查看完整版本: Negative values

Negative values

[size=2]I receiving negative values for this experiment (in theory this is not correctly). C%nB%t_:Vq&q


X9p'[xM$FK The experiment consist in plates parallel bars with a viscou fluid between. w{O+iKq\3]
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Exist an analytical solution for this problem, but I can't obtain.
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Other question is how I make the scalar value inside of the solid bars (in x y x) equal to zero? `&M
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*?~^5F%vn _ Thanks again Mr. Nelson
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TITLE 'Bars 3D' y7vD@'OR

%k1pcA`%yY \%X COORDINATES cartesian3 xRj3S]1~!N7wn+H
T5G}7r}6C6r|i
VARIABLES
J!MDYB*E vx(1e-6) vy(1e-6) vz(1e-6) p
(W xf9a#Y0Qa.]
!n~S#C/F"VO SELECT { method controls }
Z
H0{{9rq ngrid = 10.0 St
l.G8xad^:N
errlim = 0.001
h+s|P0~F3B stages = 1
F9dX^"jDI regrid = off
#a eD#lp9O7}E |&rGG jjn0k/mj8y
DEFINITIONS { parameter definitions }
f`-g!a8iw LIx = 0.0 ^/\rsq)^-Q8G1O
LIy = 0.0
J0s*_R} LSx = 3.0 ^,}8o*Jp&[i
LSy = 3.0 3] Sp2HX)}5Rb7E
RPT = 2 o'Cj,`6F
Am9qo8p,Z%|$Ea
dens = 1.0 7l{c/wt'y`0@
visc = 0.001
NOl5C"N%r3` penalty = 1.0
cA:Y*s$kS Pin = 0.001 4}1hn6@_qd

M.Bq k:|5q]Df INITIAL VALUES
4wK2i'{$Q6X&u vx = 0 vy = 0 vz = 0 p = Pin
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a1F#Rj%H"Z`S E D#g EQUATIONS ;QS/i~"n&I
vx: div(grad(vx)) - dx(p)/visc = dens*(vx*dx(vx) + vy*dy(vx) + vz*dz(vx))/visc 7P+c)x o@#|*c#Qr)G
vy: div(grad(vy)) - dy(p)/visc = dens*(vx*dx(vy) + vy*dy(vy) + vz*dz(vy))/visc G{^*_)akn'd$O
vz: div(grad(vz)) - dz(p)/visc = dens*(vx*dx(vz) + vy*dy(vz) + vz*dz(vz))/visc cK,v;Q4@b
p: div(grad(p)) = penalty*(dx(vx)+dy(vy)+dz(vz))
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zcq)F` ! CONSTRAINTS { Integral constraints } aO,vxS@"`.Z
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EXTRUSION
t8f.]@r&H SURFACE 'A-INI' z = 0.0
O!gn+s`6f3o'X| LAYER 'LA'
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SURFACE 'A-FIN' z = 1.0
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LAYER 'LB' #n~&W.e]PT-v
SURFACE 'B-FIN' z = 2.0
k F%e RQ
k5r4m td(ic LAYER 'LC' ~7tjpH;O;`#p-`&@Q
SURFACE 'C-FIN' z = 3.0
ED|:F!J]$Eq T (X3Py:oM!t$w6r
BOUNDARIES
9rMv5kX:P;k YP!Q SSd;Vc
REGION 1
UFFJ:w`B START(LIx, LIy) 3]PR:oQ/A2Y4h
value(vx)=0 value(vy)=0 value(vz)=0 natural(p)=0
Oh gz}a2tq Z -Q@l-l:[$A.~"t*Y
LINE TO (LSx, LIy) d!yIvZ2~8l
natural(vx)=0 natural(vy)=0 natural(vz)=0 value(p)=-Pin
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LINE TO (LSx, LSy)
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value(vx)=0 value(vy)=0 value(vz)=0 natural(p)=0
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LINE TO (LIx, LSy)
,u3~P/Tj natural(vx)=0 natural(vy)=0 natural(vz)=0 value(p)=Pin rr4ukG]

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@``$` LINE TO CLOSE #BL5we$L6E{)?I
_a$~,W+j:U5m
! FIELD 1
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,LLua]U#y9iXv.u LIMITED REGION 2
9^&r pE4k
} LAYER 'LA' VOID |!TE;F DD2L
LAYER 'LC' VOID
T s&S|?Y7oq
f REPEAT i = 0 TO RPT
N M\;qM|1VX REPEAT j = 0 TO RPT 5L#j-vE_
START (0.0 + i, 0.3333333333333333 + j) (rSuX3B8?
value(vx)=0 value(vy)=0 value(vz)=0 natural(p)=0
3r,D8va'lX*f LINE TO (1.0 + i, 0.3333333333333333 + j) TO (1.0 + i, 0.3333333333333333 + 0.3333333333333333 + j) TO (0.0 + i, 0.3333333333333333 + 0.3333333333333333 + j) TO CLOSE
&H]+]2OB#E\ ENDREPEAT ])X]h(@0hj}9L}
ENDREPEAT
Qp'FlIxOb (Q&Wrlt2Ki-f
! FIELD 2
.WDg%?$@E
HJ6@+o&N LIMITED REGION 3
i6l'wPRv(JC | LAYER 'LB' VOID
v8CvbEj REPEAT i = 0 TO RPT 5IiW@2m0B
REPEAT j = 0 TO RPT
b;T"H5q-P START (0.0 + i, 0.3333333333333333 + j) w Z{3_I*f
value(vx)=0 value(vy)=0 value(vz)=0 natural(p)=0 ]
pMO@;iH#I
LINE TO (1.0 + i, 0.3333333333333333 + j) TO (1.0 + i, 0.3333333333333333 + 0.3333333333333333 + j) TO (0.0 + i, 0.3333333333333333 + 0.3333333333333333 + j) TO CLOSE "W^UB)mge
ENDREPEAT
BG&G B3qun ENDREPEAT YYcm[|*fO

o"^P1i!m(J1~1b ym ! FIELD 3 G
`;x"E,P2q
d/w8IAtq
LIMITED REGION 2 IY9N0rf
LAYER 'LC' VOID
W/gC lU8_7Bg REPEAT i = 0 TO RPT
'` F4l'CTB REPEAT j = 0 TO RPT 5d3cY,ANd'U/j
START (0.0 + i, 0.3333333333333333 + j) 3|Cf*k8G%e7q:u;b*B
value(vx)=0 value(vy)=0 value(vz)=0 natural(p)=0 zJ s'kG#R3hO
LINE TO (1.0 + i, 0.3333333333333333 + j) TO (1.0 + i, 0.3333333333333333 + 0.3333333333333333 + j) TO (0.0 + i, 0.3333333333333333 + 0.3333333333333333 + j) TO CLOSE
xI/R$KX
u ENDREPEAT
d-~T
\"N'c8mDn ENDREPEAT M%cy3Yu

rg!\T9QHf^ monitors ] [ nU ab
GRID(x,y,z) :i)L)m:x8m&U1@*}
vector(vx,vy) on z = 1
7U9ajrh)v/r/b vector(vx,vy) zoom(1.0, 1.0, 1.0, 1.0) on z = 1
g)?(o$C%X w.lR vector(vy,vz) on x = 1
0I$l5A&mE_!D vector(vz,vx) on y = 1 {]#p%Z|YX~
contour(vx) on z = 1 \#d D lZ(Sv,ER
contour(vy) on x = 1 .K%v1F[#?\/w
contour(vz) on y = 1
%o-E B7g3\grE 4Y9G_KZ)D
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plots !c5W feQ8C0V7u2]
GRID(x,y,z) Ij V}9ka~8s
VECTOR(vx,vy) zoom(1.0, 1.0, 1.0, 1.0) ON z = 1 points = 70 export format "#1,#2" file "field_2d.txt"
I4P T%N^E ! VECTOR(k*grad(vy)) zoom(1.0, 1.0, 1.0, 1.0) ON x = 0 points = 70 export format "(#x,#y) = (#1,#2)" file "FIELD_YZ.TXT" as "Vector Field YZ"
(m9lCs/V fb1\Oux ! VECTOR(k*grad(vz)) zoom(1.0, 1.0, 1.0, 1.0) ON y = 0 points = 70 export format "(#x,#y) = (#1,#2)" file "FIELD_XZ.TXT" as "Vector Field XZ" #C&Fq0neJ
! TABLE(dx(vx), dy(vy), dz(vz)) zoom(2.0, 2.0, 2.0, 1.0, 1.0, 1.0) points = 70 format "(#x, #y, #z) = (#1, #2, #3)" file "FIELD_XYZ.TXT"
iN:mI*Yhx TABLE(dx(vx), dy(vy), dz(vz)) zoom(1.0, 1.0, 1.0, 1.0, 1.0, 1.0) points = 70 format "#1 #2 #3" file "field_3d.txt"
-Z*N*u hx +^ ~8J(W }kn,b
vector(vx,vy) on z = 1 G#PvTSZ
vector(vy,vz) on x = 1 M4k%WB6{K Y
vector(vz,vx) on y = 1
6K8j+_P C contour(vx) on z = 1 U"v5PK-y2d%b(P
contour(vy) on x = 1
Ho;hc6Wl/f8AV contour(vz) on y = 1 ^:O lm7T7Eeo
end [/size]d%hJ
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[size=2]Ops the paragraph
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U'q7{} o;P3zX"G ]4A "Exist an analytical solution for this problem, but I can't obtain."
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K4Q [&|me9P Is wrong, sorry! T4S ?~D&}

-[(\4v0`&l.j$k6@ I can't generate the numerical values to compare with analytical solution!
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Thanks again![/size]

[size=2]1. *\Kw)Ko~8_
The only negative numbers I see are in Vy, which is nominally zero. These are simply numerical noise, four orders of magnitude below the dominant flow velocities. This is a numerical approximation, after all, not an analytic solution, and on a very crude mesh at that.
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2.
${)I*z};a{E Your four slabs are all disjoint. There is no point in running them all together; it just creates a larger mesh and runs longer. You can do each one individually. :Z-L:f7~!fF C'g

-b8w^"~~ 3. :MH/j&VU)O ?*u
If "the space between the bars" you refer to is the gaps between slabs, then they are already zero, because you excluded them. If you mean to stop the flow in the mid section of each slab, just exclude that as well.
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If you are using the student version, it won't work. You need more nodes than the student version allows. Try running the individual slabs. [/size]
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