- ODS: quan sdt ma tran FRF tai tan so xac dinh
b.Nhan dang sai hong
Vi$c thyc nghiem dugc tien hanh bang cich do rung liic cau o trang thii chua co sai hong va sau khi da tao ra nhimg sai hong tran ciụ
Voi pham vi bio cio nay, chiing ta de cap hai phuong phap: - Phuong phip nang lugng SEM (Strain Energy Method) - Phuong phip mem deo
Cay cau o day la 1-40 tai Albuquerque dugc lua chpn lam doi tugng thi nghiem. Cau gom 2
lan duang rieng rẹ Cau che tao voi san ba tong, dugc do boi cac ram doi ban bang thep v i 3 xa ngang thep de dọ Tii trpng tir xa ngang truyan xuong cic rim thong qua cic thanh
dam.
Cau gom 3 nhip, nhip 1 v i 3 co cimg chieu dai (khoang 39.9 m) con nhip 2 dai co 49.4 m. De CO 3 nhip cau niy chiing ta da ghep 5 rim doi thep (cin 4 moi ghep cho 5 rim va cac vat nut sau nay ciing dugc cho la giy boi hien tugng cong ciia cic rim ngang nay).
Hinh 44 Cay cau 1-40 tai New Mexico [8]
Viec bo tri diu vao dau ra dugc mo ta nhu hinh duoi daỵ Cam bien dugc gan tren than cau (vi tri ma cic thanh dam ngang dugc ban voi than cau). Vat nut dii 122 cm can nhan dien ciing nam tren thin caụ Viec kich boat diu vio sir dung miy tao rung Sandia co Ion. Miy tao rung niy co the rung voi tin hieu sin hoac tin hieu ngau nhian trong dai tan 2 toi 12 Hz.
Vet nut gan niit 7
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rung
113
(b) Mo hinh Wong MATLAB Hinh 45 Bo tri thi nghiem tren cau 1-40 [7]
Cic thao tic MA ciing dugc thuc hien ung voi cic trang thii truoc va sau hu hong cua cau 1-40. Hinh duoi day mo ta FRF tai cic niit gin diam kich thich (niit 3) v i nut xa (niit 12).
G, nut 3 G, nut 12 G, nut 12
v--^^-
tso (Hz)
Hinh 46 FRF tai nut gan (so 3) vd nut xa (so 12) Bdng 7: Tan sd cong huong tuong ung truac vd sau hu hong
Mode 1 2 3 4 5 6
Tin so cong huong (Hz) Truoc khi hu hai
2.4793 2.9493 2.9493 3.4942 4.0774 4.1668 4.6362
Tan so cong huong (Hz) Sau khi hu hai
2.2699 2.8339 2.8339 3.4874 3.9896 4.1470 4.5245
Nh$n thiy ro rang co sy khac nhau ro rang ve gii tri tin so cong huong cua cic mode tuong ling nen co the ket luan da co sy sai hong xiy rạ Hai hinh duoi day la FRF tuong ung voi tinh huong truoc va sau sai hong de co tha lam ro hon nhan xet niỵ
Hinh 47 FRF truac liic sai hong
Hinh 48 FRF sau khi sai hong
Hinh 48 chinh OS ciia cau 1-40 tai cimg 1 mode cong huong (mode 4) ma tir do ciing cho thay sy khic biet giira truoc va sau khi co khuyat tat tren cau tnic caụ Co tha nhan thay rang dimg phan tich MA co tha nhan biat dugc c6 sai hong xiy ra hay khong nhung chua chi ra dugc vi tri cua sai hong. Noi dung niy se dugc trinh bay o phan saụ
trifd^c