Coupled Eulerian Lagrangian Approach to Model Offshore Platform Movements in Strong Tidal Flows

2011 ◽  
Author(s):  
F. Van den Abeele ◽  
J. Vande Voorde
Keyword(s):  
Fluid Flow ◽  
Wind Waves ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Added Value ◽  
Inertia Force ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Operational Conditions ◽  
Tidal Flows

Offshore platforms are subjected to wind, waves and tidal flows. Tidal flow will generate a steady current, which induces a lift force and a drag force on the platform legs. In addition, water particle velocities induced by waves give rise to an oscillatory flow. As a result, the structure will experience a lift, drag and inertia force when subjected to wave-induced flow patterns. On top of that, a turbulent Von Karman vortex street can appear in the wake of the platform legs for certain combinations of dimensions and flow velocities. Vortex shedding can lead to vortex induced vibrations, which may jeopardize the integrity of the entire offshore platform. Environmental loads can cause significant deformations of offshore structures, which can in turn influence the fluid flow. Multiphysics modelling is required to capture the mechanisms governing fluid-structure interaction. In this paper, a Coupled Eulerian Lagrangian (CEL) approach is pursued to simulate offshore platform movements in strong tidal flows. In a CEL analysis, the fluid flow is modelled in an Eulerian framework: the water is described by an equation of state, and can flow freely through a fixed mesh. The offshore platform is modelled as a compliant structure in a traditional Lagrangian formulation, where the nodes move with the underlying material. Interaction between the fluid domain and the offshore structure is enforced using general contact conditions. The strongly coupled problem is then tackled with an explicit solver. Here, the CEL approach is demonstrated to simulate the movement of an offshore jack-up barge. The response of the vessel is calculated for different flow conditions. The multiphysics model allows evaluating the added value of structural redundancy, e.g. in the number of platform legs required for a safe design. In addition, it provides a valuable tool to predict the tidal windows allowed for given operational conditions.

Finite Element Analysis for Structural Performance of Offshore Platforms under Environmental Loads

2013 ◽  
Vol 569-570 ◽  
pp. 159-166 ◽  
Author(s):  
Shehata E. Abdel Raheem ◽  
Elsayed M.A. Abdel Aal
Keyword(s):  
Finite Element ◽  
Return Period ◽  
Wave Force ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Current Increase ◽  
Environmental Loads ◽  
Highly Nonlinear

Offshore structures for oil and gas exploitation are subjected to various ocean environmental phenomena which can cause highly nonlinear action effects. Offshore structures should be designed for severe environmental loads and strict requirements should set for the optimum performance. The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. The structure is discretized using the finite element method, wave force is determined according to linearized Morison equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the one year return period wave and must be able to survive the 100 year return period storm conditions. The results show that the nonlinear response analysis is quite crucial for safe design and operation of offshore platform. Fixed Jacket type offshore platforms under extreme wave loading conditions may exhibit significant nonlinear behavior. The effect of current with different angles when hitting the offshore structure with the wave and wind forces, is very important for calculate the stress, the response displacement and deformation shapes. As the current increase or decrease the effect of wave force according to the hitting angle of current.

Damage Detection in Offshore Structures by the Random Decrement Technique

1984 ◽  
Vol 106 (1) ◽  
pp. 38-42 ◽  
Author(s):  
J. C. S. Yang ◽  
J. Chen ◽  
N. G. Dagalakis
Keyword(s):  
Wind Waves ◽  
The United States ◽  
Offshore Structures ◽  
Naval Research ◽  
United States Geological Survey ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Damage Scenarios ◽  
Random Decrement Technique ◽  
Random Decrement

The Random Decrement Technique has shown promise as an inspection technique for offshore structures. The major advantage of this technique is that it requires only measurements of the dynamic response of the structure and not the input excitation causing the response. On offshore platforms, such random input forces occur from wind, waves, and currents. The Random Decrement Technique was evaluated together with a number of other NDE techniques under the NDE round robin testing program sponsored by the United States Geological Survey and the Office of Naval Research. A series of tests, damage scenarios, were conducted on a model of an offshore structure in a blind-mode by an independent neutral agent. Test data were given to the corresponding advocates to be analyzed and interpreted to predict the damages. Initial results indicated that the Random Decrement Technique was able to identify all the damage and non-damage situations with the usage of only four accelerometers mounted on each of the legs of the structure.

Downtime Analysis Techniques for Complex Offshore and Dredging Operations

2004 ◽  
Author(s):  
Remmelt J. van der Wal ◽  
Gerrit de Boer
Keyword(s):  
Wind Waves ◽  
Weather Forecast ◽  
Offshore Structures ◽  
Operational Mode ◽  
Offshore Structure ◽  
Hydrodynamic Models ◽  
Time Step ◽  
Made In

Offshore operations in open seas may be seriously affected by the weather. This can lead to a downtime during these operations. The question whether an offshore structure or dredger is able to operate in wind, waves and current is defined as “workability”. In recent decades improvements have been made in the hydrodynamic modelling of offshore structures and dredgers. However, the coupling of these hydrodynamic models with methods to analyse the actual workability for a given offshore operation is less developed. The present paper focuses on techniques to determine the workability (or downtime) in an accurate manner. Two different methods of determining the downtime are described in the paper. The first method is widely used in the industry: prediction of downtime on basis of wave scatter diagrams. The second method is less common but results in a much more reliable downtime estimate: determination of the ‘job duration’ on basis of scenario simulations. The analysis using wave scatter diagrams is simple: the downtime is expressed as a percentage of the time (occurrences) that a certain operation can not be carried out. This method can also be used for a combination of operations however using this approach does not take into account critical events. This can lead to a significant underprediction of the downtime. For the determination of the downtime on basis of scenario simulations long term seastate time records are used. By checking for each subsequent time step which operational mode is applicable and if this mode can be carried out the workability is determined. Past events and weather forecast are taken into account. The two different methods are compared and discussed for a simplified offloading operation from a Catenary Anchor Leg Mooring (CALM) buoy. The differences between the methods will be presented and recommendations for further applications are given.

Integrity Management System for Fixed Offshore Structures Inspection Strategy

2004 ◽  
Author(s):  
Mohamed A. El-Reedy
Keyword(s):  
Management System ◽  
Offshore Structures ◽  
Assessment Method ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Structure Comparison ◽  
Actual Structure ◽  
Existing Structures ◽  
Integrity Management

The GUPCO offshore structure management system was developed as a part of an integrated infrastructure management system. This paper presents a case study of providing an integrity management system for inspection, evaluation and repair of the fixed offshore platforms in Gulf of Suez. The management system procedure is presented focusing on the first step for defining the highly risky weight to the lower risky weight structure based on API criteria for assessment of the existing structures. The risk analysis methodology for developing design and assessment criteria for fixed offshore structure based on consequence of failure is illustrated. In our case study the assessment method is applied for a number of fixed offshore structures. The above methodology is performed after theoretical assessment and then verifying by using ROV subsea inspection for the fixed offshore structure. Comparison between the actual structure performance and the predicting risk assessment for the structure from the model will be studied. The overall management system will be illustrated in scope of predictive maintenance philosophy and reliability for all offshore structures.

Wave Load Prediction on a Stationary Bergy Bit Near a Fixed Offshore Platform

2017 ◽  
Author(s):  
Dong Cheol Seo ◽  
Tanvir Sayeed ◽  
M. Hasanat Zaman ◽  
Ayhan Akinturk
Keyword(s):  
Water Level ◽  
Offshore Structures ◽  
Air Gap ◽  
Offshore Platform ◽  
Load Prediction ◽  
Wave Load ◽  
Offshore Structure ◽  
Cfd Simulations ◽  
Simulation Performance ◽  
Fixed Offshore Platform

Offshore oil and gas operations conducted in harsh environments such offshore Newfoundland may pose additional risks due to collision of smaller ice pieces and bergy bits with the offshore structures, including their topsides in the case of gravity based structures particularly in extreme waves. In this paper, CFD (Computational Fluid Dynamics) prediction for wave loads acting on a bergy bit around a fixed offshore platform is presented. Often the vertical column of a gravity based structure is designed against ice collisions, if operating in such an environment. In practices, topsides are usually protected by being placed sufficiently high from the still water level, away from the reach of the bergy bits. This vertical clearance between the still water level and the topside deck is known an air gap. Hence, the amount of the air gap planned for such an offshore structure is an important factor for the safety of the topsides at a given location. In this study a CFD method is applied to estimate the dynamic response of the bergy bit and provide a reliable air gap to reduce the potential risk of the bergy bit collision. In advance of more complex collision simulations using a free-floating ice for the airgap design, CFD analysis of wave load prediction on a stationary bergy bit is carried out and reported in this paper. In the experiments and CFD simulations, the location of the bergy bit is changed to quantify the change of wave load due to the hydrodynamic interaction between the bergy bit and the platform. Finally, the results of the CFD simulations are compared with the relevant experiment results to confirm the simulation performance prior to the free floating bergy bit simulations.

Developing the Structural Integrity Management System for Ageing Fixed Offshore Oil Platforms in Indonesia

2017 ◽  
Vol 862 ◽  
pp. 265-270
Author(s):  
Raditya Danu Riyanto ◽  
Murdjito
Keyword(s):  
Management System ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Element Analysis ◽  
East Kalimantan ◽  
Ranking Criteria ◽  
Life Years ◽  
Integrity Management

Offshore structure, particularly fixed offshore structures, should be kept in the performance for the fit-for-purpose condition during their operating lifetime. For fixed offshore structures that exceed their designated life years, the proper Structural Integrity Management System (SIMS) should be developed and applied. Despite the fixed offshore platforms have their service life, there are still platforms that continue to operate exceeding their service lifetime. These ageing platforms should be taken care thoroughly to avoid the consequences that could take casualties. This paper will propose the proper initiation of SIMS development for ageing fixed offshore platforms in Indonesia, by taking an example at Bekapai Field Platforms in East Kalimantan. Using HAZID technique and several ranking criteria, the platforms are assessed and ranked. Platforms that categorized in critical condition are grouped based on similarities in geometry and function. The highest rank is analyzed in computer Finite Element Analysis (FEA) Software with modification based on latest inspection result. This method is proven to be a proper method to be used as a maintenance program for ageing fixed offshore platforms in Indonesia.

scholarly journals Development of Risk-Reliability Based Underwater Inspection for Fixed Offshore Platforms in Indonesia

2018 ◽  
Vol 147 ◽  
pp. 05002
Author(s):  
Ricky L. Tawekal ◽  
Faisal D. Purnawarman ◽  
Yati Muliati
Keyword(s):  
Structural Reliability ◽  
Structural Integrity ◽  
Damage Mechanism ◽  
Offshore Structures ◽  
Probability Of Failure ◽  
American Petroleum Institute ◽  
Offshore Platform ◽  
Risk Level ◽  
Offshore Platforms ◽  
Fixed Offshore Platform

In RBUI method, platform with higher risk level will need inspection done more intensively than those with lower risk level. However, the probability of failure (PoF) evaluation in RBUI method is usually carried out in semi quantitative way by comparing failure parameters associated with the same damage mechanism between a group of platforms located in the same area. Therefore, RBUI will not be effective for platforms spread in distant areas where failure parameter associated with the same damage mechanism may not be the same. The existing standard, American Petroleum Institute, Recommended Practice for Structural Integrity Management of Fixed Offshore Structures (API RP-2SIM), is limited on the general instructions in determining the risk value of a platform, yet it does not provide a detail instruction on how determining the Probability of Failure (PoF) of platform. In this paper, the PoF is determined quantitatively by calculating structural reliability index based on structural collapse failure mode, thus the method in determining the inspection schedule is called Risk-Reliability Based Underwater Inspection (RReBUI). Models of 3-legs jacket fixed offshore platform in Java Sea and 4-legs jacket fixed offshore platform in Natuna Sea are used to study the implementation of RReBUI.

Damping-Controlled Response of a Truss-Pontoon Semi-Submersible With Heave-Plates

2005 ◽  
Author(s):  
Nagan Srinivasan ◽  
Subrata Chakrabarti ◽  
R. Radha
Keyword(s):  
Separated Flow ◽  
Cost Effective ◽  
Added Mass ◽  
Offshore Structures ◽  
Field Application ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Scaled Model ◽  
Large Wave ◽  
Truss Spar

Hydrodynamic added mass and damping are old and popular research topics in the field of offshore structures engineering. The concept of added mass has been used very intelligently in the design of modern deepwater floating vessels. The turning point of the conventional Spar to a Truss-Spar is a typical example in which the added mass created by the heave plates in a Truss Spar efficiently reduced the steel weight and the subsequent cost of the Spar hull. However, the damping is not utilized as efficiently as the added mass in the design of the floating offshore platforms. It should be noted that at resonance damping plays an important role in controlling the response amplitude. This resonance is called damping controlled response. An offshore platform efficiently designed to reduce the wave excitation forces and increase the separated-flow damping could qualify as a platform to operate even near resonance. Such design could make this concept cost effective, as well as operationally more productive with minimum downtime. The principal purpose of this paper is to describe an offshore platform design that could face the resonance efficiently. The paper applies the concept of both hydrodynamic added mass and separated-flow damping intelligently in the design of a large floating vessel on column-stabilized principle. The platform is designed to face resonance due to extreme waves and utilizes the damping to control its motion, thereby qualifying its field application. The design is verified and justified with the help of a scaled-model study in a large wave tank. The results are presented herein.

Integrating Constrained Random Waves in Endurance Time Analysis of Offshore Structures Subjected to Sea Waves

2012 ◽  
Author(s):  
H. Matin Nikoo ◽  
M. Zeinoddini ◽  
H. Estekanchi ◽  
M. Golestani
Keyword(s):  
Time Domain ◽  
Offshore Structures ◽  
Design Stage ◽  
Offshore Platforms ◽  
Sea Waves ◽  
Base Shear ◽  
Time Analysis ◽  
Offshore Structure ◽  
Endurance Time ◽  
Damage Indices

This paper introduces a novel methodology for design and assessment of offshore structures exposed to irregular sea waves. For this, Constrained NewWave (CNW) is integrated with the Endurance Time Analysis (ETA) methodology, which is basically developed for the performance based analysis of onshore structures to earthquake loads. In this approach, the offshore structure is simulated in time-domain under a set of calibrated intensifying wave functions. They are devised to represent a gradually increasing roughness of the sea state by time. A performance index such as base shear, drift or stress in a critical structural members are monitored until they reach to a predefined maximum value. A higher endurance time (corresponding to a higher wave height) is to be interpreted as a better performance of structure. Ability to consider spectral features of waves, waves’ irregularity, the wave-in-deck impacts, utilizing a relatively simple approach, requiring relatively low computational times and capability to consider any desirable damage indices are the advantages of this novel method. The method can be used in the design stage, collapse analysis and for the assessment of existing offshore platforms. In this paper the effectiveness of this method has been examined on offshore jacket platforms. The results obviously have highlighted the potentials of this approach for the dynamic, time-domain, non-linear analysis and assessment of offshore platforms.

Response Control of TLP Using Tuned Mass Dampers

2014 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
Deepak Kumar ◽  
Ranjani Ramanathan
Keyword(s):  
Large Amplitude ◽  
Experimental Studies ◽  
Tuned Mass Damper ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Scaled Model ◽  
Response Control ◽  
Extreme Loads ◽  
Mass Damper

Offshore tension leg platform (TLP) is a compliant type offshore structure where the tendons are deployed under initial pretension to counteract the excessive buoyancy. TLPs show large amplitude response under environmental loads due to their compliancy, which poses threat under extreme loads. Use of passive dampers like Tuned Mass Damper (TMD) is common to control such large amplitude motion, however their deployment in offshore structures is relatively new. Response control of a scaled model of TLP is attempted using tuned mass damper of pendulum type under regular waves. Based on the experimental studies carried out, it is seen that there is a significant reduction in the surge response under the folded pendulum type damper. Results also show that there is a reduction in the heave response due to the control envisaged in the surge motion. The discussed method of response control is one of the effective methods of retrofitting offshore platforms whose operability at rough sea states is a serious concern.

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