Tuyin Tap Nghien Cuu Biin, 2010, XVII: 30-42
M0T SO KET QUA TINH TOAN DONG CHAY THEO MUA TRONG VUNG VINH BINH CANG - NHA TRANG BANG MO HINH ROMS
Bui Hong Long, Pham Xuan Duong
Vien Hdi duong hoc
Tom tat Bai bao trinh bay mot so ket qua tinh toan cac dac trung dong chay theo hai miia gio chinh (tay nam, dong bac) va vai tro ciia cac yeu to tao ddng chi'nh trong vung vinh Binh Cang - Nha Trang bang md hinh ROMS. Cac ket qua tinh toan cho thay dugc hai dieu quan trgng; thir nhat trong trudng ddng chay tinh toan xuat hien mot sd cac xoay d vinh Nha Trang. Cac xoay nay xuat hien khi ddng nude tir phia nam len qua eo hep mui Chut - Hon Tre vao vinh Nha Trang theo hudng ddng nam - tay bac gap ddng nude lech nam qua mui Kne Gia va ddng nude tir ngoai khoi di vao qua cira vinh phia ddng. Thu hai ket qua tinh toan ciing cho thay dugc vai trd ciia cac yeu to chinh gay ra hoan luu tai cac diem nhu viing gan bd va cira song khac mot each r5 ret vdi viing ngoai khoi; ddng mat dd (thuan tuy do nhiet mudi) ddng gop 16% (miia gid ddng bac) va 13% (miia gid tay nam) trong ddng tdng hop. Ddng mat dd va ddng nude song ddng gop tuong img 35% va 42% trong ddng tdng hop;
ddng mat dd - ddng nude song va ddng trieu ddng gop tuong irng 58% va 71%.
SOME CALCULATED RESULTS OF CURRENT SYSTEM BASE ON THE ROMS MODEL IN THE BINH CANG -NHA TRANG BAY DURING TWO
MAIN MONSOON SEASONS Bui Hong Long, Pham Xuan Duong
Institute of Oceanography
Abstract This paper presents some calculated results base on the ROMS model in the Binh Cang-Nha Trang bay during two main monsoon seasons (northeast and southwest). The received results show that some calculated current eddies were formed in Nha Trang bay. These eddies were formed when the current from the south passed along the Chut-Hon Tre straight into Nha Trang bay and interacted with both current systems: the first one came from the north passing near Kne Gia peninsular and the another one came from the open sea. The role of main elements forming circulation in different places of the research area was defined as: Gradient current (just temperature and salinity) occupied about 16% and 13% of the general current in the northeast and southwest monsoons, respectively. Gradient and river currents were 35% and 42% of general current during the northeast and southwest monsoons, respectively. Gradient - river and tide currents were 58% and 71% of general current during the northeast and southwest monsoons, respectively.
I. MO DAU
Dong chay ven ba dugc tao nen va duy tri bdi nhiing thanh phan chinh nhu thiiy trieu, nguon nude tir song sudi, gio hay ap suat khi quyen tac dung len mat nude, hay su bien doi mat do nude bien trong khong gian ciia viing nghien ciru. De co the dinh lugng mot each tot nhat cac thanh phan dong chay nay trong dong chay tong hop trong vinh Binh Cang - Nha Trang, chiing toi da su dung mo hinh ROMS de tinh toan:
- Vai tro ciia dong mat do (thuan tuy do nhiet, mudi)
- Vai tro ciia dong mat do va song - Vai tro ciia dong mat do, song va thiiy trieu
- Vai tro ciia dong mat do, song, thiiy trieu va gio (dong tong hop).
Do tinh chat quan trgng ciia viing vinh nen viec nghien ciiu dong chay trong viing vinh rat can quan tam nghien ciiu.
Cac ket qua nghien ciiu cho phep nam bat dugc cac dac trung ca ban ciia moi trudng bien nhu muc nude, thiiy trieu, song, dong chay, nhiet do, do muoi v.v. De dap irng dugc yeu cau ngay cang cao phuc vu cac hoat dong kinh te xa hoi, quoc phong, viing bien Nha Trang Khanh Hoa can dugc tien hanh nghien ciiu nhieu han nua dac biet la su dung mo hinh toan vdi cac cong nghe mdi, day la con dudng it ton kem nhat va can thiet de co dugc cac thong tin huu ich.
II. TAI LIEU VA PHUONG PHAP 1. He phuong trinh:
Cac phuong trinh dang ca ban (Blumberg & Mellor, 1987; Duong Hdng San, 2003), ciia mo hinh hoan luu bieu diln cac trudng van toe va do cao be mat.
Hai phep tinh xap xi dan gian hoa da tirng dugc sir dung; thii nhat no thira nhan trgng lugng cira chat long can bang vdi ap suat (gia thiet thiiy tinh) va thii hai, nhung su khac biet ve mat do dugc bo qua trir khi nhung khac biet do ldn do luc hut ciia trai dat (phep tinh xap xi Boussinesq).
Trong he tga dd true giao Cartesian (Vreugdenhil, 1998) vdi ox tang theo hudng ddng, oy tang theo hudng bac va oz tang tir muc nude tinh hudng len (gdc tga dd nam tai be mat bien). Be mat tu do dugc xac dinh tai vi tri z = n(x,y,t) va day tai vi tri z = - H(x,y). Neu v vector van tdc theo phuong ngang vdi cac thanh phan (u, v) va V la toan tir gradient theo phuong ngang, cac phuong trinh lien tuc va ddng lugng dugc viet nhu sau:
Phuong trinh lien tuc ddi vdi chat long khong nen dugc:
^ + ^ + ^ = 0 (1) dx by dz
Cac phuong trinh ddng luong Reynolds:
** + F+D(2) du du
tv.Vu + vc
dt dz
— + v.vv + dt
dv dz ' trinh
dx dy ddng luong dip_ = _pt>_
dz pQ
Phuong trinh trang thai p = p(s,T,P Phuong
phuong thang diing:
theo (4) va gia thiet thiiy tinh — = pg dP
dz (5)
ddi D„
Trone do: — = , dd 1 dP dx va — =
dy p0 dy ddng lugng K
A dP
dx
P7p0 la su bien
la :o phuong ngang
—(K —] va D =—(lC —
dz\ " dz) ' dz\ M dz cac thanh phan nhdt va khuech tan rdi theo phuong ngang.
Toan bd cac chuyen ddng dugc tao ra bdi cac qua trinh quy md nhd khong the giai quyet true tiep bang ludi md hinh (quy md dudi ludi) dugc tham sd hda bang cac qua trinh xao trdn theo phuong ngang. Cac sd hang Fu va Fv dai dien cho cac qua trinh khong giai quyet duoc nay va trong phep ngoai suy khuech tan phan tir, cd the viet nhu sau:
F =-£. 2A, < it dx dy
. 5u ^ dv dy dx 8 2AM
dv' 8 du SvY dx 2AM dy H
dy
(6) Viec can bang cac yeu to khac nhau de dat dugc su ket hgp tot nhat doi vdi su dem gian hoa dia hinh. chung ta sir dung he tga do Sigma, khi do cac phuong trinh viet trong he tga do nay trd nen phiic tap hon nhu sau:
8H. 8{H:u) , 8(Hy) , r j f e j _ n ( 7 )
dx dl du ,
fv + v.vu dl r -T7
/u + v.Vv a
P = P(T,S,P)
do J-gH:p ds I p0
oy 3?
dx sPo, & "
dl_ ' SP* ^ _ dy u ,
0
+ /r + D„(8)
+ (9) (10) (H)
dday:
v = (u.v.n)
v a v. v = M A + v A + Q f 02)
& dy ds Van t6c thing diing trong he tga do Sigma se la:
H. u v-dz
dt dx dy dz dz dz . , w = — + w — + v— + O.H. (13)
<3r <3x dy
Chuyen cac phuong trinh (7)-(13) sang he tga do mdi (he tga do Sigma cho phuong thang diing va he tga do cong true giao theo phuong nam ngang) vdi v.<f = u va V./J = v, khi nay cac phuong trinh chuyen dong theo (www.myroms.org), co the viet lai nhu:
dt v. mn
\- [\ mn dt v mn J d£
d_
Vd{
p = p(T,S,P) d^
~ds d_(H_
) d ( H.uv^ a ' H.uQ\
\ + — —=— +— ^—
) dp\ m , Si k mn J ) d ( n
\-u— — \H,v = M dp\m J " " I dP d£~
gp dz dc) Hz
p0d$
d ( H.uv dp d ( 1
//,v21 | d fH.vQ
bp\m - rH.u
ds v. mn ' dP f f
m _+Zpd^ + gdS_
dp p0 dp dp +!L(Fr+Dr) mn
dt y mn J d.
gH:P
Po d HM
n dp Hy
m d_
ds
H.Q = 0
Vi z la mot ham tuyen tinh ciia L\, phuong trinh (18) co the viet lai nhu sau:
I L L dt I mn
d ( HM
&4\ n
d (Hy\ | a (Hp
dp\ m ) ds 0
(14)
(15)
(16) (17) (18)
(19) Trong do: m, n la moi lien he giua do ldn ciia khoang sai phan trong cac he tga do (he tga do Sigma va he tga do theo phuong z la Sigma va phuong ngang la he tga do cong true giao Z.p. m{c.p). n{%,p)\ (ds\ =(l/m)d^, (ds)^ = (l/n)dp. Dm Dv la cac thanh phan nhdt va khuech tan roi, Fu va Fv la cac thanh phan ngoai luc.
~a~H
t, \ds dz dz v-u+s) mu nv—
1 'dt c£ dp (20) (21)
(22) dz -.dc „( xdh
— = (1 + s)-^ + C{s) — 3£ d£ d^
dz f, sdg _/ ^dh
— = (1 + s)— + C(s)—
dp. dp dp
Gia thuyet ve ap suat thiiy tinh cho phep tinh dugc thanh phan van toe theo phuong thang dirng tir phuong trinh lien tuc va vi vay cac mo hinh loai nay doi khi con dugc ggi la "tua ba chieu" de phan biet voi cac mo hinh sir dung day du ca 3 phuong trinh dong lugng.
2. Dieu kien bien:
Dieu kien bien thang dung:
Cac dieu kien bien thang dirng dugc quy dinh nhu:
dn dt'
du x l \ . dv
Tai dinh (z = n(x,y,t)): w- T!(x,y,t)(23)
Km— = r*(x,y,t) va K dz "' dz
-Tai day (z = -H(x,y)): -w + v.VA = 0, Km^ = r;(X,y,t)™Km^ = r£(x,y,t) (24)
dz dz Vdi day bien doi, z = -H(x,y), ung suat day phu thuoc vao cac thanh phan van t6c theo phuong ngang:
< = ( r , +yju2+v2)u,
*l = (ri + Yi V"2 +v2)v (25)
Trong he tga do Sigma, cac dieu kien bien thang dirng trd thanh:
- Tai dinh (s=0):
Km du . / \ ds
Tai day (s :
= Tys{x,y,t) va Q = 0(26) I):
K„
H.
Km
H.
du ds dy_
ds
= r;(x,y,t),
= T^(x.y.t) va Q = 0(27)
Cdc di'eu kien bien theo phuong
ngang: , Cac dieu kien bien dugc sir dung doi
vdi u la:
- (3 cac bien phia dong va phia tay:
d_
dx
hv d 2u^
mn dx = 0 (28) (j cac bien phia bac va phia nam:
d_
dy
hv d2u
mn dy2 = 0 (29) Doi vdi nhiet do va do muoi d bien sir dung dieu kien:
ZSJL = Q<- ^ = g ,; (30)
8N 8N
Neu tai bien cirng (bd dat lien hoac cac dao) sir dung: Q'= Qi'= 0
Trong do: Ki hieu N la phap tuyen vdi dudng bo, Tb va Sb la gia tri nhiet do va do muoi tai bien.
Tai bien mo huong khoi: Tinh dao dong muc nude trieu tai bien md co dang:
n, .F,cos[,j/ + v>, +p,{')] (N 3 1)
(32) Bien md tai ciia song:
I { uaStmg
Trong do Q : Luu lugng nude song, D : Dien tich mat cat udt ngang song.
Cac ki hieu co the dugc tham khao chi tiet hon tai (Coo. Mellor & Blumberg,
1985).
Cac dieu kien ngoai luc:
Gio la yeu to ngoai luc co tam quan trgng ldn den ddng chay bien, viec co trudng gio d cac thai diem khac nhau cung la mot van de cho bat cir ngudi lam mo hinh nao. De co dugc chuoi so lieu nay, chiing toi da sir dung nguon so lieu gio trich tir Bo so lieu khi quyen - Dai duong tong hgp (The Comprehensive Ocean - Atmospheric Data Set - COADS). Day la ca sd dii lieu dugc xay dung va duy tri bdi Trung tam nghien ciiu khi quyen Quoc gia (NCAR) va Cue khi quyen - Dai duong Quoc gia (NOAA) dac biet la Trung tam chan doan khi hau (Climate Diagnostics Center CDC), Vien hop tac nghien cuu cac khoa hgc moi trudng (Cooperative Institute
for Research in Environmental Sciences - CIRES) thuoc truong Dai hoc tong hop Colorado va Trung tam du lieu khi hau Quoc gia (National Climatic Data Center - NCDC). COADS la tdng hop sd lieu quan trac be mat bien toan cau tir nam 1784 den 1997 trong do so lieu trung binh thang duoc thong ke trong giai doan 1800 - 1997. Cac so lieu chit yeu thu thap tir cac tau bien (tau thuong mai, tau nghien cuu,
tau danh ca, hai quan. v.v.) va cac phao co dinh va tha troi. Cac gia tri con thieu se duoc tinh bang phuong phap phan tich dot tuong (objective analysis - OA) sau do no se duoc noi suy tuyen tinh hoac phi tuyen.
Cac ket qua sir dung COADS de lay chuoi so lieu gio cho hai miia gio dong bac va tay nam phuc vu cho mo hinh duoc tai hien qua cac hinh 1 va hinh 2.
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Hinh 1. So do phan bo truong gio theo thai gian d viing vinh Binh Cang - Nha Trang vao mua gio dong bac
Fig. 1. Diagram of temporal variation of wind velocity at Binh Cang - Nha Trang bay during NE monsoon period
> n i f
m m
^ m m m
/ / J Y / A / / / / / / f / / / / / / / J f / /
l l l f l l
\yr/T/r///rW/t////////'///\
/ / / / / / / / / / / / / / / / / / / / / .
»//////////>/////////
Truong gio tay nam ngay 17/7/2009 Truong gio tay nam ngay 24/7/2009 Hinh 2. So do phan bo truong gio theo thai gian a viing vinh Binh Cang - Nha Trang
vao miia gio tay nam
Fig. 2. Diagram of temporal variation of wind velocity at Binh Cang - Nha Trang bay during SW monsoon period
III. KET QUA
1. Hieu chinh va Idem djnh md hinh:
1.1. Xac djnh va hieu chinh:
Buac 1: Xac dinh buac thai gian:
Xay dung dugc ludi tinh, dua cac so lieu ban dau va cac dieu kien bien vao mo hinh thi cong viec chgn budc thai gian (dt) phai thoa man dieu kien on dinh va hdi tu Courant-Friedrichs-Levy (Durran, 2002).
De sd hda dia hinh vinh Binh Cang - Nha Trang, chung tdi sir dung ban dd CAM RANH BAY TO CAPE VARELLA, ti le 1:150.000 va dugc hieu chinh lai vdi cac sd lieu do sau trong viing nghien cuu ciia tat ca cac de tai cac du an khao sat chi tiet trong thai gian gan day. Khu vuc nghien cuu dugc phii kin bdi mot mang ludi 150x 150 nut ludi vdi Ax« 260m (trung binh), Ay » 265m (trung binh),
AZW0.4-H1&5/W va budc thdi gian At = 30s la phii hop vdi md hinh.
Buac 2: Hieu chinh cdc tham sd khuyech tan rdi, nhat rdi: De ket qua tinh toan ciia md hinh dugc sat vdi cac sd lieu thuc do thi budc hieu chinh nay rat can thiet cho cac qua trinh ddng luc hgc ciia
vimg nghien cuu. Giu nguyen cau hinh da dugc thiet lap, chiing tdi cho md hinh thu nghiem md phong hoan luu cua vung nghien ciiu vdi nhieu so do rdi khac nhau, cac ket qua md phong dugc so sanh vdi bd sd lieu thuc do (thang 9 nam 2007). Ket qua tinh toan dugc trich ra tir hai diem khac nhau ciia mien tinh (Hinh 3). Tram 1 cd tga dd nam gan vdi tga dd ciia tram do muc nude Cau Da - Nha Trang, tram 2 la diem nam d khu vuc Hon Thi. Sd lieu lay ra tir hai diem nay la chudi sd lieu muc nude, chudi sd lieu ciia cac thanh phan chuyen ddng (thanh phan u va v trung binh).
Ket qua dinh tinh: vdi cac sa dd rdi khac nhau dugc the hien qua cac hinh minh hga 4. Tir cac ket qua phan tich cho thay mot each dinh tinh la cac sa dd roi cd he so nhat rdi cho cac thanh phan ddng luc va cac thanh phan vd hudng (nhiet - mudi) bang 20m2/s va 10m2/s, ket qua nay phan anh dugc mdi lien he tdt hon giira dao ddng muc nude vdi cac thanh phin chuyen ddng va sd lieu tinh toan dua ra phii hop vdi thuc te han.
Hinh 4. Bieu do bien doi muc nuac va thanh phan it, v ciia viec hieu chinh sa do roi vai cac h? so nhat dong hoc la 20m2/s, 2m2/s va 0,2m2/s ciia diem 1
Fig. 4. Variation of water level and u, v components for adjustment of turbulent diagram corresponding to different kinetic viscous coefficients of 20m7s, 2m Is, and 0.2m /s at point No. 1
Ket qua dinh luong: Hieu chinh sa do rdi vdi cac he so nhdt dong hoc la 20m2/s, 2m2/s va 0,2m2/s thi dinh lugng sai so tinh toan so vdi thuc do ciia chudi so lieu muc nude tai tram Cau Da vao thang 9/2007 lan luat bang 10,02; 10,9 va
11,3cm. Do vay chiing toi da chgn sa do co he so nhdt roi cho cac thanh phan dong luc bang 20m2/s va cac thanh phan vo hudng bang 10m2/s dua vao mo hinh ap dung vao viing vinh Binh Cang - Nha Trang.
1.2. Kiem djnh:
Kiem dinh chuoi so lieu dao dpng muc nude giua thuc te va tinh toan:
Bo so lieu de kiem dinh lai mo hinh ROMS sau khi da dugc hieu chinh la bd so
lieu ddng bd thu thap dugc vao thang 8/2009 (bo sd lieu ve muc nude tai tram Cau Da, gid, ddng chay, nhiet, muoi tai 17 tram mat rdng), tai viing vinh Binh Cang - Nha Trang la chuyen khao sat mdi day nhat. Ket qua so sanh muc nude (rj) tinh toan va muc nude thuc do ciia tram muc nude Cau Da (Nha Trang) dugc danh gia theo dinh tinh va dinh lugng cho cac ket qua chap nhan dugc:
Danh gid dinh tinh: So sanh ket qua tinh toan ra tir chudi sd lieu ciia tram 2 cd tga dd 109°. 185, 12°.432 va sd lieu muc nude do dac tai tram muc nude Cau Da (Nha Trang) vao thang 8/2009 la phii hop d tat ca cac khoang du bao (Hinh 5).
-Thyc do -20m2/s -2,0 m2/s -0,2 m2/s
Hinh 5. So' dd ket qua danh gia giCra muc nude tinh toan vdi muc nude thuc do thang 8/2009 ciia tram Cau Da
Fig. 5. Comparative diagram between measured and computed water levels in August 2009 at Cau Da station
Danh gid dinh luong: Danh gia dinh lugng dd chinh xac ciia muc nude tinh toan vdi muc nude thuc do cung khong dan gian vi: thii nhat, xac dinh dugc su ddng bd giua sd lieu muc nude thuc do va sd lieu quan trac la van de khd; thii hai, chuyen giua sd lieu muc nude thuc do va sd lieu quan trac ve ciing mot gdc tga dd; thii ba.
chudi sd lieu cang dai thi sai sd trong danh gia dinh lugng lai cang ldn. Do vay, sd lieu diing de danh gia dinh lugng, chiing tdi xet trong khoang thai gian mot thang (thang 8/2009).
Sir dung chi sd RMSE (RMSE, sai sd binh phuong trung binh), de danh gia ve mat dinh luong sai sd tinh toan so vdi thuc
do. Tieu chuan danh gia sai sd la binh phuong nhd nhat giira ket qua tinh toan va muc nude thuc do la:
RMSE--
Trong dd qt la muc nude thuc do, n]' la muc nude tinh toan va N la sd diem thai gian ddng bd ciia cap gia tri muc nude.
Ket qua diing chi sd RSME de xac dinh dinh lugng sai sd tinh toan va thuc do ciia chudi sd lieu dao ddng muc nude trong thang 8/2009 la 10,2cm. Sai sd 10,2cm ciia chudi sd lieu dai ngay da phan anh ket qua ciia md hinh cd miic dd tin cay cao.
2. Hinh thai dac trung cua hoan luu:
Khi nghien cuu hoan luu trong vinh Binh Cang - Nha Trang bang mo hinh ROMS cho thcri gian dai lien tuc mot nam ciia bien doi tirng gid. Cac ket qua tim dugc cho thay, trudng dong chay xuat hien mot so hinh thai dac trung, do la hinh thanh cac xoay d vinh Nha Trang. Cac xoay xuat hien khi dong nude tir phia nam len qua eo hep mui Chut - Hon Tre chay vao vinh Nha Trang theo hudng Ddng Nam - Tay Bac, bi tac ddng true tiep ciia ddng nude lech nam mui Kne Gia va ddng nude tir ngoai khoi phia ddng chay vao.
Viing xoay chi dugc hinh thanh va phat trien d pha trieu len. Trong thoi gian nay, nude vung cira dang len gay ap luc nude chay vao vinh qua hai cira la cira phia ddng va phia nam. Nude d cira phia nam vdi song pha truyen trieu nhanh hon d cira phia ddng va phai di qua mot eo hep cd hudng Ddng Nam - Tay Bac chay len bac vinh, trong khi dd bd ciia vinh Nha Trang lai cd dang hinh cong ludi liem cd hudng Ddng Nam - Tay Bac. Do vay ma nude d
eo vinh Nha Trang (tao bdi bd ciia dao Hon Tre va bd nui Chut) bj hut nude manh hinh thanh ddng chay vao vinh men theo dudng bd cong ciia vinh Nha Trang cd dang mot ludng ddng chay cong d vinh Nha Trang.
Khi nude ngoai khoi phia ddng dang cao hon tao ra ddng chay manh hern hudng vao trong vinh thi mot phan luong nude den khu vuc mui Kne Gia bi hut di len viing dinh vinh Binh Cang, mot phan nguon nude chay lech hudng ve nam. Nguon nude lech nam nay tac ddng true tiep tdi ludng chay cong tir phia ddng nam len budc ludng chay nay bi lech hudng cd xu the quay dau trd lai, trong khi dd lai cd khdi nude tir phia ddng tac ddng tdi ludng chay cong lam lech hudng dan ludng chay nay. Den mot giai doan nao do cac ludng chay phuc tap nay se hinh thanh mot viing chay xoay trong vjnh Binh Cang - Nha Trang.
Hinh 6 la hinh minh hoa xu hudng hinh thanh viing xoay va hinh 7 minh hoa vung xoay da hinh thanh va phat trien day dii.
109 07'
Hinh 6. So dd xu hudng hinh thanh xoay trong vinh Fig. 6. Diagram of the forming process of eddy in the study area
109 07'
Hinh 7. So do xoay trong vinh Fig. 7. Diagram of eddy in the study area
109°24'
Cdc tinh chat dgc trung cua vung xoay:
-Viing xoay chi dugc hinh thanh tai mot viing nhat dinh cira vinh Binh Cang - Nha Trang, do la kfiu viing vinh Nha Trang.
-Chi xuat hien d pha trieu len khi ma dong nude tir phia dong chua hoan toan chiem uu the.
-Viing xoay thudng xuat hien ro ret khi do cao muc nude dat khoang tir 1.90 den 2,5m.
- Thai diem thudng hay xuat hien tuy vao thai gian trong nam tir thang 10 den thang 2 nam sau, cac xoay hay xuat hien vao ban dem ve sang. Tir thang 4 den thang 9 thudng it khi xuat hien xoay han va khi xuat hien thi thudng xuat hien vao budi chieu nhieu hon.
- Viing xoay ton tai trong thai gian khoang 2 gid.
- Miia chuyen tiep viing xoay lan dan ve phia dau mui ciia dao nhieu hon.
- Nhieu thai diem tang mat chua xuat hien nhung cac tang dudi xuat hien viing xoay.
- Mot vai thai diem trong cac miia co the xuat hien tdi ba xoay trong vjnh, bao gom hai xoay nghich va mot xoay thuan.
3. Vai tro cua cac nhan to chinh hinh thanh hoan luu trong vinh Binh Cang - Nha Trang:
De co the dinh luong mot each tot nhat cac thanh phan dong chay trong dong chay tong hgp, chiing tdi da sir dung md hinh ROMS chay vdi cac phuong an sau:
- Chi nghien ciiu ddng mat dd (ddng mat dd).
- Nghien ciiu ddng mat dd va them tac ddng ciia nguon nude tir luc dia chay ra (them song).
- Nghien ciiu ddng chay bao gdm:
ddng chay do mat dd, nude song va trieu tac ddng (them trieu).
- Ddng chay tdng hgp
Ket qua nghien ciru cac thanh phan nay cho thay, a cac vi tri khac nhau thi tirng thanh phan gay ra dong chay se khac nhau. C1 viing gan bd va cira song khac vdi viing ngoai khoi rat nhieu, do vay chung toi chon ra ba diem dac trung ciia vung nghien cuu va tien hanh phan tich chudi sd lieu lien tuc nhieu ngay ciia cac tram nay vao hai miia gid dien hinh. Cac ket qua phan tich cho biet:
a. Tram vung cua song Dong Bd:
- Ddng mat dd ddng gdp 1,2% (miia gid ddng bac) va 0,4% (miia gid tay nam) trong ddng chay tdng cdng.
- Ddng mat do va ddng nude song ddng gdp tuong ung la 25% va 32%.
- Ddng hon hop mat do - nude song, thuy trieu ddng gdp 55% va 66%.
Hinh 8, 9 minh hoa bieu dd bien ddng ddng chay theo thai gian cua tram cira song Ddng Bd vao mua gid ddng bac va miia gid tay nam.
- Met DO Tlifem Song Hl6m Tri^u - T6ng Hqip
0 5 10 15 20 25 30 35 Hinh 8. Bieu do bien ddng dong chay theo thai gian ciia tram cira song Ddng Bd
vao miia gid ddng bac
Fig. 8. Diagram of temporal variation of current velocity at Dong Bo river mouth station during NE monsoon period
Hinh 9. Bieu do bien dpng ddng chay theo thai gian cua tram cira song Ddng Bd vao miia gid tay nam
Fig. 9. Diagram of temporal variation of current velocity at Dong Bo river mouth station during SW monsoon period
b.Tram vung giua cua vinh Binh Cang - Nha Trang:
- Ddng mat dd ddng gdp 22% va 29%.
- Ddng mat do va ddng nude song ddng gdp 40% va 59%.
- Ddng hdn hop mat dd - nude song, thuy trieu ddng gdp 56% va 83%.
Hinh 10, 11 minh hoa bieu dd bien ddng ddng chay theo thai gian ciia tram giua cira vjnh Binh Cang-Nha Trang vao miia gid ddng bac va miia gid tay nam.
c. Tram ngoai khoi phia nam vinh Binh Cang- Nha Trang:
- Dong mat do dong gop 25% va 11%.
- Dong mat do va dong nude song dong gop 40% va 34%.
- Dong hon hop mat do, nude song.
thiiy trieu dong gop 62% va 64%.
Hinh 12, 13 thd hien bieu dd bien dong dong chay theo thai gian ciia tram ngoai khai phia nam vao miia gio dong bac va miia gio tay nam.
Hinh 10. Bieu do bien dong dong chay theo thai gian ciia tram giua cua vinh vao mua gio dong bac
Fig. 10. Diagram of temporal variation of current velocity at bay mouth station during NE monsoon period
Hinh 11. Bieu do bien dong dong chay theo thai gian ciia tram giua ciia vinh vao miia gio tay nam Fig. 11. Diagram of temporal variation of current velocity at bay mouth station
during SW monsoon period
Hinh 12. Bieu do bien dong dong chay theo thai gian ciia tram ngoai khoi phia bac vao miia gio dong bac
Fig. 12. Diagram of temporal variation of current velocity at northern station in offshore region during NE monsoon period
Hinh 13. Bieu dd bien ddng dong chay theo thoi gian ciia tram ngoai khai phia bac vao mua gid tay nam
Fig. 13. Diagram of temporal variation of current velocity at northern station in offshore region during SW monsoon period
IV. KET LUAN
Cac ket qua nghien ciru ddng chay bien ddi theo tirng gid d vinh Binh Cang - Nha Trang da xac dinh dugc mot sd trudng hop trudng hoan luu cd hinh thai dac trung. dd la hinh thanh mot viing xoay d vinh Nha Trang. Viing xoay nay xuat hien khi ddng nude tir phia nam len theo hudng Ddng Nam - Tay Bac chiu tac ddng ciia hai ddng nude chii yeu, ddng nude lech nam ciia khu viing phia nam mui Kne Gia ket hgp ddng nude true dien tir cira phia ddng chay vao va viing xoay chi dugc hinh thanh trong pha trieu len.
Vai trd nhirng nhan to chinh hinh thanh hoan luu viing vinh Binh Cang - Nha Trang anh hudng tdi ddng tdng hop la kha phiic tap. 0 nhirng vi tri khac nhau thi anh hudng ciia cac nhan to nay trong ddng tdng hgp la khac nhau. De danh gia miic dd ddng gdp cira cac nhan to nay tdi he ddng chay tdng hop can xem xet theo chuoi thai gian.
Viec hinh thanh cac viing xoay trong viing nghien ciiu va thai gian ton tai tuong ddi ngan ciia chiing can dugc kiem tra va danh gia them bang viec so sanh cac kdt qua tinh toan va sd lieu do dac thuc te.
Cac ket qua nghien ciiu ung dung cho thay md hinh rat cd trien vgng ap dung cho nhieu viing khac nhau phuc vu tdt cho nghien ciru khoa hgc ciing nhu vide xay dung tien kha thi cho qui hoach phat trien kinh te bien va cac cdng trinh ven bd. Ket
qua tinh toan dugc kiem chiing thdng qua cac ket qua do dac thuc te d trong viing nghien ciiu, cho thay cd su phii hgp tuong ddi vdi thuc te do dac.
TAI LIEU THAM KHAO
Blumberg, A. F. and G. L. Mellor, 1987. A description of a three-dimensional coastal ocean circulation model. In:
Heaps N. (Ed.), three - dimensional coastal ocean models, American Geophys. Union, 1-16.
Coo. Mellor, G. L. and A. F. Blumberg, 1985. Modeling vertical and horizontal viscosity and the sigma coordinate system. Mon. Wea. Rev., 1 13: 1,379- 1,383.
Durran, D. R. 2002. Numerical methods for wave equations in geophysical fluid dynamics. Spinger publishers New York. Berlin. Heidelberg. Barcelona.
Budapest. Hong Kong. London. Milan.
Paris. Singapore. Tokyo. 465 p.
Duong Hong Son, 2003. Nghien cuu phan bd ba chieu trudng ddng chay va nhiet do Bien Ddng bang phuong phap sd tri.
Phan vien Khi tuong Thiiy van phia Nam, Thanh phd Hd Chi Minh. Tr. 115 - 126.
Vreugdenhill, C. B. 1998. Numerical methods for shallow - water flow. Kluwer Academic Publishers, Netherlands. 261 p.
http://www.mvroms.org Ngudi nhan xet: TS. La Van Bai
