Yu, Tongqiang (Jiangsu University of Science and Technology) | Liu, Kun (Jiangsu University of Science and Technology) | Wang, Qingfeng (Jiangsu University of Science and Technology) | Wang, Jiaxia (Jiangsu University of Science and Technology)
The fully opening of the northern shipping line puts forward a great challenge for the safety of polar ships, the presence of floating ice and icebergs increases the possibility of collision between ship and sea ice. However, due to the complex mechanical properties of sea ice, a reasonable description of its material constitutive relation is the main factor affecting the accusation of calculation and analysis.
In this paper, a constitutive model of ice material considering the effect of temperature is presented, a user-defined subroutine is developed and embedded into the finite element software LS-DYNA. The experimental and numerical studies of marine steel are carried out. Based on this, the collision scenario is established, the damage and deformation characteristics of the ship structure and ice are studied, The effects of collision scenario parameters are discussed. The results of this paper can provide reference for the design and manufacture of polar ships.
Arctic sea ice, especially summer sea ice, is declining at a rate of 10% every ten years (Richter M J, 2008a). The fully opening of the Arctic sea lanes is becoming possible and the polar shipping industry is bound to boom. However, due to the complicated environmental features in polar water, the strength of ships in polar waters is gaining more and more attention due to numerous ice floe and icebergs even in summer. Ship-ice collision will cause damage to ships, water or even sink and other consequences, bringing about significant loss of life and property. Therefore, the research on the collision performance of polar ships is essential to reduce the accident loss of polar ice collision and as well as the design of polar ships.
A reasonable description of sea ice's material properties plagued the scholars for years, the main obstacles are its various components and random inherent effects. Dozens of studies has been done in this area (Paige R A, 1967; Peyton H R, 1968; Timco G W, 2010). Full scale real ship-ice collision tests or ship model tests are also carried out in order to study the loading force during the collision process (Ritch R, 2008b; Valanto, 2001c). These results is available in deducing empirical formulas and analytical equations. For example, Dempsey (2001a) and Ian J. Jordaan (2001c) proposed the analytical methods for ice loading and ice pressure calculation and pointed out that sea ice had a clear scale effect. Frederking R. (2011b) studied the effect of strain rate on ice loading through comparative experiments. In recent years, with the rapid development of computer simulation technology, commercial finite element analysis software is increasingly used to simulate sea ice material and ice load as a more concise and effective way. Many material constitutive models are modified or justified to describe the iteration between the structure and sea ice reasonably(Gagnon, 2006a; Shunying Ji, 2002; Carney, 2006b ). Among them, crushable foam materials is widely accepted as for its rationality to reflect the brittleness of ice and good consistency with the experiment, but it does not have physical definitions as well as neglects the impact of damage. Other material constitutive models like Viscouselastic- plastic, elastic-plastic, and elastic-brittle sea ice material(Liu, 2012; Derradji, 2000a; Derradji, 2001b) are also detruded by different scholar in accordance with their focus point and research content.
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.
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.
Huang, Shuo (Guangzhou Institute of Energy Conversion) | Sheng, Songwei (Guangzhou Institute of Energy Conversion) | You, Yage (Guangzhou Institute of Energy Conversion) | Wu, Bijun (Guangzhou Institute of Energy Conversion) | Bai, Xu (Jiangsu University of Science and Technology)
Exploitation of floating wave energy converters (WEC) are boosted into deep water zones surrounding islands, and the encounters problems cannot be solved successfully in techniques by using conventional mooring systems. The difficulties and key factors on designs of mooring systems of the WECs in deep water sea area with large slope should be paid more attention. Meanwhile, the force of anchor lifting due to variation of bathymetry of islands surrounding seas cannot be ignored in deep water. In order to reduce the difficulties and costs of mooring system's construction in deep water, the features of the landscape should be taken into account. According to these special needs, the selection of mooring system material, size and layout are analyzed. Three design schemes obtained by specific study object of floating ”Sharp Eagle” WEC (Sheng, 2015) are put forward, which can effectively reduce the construction costs. Mixed catenary, synthetic cable taut and suspension type mooring system are proposed. Critical conditions include environmental conditions and directions in which the mooring system produces the maximum tension. For a complete condition, the mooring analyses are established in survival sea-state 50- years return. The dynamic analysis of the WEC and mooring system coupled motion in time-domain are implemented. The above experience will be significant for other mooring system of floating WEC design in deep water with a sloping bottom.
With the wave energy exploitation of islands surrounding sea, encounters problems of the mooring systems of floating wave energy converters (WEC) in deep water cannot be solved successfully either in economics or techniques. In present years, the working water depths of floating WECs are mostly less than 100m (Yu et al., 2015). It should take the reference from the experience of mooring systems of offshore production platforms and oceanographic buoys (Garrett, 2005). However, the working principle, installation method and launching areas of WECs are different from them. The project cost of WEC is far less than an offshore production platform, and the construction cost is the primary consideration, so it can't directly copy designs of offshore production platform.
Structure design technology based on the limit state is becoming the mainstream technology. It is significant for carrying out researches on the Ultimate Limit State (ULS) for semi-submersible drilling platform. The author of this paper has conducted researches on the finite element analysis technology of semi-submersible drilling platform by the ABAQUS finite element package and proposed the engineering numerical techniques for ultimate strength of semi-submersible platform. In order to simplify the problem, the structures and equipments on the upper hull deck are omitted. This will significantly affect the reliability of the result. So, the influence of the accommodation structure on the ultimate strength of the semi submersible platform was studied. Based on the previous research results, the deformation modes and ultimate bearing capacity, under the load modes due to split force between pontoons, longitudinal shear force and torsion moment about transverse horizontal axis, were analyzed by the non-linear finite element code ABAQUS respectively. The comparison between the platform without accommodation was made from the progressive buckling, including the stress distribution, strain distribution, deformation modes and the bearing load. Then, the different designs of general arrangement for accommodation were put forward. By comparative studies, the structural optimization design and the recommendation for the semi-submersible drilling platform were put up. Lastly, considering the significant change in the stiffness of the connection between accommodation and upper hull, the fatigue crack is easily generated in the joints under wave loading. The damage deformation mode and the ultimate strength under above load modes of semi-submersible drilling platform with failure crack were calculated. Further, the comparative analysis between the damaged structure and the intact structure was performed, and the effects of crack on ultimate strength were discussed.
Zhang, Yanchang (Marine Design & Research Institute of China) | Wang, Pu (Marine Design & Research Institute of China) | Liu, Kun (Jiangsu University of Science and Technology) | Li, Xiaoping (Marine Design & Research Institute of China)
The research on the design method based on Ultimate Limit State(ULS) for the semi-submersible drilling platform was carried out. This paper introduced the ULS, analysis methods for ultimate strength. Then, based on the ABAQUS finite element package, numerical simulations on stiffened plates were performed, especially on analysis methods, effects of initial deflection, results analysis technologies and so on. The numerical simulation technologies were summarized. Furthermore, the structural models, load models and boundary conditions of the semisubmersible drilling platform were analyzed; the ultimate forces and damage modes of the target platform under the load modes due to split force between pontoons, longitudinal shear force and torsion moment about transverse horizontal axis were analyzed; the equivalent models and effects on the results and computational efficiency of stiffened models, and the engineering numerical techniques for ultimate strength of semi-submersible platform were proposed. The structural design technology for semi-submersible platform based on the ULS was proposed. The recommendation for the semi-submersible drilling platform structural design was put up.
Since the recent twenty years, the ship structure design method is changed from the traditional allowable stress criterion design to the limit state design. The limit state design can make the design more accurate, economical and safe because it considered the various failure modes of structures in the service life. The limit state design are widely used for marine and land structures. The ultimate strength (ultimate moment) of ship hull girder are ruled by the ISO (2007), IACS(2008) and many classification society rules. Furthermore, the ISSC (2003,2006,2009) provided consecutive special reports of ultimate strength. It is a new and different topic for semi-submersible drilling platform to carry out the design based on ultimate limit state. This paper summarized the use of ULS in semi-submersible drilling platform based on the research findings of Marine Design & Research Institute and Jiangsu University of Science and Technology.
As the main drilling unit using to the deep sea drilling, the research and design of the semi-submersible drilling platform becomes a hot research topic at home and abroad. Chakrabarti(2007) calculated the residual strength of a semi-submersible drilling platform with brace damage by numerical simulation method, and discussed the difference of loading conditions and calculation methods between the offshore structures and the monohull ship structures. Estefen(2007) studied the damage mechanism of the stiffeners on the column frame of a semisubmersible platform, and compared the numerical solution of the ultimate strength of stiffened plate with the small scale experimental solution. Zeng(2005) and Yang(2011)calculated the ultimate strength of a semi-submersible platform using a simplified progressive collapse analysis method. Jiang(2010) calculated the ultimate strength of the local structures of semi-submersible platform using nonlinear finite element method. Liu and Zhang(2012,2014)analyzed the ultimate strength of stiffened plate, brace and upper hull structure of semisubmersible platform by non-linear finite element method. As the ultimate limit state design is a new and difficult topic, its studies are still in the initial stage, the analysis methods and standards of semisubmersible platform are in the research progress, meanwhile, there is little rules for reference.
Generally the multidisciplinary design optimization in ship design only considers the impact of certainties with ignoring the existence of uncertainties in the design. The results of the optimization obviously cannot really guarantee the feasibility of ship hull and excellence of sailing performance. Currently, uncertainty multidisciplinary design optimization of ship focuses on one dimension of uncertainty analysis. To obtain the optimal solution of ship design, the problem of Multidisciplinary Robust Design Optimization (MRDO) under multi-dimensional uncertainties is studied in the paper by analyzing and considering uniform distribution and normal distribution of random uncertainties. It deduces a new multi-dimensional polynomial chaos approach based on Legendre polynomials and Hermite polynomials. It is established the mathematical models of multi-dimensional uncertainty quantification while considering the speed reducer and bulk carrier optimization as the research objects. By analyzing the influence of multi-dimensional stochastic uncertainties to the ship design optimization, the research of ship robust multidisciplinary design optimization is completed. The possibility of failure in ship design optimization is effectively reduced and avoided.
Over the years, optimization has been playing an increasingly important role in engineering. Complex systems like ships and other marine structures must fulfill multiple, often conflicting objectives (Knight Joshua T., 2014). Multidisciplinary Design Optimization (MDO) can be used to evaluate multiple, conflicting objectives simultaneously and reveal useful tradeoff information for decision-making purposes (Dong Suzhen,2014). However, real world applications are affected by uncertainty and require uncertainty analysis and uncertainty quantification (UQ). Uncertainty exists in many of the design variables and system parameters for ship and marine structure design. This is especially true in the early stages of design. For this reason and others, optimization of a ship's performance characteristics is often delayed until later in the design process, after uncertainties have been at least partially resolved.
In this paper, firstly we investigate the prerequisites of the repeatable signals, which must be satisfied when a short signal is used repeatedly. Secondly, based on the prerequisites two available type of methods are presented and discussed. One is called interception method (IM) which can preserve all the original information of objective waves, but can only be used by single-paddle wave-maker and multi-paddle wavemaker to make regular waves. The other one is called as quintic polynomial method (QPM) which will introduce small amounts of unreal waves into tests but can be used for all types of wave-maker while also can ensure enough experimental precision and some other nice merits.
The generation of waves in laboratories is normally made by moving the paddles of wave-maker in water under the control of corresponding signals which are based on the objective waves. For some model tests, such as the stability tests of rock slope (van der Meer, 1987) or the overtopping tests of seawall (Franco et al, 1999), etc., to get stable and reliable results thousands of irregular waves must be made uninterruptedly, so a fairly long length of signals should be prepared in advance. But in fact especially to the electromechanical type wavemaker the available length of the signals are often much shorter than need for the cause of technique, efficiency and cost. So applying the shorter signals repeatedly in an uninterrupted way is often necessary. However, to make the signals repeatable some prerequisites must be satisfied.
Firstly, the repeatable signals must have the characteristics of closure and smoothness. Closure means that the beginning and end points of the paddle motion have to share the same location. Without this feature, the centre of movement of the paddles will deviate towards one direction gradually and continually until impacting the borders, which is very harmful to safety and test precision. Smoothness means the variations between two adjacent signals small enough, to prevent the failure of the related equipment from too sudden changing of the motor rotation. Furthermore, for the wave-maker with multi-paddle to make the relations of wave phases correct, the repeatable signals for each channel must take the same length and derived by local wave time sequence.
Zhang, Jian (Jiangsu University of Science and Technology) | He, Wen-xin (Jiangsu University of Science and Technology) | Yuan, Zhi-ming (University of Strathclyde) | Chen, Cong (Jiangsu University of Science and Technology)
In order to investigate the water media effect on Structure response under ship-ice collision load. This paper presents a study on ship-ice collision considering the effect of water media for the first time. The ship-ice collision is simulated in aqueous medium and the coupling behaviors between the ship, water and ice was considered. The calculation model is applied to various working conditions of ship-ice collision calculation. The parametric study on the thickness of shell and transverse diaphragm and the spacing of the frames is then conducted. The damage deformations, collision forces, structural energy absorptions varying with thickness of shell plate, thickness of the transverse diaphragm and different spacing of frame are discussed. The capability and contribution of each major component in the shoulder of the ship on the resistance of ice loads is analyzed. The conclusions are of great significance in improving anti-ice load ability of ship structure.
It is shown that this design tool is capable of analyzing the effect of wake controlling algorithms in the upstream turbine.
In the recent years, with the discovery and exploitation of oil and gas resources in arctic area as well as the development of Northern Sea Route (NSR), more and more attentions has been paid to the study on ship-ice collision in the field of naval architecture and ocean engineering.
Ship-ice collision has been a topic of interest among researchers especially those from Canada, Norway, America. Gagnon (2006) investigated the ship-ice collision through both the experimental and numerical methods. However, the structural damage was not reported. Wang and Yu (2008) used a coupled model to siumlate ice-LNG collision. The floating ice model with inducted ice failure model, Liu , Amdahl and Løset (2010; 2011) systematically studied the external and internal dynamics of a ship collision. They got the pattern of the energy dissipation during the collision by using a simplified method. They also simulated the ship-ice collision by a numerical method. Lee and Lee (2009) conducted a collision test between a cylindrical ice a and grillage structure. Special efforts were put on the failure law of the ice model. Zhang, Wan and Chen (2014) used both numerical and experimental methods to investigate the collision between the side grillage and ice to validate the feasibility of the ice material model, as well as the numerical method.
Xu, Gang (Jiangsu University of Science and Technology)
In order to exactly predict hydrodynamic forces acting on a floating structure, a time-domain second-order method was formulated to simulate a three-dimensional wave-body interaction problem. In the approach, Taylor series expansions are applied to the free surface boundary conditions, and Stokes perturbation procedure is then used to establish corresponding boundary value problem at first-order and second-order on the time-independent surfaces. Desingularized boundary integral equation method (DBIEM) is used to calculate wave field at each time step. A hybrid radiation condition, which is the composition of the multi-transmitting formula (MTF) method and damping zone (DZ) method, is employed to minimize the wave reflection. A stable integral form of free-surface boundary condition (IFBC) is used to update velocity potential on the free surface. The numerical precision of the method was then investigated. The results were also compared with analytical solutions. It is shown that long time simulation can be carried out with stability and accuracy.