Shaft Alignment Powertrain Vibration - · PDF fileC2 Shaft Alignment Definition “Most shipboard configurations of shafts and bearings are likely to be aligned when some or all of

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Chris LeontopoulosChris Leontopoulos

Shaft AlignmentShaft Alignment

andand

Powertrain VibrationPowertrain Vibration

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Shaft Alignment

Definition

� “Most shipboard configurations of shafts and bearings are likely to be aligned when some or all of the centrelines of the bearings are offset from the theoretical straight line condition, so as to achieve an acceptable bearing load distribution and shaft slope.”

Design Process

� “The classic alignment technique would involve the calculation of the bearing reactions following a quasi-static analysis and varying of the bearing offsets until an acceptable set of bearing reaction loads and shaft slope is achieved.”

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Influence Parameters on Shaft Alignment

1. Bearing offsets

2. Thermal Effects

3. Loads (propeller, gear)

4. Crankshaft model

5. Hull Flexibility

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Case Studies

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Design Trends

1. Increased engine power and reduced rpm

2. Increased propeller weight and efficiency

3. Shorter shafts (except container vessels)

� Hence, increased bending moments and stiffness and sensitivity on bearing influence coefficients

1. Changes in propeller design

2. Changes in hull design

3. Increased propeller weights

� Hence, increased propeller loads, which affect shaft slope and hence slope boring

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5

10

15

20

25

30

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Bulk Carrier Chemical

Carrier

Container

Carrier

General

Cargo

Carrier

High Speed

Craf t

Of f shore

Supply

Vessel

Oil Carrier Passenger

Vessel

Special

Purpose

Vessel

Tug Yacht

z

Alignment Related Failure Statistics

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Stern Tube Bearing

Stern tube bearing damage

White Metal Bearing Damage

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Stern Tube Bearing

Teflon Bearing Damage

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Alignment Related Failures

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“The alignment process is critical as it involves high risk consequences, which usually immobilise the vessel.”

“ABS possesses extensive practical and design experience on shaft alignment.”

Shaft Alignment

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� The “simply supported beam”

g

Shaft Alignment – Fundamental Principles

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� The “simply supported beam”

g

Shaft Alignment – Fundamental Principles

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IntroductionIntroduction

� Demonstrate AVI

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Dry Dock

In Service -Waterborne

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Positioning the Bearings to Actual Design Values

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� Optical/Laser/Telescope

Alignment Procedure

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Alignment Procedure

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Critical Areas

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Stern Tube Bearing Alignment

Ideal contact between the shaft and the bearing

Edge contact.

Desired: Even load distribution throughout the bearing length.

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Shaft Alignment Analysis

� Modelling of the bearing reaction

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Propeller operation in wake

field behind the ship

Propeller Loads

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Alignment Acceptance Criteria

1. Bearing loads (force, pressure)

a) 8 bar white metal

b) 6 bar synthetic material

c) 5.5 for water lubricated

2. Relative shaft slope inside stb bearing:

a) <0.3 mrad then slope boring is not required

b) >0.3 mrad then slope boring is required

3. Engine Flange bending moments in accordance with manufacturers’ limits

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Alignment Analysis – ABS Capabilities


Optimization for Shaft Alignment

Alignment Investigation

Hull Deflection – Shaft Alignment

Interaction


Shaft Alignment Procedure

Expertise in Installation and Build

Process

ABS Capabilities Shipyard Capabilities

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� Sterntube Frame Boring

• Vertical / Horizontal boring of

Stern tube frame

Alignment Procedure

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� Reactions Measurements

• Bearing reactions are measured directly or indirectly or both. The most commonly applied methods that measure the alignment condition are:

– Gap and Sag

– Jack-up

– Strain gauge method

• The Sag and Gap

and the strain

gauge procedures

are indirect methods

to measure the

deflections and

correlate shaft

strain to the

bearing reactions,

in a “reverse

engineering” way.

Alignment Procedure

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� Jack up method

Lifting curve

Lowering curve

Hysterisis: difference in

jack load between lifting

and lowering

Resultant line - average

between lifting and

lowering curve.

Bearing reaction is then:

mm

Alignment Procedure

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“Correlation between measurements and design calculation is top priority”

Shaft Alignment – Correlation

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� Strain Gauges

Alignment Procedure

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� Strain Gauge Installation Procedure

Alignment Procedure

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Alignment Procedure

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Alignment Procedure

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Shafting Alignment Measurements

Problems with alignment verification are often related to our ability to have control over the following:

� accuracy and reliability of the applied alignment procedure

� reliability of the alignment calculation (modeling, loads,..)

� ability to control factors which may affect/change the preset alignment parameters (stern tube bearing slope angle, bearing offset, etc.)

� accuracy of the applied alignment verification method alignment condition monitoring

� skills of the engineers conducting alignment procedure and measurement

� ability to validate measurement method and obtained results

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� Crankshaft deflection measurements

Indirect Indications of Misalignment

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� Shaft Eccentricity diagnosed through vibration monitoring

Axial

Radial

Tangential

Indirect Indications of Misalignment

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Dynamic Measurements

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Hull Deflection

� ABS have established correlation among hull deflections and use the same data to predict the hull deflections of the newly designed vessel of the same type.

� Collected data is to be applied in the ABS Shaft Alignment Optimization software to provide a basis for more robust shaft alignment design, which will be less susceptible to the alignment condition change during the operation of the vessel.

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Hull Deflection

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Refined FE model of the stern structures

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� Alignment optimisation

� Optimised shaft line

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“ABS possesses extensive practical and design experience on vibration of marine powertrains.”

Powertrain Vibration

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Vibration Acceptance Criteria

1. Torsional Stress limits (IACS)

2. Lateral and Axial Vibration

3. Torsio-axial Vibration (direct drives)

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IntroductionIntroduction

� Demonstrate AVI

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�

Torsional VibrationTorsional Vibration

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Torsional Vibration – Barred Speed Range

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Powertrain components affected by torsional

vibration

Torsional Vibration

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� VIBRATION FAILURE

Torsional Vibration

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� VIBRATION FAILURE

Lateral Vibration

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Lateral Vibration

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Coupling bolts

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Vibration Training using the Rotor-kit

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Practical Vibration Problems

� propeller induced vibration,

� engine misfire,

� barred speed range,

� gear hammer,

� coupling bolts failure,

� crankshaft failure,

� bearing failure,

� tailshaft torsional fracture

� vibration due to misalignment

� propeller cavitation

� shaft whirling

…………and many more

Within the Classification Rules and beyond we have tackled a variety of powertrain vibration problems

and issues, such as:

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ANSWERSANSWERS

&&

Shaft Alignment and Powertrain Vibration

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Thank you for your attention

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Shaft Alignment Powertrain Vibration - · PDF fileC2 Shaft Alignment Definition “Most shipboard configurations of shafts and bearings are likely to be aligned when some or all of