I Journal of transportation science and teciinoiogy, Vol 15, May 2015
TINH TOAN DONG CHAY BAO QUANH THAN TAU BANG PHAN MEM ANSYS FLUENT
CACULATING THE FLOW AROUND THE HULL USING THE ANSYS FLUENT SOFTWARE
TS. Dd Quang Khdi, ThS. Nguyin Tiin Cong Khoa ddng tdu, Tncdng BHHH Viet Nam, Viet Nam, khaidq&yimaru edu.vn Khoa ddng tdu, Trudng BHHH Viet Nam, Viet Nam, congnt0lvimani. edu. vn
Tom tdt: Bai bdo ndy gidi thiiu phuangphdp tinh todn cdc ddc tinh ddng chdy bao quanh thdn tdu bdng phuang phdp sd dudi su hd trp cua phdn mem Fluent. Bdy phuang phdp hieu qud dephdn tich ede dgc tinh thuy ddng luc hgc thdn tdu, phuangphdp ndy cd the kit hpp vdi cdc thic md hinh tdu de gidl quyit bdi todn tdi icu hinh ddng thdn tdu ve mat thuy ddng lue hge.
Tie khda: Bdng chdy bao quanh thdn tdu, cde ddc tinh thiiy dong lue hpc tdu, phuang phdp the tich chdt Idng, phuang trinh he sd the tich, phuang trinh Navier-Stokes.
Abstract. This article presents a method in calculating the characteristics of flow around ship hull, using numerical method by Fluent software. This is a efficient method for analysing ship hydrodynamics. This method be able to combine with ship-model testing to optimize the ship hull for hydrodynamics purposes.
Keywords: Flow around the ship hull, ship hydrodynamics characteristics, volume of fluid method, volume fraction equation, Navier-Stokes equations.
1. Ddt van d i
Tinh toan ddng chay bao quanh thdn tau Id gidi bdi toan ddng chdy c6 mat thodng, vdi sy tuong tac giiia cdc pha rdn - long - khi.
Phuong trinh Navier-Stokes cho cho bdi toan ndy Id phuong trinh phi tuygn. Dg gidi dupc bai todn, ngudi ta thudng kgt hgp, so sanh va phan tich kgt qua tu qua trinh gidi bdng phuong phap sd phii hgp vdi qua trinh thir nghiem. Phuang phap sd dp dyng cho giai bai toan nay la phuang phdp thi tich chdt Idng - "Volume of Fluid".
Fluent la mgt trong nhiing chuong trinh ung dung phuang phap sd nay d i giai quyit mdt cdch hieu qua cac bai toan thudc Imh vyc ddng chdy nhieu pha, dugc img dung rpng rai trgn thg gidi hien nay.
Bai vigt dudi day tiinh bay qua ttinh tinh todn ddng chay bao quanh than tau ddu 4950 DWT vdi su hd trp cua phdn m i m Ansys Fluent nhu mdt vi du minh hga.
2. Mo hinh bai toan nghidn cmi 2.1. Mo hinh bai toan
Tdu chay ttong kenh md, cd sdng vdi van tdc khdng d i i v(m/s). Ta qui ddi thanh
md hmh bai toan tau diing yen tren mdi trudng nudc chdy dgu vdi van t i e v(m/s), van tdc sdng bang v(m/s).
Hinh 1. Mo hinh bdi todn chay tren song 2.2. M6 hinh tau
Dg giam kich thudc cho bdi toan, mo hinh tinh toan dugc thu nhd vdi ty le 1/100.
Kich thudc tdu thyc, tdu md hinh nhu sau:
Bang 1. Thong so tdu thirc vd tdu mo hinh Cac thong so chinh cua tau
Chieu dai I6n nh3t: Loa [m]
Chieu dai giita hai duong vuong goc: L„ [m]
Chieu rpng. B [m]
Chieu cao man. D [m]
Chieu chim thi6t kk d [m]
He so beo thS tich: C B Trpng tai: DWT [t]
Toe dp ion nhiit [Knots]
Toe dp dinh rauc [Knots]
Tau thuc 90
84.3 17.5 8 6 0.765 4950 13 12
IVI6 hinh 0.9
0.843 0.175 0.08 • 0.06 0.765
1.3 1.2
TAP CHl KHOA HOC CONG NGHE GIAO THONG VAN TAI, S 6 15-5/2015
- = 0 3. P h u a n g trinh Navier-Stoekes va phirong p h a p t h i tich chdt long (Volume of Fluid-VOF)
3.1. Phurffng trinh Navier-Stockes Hg phuong trinh Navier-Stockes bao gdm phuang tiinh lien tyc, phuong tiinh ddng lugng va phuang ttinh nang lugng. He phuang trinh nay d dang khai trign theo cac tga do x,y,z nhu sau:
Phuong tiinh lien tyc:[2]
dp ^ d(pu) ^ d(pv) ^ d(pw) dt dx dy dz Phuang trinh ddng luong theo phuang x:[2]
d(pu) djpu^) d(puv) 8(puw) _ dt dx dy dz
dx Re^ |_ Sx dy dz j Phuang trinh ddng luong theo phuong y:P]
5(/3v) ^ d{puv) d{pv~) , d(^pvw) _ dt
(5)
(6)
dy [ dx
(7) dz
(8) dy Re, \_ dx dy
Phuang ttuih dong luong theo phuong z:[2]
d{pw) djpuw) d(pvw) djpw^) _ dt dx dy dz _dp_ 1 \dr.^ dz^_ dr^
dz Ke^l dx dy dz + Phuang trinh nang lugng: [3]
djE,) ^ djuE,) ^ djvE,) ^ djwE,) dt dx dy dz B{up) d(vp) d(wp)
dx dy dz
Re^PrJ dx dy dz
Trong do: u, v, w la cac thanh phan van tdc ciia phan tir Idng Ian lugt theo cac phuang X, y, z [m/s]
.-„,T^., c^,r^,,r,^,T^^,T^,T^,T^la cdc tiidnh phdn thuc nhdt giija cac phdn tir long [N]
3.2. PhiroTBg p h a p t h i tich chdt long- Volume of Fluid-VOF
Md hinh bai toan VOF giai quyet cac bai toan hai hoac nhigu pha, mdi pha dugc gpi Id pha thdnh phdn. The tich mdi pha thanh phan dugc quy dinh thdng qua gid tri Cq nhu sau:
Oq = 0 la vimg nghien cuu la vimg rdng, khdng chua chdt Idng pha thii q*; Oq ^ 1 la vung nghign cim chira 100% chat Idng pha thu q*'\ 0 <aq< 1 la vimg nghien cuu gdm chdt Idng thupc pha thii q* vd 1 hoac nhigu cac pha thdnh phdn khac.
Phucmg trinh h^ sd the tich Vigc nghign cim cua mat tigp xuc giiia cac pha dugc thuc hien bdi viec gidi phuong trinh lien tyc cho hg sd thg tich cua mdt hay nhiiu pha. Vdi pha thii q"*, phuang trinh cd dang sau: [1]
<cc p) + V.{a py,)^
(10) S,+t{m^-m^
J fa
Re, [ &
(9) (wr„ + vTg, + wc^ ) +
—(wr +vr +ivr ) + Qy ^ y> y^
— (wr^+vr_^+MT^)
dt
Trong dd:/77^Ia khoi lugng chdt Idng dich chuyen tir pha p sang pha q; m^^ la khdi lugng chdt Idng djch chuygn tir pha q sang pha p\ pq Id ty trgng cua pha q; 5„^ la nang lugng ngudn.
Vdi pha CO sd, he sd the tich se dugc tinh toan dya tign phuang ttinh sau: [1]
Z a , = l (11)
Trong bai toan hai pha (pha 1 va pha 2), ty trgng ciia mdi viing dugc dac trung bdi ty tipng cua timg pha va he sd the tich tuang ling cua cac pha do, theo cdng thdc sau: [1]
/7 = a 2 A + 0 - « 2 ) A (14) Trong bai toan gdm n pha, ty trpng cua
viing dugc tinh qua cdng thiic sau: [1]
P = Y.ao (15)
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I Journal of transportation science and technology, Vol 15, May 2015
4. Md hinh hinh hoc va chia lydi 4.1. Md hinh hinh hoc
Tau dugc dua vdo frong Autoship de md hinh hda lai vd bao than tau: [4]
4.2. Chia ludi
Kieu ludi: unstructured mesh. Chia ludi nhd hon d nhiing viing co dp cong phiic tap, vi du nhu viing cong ciia vd bao than tdu:
Sd mit: 190342, Sd phdn tii: 929054
Hlnh 3. Xdy dipig THtdu trong Autoship Mat vd bao tau dyng ttong Autoship dupc xudt sang module Geometry ttong Ansys:
Hinh 5. Mo hinh hinh hgc Gdc tpa dp dat tai vi tri giiia tau, giao giua dudng ca ban vd mat phdng dpe tdm tdu.
Vi tin mat thoang tai: z = 0,06 [m];
Day ludng tai: z = - 1,5 [m];
Gidi ban tign cua vimg khdng khi tinh toan: z = 0,02 [m].
Hinh 7. Chia lucn nho hon o vdng cong phuc tgp 5. Cac thiet lap ban ddu va dieu kien bien
Md hinh bai toan: bai toan tau chay trong kgnh cd sdng; chdt Idng thyc.
Thdng sd sdng:
- Loai sdng: Shallow wave (sdng ndng);
Van tdc sdng: 0,617333 [m/s];
Bien dp sdng : 0,0122[m];
Bhieu cao sdng: 0,0244 [m];
Gdc lech pha: -270°;
Chiiu ddi sdng: 0,3962 [m].
Dieu kien bign tai dau vao: van tdc = 0,617333 [m/s], mixture;
Digu kien bien tai ddu ra: chudn dp sudt, vi tri mat thoang = 0,06 [mj, vi tii day Iudng=-1,5 [m].
Digu kien bign tai vd bao thdn tdu:
tudng cd dinh, dp cao nhdm = 0,00007 [m], hang sd nham ^ 0,012.
Tai day ludng vd hai bd: tudng cd dinh, dp cao nham= 0, hdng sd nham = 0,012.
Budc thdi gian: 0,001 [s]; sd budc thdi gian:
2000.
TAP CHf KHOA HOC C O N G NGHE GIAO T H O N G VAN TAI. SO 15-5/2015
6. Kit qua
Trudc hit, ta khao sat trang thai hai pha tai mat thoang:
Hinh 8. 5(f trdn ldn giUa hai pha Igi mdi thodng Hinh 8 cho thay, tai vimg mui tau, nudc ddn len cao, chiim he sd thi tich ldn. Ngay sau vung miii vd vimg chuyin giao giiia doan thdn dng cua tau va doan thon mui, thon dudi va doan sau dudi tau, he sd thi tich cua nudc deu giam he so the tich cua khdng khi tang.
Hinh 9. Ap sudt tinh tren vo bao tdu Hinh 9 cho thdy, dpe theo chiiu dai tdu, dp suat tinh giam dan. Theo chigu cao, dp suat tinh tang ddn tir mep boong den day tau.
Gid tri ldn nhdt ciia dp sudt tinh la d vi tri dinh xa nhat theo phuang chigu ddi vg phdi miii cua miii qua le, xap xi 983 pascal.
Hinh 10. Ap sudt thuy dong trin mgi vo bao tdu Hinh 10 cho thdy su phan bo dp suat dgng ttgn vd bao thdn tau. Gia tri dp suit ddng tang nhanh vd dot nggt tai vi tri giao gi&a doan thon mui vd doan thdn dng ciia tau, dat gid tti ldn nhdt tai vimg gdn vdi day tau, xdp xi 264 pascal.
Hinh 13. Ap suat tong trin mgtz = 0.01m Cac hinh 11 din 13 cho thdy su phdn bd dp suat ttgn dien tich mat cat iing vdi cac mdn nudc khac nhau cua tau. Nhin chung, cdc gia tti ap suat thiiy dpng deu cd quy luat phdn bd tuang ty nhau. Ap sudt tang manh tai vimg giao giiia doan thon miii vd doan than dng ciia tdu. Ap sudt thiiy ddng gidm tai viing dinh mui qua lg va dac biet gidm manh, dat gia tri nhd nhat tai vimg sau dudi tdu.
Hinh 14 va 15 cho thdy quy luat phan bd vdn tdc tren cac mat cat nhin chung tuan theo quy ludt tuong ddi gidng nhau.
Van tdc Vx cd dp Idn giam manh tai vimg xa nhat ve phia miii tdu vd t^i vimg sau dudi tdu. Tai cac vimg nay, van tdc Vx cd chiiu ngugc Iai so vdi chieu chung cua ddng chdy.
Van tdc Vy cd dp ldn tdng manh vg hai phia man tau tai vimg giao ^iiia doan thon mui, thon dudi vdi doan thdn dng cua tau. Dp ldn ciia van tdc nay gan nhu khdng ddi dpe theo viing chdt Idng chdy qua doan than dng cua tau.
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Journal of transportation science and technology, Vol 15, May 2015
Hinh IS. Phdn bo vgn toe tren mgiz = 0.02 m Van tdc Vz cd dp ldn tang manh tai vimg thon mui va vimg thon dudi cua tau. Tuy nhign, tai hai vimg nay, chiiu ciia van tdc Vz ngugc nhau. Dp Idn ciia van tdc Vz tai cdc vung trung gian nhu vimg thdn ong cua tau gdn nhu khdng thay ddi va cd gia tti rdt nhd.
7. Kitlu^n
Ket qua tfnh todn dugc v i trudng van tdc va dp suat cung phii hgp vdi thyc te vd ly thuygt Idp bien da dugc cdng bd trudc day.
Hon niia, bai bao cdn chi dugc ra pham vi chinh xac ve hinh hgc ciia vung ldp bign, vimg vgt thuy dpng sau dudi tau, hay vung ngoai ldp bien cua tdu khi chuyin dgng.
Dieu nay cung cap mdt each tryc quan va chinh xac ve cac d^c tinh ddng chay sau dudi tau, gia tti vdn tdc ddng chay vao mat hiit chong chdng, giiip ich cho qua trinh nghign ciru sy Iam vigc cua chong chdng, ciing nhu qua trinh thiet ke tdi uu hinh dang tdu ve mat ddng lyc hgc.
Tu md hinh bai toan nay, cd the tien hdnh qua ttmh md phdng vd bao thdn tau cimg td hgp thigt bi ddy, thiet bi Iai ngay d budc thiet kg lya chgn phuong an de tinh toan nghign Cliu cac ddc tinh thuy ddng lyc hgc cua tau khi hanh hdi, giiip phdn tich cac bai toan ve ddng lyc hgc ddng chay, giiip tdi uu hda hinh dang than tau cimg sy lam viec ciia td hgp thiet bi ddy, thiet bj Idi sau dudi tau. Ddng thdi, qua trinh nay ngn k i t hgp vdi qua ttinh che tao va thir md hinh tau trong bg thic de phuc vy cho qua trinh thiet kg tdi uu tau, dam bdo tinh chinh xac, thu dugc thdng sd kich thudc va hinh dang con tau tdi uu nhdtG
Tai liSu tham khao
[1] ANSYS, hic (January 29, 2009), ANSYS Fuent theory guide.
[2] Satu Hannien (2012), Rons computations of the flow field around a ship advancing at constant speed in still water. Ship Laboratory, Helsinki University of Technology.
[3] Tom Benson (June 12, 2014), Navier- Stockes equations 3- dimensional unsteady, NASA Official.
[4] Ts. Bh Quang Khai, Ths. Le Thanh Binh, Ks. Trinh Thanh Hiiu, Huong ddn su dung AutoShip, Nha xudt ban Hang hai 2014.
J Ngdynh^n bdi: 10/3/2015 •^-'^-••ry^njr.
f' Ngay chap nh^n dang: 15/4/2015 ""^
\^ Phan bien: FGS.TS. Vfi Ngoc Bich
