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This paper presents a three-dimensional hybrid model that couples the weakly compressible smoothed particle hydrodynamics (SPH) and the quasi-arbitrary Lagrangian-Eulerian finite element method (QALE-FEM) for modelling the wave-structure interaction (WSI) in extreme sea states. The former is a fully Lagrangian mesh-free approach that solves the one-phase incompressible Navier–Stokes model and has shown satisfactory performance in simulating the WSI. The latter is an arbitrary Lagrangian-Eulerian approach based on the fully nonlinear potential theory and can accurately simulate highly nonlinear nonbreaking water waves in a large scale with high computational efficiency. These two models are coupled using a one-way zonal approach, in which the SPH uses a small computational domain near the structure, whereas the QALE-FEM covers the rest of the computational domain and provides wave conditions at the inlet of the SPH domain. The present hybrid model is validated against the experimental results and applied to the CCP-WSI blind test on modelling wave energy converters subjected to extreme focusing waves. The accuracy and convergence of the presented model are discussed.
The wave-structure interaction (WSI) in extreme sea status has been receiving extensive attention in the design and operation of the offshore and marine structures for their safety and survivability. The wave in such a condition is typically highly nonlinear and may exhibit local wave breaking, typically exceeding the range of applications of the linear, second-order, or Stokes wave theories. For a full development/formation of the extreme wave, the associated wave fetch length or propagation distance must be sufficiently large (Wang, Ma, and Yan, 2017, 2018). On the other hand, the structures subjected to such waves normally undergo significant motions and/or deformations. Consequently, small-scale physics, such as the viscous/turbulent effects, breaking wave impact, and aeration, may be important. This calls for numerical models with a capacity of dealing with both the large-scale wave propagation and the small-scale near-field physics simultaneously to deliver a reliable prediction on WSI in extreme sea conditions. Conventionally, two types of numerical models have been developed and applied in the engineering practices.
In this work, our computational fluid dynamics (CFD) solver naoe-FOAM-SJTU is adopted to simulate the interaction between focused waves and a moored hemispherical-bottomed buoy. This solver adopts a two-phase Navier–Stokes model and a spring mooring system. Three crest-focused wave groups, based on NewWave theory, are generated and validated against the experimental measurements from the Collaborative Computational Project in Wave–Structure Interaction (CCP-WSI) working group. Numerical results for the buoy’s heave and surge displacement, pitch angle, and mooring load are compared against corresponding physical data. The effects of wave steepness on the behavior and mooring loads are discussed.
Under extreme wave conditions, strong nonlinear impact phenomena such as severe wave runup, relative motion, and green water may occur, which will cause a large local impact load on wave energy converters (WECs). Exploring the interaction between extreme waves and WECs has great importance for the design and protection of these kinds of structures. As an extreme wave is highly nonlinear and can arise as a highly transient event within a multifrequency sea state, a focused wave group is typically adopted to model an extreme wave in physical or numerical modeling. The focused wave group where many wave components in a spectrum focus simultaneously at a position in space can represent an extreme wave profile with a specified wave energy spectrum. Thus, a focused wave can play the role for extreme wave conditions. The accurate prediction of the motion of a WEC under extreme wave conditions can be viewed as that under the focusing wave.
The paper presents the contribution to the CCP-WSI Blind Test, in which the responses of wave energy converters subjected to extreme waves are considered, by a hybrid model, qaleFOAM, coupling a two-phase Navier–Stokes (NS) model and the fully nonlinear potential theory (FNPT) using the spatially hierarchical approach. The former governs a limited computational domain (NS domain) around the structures and is solved by the OpenFOAM/InterDyMFoam. The latter covers the rest of the domain (FNPT domain) and is solved by using the quasi Lagrangian-Eulerian finite element method. Two numerical techniques have been developed to tackle the challenges and maximizing the computational efficiency of the qaleFOAM, including a modified solver for the six-degree-of-freedom motions of rigid bodies in the NS model and an improved passive wave absorber imposed at the outlet of the NS domain. With these developments, the accuracy and the computational efficiency of the qaleFOAM are analyzed for the cases considered in the blind test.
A reliable prediction of the responses of the offshore structures in a realistic extreme sea plays a fundamental role in the safe and cost-effective design of such structures. Numerous numerical models and software have been developed based on wide ranges of theoretical models, including the Navier–Stokes (NS) models and the fully nonlinear potential theory (FNPT), which assumes that the flow is incompressible, inviscid, and irrotational.
The electricity in Indonesia still dominated by fossil energy which might cause many losses, especially to the environment. Renewable energy such as geothermal is needed to replace the fossil energy. It is the right choice in today's global sustainable development due to low carbon emissions. Indonesia has 40% of all geothermal potential all over the world. Geothermal energy potential in Indonesia is widespread in areas that traversed by the ring of fire or areas with active volcanic activity, one of them is Mount Tangkuban Perahu in West Java. Geothermal potential in an area could be known by the anomalies on surface manifestations such as fumaroles, hot spring, mud pools, steaming ground, sinter, and hydrothermal alteration. It is possible to identify areas that have the potential of geothermal energy based on their surface relief through remote sensing. Identification of anomalies obtains through the processing of Landsat 8 satellite imagery using thermal bands 10 and 11 with Thermal Infrared (TIR) sensors. Remote sensing is very effective in identifying manifestations and potential of geothermal energy because it can cover data on a wide area, time, and cost-efficiency. In addition to fluid manifestations, remote sensing can also identify the distribution of minerals in areas to estimate the reservoir characteristics of a geothermal system. This study aims to estimate the geothermal reservoir characteristics in Mount Tangkuban Perahu area that used as an initial consideration in geothermal exploration and further geothermal research in other areas. The methods use in this research are Split-Window Algorithm (SWA) to find the distribution of manifestations, calculations of Radiative Heat Flux (RHF) to obtain an estimation of geothermal resource potential, and bands ratio to identify the distribution of the hydrothermal alteration minerals. The results will provide information about surface temperature and heat losses based on anomalous manifestations, estimation of power electricity resource, surface mineral distribution, geomorphological features, and a conceptual model of Mount Tangkuban Perahu geothermal system.
Hase, Kazukuni (JFE Steel Corporation) | Ichimiya, Katsuyuki (JFE Steel Corporation) | Ueda, Keiji (JFE Steel Corporation) | Handa, Tsunehisa (JFE Steel Corporation) | Eto, Taiki (JFE Steel Corporation) | Aoki, Masahiro (JFE Steel Corporation)
A YP460 N/mm2 class steel plate with a thickness of up to 100 mm for ultra-large container carriers has been developed by thermo-mechanical control process (TMCP). The developed YP460 steel plate has an excellent brittle crack arrest toughness of over 11,000 N/mm3/2. The characteristics of the plate include a highly oriented texture and excellent Charpy impact toughness by means of an advanced TMCP for the prevention of brittle crack propagation. The alloy design of the plate is a relatively high carbon equivalent to satisfy the required tensile properties; however, good weldability is achieved as a result of its low weld cracking parameter alloy design.
Recently, the size of container carriers has increased as the volume of container freight between Asia and Europe expanded. The first large container carrier with a capacity of more than 10,000 TEU (twenty-foot equivalent unit) was constructed in 2005 for transport efficiency improvement. However, the size of container carriers is continuing to expand, and construction of ultra-large container carriers with capacities of more than 20,000 TEU began in 2016. The thickness and strength of the steel plates applied to the upper hull structure of large container carriers—for example, the hatch-side coaming and upper deck—have been increasing in order to secure the structural strength required by the large cargo opening deck structure.
Inverse kinematics was studied to compute the joint parameters of rotary crane systems with two Degrees of Freedom (2-DOF) and the lengths of the wire ropes that would enable a target structure to reach the desired position and orientation during the performance of collaborative tasks in offshore installation operation using two floating cranes. First, the connecting positions between the wire ropes and the target structure in a local coordinate system of the structure were described in a global coordinate system. The forward kinematic equations of two rotary crane systems were modeled with the joint parameters of the crane systems and the lengths of the wire ropes. Inverse kinematics reverses these equations to determine the joint parameters of the crane systems, making the wire ropes perpendicular to the base or water plane. The connecting positions between the wire ropes and the boom of each crane system were computed using these joint parameters, and the lengths of the wire ropes considering their tensions were also computed using the balance equations of the forces and moments acting on the structure and the wire ropes, including the gravitational forces and tensions. Convergence problems such as singularities and out-of-reach targets were considered. Multiple solutions were also considered to achieve the desired posture and to determine how to choose an optimal one. Finally, the inverse kinematics was validated by applying it to monopile installation simulation using two floating cranes.
A floating crane is almost essential for installing an offshore structure. Depending on the shape of the offshore structure and the environment of the installation area, some cases may require more than one floating crane. As carrying out collaborative tasks with two floating barges at an offshore site is quite dangerous, however, it is necessary to verify the safety of the collaboration by conducting a simulation before the real operation. To perform the simulation, the length of the wire rope and the joint angle of the crane according to the installation position and posture of the object structure are required. Currently, iteration work is necessary to confirm correctness by calculating the joint angle of the crane and the wire length manually. Therefore, in this study, inverse kinematic analysis was performed to automatically calculate the rotation angle and wire length of the two-axis rotary crane according to the position and attitude of the installation structure.
Li, Bowei (School of Navigation / Wuhan University of Technology) | Xu, Yanmin (School of Navigation / Wuhan University of Technology) | Chang, Zheng (School of Navigation / Wuhan University of Technology) | Wang, Jianyu (School of Navigation / Wuhan University of Technology)
This paper carried out a research of the dynamic route-planning of the ship. Using Memetic algorithm and with collision regulars on the sea, the format of ship-encounter is analyzed and furthermore, the ways to evade is determined. Finally, the constraints of the obstruction cost and the length cost, the dynamic path planning is conducted. According to the results of the path planning, the ship simulation manipulator is used to simulate and verify the two situations including crossing and head-to-head, and then analyze the path planning process. From the perspective of maritime practice, the empirical results of avoidance are used as a comparison to verify the validity and applicability of the algorithm.
With the development of the world economy, the “One Belt, One Road” initiative and the “Ocean Power” strategy, the marine economy has become a new economic growth point. The development of the marine economy has reached an unprecedented height. With the full implementation of the global E-navigation strategy, navigation is shifting towards to “intelligent maneuvering, intelligent decision-making, unmanned driving, and wide-scale navigation protection”. The era of unmanned cargo ships has arrived. The technology mentioned above requires high-end scientific theoretical methods for support and highly intelligent navigation technology as a guarantee to achieve unmanned driving. At the same time, maritime tasks are becoming more frequent, so issues such as maritime safety and efficiency of offshore operations have received much attention. In the face of complex time, space constraints and sudden task sets, more situations require multiple ships to work together to maximize efficiency.
In the case of ship path planning, Chang(Chang K Y, Jan G E. Parberry I.2003) designed a novel calculation model, which uses the maze routing algorithm to achieve accurate analysis of the collision avoidance route that may occur in the event of an accident. Ito M( Ito M, Zhang F, Yoshida N.1999) adopted the concept of the security domain to create and simulate the space, and then determine the optimal path adjustment algorithm through four different and meaningful parameters. Yang and Gao (Yang Ke. 2015)( Gao RJ. 2016) implemented a more accurate path planning by establishing a model of the turbulent region of the pier and using hybrid intelligent algorithms under multiple constraints such as steering angle and navigable water boundary. The study provides a scientific basis and theoretical basis for decreasing bridge impact accidents. Based on the characteristics of motion, Wu (Wu Bo, Wen YQ, Xiao CS.2013) explored the autonomous collision avoidance algorithm of unmanned boats when performing tasks in relatively harsh environments. Xiang (Xiang ZQ, Zhai Chao, Du KJ, et al.2015) used the heuristic algorithm to initialize the particles and used the path smoothing optimization method, then he integrated the maritime rules to realize the static and dynamic path planning of the surface unmanned boat.
Liu, Zhen (Jiangsu University of Science and Technology) | Ma, Xiaojian (Jiangsu University of Science and Technology) | Zou, Yucheng (Jiangsu University of Science and Technology) | Wang, Guohui (Jiangsu University of Science and Technology) | Wang, Qingyang (Jiangsu University of Science and Technology)
The Longuet-Higgins wave model is introduced to study the motion response of a moored JIP Spar interaction with freak waves using timedomain method. The wave characteristics of the freak waves are analyzed. The results show that the maximum of the sway motion appears at the back side of spar, while the maximum of the pitch motion appears at the front side. The maximum of the sway motion increases with the initial phase, spectral widths and spectral periods for the focus points located at the front side of the spar. The finding is helpful to the structural design of JIP Spars.
Ocean waves are irregular and nonlinear, the regular wave can not accurately reveal the real wave condition. Freak waves, also known as rogue waves, are large, unexpected and suddenly appearing surface waves that can be extremely dangerous to offshore platforms. In physical oceanography, the significant wave height (SWH or Hs) is defined as the average of the highest one-third (33%) of waves (measured from trough to crest) that occur in a given period. Nowadays, it is usually defined that waves with maximum height larger than 2.2 times of significant wave height value are called freak waves(Lavrenov and Porubov, 2006). A great deal of efforts have been made by experimentally and numerically study to find the generation mechanisms and the physical properties of freak waves (Baldock, 1994; Fochesato, 2007). Also, long time simulation is required to generate the suitable waves if random waves are used. However, focused waves generated by the superposition of component waves with different frequencies can well simulate the largest transient wave in a short time(Liu, 2010). One of the possible mechanisms of freak wave generation may be energy focusing, i.e., the wave energy is concentrated in a small spatial area during a short time, resulting in an abnormally large wave (Kharif, 2003; Yan, 2009; Mori, 2002; Clovanangeli, 2004; Kharif, 2008; Touboul, 2006; Baldock, 1994; Yan, 2010). Two kinds of numerical theories to get freak waves are linear and non-linear theory. Freak waves are usually simulated based on the Longuet-Hinggins model by phase modulation method or linear wave superposition(Liu, 2010; Huang, 2002; Kriebel, 2000; Pei, 2007; Li, 2007; Zhao, 2009). In non-linear theory, freak waves are usually generated by high order spectrum method. In general, the linear method can capture the main characteristics of freak waves to satisfy the basic engineering requirements, which can bypass the complex non-linear theory.
Wang, Ruimin (Ocean University of China) | Jiang, Zhenqiang (Powerchina Huadong Engineering Corporation Limited) | Tian, Zhe (Ocean University of China) | Lu, Hongchao (Ocean University of China) | Wang, Xujie (Ocean University of China) | Liu, Fushun (Ocean University of China)
Dynamic response analysis is becoming an essential part in the stage of structural design and is significant to the safe operation of floating platforms during the service life. In this paper, a method of dynamic response analysis for fully symmetric floating platforms is proposed, which is based on Laplace transform and complex exponential decomposition. Two numerical examples are used to investigate the performance of the proposed method. Compared with the traditional New-mark-β method, the proposed method is more efficient.
With the increase of population and the development of the society, the demand for resources is rising sharply. As a result of the extensive exploitation and consumption of land resources, people turned their attention to the vast ocean which contains abundant resources including petroleum, mineral and marine wind energy. Gradually, the coastal countries of the world have been engaged in the development of marine energy, and the design and use of platforms is an essential part closely related to oil exploitation. As oil production is moving from shallow water to deep-sea, traditional fixed jacket platforms are no longer suitable, which leads to the application of many floating platforms. However, considering the severe environment in deep waters, floating platforms may be destroyed easily, causing significant loss of life and property. Therefore, it is vital to carry out the analysis of dynamic response at the design stage to improve the service performance of floating platforms.
The time domain method can be used to obtain the dynamic response of floating platforms by solving the differential equations of motion in time domain by using a numerical approach. When the time domain method is adopted, all the matrices of the differential equation of motion are required to be known. Oglivie (1964) found that the retardation function can be obtained by the cosine transform when the hydrodynamic parameters are known.
The first order potential theory method can be used to analyze the dynamic response of floating structures depending on assumption of Gaussian process in frequency domain(Newman, 1997; Faltinsen, 1990; Faltinsen, 2005). The well-established theory for Gaussian process is used to obtain the response statistics. The method based on the linear theory suggests that the step of the wave is small, and the response due to the wave excitation is proportional to the wave amplitude (Faltinsen, 2005).