energies

The propagation potential over a variable bathymetry, in the absence of the floating body spreader, is based on the following local-mode representation. For evaluation of the absorbed power of the units, a typical PTO has been assumed.

Figure 1. Computational meshes on (a) free surface, (b) bottom, and (c) WEC surface.

Sloping Seabed Eﬀect

Conclusions

Coupling method for investigating the far-field effects of wave energy converter arrays over a varying bathymetry.Energies. A new method for estimating wave energy converter performance in variable bathymetry regions and applications.Energies.

Sealing Performance Analysis of an End Fitting for Marine Unbonded Flexible Pipes Based on

Hydraulic-Thermal Finite Element Modeling

Introduction
Sealing Analysis
FE Modeling Procedures
Results and Discussion
Conclusions

The sealing ring is designed in advance according to the specifications of the flexible pipe and the end ﬁtting. The contact seal between the sealing ring and the polymer material in the inner layer of the flexible pipe is a form of static seal [27].

Figure 1. Typical cross-section of ﬂexible pipeline end ﬁtting [9].

An Assessment of Wind Energy Potential in the Caspian Sea

Materials and Methods

Thus, Figure 1a,b presented the distribution of the water depth, in general, and for the reference sites considered for evaluation. Apart from the assessment of the wind energy potential, another objective of the present work is to estimate the performance of some offshore wind turbines, and therefore the U10 values must be adjusted to the hub height of a specific system.

Figure 1. The Caspian Sea and the reference sites considered for assessment, where: (a) bathymetry map [25]; (b) water depths corresponding to each reference site [25]; (c) number of inhabitants corresponding to the reference area considered [26].

Results

The variation of wind speed between different distances from the coastline (5 km-25 km-50 km) is shown in Figure 5b. This distribution closely followed the wind speed evolution with better results expected in the north.

Figure 3. Spatial distribution of the U80 parameter (average values) considering the 20-year time interval (January 1999 to December 2018) of ERA-Interim data.

Discussions and Conclusions

Joint evaluation of the wave and offshore wind energy sources in the developing countries.Energies. Evaluation of the wind energy potential in the coastal environment of two enclosed seas. Adv.

Figure 12. The classiﬁcation of the wind turbines selected for the sites Atyrau and Baku, taking into account the power output per swept area

Volume-Based Assessment of Erosion Patterns around a Hydrodynamic Transparent Oﬀshore Structure

Experimental Setup

The sediment pit is located in the center of the pool and provides an additional depth of 1.2 m, a length of 8 m and a width of 6.6 m. The piles below the lowest nodes were made of aluminum and connected to the bottom of the wave pool. Since the mantle structure was not rotated during the laboratory experiments, only one orientation of the model with respect to current and wave direction was investigated in this study.

Consequently, a substantial influence of the jacket structure on the flow and therefore on the sediment bed was envisaged. No general starvation of the bed (general seabed lowering) was observed in the present study.

Figure 2. Schematic view of the jacket model (a) plan view on the model, including dimensions, the mounted echo sounding transducer, the reference structure footprint a 1 and the increasing interrogation area a i to compute the erosion volume (b) side view

Calculation of Erosion Volumes

The incremental erosion volume VI, and the incremental erosion depth DV, are both a net gradient volume, related to an area between two adjacent interrogation areasaiandai−1. The incremental erosion volume VI,i Equation (5) is directly related to equations (3) and (4) and represents an erosion volume in relation to an area. On the other hand, the incremental parameter DV represents an erosion depth for an interrogation area, calculated by normalization with the pile diameter.

Results

Figure 6a illustrates the dimensionless eroded sediment volume VD,i with increasing distance from the center of the structure. With increasing distance from the structure, the influence of the global sanding process on the erosion volume decreases. Consequently, it is possible to estimate sediment volumes or scour depths in relation to the hydraulic condition or the distance to the center of the structure.

With distance from the pile, the erosion depth resembles that of the global erosion value. Global erosion causes a lowering of the seabed at the same time as the deepening of the local scour hole.

Figure 4. Exemplary photo of the model setup and scour pattern after test 4; the dashed line illustrates the extent of the global scour, current is coming from left to right with 0 ◦ , waves are propagating perpendicular in 90 ◦ .

Remarks Regarding Practical Application and Scale Eﬀects

12] concluded that at the end of the tests, approximately 90% of the equilibrium depths were reached for local treatment processes. With a scale factor of 1:30, current test durations correspond to storm durations of ~20–45 h, depending on wave period. However, the results also show that local and global scratching processes are affected by a characteristic depth ratio, but are interconnected through intertwined feedback mechanisms, which likely leads to the influence of global scratching on the development of local scratching and vice versa (see [12]).

In particular, the timing of global scratch development and the impact on local scratch development in this context appear to be an important research question that remains unresolved. To better assess the differences with respect to prototype conditions, scale effects were discussed and measurements from this study were compared to available field studies on scratch development around mantle structures (see Figure 11).

Summary and Conclusions

In Proceedings of the Second International Conference on Scour and Erosion, ICSE 2, Singapore, Singapore, 14–17 November 2004. In Proceedings of the Ninth International Conference on Scour and Erosion, ICSE 9, Taipei, Taiwan, 5–8 November 2018. In Proceedings of the Sixth, France and Erosion of the Sixth, France and ER International Conference on Scour and Erosion, 6 31 August 2012.

In Proceedings of Fourth International Conference on Scour and Erosion, ICSE 4, Tokio, Japoni, 5–7 nëntor 2008. Në Proceedings of Third International Conference on Scour and Erosion, ICSE 3, Amsterdam, Holandë, 1–3 nëntor 2006.

Control Strategies Applied to Wave Energy Converters: State of the Art

Wave Energy Technology

This classification is somewhat qualitative due to the many differences between continental shelves around the world. This classification is according to the orientation of the wave energy device with respect to the wave propagation front (Figure 1). Therefore, the air turbine can take advantage of the complete wave oscillation cycle.

They take advantage of the potential energy of the waves to convert it, through synchronous generators, into electricity (Figure 5). As a result, this PTO solution presents a challenge stemming from the bidirectional nature of the flow.

Figure 1. Classiﬁcation according to device dimensions and orientation.

Control Strategies

Conventionally, you only need to know the instantaneous value of the PTO speed, for which measuring instruments are usually available on the market. In addition, the optimum value of the PTO damping, the value of Bpto that maximizes the instantaneous absorbed power, can be easily calculated for regular waves. For this solution, the damping coefficient is time-varying and instantaneously tuned, based on the frequency of the excitation force.

A critical point for this control strategy is the calculation of the lock and release time periods. The solution is based on the spectral decomposition of the measurement signal, which is used to construct the optimal solution.

Figure 8. Variation of WEC oscillator velocity (no PTO) for a set of regular wave frequencies with Reference Model 3 [29] geometry with minor variations; simulations performed in WECSIM [30].

Conclusions and Further Research

Passive real-time control of wave energy converters using the Hilbert-Huang transform.IFAC-PapersOnLine. Optimizing Wave Energy Converter Control with Power Losses and Fatigue Remove. IFAC-PapersOnLine. Estimation of damping coefficients of power take-off systems of wave energy converters: A hybrid approach. Energy.

Economic aspects of latching control for a wave energy converter with direct drive of a linear power take-off generator. Restore. Stochastic control of wave energy converters for optimal power absorption with limited control force. Appl.

Figure 11. Recent studies for diﬀerent WEC control strategies, 2017–2019.

Impact of Electrical Topology, Capacity Factor and Line Length on Economic Performance of

Description of Electrical Topologies Considered

It consists of an indoor collection system with 25 and 75 turbine system sets, respectively, connected to an onshore substation in the island and high voltage (HV) submarine transmission cables between the onshore substation and the point of common coupling rail in the mainland. The collector system consists of several radial branches connected via submarine cables to an onshore substation. In this conﬁguration, each turbine is connected to AC-DC and DC-DC converters that create a medium voltage (MV) DC bus in the collection system.

The collection system is connected to another multilevel DC-DC converter on an onshore platform via 30 kV DC monopolar submarine cables. The radial design for an OWF collection system was shown to be the most cost-effective option in a previous study [8].

Figure 1. Conﬁguration of proposed AC OWF.

Annual Energy Yield and Electrical Losses Estimation

The power electronics (PE) losses for the AC offshore configuration include the losses in the turbine inverters within the collection system, while the PE losses for the DC counterpart include the losses in the turbine inverters, the onshore DC-DC and DC-AC converters. IN and I are the average currents in the top and bottom stacks, respectively. λ refers to the ratio of conduction time to switching period. The corresponding PE losses in the IGBT modules (PIGBT-HVAC) and (PFWD-HVAC) can be calculated as given by (1) and (2) respectively.

As transformerless multilevel inverter topologies are considered in the DC offshore wind configuration, transformer losses are therefore a concern in the AC offshore wind configuration. Pcable-AC and Pcable-DC are the total losses of the collector and transmission lines in AC and DC offshore configurations.

Table 1. Rated values for Parameters of the IGBTmodules used in the converters [33].

Economic Analysis

CAPEX
OPEX

Today, the VCS-based inverter is the most promising technology dominating the market [40,41]. The total cost components of the electrical system for the DC configuration include: (1) medium voltage DC submarine indoor cables with installations; (2) onshore substation with inverters and other necessary components; (3) submarine high voltage direct current cables and their installations connecting the onshore substation on the island to the mainland; (4) mainland converters; and (5) a grid connection unit including other substation components such as reactors. Cable costs of the collection system: The wind turbines are connected to each other as well as to the onshore substation via submarine cables. Onshore DC/AC Converter Substation: The onshore onshore substation is a DC/AC substation that converts 150 kV DC to 154 kV AC national transmission voltage.

A comparison of AC and HVDC options for connecting offshore wind generation in Great Britain.IEEE Trans. Daniel Manrique, O. Design of the HVDC Connection of a 425 MW Offshore Wind Farm to the German Grid;.

Table 2. DC cable costs considered for collection and transmission systems.

Ocean Renewable Energy Potential, Technology, and Deployments: A Case Study of Brazil

Targets, Materials, and Methods

Maritime areas under Brazilian jurisdiction include the Territorial Sea, with a limit of 12 nautical miles; Exclusive Economic Zone (EEZ), with 12 to 200 nautical miles; and the Continental Shelf, which includes the seabed that extends beyond the Territorial Sea, along the natural extent of land territory outside the continental shelf. Others, describing different concepts from the above categories, e.g., wave carpet [91] and rotating mass[92,93], which uses the motion of a hull to accelerate and sustain the rotations of a rotating mass inside. Flood production - the process of energy production begins when water enters the tidal basin (flood tide);

Bidirectional generation—the tidal power plant produces power during the high and low tides. The TRL system quantifies the development of ocean energy devices from an initial stage of research and development (R&D) to industrial deployment, which involves the mass production of off-the-shelf components and devices.

Figure 2. Brazilian coastline and the main marine areas delimited.

Case Study of Brazil 1. Resource Assessment Results

The back shows the variability of the energy source and provides a holistic view of the wave climate along the Brazilian coast. It can be observed that, regardless of the water depth, the seasonal variability (SV) of regions A and B is always smaller than that of regions D and C. His plant had problems and stopped working off the coast of Rio de Janeiro due to the fatigue of its long intake pipes [184].

The second project is a nearshore wave energy converter, also developed by the UFRJ, which will be installed in relatively shallow water (water depth of 25–30 m) on the Rio de Janeiro coast. The vertical movement of the buoy is transmitted to the gearbox by means of a central rod (lifting stem).

Table 3. Average values of the ocean current power density (W/m 2 ), standard deviation (±), seasonal variability (SV), and coeﬃcient of variation (COV) for each coastline region—A, B, C and D—for each season (summer, autumn, winter, and spring) between Ja

Discussion and Open Question

Geometric evaluation of the main operating principle of a redundant wave energy converter by means of Constructional Design. Renew. Wave energy potential assessment in the central and southern regions of the South China Sea. Renew. Built-in Force Reduction in Hinged, Modularized Floating Platform for Wave Energy Harvesting and Pitch Motion Suppression. Renew.

Control, power and electrical components in wave energy conversion systems : an overview of the technologies. Refresh. Review of control strategies for wave energy conversion systems and their validation: the wave-to-wire approach. Refresh.