A deep draft semi-submersible hull has been developed as a standardization concept which can support the topside structures up to the facility weight for the specific level of daily oil production in GOM (Gulf of Mexico). The designed hull has the optimized dimensions of ring pontoon and four columns for coping with the weight change of topside and the innovated hull shape to eliminate the casting which is normally used at the corner node area where high stress concentrated on. The hull form also has the good global motion in waves, winds and currents to be able to use the SCR (Steel Catenary Riser). The mooring systems are designed for water depths of 1,500m as a standard design concept of hull including mooring lines (3 × 4). The global performance is validated for the maximum offset, the mooring line tension and the acceleration. The possibility of SCR usage is also investigated with the fully coupled time-domain analysis to confirm that the designed hull form has the suitable hydrodynamic characteristics to permit the minimum vertical motion performance for SCR. Throughout the global performance and mooring analysis, the designed Semi-FPU fulfills all stability requirements of rules and codes specified in design of basis for both intact and damaged conditions, and has good motion characteristics such as inclination, acceleration, sectional loads and air gap and mooring system compliance with design criteria in the view point of mooring tension, offset and fatigue damage. Also, the global structural strength analysis has been performed to extract stresses and displacements where local points which are pontoon-column connection areas from the global model. The local points need to reinforce during detail design stage from buckling, yielding and fatigue analysis for normal operating and extreme storm conditions.

This paper presents the first iteration design of the Flotant concept developed within the framework of a Cooperation Research Project funded by the European Union’s Horizon 2020 research and innovation programme. The Flotant concept is a hybrid concrete-plastic barge-type floating offshore substructure holding a 12MW wind turbine with the singularity of getting floatability by using plastic foam material fitted within the floater substructure. The INS12MW generic wind turbine, an upscaling exercise based on the DTU10MW reference wind turbine, is presented and simulated using open-source certified aeroelastic code. The floating platform and the mooring system are designed for two different sites, West of Barra and South East of Gran Canaria island. The principal dimensions are presented along with the hydrostatic and hydrodynamic properties of the floating system. A relevant subset of design load cases derived from International Electrotechnical Commission and Det Norske Veritas standards was simulated using an open-source aeroelastic code (NREL FAST) to check the coupled aero-hydro-elastic behaviour of the floating system and to generate the required load-matrix for the structural assessment of the different components. The evaluation of the design includes the seakeeping performance, the stability of the floating platform and the global performance analysis for the abovementioned sites. It demonstrates the technology developed within the Flotant project is feasible even in rough conditions like the ones in the West of Barra site.

The Prelude Floating Liquefied Natural Gas (FLNG) facility is moored with an internal turret allowing it to perform offloading operations of liquefied natural and petroleum gas products. It does so in either a Free Weathervaning (FW) mode, i.e. by allowing the unit to rotate according to environmental loads, or in a Thruster-Assisted (TA) mode, i.e. by using the stern thrusters to maintain a fixed heading deemed preferable for the entire operation, or a particular phase. An accurate estimation of the various environment effects, in terms of forces on the FLNG and LNG carrier, is critical to ensure a correct prediction of its heading or the required thruster forces, depending on the selected operating mode. The predominant loads driving the weathervaning behavior are wind and current loads. These loads have been estimated from wind tunnel tests during the engineering phase. Since the Prelude FLNG has been installed on-site, field measurements have provided an opportunity for comparison and shown some differences with the numerical predictions based on the estimated loads, prompting a need for verification of current loads by an independent method. For the Prelude FLNG application, current loads play an important role due to facility size and significant tidal currents. It has been shown in some previous studies that wind tunnel tests for a model of under-water geometry may underestimate current loads compared to those on a full-scale vessel. There is a boundary layer along the wind tunnel floor in wind tunnel tests, while the current profile is relatively uniform over the hull draft in the real ocean condition. Moreover experimental tests present some additional drawbacks: they are performed at a reduced scale (1:225), the Reynolds number is lower than full-scale even with a large wind tunnel speed, and it is difficult to model the long (150m full-scale) Water Intake Risers (WIR) extending below the hull bottom. In order to investigate these effects, state-of-the-art full-scale CFD simulations were performed for the Prelude hull and WIR. The test program included different current speeds and directions, and several sensitivity studies: Reynolds number effect between model- and full-scales, effect of current speed profile (comparing uniform and boundary layer profiles at model scale), effect of FLNG rotation in yaw, impact of unsteady current, and presence of marine growth. Extreme dimensions of Prelude FLNG and requirements for accuracy of this study called for the CFD calculations to be performed on the High Performance Computing (HPC) clusters - Stampede2 and Frontera - at the Texas Advanced Computing Center (TACC), which are both amongst the world’s largest supercomputers. This paper describes the assumptions and challenges of the CFD study and discusses the results of the main program and various sensitivities. The main conclusions and lessons learnt are also discussed.

The FOWTs (Floating Offshore Wind Turbines) projects are spreading, especially in Europe. Some of FOWTs are doing commercial activities, on the other hand, many new concepts of FOWTs are still published in the world. This may mean that there is room for the reduction of the construction cost of the floater, therefore the development of more reasonable design of the floater would give rise to big business opportunities. These new concept of FOWTs are thought to be optimized regarding the safety and economic efficiency, but there are a few studies for the comparison in the safety, economic efficiency, and parameters which effect to them between different types of floater concepts. Therefore, authors carried out the parametric study in terms of the motion in waves and wind and construction cost for the semi-submersible type and the spar type. In this study, 2, 5, 10, 15MW wind turbines are assumed to be installed on the floater, and dimensions of the floater and an inclination angle because of the maximum thrust force are set as constraint conditions. The construction cost is estimated as a product of material weight and unit cost of material. Authors found the solution regarding the relationship between the construction cost and the performance of the FOWTs through this study. the distance between the columns and the lower pontoon breadth were effective parameters to ensure he performance in waves and to reduce the construction cost of semi-submersible floater.

The potential for coupling a cylindrical point absorber type wave energy converter (WEC) to a 5MW spar type floating offshore wind turbine is investigated. The wind and WEC system is modelled in the frequency domain and in two dimensions under the simplifying assumption that wind and waves propagate in the same direction. Coupling of the bodies is considered with respect to all theoretical combinations that might be achieved rather than a single specific design. Results are analysed with respect to the maximum power that the WEC coupling can achieve. It is shown that for mild waves the WEC can theoretically produce power in the range of 0.2 to 0.6 MW, its optimal dimensions are such that the draft and radius are approximately 18.8 m, and that obtaining this power tends to marginally amplify the pitch of the spar.

Mechanistic models are necessary for understanding and predicting the behavior of liquid-liquid flow for multiple pipe dimensions, mixture properties, and flow patterns. In this paper, a mechanistic model is proposed to calculate pressure drop across circular channels for liquid-liquid two-phase flow. The developed model considers several key aspects of liquid-liquid flow, such as mixed and wavy liquid-liquid interfaces and dispersion within each liquid’s layers. Unique identifiers, such as height, turbulence, and dispersion, are calculated for each phase, using an augmented separated flow model and nonlinear optimization. Comparison of the proposed model with experimental data, comprising of multiple inclination angles and flow patterns, shows accurate predictions for a variety of liquid-liquid flow patterns, including double- and triple-layered flow.

An integrated optimization model of EEDI and minimum propulsion power has been established in this paper. EEDI optimization needs to meet IMO requirements for minimum propulsion power. Installed power reduction is one of the most effective way to optimize EEDI, but it will make the installed power lower than IMO requirements. From the view of security, it is not allowed. In order to coordinate the contradiction between the reduction of EEDI and the minimum propulsion power of the ship, this paper is devoted to the development of an effective and efficient EEDI optimization method under the minimum propulsion power constraints of the ship. The evaluation method of the objective function EEDI is a digital pattern of hydrodynamics performance for tanker series developed by the China Ship Science Research Center. In order to illustrate the method, the VLCC is selected as the research object, and Non-dominated Sorting Genetic Algorithms II is selected to optimize the EEDI. The calculation results show that energy efficiency has been optimized about 4%, so the EEDI and minimum propulsion power integrated optimization model are reasonable and effective.

New types of fish farms are often larger and structurally more complex than conventional fish farming structures, and associated challenges concerning safety and costs increase correspondingly. Thus, increased precision in structural design is required, with estimation of hydrodynamic loads on nets as an important topic. Today, both load coefficients for nets and measured netting dimensions are given with relatively high uncertainties. New knowledge for netting materials with high solidities as well as scaled netting commonly applied in model tests are included in the presented study. Results from towing tests and the development of a new mathematical expression for local drag coefficients (for netting twines) indicate that drag coefficients are not only dependent on solidity and Reynolds number, but may also be affected by the velocity reduction and the local velocity at the twines.

Understanding the behavior of the multiphase flow in the porous media near the wellbore region is essential for increasing wells’ productivity and oil recovery. In this paper, an experimental and numerical study of multiphase flow in porous media near a perforation tunnel is presented. The effect of properties on the flow, such as porosity and permeability, are crucial for increasing oil and gas production. Two-phase flow through a cylindrical porous media with a perforation tunnel samples experimentally and numerically tested. Five sandstone samples were created at Memorial university labs, the sample dimensions are 30.48 cm high, 15.54 cm diameter, and a perforation tunnel has a 25.54 cm depth and 2.54cm diameter. The air and water injected into the sample radially at different flow rates, the water flow rate ranged from 1 to 3 LPM, and the air 3 to 9 LPM. The simulation carried out using ANSYS-Fluent 18.1 commercial software simulates the Volume Of Fluid method VOF coupled with the different turbulent models used to simulate the flow. The results showed that the porous media’s pressure buildup is greatly affected by the gas flow rate and its permeability. The wellbore pressure and porosity have more negligible effect on the pressure buildup profile in the porous media. The dominant factor for the breakthrough of a fluid in a core sample is the gas flow rate. Incorporating the gas flow in a porous system will reduce hydrostatic pressure loss, and less time is required to activate the breakthrough time.

The plug and abandonment (P&A) operation is the final stage in the life cycle of oil and gas wells. The aims of the P&A operation are to seal the well and permanently maintain the well-integrity similar to that of the original natural caprock. Using this approach, it is possible to isolate fluids movement between different strata, to prevent environmental disasters. Generally, the main steps in the P&A operation are (i) accessing the annulus section of the well, (ii) cleaning the defected area, and (iii) placing the cement plug barriers into the target area. To prepare the target area and avoid cement plug contamination, a cleaning process is required inside and outside the casing. The jet cleaning process is one of the effective methods for the cleaning step, in which a liquid of a higher density is usually injected into the target area to displace a lighter ambient fluid. During the jet cleaning process, several forces affect the cleaning efficiency, including inertial, viscous and buoyancy forces. In this work, we analyze a fundamental component of the jet cleaning process in the P&A operation, via experimentally studying the characteristics of a miscible positively buoyant jet. In our work, a heavy fluid is injected downwards into a large rectangular tank filled with a light ambient fluid. Due to the large dimensions of the experimental tank, the wall effects on the flow are neglected, i.e. we consider a free jet. We investigate some of the parameters affecting the behaviour of our positively buoyant jets, such as the injection velocity, the nozzle diameter, and the ratio between the viscosity of the jet fluid to that of the ambient fluid. In the parameter ranges of our interest, the jet flow exhibits certain critical flow features, such as the laminar length (i.e. the initial stable part of the jet where the injection fluid remains laminar and does not mix with the ambient fluid) and the spread angle (i.e. the area occupied by the jet). Our results show that both the laminar length and the spread angle decrease by increasing the injection velocity. In addition, increasing the viscosity ratio results in increasing the maximum laminar length and decreasing the spread angle. These results can help to better design an efficient cleaning in the P&A operation of oil and gas wells.

This paper covers the generic procedure for the creation and usage of a complete system simulation for propulsion systems of ships with focus on complex hybrid systems. Due to the large number of available components and challenging operational profiles, there is no longer a single best solution, especially in specialized shipbuilding. On top of that even minor changes in the propulsion system can have a substantial impact on plant performance and vessel behavior. Thus, the early design stage is crucial. The design procedure usually incorporates the selection and dimensioning of available components and concepts. Once this has been done, the dynamic behavior can be analyzed using the developed system simulation environment. With the knowledge gained the needed alterations in the concept can be identified and implemented in the subsequent design iteration circle. Based on the example of an offshore anchor handling vessel, the integration potential of a hybrid propulsion system is examined and evaluated according to the aforementioned procedure. The applied tool is a system simulation environment developed in the Department of Marine Engineering, consisting of a distributed co-simulation of the existing ship design environment E4 and Matlab ® Simulink ® .

With the increasing demand for renewable energy sources in the past years, the interest in expanding the use of wind energy has grown. The next frontier in this expansion process is the use of floating wind turbines offshore. One of the main factors dictating the economic feasibility of such wind turbines is the complexity of their installation process. The dimensions of modern offshore wind turbines, the distance from the installation sites to the coast and demanding environmental factors all contribute to the difficult of developing an efficient installation concept for this kind of structures. In this work, we present a new concept for a catamaran vessel capable of handling the deployment of offshore wind turbines on floating spar platforms using a low-height lifting system that connects to the lower end of the wind turbine. The low-height lifting system is controlled by an active heave compensation system and constant tension tugger wires attached to the turbine mid-section are used to ensure the balance of the tower during the installation process. We conducted a series of hydrodynamic analysis using the software suit SIMA to study the dynamic response of the proposed system under different weather conditions and different operational layouts. This preliminary concept was proven feasible from a hydrodynamic point of view and can now be pushed forward for further studies regarding other aspects of the operation, such as impact and structural loads and mechanical design of components.

With commercialization, marine science and military applications in offshore and shallow waters is increasing, the development of the small surface vessels are getting greater, and that design targets are focus on multi-functional platforms, smart navigation and autonomous, etc. Therefore, the goals of multi-purpose small surface vessels such as the coastal patrol, offshore observation and data collection, intelligence reconnaissance, anti-mine warfare, marine shooting training targets, and so on. In currently, to achieve these missions, the length of most small surface vessels were designed less than 10 meters. Furthermore, based on these multi-propose requirements, this study will explore the configuration design of monohull and trimaran, combine the research source of the Horizontal Circulating Water Channel (HCWC), through the ship model test to acquire experimental data. In addition, to promote the study quality and experimental efficiency, we applied Taguchi design of experimental (DOE) and the variance of analysis (ANOVA) to compare the resistance and payload of various configurations ship design. In this study, we defined two control factors (such as factor-A is Longitudinal distance, factor-B is Lateral distance) and set up three-level factorial design, and planned factorial experiment based on Taguchi orthogonal array L 9 (3 4 ). Also used the neural network and training metamodeling. This metamodeling was decided by relative coefficient (R) and decision coefficient (R 2 ). According to this metamodeling, and then, applied the genetic algorithm to search the best solution such as A 2 B 3 . The results of this study showed that the resistance performance of the trimaran is better than the monohull while the volume Froude number Fr ∇ > 0.95, and the optimum configuration has greater resistance performance at both higher and lower speed fields to achieve robust design. In the other hand, this paper will also discuss the feasibility and effectiveness of the installation space and multi-function performance on platform. Hence, for payload study, we also applied ANOVA to analyze these nine different configurations, and indicated a significant main effect for factor-B. However, no significant main effect for factor-A and interaction effect were found. To conclude, this study may be of importance in explaining small surface vessel design, as well as in providing ship designer with a better understanding of trade-off about speed and payload. While this study has its limitations (such as HCWC characteristic dimension), it is hoped that it could as a basis for further study in the multi-functional small surface vessel.

A three-dimension (3D) re-entrant honeycomb structure which exhibits negative Poisson’s ratio in all three principal directions is modeled from a classical two-dimension (2D) auxetic material. In this work, on the basis of the Castigliano’s second theorem and Timoshenko beam model, the shear deformation and axial deformation of this structure are investigated. And the analytical formulas of the effective modulus and Poisson’s ratio in each principal direction of the honeycomb structure are derived. By comparing the analytical results with the finite element analysis results, the rationality of the formula is verified. Then, the collapse characteristics of honeycomb structures with different mechanical properties under variation impact velocities are studied. The results show that, the deformation of honeycomb structure can be divided into three patterns, “quasi-static” deformation, “transitional” deformation and “local” deformation varied with impact velocities. And due to inertial effect, with the increase of impact velocity, the load-bearing capacity and energy absorption of the structure also increased. In addition to the impact velocity, the cells’ configuration is also a non-negligible factor, and its turns out that the decrease of angle accelerates the deformation state of the honeycomb structure and strengthen the energy-absorption capability after being subjected to impact load.

The Yme oilfield is located approximately 100 km from the Norwegian coastline in the Egersund basin. The original field development in 2008 consisted on a jack-up type platform (MOPU) and a subsea storage tank at 93 m depth. Both are interconnected through a caisson containing all risers, piping and umbilicals which also supports a wellhead platform (WHM). That original MOPU was removed in 2016 [1] and a redevelopment of the field is currently under execution making use of some of the remaining facilities. In order to re-use the existing tank and caisson, advanced structural fatigue analyses including fracture mechanics, probabilistic assessment, motion monitoring and regular NDT inspection concluded with the requirement for a support structure to extend the service life of the old structure, which fatigue life was limited. A screening process that covered different alternative solutions lead to a design (called Caisson Permanent Support or CPS) with overall dimensions (L.B.H) of approx. 70m × 50m × 40m and a dry-weight of 1300 t (figure 9). It consists on a beam structure composed of steel tubular braces with diameters ranging from 1,1 to 2,7 m that supports a clamp (6 m height and 5,15m diameter) connected to the caisson. In an iterative process between structural, fabrication and installation designers the optimal final concept was selected after detailed analyses to demonstrate that is capable of meeting the requirement of 20 additional years of structural service life for Yme facilities. The CPS was successfully installed in June 2019 ensuring the integrity of the offshore structures and enabling the further re-development of the Yme field. Given its dimensions and its particular design purpose, the CPS is regarded as a unique project in the industry. This paper describes the challenges and the engineering work required for the design of the CPS.

This paper explores optimal configuration of both dimension and layout of Wave Energy Converter (WEC) arrays with full interaction and exact hydrodynamics. Arrays in this research contain devices that operate in heave mode and also devices that operate in pitch mode. The hydrodynamic interaction between buoys in the array is studied and higher q-factors is achieved using optimization. This study includes optimization results for arrays of only heave-mode buoys and hybrid arrays of 2 types of devices that has been mentioned above. Each of the heave-mode arrays contain 3, 5, and 7 buoys respectively while the hybrid arrays have arbitrarily selected configurations of the type of devices for comparison. This simulation uses impedance matching control which provides theoretical maximum level of power. The results indicates it is essential to optimize array layout simultaneously with the dimension of each buoy. Meanwhile, the mode of motion of the devices in an array is a significant factor in designing the array under complex ocean environment, and better performance of the array is achieved when the configuration is selected properly.

Results from cuttings transport tests in laboratory using different field applied oil-based drilling fluids with similar weight and varying viscosities are presented in this paper. The fluids are designed for highly deviated wells, and the cuttings transport performance at relevant wellbore inclinations was investigated. The experiments have been performed in a flow loop that consists of a 10 meters long test section with 2″ OD freely rotating steel drill string inside a 4″ ID wellbore made of cement. Sand particles were injected while circulating the drilling fluid through the test section. Experiments were performed at three wellbore inclinations: 48, 60 and 90 degrees from vertical. The applied flow loop dimensions are designed so that the results are scalable to field applications; especially for the 12,25″ and 8,5″ sections. The selected setup provides correct shear rate ranges and equal Reynolds number to the field application when the same fluids are applied. Results show that hole cleaning abilities of the tested fluids vary significantly with well angle, drill string rotation and flow rate. Results support field experience showing that low viscous fluids are more efficient than viscous at higher flow rates and low drill string rotation. As well as per field experience more viscous fluids are efficient in combination with high drill string rotation rates. The results show the effect of cuttings transport efficiency as function of hydraulic frictional pressure drop, demonstrating methods to achieve more optimal hydraulic design in the tested conditions. The key findings have direct relevance to drilling operations.

A successful primary cementing job requires an efficient fluid displacement process in order to place cement in the annulus between a casing or liner and the formation around the wellbore. This operation is a critical part of the well construction and due to the hardening properties of cement there will be no second chance with this operation. Once hardened, the cement should provide zonal isolation and pressure containment and should do so through the lifetime of the well. Furthermore, the cement shall anchor and support the casing string and protect it against corrosion due to formation fluids. A good quality cement job is important both from an environmental and from an economical perspective. In order to improve recommended cementing practices, and thus also the quality of cementing process, it is necessary to develop cementing simulation software for proper engineering. Detailed data on the displacement efficiency from practical operations are difficult or impossible to obtain. Furthermore, field operations do not allow for a systematic change in fluid properties. To be able to validate the engineering tools it is therefore necessary to perform laboratory measurements with fluids with relevant properties. It is also important to perform these experiments in laboratory equipment of sufficient diameter dimensions to facilitate scale up of the results. The purpose of the present article is to give an overview of cement displacement experiments which were conducted using a large diameter annular flow loop using model fluids with relevant rheological properties. While some results from these experiments have been presented in previous articles, this article is intended to give an overview of all the experiments, including the setup and experimental approach, and provides in more detail results not presented previously. In particular we show results from video recordings which confirm previous conclusions based on conductivity measurements. It is found that eccentricity affects the displacement physics significantly. In washout sections the effects of eccentricity are different and generally smaller since the eccentricity is also reduced. Drill string rotation improves displacement efficiency in all tested cases both within and outside the washout cavity. Since the amount of publicly available experimental data of this type is very limited, the detailed information presented here should be of great interest and relevance for the development and validation of industrial cementing simulation software.

Due to the ever higher demands from the energy market, the quantity, dimension and power capacity of newly installed offshore wind turbines are continuously increasing. In terms of logistical management, economic feasibility and engineering difficulty, the traditional installation methods, predominantly represented by using Jack-up vessel and offshore cranes, will hit their limitations soon in the future. Offshore turbines have a relatively fixed geometric profile and physical characteristics: a slender cylindrical tower with huge blades attached on the top end. In this work, we exploited these features and designed a low-height lifting system for deploying wind turbine onto a floating spar platform. The low-height lifting system lifts the wind turbine with wires attached to the bottom of the tower, and keeps the balance of the tower with extra tug lines on the mid-section. The wires and tug lines are controlled by an active 6DOF compensation system. The low-height lifting system removes the necessity of a huge offshore crane onboard and can scale well to even larger wind turbines. The design is virtual prototyped in the simulator of Offshore Simulator Centre using FATHOM simulation software. Different design configurations are discussed in terms of the general arrangement, system dimensions and control methods.

In this paper, we apply a CFD computer code to study the hydrodynamic behavior of a stand-alone cylinder and a dual coaxial-cylinder system (DCCS) via free-decay motion tests. The geometric proportions of a stand-alone cylinder and the inner and outer cylinder of the DCCS are chosen to be the same as those in [1] and [2], respectively, as ocean wave-energy converter (WEC) devices. Overset mesh based on the commercial code ‘Star-CCM+ 11’ is used to simulate the free-decay motion of the two systems. Five parameters chosen for the CFD implementation are: turbulence model, initial displacement, time step, number of prism layers and mesh size. Results obtained from using different values of these parameters are compared so as to confirm the validity of choices made. The hydrodynamic performance of the stand-alone cylinder and outer cylinder in the DCCS are compared with the experimental results to assess and validate the CFD models. In addition, the heave hydrodynamic coefficients, namely, the added mass and total damping, and ‘resonance’ frequency of the stand-alone cylinder and those of the inner cylinder of the DCCS, with the outer cylinder being fixed, are obtained by using the CFD procedure. The hydrodynamic coefficients of another stand-alone cylinder with the same dimensions as the inner cylinder of the dual-coaxial cylinder are also obtained by simulations. The vorticity-contour plots for the stand-alone cylinder and the outer cylinder in the DCCS in free-decay motion are presented and analyzed. Finally, the results of the three cases are compared to examine the effect of the outer cylinder on the heave hydrodynamic coefficients of the inner cylinder.