1. Gii thiu1.1Trnh by v c tnh thit k hnh hc ca chn vtChn vt c nhiu chng loi khc nhau: chn vt bc c nh, chn vt bin bc, chn vt li gp, nhng tt c chn vt u c nhng c trng hnh hc c bn chung phc v cho nhu cu tnh ton v s dng. []Mi li ca chn vt c hai mt kh ng hc chnh. Mt hng vo thn tu gi l mt sau, mt hng v ph sau tu gi l mt trc. Thng thng, chn vt quay theo chiu kim ng h khi nhn vo mt trc. Giao tuyn ca mt trc v mt sau gi l cc bin, bin trc l bin pha bn phi mt trc, bin sau l bin pha bn tri mt trc. []

By gi chng ta s xem xt mt dim P trn b mt hnh tr c bn knh r, xt mt im bt u v t bt du di chuyn to thnh mt hnh xon c quanh b mt ca hnh tr. Phng trnh th hin s chuyn ng ca im P trn b mt ca hnh tr (cc im ) trn c m t l:

Trong l gc ca phng quay trong mt phng Y-Z ca bn knh r ph thuc vo tia OZ trong ton b mt phng. Khi gc = hoc radians, khi ng xon c, th hin nh l qu tch ca im Pn, hon thnh mt vng xoay quanh hnh tr.

Li cnh ca chn vt c to ra mt cch y bi cc tit din c sp xp c th t qua v tr v mi tit din s c mt ng dy cung ring v tr c so snh vi phng X trong mt phng XZ (hnh 2-3). Gc c gi l gc pitch, chiu dng c xc nh theo quy tc bn tay phi, tc l ngc chiu kim ng h, theo phng Y hoc ta pitch. Gc nhn ca mt phng XZ cng c th hin qua hnh 2-4, qua hnh ny chng ta cng s thy c b mt mt hnh tr c to ra bi bn knh , quay mt vng c chiu di . Trong khi b mt chung ca chn vt c bao bc bi mt hnh tr c bn knh , th ng dy cung v phn m rng to thnh mt hnh xon c hon chnh. []

Figure 23 Tit din cnh theo phng XZ.Ch thch hnh 2-3:RP=section ref point:Mt ct tit din ti im c bit ref

=pitch angle:Gc PitchS=Developed chord length: di ng dy cung

Figure 24 - Pitch ca mt tit din c to ra trong mt phng XZ t b mt ca hnh tr

Ch thch hnh 24:Pitch axis:Ta PitchPitch angle:Gc PitchChord line:ng dy cungFully developed section: Mt mt tit din hon chnhDistance traveled along helix in one revolution:Khong cch i dc theo ng xon c trong mt ln quay y

Trong mt qu trnh to ra mt b mt hnh tr, mt im trn hnh xon c di chuyn c mt on l .

Trong : - pitch ca tit din i

- Bn knh hnh tr ti tit din i

- Gc pitch ti tit din I.

Ngi thit k chn vt khi y phi xc nh pitch hoc gc pitch cho mi tit din ng vi bn knh . Ngoi ra cn phi xc nh r ng knh D ca chn vt. Ngoi ra phi ch ti t l c gi l t l Pitch/ ng knh mi v tr bn knh . Nu gc pitch khng c cho trc,c th tnh ra t nhng thng tin trn.

th pitch (hnh 2-5) c th c v cho thy r s phn b pitch theo bn knh ca hnh tr. th th hin dng nhng ng cong mt trong l honh v l tung .

Figure 25 th bc chn vt.

1.2Vic gia cng chn vt dng cho tu thy ni a Vit NamVi nhu cu rt ln v chn vt cho th trng trong nc nhng vic sn xut chn vt hin nay li phn ln da trn cc khun mu truyn thng sn c (thm ch mt s thit k khun hon ton da trn kinh nghim) nn c tnh y ni ring cng nh c tnh cng sut, hiu sut ca chn vt ni chung vn cn nhiu hn ch. iu ny dn n tn km v chi ph vn hnh, v s l thuc ln vo th trng cung cp (ngi tiu dng khng c nhiu la chn tt hn cho chn vt mun mua).Trc nhng kh khn v ti liu, iu kin nghin cu, c s vt cht, nn cng tc ch to chn vt nc ta cha c ng b. a s tu ng mi cha thc hin vn thit k ch to chn vt, hu ht lp cc my c km theo chn vt, hoc lp chn vt theo kinh nghim da trn mu sn c ca cc c s ng tu. Phng php ch to chn vt ch yu ca cc c s sn xut chn vt Vit Nam l phng php c. a s sn phm l chn vt bc c nh c 3-4 cnh, c ch to t ng thau, chn vt gang v thp chim t l thp. Chn vt gang v thp thng c sn xut theo n t hng. Cht lng chn vt ph thuc vo tay ngh, cng ngh c da trn kinh nghim mu chn vt dn giang []. Do , cc chn vt c ra cha tht tt, cc thng s cha chnh xc. Vic ch to chn vt theo cng ngh ny c cc nhc im chnh nh sau: chnh xc v nhm b mt chn vt thung khng t yu cu, do phi qua giai on gia cng tinh v nh bng nn mt nhiu thi gian, cng sc, ph thuc tay ngh cng nhn v trong nhiu trng hp chn vt c th khng ph hp vi tu. ch to ra mi chn vt, truc tin phi cn ch to mt chn vt mu v mt khun c nn gi thnh cn cao. Hn ch vic ch to cc mu chn vt c ng knh ln v c yu cu chnh xc cao nh chn vt ca cc tu cao tc, tu cnh ngm v..v Sau khi ch to, khng th sa cha uc khi chn vt khng ph hp vi tu thit k.V vy, chng ta cn kho st li c tnh hnh hc ca mu chn vt Vit Nam xem s tng quan vi chun thit k trn th gii.

1.3Nhu cu cn nh gi c tnh ca chn vt ng thy ni a la chn chn vt v ng c ph hp.Khi thit k thit b nng lng tu , chn thit b y v chn s vng quay ti u ca n , ngi ta s dng cc c tnh ti tc ca chn vt ( c tnh chn vt ) . chnh l s ph thuc ca cng sut truyn n chn vt hoc mmen xon vo s vng quay hoc tc tu .Cc h s KT , KQ , c biu din di dng cc ng cong ph thuc vo h s tin J ( hnh ) , gi l ng c tnh chn vt . T th c th nhanh chng xc nh lc y , mmen quay v hiu sut chn vt cho mi ch lm vic. ng c tnh trn y l th ghi li kt qu th m hnh hoc o trn tu thc i vi chn vt bin bc , tu vo v tr ca cnh m bc xon ca chn vt c gi tr khc nhau . Nh vy c tnh chn vt ca loi chn vt ny c th xem nh tp hp cc c tnh ca nhng chn vt c bc xon khng thay i , trong khi ng knh vn gi nguyn .2. Gii thiu phng php kho st bin dng chn vt bng my qut laser2.1 phng php kho st2.1.1Vi nt v cng ngh Scan LaserCng ngh Scan laser l mt trong nhng ng dng ca cng ngh o khng tip xc. Trong qu trnh o my s dng chm sng Laser chiu vo b mt chi tit cn o, chm tia sng c phn x li t b mt chi tit c cm ng o thu li a vo b phn bin i ca my o v vi s h tr ca my tnh v phn mm iu khin cho ra kt qu ca chi tit di dng m my im [7]. Thit b Scan Laser c chn s dng trong nghin cu ny l thit b NextEngine 3D Laser Scanner (xem Hnh 2) ca hng NextEngine [8][9].

Hnh 2. My NextEngine 3D Laser Scanner2.1.2Quy trnh qut chong chng Master Airscrew E96Quy trnh qut chong chng Master Airscrew E96 c thc hin qua nhng bc sau: Chun b mu v g . Ci t thng s trn phn mm. X l s liu qut c. Xut kt qu: chn d liu xut ra dng m my im c th tin hnh x l kt qu sau khi qut bng cc cng c h tr khc.

x[1](2014, May) Wikipedia. [Online]. http://en.wikipedia.org/wiki/Propeller_(marine)

[2]KS. Nguyn Bn PGS.TS. Nguyn c n, L THUYT TU THY (tp 2). H Ni: NXB Giao thng vn ti, 2005.

[3]Donald R. Smith and John E. Slater, "The Geometry of marine propellers," Dartmouth, NS, 1988.

[4]TS Trn Gia Thi, "Nghin cu xc nh ng c tnh chn vt trong iu kin thc t,".

[5]J. S. Carlon, Marine Propeller and Propulsion. Oxford, Britain: Butterworth - Heinemann, 1994.

[6]V Vn Lot, " n Phn tch quy trnh ch to chn vt trong nc hin nay," Nha Trang, 2007.

[7]Thng L Vit Nguyn and Nguyn Khi Nguyn, "KHO ST C TNH HNH HC CA CHONG CHNG MY BAY M HNH," 2013.

[8]M. M. Bernitsas, D. Ray, and P. Kinley, KT, KQ and Efficiency Curves for the Wageningen B-Series Propellers. Michigan: The University of Michigan, 1981.

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