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We frame the mechanical stress tensor decomposition in a general procedure which involves the Helmholtz–Hodge decomposition. We highlight the impact of the mechanical stress tensor decomposition on the Navier–Stokes equation, with emphasis on the dissipation function. For fluids with low compressibility, we draw some insights on the Reynolds Averaged Navier–Stokes equations, and on the Reynolds stress tensor decomposition. We derive a turbulent potential flow model, and investigate the transition from viscous potential flow to turbulent potential flow. Under low Mach number approximation, we apply the turbulent potential flow model to one-dimensional propagation of large amplitude pressure waves in liquid-filled pipe. [ABSTRACT FROM AUTHOR]

An understanding of the hydroelastic response of a flexible circular plate to water waves is relevant to many problems in ocean engineering ranging from offshore wave energy converters and solar wind devices to very large floating structures such as floating airports and ice sheets. This paper describes results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Response amplitude operators (RAOs) of a floating flexible circular disk are determined for incident monochromatic and irregular wave trains, the latter defined by JONSWAP spectra. Free-surface displacements are measured using wave gauges, and the plate motion recorded using a QUALISYS® motion tracking system. Different basin depths and plate thicknesses are considered in order to quantify the effects of water depth and flexural plate rigidity on the overall dynamic behaviour of the circular disk. We present synchronous and subharmonic nonlinear responses for monochromatic waves, and displacement spectra for irregular waves. The measured wave hydrodynamics and disk hydroelastic responses match theoretical predictions based on linear potential flow theory. [Display omitted] • Experimental data on floating flexible disk dynamics in water waves. • Potential flow theory provides close match to experimental data. • 2nd & 3rd harmonic responses in regular waves are identified. [ABSTRACT FROM AUTHOR]

To efficiently utilize the abundant wave power in the ocean, it is necessary to deploy a wave farm. This paper considers a wave farm of oscillating water columns (OWCs) integrated into tubular structures. Each OWC device within the wave farm is constructed with a vertical tubular design, incorporating a partially open submerged side that faces the sea. At the top of each device, an air turbine is installed to harness the pneumatic power generated by incoming water waves. To assess the performance of the wave farm, an analytical model is developed using the eigenfunction matching method within the framework of linear potential flow theory. Subsequently, this model is utilized to assess the efficiency of two wave farm setups: a line array with varying numbers of devices and a square array consisting of four devices. When the openings of the OWC devices are deployed on the exterior side of the square array, the majority of the wave power captured by the wave farm is contributed by the windward OWC devices, over a wide range of wave conditions examined. However, when the openings are placed on the interior side of the square array, wave resonance among the OWC devices becomes a significant factor affecting the wave farm's performance. In this case, the leeward devices could capture more wave power compared to the windward ones. Large wave excitation forces acting on the OWC devices can be excited when the near-trapping of waves arises in a wave farm consisting of a circular array of OWC devices. The physical findings in this paper highlight the importance of the array configuration and opening arrangement for optimizing wave power extraction in wave farms. • We consider an array of oscillating water columns integrated into tubular structures. • An analytical model is developed to solve hydrodynamic problems. • We consider a line array of devices and a square array with four devices. • Windward devices capture most wave power in square array with exterior openings. • Wave resonance crucially impacts square array performance with interior openings. [ABSTRACT FROM AUTHOR]

We consider a finite array of floating flap gates oscillating wave surge converter (OWSC) in water of constant depth. The diffraction and radiation potentials are solved in terms of elliptical coordinates and Mathieu functions. Generated power and capture width ratio of a single gate excited by incoming waves are given in terms of the radiated wave amplitude in the far field. Similar to the case of axially symmetric absorbers, the maximum power extracted is shown to be directly proportional to the incident wave characteristics: energy flux, angle of incidence and wavelength. Accordingly, the capture width ratio is directly proportional to the wavelength, thus giving a design estimate of the maximum efficiency of the system. We then compare the array and the single gate in terms of energy production. For regular waves, we show that excitation of the out-of-phase natural modes of the array increases the power output, while in the case of random seas we show that the array and the single gate achieve the same efficiency. [ABSTRACT FROM AUTHOR]

Many marine structures are composed of vertical axisymmetric floats. In this paper, a semi-analytical model based on the linear potential flow theory and an eigenfunction expansion method is developed to study wave diffraction and radiation by an array of cylindrical structures. Each structure can be formed by three coaxial cylinders of different dimensions. Based on the semi-analytical model, a constrained matrix equation of motion is presented and solved to evaluate the performance of multiple interconnected cylindrical structures. In order to verify the accuracy of the semi-analytical model, a typical OC4-DeepCwind floating offshore wind turbine (FOWT) is selected for validation. The validated model is, then, applied to study the effect of base column submergence depth, radius, and thickness on the motion response of a semi-submersible platform. Although the results of this study are of significance for the selection of the optimum semi-submersible FOWT for specific locations (with specific prevailing wave directions), the focus of this work was placed on the semi-analytical model itself, which is efficient in modeling the interaction of the wave field and can be used in future FOWT projects. [ABSTRACT FROM AUTHOR]

We review wave energy conversion technologies for niche applications, i.e., kilowatt-scale systems that allow for more agile design, faster deployment and easier operation than utility scale systems. The wave energy converters for niche markets analysed in this paper are classified into breakwater-integrated, hybrid, devices for special applications. We show that niche markets are emerging as a very vibrant landscape, with several such technologies having now achieved operational stage, and others undergoing full-scale sea trials. This review also includes flexible devices, which started as niche applications in the 1980s and are now close to commercial maturity. We discuss the strong potential of flexible devices in reducing costs and improving survivability and reliability of wave energy systems. Finally, we show that the use of WECs in niche applications is supporting the development of utility-scale projects by accumulating field experience, demonstrating success stories of grid integration and building confidence for stakeholders. [ABSTRACT FROM AUTHOR]

We present a novel mathematical model to investigate the extraction of wave power by flexible floaters. The model is based on the method of dry modes, coupled with a matched eigenfunction expansion. Our model results compare satisfactorily with preliminary data obtained from a demonstrator device, developed at the University of Groningen. We show that the role of elasticity is to increase the number of resonant frequencies with respect to a rigid body, which has a positive effect on wave power output. The mathematical model is then extended to irregular incident waves, described by a JONSWAP spectrum. Our results show that the peak capture factors decrease in irregular waves, as compared to the monochromatic case. However, the system becomes more efficient at non-resonant frequencies. This work highlights the need to scale-up experimental investigations on flexible wave energy converters, which are still a small minority, compared to those on rigid converters. [ABSTRACT FROM AUTHOR]

We analyse the nonlinear behaviour of an array of curved surge-type wave energy converters(WECs) in a semi-infinite channel of constant depth. Surge-type WECs have attractedinterests by researchers and industry, mainly because of their capability to absorb energy withpotentially large efficiency when excited by incident waves. The vast majority of the theoretical models developed so far on the dynamics of this kindof devices neglect nonlinear contributions. This can be unjustified when nonlinearresonances of trapped modes occur. Indeed, Michele et al. (2018b) recently showed thatsubharmonic resonance and mode competition of trapped modes can increase energyproduction of a system of surging WECs. Moreover, recent investigations on curvedflap-type gates suggest that using curved structures could further improve wave energyextraction efficiency. Motivated by these new aspects, in this work we investigate theeffect of gate surface curvature on the nonlinear dynamics of an array of surge-typeWECs. We show that a small horizontal deviation of the gate surface produces significantchanges in the dynamical behaviour of the system. Using perturbation-harmonic expansionup to the third order, we decompose the nonlinear governing equations in a sequence oflinearised boundary-value problems of order n and harmonic m. The gate shape effectsresonate the first harmonic at the second order, so that three timing with two slow time scalesis necessary. First, we consider the synchronous excitation of a single trapped mode. Products betweenthe gate shape function and the second-order terms force the first harmonic at the third order.We point out that this particular excitation is not possible for flat gates, because in that casethe corresponding evolution equation would be damped and unforced. We also show theoccurrence of new terms in the Ginzburg-Landau evolution equation, which are notpresent in the case of flat gates. We show that nonlinear synchronous resonance ofcurved WECs yields constructive interactions that can be significant for designpurposes. Finally, we analyse the occurrence of subharmonic nonlinear resonance bymonochromatic incident waves. Perturbation expansion of the unknowns leads to anevolution equation similar to that obtained for the synchronous case. Then we define anoptimized PTO coefficient which maximises power extraction under subharmonic resonance.The capture factor reaches much larger values than the theoretical maximum of aWEC in a channel described by the linearised theory. Furthermore, we show thatsubharmonic resonance is associated with increased efficiency of wave power extraction,though the effects of curvature are not always beneficial as we initially thought. [ABSTRACT FROM AUTHOR]

Combined floating offshore wind turbines (FOWTs), wave energy converters (WECs), and floating solar photovoltaics (FPVs) systems have the potential to provide cost-effective solutions for offshore multi-energy complementation and structure protection. In this study, a theoretical model based on the potential flow theory and eigenfunction matching method is utilized to study wave diffraction and radiation by a co-located system, in which the main components of the wind platform and WECs are made of vertical cylindrical floats. Based on the displacement constraint matrix, coupled equations of motion are developed to calculate the kinematic response of the co-located systems. After running the convergence analysis and model validation, the present model is employed to perform a multiparameter impact analysis. Case studies are presented to clarify the effects of the WEC radius, draft, layout, power take-off (PTO) system, and incident wave heading and frequency on the hydrodynamic coefficient, wave energy capture width, and motion response of the wind platform. Our findings highlight that several factors play a crucial role in the performance of the co-located system, more importantly, that the theoretical model developed in this study is capable of effectively predicting the wave-structure interactions in wave fields, making it applicable to future wave farm projects. • A theoretical model is presented to calculate the hydrodynamic coefficients. • A dynamic motion equation is developed to evaluate the motion response. • A multiparameter impact analysis is conducted on the co-located system. • Our study demonstrates the synergistic benefits of combining wind-wave system. [ABSTRACT FROM AUTHOR]

A mathematical model is developed to investigate the performance of a hybrid system comprising semi-submersible floating offshore wind turbines (FOWT) coupled to an array of point-absorbing wave energy converters (WECs) under irregular waves and dynamic winds. In this study, the hydrodynamic interaction of the hybrid system is conducted by applying the matching-method of eigenfunctions to solve the diffraction and radiation velocity potentials. Non-linearities of the hybrid system are taken into account in the Cummins framework, covering aerodynamic, catenary mooring, PTO system, fluid viscosity modeling, and frequency–time domain transformation of hydrodynamic coefficients. After running the convergence analysis and model validation, the present model is employed to perform a multiparameter effect analysis. Case studies are presented to clarify the effects of WEC parameters (including radius, draft, PTO damping, and layout) on the performance of a hybrid system. Nevertheless, a significant aspect of this work revolves around the development of a precise and efficient mathematical model, capable of accurately computing hydrodynamic coefficients for specific marine structures and evaluating the motion response of the interconnected floaters. Additionally, the study offers valuable insights into the preliminary design of hybrid systems and lays a mathematical foundation along with corresponding code for hybrid system projects. • An accurate and efficient model is presented to calculate the hydrodynamic coefficients of hybrid systems. • A practical mathematical model has been developed to evaluate the dynamic performance of coupled marine structures. • Integrating WECs significantly reduce the power spectrum density in pitch mode of the wind platform. • Linear PTO contributes more to platform stability than quadratic and constant PTO systems. [ABSTRACT FROM AUTHOR]

The new means and modalities of communication and information technologies have significantly revolutionized access to surgical education. The introduction of the Internet information highway into mainstream clinical practice as an information sharing medium offers a wide range of opportunities to healthcare professionals. High‐speed Internet broadcasting allows the display of high‐quality full‐screen videos. Access to surgical procedures through the Internet already plays a major role in continuing medical education nowadays and will undoubtedly be gaining grounds in the future. WebSurg.com, the World Virtual University, a web‐based surgical university, is dedicated to minimally invasive laparoscopic surgery. Using brand‐new multimedia data, the electronic university provides thorough descriptions of over 150 procedures in minimal access surgery and 265 videos of surgical interventions. Such a teaching tool recreates all the prerequisites and requirements of a traditional School of Medicine, incorporating the manifold standpoints of world‐renowned experts about specific topics and hands‐on hints in various surgical specialities. Following the evolution of technologies, recent advances have made it possible to display items of Websurg.com on handheld devices (personal data/digital assistance also known as PDAs, Pocket PCs, and smart phones). Integrating all these elements into a unique World Virtual University, Websurg.com epitomizes the concept of a unified academic center providing teaching and tutorials administered by international experts. The Internet assuredly contributes to the worldwide diffusion of scientific information in an easy and user‐friendly way. [ABSTRACT FROM AUTHOR]

A practical model is developed to investigate the performance of a hybrid system with semi-submersible floating offshore wind turbines (FOWT) coupled to an array of point-absorbing wave energy converters (WECs). In this study, the boundary value problem is solved by applying the matching-method of eigenfunctions to solve a complex-shaped hybrid system and the velocity potential can be decomposed into radiation and diffraction problems. For each component in the structure, we consider it consists of three coaxial cylinders of different dimensions, making our mathematical model applicable to many marine structures. Within the framework of a linearized theory, We develop the coupled equations of motion to model the stiffness and damping constraints and to evaluate the effect of coupled motion between the floating platform and vertical truncated cylinders, taking into account wind forces, mooring lines, power take-off (PTO) systems and viscous effects on the hybrid system. For such a system, the combination of the OC4-DeepCwind platform with an array of point-absorbing WECs is investigated in this study. After running the convergence analysis and model validation, the present model is employed to perform a multiparameter effect analysis. Case studies are presented to clarify the effects of WEC parameters (i.e. radius, draft, PTO damping and layout), base column submergence, wave heading and frequency on the motion response of wind platform and mean capture width ratio of the WECs array. Our results provide insights into the relationship between the variables analyzed and the performance of the hybrid system. Moreover, the theoretical model developed in this study accurately calculates the hydrodynamic coefficients and motion performance of some marine structures. • A practical model was presented to accurately calculate the hydrodynamic coefficients. • A coupled motion equation was developed to model the rigidity and damping constraints in a hybrid system. • The study examined the synergistic effects between a wind platform and PTO damping. • Added WECs significantly reduce the pitch motion response of the wind platform. • Increasing the submergence depth of the base column has a negative impact on the hybrid system. [ABSTRACT FROM AUTHOR]