15 au a2 a2u at po ao l(0)=0=f(p) u=tg Td"=0 自然周期边界条件 u=7g T=0 a mt -= exp u=2(Am cos mp+Bm, sin mp)exp/Q2m't n=0 dnJ/(o)cos mgdg f(o)sin modo15. 0 0 2 2 2 0 2 =   −     a u t u ( ) ( ) u  t=0 = f  u =T ' '' 0 2 0 2  − T = a T  自然周期边界条件： u =T ' 0 2 0 2 2 + T = a m T  exp[ ] 2 0 2 2  a m t Tm = − ( cos sin ) exp[ ] 2 0 2 2 0    a m t u A m B m m =  m + m −  =        A f m d m m ( )cos 1  − =       Bm f ( )sin m d 1  − =