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The installation of offshore structures and facilities in the marine environment, usually for the production and transmission of oil, gas exploration, electricity, and other natural resources is referred to as offshore construction. Since offshore structures are subjected to changing threats to the environment year-round. Fatigue behavior prediction noticed on these structures should be considered during the design stage. Fatigue is one of the failure mechanisms of offshore steel structures, and it must be investigated properly during system design. The fatigue analysis of offshore structures under drag wave force, total wave force, total moment about the sea bed, and other variables are reviewed thoroughly. The structure's dynamic response becomes a critical aspect in the whole design process. The fatigue analysis was carried out using MATLAB software, material properties of the offshore structure, and wave spectrum characteristics in this study. This study shows the JONSWAP spectrum and stress concentration analysis prediction. The offshore support structure that is predicted during the design phase will help to keep the stress concentration factor below the fatigue threshold and anticipate safe life design, according to the results of the fatigue study. The fatigue performances of tripod and jacket steel support structures in intermediate waters depth are compared in this project (20-50 m). The North Atlantic Ocean is used as a reference site, with a sea depth of 45 meters. The tripod and jacket support structures will be designed by using current industry standards. Keywords: [Fatigue evaluation, North Atlantic Ocean and Failure].

The misalignment of wind and waves is of special interest for various engineering applications, i.e. for structural fatigue load analyses, for work vessel operations for offshore construction or maintenance, and for floating wind turbines. In addition to the normal or frequent boundary conditions, the combination of extreme loads and their directions is essential for coastal and offshore designs. These aspects are addressed by analyzing ten years of field measurements in the German Bight of the North Sea, which is intensively used for offshore wind energy production. This paper focuses on the occurrence and amount of wind and wave misalignment as well as the direction dependency of the wind-wave correlation for normal conditions and extreme storms. Subsequently, the influence of statistical distribution functions for the estimation of extreme wind and wave values is presented. Based on these results, a method is developed to combine direction dependent extreme wind and wave incidents for return periods of several decades.

This paper presents an overview of quality control issues of submarine cables in project cycle of offshore wind power projects in Jiangsu. After analyzing all stages of the overall process of an offshore wind power project cycle, different focus quality control issues related to submarine cable, such as design flaw, reinstallation, harsh offshore construction conditions, damage by external force, application of land cable accessories, excessive ground current and uneven distribution between layers are listed in detail following accident cases. In the end, several practical advices and methods such as the preferences of three-core submarine cable and dry pluggable terminal, improvement of standards of quality control test methods and life cycle management measures are given, in order to improve the quality control of submarine cables.

This chapter presents an overview of oil and gas investment and different types of offshore structures, from shallow water to deep water, and other structure configurations such as floating, production, storage, and offloading and tension-leg platforms. The offshore project phase, focusing on control of the engineering from appraisal, selection, definition, and execution, is discussed in this chapter. The offshore project investment and the cost estimate corresponding to each phase of the project are also discussed. To understand the oil and gas business, the first step is to define the offshore project target and objective, and then how to provide a project which is technically matched throughout all phases with the business requirements.

This paper describes an experimental and numerical investigation of the Iberdrola TLP wind turbine concept, TLPWIND, in realistic wind and wave conditions. The TLP was coupled to the NREL 5 MW reference turbine and was designed to operate in a water depth of 70 m. The test campaign included free oscillation tests, tests in regular and irregular waves and simulated wind conditions. A Software-in-the-loop approach was adopted to account for the time-varying aerodynamic forces produced by the turbine during the physical experiments. The effect of wind was found to have a significant contribution to the overall response of the platform whilst variation in wave conditions was found to have a relatively small effect on the platform response. A comparison of results from physical and numerical simulations show that, the numerical predictions from FAST were very close to the results obtained from the experiments in some cases, but in other cases the numerical model failed to accurately predict the platform response. The results from both studies show the benefits of such TLP structures in terms of motions which are vital to obtain a high power output from a floating offshore wind turbine.

This paper develops a methodology to determine the installation costs of a floating wind farm installed offshore, the value of which depends on the type of floating offshore wind platform installed. In this context, several costs in the installation process have been defined: installation of the offshore wind generators, installation of the floating offshore wind substructures, installation of the anchoring and mooring, installation of the electric systems and the commissioning or start up of the floating offshore wind farm. Furthermore, several installation scenarios have been taken into consideration regarding the shipyard surface and draught, the number of lifts, the transport, the mooring strategy and the substation configuration. The method, tested for the region of Galicia and for three sorts of floating substructures: spar, semisubmersible and tensioned leg, allows to compare different alternatives of installing a floating offshore and the most important aspects of the costs proposed. It can be useful for investors who decide to use this type of offshore renewable energy in the future.

The present paper compares in economic terms, four technological alternatives to use offshore renewable energies: floating offshore wind energy technology, floating offshore wave energy systems, floating offshore co-located systems and floating offshore hybrid systems. These alternatives are compared considering different locations and sizes of the farms. Studies such as this can be useful for planning strategies and decision-making, particularly to investors that have to decide if and how to develop and deploy particular technologies in deep waters. The results indicate that the best alternative considering the life-cycle cost and LCOE is the floating offshore wind energy technology. Floating offshore co-located systems have the second best result, being a better alternative than floating offshore wave energy devices or floating offshore hybrid systems.

One of the advantages of floating offshore wind turbines (FOWTs) is that they can be designed to be easily wet towed and installed to reduce the cost of offshore construction. In this paper, a fully coupled towing system numerical model is established for a novel 10 MW FOWT concept, namely, a submerged floating offshore wind turbine (SFOWT) to investigate the towing performance. Firstly, the numerical simulation is validated by comparison with model experiment results. Then, a series of numerical simulations are conducted to predict and compare the towing performance for a three-column SFOWT (TC-SFOWT) and a four-column SFOWT (FC-SFOWT) under different wave conditions. The results show that the two forms of SFOWT have good towing performance when the significant wave height is less than 5 m, which is the maximum wave height for the allowable towing condition. The FC-SFOWT shows relatively better performance in heave motion and roll motion, but the towing force is relatively larger compared with the TC-SFOWT under the same condition. When the significant wave height is 5 m, the maximum values of heave motion, pitch motion, and roll motion of the TC-SFOWT are 2.51 m, 2.14°, and 1.38°, respectively, while they are 2.25 m, 2.70°, and 1.21°, respectively, for the FC-SFOWT. Both the roll motion and the pitch motion are satisfied with the requirement that the roll and pitch are less than 5° during the towing process. The mean towing force of FC-SFOWT is 159.1 t at the significant wave height of 5 m, which is 52.8% larger than that of TC-SFOWT. The peak period mainly influences the frequency where the response peak appears in power spectra. The findings in this paper could provide some guidelines for wet towed operations.

Despite the fact that offshore wind energy will tend towards the floating technologies their economic impact has not been practically evaluated yet. In this context, the aim of this article is to characterize the possible economic alternatives which can be considered in the life-cycle of floating offshore wind farms based on their life-cycle costs. Several groups of variables have been considered for determining these alternatives: wind turbines, floating platforms, mooring system, anchoring process, kind of seabed, electric system, installation, shipyard and maintenance. The method proposed has been applied to the case of the North-West coast of Spain (Galicia region). For this case test three different platforms have been analyzed: Tensioned Leg, Spar and Semisubmersible platforms. Results, which are presented by using maps of the area, conclude that offshore substation, string electric configuration and “tree fall” decommissioning method are the best options for minimizing the costs. In addition, the installation method will be conditioned by the type of floating platform and mooring material, whereas the disposition and anchor decisions are dependent on the geographic location. Results show how the methodology proposed is useful to characterize economically the life-cycle of a floating offshore wind farm.

The radiated acoustic waves from impact pile driving produce high noise level into the water which may cause damage to marine mammals living close to the offshore construction location. In this paper, a linear, axisymmetric finite element (FE) model is applied to predict pile driving noise in the water. Measurement from bottom-mounted hydrophone deployed at a site 230 m from the source is used to validate the model results. The comparisons between model results and measurement, such as structure modal analysis, sound exposure level at different pile penetration and unweighted one-third octave band level, are presented and show useful predictions of noise level from the model. Furthermore, a time domain case is demonstrated to show Mach wave associated with the radial deformation of the pile and supersonic speed. Finally, analysis of variance (ANOVA) and linear regression are made after verifying the model prediction. The ANOVA results identifies some significant parameters on pile driving noise and the empirical equation from linear regression represents the noise level from pile driving impact at close range. These are possible metrics on offshore wind farm environment assessment in Taiwan.

Lifting operation though the wave splash zone is challenging. Careful numerical analysis in the design phase is needed to minimize associated risks. This study addresses numerical modeling and analysis of the splash zone lowering of a large subsea spool. A typical offshore construction vessel is used for the operation. The objective is to compare the effects from different numerical methods and parameters on the allowable sea states and the operability. These methods and parameters include wave short-crestedness, shielding effects from the vessel, wave direction and wave seed number. A coupled numerical model of the spool-vessel system is established in SIMO program, which is a simulation tool for marine operations. Slamming and submergence-dependent loads on the spool during the transient lowering process are calculated. A large number of time-domain simulations has been performed to derive the allowable sea states. The operational criteria for assessment of the sea states include slack sling, snap loads in wires and clearance between spool and the vessel. Operability analysis of the operation at one reference site in the Barent Sea is established using 50-year hindcast data. The influences from different methods on the allowable sea states and the operability are compared and discussed in detail.

The offshore construction environment can be very difficult to be accurately predicted, due to various uncertainties in the geotechnical elements, and highly probabilistic events at which ocean conditions govern the design. The integrity assessment and life extension activities towards end of field life is becoming very common in older fields surrounding Malaysia, and other areas such as the Arabian Gulf and the North Sea. The in-line measurement of the existing residual stresses on these assets is very critical for the remaining life assessments, and also to categorise assets for shutdown to undergo rehabilitation work. The novel idea of using ultrasonic waves is developed and explained in detail in this paper. This method is based on the measurement of the time of propagation of the critically refracted longitudinal wave components travelling along the subsurface region of the specimen. Numerical validation is backed up by experimental work to verify this method to be fit-for-purpose for the intended application, through the development of an acoustoelastic calibration curve for several sectional shape/sizes of carbon steel material. These tests show good correlation between the numerical and experimental work, and this has the potential to be a reliable tool for use in the offshore/marine engineering sector where shutdowns are expensive.

This study is aimed to develop the dynamic analysis technique for a floating aquaculture in a shallow water region under the harsh sea condition. In case of the installation region to transform from a coastal area to the offshore area, the influence of sea bed with sea waves on the mooring lines was announced to be significant by other authors. In this study, the numerical tool was developed to solve dynamic behavior of the floating barge coupled with mooring lines in a shallow zone of the sea considering the influence of sea bed on the floating system.Copyright © 2016 by ASME

In the early stages of oil and gas exploitation, it is important to rapidly identify which production platform is likely to deliver its utmost value. This study first explores the key features and constraints of the most commonly used fixed and floating offshore platforms then proceed to discuss the current available production technology. Platform selections are based on several factors such as stability, water depth and environmental conditions. Drilling can be done from the platform or another mobile unit. As most new offshore operations turn to semi-submersible platform and drill rigs, it is perceived as the most promising platform by oil and gas industry.

With the constant increase of known oil reserves in deep and ultra-deep waters, floating production systems (FPS) have been established as the main option for offshore production activities. This work presents recent advances regarding an innovative application of evolutionary optimization methods to the design of mooring systems for FPS. Here the focus in in the consideration of actual scenarios with seabed obstacles and other restricted areas where anchors cannot be positioned. The optimization tool employs the Particle Swarm Optimization (PSO) method. The constraints are treated by specialized constraint-handling techniques, and each candidate solution is evaluated through nonlinear analyses coupling the hydrodynamic model of the platform hull with a Finite Element model of the mooring lines and risers. A case study illustrates the application of the optimization for a real-world scenario.

There is significant evidence that the low-frequency mean acoustic noise pressure level in the ocean has been constantly increasing in the last decades. The main noise sources responsible for this increase were identified as ship traffic, offshore construction and oil & gas surveying. The Portuguese Navy funded SUBECO project aims at deploying a network of multiparametric offshore buoys for environmental and acoustic monitoring. A preferred location for the individual buoys is within or close by the ship traffic separation lanes along the west coast of Portugal. It is therefore expected that the received acoustic field will be dominated by shipping noise as a mixture of both short and long range ships. Most ships will have an AIS so their position may be known at all times. One of the objectives of this network is to use the recorded sound to infer and calibrate model predicted noise in a wider area. This work proposes a relatively simple technique for estimating the radiated noise level of ship tracks within acoustic reach of a single (or a small number of closely localized) hydrophone(s). It is expected that the data constrained predicted field with the estimated source levels will provide a better fit to the actual wide area acoustic field. This work is a contribution to fulfill the requirements of Portugal to the European Union Marine Strategy Framework Directive (MSFD) aiming at a good environmental status.

The paper is in support of the effort by the Marine Renewable Energy (MRE) Committee of the ASCE Coasts, Oceans, Ports, and Rivers Institute (COPRI) for setting up a guide document for offshore renewable energy foundations. The guide would use standard design codes for fixed foundations and mooring anchors in API, ISO and DNV. This paper focuses on specific aspects of design of offshore wind turbines that distinguish them from oil and gas installations. Emphasis is placed on the source of loading and the corresponding response of soil resistance. The paper also how soil investigation for offshore windfarms differ from oil and gas and economic procedures for carrying out such investigation. Foundation design of offshore structures requires identifying the critical loads. In the case of oil and gas foundations, the source of the load is the wind or wave or a combination of both. For offshore wind towers on fixed foundations, an additional source of dynamic load is the turbine blade rotation during operation. The frequencies of the rotor revolution and that of the blade passing the tower, need to be checked in relation to the resonance frequency of the foundation. The foundation dynamic response therefore depends largely on the stiffness and dampening characteristics. Most offshore wind turbines tend to be located in relatively shallow water depth where difficult multi-layered soils tend to be dominate. This paper also discussion installation suction buckets of fixed foundation in difficult multi-layered soils.

Platform construction GTS (Gathering Testing Sattelite) is offshore construction platform with fix pile structure type/fixed platform functioning to support the mining of petroleum exploitation. After construction fabrication process platform was moved to barges, then shipped to the installation site. Moving process is generally done by pull or push based on construction design determined when planning. But at the time of lifting equipment/cranes available in the work area then the moving process can be done by lifting so that moving activity can be implemented more quickly of work. This analysis moving process of GTS platform in a different way that is generally done to GTS platform types by lifting using problem is construction reinforcement required, so the construction can be moved by lifting with analyzing and checking structure working stress that occurs due to construction moving process by lifting AISC code standard and analysis using the SAP2000 structure analysis program. The analysis result showed that existing condition cannot be moved by lifting because stress ratio is above maximum allowable value that is 0.950 (AISC-ASD89). Overstress occurs on the member 295 and 324 with stress ratio value 0.97 and 0.95 so that it is required structural reinforcement. Box plate aplication at both members so that it produces stress ratio values 0.78 at the member 295 and stress ratio of 0.77 at the member 324. These results indicate that the construction have qualified structural reinforcement for being moved by lifting.

Underwater noise caused by pile-driving during the installation of offshore foundations is potentially harmful to marine life. In Germany, the regulation authority BSH set the following protection values: Sound Exposure Level SEL = 160 dB and Peak Level LPeak = 190 dB for Harbor Porpoises that must be complied with at a distance of 750 m to the construction site in order to avoid temporal threshold shifts. The experience over the last years shows that underwater sound produced during pile-driving, depending on many parameters and measurements, shows values of up to 180 dBSEL and up to 205 dBL Peak in a distance of 750 m. Therefore, Noise Mitigation Systems (NMS) are required to significantly minimize the underwater sound. Since 2011, NMS must be applied during all noisy offshore construction work in Germany. The Institute of Technical and Applied Physics GmbH (itap) was involved in many offshore wind farm (OWF) projects with pile-driving activities (>1000 pile installations without and with different NMS). Based on these underwater noise measurements, the tested NMS were evaluated. In this paper, a general overview of existing and tested NMS including tested system variations is provided and the measured data and influencing factors on the resulting noise reduction are discussed. Additionally, combinations of two or more NMS are measured during the construction phase, if monopiles with diameters of up to 8 m are installed. It is demonstrated what level of effect one or more NMS have on the emitted noise. However, it is shown that it is possible to install monopiles with a diameter of >6 m with noise levels below 160 dBSEL at a distance of 750 m, if combinations of suitable NMS are used. Nevertheless, any kind of noise mitigation will have a significant influence on the ‘disturbed’ or treated area from pile-driving noise for marine mammals. The question of whether a state-of-the-art measure to reduce pile-driving noise exists will be explored, based on measured data and experiences with NMS under real offshore conditions.

The scope and ambition of marine geotechnical investigations have greatly evolved over the last years. Offshore foundations, dredging operations of harbours and channels, sub-seabed installations all place new demands on acquiring more reliable knowledge on the composition of the seabed to address cost-effectively the issues of buried geo-hazards, sediment property discontinuities and trapped pollutants. This chapter shows the potential of physical sampling and different remote sensing approaches, but also their limitations. The technology gap can be addressed by designing an Acoustic Sub-seabed Interrogator (ASI), ideally combining a range of low frequencies (to penetrate deeper into the seabed) and a range of high frequencies (to enable higher vertical resolutions closer to the surface). The use of a dense network of broadband receivers should allow capturing of specular and non-specular returns, and bespoke data acquisition and processing should give access to 3-D volumetric measurements. Its design should allow deployments at all depths. The resulting acoustic corer should expand the horizontal and vertical ranges of existing tools whilst preserving the best spatial resolutions currently achievable.

The dynamic loads experienced when deploying structures with large suction anchors from an offshore construction vessel has been studied. Both model tests and CFD-analyses have been used to calibrate a numerical model of a typical Integrated Template Structure (ITS). The numerical model has then been used in time domain analyses in order to study the dynamic loads in the main lift wire when the ITS is lowered through the splash zone. An overall conclusion from this study is that from a lifting point of view neither the structural integrity of the ITS nor the crane will be jeopardized when crossing the splash zone in a typical deployment operation on the Norwegian Continental Shelf (NCS). The CFD analyses reveal the importance of entrapped air and water when the top of the suction anchor is crossing the splash zone. For the Gjoa ITS suction anchors used in the study, the openings on top of the suction anchors are quite large (perforation of 6%) which limits the amount of entrapped air during the water entry phase and also the amount of entrapped water in the water exit phase.

Recently, a number of wind turbines are being installed due to the increase of the interest in green energy. Such wind turbines are installed on land or offshore, and most of them are being installed on land because of easy installation. However, because it is possible to get better wind quality in offshore, the request for an offshore wind turbine is increasing and some heavy industries including shipyards are producing different sizes of offshore wind turbines. A floating crane is used for constructing the offshore wind turbine because its weight amounts to several hundred tons. Thus, it is very important to secure the safety during the construction. In this study, a dynamic response simulation of the offshore wind turbine suspended by the floating crane is performed. For this, we supposed that the motion of the floating crane and the wind turbine has 14 degrees of freedom, and there is the interaction by constraints among them. In addition, hydrostatic and hydrodynamic forces which are independent of e...

To increase the lifting capacity and minimize the cost and time for building a ship and offshore structure, block lifting with multi-cranes becomes more and more important. In this paper, therefore, dynamic response analysis of the multi-cranes is performed for block lifting operation. By this simulation, one can confirm the dynamic effects, such as dynamic motion and load, to prevent fatal accidents during the multi-crane operation. There are several types of crane and the crane systems consist of several rigid bodies. These rigid bodies are connected with various types of joints and wire rope, and the crane system is called as multibody system. To carry out the dynamic simulation of the crane system, therefore, the program for dynamic analysis of multibody system is developed. Among the several types of the cranes, the floating crane is operated on the sea water. Therefore, the developed program includes the function for calculating the hydrostatic and hydrodynamic forces. Using the dynamics simulation program developed in this paper, a dynamic response simulation of several cases of block lifting with multi-cranes are carried out, and the simulation results are validated by comparing them with the measured data from the shipyard.

Handling Increased Tensions in Deeper Water Depths With ultradeep installations reaching deeper than 2000 m, laying pipe on the seafloor can present challenges, such as increased holding tensions on the pipe during installation. Proper tension must be maintained to prevent the buckling that can be caused by the hydrostatic pressures acting on the pipe.

Because offshore plant industry needs to design, deploy and operate much of equipment especially, the latest trend shows the installation of production facilities is augmented in the subsea. The installed facilities are very difficult to be repaired or changed because they are located in the subsea. For solving these problems, both the directly related information of the production like the optimal number, position and depth of wells and the distribution for effective operation and safety of equipment of subsea should be considered at the preliminary stage of FEED (Front End Engineering Design). The marine exploration is introduced in this paper for providing the fundamental technology to answer the questions related to above considering points. First, some kinds of the offshore plant facilities are enumerated and aims of marine exploration for the offshore oil/gas development are summarized. In addition to it, the main roles of marine survey, in the step of designing and installing offshore oil-gas plant, development are briefly listed. And then foreign examples are shown to help the reader’s understand. This paper is hoped to be helpful for understanding the marine exploration that can be applied to offshore oil/gas plant and to be contributed to developing the domestic techniques in this field for the future.

There are many applications in marine engineering where two or more floating vessels are in close proximity. Probably the most significant one is related to the offshore installation engineering. On the background of the upper module installation operation of spar platform, this paper investigates the hydrodynamic interaction effects of multiple floating bodies in offshore installation engineering. The numerical simulation bases on the 3-D frequency domain linear potential theory. The calculations are carried out for the crane ship, the transport ship and the spar platform. Finally the best environmental parameters and the relative position of floating bodies are selected, which can provide good advice on installation operation scheme design.

The offshore wind turbine, especially the floating offshore wind turbine in the deep sea is a perspective technology in the context of increasing energy demands. Mooring system, as an important unit of the floating offshore wind turbine is emphasized. The methods of in-situ test and the laboratory experimental tests are reviewed. Some new testing methods are discussed. The most commonly used anchor systems are explored. The paper aims to present some future research work that is important for the development of the floating offshore wind turbine technology.

Recently, a number of wind turbines are being installed due to the increase of interest in renewable, environment-friendly energy. Especially, an offshore wind turbine is being watched with keen interest in that it has no difficulty in securing a site and can get high quality of wind, as compared with a wind turbine on land. The offshore wind turbine is transferred to and installed on the site by an offshore floating crane after it was made in a factory on land such as shipyard. At this time, it is important to secure the safety of the turbine because of its huge size and expensive cost. Thus, a dynamic analysis of the offshore wind turbine which is connedted with the offshore floating crane was performed based on the multibody systems dynamics in this study. As a result. it is shown that the analysis can be applied to verify the safety of a method for the transportation and installation of the offshore wind turbine suspended by the crane.

Compared with onshore drilling, offshore drilling condition is extremely complex,more security requirements are needed. According to the characteristic of offshore drilling, this paper states the ruler and safety requirement selection of offshore device, including: types of platform, load of rig, position system, BOP, and riser system. List the relevant calculation formula, technical parameters, presents the main requirement of the equipment selection.

Electric power supply to oil and gas platforms is conventionally provided by gas turbines located on the platforms. As these gas turbines emit considerable amounts of CO 2 and NO x , it is desirable to find alternative solutions. One alternative is to feed the platforms from the onshore power system via subsea power cables, which already have been implemented on some platforms in the Norwegian part of the North Sea. The paper studies a cluster of petroleum installations in this geographic area, connected to the Norwegian onshore power system through an HVDC voltage link. In the study, an offshore wind farm is also connected to the offshore AC power system. The main focus is investigation of transient stability in the offshore power system, and several fault cases have been studied for different levels of wind power generation. Simulations show that faults on the offshore converter platform can be critical due to the dependency of the reactive power delivered by the HVDC link to the offshore AC system. However, it is shown that local wind power production matching the offshore power demand will improve both voltage- and frequency-stability. Further on, it is indicated that offshore reactive power injections or alternative wind farm control topologies could improve voltage stability offshore.

This paper examines the risk to subsea gas pipeline during hot-tapping installation process. Hot tapping is one method to connect new pipeline to existing pipeline while they remain in service. In this study it is considered that hot tapping is installed using crane barge. To assure the crane barge in steady position, the crane barge is moored by means of mooring chain at several locations. These mooring activities and hot tapping installation possess potential risk to existing subsea facilities. Hence, in general there are two objectives in this study such as: determining the safe distance between mooring chain for and the existing facilities, and performing risk level due to external load that may occurs during installation. The risk level is determined by analyzing frequency and its consequence then will be mapped into risk matrix according to DNV-RP-F107. From mooring distance analysis, the result can be used as a reference for positioning the mooring point of crane barge. Based on the result of risk assessment to facilities, risks due to external load such as dropped anchor, dragged anchor, ship sinking and dropped object are in the as low as reasonably practicable (ALARP) region which mean, in the practical life risks are acceptable as long as the frequency is maintained in the lowest rank.

Moored offshore floating units may operate in regions where the bathymetry changes significantly over the mooring spread. Traditional mooring analysis methods make the assumption that the seabed slope is constant along the azimuth direction of each mooring line. This assumption, while reasonable for a seabed with nearly constant slope, can lead to significant errors with respect to the line tensions and vessel offsets in the mooring design assessment when the seabed slope is variable. This paper demonstrates the impact of bathymetry changes on the mooring design with the help of numerical analysis examples. The floating vessel considered is a semi-submersible moored by an eight point all chain catenary mooring system. Two methods of analysis are compared. In the first method, a true representation of the seabed surface that accounts for all variations in the bathymetry is used. In the second method, the anchor depths and the seabed slopes at the anchor locations estimated in the previous method are used, however, with the assumption of constant seabed slopes along the line azimuth directions. The dynamic analysis program Orcaflex is used for performing the numerical analyses in the time domain for both the methods. Differences in the performance of the mooring system are demonstrated by comparing the static and the dynamic line tensions as well as the vessel offsets in different environmental conditions. The paper also discusses how maximum offsets and line tensions are estimated.

The wind regime offshore is better for wind power generation than onshore and gaining authorization for offshore construction is often easier, but the cost of building offshore is much higher than onshore. Most offshore wind farms are in European waters. The technology for offshore wind turbines is the same as for large onshore wind turbines but sizes tend to be larger because it is easier to erect larger wind turbines offshore and because economics favor larger turbines. Foundations for offshore wind turbines are more complex than onshore. Some use gravity bases but the most common is the monopile foundation. In deeper water some tripod or multipile structures have been used. Meanwhile the development of floating wind turbine supports will eventually enable much deeper water sites to be utilized. Bringing power ashore from an offshore wind site is expensive. To reduce costs consideration is being given to the development of offshore grids that can collect power from a number of wind farms and bring it ashore at several key interconnections. For operation far offshore, a grid will have to be based on high voltage direct current technology to avoid reactive losses or high compensation costs.

The chapter introduces the platform types designed for supporting the tower, nacelle and turbine assembly of floating offshore wind turbines. Basic information on hydrodynamics is presented to provide an understanding of platform behaviour in waves. The classification method that distinguishes the platform types is stabilization. Covering this topic, buoyancy, mooring and ballast stabilized platform types are illustrated and briefly explained. The advantages and disadvantages of each approach are considered and summarized. The areas in which the benefits of each type are the most evident are clarified through various comparative studies. Most platform models are currently still at demonstration or conceptual stages. For this reason, computer codes that aim to capture their motions become particularly significant in design stages, and they are discussed next. A significant number of projects at the initial stages of planning and application are being developed in Japan, Europe and the United States. The platform types observed in these projects are presented. The chapter concludes with newly evolving design standards and a brief discussion on the optimization of platform shapes.

Europe, USA and Japan are positioning for offshore wind renewable energy becomes an option in order to reduce their energy dependence on fossil fuels. This is especially a key factor in countries that does not have its own fossil fuel resources. Given the characteristics of our continental shelf, it is expected that these platforms for harnessing the wind energy will be installed in locations away from the coast (offshore) and in 50+ deeper waters. This will lead to a new scenario that request new concepts and engineering solutions based on become floating structures (moored and anchored to the seabed). These new requirements and the economical constrains of this type of energies has made that nowadays we are in a stage of proof of concepts without a clear candidate to become the dominant technology in the near future. Therefore, in this chapter an overview of present and future trends in floating offshore wind technology is presented. The objective of this overview is to structure the different concepts and clarify the advantages and disadvantages of each.

The Italian national project MARIS (Marine Robotics for Interventions) pursues the strategic objective of studying, developing, and integrating technologies and methodologies to enable the development of autonomous underwater robotic systems employable for intervention activities. These activities are becoming progressively more typical for the underwater offshore industry, for search-and-rescue operations, and for underwater scientific missions. Within such an ambitious objective, the project consortium also intends to demonstrate the achievable operational capabilities at a proof-of-concept level by integrating the results with prototype experimental systems.

An accurate assessment of the offshore environment, including the meteorological, oceanographic and other relevant environmental conditions, is fundamental to the design of FOWTs.

The appearance of the offshore constructions will affect the hydrodynamic environment greatly. The direct effect is the change of hydrodynamic environment, which will affect the silt migration path and cause local scour. So a local refined calculation model of tidal distribution is developed in this paper to study the tidal current distribution and sediment scouring and deposition around the offshore constructions. Then an artificial island at Shengli Oil filed is taken for example. The developed model above is adopted to simulate the tidal distribution and local scouring change before and after the construction of the artificial island. The results of calculation show that excessive flow velocity appears near the construction, which cause sever local scour. And the calculation results can also provide technical support for the safety evaluation of the offshore constructions.

As exploration for new offshore oil and gas fields pushes into ever deeper water, upstream assets require ever more power for marine operations and commercial activities related to exploration, development, completions, and production. This paper will briefly introduce the different activities and conditions required for the energy assets, some of the current designs, and respective typical power plant characteristics. Comparisons will be also discussed with how drilling power plants are similar and different in design to other power plants such as production platforms and integrated electric military and commercial vessels. To successfully design the next-generation offshore energy vessels, electrical engineers will be required to leverage best practices and technology across all marine-integrated markets. An in-depth understanding of the operational mission of the vessel and the equipment required is absolutely necessary to ensure optimization of the plant and efficient distribution.

This article presents an overview of the challenges and application possibilities of deploying underwater sensor networks nearby oil rigs drilling operations areas and offshore construction sites surroundings using Remote Operated Vehicles (ROVs). We have started to develop a simulation scenario using a VMAX PerrySlingsby ROV full-up simulator in order to detect and solve any possible problems that may occur.

This chapter contains sections titled: Feasibility Study Offshore Wind Energy in Europe Under Sea Tunnel System Offshore and Onshore PTPTM Constructions Next-Generation Technology Offshore Environment ]]>