Non-Harmonic Decomposition of Sea Measured Data of Offshore Platforms

2016 ◽  
Author(s):  
Fushun Liu ◽  
Jinchao Cao ◽  
Jiefeng Chen ◽  
Wenlong Yang ◽  
Wei Li
Keyword(s):  
Model Updating ◽  
Wave Force ◽  
Offshore Structures ◽  
Measured Data ◽  
External Loading ◽  
Offshore Platforms ◽  
Modal Parameter ◽  
Application Performance ◽  
Harmonic Decomposition ◽  
Harmonic Components

The measured data are often required and taken as the input of different kinds of algorithms for modal parameter identification, model updating and/or damage detection of offshore platforms. This paper investigates the application performance of the approach to offshore platforms, by using real measured data. Considering the fact of a recorded loading is always finite in duration, most likely aperiodic, and even damped because of the existence of damping of the structures, a recent developed complex exponential decomposition method [1] was employed to deal with real measured data. Therefore, in this article, three kinds of measured data will be used. The first one is a measured wave force that was collected through an experiment conducted in the lab of Ocean University of China, to investigate the feasibility of original external loading decomposition. To study the performance of the proposed method when applied to offshore structures, two sets of typical signals are used: one set was collected from the JZ20-2MUQ offshore platform when it was excited by ice, and the other was collected from the WZ11-4D platform when it was excited by waves. The results show that the approach can decompose the real measured data into a series of non-harmonic components, and a large model order is often suggested.

Study of Offshore Jacket Platform Attached With Tuned Liquid Column Gas Damper

2017 ◽  
Author(s):  
P. Sathish ◽  
A. S. Sajith
Keyword(s):  
Natural Resources ◽  
Wave Theory ◽  
Wave Force ◽  
Offshore Structures ◽  
Liquid Column ◽  
Offshore Platforms ◽  
Jacket Platform ◽  
Tuned Liquid Dampers ◽  
Offshore Jacket Platform ◽  
Gas Damper

With increase in need of energy, scarcity of natural resources also increases. Need for energy has led the people to move into the ocean since they contain abundant natural resources. Offshore platforms play a major role in exploring and exploiting these resources. Jacket platform being a fixed offshore jacket platform is used in water depths 300 to 400 m. The study of behavior of these offshore structures is vital part in the design since they are subjected to dynamic loading of waves, wind, earthquake, ice etc. These structures in hostile environment are subjected to heavy loads. There is need for controlling the response of these structures. This can be achieved by providing external dampers. There are various dampers available to control the response of structures. Tuned liquid dampers (TLD)s and Tuned Liquid Column Damper (TLCD)s use liquid inside to tune its frequency to natural frequency of structure. Tuned Liquid Column Gas Damper (TLCGD) is latest version of dampers. It has a unique flexibility of tuning frequency compared to all other dampers. In the present study, jacket platform is modeled as Multi degree of freedom (MDOF) system. At later stage, for simplistic analysis, MDOF system is reduced to SDOF system using static condensation. Performance of TLCGD for both the systems is compared. Airy’s wave theory is used for wave force excitation. Equations of motions for Jacket platform models attached with TLCGD are developed and solved using Newmarks β method in MATLAB. TLCGD is found to be very flexible in tuning the frequency and maximum reductions in response, 21.3% and 23.14% are observed at 0.3 MPa for MDOF and SDOF systems respectively. Work done shows that the results for MDOF and SDOF are comparable and hence, jacket as SDOF can be used for analysis for reducing the complexities.

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.

A method of technical diagnostics for offshore structures

1994 ◽  
Vol 16 (2) ◽  
pp. 43-48
Author(s):  
Do Son
Keyword(s):  
Diagnostic Method ◽  
Joint Venture ◽  
Oil And Gas ◽  
Residual Life ◽  
Life Time ◽  
Offshore Structures ◽  
Technical Diagnostics ◽  
Offshore Platforms ◽  
South Vietnam ◽  
Local Destruction

This paper describes the results of measurements and analysis of the parameters, characterizing technical state of offshore platforms in Vietnam Sea. Based on decreasing in time material characteristics because of corrosion and local destruction assessment on residual life time of platforms is given and variants for its repair are recommended. The results allowed to confirm advantage of proposed technical diagnostic method in comparison with others and have been used for oil and gas platform of Joint Venture "Vietsovpetro" in South Vietnam.

Validating and Updating Finite Element Models Using Experimental Measurements of Dynamics

1990 ◽  
Vol 204 (1) ◽  
pp. 45-50
Author(s):  
C F McCulloch ◽  
P Vanhonacker ◽  
E Dascotte
Keyword(s):  
Finite Element ◽  
Structural Dynamics ◽  
Model Updating ◽  
Measured Data ◽  
Physical Parameters ◽  
Experimental Measurements ◽  
Finite Element Models ◽  
Data Sets ◽  
Modal Data ◽  
Modelling Assumptions

A method is proposed for updating finite element models of structural dynamics using the results of experimental modal analysis, based on the sensitivities to changes in physical parameters. The method avoids many of the problems of incompatibility and inconsistency between the experimental and analytical modal data sets and enables the user to express confidence in measured data and modelling assumptions, allowing flexible but automated model updating.

Multi-State Transient Rotor Vibration Control Using Sampled Harmonics

2002 ◽  
Vol 124 (2) ◽  
pp. 186-197 ◽  
Author(s):  
P. S. Keogh ◽  
M. O. T. Cole ◽  
C. R. Burrows
Keyword(s):  
Magnetic Bearing ◽  
Measured Data ◽  
Rapid Decrease ◽  
Flexible Rotor ◽  
Rotor Vibration ◽  
Transient Vibration ◽  
Stability Boundaries ◽  
Vibration Attenuation ◽  
Harmonic Components ◽  
Bearing System

A technique is introduced to achieve transient vibration attenuation in a multi-input, multi-output flexible rotor/magnetic bearing system. The strategy employs feedback control of measured harmonic components of rotor vibration. Whereas previous harmonic controllers have been based only on steady state vibration characteristics, the new controller also incorporates the transient dynamics. The controller may still be designed from measured data and is determined from target transient vibrational responses arising from step changes in particular disturbances. Account is taken of delays arising from evaluation of harmonic components. Furthermore, stability boundaries for the controller are shown to have significant tolerance to measurement error. The controller is validated experimentally in a flexible rotor/magnetic bearing system and mass loss tests are used to demonstrate rapid decrease in vibration levels with near elimination of transient overshoot.

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.

scholarly journals Icebergs: Their Physical Dimensions and the Presentation and Application of Measured Data

1983 ◽  
Vol 4 ◽  
pp. 116-123 ◽  
Author(s):  
I. Stuart Hotzel ◽  
John D. Miller
Keyword(s):  
Engineering Design ◽  
East Coast ◽  
Offshore Structures ◽  
Measured Data ◽  
Hydrocarbon Exploration ◽  
Morphometric Data ◽  
Grand Banks ◽  
Functional Relationships ◽  
Linear Dimensions ◽  
Physical Dimensions

A knowledge of the dimensional characteristics of icebergs off the east coast of Canada is required for both scientific and engineering purposes. To fulfil this need, hydrocarbon exploration in the region has been supported by a program aimed at collecting morphometric data on icebergs, in addition to providing operational support for activities such as ice-berg towing, this program has yielded information which will be useful for the engineering design of offshore structures. Functional relationships between the dimensions of icebergs are presented and ratios between the linear dimensions are examined. These ratios are used to calculate preliminary values for draft and mass on the Grand Banks and are demonstrated to give reasonable values for draft of icebergs off Greenland.

Model Simplification for Offshore Platforms Using Model Refinement Scheme

2013 ◽  
Vol 284-287 ◽  
pp. 1436-1440 ◽  
Author(s):  
Min Zhang ◽  
Shu Qing Wang ◽  
Jia Li Fu ◽  
Xiao Long Xu
Keyword(s):  
Experimental Model ◽  
Degrees Of Freedom ◽  
Oil And Gas ◽  
Model Updating ◽  
Experimental Models ◽  
Offshore Platforms ◽  
Model Refinement ◽  
Jacket Platform ◽  
Cross Model ◽  
Offshore Oil And Gas

Offshore jacket platforms have been widely used in offshore oil and gas exploitation under hostile ocean environments. Finite element models of such structures need to have many degrees of freedom (DOFs) to represent the geometrical detail of complex structures, which leads to more computing power when performing the analysis and what’s more, the incompatibility in the number of degrees of freedom to the experimental models. Therefore, there is a need to simplify the analytical model by reducing the DOFs and in the process, making the essential eigen-properties agree with those of the experimental model is desired. In this paper, a scaled physical experimental model of an offshore jacket platform is simplified using the recently developed model refinement scheme. Mathematically, the procedure to implement the model refinement technique is an application of cross-model cross-mode (CMCM) method for model updating. The master degrees of freedom are chosen according to the placement of accelerometers in the experiment. Upon the completion of the refinement, the improved reduced jacket platform model matches the dynamic characteristics of the experimental model quite well.

Water Deluge System Design for Fire Fighting

2016 ◽  
Author(s):  
Jin Lee ◽  
Sang Hwan Kim ◽  
Jung Kwan Seo ◽  
Jeom Kee Paik
Keyword(s):  
Fluid Dynamic ◽  
Design Procedure ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Probabilistic Sampling ◽  
Spray System ◽  
Safety Design ◽  
Fire Scenarios ◽  
Fire And Explosion ◽  
The Cost

The ships and offshore structures are exposed to inherently the risk of fire and explosion. These fire and explosion, accident caused by grave consequences not only to the ships and offshore platforms on the sea but the environment all mankind. The aim of this paper is to focus on an optimization of water deluge and mist spray system locations subjected to jet on the ships and offshore platforms. A trustworthy set of fire scenarios is identified and classified using probabilistic sampling methods calling for Latin Hyper Sampling. These events of fire are numerically calculated for selected scenarios by the computational Fluid Dynamic (CFD) code using a KFX. The Water Deluge Location Index (WLI) is then calculated by using the frequency and consequence of fire scenarios. And then, WLI are utilized to prioritize the optimal locations of water deluge and mist spray systems. The recommended methodology believes that can increase to certainties in the design procedure of unreliability and can regard the cost-effectiveness of safety design.

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