Damage identification in ship structures is traditionally performed through on-site inspections. In this work, a first step is made towards assessing an in-line with operation ship hull Structural Health Monitoring system by registering onboard sensor data. Specifically, an optimization-based approach is proposed for solving the inverse problem for damage identification through processing static response data. Idealized geometry and loading conditions are considered for the deck and shell plating. Damage is abstractly represented as a single circular hole randomly located within the defined domain. Strain readings representing onboard measured data are provided by a FE model developed for this purpose. These correspond to zero-strain paths for each considered case: axial strains along the ship’s neutral axis on the side shells and shear strains along the deck’s centerline. Damage detection amounts to predicting its location, essentially considered the design variable of an optimization problem seeking to minimize an error function between strains measured for various damage scenarios and an indicative target scenario. Three established optimization algorithms are used for this task: a gradient-based, a Genetic Algorithm-based and a statistics-based method (Design of Experiments and Response Surface Methodology). Results indicate that the gradient and GA based approaches are more efficient while the less efficient statistics-based approach proved less computationally demanding.

Tubular members are widely used in oil and gas offshore production and drilling structures either fixed or mobile units. Due to complex operational conditions, the tubular members are subjected to both age and mechanical related damage, which in turn affect the ability of the structure to withstand the applied loads. This motivates the importance of investigating the behavior of tubular members considering the presence of dentation resulting from collision or falling objects and consequently assessing the residual strength of the damaged members accurately. A series of finite element analysis are performed to study the pre- and post-ultimate strength behavior of intact and locally dented un-stiffened steel tubular members subjected to four-point bending. The effects of dent geometrical parameters; length, width, depth, orientation, and location on the ultimate load carrying capacity are analyzed. The ratio between the diameters to the shell thickness is varied, where combined local and global initial imperfections are considered. Buckling and post collapse analysis as well as modes of failure are studied. Parametric diagrams for the ultimate residual strength as a function of dent geometry and the location of damage are also presented. Several concluding remarks are stated which benefit the structural integrity assessment of tubular steel members.

This paper focuses on the bending deformation experienced by metallic materials and its characterization during the crash analysis of ship structures. These analyses are conducted with plane stress shell elements for computational reasons. The inherent nature of through thickness plane stress poses restrictions on how the bending associated stress and strain distribution are resolved. Namely, fracture criteria used in crash analysis account bending damage accumulation differently. Most criteria do not specifically address the issue as element erosion is activated once all through thickness integration points have reached the predefined failure condition. However, when elements are bent, material layers (top and bottom) display strong variations in mechanical field variables that are commonly used to control element deletion. Therefore, the focus of current analyses is to show how different fracture criteria account bending deformation and how sensitive are the results depending on the chosen element size.

Considerable work has been done on the modelling of fracture and necking for accidents in the maritime and offshore industry, but very little has been done to find the crack orientation during this failure. Such information will be required in future analyses which use the eXtended Finite Element Method (XFEM), rather than the element deletion approach which is typically used. It also offers a more realistic portrayal of the extents of damage, which will be useful in assessments of salvageability and residual strength analysis in maritime structures. This paper reviews the current state of the art on the direction of necking and fracture relative to the main in-plane loading axes. It was found that necking and fracture can both evolve under different angles relative to the first principal stress, depending on the ratio of inplane strains, material anisotropy, and other effects. Traditional analysis has given an easy relationship between necking orientation and strain ratio for negative second principal strains. Anisotropy is found to have a very important role for the necking angle for strain ratios (ε 2 /ε 1 ) greater than 0.5. Fracture theory predicts a fracture angle perpendicular to the first principal stress for states of stress between uniaxial tension and equi-biaxial tension, but it predicts in-plane slant fracture for strain ratios less than −0.5.

In subsea installation operations, the hydrodynamic forces on the subsea module are important considerations when designing the structure and choosing slings. In this paper, the hydrodynamic forces and flow field of a subsea module with deflated cavity shells during forced water entry operation were investigated numerically. The numerical simulation was carried out based on Reynolds-averaged Navier–Stokes equations, with a constant lowering velocity of the module. The results of the numerical simulation were validated by experimental data and they showed good agreement. The relationship between hydrodynamic forces and draft was presented. Furthermore, the slamming positions, free surface variation, pressure variation in deflated cavity shells, slamming coefficient and the influence of holes were studied based on flow field scenes. It was found that the hydrodynamic forces varied with draft non-linearly. Moreover, the change of draft altered the form of the free surface due to the complex steel frame structure of deflated cavity shells. The present study can be further extended to assess the operating conditions of lifting operations and to advise on the design of the subsea module.

This paper consists of two parts. Part one presents a thin-shell analytical solution for calculating the conical transition junction loads. Design equations as contained in the current offshore standards are based on Boardman’s 1940s papers with beam-column type of solutions. Recently, Lotsberg presented a solution based on shell theory, in which both the tubular and the cone were treated with cylindrical shell equations. The new solution as presented in this paper is based on both cylindrical and conical shell theories. Accuracies of these various derivations will be compared and checked against FEM simulations. Part 2 of this paper is concerned with the ultimate capacity equations of conical transitions. This is motivated by the authors’ desire to unify the apparent differences among the API 2A, ISO 19902 and NORSOK design standards. It will be shown that the NORSOK provisions are equivalent to the Tresca yield criterion as derived from shell plasticity theory. API 2A provisions are demonstrated to piecewise-linearly approximate this Tresca yield surface with reasonable consistency. The 2007 edition of ISO 19902 will be shown to be too conservative when compared to these other two design standards.

A series of ultimate strength analyses of ring-stiffened cylindrical shells with various dimensions and scantlings is carried out applying the nonlinear finite element method. The detailed buckling/plastic collapse behavior including the influence of initial deflection applied in the ultimate strength analyses is investigated. In most past studies, detailed classification of collapse modes and investigation of the influence of the initial deflection mode have not been sufficiently conducted. In this study, firstly the ultimate strength analyses of 288 cases varying the dimensions of the ring-stiffened cylindrical shell and the attachment direction of the stiffeners, inside or outside, are performed. From the results, the collapse modes are classified into five modes, which are stiffener-torsional buckling collapse (localized deformation mode and mode to keep strength after the ultimate strength), shell buckling collapse (localized deformation mode and mode with kinking lines), and combined collapse of the buckling modes. A slenderness ratio is proposed using elastic buckling strength and pressure when the circumferential stress reaches the yield stress, and the possibility of estimating the ultimate strength is indicated.

In the construction of ships and ocean structures, thin steel plates are welded in order to join parts. Due to the welding, deformations and residual stresses may occur. These deformations and residual stresses can cause problems in the assembly process. Therefore, the prediction of welding deformations and residual stresses is necessary in advance of production. Welding deformations and residual stresses can be predicted using thermal elastic plastic (TEP) finite element analysis (FEA). However, solid elements are used in the conventional analysis method of TEP-FEA. The modeling of the thin-plate structures using solid elements is very complicated and difficult. In addition, the number of elements increases when using solid elements compared to shell elements. This leads to an increase in the required computing resources. Therefore, an efficient modeling method is necessary for thin-plate structures. In the present research, in order to realize an efficient welding mechanics analysis method for thin-plate structures, the authors proposed an efficient FEA method for the welding mechanics problem for thin-plate complex structures using the proposed shell-solid mixed analysis method. For the shell-solid mixed analysis method, the multipoint constraint (MPC) technique was used in the finite element analysis to connect shell elements and solid elements. In order to compare the analysis accuracy with the conventional analysis, which uses solid elements, the proposed shell-solid mixed analysis method was applied to the fundamental welding mechanics problem of thin-plate structures. The results revealed that the proposed method has approximately the same analysis accuracy as the conventional method. These results indicated that the proposed method can effectively analyze the welding deformations and residual stresses in thin-plate complex structures.

Prediction of large-scale marine structures under extreme loading conditions (e.g. impact, fire) requires the use of computational tools that are both accurate and efficient. To resolve models at this scale, engineers normally use shell elements in which two of the (in-plane) dimensions are much larger than the third (thickness) one. Herein, we propose a consistent characterization framework for shell-element models commonly used in metal marine structures. The underlying model is based on a three stress-invariant plasticity model that accounts for the effects of stress triaxiality and shear-dominated stress states and accounts for the micromechanical void growth and coalescence that leads to fracture. This framework serves as both a constitutive model as well as a back-end calibration engine which outputs material cards that can be readily used with commercial finite element solvers like LS-DYNA and Abaqus. The calibration framework supports data-driven constitutive models that require engineers to prescribe the Fracture Locus (FL) and Instability Curves (IC) from experimental data, such as the Johnson-Cook model. Moreover, the calibration framework uses the underlying physics based model to computationally generate additional surrogate data that compliments the experimental testing. Thus, it allows the analyst to calibrate a material model based on limited experimental data, hence, reducing the costs associated with data acquisition and processing. A standalone calibration tool (VistaCal) that highlights the benefits of this characterization framework is also presented.

Subsea 7 is currently planning for the installation of PiP flowlines in the Norwegian Sea. A case study has been performed for a 8 × 12in PiP to be installed in a water depth between 320 m to 420 m. Fishing activities are frequent in this area. Therefore, the integrity of the pipeline in case of trawl pull-over must be checked. It is found that pipelines with residual curvatures could behave very differently from pipelines without residual curvatures when they are pulled over by trawl gear. However, the effect of residual curvature on pull-over resistance capacity of rigid pipelines has not been mentioned in DNVGL-RP-F111 [1]. Therefore, an optimised methodology involving FE analyses and Monte Carlo simulation has been used in this project to check the integrity of the pipe-in-pipe flowline for the trawl pull-over load case. This paper focuses on the FE analyses of the pipe-in-pipe flowline pulled over by trawl gear. The related Monte Carlo simulation has been discussed elsewhere [2]. To understand in detail the behaviour of the pipeline with trawl pull-over loading, the pipeline was modelled using a combination of beam, shell and brick (solid) elements. The advantage of the model was demonstrated by comparing output from the model with corresponding output using beam elements. The effects of some result-sensitive parameters were studied, which include centralizer location, pressure, trawl contact area and wall thickness. Special attention was paid to these parameters because their effects are not able to be captured with the normal beam element. Finally, the impact of residual curvatures on the trawl pull-over behaviour was studied. It was found that the pipeline pull-over resistance capacity is sensitive to residual curvature direction and contact location, but not sensitive to RC spacing and RC shape. Based on the advantage of this analysis methodology, it is believed to be a good option for pipeline trawl pull-over analysis, especially with complex pipeline configuration.

Fatigue is a primary challenge in the design of steel catenary risers (SCRs) and different measures and methods are utilized to mitigate it. Traditional upset ends and steel lazy wave risers (SLWRs) are such methods to mitigate fatigue. SLWRs were first used in 2009 on the Espirito Santo floating, production, storage, and offloading (FPSO) vessel of Shell Company’s Parque das Conchas (BC-10) project offshore Brazil. SLWRs have been used increasingly since then and gained popularity especially in recent years. A novel patented tubular connection assembly is presented herein which improves the fatigue life of SCRs and welded connections in general. This novel tubular connection assembly has many advantages. It overcomes the thickness limitation of welding traditional upset ends and reduces offshore welding time, cost, and risk. When used in simple SCRs, this novel tubular connection assembly renders simple SCRs an alternative robustly viable at significantly lower cost, shorter schedule, and many additional advantages as compared to SLWRs. Of such many advantages, simple SCRs are simpler to configure, analyze, design, and install using wider installation methods and vessels. They also use less material and offer better short- and long-term integrity especially for insulated SCRs. In addition, they have smaller footprint and are less prone to clashing.

This paper summarizes the assessment of the structural analysis and design of a floating foundation for offshore floating wind turbine (FWT) based on DNVGL standard and Eurocode in terms of economy and reliability. The wind loads are calculated using empirical equations. The wave loads are obtained and verified using various methods including hand calculation, AQWA and Flow-3D. It is found that the shell thickness could be reduced significantly by introducing the stiffeners (stringer or ring), which can decrease the weight of the hull and lower the cost. While DNVGL and Eurocode yield similar design solutions if using plane shell structures, Eurocode significantly underestimates the buckling resistance of stiffened cylindrical shells.

In 1950’s and 1960’s, Mihama beach in Heda Bay located on western coast of Izu peninsular had been famous for the richness in shell fauna, for example, about 400 species including rare ones were collected. In 2000’s, however, the impoverishment of ecosystem function has become considerable, which led us to project the investigation on the origin and restoration. The authors carried out field survey in 2007–2008 and found that the impoverishment of Mihama is derived not from surface water but from the benthic environment. The measured water current at the site was quite small, which indicated the water exchange was very weak. It must be one of the main causes of unfavorable benthic environment. Thus environmental regeneration plans for Mihama was proposed in which the pears blocking the water current be removed. In order to assess the effect of proposed plans, simulation-based habitat evaluation was conducted. A three-dimensional hydrodynamic and sediment transport models were developed to reproduce the characteristics of currents and predict the sediment size around Mihama . For the assessment of the ecological status, HEP (Habitat Evaluation Procedure) was employed, in which one of the typical species of bivalves is chosen as a target species. Water depth, sediment size, friction velocity at the bottom, etc. were considered as the environmental factors for the target species. The suitability indices (SI) for each environmental factors were calculated by using the results of hydrodynamic and sediment transport simulations. By using the developed scheme, total habitat unit was evaluated for the proposed regeneration plans and compared to that without countermeasures. It was predicted that the removal of the piers will improve the habitat condition in the target site. Based on the proposal by the authors, a water pathway under the pier was built in 2009. The authors conducted field survey again in 2014 and confirmed that the benthic environment has been improved.

Submerged pressure shell’s corrosion situation is more serious due to bad work environment, complex structure and difficulty of maintenance. Based on the analysis of calculation method of submerged pressure shell structures with non-corrosion, the calculation formula of pressure shell with pitting corrosion is given. The Finite Element Model is constructed and its residual strength is investigated. The relationships between shell stress and some parameters, such as radius of corrosion pit, depth of corrosion pit and location of corrosion pit are studied. Based on the finite element analysis results, the effect of radius of corrosion pit on the stress of pressure shell with pitting corrosion is analyzed. Furthermore, the influence coefficients of residual strength of pressure shell due to depth and location of pitting corrosion are determined, which provide a reference for the strength evaluation of submerged pressure shell with pitting corrosion.

Environmental contours are used in structural reliability analysis of marine and coastal structures as an approximate means to locate the boundary of the distribution of environmental variables, and to identify environmental conditions giving rise to extreme structural loads and responses. There are different approaches to estimating environmental contours, some directly linked to methods of structural reliability. Each contouring approach has its pros and cons. Although procedures for applying contours in design have been reported in articles and standards, there is still ambiguity about detail, and the practitioner has considerable flexibility in applying contours. It is not always clear how to estimate environmental contours well. Over four years, DNV-GL, Shell, the University of Oslo and HR Walling-ford worked together to review current practice regarding the use of design contours. In this paper, we present a summary of our findings. We overview the motivations for different approaches to contours, and their resulting characteristics. Using different marine applications, we also explore the various sources of uncertainty present, their impact on contour estimates and the estimation of extreme environmental loads and responses.

The eggshell is a multifocal, rotary thin-walled structure that satisfies the positive Gaussian curve. The eggshell meets the dome principle and requires no additional rib support to achieve sufficient strength and stability with minimal material. Some scholars have applied this bionic prototype to the pressure-resistant shell, which proves that it has good comprehensive performance. However, there is less in-depth discussion of the buckling characteristics of this new pressure-resistant shell yet. In this paper, the dangerous situation of collision, reefing and other accidents during the use of deep submersibles is considered, the residual strength of the shell with partial damage is studied, which is of practical engineering significance. Firstly, the ABUQUS finite element software is used to calculate the buckling of the egg-shaped pressure shell with local deformation, and the influence of local deformation on the buckling mode and ultimate bearing capacity of the pressure shell is analyzed. Secondly, by designing the pressure-resistant shells with different concave amplitudes and recessed positions, the influence of the pressure-resistant shell on the stability of the pressure-resistant shell is analyzed. Finally, according to the calculation results, the sensitivity law of different concave positions to the concave amplitude is summarized, and the beneficial engineering opinions are given.

The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention/remediation system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting. As part of a Joint Industry Project (JIP) between TechnipFMC, Shell and Total, full-scale thermal testing of an ETH-Blanket prototype was carried out in Artelia facilities (in Grenoble, France). This testing was performed to verify the capability of the ETH-Blanket system to increase the temperature of the fluid inside a pipe sample above a target temperature (hydrate dissociation temperature or wax disappearance temperature) for various conditions. The impact of lateral misalignment of the ETH-blanket on the pipe and of the pipe burial depth were studied. Moreover, the tests were carried out on two pipe samples, with different designs and insulation properties. In parallel, CFD models of the test set-up were built to replicate the thermal behaviour of the ETH-Blanket. The combination of these models with the measured heating efficiency of the prototype allowed characterising the performances of the system in real subsea conditions. This paper presents the description of the full scale thermal testing conditions. Results of the different tests are detailed and the impact of the different parameters on the ETH-Blanket thermal performances are assessed, focusing on natural convection effects, thermal losses and the overall data gathering process.

The Electrically Trace Heated Blanket (ETH-Blanket) is a new offshore intervention/remediation system currently in development by TechnipFMC for the efficient remediation of plugs due to hydrates or wax in subsea production and injection flowlines. The ETH-Blanket consists of a network of heating cables placed underneath an insulation layer which is laid onto the seabed above the plugged flowline. By applying electrical power to the cables, heat is generated by Joule effect which warms up the flowline content until hydrate dissociation or wax plug remediation through softening or complete melting. As part of a Joint Industry Project (JIP) between TechnipFMC, Shell and Total, full-scale thermal testing of an ETH-Blanket prototype was carried out in Artelia facilities (Grenoble, France). This testing was performed to verify the capability of the ETH-Blanket system to increase the temperature of the fluid inside a pipe sample above a target temperature (hydrate dissociation temperature or wax disappearance temperature) for various conditions. The impact of lateral misalignment of the ETH-blanket on the pipe and of the pipe burial depth were studied. Moreover, the tests were carried out on two pipe samples, with different designs and insulation properties. CFD models of the test set-up have been built to replicate the thermal behaviour of the ETH-Blanket prototype. Once validated against the test results, the final aim of CFD modelling is to be able to calculate the performances of the system in real subsea conditions. The modelling of the prototype includes a 3D geometry of the system including the soil, natural convection of water between the ETH-blanket and the pipe sample and natural convection of fluid in the pipe sample. The present paper focuses on the CFD work performed to match the full-scale thermal test results and to predict the ETH-Blanket performances for real subsea operating conditions. It will describe the various CFD models used, the sensitivities and findings in terms of local and global heat transfer and flow effects and the comparison to the experimental data.

Prelude floating liquefied natural gas (FLNG) facility reached a significant milestone in June 2018 when gas was introduced onboard for the first time as part of the facility startup process, loaded from an LNG Carrier (LNGC) moored in side-by-side (SBS) configuration. This first offshore LNG SBS operation allowed Prelude’s utilities to switch from running on diesel to running on gas. SBS mooring is the base case configuration for offloading both LNG and Liquefied Petroleum Gas (LPG) into product carriers using Marine Loading Arms (MLA) once the Prelude FLNG facility is fully operational. These complex and weather sensitive operations are expected to take place on a weekly basis. This means critical decisions about weather-window and timing should be supported as much as possible by predictive analysis and modelling of forecast environment to reduce the risks. There are multiple criteria for evaluating the operability of LNGC or LPGC SBS offloading. These criteria cover the various phases of an operation, such as personnel transfer to the visiting carrier, Terminal Team Leader (TTL) transfer, spool fitting and fender lowering, approach and mooring, connection and testing of the loading arms, ramp-up of product transfer, full rate cargo transfer, loading arm purging and recovery, de-berthing, and people and hardware recovery. The criteria have been tailored to be appropriate to the phase of the operation. They comprise both environment-based criteria (maximum acceptable wind and waves conditions), and criteria related to motion or mooring (carrier roll, MLA envelope, mooring line tension, fender deflection). Motion and mooring criteria are evaluated through dynamic time-domain simulations. This allows an accurate modelling of non-linear effects, including mooring characteristics and partially filled cargo tanks. Thrusters can be used to control Prelude FLNG facility position if needed. The required thruster force to maintain the selected heading is calculated with frequency-domain calculation for all possible headings. This paper presents a visual reporting tool, developed by TechnipFMC in partnership with Shell. This tool has been used to support operational decisions during commissioning and startup, for SBS LNG and LPG import to Prelude FLNG facility. The daily reports used weather forecasts, in combination with numerical simulations, to predict the maximum motion and mooring criteria which contribute to determine both the timing and the decision to proceed with the operation. The format of the report has been designed to be user friendly for offshore operational staff, summarizing efficiently and in a visual manner the usage factors for each criterion separately. An overall operability is also presented for a quick overview. This paper also presents the details of numerical simulations, summarizes the different studies carried out to ensure the reliability of these simulations and discusses the possibilities for future development.

In offshore jacket design, it has long been recognized that an accurate global structural model requires implementation of the effects of local joint flexibility (LJF). However, there is still no general method for implementing these effects accurately and efficiently without complicating the application of loads. The literature describes several techniques for determining LJFs using parametric formulas and implementing these in global models of a jacket structure. These techniques are simple but associated with uncertainties and a risk of compromising the accuracy of the global model. Alternative methods, such as the use of superelements, provide very accurate results but complicate the consistent application of external loads as well as postprocessing. This paper introduces a new methodology which is called the Correction Matrix Methodology. This allows the effects of LJF from detailed three-dimensional (3D) finite-element (FE) shell or solid models to be incorporated in a global beam FE model via a simple correction matrix. The effectiveness of the methodology is improved by using interpolation between a limited number of correction matrices. The new methodology provides exact results when correction matrices associated with the actual geometry are applied. When using the interpolation procedure, the methodology provides accurate results and computational efficiency when the database has been established. The Correction Matrix Methodology is a significant improvement of the conventional methods for modelling LJF and is currently being implemented in a general form for arbitrary joints in Rambolls Offshore Structural Analysis Program (ROSAP).