IS Hdi nghi Khoa hoc vd Cdng nghe Bicn lodn qiiik- Idn^ '''d_^
PHAN TICH MOI TREN QUAN DIEM DO TIN CAY SU DUNG MO PHONG SONG NGAU NHIEN TUYEN TINH
Diio Nhu- Mai, Nguyen Viet Khoa, T r i m T h a n h Ihii va Nguyen Van Q u a n g Vien Ca hoe, Vien Khoa hoc va Cong nghc Viet Nam
264 - Doi c a n . Ba Dinh. 1 la Ngi Email: dnmai'g/imcch.ac.vn. maidao.vcoiffmmail.com
Tom tat:
C 'dng trinh ngodi kluri cd xu hudng hi phd huy mdi dudi tdc ddng ciia tai trong sdng theo chu ki. Do linh bat dinh xudt hien a mot sd tham sd quan trong. tudi iho moi cd the md phong nhu mot hicn ngdu nhiin. nhu vay dd lin cdv ddi vdi hu hong moi cd the dmrc ddnh gid mdi cdch cd he thdng iheo xdc .sucil Trong nghien cuu ndy dp dung qui Irinh phdn lich moi tren cjuan diC'iu do tin cdy cua Ang .-i 11.- S vdi gid ihiel tai trong ngdu nhien cd phdn hd Beta Ddng gdp chinh <r ddy Id tinh todn mien ung sudt Id phdn ung ciia cdng trinh dudi tdc ddng cua sdng ngdu nhien luyen linh. lie dd xdy dimg phdn bd Beta cua lai irong
FATIGUI- ANALYSIS UNDER LINFIAR R A N D O M W A V E S LOADING Ab.stract:
Under periodic wave loadings offshore structures lends to he damaged due lo culmulalive fatigue damages. Due to uncerlancies of several main parameters, the fatigue life itself can he modeled as random variable, in results the reliability of fatigue failure can he systematically evaluated in terms of probahility. In this .study, the Ang A. 11 - S. procedure of reliability based faiigue analysis is applied with the assumption that random loading is modelled with Beta distrihution The main contribution is calculation of stress ranges as structural responses under linear random waves, then the Beta dis.slribution of the loading is established.
M O DAU
Phan tich moi ciia eong trinh bien la yeu cau eua cac lieu chu5n thiat kd cong trinh bien.
Cae cong trinh bien ngay cang d u o c dua ra khai thae 6 eae vung bi£n xa va sau ban. do vay cung duoc thiel ke sao cho phii hgp de dap u n g eac didu kien khde nghiet cua moi Iruong tir nhien. Khi do cae yeu to phi tuyen va tinh b i t dinh eiia eae tham s6 ddu vao khong the bo qua trong tinh loan.
Ban than tuoi thp moi eo the mo phong nhu bidn ngau nhien, do vay ta co thd phan tich moi theo quan diem dp tin cay. Ang A. H. - S (1977) [1] d u a ra mpt qui trinh phan lich moi ket cau tren quan didm do tin cay. Co nghTa la xel tu6i thg moi nhu- mot bidn ntzau nhien. nen dp an loan khi c6 pha buy moi co thd danh gia mgt each he th6ng tren quan
Tieu ban Ndng luang, Ky ihudt cdng Irinh. Van tai vd Cdng nghe Bien
diem xae suat Vai gia thidl tai trong ngau nhicn mo phong bang phan bd Beta con hien tugng moi dae trung bang duong eong SN (quan he giiia ung sual pha hiiy do moi S va chu trinh dat tai N). Sir dung phan bo Weibull de thiel lap ham dp lin eay (bicu dien xac suat khong pha hiiy). Caeh lidp can cho la each nhin tong quat hon ve dp bdn moi. Tuy nhien cGng doi hoi chi phi tinh loan cao hon.
Bao cao gom ba phan:
- Dau lien gioi thieu ca so li thuyet phan tich moi theo quan didm dp tin cay - Sau do trinh bay ca sa mo phong song ng3u nhien luydn linh
- Cuoi cung ap dung qui trinh linh loan moi cho mot gian cu thd va so sanh vcri ket qua da cong bo khi mien ung suat dugc tinh eho cac Iruong hgp song da dugc thong ke cho vLing bien Viet Nam [5]
I. TINH TOAN DO TIN CAY 1.1. Co" SO" vat li cua hicn tagng moi
Quan he S-N duge xay dung lir ket qua thirc nghiem cho dang moi noi va vat lieu cu the
l n n = l n c - m l n s hay n - c / s " ' (1) trong do n so chu trinh du doan bi pha hiiy ung vol ehenh lech so ung suat s, s chenh
lech irng suat (ung suat max trir di ung suat min), m dp doc am eua ducmg cong S-N (voi phan tir hinh ong m=3), In c giao diem eua duong S-N vai true In n
Ton thuang tich luy dirai lac dpng cua tai trpng thay doi tinh bang luat pha hiiy Miner's
D = y _"' , trong do n, so chu trinh eo chenh lech ung suat thu i (2)
^ n ( s , )
(3) va hu hong se xuat hien khi
£ ( D ) - £ S ^ S " ' ' "^^^' la ky vpng hay trung binh cua D.
\_ " \^i /J
Khi mien ting suat S la ngau nhien vai ham mat dp xae suat (PDF) / ( s ) , thi
i ti(s,) I c
trong do Jl = '^ _ '^ , 6 day E[S"' ) la moment thii m cua S [5]. (5)
\s f,{s]dr
0
1.2. Tai trong moi
Ta su dung phan bo beta de mo phong cac tai trgng gay ra moi; vi tren Ii thuyet cac tai h-png nam trong mpt gicri han deu la nguyen nhan gay ra hu hong moi. Phan b6 beta co cac giai han hiiii ban tren va duoi, do vay du linh boat dk ap dung vcri bieu d6 dfl- lieu chenh
Hdi nghi Khoa hoc vd Cdng nghe Bicn lodn qudc Idi 'id V
lech irng suit bit ky. Phan bo xac suat ciia phan bo bela voi bien dual =0 va bicn tren -= SQ eo dang
fXs)- WnT
B(q,r) fi<s<s„
trong do B(q,r) la ham Beta co dang B{q,r) -
r(^;)r(r)
(6)
nq + r) (7)
q va r la cac tham s6 cua phan bo va chung duoc xac dinh boi cac bleu thuc sau
Vol phan bo bela a tren thi moment thir m cua S co dang
„„, r{m+q)r(q + r)
° r{q)r{m + q + r)
1.3. Tinh toan moi tren quan diem do tin cay
Moi la qua trinh tich liiy ton thuong, nen xac sual co dieu kien de moi xuat hien hong chu trinh dat tai tiep theo co tinh dem dieu va tang dan cirng voi tuoi thp, co nghTa ham hu hong la ham don dieu tang [1]. Phan bo Weibull co tinh chat tren va ham hu hong c6 dang
EiS"
(8)
(9)
h{n) , k>l.O w -Eyw-z)
Ham dp tin cay tuong irng co dang [1]
L{n) = exp ^ \h{n)dn = exp w-e)
10)
(11) trong do w tuoi thp Ion nhat c6 the, E tuoi thp tpi thieu va k tham so dang. Gia thi& tu6i thp toi thieu E = 0, hai tham so w va k quan he voi ki vpng va phuang sai cua tu6i thp moi qua
if=u)r|;+f I v a a „ = u j | r | i + i | + r ' | i + ^ | | (12) <4)--+(4)-i4)r
til day he so tuong quan COV c6 dang n „ = a„ /n = It' °', suy ra it = n ' eay (11) se co dang nhu sau
L{n)=exp - | | r ( i + « ' • » •
' va ham dp tin
(13) Vay khi mien iing suat la ngSu nhien vol mat dp xac suat / ( s ) va tinh duac moment thiim fi^S" j ciia S, thi dp tin cay ciia tuoi thp n danh gia bing phuang trinh (13).
1.4. Tinh toan chenh lech ihig suat thiet ke cho phep
Thuc chat la xac djnh mien ling suit cho phep d6 thiSt ke chi tijt mpt diSm n6i hoac mot ket cau cu the cung nhu dam bao d?t tu6i thp thi^t ki no voi do tin cay L(no). Tit phuong trinh (13) ta co dp tin cay iing vai tuSi thp moi ma ta quan tam
Tieu han^Ndn^luony. Ky thudl cdng trinh. Van tai vd Cdng nghe Bien
'-(n) = /,(n„) = l - p , ( n j (14) oday pi-(n„) la kha nang xay ra hu hong trong pham vi tu6i thp no. Nghich dao (13) vii
xiip XI
H^-Pi:^n„)\s~p,in„) (15) ta dupe tuoi thp binh quiin
I'(l+n"") , , , , n=-n„-^ rr-^ = n,.-y,. • (16)
(P,.)"
Doi vol tai trpng co bicn dp la hang so, chenh lech irng suat Ihia Wi cho phcp xdc dinh boi;
Doi vai lai Irong ngau nhien eo phan bo beta Ihi:
phuang trinh (16) co the duoc viet lai la.Vi, =.?,^, trong do ^ la he s6 uuig suit ngdu nhicn
IL SONG NGAU NHIEN TUV£N TINH 2.L Mo phong so song ngau nhicn tuyen tinh
Tir du: lieu song ta eo the gia thidt mat song la mpl qua trinh Gauss dirng. Ta eo thd mo ta mat song bang to hgp cae eon song vai buoc song, bien dp va chu ki khac nhau va truyen di voi van loc va huong khac nhau. Voi song mpt huong mat song luc thai so voi mirc nuac trung binh ri{f) tai mot diem nao do trong khong gian co the vidt duoi dang
N
Ti(f) = 2 ] c„cos(co„f+ ((>„) (19) trong do o)„ va (j)^ la tan so va pha song ngau nhien ciia eon song thti n. Bien dp song c^
c„=72S„,(co„)dco (20) trong do S,|,, (©„) la thanh phan thir n eua pho nang lugng va c/o) la gia so tan so. Tong
cac thanh phan nay se eho ta bieu ghi song cho chu ki t - 0 den T = 2n/d(i). Tinh chat ngau nhien lao ra boi pha song ^„ ung vai moi thanh phan cosin va co phan bo deu trong khoang tir 0 den 27t.
2.2. Ph6 nang lug-ng song
SiJ dung pho nang lugng song tiiy theo vi tri va dieu kien bien. Pho Pierson-Moskowitz va JONSWAP dugc sir dung rong rai. Trang thai bidn dugc mo ta bang hai tham so do la chidu cao song dang ke H^ va ehu ki cit khong T^.
Phd Pierson-Moskowitz co dang
licit iighl Klicici hoc vd ( 'dug nghe Hien lodn cjiick ldn llnr V
A
1 J'"
271 ^-nr, Pho .lONSWAP cii dang
, , 1 IllKk OTIV ' V>' ..
s 0))= —'A - \'^ '<
""* ' 271 47ir,; [ (•) j
Irong do fo lii uin .so phii dai cue dai \ a
(21)
i22)
•/; = Jt,,T,. a = e " "•'" . 7 = 3,3 . k„ = 1,4085.
* : , , = 0 , 3 2 7 c ' " • ' " ' = 1,17. k = 1 - 0 , 2 8 5 l n ( y )
111. Vi DII T I N I I T O A N
(23)
3.1. Qui trinh toiin tinh
Buoc I Phiin lich dpng kcl ciiu cho song- ngiiu nhicn lu} en tinh co mat song Ihco (19) vai phi) nang luong song phii hgp (21 hoiic 22). Trong nghien ciru niiy chiing liii kc Ihini Ciic kcl qua linh lai Irpng dpng. cac nghiiJn ciru dii co vc mo phong kiil ciiu co kc diin cac hicu irng phi uiycn ciia ban ihan kcl ciiu \ a ciia luong hie giira kiil ciiu vii nen mong. Kcl qua lii liip Ciic giii Iri chenh lech irng suiil va Ciic giii Iri can lri:n \ a can duoi ciia chenh lech irng suiil
Buoc 2. Xiiy dung ham mill dp pho ciia chenh lech irng suiil lit lap kel qua chenh lech irng sual dii tinh dupe trong buoc I. Lira chpn he so tuong quan ki; den linh biit dinh do die tao. do mo phong kcl cau. cua lira chpn ducmg
cong moi Vii mo hinh linh loiin lich luy ton thuong moi. Cac tham so q \'ii r ciia ham beta duoc linh Ihco (8). Mo men bac m ciia chiinh lech img sual duac linh Ihco (9)
Buoc 3. Vol moment bac m ciia chenh lech irng suat tinh duoc 6 buoc 2 Tinh trung binh n ciia luoi thp moi Iheo (5). Sau do dp tin cay Ihco tuoi thp moi tinh duoc theo (13). Chenh lech img suat eho phcp duoc tinh Ihco cong thirc (18)
3.3. Vi du tinh toan
Phan lich dpng cho gian tu nang duoc tien hanh sir dung chuong trinh phan tich dpng gian tu nang JACKUP V. Chan ii dupe mo phong sir dung phan tir ddm cot - Euler dfi mo lii duoc dnh huong ciia luc dpc true len dp cimg chong uon eiia kk cSu. T u a n g tac ii mong vol nen dimg mo hinh 16 xo dan h6i co
J^l^^^---^^
(14)
(13) 9
(13)
6
(11)
3
J3—-^^
(.6 14 (9) 11 (8) 8
U)
5
(6)
2
——i2^i\
3 Cong nghe Bien
ki dir\ tuang tac giira luc dpc va moment xoay. Chuong trinh nay la ket qua de tai cap Vien Khoa hpc va eong nghe Viet Nam (2005-2006) [i].H.I gidn khoan Tam Ddo
Vi du la gian Tam Dao co ba chan de la he khung khong gian co mat cat hinh tam giac.
ChiSu cao chan di 1 lOmet, chiSu cao thap khoan 64 met. Khoang each giira cac chan 43,2 met (tinh tir tiim m6i chan). Gian ^6m 3 chan, m6i chan duoc cau tao dang thanh giang gdm 3 6ng thep chinh duac lien ket boi cac thanh giang tai cac diem nut. Khoang each giiia cac 6ng thep chinh trong mpt chan la 12 met. Gian tu nang Tam Dao lam viec o vimg bien CO dp sau 62 met, khoang each tir than gian den mat nuoc bien la 14 met. Ta c6 the dua gian vi mo hinh gian khong gian moi chan mo ta bang cae phan tir dam tuang duong (hinh 1) voi dac tinh nhu sau; D=4m, F=0.2m^ I=4.84m'', J=9.68m*', Than gian-700Tan.
Gian cao 90m. Mo hinh tinh quy doi co 19 nut va 21 phan hi dam cot Euler. Phan tii nen mo ta biing cac 16 xo dan hoi co ke den tuong tac giira lire dpc va moment xoay dat vao cac nut 1 sin 3.
It tilt .J u
wssmsmmns
»j* I Y r r|** H* 1,
;iini'"ifTiii!nii
ililiJilMIIIIILliiU
Hinh 2. Mat sdng nhu hdm thdi gian cua 600s ddu Hinh 3. Pha sdng duac tao ngdu nhien
Hinh 4.PhS mat sdngHinh 5. So song kMinh 6. Bien do c„
Mo phong s6 song nglu nhign tuySn tinh sir dung ph6 Pierson-Moskovit vol tham so H,=I2m va Tj=10s cho trang thai bien trong 1 gia. Chia dai tjn lam 512 diem. Hinh 2-6 cho ta mo phong s5 ciia trang thai bi6n nay. Khi tinh tai trpng ta tinh cho timg thanh ngap nuac sau do qui vi cac nut Wang duang (4-12) co tinh ca kh6i lupoig nude kem cho tirng nit. Sii dung chuang ttinh WE2000 phat triSn modul mo phong so frang thai bien ngau nhien.
lien nglu Khou hoc vd Cdng nghe Bien loan qudc ldn I'lii V
Hinh 7. Ung suat trong 600s dau
Phan tich dong cho glim dupe tinh voi tai trpng dH linh duac cho trang thai bicn keo diii trong I gia nen doi hoi linh loan kha lau (6 gia). Tren ca so img suat tai moi noi chan cpl dii tinh dupe (Hinh 7) diing phuong phap dong mua ta dung duoc ham mat dp pho irng suiit f(s) vol he so tuong quan ciia tai trpng tinh dupe ~0.5. Tir ta co cac dai lupng s0=68,5MN/m^ n=22.758, n=0.5. Theo cong thuc (8) tinh duac q=2.3388, r=4.70089. Mo men bac m ciia chenh lech img suat E(Sm) theo eong thire (9). Tir day ta tinh dupe tuoi thp mdi ihco (5) n=28 nam, dp tin cay theo (13) R=0.864 va chenh lech irng suit eho phep theo (l8)s=ll7.568MN/m-
KET LUAN
Da tien hanh mo phong so cho song ngau nhien tuySn tinh. Xiiy dung chenh lech irng suat cho diem nong la moi n6i duoi chan cot ap dung qui trinh phan lich moi tren quan diem dp tin cay eiia Ang A. H.-S. Ket qua nhan dupe cho thSy mo phong ngSu nhien cho moi thp, dp tin cay va chenh lech img suSt cho phep dSu nho hon mo phong ti6n dinh thuc hien trong [5].
L61 cam on
Nhom lac gia cam on su tai tra cua Vien Khoa hpc va Cong nghe Viet Nam qua ii tai
"Phdn tich moi vd ddnh gid tuoi thg con lgi cua cdc cdng trinh bien cd xet den cdc yeu to bat dinh " de hoan thanh nghien cim nay.
TAI LIEU THAM KHAO
1. Ang AHS. Bases for reliability approach lo structural faiigue. Proceedings of ICOSS AR 77, Munich, September 1977. pp. 97-114.
2. A.H.-S. Ang, M.C. Cheung, T.A. Shugar, J.D. Femie (2001), Reliability-based fatigue analysis and design of floating structures. Marine Structures 14, pp. 25-36
TmijMnNdnglu-cmg. Ky Ihiiiil ccjiig ninh Van lai vd Cdng nghe Hiin
3. Bao de tai cdp Vien Khoa hoc va Cong nghc Viel Nam (2007). Phan lich lac dpng ngau nhien phuc vu Ihi^t ki, xay dung va danh gia cac gian tu nang hoat dpng tren bien Viet Nam
4. Dao Nhu Mai. Trin Thanh Hai, (2007), Fatigue Analysis of Jack-up Units Using Large Deformation Approaches liiyHn Icip cdng Irlnh Hoi nghi Ca hoc lodn qudc ldn thir VIII, Tap 2 Ctr hoc Vdt rdn Bidn dang, tr 314-323
5. Dao Nhu Mai, Le Viet Anh, Nguyin Viet Khoa va Nguyin Hiiu Cuong (2010) Phan tich moi tren quan diem dp lin eay, Tuyen tap Hpi nghi Hpi nghi Khoa hpc loan quoc Co hpc Vat rin bifa dang ISn thir muai Thai Nguyen, 12-13/11/2010, ISBN 978-604-915- 000-5. tr 482-489.