CFD-FEM Modeling of a Floating Foundation under Extreme Hydrodynamic Forces Generated by Low Sea States

The high development of the offshore industry for supporting new marine and renewable energy projects requires a constant improvement of methods for structure designing. Because recent studies warned that maximum environmental loads occur during low sea states and not during extreme sea states as recommend by the offshore standards (e.g., RP 2AWSD-2014), this study used measured wave and current data for analyzing that warning. The Colombian Caribbean coast was selected as the study area, and in situ ADCP data combined with Reanalysis and numerical data was used for identifying proper sea states for the analysis. Then, two low and one extreme sea states were selected and their associated current profiles were extracted, for providing input data for Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) simulations to evaluate the effect of the hydrodynamic forces over a floating structure. The results showed that low sea states generated maximum loads and rotations in the floating structure, and the extreme sea states caused high-frequency vibrations that could provoke structural dynamics problems such as failures due to fatigue or sudden collapse by resonance and amplification.

FLOW FIELD ON HELODECK OF A FRIGATE: A REVIEW

The various functions desired from a frontline warship such as a frigate, corvette or a destroyer, coupled with the requirement of very high speeds and economic viability restricting the size, necessitates a very dense arrangement of weapons and sensors on the top deck and superstructure. Accordingly, Navies across the world have faced several problems with respect to functions for which a good aerodynamic design for these structures is essential. Major issues include smoke nuisance created due to impinging of the ship's exhaust gases on to the top deck leading to possible suction by engine intakes and high turbulence in the ship's air-wake leading to ship aircraft interface concerns. The flow field on the helodeck is extremely complex due to its geometry and interaction with the wake of the ship’s superstructure. A knowledge of this complexity is essential for ensuring safe helo operations on the helodeck. The problem of ship helicopter interaction has hogged the lime light in recent times, due to rising demand for design of warships for increased stealth, especially in the past two decades. Consequently, several researchers in countries with advanced Navies have invested considerable resources towards evolving both experimental and numerical solutions for the problem. However, given the military nature of the operations, open literature on the subject containing details of such research, which can be used as reference material for present work, are limited. Considering the complexities involved in the problem, an attempt has been made in this paper to holistically review the widely scattered and limited literature in this field. A good amount of literature on marine helo applications emerge from the offshore industry. Keeping in mind that the fields of warship design and offshore structures are dissimilar and have their peculiar problems, informed conclusions have been made in drawing lessons from available literature.

A Comparative Emissions Assessment - Drill Cuttings Treatment Alternatives

The offshore industry has for many years been cognisant of its impact on the marine environment. Since 1991, strict regulations relating to oil-based drill cuttings discharge have been in force in the signature countries to the OSPAR (Oslo/Paris) Convention. As the impact of greenhouse gas (GHG) emissions on climate change has become better understood, global carbon dioxide (CO2) emission reduction targets and how to meet them have risen up operators’ agendas. Offshore operations, which involve marine logistics, are also subject to limits on nitrogen dioxide (NOx) emissions, an indirect GHG that's toxic to humans and contributes to soil and water acidification. The choices that operators make today in how they operate, including the disposal of drill cuttings, must therefore address an increasing number of environmental and climate targets, in addition to health, safety and cost. This paper will outline the results of a comparative study between the offshore processing of drill cuttings and relevant conventional alternatives, including skip and ship, bulk transfer and cuttings reinjection (CRI). It is the first paper to show a direct emissions comparison between offshore processing and all other alternative methods for drill cuttings processing. The study assessed the carbon footprint and NOx emissions for each of the different alternatives for the treatment of drill cuttings. The values were then used to create an interactive emissions calculator that can be easily applied to specific projects to clarify the actual potential for emissions reduction within the drilling waste management process. A number of case studies were then run, comparing the different alternatives. For the examples run, the comparative assessment showed that wellsite thermal processing technology was the favourable alternative in terms of emissions, with an emission reduction in the order of 14 - 48%, compared with the onshore alternatives. Emissions of the alternatives, skip and ship and bulk transfer, were highly dependent on sailing and road transport distances, as well as power source for the onshore treatment facility. The assessment showed that CRI has the highest emissions of CO2 per tonne of cuttings. Alternatives involving onshore treatment had the highest NOx emissions when sailing distance was high, however this was highly dependent on the machinery and fuel source of the transport vessel - and for the offshore alternatives, the on-site energy production solution.

Overview of Possibilities of Solar Floating Photovoltaic Systems in the OffShore Industry

The demand for energy has rapidly grown around the world. Solar floating photovoltaic (FPV) systems are an efficient solution to solve the issues from nonrenewable energy sources, such as reduction of CO2 emission, limitation of global warming, environmentally friendly, a great innovation in sustainable aquaculture, and a new ecofriendly technique, along with reducing production costs, especially regarding the scarcity of habitable land. A large number of installation projects using FPV technology have been operated in water bodies such as lakes and dams/reservoirs. However, deployment of FPV offshore is still limited because of the existing characteristics of marine/sea environments that are different from onshore, such as wind loads and wave loads. Despite these difficulties, there are several projects that have been installed in some countries and gained many significant achievements. It opened possibilities to apply FPV systems offshore worldwide. In this review, we present a brief overview of FPV systems both onshore and offshore, analyze advantages and disadvantages of offshore FPV systems, and provide an overview of their future.

The social structure of 70 years of literature on Human Reliability

From its first applications to the military domain, HRA progressed to applications in Nuclear Power Plants (NPPs) operations, when development and validation of methods mainly targeted their use in Probabilistic Risk Assessments. In recent years, advances in HRA include the extension to various application fields, the development of new methods or enhancement of existing ones, data collection efforts, among others. These advances are possible due to the increasing number of authors on HRA and collaboration between them. Systematic literature reviews have been increasingly used for understanding various aspects of a research field. While recent reviews have provided an overview of the topics addressed by HRA research, the social structure of the field has not yet been fully explored. This paper discusses the social structure of HRA through 70 years of literature. The review aims at responding to how the links between different authors groups were created, that is, which large-scale projects, geographical proximity, or research topics contributed to these connections. The results indicate that (1) while the research on HRA was mostly based in the U.S.A. before 2000, China, Japan, and South Korea are significant contributors to the recent literature; (2) despite the increasing diversity of application fields, such as applications to the maritime and offshore industry, the main focus on NPPs operations is persistent since the 1980s; (3) due to large research projects, favored by a connected world, the physical workspace does not limit current collaboration among authors.

The Next Generation Fast Marine Access Solution

The long distance transport of offshore personnel has traditionally been undertaken by air. However, the desire for increased safety and efficiency in combination with the drive to lower operational cost in the offshore industry opens up new possibilities for fast marine access solutions. This article presents the development of the next generation Fast Crew Supplier that combines high transit speeds at high comfort levels with a reliable, safe and comfortable method of personnel exchange to the platform using a Walk-to-Work solution. The results of an integrated design approach are presented which are used to optimize the main transfer systems and their controls. It is shown that optimization of these systems allows a high workability for a Walk-to-Work solution on a fast and relatively lightweight ship in challenging wave conditions.

At the Interface of Marine Disciplines: Use of Autonomous Seafloor Equipment for Studies of Biofouling Below the Shallow-Water Zone

Biofouling of artificial substrates is a well-known phenomenon that can negatively impact offshore industry operations as well as data collection in the ocean. Fouling communities worldwide have mostly been studied within the top 50 m of the ocean surface, while biofouling below this depth remains largely underreported. Existing methods used to study biofouling are labor intensive and expensive when applied to the deep sea. Here, we propose a simple and cost-effective modification of traditional methods for studying biofouling by mounting test plates on autonomous seafloor equipment and preserving them in ethanol upon retrieval for transport to the laboratory. This method can greatly advance our understanding of biofouling processes in the deeper ocean, including fouling community biodiversity, recruitment, and seasonality. We present two case studies from the Laptev Sea and the Sea of Okhotsk in support of this method. In the first study, we looked at fouling communities on the surfaces of ocean-bottom seismometers deployed for one year in the 36–350 m depth range. In the second study, we tested metal and plexiglass (poly(methyl methacrylate) plates mounted on autonomous bottom stations and found evidence of both micro- and macrofouling after three months of deployment. Our results demonstrate that various autonomous seafloor equipment can be used as supporting platforms for biofouling studies.

Dropped Object Impact Analysis Considering Frequency and Consequence for LNG-FPSO Topside Module

Recently, quantitative risk assessment (QRA) has been widely used as a decision-making tool in the offshore industry. This study focused on analyzing dropped objects in the design of a modern offshore platform. A modified QRA procedure was developed for assessing production module protection against accidental external loads. Frequency and consequence analyses were performed using the developed QRA procedure. An exceedance curve was plotted, and a high-risk management item was derived through this process. In particular, simulations and experiments were used to verify the difference between the potential and impact energies according to drop orientation. When the object dropped in a specific orientation, the impact energy was confirmed to be up to 4.7 times greater than the potential energy. To reflect the QRA results in structural design, the proposed procedure should be used to calculate the maximum impact energy. The proposed procedure provides a step-by-step guide to assess the damage capacity of a production area as well as the damage frequency and consequences.

MACRO-GOM: Long Term Multi-Resolution Ocean Current Reanalysis Dataset for the Gulf of Mexico

The Gulf of Mexico's unique circulation characteristics pose a particular threat to marine operations and play a significant role in driving the criteria used for design and life extension analyses of offshore infrastructure. Estimates from existing reanalysis datasets used by operators in GOM show less than ideal correlation with in situ measurements and have a limited resolution that disallows for the capture of ocean features of interest. In this paper, we introduce a new high-resolution long-term reanalysis dataset, Multi-resolution Advanced Current Reanalysis for the Ocean – Gulf of Mexico (MACRO-GOM), based on a state-of the-science hydrodynamic model configured specifically for ocean current forecasting and hindcasting services for the offshore industry that assimilates extensive non-conventional observational data. The underlying hydrodynamic model used is the Woods Hole Group – Tendral Ocean Prediction System (WHG-TOPS). MACRO-GOM is being developed at the native resolution of the TOPS-GOM domain, i.e. 1/32° (~3 km) hourly grid for the 1994-2019 time period (25 years). A 3-level downscaling methodology is used wherein observation based estimates are first dynamically interpolated using a 1/4° model before being downscaled to the 1/16° Inter-American Seas (IAS) domain, which in turn is used to generate time-consistent boundary conditions for the 1/32° reanalysis. A multiscale data assimilation technique is used to constrain the model at synoptic and longer time scales. For this paper, a shorter, 5-year reanalysis run was conducted for the 2015-2019 time period for verification against assimilated and unassimilated observations, WHG's proprietary frontal analyses, and other reanalyses. Both the frontal analyses and Notice to Lesses (NTL) rig mounted ADCP data was withheld from assimilation for comparison. Offshore operations in the GOM can benefit from an improved reanalysis dataset capable of assimilating existing non-conventional observational datasets. Existing hindcast and reanalysis model datasets are limited in their ability to comprehensively and reliably quantify the 3D circulation and kinematic properties of the main features partly because of limited assimilation of observational data. MACRO-GOM incorporates all the advantages of available HYCOM-based reanalyses and further enhances the resolution, accuracy, and reliability by the assimilation of over three decades of WHG's proprietary datasets and frontal analyses for continuous model correction and ground-truthing. The final 25-year high resolution dataset will provide highly reliable design and operational criteria for new and existing infrastructure in GOM.