Zemlyak, Vitaliy Leonidovich (Sholom-Aleichem Priamursky State University) | Kozin, Victor Mikhailovich (Institute of Machining and Metallurgy FEB RAS) | Baurin, Nikita Olegovich (Sholom-Aleichem Priamursky State University) | Ipatov, Konstantin Igorevich (Sholom-Aleichem Priamursky State University)
The given article is devoted to the experimental research on the topic of deformed state of hummocked ice caused by motion of a submarine vessel near its surface. Experiments were carried out in the ice basin. The model of ice cover was made by natural freezing on up to the required depth. Ridge ice hummocks were modeled by freezing stripes of ice of the given thickness into the ice field. Assessment of icebreaking capacity of flexural-gravity waves with using the criterion of ice failure is performed. Modes of motion at which ice breaking was most intensive are detected.
Effect of wind and currents in the ice fields can cause the compression processes leading to hummocks. When necessary, a submarine vessel may appear above water in case of emergency or when performing various motions in hummocked ice. In this case it is possible to use hydrodynamic loads.
It is known that motion of a submarine vessels (SV) under ice cover causes the appearance of a system of flexural-gravity waves (FGW), whose amplitude reaches its maximum when the SV velocity exceeds the so-called crest velocity corresponding to the most intensive wave formation during motion in ice-free water, then in the ice cover progressive FGW will develop with crack formation, or will cause complete ice failure with minimum effort.
Kheisin (1967) studied the plane steady-state problem of the motion of vortex under a layer of broken ice. Bukatov and Zharkov (1995) studied the steady motion of a point source of mass under a floating elastic plate and analyzed the effect of the velocity of motion, the depth of the source and the thickness of the plate on its deflection. In Sturova's work (2012) the solution of the linear steady problem of the flow of nonviscous liquid around a sphere under the ice cover, broken ice, a membrane, and also under the free surface is performed. Korobkin (2012) considers the nonlinear problem of non-stationary waves caused by the submerged elliptic cylinder, moving under the ice cover. With the help of FGW in the ice cover caused by a SV, partial or complete ice failure can be achieved, which will allow submarine vessels emerge in thicker ice as compared wth the traditional method of surfacing (Kozin et al, 2005).
It is general consensus that set-down should be considered in airgap assessment for a deep-water Tension Leg Platform (TLP). The set-down is caused by compliant modes in horizontal planes (surge, sway and yaw) which has profound implications in various aspects of TLP design. During the design of a TLP, the tendons are usually treated as a steel cable, and the Jain's stiffness matrix is employed in the calculation of tendon stiffness. In this study, a new methodology of statistics is proposed to calculate the probability of slamming by taking into account of the set-down for the analysis of airgap. The probability of the slamming occurrence is evaluated based on the reduced air-gap caused by set-down. By comparing the results with that of the conventional TLP airgap design assessment, the impact on airgap design is further examined.
Tension leg platform (TLP) is a kind of compliant system whose mooring system is pre-tensioned attached to the seabed. The tendons are stretched tight by the excess buoyancy of the platform. For this reason, the heave, roll and pitch motions are effectively restricted. The horizontal motions whose natural periods are much longer than that of the vertical motions often cause a phenomenon called set-down occurring to TLP. It is crucial that set-down should be taken into account in airgap assessment.
Dynamic analysis is fundamental to the design of TLP. In early stage of TLP dynamic analysis, tendons are treated as a kind of massless springs and the dynamic analysis of the TLP is carried out as uncoupled analysis. One of the challenging issues of TLP dynamic analysis is the combination of wave frequency, low frequency and high frequency coexisting in TLP response. The high frequency effect is usually only considered in vertical plane motions.
The term of stiffness which contain restoring stiffness from tendons and hydrostatic stiffness in the equation of TLP dynamics is usually treated as a static stiffness.
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).
Ship-mounted cranes are widely used in transportation and installation of heavy loads to the seabed. To minimize adverse effect caused by harsh environment, the cranes are equipped with compensation equipment for the motion. When we design the compensation equipment for the cranes, anti-sway control algorithms in the equipment should be included. To test the feasibility of the algorithms effectively at the early design stage, the hardware-in-the-loop simulation (HILS) framework can be used as one of alternatives. The proposed method consists of several components: virtual mechanical system based on multibody system dynamics, virtual actuator and sensor, and hardware controller. In this study, it is applied to an example of the anti-sway control of the crane on an offshore supply vessel (OSV) during the installation operation of a subsea equipment using the proposed HILS framework.
Cranes on the offshore supply vessel are used for offshore construction including transportation and installation heavy loads in a marine environment. During the transfer operations, the swing problem is inevitable, in addition, harsh and changeable sea condition can be regarded as a persistent external disturbance and be further intensified the swing motion. Meanwhile, waves induce the motion of the OSV. The OSV induces similar effects on the subsea equipment suspended by the OSV. For the safety, the transfer operation by the crane should be paused in harsh environment conditions to avoid collisions between the load and hull of the vessel which was attributed to insufficient capability of the controller. Therefore, in order to improve safety and increase transportation efficiency, controller with suitable anti-sway control algorithm should be developed, which make it possible to reduce residual swing motion significantly by controlling the angles of the knuckle boom. When we design the compensation system for the cranes, suitable control algorithm should be included. For this reasons, some literatures (Xu, et al., 2012, Gjelstenli, 2012, Chu et al., 2015) are recently focused on the control of cranes. In this study, we considered anti-sway control for the crane on the OSV, which is shown in Fig. 1. Since the controller performance should be evaluated in advance of operation, the Hardware-In-the-Loop Simulation concept used as an effective method to test the controller. Therefore, this study proposes the HILS framework which consists of several components: virtual mechanical system based on multibody system dynamics, virtual actuator, virtual sensor, and hardware controller. At first, the configuration of the simulation framework aforementioned was introduced. Then, the application of the simulation for anti-sway of the OSV crane was presented. Finally, conclusion and future work discussion were summarized in the remainder of this paper.
Helium is one of the best shielding gases or their partial components to protect and boost automated welding processes. The right shielding gas composition creates many advantages. Helium, however, has been considered expensive and difficult to get. This study evaluates helium availability in both short and long term, its cost structure, recovery and recycle options, as well as its positive effects on welding processes with different materials and varying gas blends. The study consists of a review of scientific articles, interviews with specialists in different companies, a review of presentations and experiments.
The shielding gas and its composition have a remarkable significance to the end result in the welding process. Especially in challenging and demanding fabrication projects and processes the right shielding gas can offer great advantages to the quality, cost and lead time. The storage industry of liquefied natural gas (LNG) and shipbuilding use both highly alloyed austenitic and non-austenitic steels. Normally the projects consume huge amounts of materials and lead times are tight. Helium itself or its mixtures with argon, carbon dioxide, hydrogen, or oxygen offer improvements and speed up automated welding processes. Helium has been underrated mainly because of the uncertainties in its availability and price.
The availability of helium has been risky and the output of many of the earlier main sources has been declining. New sources have recently been found and many projects have been realised, thanks to which the availability is stabilising and increasing. Since 2000, helium recovery and recycle systems have been developed. The first systems were built for pure helium applications, e.g. in magnetic resonance imaging (MRI) research centres as university cold labs and in big hospitals using MRI. Impure helium is collected from exhaust pipes and compressed into high-pressure cylinders, bundles, or cylinder containers, which are delivered to the liquefaction plant, where the impurities are removed and the helium molecules are liquefied and redelivered to customers. Some studies have also been conducted to build up purification units to purify gaseous helium for reuse in welding applications.
In this paper, we describe how to use multi-variable decision analysis to facilitate offshore oil and gas platform decommissioning. We implemented decision analysis as a software tool (PLATFORM) to clarify and evaluate decommissioning alternatives against a comprehensive set of objectives, including both market and non-market values. Decommissioning options selected for in-depth analysis were complete platform removal and partial removal to 85 feet below the water line, with the remaining structure converted to an artificial reef. PLATFORM performed key analyses of the impacts of each option (e.g., on costs, fishery production, air emissions). The analysis found a near-consensus of stakeholders in support of partial removal and a “rigs-to-reefs” program.
Defining the most practicable and appropriate way to decommission offshore oil and gas platforms requires consideration of various critical factors and a range of alternatives, including complete removal and partial removal with artificial reefing. Conventional cost-benefit analysis often neglects important complexities inherent in platform decommissioning. An effective decommissioning process must adequately address aspects that are inherently difficult to monetize, such as the production of greenhouse gasses, gains and/or losses of ecological services, and regulatory compliance.
Differences in stakeholder perspectives regarding the value and importance of non-market factors can result in distrust when choices are considered in purely financial terms. The resulting tensions between stakeholders about the proper basis for evaluating options are all too common in negotiations at the nexus of science and public policy (Fowler et al. 2014).
We demonstrate how multi-attribute decision analysis (MADA), incorporating market and non-market-value elements, provides an alternative to traditional cost-benefit analysis which requires all factors to be monetized. Not only does it enable rigorous and technically defensible assessment of the science and economics of both market and non-market values, it empowers stakeholders to explore and understand the relationships between economic factors and other effects that might otherwise be poorly represented or ignored— such as air and water quality, biological productivity, and ocean access (McCann et al. 2016; Bernstein 2015).
A 2D and 3D hybrid simulation technology is presented for the vortex induced vibration of a very long cable system, modeled by a circular cylinder whose aspect ratio (L/d) is in the order of 1,000. Flow around a circular cylinder is modeled by 2D unsteady simulation driven by recently developed high-order finite volume method, and the computed unsteady hydrodynamic forces are transferred to the nonlinear cable dynamics solver, and simultaneously the motion of the cylinder is also transferred to the flow simulation solver concurrently. Through this strategy, the unsteady excitation force due to the vortex shedding could be coupled to the accurate prediction of the 3D nonlinear cable motion. The solution strategy and efficacy of the current approach will be presented by results of the various test cases including the vortex-induced vibration of a long cable system.
Vortex-induced vibration (VIV) of a circular cylinder is a highly nonlinear phenomenon occurred by the interaction between risers and surrounding fluid flow. This phenomenon is considered as a representative example of more general class of problem, namely fluid-structure interaction(FSI)[Ahn and Kallinderis 2006]. The nonlinearities of the VIV simulation can be classified into three categories, first the inherently nonlinear behavior from the high Reynolds number vertical flow around the riser[Kallinderis and Ahn 2005B], second from the geometric nonlinearity of the oscillating riser with large displacement compared to its initial riser configuration[Lee et al. 2016], and finally the nonlinear response of the long riser interacting with the surrounding fluid which may terms as boundary-condition nonlinearity[Ahn and Kallinderis 2006]. Full three dimensional time-domain simulation of VIV of a riser based on fully three-dimensional FSI simulation is still challenging mainly due to tremendous amount of computational cost from the fluid solver[Ahn and Kallinderis 2006, Kallinderis and Ahn 2005A, Ahn Kallinderis 2005], rather than the structural part.
A very efficient methodology, composed of two-dimensional CFD simulation and three-dimensional riser dynamics, was proposed by Schulz and Meling[Schulz and Meling 2004] which can be applied to a very large scale VIV simulation, that might be prohibitively expensive for full three dimensional FSI approach. Their approach is based on the determination of hydrodynamic force by a two-dimensional CFD simulation, and its application to the riser structural dynamics code. Their coupling algorithm was sequential and the fluid and structural solver is being integrated in time with in a staggered manner with a fixed time step interval. In this paper, we utilize the same philosophy of 2D/3D hybrid computation proposed by [Schulz and Meling 2004], with more advanced numerical algorithm in all three components of simulation technology involved in the riser FSI simulation. First, for the CFD simulation we utilized recently extended third-order cell-centered finite volume method[Lee and Ahn 2016]. The method is an extension from the previous work of Kallinderis and Ahn[Kallinderis and Ahn 2005B] incorporating high-order solution reconstruction using robust wrapping-stencil. Secondly, the motion of a very long riser with aspect ratio L/D≈O(l,000) is modeled with sable element and discretized by recently developed nodal-position finite element method[Sun et al. 2011], which is accurate and efficient for the large displacement of riser form its initial configuration[Lee et al. 2016], Finally, a more stable and accurate coupling algorithm based on predictor/multi-corrector Newmark method is employed. By using the PC-Newmark coupling algorithm, the interaction between the flow and riser motion is strongly coupled and integrated simultaneously without a time lag.
Gao, Song (Shanghai Jiao Tong University) | Kou, Yufeng (Shanghai Jiao Tong University) | Peng, Tao (Shanghai Jiao Tong University) | Lu, Chao (China Ship Development and Design Center) | Sun, Jianglong (Huazhong University of Science and Technology, Shanghai Jiao Tong University) | Zhang, Wenxu (China Ship Development and Design Center)
This paper presents a novel semi-submersible concept, namely multiple-column platform (MCP), which features a center column and middle pontoon to satisfy its function as a mobile offshore nuclear power plant. This unique design makes it differ from the conventional semi-submersibles significantly, so that the hydrodynamic performance of this novel design should be fully investigated. In this paper, the numerical and experimental study have been carried out to examine the hydrodynamic performance of MCP. Numerical simulations are conducted in frequency domain based on 3D potential theory, and be validated by model tests, including free decay tests and wave tests. Moreover, a comparative study on MCP and two conventional semi-submersible models have been numerically executed. The hydrodynamic characteristics, including hydrodynamic coefficients, natural periods and motion response amplitude operators (RAO) have been investigated.
The new invention, MCP, showed in Fig. 1, is a new type semi-submersible, providing an attractive possibility that serve as a mobile offshore small nuclear power plants. It can serve the functions including energy supply for offshore industry, remote islands, high-power ships and seawater desalination as well. The strong and durable nuclear energy make these advantages come true. The MCP novel semi-submersible concept shows a unique characteristic that it has a center column with a middle pontoon supporting it. The watertight center column and middle pontoon consist of the nuclear reactor generator module, the central plant module and the power plant main control module. All of these can serve as the ballast as well, which provides significant weight displacement for the whole hull to reduce the heave response, increase the platform stability, the topside decks capacity, and enhance the reactor thermal efficiency due to the external cold water. This invention provides exceptional economic, environmental, sustainability, security and operational advantages over the current power generator for offshore industry.
In order to optimize the hydrodynamic performance of semi-submersibles, lots of work have been carried out. Bindingsbø and Bjørset (2002) investigated a novel deep draft semi-submersible, which owns a draft of 40 m. Compared with the conventional semi- submersibles, which have the draft of 20-25 m, the heave and pitch RAO of deep draft semi-submersible will approximately reduce by 50%. Another way is to install heave plates at the bottom of the semi-submersibles. The heave plates will increase added mass and viscous damping of the platforms, which in turn give rise to the decrease of heave responses. Cermelli et al. (2004) proposed a novel design MINIFLOAT, which has an extended plate area, namely heave plates, at the bottom of the columns to improve the motion performance in heave and pitch response. Truss pontoon semi-submersible (TPS) is another novel floating concept that includes the advantages of conventional semi-submersibles and truss-spars, which utilizes the added mass and the separated flow damping introduced by heave plates at the bottom of the truss columns (Srinivasan et al., 2005). Model tests (Srinivasan et al., 2006) and numerical study (Chakrabarti et al., 2007) both illustrated the improvement of its motion characteristics. Some other innovative concepts were also investigated to improve the hydrodynamic performance. The H-pontoon semi-submersible, which includes a pair of secondary central pontoons supported by the two main pontoons, presents better hydrodynamic performance when compared with conventional ring pontoon structures (Mansour and Huang, 2007). The Free-Hanging Solid Ballast Tank semi (FHS) using the free-hanging SBT significantly increases the heave natural period while controls the heave response in the wave frequency range (Mansour, 2009); Deepwater tumbler platform (DTP), which has double tier pontoons to improve heave performance and to enhance the platform stability by installing ballast in lower tier pontoons (LTPs) (Jiang et al., 2016).
Measured post-storm beach recovery was simulated using the process- based, depth-averaged 1-D cross-shore numerical model CSHORE over 30 tide cycles. The field data were collected during a 3-week experiment along the Delaware coast of the United States following a Nor'Easter storm. A pronounced ridge formed immediately after the storm and rapidly grew in height and shoreward extent. The model was able to capture the ridge accretion process (crest location, elevation, and ridge slope) accurately once sediment transport related parameters were calibrated. A sensitivity analysis of the most important numerical parameters is presented in addition to profile evolution results.
Intertidal sand bars are a common morphological feature often observed along sandy coasts with micro/mesotidal beaches. The formation and dynamic behavior of bars, or bar and trough systems, located in the surf and swash zones of the beach are controlled by a variety of morphological and hydrodynamic characteristics of the surrounding environment. The dynamic evolution of these features is thought to play a critical role in beach recovery mechanisms after erosive storm events. Especially, the ridge and runnel (RR) type swash bar is a single bar and trough system, asymmetric in shape and generally found in the upper intertidal zone on sandy beaches subject to relatively small tidal range (<3 m, Kroon and Masselink, 2002). Wave runup coinciding with the rising storm tide carries a large amount of sediment landward that is left on the inner swash zone building a pronounced berm face, or a ridge, followed by the landward slip-faced dipping, or runnel (King, 1972). The formation and onshore migration of ridge and runnel type bars is linked to beach recovery process since the onshore migration of a (partially) submerged nearshore bar during low-energy wave conditions following a storm can carry large amounts of sediment back up on the subaerial portion of the beach.
Yu, Xichong (CNOOC Research Institute) | Xie, Bin (CNOOC Research Institute) | Li, Yuxing (China University of Petroleum) | Wu, Yaling (China Huanqiu Contracting &Engineering Corporation) | Wang, Qing (CNOOC Research Institute) | Li, Yan (CNOOC Research Institute) | Zhu, Jianlu (CNOOC Research Institute) | Zhu, Xiaosong (CNOOC Research Institute) | Chen, Bing (CNOOC Research Institute)
In recent years, Liquefied Natural Gas ship (Floating Liquid Natural Gas, referred to as ”FLNG) was presented in ocean engineering. It is a new kind of FPSO equipment with the combination of the liquefied, storage and loading of offshore LNG/LPG. The FLNG system has many advantages, such as short production cycle, flexible production, independently development, easy to recycle and transport. FLNG topside module is one of key components, and pretreatment and natural gas liquefaction are most important modules in the FLNG topside. Natural gas must be pretreated to remove acid, dehydration and mercury removal and heavy hydrocarbon recovery. Heavy hydrocarbon recovery is one of key processes in offshore FLNG, and has many different from onshore LNG plant, such as liquefaction process of refrigerant self-product, space, products and offshore adaptability and so on. In this paper, aiming at the specific characteristics of the deepwater gas field in the South China Sea, and propane pre-cooling and dual nitrogen expansion liquefaction process with independent intellectual property rights, seven heavy hydrocarbon recovery processes are studied for products recovery, products composition, equipment number, the mutual influence of heavy hydrocarbon recovery process and liquefaction process, and finally the heavy hydrocarbons recovery process of propane auxiliary cooling with no contact tower is recommended for the target gas field in the South China Sea. The recommended heavy hydrocarbon recovery process has the advantages of high yield of heavy hydrocarbon products, pure product components, small space, less equipment, and no effect on liquefaction process.
The South China Sea is rich in petroleum resources, There are about 1.37 billion tons oil resources (about 17%) and 6.62 trillion Nm3 natural gas resources, about 70% of which is from deep water. Now in the world the main development mode for deep water and super deep water gas fields is the mode of sub-sea tie-in system, but it has a long offshore distance, a high investment of pipeline and the needs of safety, remote control from down streams. So a new industrial development mode needs to be developed urgently. In recent years, Liquefied Natural Gas ship (Floating Liquid Natural Gas, referred to as “FLNG”) was presented in ocean engineering. It is a new kind of FPSO equipment with the combination of the liquefied, storage and loading of offshore LNG/LPG. The FLNG system has many advantages, such as short production cycle, flexible production, independently development, easy to recycle and transport. This system can be applied in small, medium, and large gas fields development, and also can be suitable for shallow and deep water gas field development (Iversen et al., 2009; Ganielsen et al., 2009). FLNG device research and development in recent years become the focus of world's major oil companies and research institutions, which is listed as one of the international oil top ten science and technology progress in 2013. 19 projects are at the implementation stage, and 5 of them are at the project cost stage. The first FLNG SATU in the world has been put into production formally in Kanowit gas field in November, 2016. And there are 4 of the other ones at the project cost stage.