Liu, Lei (Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration) | Lu, Haining (Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration) | Yang, Jianmin (Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration) | Peng, Tao (Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration) | Tian, Xinliang (Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration)
Numerical study of the free-fall of a single sphere at different Reynolds numbers has been conducted with Computational Fluid Dynamics(CFD) method based on the engineering concerns of the dynamics of ore particles in vertical pipes in deep sea mining. A combination of Detached Eddy Simulation (DES) and the six-degree-of-freedom (6-DOF) motion solver was adopted. The sphere motion, the hydrodynamic forces on the sphere and the characteristics of the surrounding flow field were analyzed in detail. Different falling trajectories of the sphere were observed. The surrounding flow field gradually lost the symmetry with the increase of Reynolds number. The results of this article would provide a basic reference for the further investigation on motion of the multiple ore particles.
As the increasing demand of the natural sources in the world, deep sea deposits are considered as the most valuable alternative sources. Deep sea mining applications has been proposed since 1960s (Mero, 1965; Willums and Bradley, 1974; Chung, 1999; Chung, 2005; Chung, 2009). One of the most important issues in deep sea mining is the ore transportation from seafloor. Typically, ore particles can be transported vertically to the support vessels in the upward flow of water in a riser. Significant efforts have been dedicated to the vertical hydraulic transport system in deep sea mining (Engelmann, 1978; Bournaski et al., 2001; Xia et al., 2004; Chung et al., 2007; van Wijk, 2016).
Engelmann (1978) conducted experimental investigation on the hydrodynamic behaviors of ore particles in a vertical tube, and established the empirical equations for designing the hydraulic transport system in deep sea mining. Chung et al. (1998), Chung et al. (2001) and Chung et al. (2007) had a thorough investigation on the vertically upward transport in deep sea mining, including the transportation of spherical bead and non-spherical particles, the effects of particle shape and size, different particle behaviors over a wide range of Reynolds number in both Newtonian fluid and non-Newtonian fluids. Yoon et al. (1999), Yoon et al. (2001) and Yoon et al. (2008) studied the flow characteristics of the solid-liquid two-phase mixture in both vertical tubes and flexible hoses. Bournaski et al. (2001) and Xia et al. (2004) studied the hydraulic gradient caused by the fluid, the coarse particles and the collisions in the vertical pipes. Parenteau (2010) carried out numerical simulations to investigate the transient behaviors and pressure predictions for the risers by using Computational Fluid Dynamics (CFD) methods. Talmon and Rhee (2011) designed a close-loop system in the laboratory to conduct experiments on ore transport over large vertical distances. Sobota et al. (2013) experimentally investigated the velocities of ore particles and carrier liquid to determine the slip velocities for the artificial nodules in the vertical pipe. Vlasak et al. (2014) studied the influence of pipe inclination, solid concentration and mixture velocity on the characteristics of particle-water mixtures by using a pipe loop system. van Wijk (2016) carried out a study into flow assurance of the hydraulic transport system in deep sea mining and proposed a onedimensional flow model to investigate the mechanisms leading to the riser blockage.
The characteristics of flow field and force of a single spherical ore particle in the hydraulic collecting have been investigated. Researches of hydraulic collecting spherical particles in various collecting heights and flow velocities have been carried out with numerical method and testing method. It is verified that the vertical force prediction for single ore particle in collecting condition based on numerical simulation is feasible. The study reveals that the variation of the wake vortex is the dominant factor of force vibration. The drag coefficients of the sphere are defined as empirical equations using dimensionless quantities.
The world's growing economy demands more mineral extracted from the ocean. This demand requires the development of the deep-ocean mining technology. Polymetallic nodules are deposited over the ocean floor at water depth of 4,000~6,000 m. They are mostly spherical or ellipsoidal, with their long-axis length varying from 2 cm to 10 cm and a density of 2,100 kg/m3 (Liu et al., 2014). However, a profitable exploitation of deep-ocean mining is feasible on the premise that there is a nodule collector with maximum collecting capacity of 140 kg of wet nodules per second (Herrouin et al., 1989). As a result, effective collecting of manganese nodules out of sediment upper layer of deep seafloor is not only one of the key processes of the deep-ocean mining technology, but also the beginning of an economic and environmentally acceptable mining operation.
To pick up these nodules, a variety of collecting methods such as hydraulic methods, mechanical methods and hybrid collection methods have been developed. Commercial production must achieve high sweep efficiency (Chung, 1985). A sea test (the OMI Test, 1978) showed that hydraulic methods had a higher collecting efficiency than mechanical methods. It is also found that the hydraulic methods have better adaptability to the variation of seabed height than other methods (Zhao et al., 1995).
Kou, Yufeng (Shanghai Jiao Tong University) | Lu, Haining (CISSE - Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration) | Yin, Hanjun (Shanghai Jiao Tong University) | Cai, Yuanlang (CISSE - Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration)
Vortex Induced Motion (VIM) of Tension Leg Platform (TLP) can cause fatigue stresses on the risers and tendons and must be taken into account in design. The VIM response of a TLP hull with 4 round columns is investigated by tow model test, which was conducted by State Key Laboratory of Ocean Engineering in Shanghai Jiao Tong University (SKLOE, SJTU) from August to September of 2015. A 1:50 TLP hull model is built accurately in geometry, including the appurtenances such as anodes, tendon porches, fenders, supports, caissons and other pipe-like structures running on the hull. However, the topsides are neglected and replaced by an aluminum deck which is strong enough to support the air bearing system and horizontal mooring system. The air bearing system composed of six air bearings and a smooth flat-plate is applied to simulate the vertical load of tendons and TTRs, which allows matching the same mass ratio with prototype in model test. The horizontal restoring force and moment of initial tendon and TTR system are modeled by 4-spring horizontal mooring system mounted above water, ensuring the correct natural periods for surge, sway and yaw motion of the TLP. The current is simulated by carriage speed in towing tank. Screening tests for 16 current headings with the interval of 22.50 show different VIM response in every heading. The comparatively larger VIM amplitude in transverse direction, about half of column diameter, occurs in 900 and 337.50 current headings. The lock-in range of reduced velocity between 6 and 8 is also observed in 900 and 337.50 current headings.
Due to the increasing draft, VIM of multi-column floating platforms under sea current may become notable, and cause fatigue stresses on the risers and mooring systems. The interference among columns makes more complex VIM phenomenon than Spars and mono-columns. Liu et al (2015a) experimentally investigated the flow and force on fixed four-square-cylinder array, revealed that the downstream cylinders experience smaller mean drag force but higher fluctuating force than the upstream ones, and that the interaction was highly related to current heading and spacing ratio. Gonçalves et al (2012a, 2012b, 2013) studied a lot on VIM of Semi-submersible with four square columns by tow model test. It was found that not only VIM in transverse direction but also considerable yaw motion oscillation occurred. The largest transverse amplitudes can reach 40% of column width for 300 and 450 incidences. However, the maximum yaw motions were found about 4.50 for 00 incidence. Comparatively, the largest in-line motions were no more than 15% of column width. It was also found that the hull appurtenances had some influence on the VIM response of Semi-submersible, especially the pipes located at columns. The external damping was proven another critical factor to determine the VIM performance, 20% extra damping can decrease 50% of VIM amplitude for some specific response frequencies. Gonçalves et al (2015) also discovered the different behavior of round and square-rounded columns in terms of transverse and yaw response for different incidence angles. Bai et al (2013) studied the VIM of new type Deep Draft Semi-submersible (DDS) with four rectangular columns by tow model test and 2D numerical simulation. The lock-in range of reduced velocity between 6 and 8 was obtained for 1350 incidence. Because of over-simplified model, the numerical simulation predicted broader lock-in range and larger response amplitude. Actually, even the 3D CFD method is hard to accurately predict the VIM performance of multi-column floaters with consideration of the appendages, because of the great difference in size between the hull and attached structures. The model test is the preferred solution to investigate the VIM response of a new platform. The effect of current velocity and heading, hull appurtenance, and external damping should be taken into account in model test, and the transverse and yaw motion must be mainly focused on.
Guo, Xiaoxian (Shanghai Jiao Tong University) | Lu, Haining (Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration(CISSE),) | Yang, Jianmin (Shanghai Jiao Tong University) | Peng, Tao (Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration(CISSE),)
As the exploration of offshore oil and gas resources are moving into larger depth, many mobile drillships have been widely applied to the offshore drilling operation, thanks to the good mobility, large variable deck loads and storage volumes. Large motion responses of the drillship and the water motions inside the moonpool were reported, which introduced safety concerns. In this paper, both numerical simulations and physical experiments have been carried out to investigate the hydrodynamic performances of a newly designed deep-water drillship, and the resonant water motions inside the moonpool with submerged recess structure. The three modes of water motions coexist in the moonpool even when there is only one external excitation source provided by a regular wave train. The submerged recess structure clearly introduces the obstacle effects leading to exacerbation of the water motion inside the moonpool.
Moonpools are designed as vertical openings through the decks and the hull structures to support the required underwater operations on marine vessels and offshore platforms. The water inside moonpool is required to provide a moderate environment for operation rather than being exposed to the violent metocean conditions. However large water motions may occur inside the moonpool under some resonant conditions, including the vertical piston motions, and the longitudinal sloshing motions. The effects on 6 degrees of freedom (DOF) RAOs of the drillship which are caused by moonpool also need to be investigated. Recently, the recess type moonpool appears in drillship’s moonpool design, which has advantage on drilling equipment arrangement. The impacts introduced by the recess type structure on relative water motions inside moonpool need to be clarified.
Fukuda (1974) carried out a set of physical experiments to investigate the water behavior inside the moonpool and the effects on the vessel motions in a towing tank. He obtained an empirical formulation which could be used to identify the resonant frequency of the water motions. A mathematical model was developed later to describe the water behavior inside moonpool , and also corresponding model tests with respect to the damping mechanisms and motion behavior were conducted (Aalbers, 1984). Molin (2001) treated this problem in the framework of linear potential theory under the assumption of a infinite length and beam of a barge equipped with a moonpool, and brought out the oscillation natural frequency formulation. It was believed that the water motions response inside the moonpool is overestimated with respect to the experimental results without considering the fluid viscosity (Kristiansen and Faltinsen, 2008). Kristiansen and Faltinsen (2008) set up a fully nonlinear numerical wave tank coupled with an inviscid vortex tracking method to investigate the impacts caused by fluid viscosity and the nonlinear effects that associate with free surface. More recently, computational fluid dynamics (CFD) has been utilized to study the sloshing phenomenon. Zhang (2012) applied Moving Particle Semi-Implicit (MPS) method to study the sloshing phenomenon. Large impact pressure was observed, and it was shown a periodic impact had two pressure peaks in each period.
Xiong, Lingzhi (Shanghai Jiao Tong University) | Lu, Haining (Shanghai Jiao Tong University) | Yang, Jianming (Shanghai Jiao Tong University) | Zhang, Wei (Offshore Oil Engineering Co., Ltd, Engineering Company) | Yang, Guang (Offshore Oil Engineering Co., Ltd, Engineering Company)
Floating vessels moored in shallow water are at risk of possible bottom grounding and collision between the vessel and the subsea pipelines. Their dynamic responses are of great concern in offshore engineering. In this study, experiments were conducted to investigate the motion response of a large floatover barge moored in ultra-shallow water. White noise wave tests with five different incident angles were carried out in four different water depths. Shallow water effects were observed in the experiment. The motion characteristics of the moored barge in shallow water were also clarified in the analysis. The barge motions in the horizontal plane and the mooring line tensions increase with the decrease of the water depth, while the heave and pitch motions reduce. Results obtained from this study were provided to support the floatover installation operation.
Liu, Lei (Shanghai Jiao Tong University) | Yuan, Hongtao (Shanghai Waigaoqiao Shipbuilding Co., Ltd.) | Yang, Jianmin (Shanghai Jiao Tong University) | Tian, Xinliang (Shanghai Jiao Tong University) | Li, Chunhui (Shanghai Waigaoqiao Shipbuilding Co., Ltd.) | Lu, Haining (Shanghai Jiao Tong University)
Offshore platforms under construction are normally moored on the dock during the outfitting stage. The safety of the platforms must be guaranteed during the whole stage of outfitting which may last for several months. This paper presents a wave basin model test study of a jackup moored on the dock in Shanghai Waigaoqiao shipyard in China. In the model test, the jackup and the sea states were scaled based on the Froude similarity law. The dynami c responses of the system, including the six degrees of freedom (6DOF) moti ons of the jackup and the barge, tensions on the mooring lines and the collision forces on the fenders, were measured in various sea states. Meanwhile, the current-and-wind-only sea states were simula ted and the dynamic responses were measured for comparison with those in the wave conditions. The mooring line tensions were found to excee d the strength of the lines in offshore wind conditions. And this phenomenon may be attributed to the decrease of the jackup's yaw m otion stiffness. In addition, several suggestions are proposed for optimizing the mooring system performance.
The seakeeping of the floatover barge in waves is extremely significant to the design of installation and transportation. The T-shaped barge is a new concept with some unique characteristics dissimilar from conventional barges. In this paper, numerical analyses in frequency domain and time domain were carried out for transportation configuration. The frequency domain analysis used 3D potential flow code WAMIT, and obtained motion response amplitude depending on frequency and other hydrodynamic parameters. In addition, the time domain analysis was also performed using self-made program with FORTRAN code. Based on the convolution theory, a 6-dof time domain equation of motion was built and solved by 4-order Runge-Kutta method, and instantaneous hydrostatic restoring force was calculated to take large amplitude roll motion into consideration. Corresponding model tests were also carried out in the ocean basin of Shanghai Jiao Tong University. Comparison between numerical and experimental results shows that the response amplitude operators agree quite well and the effect of viscous roll damping is obvious. The time domain analysis program was validated by experiment comparing statistic and time series. Furthermore, sensitivity analysis on wave parameters was also executed to find the worst condition.
Li, Jun (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Li, Xin (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Chen, Gang (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Lu, Haining (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University)
Lu, Haining (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Xiao, Longfei (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Li, Xin (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Xie, Wenhui (China National Offshore Oil Corp. Research Center)
Zhang, Hui (State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University) | Xiao, Longfei (State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University) | Yang, Lijun (State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University) | Lu, Haining (State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University)