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Bi tp thy lc i cng
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Nguyn Thnh Trung 2461.53 Tr. 1
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Nguyn Thnh Trung 2461.53 Tr. 2
BI TP THY LC I CNG
H v tn: Nguyn Thnh Trung
Lp: 53CG2
MSSV: 2461.53
Bi tp chng 2: Thy tnh hc
Bi 2.4 : Theo bi ra ta c s nh hnh v:
p sut ti im A l:
p sut ti im B l: Ly (1) (2) ta c chnh p sut ti A v B
Mt khc ta li c: ; Vy ta suy ra c:
Du - ngha l
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Nguyn Thnh Trung 2461.53 Tr. 3
Bi 2.11 :
Xt p sut d ti 2 im A v A thuccng
1 mt ng p 0-0: Vi: T ta c
Hay Theo hnh v trn ta c:
Bi 2-12 (28)
p sut d ti im A c tnh bi:
Xt p sut d ti 2 im C v C thuc cng 1 mt ng p 0-0:
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Nguyn Thnh Trung 2461.53 Tr. 4
M:
Hay : Bi 2-23:
Ta tnh cao trng tm ca tit din ca van:
Xt p lc do khi nc c cao h1 gy ra ln ca van:
Ta c:
Nu ta chn trc Oz nm nghing theo mt vi hng nh hnh v, im O nm timt thng lu th v tr ca im t lc P1 s tnh theo cng thc:
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Vi
T ta c :
Xt p lc do khi nc c cao h2 gy ra:
cao trng tm phn tip xc vi nc ca ca van l:
Din tch mt tip xc vi nc l:
Do ta c:
im t lc l: (xt trong h trc Oz)
Trong h trc Oz th im D c ta :
Vy t ta c c p lc ca ton b nc tc dng ln ca van l:
ln:
im t lc c xc nh theo phng ph p xc nh im t khi c hp lc 2 lc song song:
Khong cch gia 2 im t D v D l:
Gi a l khong cch t D n im t G ca hp lcP v b l khong cch t D n im t G ca hp lc P.
Ta lp c h phng trnh sau t phng trnh cn bngmoment quanh O
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Gii ra ta c:
T ta xc inh c im t G ca hp lc P cch O mt on:
Bi 2-24:
Xt p lc P1 do khi nc thng lu gy ra
Chn trc AZ nh hnh v
Din tch phn nc tip xc vi nc l:
Trng tm c cao: p lc:
im t: T ta suy ra khong cch gia D v O l:
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Xt tng t cho khi nc h lu ta c:
Khong cch gia D v O l:
Xt iu kin cn bng momen quanh O:
Van bt u m khi:
Gii phng trnh trn ta suy c gi tr ca
Bi 2.27:
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Nguyn Thnh Trung 2461.53 Tr. 8
Nhn trn hnh v ta c nhn xt rng h c xu hng quay quanh im K ( nm chn ca trchng). Do vy h cn bng th lc P do nc tc dng vo thnh van phi c phng i qua Khay im D chnh l im t lc ca P
Chon trc ta Oz nh hnh v:
Ta im t lc P c tnh theo cng thc:
Vi:
l phn din tch phn mt tip xc vi nc.
: l moment qun tnh ca mt tit din tip xc vi nc
l cao ca trng tm tit din tnh t mt thong
T ta suy ra: (1)Mt khc theo hnh v ta thy:
; (2)
T (1) v (2) ta suy ra gi tr ca H=1,04(m)
Ta tnh c ln ca P l: P=24503,9 (N) = 24.3 (kN)
Bi 2.39:
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Bi tp chng 3:
Bi 3-26:
Chn mt O-O l mt phng chun so snh:
Vit phng trnh Becnulli cho mt ct ti 2-2 v 3-3 vi gi tr p sut d ta c:
Ta c th b qua gi tr tn tht ct nc D2/2 rt nh nn ta c th b qua
Vit PT nh lut Becnulli cho 1-1 v 4-4 ta c:
Thay (2) vo (1):
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Vi v4 v v1 l:
Ta c : Vy lu lng nc clo trong ng l:
2) Lu lng nc Clo trong ng l 0.5 l/s
T (*) ta c:
3)
T (*) ta c:
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Nguyn Thnh Trung 2461.53 Tr. 11
Bi 3.27:
Chn mt chun 0-0 nh hnh v
Vit phng trnh Becnulli cho m t ct ti 1-1 v 2-2 vi gi tr p tuyt i ta c:
M:
; n ; n
T ta c c gi tr ca v:
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Bi 3.35:
Chn mt chun 0-0 l mt i qua y di ca van x nh hnh v:
Vit phng trnh Becnulli cho m t ct ti 1-1 v 3-3 vi gi tr p sut tuyt i ta c:
T ta c:
Vy:
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Bi 3.36:
Vit phng trnh nh lut Becnulli cho mtct 2-2 v 3-3 vi mt phng so snh l mt0-0 nh hnh v:
Vi cc gi tr:
Tn tht ct p s bng tng cc tn tht dc ng v cc b: (do tn tht dc ng t l vi chiu di)
Vit phng trnh nh lut Becnulli cho mt ct 2-2 v 1-1 vi mt phng so snh l mt 0-0:
V ng o p
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Bi 3.39:
Chn mt O-O l mt phng chun so snh:
Vit phng trnh Becnulli cho m t ct ti 1-1 v 2-2 vi gi tr p tuyt i ta c:
T ng o p ta c phng trnh:
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Thay (2) vo (1) ta suy ra c:
Vi:
Lu lng nc l:
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Bi 3-41:
Chn mt phng chun O-O nh hnh v
Vit phng trnh Becnulli cho m t ct 1-1 v 2-2 vi p sut d:
Phng trnh lin tc p dng cho knh ti on u v on thu hp;
Thay (2) vo (1) ta c:
Sau khi thay s vo v gii ra ta c gi tr ca v2 l:
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Bi 3.46:
Phng trnh ng lng cho on dng chy c gii hn bi 2 mt ct 1-1 v 2-2 i vi trcchiu s nm ngang hng t tri sang phi:
Coi:
Lc ngoi gm c:
Lc khi trng lng ca on dng chy l G tuy nhin Gs = 0
Lc mt:
Lc ma st trn thnh ng. Tuy nhin ta ch xt 1 phn ng ngn nn coi lc ma st l nhnn c th b qua
p lc nc xung quanh tc ng ln mt ng 1-1 v 2-2:
Phng trnh inh lut Becnuli cho 2 mt 1-1 v 2-2 vi mt O-O l mt chun:
Tuy nhin do Q v l khng i nn:
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Nguyn Thnh Trung 2461.53 Tr. 18
Vit li phng trnh trn ta c :
Goi phn lc ca van tc ng vo dng nc l R
Ta c:
Gi tr R = gi tr p lc tc dng ln ca van: Vi:
p dng thay s: P=112.5 (kN)
Chng IV: Tn tht ct nc trong dng chy
Bi 4-14:
S Vi nc c nhit Vy ta c Vy nc chy ri
Chiu dy ca lp mng st thnh
Ta thy:
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Nguyn Thnh Trung 2461.53 Tr. 19
Nn nc chy ri trong khu thnh trn thy lc
Bi 4-20:
Tn tht dc ng hd tnh theo cng thc Darcy:
Ta gi s rng nc trong ng chy khu sc cn bnh phng
Ta tnh C theo cng th c Maninh: Vi
(tra bng vi ng thng)T ta c : Mt khc ta c:
Thay vo cng thc hd:
Vi
ta kim tra li iu kin chy ri trong khu sc cn bnh phng
Ta kim tra li iu kin chy ri trong khu sc cn bnh phng
y
Vy gi thit ng.
Lu lng nc chy qua l:
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Bi 4.26:
Vit
phng trnh nh lut Becnulli cho mt ct 1-1 v 2-2 vi mt phng so snh l mt 2-2:
Tn tht dc ng:
Ta xt:
Vy nc chy ri
Xt:
Ta c: Chy ri trong khu sc cn bnh phngCng thc Niucrat
Tn tht cc b ti ch vo ng l:
Tn tht cc b ti ch m rng ra t ngt
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Vy ta c:
Vy chnh cao: Bi 4.30:
Vit phng trnh nh lut Becnulli cho mt ct 1-1 v 2-2 vi mt phng so snh l mt O-O:
Tuy nhin do ta b qua tn tht dc ng nn: Ta tnh ton cc tn tht cc b:
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Nguyn Thnh Trung 2461.53 Tr. 22
Thay cc gi tr trn vo phng trnh Becnuli:
T ta tnh c lu lng:
v ng o p ta xt them gi tr :
Bi 4.31:
Ta tm lu lng xng t a m phu cho php chyqua. Xt phu trng thi ngp xng hon ton.
Vit phng trnh nh lut Becnulli cho mt ct 2 2v 2-2 vi mt phng so snh l mt 2-2:
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Lu lng ti a cho php qua ph u m phu khng b trn l:
Hay:
Xt b cha
Vit phng trnh nh lut Becnulli cho mt ct 1 1 v 1-1 vi mt phng so snh l mt 1-1:
Trong tng ng l cc tn tht cc b ti v tr I, II, III trn hnh v
Thay vo phng trnh Becnuli trn
Do lu lng ti a l Q=4.9(l/s) nn vn tc ti a trong ng l:
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Vy ta c:
Bi 4.33: