Footprints were left on the seabed due to previous operations, and the problem of the spudcan-footprint interactions gradually becomes one of the major concerns of jack-up unit installation. The spudcan is subjected to eccentric loading conditions, which can lead to structural failure and the overturn of the jack-up unit. This paper reports the global behavior of the three-legged jack-up unit with a novel rectangular-shaped spudcan when it needs to reinstall near an existing footprint. The coupled Eulerian-Lagrangian (CEL) approach was used. A simplified three-legged jack-up unit model was developed and the flexible stiffness between the hull and legs was considered. The free-rotation heading and force-controlled loading conditions were also adopted. The bending moment distribution along the legs, horizontal force and the overturn of the jack-up unit are discussed to assess the potential of the jack-up unit sliding toward the footprint center. The critical offset distance was found at 0.3D and an offset distance of at least 1 times of the spudcan diameter is able to diminish influence of the footprint. The ability of the novel rectangular large spudcan with a flat base is shown to be effective at easing spudcan-footprint interactions, compared with generic circular spudcan.

In the same sea area, with the increase of the number of operations, the situation of jack up offshore drilling platform carrying out secondary or multiple Jack-up leg embedment operations in the vicinity, or even in the same location will increase year by year. Therefore, the operation of jack up offshore drilling platform makes the sea area “step on the footprints” The problems become more and more frequent, and have a significant impact on the operation safety of offshore platforms. During the “footprint” process of jack-up drilling platform, the spudcan will slide transversely along the direction of Jack-up leg pits to varying degrees. If the sliding distance is too large, the leg or platform structure will be damaged. Based on the symmetrical structure of the three-leg jack-up offshore platform, the bow and the starboard spudcan are slided along x-axis at different angles, respectively. According to the critical bearing capacity of the platform legs, the critical distance of spudcans sliding is calculated. Finally, the relationship between the sliding distance of spudcan in different directions and RPD (Rack phase difference) is obtained by monitoring the RPD value of legs. It provides meaningful guidance for platform designers and operators.

A new generation of subsea production system with the suspended manifold as the major characteristic was proposed to solve the disadvantages for hard to be discarded and recovered for the traditional subsea manifold fixed in seabed. Here, the flexible jumpers connecting the dry trees in the subsea functional chamber to the suspended manifold, can not only provide enough mooring forces as the mooring system, but also transport oil and gas from dry trees, which is an indispensable part of a complete new generation of subsea production system. So how to optimize the flexible jumpers to guarantee a good hydrodynamic performance is quite essential. In this paper, a steep wave type of flexible jumper is optimized by changing the suspended height, connection width, and position and diameter of the buoyancy block. The result shows that the location and the size of the buoyancy block both have a great influence on the distribution of the mechanical property and the line type of the flexible jumper while the influence of suspended height and connection width is very small. Calculations and analysis demonstrated that changing the position of the buoyancy block has no effect on the maximum tensile force of the flexible jumper, but the farther the buoyancy block is from the seabed, the larger the minimum bending radius of the flexible jumper is. Meanwhile, the larger the diameters of buoyancy block becomes, the larger the maximum tensile force is, and the smaller the minimum bending radius will be.

In this study, a new higher-order Euler-Bernoulli beam element of Absolute Nodal Coordinate Formulation (ANCF) is developed for geometrically nonlinear analysis of planar structures. The strain energy of the beam element is derived by applying the definition of the Green–Lagrange strain tensor in continuum mechanics. The first contribution of this research is to realize the accurate calculation of curvature on the beam element node by additionally considering the second derivative of the position vector obtained by quintic Hermite interpolation function. Furthermore, in traditional theory, the independent variable of finite formulation is arc-length coordinate s, while in this work, a correction is come up with and proven that it is actually an equivalent parameter. Some benchmark problems of straight beams are solved by the proposed element and accurate results are obtained by just fewer elements when compared with the other works including the traditional ANCF element and B23 element of ABAQUS. What leads to this accuracy result is that the precise calculation of nodal curvature is obtained from higher order interpolation scheme. The correctness and accuracy of the proposed element are validated in this work and it can be further developed for tackling large deformation and large rotation problems of spatial curved beams.

As the exploitation of oil and gas gradually enters the deep sea, the low-temperature and high-pressure deep-sea environment poses a huge challenge to the flow protection of pipelines (2014a). In this paper, the phase change material sandwich pipeline which uses phase change heat storage and exothermic to maintain the pipeline temperature is taken as the research object, the heat transfer characteristics of the deep-water phase change material sandwich pipe are studied through the combination of theoretical analysis and numerical simulation (2014b). The main contents include: Firstly, through the establishment of two-dimensional and three-dimensional pipe models, analyzed the temperature distribution along the pipeline and the radial temperature distribution of the pipeline under steady oil flow conditions. Secondly, by using transient heat transfer, the effects of phase change material parameters, the proportion of phase change material in the insulation layer, and the difference in the ratio of phase change materials in the insulation layer on the insulation performance are analyzed to obtain the best results. Insulation material and optimal insulation layer layout; finally, the thermal storage and the phase change conditions of the phase-change material sandwich pipe is studied under the re-starting condition. The results show that the effective holding time of the phase change material insulation layer is close to 1.4 times that the non-phase change material insulation layer, and the melting point size has little effect on the insulation material. The closer the phase change material is to the inner tube, the better the insulation effect. This study provide guidance for the design and utilization of phase change material sandwich pipe.

Mechanical behavior of flexible risers can be challenging due largely to its complex design generating strong nonlinear problems. Nonlinear material properties, as one of them, from polymer layers dominate the overall viscoelastic responses of flexible risers which may play an inevitable role on the global analysis in deepwater application. An alternative to predict the viscoelastic behavior comprising of the time domain and the frequency domain has been proposed recently by the authors (Liu and Vaz, 2016). Given the fact that polymeric material properties are temperature-dependent and that the temperature profiles in flexile risers vary continuously in both axial and radial direction, the temperature of the internal hydrocarbons must affect the viscoelastic responses. However, such phenomenon dose not draw much attention in previous studies. This paper presents an improved model for overcoming some drawbacks in the proposed model involving assumption of steady temperature distribution in polymer layer and no gap appearance between the adjacent layers. The computing method of model is developed by using a step by step test approach. Consequently, some important parameters like equivalent axial stiffness, contact pressure or gap between the near layers, and force-deformation relationship can be observed. Parametric studies are conducted on the axisymmetric viscoelastic behavior of flexible risers to study the role of input temperature and loading frequency. Results show that equivalent axial stiffness given by the improved model is smaller than before. It can also be found that the gap between metal layer and polymer layer appear easily and increases as time goes on.

The sheave installation method (SIM) is an effective and non-conventional method to solve the installation of subsea equipment in deep water (>1000m), which has been developed to deploy the 175t Roncador Manifold I into 1,885 meters water depth in 2002. With the weight increment of subsea cluster manifold, how to solve its installation with the high reliability in the deep sea is still a great challenge. In this paper, the installation of the 300t subsea cluster manifold using the SIM is studied in the two-dimensional coordinate system. The mathematical model is established and the lumped mass method is used to calculate the hydrodynamic forces of the wireropes. Taking into account the complex environment loads, the numerical simulation of the lowering process is carried out by OrcaFlex. The displacement and vibration of the subsea cluster manifold in the z-axis direction and the effective tension at the top of the wireropes can be gotten, which can provide guidance for the installation of the cluster manifold in the South China Sea.

The cluster manifold becomes an essential part in a subsea production system and it has been widely used in the development of ultra-deepwater oil and gas fields. One hand, it can gather the production fluid from subsea wells. On the other hand, it can distribute water, gas and chemical agents from the floating production system to each subsea well. Hence, the failure of subsea cluster manifolds may not only lead to the stagnation of production wells and economic losses but also cause environmental pollution and human health in severe cases. Therefore, the reliability of subsea cluster manifolds is quite of importance and it should be studied for the safety service of the subsea production system. Based on the fault tree analysis (FTA), this paper will discuss the failure cause of six well slots subsea cluster manifolds in LiWan 3-1 gas field in China South Sea. Considering the pipeline structure, control system and flow assurance, the fault trees of subsea cluster manifolds are built. Meanwhile, the importance degrees of each elementary event are ranked orderly and the minimum cut sets are obtained through analyzing the structure important of the FTA. The failure major reasons are obtained and the preventive measures are proposed, which could have some guiding significance for the operations of subsea cluster manifolds system in China South Sea.

Subsea connector is an important connection facility in subsea production system. Once destroyed, it will cause sealing failure which could lead to leakage accident, so the connectors must have high degree of damage-resistance capacity. Ultimate bearing capacity is composed of a set of important parameters measuring subsea connectors’ damage-resistance capacity, such as ultimate bending strength, ultimate torsional strength, etc. However, these data are usually obtained by carrying out destructive tests, which will bring heavy cost to subsea connector products in order to obtain the required technical data. Considering reducing the cost of destructive testing, a theoretical calculation method is needed to be developed. In addition, during the stage of product design, it is also necessary to estimate ultimate bearing capacity to verify whether the structural design parameters meet the anticipated requirements. In this paper, only the ultimate torsional strength of subsea connectors was studied, and based on finite element analysis, a calculation method of ultimate torque was put forward, which consists of using finite element software to build the 3D subsea connector model, loading different pure torsional moment, analyzing the calculation results and establishing torsional failure criteria to determine ultimate torsional strength. The results show that sealing failure will be ahead of structural strength failure under the pure torsional loads, and traditional strength failure criterion is not suitable for determining ultimate torsional strength of subsea connectors; the numerical solution of ultimate torque is 60KN·m based on the sealing failure criterion in this paper. In the end, a simplified mechanical model of subsea connector was established, the limit state equation of sealing failure was built in the action of pure torsional load, and the analytical solution of ultimate torque was calculated. The calculation method of ultimate torsional strength established in this paper was verified through comparative analysis.

Subsea pipelines have been widely used to transfer oil from platforms to the mainland near harbor anchorage zone, and they become increasingly susceptible to risks stemming from dropped object impact damages. The impact from dropped objects may lead to local deformation and fracture in the pipeline and vast economic and environmental consequences. In this research, the responses of continuously supported offshore pipelines subjected to transverse impacts caused by dropped objects are studied. For this, the impact on an internally pressurized pipeline resting on a flexible bed has been numerically simulated. A relatively extensive parametric study has then been carried out to examine effects from variations in the cement coating thickness, internal pressure, indenter shape, impact velocity and subsoil mechanical properties on the pipeline response. It has been noticed that the presence of internal pressure results in substantial decrease in the impact dent depth, causing the deformation to become spatially more localized. It has also been shown that the flexibility of pipe bed plays an important role in the impact energy dissipation.

Pipe-soil interaction has been intensively investigated both theoretically and experimentally due to its importance in the design of seabed pipelines. In recently years, the effects of single phase, steady internal flow on the dynamic response of seabed pipelines have received increasing attention. However, the effects of transient two-phase flow on the vibration behavior of seabed pipelines have been seldom studied. In this work, a physical model for analyzing the dynamic behavior of a seabed pipeline conveying gas-liquid two-phase flow is proposed. Slug flow regime is considered as it causes most violent vibrations. An analytical model is adopted for the prediction of important flow characteristics of the gas-liquid slug flow. The dynamic behavior of pipelines is analytically and numerically investigated by using the generalized integral transform technique (GITT), by which the transverse vibration equation is transformed into a coupled system of second order differential equations in the temporal variable. Good convergence behavior of the proposed eigenfunction expansions is demonstrated for calculating the transverse displacement at various points of pipelines conveying gas-liquid slug flow. Parametric studies are performed to analyze the effect of the internal two-phase flow on the dynamic behavior of pipelines.

Polymer properties, i.e. viscoelastic characteristics, may pose a non-negligible impact on the axisymmetric analysis, especially on the axial structural damping behavior. An available mechanical model taking viscoelastic into account is established for capturing such parameters as axial strains and forces on each layer, axial stiffness and so on. In this paper, the flexible riser is divided into helical and cylindrical elements to carry out the mechanical analysis due to the complexity of structure and material property. Prony Series is used to describe the creep and relaxation behavior of material viscoelasticity. A viscoelastic solution is obtained using the correspondence principle. Finally, a case study is performed and some interesting results are presented.

Analysis of dynamic response of a fluid-conveying riser is an important aspect in subsea production system. In the present paper, dynamic response of a pinned-pinned riser subject to external fluid force was solved by the generalized integral transform technique (GITT). A nonlinear wake oscillator models was used to represent the cross-flow and in-line force acting on the riser, leading to a coupled system of second-order Partial Differential Equations (PDEs). The GITT approach was used to transform the system of PDEs to a system of Ordinary Differential Equations (ODEs), which was numerically solved by using the Adams-Moulton and Gear method (DIVPAG) developed by the International Mathematics and Statistics Library (IMSL). Numerical results were presented for comparison to those given by the numerical and experimental results, allowing a critical evaluation of the technique performance. The influence of conveying fluid velocity and mean top tension were evaluated to show that they should not be negligible in numerical simulation of Vortex-Induced Vibration of a long flexible riser.

The finite element model of ABAQUS combined with FORTRAN subroutines was developed to predict the residual stress and deformation of T-joint welds under different preheat and inter-pass temperature. A calibrated and sequentially coupled thermal and mechanical 3D finite element (FE) model is developed, and Goldak’s double ellipsoidal heat source model is implemented into the numerical model. The welding induced imperfections, including the residual stress and distortion are discussed in this paper. The results show that vertical deformation depend significantly on the preheat temperature and inter-pass temperature. The influences of preheat and interpass temperature on the residual stress are not significant.

Sandwich pipes (SP) can be an effective solution for ultra-deepwater submarine pipelines, combining high structural resistance with thermal insulation. Most research work on this subject has been conducted at the subsea technology laboratory (LTS) of COPPE/UFRJ, with the aim of developing qualified pipes to transport deepwater oil and gas, especially for the pre-salt reservoirs at Offshore Brazil. This article reviewed most of the research done in recent years (2002–2012) on the buckling, collapse and buckle propagation of SP, which emphasized on the development of theoretical, experimental and numerical methods adopted to analyze such structural behavior of SP with different core materials. The main mechanical and thermal properties of the previously considered core materials were also given, together with the elastoplastic constitutive model for each material. The experimental and numerical results of collapse and buckle propagation under external pressure for SP were summarized. A general discussion of the mechanical failure modes of SP under external pressure was also provided. Besides, some suggestions for future work on collapse behavior and buckle propagation of SP were given.

Sandwich Pipes (SP) can be an effective solution for the ultra-deepwater submarine pipeline, combining high structural resistance with thermal insulation. Besides polymer, strain hardening cementitious composites (SHCC), a micromechanically designed material with the characteristic of high tensile ductility, can be another choice for the annular material. The purpose of this work is to investigate numerically the limit strength of SP with SHCC under external pressure and longitudinal bending. The mechanical behaviour of SHCC is simulated using a Concrete Damaged Plasticity (CDP) model provided by Abaqus/Standard. The finite element (FE) model is employed to better understand the structural behaviour of SP in different conditions of geometry, adhesion and loading. The pressure-curvature (P – K) failure envelopes for SP with unbonded and fully bonded interface conditions are presented. The results show that the resistance of the annulus layer has a great contribution for the overall structural behaviour. The interface condition and the thickness of the annulus are important influence factors on the overall structural behaviour. Besides, the lateral confinement effect on SHCC caused by the inner and outer steel tubes and the ultra high ductility of the SHCC have strong influence on the results for the pressure-curvature collapse envelopes.

Dynamic response of a vertical flexible cylinder vibrating at low mode numbers with combined x – y motion are investigated in this paper. The uniform flow was simulated by towing the flexible cylinder along the tank in still water, therefore the turbulence intensity of the free flow is negligible in order to obtain more reliable results. The dominant frequencies, maximum attainable amplitude, modal analysis and x – y trajectory in cross-flow and in-line directions have been reported and compared with literatures, some good agreements and justifiable discrepancies are obtained. These results could benefit the future experimental and numerical work in this area.

There are four typical layout types for the subsea production system. These include single well tie back, the daisy chain, the template manifold and the cluster manifold. In the early development phase, an appropriate layout type needs to be selected. The layout design of the subsea production system is based on the data of oil and gas fields. Due to many advantages, such as less initial investment, being installed in advance, flexibility for development schedule and so on, the cluster manifold is becoming more popular and has been applied extensively in the layout of deepwater subsea production systems. In this layout type, the number and locations of cluster manifolds, and the connection types between subsea production facilities have a direct effect on the safety, flexibility and cost of the target deepwater oil and gas fields. Hence, how to design the optimal layout of the cluster manifold is of key importance. This paper will focus on the cluster manifold layout by the math means programmed using C++. For any given subsea well and the floating production system, the basic layout of the cluster manifold with the lowest cost can be obtained based on the assumptions, including the number, locations and cost of the jumpers, PLETS and flowlines. This mathematical method can reduce subjective bias from the engineers and provide a more scientific reference for obtaining the optimal cluster manifold layout.

The penetration of the jackup platform will be much deeper, and the weight of the backfill above the spudcan will make more contribution to the resistance of jacking up of the platform. The prediction of the depth of the shoe pits is most important in estimating the weight of the backfill over the spudcan. This paper presents a method for predicting the depth of the shoe pits on the basis of superior limit theorem of ultimate analysis by comprehensively investigating the non-drained shear strength of backfill soil, the penetration depth and the spudcan shape. An experimental device is set up to verify the predicting formula, and very good results are obtained.