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.

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.

Computing Large Amplitude Motions of a Floating Offshore Structure in the Time Domain

2008 ◽  
Author(s):  
Wei Qiu ◽  
Hongxuan Peng
Keyword(s):  
Time Domain ◽  
Large Amplitude ◽  
Offshore Structures ◽  
The Body ◽  
Surface Boundary ◽  
Offshore Structure ◽  
Floating Structure ◽  
Time Step ◽  
Large Amplitude Motions ◽  
The Time Domain

Based on the panel-free method, large-amplitude motions of floating offshore structures have been computed by solving the body-exact problem in the time domain using the exact geometry. The body boundary condition is imposed on the instantaneous wetted surface exactly at each time step. The free surface boundary is assumed linear so that the time-domain Green function can be applied. The instantaneous wetted surface is obtained by trimming the entire NURBS surfaces of a floating structure. At each time step, Gaussian points are automatically distributed on the instantaneous wetted surface. The velocity potentials and velocities are computed accurately on the body surface by solving the desingularized integral equations. Nonlinear Froude-Krylov forces are computed on the instantaneous wetted surface under the incident wave profile. Validation studies have been carried out for a Floating Production Storage and Offloading (FPSO) vessel. Computed results were compared with experimental results and solutions by the panel method.

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 Near Fault Effect on the Response of Single Hinged Compliant Offshore Tower

2018 ◽  
Vol 203 ◽  
pp. 01015
Author(s):  
Syed Yusuf Javed
Keyword(s):  
Offshore Structures ◽  
Dynamic Responses ◽  
Simultaneous Action ◽  
Integration Scheme ◽  
Random Waves ◽  
Sea Waves ◽  
Offshore Structure ◽  
Wave Condition ◽  
Near Fault ◽  
Time Histories

The response of compliant offshore structure under simultaneous action of random waves and earthquake loading has been analyzed. Since earthquake forces play a significant role in affecting the response of these offshore structures, comparative studies have been carried out considering near fault and far fault seismic excitations in the presence of moderate random sea waves. The offshore tower is modeled as an inverted pendulum with a cylindrical shaft connected by an articulated joint at the base. Seismic forces are evaluated by dividing the tower shaft into finite elements with masses lumped at the nodes. The nonlinearities associated with the system owing to variable submergence, drag force, variable buoyancy along with the geometry are considered in the analysis. The nonlinear dynamic equation of motion is formulated considering Lagrangian approach, which is solved in time domain by the Newmark-beta integration scheme. The sea state conditions, more precisely the water particle kinematics are evaluated using Airy’s wave theory along with the stretching modifications, as suggested by Chakrabarti. To minimize the dynamic responses, emphasis has to be given to the variations in height and position of the buoyancy chamber in extreme wave condition. The results are expressed in the form of time histories of deck displacement, hinge rotation, hinge shear and the bending moment. Parameters like maximum, minimum, mean and standard deviation are also determined by statistical analysis of response time histories of the dynamic responses at articulated joint.

Reliability Analysis of Offshore Wind Turbines Using Copula

2018 ◽  
Author(s):  
Weifei Hu ◽  
Zhiyu Jiang ◽  
Yeqing Wang
Keyword(s):  
Reliability Analysis ◽  
Environmental Conditions ◽  
Joint Distribution ◽  
Environmental Parameters ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Design Stage ◽  
Offshore Structure ◽  
Distribution Models ◽  
Restricted Form

Offshore structures are subject to severe environmental conditions and require high operating and maintenance costs. At the design stage of an offshore structure, it is necessary to perform load analysis and to consider representative environmental conditions characterized by statistical models. However, many available joint distribution models of the environmental parameters can only describe the correlation of these parameters in a very restricted form. The use of simple probabilistic models without correctly addressing their correlation may lead to significant bias in the reliability analysis. Here, the correlation between three offshore environmental parameters including the significant wave height, wave peak period, and mean wind speed is described by copula. The copula density functions and theoretical derivations of copula correlation parameters using actual sea state data are provided for general applications of reliability analysis of offshore structures. Hindcast data of two representative sites are used to fit the best copula. The developed copula-based joint distribution can be used for accurate reliability analysis of offshore structures considering long-term fatigue loads and extreme responses.

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.

Application of Direct Boundary Element Method to Three Dimensional Hydrodynamic Analysis of Interaction Between Waves and Floating Offshore Structures

2004 ◽  
Author(s):  
Saeid Kazemi ◽  
Atilla Incecik
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Three Dimensional ◽  
Offshore Structures ◽  
Sea Waves ◽  
Offshore Structure ◽  
Hydrodynamic Analysis ◽  
Hydrodynamic Behaviour ◽  
Direct Boundary Element Method ◽  
Element Method

A three-dimensional hydrodynamic analysis of interaction between a floating offshore structure and sea waves has been carried out using a novel approach which is based on the weighted residual technique and the direct boundary element method. The main advantage of the direct boundary element method is the fact that one can determine the total velocity potential directly. Direct BEM is more versatile and computationally more efficient than indirect BEM. Besides, the BEM can easily be coupled with other numerical methods, e.g. finite element method (FEM) in order to carry out structural analysis of deck of the platform due to impact. Firstly, the boundary value problem of three-dimensional interaction between regular sea waves and a semi-submersible will be described. Secondly, the direct boundary element method has been applied to predict hydrodynamic behaviour of Khazar Semi-Submersible Drilling Unit (KSSDU), which is the largest semi-submersible drilling platform under construction for a location in the Caspian Sea, North of Iran. The rigid body motion responses in six degrees of freedom of KHAZAR semi-submersible in response to encountering waves have been calculated by using the direct boundary element method. The results obtained from the direct BEM will be compared with those obtained by the results based on the conventional boundary element method (indirect BEM) which were obtained by the designers of KHAZAR semi-submersible.

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.

Analysis of Offshore Structures Subjected to Various Types of Sea Wave

2004 ◽  
Author(s):  
K. Kuntiyawichai ◽  
S. Chucheepsakul ◽  
M. M. K. Lee
Keyword(s):  
Finite Element ◽  
Wavelet Analysis ◽  
Dynamic Behaviour ◽  
Time History ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Offshore Structure ◽  
Finite Element Software ◽  
Jacket Structures

The principal aim of this paper is to study the dynamic behaviour of offshore platforms subjected to wave loading. A general review of offshore structure, wave loading and their effects on offshore structures are presented. A brief review on the basics of Wavelet analysis is also mentioned in this study. The techniques for modeling wave loading in finite element analyses are described and discussed in detail. A series of 3D analyses were carried out using the ABAQUS finite element software to study the effects on the dynamic response of the change in support conditions at the seabed. The effects of wave height, wave period and wave velocity on platform behaviour were studied. The results from time history analysis are characterized using Wavelet Analysis in order to obtain the response pattern due to wave loading. These analyses allow the frequency response of the jacket structures to be described in the time domain. These results give a clear view on the response of jacket structure. The important parameters on offshore modeling have also been identified and discussed in this paper. The results presented in this study can be used as a guidance for engineer in order to understand the dynamic behaviour of jacket structures subjected to wave loading.

Onshore Yard Readiness for Upcoming Oil and Gas Offshore Structure Decommissioning Projects in Indonesia

2021 ◽  
Author(s):  
Sari Amelia ◽  
Jing Shuo Leow ◽  
Bisri Hasyim ◽  
Dega Damara Aditramulyadi ◽  
Hooi Siang Kang ◽  
...  
Keyword(s):  
Southeast Asia ◽  
Oil And Gas ◽  
Offshore Structures ◽  
Research Data ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Heavy Lift ◽  
Waste Handling ◽  
To Receive ◽  
Waste Handling Facilities

Abstract More than a thousand fixed oil and gas offshore structures were installed in the Southeast Asia region. Indonesia currently has more than 600 offshore oil and gas platforms, nearly half of which need to be decommissioned within the next few years. While the regulators and operators are developing procedures and regulations for the decommissioning process of the offshore platforms, there is also a need to ensure that onshore facilities are available to receive the decommissioned structures and equipment and subsequently process them safely. At the moment, there is no yard in Indonesia that is well-placed to undertake onshore decommissioning activities. The aim of this study is to develop recommendations for yard owners to assure their yards are ready for the upcoming decommissioning projects. Research data was collected directly from field survey in an offshore fabrication yard, owned by PT. Meitech Eka Bintan, Indonesia. In the current study, research data was analyzed by comparing with decommissioning yard facilities in ABLE Seaton Port, United Kingdom which was used as offshore structure decommissioning yard since 1985. Recommendations include the work required to assure the yard comply with respective guidelines and industry best practices. The research begun with identifying the yard's potential to receive onshore decommissioning work based on current primary facilities which are quay and fabrication area properties. After that, a yard modernization assessment was carried out as to identify the best location for the upgrade on the missing required facilities. The results indicate that the primary facilities of the yard are comparable to ABLE Seaton Port with both having similar depth at quayside, capable of mooring barges and Heavy Lift Vessel (HLV), both having liquid containment system at the fabrication area and the large fabrication area at PT. Meitech Eka Bintan yard is sufficient similar to the area utilized by ABLE Seaton Port for Brent Delta topside decommissioning works. However, since the yard's main business is currently on offshore structure fabrication, hence there is a lack of waste handling facilities such as waste handling workshop and covered waste storage area to fulfill the respective guidelines and regulations. A case study was carried out to identify the onshore decommissioning working area and the location of the waste handling facilities on the yard. This study is expected to assist towards improving the readiness of yards to carry out onshore decommissioning not only in Indonesia but also in Southeast Asia region.

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