Tuygn tap bao cao Hgi nghj KHCN "30 nam DSu khi Viet Nam Cff hdi mdi, thach thde mdi" 251 Sir DUNG PHirONG P H A P P H A N T I C H MOI N G A U NHIEN DE HOACH DINH KE HOACH K H A O S A T CHI TIET KET C[.]
Trang 1Tuygn tap bao cao Hgi nghj KHCN "30 nam DSu khi Viet Nam: Cff hdi mdi, thach thde mdi" 251
Sir DUNG PHirONG P H A P P H A N T I C H MOI N G A U NHIEN DE
HOACH DINH KE HOACH K H A O S A T CHI TIET KET C A u CHIU
L i r e G I A N KHOAN BIEN CO DINH CUA XNLD VIETSOVPETRO
Hoang Le Ngge VTnh, Vu Xuan Lai
Bui Van Ngan, Tu Le Trung
XNLD Vietsovpetro
TOM TAT
Di phuc vu cho cdng tdc khai thde ddu khi a md Bgch Hd vd md Rdng, XNLD Vietsovpetro da xdy dung dugc trin 30 cdng trinh biin ldn nhd, tap trung chii yeu vdo giai dogn 1985 - 1995 vd keo ddi den ndm 2000 Do thudng xuyin phdi chiu su tdc dpng khdc nghiet ciia mdi trucmg biin, ddc biet Id su tdc dpng ngau nhien liin tuc mang tinh chdt chu ky ciia sdng biin nin qud trinh tich lUy tdn thuang do mdi ciing xdy ra liin tuc trong sudt dai sdng ciia cdng trinh, ldm dnh hucmg ldm din tudi thg ciia chimg Vi vay vdn di ddt ra cho XNLD Vietsovpetro Id phdi dinh ky thuang xuyin thuc hien cdng tdc khdo sdt vd ddnh gid lgi tinh trgng chiu luc cua kit cdu cdc cdng trinh biin, ddy Id mpt cdng viec cd khdi lugng rdt ldn, khd khan, phirc tgp vd rdt tdn kem Di gidm thiiu chi phi khdo sdt ciing nhu ndng cao mirc dp chinh xdc, tin cay cua cdng tdc khdo sdt, cdn cd mdt phuong phdp tinh todn, phdn tich khoa hgc Viec sir dung phuong phdp phdn tich mdi ngdu nhiin di hogch dinh ki hogch khdo sdt chi tiet cho kit cdu chiu luc gidn khoan biin
cd dinh cua XNLD Vietsovpetro nhdm ddp img nhu cdu thuc ti trin Id vdn di chii yiu md bdo cdo ndy di cap din
TONG QUAN VE PHLTONG P H A P
Ket cau eae cdng trinh gian khoan bien dugc su dung phd bien la he khung khdng gian dugc che tao tu cac dng thep lien ket vdi nhau bang cac mdi han, do dd trong qua trinh chiu lyc, cac nut eua ket eau la noi cd trang thai ung suat phuc tap va tap trung nhat Vdi sy tae ddng ngau nhien, thay ddi lien tyc cua tai trgng sdng trong sudt ddi sdng cua cong trinh da tao ra sy tdn thuong tich luy mdi d cac nut, khi cac tdn thuong tich luy nay dat den mdt ngudng nao dd se lam xuat hien eae vet nut, cac vet ntJt dd neu khdng duge phat hien va kip thai xu ly thi cac lien kit dd se bi pha buy nhanh chdng Vi vay, trong suot ddi sdng cua cdng trinh can phai cd sy phan tich, danh gia de lap ke hoach cho viee khao sat va sua ehua, dam bao cho edng trinh hoat ddng an toan
Su dyng phuong phap phan tich mdi ngau nhien de hoach dinh ke hoach khao sat ehi tiet cho ket cau chiu lyc gian khoan bien dugc the hien qua so dd sau:
Trang 2252 Sd dung phtfong phap phan tich mdi ngau nhign dg hoach djnh ke hoach khao sat chi tiet
Hinh 1 PHLTONG P H A P PHAN TICH MOI N G A U NHIEN
1 Twffng tac ngau nhien cua tai trong sdng
Qua trinh ngau nhien dac trtmg eho su phan phdi nang lugng sdng theo cac tin sd lien tuc tai mdt vung biin nao dd la ham mat do phd sdng
• Ddi vai trgng thdi biin ngdn hgn, cdc dgng phd sdng thudng dugc sir dung di phdn
tich kit cdu cdc cdng trinh biin la phd Pierson-Moskowitz vd pho Jonswap
Phd sdng Pierson-Moskowitz:
HtT
%7f
( T,co \ 2n exp
1 (T,co
trong dd: T^ la trung binh chu ky cit khdng,
Hs la chieu cao sdng dang kl
• Phd sdng Jonswap:
^^^i^) = cig'^^'^ exp (O
exp
(2)
trong dd:
a, Wp y\k cac tham so phy thudc vao H^ va T^ cua trang thai bien ngin ban d vung
dang xet
crdae trung cho do nhgn cua dinh phd,
Wp la tan sd gdc cua dinh pho Pierson-Moskovitz tuong ung
Khi y= 1 phd Jonswap trung vdi phd Pierson-Moskovitz
Ddi vdi vung md Bach Hd, cac tham so tren dugc xac dinh nhu sau: a - 0,0097; y=
1,45; Wp= 0,465; o-= 0,092 khi w < w^ va (T= 0,102 khi w >W/,
• Ddi vai trgng thdi biin ddi hgn
Trang 3Tuyen tgp bao cao Hgi nghj KHCN "30 nam Dau khi Viet Nam: Cff hgi mdi, thach thde mdi" 253
Tap hgp cac trang thai biin ngin han trong mdt khoang thdi gian dai tao thanh mdt
trang thai biin dai ban Tu tap hgp cac sd cap gia tri (//,, Tf) ngudi ta thiet lap dugc bilu
do phan tan sdng, dya vao bieu dd phan tan sdng ta cd the xac dinh dugc ham phan phdi
xac suat hai chieu dai ban cua Hs va 7^:
P[{H, < / / , < / / , ) , ( r , < r, < T,)]= jjf, ,,{H,T}lHdT (3)
H,T,
trong dd: F„ , {H,T) - la ham mat do xac suat hai chieu cua chieu cao dang ke va chu ky
cit khdng Tuy nhien de don gian, trdng thuc te ta thudng quan tam den ham phan phdi
cua chieu cao sdng dang ke / „ , (H)
Theo kinh nghiem thuc te khi chieu cao sdng dang ke xay ra trong khoang thdi gian
dai thudng phan phdi theo quy luat Weibull:
P',.iffs)= j / « „ ( / / > / / / = ! - e x p ( H-H, (4)
trong dd: a, p la cac tham sd hinh dang va kich thudc cua phan phdi dugc xac dinh tu cac
sd lieu quan trac cd dugc tai vung bien dang xet
Khi chieu cao sdng rieng biet d mdi trang thai bien phan phdi theo quy luat Rayleigh
thi phan phdi xac suat dai ban cua chieu cao sdng rieng biet cung tuan theo luat Weibull:
^ / / ^ "
trong dd: C va Z) la cac tham sd phu thudc vao cc, cdn or va y5 la cac tham sd Weibull cua
chieu cao sdng dang ke H^
• Sd sdng cd chiiu cao vugt mpt chiiu cao sdng rieng biet cho truac trong N ndm:
Neu Nl la tdng sd sdng trong 1 nam va Nei la sd sdng cd chieu cao vugt mdt gia tri
cho trudc H cua chieu cao sdng rieng biet thi tan suat cua sy kien dd se la N^i/N, va xac
suat cua su kien dd dugc bieu dien theo cdng thuc:
e , ( ^ ) = l - ^ / ( ^ ) = e x p Tir dd suy ra:
cff
H
cfi
N,
(6)
(7)
Tir bieu thuc (7), khi da biet cac tham sd fi C, D va N; ta thiet lap dugc bieu do the
hien mdi quan he giua chieu cao sdng H va /gTVg/ Tu bieu dd nay ta cd the xac dinh dugc
sd sdng cd chieu cao nam trong khoang (//,, //,+/) va do dd xac dinh dugc sd chu trinh
thay ddi ung suit trong kit ciu dl phuc vu cho tinh toan mdi
• Tdi trgng sdng tdc dpng len cdng trinh dugc xdc dinh theo phuang trinh Morison
Luc thuy ddng phan bd tren mdt don vi chilu dai tac dung len mdt phan tu manh
{D < 0,2A, vdi D la dudng kinh cua phin tu, A la chilu dai bude sdng) dugc xac dinh theo
cdng thuc:
Trang 4254 Su' dung phuong phap phan tich moi ngau nhien dg hoach dinh kg hoach khao sat chi tiet,
trong do: ^ - dien tich mat cit ngang cua phan tu ket cau
w„ - vecto gia tdc phap tuyen cua phan tu nude vudng gdc vdi true cua phan tu
CM - he sd khdi lugng nude kem
CD - he sd can
ii„ - vecto van toe phap tuyin cua tu nude, vudng gdc vdi tryc cua phan tu ket cau
p - la ty khdi cua nude bien
Trong cdng thue (1-8) thanh phin lyc can la mgt sd hang phi tuyen Do do trong tinh toan ddng lyc ta cin phai tuyin tinh hda thanh phin nay Ap dyng phuong phap binh phuang tdi thilu ddi vdi qua trinh chuin trung binh bang khdng ta ed the viet phuang trinh Morison nhu sau:
trong dd cr„ la do lech chuan cua phan phdi van tde
2 iTng suat ngau nhien
Trong qua trinh phan tich mdi cua cac gian khoan bien cd dinh bang thep, chu yeu ta quan tam din ung suat d eae mdi han va do dd can quan tam den qua trinh thay ddi ung suat eye bd ldn nhat do tae dyng eua tai trgng gay ra d eae lien ket Do tac ddng eua mdi trudng bien la mdt qua trinh ngau nhien nen phan ung cua ket cau cung la mdt qua trinh ngau nhien Cac sd lieu dau vao cho phan tich la tap hgp cae trang thai bien ngan ban theo cac hudng sdng nhat dinh Mdi trang thai bien dugc dac trtmg bdi hudng sdng, chieu cao
sdng dang ke Hj, chu ky trung binh cat khdng F bay phd nang lugng sdng S,j^(co) cua trang
thai bien dd Qua phan tieh ddng lyc ket cau ket qua nhan dugc la ham mat do phd ung suat
Sss((o), nhu vay qua trinh ung suat cd lien quan vdi qua trinh sdng thdng qua bam truyen
tuyen tinh (cac sd hang phi tuyen trong cdng thuc Morison da dugc tuyen tinh hda)
Qua trinh tuong tac cua sdng bien dugc gia thiet la mdt qua trinh Gauss trung binh bang khdng, nen ung suat trong ket eau cung la mdt qua trinh Gauss trung binh bang khdng
Ss!i";t
Vf, '"ft
Qud trinh img sudi ddi liep
^i'nham-^ I L A *
Qud Irifili img sudi ddi rdng
Hinh 2 Cac dac trung quan trgng cua mat do phd phan ung dugc su dyng trong phan tich moi:
Mdmen bgc k ciia phd
Trang 5Tuygn tap bao cao Hgi nghj KHCN "30 nam Pau khi Viet Nam: Cff hgi mdi, thach thuc mdi" 251
M, = jo)''S^X'^)d(o voi k= 0,1,2
0
Phuong sai cua qud trinh img sudt, khi S„ = 0
CO
Tham sd bi rpng ddi tdn
He sd diiu hda
s^
, "'-M,M,
M,
= i
^MJ^,
1-r'
: V 7 ^
(10)
(11)
(12)
(13)
Trudng hgp phd ddi hep
Can eu vao tham sd s de xac dinh be rdng cua ham mat do phd, thdng thudng khi
e< 0,4 tbi qua trinh dugc coi la dai hep Ddi vdi qua trinh nay cd cae dac trung sau:
Ham mat do cua ung suat bien Sa (gia tri cue dai) la mdt bien ngau nhien phan phdi
theo luat Rayleigh, xac dinh theo cdng thuc:
^(S) = 4exp
trong dd tham sd o^ bang phuong sai cua qua trinh ung suat a^ = MQ
Sd gia ung suat danh nghia trong trudng hgp giai tan hep ed gia tri gan dung:
Sr — Smax " Smin — 2 S a ( i 5 )
Phan phdi Rayleigh cua sd gia ung suat vdi do lech chuan bang 2Sa se la:
/Js)=
4c7: -exp ^ 15^^ (16)
Chu ky cua qua trinh ung suat nay la chu ky cit khdng vdi do ddc duong Nd ciing
la mdt bien ngau nhien cd gia tri trung binh gan dung:
T.=2n^
Sd chu trinh ung suat iing vdi trang thai bien dang xet dugc xac dinh bang:
T
« = •
T
(17)
(18) Trong dd: T^ la khoang thdi gian cua trang thai bien ngan ban dang xet
Tru&ng hgp phd ddi rdng
De don gian cho qua trinh phan tich kit ciu cac MSP ngudi ta thudng gia thiet qua
trinh ung suat la dai hep Tuy nhien, trong mdt sd trudng hgp qua trinh sdng khong phai la
Trang 6256 Sddung phu-QTig phap phan tieh mdi ngau nhien dl hoach djnh ke hoach khao sat chi tiet
qua trinh Gauss, bien do ung suat khdng phan phdi theo luat Reyleigh va sd gia ung suat
khdng cdn thda man bilu thuc (15) Trong qua trinh phan tich dgng luc hgc ket cau, ddi
khi cd thi nhan dugc qua trinh ung suat vdi ham mat do phd cd bai dinh quan trgng: mdt
dinh ung vdi tin sd dinh cua phd mat sdng, cdn dinh kia ung vdi tin sd dao ddng rieng thu
nhit cua kit ciu tuc la ung vdi dinh cua ham truyen Khi nhin vao bieu dd md ta qua trinh
ung suit, ta thiy ed mdt sd cue dai va cyc tieu dia phuong nam d ca hai mien (-), (+)
Trong trudng hgp dd nlu ap dyng cdng thuc (18) de tinh sd chu trinh ung suat se khdng
cdn phu hgp nua, do dd khi phan tich mdi va do tin cay can phai xet den anh hudng cua be
rdng dai, tuc la anh hudng cua chung tdi sd gia ung suat va sd chu trinh ung suat
D I khic phuc, ngudi ta su dung he sd hieu chinh p(m,a), trong dd cd ke den tham sd
m cua mdi quan he S-N va su phan phdi mat do phd trong mien tan sd co
Dua vao phuong phap dem ddng mua ddi vdi cac the hien cua qua trinh ung suat
nhan dugc bang md phdng, Monte Carlo, Wirsching va Ligh da dua ra kien nghi chinh
p(m,o)), khi qua trinh ung suat la qua trinh Gauss dai rdng cd he sd dieu hda r va tham sd
be rdng e da biet:
p{fn,(o) = A{m) + \[ - ^(m)](l - V l - r ' j ' (19)
Vdi: 4 w ) = 0.926- 0.033W ; 5(w) = 1.587-2.323m
Trong dd: OT la tham sd dudng cong mdi S-N
Tuy nhien, viec xac dinh he sd hieu chinh tren chi dua vao su md phdng mgt so it
kieu phd nen trong thuc te neu thieu thdng tin ta cd the xac dinh chung dua tren gia thilt
ung suat la qua trinh Gauss dai rdng tdng quat, hoae qua trinh Gauss dn tring
3 He so tap trung irng suat
Lien ket cua ket cau cdng trinh bien la cac lien ket dng ndi vdi nhau bing mdi ban
Trong qua trinh chiu lyc su phan bd timg suit va biin dang d phin giao tuyen mdi ban la
rat phuc tap Nhung dilm cd ung suit ldn nhit ggi la cac dilm ndng, cac dilm ndng dd cd
the xay ra tai chan mdi ban ve phia ong chu hoae phia ong nhanh D I dac tnmg cho cac
diem ndng ung suit dd ngudi ta dua ra cac khai niem la he sd tap trung timg suit SCF va
he sd tap trung bien dang SNCF:
SCF = ^22^ (20)
trong dd: S„ax la ung suit cue bd ldn nhit va S„ la ung suit danh nghia d dng nhanh
SNCF^^^^ (21)
trong dd: f„^ la biin dang cue bd ldn nhit va £„ la biin dang danh nghia d ong nhanh
Quan he giua SCF va SNCF:
1 + ^
SCF = SNCF ^ (22)
trong dd: v la he sd Poisson cua vat lieu; £2 la biin dang vudng gdc vdi f„^
Trong trang thai ting suit phang, ung suit cue bd ldn nhat se la:
Trang 7ruygn tap bao cao Hgi nghj KHCN "30 nam Dau khi Viet Nam: Cff hdi mdi, thach thde mdi" 251^
1 + i ^
<7 - FF
"-"max ~ •^'^max \-v' (23)
He sd tap trung ung suat {SCF) cd the dugc xac dinh bang phuong phap thyc
aghiem hoae tinh toan theo phuong phap PTHH vdi cac phan tu ban la phan tu khdi cac phin tu dng la phan tu vd Cac he sd nay phy thudc vao dang va tuong quan hinh hgc cua
lien ket Hien tren the gidi cd rat nhieu tac gia da nghien cuu va dua ra cac he sd SCF cho
cac dang lien ket nhu Kuang, Smedley-Wordwortb, Gibstein, Marshall, Efthymiou, v.v Theo tieu chuan API RP2A-WSD (2000) cac he sd tap trung ung suat tuong iing vdi cac dang lien ket dugc quy dinh trong Bang 1:
Bang 1
Dgng lien kit
F K
T & Y
X; vdi p<0.98
X; vdi P>0.98
a
1.0 1.7 2.4 1.7 Brace SCF
Axial Load SCFa,
a A
vdi
A = \.%^Tsme
In-Plane bending
SCFipb
^A
3 vdi
^ = 1.8^7^ sin 6*
Out-of-Plane bending SCFopb
\.5A
• vdi
^ = 1.8^7^ sin ^
1.0 + 0.375(l + ^ 5 C F ^ , „ , J > 1 8
a = YP^ ; P = yCj; y = y^; r = ' ^ ; G la goc nghieng giiia dng nhanh va ong chu
4 Ung suat cue bd ldn nhat tai cac lien ket
Do giao tuyen giua dng ehu va dng nhanh la mdt dudng cong ghenh hinh yen ngya nen viec xac dinh chinh xac tai hai phia eua giao tuyen la rat phuc tap Nen trong tinh toan
thudng su dung cac bieu thuc sau day de tinh iing
suat tai 8 diem dge theo giao tuyen:
S) = ajSCFaxSax + biSCFipbSjpb
52 = a2SCFaxSax " b2SCFjpbSipb
53 ~ ^sSCFa^Sax + CsSCFopbSopb
54 — a4SCraxSax " C4SCropbSopb
55 = a4SCFaxSax + bsSCFjpbSjpb + CsSCFopbSopb
§6 ~ SgSCFaxSax - bgSCFjpbSjpb - CgSCFopbSopb
S7 ~ aySCFaxSax " bySCFjpbSjpb + CySCFophSopb
Sg = agSCFaxSax + bgSCFjpbSjpb - CgSCFopbSopb
Trong dd: ai, bj, Cj la cac he sd xet den vi tri eua
cac diem ung suat; Sax, Sjpb, Sopb la eae thanh phan ung suat danh nghia; SCFax, SCFjpb, SCFopb la cac he sd tap trung ung suat
5 He th6ng dirdng cong mdi
Phuong trinh dudng eong mdi thi hien moi quan he giua sd chu trinh tdi pha buy N vdi sd gia iing suat Sr dugc viet dang sau:
beminq momtdl
Trang 8258 Sd dung phuong phap phan tieh mdi ngiu nhign dg hoach djnh ke hoach khao sat chi tiet
\gN = \ga-m\gS^ (24)
Trong dd: a va m la cac hang sd thyc nghiem
Do bin mdi cua kit ciu phy thudc vao kieu lien ket, hinh dang cua phan tu, tinh chat
ung suit, phuang phap ebl tao va kiem tra Ngoai ra chung cdn phu thudc vao chieu day
cua thanh dng, cac dudng cong S-N co ban da cho phu hgp vdi chieu day 32mm ddi vdi
mdi noi dang T, cdn cac loai mdi ndi khae la 22mm Vi vay, khi cac mdi ndi cd chieu day
khae chuin tren thi cdng thuc (24) phai ed sy dilu chinh
K^B J
mlgS^
Trong dd: t la chilu day thyc cua phin tu dang xet; ts la chilu day chuan ung vdi
dudng cong S-N 32mm hoae 22mm
iriN/mnt)
Cdc ducmg S-N cua moi noi ong
Hinh 4
6 Tinh toan tudi tho mdi theo quan diem tdn thtrong tich IQy
Theo Miner, mdi bae ting suat cao hon gidi ban mdi deu gay ra mgt phan tdn thuang
cho vat lieu Neu phan tu ket cau chiu tap hgp ung suat gdm k bae khae nhau thi sd do ton
thuang tich luy tdng cdng cho phep la:
(25)
trong dd: n, - sd chu trinh ung suat ma phan tu phai chiu vdi ung suat S,
[D] - tdn thuong mdi cho phep
A', - sd chu trinh tdi pha buy lay theo dudng cong mdi S-N ung vdi S,
Tudi thg mdi cua phan tu ket cau dugc tinh theo cdng thuc:
L = - ^ (nam)
A
I nam
1 Tinh toan tuoi tho mdi theo quan diem co* hoc pha hiiy
a Lugt tdc dp phdt trien vet nut cua Paris-Erdogan
Mdi quan he giua tdc do phat triln vlt nut da/dN va sd gia yeu td cudng do ung suit
AK = AcTF4na dugc ggi la dudng cong tde do phat trien vet nut:
(26)
Trang 9Tuygn tap bao eao Hgi nghj KHCN "30 nam Pau khi Viet Nam: Cff hdi mdi, thdeh thde mdi" 251_
- Vung A la vung ngudng, vlt nut bit diu hinh
thanh AK,h la gia tri ngudng cua ylu td cudng do ung
suit Khi AK < AK,h vlt nut khdng phat triln Khi
AK > AK,h vet nut phat trien cham dan
- Vung B la vung tdc do phat trien vet nut dn dinh
- Vung C la vung pha buy Khi AK > Kjc kit ciu bi
pha buy
.iO^d.M -ruT :'.chi; trinh]
( /
Vijng B
/ i
Vijmj C
dN
(27)
Di/dng cong td'c dd phjt Irien vei nift
Hinh 5
da
dN Ana^E
(28)
(29)
Trong dd: R la he sd bat ddi xung cua chu trinh ung suat R = '^"^/i^^', cTy gidi ban
chay eua vat lieu; E module dan hdi cua vat lieu; C, m la cac tham sd phat trien vet niit, dugc xac dinh tu thyc nghiem
Ta cd the thay rang phuang trinh Paris an toan cho vung A ma khdng an toan cho vung C Tuy nhien, hau bet tudi thg mdi deu nam trong vung A va B nen khi tinh toan tudi thg mdi thi su dyng phuong trinh Paris la an toan Neu khi thieu cac sd lieu ve C va m thi
su dyng cdng thuc (29) la tien lgi
Khi da xac dinh duoc tdc dd phat trien cua vet nut — , ta cd the xac dinh duoc sd
dN chu trinh can thiet de vet nut phat trien tu chieu sau a, den a^:
\da
' - 2 J d o /
a /d"
(30)
Viec xac dinh sd chu trinh lam vlt nut phat triln ttr chieu sau a, tdi chieu sau pha buy a^ cung ddng nghia vdi viec xac dinh tudi thg mdi
b Trudng hop irng suat cd bien dp fihdng ddi
Lien quan den bai toan dang xet, ta chi xet trudng hgp khi vet nut da xuat hien, su dung phuong trinh Paris ta cd:
da
^ ir UvY J
}c{AKr ^ },c(Aa^Ff ^ Cn^^ },c(Aa^Ff
trong dd: AK - sd gia cua yeu td cudng do iing suat: AK = AaFyfm
A CT - sd gia ung suit Ao- = a^^ - o-,,„
a - ung suat danh nghia d phin tu, vudng gdc vdi hudng lan truyen nut
F - ham sd phy thudc cac ylu td hinh hgc Theo tieu chuan cua DNV thi cdng thuc (31) thi hien sd chu trinh tdi pha huy dugc viet thanh:
Trang 10260 Sd dung phu-ong phap phan tieh mdi ngiu nhien di hoach djnh ke hoach khao sat chi tiet
' CT'"'''''ACT"' }JFJ^ CT''-'Aa"
(32)
Trong dd: a,=-^, a^ =^-,T la chieu day cua thanh dng
'J
da
a, \F4naJ
(33)
Vdi gia thilt kit ciu bi pha buy khi vlt nut an sau bet chieu day («/= 1), thi sd chu
trinh dl vlt nut phat trien tu chieu sau a, tdi chieu sau aj la:
N{a^ -> «2) =
Cr'^^-'Acr"'
a, \F4na) a, \F4na]
(34)
D I thuan tien cho tinh toan, cac tich phan / dugc xay dung thanh cac toan dd cho cac dang moi ban khi chung nam trong khdng khi cung nhu khi chung ngap trong nude bien
c Trudng hpp irng suat co bien dp thay ddi ngdu nhien
Khi ling suat dugc biet dudi dang the hien, bang phuong phap dem chu trinh ta se nhan duge mdt tap hgp ung suat (ACT, - nJ vdi i = 1 H- I, Ila sd bae ung suat
Khi ung suat dugc biet dudi dang ham mat do xac suat /(Acr), bang phep tinh xac suat va thdng ke, ta cung bien ddi thanh mdt tap hgp ung suat (ACT, - « , ) nhu tren hinh bieu dien Hinh 6 Trong dd: ACT, la trung diem cua bae ung suat thu i, nj la sd chu trinh cua bae i, ni = nn/tAcr,)
f(A5)
f^50=S
A5 4 A5max
A5i
Oi
Hinh 6
Tu each lam tren, ta se xac dinh dugc so gia ung suit tuong duong Aa theo cdng
thuc:
Ao- =
eq
i I \
Z«-Ac7;
(35)
Bai toan trd ve trudng hgp ung suit cd bien do khdng doi vdi Ao- dugc thay bing Ao-^,
d Tieu chudn phd hiiy
Tren co sd ly thuyet vl do tin cay, co hgc pha huy dua ra tieu chuin danh pha buy
do qua trinh phat trien cua vlt nut la: