Influence of rudder location on propulsive characteristics of a single screw container ship

Transcription

1 First Internatinal Sympsium n Marine Prpulsrs smp 09, Trndheim, Nrway, June 2009 Influence f rudder lcatin n prpulsive characteristics f a single screw cntainer ship Maciej Reichel Ship esign and Research Centre (CTO S.A.), Gdańsk, Pland ABSTRACT This paper presents the experimental study n the influence f the rudder lcatin n prpulsive characteristics f a single screw, single rudder cntainer ship. A wide mdel tests prgram was carried ut in accrdance with the standard ITTC prcedure. The twing velcity, prpeller revlutins, thrust and trque were measured. Six types f rudders were tested during the experiments: spade, Schilling with fishtail, hrn type, Becker type, hrn and Becker type with efficiency bulb. uring the tests the rudderstck was lcated in three different psitins alng the hull centreline in the distance t prpeller equal t 59, 65, 71 percent f prpeller diameter. The different cmbinatins f the rudderprpeller arrangement allwed t frmulate sme cnclusins abut the influence f the rudder lcatin n the prpulsive characteristics. The wake fractin, thrust deductin fractin, hull, rtative and prpulsive efficiency are cmpared. Keywrds rudder lcatin, prpulsive efficiency, mdel tests 1 INTROUCTION Minimizing fuel cnsumptin was always imprtant during explitatin f ships. One f the reasns was envirnment prtectin, which is cnnected with emissin f exhaust gases like NO x, SO x and CO 2, but the main cause was csts minimizatin. uring last years the necessity f fuel cnsumptin reductin was intensified because f increasing f il prices and the financial crisis. The shipbuilding industry is ne f the victims f the glbal crisis as well. Therefre it is very imprtant t minimize csts f design, prductin and explitatin f ships and ther flating structures. Many shipwners made effrts t reduce the energy cnsumptin f their vessels, what have led t varius studies and subsequent decisins t invest in fuel saving prjects. The best way t reduce csts f ship explitatin is increase f ttal efficiency f prpulsin system. This will guarantee the same ship speed with lwer fuel cnsumptin. It is well knwn that rudder behind the hull and the prpeller has a great influence n the prpulsive perfrmance. Sme experiments, which determine influence f rudder prfile thickness n prpulsive characteristics, have been carried ut (Mriyama & Sugai, 1981). It is als knwn that rudder prfile has an influence n the prpulsive characteristics and fuel cnsumptin (Hasegawa et al. 2006). Fllwing assumptin culd be made, that besides the thickness and prfile f the rudder blade, als the lcatin f rudder culd have large influence n prpulsive characteristics. A set f selfprpulsin mdel tests with varius rudder types have been carried ut t determine the influence f rudder lcatin n the prpulsive characteristics. On this basis sme cnclusins regarding prpulsive efficiency fr different ship speeds are frmulated. 2 PROPULSIVE CHARACTERISTICS Fr the analysis f prpulsive characteristics changes caused by rudder lcatin and fr descriptin f mdel test results, standard cefficient frms are used: wake fractin thrust deductin fractin hull efficiency rtative efficiency prpulsive efficiency J n w = (1) V RT F t = (2) T 1 t η H = (3) 1 w KQ 0 η R = (4) K Q η = η R η H (5) Where J = advance cefficient, = prpeller diameter, n = prpeller revlutins, R T = mdel ttal resistance, F = additinal twing frce, K Q0 = trque cefficient in pen water cnditins, K Q = trque cefficient in behind hull cnditins, η 0 = free stream prpeller efficiency. η 0

2 3 MOEL TESTS Experiments were carried ut using a wden mdel f a panamax cntainership built t a scale f 1:27.2. All mdel tests were cnducted at Ship Hydrmechanics ivisin f Ship esign and Research Centre in Gdańsk accrding t the standard ITTC prcedure. 3.1 Ship and rudder mdels The principal particulars f the cntainership mdel are presented in the Table 1. The wden mdel shwn in the Figure 1 had n appendages, but was equipped with ne bw thruster. A wire n the frame 19, with a diameter f 1mm was used fr turbulence simulatin. Stern part f the mdel was designed in a way, which allwed t mve the rudderstck in different psitins alng the hull centreline. Three lcatins fr rudderstck have been chsen, with the distance t prpeller, shwn in the Figure 2, equal t 59, 65, 71 percent f prpeller diameter. The whle research prject dealt bth with prpulsive and maneuvring characteristics f a cntainership fitted with different rudder types. Therefre the rudders, which culd be favurable n the ne hand frm prpulsive and frm the ther hand frm maneuvring pint f view, were chsen fr experiments. Six types f rudders were tested during the experiments: spade (SPA), Schilling with fishtail (SCH), hrn type (HOR), Becker type (BEC), hrn and Becker type with efficiency bulb (HOR E, BEC E ). Gemetry f rudder blades and prfiles at shaft height is shwn in the Figure 3. Generally fr all rudder types the same lateral area and aspect rati (Λ) was assumed. Hwever, size f the efficiency bulb n the HOR E and BEC E rudders varied accrding t actual distance between the rudderstck and the prpeller disk. This has invlved different values f fixed part (A RX ) and ttal rudder area (A RT ). Particulars f rudders and differences in lateral areas are shwn in the Table 2. Table 1. Principal particulars f the cntainership mdel Length between perpendiculars (m) Breadth (m) raft (m) isplacement (m 3 ) Blck cefficient Scale L PP B T V C B λ 1:27.2 Figure 3. Rudder blades and prfiles Figure 1. Hull sectins f tested cntainership Table 2. Particulars f rudders Cefficients A RT A RX A Rmv A RF Λ SPA SCH HOR HOR E BEC BEC E Figure 2. Rudderstck psitins twards prpeller

3 3.2 Prpeller ata Fr the experiments a fivebladed fixedpitch prpeller was used. The prpeller was designed in a cmbined way, using lifting surface thery and a data base f similar ships. The particulars f the prpeller are shwn in the Table 3. Table 3. Particulars f prpeller iameter (mm) Pitch rati at r = 0.7 R Expanded blade area rati Hub diameter rati Number f blades irectin f rtatin P 0.7 / A E /A 0 d h / z right The pen water characteristics f the designed prpeller are shwn in the Figure 4. Selfprpulsin tests were the main part f the experiment prgram. A systematic series f selfprpulsin mdel tests was carried ut fr rudders described in the item 3.1. Fr all rudders, experiments have been carried ut fr three rudderstck psitins and fr the same Frude number range as in resistance tests. uring the tests, the mdel was running with a driven prpeller at speed f the twing carriage. In rder t achieve demanded lad f the prpeller, an additinal twing frce, taking int accunt differences between Reynlds numbers f ship and mdel and assumed resistance increase in service cnditins was applied accrding t the frmula: F 2 M = 0.5ρ V S ( C C ) (6) M Where ρ M = water density, V M = mdel speed, S M = wetted surface, C TM, C TS = ttal resistance cefficient fr mdel and ship respectively. uring these tests the prpeller revlutins (n), trque (Q) and thrust (T) have been measured. 4 TEST RESULTS 4.1 Open Water Rudder Tests Hydrdynamic characteristics f all rudders were determined frm pen water tests. Results f the pen water tests are shwn in the Figure 5 in standard nndimensinal frm: C M TM RT TS = 2 (7) 0.5ρV A Where = drag frce, V = water inflw velcity, A RT = ttal area f rudder. It can be seen that fr very small angles f attack almst all rudders have the same value f drag cefficient. Only SCH rudder has significantly, apprximately furtimes, higher drag. At larger rudder angles the drag cefficient fr BEC, BEC E and SCH rudders is higher than fr SPA, HOR and HOR E, but this angle range is nt in the interest area f current analysis. Figure 4. Open water characteristics f used prpeller 3.3 Tests setup and experiment prgram The whle test prgram cnsisted f three stages: the pen water tests f rudder blades, resistance tests f the hull and selfprpulsin tests. The pen water experiments f rudder blades were carried ut at water inflw velcity f 1.5 m/s and the Reynlds number apprximately uring these tests the drag () and lift (L) frces and mment (N) abut the vertical axis have been measured. Resistance tests have been dne in the Frude number range , crrespnding t twing speed m/s. Figure 5. rag frce cefficients fr rudders in pen water cnditins

4 4.2 Resistance Tests Resistance tests have been carried ut nly fr bare hull because f tw reasns: it is purpseless t measure resistance with rudders because f different wake field in the rudder lcatin in and ut f behindprpeller cnditins, small difference between ttal resistance cefficients f the hull equipped with different rudders was assumed (Nagarajan et al., 2008) The resistance test results are shwn in the Figure 6. Figure 7. Thrust deductin fractin fr Fr = Figure 6. Resistance test results 4.3 Selfprpulsin Tests The selfprpulsin tests were carried ut accrding t standard ITTC prcedures. On the basis f the tests thrust deductin fractin (t), wake fractin (w), hull (η H ), rtative (η R ) and prpulsive (η ) efficiency have been determined. All the characteristics are presented in the functin f distance t prpeller disk, which is defined in percents f prpeller diameter. All the results are shwn in mdel scale values. In all the figures a reference level, which defines the current characteristic in withut rudder cnditin is presented. Because f similarity f analysed prpulsive characteristics behaviur fr different ship velcities in the tested range, nly ne speed equal t Fr = has been chsen fr the results presentatin. Hwever in the Figures the prpulsive efficiency is shwn fr all tested ship speeds. Figure 8. Wake fractin fr Fr = Figure 9. Hull efficiency fr Fr = 0.249

5 Figure 10. Rtative efficiency fr Fr = Figure 13. Prpulsive efficiency fr Fr = Figure 11. Prpulsive efficiency fr Fr = Figure 14. Prpulsive efficiency fr Fr = Figure 12. Prpulsive efficiency fr Fr = Figure 15. Prpulsive efficiency fr Fr = 0.225

6 4.4 Cavitatin Tests Fr all rudder types and rudderstck psitin, cavitatin mdel tests have been carried ut. The pssible cavitatin patterns have been bserved n the rudder and n the prpeller as well. The experiments were dne fr the cavitatin number σ = In all psitins, bth rudders and prpeller were free f cavitatin. 5 CONCLUSIONS This paper presents mdel tests f a singlescrew, single rudder cntainership. Particularly the influence f rudder lcatin n sme prpulsive characteristics has been studied. Six types f rudders were used fr the experiments. The rudders had the same lateral area, but different prfile and cnstructin. Tw f these rudders were equipped with an efficiency bulb. uring the tests the rudderstck was lcated in three different psitins alng the hull centreline in the distance t prpeller equal t 59, 65, 71 percent f prpeller diameter. The selfprpulsin mdel tests have been dne fr a Frude number range A big difference between ttal values f thrust deductin fractin fr different rudder prfiles can be bserved. Hwever fr the tested ship speed range, fr all rudder prfiles and all rudderstck lcatins n tendency in thrust deductin fractin can be seen. Wake fractin fr all tested cnfiguratins was in the range frm 0.3 t 0.4 and had a tendency t increase with appraching t the prpeller. The character f hull efficiency characteristics is mstly an effect f wake fractin and in mst cases increase with appraching t prpeller. It has a direct influence n the ttal prpulsive efficiency. In almst all cnfiguratins a small difference in rtative efficiency can be seen in the functin f prpeller rudder distance. A slight tendency t increase with appraching t prpeller is bserved. It can be seen that fr almst all rudder types, fr all tested ship velcities the best rudder lcatin frm the prpulsive efficiency pint f view is the clsest t the prpeller. Fr the sake f nearly the same rtative and small differences in free stream prpeller efficiency it is mainly caused by increase f hull efficiency. ACKNOWLEGMENTS Experiments described in this paper were a part f the research prject N. R entitled Optimisatin f rudder prfile gemetry and the lcatin f the rudder twards hull and prpeller frm the viewpint f cavitatin f prpulsin system and the prpulsive and maneuvring characteristics f ships funded by Plish Ministry f Science and Higher Educatin. REFERENCES Hasegawa K., Nagarajan V., Kang. H. (2006). Perfrmance evaluatin f Schilling rudder and mariner rudder fr Pure Car Carrier (PCC) under wind cnditin. Prceedings f the Internatinal Cnference n Marine Simulatin and Ship Maneuvrability, Terschelling, the Netherlands Mriyama, F., Sugai, N (1981). On the Prpulsive Perfrmance f a Ship with Rudder'. Papers f Natinal Maritime Research Institute f Japan 18(3), pp Nagarajan V., Kang. H., Hasegawa K., Nabeshima K. (2008). Cmparisn f the mariner Schilling rudder and the mariner rudder fr VLCCs in strng winds. Jurnal f Marine Science and Technlgy 13:2439