Study of the functional design of a floating offshore breakwater

These days, green energy is getting more and more attention in our society, and with this, the construction of offshore wind farms is gaining interest. With the development of these farms, a need for constant maintenance is created. This means a constant presence of maintenance vessels, crew boats, and equipment in the wind farm area will be necessary. In view of this, it is interesting to investigate the concept of an offshore shelter location. This location would have two main functionalities: a sheltering location for the vessels, and a logistic function. One solution to this problem could be the creation of an offshore harbour based on floating breakwaters (FB). This option is investigated in this dissertation. The starting point of this report is the determination of the hydraulic and structural boundary conditions. Hydraulic boundary conditions were obtained by analyzing time series of measured wave heights and directions, provided by IMDC. Structural boundary conditions were determined based on the new offshore support vessel presented by Offshore Wind Assistance N.V. (OWA). After these boundary conditions are defined, a preliminary design, based on previous research, is made. This preliminary design is then modeled in MILDwave software, which lead to an optimization of the FB length, and a study of different FB layouts. Since the motions of the FB need to be limited to assure safe working conditions, a motion analysis is performed using AQUA+ software. From this it will become clear that there will be a problem regarding the limitations of these motions. In view of these findings, the design of a heave FB is proposed.

Study of the functional design of a floating offshore breakwater Karen Merlevede Promotor: prof dr ir Peter Troch Begeleiders: ir Vicky Stratigaki, Piet Haerens (IMDC) Masterproef ingediend tot het behalen van de academische graad van Master in de ingenieurswetenschappen: bouwkunde Vakgroep Civiele Techniek Voorzitter: prof dr ir Julien De Rouck Faculteit Ingenieurswetenschappen en Architectuur Academiejaar 2011-2012 Study of the functional design of a floating offshore breakwater Karen Merlevede Promotor: prof dr ir Peter Troch Begeleiders: ir Vicky Stratigaki, Piet Haerens (IMDC) Masterproef ingediend tot het behalen van de academische graad van Master in de ingenieurswetenschappen: bouwkunde Vakgroep Civiele Techniek Voorzitter: prof dr ir Julien De Rouck Faculteit Ingenieurswetenschappen en Architectuur Academiejaar 2011-2012 A good traveler has no fixed plans, and is not intent on arriving - Lao Tzu i Dankwoord Als eerste wil ik graag mijn begeleider, Piet Haerens, bedanken voor het aanreiken van dit onderwerp Natuurlijk heb ik van tijd tot tijd zitten vloeken op het concept ’thesissen’, maar ik mag mij gelukkig prijzen dat ik het steeds een boeiend thema ben blijven vinden! Verder wil ik ook mijn promotor, Peter Troch, bedanken voor de begeleiding aan de start van het academiejaar Dankzij hen kon ik een vlotte start maken, wat ervoor gezorgd heeft dat die typische laatste thesis stress mij bespaard gebleven is, OEF! Peter Mercelis wil ik graag bedanken voor zijn begeleiding tijdens de dagen die ik op IMDC doorbracht en het nalezen van de hele boel, Joris Rooseleer voor de input in verband met het verankeringssysteem en Phillipe de Schoesitter voor de aangename babbels op IMDC en de info over moonpools ed Evert Lataire wil ik bedanken om mij als bouwkundig studentje in te leiden in een stukje van de maritieme wereld Verder wil de belangrijkste mensen in mijn leven bedanken, mijn familie In het bijzonder mijn ouders, voor hun onvoorwaardelijke steun en omdat ze mij de kans hebben gegeven om burgerlijk te gaan studeren Mijn zus, Anne, voor het tussen-thesis-door-tripje en de vele tips over maritieme toepassingen, Torretje, voor de uitleg over verankeringen, mijn broer Stijn, voor de fietstelefoontjes! Ook bedankt aan de BWC, het waren aangename middagen op de magnel Ann sorry als ik je gefrustreerd heb door teveel snipperdagen te nemen! Verder wil ik ook een zot leuk mannetje bedanken, Wally! Danku om altijd te luisteren naar mijn ’zottigheid’, ik ben blij dat je onder mij woont! Djanxke, bedankt om zo geduldig te zijn Dat kan niet altijd even gemakkelijk zijn, maar voor familie heb je natuurlijk wel iets over! And last but not least, wil ik mijn partner in crime, Bo, bedanken omdat we samen altijd zulke goede mopjes en plannen maken Ooit gaan we de nacho’s terugvinden! Copyright The author gives permission to make this master dissertation available for consultation and to copy parts of this master dissertation for personal use In the case of any other use, the limitations of the copyright have to be respected, in particular with regard to the obligation to state expressly the source when quoting results from this master dissertation ii Study of the functional design of a floating offshore breakwater by Karen Merlevede Master dissertation submitted in order to obtain the academic degree of Master of Civil Engineering (major Water and Transportation) Head supervisor: Prof Dr Ir P Troch Supervisor: Ir P Haerens Department of Civil Engineering Head of department: Prof Dr Ir J De Rouck Faculty of Engineering Ghent University Academic year: 2011–2012 Summary These days, green energy is getting more and more attention in our society, and with this, the construction of offshore wind farms is gaining interest With the development of these farms, a need for constant maintenance is created This means a constant presence of maintenance vessels, crew boats, and equipment in the wind farm area will be necessary In view of this, it is interesting to investigate the concept of an offshore shelter location This location would have two main functionalities: a sheltering location for the vessels, and a logistic function One solution to this problem could be the creation of an offshore harbour based on floating breakwaters (FB) This option is investigated in this dissertation The starting point of this report is the determination of the hydraulic and structural boundary conditions Hydraulic boundary conditions were obtained by analyzing time series of measured wave heights and directions, provided by IMDC Structural boundary conditions were determined based on the new offshore support vessel presented by Offshore Wind Assistance N.V (OWA) After these boundary conditions are defined, a preliminary design, based on previous research, is made This preliminary design is then modeled in MILDwave software, which lead to an optimization of the FB length, and a study of different FB layouts Since the motions of the FB need to be limited to assure safe working conditions, a motion analysis is performed using AQUA+ software From this it will become clear that there will be a problem regarding the limitations of these motions In view of these findings, the design of a heave FB is proposed Keywords: floating breakwater, offshore wind farms, offshore harbour, heave floating breakwater iii Study of the functional design of a floating offshore breakwater Karen Merlevede Supervisor(s): Peter Troch, Piet Haerens Abstract— This article discusses a theoretical approach in the design of an offshore floating breakwater (FB) The choice of hydraulic and structural boundary conditions is discussed, after which a preliminary design is made This design is then optimized using MILDwave software A motion analysis is performed with AQUA+ software Finally, a design for a heave floating breakwater is proposed Keywords— floating breakwater, offshore wind farms, offshore harbour, heave floating breakwater I in the the design of the mooring system and are therefore only determined for case conditions TABLE I: Hydraulic boundaries Hdes Tdes Waterlevel Wind speed Current speeds Return period I NTRODUCTION OWADAYS , green energy is getting more and more attention in our society The European directive 2009/28/EC [1] states that Belgium needs to obtain 13% of the electricity consumption from renewable energy sources by 2020 To accomplish this, the installation of offshore wind farms (OWF) is gaining interest With the development of these offshore wind farms, a need for constant maintenance is created This means a constant presence of maintenance vessels, crew boats, and equipment in the wind farm area will be necessary In view of this, it is interesting to investigate the concept of an offshore shelter location This location would have two main functionalities: a sheltering location for the vessels, and a logistic function One solution to this problem could be the creation of an offshore harbour based on floating breakwaters (FB) N II H YDRAULIC BOUNDARY CONDITIONS Time series of registered wave heights and directions over a period of 20 years have been provided by IMDC By constructing several JAVA tools, this data was analyzed using ACES software, and afterwards presented graphically in excel The boundary conditions will be determined for two cases • Case 1: working conditions, for which 95% workability in normal weather conditions is intended in this design These boundary conditions will be used for the preliminary design and the motion analysis It is noted that case circumstances also assume that waves incident perpendicular to the longitudinal axis of the FB The design wave height and period are different for each direction However, it is seen that most waves are coming from the SW direction, which is why the FB will be oriented perpendicular to this direction The design wave height and period for case circumstances will be those of the SW direction In the analysis of possible FB layouts, the individual wave heights and periods per direction will be taken into account • Case 2: a storm with a return period of 50 years, used for the design of the mooring system Table I summarizs the applied hydraulic boundaries both case and Water level, wind and current speed are only important K Merlevede is with the Civil Engineering Department, Ghent University (UGent), Gent, Belgium E-mail: Karen.Merlevede@gmail.com III III-A Case 2,5 m 9s - Case 5,0 m 10 s 6,25 m TAW 25 m/s m/s 50 y S TRUCTURAL BOUNDARY CONDITIONS Design vessel In [2], a new Offshore Wind Assistance (OWA) support vessel is presented This vessel will not only be used for crew transfer, but also for seabed survey, scour monitoring and cable inspection, etc It has a beam over all of 10,04 m, a length over all of 25,75 m, and a draught of 1,75 m The preliminary design will be influenced by the design vessel in length It will be assumed that only one OWA vessel will be mooring at the floating breakwater, and that this requires a minimum length of 50 m III-B Safe working criteria The criteria to ensure safe working conditions are listed here The waves on the lee side of the structure need to be attenuated to m to ensure a sheltering environment [3] The directional maximum value of C can be determined by dividing m by the directional design wave height • The heave motion needs to be limited to 1m, the roll motion to 5° and the pitch motion to 1° [4] • The wave overtopping needs to be limited to 0,01 m /m/s [5] • IV P RELIMINARY D ESIGN The preliminary design will be based on case boundary conditions Two processes of energy transportation are important for the preliminary design: diffraction and transmission Diffraction considerations will lead to an optimal length, while transmission will lead to an optimal width/draught ratio IV-A Diffraction Diffraction can be quantified using Wiegel diagrams [6] However, these are developed for semi-infinite breakwaters In this case of an offshore floating breakwater, the gap method as described in the Shore Protection Manual [7] is applicable Using this method, it can be determined that the minimum FB length will be 225mm IV-B Transmission [8], [9], [10], and [11] developed approaches to quantify the transmssion process These approaches are applied to testcases by [12], [13], and [14] From this it is found that the equation by [11] provides the most accurate results The transmission according to [11] is given by Ct = gT sinh(k(d − D)) 2π (W + d tanh(3, D d )) cosh(kd) (1) Using this equation, and assuming an initial width of 40 m, leads to a minimum draught of m IV-C VI-C Overtopping The mechanism of overtopping will determine the necessary freeboard of the structure Using equations proposed by [15] and the limitations for overtopping discharge leads to a minimum freeboard of m V MILDWAVE M ODEL MILDwave [16] is a wave propagation model based on the depth-integrated mild-slope equations of [17] To model an object in the wave field, the cells are assigned a certain absorption coefficient (S) This coefficient ranges from zero to one; zero meaning the cell consists out of water, and one meaning the cell is fully reflective and does not absorb any energy The difficulty is that MILDwave does not offer a specific input for floating objects [18] studied the layout of a farm of floating wave energy converters (WEC) using MILDwave, and found that the best way to model a floating object is to assign a linearly varying S over the width of the structure This approach is verified by applying this technique to the same testcases that were used to determine the best applicable equation VI why L/150/100 is studied This layout suffices for the same directions as the L/150/150, except for the north Again, it is seen that C is well beneath the maximum allowable value for SSE-W directions This is why the last L-shape modeled is L/100/100 In this case, the FB is efficient for waves coming from the SSWNWN segment However, waves coming from the first quadrant are not attenuated sufficiently This is why the U-shaped FB will be studied in the next section In every L-shaped layout, problems with reflecting waves are present This is the case when waves are attacking the leeward side of the structure The reflection decreases when reducing the length of the legs The asymmetrical layout showed the most negative reflection properties Generally, the L/100/100 layout was found to be the most satisfying U-shaped FB The final layout modeled, is a U-shaped FB of which the parallel sides measure 100 m, and the connecting side 155 m This layout offers sufficient attenuation for waves coming from the SW to the NE However, for waves coming from the south, the attenuation is significantly lower that in the case of an L-shape This is because the waves are reflected inside the U-shape, amplifying the resulting wave heights For waves coming from the SSE, SE, and ESE, the resulting wave heights are even higher than the incoming wave heights A comparison between the beam shaped FB, the U-shaped FB and the L/100/100 configuration is shown in figure S TUDY OF THE LAYOUT USING MILDWAVE Three types of FB layout will be modeled in MILDwave A beam shape, an L shape, and a U shape VI-A Beam shaped FB The beam shaped structure is oriented perpendicular to the SW direction, where most waves are coming from The results show that the length of the FB can be reduced to 150 m Fig 1: Comparison between the beam shaped FB, L/100/100, and U-shaped FB VI-B L-shaped FB Since the fourth quadrant on the wind rose also produces relatively high waves, an L-shape is the subject of this section Three types in particular are studied: L/150/150, L/150/100, and L/100/100 The first number stands for the length of the side perpendicular to the SW, while the second number is the length of the leg perpendicular to the NW The L/150/150 layout attenuates waves coming from the SSE-N segment sufficiently It is noticed that the attenuation coefficient, C, is often only half of the maximum allowable value for the SW-N segment This is This figure shows that the directions of sufficient attenuation and the directions for which C exceeds one are different for each layout It is found that the wave amplifying directions in the case of L/100/100 are more harmful than in the case of the U-shaped FB, because the incoming waves are smaller in the latter case Nonetheless, this reflection is to be damped as much as possible, for example by adding wave absorbing structures on the leeward side of the structures Extensive theoretical and experimental research on this topic is recommended VII M OTION A NALYSIS VIII-B The motions of the FB need to be limited [4] states that three motions in particular have to be studied: heave, roll, and pitch The period of resonance of floating bodies for these motions is usually found somewhere between s and 20 s, an interval that also contains the design wave periods The motion analysis is performed using AQUA+ software, and results in Response Amplitude Operators, or RAO’s They are defined by [19] Response(t) = (RAO)η(t) (2) where η(t) is the wave profile as a function of time, t The calculations were performed for different wave incidences: 0°; 22,5°; 45°; 67,5°; and 90° The results of this analysis are listed here • The maximum heave RAO amplitude equals 1,61 m/m for a wave period of 10 s; case conditions will result in a heave motion of m, • the maximum pitch RAO amplitude equals 1,18 °/m for a wave period of 10 s; case conditions will result in a pitch motion of 2,95°, • the maximum roll RAO amplitude equals 2,2 °/m for a wave period of s; case conditions will result in a roll motion of 5,5° None of these motions fall within the limits proposed by [4] A mooring line anchoring system will not be able to restrain these motions sufficiently Reducing the motions is possible by changing the FB layout, adding a moonpool, or adding a skirt Furthermore, the mooring system can be designed in such a way that the motions can be restrained Two possible alternatives are proposed: a tension leg mooring system, and a heave FB The latter will be researched extensively in the next section VIII H EAVE F LOATING B REAKWATER [12] performed research on this type of FB, and compared it to a regular fixed breakwater According to his research a heave FB will always be more efficient than the fixed type because of the extra damping by the heave motion itself, causing additional loss of wave energy In this section, the piles will be designed to make sure their dimensions are realistic First the forces acting on the FB and the piles need to be determined In both cases these are forces due to wind, current and waves VIII-A Forces acting on the floating breakwater VIII-A.1 Wind and current Wind and current forces are calculated using the approach described in [20] This leads to a wind force of 485 kN and a current force of 231 kN The approximating points of application are 38,25 m and 32,25 m above the sea bed, respectively VIII-A.2 The pile diameter is assumed to be 4,5m VIII-B.1 Wind and current Wind and current forces are again calculated using the approach in [20] This leads to a wind force of 91 kN and a current force of 263 kN VIII-B.2 Wave forces According to [22], wave forces on piles can be calculated using the Morison equation This leads to a total wave force of 323 kN, with a point of application of 19,70 m above the sea bed VIII-C Pile design Assuming piles are present in the design of the heave FB, means each pile will take on 1/6 of the total force acting on the FB itself The total bending moment for one pile at the sea bed equals 573 839 kNm VIII-C.1 Wall thickness Using the approach described in [23] a wall thickness of 0,08 m can be determined VIII-C.2 Penetration depth In [23] methods of Vandepitte [24] are described to determine the penetration depth Following this approach leads to a minimum depth of 28 m below the sea bed VIII-C.3 Pile length The total pile length consist out of the penetration depth, the water depth, and the extreme water level This leads to a total length of 68,25 m VIII-C.4 Results The design for the heave floating breakwater is shown in figure IX C ONCLUSIONS AND R ECOMMENDATIONS In this text, a design is proposed for a heave FB Although roll and pitch motions are restrained in this concept, the heave motion is not A system will need to be designed to allow safe mooring at the FB, despite these up- and downward motions Alternatively research can be done on how to restrain the heave motion completely Wave basin experiments are strongly advised, since the approach in this text is purely theoretical Only experimental observations can map the behaviour of different layouts, wave incidences, etc Wave forces Wave forces are calculated by the Froude-Krylov theory as described in [19] However these equations are only valid for fully submerged objects, which leads to an overestimation The approach by Goda [21] delivers a more realistic result, 93 949 kN, with a point of application of 34,16 m above the sea bed Forces acting on the piles R EFERENCES [1] [2] [3] [4] European Parliament and Council, “Directive 2009/28/ec of the european parliamant and of the council,” Official Journal of the European Union, pp 16 – 61, April 2009 the GeoSea Newsflash, “Owa fast crew transfer vessel,” Stan Messemaekers, p 11, 2011 J De Rouck, Zee- en Havenbouw, Universiteit Gent, 2011 Pianc, “Criteria for movements of moored ships in harbours,” Supplement to bulletin n° 88, 1995 [23] L De Vos, Optimalisation of scour protection design for monopiles and quantification of wave run-up, Ph.D thesis, Universiteit Gent, 2008 [24] D Vandepitte, Berekeningen van constructies, Universiteit Gent, 1979 =2 Fig 2: Heave Floating Breakwater [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] T Pullen, NWH Allsop, T Bruce, A Kortenhaus, H Schăuttrumpf, and JW van der Meer, “Wave overtopping of sea defences and related structures: Assessment manual, Die Kăuste: Archive for research and technology on the north sea and baltic coast, 2007 R.L Wiegel, “Diffraction of waves by semi-infinite breakwaters,” Journal of Hydraulic Div., 1962 Corps of Engineers US Army, Shore Protection Manual, Coastal Engineering Research Center, 1984 E.O Macagno, “Experimental study of the effects of the passage of a wave beneath an obstacle,” Proceedings of Acad´emie des Sciences, Paris, 1953 D.B Jones, “Transportable breakwater - a survey of concepts,” Naval Civil Engineering Laboratory, 1971 J.J Stoker, Water waves The mathetmatical theory with applications, Interscience Publishers New York, 1957 H Wagner, A Găotz, R Reinsch, and HJ Kaiser, Schwimmende wellenbrecher im einsatz in einem tagenbaurestsee mitteldeutschlands,” Binnenschifffahrt ZfB, 2011 E Tolba, Behaviour of Floating Breakwaters under Wave Action, Ph.D thesis, Bergische Unversităat, 1999 E K Koutandos and C Koutitas, “Floating breakwater response to wave action using a boussinesq model coupled with a 2dv elliptic solver,” Journal of Waterway, Port, Coastal and Ocean Engineering, pp 243–255, 2004 T Nakamura, N Mizutani, N Hur, and D S Kim, “A study of the layout of floating breakwater units,” in proceedings of The International Offshore and Polar Engineers Conference, 2003 C Franco and L Franco, “Overtopping formulas for caisson breakwaters with nonbreaking 3d waves,” Journal of waterway, port, coastal and ocean engineering, pp 98–108, march/april 1999 P Troch, V Stratigaky, and L Baelus, “Reference manual of mildwave,” 2011 AC Radder and MW Dingemans, “Canonical equations for almost periodic, weakly nonlinear gravity waves.,” Wave motion, pp 473–485, 1985 Charlotte Beels, Optimization of the Lay-Out of a Farm of Wave Energy Converters in the North Sea, Ph.D thesis, Ghent University, 2010 S.K Chakrabarti, Hydrodynamics of Offshore Structures, WIT Press, 1987 Pianc, “Floating breakwaters, a practical guide for design and construction,” Supplement to bulletin n° 85, 1994 Y Goda, Random Seas and the Design of Maritime Structures, World Scientific Publishing Company, 2000 J De Rouck, Offshore constructions, Universiteit Gent, 2011 Appendix G MILDwave optimization Figure G.41: U shaped FB - Wave direction: ENE Figure G.42: U shaped FB - Wave direction: E 171 Appendix G MILDwave optimization Figure G.43: U shaped FB - Wave direction: ESE Figure G.44: U shaped FB - Wave direction: SE 172 Bibliography A.B Aalbers The water motions in a moonpool Ahmed Ali Floating transshipment container terminal, 2005 H.A Ardakani and T.J Bridges Shallow-water sloshing in rotating vessels part three dimensional flow field Under consideration for publication in J Fluid Mech., 2009 E.R Armstrong Seadrome Time magazine, 1929 Charlotte Beels Optimization of the Lay-Out of a Farm of Wave Energy Converters in the North Sea PhD thesis, Ghent University, 2010 V Carri¸co and J.J Maisonneuve Aqua+ user’s manual Sirehna, 1995 CEM Coastal Engineering Manual EM 1110-2-1100, U.S Army Corps of Engineers U.S Army, 2008 S.K Chakrabarti Hydrodynamics of Offshore Structures WIT Press, 1987 H Cozijn, R Uittenbogaard, and E ter Brake Heave, roll and pitch damping of a deepwater calm buoy with a skirt in proceedings of the fifteenth (2005) international offshore and polar engineering conference, 2005 J De Rouck Zee- en Havenbouw Universiteit Gent, 2011a J De Rouck Offshore constructions Universiteit Gent, 2011b L De Vos Optimalisation of scour protection design for monopiles and quantification of wave run-up PhD thesis, Universiteit Gent, 2008 M.C Deo Waves and structures Indian Institute of Technology, 2007 Det Norske Veritas Global performance analysis of deepwater floating structures Recommended practice DNV-RP-F205, 2010 G Dong, Y Zhen, B Teng, and D Lin Experiments on wave transmission coefficients of floating breakwaters Ocean Engineering, pages 931–938, 2008 173 Bibliography Anthony Lee Farmer Investigation into snap moading of cables used in moored breakwaters, November 1999 M Fousert Floating breakwater: A theoretical study of a dynamic wave attenuation system, 2006 C Franco and L Franco Overtopping formulas for caisson breakwaters with nonbreaking 3d waves Journal of waterway, port, coastal and ocean engineering, pages 98–108, march/april 1999 N Garceau Combined transmission and diffraction around a floating breakwater, 1997 Ben C Gerwick Construction of Marine and Offshore Structures CRC Press LLC, 2000 M R Gesraha Analysis of a pi shaped floating breakwater in oblique waves Applied Ocean Research, pages 243–255, 2006 Y Goda Random Seas and the Design of Maritime Structures World Scientific Publishing Company, 2000 http://www.c power.be/, may 2012 IMDC Hydraulisch randvoorwaardenboek Vlaamse Kust Ministerie van de Vlaamse Gemeenschap, Departement Leefmilieu en Infrastructuur, Administratie Waterwegen en Zeewezen, Afdeling Waterwegen Kust, 2005 Sten Magne Eng Jakobsen Passive heave compensation of heavy modules, 2008 D.B Jones Transportable breakwater - a survey of concepts Naval Civil Engineering Laboratory, 1971 J.M.J Journ´ee and W.W Massie Offshore Hydrodynamics Delft University of Technology, 2001 C Kim, C Lee, and J Goo A dynamic response analysis of tension leg platforms including hydrodynamic interaction in regular waves Ocean Engineering, 207 E K Koutandos and C Koutitas Floating breakwater response to wave action using a boussinesq model coupled with a 2dv elliptic solver Journal of Waterway, Port, Coastal and Ocean Engineering, pages 243–255, 2004 E K Koutandos, P Prinos, and X Gironella Floating breakwaters under regular and irregular forcing: Reflection and transmission characteristics Journal of Hydraulic Research, pages 174–188, 2005 E.O Macagno Experimental study of the effects of the passage of a wave beneath an obstacle Proceedings of Acad´emie des Sciences, Paris, 1953 174 Bibliography V Martin Findon village Findon News, 2004 L Martinelli, P Ruol, and B Zanuttigh Wave basin experiments on floating breakwaters with different layouts Applied Ocean Research, pages 199–207, 2008a L Martinelli, P Ruol, and B Zanuttigh Loads on floating breakwaters: Effect of layout under irregular waves Coastal Engineering, pages 3875–3887, 2008b NL) Minnes, Roelof Arnoldus (Tolkamer Semi-submersible, mobile drilling vessel with storage shaft for tubular drilling equipment, February 2003 URL http://www freepatentsonline.com/6524049.html J.R Morison, M.P O’Brien, J.W Johnson, and S.A Schaaf The force exerted by surface waves on piles Petroleum Transactions, pages 149–157, 1950 T Nakamura, N Mizutani, N Hur, and D S Kim A study of the layout of floating breakwater units in proceedings of The International Offshore and Polar Engineers Conference, 2003 European Parliament and Council Directive 2009/28/ec of the european parliamant and of the council Official Journal of the European Union, pages 16 – 61, April 2009 E Pe˜ na, J Ferreras, and F Sanchez-Tembleque Experimental study on wave transmission coefficient, mooring lines and module connector forces with different designs of floating breakwaters Ocean Engineering, pages 1150–1160, 2011 Pianc Floating breakwaters, a practical guide for design and construction Supplement to bulletin n➦ 85, 1994 Pianc Criteria for movements of moored ships in harbours Supplement to bulletin n➦ 88, 1995 T Pullen, NWH Allsop, T Bruce, A Kortenhaus, H Schă uttrumpf, and JW van der Meer Wave overtopping of sea defences and related structures: Assessment manual Die Kă uste: Archive for research and technology on the north sea and baltic coast, 2007 AC Radder and MW Dingemans Canonical equations for almost periodic, weakly nonlinear gravity waves Wave motion, pages 473–485, 1985 N.A Siddiqui and S Ahmad Fatigue and fracture reliability of tlp tethers under random loading Marine Structures, pages 331–362, 2001 J.J Stoker Water waves The mathetmatical theory with applications Interscience Publishers New York, 1957 the GeoSea Newsflash Owa fast crew transfer vessel Stan Messemaekers, page 11, 2011 E Tolba Behaviour of Floating Breakwaters under Wave Action PhD thesis, Bergische Unversită at, 1999 175 Bibliography P Troch, V Stratigaky, and L Baelus Reference manual of mildwave, 2011 http://www.marbef.org/wiki.Floating_Breakwaters, november 2011 Corps of Engineers US Army Shore Protection Manual Coastal Engineering Research Center, 1984 D Vandepitte Berekeningen van constructies Universiteit Gent, 1979 H Wagner, A Gă otz, R Reinsch, and HJ Kaiser Schwimmende wellenbrecher im einsatz in einem tagenbaurestsee mitteldeutschlands Binnenschifffahrt ZfB, 2011 C Wang and Z Tay Very large floating structures: Applications, research and development, 2011 H Wang and Z Sun Experimental study of a porous floating breakwater Ocean Engineering, pages 520–527, 2010 E Watanabe, C.M Wang, T Utsunomiy, and T Moan Very large floating structures: applications, analysis and design Centre for Offshore Research and Engineering, National University of Singapore, 2004 R.L Wiegel Diffraction of waves by semi-infinite breakwaters Journal of Hydraulic Div., 1962 A Williams and A Abdul-Azm Dual pontoon floating breakwater Ocean Engineering, pages 456–478, 1997 A Williams, H Lee, and Z Huang Floating pontoon breakwaters Ocean Engineering, pages 221–240, 2000 176 List of Figures 1.1 General approach 2.1 Seadrome (Armstrong, 1929) 2.2 Bombardon Floating Breakwater (Martin, 2004) 2.3 Semi-submersible structure (Minnes, 2003) 2.4 Mega float structure (Watanabe et al., 2004) 2.5 Tension leg platform (Siddiqui and Ahmad, 2001) 10 2.6 Catamaran floating breakwater 12 2.7 Dual pontoon floating breakwater 12 2.8 Mat floating breakwater 13 2.9 Aframe floating breakwater 13 2.10 Tethered floating breakwater 13 2.11 Diffraction process (US Army, 1984) 14 2.12 Transmission process 14 2.13 Six independent motions of a freely floating structures (Ardakani and Bridges, 2009) 15 2.14 Model Gesraha (2006) 17 2.15 Models Pe˜ na et al (2011) 17 2.16 Breakwater Layout Nakamura et al (2003) 18 2.17 Martinelli Layout: I-shapes and J-shape (Martinelli et al., 2008a) 19 2.18 Hydrodynamic mass-spring system (Fousert, 2006) 21 3.1 Storm demands 26 3.2 Wave rose (probablity of non exceedance) 27 177 List of Figures 3.3 Directional significant wave height (m) 29 3.4 Influence threshold value - northern direction 30 3.5 Table of occurrence 30 3.6 Extreme water levels (IMDC, 2005) 32 3.7 Thorntonbank North current forecast MUMM 33 3.8 Extreme value distribution for the wind speed (IMDC, 2005) 34 4.1 OWA support vessel 36 4.2 Six degrees of motion 38 5.1 Diffraction process (US Army, 1984) 40 5.2 Definition of the parameters in equatino 5.5 43 5.3 Transmission coefficient for rigid, rectangular surface barrier, L/d = 1.25 (Jones, 1971) 5.4 Transmission coefficient for rigid, rectangular surface barrier, L/d = 2.5 (Jones, 1971) 5.5 44 44 Transmission coefficient for rigid, rectangular surface barrier, L/d = 5.0 (Jones, 1971) 45 5.6 Comparison equation 5.6, 5.8, 5.10 T = s, h = 12 m, d = 30 m 46 5.7 Tolba (1999) Restrained body D/d = 1/6, Hi/L = 0,014-0,048, B/d = 1/2 47 5.8 Koutandos et al (2005) Ct 48 5.9 Sketch of the preliminary design 52 6.1 Preprocessor MILDwave 54 6.2 Calculator MILDwave 54 6.3 Homogeneous model 55 6.4 Non homogeneous model 56 6.5 Contour plot MILDwave model, Tolba testcase, model with heterogeneous S 56 6.6 Results MILDwave model, Tolba testcase 57 6.7 Results MILDwave model, Koutandos testcase 58 6.8 Results MILDwave model, Nakamura testcase 58 7.1 Input MILDwave preliminary design 61 178 List of Figures 7.2 MILDwave: contour plot of the preliminary design 61 7.3 Results for the beam shaped floating breakwater —: CM ILDwave , - - -: Cmax 64 7.4 Reflection in the case of the beam shaped FB 64 7.5 Results for L/150/150 —: CM ILDwave , - - -: Cmax 66 7.6 Results for L/150/100 —: CM ILDwave , - - -: Cmax 67 7.7 Results for L/100/100 —: CM ILDwave , - - -: Cmax 69 7.8 Comparison L/150/150, L/150/100, and L/100/100 70 7.9 Comparison L/150/150, L/150/100, and L/100/100 for the NNE direction 70 7.10 Results for the U shaped FB —: CM ILDwave , - - -: Cmax 71 7.11 Comparison between L/100/100 and the U-shaped FB layout 72 7.12 Reflection in the case of the U shaped FB, direction SE 73 7.13 Comparison between the beam shaped FB, L/100/100, and U-shaped FB 75 8.1 Definition angle of incidence 78 8.2 RAO modulus - Pitch 79 8.3 RAO modulus - Roll 80 8.4 RAO modulus - Heave 80 8.5 Definition sketch of a moonpool 81 8.6 Definition sketch of a skirt 82 9.1 Regions of applicablity according to Deo (2007) 87 9.2 Wave force per meter in depth 89 9.3 Wave pressure distribution on an upright section of a vertical breakwater (Goda, 2000) 90 9.4 Wave pressure distribution on the FB 91 9.5 Wave force on one pile in function of time 95 9.6 Forces acting on one pile 97 9.7 Lateral bearing capacity (De Vos, 2008) 98 9.8 Heave Floating Breakwater 100 10.1 Non homogeneous model 103 10.2 Comparison between the beam shaped FB, L/100/100, and U-shaped FB 104 179 List of Figures A.1 Concessions Belgian coast 109 C.1 Cumulative wave height - direction N 117 C.2 Cumulative wave height - direction NNE 118 C.3 Cumulative wave height - direction NE 118 C.4 Cumulative wave height - direction ENE 119 C.5 Cumulative wave height - direction E 119 C.6 Cumulative wave height - direction ESE 120 C.7 Cumulative wave height - direction SE 120 C.8 Cumulative wave height - direction SSE 121 C.9 Cumulative wave height - direction S 121 C.10 Cumulative wave height - direction SWS 122 C.11 Cumulative wave height - direction SW 122 C.12 Cumulative wave height - direction WSW 123 C.13 Cumulative wave height - direction W 123 C.14 Cumulative wave height - direction NWW 124 C.15 Cumulative wave height - direction NW 124 C.16 Cumulative wave height - direction NWN 125 D.1 H1 / North to East 127 D.2 H1 / East to South 128 D.3 H1 / South to West 129 D.4 H1 / West to North 130 E.1 Wiegel Diagram head on waves 132 E.2 Goda Diagram head on waves 133 F.1 Results MILDwave model, Tolba testcase, Model with S = 0,94 135 F.2 Results MILDwave model, Tolba testcase, Model with S = 0,95 135 F.3 Results MILDwave model, Tolba testcase, Model with S = 0,96 136 F.4 Results MILDwave model, Tolba testcase, Model with S = 0,97 136 F.5 Results MILDwave model, Tolba testcase, Model with S = 0,98 137 180 List of Figures F.6 Results MILDwave model, Tolba testcase, Model with S = 0,99 137 F.7 Results MILDwave model, Tolba testcase, Heterogeneous model 138 F.8 Results MILDwave model, Koutandos et al (2005) testcase, Model with S = 0,94139 F.9 Results MILDwave model, Koutandos et al (2005) testcase, Model with S = 0,95140 F.10 Results MILDwave model, Koutandos et al (2005) testcase, Model with S = 0,96140 F.11 Results MILDwave model, Koutandos et al (2005) testcase, Model with S = 0,97141 F.12 Results MILDwave model, Koutandos et al (2005) testcase, Model with S = 0,98141 F.13 Results MILDwave model, Koutandos et al (2005) testcase, Model with S = 0,99142 F.14 Results MILDwave model, Koutandos et al (2005) testcase, Heterogeneous model142 F.15 Results MILDwave model, Nakamura et al (2003) testcase, Model with S = 0,94143 F.16 Results MILDwave model, Nakamura et al (2003) testcase, Model with S = 0,95144 F.17 Results MILDwave model, Nakamura et al (2003) testcase, Model with S = 0,96144 F.18 Results MILDwave model, Nakamura et al (2003) testcase, Model with S = 0,97145 F.19 Results MILDwave model, Nakamura et al (2003) testcase, Model with S = 0,98145 F.20 Results MILDwave model, Nakamura et al (2003) testcase, Model with S = 0,99146 F.21 Results MILDwave model, Nakamura et al (2003) testcase, Model with varying S146 G.1 FB length 100m 148 G.2 FB length 150m 149 G.3 FB length 200m 149 G.4 Beam shaped FB - Wave direction: SW 150 G.5 Beam shaped FB - Wave direction: WSW 151 G.6 Beam shaped FB - Wave direction: W 151 G.7 Beam shaped FB - Wave direction: WNW 152 G.8 Beam shaped FB - Wave direction: NW 152 G.9 L/150/150 - Wave direction: SW 153 G.10 L/150/150 - Wave direction: WSW G.11 L/150/150 - Wave direction: W 154 154 G.12 L/150/150 - Wave direction: NWW 155 G.13 L/150/150 - Wave direction: NW 155 181 List of Figures G.14 L/150/150 - Wave direction: NWN 156 G.15 L/150/150 shaped FB - Wave direction: N 156 G.16 L/150/150 - Wave direction: NNE 157 G.17 L/150/150 - Wave direction: NE 157 G.18 L/150/150 - Wave direction: ENE 158 G.19 L/150/150 - Wave direction: E 158 G.20 L/150/100 - Wave direction: SW 159 G.21 L/150/100 - Wave direction: WSW G.22 L/150/100 - Wave direction: W 160 160 G.23 L/150/100 - Wave direction: NWW 161 G.24 L/150/100 - Wave direction: NW 161 G.25 L/150/100 - Wave direction: NWN 162 G.26 L/150/100 - Wave direction: N 162 G.27 L/150/100 - Wave direction: NNE 163 G.28 L/150/100 - Wave direction: NE 163 G.29 L/150/100 - Wave direction: ESE 164 G.30 L/150/100 - Wave direction: E 164 G.31 L/100/100 - Wave direction: SW 165 G.32 L/100/100 - Wave direction: WSW G.33 L/100/100 - Wave direction: W 166 166 G.34 L/100/100 - Wave direction: NWN 167 G.35 L/100/100 - Wave direction: N 167 G.36 L/100/100 - Wave direction: NNE 168 G.37 L/100/100 - Wave direction: NE 168 G.38 U shaped FB - Wave direction: SW 169 G.39 U shaped FB - Wave direction: NW 170 G.40 U shaped FB - Wave direction: NE 170 G.41 U shaped FB - Wave direction: ENE G.42 U shaped FB - Wave direction: E 171 171 G.43 U shaped FB - Wave direction: ESE 172 182 List of Figures G.44 U shaped FB - Wave direction: SE 172 183 List of Tables 3.1 Directional H95% 27 3.2 Directional probability of occurrence (m) 28 3.3 Directional significant wave height (m) 28 3.4 Summary peak wave periods (IMDC) 31 3.5 Hydraulic boundaries 35 4.1 OWA support vessel 37 4.2 Motion Criteria (Pianc, 1995) 37 5.1 Hydraulic boundaries: case 39 5.2 Dimensions experiments Tolba (1999) 47 5.3 Analytical results testcase Tolba 47 5.4 Dimensions experiments Koutandos et al (2005) 48 5.5 Analytical results testcase Koutandos et al (2005) 49 5.6 Dimensions experiments Koutandos et al (2005) 49 5.7 Analytical results testcase Nakamura et al (2003) 49 5.8 Boundary conditions preliminary design 51 5.9 Dimensions preliminary design 52 7.1 Dimensions preliminary design 60 7.2 Influence of the floating breakwater length 62 7.3 H95% per direction 62 7.4 Influence of different wave incidence angles for the beam shaped FB 63 7.5 Inlfuence of different wave incident angles for the symmetric L shaped FB 150x150 65 184 List of Tables 7.6 Inlfuence of different wave incident angles for the asymmetric L shaped FB 7.7 Inlfuence of different wave incident angles for the symmetric shaped FB 100x100 68 7.8 Inlfuence of different wave incident angles for the U shaped FB 71 8.1 Motion Criteria (Pianc, 1995) 76 9.1 Parameters for wind and current force calculation 84 9.2 Dimensions Heave FB 84 9.3 Parameters for wind and current force calculation 85 9.4 Wind and current load calculation 85 9.5 Parameters for wave load calculation 89 9.6 Wave pressures according to Goda 92 9.7 Results wave force calculation according to Chakrabarti and Goda 92 9.8 Total force acting on the FB 93 9.9 Total force acting on one pile 95 9.10 Forces on heave floating breakwater 67 96 9.11 Pile properties 99 10.1 Dimensions preliminary design 102 E.1 Hydraulic boundaries case 131 F.1 Dimensions experiments Tolba (1999) 134 F.2 Dimensions experiments Koutandos et al (2005) 139 F.3 Dimensions experiments Koutandos et al (2005) 143 G.1 Results MILDwave simulations to study the FB length 148 G.2 Influence of different wave incidence angles for the beam shaped FB 150 G.3 Inlfuence of different wave incident angles for the symmetric L shaped FB 150x150153 G.4 Inlfuence of different wave incident angles for the asymmetric L shaped FB 159 G.5 Inlfuence of different wave incident angles for the symmetric shaped FB 100x100 165 G.6 Inlfuence of different wave incident angles for the U shaped FB 169 185