请教velocity矢量方向和displacement矢量方向相反，是否对？

sz007

各位高手：

   你们好！我计算了一地下连续墙，但是加载后速度的矢量方向和位移的矢量方向刚好相反，不知是什么原因？各位大侠能指点一二吗？

附命令流：
;※※※※※土体※※※※※※

gen zone radcyl p0 (0 0 0) p1 (20 0 0) p2 (0 0 -20) p3 (0 20 0) &
                size 5 20 8 10 ratio 1 1 1 1.15 dim 3.5 3.5 3.5 3.5
gen zone radcyl p0 (0 0 -20) p1 (20 0 -20) p2 (0 0 -50) p3 (0 20 -20) &
                size 5 20 8 10 ratio 1 1 1 1.15 fill dim 3.5 3.5 3.5 3.5
gen zone cylin p0 (0 0 0) p1 (2.8 0 0) p2 (0 0 -20) p3 (0 2.8 0) &
               size 4 20 8
;*****左右对称******
gen zone reflect dip 90 dd 270 origin (0 0 0)
;*****前后对称******
gen zone reflect dip 90 dd 180 origin (0 0 0)
group loess

;******************************************************************************
;※※※※※接触面※※※※※※

interface 1 face range cylin end1 (0 0 -0.001) end2 (0 0 -20.01) radius 3.52 &
                       cylin end1 (0 0 -0.001) end2 (0 0 -20.01) radius 3.48 not
interface 2 face range cylin end1 (0 0 -0.001) end2 (0 0 -20) radius 2.81  &
                       cylin end1 (0 0 -0.001) end2 (0 0 -20) radius 2.79
interface 3 face range cylin end1 (0 0 -19.99) end2 (0 0 -20.01) radius 3.51

;******************************************************************************
;※※※※※墙体※※※※※※

gen zone cshell p0 (0 0 22) p1 (3.5 0 22) p2 (0 0 1) p3 (0 3.5 22) &
                size 1 21 8 4 dim 2.8 2.8 2.8 2.8
;*****左右对称******
gen zone reflect dip 90 dd 270 origin (0 0 0) range z 1 22
;*****前后对称******
gen zone reflect dip 90 dd 180 origin (0 0 0) range z 1 22
group wall range z 1 22
ini z add -21 range group wall
;*******************************************************************************
;※※※※※承台※※※※※※

gen zone brick p0 (-3.5 -3.5 3) p1 (3.5 -3.5 3) p2 (-3.5 -3.5 1) p3 (-3.5 3.5 3) &
         size 10 2 10 group chengtai
attach face range z 0.9 1.1
save geo.sav

;==============================================================================
res geo.sav
model mohr range group loess
prop bulk 18.61e6 shear 7.52e6 coh 70000 fric 30 range group loess
model elas range group wall
prop bulk 18.61e6 shear 7.52e6 range group wall
model elas range group chengtai
prop bulk 18.61e6 shear 7.52e6 range group chengtai
;
inter 1 prop kn 2e8 ks 2e8 fric 20 coh 70000
inter 2 prop kn 2e8 ks 2e8 fric 20 coh 70000
inter 3 prop kn 2e8 ks 2e8 fric 20 coh 70000
;
ini dens 1610.4 range group loess
ini dens 1610.4 range group wall
ini dens 1610.4 range group chengtai
model null range z 0 3

;*********************************************************************
;※※※※※边界条件※※※※※※
fix x y z range z -49.9 -50.1
fix x range x -20.1 -19.9
fix x range x 19.9 20.1
fix y range y -20.1 -19.9
fix y range y 19.9 20.1
set grav 0 0 -10
ini szz 0.0 grad 0 0 16104.0 range z -50 0.0
ini sxx 0.0 grad 0 0 8052.0 range z -50 0.0
ini syy 0.0 grad 0 0 8052.0 range z -50 0.0

hist unbal
plot cont szz
solve ratio 1e-6
save grav0.sav

;======================================================
res grav0.sav
model elas range group chengtai
prop bulk 14.3e10 shear 13e10 range group chengtai
model elas range group wall
prop bulk 14.3e9 shear 13e9 range group wall
ini dens 2500 range group chengtai
ini dens 2500 range group wall

hist unbal
plot cont szz
solve ratio 1e-6
save grav1.sav

;==========================================================
res grav1.sav
apply szz -1e5 range z 2.8 3 group chengtai
ini state 0
ini xdis 0.0 ydis 0.0 zdis 0.0
hist unbal
hist gp zdis 0 0 3
plot cont szz
solve ratio 1e-6
save 1e5.sav

savage

最近我做模拟也发现了这个问题，VELOCITY到底是个什么东西，它表示什么，说明了什么问题？求高手解答。