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6.3.4Gidm sdt cong trinh xay dimg: cau
Vi khuon kho giai ban cua mot da tai va vi viec thuc hien cac thi nghiem gan cam bien len cau roi tac dpng len cau bang bua ta hay may tao rung dpng la khong kha thi (kinh phi, sir cap phep). Nhimg thi nghiem ke tren co the thuc hien dugc khi da tai dugc mo rpng, lien ket voi cac co quan huu quan de dugc phep thuc hien thi nghiem tran mot doi tugng cau cu thẹ Khong lam mat tinh tong quit cua mot cong trinh nghien cuu, chiing toi da sir
dung cac tap du lieu va cong cu DIAMOND tir thu vien mian phi cua nhom nghian cuu My
Los Alamos National Laboratory (LANL). Cong cu DIAMOND la cong cu nguon mo phat trien tren moi truong MATLAB (nguoi dimg khong phai tra tien mua DIAMOND ma chi phai tra tien mua MATLAB). Vi DIAMOND cung dang trong qua trmh phat trien nen nguoi su dung co the tuy y phat trien cac thuat toan SHM tren DIAMOND nhung ciing khong nhan dugc sir ho trg nao tir LANL. Ngoai ra chung toi se con sir dung phan mam thuong mai CIVIL/ANSYS la phan mem ho trg cho viec mo hinh boa cac cong trmh xay
d\mg (o day chung ta quan tam toi cau) trong cac nghien cuu tiep theọ Be xuat cua nhom
tac gii do la kat hgp CIVIL va DIAMOND, do la su kat hgp mai va hieu qua trong viec nghien cim va SHM.
Phep phan tich dao dpng riang (MA) la cong cu hieu qua cho viec mo hmh hoa dac
trung dpng cua mpt he thong xac dinh. MA dugc thiat lap dua tran ly thuyat ve gia tri riang
va vecto rieng cua he thong. Dua tran ly thuyet MA ma cac thuc nghiem tuong ung ciing da dugc thuc hien rat hieu qua va kha don gian. Phep phan tich MA se cho phep tinh dugc tan so dao dpng rieng, he so suy hao va dang dao dpng cua cau truẹ
Phuong trinh vi phan mo ta dao dpng cua cau true tuan theo dinh luat Newton ap dung tren tat ca cac bac tu do cua cau true dọ Voi mot bac tu do xac djnh thi phuong trinh dugc mo ta nhu sau:
[A/Jx(/)+[cMr)+[/:MO=/(0 (11)
Voi cac ma tran [M], [C], [K] la cac hang so; f(t) la vecto ngoai luc tac dung theo thai gian
t lien tuc.
Khi cau true chiu tac dung boi ngoai luc f(t) co nhiin^ tan so khac nhau thi co the chia thanh hai loai dao dpng: (1) tan so dao dpng khac voi cac tan so cong huong cua cau tnic va (2) tan so dao dpng trimg voi tan so cong huong cua cau truẹ Mot cau true c6 the c6 nhieu tan so cong huong khac nhau, tir do c6 nhiau dang dao dpng khac nhaụ Mot dang dao dpng lai dugc dinh nghia bao gom tan so cong huong (tan so dao dpng rieng) tuong ung, he so suy hao, va hinh dang dao dpng riang (mode shape - MS).
Khi tin so luc tic dung bang tin so dao dpng riang chung ta co mot MS tuong ung, con neu khic chung ta co mot hinh dang dao dpng ODS yau hon. Co tha coi MS la mot truong hgp dac biet cua ODS. Khi tian hanh thuc nghiem bang cich chii dpng tie dpng vao cau tnic cic rung dpng xac dinh, cai ma chung ta do dugc li ODS, tir do moi xic dinh cic thong so trong phep phan tich MẠ
Co hai ky thuat thuong dugc sir dung de uoc lugng cac tham so MA la phuong phip mo phong Monte Carlo va phuong phap lap.
Phuong phip Monte Carlo: lap di lap lai thi nghiem da thu dugc cic tap dir lieu nhieu lin voi gia thiat rang c6 su bian doi ngau nhian tran cic lan dọ Tir do xay dung phep phan tich MA tuong ung da thu dugc cic tham so MA co phan bo thong ka xic dinh.
. - Phuong phap bootstrap: sir dung cic dip img tan so (FRF) do dugc (bang cich do lap di lap lai) de to hgp thanh mot dip ung trung binh voi cic trpng so khic nhaụ Cic trpng so nay se dugc sir dung de xiy dung cic tham so ciia phan tich MẠ
Sir khic biet co bin cua hai phuong phip niy do la phuong phap Monte Carlo yau cau phai CO phan bo dir lieu do xic dinh con phuong phip lap thi khong. Phuong phip Monte Carlo chi co the uoc lugng cic loi ngau nhian trong khi phuong phip lap thi c6 the uoc lugng loi ngau nhian va ca cic loi he thong vi du nhu moi truong thay doị Tuy nhien, phuong phip bootstrap lai yau cau dp phuc tap cao ban phuong phip Monte Carlo do luon phai thuc hien viec tinh toin va luu trir FRF trong qui trinh thu thap du: lieụ
. R6 rang, buac dau tien cua phan tich MA do la phai thu dugc tin hieu tic dpng dau
vao x(t) va dip img ra y(t). Tir do co the chuyan tin hieu sang mien tin so: ham mat dp pho Gxx(tt)) va Gyy(ft)), ham mat dp pho cheo Gxy(co). Sau do tinh cic FRF nhu sau:
H^{co) = - ^ (12)
hoac CO the tinh cic ham lian ket:
Ham lien kat phin inh su tuong quan giira tin hieu vio vi ra, nau cau true dugc xem la mot he thong tuyen tinh bit bian LTI thi him lien kat nhan gii tri thuc bang 1. Con nau tin hieu ra la nhieu chang ban thi ham lian ket bang 0. Thong thuong thi no nhan gii tri thay doi trong dii 0 toi 1.
Nhan xet rang cic FRF trong cic phuong trinh tren moi khi tien hanh do dac va tinh toin lai cho nhung ket qua khac nhaụ Dieu nay thuc su da giii thich vi c6 rit nhieu nguyan nhan gay nen su sai khic niy, nhung nhin chung co tha phan thanh 2 loai la tit dinh (tir viec lech offset cim bian va mach dien, lay mau tin hieu, uoc lugng pho) va ngau nhian (tir cam bien, mach dien, nguon kich thich phu khong do dugc, he phi tuyan).
Viec xir li sai so tat dinh luon de dang hon loi ngau nhien. Nhirng no luc cua cic nha nghien cuu vi tha dugc tap trung da xir ly loai sai so ngau nhian naỵ Voi nhirng sai so co su tuong quan voi nguon kich thich (da dinh gii cong trinh) thi rat kho xir li nan trong khuon kho da tai niy chung ta chap nhan gia dinh la cic loi ngiu nhian la dpc lap voi kich thich dau vao (gii dinh niy ciing thuan Igi nhu khi lay trung binh FRF ciia cic lan do khac nhau thi gii tri thu dugc se giam dugc loi ngau nhian).
Dp lech chuan cua mot phep do dugc tinh theo cong thirc
74^-/^)1 (14)
C5 do a la dp lech chuan (68% dp chac chan, xem hinh 31), X li bian ngau nhien, |i=E(X) la tri trung bmh.
Neu th\rc hien phep do X trong n lan thi ta co tha tinh dugc dp tin cay ciia phep do nhu sau
Voi n>l thi de nhan thay (yn^<y ). 3 0. 4 1 J .0 0. 1 0. 2 C 1 _ L O 0.1% ^(•' 1 ,J^--i - 3 a r P^13,6% - 2 a - Jk 34.1% l a 1 34.1% ^ 1 Hlfeiwi^^ 0.1% ; 1 a 2a r 3a
Hinh 31 Minh hog ve phan bo chuan [11] (adsbygoogle = window.adsbygoogle || []).push({});
Liic nay, theo [1,2] thi chiing ta co the tinh dugc dp lech chuan cua uoc lugng dac trung bien dp va pha cua ham truyen Hxy(co) nhu sau:
^ « ( ' ^ ^ ^ M ) = a r c s i n Vi^^>)
{\c^{co}j2^
Hmh 32 minh boa cho truong hgp tien hanh do dac FRF mot cich tong quit, co nghia la xay dung dugc thanh mot ma tran do FRF.
x3(t)->X3(w) x1(t)->X1(w)
(16)
(17)
Hinh 32 Do cdc FRF tren mot cau true xay dung
Tren th\rc ta thi do FRF co the tien hanh theo cich don giin hon, sir dung mot trong hai loai thiet bi de kich thich diu vio la bua dap chuyan dung va bp tao rung (hinh 33) nhu sau:
1) Co dinh diem do diu ra (vi du nhu co dinh cam bien gia toe tai nut 1), thay doi cic diem kich thich (tir niit 2 den 6 trong hinh 32). Thi nghiem kiau niy phii hgp voi thiet bi de kich thich dau vao la biia dap chuyen dung vi co the di chuyen de ding.
2) Co dinh dau vao kich thich (vi du nhu dat co dinh mot miy tao rung tai mit 1), thay doi ^ cic diem do (tir niit 2 toi niit 6 trong hinh 32).
3) Neu thiet lap co 2 dau vao va 2 diem do tro len thi gpi la phep do MIMO (nhieu dau vio nhieu dau do).
Hinh 33 Biia chuyen dung vd bo tao rung [5]
De thuc hien phep phan tich MA theo phuong phip Monte Carlo va Bootstrap, chiing ta can tinh dugc cic tan so dao dpng rieng, he so suy hao, va MS nhu sau:
;,;T Phuong phap Bootstrap Phuong phap Monte Carlo
1. Do va luu n mau FRF Hxy(co) tran L Tinh tri trung binh va dp lech chuan timg diem do dau rạ cua dac trung bian dp v i pha cua FRF 2. Lay to hgp trung binh ngau nhian nid Hxy(a))
mau FRF tir n mau thu dugc Hi(co). 2. Thu dugc tri trung binh Hi(co) dua 3. Dimg thuat toin nhan dang ciia tren dac trung bian dp va pha co thong so
phuong phip phin tich dao dpng thong ke xic dinh nhu sau: rieng de tinh tan so dao dpng riang
cOj, he so suy hao C,[ v i MS.
4. Lap cic buoc 1-3 da tinh histogram cua cic thong so tran (kiem tra hoi tu).
5. Thuc hien phep tinh thdng ke |i(Wi), ăcoi),... v" R = va phuong sai o-Ml//. ( - * óizHJco))
3. Tinh cOj, Q v i MS tir Hi(co)
4. Thuc hien cic phep tinh thong ka cac thong so tran va kiam tra tinh hoi tụ
5. Cho ra ket qui cuoi cimg cua |ăcOi),
0 ( C D , ) v "
Su- dung cong cu DIAMOND/MATLAB trong bai toan chan doan tinh trang can
Cong cy DIAMOND la cong cu mo ma bat cu nguoi sir dung nio ciing dugc phep thay doi v^ phat trien them cac thuat toin dua tran phan tich dao dpng rieng. De minh hoa cho cac
thu§t toan thi cic d\i lieu thuc nghiem dugc sir dung la dij lieu do tren cac cay cau thyc te [6,
7]. De tien hanh nhirng nghien cuu SHM thi nhirng kian thuc co bin ve ciu (cy the 6 day li be tong c6t thep) la rit can thiat [10].
Diamond gom 3 modun (adsbygoogle = window.adsbygoogle || []).push({});
ạ Phan tich dao dpng rieng b. N h ^ dang sai hong
c. Hi^u chinh dimg mo hinh FEM (phan tir hiru ban): khong de cap trong bio cio niy, se la su phat trien ke tiep khi ket hgp DL\MOND/MATLAB voi CIVIL/ANSYS.
ạ Phan tich dao dong rieng
Co nhiau phuong phip phan tich dao dpng riang, trong pham vi bio cio niy thi ap dung cic phuong phip sau:
- ODS: quan sat ma tran FRF tai tan so xic dinh [34]
- RPA: Xap xi theo da thuc hiru ty: uoc lugng bac cao tren mien tan so [14]
- ERA: uoc lugng tham so theo phuong phip dao dpng rieng tren mian thai gian (bac thap) Luu y rang voi cic thuat toin ke tran thi dau diing voi phuong phip Monte Carlo nhu da
trinh biy a tran. Cic kat qua thong ka sau do dugc dimg de xic dinh dp tin cay cua cic
thong s6 MẠ
De kiem chimg thuat toin, doi tugng nghien cuu o day la cay cau Alamosa Canyon tai phia nam cua New Mexico (hinh 34). Cay cau dugc xay dung voi muc dich de thir nghiem SHM. Day la cay cau co 7 nhip, moi nhip dai 15.2 m vi rpng 7.3 m. Giira hai nhip cau lian tiep 6 phia duoi li mot try caụ Moi nhip cau co 6 ram cau bang thep (hinh 35). Viec do luong dugc tien hanh tran nhip cau dau tian, cu 5 cam bian gia toe dugc lap dat dpc theo mot ram caụ Cam bian khong dugc lap dat tai vi tri mo cau hay try cau (xem hinh 35). Tran hinh nay ciing mo t i 2 dau vao kich thich boi biia chuyan dung va 30 diam do tuong ung.
Hmh 35 mo ta cich bo tri diem kich thich vi cic dau do tran cau trong do hinh (a) li nguyen ly, hmh (b) la mo hmh xay dung troiig DIAMOND/MATLAB. Luu y trong hinh (b) thi cac niit tir 38-43 tuong ung voi vi tri m6 ciu (khong dat cam biln do) va 32-37 tuong ling voi vi tri try cau (ciing khong dat cim bien do). Nhiing diem niy nau co dat dau do thi tin hỉu ciing co the coi la rat nhọ
aSu vSo 2 trSn mat c^u
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