Ocean Renewable Energy Research Articles

Internal waves

Internal waves are ubiquitous oceanographic features that occur in various forms across the world’s oceans. They manifest themselves as interface waves across ocean density layers that represent the interplay between buoyancy and gravitational forces, and are typically classified as linear and nonlinear internal waves. Nonlinear internal waves are characterized by isopycnal displacements that can exceed 30 m, and current velocities that approach 1 m/s. Internal wave energy converters, if developed, could have the advantage of no surface expression and provide for the availability of renewable ocean energy in regions of scant surface wave energy resources.
 Here, internal wave energies were computed at two locations: the New Jersey continental shelf and the coast of Central California. The available energy resource calculated for internal waves was then compared against surface gravity wave resources at each of these locations. Results suggest that the internal wave energy flux is comparable to that of surface waves on the New Jersey continental shelf during the summer of 2006 but is two orders of magnitude lower than that of surface waves in Central California during the summer of 2017. When expressed in terms of forces on a cylindrical structure, internal wave forces are an order of magnitude lower than that of surface waves on identically sized cylinders. However, the forces of the two resources are comparable when the diameter of the cylinder is doubled for the internal wave calculations. This suggests that while a larger energy converter would be required to harness internal wave energy, the larger size could be a reasonable tradeoff for advantages such as the lack of surface expression and the availability of energy in regions of limited surface wave energy resources.
 These results could potentially pave the way for longer-time scale characterization of internal waves and the development of devices to harness this energy resource (thereby powering the Blue Economy), while augmenting the portfolio of marine renewable energy resources. Further, the dominance of internal wave energy resources during summer seasons when the water column is stratified can augment the surface wave energy resource that can be diminished during the summer season.

ANTIFOULING AND ANTICORROSIVE PREVENTION WITH CERAMIC COATINGS ON OFFSHORE STRUCTURES FOR RENEWABLE ENERGY

In the past, ships, port facilities and offshore platforms dedicated to the exploitation of fossil resources were the only man-made structures that were exposed to seawater, currently the exposed structures are extended to all those used in the field of renewable ocean energy sources, such as waves, tidal flows or oceans streaming and offshore wind energy. Therefore, this study highlights the need for offshore structures to consider the choice of ceramic coatings in the field of surface treatment and marine corrosion control without neglecting another of the main problems that affects structures in contact with seawater, which is the phenomenon known as biofouling. Corrosion is a major problem in offshore environments due to extreme operating conditions and the presence of aggressive corrosive elements. The corrosion resistance can represent the difference between trouble-free long-term operation and costly downtime. On the other hand, biofouling, which is defined as the undesirable phenomenon of adherence and accumulation of biotic deposits on an artificial surface that is submerged or in contact with sea water, can cause variations in the weight distribution of a floating structure, affecting its stability. In addition, biofouling leads to corrosion in the same way that corrosion leads to biofouling, so both factors are studied in parallel.
 This study evaluated differences in the total of seawater biofouling attached on coated paints and ceramic coatings in carbon steel for offshore structures. All three different ceramic coatings were made of incorporating active ceramic particles against biofouling as titanium, cobalt and manganese. In this study, the ASTM-D3623 test method, for the protection of submerged marine structures, was used. This method covered the procedure for testing antifouling coatings exposed for a period of two year at an immersion site with a high biological activity in shallow marine environments.
 The results of the investigation showed that the cobalt-based coating had the best antifouling properties at the end of the experimentation, although there was no significant difference in the biofouling attached during the two years of exposure, but great differences were shown with respect to the antifouling paints. Biofouling adhesion resistance was greatest when a coating thickness of 217 μm was used and when the substrate surface roughness (Ra) was 0.245 µm. The results indicated up to more 30% total area covered by biofouling in paint coatings than ceramic coatings. On the other hand, the results showed a progressive degradation of the antifouling paint coatings, which meant an exponential increase of biofouling adhered to the samples, but not in ceramic coatings during the two years experiments.

Optimal Design of a Submerged Tidal Device for Low Current Environment

The tidal current power is one of the reliable renewable ocean energy resources that can be deployed at the region having ocean current. The feasible current speed for the application of tidal device is known to be more than 2m/s. As there are many islands in Asia where the current speed is below than the feasible speed, the submerged device that can produce the power at lower current speed with easy deployment and retrieve is introduce. To simplify the installation and O&M operations, the 4-point taut mooring system is applied that can also secure the designated position. In this study, a HAT (horizontal axis turbine) of 5-kW submerged tidal device is designed and analyzed for a low current region that consist of two buoyancy tanks, a yaw control strut, and a diffuser-type brimmed duct. To analyze the most stable condition, 9 different cases of width and height of the device and 8 different mooring arrangements (total 72 different cases) are investigated both by frequency and time domains. The results show that the dynamic behavior that mainly affects the turbine performance decreases with lower strut height. However, it was observed that the device width has little effect on the dynamic response of the device. The device dynamic motion decreases with decreasing azimuth angle and increasing hang-off angle of the mooring configuration. The optimal design configuration that can produce the maximum power is found that of 4.42 m width, 2 m height, 30° azimuth angle and 60° hang-off angle. According to API RP 2K code, the mooring system is also designed in both intact and damaged conditions. The proposed tidal device could be applied for the low current speed areas with easy implementation and maintenance.

Optimization and evaluation of a semi-submersible wind turbine and oscillating body wave energy converters hybrid system

A hybrid system consisting of a floating offshore wind turbine and wave energy converters (WECs) is promising for multiple extractions of ocean renewable energy. Optimization of the layout and an evaluation of the performance of the hybrid systems are important before practical use but are not well done due to limited simulation tools. This study fills these gaps by proposing a complete toolkit based on the OpenFAST-AQWA framework together with a code that can deal with the full couplings in the problem. A novel DeepCWind-Wave Stars hybrid system is proposed as a representative to validate and practice the new tool. The key parameters of the WECs are optimized using an easily performed method based on the local wave contour disturbed by the platform. Motions, mooring loads, and power of the hybrid system are evaluated under a wide range of wind and wave conditions to examine the influence of the WECs. Results show that the integration of the WECs brings no harm to the stability of the system. The WECs reduce the fluctuation in the mooring force but slightly increase the average mooring force. The generated wave power is an adequate supplement to wind power, especially at a small wind speed.

A robust planning model for offshore microgrid considering tidal power and desalination

Increasing attention has been paid to resources on islands, thus microgrids on islands need to be invested. Different from onshore microgrids, offshore microgrids (OM) are usually abundant in ocean renewable energy (ORE), such as offshore wind, tidal power generation (TPG), etc. Moreover, some special loads such as seawater desalination unit (SDU) should be included. In this sense, this paper proposes a planning method for OM to minimize the investment cost while the ORE’s fluctuation could be accommodated with robustness. First, a deterministic planning model (DPM) is formulated for the OM with TPG and SDU. A robust planning model (RPM) is then developed considering the uncertainties from both TPG and load demand. The Column-and-constraint generation (C&CG) algorithm is then employed to solve the RPM, producing planning results for the OM that is robust against the worst scenario. Results of the case studies show that the investment and operation decisions of the proposed model are robust, and TPG shows good complementarity with the other RESs.

Ocean Renewable Energy: A Comparative Study of Indian and Global Collaborative Research for Sustainability and Policy Implications

Ocean Renewable Energy: A Comparative Study of Indian and Global Collaborative Research for Sustainability and Policy Implications

Design optimization of ocean renewable energy converter using a combined Bi-level metaheuristic approach

Design optimization of ocean renewable energy converter using a combined Bi-level metaheuristic approach

Review of Resources from the Perspective of Wave, Tidal, and Ocean Thermal Energy Conversion

The conversion of Ocean Renewable Energy (ORE) sources to electricity could meet increasing energy demand and diversify the energy supply in Malaysia. Possessing a long coastline overlooking the South China Sea (SCS) and the Malacca strait has encouraged the Malaysian government to promote ORE and assess available resources to reduce its dependence on fossil fuels. However, most of the previous attempts to assess the potential of Malaysian ORE resources have focused primarily on theoretical resource assessment, which in practice may not reflect the viability and suitability of the resource. Other technical and practical issues must be accounted for as well. This paper presents a brief description of ORE conversion technologies and reviews the existing studies on regional ORE resources in Malaysia with an emphasis dedicated to wave energy, tidal energy, and Ocean Thermal Energy Conversion (OTEC). It also highlights the essential technical and practical constraints limiting or excluding the utilization of ORE sources. While some ORE resources, particularly the OTEC, appear to be theoretically promising for exploitation in Malaysia, this review has shown a lack of precise resource mapping linked to socio-economic and environmental constraints.

Analysis of energy variability and costs for offshore wind and hybrid power unit with equivalent energy storage system

Offshore wind and wave energy are largely untapped renewable resources. However, the intermittency and the high cost of energy of these resources pose a few major challenges for their wide-scale developments. Although energy storage systems are considered to mitigate or reduce the energy variability to support a reliable power network, the proposed solutions have further increased the capital expenditure. This is primarily due to a lack of systematic techno-economic assessments of offshore renewable systems with energy storage. In addition, the integration of offshore wind and wave energy systems reported in previous literature showed a number of benefits, such as power smoothing and cost reduction. This paper investigates the offshore wind and wave energy intermittency and their dispatchability and proposes an equivalent energy storage system to achieve the same level of energy variability as the combined wind and wave system. This provides a thorough understanding of the power smoothing performance and firmness of energy supply in an offshore energy farm. The economic assessment of the stand-alone offshore wind system, the wind turbine with an energy storage system and the hybrid power unit system are conducted and compared via high-fidelity cost models. In addition, the sensitivities of three system configurations are investigated at multiple locations around the world, which are selected to address typical wind and sea states. The results indicate that the hybrid wind and wave power system has merits in reducing energy variability and enhancing ocean energy dispatchability while offering highly competitive cost, compared to the other two system configurations. Furthermore, the research aims to provide a guidance and support for the developers, investors and policymakers at the pre-planning stage of developing ocean renewable energy systems.

Study of Supply Chain Management of Industrial Plan Manufacturing Development of Marine Power Turbine in Indonesia

Indonesia had announced its target to reduce carbon emission by achieving 0% Net Zero Emission (NZE) by 2060. So starting in 2022, the Government must update the regulations governing the energy sector to encourage the implementation of renewable energy. As an archipelagic country, one of the renewable energy potentials is Ocean Renewable Energy (ORE). The contribution of the ORE to Indonesia’s National Energy Mix is almost none. Thus, it is a good chance for the government to give more incentives for implementing ORE, especially in eastern Indonesia where they are abundantly available. Since the infrastructure and supporting facilities there, including industries, are sparse and the supply chain management depends on Java Island, it needs special regulations to speed up the implementation of ORE. This paper studies the supply chain management of the implementation of marine current turbines base on secondary data and the experience of engineers from the National Research and Innovation Agency when they implemented the converter technology of the marine current turbine at Larantuka Strait, Nusa Tenggara Timur. Results In this study, the implementation of ocean current turbines must be integrated with government policies related to maritime connectivity and security because the energy produced is large enough and suitable for execution.

Experimental Study on Hydrodynamic Aspects of Turbine which Convert Hydrokinetic and Potential Coastal Wave Energy

Currently, the exploration of ocean renewable energy sources was mostly carried out to obtain optimal results and low cost. The waves that arrive on the beach consist of both potential energy where the water surface moves up and down and hydrokinetic energy where the volume of water comes and goes into the beach sand. They had the potential to be converted to electricity. This paper explained the study of the hydrodynamic aspects of turbines that convert hydrokinetic and potential coastal wave energy. The vertical axis darrieus turbine was modified to catch both energies. It could convert energies from hydrokinetics and the potential of waves simultaneously, whereas a vertical axis turbine with 6 horizontal blades and 3 vertical blades in a shaft. Testing was done at the testing Tank, Hydrodynamic Technology Research Center, National Research and Innovation Agency. The hydrodynamic tests were with 3 turbine variations, wave variations, and current velocity. The test results, vertical axis turbines with horizontal blades could receive wave energy, due to the orbital motion of water particles and vertical blades were very effective in receiving current energy so that turbines with 2 types of vertical and horizontal blades could convert wave and current energy.

Numerical simulation of a floating-type point absorber wave energy converter

Wave energy converters (WEC) have been researched extensively to harvest large amounts of untapped ocean renewable energy. Floating-type point absorbers are a type of WEC that converts the ocean wave energy to electrical energy, by utilizing the relative motion of multi-body system mainly consisting of a floating section and a reaction section. The design of floating-type point absorbers is not straightforward and needs special attention to understand the dynamics of the multi-body system, and power take-off (PTO) mechanism placed in the reaction section. The purpose of this study is to develop a numerical simulation tool which can help understand various dynamics of a floating-type WEC and aid in the practical design of PTO systems. The PTO mechanism is represented using a spring-damper system and theoretical modelling of mean absorbed power is presented. The numerical simulation is developed in Orcaflex and is carried out on a demonstration model to show the usefulness of the developed tool. The heave displacement shows the effect of damping (PTO) on the motion response of the floating-type WEC. It is found that the maximization of absorbed power is possible using the developed simulation tool for a specific sea state. Furthermore, the results show the potential use of the developed tool for other floating-type WEC concepts.

Numerical study of a novel hybrid system with the Wavestar wave energy converter array and a SPIC semi-submersible floating platform

To improve power generation efficiency and reduce costs in the industry of ocean renewable energy, one of the optimal strategies is the addition of wave energy converters (WECs) into the floating wind turbine. This paper proposes a novel hybrid wind-wave energy concept that comprises multiple Wavestar point absorption wave energy converters (WECs) and a SPIC semi-submersible floating wind turbine (FWT). ANSYS/AQWA software is used to perform numerical simulations based on three-dimensional potential flow theory. Three hybrid systems are designed with different numbers of Wavestar WECs, which are symmetrically arranged on the platform. Before the study, the hydrodynamic responses of the Wavestar WEC and the SPIC concept platform are simulated separately and compared with existing experimental data. After the validation of numerical models, the platform motions and the absorbed power of the WECs are investigated, which are the main factors in evaluating the performance of a hybrid system. After a series of numerical simulations, the results show that the absorbed power increase significantly with the increase in the number of the Wavestar WECs, while the platform motions also increase. It can be concluded that the wind-wave energy hybrid design needs to find a balance between the platform motions and the absorbed power of the WECs. Overall, this study can be used as a reference for the design of other novel hybrid ocean energy concepts.

A review on the progress and research directions of ocean engineering

This paper reviews research in ocean engineering over the last 50+ years with the aim to (I) understand the technological challenges and evolution in the field, (II) investigate whether ocean engineering studies meet present global demands, (III) explore new scientific/engineering tools that may suggest pragmatic solutions to problems, and (IV) identify research and management gaps, and the way forward. Six major research divisions are identified, namely (I) Ocean Hydrodynamics, (II) Risk Assessment and Safety, (III) Ocean Climate and Geophysics: Data and Models, (IV) Control and Automation in the Ocean, (V) Structural Engineering and Manufacturing for the Ocean, and (VI) Ocean Renewable Energy. As much as practically possible research sub-divisions of the field are also identified. It is highlighted that research topics dealing with ocean renewable energy, control and path tracking of ships, as well as computational modelling of wave-induced motions are growing. Updating and forecasting energy resources, developing computational methods for wave generation, and introducing novel methods for the optimised control of energy converters are highlighted as the potential research opportunities. Ongoing studies follow the global needs for environmentally friendly renewable energies, though engineering-based studies often tend to overlook the longer-term potential influence of climate change. Development and exploitation of computational engineering methods with focus on continuum mechanics problems remain relevant. Notwithstanding this, machine learning methods are attracting the attention of researchers. Analysis of COVID-19 transmission onboard is rarely conducted, and 3D printing-based studies still need more attention from researchers.

Stability analysis of parametric resonance in spar-buoy based on Floquet theory

Parametric resonance is a phenomenon caused by time-varying changes in the parameters of a system which may result in undesirable motion responses and instability. Floating bodies like ships and spar-buoys are prone to Mathieu instability mainly due to the instantaneous change of the metacentric height. With the fast-growing developments in Ocean Renewable Energy systems, spar-buoys are commonly used for wave energy convertors and floating wind turbines. Undesirable, unstable motions as a result of the parametric resonance can be problematic as it may cause inefficiency in operations and structural risk integrity. In this research, a new approach has been developed to investigate these nonlinear oscillations and analyze the conditions when parametric resonance occurs. The hydrodynamic loads are calculated using the linear approach, and the motion responses of the floating body coupled in heave, pitch and surge are determined. It is shown that the eigen values obtained from Floquet Theory can be used as indicators of stability under different wave conditions. This procedure can be practically used with little computational cost to determine factors affecting the equilibrium status of a system in regular waves.

Anaconda-shaped spiral multi-layered triboelectric nanogenerators with ultra-high space efficiency for wave energy harvesting

<h2>Summary</h2> Shifting from fossil fuels to clean energy is urgently needed to reduce anthropogenic carbon emissions. The ocean is recognized as an important source of renewable energy (i.e., wave and tidal), yet remains underutilized due to several technical barriers such as low energy conversion efficiency. The triboelectric nanogenerator (TENG), which can efficiently convert wave energy into electricity, has emerged as a potential solution. However, the low output performance and space utilization of existing TENGs impede commercial applicability. Here, we design an anaconda-shaped spiral multi-layered triboelectric nanogenerator (ASM-TENG) to overcome those two shortcomings. Benefiting from the tandem structure, compared with conventional TENGs, the ASM-TENG can enhance total power output by 2- to 30-fold with a peak power density at 347 W m⁻³, it can also enlarge the space utilization by 2- to 8-fold up to 93.75%. Our ASM-TENG provides a new strategy to improve the overall performance of TENG, strengthening its commercial applicability and further facilitating the development of ocean renewable energy.

Nanofiber-Enhanced "Lucky-Bag" Triboelectric Nanogenerator for Efficient Wave Energy Harvesting by Soft-Contact Structure.

Developing clean and renewable ocean wave energy is a top priority and an effective way to achieve carbon neutrality. Triboelectric nanogenerators (TENGs) have emerged as promising green and clean energy-harvesting devices. To harvest low-frequency wave energy efficiently, much effort has been made on the modification of the contact surface, which leads to a higher fabrication cost. In this work, we designed a novel “Lucky-Bag” core (LBC) for spherical TENGs with a low-cost and easy fabricating process. The nanofiber/silicone hybrid porous outer layer of the LBC can switch freely from plane to surface and improve the output performance of both the plane and spherical TENGs. Several factors, such as the input frequency, direction, and resistive load, together with the thickness were systematically investigated; the unique porous soft-contact structure increased the triboelectric contact area, and the working mechanism was studied by using the COMSOL software. The experimental results showed that the peak-to-peak open-circuit voltage (V) and short-circuit current (I) could reach 580 V and 23.5 A at 1.5 Hz, even under 2D linear motion. Besides, the maximum output power of the spherical TENGs reached 9.10 mW, which can fully power electronic devices such as capacitors and LEDs under water wave triggering. These findings provide useful guidance for optimizing the performance of spherical TENGs for practical applications in harvesting water wave energy.

Compression-assisted absorption refrigeration using ocean thermal energy

Renewable ocean energy is regarded as an attractive candidate resource for the development of maritime cold chain systems. To meet the refrigeration requirement of seafood freezing and preservation storage, this study proposes two-type compression-assisted ammonia-water absorption refrigeration cycles using ocean thermal energy. The effects of intermediate pressure on the exergy efficiency and primary energy rate ratio are analyzed and discussed. Moreover, the role of the heat source and sink temperatures on the primary energy rate ratio was examined. The results indicated that the absorption refrigeration system with a compressor in the low-pressure stage has a higher exergy efficiency and a higher primary energy rate ratio than the corresponding compressor in the high-pressure stage. For a warm seawater temperature of 29 °C and cold seawater temperature of 8 °C, the low-pressure compression-assisted refrigeration cycle is the best solution with an exergy efficiency up to 0.284, and the optimal primary energy rate ratio equals 1.392. Furthermore, a higher primary energy rate ratio can be realized by increasing warm seawater temperature or reducing cold seawater temperature.

Marine research: EU and ukrainian legislation

The article analyzes the regulatory legal acts of the European Union and Ukraine in the field of marine research and identifies key gaps in Ukrainian legislation. It has been established that the EU legislation provides for the observance of the principle of integration of science, industry, politics and society and pooling their resources for the financing of marine research. The priority thematic areas of European legal support in this field are: research on climate change, protection and recovery of marine biodiversity, ecosystem approach to resource management and spatial planning, renewable ocean energy, impact of human activity on coastal and marine ecosystems, generation of digital scientific knowledge about seas and oceans and free access to them, forming the foundations of a carbon-neutral and cyclical EU’s “blue” economy. It is noted that, despite the wide range of legislative acts adopted in Ukraine, which regulate the field of marine research, there is a dispersal regarding the directions of these researches, and the basic principles of their conduct are not defined. The priority areas of scientific marine research need to be determined. It is concluded that there is a need to form a more consistent policy regarding marine scientific research, to strengthen partnerships with the participation of all interested parties who mobilize and distribute knowledge, experience, technologies and financial resources in the interests of the sustainable development of water resources of Ukraine. This requires establishing the basic principles of conducting marine scientific research, applying a foresight approach to determine the priority areas of marine scientific research for Ukraine. After the approval of the Foresight’s results by the Decree of the Cabinet of Ministers, the main tasks are focus on these priority areas during forming a state order for conducting marine scientific research and annually monitor the implementation of the identified priorities and provide a report on the monitoring results.

Bias Correction Techniques for Uncertainty Reduction of Long-term Metocean Data for Ocean Renewable Energy Systems

Bias Correction Techniques for Uncertainty Reduction of Long-term Metocean Data for Ocean Renewable Energy Systems