The NOEL, Natural Ocean Engineering Laboratory, of Reggio Calabria (Italy)

Transcription

1 July 2011 NOEL, Lungomare Falcomatà, Rada delle Mura Greche, Reggio Calabria The NOEL, Natural Ocean Engineering Laboratory, of Reggio Calabria (Italy) Felice Arena Professor of Ocean Engineering Mediterranea University Director of NOEL

2 The first ocean engineering laboratory working in the field rather than in wave tanks equipped with wavemakers based on the successful experience of some pionieeristic small-scale-field- experiments directed by Professor Paolo Boccotti off the beach of Reggio Calabria (Italy), since NOEL, prof. Felice Arena

3 L O C A T I O N Messina Tyrrhenian Sea STRAITS OF MESSINA Ionian Sea NOEL lab Calabria Reggio Calabria Messina Reggio Calabria Sicily

4 LOCATION Beach of Reggio Calabria on the East coast of the Strait of Messina. Peculiarity. A local wind from NNW often generates sea states consisting of pure wind waves with the typical size of a big laboratory tank (significant wave height 0.20m<H s <0.80m, peak period 2.0s<T p <3.6s). This local wind is very stable, and sometimes keeps steady from morning to evening. The tide amplitude is small (typically within 0.10m). The water is very clear because of the current which flows twice in a day.

5 THE ORIGIN OF LABORATORY On 1989 Professor Paolo Boccotti directed the first experiment aimed at verifying the possibility to work in the sea as in a big wave tank. In 1990 a small scale field experiment was carried out off the beach of Reggio Calabria to verify the theory of Quasi-Determinism, that defines the mechanics of three-dimensional wave groups when a very high wave occurs. The results of the experiment gave a full confirmation of the theory (Boccotti et al. 1993) and showed that the sea off the Reggio Calabria promenade is a natural lab for small scale field experiments (Phillips et al. 1993). Here a local wind blowing from Messina toward Reggio Calabria generates wind waves with spectra very close to the mean JONSWAP, spectrum during most time of a year.

6 THE ORIGIN OF LABORATORY.. After three more experiments the Mediterranea University of Reggio Calabria decided to build a laboratory in the promenade of Reggio Calabria. The municipality of Reggio Calabria included the laboratory in a big project for the city seaside. This includes an open theatre and a new promenade with a splendid sight of the Straits of Messina and Sicily. The new laboratory has its own beach, and its own water sheet within 50m from the shoreline. It includes a conference room, a room with the electronic station and a P.C. network, offices and a small workshop. The small scale field experiments are performed in the water sheet off the beach. The instruments are connected by cables to the electronic station. People attending symposia held in this lab can get a real time view of the experiments.

7 The new management and the N.O.E.L. In March 2009 the Mediterranea University of Reggio Calabria assumed direct management of the laboratory, and Professor Felice Arena was designated as Director of the Lab, supported by the Scientific Supervision of Professor Paolo Boccotti (they are both full professor of Ocean Engineering). In this new phase of the lab, activities are run with the support of the PhD students of the ocean engineering program, as well as graduate students, which participate to the experiments. In the lab academic activities, as lectures for under graduate students, are also held.

8 The Staff of the N.O.E.L. (2009/2010): Professors and researchers of the Mediterranea University (Alessandra Romolo, Giuseppe Barbaro, Paolo Boccotti, Vincenzo Fiamma, Felice Arena)

9 The Staff of the N.O.E.L.: With some PhD students and PostDoc of the Mediterranea University

10 Lectures in the N.O.E.L. ( ): Prof. Pol D. Spanos (Rice University, USA) Prof. F. Einaudi Prof. P. Boccotti NASA,USA

11 Prof. Carlos Guedes Soares, Instituto Superior Tecnico, Lisbon

12 Professor Franco Einaudi Goddard Space Flight Center NASA, USA May, June 2011

13 Professor Pol D. Spanos, Rice University, Houston Texas, USA - April 2011

14 Professor Francesco Fedele Georgia Institute of Technology, USA June 2011

15 PhD in Ocean Engineering Final exams cicle XXI XXI

16 PhD in Ocean Engineering Final exams cicle XXII PhD in Ocean Engineering Final exams cicle XXIII XXII XXIII

17 Early experiments of Professor Paolo Boccotti in the natural ocean engineering laboratory of Reggio Calabria

18 NOEL experiment RC1990, on mechanics of three-dimensional wave groups in the open sea, and formation of exceptionally high waves. There were nine vertical piles of small section on deep water, each with instruments for measuring the free surface displacement, and pressure transducers for measuring the fluctuating pressure head beneath the water surface. The experiment aimed to check the basic predictions of the quasideterminism theory: an exceptionally high wave in a wind generated sea-state occurs because of the transit of a characteristic wave group at the apex of its development. The theory is based on a closed-form solution of probabilistic wave mechanics, and describes in details this three dimensional wave group, giving not only the free surface displacement but also the velocity potential.

19 1990 Mechanics of three-dimensional wave groups in the open sea, and occurrence of exceptionally high waves... In particular the theory shows that, whichever the spectrum of the sea state, the wave group has a development stage which is followed by a decay stage. During the development stage, the envelope and the wave crest shrink and as a consequence the height of the central wave of the group grows up to a maximum. The opposite occurs during the decay stage. The individual waves have a propagation speed greater than group s speed, so that each of them runs along the envelope from the tail where it is born to the head where it dies. As a consequence each individual wave experiences some great transformations during its evolution, especially when the three dimensional wave group is close to the apex of its development.

20 NOEL experiment RC1991. Mechanics of three-dimensional wave groups interacting with a vertical breakwater, and formation of high waves at the breakwater and in the water sheet before the breakwater. A special vertical breakwater 12m long was built on 1.5m water depth. Thirty wave gauges were assembled in the water sheet before the breakwater. The experiment aimed to check the quasi-determinism theory for what concerns waves interacting with a reflecting wall. In particular the theory predicts that an exceptionally high wave at the wall, most probably is the central wave of a three-dimensional group hitting the breakwater, at the apex of its development stage.

21 NOEL experiment RC1991. Mechanics of three-dimensional wave groups interacting with a vertical breakwater, and formation of high. The theory predicts that, an exceptionally high wave at a point far from the breakwater, most probably, is the outcome of two wave groups at the apex of their development, which strike each other in full at this point. The experiment also aimed to verify some predictions on the frequency spectrum as a function of the distance from the breakwater.

22 NOEL experiment RC1992. Mechanics of random wave forces on gravity offshore platforms. The 1:50 scale model of a gravity offshore platform was towed and sank on 2.5m water depth. A first set of transducers was placed at the base and at a column of the platform. A second set of transducers with the same configuration of the first set, and on the same water depth, was placed at some distance from the platform. Thus it was possible to get a real time comparison between the wave force on the solid body and the wave force on an equivalent water mass (Froude Krylov force).

23 NOEL experiment Wave forces on large horizontal cylinders. This experiment was similar to RC1992 with the difference that here the solid body was the 1:30 scale model of a submerged tunnel. Like in RC1992 there were two sets of pressure transducers, one at the solid body (tunnel) and one with the same spatial configuration, at some distance from the solid body so as to get a real time comparison between the wave force and the Froude-Krylov force. Two kinds of tunnels were tested. First: a tunnel of 27m diameter for the railway and the highway. Second: a tunnel of 13.5m diameter for the railway only. The most typical Hs (significant wave height) of the small wind waves of Reggio Calabria is 0.30m, and we fix the model scale as equal to the quotient between this most typical Hs and the design Hs of the prototype. In the case of the experiment RC1992 (model of the gravity offshore platform) the design Hs of the prototype was 15m so that the model scale was 1:50. In the case of the experiment RC1993 (model of a submerged tunnel) the design Hs of the prototype was 9m so that the model scale was 1:30.

24 NOEL experiment Mechanics of random wave forces on vertical breakwaters. A small vertical breakwater 12m long was assembled like in the experiment RC1991. This time a set of transducers was put at various elevations at the wall centre. The aim was to analyze the wave pressure on this kind of structure, both under wave crests and wave troughs. The effects of high water jets like that of the photo were deeply investigated.

25 NOEL exp Submerged caisson for absorbing sea wave energy. In autumn 2001 we assembled a 1/10 scale model of one caisson of the so called invisible breakwater disclosed by Professor Boccotti. This breakwater consists of caissons well beneath the water level (at full scale: 3-5m beneath the mean water level). Hence, we are dealing with a breakwater with a very low environmental impact. Under wave action water enters into (or exits from) the caissons, and as a consequence an air pocket (1) in a room inside the caisson is compressed or expands B B SECT A-A

26 NOEL exp On tuning the height of the air pocket, it is possible to induce resonance. Thanks to resonance the plant can absorb a large share of the incident wave energy. This energy is wasted inside the caissons. The experiment showed that, on tuning the height in the air pocket, it is possible to get an impressive amplification of the random pressure fluctuations inside the plant. Moreover the experiment confirmed that the height of the waves off a beach can be controlled on opening or closing two valves on the beach. Air compressor compressore Air pocket polmone d'aria x

27 NOEL exp Vertical breakwaters for converting sea wave energy into electric power. On spring 2005 we assembled a 1/10 scale model of a caisson breakwater with a U-OWC embodied (size of the model: 16.2m length, 2m water depth, weight about 300tons). The U-OWC converts the chaotic wave energy into the energy of a high speed air current in a tube. The energy of this air current can be converted into electric power by means of a Wells turbine. In the experiment 2005 there was no turbine, so that there was only the first step: from the chaotic wave energy to the energy of the air current in the tube.

28 NOEL exp Vertical breakwaters for converting sea wave energy into electric power. The aim of the experiment was not to improve the design empirically on changing size and shape of the various part of the plant. On the contrary, the design had be performed up to details, analytically, on exploiting a powerful tool for design which is the Quasi Determinism of the largest sea waves (Boccotti, 2000; chaps. 9-10). The experiment aimed to verify two things of general interest, which emerged from the Boccotti s solution (2007) for the interaction waves U-OWC. Specifically, the experiment aimed to verify whether or not the plant can convert the very 100% of the energy of the long swell, thanks to a super amplification of these swell, amplification that cannot expand towards the open sea, since the propagation speed of the reflected wave energy approaches zero. This time the confirmation was really spectacular: in a number of records of long swell, nearly the 100% of the wave energy was converted into the energy of the air current in pressure, and this occurred thanks to some super amplifications of the waves at the breakwater embodying the U-OWC, just as it was predicted.

29 NOEL exp Vertical breakwaters for converting sea wave energy into electric power. Mare Seaward tube 2 Saracinesche / turbine Blocchi zavorra in calcestruzzo Concrete ballast Terra Comparison: a traditional caisson massi guardiani And a REWEC3 caisson II 1 5 φ F 1 φ III larg h ez za m ed ia co n d o tto : III 2 0 II S ez. I

30 Experiments in the NOEL with the new management of the Mediterranea University Director: Professor Felice Arena Scientific Supervisor: Professor Paolo Boccotti

31 NOEL exp 2009 a. Directional spectra in coastal area measured by two gauges The first experiment (of May 2010) dealt with the directional spectrum recorded by wave gauges, either ultrasonic probes measuring the free surface elevation or the transducers, measuring the wave pressure.

32 NOEL exp 2009 b/c. Sea wave forces on a vertical wall The experiment dealt with the wave pressures and the wave forces on vertical walls at sea. This experiment was carried out for different relative water depths, in May (exp b) and in October-December, (exp c) to analyze the extreme pressures and forces on the wall when high waves occur. The wave force was measured by means of a set of pressure transducers, on the mid vertical section of the wall.

33 NOEL exp spring 2009d. Hydrodynamic forces of sea waves on horizontal submerged cylinders At the end of September 2009 a new experiment started, to analyze the wave forces on cylinders. The first experiment was carried out by considering a vertical cylinder. The wave force is measured by means of a set of pressure transducers in a horizontal section of the cylinder z 0.75m ultrasonic probes 1.8m x wave pressures 2.0m 1.45m 1.2m

34 NOEL exp spring Waves and QD in space-time domain In the spring of 2010, an experiment was carried out on the wave group mechanics and statistics in space time domain. The Boccotti s Quasi-Determinism theory predicts that the high waves during storms are joined in groups; all wave groups with high waves have the same characteristics and have similar changing during they propagation. During this experiment, 26 wave gauges were used for recording waves simultaneously. The result is a full and spectacular validation of the QD theory. It has been found that wave groups, when a very 0.0 high wave occurs (very high with respect to the mean wave height), recorded in different days, are very close to each other! A very important consequence in ocean -5.0m engineering: freak waves (or giant waves) during a storm have all the same characteristics and have the same evolution during they propagation. 1.20m 15.0m m θ 22.0m y -2.0m y horizontal beam wave direction

35 NOEL exp autumn 2010-spring Hydrodynamic forces of sea waves on horizontal submerged cylinders In October 2010 a new experiment has started, on hydrodynamic forces of sea waves on horizontal submerged cylinders (tunnels of pipelines). A submerged cylinder is supported by the structure shown in the picture (in the Northern part of the Lab). It is possible to see two ultrasonic probes which record the free surface displacement (red circles). The forces on the cylinder are recorded by means of eight pressure transducers in the vertical mid section of the submerged cylinder. It is the first experiment in the world on sea wave forces on submerged pipelines, carried out at sea with techniques of laboratory

36 NOEL exp spring Waves and QD in space-time domain in front of a vertical breakwater.. Ongoing

37 Selected papers on historical experiments in the natural ocean engineering laboratory (up to 2007) P. Boccotti, G. Barbaro, L. Mannino, A field experiment on the mechanics of irregular gravity waves, Journal of Fluid Mechanics, 252, , 1993 P. Boccotti, G. Barbaro, L. Mannino, V. Fiamma, A. Rotta, An experiment at sea on the reflection of the wind waves, Ocean Engng., 20, , 1993 P. Boccotti, A field experiment on the small scale model of a gravity offshore platform, Ocean Engng., 22, , 1995 P. Boccotti, Inertial wave loads on horizontal cylinders: a field experiment, Ocean Engng., 23, , 1996 P. Boccotti, A general theory of three-dimensional wave groups., Ocean Engng., 24, , 1997 F. Arena, Statistics of wave forces on large horizontal cylinders, Ocean Engng, 29/4, , Arena, F. & Fedele, F. (2002). A family of narrow-band non-linear stochastic processes for the mechanics of sea waves. European Journal of Mechanics - B/Fluids, Vol. 21, Issue 1, pp Boccotti, P., On a new wave energy absorber, Ocean Engineering, 30, , 2003 Arena, F. (2006). Interaction between long-crested random waves and a submerged horizontal cylinder. Physics of Fluids, Vol. 18, Issue 7, paper , pp. 1-9, doi: / Boccotti P., Filianoti P, Fiamma V, Arena F., Caisson breakwaters embodying an OWC with a small opening Part II: A small-scale field experiment. Ocean Engineering. vol. 34, pp ISSN: Arena, F. & Filianoti, P. (2007) A small-scale field experiment on a submerged breakwater for absorbing wave energy, ASCE Journal of Waterway, Port, Coastal, and Ocean Engineering, Volume 133, Issue 2, pp , doi: /(asce) x(2007)133:2(161) Boccotti P., Quasi-determinism theory of sea waves, ASME Journal Offshore Mechanics and Arctic Engineering JOMAE, Vol. 130, pp paper JOM (the paper was the invited lecture given at the 2006 OMAE Congress in Hamburg).

38 Selected papers on historical experiments in the natural ocean engineering laboratory (up to 2007) Books Boccotti, P., Idraulica Marittima, UTET, 1997, Boccotti, P., Wave Mechanics for Ocean Engineering. Elsevier, Amsterdam, 2000.

39 Selected papers on experiments in NOEL Boccotti, P., Arena, F., V. Fiamma & G. Barbaro (2010) Drag and inertia coefficients for the Morison equation, being obtained from a small scale field experiment, Proc. of the 6th Computational Stochastic Mechanics Conference, Rodhos, Greece, June 2010, Research Publishing :: ISBN: , pp Boccotti, P. (2010) field experiment on random-wave forces on vertical cylinders. part i: possibility of simulating the random process, Proc. of the 6th Computational Stochastic Mechanics Conference, Rodhos, Greece, June 2010, Research Publishing Romolo A., Arena F. (2010) A Small-Scale Field Experiment for the Validation of a Theory on Reflection of Nonlinear Short-Crested Wave Groups, Proceeding 32st International Conference Coastal Engineering (ICCE 2010) - ASCE, 30 June - 5 July 2010, Shangai, China. Arena, F. (2010) Nonlinear ocean wave groups with high waves, Instituto Superior Tecnico - CENTEC research center, Taylor & Francis, in press. pp Boccotti, P., Arena, F., Fiamma, V., Romolo, A. & Barbaro, G. (2011) Estimation of mean spectral directions in random seas, Ocean Engineering, Vol. 38, Issue 2-3, pp Boccotti, P. (2011) A field experiment on the recurrence of large waves in wind seas, Ocean Engineering, in press Boccotti, P., Arena, F., Fiamma, V., Romolo, A. & Barbaro, G. (2011) A small scale field experiment on wave forces on upright breakwaters, ASCE Journal of Waterway, Port, Coastal, and Ocean Engineering, in press Boccotti, P., Arena, F., Fiamma, V., Barbaro, G. (2011) Field experiment on random-wave forces on vertical cylinders, Probabilistic engineering mechanics, in press Boccotti, P., Arena, F., Fiamma (2011) Distributions of wave heights on the time domain and on the space domain, in a stationary sea state, under peer review

40 For further information, please visit or contact the Director, Professor Felice Arena (telephone , Thank you!