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Similitude laws for scaling the vibration response of flat panels to a turbulent boundary layer excitation are proposed and analyzed in this paper. Their relevance is studied from an analytical, experimental and numerical perspective. It is first shown that a perfect similitude, in terms of vibration response scaling, can theoretically be achieved between plates of proportional sides and of variable thicknesses. Vibration auto-spectral and cross-spectral density functions, measured in a wind-tunnel facility on a set of three plates, are then successfully scaled: the plates dimensions and test flow speeds are a priori defined using the proposed similitude laws. Finally, the applicability of the suggested strategy for different boundary conditions, for different types of materials and properties and for distorted models is also numerically studied and confirmed. (C) 2019 Elsevier Ltd. All rights reserved.

Nell'ultimo decennio è cresciuta sempre più la consapevolezza del ruolo imprescindibile rappresentato dal mare sulla vita del nostro pianeta. La maggior consapevolezza è stata accompagnata da un crescente senso di preoccupazione scaturito poi in uno stato di allarme a livello mondiale. L'allarme è stato generato dall'evidente stato di depauperamento delle risorse, delle funzioni e dei servizi eco-sistemici forniti dal mare, sui quali da sempre si sono basati gli equilibri del mare stesso e su cui, peraltro, si fonda lo sviluppo socio economico di una cospicua porzione del pianeta. Le condizioni di allarme si sono manifestate dapprima in sordina e poi via via in maniera più eclatante nel momento in cui il mare ha iniziato a riproporre, tal quali, i prodotti di scarto per secoli scaricati indiscriminatamente in esso, uno tra tutti la plastica, sfatando quella concezione errata ampiamente diffusa che il mare fosse un recettore e digestore inesauribile. L'approccio migliore per affrontare una tale questione di portata planetaria, generato di fatto da una profonda carenza culturale, non può che basarsi su una nuova concezione culturale della risorsa rappresentata dal mare.

The BlueMed Strategic Research and Innovation Agenda (SRIA) outlines a set of key challenges for the Mediterranean and particularly knowledge gaps, specific activities enabling the blue growth as well as measures for capacity creation and skills' enhancement. Sectors of interest include ecosystems, climate change, biotechnologies, aquaculture, fisheries, tourism, shipbuilding, transportation, observing systems, data, off-shore platforms, cultural heritage, spatial planning. Drafted by engaged stakeholders from EU and non-EU Mediterraenan countries, this version was reviewed in 2020, in connection with the Implementation Plan and the Euro-Mediterranean context development

The present deliverable LIFEMEDECA Action A2 "Additional socio-economic assessment" aims at carrying out the additional socio-economic assessments (as mandated by the road map agreed at COP21) and at dealing with emerging relevant technical and/or scientific issues which might jeopardise an appropriate assessment of needs and bottlenecks toward the establishment of a MED ECA. Action A2 also aims at defining the baseline scenario with the results of the assessments and will be the basis for an interim report at COP22.

In the second half of the year, CNR activities focused on the development of additional studies (action A2) to support the establishment of the ECA in the Mediterranean and on the networking with other projects and initiatives (action B3). Moreover, the communication and dissemination activities (action B1) performed include the participation to events, the organization of a workshop and a press conference and the submission of an abstract for the Transportation Research Arena (TRA) conference. Finally, CNR support the management of stakeholders, started the design and the implementation of the Knowledge Centre (action B2) and hosted a project and Steering Committee meeting (action C1).

Scope of deliverable B.3.D.1 is to provide the 2021 annual "Networking Progress Report" which summarizes the work carried out within Act.A3 during the year with reference to: a)relevant past and/or ongoing, LIFE and non-LIFE projects and other initiatives will be identified during the whole Action's duration; b)after assessing each identified project/initiative, the most relevant in view of their potential contribution to / synergy with LIFE4MEDECA will be networked with; c)ad hoc one to one interface/meeting will be organized as appropriate to collect/gather relevant input for LIFE4MEDECA actions in general and with a special focus on actions A1, A2, A4 and B2.

Similitude laws for the vibration response of simply supported plates under random excitations are derived and tested numerically and experimentally for the case of a turbulent boundary layer. Analytical calculations show that under the assumption of proportional sides, perfect similitude in terms of vibration response scaling can be achieved between plates of variable thicknesses. It is also highlighted that even if the similitude conditions are not all satisfied (i.e., a complete scaling of all the involved parameters, from panel dimensions to flow speed), an approximation can be made in the mid-high-frequency domain that leads to satisfactorily scaled results. Based on the analytical study, a series of tests is performed in an anechoic wind tunnel on three-scaled simply supported panels at different flow velocities. Applying the proposed procedure to this set of vibration measurements leads to satisfactory scaling of results between each other.

La Strategia per l'Economia Blu riconosce che i mari e gli oceani rappresentano un motore per l'economia europea con enormi potenzialità per l'innovazione e lo sviluppo sostenibile nei settori marino e marittimo. Nell'ambito della terza edizione del BUIG-Mare, un lavoro corale insieme alle istituzioni con cui quotidianamente si lavora "sul" mare e "per" il mare, il contributo delinea lo stato dell'arte dell'iniziativa di ricerca e innovazione BlueMed per lo sviluppo dell'economia sostenibile dal mare nell'area del Mediterraneo valorizzando la dimensione nazionale.

In structural dynamics, similitude laws usually deal with simple configurations as thin flat plates with point forces. Only recently, few papers have analyzed stiffened shells or stochastic pressure loads. This research activity extends the applicability of some similitude laws, developed for thin flat plates under a turbulent boundary layer load, to ribbed plates forced by the same wall pressure fluctuations. The work addresses the problem of designing a scaled experimental test-article and, successively, of re-modulating the measured data in order to get the structural response of an original (unscaled) configuration. Due to the complexity of the structural domain, the design of a scaled configuration leads to a distorted similitude. Then, a simple approach, to circumvent the distortion effects, is proposed.

The paper presents an overview of technology trends for disruption in short and medium terms related to naval science and engineering, such as everywhere computing, predictive analytics, unmanned and autonomous vehicles, mixed reality, every¬where sensors, artificial intelligence and marine robotics.

In order to ensure the efficient implementation of BLUEMED key priorities identified in the BLUEMED Implementation Plan, research infrastructures (RI) are key tools. This roadmap aims at giving an overview of the actions to be carried out at the Mediterranean level to further support the scientific needs of research and innovation communities and it results from a long bottom-up process carried out throughout the whole CSA.

In questo documento viene analizzato lo stato delle conoscenze attuali per ciascuna delle 3 macro-tematiche al fine di individuare gli aspetti conoscitivi su cui indirizzare gli sforzi futuri, identificando benefici specifici attesi, diretti ed indiretti, delle azioni per colmare le principali lacune conoscitive. In particolare vengono definite le principali tecnologie con maggiore potenziale di innovazione. Sono poi identificati i principali fattori abilitanti l'implementazione delle tecnologie individuate e le ricadute attese su politiche, strategie e normative, azioni di marketing, ricerca, finanziamenti, skills, il tutto in un contesto nazionale, inserito nel più vasto contesto EU e Mediterraneo. Considerata la molteplicità ed eterogeneità dei temi trattati nei 29 task del progetto ITEM, la redazione del documento oggetto delle prime due deliverable è stata organizzata accorpando temi simili sia all'interno dello stesso WP che, nel caso dei sistemi produttivi tecnologici e biotecnologici, fra WP diversi. Il documento è diviso quindi in due parti: quella relativa al WP3- Sistemi osservativi e quella relativa ai WP 4 e 5, Sistemi produttivi tecnologici e biotecnologici, che presentano alcuni argomenti comuni. Inoltre, per facilitare la lettura del documento, per ogni argomento individuato, il risultato dell'analisi dello stato delle conoscenze e dei gap conoscitivi viene presentato congiuntamente a quello dell'analisi dei potenziali di tecnologie per colmare le lacune individuate ed indirizzare le normative, di fatto unificando i risultati del task 1 e del task 2 per ciascun argomento.

This work presents an investigation on the definition and applicability of distorted similitudes and the related scaling laws for the analysis of the dynamic forced response of rectangular composite plates. Such responses are determined from a generalization of the modal approach, which allows the use of the mode shapes and natural frequencies in order to establish the proper scaling laws. The cases, herein discussed, are exclusively theoretical and form the basis for the application of numerical methods such as the Finite Element Method. Analytical models of simply supported rectangular plates are used to produce both the original and distorted model responses. The results show that even in the case of distorted models it is possible to reproduce with reasonable accuracy the response of the original plate.

50% of the total drag of many ships and submarines [1]. Thus, researchers have devoted their efforts to the quest for surfaces with reduced drag to be applied on marine vessels. Bioinspired, liquid-repellent surfaces have been intensively investigated for this application. However, the well-known superhydrophobic surfaces have proven unsuitable for underwater conditions, due to the loss of trapped air pockets. On the other hand, Slippery Liquid-Infused Porous Surfaces (SLIPSs) have provided encouraging results in terms of drag resistance reduction and long-term stability [2]. However, further studies are needed to establish more solid relationships between SLIPS engineering and their drag resistance properties. In this work, we have fabricated and tested SLIPSs with different infused oils. All these SLIPSs were based on a randomly oriented, nanostructured boehmite coating combined with an organic layer to promote retention of the infused liquid. Perfluoropolyethers, silicone oils and n-hexadecane were used as infused liquids. The drag resistance behavior of SLIPSs has been tested in three experiments involving different scales and flow régimes: ? Visualization of the rolling/sliding motion of a single drop on a tilted surface ? Measurement of the torque in a Couette-like flow apparatus (laminar conditions) ? Measurement of the wall shear force in a high-speed boundary layer over a large flat plate (turbulent conditions). Preliminary results indicate that a careful design of SLIPSs is necessary to achieve the best compromise between drag reduction and long-term stability, particularly when the more challenging requirements typical of real, high-Reynolds number flows must be considered. [1] Perlin, M.; Dowling, D. R.; Ceccio, S. L. Freeman Scholar Review: Passive and Active Skin-Friction Drag Reduction in Turbulent Boundary Layers. J. Fluids Eng . 2016 , 138 (9) , 091104. [2] Rosenberg, B. J.; Van Buren, T.; Fu, M. K.; Smits, A. J. Turbulent Drag Reduction Over Air- and Liquid-Impregnated Surfaces. Physics of Fluids 2016 , 28 , 015103.

This communication investigates exact and distorted similitudes and the related scaling laws for the analysis of both dynamic response and radiated power of rectangular plates. The response of a given panel in similitude from another one is determined from a generalization of the modal approach, allowing the use of mode shapes, natural frequencies and nally radiation functions in order to establish appropriate scaling laws. Analytical models of simply supported rectangular plates are used to produce both original and replica model responses under point mechanical excitation. Emphasis is then especially put on laboratory experiments which are performed on baed simply supported aluminum panels under mechanical excitations. All the six possible scaling directions, i.e. predicting a plate vibroacoustic reponse from another plate, are reported. All obtained results show that structural response or radiated sound power of a given plate can be both recovered with satisfactory accuracy by using the related scaling laws, even if parent models are used.similitude; plates vibration; scaling

The analysis of the response of a stochastic system, through a discrete coordinate set, can become computationally challenging, even when using a full modal representation. Nevertheless, many dynamic load cases, in engineering applications, have stochastic behaviour as the wall pressure fluctuations due to the turbulent boundary layer. In this work, a new method is proposed: it is named as frequency Modulated Pseudo Equivalent Deterministic Excitation, PEDE M , and it is based on the Pseudo Excitation Method, PEM. This latter can be considered as an exact representation since it uses a modal decomposition of the cross-spectral density matrix of the excitation; the extraction of the eigensolutions of the load matrix, at each frequency step, is a computational disadvantage. PEDE M overcomes this issue by introducing some approximations based on the analysis of the eigensolutions of the dynamic load matrix versus frequency. Mainly, two different approximations are proposed with reference to extreme frequency ranges (low and high) wherein the dynamic matrix of a random and convective load has different characteristics. A criterion to identify these frequency ranges is proposed versus a dimensionless representation of the frequency. Moreover, it is shown that the proposed approximations represent the bounding curves of the response for the whole frequency range. Fruitful comparisons with a full stochastic approach is discussed. The proposed approximations combine a good accuracy and representation of the stochastic system together with a significant reduction of the computational costs if compared to a full stochastic response or a PEM solution. The method is applied over two simple configurations (a chain of oscillators and two flexural plates) but the possible extensions to more complex cases are motivated by the quality of these preliminary results.

This report represents an overview and analysis of recent R&I strategies and programmes and funding schemes of interest for the BLUEMED Initiative at international, European, regional and national level, a background document to initiate and facilitate dialogue and interaction between research funding agencies of different countries and European Institutions. Once the strategic alignment of agendas on areas of mutual interest has been identified, the aim is to lay the groundwork for operational alignment towards the launch of transnational actions. It will also provide an auxiliary tool to design the BLUEMED Implementation Plan.

L'agenda strategica per la ricerca e l'innovazione è lo strumento di riferimento dell'iniziativa intergovernativa BlueMed per lo sviluppo della crescita blu nel Mediterraneo, alla quale aderiscono 16 paesi europei e non europei del bacino. Sviluppato nell'ambito del progetto BlueMed CSA coordinato dal CNR, a partire dalla prima edizione del 2015 e a valle di una consultazione capillare degli stakeholder di riferimento per le attività marino-marittime, il documento definisce priorità strategiche di ricerca cross-disciplinari e multi settoriali intorno ai pilastri della conoscenza, economia, tecnologia e policy. Esso è dunque pensato, anche nella forma comunicativa, per facilitare il successivo intervento dei policy makers nella definizione dei programmi di ricerca.

Rendicontazione scientifica SP1_LI1_WP1: UO01 Rumore subacqueo UO03 Riduzione dell'impatto del wave wash sull'ambiente costiero UO04 Valutazione di superfici super-idrofobiche in condizioni reali UO05 Utilizzo di vernici sensibili alla temperatura per la determinazione dell'attrito a parete

Skin-friction drag is a major source of energy dissipation in marine vehicles. In addition, self-induced noise generated by turbulent boundary layer can strongly limit the operation of on-board sensors. Therefore, designing surfaces with friction drag reduction and vibration control properties is a research topic of great interest for the marine transportation field, both in civil and military segments. Liquid-repellent surfaces have been identified as potential solutions for drag reduction and some papers have already proved their positive effects on drag1,2, but also their inherent limits3. Moreover, no one has ever investigated the potential of liquid-repellent surfaces in terms of self-induced noise attenuation. In our study, we first fabricated water-repellent surfaces following two well-known biomimetic approaches, namely the SuperHydrophobic Surface (SHS) approach and the Liquid-Infused Surface (LIS) one. Then, we performed experiments in a high speed water channel to evaluate frictional drag and vibration induced by the turbulent boundary layer (Re?106). Drag experiments were performed on floating aluminum surfaces (48x28 cm2) bearing a flexural load cell that measured the frictional force exerted by water flow. Meanwhile, in noise experiments a tray-shaped surface was fixed to a rigid frame while 8 piezoelectric accelerometers measured its vibrational response to water flow. On one hand, SHSs showed quick air plastron depletion during the tests, leading to no drag reduction and higher vibration level compared to a reference uncoated panel. On the other hand, LISs showed remarkable drag reduction (up to 16%) in the 1.0÷3.5 m/s velocity range and reduction of the acceleration response spectra at medium and high frequencies, regardless of flow velocity. These preliminary results suggest LISs as potentially relevant surfaces to reduce friction drag and self-induced noise, with perspective huge impact in marine transportation. Further experiments are needed to explain the observed noise attenuation and drag reduction effects, which indeed overcame expectations.

In this paper, some possible applications of scaling-laws for the vibroacoustics of structures are studied. Two experimental works conducted on simply-supported plates submitted to different mechanical and acoustic loadings are described. The first concerns similitudes for the dynamic vibration response and radiated acoustic power of flexural plates under point mechanical excitations. Exact and distorted similitudes and the related scaling laws are investigated from analytical and experimental points of views. All obtained results show that structural response or radiated power of a given plate can be both recovered with satisfactory accuracy by using the related scaling laws, even if parent models are used. The second work concerns similitudes for the vibration of plates under a turbulent boundary layer excitation. Both analytical and experimental analyses are again conducted. It is shown that under the assumption of proportional sides, perfect similitude in terms of vibration response scaling can theoretically be achieved between plates of variable thicknesses. This is experimentally confirmed with the satisfactory scaling of the acceleration autospectral density measured at several discrete points on three parent panels at different flow speeds. The extension of the scaling procedure to cross-spectral density functions is finally studied. As for the autospectral density, the cross-spectral density of acceleration between two points can be effectively retrieved from one panel to another using similitude laws. This opens the possibility of predicting the radiated acoustic power for scaled flow-induced problems, as a bridge between the two summarized works.

The study of the interaction between elastic structures and turbulent boundary layer still presents some uncertainties. This is true even assuming a one-way coupling and stationary turbulent boundary layer (TBL) over smooth and flat plates in subsonic flow. The reasons are mainly related to (i) the limitation for the direct numerical simulations of Reynolds number value of the Navier-Stokes equations, (ii) the high frequency structural and acoustic numerical and modelling difficulties and (iii) the lack of experimental data representative of all frequency-wavenumber pressure fluctuation regions, needed for the direct validation of the semi-empirical pressure models. In fact, when the pressure convective terms are the dominant sources of vibrations and radiated noise, consolidated and almost case independent formulations exist; on the contrary, when the subconvective terms are of concern, the definition of models seems to be strongly dependent on the flow conditions and the characteristics of the fluid-structure interaction. In order to find a general procedure for the estimation of the response of elastic thin panels to TBL excitation, some scaling laws derived using dimensional analysis and energetic considerations are proposed. These dimensionless relations contain a combination of both flow and structural parameters yielding to simple analytical expressions relating a dimensionless structural response metric and a dimensionless frequency. The found scaling expressions are validated with wall pressure fluctuations and vibrational response data acquired in wind tunnels and towing tank for the case of thin flat plates made of homogeneous isotropic and composite materials.

The quality of the predictive structural (and structural-acoustic) response of an elastic (structural) domain, under a random and convective load, is analyzed here through a discussion of the main steps of a numerical procedure. The structural response of a plate, due to a known wall pressure distribution, is derived in modal coordinates according to a finite element scheme. The modal basis can include the dry or wet (aeroelastic) structural mode shapes: in the present analysis only the in vacuum eigenvectors are used. For this problem, the transformation of the pressure distribution into discrete locations is one of the most critical steps that depends on (i) the model assumed for wall pressure fluctuation description (the assumed turbulent boundary layer model), (ii) the integration scheme and (iii) the frequency range. These three aspects are the main goals of this work. In particular, it is presented the sensitivity of the structural response toward the adopted numerical approximations. The transformation of the pressure distribution into discrete locations can be computationally expensive for the desired level of the required numerical approximation. The use of consistent formulation, in the finite element scheme, can be sometimes unfeasible. Some numerical approaches, dealing with the high frequency bands, are analyzed and some enhancements are proposed aiming at a reduction of the computational cost. © 2013 Elsevier Ltd.

The analysis of the response of a stochastic system, through a discrete coordinate representation, can become computationally challenging, even by using a full modal representation; in fact, many dynamic load cases have stochastic behaviour as the wall pressure fluctuations due to the turbulent boundary layer. In the present work, a new method is presented and discussed and it is named frequency modulated pseudo equivalent deterministic excitation (PEDEM). PEDEM is based on the pseudo excitation method (PEM), but it tries to overcome the computational neck-bottles of this latter by introducing some approximations which are based on the analysis of the eigensolutions of the dynamic load matrix versus frequency. The solution approach uses three different approximations for the load matrix with reference to three frequency ranges, named low, mid and high; these approximations derive from the eigenanalysis of the load matrix. A criterion to identify the three frequency ranges is proposed, too and it is expressed in terms of a reduced dimensionless frequency. PEDEM is thus applied to a plate response; this test case that contains the most relevant parameters of a structural problem. The results herein discussed show that the correlation area can play a fundamental role in discriminating the quality of the approximation. A good level of accuracy and representation of the stochastic system together with a significant reduction of the computational costs are obtained if compared to a full stochastic response (FSR) or PEM solution.

Deliverable 3.2 "Final report on towing tank experiments" contains the results of the experimental activities performed in the CNR-INSEAN towing tank, devoted to the characterisation of the flow in correspondence of the test section of the Flame model, of the velocity field beneath the boundary layer, of wall pressure fluctuations and of the vibro-acoustic response of a reference metallic plate and of other three covered with different materials. In particular, the influence of the flow history in the test section, located approximately 2.5 m downstream the bow of the model has been analysed. Mean and fluctuating velocity quantities, scaling laws and models for the single point pressure spectra, cross spectral density and related semi-empirical models as well as wavenumber-frequency spectra are reported. Moreover, results relative to acceleration and acoustic pressure measurements, modal and data analyses are discussed. The main achievements and conclusions are summarised below. * The measured mean pressure difference acquired at the beginning and at the end of the wall pressure sensors array shown a very mild adverse pressure gradient most likely due to flow deceleration. * Velocity measurements indicated that the memory effects of the strong acceleration around the bow are confined to the outer layer. In fact, the mean velocity profile shown an higher values of the outer velocity with respect to the nominal carriage speed and a thicker boundary layer, if calculated in the position of the maximum stream-wise mean velocity. However, pressure gradient value is not sufficient to provide any shift from the log law as well as any difference in velocity statistics with respect to classical flat plate results. * Wall pressure spectra show some typical behaviours in the low frequency region that can be related to outer flow effects. The main findings of the present analysis are: i) a higher value of the scaled PSD amplitude in the low frequency range, below the logarithmic scale independent region, is observed, ii) the introduction of the dimensionless parameter D=d/d* seems to reduce the gap between ZPG and APG curves, iii) the stream-wise decay is faster and iv) the Goody model still gives a satisfactory representation of the single point pressure spectrum. Some confirmation of the above consideration can be found in literature, however the development of an analytical model able to take into account for pressure gradient effect needs some further effort and systematic comparisons between all the available data sets. * Semi-empirical models for the CSD can be used with suitable values of the free coefficients. In this regard, the sensitivity analysis performed on the values assumed by the coefficients of the Chase model, shown that they are significantly different from the original ones also in the case of ZPG equilibrium flow over a flat plate. Moreover, they depend on flow conditions even for very mild pressure gradient. However, if experimental data are not available, it is possible to define a reasonably small range of variation that can be useful to perform sensitivity analyses of the vibro-acoustic response. * The vibro-acoustic experimental campaign performed on a bare aluminium panel and on three metallic panels covered by different materials of same thickness had two main scopes: i) provide reference data for the development and validation of numerical and reduced order models and ii) analyse the different behaviour of material coatings usually adopted for this kind of applications.

In this work high Mach number aerodynamic and structural measurements acquired in the CIRA (Italian Aerospace Research Center) transonic wind tunnel and the models used to analyze the response of composite panels to turbulent boundary layer excitation are presented. The two investigated panels are CFRP (Carbon Fiber-Reinforced Polymer) composite plates and their lay-up is similar to configurations used in aeronautical structures. They differ only for the presence of an embedded viscoelastic layer. The experimental set-up has been designed to reproduce a pressure fluctuations field beneath a turbulent boundary layer as close as possible to those in flight. A tripping system, specifically conceived to this aim for this facility, has been used to generate thick turbulent boundary layers at Mach number values ranging between 0.4 and 0.8. It is shown that the designed setup provides a realistic representation of full scale size pressure spectra in the frequency range of interest for the noise component inside the fuselage, generated by turbulent boundary layer. The significant role of the viscoelastic layer at reducing panel׳s response is detailed and discussed. Finally, it is demonstrated that at high Mach number the aeroelastic effect cannot be neglected when analyzing the panel response, especially when composite materials are considered.

Deliverable 3.1 contains the description of the experimental setups designed and constructed to perform PIV velocity measurements, wall pressure fluctuations measurements and vibro-acoustic tests devoted to the analysis of the response of plates, made of different materials, to turbulent boundary layer excitation. The characteristics of the Flame model built for towing tank measurements are also described. Moreover, some additional mean velocity and pressure measurements aim at characterising flow conditions about the Flame model, to be compared to those numerically reproduced, are presented. Some details are summarized below. Same size as the original Flame have been chosen in order to: i) be able to identify common test cases for towing tank and free field measurements and ii) obtain a thick, stationary turbulent boundary layer. This last is a fundamental requirement to perform accurate PIV measurements of the velocity field, close to the wall and to extend the correlation length range of measured wall pressure fluctuations. As a consequence, taking into account Flame size and the need to avoid free surface and floor effects, all test campaigns have been performed in the CNR-INSEAN largest towing tank, which is 470 m long, 13.5 m wide and 6.5 m deep, for carriage speeds of 2.5 and 5.1 m/s. Some additional data have been acquired for lower velocities starting from 0.5 m/s. The inner part of the Flame model is made of steel and contains an aluminum watertight box in correspondence of the test section for instrumentation placement. The box frontal area is 746 x 647 mm. The PIV setup has been designed with the aim to minimize the interaction between the laser light and the wall, making available data very close to the wall itself. Two PIV cameras have been placed inside the model, with two parallel points of view at about 120 mm of distance. The PIV field of view extends 40 mm in the streamwise direction and 45 mm spanwise for one camera and 35x42 for the other camera. Concerning wall pressure fluctuation measurements, a basic configuration has been designed for a number of 20 sensors that cover a maximum distance of 0.133 m is stream-wise direction and 0.025 m in cross-stream direction, respectively. Some additional points have been provided in order to have the possibility to investigate the evolution of the pressure field in stream-wise direction up to 0.25 m. An array of pitot tubes has been arranged to identify the turbulent boundary layer thickness and the flow behavior at the outer edge. Moreover, a couple of absolute pressure transducers have been installed upstream and downstream the measuring section in order to estimate the amplitude of the stream-wise pressure gradient. Five panels have been selected for the vibro-acoustic tests: the first one is a 5 mm thick aluminum bare panel, the second is a 3 mm thick aluminum panel ribbed by 3 stiffeners with al L section. The second set of panels consists of a 5 mm thick aluminum panels coated with two different kinds of polyurethane and a foam, respectively. To connect the plates to the rest of the system, an outer rigid frame fixed to the model and an inner rigid one, specific for each panel, have been designed and constructed. Panels are glued to the inner frame, the maximum dimensions in stream-wise and cross-stream direction are for all panels 0.6x0.5 m, the effective dimensions are 0.5x0.4 m. The instrumentation used includes 12 piezoelectric ICP accelerometers and 3 microphones placed inside the watertight box. Finally some information about the experimental modal analysis is provided.

In this work experimental and numerical methodologies for the calculation of vibrations induced by turbulent boundary layer (TBL) on ship structures are presented. In particular, analytical expressions for the hydrodynamic load are derived on the basis of direct pressure measurements on ship models, in a towing tank and, to avoid the limitations of experimental data in the low wavenumber range, by an inverse method based on the use of the structural response. The models are discussed for the case of hull form where the assumptions of stationary and zero pressure gradient flow over flat surface are often not applicable. Moreover, taking into account the characteristics of the fluid-structure interaction for naval applications, formulations for WPF spectra representation that highly reduce the computational time needed for the calculation of the structural response are provided. However, the possibility to correctly identify the pressure load passes through the accurate identification of boundary conditions and structural properties in terms of wet modal parameters. The problem is here solved applying classical modal analysis and an output-only identification technique based on an appropriate formulation of POD (Proper Ortogonal Decomposition) and on the use of the TBL load as ambient load. The application of this method provides an accurate calculation of wet natural frequencies and mode shapes as well as a robust estimation of the total damping coefficient. Moreover, the methodology is particularly fruitful for full scale size problems for which the use of a classical modal analysis is clearly unfeasible. Examples of application of the developed numerical and experimental methodologies are given considering the response of ship structures, at model and full scale size, to TBL excitation.

This work presents an investigation on the definition and applicability of distorted similitudes and the related scaling laws for the analysis of the dynamic forced response of rectangular composite plates. Such responses are determined from a generalization of the modal approach, which allows the use of the mode shapes and natural frequencies in order to establish the proper scaling laws. The cases, herein discussed, are exclusively theoretical and form the basis for the application of numerical methods such as the Finite Element Method. Analytical models of simply supported rectangular plates are used to produce both the original and distorted model responses. The results show that even in the case of distorted models it is possible to reproduce with reasonable accuracy the response of the original plate.

Hydro/vibro-acoustical modelling in CAPEM is performed at Atlas Elektronik, FAU, FFI, and CNR-INSEAN. The goal is to estimate the vibro-acoustical response of flexible structures to turbulent boundary layer (TBL) excitation. Different modelling strategies are applied, and different numerical simulation tools are used. Combined, this provides a broad range of experiences towards the goal of the project, which is to improve modelling of conformal array performance. PIN 2.2.1 collects the work done on hydro/vibro-acoustic modelling in the different research groups to date. A full report with comparisons of results, conclusions, and recommendations will be issued at the end of the project. All the simulation approaches are so far based on the fundamental assumption that the vibration of the structure has negligible effect on the turbulent motion of the fluid surrounding it outside FLAME. This means that the structural computations can be fully decoupled from the simulation of the TBL, and only time-dependent data values at the surface are transferred to the structural simulations. FFI uses a structural code from MSC Software to do a coupled calculation of the flexible structure and the nearby water volume inside FLAME. As a first estimate, the details of the sensor box inside FLAME are omitted, and open boundary conditions are applied to the water volume inside FLAME. The first structure to be modelled in this approach is the silicone membrane used in Sea Trial 1, with material parameters estimated from experiments and assumptions. FAU use their own TBL simulation results, and the Finite Element solver CFS++ for the structural simulations. Eigenmodes have been calculated for the 0.8 mm steel plate used in Sea Trial 1, and the velocity at the inside of the plate is taken as a boundary condition for the linear wave equation, to describe the signal propagation inside FLAME. The first results show that the first eigenmode of the steel plate dominates. Atlas Elektronik solve the bending wave equation by a Finite Element method to find the eigenmodes of the 0.8 mm steel plate, the wave-frequency spectrum of the plate displacement induced by the TBL, and the corresponding wave-frequency spectrum of the acoustics inside FLAME. The geometry of the sensor box inside FLAME is included in this approach. It is also demonstrated, as indicated by FAU, that the wall shear stress from the TBL has negligible effect on the wall displacement and interior acoustics, compared with the TBL wall pressure. CNR-INSEAN present scaling laws that relate the power spectral density (PSD) of the surface displacement to the PSD of the wall pressure fluctuations from the TBL. Scaling laws based on dimensional analysis and energetic considerations are presented.

Nowadays, the problem of the computational cost vs. the accuracy of the results is an important field of research in engineering, particularly for the analysis of the response of a stochastic system. By using a set of discrete coordinates, this response can become computationally challenging, especially when using a modal representation. Many dynamic load cases, significant for engineering applications, have random and convective properties such as wall pressure fluctuations due to the turbulent boundary layer (TBL). In this work, a new method for the evaluation of the dynamic response of a linear system excited by a TBL like load is proposed: it is named as frequency modulated pseudo-equivalent deterministic excitation (PEDEM) and it is based on the pseudo-excitation method (PEM). The latter is an exact representation since it uses the modal decomposition of the cross-spectral density matrix of the load. Unfortunately, the extraction of the eigensolutions of the load matrix is required at each frequency step and thus can become computationally unacceptable when a large number of eigensolutions is required. PEDEM tries to overcome this computational bottleneck by introducing some approximations, which are based on the analysis of the eigensolutions of the dynamic load matrix vs. frequency. Three different approximations are proposed and thus modulated for the three frequency ranges wherein the dynamic matrix of the considered random and convective load has different characteristics. A criterion to identify the above-mentioned frequency ranges is also proposed by introducing a dimensionless representation of the frequency. The results show that the proposed approximations combine a good accuracy in representing the stochastic system response with a 40 per cent of reduction of the computational costs if compared to a full stochastic response. The method is successfully applied to a simple 1D configuration, a chain of oscillators, which still presents the main features of a generic system. The extension to 2D systems is also analysed considering a preliminary test case with a flexural plate.

In the last years, several research projects have been devoted to the understanding of the characteristics of the self-noise induced by turbulent flow around the hull of military surface and underwater vessels. Experimental setups and test campaigns have been designed to measure, in the CNR-INSEAN towing tanks, wall pressure fluctuations on surfaces of different geometries and the induced vibro-acoustic response, varying flow conditions and structural material properties. In particular, experimental data concerning a bulbous bow of a military vessel and a catamaran model are used in this work to analyze the case of non-stationary and inhomogeneous boundary layers. These flow conditions typically occur when free surface effects, as well as surface curvature and transitional phenomena cannot be neglected. The results are compared with some literature data and with other measurements acquired in the towing tank in nearly canonical flow conditions. The possibility to provide predictive case independent semi-empirical models for the different frequency ranges of interest is analyzed. Finally, different approximations for the spatial variation of the pressure load are proposed and validated through the comparison between the numerical and experimental structural response.

An experimental campaign devoted to the vibro-acoustic characterization of turbulent boundary layer excitation has been performed in the CNR-INSEAN towing tank, using the Flame model. Different configurations have been tested varying structural geometry and material properties as well as flow conditions. In particular five panels have been considered: * a 5 mm thick aluminium bare panel; * a 3 mm thick aluminium panel ribbed by 3 stiffeners with an L section; * two 5 mm thick aluminium panels coated with two different kind of polyurethane; * a 5 mm thick aluminium panel coated with a foam. Acceleration and acoustic pressure have been acquired for tow speed ranging between 0.5 m/s and 5.1 m/s. Moreover, experimental modal analysis has been carried out to support the interpretation of the towing tank experimental data and to provide the information needed for the numerical structural and acoustical analysis. Most of the panel experimental vibration analysis is completed, in particular comparisons between different panel responses seem to be coherent with the panel characteristics. Moreover, dry and wet modal analysis performed experimentally and numerically on the bare aluminium panel gave satisfactory results in terms of identified natural frequencies. Dry modal parameters have been identified also for the composite panels, however, the possibility to perform a wet analysis and to design a numerical FEM model deserves some additional tests. In particular modal analysis with free boundary conditions is probably necessary to evaluate the exact material properties of the composites. The analysis of microphone signals has been performed only qualitatively, little is known "a priori" about the acoustic performance of these composite materials (aluminium + polyurethane and aluminium + foam) therefore, the possibility to perform acoustic measurements in an anechoic room for the evaluation of their properties is under consideration.

In this paper the statistical properties of the slamming impact process are analyzed with the help of experimental data acquired in the towing tank on a high speed ferry model. The physical model is a segmented-hull with a flexible backbone-beam equipped, among other devices, with sensors to measure the wetness of hull sections and strain gauges to estimate the induced vertical bending moment. This setup allows us to analyze the slamming process not only on the basis of the detected slamming events but also on the basis of the whipping response produced by the impacts. Moreover, due to the particular model selected for the present analysis, characterized by a V-shaped hull, bottom as well as bow flare slamming contributions are investigated. One of the major findings is the evidence that the impact statistics are largely affected by the grouping of slams into clusters thus violating the hypothesis of mutual independence between successive impacts that is at the basis of most of the statistical models. The dependence of the whipping response on the impact velocity is also investigated. Finally, the definition of a new criterion for slamming identification based on the evaluation of the whipping bending moment is discussed (C) 2013 Elsevier Ltd. All rights reserved.

In this report some further considerations concerning towing tank wall pressure fluctuations (WPF) data analysis are presented. The main objective of the present work is to investigate the capabilities and the limitations of available semi-empirical models for the representation of WPF power spectral density (PSD) and cross spectral density (CSD) by comparison with experimental data acquired during the FLAME towing tank test campaign. The performed analysis reveals that when suitable values of the free model parameters are chosen it is possible to derive analytical formulations for the single point pressure spectrum and for its spatial behaviour. These results are fundamental to provide the input for the structural analysis.

Dimensional analysis and energetic considerations are used to determine the functional dependence of the response of homogeneous and composite panels, excited by the turbulent boundary layer, on structural and flow parameters. The derived relations are expressed in dimensionless form providing a general description of the panel response amplitude in the frequency domain. The validity of the theoretical findings is demonstrated using experimental data acquired at full scale and, at model scale, in different facilities (wind tunnels and towing tank), for different flow conditions (Reynolds number values, boundary layer thickness etc.), for different structural materials and characteristic panel dimensions in order to have a significant range of variation of the dimensionless parameters. The basic hypothesis underneath this analysis is to have a fully developed turbulent boundary layer, negligible pressure gradients and a thin flat plate. The results of this study not only yield simple analytical expressions relating the dimensionless panel response and the dimensionless frequency, providing a drastic reduction of the computational burden associated to the numerical solution of the coupled problems, but also offer new physical insights in the mechanisms of structure-fluid interaction.

The correct characterization of wall pressure fluctuations (WPF) and of the response of an elastic structure subjected to turbulent boundary layer (TBL) represents one of the most challenging problems in the fluid structure interaction field. This kind of excitation for an elastic structure is encountered on a number of different engineering applications: in naval field WPF acting along the ship hull impinge on comfort on board high speed vessels and they are also responsible for strong vibrations of the sonar dome, which can degrade the correct functioning of the sensors mounted inside the dome itself. Moreover, the sound pressure levels produced by TBL load acting along the aircraft fuselage can be intense enough to result in an unacceptable cabin noise and can cause a reduction of the lifetime of fuselage panels due to structural fatigue. The study of WPF induced by TBL load in the naval and aeronautical fields are characterized by important differences in terms of both flow and structural characteristics, which provide highly different dynamical responses of a typical naval and aeronautic panel. Nevertheless, the characterization of the TBL load using model scale tests of a ship and an aircraft or sections of them have also strong similarities and for a great number of problems can be analysed using parallel experimental approaches in towing tanks, water channels and wind tunnels. The base of this approach is given by the identification of the most appropriate scaling laws for wall pressure fluctuation spectra and spatial models in the frequency domain, which allow to obtain in principle the full scale spectra from the sole knowledge of few mean flow parameters. Unfortunately, these models are based on very restrictive hypotheses on the nature of the flow and the structure, basically canonical flat boundary layer. Aim of this work is to show how some of the typical perturbations from the canonical flat plate boundary layer, encountered when studying a real structure in naval and aeronautical fields, can interfere in the modelling of this load and to show possible solutions to these specific problems. To examine these features for complex boundary layer, the results of three different experimental campaigns performed at CNR-INSEAN towing tank and CIRA PT-1 transonic wind tunnel are here discussed.

The computational costs associated to the analysis of a stochastic response of a linear system can become unacceptable high, even using a full modal representation. Here, a new approach is proposed by invoking a pseudo equivalent deterministic excitation (PEDE). This is based on the given spectral load representation. The load used in a deterministic loop is derived from the column of the spectral load matrix. The method allows a good representation without using the eigenvalues and eigenvectors of the spectral load matrix; in fact the pseudo excitation method, (PEM), is just based on these, and the PEM is an exact representation being based on the modal decomposition of the spectral excitation. The two methods, PEM and PEDE, are then compared with a full stochastic response for two simple systems: a chain of five oscillators (mass and stiffness) and a plate. Both the system are considered excited by a spectral load representing the classical form due to Corcos for the wall pressure distribution due to a turbulent boundary layer: a random and convective excitation. A dimensionless representation of the frequency axis is also used; on this scale, the results demonstrated that in the first frequency ranges the PEDE is a very useful approximation.

The high computational costs, associated to the numerical solution of the fluctuating pressure field generated at the wall by the turbulent boundary layer and of the induced structural response, push for the exploration of alternative methodologies of analysis. Wall pressure fluctuations spectra are often modeled using semi-empirical expressions based on the experimental evidence and on the identification of universal scaling laws. In this work the possibility to adopt a dimensionless representation, able to provide a universal expression for the structural response of plates under turbulent boundary layer excitations, is investigated with the help of pressure fluctuations and acceleration experimental data sets. The test article is a plane thin plate wetted by a fluid over one face, the boundary layer is fully developed and pressure gradient effects are negligible. The attention is devoted to the investigation and the definition of a normalization of the required axes: the excitation frequency and the power spectral density of the structural response. The analysis is initially based on analytical models for the structural response under turbulent boundary layer excitations. The proposed scaling laws are successively and successfully applied to four data sets measured in different conditions both in wind tunnels and in a towing tank.

Turbulent flow around the ship is one of the main sources of vibrations for hull, appendages and propeller. In particular, vibrations induced on the wetted hull panels by the turbulent boundary layer can propagate through the ship structures generating undesirable noise in a quite large frequency range. To investigate and quantify TBL effects on noise level on board, acceleration measurements have been performed on a hull ribbed panel of Ro-Ro Pax ship and used to validate the results obtained by two different numerical procedures developed to characterise the hull panel response. The wall pressure fluctuation load has been modelled using semi-empirical models specialized for the present case on the basis of full scale pressure measurements performed on the same ship. The first numerical analysis, based on Finite Element and on in house codes, is aimed at validating models for wall pressure spectra description. In a second phase, the application of the Statistical Energy Analysis allows to determine the response of a larger portion of the ship hull in correspondence of the bow region and to estimate the noise radiated on board.

Measurements of the acceleration response of typical homogeneous and composite aeronautical panels with different lay-up to turbulent boundary layer excitation have been performed in a transonic wind tunnel for Mach number values ranging between 0.4 and 0.9. Artificial boundary layers of different thickness have been generated using the setup described in PART 1. Aim of this experimental campaign was the understanding of the influence of different materials and geometrical properties on the response of aeronautical panels to random convective loads as a starting point for a following acoustical optimization. Numerical simulations of the panel response have been performed by FEM and in house codes using, as a forcing function, the modeled pressure field and have been validated by comparisons with measured acceleration data. The numerical determination of the structural response is also fundamental to understand how and when the theoretical models developed for the representation of wall pressure fluctuation spectra can be considered predictive thus, independent on the particular flow conditions.

In this paper a summary is presented concerning several experiences in predicting and measuring the structural response under turbulent boundary layer excitations. The theoretical, numerical and experimental evaluations involved both wind tunnel and towing tank (water) tests in which a flow wetted a plane plate over one face. A critical review of all these sets is presented together with the possibility to adopt a dimensionless representation for the response. This is done in order to tentatively compare measurement sets and/or predictive results obtained in nominally different conditions. Specifically, the attention is devoted to the definition of the possible normalisation of the required axes: the excitation frequency and the response metric. To this aim relations suggested by the dimensional analysis are applied to four distinct data sets finding the best choice of dimensionless parameters that allow the collapse of the different curves in a single one. The functional relations between these parameters are discussed and an analytical expression for the dimensionless plate response is obtained.Copyright © 2010 by ASME

The quality of the predictive response of a structural domain, under a random and convective load, is here analyzed by discussing each step of the numerical procedure. The structural response, due to a wall pressure distribution, is derived in modal coordinates according to a finite element scheme. The modal basis can include the dry or wet (aeroelastic) structural mode shapes: in the present analysis only the in vacuum eigenvectors are used. For such a problem one of the most critical points is the transformation of the pressure distribution into discrete locations. In fact, this step depends on (i) the assumed TBL model, (ii) the integration scheme and (iii) the frequency range. These three points are the goals of the present work where the specific sensitivity to each of them is investigated. The transformation of the pressure distribution into discrete locations can be computationally expensive for the desired level of the required numerical approximation. The use of consistent formulation in the finite element scheme can be unfeasible. Moreover the approximations, in expressing the pressure field, can have a different influence on the structural responses according to the chosen TBL models. This is another key aspect of the present work.Copyright © 2010 by ASME

For the effective operation of sonar system mounted inside the bulbous of a fast ship, it is important to reduce all the possible noise and vibration sources that cause the dome to vibrate thus radiating noise and interfering with sonar sensor response. In particular, pressure fluctuations induced by the turbulent boundary layer on the surface of the sonar dome represent one of the major sources of self-noise for the on board sensors. Calculation of the structural vibrations and of the noise radiated inside the dome requires as a first step the characterization of the frequency spectra of turbulent boundary layer excitation. Most of the literature related to wall pressure fluctuations is devoted to the study of equilibrium turbulent boundary layers on flat plates in zero pressure gradient (ZPG) flow, for which scaling laws for the power spectral densities and empirical models for the cross spectral densities are well established. The turbulent boundary layer on the bulbous can present several differences with respect to the canonical case because of the presence of hull surface curvatures and of the free water surface that produce pressure gradient variation along the bulbous surface. Moreover, hydrodynamic coincidence effects play a markedly different role in the underwater problem than in the aerodynamic problem. Therefore, an experimental campaign was performed in a towing tank to measure wall pressure fluctuations at different locations along a large scale model of a bulbous and to investigate their spectral characteristics in terms of auto and cross spectral densities. Boundary layer mean flow parameters were obtained with a finite volume code solving the Reynolds Averaged Navier Stokes Equations. The auto spectral densities (ASD) of the measured wall pressure fluctuations were scaled using different combinations of inner and outer flow parameters in order to make ASD independent of the tested conditions i.e. of Reynolds number. The modelled load was used as input for a numerical procedure aimed at evaluating the dynamical response of a section of the bulbous under analysis. The validation of this procedure was experimentally obtained through the measurements of the vibrational response of an elastic section inserted into the bulbous model. Moreover, this comparison indirectly provides additional insights on the physics of wall pressure fluctuations for complex flows.Copyright © 2010 by ASME