning wheel, TV damper2) Shipyard : Propeller particulars, Shafting arrangement,

Intermediate/Propeller shaft

2. Output data1) Torsional stress2) Torsional acceleration and torque

3. Optimization1) Tuning Wheel or Heavy turning wheel2) TV damper

Viscous damper : 10 months (lead time) Spring damper : 12 months (lead time)

3) Improve shafting

4. TV calculation should be verified by TV measurement during sea trial

5. After shaft drawings is received from shipyard, TV damper is applied or not according to TV calculation.

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E.O.D.

18

Appendix 1. Optimization of Torsional Vibration

1 Casing2 Cover3 Inertia ring4 Bearing5 Silicon oil

Oil spray cooling system (only if needed)

1. Viscous Damper

19

Appendix 2. Optimization of Torsional Vibration

2. Spring Damper (Geislinger Damper)

Outer ring Middle pieceInner star OilBrass shim Support piecesspring

TorsionalVibration Presentation

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