energies Article Simulation and Experimental Studies of a Multi-Tubular Floating Sea Wave Damper Leszek Chybowski ID , Zenon Grz ˛adzieland Katarzyna Gawdzi ´nska* ID Faculty of Marine Engineering, Maritime University of Szczecin, 70-500 Szczecin, Poland; [email protected] (L.C.); [email protected] (Z.G.) * Correspondence: [email protected]; Tel.: +48-914-809-941 Received: 26 March 2018; Accepted: 11 April 2018; Published: 20 April 2018 Abstract: This article explores the issue of shore protection from sea waves and has presented the main methods used for coastal protection. It discusses the construction and operation of the multi-tubular floating sea wave damper that has been developed at the Maritime University of Szczecin by Professor Bolesław Ku´zniewski.This paper presents the results of the research project aimed at creating and examining a prototype of the device. The research aimed to confirm the two hypotheses: “the largest damping force should occur when the damping units are placed at an optimal distance equal to half the length of the wave to be damped” and “a compensation of the horizontal forces caused by the rippling of water should occur in the damping device”. Simulation studies of the behaviour of the device’s buoyancy elements when floating on waves were performed using the ANSYS AQWAWB and AQWA software. The buoyancy components were modelled as TUBE elements with a diameter of 0.11 m and a length of 1.5 m and as triangular and square surface elements. The results of the experimental research and the computer simulation of the operation of the prototype device have also been presented. The external conditions adopted corresponded to the frequency of a wave equal to 0.807 Hz and to the wave height in front of the device which was equal to 0.1 m. Experimental studies were conducted in an auxiliary model basin with dimensions of 60 m × 7 m × 3.12 m at the Ship Hydromechanics Division, Ship Design and Research Centre (CTO S. A.) in Gda´nsk(Poland). The study recorded the distribution of the vertical and horizontal forces acting on the prototype device as well as the wave height both in front of and behind the device. Both hypotheses were proven. Simulation and experimental studies have been summarised. A proposal for future works has also been presented. Keywords: sea waves; damping; shore protection; model basin; load simulation; multi-tubular floating damper; Ku´zniewski’sdamper 1. Introduction Effective protection of the sea shore remains a valid but still unsolved social issue that forms part of the responsibilities of any public authority. The coastal area is a space of human expansion which includes the majority of hydrotechnical facilities. Furthermore, it is estimated that more than 60% of the world’s population inhabit coastal areas [1]. These areas are directly related to many fields of human activity, such as industry, trade, agriculture, fishing and tourism. As a rule, hydrotechnical facilities are structures that are subjected to complex mechanical loadings [2–8], among which of primary importance are the hydrotechnical forces associated with water movement [9,10]. The most important factors that cause water movement in coastal zones are surface waves and wave-driven currents [11–13]. Dynamic phenomena occurring in coastal zones [14], including wind-driven sea waves which are a major cause, contribute to coastal erosion and abrasion [15]. Figure1 shows an overview map of the impact of erosion processes on European sea shores. Particularly great coastal Energies 2018, 11, 1012; doi:10.3390/en11041012 www.mdpi.com/journal/energies Energies 2018, 11, 1012 2 of 20 Energies 2018, 11, x 2 of 20 Energies 2018, 11, x 2 of 20 damage can be observed in Belgium, Denmark, Estonia, France, Spain and Italy. Interesting case Particularly great coastal damage can be observed in Belgium, Denmark, Estonia, France, Spain and studies regarding Mediterranean islands can be found in references [11,12,16]. Italy.Particularly Interesting great case coastal studies damage regarding can be Mediterranean observed in Belgium, islands canDenmark, be found Estonia, in references France, [11,12,16]. Spain and Italy. Interesting case studies regarding Mediterranean islands can be found in references [11,12,16]. FigureFigure 1. ExposureExposure to to coastal coastal erosion erosion in Europe [17]. [17]. Figure 1. Exposure to coastal erosion in Europe [17]. For example, the Polish sea annually claims about 50 hectares of land which have a total value For example, the Polish sea annually claims about 50 hectares of land which have a total value of of 500For million example, zlotys. the The Polish worst sea situationannually isclaims on the about western 50 hectares coast, on of theland Hel which Peninsula have a and total on value the 500 million zlotys. The worst situation is on the western coast, on the Hel Peninsula and on the Vistula Vistulaof 500 millionSpit [1]. zlotys.There areThe areas worst where situation coastal is onregression the western exceeds coast, one on meter the Hel per Peninsulayear. Approximately and on the Spit [1]. There are areas where coastal regression exceeds one meter per year. Approximately 60% to 60%Vistula to 70% Spit of [1]. the There Polish are coastline areas where is exposed coastal to regression erosion caused exceeds by one wave meter movement. per year. EveryApproximately year, the 70% of the Polish coastline is exposed to erosion caused by wave movement. Every year, the country’s country’s60% to 70% territory of the Polishis reduced coastline by about is exposed 340,000 to erosionm2 [18]. caused In recent by wavedecades, movement. more than Every 70% year, of thethe territory is reduced by about 340,000 m2 [18]. In recent decades, more than 70% of the Polish coast has Polishcountry’s coast territory has been is affected reduced by by erosive about processes.340,000 m The2 [18]. average In recent annual decades, rate of more coastline than recession 70% of thein been affected by erosive processes. The average annual rate of coastline recession in the years from thePolish years coast from has 1975 been to affected 1983 was by 0.9erosive m/year. processes. Furthermore, The average it is important annual rate to ofrealise coastline that recessiona coastline in 1975 to 1983 was 0.9 m/year. Furthermore, it is important to realise that a coastline recession at the recessionthe years atfrom the 1975rate ofto only1983 0.10 was m 0.9 per m/year. year means Furthermore, a loss of it land is important area equal to torealise about that 37,000 a coastline m2 per rate of only 0.10 m per year means a loss of land area equal to about 37,000 m2 per year. There are a year.recession There at are the a ratenumber of only of methods0.10 m per of coastalyear means protection a loss whichof land vary area in equal efficiency, to about implementation 37,000 m2 per number of methods of coastal protection which vary in efficiency, implementation and operation costs andyear. operation There are costs a number and level of methods of environmental of coastal protectioninterference which [19–22]. vary A in brief efficiency, overview implementation of the basic and level of environmental interference [19–22]. A brief overview of the basic methods is presented in methodsand operation is presented costs and in Figure level of2. environmental interference [19–22]. A brief overview of the basic Figure2. methods is presented in Figure 2. Figure 2. Technical methods of shore protection [22]. Figure 2. Technical methods of shore protection [22]. Figure 2. The following methods are amongTechnical the most methods popular: of shore protection [22]. The following methods are among the most popular: TheBreakwater—this following methods consists are among of concrete, the most stone popular: or prefabricated structures placed parallel or at anBreakwater—this angle to the consistsshoreline. of concrete,Figure 3 stone shows or prefabricatedexample breakwaters structures placedmade ofparallel patented or at ­ Breakwater—thisprefabricatesan angle to ofthe consists various shoreline. of types. concrete, Figure One stone disadvantage 3 shows or prefabricated example to this structuressolutionbreakwaters is placed the made deepening parallel of patented or of at the an anglewaterprefabricates to thebasin shoreline. directlyof various Figure in types.front3 shows Oneof examplethe disadvantage structure breakwaters fromto this the made solution side of patentedof is the deepeningopen prefabricates sea, ofhuge the of implementationwater basin directly cost and in limitsfront ofto thewater structure exchange from between the sidethe seaof theand openthe areasea, beinghuge protected.implementation cost and limits to water exchange between the sea and the area being protected. Energies 2018, 11, 1012 3 of 20 various types. One disadvantage to this solution is the deepening of the water basin directly in front of the structure from the side of the open sea, huge implementation cost and limits to water Energiesexchange 2018, 11 between, x the sea and the area being protected. 3 of 20 ­ Components installed on the sea bed, below the water surface—barrages, artificial reefs. Components installed on the sea bed, below the water surface—barrages, artificial reefs. The The drawbackdrawback to to these these kinds kinds ofof structures is is the the deepening deepening of ofthe the water water basin basin directly directly in front in frontof of the structurethe structure and the and need the for need maintenance for maintenance and systematic and systematic monitoring monitoring of its of technical its technical condition. ­ Structurescondition. placed in the beach area—plants, fences, brushwood, geotextiles and geosynthetic materials. Structures The disadvantage placed in the of thisbeach type area—plants, of solution isfences, the extent brushwood, of intervention geotextiles in the and natural ecosystemgeosynthetic of the dunes.