scholarly journals A Numerical Study on a Flopper Stopper for Leg Positioning of a Jack-Up Barge

2017 ◽  
Author(s):  
Zhiyu Jiang ◽  
Wilson Guachamin Acero ◽  
Zhen Gao ◽  
Lin Li
Keyword(s):  
Wave Height ◽  
Structural Damage ◽  
Oil And Gas ◽  
Numerical Study ◽  
Coupled System ◽  
Offshore Wind ◽  
Maximum Increase ◽  
Peak Period ◽  
Global Dynamic ◽  
Jack Up

Jack-up barges are commonly used for marine operations in the offshore oil and gas, and offshore wind industries. A critical phase within the marine operation activities is the positioning of the jack-up legs onto the seabed. During this process, large impact velocities and forces may arise from the barge’s heave, roll and pitch motions, and structural damage of the legs can occur. This paper numerically investigates the effect of a flopper stopper (FS) on the motion responses of a jack-up barge from the offshore wind industry. The FS is known as a passive roll compensation device. It is suspended from the side of the barge by means of wire ropes and cantilever beams. A simple geometry of an FS is proposed, and the working principle introduced. For the loading condition before the leg-soil impact occurs, global dynamic analyses of the coupled system are conducted. Characteristic values of impact velocities are used to establish the jack-up operational limits in terms of the significant wave height and peak period. By comparing the operational limits for the barge with and without FS, it is found that FS should be placed on the weather side. At beam seas, the current FS can lead to a maximum increase in the operational wave height limit of 35%, whereas for the other wave headings, it may not be beneficial to use FS.

scholarly journals Sensitivity Analysis of a Bottom Fixed Offshore Wind Turbine Using the Environmental Contour Method

2019 ◽  
Author(s):  
David Barreto ◽  
Abdolmajid Moghtadaei ◽  
Madjid Karimirad ◽  
Arturo Ortega
Keyword(s):  
Wind Turbine ◽  
Wave Height ◽  
Environmental Conditions ◽  
Stochastic Dynamics ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Contour Method ◽  
Exceedance Probability ◽  
Offshore Wind Turbine ◽  
Peak Period

Abstract In the field of stochastic dynamics of marine structures, environmental conditions play a vital role. Considering wind and waves as random processes, determining the environmental parameters which correspond to an annual exceedance probability for a certain structural concept is of vital importance for the respective assessment of the loads and their effects. The accuracy in predicting the conditions, especially those corresponding to the sea, is of a great relevance when a probabilistic design is performed in order to ensure the structural integrity of an offshore wind turbine. In particular, models are not always completely perfect and accurate data is not always available. The Environmental Contour Method (ECM), which is based on the IFORM methodology, is one of the most popular methods in the offshore industry when determining the environmental conditions, for a given annual exceedance probability, is required. The ECM allows analysing proper sea states for operational and extreme conditions with lower computational efforts than the most accurate method (Full Long-Term Analysis). In the present study, effects of progressive variations (uncertainties) of the sea states parameters (i.e. significant wave height, spectral peak period) on the dynamic response of a Monopile Wind Turbine (NREL 5MW) are analysed. Two operative conditions are considered: rated wind and cut-out wind speed. In each case, the 50-year environmental contour (EC) is plotted for a site located in the North Sea. Some sea states are selected from the EC (base cases) and then derived cases with percentage variations are generated. All the cases are simulated in FAST (NREL) and the standard deviations of the time series are compared with its respective values of base cases. The results for the dynamic responses at mudline (e.g. overturning moments and shear forces) are presented as the most important parameters governing the design of the monopile. In this analysis, the wave height shows more influence on the response variation percentage than the peak period. This work shows the importance of accurately setting up the input parameters and their impact on the calculation of the dynamic responses.

Numerical Simulation of Spudcan Penetration Into Silica Sand and Prediction of Bearing Behaviour

2012 ◽  
Author(s):  
Tim Pucker ◽  
Britta Bienen ◽  
Sascha Henke
Keyword(s):  
Bearing Capacity ◽  
Oil And Gas ◽  
Cone Angle ◽  
Oil And Gas Industry ◽  
Friction Angle ◽  
Offshore Wind ◽  
Silica Sand ◽  
Gas Industry ◽  
Jack Up ◽  
Bearing Behavior

Prediction of the bearing behavior of vertical loaded shallow foundations is typically done using the classical bearing capacity approach. This approach is very sensitive to the friction angle assumed in the calculation. A conservative estimate of the bearing capacity is required for most applications, hence uncertainties in the friction angle may be absorbed by the safety factor applied. Spudcans are used to found mobile jack-up platforms in the oil and gas industry as well as in the offshore wind energy industry. Contrary to the classical approach, the bearing capacity of spudcans has to be predicted accurately. Spudcans are penetrated into the seabed and a continuous bearing failure proceeds until the target capacity is met. A Coupled Eulerian-Lagrangian (CEL) approach is used to simulate the penetration process of spudcans into silica sand. The sand is modeled using a hypoplastic constitutive model to capture the influence of the void ratio and stress state for example. A parametric study of foundation diameter and enclosed cone angle is presented. The numerical model is validated against results from centrifuge experiments of flat and conical circular footings penetrating into silica sand. A first empirical approach to estimate the bearing capacity depending on the diameter and enclosed cone angle is given for silica sand.

scholarly journals Numerical Simulations for Installation of Offshore Wind Turbine Monopiles Using Floating Vessels

2013 ◽  
Author(s):  
Lin Li ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Time Domain ◽  
Coupled System ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Support Structures ◽  
Offshore Wind Turbines ◽  
Motion Responses ◽  
Sensitivity Studies ◽  
Jack Up

Monopiles are the most commonly used support structures for offshore wind turbines with up to 40m water depth due to the simplicity of the structure. The installation of turbine support structures can be carried out by a jack-up vessel which provides a stable working platform. However, the operational weather window using jack-up vessels is very limited due to the low sea states required for jacking up and down. Compared to jack-up installation vessels, floating vessels have more flexibility due to fast transportations between foundations. However, the vessel motions will affect the motion responses of the lifting objects, which might bring installation difficulties. Therefore, it is necessary to examine the dynamic responses of the coupled system to ensure safe offshore operations. In this paper, the installation operation of a monopile using a floating installation vessel is studied by a numerical model. Time domain simulations were carried out to study the installation process of a monopile, including lowering phase, landing phase and steady states after landing. Sensitivity studies were performed focusing on the effects by the gripper device stiffness and landing device stiffness. Comparisons of critical responses by using floating vessel and a jack-up vessel were also studied in the paper.

scholarly journals Numerical Study on the Hydrodynamic Characteristics of Submarine Pipelines under the Impact of Real-World Tsunami-Like Waves

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 221 ◽  
Author(s):  
Enjin Zhao ◽  
Ke Qu ◽  
Lin Mu ◽  
Simon Kraatz ◽  
Bing Shi
Keyword(s):  
Solitary Wave ◽  
Wave Height ◽  
Real World ◽  
Oil And Gas ◽  
High Efficiency ◽  
Numerical Study ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Characteristics ◽  
Tsunami Waves ◽  
The Impact

Submarine pipelines have been extensively used for marine oil and gas extraction due to their high efficiency, safety, and low price. However, submarine pipelines are vulnerable to extreme waves (i.e., tsunami waves). Previous research has often used solitary waves as a basis for studying the impacts of tsunami waves on submarine pipelines, although the hydrodynamic characteristics and wave properties drastically differ from those of real-world tsunami waves. This paper numerically investigates the hydrodynamic characteristics of tsunami waves interacting with submarine pipelines, but instead uses an improved wave model to generate a tsunami-like wave that more closely resembles those encountered in the real-world. The tsunami-like wave generated based on a real-world tsunami wave profile recorded during a 2011 tsunami in Japan has been applied. Given the same wave height, simulation results show that peak hydrodynamic forces of the tsunami-like wave are greater than those of the solitary wave. Meanwhile, the duration of the acting force under the tsunami-like wave is much longer than that of the solitary wave. These findings underline the basic reasons for the destructive power of tsunamis. It is also noted that the hydrodynamic forces of the pipeline under the tsunami-like wave increase with wave height, but will decrease as water depth increases. In addition to the single pipeline, the complicated hydrodynamic characteristics of pipelines in tandem arrangement have been also numerically studied. It is believed that the findings drawn from this paper can enhance our understanding of the induced forces on submarine pipelines under extreme tsunami waves.

Three-Dimensional Pushover Analysis of a Jack-Up Platform

2012 ◽  
Author(s):  
Ning Cheng ◽  
Mehrdad Kimiaei ◽  
Mark J. Cassidy
Keyword(s):  
Oil And Gas ◽  
Numerical Solutions ◽  
Progressive Failure ◽  
Pushover Analysis ◽  
Three Dimensional ◽  
Offshore Wind ◽  
Foundation Soil ◽  
Oil And Gas Exploration ◽  
Plastic Behaviour ◽  
Jack Up

Jack-ups, as the name indicates, are self-elevating units consisting of a floatable hull and, usually, three truss work or circular legs. As a mobile structure, jack-ups are mainly utilized for oil and gas exploration and maintenance purposes in shallow to medium water (up to 120 meters), though they have recently seen application in the construction of offshore wind energy infrastructure. The use of the finite element method for structural analyses of jack-ups is a common practice. However, most jack-up models remain elastic with the yielding of structural members or even the soil around the spudcan not accounted for. This paper describes the development of a comprehensive and integrated elasto-plastic jack-up model in ABAQUS [1]. This model is representative of a modern jack-up structure, and it can capture geometrical nonlinearities and plastic behaviour of the structural and soil materials. In this study, the discretisation of the structural elements, the choice of elements, the elasto-plastic behaviour of the material, and the mesh generation are described. Numerical results of a series of static pushover analyses for this sophisticated model under extreme loads are presented. The sensitivity of the results to the structural configurations is discussed. For instance, the choice of sectional properties of the chord member and the assumption of the behaviour of the spudcan (jack-up foundation)-soil interaction are shown to be critical to the prediction of the ultimate strength of the platform and the progressive failure mechanism. In conclusion, generic issues associated with static pushover analyses of jack-ups are discussed and possible numerical solutions are proposed.

Semi-Empirical Crest Distributions of Long-Crest Nonlinear Waves of Three-Hour Duration

2017 ◽  
Author(s):  
Zhenjia (Jerry) Huang ◽  
Qiuchen Guo
Keyword(s):  
Nonlinear Wave ◽  
Wave Height ◽  
Model Test ◽  
Significant Wave Height ◽  
Spectral Peak ◽  
Wave Crest ◽  
Empirical Formulas ◽  
Peak Period ◽  
Significant Wave ◽  
Semi Empirical

In wave basin model test of an offshore structure, waves that represent the given sea states have to be generated, qualified and accepted for the model test. For seakeeping and stationkeeping model tests, we normally accept waves in wave calibration tests if the significant wave height, spectral peak period and spectrum match the specified target values. However, for model tests where the responses depend highly on the local wave motions (wave elevation and kinematics) such as wave impact, green water impact on deck and air gap tests, additional qualification checks may be required. For instance, we may need to check wave crest probability distributions to avoid unrealistic wave crest in the test. To date, acceptance criteria of wave crest distribution calibration tests of large and steep waves of three-hour duration (full scale) have not been established. The purpose of the work presented in the paper is to provide a semi-empirical nonlinear wave crest distribution of three-hour duration for practical use, i.e. as an acceptance criterion for wave calibration tests. The semi-empirical formulas proposed in this paper were developed through regression analysis of a large number of fully nonlinear wave crest distributions. Wave time series from potential flow simulations, computational fluid dynamics (CFD) simulations and model test results were used to establish the probability distribution. The wave simulations were performed for three-hour duration assuming that they were long-crested. The sea states are assumed to be represented by JONSWAP spectrum, where a wide range of significant wave height, peak period, spectral peak parameter, and water depth were considered. Coefficients of the proposed semi-empirical formulas, comparisons among crest distributions from wave calibration tests, numerical simulations and the semi-empirical formulas are presented in this paper.

A numerical study on the influences of underlying soil and backfill characteristics on the dynamic behaviour of typical integral bridges

Bauingenieur ◽  
2020 ◽  
Vol 95 (11) ◽  
pp. S 2-S 11
Author(s):  
H. D. B. Aji ◽  
M. B. Basnet ◽  
Frank Wuttke
Keyword(s):  
Soil Structure ◽  
Dynamic Behaviour ◽  
Numerical Study ◽  
Coupled System ◽  
Soil Structure Interaction ◽  
Dynamic Resistance ◽  
Soil Characteristic ◽  
Structure Interaction ◽  
Integral Bridges ◽  
Underlying Soil

Abstract The identification of the dynamic behaviour of a structure is one of the crucial steps in the design of the dynamic resistance of the structure. The dynamic behaviour is represented by the natural frequencies and damping which are subsequently used along with the considered dynamic actions in the design process. In regard of integral bridge concept, one of the consequences of the omission of joints and bearings is the substantial soil-structure interaction which in turn increases the sensitivity of the dynamic behaviour of the bridges to the surrounding soil characteristic. In this article, we extended our hybrid BEM-FEM steady-state dynamic numerical tool to the 3D regime, developed by utilizing an in-house BEM and the commercial FEM software ABAQUS and use it to analyse the dynamic interaction between the bridge and the underlying soil as well as the backfill. The numerical results from four typical integral bridges show that underlying soil characteristic has great effect on the resonant frequencies and the damping. The backfill material properties tend to have less significant role due to the abutment wingwalls dominating the force transfer between the soil and the superstructure. The results also show that the degree of influence of the soil-structure interaction on the coupled system is affected by the type of load pattern in addition to the flexural stiffness of the superstructure.

Prevention of Offshore Wind Power Cable Incidents by Employing Offshore Oil/Gas Common Practices

2021 ◽  
Author(s):  
David McLaurin ◽  
Alan Aston ◽  
John Brand
Keyword(s):  
Wind Power ◽  
Oil And Gas ◽  
Early Stage ◽  
Offshore Wind ◽  
Power Cables ◽  
Manufacturing Testing ◽  
Static Conditions ◽  
Offshore Oil ◽  
Oil Gas ◽  
Oil And Gas Sector

Abstract It has been observed that, although submarine power cables have a critical role to wind power arrays and power export to shore, they are often overlooked at early stages of projects and oversimplified during late stages. This leads to lack of attention given during cable design and planning, as well as pressured schedules during manufacturing, testing and installation. The significant number of incidents attributed to offshore submarine cables during construction has increased overall project risk, lowered system average power availability and increased insurance costs. Lack of proper routing can also result in an inability to maintain asset integrity for the project design life. Despite the attention that submarine power cables have received over the past few years, the number and cost of incidents does not appear to be decreasing. A comparison can be made between offshore HVAC and HVDC cables used for wind power and offshore umbilicals and MV cables used in the oil and gas sector. These umbilicals are often similar in weight, size and bending stiffness, and have similar design, manufacturing, routing and installation challenges, but with a fraction of the incidents observed with offshore wind array and export cables. An additional caveat is that the offshore oil and gas sector has achieved a reliable track record while installing and maintaining these umbilicals and cables in fully dynamic conditions (ultra-deep water) as well static conditions. One primary difference between how the oil and gas sector executes these systems are design, planning and specification from an early stage of the project. Significant attention is given at an early stage to quality control, including offshore routing and umbilical testing specifically to avoid incidents resulting in umbilical damage due to the tension and crushing forces during installation as well as ambient seawater and seabed interaction. Management of these risks are documented, and optimal mitigation strategies are implemented early in the design phase. This paper will discuss the types of incidents which have been observed during construction and installation of submarine HVAC/HVDC cables in the wind power sector and how they could have been prevented by normal practices of the offshore oil/gas sector from early design and planning all the way to installation and commissioning.

PyraWind™: An Innovative Floating Offshore Wind Turbine (FOWT) Global Performance Analysis

2021 ◽  
Author(s):  
Zhiyong Yang ◽  
Xiaoqiang Bian ◽  
Yu Shi
Keyword(s):  
Wind Turbine ◽  
Hydrodynamic Model ◽  
Coupled System ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Floating Offshore Wind Turbine ◽  
Offshore Wind Turbines ◽  
Ongoing Work ◽  
Heavy Lift ◽  
Solid Foundation

Abstract In the near future, the offshore wind industry will experience a significant increase of turbine size and of floating wind development activities. A floating offshore wind turbine foundation offers many advantages, such as flexibility in site selection, access to better offshore wind resources, and quayside integration to avoid a costly heavy lift vessel offshore campaign. PyraWind™ is a patented three canted column semisubmersible floating foundation for ultra large offshore wind turbines. It is designed to accommodate a wind turbine, 14 MW or larger, in the center of the interconnected columns of the hull with minimal modifications to the tower, nacelle and turbine. The pyramid-shaped hull provides a stable, solid foundation for the large wind turbine under development. This paper summarizes the feasibility study conducted for the PyraWind™ concept. The design basis for wind turbine floating foundations is described and the regulatory requirements are discussed. Also included are the hydrodynamic analysis of the hull and ongoing work consisting of coupling hull hydrodynamics with wind-turbine aerodynamic loads. The fully coupled system was analyzed using OpenFAST, an aerodynamic software package for wind turbine analysis with the ability to be coupled with the hydrodynamic model. Due to the canted columns, a nonlinear analysis was performed using the coupled numerical hydrodynamic model of the platform with mooring system in extreme sea states.

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