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Purpose This study aims to investigate the collective perception regarding the future of offshore platforms and frame the main categories of meanings associated by the community with the investigated phenomenon. Design/methodology/approach A data driven approach has been conducted. The collection of the peoples’ opinions has been realized on two specific social network communities as follows: Twitter and Instagram. The text mining processes carried out a sentiment and a cluster analysis. Findings The sentiment analysis of the most frequent words has been shown. The following four main homogeneous categories of words are emerged in relation to the decommissioning of offshore platforms: technological areas, green governance (GG), circular economy and socio-economic sphere. Research limitations/implications The alternative use of the offshore platforms, including tourism initiatives, aquaculture, alternative energy generation, hydrogen storage and environmental research, could improve the resilience of communities by offering the development of new jobs and the growth of local and innovative green businesses. Practical implications The adoption of a circular model and GG initiatives aims to limit the input of resources and energy, minimize waste and losses, adopt a sustainable approach and realize new social and territorial value. Originality/value The analysis underlines the importance to adopt a systems perspective, which takes into account the social, economic and environmental system as a whole, the different phenomena that occur and the variety of categories of stakeholders, from users to local governments that participate in the territorial development.

This paper deals with the assessment of fatigue crack propagation on the connection between column and brace for a semi-submersible. The analysis of global and local structural responses under different sea states are performed to acquire the transfer functions of stresses. Based on an existing crack the Failure Assessment Diagrams (FAD) are applied as criterion of acceptance for the safety of crack and structure during the crack growth calculation cycle. The crack growth rate considering threshold stress intensity factor and stress ratio is used. During safety assessment the stress response from ultimate sea state is outlined. A comparison of fatigue crack growth using ultimate stress and normal stress data with different crack growth rate is presented. The results show the reliability of fatigue assessment using FAD as a measurement of acceptability of crack propagation.

Multi-purpose offshore structures are very complex systems to be designed as many different requirements have to be taken into account simultaneously. Experimental tests on scaled models can be very useful to verify structural behavior and to validate numerical models. The definition of the scale can play a key role in performing tests as high scales, closer to full-scale, are generally related to more reliable results. The present paper concerns the design of a wind turbine model for a large-scale model of a Multi-purpose offshore Platform developed within the EU project H2020 Blue Growth Farm. This project aims at developing an offshore farm, based on a modular floating structure that integrates wave energy converters and a wind turbine with aquaculture. The scale model of the complete structure will be deployed at the Natural Ocean Engineering Laboratory (NOEL). The paper will focus on the strategies adopted to scale 1:15 the DTU 10 MW wind turbine in order to represent both the main aeroelastic features and all the functionalities of a real machine. The complete design of the machine and its control will be also provided.

The high-efficient development of heavy oil is difficult for offshore oil field. Based on the mature technology of onshore heavy oil thermal recovery, a new rod pumping technology of “heavy oil steam stimulation along with conventional sucker rod pumping system” is proposed. According to the structure space of aimed offshore platform, we designed one new kind of miniature hydraulic pumping unit with long-stroke, low pumping speed and compact structure. The paper also studies the offshore heavy oil thermal recovery well safety technology, establishes a leakage model of wellhead sealing and a mechanical model of sealed rubber sleeve on downhole nonlinear large deformation. The study shows that a series of equipment for offshore rod pumping oil recovery and the key technology of well safety lay a solid foundation for carrying out rod pumping of offshore heavy oil thermal recovery.

Grouted connections are frequently used as structural detail of offshore wind turbines and platforms for the load transferring connection between piles and support structure. At latticed substructures this connection is commonly located at mudline. However, a potential influence of the surrounding water on the connection's fatigue behaviour was neglected in earlier tests and consequential design methods. Herein described experimental investigations at small and large-scale fatigue tests in submerged conditions showed a significant reduction of endurable load cycles. In addition, the water impact caused varied damage mechanism in the connection. © 2017 The Author(s).

The growing complexity of environmental challenges has progressively led to the emergence of Sustainable Business Models (SBMs) able to embed economic, environmental, and social flows in a unified value network. All sectors are demanding innovative and sustainable solutions, including the oil and gas industry, which aims to address the issues about the decommissioning of offshore platforms. However, although the relevant literature highlighted the potentialities related to a multi-reuse of these structures, the effect of Sustainable Decommissioning (SD) on macro-environmental factors is still an open question. Based on these considerations, this study follows a Political, Economic, Social, Technological, Legal, and Environmental (PESTLE) analysis according to semi-structured interviews conducted with oil and gas key informants and stakeholders in the Italian context. The results of the analysis can provide a novel thinking for addressing the challenges related to a sustainable decommissioning of offshore platforms and shed light on the importance of synergistic efforts by local entrepreneurship and institutional arrangements to combine economic and environmental sustainability with social needs. This paper can contribute to the emerging field of sustainable business models related to the decommissioning of offshore platforms and suggests avenues for future research.

International audience; Tensegrity systems are a class of reticulated space structures composed of compressed bars maintained in equilibrium by a network of tensioned cables. Their stiffness depends both on elements’ mechanical properties and their internal self-stress state. Taking advantage of their structural properties, we respond to the challenge of accessibility for everybody to the sea with a new concept of modular lightweight and deployable platforms. Variable configurations are developed to fit ecologically into the marine environment thanks to the transparency of double layer tensegrity structures. Moreover, allowing practical assembly and disassembly is considered in the design to respect the coastal law. Through a numerical study, we demonstrate in this paper the capability of this solution under various representative load cases and support conditions.After the structural and design optimization of elements constrained by weight and stiffness, we detail the design of the nodes, which are the key components ensuring geometry and foldability of the structure. Finally, on-site setting and interfacing with ground supports is experimented in marine conditions to proof the feasibility of this concept.

The overall objective of this study was to develop a biological early warning system (Mosselmonitor®) on offshore platform to detect critical environmental situations. The experiment was conducted on oil off-shore platform called Rospo Mare B. This structure is located in the area in front of Molise coast line (Italy, Adriatic Sea), characterized by a depth of about 77 m and a bathymetry between 65 and 80 m. The Mosselmonitor® works with eight mussels connected via specific sensors to PC for recording opening values of valves. A probe was installed inside the instrument to daily control of water pH, dissolved oxygen, salinity and temperature. Water samples are weekly analyzed for heavy metals, organochlorine pesticide and suspended matter. During the entire observation period, closure alarms were predominantly detected (99.9%) and a decrease of 65% in alarms maximum duration was recorded from the fifth week. During the first month, none changes in water physico-chemical parameters were observed so that affect the bivalves behavior. The only chemical parameter steadily detected in water was copper; its average concentrations were of 10 ppb. Detected alarms were not comparable to those recorded in the first month: this observation could be explained considering that mussels will be adapted to copper constant presence.

The vibration reduction device for the offshore platform truss structure has exposed to long term high-energy ultraviolet light and salt spray radiation, the traditional viscoelastic damping technology is easy to aging and failure, and its operational lifetime is limited. The semi-active particle damping technology has the advantages of high temperature resistance, anti-aging and so on, at the same time it is also able to adapt the changes of external complex load. The coupling simulation algorithm was used in this paper to study on vibration reduction performance of semi-active particle damping technology for the offshore platform truss structure. The control strategy, simulation algorithm and key parameters of semi-active particle damping are investigated to analyze the vibration reduction effect of the offshore platform truss structure with semi-active particle damper. The results have shown that the semi-active particle damping has a better effect of vibration reduction compared with the passive particle damping. In addition, the control strategy in different frequency bands has different vibration reduction effects to the system; and the simulation has a good agreement with the experimental results.

To improve the anti-explosion performance of blast wall in offshore platforms, an auxetic re-entrant blast wall (ARBW) was proposed and designed based on the indentation resistance effect of an auxetic structure. Based on the numerical nonlinear dynamic analysis method verified by the explosion experiment of a conventional steel corrugated blast wall (CBW), the failure mechanisms of ARBW, steel honeycomb sandwich blast wall (HSBW) and CBW were investigated under distributed impulse loads. Computational results demonstrated the excellent anti-explosion performance of the proposed ARBW design. Concerning the minimal deformation at the mid-point of the proposed protective structures, the ARBW performed best. As regards the minimal deformation at the connection, both ARBW and HSBW worked well. The stress distribution of the connection illustrated the different energy absorption and transmission modes of the three blast walls.

Multi-use offshore platforms (MUPs) combining renewable energy from the sea, aquaculture and transportation facilities can be considered as a challenging way to boost blue growth and make renewable energy (especially wave energy) environmentally and socio-economically sustainable. MUPs allow sharing the financial and other market/non-market costs of installation and management, locally using the produced energy for different functionalities and optimizing marine spatial planning. The design of these solutions is a complex interdisciplinary challenge, involving scientists and technical experts with different backgrounds. This paper presents a new methodology for the design of a MUP based on technical, environmental, social and economic criteria. The methodology consists of four steps: a pre-screening phase, to assess the feasibility of different maritime uses at the site; a preliminary design of the alternative schemes based on the identified maritime uses; a ranking phase, where the performance of the MUPs is scored by means of expert judgment of the selected criteria; a preliminary design of the selected MUP selected. An example application of this procedure to a site offshore the Western Sardinia coast, Mediterranean Sea, Italy, is provided. In this site the deployment of a MUP consisting of wave energy converters, offshore wind turbines and aquaculture is specifically investigated.

This paper documents developments in fatigue cracking of a floating platform that required repair and upgrading during 1999–2000. The Veslefrikk B (VFB) platform was built in 1985 for drilling exploration but was converted to a production platform in 1989. Shortly thereafter extensive fatigue cracking was discovered and several repairs were made. However, extensive fatigue cracking continued and a retrofitting program was implemented, using various types of grinding and peening techniques. In 1999 the platform was temporarily decommissioned and dry-docked for a comprehensive repair and upgrading program, following the International Institute of welding (IIW) guidelines for weld improvement methods [1] , this was completed in only four months. However, after a few more years of service fatigue damage again necessitated new repairs. The majority of cracks occurred in the hull skin plates and caused water leakage. It is noteworthy that cracking this time occurred only in areas of the structure that were left untreated in the first retrofitting program due to low levels of stress from FE analyses in these areas. The paper describes the original repair and strengthening program, and the types of subsequent fatigue damage that necessitated new repairs. The recent life extension program has resulted in the safe operation of the platform for an estimated additional period of 20 years.

Prototype monitoring techniques play an important role in the safety guarantee of mooring systems in marine engineering. In general, the complexities of harsh ocean environmental conditions bring difficulties to the traditional monitoring methods of application, implementation and maintenance. Large amounts of existing mooring systems still lack valid monitoring strategies. In this paper, an underwater monitoring method which may be used to achieve the mechanical responses of a multi-point catenary mooring system, is present. A novel self-contained assembled water depth-inclination (D-I) sensor is designed and manufactured. Several advanced technologies, such as standalone, low power consumption and synchronism, are considered to satisfy the long-term implementation requirements with low cost during the design process. The design scheme of the water resistance barrel and installation clamp, which satisfies the diver installation, are also provided in the paper. An on-site test has previously been carried out on a production semisubmersible platform in the South China Sea. The prototype data analyses, including the D-I value in the time domain (including the data recorded during the mooring retraction and release process) and spectral characteristics, are presented to reveal the accuracy, feasibility and stability of the sensor in terms of fitting for the prototype monitoring of catenary mooring systems, especially for in-service aging platforms.

Airborne Wind Energy Converters (AWECs) are promising devices that, thanks to tethered airborne systems, are able to harvest energy of winds blowing at an altitude which is not reachable by traditional wind turbines. This paper is meant to provide an analysis and a preliminary evaluation of an AWEC installed on a floating offshore platform. A minimum complexity dynamic model is developed including a moored heaving platform coupled with the dynamics of an AWEC in steady crosswind flight. A numerical case study is presented through the analysis of different geometrical sizes for the platform and for the airborne components. The results show that offshore AWECs are theoretically viable and they may also be more efficient than grounded devices by taking advantage of a small amount of additionally harvested power from ocean waves.

WOS; International audience; In offshore tubular structures, a typical tubular joint may be subjected to three different types of basic loadings: axial, in-plane bending and out-of-plane bending, through its brace members. Each type will cause a different stress distribution at the joint intersection of structures. Moreover, the actual load condition of a tubular joint can be any combination of the above three basic load cases, for this reason, a combined loading was investigated in addition to these three basic loadings. This load is composed of an axial loading combined with a continuation of rotational bending loading obtained while rotate center of the brace around a circle. Different types of planar joints such as T, Y, X, K, DT, DY, DX, TY, TK, DTX, DTDY, and DTDK, with braces subjected to combined loading, were numerically analyzed to study the effect of those different cases of loading and different types of joints, on the stress concentration zone and values.

Role of mini tension leg platforms (TLP) in oil exploration and production in marginal deepwater fields is becoming increasingly important. Mini TLP combines the simplicity of a spar and favorable response features of a TLP. In this paper, the results of a detailed experimental and numerical investigation of the coupled dynamic behavior of a mini TLP are reported with special attention to hull-tether coupling. The experimental study has been carried out using a scaled model in wave flume with specially designed tethers whose first two "string" natural frequencies are excited by waves, thus achieving strong hull-tether coupling. The numerical study has been carried out using a nonlinear time domain finite element method specifically addressed to compliant offshore platforms using a combination of potential theory based wave loading and Morison-type wave loading. Extensive comparisons between numerical and experimental results have been made both for platform motions and deflected shapes of the tethers and conclusions drawn. Copyright ? 2004 by ASME.

This paper describes a group model building activity designed to elicit the potential effects a projected multi-use deep water offshore platform may have on its local environment, including ecological and socio-economic issues. As such a platform is proposed for construction around the island of Hsiao-Liu-Chiu, Taiwan, we organized several meetings with the local stakeholders and structured the debates using group modeling methods to promote consensus. During the process, the participants iteratively built and revised a causal-loop diagram that summarizes their opinions. Overall, local stakeholders concluded that a multi-use deep water offshore marine platform might have beneficial effects for Hsiao-Liu-Chiu because more tourists and fish could be attracted by the structure, but they also raised some potential problems regarding the law in Taiwan and the design of the offshore platform, especially its resistance to extreme weather. We report the method used and the main results and insights gained during the process.

TNT Equivalency methods are widely used for vapour cloud explosion blast modeling. Presently, however, other types of models are available which do not have the fundamental objections TNT Equivalency models have. TNO Multi-Energy method is increasingly accepted as a more reasonable alternative to be used as a simple and practical method. Computer codes based on computational fluid dynamics (CFD) like AutoReaGas, developed by TNO and Century Dynamics, could be used also in case a more rigorous analysis is required. Application of the Multi-Energy method requires knowledge of two parameters describing the explosion: a charge size and a charge strength. During the last years, research has led to an improved determination of the charge strength (i.e., the class number or source overpressure) to be chosen to apply the blast charts. A correlation has been derived relating the charge strength to a set of parameters describing the boundary conditions of the flammable cloud and the fuel in the cloud. A simple approach may not be satisfactory in all situations. The overpressure distribution inside a vapour cloud explosion is generally not homogeneous and the presence of obstructions causes directional blast propagation in the near field. A CFD approach, in which the actual situation is modeled, supplies case-specific results. An overview of the key aspects relevant to the application of the Multi-Energy method and CFD modeling is provided. Then the application of the two methods is demonstrated for an example problem involving the calculation of the explosion blast load on a structure at some distance from the explosion in an offshore platform complex. Copyright (C) 2000 Elsevier Science B.V.

In this paper, a relatively novel approach is established to estimate different limit states and accurate behavior of jacket platforms against environmental wave loading. This novel approach which is called Incremental Wave Analysis (IWA) can be an appropriate substitute to current pushover practice. The IWA can take into account the effects of variation in wave height and wave-in-deck loading in the estimating of platforms' behavior. This paper aims to introduce the applications of this approach in deterministic assessment of offshore platforms, comprehensively. The IWA can estimate the collapse-prevention limit state of jacket platforms properly. In addition, an appropriate parameter for ultimate capacity of offshore platforms is introduced which is called Collapse Wave Height (CWH). It is illustrated that the CWH can be utilized as a substitute to RSR parameter in the design and assessment of jacket platforms. Moreover, this novel indicator is able to exceptionally estimate the collapse probability of offshore platforms utilizing a deterministic practice. This is a unique feature that can never be achieved by current pushover method utilizing RSR parameter. The IWA can be carried out using either nonlinear static or dynamic wave analyses. Therefore, in this paper, both Static and Dynamic Incremental Wave Analyses (SIWA and DIWA) will be systematically explained. Before conducting DIWA, some fundamental questions such as importance of dynamic analysis and also proper methodology for conducting dynamic analysis, will be investigated. Comparison between SIWA and DIWA will also bring about worthwhile results which will be discussed thoroughly.

A challenging problem in structural health monitoring systems is the requirement of a systematic, effective method for damage localisation and assessment severity of structures, based on vibration data measured by sensors. To address this issue, a novel technique, referred to as damage estimator with modal parameters of structure before and after damage, is applied to detect the location and estimate the severity of existing damage of complex structures. Specifically, a series of experimental tests using a scaled offshore platform model of a 4-story jacket type has been conducted to verify the efficiency of proposed approach, with white noise excitations applied to the top plate of test model. For 6 scenarios of damage conditions simulated by bolt adjustment in the 3rd layer, vibration-based impulse data are induced by an impact hammer and recorded to analyse the variations of modal parameters. Upon the investigation, the results highlight that damage estimator is capable of tracking damage orientation and severity longitudinally, using data from only the fundamental mode shape before and after damage. However, detection accuracy declines considerably for small-scale damages.

International audience; When performing risk analysis, it is often uneasy to find the link between limit state and consequences. This paper focuses on efficiency based limit states in case of large cracks on offshore structures. Randomness and uncertainties on loading as well as on crack measurement and detection are introduced.; Les analyses de risque sont souvent délicates par manque de lien direct entre la fonction d’état et les conséquences. Cet article propose des fonctions d’état de type performantiel (déplacement) dans le cas d’apparitions de fissures traversantes dans des tubes métalliques de structures offshore. Les aléas sur le chargement, la mesure de la fissure et la performance des inspections sont intégrés dans l’analyse de risque.

Monitoring offshore platforms, long span bridges, high rise buildings, TV towers and other similar structures is essential for ensuring their safety in service. Continuous monitoring assumes even greater significance in the case of offshore platforms, which are highly susceptible to damage due to the corrosive environment and the continuous action of waves. Also, since a major part of the structure is under water and covered by marine growth, even a trained diver cannot easily detect damage in the structure. In the present work, vibration criterion is adopted for structural monitoring of jacket platforms. Artificial excitation of these structures is not always practicable and ambient excitation due to wind and waves may not be sufficient for collecting the required vibration data. Alternate methods can be adopted for the same purpose, for example, the application of an impact or a sudden relaxation of an applied force for exciting the structure. For jacket platforms, impact can be applied by gently pushing the structure at the fender while relaxation can be accomplished by pulling the structure and then suddenly releasing it using a tug or a supply vessel in both cases. The present study is an experimental investigation on a laboratory model of a jacket platform, for exploring the feasibility of adapting vibration responses due to impulse and relaxation, for structural monitoring. Effects of damage in six members of the platform as well as changes in deck masses were studied. A finite element model of the structure was used to analyze all the cases for comparison of the results as well as system identification. A data acquisition and analysis procedure for obtaining the response signatures of the platform due to the impulse and relaxation procedure was also developed for possible adoption in on-line monitoring of offshore platforms. From the study, it has been concluded that both impulse and relaxation responses are useful tools for monitoring offshore jacket platforms. The present work forms the basis for the development of an automated, on-line monitoring system for offshore platforms, using neural networks. ? 2000 Elsevier Science Ltd. All rights reserved.

The dynamic pressure distribution around a cylinder tilted along and against the principal wave direction is measured. The cylinder was exposed to the action of random waves in the presence and absence of extreme waves. Six inclinations from the vertical plane, three along and three against the wave direction, were considered. The cylinder in upright position was also studied. The variation of dimensionless peak pressure (pressure maximum/average highest one-third wave height, H(1/3)) with the relative wave height (maximum wave height/H(1/3)) for locations facing the wave and at the rear of the cylinder for different angles of inclinations of the cylinder are reported for the two kinds of waves mentioned earlier. The statistical properties of the different asymmetries in the pressure traces are also discussed.The dynamic pressure distribution around a cylinder tilted along and against the principal wave direction is measured. The cylinder was exposed to the action of random waves in the presence and absence of extreme waves. Six inclinations from the vertical plane, three along and three against the wave direction, were considered. The cylinder in upright position was also studied. The variation of dimensionless peak pressure (pressure maximum/average highest one-third wave height, H1/3) with the relative wave height (maximum wave height/H1/3) for locations facing the wave and at the rear of the cylinder for different angles of inclinations of the cylinder are reported for the two kinds of waves mentioned earlier. The statistical properties of the different asymmetries in the pressure traces are also discussed.

The applicability of the notch strain approach to the assessment of the fatigue strength and service life of a K-shaped tubular joint is investigated. The structural stresses in the hot spot area are calculated by the finite element method and compared with the results of relevant parametric formulae as well as of strain gauge measurements. The stress concentration factor at the weld toe is determined on the basis of a plane cross-sectional model of the weld at the hot spot. The elastic–plastic notch strains are derived therefrom using the cyclic stress strain curve of the material (finite element results and approximations according to Neuber and Sonsino). The fatigue strength of the tubular joint under constant-amplitude loading is predicted on the basis of the strain S–N curve. The service life under variable-amplitude loading in seawater is derived using the Miner rule. The notch strain approach for welded joints results in unacceptably large differences in the predicted strength and life values under similarly acceptable assumptions in respect of material state, local hardness and residual stress. The inhomogeneity of material and hardness at the weld toe seems to be the main reason for the discrepancies.

Many offshore structures are subjected to overturning moments due to wind load, wave pressure, and ship impacts. For foundations in such structures, usually a combination of vertical and batter piles is used. Little information is available in the literature about estimating the capacity of piles under uplift. In cases where these supporting piles are not vertical, the behavior under vertical pullout is not well established. In this article the vertical pullout behavior of batter piles is examined through an experimental investigation carried out on model batter anchor piles. The tests are conducted on model aluminum pipe piles of 19 mm diameter with different embedment ratios in a soft marine clayey bed at different consistencies and with various batter angles of 0�, 10�, 20�, and 30�. Results indicate that the pullout capacity of a batter pile is less than that of a vertical pile. This reduction is explained in terms of reduced area available for skin friction. Based on this, pullout behavior of batter anchor piles is described as "short anchor" and "long anchor" failures. However, with increase in the embedment length, the capacity of batter pile remains unaffected.

The normal subsidence monitoring technologies, used in civil engineering, are hard to apply in ocean engineering. Because it is hard to find a fixed reference for subsidence monitoring. A new method, which is suitable for subsidence monitoring of offshore platforms, is proposed in this paper. Firstly, the compression characteristic of the soil was analyzed and the harms of subsidence are discussed. Based on the analysis, the subsidence monitoring method was given. Finally, an real application is shown. Some advanced measurement technologies, such as the FBG strain measurement techniques and so on, were used in this application. The real application indicates that the new method is suitable for the subsidence monitoring of offshore platforms.