Kul Ship Project A Course project Resistance, propulsion and machinery Post-Panamax cruise ship with two-floor loft cabins

Transcription

1 Kul Ship Project A Course project Resistance, propulsion and machinery Post-Panamax cruise ship with two-floor loft cabins Aleksi Airinen, 81809S Andres Rene Kurmiste, Rainer Klein, Aalto 2014

2 Contents 1. Resistane Methods Model input Holtrop-Mennen method ITTC-78 method Comparison and discussion Machinery Main diesel engines, generators and backup power Main propulsors, transverse thrusters, other components Electrical balance Propulsion General Propeller efficiency Cavitation References Appendix Appendix Appendix

3 1. Resistane 1.1. Methods We aimed to find a method which has been proven to provide the best results. That way ITTC-57 was ruled out for being too simplistic, from a time even before the bulbows bow. A consultation with J. Matusiak led us to evaluate using Taylor Standard Series method which was soon deemed unfit for its limited B/T range. Next we looked into using others systematic series methods such as MARAD, Series-60 and SSPA but again our high B/T ratio lay outside of the models limits. ITTC- 78 method was chosen because it was able to provide a rough estimation with little chance of application error. Holtop-Mennen method (HMM) [1] [2] was chosen as it was sufficiently simple to implement and we could find software (NavCad) to test the quality of our implementation. Input parameters used for the estimations are presented in Table 1, Table 2 and Appendix 1. Water properties those of ocean water Model input Table 1: HMM input data Variable Abbrev. value unit Reference Density of water Ρ 1025 Gravity acceleration G 9.81 Kinematic viscosity of water Μ 1.19E-06 Length between perpendiculars kg - m 3 m s 2 - m 2 L bp 334 m - Overall length L oa 359 m - Waterline length L wl 349 m - Draught at aft T a 9.4 m - Draught at bow T b 9.4 m - Beam at waterline B 48 m - s - 3

4 Speed V 12.6 m/s - block coefficient C b [3] [4] Prismatic coefficient C p [3] [4] Midship sectional area [3] [4] C m coefficient Waterplane area coefficient C wp [4] Stern shape coefficient C stern 0 - [2] Longitudinal center of [5] LCB 0 % buoyancy Bulb transverse sectional area A bt 30.6 m 2 [6] Wetted area of appendages S app 1750 m 2 [4] Appendage resistance factor 1 + k [1] Bulb transverse area center [6] h b 5 m above keel line Half-angle of entrance i e 30 [4] Transom area A t 0 m 2 [7] Table 2. ITTC-78 input data Variable Abbreviation Value Unit Referecnce Design length L 334 m Delftship Breadth B 48 m Draught T 9,4 m Block coefficient CB 0,73 [4] Speed V 13,12 m/s Kinematic viscosity ν 1,19*10^-6 m^2/s Prismatic coefficient cp 0,75 [4] 4

5 Length and volume s cube root relation Volume L PP 3 6, m^ Holtrop-Mennen method First we shall calculate the frictional resistance R F sccording to ITTC-57 method [8]. For this purpose we need to find the wetted surface area S and Reynolds number Re of our ship. Reynolds nr of the ship is found by dividing the ships speed V and length L by the kinematic viscosity of the water μ. Re = E 6 = (1) This allows us to calculate the frictional resistance coefficient C F of our ship. C F = (log(3.61e+9) 2) 2 = (2) The wetted surface area of the hull is found from a 3D model of the hull prepared in DelftShip (Appendix 1). S = m 2. (2) Now we can calculate the frictional resistance R F. R f = = N. (3) As our ship has a bulbous bow we must also calculate its resistance. First we need to calculate bulb characteristics such as bow emergence P b and immersion Froude number F ni 30.6 P b = = F ni = = ( ) Thus we can calculate bulb resistance R b = 0.11 EXP( ) = N In the following step appendage resistance R app is calculated. This resistance is dependent on the total area of appendages S app, coefficient 1 + k 2, which describes the severity of resistance increasing effect of various appendages such as bilge keels and rudders, and the frictional resistance coefficient. 5

6 R app = = N Transom resistance R tr also plays a part in the HMM but according to our research it has no significant effect for our ship [7] [1]. R tr = 0 Next we shall calculate the wave resistance of the ship. This requires the use of 12 coefficients c 1, c 2, c 3, c 5, c 7, c 15, c 15, λ, m 1, m 4, d, F n which are described in [1] and [2]. R w = EXP ( cos ) = N (1) The final part of resistance calculations is finding the model-ship correlation resistance. This is dependent on coefficients c 2, c 4 which can be found in [2] [1]. R a = ( ) ( ) = N Total ship resistance in HMM R T is a sum of frictional resistance R F, appendage induced resistance R APP, wave resistance R W, bulb induced resistance R B, underwater transom resistance R TR and R A, which is model-ship correlation resistance. 1 + k 1 is here called form factor of the hull. R T = R F (1 + k 1 ) + R APP + R W + R B + R TR + R A (1). The hull form factor is a function of waterline dimensions breath B, length L and draft T as well as ship shape coefficients c 14, L R. (1 + k 1 ) = ( ) ( ) ( ) ( ) ( ) = (2) For the value of ship resistance at a speed of V=24.5 kn we obtain R T = (1.203) = N (1). Total effective power for our ship at 24.5 kn is P e = = 67.1 MW For comparison, we also calculated the resistance with NavCad software. As our demo version was not capable of calculating wave resistance, we could not fully compare the results yet were able to get a general idea by removing the wave components from our calculations. 6

7 Ship effective power, MW According to our Excel implementation, the resistance would be R 1 = N Whereas the NavCad implementation leads us to R 2 = N. We believe this difference is relatively small and can be attributed to the different manner that ship parameters are presented and modified. Chart 1: Ship resistance estimation by HMM Ship speed, kn 1.4. ITTC-78 method The total resistance coefficient of a ship without bilge keel is [9]: C T 1 kc C C C 1 0,074 0,0013 0, , , , F R F AA, where k form factor CF frictional coefficient of the ship according to the ITTC-1957 ship-model correlation line CR residual resistance coefficient ΔCF roughness allowance CAA air resistance 7

8 We are using the equation where the bilge keel is not included due to not having bilge keels, but instead stabilizers, which can t be compared with bilge keels. We can estimate the form factor by Watanabe s equation [4]: C B 0,730 k 0,095 25,6 0,095 25,6 2 LWL B 348,98 B T 48, ,07 9,38 0,074 The frictional coefficient comes from ITTC-57, which is the following [4]: C F, where R n 0,075 0, log Rn 2 log 3,69 10 V L WL , , ,00131 The residual resistance coefficient can be taken from Guldhammer and Harvald s method graphs, which gives us the following result from graph where L PP 3 =7,0 [10]. C R 0,00057 Our ships Froude number: F n V g L PP 12,6 9, ,22 Now we need to calculate the roughness allowance [9]: C F k 105 L WL 1 3 0,64 10 ks = 150*10^-6 roughness [m] S , , ,00015, where Finally we need to estimate the air resistance coefficient [9]: 8

9 C AA AT ,001 0,001 0,00066, where S AT ship s transverse cross-sectional area above waterline S - wetted surface area The wetted surface area was found from DelftShip model and transverse sectional area estimated based on known superstructure measurements. The total resistance of the ship is at the maximum speed of 24.5 knots is: R T V S CT , , kN 2 2 The effective power of the ship at 24.5 knots is [11]: P R V , ,4 57. MW E T Comparison and discussion Between the two methods and three implementations tested, Holtrop method in NavCad delivered the highest result at 71.6 MW, Holtop-Mennen method in our Excel implementation gave an estimate of 67.1 MW and ITTC-78 implemented in Excel 57.6 MW. Both methods use the ITTC- 57 method of frictional resistance calculation but with different wetted surface area calculations. ITTC-78 uses the ITTC-57 frictional coefficient as to many other empirical methods. It s residual resistance was taken at the moment from Guldhammer-Harvald method graphs, but it seem that this method greatly underestimates the residual resistance component, which lead to such high differences between the two methods. 2. Machinery We have decided to use a power plant type arrangement with six medium-speed diesel engines and electric generators. The power generated is used both for on-board consuming and electric propulsion. The system consists of Wärtsilä medium-speed HFO diesel engines and bow thrusters, ABB electrical power generators, switchboards, transformers, frequency converters and Azipod electric propulsion units [12] as shown in Figure 1 and Figure 2. 9

10 Comparison of advantages and disadvantages of a diesel electric power system with Azipod propulsion units [12] [13]: Improved life cycle cost by reduced fuel consumption and maintenance (up tp 20% less fuel consumed compared to conventional shaftline propulsion system). Reduced vulnerability to single failure in the system. Less space consumption and more flexible utilization of the on-board space. Improved maneuverability by utilizing azimuting thrusters (smaller turning radius and shorter crash stop distance). Decreased propulsion noise and vibration due to shorter shaft lines and less cavitation. Even wakefield due to the use of pulling propellers and greater freedom in choosing the location of the propulsors. Less resistance arising from the lack appendages such as stern thrusters, rudders and shaft brackets. Proven technology (currently used on 108 vessels, 48 of which are cruise ships) - Increased investment costs. - Increased transmission losses at full load caused by additional components. - Extra crew training might be required due to more complex machinery. - Less damage to underwater surface from anchoring as the propulsors can be used to keep this ship in place. Figure 1. Power flow in a simplified electric power system [12] 10

11 Figure 2. Simplified single line diagram of the power plant with a propulsion system [13] Estimation using the ITTC-78, Holtrop-Mennen method and case studies of similar ships proved the required power to be roughly 54 MW. This can be met by three Azipod XO2100 propulsion units providing a maximum of 21 MW each [14]. Analysis of reference ships concluded that the electric propulsors best fitting our needs are the R-R Mermaid series and ABB Azipod series, demonstrated in Table 4. Further research revealed that the mermaid propulsors suffer from serious reliability issues compared to more popular and proven Azipod units 2.1. Main diesel engines, generators and backup power Having compared the most powerful medium-speed diesel engines of Rolls-Royce (R-R), Wärtsilä, MAN Diesel & Turbo SE (MAN) and Caterpillar Maschinenbau Kiel (CAT), we concluded that the best option is to use Wärtsilä products. It appears that R-R does not produce marine engines of sufficient power output. MAN products had the benefit of including a generator developed and tested by the same company thus decreasing the probability of compatibility errors. Nevertheless the greater cost made the sets incompatible for our design. CAT engines were discarded in favor 11

12 of Wärtsilä engines to keep the production in Finland for job creation and logistical purposes and because the Wärtsilä and ABB diesel-electric setup has been proven to work well in reference ships that best resemble our concept (largest cruise ships produced). The required electrical power output is kva. The generators were chosen to fit the revolution speed of the shaft and the required output power. Our chosen diesel-electric generator system employs six Wärtsilä 14V46F engines and six ABB AMG 1600 generators. Using six identical engines and generators reduces the total number of necessary spare parts needed onboard as the reserves are interchangeable. The machinery system also becomes simpler to design and easier to maintain which reduces the probability of malfunction and misuse. Table 3: Diesel-electric set comparison Engine maker Wärtsilä MAN Diesel & Turbo CAT MaK Engine model Engine power, KW Gen output, kw Gen maker Gen model nr required SFOC, g/kwh Single engine weight, t Single generator weight, t Total weight, t 12V46D ABB AMG V46D ABB AMG V46F ABB AMG AMG 14V46F ABB V46F ABB AMG V genset V48/ genset V48/ genset V48/ genset M43C genset M43C genset The ship will also need emergency generator diesel engines to ensure power in case of a catastrophic main engine room failure. In the forward part of the ship two MTU 16V4000 units providing 5000 kw of power Main propulsors, transverse thrusters, other components Analysis of reference ships concluded that the electric propulsors best fitting our needs are the R- R Mermaid series and ABB Azipod series, demonstrated in Table 4. Further research revealed that 12

13 the mermaid propulsors suffer from serious reliability issues compared to more popular and proven Azipod units, shown in Figure 3. Table 4. Reference comparison of diesel engines and main propulsors. Ship name Diesel engine Main propulsor Manufacturer Type Nr Manufacturer Type Nr Oasis of the Seas Wärtsilä 12V46 3 ABB Azipod XO 3 Wärtsilä 16V46 3 Queen Mary II Wärtsilä 16V 46C-CR 4 R-R Mermaid 4 GE LM Norwegian Epic Cat 16M43 3 Wärtsilä FP Cat 12M43 3 Freedom of the Seas Wärtsilä 12V46 6 ABB Azimuth 2 ABB FP 1 Figure 3. Azipod propulsor concept [15] We chose to use five Wärtsilä CT3500 bow thrusters. Our choice was based on reference ships of similar wind area and operational conditions presented in Table 5. Seeing that Wärtsilä and Rolls Royce are the main proven manufacturers in the market segment we researched their portfolio and 13

14 concluded that as the products made by the two companies are both very competitive, we will choose Wärtsilä for their greater experience in similar projects. The number of thrusters was determined by extrapolation. Table 5. Reference comparison of transverse thrusters. Transverse thruster Ship name Manufacturer Type Nr Wärtsilä CT Oasis of the Seas Queen Mary II Norwegian Epic Freedom of the Seas No info 3 Wärtsilä CT Wärtsilä CT R-R TT The electrical drive system components shown in Figure 1. and Figure 2 will be supplied by ABB to minimise compatibility problems and simplify system maintenance. The fuel distribution components will be ordered from Wärtsilä to ensure the most efficient work mode for their engines. The control systems of a cruise vessel are composed of a fieldbus network, control network, power distribution network, plant network, terminals, a communication, positioning and vessel automation system. The switchboards and transformers are necessary for the management of electrical power distribution in the vessel and are usually located near the generators. As the generators and propulsors are produced and fitted by ABB, the abovementioned equipment should also fitted by the same company as an integrated solution in order to ease manufacturing and increase compatibility. The Water treatment, waste management and climate control systems shall be built by Aalborg Industries, United Technologies and MTU on-site energy. The preliminary setup is presented in Figure 4: Machinery setup. 14

15 Figure 4: Machinery setup 3. Electrical balance Electrical balance is of crucial importance in the diesel-electric ship because the energy use can be optimized much more flexibly. The electrical balance has to be calculated for different operating situations, as the electricity consumption varies depending on the conditions. Usage profile different conditions and power consumptions in those conditions is presented in Appendix 3 Table Propulsion 4.1. General The thrust is provided by 3 fixed pitched propellers. Each propeller has 5 blades. More propeller blades leads to smaller propeller peak loads, thus there is a decrease in the vibrational response of the hull caused by pressure pulses from the propellers. Fixed pitch propellers were chosen, due to the usage of Azipod propulsion. Azipods provide exceptional maneuverability and since they are electrical propulsion units the thrust can be easily controlled by changing the propeller revolutions. The propellers are operated by ABB XO2100 Azipod propulsion units, which each produce a maximal power of 21 MW at ~170 rpm (Figure 5). However, the operational point of the propeller 15

16 is at ~120 rpm, where each Azipod produces ~14 MW of power, which is required to propel the ship at the cruising speed of 22,5 knots. The required propulsive power at 22,5 knots is 41 MW. Figure 5. ABB Azipod XO product series [16] The propeller diameters available for XO2100 Azipods are from 4,4 to 6,4 m [13]. The optimal solution would be to choose the largest propeller possible as larger propellers are more efficient. However, we have to check if will be able to fit the propeller under our ship. According to [17] the clearance between the hull and the propeller blade tip should be % of the diameter of the propeller and the propeller tip should not extend beyond the bottom of the ship. Thus we can calculate the minimum required clearance for the largest available propeller as follows: m C 0,25 6,4 1, min Now me need to make sure that the tip of the 6,4 m propeller is not extending beyond the bottom of the hull, i.e. that propeller tip is not lower than the draft. The draft of the ship is 9,4 m. As our hull bottom at the location the Azipods is very close to the waterline, we can assume that the distance to the hull bottom is equal to the draft. Thus we can use the propeller if the following equation is satisfied: T C D 9,4 1,6 6,4 9, min 16

17 As we can see the equation is satisfied, thus we can use the 6,4 m propeller. However, it would beneficial if the propeller tip would be as far away as possible from the hull. This would lead to an additional reduction of the vibrations caused by propeller pressure pulses and in addition the propeller would be operating in a more uniform wake, thus being more efficient. Therefore, let us maximize equation 4.2, with respect to the clearance: T C D C T D 9,4 6, min max m We can see that the maximum clearance of the propeller tip from the hull can be 3 m for a 6,4 m propeller Propeller efficiency The propeller efficiency is evaluated for the operation point, which is defined at the cruising speed of 22,5 kn and at propeller revolutions of ~120 rpm. Propeller efficiency can be evaluated using the Wageningen B-series graphs. To select the right graph we need to know the number of blades of the propeller and the blade area ratio. In the previous paragraph 4.1, we mentioned that we are using 5-bladed propellers. The blade area ratio can be calculated with the following equation [17]: Z D 3 AE 1,3 0,3 T 1,3 0, k 0,1 0, A p p ,4 0 0, where Z number of blades = 5 v T thrust produced by one propeller at operation point = 1 R T kn 3 1 t 3 1 0,253, where RT total resistance of the hull at cruising speed = 3542 kn t thrust reduction coefficient = 1,25w 1,25 0,202 0, 253, where w wake fraction = 0,55C 0,2 0,55 0,73 0,2 0, 202 D propeller diameter = 6,4 m B 17

18 Ph hydrostatic pressure = gh pa 10259,81 6, Pa, where h distance from waterline to propeller axis = C + D/2 = 3 + 6,4/2 = 6,2 [m] pa atmospheric pressure = Pa pv vapor pressure of water (at T = 20 ºC) = ,7 t 5,78t k constant dependent on the ship type (not specified for 3 propeller ship closest is 2 propeller ship) = 0,1 From the number of blades and the blade area ratio we can see that we need the Wagenigen B- series graph for 5 blades and Ae/A0 = 0,750 (Wagenigen B-series for 5 blades and Ae/A0 = 0,750 Figure 6), as it is the closest to our blade area ratio. Finally we need to calculate the advance number, which is done as follows: VA 9,3 J 0, nd 2 6,4, where VA advance speed at the cruising speed = V 1 w 11,6 1 0,202 9,3m / s n propeller revolutions at operation point = 120 rpm = 2 s -1 The propeller pitch ratio and efficiency can be read from Figure 6. We can see that the at the cruising speed of 22,5 kn the P/D ratios of 0,9 and 1,0 would give the same efficiency of ~0,63. However, P/D ratio of 1,0 would be a better choice, as operating at the maximum speed of 24,5 kn a propeller with P/D ratio of 1,0 would be more efficient. 18

19 Figure 6. Wagenigen B-series for 5 blades and Ae/A0 = 0,750 [18] 4.3. Cavitation Cavitation is the formation of gas phase in the fluid due to pressure decrease. Cavitation happens when locally the critical pressure pcr is reached i.e. when the smallest possible pressure present in the fluid is reached [17]. Problems caused by cavitation are corrosion of propeller blades, increased vibrations and noise. To get an idea if we might have problems with cavitation we need to calculate the cavitation number. The dimensionless cavitation number is calculated as follows if the reference speed is the advance speed and the reference pressure is the hydro static pressure [17]: p p V , ,3 2 h v A 4.6 From Figure 7 we can see that for a cavitation number of 3,64 the hashed area cavitation free area is from angles of attack of about -4 to 7. As we have a fixed pitched propeller the angle of attack is always the same. Thus the blade tips most cavitation prone areas which usually have an angle of attack of 0 degrees should not experience any cavitation at operation point. Even at maximum speed of 24,5 kn our cavitation number is ~3, thus no cavitation should occur also at maximum operational speed. 19

20 Figure 7. Cavitation number and angle of attack relation to cavitation [17] 20

21 References [1] J. Holtrop and G. G. J. Mennen, "An Approximate Power Prediction Method," [2] J. Holtrop, "A Statistical Reanalysis of Resistance and Propulsion Data," [3] G. Jensen, "Moderne Schiffslinien.," in Handbuch der Werften Vol XXII, Hansa, 1994, p. 93. [4] H. Schneekluth and V. Bertram, Ship Design for Efficiency and Economy, [5] A. F. Molland, S. R. Turnock and D. A. Hudson, "Hull Form Design," in Ship Resistance and Propulsion, p [6] A. M. Kracht, "Design of Bulbous Bows," SNAME Transactions Vol. 86, pp , [7] V. Bertram, Practical Ship Hydrodynamics, [8] ITTC, Performance, Propulsion 1957 ITTC Performance Prediction Method. [9] ITTC, "1978 ITTC Performance Prediction Method," [Online]. Available: [Accessed ]. [10] "Noppa, Introduction to Marine Hydrodynamics, Weekly Exercises, figures in GH," [Online]. Available: [Accessed ]. [11] J. Matusiak, "Noppa, Introduction to Marine Hydrodynamics, osa 1b kurssimaterialista," [Online]. Available: [Accessed ]. [12] ABB AS, "Maritime electrical installations and diesel-electric propulsion". [13] ABB, "Azipod XO Product Introduction," August [Online]. Available: [Accessed ]. [14] ABB, "Azipod XO data sheet," [Online]. Available: [Accessed 20 September 2013]. [15] J. Varis, "Azipod energy efficiency in marine propulsion". [16] ABB, "Azipod XO," June [Online]. Available: [Accessed ]. 21

22 [17] J. Matusiak, Laivan Propulsio, Otaniemi, [18] M. M. Bernitsas, D. Ray and P. Kinley, "KT, KQ and Efficiency Curves for the Wagenigen B-Series Propellers," The University of Michigan, Michigan,

23 Appendix 1 Delftship hydrostatics report 23

24 Appendix 2 NavCad Holtrop resistance estimation 24

25 Appendix 3 Table 6. Electrical balance Maximum speed Cruising speed Coastal waters Manoeuvri ng Harbor Emergency Time spent % Speed kn Aux. Mach. For propulsion, cc KW Aux. Mach. For propulsion, pe kw Electric propulsion kw Heating, ventilation kw Deck machinery kw Household equipment kw Working machinery kw Lighting kw Navigation, radio kw Thrusters kw Stabilization kw Total load kw Power factor Required power kw Main generators in use Generated electrical power kw Emergency generators in use Generated el. emergency power kw Diesel generator loading %