Article presents the methodology for operational research on the polymetallic nodules mining value chain and the assessment of crucial factors influencing its feasibility. Value chain has been analyzed and boundary assumptions having a substantial influence on the decision making process were identified. Geological, technical, economic, environmental and legislative components are related within the unambiguous framework of their functional interactions. Several decision-making tools are presented and the system of SWOT analysis was applied to identify positive and negative aspects. It should be understood, that project conditions are unique for particular evaluated mineral deposit and evaluation is linked to a particular time period.
The deep seabed became one of the most potentially rewarding frontiers challenging mankind in minerals exploration. Mineral resources found in deep seabed area represent potential for enormous contribution to the world resource base and their exploitation can affect world metal markets. In 2013, International Seabed Authority (ISA) commenced the development of regulations to govern the future exploitation of seabed minerals, starting with polymetallic nodules (PN).
Deep sea mining (DSM) activities represent value chain similar to the structure of activities performed in land-based mining. However, there are no deep seabed mining activities yet on commercial scale (excluding oil and gas mining, where today's technology allows to extract gas and oil from water depths of almost 3000 meters). Existing offshore mining operations are performed in shallow waters up to 500 meters depth (tin, diamonds, phosphate rocks).
Before DSM commencement it is necessary to investigate the potential sequence of steps for the purpose of developing legal frameworks for future exploitation and business models creation. Value chain analysis can be applied to study how work selection, planning, scheduling and execution can drive different business approaches to close-to-optimal solutions, when considered as elements of a chain. Those solutions can be related to the available options in scope of technical means, legal frameworks, taxation schemes, CSR policies and building of an overall enterprise model. This approach could also offer an important alternative for the evaluation of enterprises in the absence of real-life data from operations involving direct competition, as is the case of deep seabed mining (Abramowski, 2016).
The ringing of a two dimensional (2D) floating barge under focused waves has been investigated based on the potential theory. A fully nonlinear numerical wave tank is developed using a higher-order boundary element method (BEM) including a mixed Eulerian-Lagrangian technique. Simulations are made to study focused waves interaction with a floating barge. The focus is on the roll motion principally excited by higher harmonic wave loads. The effect of wave amplitude and wave frequency on the ringing phenomenon is investigated.
Roll motion has been attracting considerable attention during these years because it is the most critical motion leading to ship or platform capsizing in comparison with other five degrees of freedom motion. The nonlinear roll motion of a 2-D rectangular barge within the framework of potential flow theory has been investigated by Cointe & Geyer (1990) and Koo & Kim (2004). Chen et al. (2016) and Li & Teng (2015) presented the roll motion of a 2-D rectangular barge and twin rectangular barges based on OpenFOAM respectively. A barge is requested to be steady or with limited motion amplitude when handling cargos or performing specific missions. The large-amplitude motion due to resonance will occur when the encounter wave frequency is close to the natural frequency of the barge, which has been investigated extensively by previous studies based on linear theory.
However, the nonlinear wave force becomes remarkable when wave amplitude increases. The resonance caused by higher order components has always been ignored. It was observed in model tests and prototype experiments that tension leg platforms (TLPs) and gravity-based structures (GBS) experienced sudden bursts of highly amplified resonant behavior in irregular waves (Report 1993; Chaplin et al., 1997; Scolan et al., 1997). This phenomenon is called as the ‘ringing’, which is closely related to large and steep waves interacting with the structure. This ringing of a structure typically occurs when its natural frequency is about three to five times of the incoming dominant wave frequency and is most likely to be excited by the third harmonic wave force. Typically when a transient wave passes through the structure, it will continue to oscillate over a period of time at its high natural frequency even the wave excitation has diminished. This oscillation can be persistent when the damping level is low. Understanding of such ringing behaviour is important because of the high level of stress generated. So far, most adopted numerical method is based on second-order theory, which is valid only for second-order problem with moderate wave amplitude. Ringing is due to third-order or higher order harmonic components of the nonlinear wave force, a fully nonlinear numerical method is needed. Zhou & Wu (2015) developed three-dimensional fully nonlinear numeical model to simulate the resonance of a TLP excited by the third order wave force component in regular wave. Since irregular wave is believed to be most likely to generate ringing phenomena but not well understood, we propose a fully nonlinear method to study the irregular wave case in this paper.
The phase-averaged wave action equation (WAE) is extended to include the effect of submerged porous media in this paper. The wave dissipation coefficient for submerged permeable media is incorporated in the WAE of wind wave model. The coefficient of the turbulent flow resistance is obtained based on Lan et al. (2016). An estimation method for the characteristic parameter of turbulent frictional resistance in permeable media is proposed in this study. Reasonable comparisons with experiments and numerical results show the present model can be applied to propagating waves over porous beds, reefs and vegetation.
Wave model simulation is one of the main ways for the marine and coastal engineering practitioners to obtain the design wave conditions. Wave generation, transformation and dissipation are influenced by many complex physical mechanisms (wind forcing, wave-currents and wave-wave interactions, shoaling, breaking, bottom friction, porous flow inside the seabed and through reefs, vegetation etc.). The combined effect of the wave refraction and diffraction on the wave transformation can be accounted for by using mild-slope equation (MSE) approaches, Boussinesq-type equation (BE) models or wind wave models (WWM). The MSE and BE are phase-resolving wave models to account for nearshore wave processes (Rojanakamthorn et al., 1989; Gobbi et al., 2000; Behera et al., 2015; Su et al., 2015). On the other hand, the phase-averaged models are used for the simulation of the variation of wave spectra for random short-crested waves in large-scale oceanic deep water and small-scale shallow water regions. Typical examples of commonly used models are WAM (WAMDI Group, 1988), SWAN (Booij et al., 1999a, 1999b), STWAVE (Smith et al. 2001), TOMOWAE (Marcos, 2003) and WWM (Hsu et al. 2005; Liau et al., 2011; Lan et al., 2015, 2016). The phase-averaged wave action balance equation was formulated by Holthuijsen et al. (2003) and Liau et al. (2011) to include wave refraction- and diffraction-induced directional turning rate of the components. The processes of wave generation, dissipation and nonlinear wave-wave interactions are well accounted for in these models based on WAE. The main effects taken into account include wind-wave generation (Komen et al., 1984; WAMDI Group, 1988), nonlinear wave-wave interactions (Hasselmann et al., 1985; Eldeberky and Battjes, 1995; Eldeberky, 1996), whitecapping (Hasselmann, 1974; Komen et al, 1984), bottom friction (Young and Gorman, 1995), and wave breaking (Battjes and Stive, 1985; Eldeberky and Battjes, 1995). Toledo et al. (2012) constructed an extended WAE in terms of linear wave theory of MSE that has an improved behavior for rapid spatial bottom changes as well as ambient current changes. Lan et al. (2015) proposed a theory of WAE for spectral evolution over porous bottom (e.g. sand beds) in the presence of currents, by taking into account the energy dissipation effect induced by porous bottom media. This model was validated through comparisons with the experimental data for wave propagation over porous beds with low permeability. Lan et al. (2016) further proposed a extended WAE with the effect of submerged permeable reefs. However, in terms of the effect of high permeability, they did not make an appropriate method for estimating turbulent friction parameter but followed the past relevant literatures.
This paper presents a numerical investigation on the significance of the role of the compressibility of the fluids associated with water entry problems using a multi-phase solver OpenFOAM, in which the water and air are treated as either compressible (compressible solver) or incompressible (incompressible solver). The models are validated by using the experimental data of a 3D plate dropping case, whereas the detailed investigations focus on 2D wedge dropping with different dead-rise angles and/or tilting angles. The effects of the compressibility are examined by comparing the results of the compressible solver and that of the incompressible solver. It is concluded that the free surface profiles during the impact are significantly influenced by the compressibility of the fluids, leading to different patterns of impacts (convective motion between fluids and dropping wedge); even in a case with large dead-rise angle, the incompressible solver may lead to incorrect predictions on the peak pressure and the force acting on the wedge surface.
Large impulsive pressure and slamming forces may lead to the damage of the offshore structure, and are of interest for the engineering purposes. Typical examples include breaking wave impacts on quay walls/breakwaters, slamming of the ship bow during extreme weather condition. The experimental (e.g. Miyamoto and Tanizawa, 1985; MOERI, 2013; Mai et al, 2015), numerical or analytical studies (either based on the potential theory, e.g. Zhao and Faltinsen, 1993; Zhao et al. 1996, or viscous flow theories such as Gao et al., 2012; Oger et al., 2007; Skillen et al., 2013) on the water entry problems, initiated by Von Karman (1929) and Wagner (1932), provides useful references for reliably predicting the slamming loads and exploring associated small-scale physics, such as the air trapping, spray and extreme free surface deformation. Significant advances have been recently made on computational fluid dynamics (CFD) modelling on such problems. Both single-phase (e.g. Gao et al., 2012; Oger et al., 2007; Skillen et al., 2013) and multiphase models (Kleefsman et al 2005; Sussman et al, 1994; Soulhal et al, 2014) have been attempted, and a promising accuracy was demonstrated on predicting slamming loads.
A suitable mooring system significantly influences the motion response of the Very Large Floating Structure (VLFS). The motion response of a single module (SMOD) of a semi-submersible VLFS with tension leg mooring system near island was investigated by numerical study. A model test was also conducted to validate the results of time domain simulation. The numerical calculation coincides the experimental results well. It has been demonstrated that the heave and roll motion decrease as the water gets shallow, while the motions increase in extremely low frequency.
The concept of very large floating structure (VLFS) such as mat-likes and semi-submersibles has attracted many researchers’ interest in the last few decades (Wang and Wang, 2015; Lamas-Pardo et al., 2015). The mat-like VLFS is a structure similar to pontoon-like ship hull, while the semi-submersible VLFS is similar to the semi-submersible platform, consisting of several modules interconnected. The mat-like VLFS is designed to located near the shore using the breakwaters to reduce the wave impacts. Because of the small waterline-area and good mobility, the semi-submersible VLFS is more suitable for deep sea.
It's important to estimate the hydroelastic of the VLFS accurately and effectively, especially for mat-like VLFS. Mode-expansion method (Kim and Ertekin, 1998; Ohmatsu, 2000) and mesh method (Yago and Endo, 1996; Motohiko et al., 1999) is two representative methods for calculating the mat-like VLFS's hydroelastic response. The B-spline Galerkin scheme developed by Kashiwagi (Kashiwagi, 1998a) is a typical mode-expansion method. It uses B-spline function to represent the pressure and Gakerkin scheme is applied for meeting the boundary conditions. This method reduces computational time well and the accuracy of the results is acceptable for practical use. The mesh method uses the boundary element method (BEM) and finite element method (FEM) to acquire the hydroelastic response of mat-like VLFS. This method consumes huge computational time and needs quantities of computer memory.
This paper reports on an investigation of the feasibility of decommissioning offshore tubular piles with vibration. A series of 1g model pile tests using a scaled vibration source and a 400mm long open-ended steel pile were conducted in loose and dense dry sand. Under forced vibration, the pull-out load of the pile was reduced by 36% in dense sand and to the self-weight of the pile in loose sand. Back-calculation reveals a correlation between the lower tensile capacity of the pile and reduced interface friction angles during the application of vibration indicating that such a method may be valuable in future decommissioning projects.
Decommissioning the infrastructure used in the production of oil and gas is fast becoming an important field of activity and research as some of the World's most prolific oil and gas fields approach the limit of economic production. The North Sea, with infrastructure in place since 1967 (Oil and Gas Authority, 2016) is one such area, with many installations approaching or exceeding their 25-year design life (Stacey et al., 2008).
The decommissioning of these structures is regulated by UK law and by the OSPAR Decision 98/3 on the Disposal of Disused Offshore Installations (OSPAR Commission, 1998). Currently, the removal of offshore piles is not required under legislation. Instead, the piles are cut below the seabed, at a distance deemed appropriate in preventing any remaining pile becoming uncovered (DECC, 2013). Anecdotally, this distance is around three metres below the natural seabed, in line with current well abandonment procedures. Severance of the piles is normally achieved by abrasive waterjets or mechanical cutting techniques (Orszulik, 2016). This treatment of piles is currently seen as the most beneficial approach regarding cost, technical ability and environmental impact (Ekins et al., 2006), although this may not always be the case and pile extraction may become necessary or prove to be beneficial in some instances where future structures are designed to be fully recoverable.
You, Hwalong (Korea Advanced Institute of Science and Technology) | Ahn, Junkeon (Korea Advanced Institute of Science and Technology) | Jo, Choonghee (Korea Advanced Institute of Science and Technology) | Bergan, Pål G. (Korea Advanced Institute of Science and Technology) | Chang, Daejun (Korea Advanced Institute of Science and Technology)
This paper proposed a novel concept of a prismatic pressure vessel with internal lattice structures, so called the Lattice Pressure Vessel (LPV). The design principle of the LPV was described, considering compliance with the international codes of IGC and IGF. A hydrostatic test was conducted to measure the strain under pressure load and verified the design principle of the LPV. Several analyses conducted proved the structural safety of the LPV against all the conceivable loads including pressure, sloshing, thermal stress, fatigue, etc. Since the internal loadbearing lattice structure reduced the fluid dynamic load caused by ship motion, the LPV showed excellent performance in terms of structural safety including fatigue and crack propagation. Other important characteristics of the LPV were scalability and space fitness. Unlike conventional cylindrical pressure vessels, the thickness of structural components of the LPV remained invariant with size and the scale-up was achieved by increasing the number of the repeated units, meaning that the LPV could be scaled up to a significantly large capacity. Several designs of the LPV demonstrated that the LPV could fit boxshaped spaces perfectly and even spaces that was far from rectangular shape. All these designs resulted in far better volume efficiency than conventional cylinder-based tank solutions. Further, various practical uses of the LPV in LNG field were presented: onshore and offshore storage tanks, cargo tanks for gas carrier, and fuel tanks for ships.
Liquefied Natural Gas (LNG) is promising fossil fuel thanks to its environmental friendly characteristics. In addition to its land-based use, LNG finds its use as marine fuel as the Marine Environment Protection Committee (MEPC) of the International Maritime Organization (IMO)'s decision that the 0.5 % global sulphur cap should be implemented from 2020 (IMO, 2016). The LNG solution is free from sulphur and particulate matters with low carbon content. However, there are several challenges for LNG to be fully accepted as marine fuel. First, the storage tank should take as small space as possible with high volume efficiency and flexible space fitness. Second, heat ingress into the tank causes boil-off gas (BOG) generation that pressurizes the tank unless removed from the tank.
Metallic strips flexible pipe has been favored in the offshore pipelines engineering for its good corrosion resistance, high strength, easy installation etc. This new composite pipe can be regarded as promising alternative for submarine pipelines. In this paper, the cross-sectional design process for this specific kind of pipe is illustrated. Three formulas for calculating the individual strength capacities of the pipe when subjected to internal pressure, external pressure and pure bending are presented for initial screening assessment. And then a case study for an 8 inch metallic strip flexible pipe based on a shallow water application is carried out. Several FE models are established by using commercial software ABAQUS to verify the designed cross section. The two methods presented could be used to assess the structural performance of the pipe in the early design phase, which might be interesting to the manufacture engineers.
Composite pipes are extensively used in the offshore oil/gas industries for decades. Typical composite pipe, take reinforced thermoplastic pipe (RTP) as example, is favored in engineering for its good corrosion resistance, high strength, high flow rates and etc. Recently, metallic strips flexible pipe is emerging in the offshore application. It has the same advantages as RTP. Furthermore, it exhibits better on-bottom stability due to its relatively greater weight and the production costs are quite low. Fig.1 shows the typical configuration of metallic strips flexible pipe. Generally, it can be divided into three components: (1) an inner extruded thermoplastic tube that seals the transported products. (2) metallic strips reinforced layers with winding structure that provide the strength against internal pressure and tension. (3) an outer PE sheath that isolates the underlying layers of the pipe from external environments. The winding angle and the geometry of the metallic strips can be selected based on the design pressure and the corresponding functional requirements. During the metallic strips flexible pipe's installation and service periods, it will inevitably carry operational and environmental loads such as external pressure, internal pressure, bending, tension, torsion and etc. The requirements of these capacities of metallic strips flexible pipe have a significant impact on the cross-sectional design. The derivations of the individual capacities for the metallic strips flexible pipe are illustrated step by step in this paper, which may be of interest to manufacturer engineers.
Hao, Hongbin (College of Shipbuilding Engineering, Harbin Engineering University) | Ma, Qingwei (School of Engineering and Mathematical Sciences, City University London, College of Shipbuilding Engineering, Harbin Engineering University) | Liao, Kangping (College of Shipbuilding Engineering, Harbin Engineering University) | Zheng, Xing (College of Shipbuilding Engineering, Harbin Engineering University)
Wave propulsion device (WPD) is a device that can directly absorb wave energy and convert it into forward thrust by using an oscillating hydrofoil. The concept of WPD has been proposed for many years and has been proved to be feasible as the dominating or assistant propulsion of ships. The main problem of such device is its low efficiency. A new idea to improve its efficiency is investigated in this paper by using small floaters to adjust the attack angle of the hydrofoil, which is halfactive and named as floater-adjusted wave propulsion device (FAWPD). The experimental tests show that the FAWPD can generate significantly more thrust compared with conventional designs.
New technologies have been proposed widely in industrial practices in order to promote green energy and reduce emission. For example, green ship technologies have received more and more attention and the EEDI (Energy Efficiency Design Index) becomes an international convention in 2011 and takes into effect in 2013. It is enforced since 2015 and the ships failed to meet the EEDI standard will not be allowed by classification society or IMO. Thus developing new green ship technologies can be very helpful in the concept or initial design.
WPD is one of the green ship technologies, which can directly absorb wave energy and convert it into forward thrust. Generally speaking, the resistance of ship will increase when it navigates in waves, which leads to a speed loss and needs more power, meanwhile the responses of the ship due to waves will become violent.
However, some sea animals (i.e. whale and dolphin) can utilize the wave energy to swim, which was found firstly in the middle of the 18th century by an English whale catcher. They found that the floating dead whale swims faster than the ship in waves. This inspired many researchers investigate how to utilize wave energy to drive ships.
Wave impact load is of particular concern to ships and offshore structures, especially when they serve in rough seas. Extreme wave impact is catastrophic and may lead to structural failure, crew injuries and economic loss. Therefore, it is very important to determine wave impact load accurately in the design of ships and offshore structures. In this paper, we present the method that we use to measure wave impact force. To validate the reliability of this method, we conducted a well- controlled wedge drop test, and compared the experimental results with CFD simulations and the simplified analytical solution (the Wagner solution). The design of the device in combination with force transducers, the wedge drop test, the analysis of the experimental data, and the comparison with numerical and analytical solutions are discussed in detail. In addition, some shortcomings and corresponding improvements are also presented. It is shown that the device can be used to measure wave impact force over a certain area well.
Wave impact can cause very large and localized force on ships and offshore structures, which may lead to structural failure. Buchner and Voogt (2004) presented two FPSOs experiencing wave impact damage. The accurate determination of wave impact load is very important for the structural design of both deep-water offshore structures and shallow-water coastal structures. Wave impact is a strongly nonlinear transient two phase problem, which is hardly to obtain an analytical solution. It was noted that (Chan and Melville, 1988) air will be trapped when wave impacts structures, which introduces randomness to wave impact load, increasing the difficulty to predict wave impact load theoretically.
The characteristics of wave impact or slamming load are often studied by the problem of wedge entry into water. For the wedge water entry problem, Von Karman (1929) firstly proposed a simplified solution by neglecting the local uprise of the water. Taking into the local uprise of the water, Wagner (1932) developed the Wagner solution, which assumes that the wedge drops into water with constant velocity. In this paper, the Wagner method was modified to be applicable for time- varying velocity. There are a lot of other analytical works for the water entry problem and most of them are based on the potential assumption. Therefore, with these methods, the effect of viscidity and air cannot be considered.