Design and Analysis of Suction Anchor Foundations for an Integrated Offshore Renewable and Aquaculture System

Berücksichtigung von dynamischen Verkehrslasten beim Tragsicherheitsnachweis von Strassenbrücken

Assessment of foundation design for offshore monopiles unprotected against scour

The design of foundations is often governed by the serviceability limit state (SLS) requirements of the supported structure, particularly for large spread foundations. This paper aims to develop a reliability-based SLS design method for spread foundations under uplift loading in cohesionless soils. A probabilistic framework was adopted for the empirical characterisation of the compiled load-displacement curves and the quantification of the associated uncertainties. By using the obtained statistics of the curves, reliability analysis was carried out with Monte-Carlo simulations to calibrate the resistance factors within the load and resistance factor design (LRFD) framework. The calibration results showed that the embedment ratio of the foundation and the fitting errors of the empirical model, which were previously unaddressed in the literature, had notable effects on the calibrated SLS resistance factors. The relationship of the SLS with the ultimate limit state was assessed, including the governing limit state at each allowable displacement level, and the probability of ultimate failure of the foundation at the SLS condition. By considering the relationship between the limit states, the procedures for determining the design resistance factor and foundation capacity were proposed.

The TLP requires a complicated and time-consuming design process. Principal dimension of hull form and tendons should be carefully determined with the consideration of many design requirements which dominantly affect the safety of the platform. In this paper, a global optimization system for both the hull-form and tendon system is developed. The maximum heave response and total weight of hull and tendons are formulated as an objective function with the several constraints related to the safety of platform. In order to find a technically and economically feasible design, a modelling and assessment processes are fully automated, which enables the algorithm can controls the modelling and analysis process while varying a set of design parameters until it figures out an optimum design. Major design requirements related to the safety of platform is assessed by ultimate limit state (ULS) and fatigue limit state (FLS) approach to ensure the accuracy of analysis. In the ULS approaches, every safety requirement is checked on the basis of the most unfavorable environments. FLS approach is conducted for all tendons since they suffer cyclic deformation for their service life, which results in collapse of mooring system with the relatively small wave loads. In the optimization module, a better set of design parameters is investigated by using a simulated annealing (SA) algorithm. Throughout the optimization system, both the heave responses and total weight of hull and tendons are improved while satisfying the all constraints related to the design requirements.

The Paper presents the methodologies adopted for the design of mooring and riser anchors of the P43 and P48 FPSOs due to be installed in 2003 in deep water Campos Basin, offshore Brazil. It is shown how an efficient semi-analytical 3D finite element model can be used as a routine design tool for calculating the pull-out capacity of cylindrical suction anchors under combined horizontal and vertical loading. The speed of the FE model has allowed pull-out capacity contours to be developed which help in the selection of limiting installation tolerances. Fully coupled axisymmetric finite element consolidation analyses of the set-up phenomenon have been described in which the initial excess pore pressure field is established by simulating the final penetration stages of the skirts. Introduction The Barracuda and Caratinga fields are located in deepwater Campos Basin, some 150 km offshore Brazil. The average water depth is 825m at Barracuda and 1030m at Caratinga. A taut-leg spread mooring system has been adopted for both the Barracuda (P43) and Caratinga (P48) FPSOs. Each FPSO is moored by 18 lines, ten at the stern and eight at the bow. The mooring lines are made of polyester rope, combined with lengths of chain at the fairlead and seabed ends, Wibner1. Various types of anchor were considered in the initial phases of the project. Suction anchors were selected as the preferred option for the following reasons, Sparrevik2:Relatively accurate positioning on the seabed, which isimportant in fields congested with flow lines and subsea facilities,Economical and simple installation method, avoiding the need for pile driving in deepwater or dragging and proof loading.Reasonably well-established design methods compared to other types of anchor, even though no Standard Code of Practice is yet available. In addition to the 36 mooring suction anchors, 52 suction anchors in four different sizes were designed for restraint of the risers. The subject of this paper is the geotechnical in-place capacity of mooring anchors only and excludes installation aspects. The suction anchors were designed to comply with ABS Rules3 and current industry practice for 20 years service life. Site Investigation An integrated approach to SI was taken4,5. A comprehensive geophysical and geotechnical site investigation was performed in spring 2001 from the vessel Rockwater-1. Subsea7 (formerly Halliburton Subsea), performed the geophysical surveys consisting of swathe bathymetry, ROV high resolution sub-bottom profiling and side scan sonar imaging, while Fugro BV performed the following geotechnical SI from the same vessel:66 WHEELDRIVE Piezo-cone penetration testing (CPTU) to 30m penetration,12 WHEELDRIVE insitu vane tests up to 20m. One test every 0.4m and remoulded shear strength determination every second test,39 Push-in Piston cores up to 20m. The SI was followed by a programme of monotonic and cyclic laboratory testing both in Holland and the UK.

Summary. The main calculation methods for designing foundations and foundations in Central Africa are considered. The methodology for calculating foundations and foundations in Central Africa is analyzed and compared. Geotechnical calculations are an integral part of the design of foundations and foundations of buildings, especially in Central Africa, where geological, climatic and environmental factors can significantly affect the stability of structures. This work considers the main aspects affecting geotechnical calculations, including a detailed geological survey of the site, which allows determining the types of soils, their physical and mechanical properties and the level of groundwater. An important stage is the assessment of the mechanical properties of soils, such as bearing capacity, water permeability and compressibility, which affect the choice of the type of foundation. The work also analyzes different types of foundations, in particular strip, slab and pile, taking into account the loads that they must withstand, as well as the specifics of soil conditions. The article analyzes the existing methods for this region, in particular the use of drilling and laboratory soil testing. Effective approaches to the selection of foundation types for various geotechnical situations are identified. The article also describes soil investigation methods and principles of foundation design that ensure the stability and safety of buildings in conditions typical of Central Africa. Geotechnical calculations are a crucial component in the design of foundations for buildings, especially in regions with complex geological and climatic conditions, such as Central Africa. This region presents unique challenges for engineers due to the variety of soil types, seasonal rainfall, high temperatures and different groundwater levels. Proper geotechnical analysis ensures the stability, safety and durability of structures. The main factors affecting the design of foundations include soil properties such as strength, compressibility and shear resistance, as well as the state of groundwater, which affects soil stability. Areas with weak or expansive soils often require deep foundations, such as piles or bored piles, while strong soils may allow for shallow foundations. Fluctuations in groundwater levels due to seasonal rains or droughts require special attention to prevent erosion, flooding, or weakening of the foundation base. Geotechnical studies also consider environmental impacts, such as the impact of construction on surrounding ecosystems and local water resources. In addition, compliance with local and international standards ensures that structures meet safety standards. Engineers must also assess climatic factors, such as thermal expansion and contraction, which can affect soil behavior over time. The use of advanced software tools such as PLAXIS and GeoStudio a vital role in modeling soil behavior and predicting potential foundation performance under different conditions. Ultimately, successful geotechnical calculations in Central Africa require a comprehensive approach that takes into account regional soil types, climate and environmental considerations, ensuring the durability and structural integrity of buildings in this challenging environment. Foundation reinforcement is a mandatory stage in the construction of reinforced concrete structures. Its purpose is to strengthen the concrete, allowing it to resist the tensile, bending and shear forces that can act on the foundations. Reinforcement consists of inserting steel bars (rebars) into the concrete to increase its load-bearing capacity. Foundations can be of different types, such as isolated foundations, strip foundations or slab foundations, and the reinforcement varies depending on each type and the constraints of the project. For isolated foundations, for example, the reinforcement usually consists of longitudinal bars arranged in the main direction to resist tension and bending, and transverse bars arranged perpendicularly to counteract transverse forces. This reinforcement must be carefully positioned and positioned to ensure the strength of the foundation. Reinforcing the foundation is also crucial to prevent cracking and warping of the concrete over time. The concrete coating around the reinforcement protects it from corrosion and ensures its durability. Finally, the reinforcement is carried out according to strict standards that take into account the characteristics of the soil, the loads to be supported, and the dimensions of the foundation to ensure safety and stability.

Local scour around bridge piers poses significant challenges to the stability and safety of bridge structures. Local scour results from the combined effects of increased longitudinal flow velocity, the direct impact of the flow in front of the pier, and the suction effect of horseshoe vortices. This study utilizes a three-dimensional mathematical model to simulate the flow field around the pier, employing the SWASH (simulating waves till shore) model. Experimental observations in a bed load flume were conducted to analyze the contribution of different factors to local scour. The results indicate that the scour depth caused predominantly by the flow accounts for approximately 75–80% of the total scour depth. Analysis of the longitudinal flow velocity distribution suggests that the scour depth due to the redistribution of longitudinal flow velocity generally accounts for 15–30% of the total scour depth. These findings provide insights into the local scour mechanism and have implications for the design and maintenance of bridge foundations.

A new riser code, ISO 13628-12 "Design of Dynamic Risers for Floating Production Installations" has recently been updated as part of an industry JIP and is scheduled for ISO ballot in 2010. Once approved, the new ISO 13628-12 will replace the current edition of API RP 2RD as the Code of Practice for the design of dynamic metallic risers for floating production installations. This paper summarizes the four design methods in draft ISO 13628-12 and investigates their implications on the design of future SCRs. The implication of the new riser design code is illustrated by an example of an SCR design in the Gulf of Mexico. Three of the four design methods allow for certain plastic utilization of the riser cross section, which requires additional considerations for design, analysis, material selection and fabrication. Combined loading code checks with the four different methods are performed and the results are compared. Additional material specific considerations including design stress-strain curve and fabrication requirements are also presented. Introduction The design methods in the updated draft ISO 13628-12 reflect an evolutionary progression from working stress design to limit state design. Limit state design ensures a consistent safety level, based on acceptable failure probabilities, with due considerations to the inherent uncertainty in the design loads and resistance to such loads. Typical limit states for deep water riser design application include:–Accidental limit state (ALS)–Ultimate limit state (ULS)–Serviceability limit State (SLS)–Fatigue limit state (FLS) The ALS is associated with events with an annual probability of less than 10-2 and larger than 10-4, while the ULS corresponds to 100 year return period events or events with 10-2 annual probability. The SLS criteria define the loads during the normal operational conditions and normal temporary events. FLS is an ultimate limit state from accumulated excessive fatigue crack growth or damage under cyclic loading. The performance criteria for the riser design depend on the specific limit state. For example ULS requires that the riser system must survive the design event with no damage, i.e. remain intact and avoid rupture, but not necessarily be able to operate. For ALS the riser system must survive, and may sustain some damage without any rupture i.e. no release of hydrocarbon is allowed. Typical load cases for strength design of SCR are presented in Table 1. The paper presents a summary of the design equations to assess the capacity of the pipe. The performance of an 18 inch oil (X70 grade steel) export SCR suspended from a semi-submersible in 2000 m water in the Gulf of Mexico is assessed for ULS and the ALS conditions using combined loading equations for internal overpressure conditions. Potential for buckling due to compression in the touchdown zone (TDZ) is also investigated.

Determination of scour depth is needed for economical design of bridge pier foundation. Currently, determination of design scour depth is mainly based on use of relationships for maximum scour depth in steady flow along with the design discharge. Computations have revealed that time taken by the design discharge to scour to its full potential is generally larger than the time for which it runs. Hence, the computation of temporal variation of scour depth should form the basis of the design. Experiments are conducted on temporal variation of scour around circular bridge piers placed in uniform, nonuniform, and stratified beds under steady and unsteady clear-water flows. Considering the primary vortex in front of the pier to be the prime agent causing scour, a procedure is developed for computing the temporal variation of scour depth under these conditions. Since the maximum scour depth is the scour depth at large time, the procedure is logically extended to obtain an expression for the same. Sediment nonuniformity and stratification are shown to have a significant effect on scour depth. The effect of these elements as well as that of unsteadiness of flow on scour depth are studied and taken into account in the proposed method of scour calculations.

Scour protection assessment of monopile foundation design for offshore wind turbines

This paper provides a methodology for optimizing a deepwater mooring layout with respect to ground conditions and gives limitations of the method. Specifically, this paper:describes development of a predictive soil model based on integration of AUV geophysical survey and geotechnical data in an area characterized by complex and discontinuous sand strata interbedded with clays;describes using the predictive model to help optimize a FPSO mooring layout to meet design criteria;presents as-installed results for the suction anchors and demonstrates reliability of the predictive soil model;describes learnings from this project; anddiscusses limitations of the methodology. Suction-anchor installation was completed successfully and no problems were encountered with respect to soil conditions. The as-installed results thus confirmed the general reliability of the predictive soil model. Sand strata as thin as about 30 cm thick were predicted by the model and their presence was confirmed by increased pump underpressures recorded during anchor installation. The fact that the 5-m-diameter suction anchors " felt?? such thin sands was instructive. We demonstrate that, by using appropriate geophysical survey data calibrated with geotechnical information, a model of soil conditions can be developed and used as a tool to predict soil conditions away from geotechnical control points. Confidence in the predictions depends on the amount, type, spatial distribution, and quality of the data available and on the geology of the site. This case history is useful as a model approach for optimizing mooring layout with respect to ground conditions or for other applications where shallow soil conditions are sufficiently complex and variable to affect layout of foundation elements or design. Integrated study of the geophysical/geotechnical data was concurrent with mooring system design in a collaborative effort that directly influenced design iterations. Use of the integrated and iterative approaches described here will help future project teams develop more reliable mooring or other foundation solutions faster and thereby reduce costs. Introduction Background. The Parque das Conchas development is located off the coast of Brazil in the Campos Basin in Block BC-10 (Figure 1). Shell is the operator of BC-10 with 50% equity share with co-venturers Petrobras (35%) and ONGC (15%). The site is on the continental slope and is characterized by hummocky topography (Figures 2 and 3a) caused by buried mass-transport deposits (MTDs). Water depths across the mooring spread range from about 1740 m to 1800 m (Figure 3a). Production facilities feature the FPSO Espirito Santo with a clustered 3x3 suction-anchor mooring system; the mooring layout is shown in Figure 3a. Mooring radius varies slightly from cluster-to-cluster and ranges between about 2500 to 2700 meters. More details and other aspects of the FPSO Espirito Santo are discussed by Howell and others (2010).

The use of cost-effective construction design approaches is an emerging concept in the field of sustainable environments. The design of the foundation for the construction of any infrastructure-related building entails three basic requirements, i.e., serviceability limit state (SLS), ultimate limit state (ULS), and economics. Engineering economy coupled with safety are the two main essentials for a successful construction project. The conventional design approaches are based on hit and trial methods to approach cost-effective design. Additionally, safety requirements are prioritized over the economic aspect of foundation design and do not consider safety requirements and cost simultaneously. This study presents a design approach that considers foundation construction costs while satisfying all the technical requirements of a shallow foundation design. This approach is called an optimization process in which the cost-based isolated foundation design charts were developed based on the field SPT N data. The design charts are the first of their kind for the robust design of foundations and can be used to compare the economic impact of different bearing capacity models. Furthermore, the design framework considers the quantitative impact of the different applied factors of safety values in terms of cost. The results show that Vesic’s equation yields higher values of bearing capacities than Terzaghi and Meyerhof. On the other hand, Vesic’s theory offers a 37.5% reduction in cost as compared to the conventional design approach of the foundation for isolated footing.

The design of large diameter monopiles (8–10 m) at intermediate to deep waters is largely driven by the fatigue limit state and mainly due to wave loads. The scope of the present paper is to assess the mitigation of wave loads on a monopile by perforation of the shell. The perforation design consists of elliptical holes in the vicinity of the splash zone. Wave loads are estimated for both regular and irregular waves through physical model tests in a wave flume. The test matrix includes waves with Keulegan–Carpenter ( K C ) numbers in the range 0.25 to 10 and covers both fatigue and ultimate limit states. Load reductions in the order of 6%–20% are found for K C numbers above 1.5. Significantly higher load reductions are found for K C numbers less than 1.5 and thus the potential to reduce fatigue wave loads has been demonstrated.

The purpose of the research presented in this paper is to develop and implement an efficient method for analytical gradient-based sizing optimization of a support structure for offshore wind turbines. In the jacket structure optimization of frame member diameter and thickness, both fatigue limit state, ultimate limit state, and frequency constraints are included. The established framework is demonstrated on the OC4 reference jacket with the NREL 5 MW reference wind turbine installed at a deep water site. The jacket is modeled using 3D Timoshenko beam elements. The aero-servo-elastic loads are determined using the multibody software HAWC2, and the wave loads are determined using the Morison equation. Analytical sensitivities are found using both the direct differentiation method and the adjoint method. An effective formulation of the fatigue gradients makes the amount of adjoint problems that needs to be solved independent of the amount of load cycles included in the analysis. Thus, a large amount of time-history loads can be applied in the fatigue analysis, resulting in a good representation of the accumulated fatigue damage. A reduction of 40 % mass is achieved in 23 iterations using the CPLEX optimizer by IBM ILOG, where both fatigue and ultimate limit state constraints are active at the optimum.

The U.S. Army Corps of Engineers is working to develop rational policies for prioritizing in-service inspection, maintenance, and repair policies for aging locks and dams on the inland waterway system using structural reliability methods and principles of risk management. Comparisons of miter gate design criteria and performance observed in service reveal differences that are examined through finite-element-based reliability analysis. Finite-element analyses show that miter gates are overdesigned for ultimate strength limit states and have low-to-moderate stresses. However, premature fatigue damages have been found in a number of miter gates. Stochastic fracture mechanics identified contributing factors that significantly impact the probability of reaching the fatigue limit state: initial flaw size at weld details, inspection frequency, and inspection quality. The role of parameter uncertainty in gate fatigue performance during service life is depicted by a fragility that includes uncertainties in the strength of the gate structure, loads due to gate operations, and initial flaw size. Fragility assessment of the fatigue performance observed in two miter gates provides a means to evaluate observed performance. Fatigue performance can be enhanced by modest improvements in detailing practices and inspection methods.