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15 21998 5
ENGINEERING MECHANICS
Vol. 15 No. 2
May . 1998
(, 100084)
, 30 ,,, , ,
,, ,,
,,
[ 1- 5], ,,,
30,
, : 1997 7
1
1 u ( t ),
[ M ] { x } + [ C ] {} + [ K ] { } = {0} (1){ }, { x }
x i = i + u, x i = i + u (2)( 1)
[ M ] { } + [ C ] {} + [ K ] { } = - [ M ] {1} u (3)- [ M ] {1} u
, { }
[ S] = [ H * ] [ S f f ] [ H ] T (4)[ H ], [ H * ]
[ H ] = [ ] [ Y r ] [ ] T[ ] = [ { 1} { 2} { n} ][ Y r ] = diag[ Y 1 Y 2Y n ]Y i = [ k r - m r2 + j cr ]- 1
k r, m r, cr , r = kr / mr , r = c r
2 m rk r
{ r } r { r } = [ 1 r 2 r nr ] T
, { r } , r r
[ Sf f ]( PSD), [ S f f ] = [ M ] [ I ] [ M ]
TSuu (5)
Suu:Ruu ( ) = E [ u ( t ) ( u( t - ) ) ] = 4E [ u ( t ) u( t - ) ]
Suu = 12- Ruu ( ) e- j d= 4S uu (6) RuuE [ u ( t ) u ( t - ) ]( 4)( 5)( 6)
[ S] = [ H ] * [ M ] [ I ] [ M ] T [ H ] T4S uu (7) , { X } ,{ }, PSD[ S xx ]
110
[ Sxx ] = {X ( ) } { X ( ) } T = [ S] + [ Su] + [ Su] + Suu [ I ] (8) u( t ), = r ( r r ) , r { },
[ Su ] + [ Su] 0( 8)
[ Sxx ] = [ S] + S uu[ I ] = [ H * ] [ M ] [ I ] [ M ] T [ H ] T4S uu + Suu [ I ] (9)( 9)
Sxixj=
pkj
H*ikmkpmp sH j s4Suu
Sxjxj=
pkj
H*jkmkpmp sH j s4Suu + S uu
[ M ],Sx
ixj=
p
(H*ipm
2pH jp ) 4Suu
Sxjxj=
p
(H*jpm
2pH jp ) 4Suu + S uu
( 10)
r , H ij Yri rj r ,Sx
ixj
p
Y*r irp rm 2p Y rj rp r 4rSuu
= Y r2i rj r
p
( p rm 2pp r) rSuu(11a)
Sxjxj= Y r
2 jrjr p
( p rm 2pp r ) rS uu + S uu (11b)Sx
ixj
Sxjxj
=
irjr Y r 2 4r p
2p rm 2pj rjr Y r 2 4r
p
2p rm 2p + 1 ( 12),
j r = j r Y r 2 4r p
2p rm 2p( 12)
Sxixj
Sxjxj
=ir
jr + ( 1/ jr ) ( 13) = r ,
Yr2 1/ (2krr ) 2
jr = jr 14k
2r2r
k2r
m2rp
2p rm 2p = j r 1
4m 2r2r p 2p rm 2p( 14)
m r ,, m r= p2p rmp ,
111
p
2p rm 2p > m 2r( 14):
jr > j r 142r , 1/ jr