The Autonomous Underwater Vehicle (AUV) MAYA: General Description

Transcription

1 Introduction h ocans and rivrs always hav bn and still ar an important sourc of rvnu and prosprity for mankind. Du to th grat importanc of ocans and rivrs, th scintific community maks us of Autonomous Undrwatr hicls to collct scintific and bathymtric data in ordr to study and monitor th rivr and ocan phnomna. o dvlop an undrwatr vhicl allowing longtim obsrvations in th ocan it is important to improv propulsion fficincy to incras th duration of th battry for driving th propulsion unit. For th dsign of an optimizd propulsion systm th intraction paramtrs btwn propulsor and th hull of th Autonomous Undrwatr hicl should b known with rasonabl accuracy. Objctivs of th Work h main goal of th work focus on th dtrmination of th intraction paramtrs btwn th propulsor and th hull of th Autonomous Undrwatr hicl MAYA, in slf propulsion condition. h paramtrs invstigatd ar th ffctiv wak and th thrust dduction. h Autonomous Undrwatr hicl (AU) MAYA: Gnral Dscription h AU MAYA is an autonomous vhicl that is bing dvlopd undr a joint Indian- Portugus projct. h nominal spd is about. m/s and th nduranc of th propulsion systms battry at nominal spd is about 6 or 7 hours. h total propulsion fficincy is 6%, which can b considrd low, and th total wight in air is approimatly 55 kg. A propllr-typ thrustr with a duct is attachd at th rar nd of th body (tail sction). Rprsntativ picturs of th AU MAYA ar shown in Fig.. Fig. h Autonomous Undrwatr hicl MAYA h AU MAYA consists of a rmovabl torpdo-shapd nos sction, a straight cylindrical sction (mid body) and a rmovabl tail sction. h thr main sctions of MAYA ar shown in Fig..

2 Fig. h thr main sctions of th MAYA hicl h shap of th nos sction and th tail sction ar dfind according to Myring [] contour with an nclosd angl of 5 dgrs and ponnt. h Myring [] profil is a mathmatically fficint shap dvlopd by th U.S. Navy to minimiz drag on submrsibl objcts. h nos sction lngth is 0.7 and th total hull lngth, which is th sum of nos sction, mid-body and tail sction lngths, is qual to.74m. h maimum hull diamtr is 0.34 m. Propllr Hull Intraction: Effctiv Wak For a propllr oprating bhind th vhicl, th ral inflow, which is critical to th propllr prformanc, is usually considrd to includ thr componnts, namly, th nominal vlocity, th propllr inducd vlocity and th intraction vlocity. In this work, for an aisymmtric body fully submrgd in watr, th intraction vlocity is mainly du to th intraction btwn th nominal wak, vorticity and th propllr inducd flow. On this basis, a simplifid approach may b usd to stimat th propllr/nominal wak intraction (Huang and Grovs, 980), []. It should b nots that, from th propllr dsign viwpoint, it is th ffctiv vlocity fild that should b input into propllr dsign and analysis procdurs. h nominal wak is th wak fild in th propllr plan without th propllr action or without th prsnc of th propllr modifying th flow at th strn of th ship. Whn th ffcts of th propllr in th nominal wak ar takn into account about th inflow to th propllr at th propllr plan constituts th ffctiv wak. h Estimation of th Nominal Wak Fild In th prsnt work th nominal wak fild is stimatd by considring th two componnts: th potntial wak and th frictional wak. h potntial wak fild is th wak fild that would aris if th vhicl wr working in an idal fluid (without viscous ffcts). hus, th potntial wak at th propllr plan was calculatd using th panl mthod (DAWSON0 cod) following th Hss & Smith [3] formulation. h frictional wak fild ariss from th viscous natur of th watr passing ovr th hull surfac. his wak fild componnt originats from th growth of th boundary layr ovr th hull 3

3 surfac. o stimat th vlocity distribution at th propllr plan, th powr law rlationship of th form: y = δ n () was usd, whr is th nominal vlocity at th distanc y from th boundary surfac,.is th vhicl vlocity and δ is th boundary layr thicknss. o stimat th frictional nominal wak fild of th vhicl MAYA, q. () is adjustd to th rsults obtaind by Ettor Barros [4] in his viscous flow calculation by th CFD Flunt cod. h following paramtrs wr spcifid: radial position which dfins th wak thicknss ( r = ); th vlocity at th wak thicknss = r = R ) ; th hub radius Rh Rma ma ( ma r = and th vlocity at th hub is takn qual to zro. h ponnt n = 7 was usd and th quation () is writtn as: r R h R Maya R Maya = ma Rma Rh R Maya R Maya 7 () h Estimation of th Effctiv Wak Fild h ffctiv wak distribution was stimatd with th inviscid flow modl of Huang and Grovs [], basd on th intgration of a simplifid form of th Eulr quation. h mthod allows th calculation of th ffctiv wak at th propllr plan of an aisymmtric body from th nominal wak and propllr inducd vlocity. h govrning quations ar th continuity quation and Eulr quations undr th assumption of stady, inviscid and incomprssibl fluid. h quation of motion in vctor form is givn by: ω = p (3) ρ whr, θ, ) is th fluid vlocity, ω = is th vorticity vctor, and ( r th total had, with ρ th mass dnsity and p th prssur. p p = + ρ is h following assumptions ar mad to driv a thortical approimation of th hydrodynamic intraction btwn a propulsor and hull (or a thick strn boundary layr upstram of th propulsor): 4

4 a) th flow is aisymmtric and th fluid is incomprssibl; b) th intraction of propulsor and nominal vlocity profil is considrd to b inviscid in natur; thus, propulsor inducd viscous losss and turbulnt Rynolds strsss ar nglctd; r c) th convntional boundary layr assumption, << is assumd to b valid for th r nominal boundary layr in th absnc of a propulsor and; d) upstram of th propulsor no nrgy is addd to th fluid by th propulsor and th propulsor inducd vlocity fild is irrotacional. In that cas, th thortical formulation of intraction is givn by: d = d ) (4) P ( P ia whr P is th total aial vlocity and ia th intraction aial vlocity. As th ffctiv vlocity is dfind to b th total vlocity ( ) with th propulsor in opration minus th propulsor inducd aial vlocity, =, th quation (4) bcoms: P ia P d = ( + ) d (5) ia h finit diffrnc form of quation (5) can b writtn as: ( ) ( ) ) + ia ia i+ i i i + ia + ia i+ i = + + (6) i i + Sinc th vlocity nominal profil and propllr inducd aial vlocitis ia ar known, th ffctiv vlocity can b stimatd. In th prsnt work th propllr inducd aial vlocitis wr stimatd using th actuator disk approimation [5]. As th volum man ffctiv vlocity ratio within th propllr disc is calculatd by intgrating th ffctiv vlocity volum flu through th propllr disk in th form: = R R h h R R ( r ) R ( r ) d ( r ) R R (7) th man wak fraction is givn by th following quation: 5

5 w = =. (8) Propllr Hull Intraction: hrust Dduction h thrust dduction was stimatd from th incras of th rsistanc forc du to th chang in th prssur distribution on th hull surfac du to th action of th propulsor. h prssur distribution on th hull surfac with and without propulsor was dtrmind by potntial flow thory of an idal fluid with a panl mthod. h propllr, if clos to th hull may also induc a low prssur rgion on th hull which incrass its prssur drag. hus th propllr thrust must b largr to ovrcom this additional drag. h thrust dduction cofficint is dfind as: R t = (9) whr R is th total vhicl rsistanc, and is th propllr thrust. In this work th total vhicl rsistanc is basd on th primntal data from th Cntral Watr and Powr Rsourcs ow ank facility in Pun, India, [6] If th incras of rsistanc R du to th prsnc of th propllr is dtrmind by potntial flow thory of an idal fluid with a panl mthod (ProPan cod) thn th following quation: ( p p ) R = c s nds (0) holds, whr p c is th local prssur with th propllr action, p s is th local prssur without th propllr, n th aial componnt of th normal to th surfac and th intgration is carrid out ovr th vhicl surfac. h rsults of th prssur distribution on th surfac vhicl, without and with propllr action (for D = 0.0m), with thr ductd-propllr loading conditions is shown in Fig. 3. 6

6 Fig. 3 h rsults of th prssur distribution ovr th surfac vhicl, without and with propllr action In th dfinition of th propllr loading condition th J is th advanc cofficint and C is th thrust loading cofficint J = () nd C =, () ρ πr both basd on vhicl spd. h rsults show that th incras of rsistanc, R is highr whn th load is incrasing, du to dcras of prssur (suction ffcts), mainly in th vhicl tail sction causd by th propllr action. Dtrmination of Slf Propulsion Point h slf propulsion condition was stimatd by varying th propllr loading. h vhicl rquird load is also stimatd. For a fid propulsor with varying loading, thr should b a loading dlivrd to propulsor which quals th load rquird by th vhicl: 7

7 Dlivrd ( C ( ) R) = ( R + R) = R quird ρ π (3) Dlivrd R quird Eq. (3) dfins th slf propulsion condition. h rsults for such conditions ar shown in Fig.4, for propllr diamtrs in th rang of 0.6m to 0.4m. Fig. 4 h slf propulsion condition rsults h valus of propllr loading cofficint and thrust and intraction cofficints at th slf propulsion points ar givn in abl. abl h slf propulsion points D (m) C (N) ap t w h rsults show that for incrasing propulsor diamtrs th vhicl rsistanc incrass. h man wak fraction dcrass bcaus th flow fild in which th propulsor oprats (at th strn of vhicl) bcoms mor and mor charactrizd by th potntial wak rathr than by th viscous (frictional) wak ffct. 8

8 h typical total, ffctiv, nominal and inducd aial vlocity profils at th propulsor plan, in slf- propulsion condition for D = 0.84m, ar shown in Fig. 5 Fig.5 otal, ffctiv, nominal and inducd aial vlocity profils at th propulsor plan in slf- propulsion condition Conclusion his work focus on th dtrmination of th intraction paramtrs btwn propulsor and th hull of th Autonomous Undrwatr hicl MAYA, in slf propulsion condition. h paramtrs invstigatd ar th ffctiv wak and th thrust dduction. h ffctiv wak distribution was stimatd with th inviscid fluid modl of Huang and Grovs [] and th thrust dduction was stimatd from th incras of th rsistanc forc du to th chang in th prssur distribution on th hull surfac du to th action of th propulsor with a panl cod. h rsults wr obtaind stimatd for MAYA for a ductd propllr systm with diamtrs in th rang of 0.6m to 0.4m. h ffctiv wak factor dcrass from 0.9 to 0.09 and th thrust dduction factor incrass from 0.6 to 0.349, with th incras of th diamtr. 9

9 Rfrncs [] MYRING, D. F., A hortical Study of Body Drag in Subcritical Aisymmtric Flow Aronautical Quartrly, 7(3), pp , August 976. [] HUANG,.. and GROES, N.C., Effctiv wak: thory and primnt 3th Symposium on Naval Hydrodynamics, okyo, Japan, 6-0 Oct [3] HESS, J., & SMIH, A.M.O., Calculation of Potntial Flow about Arbitrary Bodis, Progrss in Aronautical Scincs, ol.8, pp. -38, 966. [4] BARROS, EORE APOLÔNIO d: Calculation of viscous flow around th RO MAYA with th Flunt cod, privat communication. [5] HOUGH, G. R. & ORDWAY, D.E., h Gnralizd Actuator Disk, Dvlopmnts in hortical and Applid Mchanics, ol., Prgamon Prss, Nw York, pp , 995. [6] R. MADHAN, ELGAR DESA, S. PRABHUDESAI, EHRLICH DESA, A. MASCARENHAS, PRAMOD MAURYA, G. NAELKAR, S. AFZULPURKAR, S. KHALAP, L.SEBASIAO, Mchanical dsign and dvlopmnt aspcts of a small AU Maya, 7 th IFAC Confrnc MCMC (Manuvring & Control of Marin Craft), 0- Sptmbr, Lisbon,