Shaft Alignment. Powertrain Vibration

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C1 Chris Leontopoulos Chris Leontopoulos

Shaft Alignment

and and

Powertrain 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

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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

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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

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Stern Tube Bearing

Stern tube bearing

damage

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Stern Tube Bearing

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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.”

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The “simply supported beam”

g

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The “simply supported beam”

g

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Introduction Introduction

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Dry Dock

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Optical/Laser/Telescope

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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

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Shaft Alignment Analysis

Modelling of the bearing

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Propeller operation in wake field behind the ship

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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

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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

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Sterntube Frame Boring

• Vertical / Horizontal boring of Stern tube frame

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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

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“Correlation between measurements and design calculation is top priority”

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Strain Gauges

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Strain Gauge Installation 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

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Crankshaft deflection measurements

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C35 Shaft Eccentricity diagnosed through vibration monitoring Axial Radial Tangential

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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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Alignment optimisation

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

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Vibration Acceptance Criteria

1. Torsional Stress limits (IACS)

2. Lateral and Axial Vibration

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Introduction Introduction

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Torsional Vibration Torsional Vibration

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Powertrain components affected by torsional

vibration

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VIBRATION FAILURE

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VIBRATION FAILURE

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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

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ANSWERS

&

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