This paper aims to numerically simulate the loading process when a moored ship is intruded by an ice ridge. Ice force caused by ice keel is calculated based on suggestions from ISO while the ice force due to consolidated layer is taken as level ice and simulated with circumferential crack method. The equation of motion is solved at each time step. A case study is given to show main features during the moored ship and ice ridge interaction. The result shows that the present numerical simulation is promising to be used in the design for moored structures in ice ridge.
In the Arctic, there exist many different types of features such as pure level ice, brash ice, ice rubble and ridges, ridge fields and icebergs, all with different structural and mechanical properties and behavior. For ships and offshore structures, first year ice ridge is a key consideration due to the extreme ice loads acting on the structures. It is crucial to determine the design load levels for offshore structures in ice-infested waters, can also bring a threat to shipping and navigation activities.
Typically, an ice ridge is formed when ice sheets are compressed against each other due to environmental factors, such as wind, current in the sea, thermal expansion etc. From geometry aspect of ice ridge, it is composed of three parts: sail, consolidated layer and keel. The above water part, called the sail, has pores filled with air and snow. The underwater part, called the keel, has pores filled with water and air pockets can exist. The ridge keel is further separated into an upper refrozen layer called the consolidated layer and a lower unconsolidated part. The consolidated layer grows through the ridge lifetime as a function of the surrounding meteorological and oceanographic conditions, air and water temperature, snow depth and the velocity of the wind, and surrounding currents are of principal importance. There was a wide variation in the shapes of the first-year sea ice ridges (Timco & Burden, 1997).
By developing general constitutive laws for ice ridge, Heinonen (2004) and Serré (2011) used finite element software to simulate the ice ridge load. At present, moored ships are often used to oil exploration and exploitation in ice-infested waters. For example, starting in the mid-1970s to the late 1980s, Dome Petroleum deployed floating drill-ships named Canmar during the summer months. In some water, the ice ridge action should be taken into consideration. A sketch of the moored ship in ice ridge is shown in Figure 1.
Niu, Jianjie (Jiangsu University of Science And Technology) | Li, Xiaomin (Ocean University of China) | Shen, Jiajia (Jiangsu University of Science And Technology) | Zhou, Li (Jiangsu University of Science And Technology)
Nonlinear dynamic vibration equation of flexible riser conveying fluid is established based on the theory of slender rod and considering the internal flow effect. With Hermitian interpolation function, all the vibration equations are discreted. The static analysis of flexible riser is solved by the Newton-Raphson method. In time domain, the dynamic analysis is calculated with the Newmark method on the basis of flexible riser's static response. The validity of the numerical simulation has been verified by Low's researches. The effect of internal flow on nonlinear response of flexible riser is studied, the result shows that the influence of internal flow on the static response of a catenary flexible riser is not obvious, however, it can change the effective tension of a moving catenary flexible riser in three dimensions, the amplitude of a flexible riser's effective tension increases with the increasing velocity of internal flow, the effect of internal flow on the surge motion of a catenary flexible riser is more significant, and the effecttive tension amplitude increases with the decreasing surge motion period.
Flexible risers conveying fluid are important in deep water oil exploration as they can accommodate the large vessel motions. Study on the dynamics of a curved flexible riser have been investigated by many researchers such as O'Brien and Mcnamara (1989), Chung JS(1996), Chai and Varyani (2002), Low and Langley (2006), Garrett (2005), Yang and Teng (2012). However, they all omit the effect of internal flow on flexible riser. Blevins (1990) has pointed out that the internal flow can affect the natural frequency of a flexible riser, thus, the riser's response will be changed. As for the internal flow's effect, a lot of researchers have focused on a two dimensional problem such as Wu and Lou (1991), Kaewunruen and Chiravatchradej (2005), Guo and Li (2008). This study focus on the static and dynamic response of a catenary flexible riser conveying fluid in three dimensions. The effect of internal flow on flexible riser is analyzed and some valuable conclusions are drawn.
Shi, Wei (Dalian University of Technology) | Tan, Xiang (Nanyang Technological University) | Zhou, Li (Jiangsu University of Science and Technology) | Ning, Dezhi (Dalian University of Technology) | Karimirad, Madjid (Queen's University)
The ice loading process has a clear stochastic nature due to variations in the ice conditions and in the ice-structure interaction processes of offshore wind turbine. In this paper, a numerical method was applied to simulate a monopile fixed-bottom and a spar-type floating wind turbine in either uniform or randomly varying ice conditions, where the thickness of the ice encountered by the spar were assumed to be constant or randomly generated. A theoretical distribution of the ice thickness based on the existing measurements reported in various literatures was formulated to investigate the response characteristics of the monopile wind turbine and spar wind turbine in such ice conditions. The effect of the coupling between the ice-induced and aerodynamic loads and responses for both operational and parked conditions of the rotor was studied. Moreover, the dynamic response of wind turbine in randomly varying ice was compared and verified with that of the wind turbine in constant ice.
So far, more than 80% of the energy all over the world comes from fossil fuels. Excessive and improper use of fossil fuels has caused climate change and threatened human security and development. The Paris Agreement, which entered into force on 4 November, 2016, is a major step forward in the fight against global warming. Due to severe smog, forty Chinese cities reel under heavy air pollution. Air pollution becomes one of the key words in China in 2016 (PTI, 2016). Renewable energies play an important role for reducing greenhouse gas emissions, and thus in mitigating climate change. Offshore wind energy is recognized as one of the world's fastest growing renewable energy resources. By the end of 2015, totally 12,107 MW of offshore wind energy was installed around the world according to Global Wind Energy Council (GWEC) report (Fried, 2016). In Europe, 3230 turbines are now installed and grid-connected, making a cumulative total of 11,027 MW (Ho, 2016). However, governments outside of Europe have set ambitious targets for offshore wind and development is starting to take off in China, Japan, South Korea and the US. The 1.2 GW of capacity installed in Asia as of the end of 2015 was located China and mainly in Japan.