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.

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.

Numerical Studies of Installation and Extraction Processes of Jack-Up Ships

2011 ◽  
Author(s):  
Gang Qiu ◽  
Ju¨rgen Grabe ◽  
Nikolai Kukolka ◽  
Hans-Werner Vollstedt
Keyword(s):  
Constitutive Model ◽  
Three Dimensional ◽  
Extraction Process ◽  
Offshore Wind ◽  
Soil Parameters ◽  
Element Analysis ◽  
Quay Wall ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Jack Up

New Jack-up ships are built to transport offshore wind turbines from harbor and assemble them with the help of cranes on the ship at the site of installation. Every ship has four stilts, which can be lowered to seabed and jack the ship up. However, penetration and extraction the stilts at the harbor area could jeopardize the existing quay wall construction. In this paper two conceptual designs of foundations, which are used to improve the strength of the seabed in front of the quay wall, are investigated using numerical methods. Through soil exchange in open-ended cylinder or bucket foundation the strength of the seabed should be improved so that jack-up ships can dock directly at the quay wall and lower the stilts into the foundations. Three dimensional finite element analysis using a coupled Eulerian-Lagrangian method (CEL) are carried out to simulate penetration and extraction process. A hypoplastic constitutive model and the Mohr-Coulomb constitutive model are used to describe the filling. The studies of influences of geometry of foundations as well as the soil parameters on the bearing capacity of stilts and failure mechanism in foundations are carried out as the design basis of the foundations.

scholarly journals Challenges and Prospects of Digital Core-Reconstruction Research

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-29 ◽  
Author(s):  
Linqi Zhu ◽  
Chong Zhang ◽  
Chaomo Zhang ◽  
Xueqing Zhou ◽  
Zhansong Zhang ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Three Dimensional ◽  
Morphological Characteristics ◽  
Research Area ◽  
Rock Properties ◽  
Reconstruction Method ◽  
Oil And Gas Exploration ◽  
Stochastic Reconstruction ◽  
Reconstruction Methods ◽  
Digital Core

The simulation of various rock properties based on three-dimensional digital cores plays an increasingly important role in oil and gas exploration and development. The accuracy of 3D digital core reconstruction is important for determining rock properties. In this paper, existing 3D digital core-reconstruction methods are divided into two categories: 3D digital cores based on physical experiments and 3D digital core stochastic reconstructions based on two-dimensional (2D) slices. Additionally, 2D slice-based digital core stochastic reconstruction techniques are classified into four types: a stochastic reconstruction method based on 2D slice mathematical-feature statistical constraints, a stochastic reconstruction method based on statistical constraints that are related to 2D slice morphological characteristics, a physics process-based stochastic reconstruction method, and a hybrid stochastic reconstruction method. The progress related to these various stochastic reconstruction methods, the characteristics of constructed 3D digital cores, and the potential of these methods are analysed and discussed in detail. Finally, reasonable prospects are presented based on the current state of this research area. Currently, studies on digital core reconstruction, especially for the 3D digital core stochastic reconstruction method based on 2D slices, are still very rough, and much room for improvement remains. In particular, we emphasize the importance of evaluating functions, multiscale 3D digital cores, multicomponent 3D digital cores, and disciplinary intersection methods in the 3D construction of digital cores. These four directions should provide focus, alongside challenges, for this research area in the future. This review provides important insights into 3D digital core reconstruction.

scholarly journals Development of a force–resultant model for spudcan footings on loose sand under combined loads

2016 ◽  
Vol 53 (12) ◽  
pp. 2014-2029 ◽  
Author(s):  
Ning Cheng ◽  
Mark Jason Cassidy
Keyword(s):  
Strain Hardening ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Plasticity Model ◽  
Loose Sand ◽  
Oil And Gas Fields ◽  
Combined Loads ◽  
Centrifuge Tests ◽  
Model Components ◽  
Jack Up

Spudcans are typical foundations used in shallow to moderate-depth water oil and gas fields to support jack-up drilling units. Understanding the behaviour of spudcans under combined loadings is crucial to the overall response of the jack-up structure. This paper presents the development of a strain-hardening plasticity model for a spudcan footing on loose sand. Most of the model components are developed from direct centrifuge observations. The centrifuge tests were performed at an acceleration of 100 times that of the Earth’s gravity on a model spudcan footing subjected to combined vertical, horizontal, and moment loads. All the experiments have been designed and conducted to allow the results to be interpreted with a strain-hardening plasticity framework. Combined loads were applied by using a novel apparatus, which enables independent vertical, horizontal, and rotational movements of the footing. Test results also revealed the existence of a three dimensional sliding surface that intersects with the conventional yield surface. This additional surface has been defined analytically. Retrospective simulation of the experimental data using the plasticity model confirms the model’s capability for use in predicting the behaviour of larger spudcan applications offshore.

Improvement of generalization capability of two-dimensional salt segmentation via iterative semi-supervised learning

2022 ◽  
pp. 1-43
Author(s):  
Lingxiao Jia ◽  
Satyakee Sen ◽  
Subhashis Mallick
Keyword(s):  
Oil And Gas ◽  
Three Dimensional ◽  
Ground Truth ◽  
Unlabeled Data ◽  
New Method ◽  
Two Dimensional ◽  
Learning Tools ◽  
Generalization Capability ◽  
Oil And Gas Exploration ◽  
Depth Images

Accurate interpretations of subsurface salts are vital to oil and gas exploration. Manually interpreting them from seismic depth images, however, is labor-intensive. Consequently, use of deep learning tools such as a convolutional neural network for automatic salt interpretation recently became popular. Because of poor generalization capabilities, interpreting salt boundaries using these tools is difficult when labeled data are available from one geological region and we like to make predictions for other nearby regions with varied geological features. At the same time, due to vast amount of the data involved and the associated computational complexities needed for training, such generalization is necessary for solving practical salt interpretation problems. In this work, we propose a semi-supervised training, which allows the predicted model to iteratively improve as more and more information is distilled from the unlabeled data into the model. In addition, by performing mixup between labeled and unlabeled data during training, we encourage the predicted models to linearly behave across training samples; thereby improving the generalization capability of the method. For each iteration, we use the model obtained from previous iteration to generate pseudo labels for the unlabeled data. This automated consecutive data distillation allows our model prediction to improve with iteration, without any need for human intervention. To demonstrate the effectiveness and efficiency, we apply the method on two-dimensional images extracted from a real three-dimensional seismic data volume. By comparing our predictions and fully supervised baseline predictions with those that were manually interpreted and we consider as “ground truth”, we find than the prediction quality our new method surpasses the baseline prediction. We therefore conclude that our new method is a viable tool for automated salt delineation from seismic depth images.

A Study on the Evolution of Distributary Channels in River-Dominated Deltas Using Numerical Simulations of Hydrodynamic Behaviors

2015 ◽  
Vol 744-746 ◽  
pp. 1050-1055
Author(s):  
Yang Jun Wang ◽  
Tai Ju Yin ◽  
Zhi Hao Deng
Keyword(s):  
Numerical Simulation ◽  
Numerical Model ◽  
Quantitative Methods ◽  
Oil And Gas ◽  
Reference Model ◽  
Three Dimensional ◽  
Hydrodynamic Characteristics ◽  
Oil And Gas Exploration ◽  
Hydrodynamic Behaviors ◽  
Distributary Channel

The Fluvial-dominated delta is one of the extremely important deposition systems in oil and gas exploration. In this paper, the three-dimensional numerical simulation of hydrodynamics has been applied to the precise analysis of the formation of fluvial-dominated deltas and the evolution of their distributary channels. The model has been created using the Delft3D program, and the conditions of the numerical model have been set according to the hydrodynamic characteristics of modern rivers and deltas. The calculation field was 20.5 km in length by 10 km in width. With the Mor-Factor set to 60, the simulation time was 45 days. The formation and the avulsion of the mouth bar, as well as the extension, migration and bifurcation of distributary channels, have been observed and studied through analysis of the simulation results. The vertical cross-section shows that the distributary channel was filled multiple times. According to distributary channel evolution characteristics combined with quantitative methods, the terminal distributary channels can be extremely developed under ideal conditions. Due to the cross-cutting and reform effort of distributary channels, sediments were spread widely and continuously. The results show that the numerical model works well in explaining the process of evolution in fluvial-dominated delta distributary channels. This study not only enables us to quantitatively understand the dynamic processes of terminal distributary channels in fluvial-dominated delta systems, but also provides a reference model for numerical simulation of hydrodynamics in sedimentology study.

scholarly journals Review of Dynamic Positioning Control in Maritime Microgrid Systems

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3188 ◽  
Author(s):  
Mojtaba Mehrzadi ◽  
Yacine Terriche ◽  
Chun-Lien Su ◽  
Muzaidi Bin Othman ◽  
Juan C. Vasquez ◽  
...  
Keyword(s):  
Wind Farm ◽  
Oil And Gas ◽  
Control Strategies ◽  
Offshore Wind ◽  
Future Research ◽  
Dynamic Positioning ◽  
Dynamic Positioning System ◽  
Oil And Gas Exploration ◽  
Advantages And Disadvantages ◽  
Progressive Technology

For many offshore activities, including offshore oil and gas exploration and offshore wind farm construction, it is essential to keep the position and heading of the vessel stable. The dynamic positioning system is a progressive technology, which is extensively used in shipping and other maritime structures. To maintain the vessels or platforms from displacement, its thrusters are used automatically to control and stabilize the position and heading of vessels in sea state disturbances. The theory of dynamic positioning has been studied and developed in terms of control techniques to achieve greater accuracy and reduce ship movement caused by environmental disturbance for more than 30 years. This paper reviews the control strategies and architecture of the DPS in marine vessels. In addition, it suggests possible control principles and makes a comparison between the advantages and disadvantages of existing literature. Some details for future research on DP control challenges are discussed in this paper.

Eulerian finite element simulation of spudcan–pile interaction

2013 ◽  
Vol 50 (6) ◽  
pp. 595-608 ◽  
Author(s):  
Kee Kiat Tho ◽  
Chun Fai Leung ◽  
Yean Khow Chow ◽  
Somsak Swaddiwudhipong
Keyword(s):  
Numerical Model ◽  
Oil And Gas ◽  
Interaction Analysis ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Gas Drilling ◽  
Pile Interaction ◽  
Offshore Oil And Gas ◽  
Jack Up

Jack-up rigs are commonly employed to perform offshore oil and gas drilling. During the installation of the spudcan foundation, the large volume of soil displaced may induce severe stresses on the piles supporting the adjacent platform. The increasing numbers of jack-up rigs being deployed at close proximity to piled platforms accentuates the need for research into quantifying the effect of spudcan penetration on adjacent piles. The main difficulty with the numerical simulation of spudcan–pile interaction lies in the need to model continuous spudcan penetration in a three-dimensional (3-D) modeling space. In this paper, the three-dimensional Eulerian numerical technique is adopted to perform a coupled interaction analysis whereby the process of continuous spudcan penetration is simulated and the corresponding pile responses are obtained. The salient features of the proposed numerical approach with particular emphasis on the incorporation of a pile in the numerical model are first described. The validation of the numerical model against centrifuge experimental data under different geometric configurations and soil profiles are then presented. The final part of this paper demonstrates the usefulness of the proposed numerical approach through a series of parametric studies. This numerical approach can be readily applied to perform site-specific assessment to mitigate the risks associated with spudcan–pile interaction.

Effect of Foundation Modeling on Extreme Response of Offshore Jack-up Unit

2010 ◽  
Author(s):  
Azadeh Jafari ◽  
Behrouz Asgarian ◽  
Mohammad Daghigh
Keyword(s):  
Ultimate Strength ◽  
Progressive Collapse ◽  
Pushover Analysis ◽  
Three Dimensional ◽  
Nonlinear Behavior ◽  
Extreme Response ◽  
Lateral Strength ◽  
Offshore Industry ◽  
Drilling Rigs ◽  
Jack Up

The demand for operation of mobile jack-up drilling rigs in offshore industry is increasing. Extreme response of jack-up platforms in sea environment requires improving the understanding of their nonlinear behavior. A sample jack-up platform located in Persian Gulf is modeled using three dimensional capabilities of USFOS considering both geometric and material nonlinearity. USFOS is a numerical tool for ultimate strength and progressive collapse analysis at frame structures such as jack-up platforms. Results of the analysis for the sample jack-up subjected to storm load pattern are compared for three different foundation modeling cases (pinned, fixed and spudcan modeling of foundation). Static pushover analysis is performed to determined jack-up behavior assuming different cases for fixity of foundation. It is observed that modeling of exact foundation by a simplified pinned model underestimates ultimate lateral strength of jack-up. A fixed based modeling overestimates lateral ultimate strength of the platform.

scholarly journals The jack-up platform for offshore oil and gas exploration overview

2017 ◽  
Vol 1 (2) ◽  
pp. 5-12
Author(s):  
L. F. Boswell ◽  
◽  
V. N. Alekhin ◽  
A. M. Budarin ◽  
◽  
...  
Keyword(s):  
Oil And Gas ◽  
Oil And Gas Exploration ◽  
Offshore Oil And Gas ◽  
Offshore Oil ◽  
Jack Up
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