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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.
Yu, Yang (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration ) | Li, Zhenmian (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration ) | Yu, Jiangxin (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration ) | Xu, Lixin (State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University / Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration )
Multi-use platform designs have been focused on in recent years with the evolution of offshore platforms. Based on the classic tension leg platforms (TLP), a multiple production offshore platform was designed by combining the TLP body with an embedded oscillating water column energy converters (EOWC). The contributions of the work include the development of a novel concept of the TLP-EOWC, a preliminary design scheme for the TLP-EOWC, implementation of a multifold nonlinear time-domain analytical model, real-valued simulation for the TLP-EOWC, and a sensitivity analysis of the design parameters. Sensitivity analysis was completed for different orifice ratios and wave heading angles in seven sea states from the LIUHUA site monitoring data. Results show that the system gains low electricity productivity in calm sea conditions and provides considerable power output in rough seas. As per this research, the offshore platform would act as a power-producing wave energy farm and contribute to the energy mix and even help achieve power self-sufficiency
As the world's energy needs continue increasing and onshore resources are reaching their limit, the seas and oceans gain extensive attention since they potentially provide an opportunity for economic growth and resource use. The European Commission indicated ocean resources, including ocean energy, aquaculture, biotechnology, deep-sea mining, and coastal tourism, also called Blue Growth sectors, as high potential components. The evolution of offshore platforms has made it possible to think of other opportunities parallel to the traditional sole function. As a pioneer, the European Union (EU) launched "The Ocean of Tomorrow" (Chandrasekaran, 2015; Koundouri, 2017), a call for proposals for multiuse offshore platforms in 2011. In this call, three projects were selected – H2OCEAN, MERMAID, and TROPOS. In 2014, Maribe developed the H2020 project to determine if there is a future for investment in combining Blue Growth sectors. Two new EU projects, Space@Sea and Blue Growth Farm, began in 2018. As a result of these projects, new concepts for the next generation of offshore platforms were proposed and examined. They included offshore wind (floating or fixed) sharing with aquaculture and shellfish farms, offshore wind sharing with wave energy, wave energy sharing with aquaculture, fixed and floating wind sharing with oil and gas, and desalination combined with other Blue Growth sectors. More related details can be found in the reference (Dalton, Bardócz, Blanch, Campbell, Johnson and Lawrence, 2019).
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.
Zhang, Hengming (College of Shipbuilding Engineering, Harbin Engineering University) | Zhou, Binzhen (School of Civil Engineering and Transportation, South China University of Technology / College of Shipbuilding Engineering, Harbin Engineering University) | Zang, Jun (University of Bath) | Sun, Ke (College of Shipbuilding Engineering, Harbin Engineering University)
This paper aims to investigate the wave resonance in the WECbreakwater gap of a dual-body hybrid system using the Star-CCM+ software. The effects of the narrow gap wave resonance on the performance of the dual-body hybrid system and the forces on the breakwater are studied. The influence of the WEC motion and the gap width of the hybrid system on the wave elevations are analyzed. Results reveal that the wave resonance in the WEC-breakwater gap significantly improves the wave energy extraction performance of the hybrid system, but has little impact on the wave attenuation performance of the hybrid system.
The high construction cost and low extraction performance of the Wave Energy Converters (WECs) reduce the economic competitiveness of the wave energy, which constrains the development of the commercialscale wave power operations. Combining WECs with the breakwater can provide an effective solution to make the wave energy economically competitive and promote the development of WECs and floating breakwaters (Mustapa et al., 2017; Zhao et al., 2019).
One of the widely studied integrated WEC-breakwater system is Oscillating-Buoy (OB) type WECs integrated with floating breakwaters, which mainly includes the single-floater integrated system (Ning and Zhao, 2016; Madhi et al., 2014; Zhang et al., 2020a) and the dual-body hybrid system (Zhao and Ning, 2018; Ning et al., 2019; Reabroy et al., 2019). The existence of the gap between two floaters of the dual-body hybrid system is one of main differences comparing with the singlefloater integrated system. The wave surface in the gap between two structures oscillates and the wave response amplitude can reach the maximum under certain wave frequency, which is called wave resonance in the narrow gap. The wave resonance in the gap between two floaters of the dual-body hybrid system can significantly affects the performance of the WEC. Thus, it is essential to study the influence of the gap wave resonance on the performance of the hybrid system.
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.
Yan, Shi (School of Civil Engineering, Shenyang Jianzhu University) | Wu, Jianxin (School of Civil Engineering, Shenyang Jianzhu University / Shandong Electric Power Engineering Consulting Institute Co., Ltd.) | Wang, Xuenan (School of Civil Engineering, Shenyang Jianzhu University) | Zhang, Shuai (School of Civil Engineering, Shenyang Jianzhu University / CSCEC Jinan Architectural Design Institute Co., Ltd)
In order to apply a PZT-based pipeline structure damage detection technology in engineering, in this paper, a PZT wave-based active detection technology as theoretical foundation was used, combining with the characteristics of pipeline structure cracking, to develop a new type of portable detection system, which is based on virtual instrument (VI) technology. The developed system was validated through testing, and the results indicated that the system is stable and reliable, enabling to identify different crack damage states of pipeline structures in real-time and online. The proposed damage detection system can be used in pipeline structures with the low cost, portable, rapid diagnose and high-precision characteristics.
Pipeline structure has been widely used in petroleum, chemical, electric power, and natural gas industries, etc. However, due to environmental impacts or man-made disoperation pipeline will have cracks, corrosion and other defects, which will cause a great threat to the pipeline system safe operation, especially in the event of an accident, will cause huge economic losses and environmental pollution. To avoid possible accidents and ensure the safe use of pipeline structures, periodic safety inspections or long-term health monitoring of the piping system are of particular and great importance. Due to characteristics of long distance and large area of pipeline structures, applications of commonly used nondestructive testing (NDT) technologies are greatly restricted. At present, a new non-destructive testing method - the use of a piezoceramic active wave sensing detection technology for pipeline structures is gradually developed and good results are achieved (Song, Gu and Mo, 2008; Song, Gu and Mo, 2007; Song, Gu and Mo, 2006; Du, Kong, Lai and Song, 2013; Gazis, 1959; Alleyne and Cawley, 1996; Yan, Sun, Song, Gu, Huo, Liu and Zhang, 2009; Silk and Bainton, 1979; Lowe, Alleyne and Cawley, 1998; Park and Payne, 2011).
Piezoceramics, (such as Lead Zirconate Titanate, PZT), is a kind of intelligent material with sensing and driving dual characteristics. It is simple in manufacture, high in strength, resistant to moisture, heat and frequency response, etc. Due to a unique piezoelectric effect, the PZT material can be used as both a sensor element and an actuator component. The basic principle of the active detection technology applying the PZT wave based method is using the piezoelectric effects of piezoceramics to manufacture transducers which are arranged in the detected structures in a form of array for transmitting and receiving detection signals, thereby establishing an excitation and sensing channel. Based on the received data combining with a special damage detection algorithm, a structural damage identification and diagnosis can be realized by analyzing the signal difference between the healthy structure and the damaged one. The principle is shown in Fig. 1.
In this study, a collision risk model was developed, based on gas model theory and Pedersen's collision and grounding mechanics. Busan north port was chosen as the area of assessment and, was divided into equal cells. Geometrical collision risk, both ship-ship and ship-structure, within each cell was analyzed following a probabilistic quantification. Moreover, bathymetry data of the port waters were analyzed to assess grounding risks. Results were plotted on Google EarthTM to identify the highest risk point and region within the area of assessment to aid safe maneuvering of vessels.
With the recent trends and advancements in maritime world, emergence of new ships is inescapable and consequently, maritime traffic density has continued to expand. Increased number of ships, as well as bigger ships in narrow passages attribute to higher volumes of traffic in already congested waterways and particularly, in port areas. This, in turn, makes ship maneuvering more difficult and complicated. Moreover, higher maritime traffic can increase the risk of collision accidents with unfavorable consequences. Although some major technological advancements such as ECDIS (Electronic Chart Display and Information System), ARPA (Automatic Radar Plotting Aids), GNSS (Global Navigation Satellite System) and GMDSS (Global Maritime Distress & Safety System) are successfully integrated with navigation, port and harbor areas are still more susceptible to collision accidents. Thus, evaluating the risk of collision has become an integral part in maneuvering supporting systems to improve safety in navigation by decreasing the risk of collision.
Collision risk in navigation is often misread due to the rarity of disastrous, individual accidents. Ylitalo (2010) discovered that the probability of an accident in a particular area would not be zero, although there is less or no records of previous incidents. Even though the probability of a direct ship-ship collision is very small, a minor incident can have unfavorable consequences, which can lead to loss of property as well as life at sea. Therefore, all risks in navigation have to be taken seriously. Identifying the risk areas, therefore, is vital to minimize and to avoid accidents. Once the risk areas are clearly identified, measures such as emergency planning can be taken for safe maneuvering of ships.
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).