GUIDELINES ON SHAFTING ALIGNMENT phần 7 pptx

Table 11.2 Calculated Bearing Reaction Changes due to Changes in Bearing Height Original bearing condition Changed bearing condition Bearing location mm Bearing height mm Bearing reactio

The change in the bearing reaction for a given change in bearing offsets of bearings No 4，No 5, and No 6 in Fig 11.9 is calculated and shown in Table 11.2, while the corresponding shafting deflection line is shown in Fig 11.10 In practice, it is not possible to determine the change in the bearing reactions because the change in the bearing offsets is usually unknown

Table 11.2 Calculated Bearing Reaction Changes due to Changes in Bearing Height

Original bearing condition Changed bearing condition Bearing

location (mm) Bearing height

(mm)

Bearing reaction (kgf)

Bearing height (mm)

Bearing reaction (kgf)

Fig 11.10 Shaft deflection curves before and after change in bearing height

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

The change in the bearing reactions is therefore determined using the above mentioned method, assuming that changes in the bending moment at three cross sections M1, M2, and M3 have been measured The changes in

the bearing offsets can be obtained from Eq (11.5) by substituting the relevant values into Eq (11.4)

(11.5)

-28154234 17284736 -12732321

18606641 -187185 -6315427

5815648 44923370 -43329799

δ4

δ5

δ6

M1 M2 M3

=

-1

i

k

− 5.237308941 × 10 − 8 − 3.17599646 × 10 − 8 2.001875716 × 10 − 8

− 1.381009923 × 10 − 7 − 2.322276437 × 10 − 7 7.442829116 × 10 − 8

− 1.502094535 × 10 − 7 − 2.450312114 × 10 − 7 5.677366995 × 10 − 8

y {

i k

− 14617630 274537

− 12830525

y {

i

k

0.4999999933

1.000000078 1.400000089

y {

=

=

3.0

4.0

Bearing location, distance from shaft left end (mm)

Original bearing condition Changed bearing condition Original shafting line Changed shafting line

The changes in the bearing reactions can be determined from Eq (11.6) using the reaction influence number matrix and the relative changes in the bearing offsets with reference to the stern tube center line, assuming that the stern tube bearing offsets do not change

(11.6)

The reactions after the changes in the bearing offsets can therefore be obtained by adding the changes to the initial bearing reactions, as shown in Eq (11.7)

i

k

139295 − 214398 81956 − 9074 8435 − 6213

− 214398 342736 − 147866 25858 − 24035 17705

81956 − 147866 86840 − 29734 33426 − 24622

− 9074 25858 − 29734 25741 − 62936 50145

8435 − 24035 33426 − 62936 287393 − 242282

− 6213 17705 − 24622 50145 − 242282 205268

y

{ i

k

0 0 0 0.5 1.0 1.4

y

{

i

k

− 4800.2 13681

− 15911.8 20137.5

− 83269.8 70165.7

y

{

Δ R 1

Δ R 2

Δ R 3

Δ R 4

Δ R 5

Δ R 6

=

=

=

=

-8 8 3 4 1 -1 7 0 6 7 -11 4 9 6 -2 4 3 4 6 -3 4 5 2 8

1 6 3 1

i

k

−4800.2 13681

−15911.8 20137.5

−83269.8 70165.7

y

{

+

+

R1

R2

R3

R4

R5

R6

Ri1 Ri2 Ri3 Ri4 Ri5 Ri6

ΔR1 ΔR2 ΔR3 ΔR4 ΔR5 ΔR6

=

-93141 -3386 -27408 -4208 -117797 71797

(11.7)

This result is completely in agreement with that directly calculated, as shown in Table 11.2

This method has the major advantage of being able to determine the reactions of the aft stern tube bearing or bearings inside the engine, on which the jack up test is difficult However, as can be seen in Fig 11.11, the bending moment caused by the change in the bearing offsets only varies linearly between any two adjacent bearings Therefore, the bending moment at any third cross section, M3, can be calculated from the previously known bending moment at any other two different cross sections M1 and M2 Therefore, only one, in case two bending moments in the adjacent span have already been used, or at most two independent bending moments between any two adjacent bearings can be used in the calculation On the other hand, because the relatively easy measurement of the bending moments is only possible before and after the intermediate bearing, it is necessary to simplify the shafting calculation model by reducing the number of engine bearings taken into account and by using the stern tube bearing as the reference line Furthermore, because the measurement of the

bending moment requires highly specialized knowledge and technique in addition to expensive equipment, the method is only employed when the reactions of the aftmost engine bearings need to be determined with high accuracy

M1 M2

M3

Fig 11.11 Bending moments in shaft caused by misalignment only

11.2.2 Measurement Method of Bending Moment

The mechanism of bending moment measurement consisting of using strain gauges to measure the axial strain from bending It is common to use four strain gauges to form a Wheatstone bridge in order to gain a larger output and to cancel out the effect of the thrust induced axial strain, as shown in Fig 11.12 It is important to glue the two sets of two strain gauges directly opposite to each other by appropriately marking the positions

G1

G2

G3

G4

13 14

23 24

M

G1

G2

G3

G4

13

24

Vin

Vout

Fig 11.12 Bending moment measurement using the strain gauge technique

Because the shaft is turning, a wireless system called a telemetry system is usually needed to measure bending moment, as shown in Fig 11.13 In the telemetry system, the firmly glued strain gauges are connected to transmitters with their own power source Therefore, the gauges and the transmitters rotate together with the shaft Signals from the transmitters are sent to a data recorder via a receiver after being received by a receiving

antenna installed around the shaft

Strain gauge

Receiver Data recorder

Receiving antenna

Transmitter

Shaft

Fig 11.13 A telemetry system used to measure bending moment

Photo 11.1 shows the glued strain gauges and installed components of the telemetry system

Strain gauges glued onto shaft

Transmitter

Receiving antenna

Batteries for transmitter

Photo 11.1 (a) Strain gauges glued onto shaft (b) Mounted essential

components comprising telemetry system

12 Conclusions

These guidelines provide methods and procedures for the design, installation and confirmation of shafting alignment in dealing with the effects of the changes that occur in bearing offsets between different load and operating conditions, after detailing the phenomena and showing the extent of the changes through measurements and calculations performed on an actual VLCC The ultimate goal of the guidelines is to help prevent improper shafting alignment related damages of bearings and shafts Although this goal can be achieved during the initial installation - bearing load measurement - readjustment cycle, the cost will be huge in the event of a major alteration of the shafting alignment at the sea trial stage Therefore, appropriate procedures are necessary that take into account actual operating conditions for the shafting alignment These may be summarized as follows:

Using an equivalent circular bar to model the crankshaft, incorporating all engine bearings in the shafting alignment calculation to improve the accuracy of the calculations

•

•

•

•

•

Optimizing the longitudinal location of the intermediate bearing to reduce the sensitivity of the shafting to changes in bearing offset

Predicting the changes in bearing offsets including the dynamic components between the installation and the representative operating conditions and compensating for these changes in the initial bearing offsets, if necessary

Directly confirming the reactions of the forward stern tube bearing, intermediate bearing, and aftmost engine bearing in the engine warm and design draught condition

If there are any recommendations by the engine manufacturer, reducing the load of the aftmost engine bearing

to nearly zero in the installation condition as a rough measure of the necessary initial compensation, and complying with the recommendation, accordingly

GUIDELINES ON SHAFTING ALIGNMENT

Rules and its Explanatory Notes

Part B

June 2006

NIPPON KAIJI KYOKAI

In the propulsion system of ships, large loads due to the weight of the propeller act on the aft edge of the shaft, which is a major characteristic of the shafting system Bending moment due to such loads results in edge loading of the aftmost bearing Consequently, Classification Societies have developed rules on shafting alignment taking into consideration the strength of the aftmost bearing ClassNK’s Rules have also been developed with a focus on the aftmost bearing Hence, shafting alignment calculations for propulsion shafting are required for shafting where the length of the aftmost bearing is shorter than the length normally set by the Rules or where the propeller shaft is intended to be classed as a Kind 1C type shaft

On the other hand, there has been a growing number of incidents of engine bearing damage reported in recent large 2-stroke cycle main engines The cause of such damage is generally thought to be attributable

to an increase in bearing loads, but may also be connected with a tendency for the span between engine bearings to become shorter In view of the contact that exists between the shaft and bearings, this tendency makes the shafting more sensitive to changes in bearing offsets Among the various cases of bearing damage reported, there have been cases in which an engine bearing becomes unloaded due to the effects of changes in temperature and hull girder deflection Therefore, in the design of shafting alignment,

it is important to give the shaft as much flexibility as possible with due consideration given to the effects of temperature changes and hull girder deflections as well as to reduce the edge loading of the aftmost bearing

ClassNK has recently amended its Rules and Guidance on Shafting Alignment These revised requirements will apply to ships that submit an application for a Classification Survey during Construction

to the Society on or after 1 July 2006 According to the amended Rules, shafting alignment calculations will be required for all shafting having an oil-lubricated propeller shaft with a diameter of 400 mm or more Furthermore, the Annex D6.2.13 to the Guidance provides clear descriptions of models of shafting, conditions to be calculated, the evaluation of calculation results and other related matters

This document gives a description of the main changes made in this revised version of the Guidance with respect to the calculation of shafting alignment and provides an explanation of the details of such calculations and the reason for the revisions made It is hoped that this information will prove useful for designers at shipbuilders and engine manufacturers as well as surveyors and other parties with an interest

in effective shafting alignment

NIPPON KAIJI KYOKAI

June 2006

GUIDANCE FOR CALCULATION OF SHAFT ALIGNMENT

1.3 Load Condition and Evaluation of Calculation Results 3

1.4.1 Sags and Gaps between Shaft Coupling Flanges 6

EXPLANATORY NOTES

1.3 Load Condition and Evaluation of Calculation Results 12

1.4.1 Sags and Gaps between Shaft Coupling Flanges 17

APPENDIX A (DERIVATION OF δB2AND δB3)

1 Approximate Calculation of Relative Displacement of the Hull 19

2 Reaction Influence Numbers determined by Relative Displacement Model 21

3 Hull Deflection that results in Engine Bearings Becoming Unloaded 23

GUIDANCE FOR CALCULATION OF SHAFT ALIGNMENT

1.1 General

1.1.1 Application

-1 This Guidance applies to shaft alignment calculations required in Sections D6.2.10, D6.2.11 and

D6.2.13 of the Rules With regard to the paragraphs in 1.3 of this Guidance, the application is to

be in accordance with Table 1.1.1-1

Table 1.1.1-1 Application of Section 1.3 of the Guidance

Paragraphs 1) 2) Type of main propulsion machinery

Notes 1) ●: Applicable -: Not applicable

2) 1.3.1: Light draught condition (cold condition) 1.3.2: Light draught condition (hot condition) 1.3.3: Full draught condition (hot condition) 3) Only applicable to oil tankers, ships carrying dangerous chemicals in bulk, bulk carriers, and general dry cargo ships, where:

● an oil tanker is a ship defined in 1.3.1(11), Part B of the Rules;

● a ship carrying dangerous chemicals in bulk is a ship defined in 2.1.43, Part

A of the Rules;

● a bulk carrier is a ship defined in 1.3.1(13), Part B of the Rules; and

● a general dry cargo ship is a ship defined in 1.3.1(15), Part B of the Rules

-2 Notwithstanding the provisions of sub-paragraph 1.1.1-1 above, paragraphs 1.1.2, 1.2.1 and 1.3.1

(excluding 1.3.1-4) below are to apply to shaft alignment calculations required in D6.2.10 and D6.2.11, where the main propulsion shafting comprises a oil-lubricated propeller shaft with a diameter less than 400 mm

-3 An alternative method of calculation different from that described in this Guidance may be

employed subject to prior acceptance by the Society

1.1.2 Calculation Sheet of Shaft Alignment

Calculation sheets for shaft alignment that include the following data are to be submitted for approval:

(a) Diameter (outer and inner) and length of shafts

(b) Length of bearings

(c) Concentrated loads and loading points

(d) Support points

(e) Bearing offsets from reference line

(f) Reaction influence numbers

(g) Bending moments and bending stresses

(h) Bearing loads and nominal bearing pressure

(i) Relative inclination of the propeller shaft and aftmost stern tube bearing or maximum bearing pressure in the aftmost stern tube bearing

(j) Deflection curves for the shafting

(k) Sags and gaps between shaft coupling flanges

(l) Procedures for measuring bearing loads (in cases where such measurement is required)

1.2 Model of Shafting

1.2.1 Loads

-1 Static loads are to be used in the shaft alignment calculations

-2 The buoyancy force working on the shafting is to be considered as a load The tensile force due to

the cam shaft drive chain specified by the engine manufacturer is also to be considered as a load for the engine

1.2.2 Bearings

-1 When only one support point is assumed in the aftmost stern tube bearing, its location is to be at

L/4 or D/3 from the aft end of the bearing When two support points are assumed, their locations are to be at the each end of the aftmost stern tube bearing When three or more support points are assumed, their locations may be decided by the designer The location of the support point in each bearing other than the aftmost stern tube bearing is to be the center of the bearing

Figure 1.2.2-1 Location of single support point in aftmost stern tube bearing

-2 Either rigid support or elastic support may be acceptable for the type of support used

-3 When the thrust shaft is integrated with the crankshaft, not less than five main bearings of the

engine are to be considered in the shaft alignment calculation

Figure 1.2.2-3 Number of main engine bearings to be considered

1.2.3 Equivalent Diameter of Crankshaft

When evaluating the shafting of a two-stroke cycle diesel engine, the equivalent diameter of the crankshaft specified by the engine manufacturer is to be used in the shaft alignment calculation,

in order to give due consideration to the lesser bending stiffness that exists in the actual crankshaft compared with simply using the diameter of the crank journal in the model

1.2.4 Shafting with Reduction Gear

For shafting with a reduction gear such as that found in main steam turbine or geared diesel engines, the shafting from the propeller to the wheel gear is to be considered in the shaft alignment calculation

#1 #2 #3 #4 #5

Aftmost engine bearing

X L

X = L/4 or D/3 X: Location of single support point from bearing aft end

L: Length of aftmost stern tube bearing D: Diameter of propeller shaft

Aftmost stern tube bearing Propeller shaft

D