ANH HU'(!rNG COA HINH DANG CCTA RA
1(3\ K H A N A N G T H A O C O A CONG TRiNH T H A O SAU
PGS.TS Huynh Ba Ky Thu$t'; 77iS. Nguyin Cong Thanh '
T6m tat: Trong tinh toSn khS nSng thSo cua cdng trinh thSo sau, ed hai yiu to cin xSc djnh dd IS h$ so luu lugng p vS cgt nudc tSe dgng Z(Zo). He so luu lux/ng tbi ehl phg thugc vSo hinh dgng ctra vSo, h$ so ma sSt, eSc hg so ton thit cue bi cda l6 thSo sSu. Trong khi dd thi cgt nudc tac dgng Z(Zo) Igi phg thugc vSo hinh dgng mSt cong cira ra vS che dg nil tiip ddng chay (vin de nSy It dugc de cgp din).
Vl^e xSe djnh ddng dSn giS tri, cgt nude tSe dung Z(ZQ) se cho kit qui khi nSng thSo cua cdng trinh phd hgp thSo sSu phu hgp vdi ly thuyit
Summary: In calculation of discharge capacity of under sluices, there are two factors to be determined: discharge coefficient and water head Z(Zo). The discharge coefficient p depends on the entrance shape, friction coefficient and partial loss coefTicient of under sluices. Whereas, the water head Z(Zo) depends on the shape of outlet section and regime of flow at downstream outlet (this problem is rarely mentioned). The determination of the proper water head value Z(Zo) would result in the suitable discharge capacity accordingly.
NhSn ngSy 17/8/2011; chinh sua 05/9/2011; chip nh$n dSng 30/9/2011
1. Gid>i t h i f u
Cdng trinh thdo lu dudi sdu cd t h i dgt dudi ddy dgp vd tren nen ( d n g nglm), di qug thdn dfp (dudng dng), eung ed t h i dgt d ben bd (dgng dudng h i m luy nen) khi diiu kifn dja hinh, dja chit cho phdp. Cdng thdo sdu cho phep chiing la thdo duge nude trong hd vdi b i t ki myc nude ndo, thf m chi cd the thdo cgn hd chira. Logi ndy la cd t h i sip dyng vdo nhiiu myc dich khdc nhau nhu: thdo lu, thdo cgn hd cliipg, d i n ddng thi cdng, thao biin cdt ling dpng, liy nudc tudi, l i y nudc vdo nhd mdy thuy difn. Do dd, tuy vdo dieu kifn cu t h i md cd t h i k i t hgp nhiiu myc dich khde nhau ddi vdi edng trinh thao nude dudi sau. So vdi edng tfinh thdo lu x l mgi thi vife vfn hdnh cipa van trong trudng hgp ndy Id khd khan vd phirc lap hgn.
Cdng tfinh thdo sdu cd mpt sd dac diem eg ban sau :
- Cipa van d sau, khi md luu tde d dudi cipa r l t ldn. Cting mdl difn lich mat eat ngang nhu nhau, luu lugng thdo qua Id thdo sdu Idn hgn r l t nhieu so vdi thao qua edng trinh xa mdl.
- Vige thdo nude tugng ddi dn djnh, khi muc nude thay ddi luu lugng thdo thay ddi il.
Myc nudc trong hd Ihip eung cd the thdo dugc luu lugng Idn.
- Do luu tdc Idn ngn ban thdn ddng chiy d luu tdc mgch ddng Idn ed the gdy nen mng dgng cu-a van vd d c b f phf n khde.
' Khoa XSy dung Cdng trinh thuy Tmdng Dai hgc XSy dung.
E-mail: thanh43d@gmail,com
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- Luc myc nudc tfong hd cao, eti-a van chju dp lyc nudc ldn d i n den lyc ddng md cu-a van cao ddi hdi (tfpng lugng) lyc nang hg cua d c thiit bj ddng md d n g Idn.
- Cipa vao d n g frinh thip, thudn Hen trong vifc xa btin d t Trong tiu-dng hgp ddng chdy mang nhieu bun d t ttii khi thdo lu hode thao bim cdt ed the gdy nen bao mdn Idp Idt cua dudng thdo nude.
- 6ng ngam vd dudng h i m chju dp lyc d l t dap hogc dd. Trong tru-dng hgp v f n hdnh thi dp lyc da k i t hgp vdi ldp do dudng ham ehju mpt phin dp lye nudc ben trong dudng h i m .
Oe xay dyng d n g thirc tinh todn kha nang xa ciia d n g tiinh thdo sau cd dp, ngudi la xult phdt tir ly thuyet ddng chay qua lo nhd thdnh mdng vd Id to thdnh mdng, chi tiet cd Ihi tham khdo [4], 2
" "
Hinh 1. Sa di tinh ddng chay qua Id nhd thanh mdng
Dudi tdc dyng cua d t nudc Z = const, ddng chdy qua khdi lo Id ddng ehay dn djnh.
Trgn eg sd phugng trinh Bemoulli viet cho 2 mat d t 1-1 vd C-C, l i y mft chuin 0-0 di qua trpng ldm Id (Hinh 1), la cd dugc phuung trinh xdc djnh luu lugng qua lo nhd thdnh mdng nhu sau (theo [4]):
Q = Vc^c=P0)j2gZ^ (1)
Vdi ^ I d hf sd luu tde, coc Id difn tich ciia mft d t co hgp, ZQ Id d t nudc tdc dyng d x6t din vfn tdc tien g i n . Gpi £ = —^ la hf sd co hgp, a>: didn t i d Id xa, cira x l vd (x = E(p Id hf s6
CO
luu lugng d a Id. Nhu vfy, d n g thirc xdc dmh k h i nang thdo d n g tfinh xa sdu d dp d dgng chung nhu sgu:
Q = f20)pgZ, (2) Trong d n g thirc tren, he sd luu lugng p. la gid tri phy thupc vdo d e h f sd tdn thit ctia
cira vdo, mirc dp eo hgp eua ddng ehay... Gid tii Zo phu ttiupe vdo nhiiu yeu id nhu hinh dgng mgt d l cira ra, che dp ndi tiip cua ddng chdy tgi cira ra vdi hg luu. V i n d i xdc djnh gid trj g ed t h i Iham khao d d e tai lifu thiiy lyc dgi eugng cung nhu thiiy lyc ehuyen ngdnh, d n d c h xdc djnh gid trj Zo ttii it duge d i cap d i n , ddc biet la tfong d c ti\fgng hgp cd hinh dgng eti-a ra Id cong (Hinh 2). Dudi ddy di sdu vdo phdn tieh d c h xdc dmh Zo eung nhu dnh hudng eiia hinh dgng cira ra tdi d t nude tde dyng ZQ.
52 S610/9-2011 TAP CHi KHOA HC)C C O N G N G H E XAY DUNG
2. Xdc djnh c$t nu'dv Zg
2.1 Khai nigm cgt nuac tac dung Zo
L i y mgt chuin Id nhu trdn hinh ve (Hinh 3), xet bd ddng phdn td dz, phugng tfinh Becnulli cho 2 mgt d t 0-0 vd 1-1 duge viet nhu sau:
(3) Ta d dQ = bgUgdz , dQ = budz; trong dd Uo,u, bo, b i l n lugt la luu tdc tmng binh, chiiu rfng tmng binh lgi mft d t 0-0 vd 1-1 ung vdi vj tfi phan td dz. Cdc ky hifu cdn lai nhu trf n hinh 3.
Nhdn d 2 ve phuang trinh (2) vdi dQ, l i y tieh phdn phugng trinh (3), ta dugc phuang trinh sau:
T,b"\u,dz = b\[z + sXdz + ^ + Y,^)b]^dz
0 i>\ y) 0 g
(4)
1-i^
H
Matchup
^
hi
dz o
\ : : ^
^ ^ ^ ^ \
Hinh 2. Sa di tinh ddng chiy dudi cira Hinh 3. Sa do xSc djnh thi nSng mSt cit ciea ra trong van trdn d$p trSn mSt cit thi/c dgng trudng hap ddng chiy qua l6 xS sSu - cd Sp
G i n ddng d t h i coi ^ = £ ^ v d theo phuang frinh lien tyc d Q = b„u„H = buh|, thay 2g 2g
vdo (5), biin ddi theo [8] ta dugc:
T =
ov" p^
Z-I- —
r)
dz• ( • - s %
Oft n id the ndng tgi mgt d t cira ra va bdng:
n !("v>
(5)
(6)
Gpi Zo = 7*0 ~ n Id d t nude ldc dung len Id xa sau vd Zfj=Z-\ ^ vdi Vo Id van tdc tiin g i n tgi mft d t 0-0. Nhu vfy, Zo, Z Id d t nude tde dyng len Id xd sau d va khdng k i den d t nudc v f n ldc tiin g i n .
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2.2 Cac truimg hgrp xic djnh cgt nuirc tac dyng 2 fZJ
Trong thyc t i d nhieu tmdng hgp ciia cua ddng chdy tgi cirg ra nhu chdy ty do, chiy ngfp, dgng cira ra Id day phing, xien hay cong. Trong phgm vi bdi bdo ndy se ehi de d p d i n 3 trudng hgp eg ban nhit, thudng gap trong thyc le.
hi
T = M^^)
Mdt chuan
T^z^(h)
hi Mdl chuan
1 hi
TRUONG HOP 1 Day ra phang
2 - - h'
TRUONG HOP 2
Dong chay phun ty do ra ngoai khong khi Hinh 4. Phan bi Sp suit tgi mSt cit cira ra trong eSc trudng hgp
Theo TL [2,3,8], trong trudng hgp ddng ehay qua Id cd ddy phdng vd phun l y do ra ngodi khdng khi (Hinh 4) thi epl nude tdc dyng se duge xde djnh theo d n g thire sau:
Trudng hap 1: Z^=T^- h^ (7)
Trong trudng hgp ndy Z (Zo) duge tinh d i n cao tfinh trin ra cua Id.
Tmong /ipp 2 ; Z„ = 7; - ^ (8)
Trong tixrdng hgp ndy Z (Zo) duge linh d i n cao tfinh lam ciia Id. Cd t h i tham khdo cdch xde d|nh Z (Zo) vdi tixrdng hgp 1 vd 2 theo hinh 5.
a) b) 0)
- I>1.5h1
Hinh 5. CSc trudng hgp xdc djnh Zo ung vdi eSc dgng ciia ra khSc nhau. TL[8]
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Trudng hgp 3 (Hinh 6) la tivdng hgp hung gian ciia trudng hgp 1 vd 2, tirc Id cira ra khdng phli Id dgng ty do md cung khdng phai dang phing md Id mdt dudng eong ndo dly.
Trong thyc t i ta hay ggp dgng ndy trong trudng hgp ddng chay qua cira van, qua Id dugc dgt frdn mgt trdn d mgt d t ttiyc dyng (Carighe-Ofixerop, dgng WES...).
hi Mdt chuin
1
- h ' -
Tiz(h)
- hi 3
p1(zl Y " ^
hi Mdt chuin
I
0
-'fh->
Hinh 6. PhSn bo Sp suit trong trudng hgp dSy cira ra IS cong (trudng hgp 3)
Nhfn thiy trudng hgp 3 Id trudng hgp tmng gian cua trudng hgp 1 vd tm-dng hgp 2.
Trong trudng hgp 1 thi dp suit phan bd tgi cii-g ra tudn theo quy luft luyin tinh cdn trong Irudng hgp 3 thi i ! i M = z(;,) tire la quy luft phdn bd dp suit theo chieu sdu khdng phli Id
r
tuyin linh md Id mft dgng hdm sd ndo d l y eiia h, d t h i Id da thire, hdm logarit, hdm sd mu...
Mft khde, ed t h i thiy gid tfj dp suit tgi ddy cirg ra eua trudng hgp 3 Id h'< h i . Gid trj h' ndy cung phy thufc vdo hinh dgng dudng cong cug mgt d t cira ra (dudng sd 3).
Trong Irudng hgp ndy, t h i ndng tgi mgt d t eti-a ra dugc xdc djnh theo cdng thirc:
hi{\ Y )
K\},\ r ]
(9)Nhu vfy, mudn b i l l dugc n thi d n phai biit dugc phan bd B^L^ = ^{h) cy t h i nhu t h i
r
ndo (h>c Id d n biit quy luft phdn bd ciia p(z) thi mdi d tiie tien hdnh liy lich phdn duge).
Hifn nay, theo d c tdi lifu tham khao ttii vifc xdc dinh Ei^ = ^{h) chua cy t h i rd rdng.
r
Do vfy vife nghidn ciru quan hf tren d n la d n thiil dugc Idm sdng Id.
3. Ket l u f n
Cd t h i nhfn thiy, d c trudng hgp tfong hinh 5 dimg vdi trudng hgp eti-a ra cd dgng ddy phing vd n i u dp dyng cdng thire (6) vd (7) se xdc djnh dugc edt nude tdc dyng Zo phti hgp vdi hinh 5 ([7]). Tuy nhidn, trong Irudng hgp cira ra d dang cong (Hinh 6) thi vife xac djnh d t nudc tdc dyng Zo v i n edn chua cy t h i , tinh lodn vdn phai chip nhfn g i n diing Id l i y d t nudc d i n tdm hof c t r i n cdng.
C h i dg ddng chdy qua Id md mgt ddy la cong thi thyc t i gid trj d t nudc tdc dyng Z (Zo) khdng phli Id dugc tinh tdi tdm ctia Id xa hay tfIn ma d diem tinh loan (OTT) ndo dd eao hgn tdm ctia id xd mgt khodng d c h n h i l djnh, dieu nay phy thupc vao vifc phdn bd dp suit cua ddng chdy theo ehiiu sdu tire Id phy thufc vdo hinh dgng cira ra trdn vd che dp ndi tiep cila ddng chdy sau Id. Trudng hgp cira ra cd dgng eong thi OTT khdng d n d dinh hogc d tdm nu-g.
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Kir QUA NGHIEN COU VA ONG DUNG
Vj tri ciia OTT d mdl y nghTa quan trpng, vi nd quyet dmh gid tii dimg d i n eiia cpt nudc tde dyng Zo. Do vfy d n phai ed cae nghien ciru tiep theo de Idm sang td v i n de ndy.
Tdi l i f u tham khao
1 Bdo d o till nghiem md hinh thiiy lyc d n g trinh tiiuy difn Ngdi Phat ti'nh Ldo Cai thdng 5/2008.
2. Fuat Senturic (1989), Hydraulic of Dams and Reservoirs, Water Resources Publications, USA 3. Hd sg thiet k i ky thugt giai dogn 1 cdng trinh thuy difn Ngdi Phdt tinh Ldo Cai thang 7/2007.
4. Hd sa thiil ke ky thuft giai dogn 2 cdng trinh thiiy difn Ngdi Phat tinh Ldo Cai thdng 5/2008.
5. Nguyin Canh C i m , el al (2007), Thdy luc I, Nxb Xay dyng. Ha Ndi.
6. McGraw-Hill Companies (1996), Handbook of Hydraulics, Seventh Edition.
7. P.G.Kixelep, et al (1960), Cim nang tinh toan thdy li/c (Ban djch).
8. Ven Te Chow (1959), Open Channel Hydraulics, McGraw-Hill Companies, USA.
9. X.M. Xlixki (1986), Tinh toSn thuy li/c cSc cdng trinh thuy cdng xa nude (Bin tiing Nga), Nxb Ndng lugng nguyen tir Moskva .
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