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Li, Jiawen (Dalian Maritime University) | Hu, Guanqing (Dalian University of Technology) | Jin, Guoqing (Dalian University of Technology) | Sun, Zhendong (Dalian University of Technology) | Zong, Zhi (Dalian University of Technology) | Jiang, Yichen (Dalian University of Technology)
A novel semi-submersible platform, referred to as HexaSemi, is proposed with a completely new designed heave plate. Compared with the WindFloat-type design, the new heave plate has a single hexagonal shape with a moonpool. From a structural point of view, its integral design can increase the integrity of the structure. In this paper, we mainly study its hydrodynamic performance for an offshore wind turbine. A numerical model is set up to simulate the motion characteristics of the floating wind turbine system, based on WADAM, Star-CCMC, and FAST. The comparative analysis of HexaSemi and WindFloat-type platforms under the storm condition is conducted and discussed. It is found that the integral design can increase the viscous hydrodynamic damping and reduce the heave response and the mooring cable force.
Offshore wind energy is a kind of clean, abundant, and renewable resource, and it has become one of the most promising power generation methods in new energy (Karimirad, 2013). Compared with the land and shallow water, the deep-water areas have the advantages of steadier and stronger wind speed. Therefore, it is an inevitable trend for future wind farms to develop from the fixed type in shallow water to the floating type in deep sea (Gao et al., 2010). The semi-submersible platform is characterized by its small draft combined with hydrostatic stability during installation and substantial waterplane restoring. The structure stability is the foundation of the safe operation of the floating offshore wind turbine. One of the common challenges to the design of floating offshore wind turbine (FOWT) is the ability to predict the dynamic load responses of the coupled wind turbine and platform system, which usually combines a wind loading wave and a stochastic wave (Jonkman, 2010; Tran and Kim, 2015). It is necessary to study the dynamic response of the floating platform under the loading of the marine environment.
Fan, Ting-Yu (Institute of Nuclear Energy Research) | Lin, Chin-Yu (Institute of Nuclear Energy Research) | Huang, Chin-Cheng (Institute of Nuclear Energy Research) | Chu, Tung-Liang (Institute of Nuclear Energy Research)
In this study, time-domain fatigue analyses of multi-planar tubular joints for a jacket-type substructure of offshore wind turbines designed for Taiwan’s local environmental conditions are performed. The potential design load cases could affect the overall calculation procedure. A series of fatigue loads from the IEC 61400-3 standard were calculated to investigate the dominant design load cases and to improve the load calculation efficiency. The stress distributions of tubular joints are computed by finite element analysis to determine the stress concentration factors. The results show that the fatigue damage caused by the power production design scenario accounts for the total cumulative fatigue damage up to 90%. This work, in addition to more efficient load calculation procedure, will be helpful for cost assessment and could accelerate the development of offshore wind farms in Taiwan.
Because of global warming and climate change, using renewable energy has become an inevitable substitute for fossil fuel and coal power. Wind power is one of the most promising renewable energy utilizations, providing an essential contribution to a clean, robust, and diversified energy portfolio. In Taiwan, the government’s reiteration of the target is that 20% of the country’s electricity will come from renewable energy by 2025, with wind power generation accounting for 15% of the renewable energy. In 2017, the first two offshore wind turbines of the 128 MW Formosa 1 Project, each a 4 MW machine, were installed, and the total installed capacity for offshore wind is predicted to reach 5.5 GW by 2025.
Flow around a rotating circular cylinder at a Reynolds number of 500 is investigated numerically. The aim of this study is to investigate the effect of high rotation rate on the wake flow past a circular cylinder. Simulations are performed at a constant Reynolds number of 500 and a wide range of rotation rates from 1.6 to 6. Rotation rate is the ratio of the rotational speed of the cylinder surface to the incoming fluid velocity. It is found that increasing the rotation rate beyond a critical value results in transition to a secondary instability regime where the oscillation of the lift force on the cylinder increases drastically. There is significant increase in the three-dimensionality of the flow inside the secondary instability regime. The flow pattern in the secondary instability regime is characterized by ring-type vortices wrapping around the cylinder. The oscillation of the force coefficient in the secondary instability regime is very irregular.
Vortex shedding flow in the wake of circular cylinders has been investigated extensively, mainly because of its increasing applications in (but not limited to) offshore oil and gas engineering. Many experimental and numerical studies have been conducted on the transition of the wake flow to turbulence (Roshko, 1954; Williamson, 1988; Hammache and Gharib, 1991; Karniadakis and Triantafyllou, 1992; Barkley and Henderson, 1996; Thompson et al., 1996). It was concluded that the transition of wake flow from two-dimensional to three-dimensional flow occurs when the Reynolds number is approximately Re D140–190. The Reynolds number is defined as Re = UD/v where U is the incoming velocity, D is the diameter of the cylinder, and v is the kinematic viscosity of the fluid. In the numerical study by Zhao et al. (2013), the critical Reynolds number was found to be 200. The critical Reynolds number varies in different experimental studies, mainly because of the end effects in the experimental condition.
May, Ruslan I. (Krylov State Research Centre (KSRC)) | Fedyakov, Valery E. (Arctic and Antarctic Research Institute (AARI)) | Frolov, Sergei V. (Arctic and Antarctic Research Institute (AARI)) | Tarovik, Oleg V. (Krylov State Research Centre (KSRC)) | Topaj, Alex G. (Krylov State Research Centre (KSRC))
Optimization of the ship route in ice-covered waters improves the efficiency and safety of navigation in the Arctic. This article describes a new wave-based approach for ice routing of a ship. Unlike grid-based approaches, which use a predefined grid to describe possible ship movements, the proposed algorithm is cell-free and extends the method of isochrones. All calculations of isochrone propagation are done using geo-algorithms and operations with geo-polygons. This allows us to use a standard vector ice data in its initial form, as well as to consider such special features as the discontinuities in ice cover, ice leads, and fractures.
Path optimization is a key challenge for safe and cost-efficient ship navigation in ice-covered waters. Recent technology developments make it possible to solve such a routing task in an automatic mode. At the same time, there are several requirements for implementing this idea. First, the formal statement of the routing problem should provide the possibility of considering the maximum number of factors and ice parameters that influence ship speed and route selection. Second, any software-based automatic routing method should serve as an additional tool, which a shipmaster or ice expert will use along with the other instruments to build the recommended route.
Chen, Hao (Manchester Metropolitan University) | Lin, Zaibin (Manchester Metropolitan University) | Qian, Ling (Manchester Metropolitan University) | Ma, Zhihua (Manchester Metropolitan University) | Bai, Wei (Manchester Metropolitan University)
This paper presents the numerical modelling of two point absorber wave energy converters (WECs) with and without a moonpool under focused wave conditions. The numerical model applies the overset mesh technique in order for the mesh to conform with the large-amplitude WEC motion induced by the focused wave groups. The incident wave group is first examined by a mesh convergence test and by comparing with the experimental data. The simulations are then carried out with the presence of the WEC. In total, three wave conditions are considered, each with the same wave period but with different wave heights. Nonlinear effects on the WEC motion are clearly exhibited when the wave steepness increases. The accuracy of the numerical results is carefully assessed against experimental data. Furthermore, the effects of the moonpool on the dynamics of the WEC are also discussed, where the WEC motion is compared for the case with and without a moonpool under the same wave conditions.
In recent years, the possibility of harnessing energy from ocean wave resources has gained great interest, where different design concepts of wave energy converters (WECs) have been proposed, such as oscillating water columns, bottom-hinged pitching devices, floating pitching devices, overtopping devices, and point absorbers. Point absorbers are one of the simplest WECs. Their characteristic length is generally smaller than the typical wavelength at the peak wave frequency. Meanwhile, they are typically subjected to large-amplitude motions close to resonance. In such a condition, a highly nonlinear wave-structure interaction is expected, where local wave breaking and overtopping may occur. Moreover, the damping coefficient of the WEC can be composed of not only the radiation wave damping but also the power takeoff (PTO) damping, as well as the viscous damping. The viscous damping force itself can be important in many cases, which are due to vortex shedding and shear stress force; see, for example, Gu et al. (2018), Palm et al. (2018), Wei et al. (2015), and Giorgi and Ringwood (2017). Such characteristics make the wave-structure interaction process highly complex and distinct from the traditional large-volume offshore structures.
Koshurnikov, Andrey V. (Lomonosov Moscow State University) | Tumskoy, Vladimir E. (Lomonosov Moscow State University) | Skosar, Vladimir V. (Lomonosov Moscow State University) | Efimov, Yaroslav O. (Arctic Research Centre) | Kornishin, Konstantin A. (Rosneft Oil Company) | Bekker, Alexander T. (Far Eastern Federal University) | Piskunov, Yuri G. (Far Eastern Federal University) | Tsimbelman, Nikita Ya. (Far Eastern Federal University) | Kosmach, Denis A. (Tomsk Polytechnic University)
There are currently many research studies on the Laptev Sea shelf permafrost distribution and permafrost thickness models. This article presents the results of field research of submarine permafrost in the Khatanga Bay area of the Laptev Sea shelf. The field work was performed in the area of the fast land ice in the Nordvik Bay by a team of experts from Moscow State University, Far Eastern Federal University, and the Arctic Research Centre, and incorporated geocryological drilling, geophysical surveying, and laboratory testing of thawed and frozen monolith rocks. The research was achieved through a combination of activities, such as the drilling of 13 core wells up to a depth of 50 m from the fast land ice of the Nordvik Bay, defining the thermal characteristics of over 300 monoliths from the Khatanga Bay shelf and the electromagnetic sounding of over 1000 holes from the ice of the Nordvik Bay. Our laboratory testing allowed identification of the permafrost roof in the Nordvik Bay and traced the permafrost foundering to a depth of 200 m, as well as an assessment of the distribution of permafrost to a depth of 500 m and modeling of the permafrost thickness dynamics for the next 50 years.
This complex multidisciplinary research project was carried out from the land fast ice in the Nordvik Bay of the Laptev Sea (Fig. 1) in order to study the geocryological conditions of the Khatanga Bay. The primary aim was to obtain and summarize data on the geocryological conditions of the southwestern part of the Laptev Sea, which is required to assess the impact of adverse environmental parameters that occurred during the industrial development of the area. The permafrost-geological structure and cryogenic processes, along with the presence of surface gas, are definitive geotechnical features of the shallow-water areas of the Arctic shelf, accounting and assessment of which are critically important at the first stages of development.
Ji, Chuanpeng (Shanghai Jiao Tong University) | Xu, Shengwen (Shanghai Jiao Tong University) | Wang, Xuefeng (Shanghai Jiao Tong University) | Liu, Xiaolei (Shanghai Jiao Tong University) | Shang, Yongzhi (Shanghai Shocktorm Ocean Engineering Co. Ltd.)
A novel conceptual telescopic pile is proposed to position a multi-modular very large floating structure (VLFS), which is supposed to serve as a movable floating airport. The telescopic piles can automatically plug in and pull out of the soil to resist the environmental forces. The demonstration of the feasibility of this conceptual design includes two parts: function verification and structure design. In the function verification, the bearing capability and dynamic responses are primarily investigated by the finite element method (FEM) using Abaqus software. The obtained results reveal that the dynamic response feature is quite good. Based on the coupled Eulerian–Lagrangian (CEL) method, the plugging and pulling processes are explicitly simulated. The results indicate that both the operations are quite safe and can be independently accomplished by vertical forces supplied by the adjustment of the ballast water and draft of the module.
Very large floating structures (VLFSs) have many important applications, of which the floating airport is one of the most valuable, as specifically described in previous relevant research (ISSC, 2006). The applications of VLFS, such as floating airports, floating piers, floating fuel storage facilities, floating hotels, floating bridges, floating stadiums, and even floating cities, have triggered extensive research in the past two decades (Kyoung et al., 2005, 2006; Wang and Tay, 2011). The first concept of VLFS that appeared in the modern world after the industrial revolution was the Floating Island described by the 19th century French novelist Jules Verne. The first VLFS promoted in earnest was the Armstrong Seadrome. It was proposed initially to enable airline routes across the world’s oceans (Armstrong, 1924). Detailed and concentrated efforts were then undertaken in the mobile offshore base (MOB) and Mega-Float projects (Suzuki et al., 2007). Shipbuilding technology had attracted the attention of architects in the late 1950s (Kikutake, 1994). Several concepts and designs of floating cities were then proposed in the 1970s and 1980s. Currently, research institutes such as the Technological Research Association of Mega-Float (TRAM) and International Ship and Offshore Structures Congress (ISSC) have paid much attention to the development and utilization of the VLFS (Suzuki, 2005). Except for the Mega-Float in Tokyo Bay, the only manufactured VLFS in existence, all VLFSs are only at the design stage (Lamas-Pardo et al., 2015).
The CCP-WSI Blind Test Series 3 have been conducted by an in-house code NEWTANK, which is a robust model solving NS-type equations by the finite difference method using the VOF method to track free surface, combing the virtual boundary force (VBF) method to simulate floating structures. In this study, the focused wave is first simulated and compared with experimental data obtained from the Coastal Laboratory at Plymouth University. Then, two kinds of tests of the floating structures under the focused wave are simulated. Float size and simulation status are the same as the experimental settings in the laboratory. Results are analyzed and compared with experimental data. Based on the reliable numerical model, this paper would supply a reasonable solution to the relevant issues of wave interaction with floating structures.
A special session titled CCP-WSI (Collaborative Computational Project in Wave Structure Interaction) Blind Test 3 was held in the ISOPE-2019 conference, which aims to supply experimental data to compare different numerical models, in order to improve related simulation techniques, to validate models, and to deepen understanding of physics in the computational fluid dynamics community. In the Blind Test 3, focused waves are generated, and focused wave interaction with a hemispherical cylinder and a moon-pool cylinder are simulated in the COAST Laboratory Ocean Basin at Plymouth University, UK. Figure 1 shows the details of the ocean basin used in the experiment. Flap-type wave makers are applied to generate waves with water depth of 4.0 m and mounted at a position with water depth of 2.0 m at still water level. The basin bottom has a slope with water depth from 4.0 m to 3.0 m at the wave-making end. A constant water depth of 3.0 m with length of 14.0 m is used for the focused wave, formed at a distance to the wave maker of 14.8 m. Floating cylinders are moored with their vertical axis at focusing position at still water level. There are 13 wave gauges set in experiment with No. 5 at focusing position, as shown in Fig. 2.
Mathematical models are essential for the effective design of wave energy converters and hence for the achievement of economic viability and industrial feasibility. Despite the fact that the wave energy field is at least 45 years old, there is still a clear lack of standardization of modeling techniques and a large amount of room for increasing confidence in hydrodynamic models. The Collaborative Computational Project in Wave–Structure Interaction (CCP-WSI) project aims to define a level playing field of comparison for a plurality of models, evaluating their performance. This paper implements a computationally convenient approach to represent nonlinear Froude-Krylov forces, along with the inclusion of nonlinear kinematics.
Accurate and reliable mathematical models are imperative in modern offshore renewable and ocean engineering applications, in order to reduce margins of uncertainty that are currently affecting every stage of the design process. On the one hand, a trustworthy prediction of structural loads is essential to ensure the safety of personnel and/or components, while avoiding oversizing the structure and excessive safety coefficients. On the other hand, in wave energy applications, the effectiveness, and hence the economic viability of the device, strongly depend on the representativeness of the mathematical model (Giorgi and Ringwood, 2018f; Ringwood et al., 2018).
During the development and optimisation of wave energy converters, numerical wave tanks are useful tools, providing detailed insight into the hydrodynamic performance of devices. Specifically, computational fluid dynamics (CFD)-based numerical wave tanks (CNWTs) can deliver high-fidelity, high-resolution results for a wide range of test conditions. However, CNWTs come at significant computational cost and require more man-hours during model setup, compared to lower-fidelity, frequency domain-based models. The computational costs can only be significantly decreased by improving the numerical solvers or by increasing expenditure on computational power. The required man-hours for the model setup, however, can be reduced by streamlining the setup of CNWTs. To this end, the formulation of best-practice guidelines can expedite this streamlining. A step toward such best-practice guidelines is blind tests. This paper presents the CNWT used for the authors’ contribution to the Collaborative Computational Project in Wave–Structure Interaction (CCP-WSI) Blind Test Series 3. In the employed numerical wave tanks, a self-calibrating impulse source wave maker is implemented for wave generation. In addition to the numerical results, and the comparison with the recently disclosed experimental data, the paper presents the spatial and temporal convergence studies, as well as results for the numerical wave maker calibration. The numerical results show average deviations with the experimental data of less than 10%. Furthermore, a correlation between the accuracy of the numerical replication of the wave and the agreement between numerical and experimental device motion is highlighted.
In recent years, growing concerns of human-induced global warming have fueled the R&D of novel technologies to harness renewable energy resources. Among these resources, marine renewable energies (MREs), and specifically ocean wave energy, show significant potential to contribute to the global energy supply (Falcão, 2010). The harsh ocean environment, in which wave energy converters (WECs) are deployed, poses challenges to the R&D of these devices. Although the energy resource is free, to be commercially viable, the price of the produced energy from a WEC, stemming from capital, operational, and maintenance costs, must be minimised.