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Fatigue has long been recognized as an important consideration for designing offshore structures and intensive cooperative industry research on tubular joints. In this paper, fatigue life assessment for welded tubular joints of aging fixed platforms is numerically assessed as part of mitigation for platform lifetime. The current paper focuses on different aspects of the remaining fatigue life assessment of an aging offshore platform. The analysis procedures are presented for numerical fatigue assessment methods based on S–N curve approach for API standard utilizing the spectral (stochastic) method. Applications have been performed on an eight-leg piled fixed type platforms located in the Persian Gulf, in order to determine the fatigue lifetime of the jacket tubular primary and secondary joints caused by the wave forces repetitively applied over the platform’s design life and to check if the platform is fit for the purpose of 20 years’ life extension or not. The structural assessment is performed based on the best estimates of the existing conditions of the structure data on the future corrosion allowance. The results are discussed and summarized through tables and plotted Figs.

Diverse forms of offshore oil and gas structures are utilized for a wide range of purposes and in varying water depths. They are designed for unique environments and water depths around the world. The applications of these offshore structures require different activities for proper equipment selection, design of platform types, and drilling/production methods. This paper will provide a general overview of these operations as well as the platform classifications. In this paper, a comprehensive review is conducted on different offshore petroleum structures. This study examines the fundamentals of all types of offshore structures (fixed and floating), as well as the applications of these concepts for oil exploration and production. The study also presents various design parameters for state-of-the-art offshore platforms and achievements made in the industry. Finally, suitable types of offshore platforms for various water depths are offered for long-term operations. An extension of this study (Part II) covers sustainable design approaches and project management on these structures; this review helps designers in understanding existing offshore structures, and their uniqueness. Hence, the review also serves as a reference data source for designing new offshore platforms and related structures.

Offshore structures exist in a variety of forms, and they are used for a variety of functions in varied sea depths. These structures are tailored for certain environments and sea depths. Different actions for suitable equipment selection, platform type design, and drilling/production processes are required for the applications of these offshore structures, as given in Part I. This paper is the second part, which outlines various processes, loads, design approaches and project management of offshore platforms. To achieve these, proper planning must be conducted for lifting, transportation, installation, design, fabrication, and commissioning of these offshore platforms. Some historical developments of some offshore structures are presented, and some project planning routines are undertaken in this research. The ultimate goal is to provide a general overview of the many processes of offshore platform design, construction, loadout, transportation, and installation. Some discussions on the design parameters such as water depth and environmental conditions were presented. It also lists various software programs used in engineering designs covering software programs for structural analysis, 3D rendering, computer-aided design (CAD), hydrodynamic design, oceanic flow analysis, offshore structures analysis, mathematical modelling, coding/algorithm development software, and programming software to aid analytical calculations. The review also includes information on cutting-edge offshore platforms and industry advancements. Ultimately, for long-term operations, various types of offshore platforms for specific seawater depths are available.

With growing concerns about the danger of global climate change and worldwide demand for energy, the interest in the investigation and construction of renewable energy technologies has increased. Fixed platforms are a type of support structure for wind turbines composed of different types of tubular joints. These structures are under different kinds of cyclic loadings in ocean environmental conditions, which must be designed and reinforced against fatigue. In the present paper, the relationships between the parameters in DKT-joints reinforced with FRP under axial loads are investigated using several models, under 16 axial loading cases, with different nondimensional parameters and different FRP materials, and orientations were generated in ANSYS (total 5184) and analyzed. The four loading conditions that cause the maximum stress concentration factors were selected. After analyzing the 1296 reinforced models, relevant data were extracted, and possible samples were created. The extracted data were used in a multivariate data analysis of maximum stress concentration factors. The Pearson correlation coefficient is utilized to study the relationship between parameters and subsequently to make predictions. To reduce the number of variables and to group the data points into clusters based on certain similarities, hierarchical and non-hierarchical classifications are used, respectively.

The northern Gulf of Mexico has been an important source for crude oil and natural gas extraction since the 1930s. Thousands of fixed platforms and associated equipment have been installed on the Gulf of Mexico continental shelf, leading to a pervasive ‘ocean sprawl’. After decommissioning, hundreds of these structures have been converted to artificial reefs under the federal ‘Rigs-to-Reefs’ program, in addition to artificial reefs specifically designed to enhance fisheries and/or benefit the recreational diving industry. Apart from a few natural banks, which reach to approximately 55 ft below the surface, artificial reefs provide the only shallow-water hard substrate for benthic organisms in the deeper waters of the northern Gulf of Mexico. This vast expansion in available habitat has almost exclusively occurred over a relatively short span of time (~ 50 years). The ecological interactions of artificial and natural reefs in the northern Gulf of Mexico are complex. Artificial reefs in general, and oil and gas structures in particular, have often been invoked as stepping stones for non-native and invasive species (e.g. Tubastrea cup corals, lionfish). The pilings are covered with fouling communities which remain largely unstudied. While the risks of these fouling organisms for invading natural reefs are being broadly discussed, other impacts on the ecological and economic health of the Gulf of Mexico, such as the potential to facilitate jellyfish blooms or increase the incidence of ciguatera fish poisoning, have received less attention. Artificial reefs also provide ecosystem services, particularly as habitat for economically important fish species like red snapper. Here we revisit the potential role of artificial reefs as ‘stepping stones’ for species invasions and for fisheries enhancement. Beyond concerns about ecological effects, some of these topics also raise public health concerns. We point out gaps in current knowledge and propose future research directions.

IntroductionThe ATL2MED mission, conducted between October 2019 and July 2020, investigated the variability of air–sea CO2 exchange in the Eastern Atlantic and the Mediterranean Sea. The main objectives were to assess the spatial and temporal variability of the seawater partial pressure of CO2 (pCO2sw), identify its controlling physical and biogeochemical processes, estimate the CO2 fluxes across the sea–air interface, and evaluate the performance of neural network-based predictions (CANYON-MED) in contrasting oceanographic regions.MethodsHigh-resolution autonomous measurements were collected using Saildrone Unmanned Surface Vehicles (USVs), complemented by fixed ocean stations, gliders, and research vessels. Data quality was ensured through cross-validation among platforms, despite challenges such as sensor drift caused by biofouling.ResultsThe results reveal pronounced regional differences in pCO2sw and CO2 fluxes, driven by thermal effects, biological activity, and physical mixing. In the Eastern Atlantic, upwelling systems off northwest Africa induced strong outgassing, while the western Mediterranean acted as a CO2 sink during the spring bloom. Conversely, the Adriatic Sea exhibited episodic CO2 outgassing, particularly in its southern and northern basins, associated with thermal stratification, river plumes, and coastal upwelling.DiscussionSaildrone measurements successfully resolved sub-mesoscale processes typically missed by fixed platforms, demonstrating their potential to enhance ocean CO2 observations in under-sampled or logistically constrained regions. The good agreement with neural network-based estimates further supports the robustness of the dataset. Overall, these findings emphasize the value of high-resolution, multi-platform approaches for accurately quantifying CO2 fluxes and improving predictive capabilities in a changing ocean.

ABSTRACT Objective The existence of offshore energy infrastructure in U.S. federal waters requires an understanding of how artificial structures impact regional fisheries. The Louisiana and Texas continental shelf in the northwestern Gulf of America (also known as the Gulf of Mexico) has a long history of offshore oil and natural gas development and harbors the penaeid shrimp fishery, the highest-valued commercial fishery in the region. Proposed wind energy areas (WEAs) on the shelf for offshore wind energy may disrupt this fishery due to spatial overlap with historical shrimping grounds and the fishery’s use of bottom trawls. Methods We used high-resolution spatiotemporal data on shrimp fishery effort developed from vessel monitoring data to investigate how development of proposed WEAs might affect the shrimp fleet. We quantified patterns of shrimp fishing effort at multiple spatiotemporal scales. We also investigated the attraction and avoidance response by shrimp vessels to existing oil and natural gas rigs to infer how future construction of fixed structures affects the spatial dynamics and behavior of the shrimp fleet. Results Less than 2.5% of the total annual shrimping effort between 2015 and 2019 occurred within the proposed WEAs in the region, and while rigs were generally avoided, shrimper trawling behavior was modified in certain regions due to spatial constrictions. The density of rigs largely controlled how closely shrimp vessels operated near platforms. In areas with high rig density, most effort occurred at distances nearly equal to the horizon, suggesting that line of sight was an important factor driving shrimper fishing behavior. Conclusions Further consideration of the responses of the fishing fleet to structures will enhance our understanding of how ocean development for multiple uses will affect regional bottom trawl fisheries and provide insight into the applicability of these methods for future marine spatial planning in and beyond this region. Lay Summary Offshore rigs affect the behavior of shrimp trawling vessels on the Louisiana–Texas continental shelf, with vessels generally avoiding rigs by modifying their trawling in areas with high rig densities. Understanding these responses can assist future marine planning to balance energy development and fisheries sustainability. Graphical Abstract Graphical Abstract

Two different concepts of wave energy converter coupled to the novel C-GEN linear generator have been studied numerically, including the evaluation of different buoy sizes. The first concept has a slack connection between the buoy and the generator on the seabed. Another concept is based on a stiff connection between the buoy and the generator placed on an offshore platform. Three different approaches to calculate the damping force have been utilized within this study: the optimal damping coefficient, R-load, and RC-load. R-load is a model for the load applied to a grid-connected generator with passive rectification. RC-load is a model for a phase angle compensation applied to a system with active rectification. The radiation forces originating from the oscillatory motion of the buoy have been approximated using the transfer function in the frequency domain and the vector fitting algorithm. A comparison of the approximation methods is presented, and their accuracy has been evaluated. The advantage of the vector fitting method has been shown, especially for higher approximation orders which fit the transfer function with high accuracy. The study’s final results are shown in terms of the absorbed power for the sea states of March 2018 at Wave Hub, UK.

In offshore engineering, a compliant offshore structure accommodates dynamic forces by flexibility rather than rigidly withstanding load effects. As an alternative to conventional fixed platforms for loading/mooring in deep waters, articulated offshore towers are highly appealing because of their reduced structural weight. This study presents the results of a probabilistic random wave with and without current force on a 500 m high articulated tower with two hinges. By using the Lagrangian approach, governing nonlinear equations of motion are derived. The motion equation has been resolved in the time domain with the Houbolt approach. Based on Stokes fifth order nonlinear wave theory, wave forces have been assessed. Hydrodynamic forces are determined using a modified Morison equation with stretching modifications developed by Chakrabarti. The study examined two marine states, i.e., 10 m/10 s and 15 m/15 s. The current intensity of 2 m/sec has been taken into account. The salient statistical parameters such as maximum, minimum, mean, and standard deviation are presented under both the ocean environments. The proposed model is feasible for both the sea states. When comparing sea states, those with a greater wave height and period and those with a smaller wave height and period have more energy in their PSDs for all responses.

BackgroundAvailable platforms for local excision (LE) of early rectal cancer are rigid or flexible [trans‑anal minimally invasive surgery (TAMIS)]. We systematically searched the literature to compare outcomes between platforms.MethodsPRISMA-compliant search of PubMed and Scopus databases until September 2022 was undertaken in this random-effect meta-analysis. Statistical heterogeneity was assessed using I2 statistic. Studies comparing TAMIS versus rigid platforms for LE for early rectal cancer were included. Main outcome measures were intraoperative and short-term postoperative outcomes and specimen quality.Results7 studies were published between 2015 and 2022, including 931 patients (423 females); 402 underwent TAMIS and 529 underwent LE with rigid platforms. Techniques were similar for operative time (WMD 11.1, 95%CI − 2.6 to 25, p = 0.11), percentage of defect closure (OR 0.7, 95%CI 0.06–8.22, p = 0.78), and peritoneal violation (OR 0.41, 95%CI 0.12–1.43, p = 0.16). Rigid platforms had higher rates of short-term complications (19.1% vs 14.2, OR 1.6, 95%CI 1.07–2.4, p = 0.02), although no significant differences were seen for major complications (OR 1.41, 95%CI 0.61–3.23, p = 0.41). Patients in the rigid platforms group were 3-times more likely to be re-admitted within 30 days compared to the TAMIS group (OR 3.1, 95%CI 1.07–9.4, p = 0.03). Rates of positive resection margins (rigid platforms: 7.6% vs TAMIS: 9.34%, OR 0.81, 95%CI 0.42–1.55, p = 0.53) and specimen fragmentation (rigid platforms: 3.3% vs TAMIS: 4.4%, OR 0.74, 95%CI 0.33–1.64, p = 0.46) were similar between the groups. Salvage surgery was required in 5.5% of rigid platform patients and 6.2% of TAMIS patients (OR 0.8, 95%CI 0.4–1.8, p = 0.7).ConclusionTAMIS or rigid platforms for LE seem to have similar operative outcomes and specimen quality. The TAMIS group demonstrated lower readmission and overall complication rates but did not significantly differ for major complications. The choice of platform should be based on availability, cost, and surgeon’s preference.