TAM CHE CO PHlTOlVG PHAP SO XAC BEWi HE SO KHI BONG MAT Dirdl CtA

XAC BEWi HE SO KHI BONG MAT Dirdl CtA TAM CHE NANG CO L 6 BAJVG PHlTOlVG PHAP SO

I S . VO T H A N H TRUNG Vien KHCN Xay dung

GS. YUKIO TAMURA, PGS. AKIHITO YOSHIDA Trudng Dai hoc Bach Khoa Tokyo, Nhat Ban

Tom tat: Bai baa trinh bay phuang phap tinh toan bang so dua tren phuang thnh Bernoulli md rong de xac dmh he so khi dong mat dudi cua tam che nang cd Id vdi hai do rong ip (ti le giita dien tich ciia cac io rong va dien tich cija tam) va cac hudng gid khae nhau td cac ap luc mat tren va ap iuc xung quanh. Cac ket qua cua thi nghiem trong ong thoi khi dong vdi hai md hinh cd tile 1:50 cua nha thap tang vdi cac tam che nang cd Id phil hgp tot vdi cac ket qua tinh toan td phuang phap nay.

TU khoa: Tinh toan so, phuong thnh Bernoulli ma rdng, tam che nang, nha thap tang, ong thoi khi ddng.

l.Datvande

Cac tam che nang duoc lap dat tren cac mai la loai ke't ca'u mdi cho viec giam su hap thu nhiet cho mai. Tai trpng gid tie dgng I6n cac tam nay dugc xae dinh tU su khic nhau giira ap luc gid mat tren dugc tao ra do ddng gid tie dung len cdng trinh va ap luc mat dudi, phu thudc vao dp ring ciia tam chan nang, cau tao giUa tam chan nang va mai.

Nhung dd'i vdi he so khi dpng mat dudi khdng d i xac djnh dugc trong cac thi nghifm trong ong thdi khi ddng do khd khan trong viec che tao md hinh thi nghiem. Do dd, mpt phuong phap tinh toan bang sd dugc diing de tinh toan he sd khi dpng mat dudi cua tam che nang.

Mpt sd nghien ciru trudc diy ve ap luc gid trong nhu: Holmes [1] da tie'n hanh nghien cUu ap luc gio trong eho nha tha'p tang vdi Id hd 6 mat ddn gio va khuat gio bang dng thdi khi ddng va phuong phap tinh toan sd. Saathoff va Liu [2] da gidi thieu phuong phap dung phuang trinh Bernoulli md rOng de xac djnh ap luc trong do gio giy ra trong nha cd mdt phdng vdi mgt l5 hd va dugc md rgng dung cho nha cd nhieu phdng vdi nhieu Id hd. Ly thuyet nay cd the dugc diing de tinh toan su thay ddi ap luc trong theo thdi gian cho tUng

phong cQa cong trinh co nhieu phdng dudi cac dieu kien khae nhau.

Trong bai bao nay, phuong phap dung phuang trinh Bernoulli md rgng (Saathoff va Liu [2]) dugc ap dung cho tinh toan. Ket qua tinh toan nay dugc so sanh vdi kdt qua thi nghiem.

2. Thf nghiem ong thoi khf dong

MOt mO hinh nha tha'p tang (200 mm cao (H) x 470 mm rdng (6) x 710 mm dai (D)) vdi mai cd cac tam che nang rdng dugc thi nghiem tai dng thdi khi dgng (cd kich thudc mat cat ngang 2,2 m rgng x 1,8 m cao) ciia Trudng Dai hgc Bach khoa Tokyo, Nhat Ban (xem chi tiet trong bai bao [3]). Ti le md hinh v i van tdc gio tuong irng la 1/50 va 1/4. Dja htnh dang III (vdi chi sd mu cua dudng profile van tdc trung binh la 0,2 - tuang duang vdi dang dia hinh B cCia TCVN 2737-1995) cua AIJ-RFLB (2004) [4] dugc diing cho cac thi nghiim nay.

Do rdi tai do cao 200 mm (tuong duong 10 m trong thuc te) la 0,26 va van tdc gid trung binh la 7 m/s. Thi nghifm dugc tien hanh vdi 17 hudng gio khae nhau (tU 0° ddn 360° vdi 30° cho tUng budc va 4 hudng gio: 45°, 135°, 225° va 315°).

Md hinh thi nghiem cd 16 tam che nang 6 tren mai vdi mdi tam co 128 Id, trong dd cd 4 tam (A, B, C va D) dugc bd tri cac dau do ap luc (hinh la). Cac tam che nang cua md hinh 1 (do rdng 5%) va md hinh 2 (do rdng 10%) vdi cac 10 co dudng kinh tuang urng la 2,8 mm va 4 mm. Khoang each giii'a cac tam che nang va dinh ciia mai ton la 1 mm (hinh 1b). Md hinh tam che nang A cd 39 dau do ap luc d mat tren va 39 dau do ap luc 6 mat dudi. Ngoai ra, xung quanh tam A cd bd tri 32 dau do ap luc (hinh Ic). Cac hieu irng ciia he sd Reynolds l§n ddng gid qua cac Id tren tam cung dugc bd qua. Tan sd lay mau cua thi nghiem la 781 Hz va tan sd Igc thdng thap la 300 Hz. Hinh 2 the hien mgt sd hinh anh cua md hinh thi nghiem trong dng thdi khi dgng.

Tap clii KHCN Xdy dicng - sd212011

KHAO SAT - THIET KE XAY DUNG

(a) Kieii thuoc mo hinh

L5 DaudoaplLfc Tam che nang Q

'Xfjjo-^-^jr//-jr/.cr^A'zjxfj:^^jjy. ••^(io'-'^^ ';j^//-v/./: •ov/zf^/^j.n r/yy/yj/jy^ W^^

fls-zi^. ^/ryzzyyy/TzyyyyX ir. fyyyji'?^ J/yyyjL . '^yyy/y..vyy/yj£h n </7yyyy/yyyyy//^. ^vyA

\ \ •- x i u c , , X V - , \ - \ ; \ , •. N

CaciS Cac dau do ap

I L/C

K / \ ,'^\, / \ ^ ° ' * / x ••*

• •

160 . „ , (b) Chi tiet mat cat mai cue mo hinh thi nghiem (c) Mat bang bo th dau do ap luc va lo cho tam che nang A

Hinh 1. Mo hinh thi nghiem (tat ca cac dan vi bang mm)

. ~-_-^_,_^^. ^ _ ^

^ ^ i ! I I » I'll* l?l"*itiS_

-. e «*(

(a) Mo hinh thi nghiem (b) Can canh cua mo hinh tam che nang Hinh 2. Mgt vai hinh anh ciia mo hinh thi nghiem trong ong thoi khi dong

3. Md hinh tinh toan

Mo hinh tinh toan dugc the hien tai hinh 3. Khdi tich giua tam A va mai dugc chia thanh 256 khdi tich nhd (khdi ao), mo hinh tuong t u n h u nha co nhieu phong (hinh 3) ma trong do ap luc gio mat dudi tam A nhu ap luc ben trong va ap li/c gio mat tren tam A nhu ap luc ben ngoai.

Khi gia thiet ddng khi qua cac Id hd n h u la ddng khi phut thi phuong trinh lien he giua ap luc mat tren va mat duoi ciia khdi tich nho / la:

2. a Uo., (1) 0 day Pa - khdi lugng neng ciia khong khi; I,, - chieu dai dao dong quy ddi cua dong khi (air slug) tai Id ho / (/e,, ~-1 + 0.8 JmJ- / 4 ); P,, - ap luc ngoai ciia khdi tich nhd / ; P, - ap li/c trong cua khdi tich nhd / ; U,, - ap van tdc cua dong khi qua Id hd /; ju - do nhdt cua khi; d - duang kinh cua Id hd; va t - chieu day ciia tam. Ky hieu ' tren cac bien the hien phep vi phan theo thdi gian.

Tap chi KllCN Xdy dmiii - sr'i2/2011

Cac lo - r ' Khd'i tich nho Duang phan chia giua cac"'-- khoi tich nho

o i i

i o i

'°\ • l 1 ot

i 0 i O ! !

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1 O i i O i 1 o 0 ' ! O ! ! O '

1 O i i O i 1 0 O ' ! 0 ! ! O '

l o t 1 b'T' 1 O

0 1 ! 0 ! ! O ' 1 O i i O i 1 O 0 1 ! 0 ! ! O '

lot i O t 1 0

0 ' ! O ! ! O 1 1 O i i 0 1 1 0

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lot 1 o |

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lot i o'

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lot 1 o"

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lot 1 0

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1 100 1

160

(a) Mo hinh tinh toan cho tam che nang

Tiu

> /+2; > /+3 :'R>

il

\ J

A.

\-t A ^.u

• • - - A - - • • A - •

:Vu.3

u,.-

'l.ltl

;+1 P..

Dudng phan chia giUa , '' cac khd'i tich nhd

A

i

-JV- - - - - A - A

* s ^ _ s , ^-.^0 ,

Tam che nang

% i^;.'.\^:;<;^\":;,-i •.••^^".^::t".i:,\'-'S^';.-^,.v:'S.-.':.'^s^.>:"

^n

Mat cat (b) Mo hinh tinh toan cho kho'i tich nho thir /

Hinh 3. Wo hinh tinh toan (tat ca cac Qan vi bang mm)

Sd hang cudi ve phai ciia phuang trinh 1 the hien su giam ap luc do ma sat (phuang trinh ma sat trong dng AP

/ A / A M . . (J..dp

= / ). He sd ma sat f = 64/Re la he sd ma sat Darcy cho dong deu (Re la so Reynolds = - - - ' ).

( 1 2 ' //

Thay vao phuang trinh ma sat trong dng, rut ra AP = - -, - U^,.

d

Phuang trinh lien he giua ap li/c be mat dual ciia khdi tich nhd / va khdi tich nhd (;+1) la:

Ai'/.i-i 1 ' ^ (,/i 1 ~ ' i '^n 1

1 1 1 0

I 2 a VI' (2) 6 day /,„i - chieu dai dao dgng quy ddi cua dong khoang each giifa tam che nang va mai; g - khoang khi (air slug) tai Id ha giua khdi tich nhd / va (/+1); P„ each giUa tam che nang va dinh ciia mai; s - chieu P„, -ap luc trong ciia khdi tich nhd / va (;+1); K- he dai^cua khdi tich nhd; w - chieu rdng cua khdi tich

\2 nhd va L/,,+ , - van tdc ddng khi giua cac khdi tich nhd sd hao hut do Id hd (= 2.78 aw 0.6 46); a - 'va(/+1).

Tap clii KllCN Xdy dung - sn 21201!

KHAO SAT - THIET KE XAY DUNG

Sd hang t h u t u d ve phai ciia phuong trinh 2 the hien SLf mat ap lire do Id h d giua cac khdi tich nhd / va (/+1).

Sd hang cudi d ve phai ciia phuang trinh 2 the hien s u mat ap luc do ma sat ciia be mat dgc theo chieu dai ciia tam. Day la phuang trinh cua s u mat ap luc cho

J r2

dong deu giua cac tam song song AP = f "^-^i-..

2a 2

He sd ma sat f = 48/Re la he s d ma sat cho dong deu L', , | M ' p ,

(Re la so Reynolds = ). Thay vao phuang M

1 O

trinh ma sat trong dng, riit ra AP = - - - — L/,,+i.

a w

Phuang trinh lien he giira ap luc be mat dudi ciia khdi tich nhd / v a khdi tich nhd (/+3) la:

P-Ju*i u*3 P. -P. P„U.,JU„,,\ ^ ' ^ ^ , . 3 ( 3 ) a .s

6 day sd hang cudi d ve phai ciia phuang trinh 3 the hien s u mat ap luc do ma sat ciia be mat dgc theo chieu rgng ciia tam.

Ngoai ra, vdi gia thiet dong khi co the nen dugc trong khdi tich nhd / dudi cac dieu kien doan nhiet, mdi lien he giua ap luc be mat duOi va van tdc cua dong khi dugc the hien qua phuang trinn lien tuc sau:

P, = {nPM{Ae,Oo, + A,,P„+A^,U.,, A>IU,:M - A : « M : « ) (4) 0 day n - - 1 . 4 cho dong khi doan nhiet; P^ - ap luc khong khi; V, - the tich ciia khdi tich nhd / ; va A... - tie't dien ciia Id h d giua cua khdi tich nhd (') va ciia khdi tich nhd (••).

Cac phuang trinh vi phan thuOng bac nhat cho ap luc ben tren tai cac Id h d va ap luc ben duOi trong cac khdi tich nhd dugc xac dinh tU cac phuang trinh 1, 2, 3 va 4. Do do, mpt tam che nang co mpt he 1056 phuong trinh vi phan thuOng. He phuang trinh nay dugc giai dua tren phuang phap Runge-Kutta bac 4 va ngon ngur lap trinh Delphi. C a c ket qua tinh toan d day dugc so sanh vol cac ket qua thi nghiem.

4. So sanh c i c ke't q u a b a n g tinh toan va bang dng thdi khi d g n g

Trong bai bao nay, cac tac gia da tinh toan cho ap luc dual ciia t a m A (d viing goc) cho hai do rdng <^ - 5% va 10% vai 17 huOng gio khae nhau ( t u 0° den 360°

vdi 30° cho tUng budc va 4 huOng gio: 45°, 135°, 225°

va 315°). Hai mo hinh tinh toan dugc sir dung:

- Mo hinh tinh toan 1 sir dung cac phuang trinh 1, 2, 3 v a 4 ;

- Mo hinh tinh toan 2 sir dung cac phuang trinh 1, 2, 3 va 4 nhung bd qua s u giam ap suat (thanh phan thU 4 trong phuang trinh 2 va cac thanh phan cudi trong cac phuang trinh 1, 2 va 3).

Cac gia tri tU thi nghiem va tinh toan thay ddi theo thai gian ciia cac he s d khi dgng mat tren va mat duOi (Cp„ va Cp) ciia cac dau do ap luc so 14, 30 va 34 (hinh 4) cho tha'y cac ket qua tinh toan tU mo hinh tinh toan 1 CO ke't qua tdt han m o hinh tinh toan 2. T u do cho thay rang cac thanh phan lam giam ap luc trong cac phuang trinh CO vai tro quan trgng trong viec tinh toan cac he sd khi dgng cua mat dudi C^i.

.14

.30 .34

(a) Vi tri cua cac dau do ap luc 14,30 va 34 ciia tam A

0.3 0

Cp„ (Thi nghiem)

' ''•..' • •[ I '.• ' • ; • ' '. • ' / " ' • , ' f- V .

-0.9 -1.2 -1.5

,' I , . " •/ C„,(Thi ngliiem) •' i ' \ ' \ ' ,'

• . ' • . / '. I • • '

^• \ . i :

C„,(Md hinhl) C„, (Mdhinh 2) •/

Gio - 700 800 900 1000 1100 1200 1300 1400 1500 So diem du lieu

(b) Dau do ap luc 14 |

Tgp chi KHCN Xdy difn^ - so 2/2011

-1.5

, V ' \ •••' ', ; \ Cp, (Thi nghiem)

\ ' Cp,(M6hinhl) \ I c),(Mohinh2)

Cp„ (Thi nghiem)

-1.2 -1.5

C,{M6Lh^)^'•; C, (Mdhinh 2) C, (Thi nghi N

2500 2600 2700 2800 2900 3000 3100 3200 3300 So diem dif lieu

(c) Dau do ap luc 30

700 800 900 1000 1100 1200 1300 1400 1500 So diem dQ lieu

(d) Dau do ap luc 34

Hinh 4. Su thay doi theo thdi gian cua cac he so khi dong mat tren va mat dudi (0^, va CJ cua tam A vdi do rdng <^=5%va hudng gid 6= 45°

Bieu dd phin bd cac he sd khi dgng mat dudi trung binh va lech chuan (C^, va c^,) cua tam A cho do rdng ^ = 5% va hudng gio 0=0° dugc the hien d hinh 5; chi cho su khic nhau nhd giffa hai ket qua va dieu nay cho tha'y hieu qua ciia ly thuyet de tinh toan cac he sd khi dgng mat dudi. Tuong t u ddi vdi tam A co do rdng <z> = 10%, ket qua tinh toan cung phu hgp vdi ket qua thi nghiem tai hudng gio 6'= 0° (ket qua khong thd hien d d i y ) .

Thi nghiem

Thi nghiem

. . -•,, % • • -

1, '' ,-- " o / , - ,

' or- •

t l l l 'T-, u .:, .. Iff, ,

(,•.<>. •

^

Mo hinh 1

M

fr-..--1! ^ M6 hinh 1

. 1

L ° c,

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i '

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\ • >

c

- ' : ^ • -

o \

\- ' • • ' /

...\ c o ^

.>P'':;'T

06

(a) He sd khi dong trung binh Cp, (b) Dp lech chuan ciia he so khi dong C^, Hinh 5. Bieu do phan to cac he so khi dgng mat dudi trung binh va lech chuan (C iVac',)

cua tam A cho do rong i^=5%va hudng gid 0=0^

Su thay ddi theo thgi gian ciia cac he sd khi dgng 6 d i y Cp,gt) va Cp,Q,t) - cac he sd khi dOng tai diem tarn ciia mat tren va mat dudi {Cup{t) va 0^,(0) dugc j va tai thdi gian t b mat tren va mat dudi; Fy - cac dien

tich hieu dung cua diemy; N - sd cac diem do ap luc va F - dien tich mat ciia tam.

tinh toan theo cac phuang trinh sau:

Cupit) = f,(c^„{JJ)-Fj)lF

y=i

C,,{t) = Y^(c^,(j,t).F^)/F

(5)

(6)

7=1

Hinh 6 the hien su thay ddi theo thdi gian cOa cac he sd khi dgng tam mat tren va mat dudi [C^p va Qp) ciia tam A vdi dd rdng tp - 5% va hudng gio 0 = 45°.

Tir hinh ve cho thay cac ket qua tinh toan tif mO hinh tinh toan 1 phu hgp vdi cac ket qua thi nghiem.

Tap cfli KHCN Xdy dimg - sd 2/2011

KHAO SAT - THIET KE XAY DUNG

A-<'^ CUP (Thi nghiem)

-1.5

CLP (Mdhinh!)

^

i

^L/P (•••) Tam che nang

I C^ (+)

>

700 800 900 1000 1100 1200 1300 1400 1500

Hinh 6. S i f ffiay cfo; theo thdi gian cua cac he so khi dgng tam mat tren va mat dudi (C^p va Cu>) vdi dp rdng ip = 5% va hudng gid 9= 45°

Hinh 7 the hien su so sanh cac ket qua tU thi nghiem va tU tinh toan cho cac he sd khi dgng tam ciia mat dudi C^^pVdi cac hudng gio khae nhau. TU hinh nay cho tha'y:

- Ddi vdi do rdng <p = 5%, co su phii hgp gitfa ket qua tinh toan va ket qua thi nghiem. Tai cac hudng gio 0 tu 30° den 90° co su khae nhau nhd giOa 2 ket qua

(khoang 0,08 va 0,02 tuong irng choC,j.vaci,,), dac biet tai hudng gio 6 = 60°. Tai cac hudng gio khae thi su khae nhau la rat nhd;

- Ddi vdi do rdng ^ = 10%, cac ket qua tU tinh toan phu hgp vdi cac ket qua tU thi nghiem ngoai trU tai cac hugng gio 0 iii 30° ddn 90° (su khae nhau tudng irng l i 0,12 va 0,02 choQ^ vac;;,).

16~

-1.2 -1 -0.8 -0.6 -0.4 -0.2 0

II--4

Thi nghiem

Mo hinh 1 \

\ /.•'

0.4

0.3

^ 0.2 -

0.1 -

0 90 180 270

H u d n g gio 6'(do)

(a) He so khi dong tam trung binh C^j, (do rong ^- 5%) -1.2

:1 -0.8 1"^^ -0.6

-0.4 -0.2 0

360

Thi r

• ''v^^y

' ^ n

. !* \

>::..:4 / \ / ^ M6 hinh 1 \

k

- -

ghiem

^^

^ • ^ - '

* ..' ,

^r'

^ / ^

f

90 . 180 270 Hudng gio <9(dp)

360

(c) H6 so khi dpng tam trung binh C^ (dp rSng <p= 10%)

- fy \ Thi nghiem

. • • / ' * » . ^

/-'' \

i 'v.

• A

M 6 hinh 1 " •

X

,-<

/ '

y

\ - ^ - - ^

0 90 180 270 360

Hudng gio ^(dp)

(b) Op lech chuan ciia he so khi dpng tam c[p (dp rPng (/S = 5%) 0.4

0.3

O 0.2

'.r

0.1

r^,^ ^{M6 hinh 1}

\

Thi nghiem ,';*'

\

0 90 180 270 360 Hudng gio 6* (dp)

(d) Dp I6ch chuan cua h6 s6 khi ddng tam c'^ (dp r5ng(ii= 10%) Hinh 7. He so khi dong tam mat dudi trung binh va tech chuan (Cij, va C'j,) ciia tam A cho cic do rong (/> = 5% va cac hudng gid 6 8 Tqp chi KHCN Xdy dung - so 2/2011

1

Hinh 8 the hien cac phd nang lugng ciia cac he sd khi dgng tam mat dudi C^^cua tam A cho cac do rdng ^ 5% va cac hudng gio 6* = 0° va 45°. Ket qua tinh toan trung vdi ket qua thi nghiem, tham tri vdi cac tan sd cao.

CO

c 10^

10"

10"

10"

Thi nghiem

e

(J

s

Mo hinh 1 tan so

be rong ciia md hinh van tdc gio tai cao dp mai do lech chuan (d^) pho nang lugng

c

10"^ 10" 10"

10^

10"

10"

10"

Thi nghiem

ne/UH

10"' 10"^

(b) Hudng gio ^=45°

10 nB/U„

10"

(a)Hudnggi6 6'=0°

Hinh 8. Pho nang lugng cua cac he so khi dong tam mat dudi CipCita tam A cho do rong ^ = 5%va cac hudng gio 0=0'va 45°

5. Ket luan

Bai bao trinh bay phuong phap tinh toan bang sd dua tren phuong trinh Bernoulli md rgng de xac djnh he sd khi ddng mat dudi ciia tam che nang co Id vdi hai do rdng v i cac hudng gio khae nhau. Cac ket qua tinh toan cho tha'y su hieu qua cOa phuang phap nay.

Ldi cam on: Cac tac gia cam an Bo Giao due, Van hda. The thao, Khoa hgcva Cdng nghe Nhat Ban thdng qua chuang tnnh Global Center of Excellence 2008- 2013, da cap kinh phi cho nghien ciru nay. Xin chan thanh cam an Vien KHCN Xay dung - Bg Xay dung - Viet Nam da tao dieu kien cho tac gia Vu Thanh Trung dugc tham gia nghien cdu nay.

T A I L I £ U THAM K H A O

1. HOLMES, J.D., "Mean and fluctuating internal pressures induced by wind". Proceeding of 5th Internastional Con-

ference on \/Vind Engineering, Fort Collins, CO, 435-450, 1979.

2. SAATHOFF, P.J. AND LIU, H., "Internal pressure of multi-room buildings". Journal of the Engineering Me- chanics Division, June, 908-919, 1983.

3. VU T H A N H TRUNG, YUKIO TAMUfRA, AKIHITO YO- SHIDA. " Nghign cUu dng thdi khi ddng hpc 66 xac dinh len tai trpng gid len cac tarn che nang vdi cac dd rdng khic nhau". Tap chi Khoa hoc Cong nghe Xay dung, so 4/2009.

4. AIJ-RLB, AU Recommendations for Loads on Build- ings. Architectural Institute of Japan, 2004.

5. CHINO, N., IWASA, Y., MATAKI, Y., HAGIWARA, T., SATO, H, "Internal pressure of double composite exte- riors", Journal of Wind Engineering and Industrial Aero- dynamics, 38, 381-391, 1991.

Ngay nhan bM: 27/5/2011.

Tqp clii KHCN Xdy dimg - so 2/2011