GUIDELINES ON SHAFTING ALIGNMENT phần 1 pps

GUIDELINES ON SHAFTING ALIGNMENTTaking into Account Variation in Bearing Offsets while in Service June 2006 the Rules and its Explanatory Notes NIPPON KAIJI KYOKAI... GUIDELINES ON SHAF

GUIDELINES ON SHAFTING ALIGNMENT

Taking into Account Variation in Bearing Offsets while

in Service

June 2006

the Rules and its Explanatory Notes

NIPPON KAIJI KYOKAI

GUIDELINES ON SHAFTING ALIGNMENT

Copyright © 2006

All rights reserved

No part of this document may be reproduced in any from, or transmitted

by any means, or otherwise, without prior written permission from the Society For information contact Research Institute or Machinery Department, NIPPON KAIJI KYOKAI

GUIDELINES ON SHAFTING ALIGNMENT

Taking into Account Variations in Bearing Offsets while in Service

Part A

June 2006

NIPPON KAIJI KYOKAI

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE

Contents

1 Introduction ··· 1

1.1 Background ··· 1

1.2 Objectives··· 1

2 General Procedure for Shafting Alignment ··· 3

2.1 Alignment Calculations··· 3

2.2 Shafting Installation ··· ··· 3

2.3 Verification of Shafting Alignment ··· 4

2.4 Uncertainties Concerning Shafting Alignment ··· 4

3 Modelling of Shafting for Alignment Calculation ··· 6

3.1 Number of Engine Bearings in Model··· 6

3.2 Equivalent Circular Bar Representing Crankshaft ··· 7

3.3 Loads···11

4 Determination of Initial Bearing Offsets ··· 12

4.1 Construction of Shafting Stiffness Matrix··· 12

4.2 Target Bearing Reactions ··· 14

4.3 Calculation of Initial Bearing Offsets··· 15

5 Optimization of Location of Intermediate Bearing ··· 19

6 Measurement of Hull Deflection ··· 22

6.1 Items and Locations of Measurement ··· 22

6.2 Method of Measurement ··· 23

6.3 Example of Measurement Results ··· 27

7 Prediction of Hull Deflection by FEM ··· 29

7.1 Objective ··· 29

7.2 FE Model ··· 29

7.3 Loads and Boundary Conditions ··· 30

7.4 Effects of Analysis Conditions ··· 32

7.5 Effects of Added Stiffness of Main Engine on Predicted Deflection··· 34

i

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE

8 Prediction of Thermal Deformation of Engine Bedplate··· 37

8.1 Temperature of Engine Structure in Running Condition ··· 37

8.2 Thermal Deformation of Engine Bedplate ··· 37

9 Dynamic Components of Hull Deflection··· 40

9.1 Dynamic Hull Deflection Related to Ship Motions ··· 40

9.2 Deformation due to Thrust··· 42

10 Determination of Final Bearing Offsets ··· 44

10.1 Prediction of Relative Displacement over Entire Length of Shafting Line ··· 44

10.2 Discontinuity in Slope of Total Deflection Curve over Entire Length of Shafting Line· 46 10.3 Determination of Final Bearing Offsets in Shafting Installation ··· 48

11 Confirmation of Bearing Reactions··· 49

11.1 Jack-up Method··· 49

11.2 Gauge Method··· 55

12 Conclusions ··· 60

ii

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE

1 Introduction

1.1 Background

The stiffness of recently designed marine propulsion shafting has been increasing remarkably, whereas hull structures have become more likely to deform as a result of cutting-age optimized design of the scantlings and the use of high tensile steel Figure 1.1 shows that the output per rpm of propulsion shafting on tankers registered with ClassNK has increased markedly since the latter half of the 1980s This result is considered to

be attributable to increased main engine power combined with slower rotational speed

The reduction in stiffness of hull and engine structures means that the offsets of the support bearings of shafting are more likely to vary under different operating conditions On the other hand, the increased stiffness

of shafting makes shafts less adaptable to any small departure of the bearing lines from the initial lines This combination is thought to be the main cause of recently reported cases of alignment related main bearing damage

1.2 Objectives

Studies on the deflection of the engine room double bottom and its effect on shafting alignment have been conducted in Japan since the earlier 1970s Due attention has been given to this problem at the design stage, and the reaction of the bearings to such deflections were usually checked under the fully loaded condition as part

of normal alignment practice at shipyards in Japan Consequently, few main engine bearing failures related to shafting alignment have been experienced However, the real causes of the reported bearing damages are not so clear that they can be prevented from recurring Moreover, discrepancies in shafting design and installation

0 100 200 300 400 500 600

1950 1960 1970 1980 1990 2000 2010

Year of build

Fig 1.1 Evolution of main engine output per revolution for tankers

1

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE

practice vary appreciably between shipyards These are potential risks to causing shafting alignment related problems

From this perspective, ClassNK has carried out intensive research in this area during the past five years, with the aim of providing the industry with consistent and comprehensive guidelines on shafting design and installation

These guidelines reflect our wealth of experience and the latest research achievement in this field and have been developed to assist marine engineers ensure the integrity of shafting alignment from design to installation

2

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE

2 General Procedure for Shafting Alignment

Shafting alignment is a process of calculation, installation, and confirmation, as well as readjusting, if necessary

in order to ensure that the all bearings are appropriately loaded and no excessive bending present in any section

2.1 Alignment Calculations

When conducting an alignment calculation, the shafting is modeled using a continuous beam supported by bearings with due offsets, as shown in Fig 2.1 The bearing reaction, bending, and shear stresses at each section are to be calculated in order to check if they are in compliance with predetermined acceptance criteria

2.2 Shafting Installation

During installation, the shafts including propeller shaft, intermediate shaft and crank shaft are decoupled from each other and laid down on the supports first, as shown in Fig 2.2 Then, necessary adjustment of the height of each support, including possible temporary supports, are made to ensure that the calculated "GAP" and "SAG" between the mating flanges are realized That is to say, although the appropriate bearing offsets can be determined by calculation, it is extremely difficult to check the offsets during installation; therefore, the gaps and sags are used as an indication of the bearing offsets actually realized When shafts cannot be stably laid down alone, temporary supports or additional external forces provided by jacks may be added as long as they are taken into account in the calculations

Fig 2.1 Calculated shaft alignment

Reference line

Bearing offset

SAG

SAG GAP

GAP

Jack force needed to stabilize the propeller shaft

Temporary support

Fig 2.2 Aligning shafts based on Gap and Sag method

Specifically, the propeller shaft is laid down first, then its flange is taken as reference to adjust the height of each support, including possible temporary supports, for the intermediate shaft to ensure that the calculated

"GAP" and "SAG" between the mating flanges are realized After the intermediate shaft has been laid down, its forward flange becomes a new reference for adjusting the position of the main engine by raising, lowering or

3

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE

tilting the engine to ensure that the calculated "GAP" and "SAG" between the mating flanges are realized The gaps and sags are measured using filler gauges The designed gaps and sags should be, therefore, as large as possible in order to achieve a high accuracy of measurement

2.3 Verification of Shafting Alignment

When verifying the shafting alignment, the forward sterntube bearing and intermediate bearing are to be jacked

up to see if they are producing satisfactory reactions A jack up test on the main engine bearings, especially the two aftmost bearings, is also highly desirable If circumstances do not allow such a test, alternatively the gauge method described in Chapter 11 is recommended, or at least crank web deflections should be measured in order

to verify that they are in compliance with the criteria of the manufacturer

2.4 Uncertainties Concerning Shafting Alignment

2.4.1 Various Errors

The following errors will inevitably exist in the shafting alignment process, including calculation, installation, and verification:

- approximation of the shafting model for calculation (for example, the number of bearings taken into account, modeling of the sterntube bearing, and the diameter of the circular bar representing crankshaft in the model, etc.);

- the accuracy of the Gap, Sag method (namely possible discrepancies between calculation results and actual installation); and

- the accuracy of bearing reaction measurements

Therefore, the results obtained should be judged after these errors have been properly estimated based on past experience

2.4.2 Difference of Conditions between Shafting Installation and Typical Service Condition

Shafting installation is usually performed in the so called launched condition with light draft and the main engine

in a cold condition However, when the vessel is in typical service condition, the draft, especially for tankers or bulk carriers, will change considerably, and the temperature in the main engine structure and nearby hull structure will rise These changes will cause additional deflections of the hull as well as the main engine structure leading to the variations in bearing offsets The bearing reactions will also change, accordingly

It is natural to make the shafting alignment fitting for the typical service condition Therefore, the initial bearing offsets should be compensated by taking account of the estimated variation as shown in Fig 2.3 in case that unsatisfactory result is predicted if without such compensation It can also be expressed by Eq (2.1)

condition) Launched

-condition loaded

(Fully -condition Launched

offset bearing

Table 2.1 shows an example of calculated bearing offsets using Eq (2.1) As can be seen from the table, the initial bearing offsets should be compensated by an amount described by the term of "Fully loaded condition - Launched condition" in the right side of Eq (2.1) represents the variation in bearing offsets between the shafting installation and the typical service condition in order to ensure that the shafting is satisfactory in its typical service condition

4

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

30000 Bearing location, distance from left end (mm)

0 5000 10000 15000 20000 25000

Launched condition Fully loaded condition Initial bearing offset Shaft deflection line (Launched condition) Shaft deflection line (Fully loaded condition) Shaft deflection line (Initial bearing offset)

Fig 2.3 Bearing offsets and shaft deflection lines under different conditions

Table 2.1 Initial Bearing Offsets to Compensate for Bearing Height Variations in Service Condition

Bearing offset (mm) Bearing location (mm)

Launched condition Fully loaded condition Initially bearing offset

15295 0.900 1.500 0.300

22375 1.600 0.800 2.400

23375 1.600 0.700 2.500

24875 1.600 0.500 2.700

26375 1.600 0.700 2.500

27875 1.600 1.000 2.200

However, if the shafting alignment is predicted to be unsatisfactory under other conceivable operating conditions such as light ballast, then the compensation may need to be reduced to an extent by which all operating conditions can be accommodated

5