Abstract In the offshore environment, aerodynamic and hydrodynamic loads induced by wind, wave and current are directly or indirectly applied to the foundations for offshore wind turbines (OWTs). To avoid resonance, the first frequency of the OWT system must keep away from the frequencies of these external excitations. The monopile foundation has a significant effect on the dynamic responses of OWT system, which should be carefully evaluated in the design. In this paper, a comprehensive numerical study has been carried out on the dynamic behaviors of the OWT supported by monopile in sand. In the numerical model, the OWT structure is simplified as an Euler-Bernoulli beam with a series of nonlinear Winkler springs, in which the soil resistance is modeled by p-y, t-z and q-z curves. The influences of dynamic loads, the dimensions of the monopile and tower (length, diameter and wall thickness) are investigated in detail, and some useful conclusions are drawn in the end. Introduction Monopile is an economical foundation option for the offshore wind turbine located in shallow water (water depth less than 30m). During its service life, the embedded monopile always sustains complicated environmental loads, i.e. the wind, the wave and other external loads. As the offshore wind turbine is a kind of dynamic-sensitive structure, dynamic loads including the wind turbulences, waves, rotational frequency of rotor (1P) and the blade passing frequency (3P for 3 bladed turbine), need to be considered in the design (Arany, Bhattacharya et al. 2015). A typical frequency range for energy-rich waves varies from 0.05 to 0.5 Hz(Bisoi and Haldar 2014). For variable speed generator in modern OWT system, the operational frequency of the rotor varies from 0.1-0.3 Hz, and thus the 3P frequency lies in the range of 0.3-0.9 Hz. Designers must keep the first natural frequency of the OWT away from frequencies of all these external loads.

Abstract The tripod foundation has been used as a popular support structure for offshore wind turbine (OWT). Typically, only deterministic computational model is considered by applying relevant standards and codes during the preliminary design of the foundations of OWT. However, uncertain parameters should also be considered in preliminary design due to complex configuration of tripod structure. In order to balance conflicting design parameters against design requirements, uncertainties from both design loads and geometric dimensions of structural components were considered to identify the dominant loads and key structural design parameters for tripod foundation. Nonlinear finite element methods were utilized to investigate the mechanical behaviors of tripod foundation and Monte Carlo simulations (MCS) were conducted to obtain sensitive design parameters of tripod foundation of OWTs. Based on the results, it is highlighted that which design parameters should be considered carefully and which design parameters can be selected relying on engineering judgment during the preliminary structural design stage of tripod foundation. Introduction The exploration of offshore wind energy has been expanding rapidly worldwide in the past five years, as shown in Fig. 1. According to statistical report studies from the Global Wind Energy Council (GWEC, 2015), the global cumulative offshore wind energy capacity has stood at 12,105 MW, after 3,392 MW were added in 2015. Besides, the development of increasingly larger OWT in deeper water highlights the trend of the future wind turbine technology, and design and construction of foundation structures have represented important safety and cost factors of offshore wind turbine (OWT) technology. Currently, most of OWTs are located in shallow water and 75% OWTs in Europe are supported by mono-pile foundations (LORC). But as turbine size and water depth increase, traditional mono-pile support structures encounter economic and technical limitations for larger wind turbines in water depth exceeding 30 m. Tripod foundations are potential alternative in offshore wind farms because of their good stability and overall stiffness in water depth ranging from 20 to 40 m (Herion, 2007). They have been successfully installed in Borkum West 2, Global Tech 1 (Fig.2) and Alpha Ventus wind farms, and total capacity is 830 MW with 166 installed turbines, 5 MW in average for each turbine (Madjid, 2014).

ABSTRACT: Based on the 5MW offshore wind turbine model developed by National Renewable Energy Laboratory (NREL), two new conceptual offshore wind turbine floating platforms with combined Tension legs- Mooring lines system were proposed in this paper. Taking the coupled dynamic responses of the top wind turbine, tower support structure and lower mooring system into consideration, the time domain hydrodynamic analysis coupled with wind loads has been done for the two offshore floating platforms: the single offshore wind turbine (SOWT) platform and the multiple offshore wind turbines (Multi-OWT) platform. According to the sea statistical historical data for China East Sea and the typical design cases in IEC61400-3 code, the motion performances of the two OWT floating platforms have been studied by numerical simulation technique, respectively. Furthermore, during the irregular wave analysis, the effects of the current force and the slow drift force on the motion responses of the two OWT platforms were also clarified. As a result, the performance of the new combined Tension legs-Mooring lines system on controlling the motion responses of the OWT floating platforms has been verified in both views of theoretical analysis and numerical simulations. In a word, the two new conceptual OWT floating platforms would play an active and instructive role in the future design of OWT floating platforms. INTRODUCTION At present, as the continued increase of energy demand of the whole world, more and more nonrenewable fossil fuels are consumed. Considering the supply limitation and the price volatility of conventional fossil fuels, many countries are paying more and more attentions to the exploitation of the offshore wind energy resource. Comparing with the onshore wind resource, the offshore wind resource has the advantages of high wind speed, low turbulence intensity, land saving, no noise annoyances and near the coastal developed areas.

ABSTRACT: When analyzing the aerodynamic loads of floating wind turbines, most professional programs didn_t consider the motions of foundation. Therefore, deviation is present inevitably. This paper is mainly focused on the effect of pitch motion on the aerodynamic loads and output power performance of the floating wind turbine. Pitching response of the floating foundation was figured out and a comparison was made between aerodynamic loads calculated under pitch motion and the calculation results of fixed wind turbines. The results show that the generator power fluctuates more widely and the flap of the blades is more acute due to pitch motion. INTRODUCTION There is a large reserve of wind energy on earth. Wind energy is a kind of clean energy which is renewable and friendly to the environment. The exploitation and utilization of wind energy is of great importance to the sustainable development of our human society. For the purpose of reducing the cost and commerce application of wind power generation, high power generator is used more and more widely. Considering the effects on environment and the quality of wind energy, installing high power generator in the deep sea has become the general trend. As the water depth increases, the cost of construction, installation and maintaining of the fixed foundation such as jacket platform and gravity platform rises sharply. There are several types of floating foundations, including TLP, SPAR, semisubmersible, etc (Jonkman, 2007). When aerodynamics of the wind generator is researched, the flow field is usually considered as a steady flow which is vertical to the rotor plane. However, the flow of wind is actually very complicated, containing both periodic components, such as mean wind speed, yaw control, influence by the tower shadow, etc, and non-periodic components, such as turbulence and wake.

ABSTRACT: Development of production platforms for promising Russian offshore areas in the Barents and Kara Seas and on Sakhalin island sets a challenge to overcome their extremely harsh environmental conditions. These are to manage ice in winter and heavy waves in other seasons (platforms and terminals in the Barents Sea) and, in addition, seismic events up to Force 9 (Sakhalin, the Sea of Okhotsk). Some experience has been gained in the design and installation of fixed ice-resistant platforms on the Russian offshore, for example, gravity-based «Vityaz» platform with a soil core («Sakhalin-II» field) deployed at a depth of 32 m. Gravitybased «Prirazlomnaya» platform for the Pechora Sea will be deployed at a depth of 19 m to operate under severe ice conditions. There is also a design of a piled platform developed by Exxon- Mobil for «Sakhalin-I» field. This paper presents an overview of general design principles for offshore ice-resistant platforms for the Russian offshore resulting from the design experience and comparison of Russian and Western codes and rules. INTRODUCTION This paper overviews design peculiarities of offshore ice-resistant fixed platforms designated for the Russian offshore (the Barents and Kara Seas and Sakhalin island). Unusually severe combination of environmental conditions in these seas is the major peculiarity of the Russian offshore. At the same time significant oil and gas reserves explored in these areas make the production reasonable and profitable. Design of these facilities calls for a new approach to standards, rules and codes and, first of all, for the development of estimation procedures and assignment of environmental loads. A difficult problem is to assign reasonable combinations of environmental loads, including those with a principally different recurrence period. Thus, a new approach to this problem is called for, an approach different from the proven western ones.

ABSTRACT: Antarctic buildings have persistently encountered serious problems stemming from the unique conditions of the harsh Antarctic environment with extreme temperatures down to -50·C and winds up to 300 km/h This leads to the on-going accumulation of snowdrifts around buildings causing problems ranging from continual snowdrift deposition at entrances to their abandonment when the buildings are rendered unusable within a year because of poor snowdrift clearance, Furthermore the short building history and rapidly intensifying occupation of Antarctica have allowed insufficient time to understand the characteristics of the environment Given this realisation, Antarctic building designers are thus confronted with minimal research data on wind loads on and snow drifting around buildings and structures. The design features affecting the performance of Antarctic buildings in terms of snowdrift clearance and design loading appear to be the building shape facing the wind and the elevation of the building from the ground, The wind induced loads on and snow drifting formation around a number of different shapes of on-ground and elevated buildings were investigated. This research provides vital information for the prediction of snow drifting around Antarctic buildings and Will play a major role in Antarctic building design in the future. 1. INTRODUCTION Snow drifting around Antarctic buildings causes a wide range of problems varying in danger and cost They include, covered windows and vents, blocked fire escapes, psychological effects (Holmes, 1982), high energy consumption and buildings being pushed off their footings Supply and construction costs often exceed 12 times those found in the construction of comparable temperate climate buildings (Rohde, 1990) Buildings and stations, because of poor snowdrift clearance, often become inundated, and sometimes rendered unusable Within a year of completion. Following the progressive obliteration of several stations in Antarctica, two alternative remedies were explored, viz. underground and elevated structures (Radok, 1977).