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.

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).

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.

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.

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.

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.

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.

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.

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).