ITTC Recommended Procedures and Guidelines

Transcription

1 I ecommeded 1978 I erformace redictio 01.4 age 1 of 9 able of otets 1. UOE OF OEDUE.... DEIION OF OEDUE.1 Itroductio.... Defiitio of the Variables....3 Aalysis of the odel est esults 3.4 Full cale redictios otal esistace of hip cale Effect orrectios for ropeller haracteristics Full cale Wake ad Operatig oditio of ropeller odel-hip orrelatio Factor VALIDAION Ucertaity Aalysis ompariso with Full cale esults EFEENE... 9 Updated / Edited by Approved ropulsio ommittee of 7 th I 7 th I Date: 0/ Date: 09/

2 I ecommeded 1978 I erformace redictio 01.4 age of I erformace redictio 1. UOE OF OEDUE he procedure gives a geeral descriptio of a aalytical method to predict delivered power ad rate of revolutios for sigle ad twi screw ships from model test results.. DEIION OF OEDUE.1 Itroductio he method requires respective results of a resistace test, a self propulsio test ad the characteristics of the model propeller used durig the self propulsio test, he method geerally is based o thrust idetity which is recommeded to be used to predict the performace of a ship. It is supposed that the thrust deductio factor ad the relative rotative efficiecy calculated for the model remai the same for the full scale ship whereas o all other coefficiets correctios for scale effects are applied. I some special cases torque idetity (power idetity) may be used, see sectio Defiitio of the Variables A AA App D F orrelatio allowace Air resistace coefficiet Appedage resistace coefficiet Drag coefficiet Frictioal resistace coefficiet F N N D FD J J J k k k N D, D Frictioal resistace coefficiet at the temperature of the self propulsio test rial correctio for propeller rate of revolutio at power idetity rial correctio for delivered power rial correctio for propeller rate of revolutio at speed idetity esidual resistace coefficiet otal resistace coefficiet ropeller diameter ki frictio correctio i self propulsio test ropeller advace coefficiet ropeller advace coefficiet achieved by thrust idetity ropeller advace coefficiet achieved by torque idetity hrust coefficiet hrust coefficiet achieved by torque idetity orque coefficiet orque coefficiet achieved by thrust idetity Form factor ropeller blade roughess roughess of hull surface Number of propellers ropeller rate of revolutio ropeller rate of revolutio, corrected usig correlatio factor ropeller pitch Delivered ower, propeller power Delivered ower, corrected usig correlatio factor

3 I ecommeded 1978 I erformace redictio 01.4 age 3 of 9 E, e B t V VA w w w w Z β ΔF ΔF Δw ηd ηh η0 η ρ Effective power, resistace power orque esistace corrected for temperature differeces betwee resistace- ad self propulsio test eyolds umber otal resistace Wetted surface Wetted surface of bilge keels ropeller thrust hrust deductio factor hip speed ropeller advace speed aylor wake fractio i geeral aylor wake fractio, torque idetity Effect of the rudder(s) o the wake fractio aylor wake fractio, thrust idetity Number of propeller blades Appedage scale effect factor roughess allowace Idividual correctio term for roughess allowace Idividual correctio term for wake ropulsive efficiecy or quasipropulsive coefficiet Hull efficiecy ropeller ope water efficiecy elative rotative efficiecy Water desity i geeral ubscript sigifies the model ubscript sigifies the full scale ship.3 Aalysis of the odel est esults he calculatio of the residual resistace coefficiet from the model resistace test results is foud i the procedure for resistace test ( ). hrust, ad torque, measured i the self-propulsio tests are expressed i the o-dimesioal forms as i the procedure for propulsio test ( ). ad D 4 D 5 Usig thrust idetity with as iput data, J ad are read off from the model propeller ope water diagram, ad the wake fractio w J D V 1 ad the relative rotative efficiecy are calculated. V is model speed. Usig torque idetity with as iput data, J ad is read off from the model propeller ope water diagram, ad the wake fractio w J D 1 V ad the relative rotative efficiecy are calculated. V is model speed. he thrust deductio is obtaied from

4 I ecommeded 1978 I erformace redictio 01.4 age 4 of 9 F t D where FD is the towig force actually applied i the propulsio test. is the resistace corrected for differeces i temperature betwee resistace ad self-propulsio tests: 1 k. 1 k. F F where F is the frictioal resistace coefficiet at the temperature of the self-propulsio test..4 Full cale redictios.4.1 otal esistace of hip he total resistace coefficiet of a ship without bilge keels is where ) F F A ( 1 k AA k is the form factor determied from the resistace test, see I stadard procedure F is the frictioal resistace coefficiet of the ship accordig to the I model-ship correlatio lie is the residual resistace coefficiet calculated from the total ad frictioal resistace coefficiets of the model i the resistace tests: (1 k) F he form factor k ad the total resistace coefficiet for the model are determied as described i the I stadard procedure he correlatio factor for the calculatio of the resistace has bee separated from the roughess allowace. he roughess allowace ΔF per defiitio describes the effect of the roughess of the hull o the resistace. he correlatio factor A is supposed to allow for all effects ot covered by the predictio method, maily ucertaities of the tests ad the predictio method itself ad the assumptios made for the predictio method. he separatio of ΔF from A was proposed by the erformace redictio ommittee of the 19 th I. his is essetial to allow for the effects of ewly developed hull coatig systems. he 19 th I also proposed a modified formula for A that excludes roughess allowace, which is ow give i this procedure. F is the roughess allowace F k.044 L WL 10 e where k idicates the roughess of hull surface. Whe there is o measured data, the stadard value of k= m ca be used. For moder coatig differet value will have to be cosidered. A is the correlatio allowace. A is determied from compariso of model ad full scale trial results. Whe usig the roughess allowace as above, the 19 th I recommeded usig A ( log e) 10 3

5 I ecommeded 1978 I erformace redictio 01.4 age 5 of 9 to give values of F+A that approximates the values of F of the origial 1978 I method. It is recommeded that each istitutio maitais their ow model-full scale correlatio. ee sectio.4.4 for a further discussio o correlatio. AA is the air resistace coefficiet i full scale AA DA A A where, AV is the projected area of the ship above the water lie to the trasverse plae, is the wetted surface area of the ship, A is the air desity, ad DA is the air drag coefficiet of the ship above the water lie. DA ca be determied by wid tuel model tests or calculatios. Values of DA are typically i the rage , where 0.8 ca be used as a default value. If the ship is fitted with bilge keels of modest size, the total resistace is estimated as follows: (1 k) B F F A AA where B is the wetted surface area of the bilge keels. Whe the model appedage resistace is separated from the total model resistace, as described as a optio i the I tadard rocedure , the full scale appedage resistace eeds to be added, ad the formula for total resistace (with bilge keels) becomes: V B ) App (1 k F F A AA here is ot oly oe recommeded method of scalig appedage resistace to full scale. he followig alterative methods are well established: 1) calig usig a fixed fractio: App 1 ) ( App where (1- is a costat i the rage ) alculatig the drag of each appedage separately, usig local eyolds umber ad form factor. App (1 wi ) (1 ki ) i 1 Fi i where idex i refers to the umber of the idividual appedices. wi is the wake fractio at the positio of appedage i. ki is the form factor of appedage i. Fi is the frictioal resistace coefficiet of appedage i, ad i is the wetted surface area of appedage i. Note that the method is ot scalig the model appedage drag, but calculatig the full scale appedage drag. he model appedage drag, if kow from model tests, ca be used for the determiatio of e.g. the wake fractios wi. Values of the form factor ki ca be foud from published data for geeric shapes, see for istace Hoerer (1965) or irkma ad löetsli (1980).

6 I ecommeded 1978 I erformace redictio 01.4 age 6 of 9.4. cale Effect orrectios for ropeller haracteristics. he characteristics of the full-scale propeller are calculated from the model characteristics as follows: where c Z D 0.3 D D c Z D 0.5 D he differece i drag coefficiet D is

7 I ecommeded 1978 I erformace redictio 01.4 age 7 of 9 where ad D D D D t c 6 3 ec0 ec0 For twi skeg-like ster shapes a wake correctio is recommeded. A correctio like the oe used for sigle screw ships may be used. he load of the full-scale propeller is obtaied from 1 J N D t w (1 ) (1 ) D t c log c k.5 I the formulae listed above c is the chord legth, t is the maximum thickess, /D is the pitch ratio ad ec0 is the local eyolds umber with empf s defiitio at the ope-water test. hey are defied for the represetative blade sectio, such as at r/=0.75. k deotes the blade roughess, the stadard value of which is set k= m. ec0 must ot be lower tha where N is the umber of propellers. With this / J as iput value the full scale advace coefficiet J ad the torque coefficiet are read off from the full scale propeller characteristics ad the followig quatities are calculated. the rate of revolutios: (1 w ) V J D (r/s).4.3 Full cale Wake ad Operatig oditio of ropeller he full-scale wake is calculated by the followig formula usig the model wake fractio w, ad the thrust deductio fractio t obtaied as the aalysed results of self-propulsio test: (1 k) F w ( t w ) ( w t w ) (1 k ) where w stads for the effect of rudder o the wake fractio. If there is o estimate for w, the stadard value of 0.04 ca be used. If the estimated w is greater tha w, w should be set as w. he wake scale effect of twi screw ships with ope sters is usually small, ad for such ships it is commo to assume w = w. F F the delivered power of each propeller: D D 10 (kw) the thrust of each propeller: J D J 4 the torque of each propeller: 5 D (N) (Nm) the effective power: E V 10 (kw)

8 I ecommeded 1978 I erformace redictio 01.4 age 8 of 9 the quasi propulsive efficiecy: E D N D the hull efficiecy: 1 t H 1 w.4.4 odel-hip orrelatio Factor he model-ship correlatio factor should be based o systematic compariso betwee full scale trial results ad predictios from model scale tests. hus, it is a correctio for ay systematic errors i model test ad powerig predictio procedures, icludig ay facility bias. I the followig, several differet alterative cocepts of correlatio factors are preseted as suggestios. It is left to each member orgaisatios to derive their ow values of the correlatio factor(s), takig ito accout also the actual value used for A. (1) redictio of full scale rates of revolutios ad delivered power by use of the N correctio factors Usig ad N the fially predicted trial data will be calculated from for the rates of revolutios ad (r/s) D for the delivered power. N (kw) () redictio of full scale rates of revolutios ad delivered power by use of F - w correctios D I such a case the fially trial predicted trial data are calculated as follows: 1 J N D t w w F (1 ) (1 ) With this /J² as iput value, J ad are read off from the full scale propeller characteristics ad the followig is calculated: (1 w w ) V J D D D 10 (r/s) (kw) (3) redictio of full scale rates of revolutios ad delivered power by use of a N correctio For predictio with emphasis o stator fis ad rudder effects, it is sometimes recommeded to use power idetity for the predictio of full scale rates of revolutio. At the poit of -(J)-Idetity the coditio is reached where the ratio betwee the propeller iduced velocity ad the etrace velocity is the same for the model ad the full scale ship. Igorig the small scale effect Δ o the thrust coefficiet it follows that J-idetity correspod to - ad -idetity. As a cosequece it follows that for this coditio the axial flow field i the viciity of the propeller is o average correctly simulated i the model experimet. Also the axial flow of the propeller slip stream is o average correctly simulated. Due to the scale effects o the propeller blade frictio, which affect primarily the torque, the poit of -idetity (power idetity) represets a slightly less heavily loaded propeller tha at J-, - ad -idetity. At the power idetity the average rotatio i the slipstream correspods to

9 I ecommeded 1978 I erformace redictio 01.4 age 9 of 9 that of the actual ship ad this coditio is regarded as importat if tests o stator fis ad/or rudders are to be doe correctly. I this case, the shaft rate of revolutios is predicted o the basis of power idetity as follows: 1000 J D V w D (1 ) J J (1 w ) V J D 3. VALIDAION N 3.1 Ucertaity Aalysis Not yet available 3. ompariso with Full cale esults he data that led to 1978 I performace predictio method ca be foud i the followig I proceedigs: 1) roposed erformace redictio Factors for igle crew Ocea Goig hips (13 th 197 pp ) Empirical ower redictio Factor ( 1+X ) ) ropeller Dyamics omparative ests (13 th 197 pp ) 3) omparative alculatios with the I rial redictio est rogramme (14 th 1975 Vol.3 pp ) 4) Factors Affectig odel hip orrelatio (17 th 1984 Vol.1 pp74-91) 4. EFEENE (1) Hoerer,.F. (1965) Fluid-Dyamic Drag. ublished by the author. () irkma,.l., löetsli, J.W. (1980) calig roblems of model appedages, 19th America owig ak oferece, A Arbor, ichiga