GUIDELINES ON SHAFTING ALIGNMENT phần 7 pptx

PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE 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) 2830 0.400 -88341 0.400 -93142 4630 0.000 -17067 0.000 -3387 8465 0.050 -11496 0.050 -27408 15295 0.900 -24346 1.400 -4208 22375 1.600 -34528 2.600 -117798 23375 1.600 1631 3.000 71796 56 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 determ ined using the above mentioned method, assuming that changes in the bending moment at three cross sections M 1 , M 2 , and M 3 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 δ 4 δ 5 δ 6 M1 M2 M3 = -1 i k − 5.237308941 × 10 − 8 − 3.17599646 × 1 0 − 8 2 .001875716 × 1 0 − 8 − 1.381009923 × 10 − 7 − 2.322276437 × 10 − 7 7.442829116 × 10 − 8 − 1.502094535 × 10 − 7 − 2.450312114 × 1 0 − 7 5 .677366995 × 1 0 − 8 y { . i k − 14617630 274537 − 12830525 y { i k 0.499999 9933 1.000000078 1.400000089 y { = = 3.0 4.0 0 5000 10000 15000 20000 25000 Bearing location, distance from shaft left end (mm) Bearing hight (mm) Original bearing c ondition Changed bearing condition Original shafting line Changed shafting line PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE 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. 57 (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 − 21 4 398 819 5 6 − 90 74 8 4 35 − 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 − 621 3 1770 5 − 24622 5 014 5 − 2 42282 2 05268 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 R1 Δ R2 Δ R3 Δ R4 Δ R5 Δ R6 = = = = -88341 -17067 -11496 -24346 -34528 1631 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 Δ R1 Δ R2 Δ R3 Δ R4 Δ R5 Δ R6 = -93141 -3386 -27408 -4208 -117797 71797 (11.7) This result is completely in agreement with that directly calculated, as shown in T able 11.2. This method has the major advantage of being able to determine th e 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, M 3 , can be calculated from the previously known bending moment at any other two different cross sections M 1 and M 2 . 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 PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE 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. M 1 M 2 M 3 Fig. 11.11 Bending m o ments 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 m easure 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 14 23 24 V in V out Fig. 11.12 B e nding 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 m o ment, 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 58 PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE antenna installed around the shaft. Strain gauge Receiver Data recorder Receiving antenna Transmitte r Shaft Fig. 11.13 A telemetry system used to measure bending moment. Photo 11.1 shows the glued strain gauges and installed co mponents of the telemetry system. Strain gauges glued onto shaft Transmitter Receiving antenna Batteries for transmitter (a) (b) Photo 11.1 (a) Strain gauges glued onto shaft. (b) Mounted essential components comprising telemetry system. 59 PART A GUIDELINES ON SHAFTING ALIGNMENT TAKING INTO ACCOUNT VARIATION IN BEARING OFFSETS WHILE IN SERVICE 12. Conclusions These guidelines provide methods and procedures for the design, installation and confir mation 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 dy namic 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, interm ediate bearing, and aftmost engine bearing in the engine warm and design draught condition. If there are any recommendations by the engine manufacturer, reducing t he 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. 60 GUIDELINES ON SHAFTING ALIGNMENT Part B Amendment of the Guidance to the Rules and its Explanatory Notes Part B June 2006 NIPPON KAIJI KYOKAI Foreword 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 CONTENTS GUIDANCE FOR CALCULATION OF SHAFT ALIGNMENT 1.1 General 1 1.1.1 Application 1 1.1.2 Calculation Sheet of Shaft Alignment 1 1.2 Model of Shafting 2 1.2.1 Loads 2 1.2.2 Bearings 2 1.2.3 Equivalent Diameter of Crankshaft 2 1.2.4 Shafting with Reduction Gear 2 1.3 Load Condition and Evaluation of Calculation Results 3 1.3.1 Light Draught Condition (Cold Condition) 3 1.3.2 Light Draught Condition (Hot Condition) 4 1.3.3 Full Draught Condition (Hot Condition) 4 1.4 Matters relating to Shaft Alignment Procedures 6 1.4.1 Sags and Gaps between Shaft Coupling Flanges 6 1.4.2 Procedures for Measuring Bearing Loads 6 EXPLANATORY NOTES 1.1 General 7 1.1.1 Application 7 1.1.2 Calculation Sheet of Shaft Alignment 8 1.2 Model of Shafting 9 1.2.1 Loads 9 1.2.2 Bearings 10 1.2.3 Equivalent Diameter of Crankshaft 11 1.2.4 Shafting with Reduction Gear 11 1.3 Load Condition and Evaluation of Calculation Results 12 1.3.1 Light Draught Condition (Cold Condition) 12 1.3.2 Light Draught Condition (Hot Condition) 13 1.3.3 Full Draught Condition (Hot Condition) 14 1.4 Matters relating to Shaft Alignment Procedures 17 1.4.1 Sags and Gaps between Shaft Coupling Flanges 17 1.4.2 Procedure for Measuring Bearing Loads 17 References 18 APPENDIX A (DERIVATION OF δ B2 AND δ B3 ) 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 3.1 In the case of elastic support 23 3.2 In the case of rigid support 23 4 Calculation Example 27 PART B AMENDMENT OF THE GUIDANCE TO THE RULES AND ITS EXPLANATORY NOTES 1 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 1.3.1 1.3.2 1.3.3 3) Two-stroke cycle diesel engine ● ● ● Four-stroke cycle diesel engine ● ● - Steam turbine ● ● - 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) PART B AMENDMENT OF THE GUIDANCE TO THE RULES AND ITS EXPLANATORY NOTES 2 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 A ftmost 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 A ftmost stern tube bearing Propeller shaft D . 1.2.4 Shafting with Reduction Gear 2 1.3 Load Condition and Evaluation of Calculation Results 3 1.3.1 Light Draught Condition (Cold Condition) 3 1.3.2 Light Draught Condition (Hot Condition). -1 i k − 5.2 373 08941 × 10 − 8 − 3. 175 99646 × 1 0 − 8 2 .001 875 716 × 1 0 − 8 − 1.381009923 × 10 − 7 − 2.322 276 4 37 × 10 − 7 7.442829116 × 10 − 8 − 1.502094535 × 10 − 7 − 2.450312114 × 1 0 − 7 5 . 677 366995 × 1 0 − 8 y { . i k − 146 176 30 274 5 37 − 12830525 y { i k 0.499999 9933 1.000000 078 1.400000089 y { =. with Reduction Gear 11 1.3 Load Condition and Evaluation of Calculation Results 12 1.3.1 Light Draught Condition (Cold Condition) 12 1.3.2 Light Draught Condition (Hot Condition) 13 1.3.3