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Cong, Peiwen (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Teng, Bin (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology) | Bai, Wei (Manchester Metropolitan University) | Ning, Dezhi (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology)
A combined concept consisting of a torus-type oscillating water column (OWC) device and an offshore wind turbine is proposed in this study for the multi-purpose utilization of offshore renewable energy resources. The wind turbine is supported by a monopile foundation, and the OWC is coaxial with the foundation. The OWC is of torus shape, and partly submerged with its bottom open to the sea. An air duct, which houses an air turbine, is installed on the roof of the chamber. The exterior shell of the OWC is connected rigidly to the monopile by four thin rigid stiffening plates. Correspondingly, the whole chamber of the OWC is divided into four fan-shaped sub-chambers by the plates. A numerical model is then developed to simulate the wave interactions with the system as well as the air-fluid interactions within the chamber by establishing an extended boundary integral equation and using a higher order boundary element method. In addition, the optimal pneumatic damping coefficient, which is expressed in terms of radiation susceptance and radiation conductance, is determined by solving a pressure-dependent wave radiation problem. Based on the developed model, a detailed numerical analysis is conducted, and the hydrodynamic characteristics related to the combined concept are explored.
The ocean is vast and powerful, enabling marine renewable energy potentially be a significant energy supply. Due to the high-power density and longtime availability, considerable efforts and advances have been made in exploiting the marine renewable energy. A variety of wave energy converters has been invented to harvest the wave energy. In the meantime, many offshore wind energy converters have been used to harvest the available enormous wind energy resources.
Among different classes of designs, the oscillating water column (OWC) device has been widely regarded as one of the most promising options (Falcão, 2010). A typical OWC device mainly consists of two key components: a collector chamber with an underwater bottom open to the sea and a power take-off (PTO) system, mostly an air turbine, on the roof of the chamber (Heath, 2012). The incident waves excite the water column inside the chamber to oscillate, and transfer energy to the air above the water column. The pneumatic power can then be converted into electricity when the air flows through the air turbine coupled with an electric generator. Due to the nature of simplicity, the OWC device can be flexibly adapted to the shoreline, nearshore and offshore through different forms.
Peng, Wei (Key Laboratory of Ministry of Education for Coastal Disaster and Protection, Hohai University / School of Mechanical Engineering, Shandong University) | Zhang, Yingnan (Key Laboratory of Ministry of Education for Coastal Disaster and Protection, Hohai University) | Liu, Chang (Key Laboratory of Ministry of Education for Coastal Disaster and Protection, Hohai University) | Chen, Renwen (State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics) | Liu, Yanjun (School of Mechanical Engineering, Shandong University)
This study investigates on the hydrodynamic efficiency of a wave energy converting device using multiple floats. The floats have the same size and mass, arranged along the wave propagation direction and close to each other. A scale model was built in the laboratory at Hohai University and then employed to study the device's performance in wave controlling and wave energy conversion. During the physical tests, the water surface fluctuation around the structures, the motion of floats, and the voltage output of the dynamos are simultaneously measured. Results show that the incoming wave energy is effectively dissipated by the interactions between waves and structures for the waves with an intermediate wave period. The energy conversion is also helpful for the wave controlling as electricity generation modules absorb part of incident wave energy. Meanwhile, the advantage of the present device in extracting wave energy efficiently at a wide range of wave frequency is confirmed. When the wave period is 1.2~1.6 s, the device's performance is optimal, and the energy conversion efficiency is about 15%.
Wave energy has the limitless foreground as a kind of newly arisen and renewable energy due to numbers of advantages, such as wide distribution and pollution-free. In previous studies, the global gross wave energy resource is estimated to be about 3.7 TW (Mørk et al. 2010). However, the development of wave energy industry is still limited due to a few factors when compared with fossil energy, including conversion efficiency and economic feasibility. Therefore, it is essential to improve the wave energy conversion efficiency and reduce the construction and maintenance cost of wave energy converters (WECs). In recent years, hundreds of patents have been issued to harness the wave energy or improve WECs' performance (Falcão, 2010; Bahaj, 2011; Vicinanza, 2019; Qiu, 2019). Among them, one category is combining WECs with other coastal structures, to save costs and avoid extra sea area fees.
The objective of this study is to design and optimize the layout of the offshore wind farms to maximize the power at a specific location. The energy production of the downstream wind turbines decreases because of the reduced wind speed and increased level of turbulence caused by the wakes formed by the upstream wind turbines. Therefore, the overall power efficiency is lowered due to the wake interference among wind turbines. This paper focuses on using the application of a Gaussian-based wake model and different optimization algorithms like the differential evolution particle swarm optimization (DPSO). The Gaussian wake model uses an exponential function to evaluate the velocity deficit, in contrast to the Jensen wake model that assumes a uniform velocity profile inside the wake. The layout optimization framework has been created for the energy production in order to provide reference for specific conditions and constraints at the Gulf of Maine and other typical projects in the future.
With the growing requirement of energy and environmental protection, the sustainable energy like wind energy has been significantly concerned in recent years. In this case, the investigations about wind farm optimization have been concerned by lots of researchers. In wind farms, one of the most critical power reduction is caused by the wake and turbulence from the blades of previous turbines. Generally, this phenomenon would drop the power production and mechanical performance of turbines. The layout optimization of wind farms according to the wake has been an essential concern for both onshore and offshore wind energy applications.
Figure 1 indicates the annual average offshore wind speeds (m/s) in the United States. From this diagram, the Gulf of Maine have one of the greatest wind energy potential on the east coast. The Gulf of Maine locates very close to the cities such as Portland and Boston with magnificent electricity requirement. So, it is considerably valuable to investigate how to develop wind power in the Gulf of Maine.
He, Zechen (The State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology ) | Ning, Dezhi (The State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology ) | Gou, Ying (The State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology )
An optimization model of buoy dimension of wave energy converter is established by using differential evolution algorithm. The linear potential flow method is used in hydrodynamic calculation. Taking the vertical oscillating cylindrical buoy as the research object, the radius and draft of the buoy are optimized under each specified volume. Through the comparison of different volume optimization results, it is found that there is an optimal buoy volume for a specific wave condition. With the increase of the volume, the optimal draft tends to a fixed value, and the optimal radius tends to be an asymptote. In addition, the influence of different damping of power take-off systems on the optimization results is also studied.
Wave energy is a kind of renewable and clean energy. The development and utilization of wave energy is attracting the attention of many scholars and research institutions around the world, which may make a significant contribution to the world' power consumption. For the commercial feasibility of wave energy, it is very important to improve the production efficiency of wave energy device and reduce its construction, installation and operation costs. Obviously, the volume of the Wave Energy Converter (WEC) is a key factor affecting both the efficiency and the cost. De Andres et al. (2015) discussed that small equipment is usually more economical due to reduced material costs and deployment. Göteman et al. (2014) and Göteman (2017) showed that the total power production can be improved if the wave energy array consists of devices of different dimensions that are similar to the WECs that have been developed at Uppsala University since 2006 (Leijon et al.,2009). Most previous optimal studies focus on the buoy dimensions instead of the buoy volume. For example, Giassi and Göteman (2017) optimized the parameters of the single wave energy converter by parameter sweep optimization of the variables and genetic algorithm, in which the radius, draft and damping of the Power Take Off (PTO) systems are optimized simultaneously in discrete parameter space. Because there are many combinations of radius and draft under a certain volume even for a truncated cylinder buoy, it' difficult to get the relationship between the volume and the efficiency directly. That means the designer couldn't balance the cost and the efficiency with the optimal dimensions.
Gu, Yifeng (School of Mechanical Engineering, The University of Adelaide.) | Ding, Boyin (School of Mechanical Engineering, The University of Adelaide.) | Sergiienko, Nataliia Y. (School of Mechanical Engineering, The University of Adelaide.)
This paper proposes a novel power maximising control strategy for wave energy conversion applications and investigates its performance against linear spring-damper control on a fully submerged heaving point absorber wave energy converter (WEC) under both regular and irregular wave conditions. Inspired by the Phi method, the developed WEC control strategy presents an analytical solution which involves a quadratic damping term accounting for the nonlinear viscous drag in the WEC hydrodynamics. Therefore, its optimal control parameters can be analytically determined without optimisation and/or linearisation, which, however, usually accompanies conventional linear control strategies such as linear spring-damper control. Simulation results show that the proposed analytical control solution can absorb almost the same power as the optimised linear spring-damper control does in both regular and irregular wave conditions.
Due to the shortage of fossil fuel and the environmental impact caused by excessive carbon emission, renewable energy has become an emerging research field nowadays. There are various categories of renewable resources such as sunlight, wind, rain, tides, waves, and geothermal heat, among which the wave energy has great potential because of its consistency, high energy density and predictability. A wave energy converter (WEC) is a type of devices which can convert the ocean wave energy into useful electricity.
Although wave energy has several superior characteristics as mentioned above, compared with other renewable energy such as solar and wind, the main challenge in commercialising WEC technologies remains in reducing their costs by taking manufacturing, installation, and maintenance into consideration. The role of WEC control accounts for not only maximizing the WEC's power absorption efficiency but also ensuring its safety operation in harsh sea environment. Therefore, indepth understanding on WEC control can help to increase the efficiency of power absorption, lower the maintenance costs, and thus guarantee competitive energy costs.
According to linear wave theory, which assumes inviscid, irrotational and incompressible fluid (Falnes and Perlin, 2003), complex conjugate control (sometimes called impedance matching control) can achieve the maximum power absorption of a WEC but requires complex linearisation, optimisation and prediction procedures in its design due to the presence of nonlinear WEC hydrodynamics. Furthermore, in practice, the wave energy conversion process is accompanied with a resonant motion and, thus, the influence of nonlinear effects in the hydrodynamics such as the viscous drag may become significant violating the linear optimal control principles. In this case, conventional linear control strategies may no longer provide optimal solutions for the WEC power absorption leading to the emerging need of nonlinear control methods. However, the concept of WEC nonlinear control and its power absorption performance against traditional linear optimal control still requires in-depth study.
Chenhao, Mao (School of Port and Transportation Engineering, Zhejiang Ocean University) | Binyu, Wang (Guangxi Vocational and Technical College of Communication) | Yunlin, Ni (School of Port and Transportation Engineering, Zhejiang Ocean University) | Yifan, Gu (School of Port and Transportation Engineering, Zhejiang Ocean University) | Hao, Zeng (School of Port and Transportation Engineering, Zhejiang Ocean University) | Wei, Chen (School of Port and Transportation Engineering, Zhejiang Ocean University)
The construction of wave dissipating platform would cause the sediment transport in the surrounding waters, changing the erosion and silting situation in the seabed, which may even lead to the abandonment of the original dock. In this paper, a 2D hydrodynamic and sediment transport model is established for Shengsi islands, Zhoushan and the surrounding area by using MIKE21. The model has well been validated through observation data of tidal level, flow velocity and direction. The influence of dissipating platform construction on the erosion and deposition of surrounding water is analyzed. The results show that the maximum diffusion envelope of suspended sediment (concentration higher than 0.02 kg/m3) in Huangsha village, Bianjiaoao and Huicheng village are 20,947.02, 19,799.04 and 5,311.35 m2 respectively. The project has little impact on the surrounding water quality environment.
The coastal construction has created enormous social and economic benefits, but the construction project has caused sediment transport in the surrounding waters, causing erosion and siltation changes which may even cause the original dock abandoned (Tsoukala et al., 2015; Plomaritis and Collins., 2013; Song et al., 2017; Zhang et al., 2005). Meanwhile, it exerts negative effects on marine ecological environment, arousing wide public concern of scholars (Sravanthi N, 2015; Yao et al., 2018; Gu et al., 2012; Tian and Xu, 2015).The suspended sediment produced during the construction process will form water masses with high suspended matter content within a certain range, weakening or even blocking the light transmission capacity of the water body, affecting the photosynthesis of phytoplankton. The reduction in the number of phytoplankton will cause a corresponding reduction of zooplankton. In addition, suspended sediment will attach to the surface of aquatic animals, interfere with their normal physiological functions, and more seriously enter the digestive system, causing death (Huang et al., 2019). Zhang (2015) used the ECOMSED model to simulate the terminal project of Shandong LNG project. The research obtained the maximum spreading range of suspended sediment produced by excavation of base trenches, stone dumping and dredging works during the spring and neap tides, and analyzed the impact of the project on marine life. Yan (2019) established a two-dimensional model by using MIKE21 FM, simulating the envelope area of the suspended sediment caused by the 10 kv submarine cable laying at Lvhua Island-Huaniao Island. The results show that the construction period has a greater impact on the marine ecological environment, and the service period has basically no impact on the marine ecology. In order to serve human life and protect the environment, numerical simulation has been widely used in engineering construction (Vu, Nguyen and Nguyen.,2020; Agrawal et al.,2019).
Wang, Yiran (School of Transportation, Southeast University) | Xu, Sudong (School of Transportation, Southeast University) | Xie, Boyi (School of Transportation, Southeast University) | Xie, Wen (School of Transportation, Southeast University) | Zhou, Jia (School of Transportation, Southeast University) | Xu, Mengxiao (School of Transportation, Southeast University)
The eastern coastal areas of China are widely distributed with flexible vegetation due to the effect of climate, which have a great influence on wave attenuation. This paper used the XBeach model to simulate the the effect of wave attenuation under flexible vegetation on slope beach by respectively changing the relative height, diameter, density and vegetation coefficient of the plants. Results show that the effect of wave height attenuation by flexible vegetation increases with the increase of relative height, diameter, density and vegetation coefficient and with the increase of each parameter, the increasing tendency of attenuation gradually weakened.
With the development of society and the deepening of the process of industrialization, human activities have made more profound changes to the global climate. Among the marine disasters caused by climate change, storm surge disasters in coastal areas are more extensive and have certain research significance. Therefore, the exploration of methods for preventing waves and attenuating waves and protecting the embankments and the shoreline along the coast has also been a hot topic. Different from traditional invasive hard coastal engineering, aquatic vegetation distributed at the boundary of sea and land is of great significance for wave mitigation in coastal zones, especially in extreme weather such as storm surge (Feagin et al., 2011). In recent years, coastal areas have been increasingly demanding protection of the ecological environment and coastal vegetation has become a good material for ecological revetment due to its certain wave-reducing effect and environmental-friendly characteristics. Research on the effect of coastal wave vegetation on wave-revetment and protection needs to be studied further. In terms of field observation, Möller et al.(1999) have shown that after going deep into the Spartina alterniflora salt marsh 20-30m, the wave height attenuates to 29% and the energy loss is about 90%. Yang et al.(2012) measured the wave parameters of 13 continuous tides on the coast of the tidal reach of the Yangtze River estuary, and calculated the wave attenuation of S. alterniflora at the edge of the coastal salt marsh. The results showed that the wave height attenuation rate per unit distance on the coastal tidal flat covered with vegetation is 1 to 2 orders of magnitude higher than the attenuation rate at mudflats.
Liu, Yihua (School of Naval Architecture & Ocean Engineering, Dalian University of Technology ) | Li, Hongxia (School of Naval Architecture & Ocean Engineering, Dalian University of Technology ) | Huang, Yi (School of Naval Architecture & Ocean Engineering, Dalian University of Technology )
In this paper, the new concept polar ocean nuclear energy platform was introduced and the influence of the moonpool on its towing resistance was studied. STAR-CCM + was used to calculate the towing resistance of the nuclear power platform at different towing speeds when the moonpool was at both open and closed. It can be found that towing resistance increased obviously with the increase of towing speed. The existence of the moonpool tends to disorder the flow field around the platform, which will cause a 20%-30% increase on the nuclear power platform's towing resistance. The research on the mechanism of increasing the resistance of the lunar moonpool can provide some guidances for the design of nuclear energy platform in the future.
In recent years, as the global warming continues unabated, the arctic sea ice gradually melts, and regular navigable waters appear in summer. It is highly possible that the arctic ocean will be ice-free in summer of 2050 (LI Z.F., 2019). The ice-free state of the arctic in summer will bring certain economic benefits to the development of the global economy: if the arctic shipping route is used, the sailing time and energy consumption of the route from China to the northern Europe or the Baltic sea will be 1/3 less than those of the traditional route. If the destination is within the Arctic Circle, the sailing time and energy consumption will be 1/2 less (CAI M.J., 2019). In addition, the arctic is rich in natural resources, including 13% of the world's proven oil reserves and 30% of the world's natural gas reserves. If the polar natural resources are to be exploited, the problem of power supply needs to be solved urgently. The ecological environment of the arctic region is fragile (LIU D.H., 2019), and it has high requirements for environmental protection of engineering equipment. The offshore nuclear power platform can provide sufficient, stable and environmentally friendly power (LI X., 2019), which is the best choice for the development of power supply equipment in the polar region and has a broad application prospect.
Methane (CH4), the primary constituent of natural gas and is the second-most abundant greenhouse gas after carbon dioxide (CO2), accounts for 16% of global emissions. The lifetime of methane in the atmosphere is much shorter than CO2, but CH4 is more efficient at trapping radiation than CO2. Pound for pound, the comparative effect of CH4 is more than 25 times greater than CO2 over a 100-year period. Natural-gas emissions from oil and gas facilities such as well sites, refineries, and compressor stations can have significant safety, economic, and regulatory effects. Continuous emission detection systems enable rapid identification and response to unintended emission events.
Halliburton announced today that it has entered a program designed for companies to reduce their greenhouse-gas emissions (GHG). The oilfield services company said it has submitted a letter of intent with the Science Based Targets Initiative (SBTI), the first step to developing a full-fledged emissions-reduction plan under the initiative. Halliburton plans to establish its first emissions targets next year with the SBTI. The SBTI is then expected to independently validate the targets by 2022. The SBTI was formed in 2015 and includes more than 1,000 corporate members.