EXPERIMENTAL STUDY ON A NEW TYPE FLOATING BREAKWATER

Transcription

1 Poceedings of he 7 h Inenaional Confeence on Asian and Pacific Coass (APAC 2013) Bali, Indonesia, Seembe 24-26, 2013 EXPERIMENTAL STUDY ON A NEW TYPE FLOATING BREAKWATER L.H Cheng 1, C.Y Fen 1, Y.H Li 2 and W.Y Jiang 3 ABSTRACT: In he aicle, a new ye floaing beakwae is oosed based on comaing he efomance of diffeen kinds of floaing beakwae ha include onoon ye beakwae, sca ie beakwae, ma floa ye beakwae ec. The ousanding feaue of he new ye beakwae is ha daming a boom of beakwae can incease wave enegy dissiaion and decease coefficien of wave ansmission and eflecion. The elaive widh and elaive submegence deh (he aio of widh o wave lengh W/L and submegence deh o wave lengh D/L) on he efomance of he beakwae ae discussed based on a seies of hysical model es in flume. The elaionshi beween ciical ansmission coefficien (C =0.5) and elaive widh is given by exeimen. In he acual design and alicaion ocess, he vaious aamees ae no indeenden, so he elaionshi beween ansmission coefficien and diffeen aamees is analyzed in his ae. Keywods: New ye, floaing beakwae, ansmission coefficien, exeimen sudy. FOREWORD Ove he as wo decades, inees in he sudy of floaing beakwaes has inceased owing o he advanage of lowe invesmen and being envionmen fiendly. Floaing beakwaes can be efeable ove ubble-mound o shee-ile sucues o educe he inciden wave enegy unde condiions include sho wave eiod and lengh, small wave heighs and lage wae deh. Floaing beakwaes can accommodae fo deh changes auomaically, and can be used o oec a boa behing o eceaional sysem, and can be used a sies wih lage wae deh o oo foundaion condiions. Floaing beakwae can be used fo offshoe oil dilling and maine aquaculue, and i has been deloyed a many sies o educe wave enegy ha eaches he shoeline o enes he o. In mos cases, he sie is locaed on dee wae aea ha is a leas dee enough o suo boaing aciviy. Ye hee ae ohe sie wih shallow wae aea and small scales ha migh also benefi fom he deloymen of floaing beakwaes ha can be consuced simly wih a sufficien low cos. In ecen yeas, floaing beakwaes moe and moe ge eole s aenion and ecogniion due o he abovemenioned advanages. RESEARCH STATUS The ealies documened on alicaions insance of floaing beakwaes is he wood floaing beakwaes ha is buil in Plymouh o, in 1811 UK. In 1944 duing Wold Wa II Biish oos landed in Nomandy by means of floaing beakwaes ha is named Bombadon and comosed of weck and caisson. The floaing beakwae is 1.6km fa fom coasline, and each uni is 600m long, 7.5m wide and 7.5 high. A floaing beakwae is laced in Aomoi o in Jaan o es hei abiliy o wihsand waves and wave absoion efomance, in Befoe his cenuy, he majoiy of he sudy and alicaion of he floaing beakwae is in develoed couny. Fo he as 10 yeas, wih he develomen of economic and echnological in China, and a vaiey of floaing beakwaes ae designed and sudied. Floaing beakwaes can be divided ino flexible floaing beakwaes and igid floaing beakwaes accoding o hei elasic oeies. Flexible floaing beakwaes can aea elasic defomaion unde wave acion wih smalle wave eflecion han ha of nomal igid floaing, he majo yes of flexible floaing beakwae is floaing af, wase ie ye, hin film ec. The igid floaing beakwae can aea elasic defomaion unde wave acion, he majo yes of igid floaing beakwae is box, fence, onoon ec. Hales (1981), McCaney (1985) and Mani (1991) classified floaing beakwae yes accoding o hei geomeical configuaion and funcional similaiies. Sucue widh in he diecion of wave oagaion ovides one means of classificaion, wide-beam floaing beakwae and naow-beam floaing beakwae. Mooing configuaions may also be used o classify he floaing beakwae. One ye is igid veical iles ha exend fom below he seafloo u o 1 Tianjin Reseach Insiue fo Wae Tanso Engineeing, Tianjin , CHINA 2 Tianjin Tianlan offshoe Science and Technology Develomen Co., Ld., Tianjin , CHINA 3 CCCC Fis Habo Engineeing Comany Ld., Tianjin , CHINA 429

2 Exeimenal Sudy On A New Tye Floaing Beakwae he wae suface, and he ohe ye is flexible mooing lines o chains ha connec he beakwae o anchos on he seafloo. (1) Rigid floaing beakwae Mos eseaches have been involved in he hydodynamics of floaing beakwaes wih ecangula coss-secion o invesigae hei efomance based on numeical model o exeimenal. Floaing box is geneally made of einfoced concee, seel o made of sca shi wih a ecangula shae, and his ye of floaing beakwae educes he wave ansmission coefficien by deceasing efleced wave enegy. A ecangula box floaing beakwae was buil in 1976 in Jaan. Gesaha (2006) invesigaed he eflecion and ansmission of inciden waves ineacing wih 2D ecangula beakwae wih wo hin sideboads ouding veically downwad. The advanages and disadvanages of diffeen yes of beakwaes wee sudied, and conduced sudies show ha acical size designs offe oecion esiced o wave heighs unde 1.5m and eiods unde 4s (Cox and Beach, 2006). Aiming o incease hese oeaional limis, einfocedconcee-onoon-ye and double floaing beakwae aeaed, and ha could suose an efficien imovemen in he hydodynamic behavio (Dong e al., 2008). The sheleing effec of floaing box ha was used in he Duch Baiona o was sudied by exeimen (E.Pena, 2010). Siassnie and Dime(2003) examined he suiabiliy of feely floaing oous box in shallow wae and showed ha he dif foces wee educed significanly. S.G Pail (2011) invesigaed he wave ansmission coefficien of hoizonally inelaced mulilaye mooed floaing ie beakwae (HIMMFPB). The deail of he HIMMFPB is shown in Fig.2. The exeimenal sudy caied ou by Kama (2010) shows hydodynamic chaaceisics of hoizonally inelaced hee and five laye floaing beakwae sysems, in which he wave ansmission is less fo five aye sysems. Wu (2002) analyzed some facos influencing he wave aenuaion effeciveness of ie-ye floaing beakwae, and he minimum wave ansmission coefficien of he floaing beakwae can each 0.22 unde unfavoable inciden wave condiions by imoving he sucue. Fig. 1 Diffeen yes of Baiona o floaing beakwae Fig. 2 HIMMFPB model layou (2) Flexible floaing beakwae Floaing af and wase ie floaing beakwaes ae he common yes of flexible floaing beakwaes. Raf floaing beakwae is comosed of inflaable nylon bag and glass fibe. This ye of floaing beakwaes educes wave ansmission coefficien by ficion beween he floaing beakwae and wae and elasic defomaion ha can absob he inciden wave enegy. Raf floaing beakwae can be used as wave dissiaion, bu also alies o oil sill sie ecovey oeaions ha have been sudied in he Univesiy of Rhode Island. Dong (2006) sudied on he boad-ne floaing beakwae, and he esuls show ha he oosed floaing beakwae has good wave dissiaion caaciy, bu is design aamee should be consideed accoding o he wave and cuen condiion in he viciniy of he beakwae. Zhang (2010) had eseach on he sca ie floaing beakwaes. Based on he hydo-elasic similaiy heoy, a hysical model wih small scale was designed and he exeimenal esuls show he nice efomance of wave aenuaion. When he beakwae widh is moe han 0.6 wave lengh, wave ansmission coefficien is less han 0.5, and he beakwae lay a good effec in dissiaing waves. Fom he exising eseach esuls, he flexible floaing beakwaes have high equiemen abou he widh o achieve he bee funcion of wave dissiaion. 430

3 L.H Cheng, e al. (3) Wave dissiaion effec of floaing beakwae The objecive of floaing beakwaes is o educe he heigh of wave ansmied H assed he sucue. I is execed ha he wave ansmission coefficien is small enough in shele of he floaing beakwae. The wave ansmission coefficien is defined by he following equaion: C H / H (1) i Whee, H i is inciden wave heigh and H is he ansmied wave heigh. If viscous effec is ignoed, he inciden wave enegy is divided ino wo as, ansmied wave enegy and efleced wave enegy. Accoding o he wave heoy, he oal enegy e uni lengh is ooional o he squaed wave heigh. So he elaionshi of wave heigh and coefficiens is as follows: C H / Hi (2) Hi H H ( 3 ) 2 2 C C 1 ( 4 ) Whee, H is efleced wave heigh and C is efleced coefficien of floaing beakwae. Unde acual sea and es condiions, due o he effec of ficion, wave beaking, wave absoion and aenuaion of floaing body, he sum of ansmied and efleced coefficien is less han 1. Many eseach esuls show ha he main facos affecing he wave ansmission coefficien including he fom of sucue, he elaive widh of floaing beakwae (he aio of widh and inciden wave lengh W/L), he floaing beakwae ino he wae deh (he aio of he heigh of beakwae in wae and wae deh, D/L) and wave seeness (H/L). The cuves of hee diffeen sucual foms floaing beakwaes ansmission coefficien and elaive widh ae shown in Fig.3. Shown as Fig.3, if he wave ansmission coefficien of onoon and box floaing beakwae less han 0.5, W/L mus geae han 0.3; on he ohe hand, when W / L 0.5, he ansmission coefficien does no vay wih inceasing widh significanly educed, and i is difficul o less han 0.2. When he elaive widh is bigge han 1, he ansmission coefficien of af floaing beakwae is less han 0.5. follows: he coss-secional shae is concave diamond, and he lengh, widh and heigh is 98cm, 24cm and19.5cm, esecively. Lengh 20cm nylon oe is insalled in he boom of he floaing beakwae o incease he daming. The inenal sace is filled wih foam, in addiion o necessay couneweigh. Two mooing lines ae laced on wave-wad side and leewad side of concave-diamond floaing beakwae, esecively. Fig. 3 Tansmission coefficien cuve of diffeen floaing beakwaes The exeimens wee caied ou in a wave flume in Tianjin Reseach Insiue fo Wae Tanso Engineeing (TIWTE). The flume is 65m long, 1.0m widh and 1.3m high, and is effecive woking deh is 1.0m. I has a igid concee bed and he sides ae lined wih glass anels fo he enie lengh of flume fo obsevaion of he exeimen inside he flume. Waves wee geneaed by a wave geneao. The wave geneao is hydaulically diven and can geneae boh egula and andom waves wih simulaneous absoion of sho waves efleced fom he fa end of he flume. Two wave heigh sensos wee laced in fon and behind of floaing beakwae, esecively, and he wave heigh senso is TK2008 ye caaciance senso wih an accuacy of 0.1mm. Each se of ess was caied ou a leas hee imes, and he numbe of eeiions would be inceased, when he diffeence of ess henomenon and measuemen beween he esuls of he hee ess. LABORATORY EXPERIMENTS Model Design and Insumenaion The model layou is shown in Fig.4. The PVC ie wih 300mm diamee is used o make he floaing beakwae, and he main design aamee is shown as Fig. 4 Model layou in he flume and icue in flume 431

4 Exeimenal Sudy On A New Tye Floaing Beakwae Wave Simulaed and Tes Aangemen Ode o sudy he elaionshi beween wave ansmission coefficien of floaing beakwae and elaive widh of floaing beakwaes and wave heigh and eiod (wave seeness), wave dissiaion effec of floaing beakwae wee esed, when wave wih diffeen heigh and eiod aced on he floaing beakwae. Model es wae deh was 0.4m, 0.5m and 0.6m ha on behalf of diffeen design wae level. Iegula significan wave heigh is 0.02m ~ 0.08m, and he significan wave eiod is 0.5s ~ 1.2s. JONSWAP secum was used o simulae he iegula wave in exeimen, and he analyical fomula is as follows: be sudied ex ( f / f 1) /2 S( f ) 1/3 ex ( ) jh T f T f 4 Whee: j ln (1.9 ) T T / ( 2.5) (5) (6) (7) 0.07 f f (8) 0.09 f f Whee: is eak faco of wave secum; f is eak fequency of wave secum, S( f) is synheically secal densiy (m 2.s), H1/3 is significan wave heigh, f is fequency, T is aveage wave eiod. TEST RESULT ANALYSIS Effec of Wave Heigh and Peiod Wave ansmission coefficiens of floaing beakwaes wee sudied when wave wih diffeen heigh and eiod aced on he floaing beakwae, wih diffeen wae deh. In ode o faciliae analysis he esul, Figue 5 shows he wave ansmission coefficien as he funcion of inciden wave heigh and eiod, unde he diffeen wae deh condiion. I can be seen fom he es esuls unde he same wave heigh condiions, he bigge wave eiod he bigge ansmission coefficien; unde he same wave eiod condiion, he ansmission coefficien is no a single incease wih wave heigh. Fom he ciical value of wave ansmission coefficien, 0.5, beakwae wave dissiaion effec is elaively oo when he wave eiod is geae han o equal o 0.7s; 0.5, beakwae wave dissiaion effec is elaively good when he wave eiod is less han o equal o 0.6s. The wave eiod is a key faco affecing he floaing beakwae ansmission coefficien. Wave eiod deemines he wave lengh and elaive widh of he floaing beakwae, so he elaive widh of he floaing beakwae is a key faco affecing he ansmission coefficien oo. The nex secion, he effec on ansmission coefficien of elaive widh will Fig. 5 The elaionshi beween C and wave heigh and eiod Effec of Relaive Widh and Relaive Wae Deh Wave ansmission is affeced by inciden wave heigh, eiod, wae deh and iself widh, ec. Accoding o hese facos, he funcion of ansmission coefficien is shown as follows: C H / H fun( L / H, d / H, D / H, W / H ) (9) i i i i i Whee: L is wave lengh, and i is he funcion of wave eiod and d wae deh; D is beakwae heigh undewae; W is beakwae widh. Pas of he faco would be fixed duing he exeimen, and he funcion of ansmission coefficien changes o as follows: fun( D / L, W / L) (10) Then we will jus change elaive wae deh and widh one by one. Figue 6 shows he wave ansmission coefficien as he funcion of elaive wae deh and elaive widh, and he elaionshi beween ansmission coefficien and elaive wae deh and elaive widh is shown as follows: 432

5 L.H Cheng, e al ( W/ L) e (11) 1.237( D/ L) e (12) I can be seen fom he fomula and figue, he smalle ansmission coefficien and he bigge W/ L. W/ L 0.3 is a ciical value, when i bigge han 0.3 he ansmission coefficien less han 0.5, and when i smalle han 0.3 he ansmission coefficien bigge han 0.5. In ode o ensue he shielded effec of floaing beakwaes, he elaive widh should emain above 0.3. On he ohe hand, he bigge D/ L and he smalle ansmission coefficien, D/ L 0.6 is a ciical value. When D/ Lis less han 0.6, he ansmission coefficien is bigge han 0.5. W/ L 0.3 is a ciical value, when i bigge han 0.3 he ansmission coefficien less han 0.5, and when i smalle han 0.3 he ansmission coefficien bigge han 0.5. (3)The bigge D/ L and he smalle ansmission coefficien, D/ L 0.6 is a ciical value. When D/ Lis less han 0.6, he ansmission coefficien is bigge han 0.5. (4) The exeimenal eseach on concave-diamond floaing beakwae gave he funcion of wave ansmission coefficien, which ovides a basis fo he design and alicaion of he new ye floaing beakwae. (5) Accoding o is flexible, simle, and easy disassembly, floaing beakwaes ae gadually favoed by eole, and he concave-diamond floaing beakwae will be used on coasal engineeing afe sysemaic and deailed es sudy. Fig. 6 The elaionshi beween and W/ L and D/ L CONCLUSIONS AND RECOMMENDATIONS Basis on he invesigaion of eseach on floaing beakwaes, he eseach ogess and alicaion osecs ae known, and he effec of wave dissiaion and sucue yes of floaing beakwaes wee comaed. Then concave-diamond floaing beakwae was designed and exeimenal sudied in flume. The exeimen was caied on, unde diffeen wave and wae deh condiions. Then he esuls wee analyzed, and he conclusions and ecommendaions ae as follows: (1) The wave eiod is a key faco affecing he floaing beakwae ansmission coefficien. Wave eiod deemines he wave lengh and elaive widh of he floaing beakwae, so he elaive widh of he floaing beakwae is a key faco affecing he ansmission coefficien oo. (2)I can be seen fom he fomula and figue, he smalle ansmission coefficien and he bigge W/ L. REFERENCES WANG Y X, WANG G Y. (2002). Reseach ogess and alicaion of floaing beakwaes [J]. Shi Building China: LIU W T. (1988). Ponoon ye and sloe ye floaing beakwae [J].Coasal Engineeing: DONG H Y. (2009) Sudy on hydodynamic chaaceisics of onoon-laes ye floaing beakwaes [D]. Dalian: Dalian Univesiy of Technology. WANG K, XU W. Tansmission coefficien and efleciviy fo beakwae of hoizonal o veical lae ye [J]. Jounal of shi mechanics, 2010, 14(5): E.Pena,J.Feeas. (2011). Exeimenal sudy on wave ansmission coefficien, mooing lines and module conneco foces wih diffeen designs of floaing beakwaes[j]. Ocean engineeing: H.Y.Wang, Z.C.Sun. (2010). Exeimenal sudy of a oous floaing beakwae[j]. Ocean engineeing: Luca Mainelli. (2008). Wave basin exeimens on floaing beakwaes wih diffeen layous[j]. Alied ocean eseach: N.K.LIANG. (2004). A sudy of sa buoy floaing beakwae [J]. Ocean engineeing: J.P. WU, R.K. WANG, X.W. ZHENG,ec. (2001). The exeimenal invesigaion of he duckweed-ye floaing beakwae [J].Jounal of Wuhan Univesiy of Technology (Tansoaion Science & Engineeing): Y. ZHANG. (2009). Exeimenal design and efomance sudy on sca ie floaing beakwae model [D]. Dalian: Dalian Univesiy of Technology. 433