Platform Hull Research Articles

Evaluation of second and third-order numerical wave-loading models for floating offshore wind TLPs

With the large-scale development in the last decades of fixed offshore wind across Europe and the ever-more present threat of climate change dominating national and global agenda, the exploitation of wind power in deep-water using floating wind turbines is gathering a significant amount of interest. Compared to other types of floating wind platforms, Tension-leg-platforms (TLPs) are less compliant systems resisting dynamic forces through their pre-tensioned tendons. Whilst this reduces the weight of the platform hull, understanding extreme loading cycles in the mooring system becomes an important design issue. Recent research has shown that including sum-frequency second-order and third-order loads is important to capture extreme events such as slack-line events on large and stiff floating systems. This article exposes a review of some of the existing numerical methods available to engineers to calculate second and third-order forces, including both potential (semi-analytical and BEM) and strip-theory approaches (Rainey and FNV). It compares their application in monochromatic waves on a truncated cylinder and a full TLP platform by evaluating forces amplitudes against CFD calculation. The results show that large fully submerged elements of the TLP floater contribute significantly to the third-order forces and are not well represented by existing engineering methods.

Numerical Analysis of Wave Load Characteristics on Jack-Up Production Platform Structure Using Modified k-ω SST Turbulence Model

One of the important stages in the offshore structure design process is the evaluation of the marine hydrodynamic load in which the structure operates, this is to ensure an appropriate design and improve the safety of the structure. Therefore, accurate modeling of the marine environment is needed to produce good evaluation data, one of the methods that can accurately model the marine environment is through the Computational Fluid Dynamic (CFD) method. This research aims to analyze the ocean wave load of pressure and force characteristics on the jack-up production platform hull structure using the (CFD) method. The foam-extend 4.0 (the fork of the OpenFOAM) software with waveFoam solver is utilized to predict the free surface flow phenomena as its capability to predict with accurate results. The Reynold Averaged Navier Stokes (RANS) turbulence model of k-ω SST is applied to predict the turbulence effect in the flow field. Five variations of incident wave direction type are carried out to examine its effect on the pressure and force characteristics on the jack-up production platform hull. The wave model shows inaccurate results with the decrease in wave height caused by excessive turbulence in the water surface area. Excessive turbulence levels can be overcome by incorporating density variable and buoyancy terms based on the Standard Gradient Diffusion Hypothesis (SGDH) into the turbulent kinetic energy equation. The k-ω SST Buoyancy turbulence model shows accurate results when verified to predict wave run-up and horizontal force loads on monopile structures. Furthermore, test results of the wave load on the jack-up production platform hull structure shows that the most significant wave load is obtained in variations with the wave arrival direction relatively opposite to the platform wall. Especially in the direction of 90° because it also has the most expansive impact surface area. Meanwhile, the lower wave load is obtained in variations 45° and 135°, which have the relatively oblique direction of wave arrival to the surface.

Evaluation of RAOs of a semi-submersible platform using field measurements: A full-scale model in Caspian sea environmental conditions

The present research investigates the motion response of a semi-submersible platform using measured field data. The Iran-Amirkabir semi-submersible platform (SSP) was considered as full-scale model in operation conditions. First, 14 accelerometer sensors were installed on the platform's hull, and measurements were made in 5 different scenarios in the Caspian Sea environmental conditions. Then, the Response Amplitude Operators (RAOs) for six degrees of motion were extracted using measured accelerator data. The Surge, Sway, and Heave RAOs processed by the Kalman estimation filter, Pitch, Roll, and Yaw RAOs were calculated from the Sensor Array method. Moreover, the boundary element method in ANSYS/AQWA software for the Iran-Amirkabir semi-submersible model was developed, and the RAO results were validated against the extracted field measurements. The obtained results from the Sensor Array method and the Kalman estimation filter are compared with the numerical simulations, which show Root Mean Square Errors of less than 3% and 4%, respectively for rotational and translational movements. The Mean Square Errors between both methods were also close to zero. Therefore, the proposed methods predicted activities of the studied SSP with relatively good accuracy by field data collected in the Caspian Sea.

Pitch stability of offshore waste collection platform hull with NACA fin stabilizers

In view of the safety problems caused by the pitch stability of the offshore waste collection platform, the three-dimensional model of the collection platform hull was established by SolidWorks software, and the influence of the installation parameters of NACA fin stabilizers on the pitch stability of the collection platform hull was discussed based on three-dimensional potential flow theory. The results show that the installation parameters of NACA fin stabilizers have an essential influence on the pitch stability of the collection platform hull. The larger the positive installation angle and the farther away the bow fin is from the midship, the smaller the peak values of pitch motion response. While the tail fin is not suitable to be installed near 600 mm of midship to avoid severe longitudinal movement of the hull.

North Pole ice-resistant self-propelled platform as an innovative complex for research in the Arctic

The Russian presence in the Arctic Region and the development of the Arctic is one of the most important geopolitical interests of Russia. At the beginning of the 21st century, the problem of using innovative methods in Arctic research came to the fore. Based on the analysis of the unique work experience of drifting stations “Severniy Polus” (“North Pole”) (1937-2015), Arctic and Antarctic Research Institute specialists have concluded that the stations should be replaced by a modern scientific complex, capable of solving a wider range of problems. As a result, it was proposed to create an ice-resistant self-propelled platform (IRSPP) – an engineering structure for permanent basing of scientific observatories. The IRSPP is designed to conduct year-round comprehensive scientific research in the high latitudes of the Arctic Ocean and should make a long drift of at least one year together with the surrounding ice massive. The scientific complex of the IRSPP includes 16 different laboratories, including an ice load monitoring laboratory. A unique ice load monitoring system (ILMS) has been developed for the IRSPP. The ILMS will be an essential part of the system of safe operation and persistence of the IRSPP and will provide the platform hull with a measurement tool for studying the mechanics of deformation and destruction of sea ice in its interaction with the engineering structures. In all respects, the IRSPP is unparalleled in the world. Its use can open a new chapter in the exploration of the Russian Arctic and in international collaboration aimed at studying the northern latitudes. The platform was put into operation in 2022.

Overview of import substitution in the houseboat market and a proposal for choosing a power unit using hydraulic drives

A study was carried out on the possibility and necessity of operating houseboats in the water areas of Russia on the basis of the concept of the development of reservoirs and small rivers, which is currently being developed by the state within the framework of national programs. A review of the operational, overall, displacement characteristics of houseboats was carried out with consideration of various options for ship power plants, suitable for the class of floating craft with registration in the State Inspection of Small Vehicles. The use of a stationary engine (JSC AvtoVAZ) in a configuration with a hydraulic drive and a swing-out column is proposed. Calculations of the resistance of the houseboat platform hull were made using several methods. A mechanism for the choice of propellers using a free software product according to empirical methods is proposed. An alternative drive scheme is selected, a detailed model of the working process of a houseboat's hydraulic drive is selected, and a mathematical model of its operation is presented.

Dynamic evaluation of jack-up platform structure under wave, wind, earthquake and tsunami loads

Nowadays, the demand for using jack-up platforms to carry out a large percentage of deep-water oil and gas exploration is steadily increasing. The response of jack-up platforms to the severe dynamic loads that may be encountered during the structure life is not examined enough. Therefore, this study attempts to investigate the response of jack-up platforms performance under the effect of dynamic loads due to wave, wind, earthquake and tsunami forces using the finite element method for two models with the lowest and highest hull elevations. The jack-up platform is located in the Gulf of Mexico. Earthquake accelerations are applied to the model in high and moderate seismic levels. In addition, tsunami waves are applied to the platform in three different directions at 0°, 45° and 90°. This study utilised Airy's linear wave approach to assess the surface elevations and wave kinematics. The reference wind velocity is 10 knots at 10 m over the mean water level. Results indicate that the dynamic response of the structure is affected by the height of the platform and by the increase of the platform hull elevation. The combination of the El-Centro earthquake, dead and live loads provides the major impact on the platform at the lowest (70 m) and highest (85 m) hull elevations. The comparison of all result proves that the jack-up platform hull under high earthquake intensity and tsunami waves with 45° has experienced maximum deformation. Moreover, raising the deck will increase the response of the dynamic load and displacements but will negatively affect the platform.

Methodology for developing the configuration of an ice load monitoring system for an iceresistant self-propelled drifting platform

The ice-resistant self-propelled platform (IRSPP) named North Pole that is currently under construction at the JSC Admiralty Shipyards is designed to carry out year-round scientific research in the Arctic Ocean. The IRSPP will be equipped with a unique ice loads monitoring system (ILMS). The technical requirements for the ILMS were developed in the Department of Ship Performance in Ice of the AARI. The ILMS should ensure a safe operation of the IRSPP in ice conditions (operational function) and serve as a measuring tool for researching of the mechanics of deformation and destruction of ice (scientific function). Analysis of ice conditions at different stages of IRSPP operation showed that the main scenario of ice interaction with the IRSPP hull will be the action of ice under compression on the middle part of the hull during drift. The monitoring of the stress-strain state of the hull is carried out by a complex system of fiber-optic strain sensors placed on different elements of the hull structures. The largest number of sensors are located on the side plating in the middle part of the IRSPP hull. The locations of the sensors were determined by finite element analysis of the stress-strain state of the IRSPP hull under the action of ice load. To monitor the stress-strain state of the surrounding ice field, up to 16 pressure sensors frozen into the ice are provided. Also, the system receives and stores data on the angles of roll, trim, yaw of IRSPP, its longitudinal, lateral and vertical accelerations, and the surrounding hydrometeorological conditions: wind speed and direction, air temperature, atmospheric pressure, and the geographical position of the platform. ILMS will significantly improve the safety of IRSPP operation during prolonged drift in ice conditions. Besides, the ILMS provides the platform hull with the functions of a measuring tool for studying the mechanics of deformation and destruction of sea ice in interaction with the engineering structures. The main purpose of this work is to create a comprehensive system for studying the processes of ice impact on structures in order to obtain new data about the parameters and nature of ice loads.

Investigation of tendon dynamics effects on tension leg platform response in random seas

This study investigated tendon dynamics effects of tension leg platform models with tendons modelled by finite element spring and beam elements for uncoupled and coupled tension leg platform in random waves and current environment. The purpose of the study is to proffering numerical solution of single mathematical equation of motion for fully integrated-coupled tension leg platform floater with tendons model. Structural modelling of complete tension leg platform is achieved with the help of ABAQUS/Standard finite element tools which is incorporated with ABAQUS/Aqua module for the application of hydrodynamic loadings on the partially submerged tension leg platform hull and fully submerged platform tendons. For the uncoupled tension leg platform model, weight, inertia, hydrodynamic force and damping forces are ignored on the tendons modelled with springs, while the stiffness of the tendons is considered as a static restoring force. The coupled tension leg platform model had all the forces applied on the tendons modelled with beam elements. Conclusively, modelling and analysis of the tension leg platform as uncoupled and coupled models have expanded our understanding to know that surge motion response is fairly predicted by the two models, however, heave and pitch motions, and variations in tendon tension differ significantly; hence, coupled tension leg platform model is recommended. The influence of a removed tendon due to accident or maintenance on the tension leg platform motions is also reported.

The Hull Strength of Marine Current Turbine Platform

Strength analysis of hull structure of marine renewable energy is crucial. The hull structure must be able to whitstand the harsh environmental load such as wave, wind and the weight of the payload and the structure itself. This paper analyzies the structural hull strength of marine current turbine platform. The platform is held by 4 mooring lines in 200 m water depth. The hull material is AISI1050 with yield stress 530MPa, the analysis consist of stress analysis which consider the dynamic motion of the platform due to wave, current, win and mooring line tension. The dynamic motion shows the maximum gravity acceleration is 1.3496G. The gravity acceleration creates additional loads due to weight multiplication of payload and structure. From the dynamic analysis using numerical software, the maximum mooring line tension due to dynamic analysis is 300.74 kN and this tension will creates stress in the moring line connection structure in the platform hull. The maximum stress of the is 126.045Pa, The mooring line tension is the highest loads compared to other factors such as weight. The safety factor of the structure based on the analysis is 4.2 which can be calculated by comparing the yield stress of the hull material and the maximum stress occurred due to dynamic load

해양작업지원선(PSV)의 기본설계 및 저항추진 성능 향상을 위한 선형개선 방안 연구

해양작업지원선(PSV)의 기본설계 및 저항추진 성능 향상을 위한 선형개선 방안 연구

Nonlinear coupled dynamics analysis of a truss spar platform

Accurate prediction of the offshore structure motion response and associate mooring line tension is important in both technical applications and scientific research. In our study, a truss spar platform, operated in Gulf of Mexico, is numerically simulated and analyzed by an in-house numerical code ‘COUPLE’. Both the platform motion responses and associated mooring line tension are calculated and investigated through a time domain nonlinear coupled dynamic analysis. Satisfactory agreement between the simulation and corresponding field measurements is in general reached, indicating that the numerical code can be used to conduct the time-domain analysis of a truss spar interacting with its mooring and riser system. Based on the comparison between linear and nonlinear results, the relative importance of nonlinearity in predicting the platform motion response and mooring line tensions is assessed and presented. Through the coupled and quasi-static analysis, the importance of the dynamic coupling effect between the platform hull and the mooring/riser system in predicting the mooring line tension and platform motions is quantified. These results may provide essential information pertaining to facilitate the numerical simulation and design of the large scale offshore structures.

Artificial Neural Networks for the analysis of spread⿿mooring configurations for floating production systems

This work presents the development of Artificial Neural Networks for the analysis of any arbitrarily defined spread-mooring configuration for floating production systems (FPS), considering a given scenario characterized by the water depth, metocean data, characteristics of the platform hull, and the riser layout. The methodology is applied to recent designs of deepwater semi-submersible platforms connected to a large number of risers with asymmetrical layout. In such cases, the design variables may include values for the azimuthal spacing and mooring radius varying along the corners of the platform, besides the pretension and material of the lines. The results of the case study indicated that, given any mooring configuration characterized by the combination of all these design variables, the ANNs provide fairly accurate values for the parameters of the response that are required for the design of mooring systems (typically platform offsets and line tensions).

The nonlinear bifurcation and chaos of coupled heave and pitch motions of a truss spar platform

This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch modes, the coupled heave and pitch motion equations of the spar platform hull were established in the regular waves. In order to analyze the nonlinear motions of the platform, three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs were constructed, the Poincare maps and the power spectrums of the platform response were calculated. It was found that the platform motions are sensitive to wave frequency. With changing wave frequency, the platform undergoes complicated nonlinear motions, including 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. When the wave frequency approaches the natural frequency of the heave mode of the platform, the platform moves with quasi-periodic motion and chaotic motional ternately. For a certain range of wave frequencies, the platform moves with totally chaotic motion. The range of wave frequencies which leads to chaotic motion of the platform increases with increasing wave height. The three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs reveal the nonlinear motions of the spar platform under different wave conditions.

Numerical study on the 3-D complex characteristics of flow around the hull structure of TLP

Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform (TLP) hull. By considering the flow field of the South China Sea and the configuration of the platform, three typical flow velocities and three flow directions are chosen to study the numerical simulation of the flow field characteristics around the TLP hull. Reynolds-averaged Navier–Stokes equations combined with the detached eddy simulation turbulence model are employed in the numerical study. The hydrodynamic coefficients of columns and pontoons, the total drag and lift coefficients of the TLP, the formation and development of the wake, and the vorticity iso-surfaces for different inlet velocities and current directions are discussed in this paper. The average value of the drag coefficient of the upstream columns is considerably larger than that of the downstream columns in the inlet direction of 0°. Although the time history of the lift coefficient demonstrates a “beating” behavior, the plot shows regularity in general. The Strouhal number decreases as the inlet velocity increases from the power spectral density plot at different flow velocities. The mean root values of the lift and drag coefficients of the front column decrease as the current direction increases. Under the symmetrical configuration of 45°, the streamwise force on C4 is the smallest, whereas the transverse force is the largest. The broken vortex conditions in current directions of 22.5° and 45° are more serious than that in the current direction of 0°. In addition, turbulence at the bottom of the TLP becomes stronger when the current direction changes from 0° to 45°. However, a high inlet velocity indicates a large region influenced by the broken vortex and shows the emergence of the wake behind the TLP under the same current angle.

Design Solutions for Jack up Platform Retrofitting

The paper is focused on the structural problems related to the retrofitting of a ship structure into a maritime self-elevating platform. The study is referred on the design of the global and local strengthening of the platform and legs structures. The joint structure built as the connection between the platform hull and the tubular legs, is designed so that to be acted by the special actuators. The total force provided by the actuators during the lifting operations is necessary to balance the total weight of the platform hull and operating equipment. The work described in the paper shows a methodology for FEM global and local strength calculation of platform structure and legs structure using site-specific parameters recommended by DNV rules, such as water depth, wave and wind loads. Also, the global static and dynamic behavior analysis of the jack up unit is presented. From the case study results it may conclude that the proposed methodology offers economic advantages to the field in which they are employed. In the paper, the platform structural capacity, incorporating yielding and buckling, is the limiting condition for the scenario under investigation.

An integrated methodology for the design of mooring systems and risers

Traditionally, the design of mooring lines and risers of floating production systems (FPS) has been performed separately, by different teams, employing uncoupled analysis tools that do not consider the nonlinear interaction between the platform hull and the mooring lines and risers. Design processes have been focused on fulfilling the design criteria of the respective component (mooring/riser) alone, with few or no consideration to the other component, and little interaction between the design teams. Nowadays the importance of employing analysis tools based on coupled formulations is widely recognized, and analysis strategies have been proposed to consider feedback between mooring lines and risers within their respective design processes.In this context, this work details a proposal of one single and fully integrated design methodology for mooring systems and risers for deep-water FPS. In this methodology, the design stages of both risers and mooring lines are incorporated in a single spiral, allowing the full interaction of different teams; mooring design implicitly considers the riser integrity, and vice-versa, leading to gains in efficiency and cost reduction.Different analysis strategies are employed, taking advantage of uncoupled and coupled numerical models. The models generated at the initial/intermediate design stages can be reused in subsequent stages: simpler models are used in the initial stages, and more refined models are gradually introduced, to reach an ideal balance between computational cost and accuracy of results. In the advanced stages, the exchange of information between mooring/riser also allows the definition of criteria for the selection of governing/critical loading cases to be revised and verified in detail. This leads to the reduction of the original loading case matrix, allowing a feasible use of time-consuming fully coupled analysis.Results of a case study illustrating the application of some of the main processes of the methodology are included.

Study on the nonlinear dynamical behavior of deepsea Spar platform by numerical simulation and model experiment

The nonlinear motion of the Spar platform hull is studied by numerical simulation and model experiment in this paper. The nonlinear differential equation for a coupled heave-pitch of a platform hull is established in a regular wave. The bifurcation pictures of response amplitude with wave frequency variation, Poincare’ maps and time histories are calculated to study the nonlinear dynamical behaviors of the platform hull. The parameters domain for unstable pitch motion is calculated numerically. It is found that the platform motion is sensitive to wave frequency. With the changing of wave frequency the platform exhibits harmonic motion, twice super-harmonic motion, 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. The nonlinear 1/2 sub-harmonic motion and the parameter domain for unstable pitch motion are qualitatively verified by the model experiment.

An Automatic Approaching Control for the Petroleum Well Re-Entry Operation in Ultra-Deep Water

Abstract Offshore Petroleum Industry regularly uses automatic control to keep the positioning of floating drilling platforms and, with a few exceptions, floating production platforms. This positioning control system is commonly denominated Dynamic Positioning System (DPS). This automatic control measures the platform position through a gyrocompass for the heading, and a Differential Global Positioning System (DGPS) and/or an Acoustic Positioning System for translational displacements. Further, the thrusters installed on the platform hull are the actuators bringing the platform to the reference position. This work presents the dynamics of semi-submersible drilling platform equipped with DPS and coupled with a drilling riser in 3000 m water depth. In addition, a special attention is paid on the drilling operation called well re-entry. During the re-entry, a safety equipment named Blow Out Preventer (BOP) is lowered down attached to the drilling riser, and the BOP shall be connected onto the wellhead. This approaching of the BOP to the wellhead is carried out controlling the floating platform manually, with the help of a camera attached to a Remote Operated Vehicle (ROV) which shows how far the BOP is from the wellhead. Then, the engaged personnel estimates this distance and changes the reference position of the DPS in order to reduce this distance. In this paper, numerical simulation results for the coupled platform and riser dynamics are featured and discussion about an extra feedback loop that could control the BOP approach automatically in the re-entry operation is presented.

Optimized Design of Pipe-in-Pipe Systems

Summary Deepwater subsea developments must address flow-assurance issues, and these increasingly form a more critical part of the design. Pipe-in-pipe (PIP) systems, one of the options available in the designers’ toolbox for overcoming these problems, are recognized as thermally efficient, reliable, and proven technology for insulated, subsea transportation of wellbore fluids. Although extremely low U values are achievable, PIP systems come at a cost, with increased weight as a penalty for use in deepwater developments. By applying an "inside-out" optimization process for the design of PIP systems, the top-tension loading on the surface vessel (installation or production) can be reduced significantly while minimizing procurement expenditure on raw materials. Specifically, the design optimization of each component reduces steel volumes as well as the overall outer diameter (OD) of the system. This paper presents the methodology for optimized design of PIP systems and illustrates the potential cost savings in terms of raw materials and installation through a case study for a typical large west African field. Commercial savings related to surface platform hull costs also are presented for a case in which the development employs PIP in catenary risers.