CHUYN
ABAQUSPhn tch truyn dn nhit v ng sut nhit
Gii thiu truyn dn nhit trong vt rnTng quan Gii thiu Qu trnh phn
tch Tnh cht nhit ca vt liu Kho phn t truyn dn nhit trong
ABAQUS/Standard iu kin bin v ti trng Phn tch trng thi n nh V d
Gii thiu
-- ABAQUS l phn mm ch yu dng tin hnh phn tch ng sut -- Nhng
ABAQUS cng c mt c tnh quan trng: chnh l c th gii vn truyn dn nhit
trong m hnh quy m ln, phc tp v nhiu b phn. Kh nng gii truyn dn nhit
l t trong vn ng sut nhit pht trin ra.
Gii thiuc tnh truyn dn nhit trong ABAQUS -- Hng ng trng thi n nh
(stability) -- Hng ng trng thi tc thi (transient), bao gm bc thi
gian di t thch ng -- y iu kin bin truyn dn nhit -- Thuc tnh vt liu
(v ti trng) c th ph thuc vo nhit -- Tip xc nhit cho php ti b mt tip
xc c nhit lu ng -- C th d dng nhp trng nhit vo trong phn tch ng sut
nhit -- c tnh * Nhit tim n (do chuyn pha to ra) * i lu cng bc * Cng
nng phn tch ngu hp ng sut truyn dn nhit * Phn t v truyn dn nhit
(thang nhit theo phng dy) * Cng nng bc x khoang rng (tng nhit l
si)
Gii thiu
ABAQUS khng th: ABAQUS khng phi l phn mm phn tch truyn dn nhit
chuyn nghip Phn tch th lng i lu t do Lc ni li dng i vi vn sc nhit
khng phn chia mng li t thch ng Phn tch truyn nhit ngc
Gii thiu So snh gia cn bng lc vi bo ton nng lng -- Trong phn tch
ng sut, ABAQUS gii phng trnh cn bng lc: Mu = P I -- Trong phn tch
truyn dn nhit, ABAQUS gii phng trnh bo ton nng sut ng thi xc nh phn
b nhit :
c = Q I qMt Density Nhit dung ring T sut thay Specific Heat i
nhit Nhit lng bn ngoi Nhit lng bn trong
Gii thiu Cc i lng vt l c bn trong phn tch truyn dn nhit-- Nhit ,
Temperature n v -- Nhit nng hay nng lng nhit, Heat energy n v J --
Nhit sut hay t sut nhit, Heat rate power n v J/t or W -- Lu lng
nhit, Heat flux = Power per unit area n v J/t/L2 -- T sut truyn dn
nhit k, kh nng nhit lng chy trong vi phn vt cht, n v J/T/L/ Lu lng
nhit t l thun vi t sut truyn dn nhit v thang nhit : T
q = k
xQ L A Tb
Ta
Q = qA = kA
Tb Ta L
Gii thiu-- Nhit dung ring, kh nng bo tn nhit trong vi phn
khi
lng vt cht, n v J/M/Qt = VcTng lng thi gian Tng lng nhit Nhit
dung ring
-- Cng thc truyn dn nhit mt chiu
2 =k 2 c t x
1 2 = 2 t x
k = cT sut khuch tn nhit
-- Tng tng sut Nhit nng
u
q
I = T dVV
I = T qdVV
D
K
T D dV V
T K dV V
Qu trnh phn tch Trong ABAQUS/Standard, thc hin phn tch truyn dn
nhit l thng qua ri rc khi hnh hc thnh phn t truyn dn nhit khuch tn,
ng thi s dng *HEAT TRANSFER la chn: *HEAT TRANSFER n nh Trong
ABAQUS/Explicit, khng c la chn phn tch truyn dn nhit n thun, tuy
nhin c th tin hnh phn tch nhit - ng sut hon ton ngu nhin. Cng nng
ny thng qua thit lp iu kin bin tng thch, c th m phng cng trnh thun
truyn dn nhit; Ngoi ti trng nhit khng u ca bc x khoang rng v ngi
dng t nh ngha, thuc tnh nhit khc c th s dng trong BAQUS/Standard u
c th dng trong Explicit. phn tch trng thi tc thi (mc nh) phn tch
trng thi *HEAT TRANSFER, STEADY STATE
nh ngha tnh cht nhit ca vt liu nh ngha tnh cht nhit ca vt liu t
t kha *MATERIAL trong inpT sut truyn dn nhit: *CONDUCTIVITY, c th
nh ngha cc hng ng tnh (mc nh) hoc cc hng d tnh (trc giao hoc hon
ton) dng tham s TYPE: *CONDUCTIVITY,TYPE=ISO|ORTHO|ANISO -- T sut
truyn dn nhit c th l hm s ca nhit , y cng chnh l mt vn phi tuyn
tnh. -- T sut truyn dn nhit cng c th l hm s ca trng bin mc nh vi s
lng ty . -- Tnh cht vt liu ca trng bin mc nh khng bao gm n phi tuyn
tnh, ABAQUS s dng phng php ni suy n gin xc nh tnh cht vt liu. V d
nh: *CONDUCTIVITY,DEPENDENCIES=1 Thit lp bao gm s lng trng bin mc
nh 63.0,20,160 70.5,200,200 Nhit Trng bin *INITIAL
CONDITIOINS,TYPE=FIELD,VAR=1 NALL,160 *STEP
*FIELD,VARIABLE=1,AMPLITUDE=TIMEVAR NALL,180 *END STEP
nh ngha tnh cht nhit vt liu
*MATERIAL,NAME=MATERIAL-1 *CONDUCTIVITY 1.0 *DENSITY 1.0
*SPECIFIC HEAT 1.0Nhit dung ring: *SPECIFIC HEAT, -- Nhit dung ring
c th nh ngha l thay i trng bin theo nhit -- Nhit dung ring ca i a s
vt liu thay i bnh n theo nhit Mt : *DENSITY, --Mt c th nh ngha l
thay i trng bin theo nhit
nh ngha phn t truyn dn nhit Phn t lin tc: Kho phn t truyn dn
nhit khuch tn lin tc trong ABAQUS bao gm: Phn t ni suy bc 1 (tuyn
tnh) Phn t bc 2 (parobol) ng dng trong 1 chiu, 2 chiu, i xng trc v
3 chiu
Hnh hc, phn t 3D
Quy cch tn gi phn t:
S im nt Khi lin tc continuum Khuch tn diffusion
DC3D20
-- Bin c bn ca im nt cc phn t ny ( t do) l vc t nhit , trong
ABAQUS dng t do 11 biu th nhit . Bin xut nhit im nt l NT11.
Phn t im Phn t nhit dung HEATCAP m phng nhit dung tp trung ti mt
im Phn t nhit dung c th l hm s ca nhit hoc trng bin Phn t ny c th s
dng trong ABAQUS/Explicit
nh ngha phn t truyn dn nhit Phn t v Phn t v u c sn trong kho phn
t. Phn t v dng m phng kt cu mng chu ti trng nhit nh: thng p lc, h
thng ng v tm kim loi nguyn kin-- trn cc im theo phng dy ca mi im nt
v phn t u cung cp t do nhit , nhit ny khng ch thay i theo mt phng
xem xt, cng thay i theo phng dy.
NT13 NT12 NT11
n
-- t do nhit phng di b mt phn t v l 11 (bin xut l N11) -- t do
nhit b mt dng l 10+n, n l s lng im mt ct s dng trn mt ct v -- Trong
v n tng (ng cht), im mt ct phn b u theo phng dy, mc nh l 5 im -- Mi
tng v bt buc s im mt ct l l, y l do s dng phng php ni suy phn on
hnh parabol trn dy quyt nh.
nh ngha phn t truyn dn nhitPhn t v vt liu phc hp V nhit vt liu
phc hp nhiu tng c th c to t cc tng c dy khng ging nhau, khng ng vt
liu theo phng chnhc trng vt liu c nh ngha trong *SHELL SECTION:
*SHELL SECTION,COMPOSITE dy ca LAYER1, s lng t do nhit (s im mt
ct), tn vt liu, dy ca LAYER2, s lng t do nhit (s im mt ct), tn vt
liu, dy ca LAYER2, s lng t do nhit (s im mt ct), tn vt liu, t4 VL1
t3 VL2 t2 VL3 t1 VL4
S im mt ct mc nh ca v nhit vt liu phc hp nhiu tng l 3 S im mt ct
n tng ca tt c cc tng bt buc nh nhau
iu kin bin v ti trngiu kin binTrong phn tch ng sut, mi mt t do u
c mt i bin: chuyn v -lc tc dng hoc phn tc dng Di trng thi mc nh
chuyn v l cha bit, lc l bit. Trong phn tch truyn dn nhit, i bin ny
l nhit --- t sut nhit (dng nng lng ca n v thi gian) Di trng thi mc
nh nhit l cha bit, t sut nhit l bit. -- T sut nhit bit = 0, tng ng
vi iu kin bin cch nhit; -- Cha c dng nng lng bn ngoi vo hoc ra im
nt. My loi iu kin bin nhit v ti trng nhit trong ABAQUS 1. Nhit mc
nh trn vi im nt no , *BOUNDARY, t do 11 2. T sut nhit q mc nh trn
vi im no hoc trn b mt no hoc trong th tch *CFLUX, *DFLUX, *DSFLUX
3. iu kin tng bin (film) trn vi im no hoc trn vi b mt no *CFILM,
*FILM *SFILM 4. iu kin bc x trn vi im no hoc trn vi b mt no
*CRADIATE, *RADIATE, *SRADIATE 5. iu kin bin t nhin (mc nh)
iu kin bin v ti trng1. Nhit mc nh Gi tr nhit bt bin*BOUNDARY
TNODE 11Tp im nt t do th nht
11 t do cui cng
500Nhit
Nhit thay i:
*BOUNDARY, AMPLITUDE = amp-1 TNODE 11 11 500Bin nhit
T
Khng ch ng cong bin nhit amp-1
1
500
0
1
t 0
1
t
ng cong bin
Nhit thay i
Phn tc dng ca nhit l t sut nhit (nhit nng i vo im nt c nhit mc
nh vi mt sut lu thng) Bin xut: RFLn
iu kin bin v ti trng2. Lu lng nhit mc nh (t sut nhit) Lu lng
nhit tp trung im nt (cng vi t do 11) thng qua t kha *CFLUX gn*CFLUX
AMP= amp-1 FNODE 11 30Gi tr tham kho t sut nhit
u vo c th tham kho 1 ng cong AMPLITUDE, t sut nhit u vo c th
thay i theo thi gian. Bin u ra CFLn c th phn nh gi tr hin ti ca im
nt *CFLUX.
Lu lng nhit phn b thng qua t kha *DFLUX hoc DSFLUX gn *DFLUX c
th gn trn mt hoc khi *DSFLUX ch c kh nng gn trn mt*DFLUX AMP= amp-1
ELHOL S1 300
*DSFLUX AMP= amp-1 SHOL S 300
q
iu kin bin v ti trng3. iu kin tng bin (film) -- Mt loi iu kin
bin thng gp nht trong truyn dn nhit l mt khi lng tng nhit hoc gim
nhit p st b mt t do -- T kha *CFLIM, *FILM *SFILM dng nh ngha iu
kin tng bin -- H s tng bin h l 1 tham s u vo ca ABAQUS, JL-2T-1q-1
-- Tnh quan trng ca h s tng bin: Tham s ny nh hng ln n kt qu truyn
dn nhit in hnh, h l hm s ca s Reynold cht lng v nhit lu thng, nhng
cng lin quan n tnh trng b mt nh th bn v phng v, v vy rt kh c trng
ha. Thng thng cn phi th nghim xc nh h.nh ngha h
qKhi lng, nhit
*FILM PROPERTY, NAME = H1 11.6E-6, 40 14.2E-6, 60 19.3E-6, 80h l
hm s ca nhit
Film, coefficient h
iu kin bin v ti trng3. iu kin tng bin (film) *CFILM gn trn im
nt*CFILM NODESET 100. 450 2.3E-3Din tch Nhit h
*FILM di trng thi hai chiu gn trn cnh phn t, di trng thi ba chiu
gn trn mt phn t*FILM ELSET F3. 450 2.3E-3Nhit h
*SFILM di trng thi ba chiu gn trn mt phn t*FILM SURSET F. 450
2.3E-3Nhit h
iu kin bin v ti trng4. Bc x hng mi trng Mt loi iu kin bin khc
trong truyn dn nhit l bc x khi en*CRADIATE
q = -A(T4 Te4)
*CRADIATE gn trn im nt NODESET 100. 450 0.1 Emissivity0~1
*RADIATE gn trn phn t*RADIATE ELSET R1. 450 0.1
M mt phn t *SRADIATE gn trn mt*CRADIATE SURSET R. 450 0.1
nh ngha iu kin bin bc x cn phi nh ngha hng s Stefan-Boltzmann v
khng tuyt i*PHYSICAL CONSTANTS, ABSOLUTE ZERO = -273.16 STEFAN
BOLTZMANN = 5.6697E-8
iu kin bin v ti trng4. Bc x hng mi trng T sut bc x emissivity l
mt loi b mt nh c nhiu ch tiu tim cn khi en l tng Mt vi t sut bc x
vt liu thng dng: Commercial aluminum sheet: 0.09 Heavily oxidized
aluminum sheet: 0.2 Polished gold: 0.02 Rusted iron plate: 0.6
Polished iron plate: 0.07 Turned, heated cast iron: 0.44 Type 301
stainless steel: 0.58 Red brick: 0.93 Black shiny lacquer on iron:
0.88 White vamish: 0.09 Water: 0.95
iu kin bin v ti trng4. Bc x hng mi trng Nhit vt cao, hin tng bc
x vt cao C cn hay khng xem xt iu kin bin bc x Te = Room temp (23oC)
h = 10W/m2/oC T sut bc x =1 Heat flux
Film
Radiation 0 100 Surface temperature 200
iu kin bin v ti trng5. iu kin bin t nhin Di nhit ty cha nh ngha
dng nhit ng thi cha c b mt ngoi dng nhit, iu kin mc nh l thng qua
q=0, tc l cha thng qua dng nhit b mt: iu kin cch nhit l tng y l iu
kin bin t nhin, dng khi gn iu kin bin i xng, nh Nhit ngun nhit bn
ngoi 800oC
Nhit ngun nhit bn trong 400oC
V d thc t phn tch trng thi n nhTruyn dn nhit hai chiuD C
Conductivity = 52W/m/oC Film coefficient = 750W/m2/oC Boundary
conditions: = 100oC C along AB Heat flux = 0 along DA Convection to
ambient temperature of 0oC along BC and CD Objective: Find q at E
Target solution: 18.3oC at E
1.0 E 0.5 y A x B 0.2
nh ngha t sut truyn dn nhit nh ngha h s chuyn nhit film
iu kin chuyn nhit
iu kin bin
Phn tch ng sut nhit
Qu trnh phn tch ng sut nhit-- ABAQUS cung cp 3 loi chng trnh phn
tch ng sut nhit: 1.Phn tch ng sut nhit ngu hp tun t, phng php thng
dng nht ng sut l do tn ti trng nhit lng to thnh, ng thi qu trnh gii
nhit khng c quan h vi trng thi ng sut, cng c th ni l ng sut ph thuc
vo nhit sinh ra cn nhit khng ph thuc chuyn v. Cn phi chy hai loi
phn tch: u tin phn tch truyn dn nhit, sau ly kt qu nhit phn tch ng
sut dn nhit. Kt qu phn tch nhit, nu nhit (hm s ca v tr v thi gian)
c a vo phn tch ng sut, xem l mt trng nh ngha trc. 2.Phn tch ng sut
nhit ngu hp hon ton ng sut ph thuc vo trng nhit ng thi nhit cng ph
thuc vo trng ng sut. Ch cn chy mt loi phn tch. 3.Phn tch cch nhit
Phn tch ny l m phng bin hnh c gii sn sinh nhit lng cc b, nhng thi
gian rt ngn, truyn dn nhit khng r rng Tt c nhit tng thm l ti ni pht
sinh cc b vt liu, ng thi ch nh hng thuc tnh c gii ca im vt liu cc
b.
Phn tch ng sut nhit ngu hp tun t-- Trong phn tch truyn dn nhit,
nhit l i lng cha bit nhit gii trng
-- Trong phn tch ng sut, chuyn v l lng cha bit Nhit ca im nt xem
l ti trng ngoi bit sn sinh bin dng nhit:
th = ( I )-- i vi bin dng tnh ton phn tch tnh: gii ng sut:
mech = th
= D( ) mech
Nh vy, trng nhit thng qua phng thc di y nh hng trng c gii: gin n
(nn co) nhit vi thuc tnh c gii c lin quan n nhit
Phn tch ng sut nhit ngu hp tun t-- Gin n nhit Di trng thi tng
nhit mt khi cha rng buc, thng thng c th pht sinh gin n th tch, nhn
t c trng gia bin dng v nhit xem l h s gin n nhit (Coefficient of
Thermal expansion, CTE) CTE c th nh ngha lin quan n nhit , cng c th
l cc hng ng tnh hoc cc hng mc d tnh S dng *EXPANSION nh ngha
CTE*EXPANSION,TYPE=ISO,ZERO=20 1.0E-6,100,1 1.5E-6,200,1
2.0E-6,100,2 2.5E-6,200,2
Cng thc tnh ton:
th = ( )( 0 ) ( I )( I 0 )0: Nhit tham kho I, Nhit ban u CTE tng
chm theo nhit tng
