Set-Up of Large Diameter Driven Pipe Piles in Deepwater Normally Consolidated High Plasticity Clays

2009 ◽  
Author(s):  
Rathindra N. Dutt ◽  
Clarence J. Ehlers
Keyword(s):  
Wave Equation ◽  
West Africa ◽  
Gulf Of Mexico ◽  
Large Diameter ◽  
Offshore Structures ◽  
High Plasticity ◽  
Mooring Lines ◽  
Pile Capacity ◽  
Trial And Error Method ◽  
Set Up

This paper will show on the basis of hindcast wave equation analysis that soil-pile set-up for large diameter driven pipe piles in clay is faster than what the current state-of-practice utilizes for design. Results of hindcast wave equation analyses utilizing observed blowcounts and hammer energy records from two deepwater sites, one in West Africa and the other one in the Gulf of Mexico, are presented to support this conclusion. For offshore structures, this increase in the rate of soil-pile set-up reduces foundation/anchor costs or reduces the waiting time until topsides can be set on the structure or mooring lines can be hooked up to anchors. Hindcast wave equation analyses were performed utilizing the observed blowcount and hammer energy information from two deepwater West Africa and Gulf of Mexico locations where pile driving was stopped and then restarted after a few days. This is a trial and error method of analysis where the soil resistance to driving (SRD) was varied until a good match was obtained between the observed blowcount at the startup of driving and the reported hammer energy using the GRLWEAP wave equation program. The set-up time for the piles ranged from about one to twelve (12) days and the piles ranged from 2134 mm to 2743 mm diameter open-ended pipe piles. The soils generally consisted of normally to slightly overconsolidated highly plastic clays. For the purpose of computing pile set-up, the ultimate pile capacity was computed using the API RP 2A (2000) guidelines. Results show that 60 to 80 percent of the ultimate pile capacity is mobilized in about 7 days, and the extrapolation of the set-up model suggests that the set-up is almost complete in about 60 days.

scholarly journals Effect of Roughness of Mussels on Cylinder Forces from a Realistic Shape Modelling

2021 ◽  
Vol 9 (6) ◽  
pp. 598
Author(s):  
Antoine Marty ◽  
Franck Schoefs ◽  
Thomas Soulard ◽  
Christian Berhault ◽  
Jean-Valery Facq ◽  
...  
Keyword(s):  
Marine Species ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Mooring Lines ◽  
Shape Modelling ◽  
Offshore Wind Turbines ◽  
Specific Effects ◽  
Hydrodynamic Loading ◽  
Floating Offshore Wind Turbines ◽  
Realistic Shape

After a few weeks, underwater components of offshore structures are colonized by marine species and after few years this marine growth can be significant. It has been shown that it affects the hydrodynamic loading of cylinder components such as legs and braces for jackets, risers and mooring lines for floating units. Over a decade, the development of Floating Offshore Wind Turbines highlighted specific effects due to the smaller size of their components. The effect of the roughness of hard marine growth on cylinders with smaller diameter increased and the shape should be representative of a real pattern. This paper first describes the two realistic shapes of a mature colonization by mussels and then presents the tests of these roughnesses in a hydrodynamic tank where three conditions are analyzed: current, wave and current with wave. Results are compared to the literature with a similar roughness and other shapes. The results highlight the fact that, for these realistic roughnesses, the behavior of the rough cylinders is mainly governed by the flow and not by their motions.

scholarly journals Corrosion of Steel Rebars in Anoxic Environments. Part II: Pit Growth Rate and Mechanical Strength

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2547
Author(s):  
Elena Garcia ◽  
Julio Torres ◽  
Nuria Rebolledo ◽  
Raul Arrabal ◽  
Javier Sanchez
Keyword(s):  
Mechanical Strength ◽  
Chloride Content ◽  
Element Model ◽  
Offshore Structures ◽  
Anoxic Environments ◽  
Electrochemical Parameters ◽  
Cathode Area ◽  
Optical Profilometer ◽  
Set Up ◽  
Corrosion Of Steel

Reinforced concrete may corrode in anoxic environments such as offshore structures. Under such conditions the reinforcement fails to passivate completely, irrespective of chloride content, and the corrosion taking place locally induces the growth of discrete pits. This study characterised such pits and simulated their growth from experimentally determined electrochemical parameters. Pit morphology was assessed with an optical profilometer. A finite element model was developed to simulate pit growth based on electrochemical parameters for different cathode areas. The model was able to predict long-term pit growth by deformed geometry set up. Simulations showed that pit growth-related corrosion tends to maximise as cathode area declines, which lower the pitting factor. The mechanical strength developed by the passive and prestressed rebar throughout its service life was also estimated. Passive rebar strength may drop by nearly 20% over 100 years, whilst in the presence of cracking from the base of the pit steel strength may decline by over 40%.

Development of a Stepped Line Tensioning Solution for Mitigating VIM Effects in Loop Eddy Currents for the Genesis Spar

2004 ◽  
Author(s):  
T. Kokkinis ◽  
R. E. Sandstro¨m ◽  
H. T. Jones ◽  
H. M. Thompson ◽  
W. L. Greiner
Keyword(s):  
Gulf Of Mexico ◽  
Eddy Current ◽  
Eddy Currents ◽  
Comprehensive Evaluation ◽  
Design Solution ◽  
Loop Current ◽  
Mooring Lines ◽  
Test Methodology ◽  
Induced Motion ◽  
High Reynolds

A number of spars are being installed in deepwater areas in the Gulf of Mexico (GoM), which are subject to loop / eddy current conditions and must be designed for Vortex-Induced Motion (VIM). This paper shows how recent advances in VIM prediction enabled an efficient and effective mooring design solution for the existing Genesis classic spar, which is installed in Green Canyon Block 205 in the GOM. The solution may also be applicable to new spar designs. During the Gulf of Mexico Millennium Eddy Current event in April 2001, the Genesis spar platform underwent vortex induced motions (VIM) which were greater than anticipated during the design of the mooring & riser systems. Analysis showed that if such large motions were to occur in higher currents in the range of the 100-year event, they could cause significant fatigue damage, and could lead to peak tensions in excess of design allowables. After a comprehensive evaluation of potential solutions, Stepped Line Tensioning (SLT) was determined to be the best approach for restoring the platform’s original mooring capacity on technical, cost and schedule grounds. SLT did not require extensive redesign of the existing mooring system of the spar. Furthermore, SLT provided a means to improve mooring integrity on an interim basis, while completing details for permanent implementation. Under SLT, the pretensions of the mooring lines are adjusted based on forecast currents in order to keep the platform below the VIM lock-in threshold at all times and for all eddy/loop current conditions up to and including the 100-year condition. High Reynolds number model tests conducted with a new test methodology were used to get a reliable prediction of the spar’s VIM response for this evaluation.

On-demand Electrohydrodynamic Jetting of an Ethylene Glycol and Water Mixture—System of Controlled Picoliter Fluid Deposition

2021 ◽  
Author(s):  
J. F. Dijksman ◽  
U. Stachewicz
Keyword(s):  
Fluid Flow ◽  
Power Amplifier ◽  
Large Diameter ◽  
Electrical Circuit ◽  
Viscous Drag ◽  
Water Mixture ◽  
Electrical Field ◽  
On Demand ◽  
Flat Substrate ◽  
Set Up

On-demand electrohydrodynamic jetting also called electrohydrodynamic atomization (EHDA) is a method to jet small amounts of fluid out of a nozzle with a relatively large diameter by switching on and off an electrical field between the nozzle and the substrate. The total amount of volume deposited is up to 5 pL. The set-up consists of a vertically placed glass pipette with a small nozzle directed downward and a flat substrate placed close to the end of the nozzle. Inside the pipette, an electrode is mounted close to the entrance of the nozzle. The electrode is connected to a high voltage power amplifier. Upon switching on the electrical field, the apparent surface tension drops, the meniscus deforms into a cone and fluid starts to flow toward the nozzle deforming the meniscus. At a certain moment the cone reaches the Taylor cone dimensions and from its tip a jet emerges that decomposes into a stream of charged fL droplets that fly toward the substrate. This process stops when the pulse is switched off. After switching off, the meniscus returns slowly to its equilibrium position. The process is controlled by different time constants, such as the slew rate of the power amplifier and the RC time of the electrical circuit composed of the electrical resistance in the fluid contained in the nozzle between the electrode and the meniscus, and the capacitance of the gap between the meniscus and the flat substrate. Another time constant deals with the fluid flow during the growth of the meniscus, directly after switching on the pulse. This fluid flow is driven by hydrostatic pressure and opposed by a viscous drag in the nozzle. The final fluid flow during droplet formation is governed by the balance between the drag of the charge carriers inside the fluid, caused by the current associated with the charged droplets leaving the meniscus and the viscous drag. These different phenomena will be discussed theoretically and compared to experimental results.

Effect of Air Fraction on Force Coefficients in Oscillatory Flow

2021 ◽  
Author(s):  
Malene Hovgaard Vested ◽  
Erik Damgaard Christensen
Keyword(s):  
High Speed ◽  
Offshore Structures ◽  
Air Injection ◽  
Wave Loads ◽  
Morison Equation ◽  
Force Coefficients ◽  
Air Content ◽  
Set Up ◽  
High Level ◽  
Spilling Breakers

Abstract The forces on marine and offshore structures are often affected by spilling breakers. The spilling breaker is characterized by a roller of mixed air and water with a forward speed approximately equal to the wave celerity. This high speed in the top of the wave has the potential to induce high wave loads on upper parts of the structures. This study analyzed the effect of the air content on the forces. The analyses used the Morison equation to examine the effect of the percentage of air on the forces. An experimental set-up was developed to include the injection of air into an otherwise calm water body. The air-injection did introduce a high level a turbulence. It was possible to assess the amount of air content in the water for different amounts of air-injection. In the mixture of air and water the force on an oscillating square cylinder was measured for different levels of air-content, — also in the case without air. The measurements indicated that force coefficients for clear water could be use in the Morison equation as long as the density for water was replaced by the density for the mixture of air and water.

Prediction of Pile Capacity by the Wave Equation

1964 ◽  
Vol 90 (2) ◽  
pp. 1-25
Author(s):  
Paul W. Forehand ◽  
Joseph L. Reese
Keyword(s):  
Wave Equation ◽  
Pile Capacity

Sour-Service Risers and Accessories for HP/HT Application in the Gulf of Mexico

2021 ◽  
Vol 73 (03) ◽  
pp. 60-61
Author(s):  
Judy Feder
Keyword(s):  
High Pressure ◽  
Yield Strength ◽  
Gulf Of Mexico ◽  
Wall Thickness ◽  
Large Diameter ◽  
High Strength ◽  
Thick Wall ◽  
Offshore Technology ◽  
Riser Pipe ◽  
Sour Service

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 30558, “Development and Implementation of Heavy-Wall, High-Strength, Sour-Service Accessory and Risers for HP/HT Application in the Gulf of Mexico,” by Carine Landier, Jonathas Oliveira, and Christelle Gomes, Vallourec, et al., prepared for the 2020 Offshore Technology Conference, originally scheduled to be held in Houston, 4–7 May. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. As oil and gas development in the Gulf of Mexico increasingly requires high-pressure/high-temperature (HP/HT) applications, the need for sour-service (SS) resistance also has grown. To meet these needs, continual innovation and improvement is needed in SS-grade materials from a technical and cost-effectiveness perspective. The complete paper discusses the material properties achieved with several large-diameter, heavy-wall SS pipes. The complete paper presents a detailed, illustrated discussion of the applications for the high-strength SS pipe and its manufacturing process. Applications The authors write that improved materials to meet HP/HT requirements such as those in the Gulf of Mexico are needed particularly for two applications: for risers, which require high-strength, thick-wall sour service; and as a substitute for corrosion-resistant alloy (CRA) with sour carbon material on defined accessories. Vallourec has developed high-strength [125,000-psi specified minimum yield strength (SMYS)] and resistant carbon steel pipes in sizes with outer diameter (OD) up to 23 in. and wall thickness up to 2.5 in. These sizes are common in lower-strength material, but meeting the high-pressure requirements with higher-grade material enables cost savings and eliminates some CRA components. It also enables the use of much-lighter-weight pipe than the 80,000-psi SMYS material that is standard for SS applications in oversize OD and heavy wall. Risers. Most deepwater drilling is performed with classic subsea blowout-preventer (BOP) systems. Access to the well through the BOP is accomplished with low-pressure, large-diameter (19-in. internal diameter) drilling riser pipe. Pipes are supplied in weldable grades (API 5L X65–X80). Large-diameter forged flanges are then welded onto the tubes. Connections are made by multiple bolts. High pressures, required as part of the drilling process, are supplied by small-diameter choke-and-kill lines. This system has served the industry well, but, as well pressures increase, so have cost and feasibility requirements of subsea BOP technology. These costs, driven by the complexity of redundant systems, have driven a desire to explore an alternative solution—a surface BOP with high-pressure drilling riser pipe. Using a surface BOP reduces the complexity and cost of the system significantly because of the ability to inspect it. The drilling riser then carries the pressure to the surface and must be able to contain it. The high-pressure environment that instigated a new solution was based on a 15,000-psi well pressure with NACE Region 2 SS performance. Because of the requirement for weldable grades for attaching the flange as well as SS, the maximum yield strength has been limited to 80,000 psi. At that strength, a very high wall thickness is required to meet 15,000 psi and greater. This becomes very heavy and can be limited by the rig hook-load capacity. Alternatives in weldable grades are nickel-based alloys with SS performance. A full string, however, is prohibitively expensive.

Optimization of the Dynamic Response of Semi-Submersibles: Influence of the Mooring System

2019 ◽  
Author(s):  
Shengtao Zhou ◽  
Frank Lemmer ◽  
Wei Yu ◽  
Po Wen Cheng ◽  
Chao Li ◽  
...  
Keyword(s):  
Life Cycle Cost ◽  
Design Space ◽  
Optimization Techniques ◽  
Optimization Process ◽  
Manufacturing Cost ◽  
Mooring System ◽  
Mooring Lines ◽  
Nsga Ii ◽  
Simulation Code ◽  
Set Up

Abstract The design and manufacturing cost of substructures is a major component of the total expenditure for a floating wind project. Applying optimization techniques to hull shape designs has become an effective way to reduce the life-cycle cost of a floating wind system. The mooring system is regarded as the component with the highest risk, mainly due to the poor accessibility. This paper extends the previous work by investigating the influences of the mooring design on the optimization process of a semisubmersible substructure. Two optimization loops are set up. In the first loop, only the main dimensions of a semi-submersible platform are parameterized without considering mooring lines (keep a constant mooring design). Nevertheless, the second loop introduces additional variables of the mooring lines. The objective is to minimize the tower-top displacement, fairlead fatigue damage, which are calculated by the in-house nonlinear dynamic simulation code SLOW, and the manufacturing cost of platform and mooring lines. The multi-objective optimization algorithm NSGA-II is employed to search for the optimal designs within the defined design space. The design space and the Pareto fronts are compared between the two optimizations. It is found that, although the mooring design does not have a significant impact on the platform design space, one obtains a different optimal set (Pareto front) if the mooring design and mooring loads are introduced into the platform optimization process. The results of this study are expected to give a better understanding in the relationship between platform and mooring design and serve as a basis for the optimization process of semi-submersible floating wind turbines.

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