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In this paper, wave power extraction from a floating Clam-type wave energy converter is investigated. The device is mainly composed of a Clam, which is formed from two pieces of floating flaps hinged at a submerged body. The Clam is closed by a flexible impermeable bag with the two hinged floating flaps kept apart by a Power Take-Off system. As waves propagate through the device, the Clam motion of the device is excited, which can be used to drive the Power Take-Off system to capture wave power. To evaluate the response and also the wave power absorption of the device, a mathematical model is developed based on the linear potential flow theory, in which a generalised mode method is adopted to model the Clam action. Theoretical expressions of the maximum wave power absorption and the corresponding optimised Power Take-Off system and mooring parameters are derived. Good agreement between the present numerical results of the device response and the physical observations is obtained. The validated model is then applied to do a series of case studies. It is revealed that the optimised Power Take-Off stiffness and mooring stiffness are independent of the Power Take-Off damping. The maximum wave power absorption can be achieved when the device is fixed in heave mode or free-floating without any constraints from the mooring system. • We developed a mathematical model to study the performance of a Clam-type device. • A generalised mode method was adopted to model the Clam action. • We derived the expressions of the maximum wave power output and the optimised PTO. • The numerical results agree well with the corresponding measured physical data. The optimised PTO stiffness and mooring stiffness are independent of the PTO damping. [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]

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]

Ocean waves are a huge and largely untapped resource of green energy. In order to extract energy from waves, a novel wave energy converter (WEC) consisting of a floating, hollow cylinder capped by a roof with a variable aperture is presented in this paper. The power take-off (PTO) system is composed of a linear generator attached to the seabed, driven by the heave motion of the floating cylinder through a tether line. The air pressure within the cylinder can be modified by adjusting the roof aperture. The hydrodynamic characteristics of this WEC are investigated through an analytical model based on potential flow theory, in which the wave diffraction/radiation problems are coupled with the air pressure fluctuation and PTO system. Analytical expressions are derived for the maximum power absorbed by the WEC under different optimization principles, revolving around the PTO damping, roof aperture damping and non-negative mooring stiffness. We find that the best power absorption is obtained when the aperture is either completely open or entirely closed, depending on the wave conditions. Intermediate values of the aperture are useful to minimize the heave motion and thus ensure survivability under extreme sea states. • A novel WEC is presented: a point-absorber with a covered moonpool. • The cover has a variable aperture which allows for controlling damping. • We develop an analytical model to investigate its performance. • The variable damping can be used to reduce heave motions and mooring forces. • This results in improved survivability relative to traditional point-absorbers. [ABSTRACT FROM AUTHOR]

Integrating wave energy converters with marine structures such as breakwaters, piles, and offshore wind turbines offers benefits in terms of wave power extraction, construction costs, and survivability. In this paper, the integration of an oscillating water column(OWC) into a vertical tubular structure is considered. The OWC chamber is enclosed by the tubular-structure with its submerged side partially open to the sea. As ocean waves propagate through the device, an air turbine installed at the top of the chamber can be driven to extract wave power. An analytical model based on potential flow theory and the eigen-function matching method is developed to solve the wave scattering and radiation problems of the device in finite water depths. Wave excitation volume flux, hydrodynamic coefficients, optimal turbine damping and power capture factor are evaluated. Upon successful validation, the model is applied to investigate the effect of the radius and finite wall thickness of the tubular-structure, the size and position of the opening on wave power extraction. We find that a thinner chamber wall thickness offers benefits to wave power extraction in terms of a broader primary band of power capture factor response, and that a broader and higher capture factor band can be achieved by increasing the height of the vertical opening. • We develop an analytical model to study an OWC integrated into a tubular structure. • The OWC lateral opening can be applied at any position beneath the mean water level. • The new analytical model eliminates the need for the thin wall assumption. • The small wall thickness of the chamber offers benefits for wave power extraction. • Increasing height of the opening leads to a broader efficiency band. [ABSTRACT FROM AUTHOR]

• We develop an analytical model of wave diffraction by multiple cylinders. • The vertical truncated cylinders can be with arbitrary cross sections. • We validate the analytical model with numerical results, with excellent agreement. • We consider the practical case of two caissons in proximity. • We perform a sensitivity analysis of incident wave direction, spacing and layout. Many marine structures are supported by piles or caissons which, from a mathematical point of view, can be assimilated to an array of truncated cylinders of arbitrary cross sections. The focus of this paper is such an array subjected to harmonic waves of small steepness. We develop an analytic method based on linear potential flow theory to solve the diffraction problem and evaluate the excitation forces and moments acting on each cylinder. The water domain is divided into the interior regions below each cylinder and an exterior region extending to infinity in the horizontal plane. A series of eigen-functions are applied to express the velocity potential in each region. The Fourier series method combined with the eigen-function expansion matching method is used to satisfy the wetted surface body conditions and continuity conditions between adjacent regions. The analytic model is validated by comparing its results with numerical modelling results and published data. It is then applied to two truncated cylinders with caisson cross sections, and results are given for the excitation forces and moments on each cylinder for different values of incident wave direction and spacing between the cylinders, and for different configurations. [ABSTRACT FROM AUTHOR]

• A WEC unit is added to an interconnected two-module VLFS. • A theoretical model is derived for optimum power take-off damping of the WEC unit. • Placing hinge at foreside of the VLFS is good for power absorption and dynamic response mitigation. • A trade off exists between vertical displacement and bending moment when evaluating effects of wave direction and structural flexibility. This paper numerically investigates the dynamic response and power capture performance of a Very Large Floating Structure (VLFS) with a Wave Energy Conversion (WEC) unit. The VLFS is composed of two hinged modules of which the relative pitch motion induced by waves is converted into electricity by the WEC unit. The discrete-module-beam-bending based hydroelasticity method is used to establish the equations of motion for the VLFS. A theoretical model is derived for optimizing the power take-off damping of the WEC unit. Based on the numerical results, it is found that (i) placing hinge near the foreside of VLFS is a good option for both the reduction of hydroelastic response and the enhancement of power absorption; (ii) for medium and long waves a larger wave incidence angle corresponds to a larger vertical displacement, a smaller bending moment and a decreased power capture width ratio of the VLFS; and (iii) the decrease of structural bending stiffness brings an increase of vertical displacement and a reduction of bending moment while its effect on power absorption is insignificant except for a very large bending stiffness. [ABSTRACT FROM AUTHOR]

A semi-analytic model based on linear potential theory is developed to solve wave radiation from an array of truncated cylinders with arbitrary cross sections, free to oscillate independently in water of finite depth. The radiated velocity potential in the interior region below each cylinder and the exterior region extending to infinity are expressed as a series of eigenfunctions in the local cylindrical coordinate system using the method of separation of variables. They are solved subsequently by imposing the continuity condition of the velocity and pressure at the wetted surfaces of the cylinders and the fluid interfaces between adjacent regions. In the process, the Fourier series expansion method is applied to the terms regarding the arbitrary cross sections. The model is successfully validated through a case study with two caissons – excellent agreement is obtained with a numerical model based on the boundary element method. The semi-analytic model is then applied to explore the influence of layout (angle and spacing between the two caissons) on the added-mass and radiation damping coefficients. It is found that the hydrodynamic interaction between the two caissons can increase or decrease the value of the coefficients depending on the wave frequency. • We develop a semi-analytic model of wave radiation by multiple cylinders. • The vertical truncated cylinders have arbitrary cross sections. • We validate the semi-analytic model vs. numerical results, with excellent agreement. • Model is applied to case study with two caissons representing mobile offshore bases. • We analyse the sensitivity of hydrodynamic coefficients to layout (angle, spacing). [ABSTRACT FROM AUTHOR]

Integrating wave energy converters into coastal structures such as breakwaters, seawalls or jetties not only offers benefits in terms of construction costs but also improves wave energy extraction. In this paper a novel theoretical model based on linear potential flow theory is developed to study the performance of an oscillating water column (OWC) integrated into a vertical structure in water of finite water depth. The model has three fundamental advantages relative to previous works: no thin-wall restriction (the thickness of the OWC chamber wall is considered), no singularities, and far fewer truncating terms in the eigen-function expansions. The OWC chamber is a vertical cylinder semi-embedded in the structure with a submerged, open bottom. As water waves impinge on the structure, the water column in the chamber oscillates and drives an air turbine installed at the chamber top to extract wave power. Using linear wave theory, the velocity potential in the water domain is decomposed into scattering and radiation potentials whose unknown coefficients are determined by the eigen-function matching method. Upon successful validation, the model is used to investigate the influence of the thickness of the chamber wall and the radius and submergence of the chamber on wave power absorption. • Analytical model of Oscillating Water Column mounted on coastal structure. • Developed without the simplifying assumption of a thin-walled OWC chamber. • Considers the three main design parameters: radius, submergence & wall thickness. • Upon successful validation using published data, model is applied. • Sensitivity analysis of OWC power performance vs. main design parameters. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a semi-analytical model for solving wave radiation from a truncated cylinder of arbitrary cross section is presented based on linear potential flow theory. The water domain is divided into the interior domain beneath the cylinder and the exterior domain outside the vertical cylinder column. Radiated spatial potentials in these subdomains are expressed as a series expansion of eigen-functions using the method of separation of variables. The continuity conditions for pressure and velocity are satisfied at the interface of the two domains, where the Fourier series expansion method is employed to deal with the radius function associated terms. Therefore, the unknown coefficients in the radiated potential expressions are determined by means of the eigen-function matching method. Hydrodynamic coefficients of the truncated cylinder are evaluated directly based on the radiated spatial potentials. Case studies on wave radiation from a truncated cylinder with "cosine" and "circular" cross sections show a good agreement between the semi-analytical results of added-mass/radiation damping and numerical ones/published data. The validated semi-analytical model is then adopted to study the hydrodynamic characteristics of truncated cylinders with "circular", "cosine", "elliptical" and "quasi-elliptical" sections. For the latter case, the influence of draft on wave radiation is also investigated. Highlights • Present a semi-analytical model of wave radiation by a truncated vertical cylinder. • Prove symmetric property of the radiation force for cylinder with "cosine" section. • Compare results of "circular", "cosine", "elliptical", "quasi-elliptical" sections. • Explore the effect of draft for the cylinder with "quasi-elliptical" cross section. [ABSTRACT FROM AUTHOR]

A novel hybrid wave energy converter (WEC) consisting of a floating oscillating water column (OWC) and several oscillating floats hinged around is proposed. Both water oscillation of the OWC and the wave-induced relative rotation of each float around the OWC are employed to extract wave power. To carry out the hydrodynamic analysis of the hybrid WEC, a theoretical model based on potential flow theory, separation of variables method and eigen-function matching method is presented. Hydrodynamic interaction between the OWC and the floats oscillating independently in surge, sway, heave, roll, pitch and yaw modes is considered. To verify the correctness of the theoretical hydrodynamic model, a specific example is computed and a numerical code based on a boundary element method is also employed as a comparison. The theoretical results are found in good agreement with ones obtained by using different approaches. The theoretical hydrodynamic model is then adopted to evaluate the dynamic response and power absorption of the hybrid WEC in frequency domain. Additionally, the corresponding isolated OWC and hinged floats are computed, respectively, and compared to demonstrate how to interact beneficially between the OWC and the floats in terms of q -factor. Effect of the geometry of both the OWC and the floats, and the spacing distance between them on power exploration of the hybrid WEC is investigated. The results reveal that the hybrid WEC holds a wider bandwidth of frequency response with a higher maximum power capture factor compared with those of the isolated OWC and hinged floats. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid wave energy converter (WEC) is proposed, consisting of a fixed inverted flume with long length and a bottom hole, and a long floating cube hinged with the flume. The inverted flume and the long floating cube works as an oscillating water column (OWC) and a rotational float, respectively, to capture power from incident waves. To study the performance of this hybrid WEC, analytical solution of the wave diffraction/radiation problems, considering the hydrodynamic interaction between the OWC and the float, is derived based on linear potential flow theory and eigen-function expansion matching method in the two-dimensional Cartesian coordinate systems. The corresponding hydrodynamic coefficients, such as wave excitation forces, added mass and wave radiation damping, are also obtained, which can be further used in evaluation of the maximum theoretical power absorption of the hybrid WEC. Results are compared with a parallel study of an isolated OWC and an isolated float. Additionally, analytical study on power capture capability of the device for various geometrical parameters is then carried out. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical model is presented to evaluate the maximum mean power that can be absorbed by a three-dimensional system of connected floating bodies in waves under a weighted global constraint. The constraint imposed on the motion amplitudes of the system can be used to limit the motions of the bodies in order to make sure that the assumption of linear theory for wave–structure interaction remains valid. The absorbed power of a structure can be considered as the difference between excitation and radiated power without consideration of practical power take off. The solutions for the maximum relative capture widths of rigidly connected two rafts have a good agreement with the calculated ones for the same rafts being seen as a single whole structure. Meanwhile, the results of maximum power absorption of two hinged slender rafts in cuboid shape give a good agreement as well with those by using slender-body approximations. Then dynamics of a hinged two rafts are studied and results show how the maximum efficiency is affected by raft width and restricting the motions. [ABSTRACT FROM AUTHOR]

In this paper an analytical model is presented for the three-dimensional wave radiation problem of a cylinder floating on a layer of water of finite depth in front of a vertical wall, based on the linearized velocity potential theory, image theory and an eigen-function expansion matching method. The image theory is utilized to transform the radiation problem from the floating cylinder beside a vertical wall of infinite length into the equivalent problem of wave radiation from two identical floating cylinders in unbounded fluid domain to derive expressions for added-mass and radiation damping. Expressions for velocity potentials are obtained by using the method of separation of variables, in which unknown coefficients are determined by applying the eigen-function expansion matching method. Added-mass and wave damping are then calculated directly from the radiated potentials. The model is validated by comparison of the present results with the numerical ones, and there is a good agreement. The influence of distance between the cylinder and the vertical wall, draft of the cylinder and water depth on hydrodynamic coefficients is given and discussed. [ABSTRACT FROM AUTHOR]

Heat pipe, a high efficient, cost effective and reliable device, is considered one of the most promising passive technologies for cooling data centres. Aiming to provide comprehensive information and focused perspective on heat pipe system for cooling data centres, the literature reviewed in this review is obtained from the Web of Science by searching the topic "heat pipe" and "data centre" conducted on Sep. 1, 2019 for the decade from 2009 to 2018. In this paper, a comprehensive review on heat pipes for use in data centre cooling systems will be carried out, starting from the working principle, heat transfer analysis and applications. The review works will be analysed in terms of the system research methodology, energy performance evaluation, and IT tasks. From the system research methodology, the heat pipe structure, simulation and testing analyses were conducted. From the energy performance evaluation, the energy consumption, energy recovery and energy saving analyses were studied. From the IT tasks, the avoidance of hot spots and thermal management in the data centres were analysed. The opportunities for further works are revealed including: developing new and efficient data centre cooling systems employing advanced technology; optimising the heat pipe structure for the data centre cooling systems; testing the data centre cooling systems under actual conditions; and evaluating the economic feasibility and market potential of the data centre cooling systems. This review provides the guidelines for the development of data centre cooling system based on the heat pipe. • The heat pipe systems for cooling data centres are summarized from the research methodology, energy performance evaluation, and IT tasks. • Opportunities of data center cooling system based on the heat pipe are emphasized. • The evaluation of economic feasibility and market potential of the data centre cooling systems based heat pipe is needed. • Further tests of the data centre cooling systems in real environment should be carried out. [ABSTRACT FROM AUTHOR]

This paper presents an analytical model to predict the three-dimensional wave diffraction of a floating cylinder located in front of a vertical wall at a finite water depth. The model is potentially used to analyze the hydrodynamic behavior of a floating wave energy device close to a steep shore. The model is based on a linearized velocity potential theory and the image theory. The wave diffraction problem is transformed into the problem of diffraction of bi-directional incident waves from two cylinders. Expressions for velocity potential are obtained by the method of separation of variables, in which unknown coefficients are determined by using the eigen-function expansion matching method. Wave elevations and wave excitation forces are calculated directly from the incident and diffracted potentials. The model is validated by comparison of the present results with the numerical ones, and there is a good agreement. The effect of wave incident angle, distance between a cylinder and a vertical wall, cylinder draft and water depth on wave run-up and wave forces is then explored. [ABSTRACT FROM AUTHOR]

To achieve cost parity with other renewables, the wave energy sector requires significant cost reduction. Increasing the wind turbine scale is one successful route to cost reduction in the wind industry. This paper aims at investigating the scalability of wave energy converters (WECs) and providing a thorough review and analysis of published data. Unlike wind turbines for which the energy absorbed increases with turbine diameter, the scalability of WECs is complicated and varies by WEC type. Here, we demonstrate that the point absorber (PA) WEC lacks scalability and has limited theoretical capture width (CW), although its theoretical capture width ratio (CWR) can exceed 100%. The CW increases with device width for terminator and length for attenuator WECs, demonstrating scalability, but CWR limits of 50% and 100% exist. Analysis of the practical performance data carried out in this work shows that: (1) due to the lack of scalability, it will be difficult for the PA unit to reach MW scale, and in most examples, the characteristic dimension is generally < 35 m; (2) the terminator could achieve MW scale by using a high characteristic dimension > 100 m; (3) the PA appears to work more efficiently than the terminator and attenuator (e.g., for the PA oscillating wave surge converters, hydrodynamic efficiencies up to 80% have been achieved in laboratory tests). • Theoretical and practical performance of wave energy converters (WECs) are reviewed. • Capture width and capture width ratio are used to assess the scalability of WECs. • The scalability of different types of WECs is analysed and presented. • Recommendations for WEC development are proposed based on the WEC scalability. [ABSTRACT FROM AUTHOR]

In this paper, a semi-analytical model is proposed to solve the diffraction problem from a cylinder with a moonpool. The cylinder and the moonpool can be in arbitrary shapes. Linear potential flow theory and eigenfunction matching method are adopted in the analytical model. After dividing the fluid domain into three regions (i.e., the region beneath the cylinder; the inner region enclosed by the cylinder; the exterior region outer the cylinder), diffracted spatial potentials in each region can be expressed by a series of eigenfunctions. The continuity conditions between adjacent regions together with a Fourier series method combined with the eigenfunction matching method are employed to determine the unknown coefficients in the expressions of diffracted potentials. The well-known potential of incident waves and the obtained diffracted potentials are then used to directly compute the wave excitation forces/moments acting on the cylinder and the wave excitation volume flux. Analytical results of wave excitation forces/moments and volume flux are compared with the numerical results obtained by using a boundary element method numerical solver. Wave diffraction from the cases with different shapes of either cylinder hull or moonpool is finally tested with the semi-analytical model. • A semi-analytical model is proposed to solve wave diffraction from a cylinder with a moonpool. • The cylinder and the moonpool can be in arbitrary shapes. • Good agreement is found between the present model and WAMIT. • Wave diffraction from the cases with different shapes of either cylinder hull or moonpool is tested. [ABSTRACT FROM AUTHOR]

Oscillating water column (OWC) devices and oscillating buoys (OBs) are two of the main types of wave energy converters (WECs). In this paper a hybrid oscillating water column-oscillating buoy wave energy converter is proposed, which we have named OWCOB. The oscillating buoy is hinged at the outer wall of the oscillating water column. As waves propagate through the OWCOB, the water column within the OWC chamber moves up and down, producing air flow to propel a turbine. Meanwhile, the oscillation of the OB drives a separate hydraulic system. To solve the wave diffraction and radiation problems of the OWCOB and investigate its energy capture performance, an analytical model is developed based on linear potential flow theory and the eigenfunction matching method. Assuming that the PTOs of the OWC and OB are both linear, the wave power extraction of the OWCOB is evaluated in the frequency domain. Of the two configurations considered, the OWCOB with the OWC opening waveward and the OB hinged leeward is found to have a broader primary frequency band of wave power capture compared to the OWCOB with the OWC opening and the OB on the same side. Further, a thorough sensitivity analysis of power capture is carried out considering the main design parameters (size and submergence of the OWC opening, distance between the OWC and the OB, OB hinge elevation, OB radius), which can form the basis of an optimization study for a particular wave climate. Importantly, we find that the OWCOB performs generally better than stand-alone OWCs and OBs, not least in terms of frequency bandwidth. • We propose a hybrid wave energy converter, OWCOB, combining two technologies. • Namely, an Oscillating Water Column (OWC) and an Oscillating Buoy (OB). • We develop a model to investigate its wave energy capture performance. • A multi-parameter sensitivity study is carried out with the main design parameters. • We find that the hybrid OWCOB performs better than stand-alone OWCs or OBs. [ABSTRACT FROM AUTHOR]

In this paper we consider hybrid wave farms, in which different types of WEC are combined, through a case study involving oscillating water columns (OWCs) and point-absorbers (PAs). A new parameter, called " H-factor ", is introduced to compare hybrid (multi-type) and conventional (single-type) wave farms in terms of wave power capture. We develop an ad hoc semi-analytical model to calculate the H-factor in a computationally efficient manner, and apply it to investigate how the H-factor and, consequently, the power capture, depend on: (i) the spacing and layout of the WECs, (ii) the type of WEC technology, and (iii) the wave conditions. We discuss the influence of these factors and, in the process, show that the H-factor is a valuable decision-aid tool. For specified wave conditions and layout limitations, a conventional wave farm may not be the most efficient option as a result of a destructive array effect, whereas a hybrid farm can be more efficient if a constructive hybrid effect occurs (if the H-factor value is above unity). This constructive hybrid effect can even overcome the destructive array effect for specified cases, demonstrating the potential advantage of hybrid wave farms relative to conventional wave farms. • Hybrid wave farm, with two types of Wave Energy Converters (WECs). • We propose the novel H-factor to compare performance with single-type farms. • We perform a sensitivity analysis: type of WECs, layout, and wave conditions. • The H-factor is proven to be a useful decision-aid tool. • Hybrid farm is advantageous relative to single-type farms in certain conditions. [ABSTRACT FROM AUTHOR]

• We propose a multi-oscillating water column (OWC) integrated platform. • We develop a semi-analytical model to evaluate hydrodynamics of the platform. • Wave power absorption and wave transmission of the multi-OWC platform are examined. • Small-draft front wall and large-draft back wall are beneficial for power absorption. • Platforms with inverse geometric constructions have the same transmission coefficient. A rectangular barge consisting of multiple oscillating water columns (OWCs) is considered in this paper, hereinafter referred to as a multi–OWC platform. Each OWC chamber is enclosed by two partially submerged vertical walls and the deck of the platform. An incident wave produces oscillation of the water column in each OWC chamber and hence air is pumped by the internal water surface to flow through a Wells turbine installed at the chamber top. The effect of the turbine is characterised as a linear power take–off (PTO) system. A semi–analytical model based on linear potential flow theory and the eigen–function expansion method is developed to solve the wave radiation and diffraction problems of the multi–OWC platform. The hydrodynamic coefficients evaluated with direct and indirect methods of the model are shown to be in excellent agreement, and the energy conservation relationship of the multi–OWC platform is satisfied. The validated model is then applied to predict wave motion, dynamic air pressure, wave power extraction, and wave reflection and transmission coefficients of the multi–OWC platform. The effects of the PTO strategies, the number of chambers, the overall platform dimensions and the relative dimensions of adjacent chambers on wave power extraction and wave attenuation are investigated. A smaller–draft front wall and a larger–draft back wall are found to be beneficial for broadening the range of high–efficiency performance of the platform. The same wave transmission coefficient can be obtained by two multi–OWC platforms with inverse geometric constructions. [ABSTRACT FROM AUTHOR]

This study concentrates on the hydrodynamics of wave energy converters (WECs) consisting of an array of periodic buoys. The interaction between the bodies and waves was solved by a precise analytical method. The intrinsic relationships between wave propagation, energy capture, and array response are analyzed. Bragg resonance was found not only in scattering waves but also in radiation waves. The radiation wave is affected by different power take-off (PTO) damping, which could lead to incoming waves travelling freely through the array or being prevented through the array. The results show that Bragg resonance reduces the extraction efficiency significantly, and each device is affected to a different degree. In addition, this study reveals that there is collective behavior in the periodic WECs, all bodies in the array oscillate with identical amplitude at the Bragg resonance frequencies. Furthermore, the parametric effects on the hydrodynamic performance are investigated. The result of the study may provide useful guidance for the practical design of the WEC array. [ABSTRACT FROM AUTHOR]

Predicting the response of point absorber wave energy converters (WECs) in extreme sea states is crucial for assessing their survivability. However, data are scarce and hydrodynamic understanding is limited. In order to simulate extreme wave conditions, laboratory-scale focused waves based on NewWave theory have been utilized. To investigate the interactions between focused waves and a point absorber WEC, a wave basin experiment has been conducted. Various parameters, including focusing amplitude and peak frequency have been examined across three different damping conditions. The motion response of the point absorber WEC and the corresponding mooring force have been measured over time. The experimental findings reveal that both the focused wave parameters and the damping values have a significant influence on the motion response and mooring force. It is shown that an increase in the focusing amplitude leads to a more intense motion response, while the mooring force is relatively insensitive to the focused amplitude/peak frequency when the end-stop spring is not compressed. The force in the connection line is maximized when the upper end-stop spring is compressed. As the peak frequency increases, the heave and surge responses decrease, whereas the maximum mooring force increases with peak frequency for a locked power take-off (PTO) system. Finally, the results indicate that optimizing the design of the power take-off system, including selecting appropriate damping values and stroke lengths for the translator, can significantly reduce the mooring load for extreme wave conditions. • We conduct experiments to study the interactions between focused waves and a point absorber wave energy device. • Peak loads in the mooring line occur when the PTO translator hits the upper end-stop spring. • Without PTO translator-end-stop spring contact, peak frequency and focused amplitude have limited impact on mooring force. • The maximum motion response varied consistently with peak frequency and focused peak. [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]

The U-Oscillating Water Column (U-OWC) is a wave energy harvester exploiting the working principle of oscillating water columns for capturing and converting energy from sea waves. U-OWC devices can be integrated into a breakwater to enable wave energy extraction and provide shelter for port activities. In this work, a coupled Smoothed Particle Hydrodynamics (SPH) model was developed and applied to investigate the hydrodynamics of a U-OWC breakwater. The numerical model is validated against the experimental results over a range of regular wave conditions. An extensive campaign of computational tests is then carried out, studying the effects of geometrical parameters on the hydrodynamic performance and wave loading over the U-OWC breakwater. It shows that the geometrical parameters of the U-shape have a significant effect on the air pressure inside the chamber and the load phase difference between the two sides of the lip wall. The minimum load and maximum capture efficiency designs for U-OWC breakwaters cannot be satisfied geometrically at the same time. This demonstrates that it is necessary to consider comprehensively the structural reliability and hydrodynamic performance in the design and construction of a U-OWC breakwater. • We develop a coupled SPH model to investigate the performance of a U-OWC. • We carry out a series of physical tests of a U-OWC in a wave flume. • Numerical results of free surface and air pressure agree well with physical data. • An air pressure–volume flux function is employed to simulate the pneumatic PTO system. • Device geometry has different effects on hydrodynamic efficiency and wave loads. [ABSTRACT FROM AUTHOR]

In this work, a wave energy converter (WEC) that reacts against an internal inverted pendulum, which works as an inertial device to provide reaction for power absorption and is potentially superior due to its natural high elevation of the internal mass compared to a normal pendulum, named IPWEC has been studied. Optimal structural configurations of the WEC have been identified by a genetic algorithm. The equations of motion have been defined and solved explicitly using a linearized model, which has been validated by experiments and a non-linearized model. When comparing IPWEC with the WEC that reacts against a normal pendulum (NPWEC), it is found that, although both WECs present almost the same wave power capture ability, IPWEC possesses several advantages in most sea states due to the naturally high elevation of the pendulum's center of gravity: (1) the pendulum mass and the angular motion amplitude of the pendulum are 35% and 50%, respectively, smaller than those of NPWEC; (2) the averaged reactive power required under complex conjugate control is 75% smaller than NPWEC; (3) the moment which holds the pendulum fixed relative to the hull in the survival mode is merely a half as large as that of NPWEC. • A WEC that reacts against an internal inverted pendulum has been studied. • The optimal structural configuration of the WEC is identified by a genetic algorithm. • The linearized model proposed is validated by experiments and non-linearized models. • An inverted pendulum possesses several advantages to a normal pendulum. [ABSTRACT FROM AUTHOR]

In this study, the flexible curtains are attached to the bottom of a rectangular floating breakwater as wave-dissipating components. Through a comprehensive experimental investigation, the wave attenuation, motion responses, and mooring forces of the proposed floating breakwater are examined, with a particular focus on the effects of wave height and the hanging length and porosity of the flexible curtain. Meanwhile, comparative analyses are conducted with the stand-alone rectangular floating breakwater and with attaching one rigid slotted barrier. Our experimental results indicate that one underhanging flexible curtain can augment wave attenuation across all tested wave conditions, which is comparable to the rigid slotted barrier. Furthermore, attaching two flexible curtains contributes to a more significant enhancement for harbor or coastal protection, especially against long waves. This can be attributed to the buffer function of flexible curtains, and the increased added mass induced by the water body confined between them, which increases the natural period of floating breakwaters. Furthermore, the attachment of the flexible curtains significantly suppresses the motion responses of the breakwater, which can alleviate the undesirable strong mooring forces. In general, increasing the length or decreasing the porosity of flexible curtains leads to similar trends in the performance of floating breakwaters. The flexible curtains have been proven to be effective wave-dissipating components for rectangular floating breakwaters. [ABSTRACT FROM AUTHOR]

Semi-Supervised Domain Adaptation (SSDA) leverages knowledge from a fully labeled source domain to classify data in a partially labeled target domain. Due to the limited number of labeled samples in the target domain, there can be intrinsic similarity of classes in the feature space, which may result in biased predictions, even when the model is trained on a balanced dataset. To overcome this limitation, we introduce a multi-view consistency framework, which includes two views for training strongly augmented data. One is a debiasing strategy for correcting class-wise prediction probabilities according to the prediction performance of the model. The other involves leveraging pseudo-negative labels derived from the model predictions. Furthermore, we introduce a cross-domain affinity learning aimed at aligning features of the same class across different domains, thereby enhancing overall performance. Experimental results demonstrate that our method outperforms the competing methods on two standard domain adaptation datasets, DomainNet and Office–Home. Combining unsupervised domain adaptation and semi-supervised learning offers indispensable contributions to the industrial sector by enhancing model adaptability, reducing annotation costs, and improving performance. • Semi-supervised learning can reduce the cost for domain shift. • The multi-view approach adopts debiased pseudo-labels and pseudo-negative labels. • It reduces class ambiguity significantly. • The cross-domain affinity learning helps feature alignment across domains. • Our approach achieves good results on well-known domain adaptation datasets. [ABSTRACT FROM AUTHOR]

The accurate evaluation of the wave energy conversion of oscillating water column (OWC) wave energy converter has consistently plagued scholars. In this paper, an original and well-validated test platform is proposed for exploring the flow characteristic of a nonlinear power take-off (PTO) damping, with which a more accurate and stable measurement of captured energy is obtained in the laboratory modelling. This study utilizes ten orifices to comprehensively investigate the impact of the PTO damping on an offshore stationary cylindrical OWC device. The joint effect of the PTO damping with wave height (H i) or draft of OWC (Dr) is examined. The damping coefficient C f = 10350 is found to be the optimal damping coefficient, in terms of both the peak wave energy conversion and the efficient bandwidth. It is revealed that the variations of the PTO damping can regulate the effect of Dr and H i on wave energy conversion. An appropriate reduction in PTO damping can alleviate the weak energy output caused by the increased Dr and H i. The effect of increased H i on wave energy conversion could be judged by the size relation of the maximum and minimum values of internal pressure data. • We propose a novel test platform to enhances OWC wave energy measurement. • Ten orifices are utilized to explore power take-off (PTO) damping impact on OWC device. • The optimal damping coefficient C f = 10350 boosts energy conversion. • PTO damping adjusts the effects of wave height and draft of OWC on power absorption. [ABSTRACT FROM AUTHOR]

Assorted novel low-reflection structures have been developed for the need of berthing safety in the harbor. The oscillating water column (OWC)-type wave absorbers offer significant benefits as they not only reduce reflected waves but also harness wave energy effectively. Based on the previous studies, a multi-factor comprehensive research on the reflection characteristics, energy extraction performance as well as the wave power dissipation of OWC-type wave absorbers is carried out. The influence of opening ratios is the key point, and the coupled effects of it with the incident wave height and the front wall draft on the hydrodynamic characteristics of the OWC are further investigated. The results indicate that though a larger opening ratio results in a smaller valley value of wave reflection coefficient within the experimental wave frequency range, an appropriate opening ratio can weaken the sensitivity of the reflection behavior of OWC to wave frequency and widens the low reflection frequency band. The existence of vortex-dissipated energy leads to a difference in the wave frequencies corresponding to the minimal wave reflection and maximum extraction efficiency. Besides, reducing the front wall draft is preferred in enhancing efficiency and reducing wave reflection, and meantime this will be accompanied by a shift in resonant frequency. A decrease in wave height has a similar effect, but the effect is not as significant as the change in the draft. The increase of wave height will cripple anti-reflection performance due to the enhancement of radiated wave energy. The OWC-type wave absorber is convincingly competitive in terms of low wave reflection, compared with other extensively studied breakwaters. [ABSTRACT FROM AUTHOR]

Oscillating water column (OWC) device is possibly the most studied among various wave energy converters and many different realizations of the technology have been investigated. To study the complex hydrodynamic behaviour of an OWC, a two-dimensional numerical wave tank based on the weakly compressible smoothed particle hydrodynamics (SPH) method is developed in this paper. A simplified pneumatic model is proposed here to simulate the effect induced by a pneumatic power take-off system within the framework of a single-phase SPH model, and implemented to determine the air pressure imposed on the free surface inside the OWC chamber. Additionally, a regional ghost particle approach, as boundary condition in SPH, is proposed to better simulate fluid dynamics near a thin wall. The overall computation cost is reduced dramatically due to the employment of the regional ghost particle boundary condition method. First, the numerical model is validated under regular waves using published physical and numerical data. An extensive campaign of computational tests is then carried out, studying the performance of the OWC for various wall thicknesses and damping coefficient under various wave conditions. The results demonstrate that the present SPH model can be used as a practical tool for the development of high-performance OWCs. • We establish a 2D SPH model to investigate the performance of an OWC. • An air pressure–volume flux function is employed to simulate the pneumatic PTO system. • We propose a regional ghost particle approach to simulate a thin front wall. • The OWC with thinner walls has a better performance in terms of power absorption. • The optimal damping coefficient is not sensitive to the dimensionless wave height. [ABSTRACT FROM AUTHOR]

• A novel MC-LHP-PV/T heat and power system was experimentally investigated. • New PV/T system achieved 18.55% higher solar efficiency compared to existing ones. • A lower inlet water temperature led to the increased solar thermal efficiency. • A higher water flow rate help increase the solar thermal efficiency. • A higher ambient temperature led to the increased solar thermal efficiency. This paper aims to experimentally investigate a novel solar Micro-Channel Loop-Heat-Pipe Photovoltaic/Thermal (MC-LHP-PV/T) system which, making its first attempt to employ the co-axial tubular heat exchanger as the condenser, PV-bound multiple micro-channel tubes array as the PV/evaporator, the upper end liquid header with tiny holes as the liquid header and liquid/vapour separator, and the upper end vapour header as the vapour collector and distributor, can create the improved condensation and evaporation effects within the loop-heat-pipe (LHP) and thus, achieve significantly enhanced solar thermal and electrical efficiencies compared to traditional PV/T systems. Based on the results derived from our previous analytical study, a prototype MC-LHP-PV/T system employing R-134a as the working fluid was designed, constructed and tested, and the testing results were used to evaluate its operational performance including solar thermal and electrical efficiencies and their relevant impact factors. It is found that solar thermal efficiency of the MC-LHP-PV/T system varied with the inlet temperature and flow rate of coolant water, ambient temperature, as well as height difference between the condenser and evaporator. A lower inlet water temperature, a higher water flow rate, a higher ambient temperature, and a larger height difference between the condenser and the evaporator can help increase the solar thermal efficiency of the system. Under a range of testing conditions with the refrigerant charge ratio of 30%, a peak solar thermal efficiency (i.e., 71.67%) happened at solar radiation of 561W/m2, inlet water temperature of 18°C, water flow rate of 0.17m3/h, ambient temperature of 30°C, and height difference of 1.3m. This set of parametrical data is therefore regarded as the optimal operational condition of the MC-LHP-PV/T system. Under these specific operational condition and the real weather solar radiation, the solar thermal efficiency of the system was in the range 25.2% to 62.2%, while the solar electrical efficiency varied from 15.59% to 18.34%. Compared to the existing PV/T and BIPV/T systems, the new MC-LHP-PV/T system achieved 17.20% and 33.31% higher overall solar efficiency. [ABSTRACT FROM AUTHOR]

Global warming caused by the emission of fossil fuel consumption has become critical, leading to the inevitable trend of clean energy development. Of the power generation systems using solar energy, the floating photovoltaic (FPV) system is a new type, attracting wide attention because of its many merits. The latest progress in the research and applications of FPVs from multiple aspects is summarized in this paper. First, the development of FPVs is briefly described with a summary of typical installed FPV systems. Innovative photovoltaic design concepts and hybrid usage with other renewable energies are emphasized for offshore applications. Furthermore, critical structural design considerations are discussed, particularly emphasizing critical aspects such as load estimations, wave-structure interaction analysis, floating structure types, and mooring system design. Finally, several significant future challenges to the development and applications of marine FPV systems are identified, including survivability in the open sea, long-term reliability, and environmental impact. It aims to provide a broad overview of the development status, offering limited insights into the trends and challenges for marine FPV systems. • Landmarks of floating photovoltaic (FPV) development are presented. • Innovative PV design concepts for marine FPV systems are reviewed. • Potential synergies of marine FPV systems are introduced. • Critical structural design considerations of marine FPV systems are discussed. • The main obstacles to developing FPV systems on the ocean are indicated. [ABSTRACT FROM AUTHOR]

• Hydrodynamics of pile-supported OWC breakwaters have been analytically modeled. • A local increase in back draft is adopted to improve performance. • Effects of chamber breadth and wall draft on hydrodynamic performance are studied. • Air compressibility on energy extraction and wave transmission are investigated. • A practical optimization strategy by setting PTO damping at two constants is tested. A pile-supported OWC breakwater is a novel marine structure in which an oscillating water column (OWC) is integrated into a pile-supported breakwater, with a dual function: generating carbon-free energy and providing shelter for port activities by limiting wave transmission. In this work we investigate the hydrodynamics of this novel structure by means of an analytical model based on linear wave theory and matched eigenfunction expansion method. A local increase in the back-wall draft is adopted as an effective strategy to enhance wave power extraction and reduce wave transmission. The effects of chamber breadth, wall draft and air chamber volume on the hydrodynamic performance are examined in detail. We find that optimizing power take-off (PTO) damping for maximum power leads to both satisfactory power extraction and wave transmission, whereas optimizing for minimum wave transmission penalizes power extraction excessively; the former is, therefore, preferable. An appropriate large enough air chamber volume can enhance the bandwidth of high extraction efficiency through the air compressibility effect, with minimum repercussions for wave transmission. Meanwhile, the air chamber volume is found to be not large enough for the air compressibility effect to be relevant at engineering scales. Finally, a two-level practical optimization strategy on PTO damping is adopted. We prove that this strategy yields similar wave power extraction and wave transmission as the ideal optimization approach. [ABSTRACT FROM AUTHOR]

Wave power absorption of a heaving-body wave energy converter (HBWEC) can be improved by making the device highly asymmetric and deploying it near a coastal wall, harbour pier, or breakwater. However, the coupling between the geometric asymmetry of the HBWEC and the partial reflecting boundaries of the various walls and the consequential influence on the power performance of the HBWEC are unclear. This research aims to fill this gap. A semi-analytical model based on the linear potential flow theory is proposed to deal with an HBWEC with an arbitrary bottom shape and a partial reflection wall. The degree of asymmetry (DoA) of the HBWEC and the reflection rate of the wall are mathematically defined. Results show that the wall increases the power performance of an HBWEC by increasing the reflected wave energy through an increase in the reflection rate. Practically, an HBWEC should have a larger DoA to make it more immune to the change of the reflection rate and therefore more adaptable to different situations. These findings could offer recommendations for the design and deployment of an HBWEC according to the properties of the wall, improving wave power absorption efficiency and avoiding unnecessary costs due to improper design. • An arbitrary heaving body WEC near a partial reflection wall is analytically modeled. • Evanescent modes are involved in mixed boundary conditions and proved nonnegligible. • The asymmetry of WEC, the reflection rate of wall, and their couplings are studied. • Design and layout of a heaving body WEC considering wall property are recommended. [ABSTRACT FROM AUTHOR]

Due to the abundant wind energy in deep water, floating offshore wind turbines (FWTs), especially for the semisubmersible FWTs, have attracted more attention these years. To reduce the heave motion of FWTs, heave plates are often attached at the bottom of the column. In this paper, experimental investigations of the hydrodynamic performance of the heave plates via the forced oscillation method are conducted. The impacts of the KC number (KC = 0.1–1.1), oscillation frequency (f = 0.4–1.43 Hz), diameter ratio- D d / D c (D d and D c are the diameter of the heave plate and column), thickness ratio- t d / D d (t d is the thickness of the heave plate), shapes of the heave plates, on the added mass, and damping coefficients are investigated. The results show that the added mass and damping coefficients are independent of oscillation frequencies, while the KC number influences significantly the hydrodynamic coefficients. Increase in the diameter ratios will decrease the added mass and damping coefficients. The thinner heave plates obtain larger damping coefficients. Comparison between the different shapes of the heave plates shows that the octagonal heave plate displays similar added mass and damping coefficients to the circular heave plate. However, square one obtains lower added mass coefficients compared to the other three shapes. And the hexagonal plate seems to have the highest damping force for different KC numbers. • Hydrodynamic performance of heave plates were investigated via an experimental approach. • The effects of the KC numbers and oscillation frequencies on the hydrodynamic coefficients were analyzed. • Diameter ratios and shapes effect of the heave plate on the hydrodynamic performance were also carried out. • KC numbers have great influence on the hydrodynamic coefficients of the heave plate. • The hexagonal plate obtains higher damping coefficients compared to other shapes. [ABSTRACT FROM AUTHOR]

For a novel vertical solar loop-heat-pipe photovoltaic/thermal system, the height difference between evaporator and condenser plays an important role in the heat transport capacity, which has significant impact on the solar thermal efficiency and parametrical optimization of this system. Therefore, based on the results derived from the authors' previous analytical investigation and computer modelling studies, a prototype of this novel system was designed, constructed, and an experimental investigation under different height difference was undertaken to study the impact of height difference on the system performance. It was found that the relationship between the solar thermal efficiency of this vertical system and the height difference is nonlinear. In present study, the optimal height difference is around 1.1 m, which was selected as an optimal value for the following experimental investigations, and below 1.1 m, the PV module surface temperature decreased with the increase of the height difference. Furthermore, the transient solar thermal and electrical performance of this system with the selected optimal height difference were investigated under outdoor real weather condition. These results of this experimentation can help optimize the system construction and thus help to develop the high thermal performance and low-cost solar PV/T system for space heating and power generation. • A novel LHP-PV/T heat & power system was experimentally investigated by varying HD. • The optimal height difference between evaporator and condenser is around 1.1 m. • New PV/T system achieved higher solar efficiency compared to most existing ones. • A lower inlet water temperature led to the increased solar thermal efficiency. [ABSTRACT FROM AUTHOR]

In this work, a mechanical power take-off system (PTO) is proposed to be installed in a small-scale wave energy converter (WEC) to transfer wave power to electricity. Two pairs of one-way bearings are respectively embedded into two transmission chains to transfer bidirectional oscillation of the primary mover to unidirectional rotation of the generator. In addition to a flywheel mounted on the output shaft, a spring is integrated into each transmission chain to further smooth the generator speed. The working principle of the PTO is discussed in detail, including the situation of the PTO at different status combinations of the one-way bearings and the rules to determine the status combination in each time instance. Compared to the case when the flywheel is the unique smoothing device, a combination of the spring and flywheel significantly reduces the fluctuation of the generator speed. Two peaks are observed for the captured power versus the PTO configuration, and the one with a small spring stiffness and suitable generator damping is superior since a high power capture efficiency is achieved with a small fluctuation of the output power. Besides, the feasibility of the proposed PTO in smoothing generator speed in irregular waves is also verified. • A mechanical PTO that is integrated with both a flywheel and spiral springs is proposed. • A combination of the spring and flywheel significantly reduces the output fluctuation. • Two peaks are observed for the captured power versus the PTO configuration. • Feasibility of the PTO in smoothing generator speed in irregular waves is verified. [ABSTRACT FROM AUTHOR]

A hybrid system integrating a power take-off (PTO) system into a floating breakwater is a promising candidate for both shoreline protection and commercial wave energy extraction. Although geometric asymmetry is important to such PTO-integrated breakwaters, its role in energy conversion efficiency and wave attenuation is poorly understood. In this study, a two-dimensional semi-analytical model dealing with floats with arbitrary bottom shapes is established based on the potential flow theory. To quantify the geometric asymmetry reflected by PTO-integrated breakwaters with different contours, the degree of asymmetry and the absolute asymmetry are newly defined mathematically. A set of symmetric and asymmetric PTO-integrated breakwaters are comparatively studied to demonstrate the effect of linear PTO damping and geometric asymmetry on the transmission coefficient, the reflection coefficient, and the energy conversion efficiency. Results show that no matter the hybrid system is symmetric or asymmetric, a larger PTO damping is beneficial for wave attenuation in longer waves, particularly at the heaving natural period of the device. On the premise that the PTO damping is optimized, an increase in the degree of asymmetry greatly improves the energy conversion efficiency. An increase in the absolute asymmetry slightly improves wave attenuation. • Interactions between waves and a float with arbitrary bottom shapes are modeled. • Installing a power take-off (PTO) on a breakwater improves its wave attenuation. • The degree of asymmetry (DoA) of a float is newly defined mathematically. • DoA greatly influences PTO-integrated breakwater's energy conversion efficiency. • DoA slightly influences PTO-integrated breakwater's wave attenuation. [ABSTRACT FROM AUTHOR]

In this work, we studied the impact of the buoy geometry on power absorption of a point absorber consisting of a cylindrical buoy. The displacement volume of the buoy is fixed while the radius to draft ratio is adopted to completely define the buoy geometry. A motion constraint that prevents the buoy from jumping out of or being submerged by the water is applied so that the absorbed power is restrained at a reasonable range. The maximum power absorption ability under reactive control has been attained, and the most appropriate buoy geometry has been identified. Passive control is also investigated to find the possible condition where it can be used as an alternative to active control. Results show that the maximum absorbed power approaches the Budal limit at low wave frequencies, and gradually departs from this limit with the increasing wave frequency. The most attractive radius to draft ratio, which shows more absorbed power and wider bandwidth, is around 1.0 and decreases with the increasing wave amplitude. At high wave frequencies, the absorbed power is identically affected by the motion constraint for both passive and reactive control, hence passive control may be an alternative to reactive control in this condition due to simpler implementation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tea polyphenols and Levofloxacin decrease HPS relative index and alleviate lung pathologic change in CBDL rats. • The network pharmacology approach reveal that TNF-α may be the potential target. • Protein and mRNA experiments verify that these effects of Tea polyphenols and Levofloxacin are possibly related to the regulation of the Endotoxin -TNF-α pathways. Hepatopulmonary syndrome (HPS) is characterized by pulmonary vasodilation and arterial blood oxygen desaturation in patients with chronic liver disease. Generally, common bile duct ligation (CBDL) rats are a suitable experimental model for studying hepatopulmonary syndrome. Our previous study demonstrated that endotoxin surges markedly, followed by bacterial translocation and the loss of liver immune function in all the stages of CBDL, thereby contributing to the pathogenesis of HPS. However, the mechanisms behind the increase of the endotoxin and how to alleviate it have not yet been elucidated. Pulmonary injury induced by increased bilirubin, endotoxin, and inflammatory mediators occurs in the early and later stages of CBDL. This study assessed the effects of Tea polyphenols (TP) and Levofloxacin on endotoxin reduction and suppression of lung injury in HPS rats in the long and short term, respectively. Morphological change of pulmonary injury, HPS relative index, endotoxin concentration, and the activation extent of Malondialdehyde (MDA) and Myeloperoxidase (MPO) were evaluated in CBDL rats with or without TP and Levofloxacin for three weeks or six weeks. The inflammation factors of serum, lung tissue, and BALF were then compared at the same condition for the two time periods. This was followed by adoption of the network pharmacology approach, which was mainly composed of active component gathering, target prediction, HPS gene collection, network analysis, and gene enrichment analysis. Finally, the mRNA and protein levels of the inflammatory factors were studied and relative signaling expression was assessed using RT-PCR and Western blot analysis. The obtained results indicated that the pulmonary injury manifestation was perceived and endotoxin, MDA, and MPO activation were markedly increased in the early and later stages of CBDL. TP and Levofloxacin treatment alleviated endotoxin infection and inflammation factor expression three weeks and six weeks after CBDL. In addition, Levofloxacin displayed a short time anti-bacterial effect, while TP exerted a long period function. TP and Levofloxacin also reduced TNF-α, TGF-β, IL-1β, PDGF-BB, NO, ICAM-1, and ET-1 expression on the mRNA or protein expression. With regard to the pharmacological mechanism, the network analysis indicated that 12 targets might be the therapeutic targets of TP and Levofloxacin on HPS, namely ET-1, NOs3, VEGFa, CCl2, TNF, Ptgs2, Hmox1, Alb, Ace, Cav1, and Mmp9. The gene enrichment analysis implied that TP and Levofloxacin probably benefited patients with HPS by modulating pathways associated with the AGE-RAGE signaling pathway, the TNF signaling pathway, the HIF-1 signaling pathway, the VEGF signaling pathway, and the IL-17 signaling pathway, Rheumatoid arthritis, Fluid shear stress, and atherosclerosis. Finally, the TNF-α level was mainly diminished on the protein level following CBDL. TP and Levofloxacin could alleviate pulmonary injury for short and long period, respectively, while at the same time preventing endotoxin and the development of HPS in CBDL rats. These effects are possibly associated with the regulation of the Endotoxin -TNF-α pathways. [ABSTRACT FROM AUTHOR]

A novel micro-channel loop-heat-pipe solar photovoltaic/thermal (LHP- PV/T) system is developed employing the co-axial tubular heat exchanger as the condenser and upper-end liquid header with tiny holes as the liquid feeder. The design facilitates an easier connection among the solar modules. It creates the improved condensation and separate evaporation effects within the LHP. A reduced evaporator area will thereby have a minor impact on the overall heat transfer performance, leading to significant potential for cost reduction. A distributed parameter model is established and validated by experimental data. The model is then applied to analyse the cost reduction potential of the LHP- PV/T via the optimization of geometrical and structural parameters. The impact of the area reduction on the LHP evaporator differs from that on the traditional integral heat pipe PV/T. The decrements in thermal and electrical efficiencies of the LHP- PV/T are 2.47% and 0.03% respectively when the width of heat pipes in the evaporator decreases from 26 to 10 mm. When the number of heat pipes decreases from 30 to 6, the decrements in thermal and electrical efficiencies are 4.63% and 0.12%, whilst the overall system cost drops by 28.58%, thus the cost-effectiveness of the system can be improved. •. A novel loop heat pipe solar photovoltaic/thermal system is built. •. An accurate distributed parameter model is developed. •. Cost reduction potential of the system is investigated. •. Influences of a reduced evaporator area on LHP differ from those on IHP. •. The system cost is reduced by 28.58% with a minor decrement in the performance. [ABSTRACT FROM AUTHOR]