iI(i−1)Ijy(t)IjyI(j−1)yIie+uex−exe+ve−eextxy3-3-1(t)I(i+1)xIixI(i−1)xIjy(t)IixI(j+1)yIjyI(j−1)y=a2e−2e+ee+2ee−2e+e(x)(y)经整理得到:(tt+)utut=1−(1−cosx+IIsinx)−(1−cosy+siny)(t)xy3-3-2atat−222(1−cosxy)−2(1−cos)(xy)()由稳定性条件:(tt+)==(t)3-3-34242atututatvtvt22xy1sinsinsinsin−+−−+−22IIxy(xy)xxyy22()对于任意复数,它的模要大于等于该复数实部的绝对值。从而,式(3-3-3)可以转变为:(t+t)=(t)3-3-44at2ut2x4at2vt2y1−2+sin−2+sin1(x)x2(y)y2要使不等式(3-3-4)对于任何可能的,值下均成立,则应该使sin2x,xy2sin2y取最小及最大值时,不等式也成立;取最小值时成立是显然的,取最大值2时成立得:从而得到该格式的稳定性条件:1t,a=3-3-52a2auv+++(x)2(y)2xy3-3用vonNeumann方法分析二维非稳态对流扩散方程显式格式n+1−nn+1−nn+1−ni,ji,j++uvi,ji−−1,ji,ji,j1txyn++11nnnnni+1,j−22i,j+i−1,ji,j+1−i,j+i,j−1=+(22)()xy