For the convenience of the cargo oil offloading process, the high-viscosity crude oil in oil tankers needs to be heated and insulated to keep the cargo oil temperature above the freezing point. The thermodynamics associated with the oil heating/insulation process needs to be well understood for optimization, especially when the oil tanker is subjected to a global motion, exciting oil sloshing inside the cargo tank. This paper presents an experimental study characterizing the heat transfer of the sloshing oil. In the experiment, a side tank of a VLCC (very large crude carrier) is considered as a prototype, and a 1/40 model is built following the Froude and Grashof similarity. The model is placed in a 6 DoF sloshing platform, which exciting periodic roll motion to simplified the wave-excited motion in the real scenario. The time histories of temperature at various monitoring points are measured. The results show that the conduction and convection are the dominated factors including the heat transfer when the oil is subjected to a sloshing condition. The characteristics of the temperature variation show different features at different locations and during different stage of the process; within the range of the consideration, larger motion angle and shorter exciting period results in more violent oil sloshing in the tank and, consequently, more significant effects on the heat transfer; as the sloshing becomes more significant, compared with the lower sloshing intensity, there is stronger forced convection above the heating coil. Forced convection makes the variation of oil temperature in the area above the heating coil more severe. Overall, the sloshing significantly influences the temperature distribution and causes a regional difference in the temperature characteristics. The experiment expects to provide a useful reference for guiding the oil heating/insulation process. INTRODUCTION Due to the high freezing point of crude oil, when oil tankers transport cargo oil in a low-temperature environment, once the cargo oil has solidified, it is not easy to unload. So, the cargo oil needs to be heated and insulated to ensure fluidity. At present, to prevent this from happening on ships, cargo oil is often overheated, which increase the transportation cost of cargo oil. In the current research on the heating process of cargo oil, cargo oil is mostly under a static environment. However, due to the influence of external wind and waves, cargo oil is always sloshing. Still, few related papers have been published on the effects of oil sloshing on the characteristics of temperature during the cargo oil heating process.

Hydrodynamic impacts of the propeller on a rudder are studied in this paper. Incompressible viscous flow around a NACA 0018 spade rudder is analyzed in open-water conditions and in the slipstream of the propeller based on a Reynolds-Averaged Navier-Stokes (RANS) method. The numerical method is validated in open-water conditions for the propeller and the rudder. For the rudder steered behind a propeller, hydrodynamic performance is compared with that in open-water conditions. The impacts of the propeller loading and the distance between the rudder and propeller on rudder hydrodynamics are studied, aiming to present a clearer description of the propeller-rudder interaction phenomenon. INTRODUCTION Rudders are widely used in the great majority of ships as steering devices, whose performance connects directly with ship maneuverings. A significant amount of effort has been made on hydrodynamics of isolated rudders in open-water conditions experimentally and numerically. However, for rudders steered behind propellers during maneuverings, the inflow into the rudder is accelerated and distorted due to the propeller slipstream. The acceleration leads to enhancement of rudder forces, while swirled inflow changes the effective rudder angles of different profiles (Molland, 2011). Such flow straightening effects cause the rudder to experience increased incoming turbulence, which brings great challenges for accurate predictions of ship maneuverability. Therefore, the investigation on how the propeller impacts rudder hydrodynamics is quite significant for ship maneuverability assessments. Some model experiments are conducted to study hydrodynamic performance of rudders influenced by propeller impacts. Molland (1991) investigated interactions of a series of all-movable rudders and a propeller. According to experimental results, increment ratios of lift and drag coefficients have raised with an increase in propeller loading, and the stall occurs later when the propeller exists. Molland (1992) tested systematic experiments on various control parameters in propeller-rudder interactions, demonstrating that the lift force of the rudder is controlled by thrust loading only. Lubke (2009) conducted PIV measurements for the velocity field of a semi-balanced rudder after the hull and the propeller, velocity fluctuations and separation regions on rudder faces can be observed.

The paper presents a numerical comparative study on the interaction between focusing waves and a cylinder using a hybrid solver, qaleFOAM, which couples a fully nonlinear potential theory (FNPT) and an incompressible two-phase Navier-Stokes model using a domain decomposition coupling approach. The former is solved by using the Quasi Lagrangian Eulerian Finite Element Method (QALE-FEM) and the latter is solved using the OpenFOAM by the finite volume method with the volume of fluid for identifying the free surface. In this paper, one-way coupling is used in qaleFOAM. For the purpose of comparison, the simulation using the QALE-FEM alone is also carried out. Both results are compared with the experimental data, contributing to the numerical comparative study organized by ISOPE 2020. Good agreements are achieved. Furthermore, the significance of the viscous and turbulent effects is also discussed. INTRODUCTION For survivability of the marine, coastal and offshore structures, the interaction between extreme waves and structures needs to be reliably predicted in engineering practices. As a typical structure, cylinders have been widely used, e.g. as the foundation of oil/gas platform and offshore wind turbines. Focusing waves, on the other hand, are widely accepted to be a representative of the extreme waves in current experimental and numerical researches. The interaction between the focusing waves and the cylinder has attracted extensive studies recently (e.g. Hildebrandt et al 2014; Yan et al, 2015). Considering the fact that the extreme waves often involves a significant nonlinearity, the linear and second order wave theories widely used in the routine design may not be sufficient for a reliable prediction. Consequently, solutions by the fully nonlinear simulations, e.g. the computational fluid dynamics (CFD), are sought for. Numerous numerical models and software have been developed based on wide ranges of theoretical models, including the fully nonlinear potential theory (FNPT) and the Navier-Stokes (NS) theories. The FNPT can be solved by the boundary element method (e.g. Ning et al, 2017), the finite element method (e.g. Wu & Hu, 2004), the quasi-arbitrary Lagrange Euler finite element method (QALE-FEM, Yan and Ma, 2007, 2010a; Ma and Yan, 2006, 2009), the spectral element method (Engsig- Karup et al, 2016), the high-order spectral method (Ducrozet et al, 2016) and the spectral boundary integral method (Wang & Ma, 2015; Wang et al 2018). The numerical methods for solving the NS model exhibit more, significant diversities compared with the FNPT models. One may categorise them into the conventional mesh-based methods, e.g. the finite volume method (Hildebrandt, et al 2014; Xie, 2012, 2013, 2015; Yang et al 2017), and the meshless (particle) methods, including the smoothed particle hydrodynamics (SPH, e.g. Lind, et al., 2012; Zheng, et al., 2014), the moving particle semi-implicit method (MPS, e.g. Khayyer et al., 2019) and the meshless local Petrov-Galerkin method based on Rankine source solution (MLPG-R, e.g. Rijas et al., 2019).

Multiphase transportation technology is widely used in subsea pipelines, while some necessary flow characteristics of the multiphase flow are difficult to obtain by traditional methods. In this study, the emulsified water fraction and equivalent viscosity of oil-water mixture under different flowing conditions were investigated with a novel stirring measurement method. Their relationship with total water fraction, temperature, and shear rate were established and analyzed based on the experimental results. This study is helpful to understand the phase distribution and flow characteristics of the oil-water two-phase flow in subsea pipelines. INTRODUCTION In recent years, the petroleum resource of offshore oil fields has become an important proportion of oil production growth. The distance of subsea gathering and transportation pipelines has been increasing substantially. The phase separation operation is usually done onshore in order to reduce the construction area and costs of offshore platform, so multiphase transportation technology is widely used in subsea pipelines. The agitation and mixing effects from the pipe fittings and shear flow disperse one phase into another, forming complex and varying flow patterns (Sharma et al., 2011; Wang et al., 2011). For oil-water two-phase flow, a small proportion of water may be entirely emulsified to form water-in-oil emulsion with oil phase (Xu, 2007; Sotgia et al., 2008; Klink et al., 2011). Nevertheless, when the water fraction is considerable, besides the emulsified water, the remaining part of water phase is co-existed with the emulsion as free water (Chen and Tao, 2005; Wen et al., 2014). The emulsified water in oil increases the effective volume of oil phase and changes the viscosity of oil-water mixture. Emulsified water fraction and viscosity, as important parameters of oil-water flow characteristics, are essential for the prediction of flow pattern and the hydraulic and thermodynamic calculation. However, they are difficult to be obtained by using traditional measurement methods. The emulsifying behaviors are not only influenced by the properties of crude oil and water, but also closely related with the shear rate and temperature. Since the emulsifying behaviors in pipe flow are different from those in the static condition, emulsified water fraction needs to be determined under flowing condition in order to reflect the flow characteristics in pipelines. However, nearly all of the current research is aimed at emulsifying properties under stationary condition (Nenningsland et al., 2011; Azodi and Nazar, 2013), which is quite different from the actual situation.

In oil and gas production and transportation systems, the particles carried with the conveying media usually exert accumulative collision on fittings such as elbows and tees in pipelines and piping section of facilities. The serious erosion damage may cause failure of the facilities and even lead to environmental disasters. In this study, the cushion effect of liquid film on the particle erosion in elbows is investigated by using a numerical procedure. The procedure performs well in estimating the erosion of elbows under annular flow conditions. The effects of macroscopic factors on the penetration rates are analyzed to further investigate the cushion effect of the liquid film. The accumulation of the liquid film on the bend extrados considerably reduces the effective collision intensity of the particles. The favorable conditions in which the cushion effect is made good use of are summarized and as the guidance for the industry. INTRODUCTION Annular flow widely appears in various facilities such as evaporators, steam heating systems, nuclear reactors and oil and gas production systems. It is produced from the condensate of the natural gas or artificially controlled as the flow pattern in long-distance transportation of oil and gas mixture. The morphological arrangement of the gas and liquid is determined by the factors such as the flow rates, the delivery ratio between the two phases, the size of pipe, the flow direction, etc. The gas phase flows in the core region with a much higher superficial velocity than the liquid phase, which is mainly attached on the pipe wall and flows as the continuous film. There are also entrained droplets or mist flowing with the gas phase in the core region. The liquid film and the droplets can be the condensate or oil or both. The thickness of the liquid film describes the morphological characteristics of the annular flow. If the flow condition stays unchanged, the annular flow in long straight pipes reaches to a developed status and the film thickness remains to be a constant value. While in elbows downstream of straight pipes, the distribution of liquid film varies all along the axial distance. The experimental researches (Anderson and Hills, 1974; Maddock et al.; 1974; Abdulkadir et al., 2014; Zahedi et al., 2018) showed that the film thickness was usually circumferentially non-uniform in the cross section. The degree of nonuniformity also varied along the axial direction of the bends. Numerical and mechanistic researches (Tkaczyk and Morvan, 2010; Tkaczyk and Morvan, 2011; Zhang et al., 2013; Zahedi et al., 2017; Liu and Liu, 2019) were also carried out to solve the thickness distribution of the liquid film in elbows.

Rust removal is a necessary step of surface coating treatment in shipbuilding and ship repairing industry. As one of the efficient and environment protecting application methods, the derusting technique using ultra-high pressure water jet is favorable in many developed shipyards. The straight cone nozzle, as a key part of ultra-high pressure water equipment which commonly used to clean the outer hull of ship vessels, is regarded as the main research object in this paper. The numerically simulates taking the internal and external flow fields of the nozzle into account was carried out via the volume of fluid (VOF) mode by CFD package. The cavitation effect which is frequently encountered in the case of high velocity flow condition was also included in this simulation. Two parameters that have a great influence on the hydrodynamics inside the nozzle are considered,including the convergence angle and aspect ratio. Some analysis results of axial velocity, turbulent kinetic energy, nozzle cavitation distribution are provided, and the influence of cavitation on water jet performance under different nozzle parameters is also briefly analyzed. Through comparing the cases in relation with different nozzle convergence angle and aspect ratio, it is found that when the convergence angle becomes larger the effect of cavitation on hydrodynamic performance becomes greater, the nozzle characterized by convergence angle of 30° and the aspect ratio of 2 has best hydrodynamic performance. INTRODUCTION The shipbuilding and ship repairing industry as one of the supporting industries in China, develops rapidly and makes great contribution to the economic growth in China. In the field of ship repairing industry, rust removal is a necessary process. However, the traditional gritblasting process are still wildly used for ship hull rust removal by far, although there are a lot of disadvantages related to it, such as inefficiency, environmental pollution and danger to operators (Qu, 2016). The ultra-high pressure water jet technique (U-HPWJT) is a unique method that uses ultra-high pressure water pump to generate highly ultra-high velocity water jet through a nozzle. The U-HPWJT has the advantages of good cleaning quality, high cleaning velocity, environmental friendly and high safety performance. The U-HPWJT is used to perform various operating processes in industry, such as surface cleaning, material cutting, and crushing (Shi et al., 2014). With the development of industrial technology, the U-HPWJT has been greatly developed and has a good application prospect in industrial cleaning, hydraulic cutting, drilling and derusting (Han and Ma, 2016).

As a calculation method to decide the shape and the installation position of fins installed at the submerged parts of a floating body for its motion reduction, we focus on the calculation method for a viscous fluid by vortex method. As a first step, by restricting 2D problems, we propose a motion calculation method for the floating body based on 2D vortex method using fluid velocity and vorticity as unknown variables. Appling this method to motion calculation of a rectangular floating body, we confirmed its effectiveness through comparison between experimented and calculated results. INTRODUCTION It is important to promote the use of ocean renewable energy because there is a possibility of not only creating a new energy source but also leading to stable power supply in regions such as remote island areas. As one of ocean renewable energies, wind energy is given. Offshore wind energy generation facilities have less restriction in location and can supply more stable wind energy than on-land facilities. Offshore wind power generation facilities are classified into a bottom mounted type and a floating one. Adoption of the latter is expected in Japan because there are few areas with shallow waters (MLIT, 2014, 2016, 2017). As calculation methods for the viscous fluid proposed previously, mesh method, particle method and vortex method etc. are given. In this research, a fluid domain around the floating body in waves is a high Reynolds number region. In calculation, since vortex generated from the body and its diffusion to the fluid domain should be accurately evaluated, we focus on vortex method. As calculation methods for the viscous fluid proposed previously, mesh method, particle method and vortex method etc. are given. In this research, a fluid domain around the floating body in waves is a high Reynolds number region. In calculation, since vortex generated from the body and its diffusion to the fluid domain should be accurately evaluated, we focus on vortex method.

A ship moving in water experiences resistances, the major component of which is frictional resistance arising from water viscosity. Therefore, drag-reduction has been an active research field in marine transportation over the last decades. A variety of innovative drag reduction techniques have been proposed, among which are riblets, microgrooves, compliant coatings, addition of polymers, air injection method, to name a few. Among them, air-injection drag reduction technique has achieved attraction increasingly in recent years owing to its overwhelming advantages, such as considerable potential drag reduction, easy operations, environmental friendliness and low costs. There are basically two types of air-injection drag reductions: Microbubble Drag Reduction (MBDR) and Air-Layer Drag Reduction (ALDR). It is interesting that they can be modeled by Eulerian-Eulerian two-fluid model and VOF (Volume of Fluid), respectively in OpenFOAM. In this paper, we show how to numerically model the two types of air-injection techniques. After that, a comparison with a recently experimental data is made for an axisymmetric body. It is surprising that such comparison reveals that MBDR and ALDR are all present in the experimental test. MBDR is dominant for low flux rate while ALDR is dominant for high flux rate. Their transition is restricted to a very narrow region, similar to a phase transition characterized by a sharp jump from one mechanism to another. Based on such observations we propose a combined numerical model based on the data-coupling method to handle the case that both MBDR and ALDR are present with a sharp transition. The combined model is a linear one in the framework of interpolation. It works well with satisfactory results obtained. Numerical results show that in the MBDR-dominant region the air void fraction around the body is the determinant factor influencing the drag reduction. In the ALDR-dominant region the formation area of the air layer around the body surface determines the amount of the drag reduction. The above results are useful for designing an effective air-injection drag reduction method.

The study on viscous-dominated flow-structure interaction (FSI) now trends towards to be popular by using the modern CFD and CSD technique, that concerns in a board range of applications for ship and ocean engineering. For example, CFD and FEA are coupled to predict the dynamic behaviour of a flexible barge in regular head waves, including the hydroelasticity of a large containership and the deformation of a thin flat plate in air flows. The particular phenomenon of interest in this paper involves scattered data interpolation on the interface between the solid and liquid by introduction of the radial basis function (RBF) technology. Additionally, the RBF-based interpolation is optimized and improved according to the region decomposition technology and the error estimate of the RBF, which helps to effectively solve the large full-rank matrix connected with the RBFbased interpolation. In this way, a new data-independent RBF interpolation point selection method is developed. Three typical cases are given by using the global RBF interpolation, the compactly supported RBF interpolation and the partitioned RBF-based interpolation, in which we analyse the bending deformation of the flat plate under the impact of airflow, which is the representative of the FSI problems. By comparison, our developed partitioned RBF-based interpolation shows the global efficiency and accuracy. In particular, the relationship between the error estimate of the RBF and the filling distance of the interpolation domain is well verified. Probably, it provides a new simple approach for data exchange in FSI. INTRODUCTION Destructive problems have arisen in many flow-structure interaction phenomena, such as fatigue failure of propellers, failure of elbow erosion, damage to high-rise buildings by strong winds and bridge deformation due to sea waves. These problems seriously threaten product life and building safety. These problems now are widely solved numerically using the partitioned coupling method due to its efficiency. In the partitioned coupling solution, independent fluid and structural modules can be used respectively. It was verified (Su, 2010; Zhang, 2017) that, fluid-solid modules can help to take advantage of the existing CFD and CSD study within this frame, which usually show different spatial-temporal discrete methods. Thus, it is necessary to develop a high-precision and efficient interface transfer algorithm on the interface between the flow field and the structure field.

Nowadays, vertical hydraulic transport (VHT) is widely recognized as the most practical and promising deep-sea ore conveying method. In this paper, the flow characteristics of solid-liquid two-phase mixture during VHT have been studied through experiments. The flow velocity of solidliquid mixture was measured by flowmeters, whereas the movement of particles was recorded by a high-speed camera. The computer vision library OpenCV and object detection library YoloV3 were applied to detect the number and position of particles, which were used to calculate the volume concentration and velocity of particles, respectively. Finally, a relation between the local flow velocity, particle volume concentration and particle velocity is summarized by fitting the experimental data into a parameter surface. INTRODUCTION With the depletion of terrestrial mineral resources and the deepening of human understanding of ocean, deep-sea mineral resources have become alternative resources for the sustainability of human society in the 21st century. As deep-sea mineral resources mainly exist on the sea floor at a depth of 1500 m ∼ 6000 m, lifting system is crucial to achieve the success of the deep-sea mining project, by which mineral resources are conveyed from seafloor to sea surface. Among the lifting methods, it proved that hydraulic pumping and air lift systems were feasible technically (Yoon et al., 2001; Yoon et al., 2003). Hydraulic pumping system is two-phase lifting technology of solid and liquid. During vertical hydraulic transport (VHT), the flow characteristics of liquid-solid two-phase mixture composed of the water and ore particles are considered as the most fundamental issues. There are considerable studies on the hydraulic transportation of solidliquid two phase mixture. In the 1970s, experts and scholars from different countries began to apply hydraulic lifting technology to deepsea deepsea mining. Germany, Japan, Poland, South Korea and China have successively established on-land hydraulic lifting test system. Since the 1990s, more studies on vertical hydraulic transport have been conducted. Sumardi and Chung (1996) performed experiments with a closed flow-loop testing system to predict the pressure drops as well as the hydraulic gradients of water-solid mixtures. Jin et al. (1997) carried out experiments to study the minimal transporting velocity of the largesize particle material in the vertical pipe. Xia et al. (1997) founded a calculating model to predict and optimize the hydraulic lifting parameters of a manganese nodule mining system.

Ocean thermal energy is a kind of renewable energy stored in the ocean. This study proposes series-type expansion zeotropic organic Rankine cycle for ocean thermal energy conversion. The R218/R125 mixture are selected as the zeotropic organic working fluid. The mathematical model of radial-inflow turbine is established to evaluate the actual efficiency. The results show that composition of zeotropic mixtures greatly effects the friction loss in radial-inflow turbine. The power output of proposed cycle is 5.16–5.39% higher than that of traditional Rankine cycle. The irreversible loss can be significantly reduced due to the temperature glide in the evaporation and condensing processes. INTRODUCTION Ocean thermal energy conversion (OTEC) technology utilizes the warm seawater at the top layer and cold seawater at the bottom to drive a thermodynamic cycle and produce power. This technology has caught great attention due to the stable and vast storage of the ocean thermal energy. However, the temperature diffidence of ocean thermal energy remains within approximately 20°C which means the energy conversion efficiency is restrained in a low level and leads to a great obstacle in its application. The advanced thermodynamic cycle is deemed as the kernel theory for OTEC. In order to improve the thermal efficiency of the cycle, a technical solution of absorption and temperature change occurrence can be adopted. There are two basic research methods. One is the use of absorbing working fluids. Kalina (1984) proposed a Kalina cycle using a mixture of ammonia and water as a working medium. This cycle achieves temperature-variable evaporation by changing the concentration of ammonia and water. Uehara (2004) proposed the Uehara cycle, which still uses a mixture of ammonia and water as working fluid. In addition, this cycle uses intermediate recuperation technology to reduce heat loss during the cycle. Its theoretical cycle efficiency is 1–2% higher than the Kalina cycle. The second is to use nonazeotropic working fluid. Currently, the research of low and medium temperature thermal energy was mostly based on pure working fluids, and the cycle performance was greatly limited in the entire circulation system (Chen and Goswami, 2010; Etemoglu, 2013; Luo and Xu., 2015). It is found that zeotropic mixed working fluids change temperature during evaporation and condensation. It broke through the isothermal phase transition process of pure working fluid in the past. Faming Sun (2012) optimized the closed-loop system. This system used output work as an evaluation index, and found that ammonia was the ideal working medium. Lecompte (2014) analyzed exergy efficiency of zeotropic mixed working fluids based on the second law of thermodynamics. Aghahosseini (2013) analyzed zeotropic working fluid and pure working fluid. Through these previous zeotropic studies, zeotropic working fluids can reduce the irreversible losses due to the temperature slip during the evaporation and condensation processes.

In deepwater wells, the cement around well casing usually does not return to the mudline. If the top of cement (TOC) is above the previous casing shoe, this can entrap drilling fluids in the annuli of the multicasing construction. High temperature fluid will heat the casing and cement during well testing and production, which will induce thermal stress and sustained casing pressure (SCP) in the annuli of the casing strings. In this paper, a method to predict the sustained casing pressure is established. This approach consists of two sub-models: a heat transfer model and a SCP model. The heat transfer model is used to provide boundary and initial conditions for the SCP model. The influence of wellbore heat transmission, casings and properties of completion fluid in the annuli is considered in the heat transfer model. A numerical simulation is given to verify the validity of the theoretical model in the framework of ABAQUS software. Good consistency has been shown between the theoretical result and the numerical simulation. In addition, both the physical parameters of the fluid in the annuli and the TOC have significant effect on the SCP. The model in this paper has important theoretical and engineering significance for deepwater drilling, especially for the casing and cementing design, and the integrity of the subsea wellbore. INTRODUCTION The casing program, wellhead equipment and geothermal gradient in deepwater wells are different from that of onshore wells, which makes the influence of SCP on deepwater wells prominent. Many accidents have occurred in deepwater wells due to SCP. For example, the production casing in Marlin A-2 well ruptured due to SCP, resulting in the well being abandoned (Bradford et al, 2004; Vargo et al., 2003). Some deepwater wells experienced casing extrusion and sticking, caused by SCP due to excessive high temperatures (Pattillo et al., 2006). In the South China Sea, technical difficulties caused by high temperature and high pressure have also been reported (Han et al., 2018; Xu et al., 2017). Therefore, it is of great significance to study SCP to ensure the safety and reliability of deepwater wells.

With the increasingly prominent energy shortage problem, offshore oil and gas fields have been rapidly developed, horizontal well production technology is increasingly valued and widely used, but horizontal well production logging technology has not been well resolved. In-depth research on the multiphase flow characteristics of oil, water, oil, gas and water in the wellbore is of great significance for improving the production logging technology of horizontal wells. Since the actual horizontal wellbore is fluctuating, the flow process of multiphase fluid in the wellbore is very complicated. At present, only a few researchers have conducted limited research on the characteristics of multiphase flow in this pipeline. In order to study the characteristics of oil-gas-water three-phase flow in different dip angle fluctuating tubes, by using the VOF model in FLUENT, simulates the oil-gas-water three-phase flow in the largediameter (124mm) fluctuating tube respectively at the dip angle θ of 0°, 5°, 10°, 15°, 20° and 30° at the inlet mixture velocity of 0.5m/s at the gas content rate (Cg) of 10% and 50%, and then analyzes and compares the evolution trend of the three-phase flow pattern in the fluctuating tube, the gas hold-up of wellbore profile, the water hold-up and the pressure distribution in the wellbore. The analysis shows that at a low gas content rate, the oil-gas-water three-phase flow pattern in the fluctuating tube is transformed from stratified-stratified flow to intermittence-stratified flow, and as the dip angle becomes larger, the partial gas hold-up becomes larger, the water hold-up becomes smaller, the curve of pressure drop oscillates more strongly, and the presence of slugs causes pressure fluctuations in the wellbore; at a high gas content rate, the oil-gas-water three-phase flow pattern is basically unchanged in the fluctuating tube, and the stratified-stratified flow, the effect of the dip angle on the gas hold-up weakens, but the greater the dip angle is, the stronger the gas-liquid two-phase slippage effect and the greater the pressure drop in the wellbore will be. Through the research work of this paper, the analysis and summary of the three-phase flow, numerical simulation and other aspects of oil, gas and water, the results have certain theoretical significance and practical guidance for improving oil and gas production on the field.

Flexible corrugated pipes as used for the transport of gas in offshore deepwater applications can generate undesired flow-induced pulsations (FLIP). This phenomenon has been also traditionally called "singing risers". The pulsations generated may result in high-amplitude cyclic stresses in the pipe systems attached to the flexible. Moreover, an HSE risk for the operators around the riser arises due to the tonal noise radiated from the system. The root cause for this phenomenon is nowadays well understood. Namely, vortex shedding at each internal corrugation of the carcass induce pressure pulsations which are eventually synchronized and amplified by an acoustical resonance along the length of the flexible. Despite this established knowledge, mitigation or suppression of the phenomenon once it occurs is hard to achieve. The purpose of this paper is describing field tests executed for a live natural gas export corrugated riser in the North Sea. The tested mitigation measure was liquid injection upstream of the gas export riser. The field tests had several objectives. First, to explore the effectiveness of this technique, for which only one prior experience is documented in open literature. According to very recent studies, the main mechanism contributing to suppression of FLIP by liquid injection is cavity fill-up, though this could not be tested in the field trial. Second, to quantify in more detail the threshold injection rates needed at different gas export rates. Third, to explore the sensitivity to export pressure. The tests consisted of measuring several variables of interest, next to the existing process conditions. These are the dynamic pressure pulsations at the riser hang-off location, as well as vibration levels at selected critical locations. The results are benchmarked with dry runs in which no liquid is injected. The injected liquid performed as expected, not only in mitigating FLIP, but even suppressing it altogether when sufficient liquid is injected. Threshold levels for the injection rates were found that, though not enough for full FLIP suppression, reduced the measured vibrations to acceptable levels. This allowed a significant increase in production capacity.

This paper presents the results from wind load CFD calculations performed on a truss leg of a typical GustoMSC designed drilling jack-up rig. The CFD model is constructed using the STAR-CCM+ software package from Siemens. The performance of two numerical models Unsteady RANSE and Delayed DES are investigated. A number of flow angles are considered. The wind force is computed using a constant and uniform flow field at the inlet boundary of the computational domain. In order to investigate the scale effects, the calculations are performed at model-scale as well as at full-scale. The results of the CFD calculations are compared with the results that can be obtained on the basis of the recommended drag force coefficients by the SNAME which are developed largely based on wind tunnel measurements. It was found that the scale effects are present for the drag force acting on truss legs due to the Reynolds number dependency of the cylindrical components. CFD results at full-scale show that the SNAME recommendation method is on the conservative side. Based on the results of the CFD calculations at model-scale and full-scale, this paper discusses the scale effects of wind drag force acting on a truss jack-up leg. INTRODUCTION A typical drilling jack-up rig consists of a buoyant platform standing on three independent truss legs, with a large forward accommodation block, several large structures and equipment, a drilling derrick and several cranes on the deck. The truss shaped leg consists of three chords with racks connected with each other through cylindrical shaped bracings and spanbreakers. Fig. 1 shows a typical GustoMSC designed drilling jack-up with three truss legs. The design of a jack-up rig requires the prediction of the forces generated by wind on the truss legs for the transit condition. In the early design stage of a jack-up, the wind forces are usually estimated by empirical methods which are given by standards such as the SNAME (2008) and ISO (2016). The standards are based on the building block approach. The total wind force on the truss leg is estimated by summing up the forces of the chords and cylindrical members considering the projected area, orientations and flow angles. This method is efficient and fast but usually the level of detail is low and shielding effects and flow interactions by the leg components are not considered. When high accuracy is required at the design stage, wind tunnel measurements are commonly carried out. However, the wind tunnel measurements are performed at model-scale and must be carefully performed to ensure that appropriate Reynolds numbers are reached for the truss legs, since scaling effects can be significant for truss legs, due to the Reynolds number dependency on the cylindrical shape components. Predicting the drag force using Computational Fluid Dynamics (CFD) is therefore of particular interest. Because, in CFD not only the drag force can be predicted, but also valuable insight can be obtained into the flow behavior through visualization of the flow field.

A steel lazy-wave riser (SLWR) is an optimized pipe configuration minimizing the top tension and fatigue for deep-water developments. This riser system may be exposed to dynamic loads when transporting internal slug flows which may cause oscillations and stresses reducing the fatigue life of SLWR. However, studies on the slug flow-induced vibration (SIV) in SLWR are rarely found in the literature. In this study, a computational code is developed to determine slug flow characteristics for a practical range of pipe inclinations. A time-domain finite element analysis has been performed to study horizontal and vertical in-plane responses of SLWR under the influence of steadily time-varying slug flows. Comparisons of oscillation frequencies, time histories and timespace varying responses are investigated. It is found that slug flows result in the reduced oscillation frequencies, but trigger multi frequencies and multi-modal interaction phenomenon, especially at higher-order modes. Further investigations should be carried out while involving the effect of external loads and considering different subsea riser configurations. INTRODUCTION In the past few years, oil and gas exploration and production have increasingly moved to deep-water developments where the steel catenary riser (SCR) was utilized as a cost-effective solution. Nevertheless, hanging a SCR from a floater with considerably large movements is regarded as an enormous challenge. The relatively high motions result in severe fatigue damage at the touchdown point (TDP) and at the fairlead. Consequently, the SLWR was developed to replace the traditional SCR configuration so that the top loads can be reduced. The SLWR differs from the SCR in the buoyancy modules installed at the mid-section of the riser. Because of the ease of engineering and distinctive performance, the SLWR had a widespread breakthrough. The buoyancy modules deployed on the SLWR effectively decrease the effective tension on the riser top and offset the floater movements from the riser TDP, which enhances the riser strength capacity and improves the fatigue performance.

ABSTRACT An effective design method to control the welding distortion of a pressure vessel constructed by HY-80 steel, especially thick plate, have been established using experiment, measurement data and FE analysis. It is found that the major factors affecting the distortion of the pressure vessel are angular distortion and transverse shrinkage. To estimate these factors, predictive equations have been derived by several experiments and the results are embedded in simplified thermo-elastic method(STEM)(Park et al., 2001) for FE analysis. Based on the results, proper quality control methods have been proposed to meet the allowance criteria without additional mechanical constraint of pressure vessel during fabrication. INTRODUCTION Welding technique is typically used for structures requiring water-tight or pressure-tight conditions such as pressure vessels. However, in case of welding, thermal deformation occurs due to heat input of welding unlike other fabrication methods. Such deformation of the structure causes an excessive gap or misalignment in the process of joining or installation of the manufactured structures. In addition, recently, as the operation conditions of large structures such as pressure vessels become severer and the thickness used becomes thicker. This increases the demand for quality control. A proper distortion control method is becoming an important issue, and it is the most efficient way to establish an appropriate production planning through the distortion assessment. In this study, the weld distortion assessment and control methods of an end-bulkhead of pressure vessel have been established to satisfy the accuracy of fitness. The welding distortions were identified with STEM and the validity of the predictions was verified by the data measured during the fabrication stage of the product. HEAT INPUT MODEL The temperature distribution, heat affected zone(HAZ) size and welding distortion were measured through the welding experiments in order to determine the optimal heat input model for FE analysis of the welding. Nonlinear thermal elasto-plastic analysis technique was used in the FE analysis. The heat transfer and thermal stress were analyzed individually. The lower surface of the welded member was assumed to be on the surface plate condition to constrain the reverse distortion caused by the welding heat input. The material was assumed as isotropic, temperature dependent and yield point was defined according to von-Mises yield stress.

ABSTRACT Taking part in the Japanese National hydrate research program (MH21, funded by METI), we have conducted examinations about flow assurance in a production well of the methane hydrate (hereinafter called the MH). In this study, we clarified distribution of the gas bubble diameter by an experiment after passing through a sand exclusion screen when dissociated gas flows from the MH reservoir to the production well. The gas-liquid separation ratio in the production system was evaluated from the experimental results. Further, numerical analysis was conducted to examine the methane gas and water two-phase flow in the production system using the estimated gas-liquid separation ratio. INTRODUCTION The MH has gained international attention as an alternative energy resource to conventional fossil fuels. In Japan, research on required production technology is carried out with the goal that private enterprises commercialize gas production from the MH. To promote MH resource development, the Ministry of Economy, Trade and Industry formulated "Methane Hydrate Development Program in Japan" in 2001, and the Methane Hydrate Resource Development Research Consortium (MH21) was organized within the same year. The initial offshore production test in 2013 and the second in 2017 have succeeded in producing gas from the MH under the seafloor by decomposing the MH into methane gas and water. In offshore production tests, the system based on the depressurizing method was used. The depressurization method lowers the bottom pressure in the production well and reduces the pressure applied to the MH reservoir, promoting the dissociation of MH into a methane gas and water. Methane gas production by the depressurization method have some obstacles. For example, the problems of sand trouble and gas-liquid separation. The MH reservoir and the production well are separated by the sand exclusion screen. The screen prevents the inflow of sand into the well. If the filtering size is reduced to prevent sand particles from flowing into the production well, the bubble diameter of the methane gas that passes through the filter also becomes finer, resulting in lower gas-liquid separation ratio. When gas flows into the water line, efficiency of the pump reduces. Furthermore, the MH may be regenerated, causing flow disruption, then leading to a blockage at downstream of the pump in the water line.

ABSTRACT A comparison of three methods for predicting wave forces on vertical structures is presented in this paper. We compare equations proposed by Goda (1985), Cuomo et al. (2010), and the American Society of Civil Engineers (ASCE) (2017). These methods were compared to experimental measurements of wave pressures and forces collected on a large scale hydraulic physical model for irregular wave conditions. The experimentally measured water depth and wave parameters were applied as inputs to each method, and the predicted forces and pressures were compared to measured pressures and integrated forces. A greater understanding of wave loading and structural response could help refine design codes and prevent over-engineering. INTRODUCTION With a majority of the world's population living in coastal areas, an understanding of wave forces and structural responses necessary to maintain existing coastal communities and ensure any new developments are properly engineered. While wave-induced loads have been studied extensively in the last half century, there is still room for improvement in the methodology of wave force estimation. There have been many studies that provide methods to estimate wave forces on coastal and offshore structures. Some of these papers exploring wave forces include Kaplan and Silbert (1976), Fenton (1990), Kaplan (1992), Kaplan et al. (1995), Kirk göz (1995), Cuomo et al. (2007), and Bea et al. (2001). Despite the large number of experiments, mathematical models, and studies done in an effort to accurately predict the wave forces and pressures on various structures, there remains a lack of understanding of wave loading and the resulting effects on near-coast structures. This study sought to examine wave forces and pressure distributions on vertical residential structures, which may be considered similar to vertical walls. These structures are commonly elevated above the ground. During a storm surge event, a structure's elevation above or below the water level, termed the structure's air gap, may be important when considering wave-induced loads and pressures. Though each of the aforementioned studies have added something new to the wealth of knowledge surrounding the behavior of ocean waves, this paper has chosen to specifically analyze methods presented by Cuomo et al. (2010), Goda (1985), modified for elevated structures by Wiebe et al. (2014), and ASCE (2017).

ABSTRACT Air lubrication method is a technique to reduce the frictional resistance by supplying air between the hull surface and seawater. Air layer is formed by the coalescence of the injected air bubbles over a certain air flow rate. The total energy efficiency is increased when the rate of decrease of the frictional resistance by the air layer is larger than the energy supplying the air. Air lubrication patterns must be confirmed and air injection position and injection flow rate should be properly controlled to improve efficiency for air lubrication system on full scale vessel. In this study, air injection experiment was performed on the plate and model line, and the lubrication diffusion angle was measured by image analysis. INTRODUCTION The reduction of ship resistance is the most effective way to reduce fuel consumption and for low CO 2 emissions. The main components of ship resistance consist of wave resistance, pressure resistance, and frictional resistance. With the improvement of hull form optimization techniques, the wave and the pressure resistance could be less than 20 percent of the total drag in most modern ships. Therefore, the advantage from the reduction of the remaining frictional drag would be enormous. The fuel consumption of global ocean shipping in 2003 was estimated 2.1 billion barrel/year (Corbett and Koehler, 2003), which corresponds to approximately 200 billion US$/year. Thus, 10% reduction of frictional drag would lead to saving of 16 billion US$/year. Air lubrication method is one of the mature technologies for commercialization to reduce the frictional resistance. Drag reduction using air can be categorized by bubble drag reduction (BDR) and air layer drag reduction (ALDR). In BDR, small bubbles are injected into the boundary layer. The dispersed bubbles act to reduce the bulk density and to modify the turbulent momentum transport, depending on the shape and distribution of air bubbles. Initial report on BDR was by McCormick & Bhattacharyya (1973). It was observed experimentally that drag reduction increases with gas (bubble) flow injection rate (Merkle & Deutsch 1992).