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XUAT VACHCfNG MINH GlA THUYET KHOA HOC
T H A N H LUAN D I ^ MTRONG NGHIEN CCOJ QUA
T R I N H OOC BE T O N G T R E N BANRUNG
PGS.TS Tran Van Tuan NCS.ThS Luu Dut Thach Khoa Ca khi XSy dt/ng Trudng Dai hge Xay dt/ng
Tdm tat: BSi bao gidi thidu vide di xuat va chimg minh gii thuyit khoa hge thanh luan diim trong nghidn eiru quS trinh due hon hgp bd tdng bing ban rung, phuc vu eho edng tSe dSo tao vS nghidn eiru cua sinh vien vS hge vidn eao hge khdi nganh ky thuat
Summary: The article introduces a method of creating and demonstrating the scientifie hypothesis to become the theoretical point in the process of casting eonstruetion concrete by vibrating platform for supporting the study and scientifie research of students and post-graduate students in technical field.
L D A T V A N D E
Phuong phdp ludn nghien ctfu khoa hpc la ly thuyit v i phuong phap, da ch? ra rang: thuc chit cda mpt edng trinh nghidn cdu khoa hpc la chtmg minh mpt gia thuyit trd thanh ludn diem khoa hpc /1,2/. l a p hpp nhiiu ludn diim ed t h i trd thdnh mpt ly thuyit khoa hpe hodn chinh.
Gia thuyit Id mpt phdn doan ein phai chtmg minh bing eae luan ed. Trong logic hpc gpi phan doan la mdnh d i vd menh d i la cdu bieu thi mpt npi dung md ta cd t h i khing dinh la dung hay sai mpt each ro rang. Phdn dodn cPn Id tim mdi lien he gida hai hay nhiiu khai nidm (hoac thdng sd). Chtmg minh Id tim cac ludn cd cd t h i lap lai, ed the ehdng minh gia thuyit bang logic bien chtmg, c6 nghTa liy thiJc tien (thi nghidm, khao sdt...) Idm thude do chan ly. Vay NCKH edn Id qua trinh di tim chdn ly. Mot cpng trinh NCKH thudng la d i xuat gia thuyit khoa hpc ve ddi tupng vd chtmg minh tinh ddng (hay sai) cua cdc gia thuyit dd.
Gia thuyit khae vdi gia thid'L Gia thiet la diiu kidn gia dinh de nghidn cdu, cdn gia thuyit khoa hpe la mpt phdn dodn c i n phai chdng minh bang cdc luan ctr, gia thuyet thudng dua trdn Cd sd quan sat, khdng trai vdi cac ly thuyit khoa hpc da biet vd phai kiem chdng dupc. Vi du, da td lau tdn tai gia thuyit; "Su sdng xuat hidn trdn trai dat, nay sinh g dai dugng". Chd tich Hdi ddng khoa hpc sinh ly, Vien hdn lam khoa hpc Nga luri Natochin da bae bd gia thuyit ndy. Ong giai thich rang y i u td then chdt d i cac sinh vat xuat hien la tdng hpp protein td cdc axit nucleic, trong nudc bien cd chda natri ngdn can qua trinh dd. Tiip d i n ong khdng dinh; N i u trong dung djch ed natri thi he thdng nay sinh su sdng kh6ng hoat dpng md dai duong luPn c6 natri. Vdy gia thuyit trdn khong dung. Theo 6ng, de tdng hpp protein td cdc axit nucleic c i n cd kali, vdn cd day du trong d i t set. Vdy dng da d i xuat gia thuyit khae "susdng nay sinh trong eSc Idp dit set
20 TAP CHf KHOA HOC CONG N G H | XAY DUNG Sd02 -12/2007
ndng, nai tieh tu nudc". Vdy tiin thdn cda t i bdo hodn ch?nh cd t h i hinh thdnh trong vung nudc mua. Ong dd so sanh gia thuyet eda minh vdi kinh thdnh, theo dd, thupng d i nan ngudi d i u tien bing dat set.
Mdt gia thuyit ndi tieng khac, dd la gia thuyit giai thich ngudn gde vu tru cua con ngudi do nd Giao su Lisa Randall HI de xuit. Ba eho rang 'Trdn trai dat tdn tai khdng gian 5 chieu vS vu tru nhu mang 3 chieu, dao dpng tu do trong mpt khdng gian vd tan". Ly thuyit dua trdn gia thuyit ndy c6 nhiiu diiu chUa dupc chdng minh, nhung nd mang nhumg chudi tU tudng Idn rat logic, nd giai thich dugc eae hien tupng nhu; vi sao cd hien tupng cdc hat co ban biin mat tdm?
nd giii thieh dupe nguyen nhan cua vu nd Big Bang. Neu gia thuyit ndy dupc eong nhdn ehinh thdc, thi lan dau tidn thuyit tuong ddi eua Einstein bj bdc bd (Din nay thuyit tuong ddi cda Einstein chUa bao gid thit bai trong vide giai thieh cae k i t qua thuc nghiem). Ly thuyit nay se giai thich dupc hidn tupng thin giao cdch cam. Giao su Lisa Randall da dupc bau Id mpt trong nhiimg thidn tdi kiet xuat cda the ky 21.
Ngodi cdc vi du minh hoa trdn, trong ly thuyit xde suit thdng kd ngudi ta thudng de xuit vd chdng minh gia thuyit d i chap nhdn hode bac bd nd, nham kiem tra su phu hpp giua phdn phdi thue nghidm vd phdn phdi ly thuyet (chinh xdc).
Trong finh viic khoa hpc cdng nghd, h i u h i t ede edng trinh dupe tiin hanh bing eae phuang phdp khdc nhau nham tim ra cdc quy ludt cda dd'i tupng; do tinh khdng chdt che cua cdc phuong phdp da dp dung (vi du cd sd dung cdc phUdng phap khai trien chudi de tim nghidm, nhung khdng t h i chtmg minh dupc tinh hpi tu cda nghiem). Cudi cung d i u phai tiin hdnh chdng minh bing thUc nghidm. Dudi ddy, bdi bdo gidi thidu mdt sd vi du cu the dien hinh.
2. CAC GlA THUYET VE QUA TRINH DUC HON HOP BE TONG
O i n nay, van cdn tdn tai cdc cupc thao luan ve mo hinh eo hpe vd todn hpc v i trang thai cda hdn hpp be tdng khi rung, tdn tai cdc tranh luan ve gia thuyit eo c h i Idm chdt va chit lupng be mat ed'u kidn bd tdng 141.
Hidu qua rung phu thude vdo nhiiu y i u td: Mdt mat phu thude vao phdi lieu va tinh chit CO ly cda hon hpp, mat khae phu thudc vao dac diem tac dpng cda luc. V i tinh chit co ly hdn hpp bd tdng n i m giufa vat ctmg vd chd't Idng. Qua trinh phdt trien cdc gia thuyit v i cd c h i Idm chat hdn hpp be tdng ehia lam hai hudng:
- Hudng thd nhit coi hdn hpp bd tdng tuoi cd cau true nhu mang tinh the: Cac ndt Id hat edt lieu to, giiJra eae nut Id vda xi mdng cd tinh ddn nhdt. Gia thuyit ndy eho phep giai thich cac qua trinh luu biin xay ra trong hdn hpp bd tdng khi mng, cd nghTa khi rung ma sat trong hdn hpp giim nhanh tdi mdt gid trj xae djnh; ngdng rung, ma sdt tdng tde thi tdi gid tri cue dai. Xdc biin Id tinh chit cda hd cd c i u trdc mang tinh the, cdn cac dae tinh luu bien thay ddi do tac dpng co khi mang tinh thuan nghjch. Td gia thuyet thtf nhit cho phep dua ra y tudng kich rung cpng hudng cae hat cd't lidu cda k i t c i u djnh hinh cd djnh, ed nghTa cd the ehpn t i n sd mng hpp ly phu thudc vdo kich thudc cdt lieu. ThUc t i ehua do dUpc, ghi Suae dao ddng cpng hudng cda hat cdt lidu, do khdng dd life ddn hdi cda vifa xi mang cd lan kh6ng khi; mat khdc, do hao tdn ndng IUpng Idn khi rung Idm chat ndn khd ghi lai dupe hien tupng cpng hudng nay.
TAP CHf KHOA HOC C O N G N G H $ XAY DUNG Sd02 -12/2007 2T
- Hudng thd hai coi hdn hpp bd tdng tuoi cd tinh chit nhu mdi trudng lien tuc cd tinh ddn nhdt do ed lan bpt khi trong do. Td gia thuyit thd hai eho phep giai thich qud trinh lam chat cpt hdn hpp bd tdng c6 ehiiu cao Idn bang phuong trinh truyin sdng.
Gia thuyet thd hai kh6ng the giai thich cho viee rung lam chat hdn hpp be tong eo cdt lieu to. Vdi gia thuyet thd hai thi md hinh Vdigdt - Kenvil va Maxwell dupe sd dung rpng rai.
Phuong trinh luu bie'n trang thdi tmg suit Vdigdt - Kenvil cho cpt hdn hpp be tdng ed t h i
de • • •
bieu dien a = E.E + n. — ; trong dd E - Modul dan hdi; E- Bien dang; r}- He s6 nhot; a- ung suat.
dt
ds ds n Phuong trinh Maxwell cd dang; a + T . — = r\. — ; trong dd; T = — t d b i e n
^ ' dt dt E
Niu coi tinh chd't co ly cua hon hpp be tdng Id ddn nhdt thi tinh luu biin cd dac diim sau:
1. Dp b i n vtfng eua eau true dupe xae djnh qua lUe can trUpt hay dng suit trupt gidi han, niu Idn hon gia tri ndy thi c i u true djnh hinh bi pha huy vd hdn hpp be tong Id chat Idng ndng cd dd nhdt xac dinh.
2. Modul dan hdi ed gia tri tdc thdi d thdi diem tac ddng rung.
Dua theo gia thuyit thd hai, tac gia 16, tr 160 -179/ da trinh bay khd d i y dd ve md hinh co hpe, todn hpc cpt be tong rung vd trinh bdy k i t qua khao sat sU h i p thu ndng IUpng cda hdn hpp be tdng tren ban rung tuyin tinh nhd phin m i m Mathematiea. K i t qua nghien edu cPn trinh bay CO sd khoa hpc xae djnh khdi lupng gia tai quan tinh, dam bao cho Idp hdn hpp bd tdng trdn cung nhan du ndng IUdng tao hinh vd Idm chdt.
Hai gia thuyit neu tren, d i u khdng cho phdp ly giai vd dUa ra dupe mpt cdch dn dinh cac ehi dp lam vide hpp ly nhd't cua cac co c i u cdng tae may rung due ed'u kidn bd tdng. Bdi vdy, tdn tai gia thuyit thd ba dua trdn kinh nghidm. Od la gia thuyit v i Cudng dp rung hpp ly.
a) Khai nidm ve eudng dp rung hgp ly: Odi vdi dao dpng diiu hoa, thi gid trj cUdng dp rung dupc xae djnh nhu sau: I = A^.ro^; trong dd A Id bien dd rung, (m); ta Id t i n sd gde, (rad/s).
b) Npi dung ciia gia thuyit IS: Cac c h i dp lam vide cd cung gia trj I = A^.ra^ thi cdng mpt hidu qua rung, co nghTa ed cdng chat lupng tao hinh va Idm chdt eau kidn be tdng. Gia thuyit nay dung khi ngudn gdy mng n i m trong long hdn hpp bd tdng. I dde trung eho ndng IUpng do ngudn gay rung tao ra vd dac trUng cho nang lupng hdn hpp bd tong nhdn dupe de tao hinh va lam chat ed'u kidn. Trong nhtfng diiu kien nha't dinh khi I cdng Idn thi hidu qua rung cang cao.
Khi ngudn gay rung nam ngodi, nhu ddi vdi bdn rung ngudi ta 141 thay rang khi gid gia tri bien dp rung trong miin cong nghd cho phep, tdng tan sd qua mpt giS trj nSo dd thi hidu qua rung lai giam (trdi vdi gia thuyit tren), cd nghTa gia thuyit cudng dp rung hpp ly khdng cdn phu hpp. Cd the giai thieh hidn tupng ndy nhUsau:
Gia thiit dao ddng dieu hod ed dang;
X = Asina)f; X = Acocosot; X'=-A.co^sin£ot (1) a = \-A<A < [a] = 70;?/,, a„,, = Aro' = 70^/^ (2)
22 TAP CHf KHOA HOC C O N G NGH6 XAY DUNG SO02-12/2007
(3) -, radls
Nhu vdy, gid tri gia tde Idn nha't a = |-'^<y^| = [s] • 0' day [a] Id gia trj gia tdc gidi han xdc dinh bang thUc nghidm cho ttmg loai hdn hpp bd tdng. Gid trj gia tdc gidi han bdi hidn tUpng tdch bd tdng khdi de, hut khdng khi vdo la giam hidu qua rung. Theo 151, gid tri [a] <70 mis' cho hau h i t cdc loai hdn hpp bd tong tuoi
Nhi^u tdi lieu dd khdng djnh rang rang, trong nhijng khoang gia trj thdng sd cdng nghe lam vide hpp ly vd trinh dp ky thuat c h i tao phu hpp, tang tan sd se ed Ipi hon tdng bien dp. Diiu ndy chung ta se xem xet ky lai td diiu kidn (2) - gia tdc dam bao cho hdn hpp be tdng khdng hut khdng khi vdo la giam hidu qua rung. Xet cac trudng hpp diiu eh?nh mdy sao cho gia tdc Idm videa = [a] = 70m/s^ vd bidn dp nam trong khoang cong nghe cho phep
/A = (0,0003-0,0008)mm
Sang 1.
a = [a]
(mis') A (m)
(0 (rad/s) / = A'w^
(mV)
70 0,0003
483 10,1
0,0005
374 13
0,0007
316 15,5
0,0008
296 16,6
Oiiu chinh t i n sd bdn rung nhd biin tan hode hdp sd, eon diiu ch?nh bien dp bang each thay ddi md men tTnh leeh tdm.
Nhin vdo bang 1 nhdn thiy ring: Trong diiu kien cung gia tdc mng dam bao khdng xay ra hidn tupng hut khi vdo vd tdch cac Idp bd tdng vdi nhau, viec sd dung tan sd thip hon hdn hpp bd tong nhdn dugc gid trj eudng dp rung Idn hdn. Oiiu ndy chtmg td vide sd dung t i n sd rung thip hdn thi hidu qua rung eao hdn.
KET LUAN - LUAN DIEM
TU gia thuyit cudng dp rung hpp ly va gia thiit khdng khi khdng the bi hut vao be tdng khi [a] < 70 mis', thi ddi vdi che dp bd tdng rung tuyin tinh vide sd dung tan sd thap se dat hidu qua Idn hdn t i n sd eao.
TAP CHi KHOA HOC C O N G NGHC XAY DUNG SO 02-12/2007 23
Tafdng hpp ldp trdn eung cua hdn hpp be tdng c6 lue dp hpp ly vd bd tdng tdch khdi d i khudn khi bdn njng lam vide, tdn tai hien tupng va cham trong dupc xem xet khd ky trong tai lidu 191.
Theo tae gia 181 ddi vdi ngudn gay rung ed t i n sd trong khoang td 2 d i n 20 Hz sd cd the xuit hien mng cpng hudng eo the eon ngudi vd nhiiu khi bidn dp ngudn gay rung kha nhd nhung lai gdy nhdng biin ddi nguy hiem hon so vdi t i n sd cao. Bdi vdy, khi dp dung may rung tan sd thip c i n ehd y dp dung nhung bidn phap bao vd chdng mng cdng hudng can thiit di an todn cho ngudi lao dpng va moi trUdng xung quanh.
Tai lieu tham khao
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3. NguySn VSn Tiin - Giao trinh Phuong phap ludn nghien cifu khoa hpe. Nxb Xdy dung. 2006.
4. Tycee 6. S. - yflapHO-BnepauMOHHafl TexHonornfl ynnoTHeHidn eeroHHbix cNieceii. MocKBa, 1982.
5.CuneH0K C. T, A. A. BopmeecKuu - MexaHMMecKoe odopyAoeaHMe npeAnpnaruM crpoMTenbHbix Marepnanoe, nsflennn M KOHcrpyKUMH. MocKBa, 1990.
6. Trin VSn Tuan - Ca sd ky thuat rung trong xdy dung va s i n xua't vat lieu xdy dung, 378 trang. Nxb Xdy dung. Hd Ndi, 2005.
7. Hoang Thuy Hai - NgUdi thdch thdc thuyet tUdng ddi. Tap chi Gido due va Thdi dai, sd 135.
11/2007.
8. Nguyen Anh Tuan - Mpt sd k i t qua nghidn ctfu ve md hinh hod co the chju tae ddng eda rung cue bp vd rung toan than. TT Hpi thao khoa hpe qude gia v i mdi trudng - sdc khoe..., trang 171- 177, Hd Ndi, 2008
9. Trin VSn Tuan - Nghidn ctfu phuong phap xde dinh li/c ep ldn b i mat cau kidn be tdng trong qua trinh ddc bang cdng nghe va rung trong. Tap chi KHCN xay dung, sd 1-9/2007, trang 21-25
24 TAP CHf KHOA HOC CONG NGHexAY DUNG Sd02-12/2007