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This paper investigates a novel micro-channel flat separated loop heat pipe system for cooling the information technology equipment in the data centres through theoretical and experimental analysis and by assessing the impact of the inlet water temperature on system performance. A computer model is developed to simulate the steady-state performance of the micro-channel flat separated loop heat pipe system. After comparing the experimental and modelling results, the new and conventional system under the same working conditions, the model is validated yielding high accuracy in predicting the performance of the micro-channel flat separated loop heat pipe system with recorded error being limited to 2.16–8.97%. The new system has better performance than the conventional system. Under the operating conditions of heat load intensity of 1,000 W/m2, water flow rate of 0.28 m3/h, refrigerant filling rate of 30%, ambient air temperature of 26°C, and evaporator and condenser height difference of 0.8 m, the performance of the system has been explored at inlet temperature from 15 to 24°C with increments of 3°C. The system's averaged heat transfer efficiency was found to decrease with the increase in inlet temperature. This research provides valuable insight into the data centre information technology equipment cooling, which is of great significance for energy saving and environmentally friendly operation of data centres. [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]

Inspired by the energy island used for energy storage, conversion, and transmission, this study explores the water wave interactions with a bottom-standing cylinder surrounded by an arc-shaped breakwater of negligible thickness. The arc-shaped breakwater can be either impermeable or porous. To analyze the problem, a semi-analytical matched eigenfunction expansion method is developed within the framework of linear potential flow theory. The fluid domain is divided into subdomains, with the velocity potentials in each subdomain expressed as eigenfunction expansions. Matching conditions, ensuring continuity in pressure and normal velocity, are imposed at the juncture boundary. The accuracy of the developed semi-analytical method is verified through comparison with results obtained using the numerically-based boundary element method. Extensive discussions are made on hydrodynamic responses, including wave exciting force and free surface elevations. When the breakwater is impermeable, fluid resonance occurs in the gap between the cylinder and the arc-shaped breakwater, leading to significantly large responses in both free surface elevation and hydrodynamic forces. A simple method is developed to estimate the resonant frequencies and mode shapes associated with these resonances. On the other hand, it is observed that the presence of the porous breakwater considerably reduces the free surface responses in the gap as well as the hydrodynamic loads on the cylinder. The porous breakwater effectively mitigates the occurrence of fluid resonance and offers an efficient means to dampen wave energy, providing valuable insights for wave energy dissipation and coastal engineering applications. [ABSTRACT FROM AUTHOR]

In this paper, the diffraction and radiation problem of multiple two-dimensional rectangular bodies floating on a layer of water of finite depth with waves is studied. An analytical model for the analysis of wave excitation forces and added mass and damping coefficients is proposed, based on a linearized velocity potential theory. Expressions for velocity potentials are obtained by the method of separation of variables, in which unknown coefficients are determined by utilizing the eigen-function expansion matching method. The model is validated by a comparison of the simulation results with the available data. The validated model is then utilized to examine the effect of the structure width, structure draft, spacing between adjacent structures, and structure numbers on wave transmission coefficient of floating structures. [ABSTRACT FROM PUBLISHER]

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]

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]

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]

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]