TECHNISCHE UNIVERSITFIT Laboratorium veer Scheepshydromechanica Archlef Mekehveg 2, 2628CD Delft DOCUMENTATIE
mr
Bibliotheek van deAfdeling Scheepsbouw- en Scheepvca
Technische Hogeschool,
3
DATUM.
02
JIM 1985;
feeolimeg7g3-Lo
Fax.aPcis
Encountered by a Controllable Pitch Propeller
Introduction
In view of future demand of energy resources, explora-tion of natural resources has been conducted in the Arctic regions during the last two decades. These activities will be continued in future also, and in its production stage, trans-portation of the products from the Arctic to industrialized areas will be a matter of concern. A high powered large ice-capable oil and gas carriers will be one of the powerful candidates(' )(2) But, since there are many aspects, which are beyond our experiences and predictions, in designing such an ice-capable tanker, extensive basic researches are necessary(3). Among them, design of propellers and pro-pulsion plant is considered to be one of the most important items to be studied, since severe propellerice interaction can not be avoided during navigation in ice-covered water-ways in the Arctic. Diesel- or turbo-electric motor driven system has been applied to most of ice breakers to avoid severe damage to propeller blades caused by propellerice floe interaction(4).
Recently, controllable pitch propellers (CPPs) were in-stalled to some ice-capable ships(5)(6), taking into account the merit of reducing fluctuating torque caused by
pro-pellerice interaction by adjustment of propeller pitch
together with controlling engine output(7). Thus, CPPs are considered to be powerful candidates of propulsion system
for a high powered large Arctic tanker.
As a part of the feasibility study of the Arctic tanker, design of CPPs were conducted. Further to study the effec-tiveness and limitation of CPPs and also to check the use-fulness and limitation of the existing method to estimate
ice-milling load, ice-milling tests were conducted by using .a stainless steel model propeller with 250 mm in diameter.
Design of propeller
In designing marine propellers, generally both hydro-dynamic performances, such as efficiency and cavitation characteristics, and strength are important factors to be taken into account. But in case of propellers for the ice-going ship, strength is of the primary importance, because severe ice load on propeller blade due to propellerice interaction (ice milling load) is expected in her navigation in ice covered sea. Fig. 1 summarizes the design procedure adopted here(8), which is constructed referring the method by Ignatjev(9). In this procedure hydrodynamic perform-ances were estimated by using existing propeller charts(1°), while ice-milling load was estimated by both ASPPR(11) and Jagodkin's method(12). Blade stress caused by the
ice-milling load was estimated by Ignatjev's method(9).
By adopting this procedure, CPPs for the Arctic tanker
Ice resistance Material of propeller aB, Strength of sea ice a,, a, diameter Ice breaking capability Blade thickness, Check of relative strength of prop. and shaft MTB170 April 1985 Rule Accumulated full scale data
Fig. I Design procedure of propellers for ice-going vessels
Table 1 Principal particulars of an Arctic tanker
Table 2 Principal particulars of propeller
Takao Sasajima*
Ice-milling tests on a controllable pitch propeller, designed for a large Arctic tanker, were conducted by use of saline ice. Thrust and torque fluctuation, blade bending moment and blade stress were measured at various ice speedpropeller shaft speed
combina-tions by changing propeller pitch.
It was shown that the ice-milling loads were severer for smaller propeller pitch setting than those for the standard pitch setting. Examination was made on usefulness and limitation of existing methods for estimating ice-milling torque and blade bending moment.
were designed, the principal particulars of which are shown in Table 1. Table 2 shows the principal particulars of the CPPs thus designed, where the strength of the sea ice and
the propeller material were chosen as follows. (1) Propeller material
In choosing the propeller material for ice-going ves-sels, it is usually said that the material, the yield strength of which is very close to ultimate strength, is better in order to avoid the deformation of the propeller blades, where operation of the propeller shaft is dangerous(13).
In this case, Mitsubishi Corrosion Resistance Steel
Center propeller Wing propellers
Diameter 10.300 m
Pitch ratio 0.620 0.640
Expanded area ratio 0.6000
Boss ratio 0.4155
Thick-chord ratio 0.05322
Number of blades 4
Cavitation Blade area criteria
Ice milling Blade section -estimationtorque Design condition Design Remarks Cruising speed,
ice breaking speed Propeller
Ship Length 350.0
Breadth 52.0 m
Draft 20.0 m
Engine Electric motor 78 MW x 3 sets Shaft speed 80 rpm Main propulsion power unit Pitch Ship resistance in open sea.
2000 1000 2 Propeller drhing motor Q.estimated from model test result
7PP. R.-350-tm
Jagodkin 1050 t m
0 20 40 N (rpm) 60
Fig. 2 Ice-milling torque estimated for propeller strength design
Fig. .5 Ice-milling lathe
Table 3 Mechanical strength of MCFtS 600 400 200 Ice-block eirria Model propeller
(MCRS) was chosen, taking into account the lower
sensi-tivity to delayed failure, even though the yield strength is not so high, and considering higher anti-erosion
capa-bility. (Table 3)
(2) Sea-ice
Strength of sea ice depends on the ice-temperature, salinity and crystal orientation. But here the crushing strength of the sea ice was assumed as follows, referring the field study data(15).
Crushing strength a, =3 MPa
Shearing strength us = 0.75 MPa
Ice-milling loads calculated by both ASPPR and Jago-dlcin's formula are shown in Fig. 2. Ice-nulling torque of 1050 ton was used for the strength design of the blades by Ignatjev's method. Thickness distribution in radial
direc-tion is shown in Fig. 3.
3. Ice-milling test
3.1 Test procedures
A model propeller with pitch changing mechanism was made from stainless steel. The scale ratio is 41.2. Fig. 4
Estimated by Ignatjev's formula
Estmated by ASPPR
Model ice
.Slip rink
Thickness distribution adopted
Polar Star
Assumed
to be 80mm
go 0 04 0.6
r/R 0.8 1.0
Fig. 3 Blade thickness distribution designed
Strain gauges
Fig. 4 Model propeller
Fig. 6 Block diagram of measurements
for ice-milling tests
shows the photograph of the model propeller.
Ice-milling tests were coducted in the low temperature room at the Wartsila Arctic Research Center (WARC) in
1983. Special lathe was designed for this test, based on the former experiences(16), as shown in Fig. 5. Block diagram of the measurements is shown in \Fig. 6. To measure the blade stress and blade bending moment, 6 one-coniponent strain gauges were put near the midchord point at 0.45 and 0.5 radius on both face and back side of the blade No. 1, as illustrated in Fig. 7. Thrust and torque fluctuation were
measured by using strain-gauge type sensors arranged on the
propeller shaft, while shaft speed and ice speed were meas-ured by counting pulse signals from the generators installed
on each shaft. Propeller shaft speed was changed, keeping the ice carriage speed constant at each test run. The ice block of about 50 cm x 40 cm x 10 cm was set under the model propeller so that milling depth is two-third of the
blade length.
Columnar ice (saline ice) was used in the preliminary tests in January 1983, by making the test ice blocks one by one in the cold room. But in the normal tests, neWly devel-oped fine-grain ice (saline ice)(17) blocks were used In order to have the ice blocks with the same ice characteri-stics, a large ice sheet was grown up to 10 cm in the ice towing tank of WARC, from which more than 120 ice MCRS less steel13 Cr stain- NiAIBZ
Ultiinate strength aB(MN/m2) 882 539 647
Yield strength ay(MN/m7) 392 343 255
Elongation e (%) 10 10 15
Impact strength (15°C) S (MNm/m7) 0.49 0.096 0.343
Fatigue strength in sea
water (2 x 107 cycle) cif OvIN/m2) 235 167 Flywheel Thrust-free joint
Toriiiie meter
Ice-block driving rnhfor
G.L.
000 000
DI De Bending moment
Blade stress
Fig. 7 Strain gauge arrangements on No. 1 blade
Table 4 Test condition
Surface
blocks were cut out and stored in the cold room.
Typical crystal structure is shown in Fig. 8 by photo-graph. Crushing strength of the model ice in horizontal direction was changed between a, = 50-250 kPa, in order to get suitable output from the strain gauges, even though
72 kPa was the target value.
The test conditions are continuous ice breaking ahead and astern with positive, neutral and negative pitch, as shown in Table 4. At least 4 runs were conducted to see the scatter of the data. Fig. 9 shows an example of ice-milling
tests.
3.2 Analysis
Total 97 runs were conducted. All the signals were re-corded at first on the tape recorder as shown in Fig. 6 and then played back for the computer analysis. A representa-tive time interval of 0.7 to 1.0 sec was choosen and signals of shaft torque, thrust, blade bending moment and blade stresses were AID-converted with sampling frequency of 500 Hz. Fig. 10 shows an example of time history of each
data.
From the sampled data, mean value (hereafter
abbre-viated as m.v.), which is a mean of signals of the intervals of
the representative time, and average peak value (hereafter, a.p.v.), which is an average of peak values picked up in the sampled data during the representative time intervals, are analyzed. In order to obtain the ice-milling loads only, signals, obtained when the propeller is running free in air just before the milling, were measured and substracted from
Bottom (b) Crystal structureoffresh fine-grain ice (a) Vertical cross section ofice in the horizontal plane
Fig. 8 Crystal structure of fine-grain ice used for the tests
.81
MTB170 April 1985
a
(b) Shear failure in the area where propeller blade comes outofthe ice (C-1-7)
Fig. 9 Examples of ice-milling tests
the signalssignals of ice-milling data.
Ice temperature was measured for all test pieces, but ice crushing strength was measured for the typical ice-blocks. Thus the crushing strength of each ice block was estimated
by using the correlation curve between ice crushing strength and ice temperature, as shown in Fig. 11.
The measured signals were corrected to corresponding theoretical model scale condition i.e. the crushing strength
111,4110
Tit
(a) Rotating propeller during ice-milling (C-1-5) Pitch ratio Propeller shaft speed Speedofice blockCase n(rps) Vice(m/s) A-1 0.64 16.1, 9.0, 4.9, 2.8 0.45 A-2 0.32 16.1, 9.0, 4.9, 2.8 0.45 0.32 16.1, 4.9
0.45
B-1 0.00 4.9 0.45 0.00 3.80.45
C-10.32
16.1, 4.9, 3.8 0.450.32
16.1, 9.0, 3.8, 3.00.45
4 200 200 600 1000 1400 1800 2200 2600 3000 o M (Nm)
ICE MILLING TEST A-1-4/3 TIME HISTORY Q 60 (Nm SHAFT TORQUE A11111111,11111111VEMIII /.1W1111,1,11 I, 111[1111111,1111,11111,111111irstinv, IIMI11,1111111111111111
MAUI
T (N) 11111'111111.11118111171=11 ITIMI'IMIIIIIIIIM:301=1111111111181111Mi1111111118111W11.MIMI AMIIIII1MI I ILIM I
111111LIIIIIMMIUMI'CM1111111114/111111111kIMMAIMIrdi
;
; 1 I
I, I
02 04 0.6 t ( s) 08
BLADE BENDING MOMENT
tt
0 1 3
(C)
Fig. 11 Relation of crushing
strength of fine-grain
ice and ice temperature
of 72 kPa and the cutting depth' of 50 mm. This is done assuming that the relationship between the signals and the crushing strength of ice, the area of the blade immersed in ice and the moment lever of the milling torque is linear.
This gives the following formulas.
Shaft torque, blade bending moment and blade
stress-es : Sice, o
aco x Amp x,Rno
Sice,0
'oice
cfc) Am x Rm Thrust : Tice,0 oco x Amp Tice, o = Tice ac x A m 40 20 0 0 S2 ( MPa ) 02 Shaft moment (N m) Thrust (N)Blade bending moment (N m)
Blade. stress. back (MPa) Blade stress, face (MPa )
04
BLADE STRESS, FACE
ILIIE111
1111MMINIII
02 04 06 t s) 0.8 0.6 t s) 08where,
Am : area of the immersed part
of blade,
Rm moment lever of milling
Vmeasured
torque
and oco, Amp, Rm 0 are theoretical values
and the ac., Am, Rm are the measured
ones.
Also the measured propeller shaft
speed is corrected so that the ice speed
becomes identical to the theoretical values of 0.45 m/s. The corrected
pro-peller speed is derived from Eq. (3).
Eitheoretical XNmeasured (3)
4. Test results and discussion
4.1 Ice-milling loads at the design pitch
At first, ice-milling test results at the design pitch were studied. Fig. 12 shows an example of all the measured data for ice-milling torque. It is easily seen. that scatter of the repeated test data is considerable, but this is common for the ice related tests. In order to make easy to compare, hereafter average values of these data points are used, as shown in the same figure, but the scatter of the data should be taken into consideration in further discussion
The average value of the analyzed data are plotted against propeller shaft speed n and shown in Fig. 13. Ice milling thrust T and torque Q are plotted for both m.v. and a.p.v., while only a.p.v. was plotted for blade bending
10 (ms) 15
Fig. 12 Ice-milling torque measured
a.p.v. 13.72 39.67 710.7 1439 4.352 41.98 5286 49.57 3.043 29.75 60 0 02 04- 0.6 t ) 08
Fig. 10 Examples of time history of ice-milling test data
Data Average point value
m.v. a.p.v.
- ---
---
_-60 SI (A4Pa BLADE STRESS. BACK
200 173 100 0.2 0.4 06 t ( s) 08 THRUST 40 20 20 40 20 40
10
5
0 5
(a) Ice-milling torque Qpe
(c) Blade bending moment
moment Mb and blade stress a. In Fig. 13(1), the prelimi-nary test results for ice-milling torque were also included
for reference.
Jagodkin'S model consists of three kinds of ice-milling torque, i.e. Qs due to shearing of the ice by blade edge, Q, due to crushing of the ice by projected area of the blade, and Qp, due to pure crushing of the ice by the mean thick-ness of the blade. The calculated results by Jagodkin's and Ignatjev's methods are shown in the figures by lines. The ratio of the crushing strength to the shearing strength was chosen to be 1.8 based on the test results in this calcula-tion, even though it is assumed to be 4 in Jagodkin's origi-nal method. It was shown that:
The m.v. of the ice torque are almost the same order as that predicted by Jagodlcin's formula at the design pitch with normal proceeding condition. Since the Jagodkin's method is constructed on the static load condition, these
results are considered to be reasonable. The a.p.v. is very
high, almost twice or three times, in comparison with the estimated value. The blade design procedure based on the estimation of ice-milling torque by Jagodkin's method was found to be useful.
Change of ice-milling thrust with shaft speed is small, except n <5rps. This range includes the pure crushing mode according to Jagodkin, but ice-milling thrust has the tendency to increase.
Blade bending moment and blade stress increase with
10 n (Ms)
0
----
---0
(rps)
A Measured (ups.)
o Calculated from Mb (a.O.n.)
ignatjev
---Q,
(MS)
Fig. 13 Change of ice-rhilling data with shaft speed
MTB170 April 1985 1 A X (2( a:p.v. A A Measured Preliminary test Jagodkin 600 200 400 5 n 10 15 0 A (5) Ice-milling thrust g o MN. A a.p.v.
10 Ao Measured (a.p.v.)Estimated from Q Caps.) Estimated from Q (m.v.)
Ignatjev
10 /
/0
(d) Blade stress
decrease of shaft speed.
In Fig. 13 (c), estimated
blade bending moment
by using Ignatjev's
method is also shown.
Symbol "0la" corre-sponds to the case where the ice-milling
torque measured was used, while "Ignatjev" corresponds to the case
where the ice-milling
torque estimated by
using Jagodkin's meth-od. It is interesting to
point out that Igna-tjev's method gives a
0 good approximation of
n (rps) the blade bending
mo-5 10 15 ment.
0 (4) Blade stresses meas.
ured (a.p.v.) are com-pared with the estimat-ed value and shown in Fig. 13(d). Measured blade stresses were a little lower than those by calculated by Igna-tjev's method, but gen-erally speaking the re-sults of the calculation give good estimation of the blade stresses. Correlation of bending moment and blade stress was good except at n 8 rps, where blade stress at the back side was compression.
(5) Based on the Jagodkin's method, full scale ice-milling torque at design point was estimated from model test data. The result is shown in Fig. 2. The ice-milling torque estimated from model test results is 1.7 times larger than that by Jagodkin's method.
4.2 Effect of propeller pitch on ice-milling loads
Fig. 14 shows the effect of propeller pitch on ice-milling torque (m.v.), thrust (rn.v.) and blade bending moment (a.p.v.), plotted on ice advance ratio (VicelnD). Again, mean value of the repeated test results are shown. It was shown that:
Due to the limited number of data, it is difficult to draw general conclusion, but there is a possibility to reduce ice-milling torque by adjusting propeller pitch in normal proceeding condition, since, for example, if the ice advance ratio is small, ice-milling torque for p = 0.32 is smaller than that for p = 0.64.
But with decrease of propeller pitch, ice-milling thrust and blade bending moment increased considerably. Thus the operation mode of the propeller should be chosen carefully, taking into account the ice-milling torque and
blade strength.
Ice-milling loads become very large when direction of the ship motion and propeller thrust is opposite.
20
1
6
10
Vie/nD
A A 0 02 0.4 0.6
0
(c) Blade bending moment
Fig. 14 Effect of propeller pitch on ice-milling data
(4) Estimated ice-milling torque by Jagodkin's method does not differ too much from the test results, even though the method is originally based on the normal proceeding condition. Blade bending moment estimated by IgnatjeV's method gave good approximation for p = 032 but not for p = 0.32. Further study is necessary
including improvement ofekisting ice-milling model.
5. Concluding remarks
Ice-millink characteristics of a CPP for a high powered Arctic tanker were studied by model tests using fine-grain ice. Ice-milling thrust and torque fluctuation, blade bending moment and stress were measured at different ice speed propeller shaft speed combinations for different propeller
pitch. Followings are conclusions obtained.
At the design pitch, ice-milling torque estimated by Jagodlcin's method is considered to be alinost the same order as that by the model tests. Ignatjev's method for estimating blade bending moment and blade stress was also found to be useful.
There is a possibility to reduce ice-milling torque by adjusting propeller pitch. But according to the test re-sults, blade bending increased with decrease of propeller pitch. Thus selection of the propeller operation model will be important. Further accumulation of the data is necessary. Even though the existing methods give rough estimation of ice milling load, further study is necessary
to simulate the milling process in general.
The author wishes to express his appreciation to Dr. E. EnkVist, Director of WARC for his guidance in conducting model tests. Thanks are extended to Mr. E. Mustarnaki, Mr. P. Valanto and Mr. S. Makinnen, of the same, for their cooperation.
References
Report of Studies on Ice-Going Vessels, Board of Shipping, Ministry of Transportation (1981)
Voellcer R.P., BeBord FN., Brennan T. and Parker C.W, Evaluating Commercial Arctic Marine Transportation with
Polar Class Icebreakers, STAR Symposium, SNAME (1981)
Talcekuma K., Technical and Economic Aspects of Arctic Marine Transportation, Proceedings of POAC '83 Helsinki (1983)
Laakso J., Propulsion Machinery Selection on Icebreakers,
Ships and Structure in Ice; WEGMET XXIV (1983):
Keinonen A. J. and Duff J., Canmar Kigoriak-Demonstration of Arctic Capability, Proceedings of POAC '83, Helsinki (1983)
Langrock D.G., Wuehrer W. and Vassilopoulos L., The Per-formance of the Controllable Pitch Propellers for the U.S. Coast Guard Polar Class Icebreakers, STAR Symposium,
SNAME (1981)
Wind J., The Dimensioning of High Power Propeller System for Arctic Icebreakers and Icebreaking Vessels, Proceeding of the 5th Lips Propeller Symposium, Drunen (1983)
Sasajirna T., Bulat V. and Glen L, An Experimental Investiga-tion of Two Candidate Propeller Designs for Ice Capable
Vessels, Proceedings of POAC '81, Quebec (1981)
Ignatjev M.A., Propellers for Ship Navigating in Ice (in
Rus-sian), S u do stroenie (1966)
Lammeren W.P.A., van Manen J.D. and Oosterveld
The Wagenigen B-Screw Series, SNAME TransactiOns Vol. 77
(1969)
Arctic Shipping Pollution F'reventions Regulations, Schedule
VII, Machinery Requirements for Arctic Class Ships (1979)
Jagodkin V.Ya, Analytic Determination of the Resistance Moment of a Propeller during its Interaction with Ice (in Russian), Problems of the Arctic and Antarctic VoL 13 (1963) Imamura S. and Teramoto K., Design Concept of Strength for Ice-Breaker Shafting, Nippon Kokan Technical Report VoL
91 (1981)
Ueda S., Daikoku T. and Matsu° S., Development of High Strength Steel for Propeller, Mitsubishi Juko Giho Vol. 15 No. 3 (1978)
Sasajirna T. et al, Field Study on Mechanical Strength of Sea Ice at East Coast of Hokkaido, Mitsubishi Technical RevieW Vol. 20 No. 2 (1983)
Airaksinen K. and Marttila M., On Propulsion of Icebreakers, 3rd Lips Propeller Simposiurn, Drunen (1977)
Enkvist E. and Malcinnen S., Experience with a New Type of Model Ice, Proceedings of SNAME ICETECH '84, Calgary
(1984) 0.6 0.4 0.2
(a) Ice-milling torque
--500 0 0.2 2 0 A 0.4 0.64 0.32 0.0 0.32 0.6 0.8 20 Qc Q, Data 0 P 0.64 0.32
