Study on a magnetorheological elastomer-base device for offshore platform vibration control

2018 ◽  
Vol 30 (2) ◽  
pp. 243-255 ◽  
Author(s):  
Dingxin Leng ◽  
Haiyan Xiao ◽  
Lei Sun ◽  
Guijie Liu ◽  
Xiaojie Wang ◽  
...  
Keyword(s):  
Wave Spectrum ◽  
Offshore Platform ◽  
Random Wave ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Magnetorheological Elastomer ◽  
Control Robustness ◽  
Resonance Control ◽  
Wave Induced ◽  
Strong Control

Wave loading is one of the leading factors contributing to fatigue damage of offshore platforms. Vibrations in marine platforms due to nonlinear hydrodynamic forces can reduce platform productivity, endanger safety, and affect serviceability. This article presents numerical evaluation of a magnetorheological elastomer device for wave-induced vibration reduction of offshore platform. Random wave loadings are estimated by wave spectrum analysis and Morison’s equations. By altering field-induced stiffness of magnetorheological elastomers and non-resonance control strategy, the wave-induced vibration of offshore platform is effectively reduced, and the magnetorheological elastomer device presents strong control robustness under various wave loadings. This work indicates that magnetorheological elastomer-base device may open a new insight for vibration mitigation of ocean structures.

scholarly journals Random wave-driven drag forces on near-bed vegetation in shallow water based on deepwater wind conditions

2019 ◽  
Vol 233 (4) ◽  
pp. 1287-1290
Author(s):  
Dag Myrhaug
Keyword(s):  
Shallow Water ◽  
Drag Force ◽  
Wind Waves ◽  
Wave Spectrum ◽  
Random Wave ◽  
Random Waves ◽  
Coastal Zones ◽  
Drag Forces ◽  
Mean Wind Speed ◽  
Wave Induced

This article provides a simple analytical method for giving estimates of random wave-driven drag forces on near-bed vegetation in shallow water from deepwater wind conditions. Results are exemplified using a Pierson–Moskowitz model wave spectrum for wind waves with the mean wind speed at the 10 m elevation above the sea surface as the parameter. The significant value of the drag force within a sea state of random waves is given, and an example typical for field conditions is presented. This method should serve as a useful tool for assessing random wave-induced drag force on vegetation in coastal zones and estuaries based on input from deepwater wind conditions.

Numerical Evaluation for Dynamic Response of Seabed Under Random Wave Loading

2009 ◽  
Author(s):  
Zhong-Tao Wang ◽  
Mao-Tian Luan ◽  
Shu-Jie Liu
Keyword(s):  
Dynamic Response ◽  
Linear Theory ◽  
Comparative Studies ◽  
Wave Spectrum ◽  
Practical Significance ◽  
Soil Parameters ◽  
Random Wave ◽  
Linear Wave ◽  
Regular Wave ◽  
Wave Loading

The analysis of dynamic response of seabed due to wave loading is of practical significance in design and construction of marine structures and offshore installations. Recently considerable efforts for this problem have been made with growing interest by many researchers and marine engineers, and many representative results have been achieved. It is obvious that wave loading plays a significant role in the evaluation of construction safety and seabed instability. But there are few results of research and engineering design that can consider the feature of wave loading and soil parameters together. The purpose of this paper is to establish a reasonable numerical model to simulate dynamic response of seabed under random wave loading. The dynamic relation between random wave and seabed can also be described through this model. Comparative studies are principally made between the proposed analysis considering actual feature of ocean situation and conventional analysis based on linear theory of regular wave. The effect of randomness of wave loading on the dynamic response of seabed is investigated. The necessity is also discussed about considering the influence of damping energy on propagating wave by porous seabed. In the conventional analyses of seabed dynamics, wave loading is basically treated as a deterministic process and is usually taken into consideration by using linear theory of regular wave. In fact, ocean wave is of intrinsic randomness in both time sequences and spatial distribution. The random nature of both wave and wave-induced loading will subsequently affect dynamic behavior of seabed. In this paper, the analyses which can consider characteristics of randomness of wave loading and dynamic interaction between seabed and random waves, are formulated in a stochastic framework. Integrated numerical analysis model is established by employing wave spectrum of AVERAGE JONSWAP. The comparative studies are conducted among the methods of conventional random analysis, proposed random analysis, and linear regular wave theory. The results show that the amplitudes of dynamic response of seabed subjected to random wave loading are larger than that of regular linear wave loading. Therefore the stochastic feature of wave loading has to be duly taken into account in the analysis for dynamic response of seabed.

Response of a Porous Seabed Under Random Wave Loading

2006 ◽  
Author(s):  
Haijiang Liu ◽  
Dong-S. Jeng
Keyword(s):  
Soil Parameters ◽  
Random Wave ◽  
Wave Loading ◽  
Random Waves ◽  
Regular Waves ◽  
Offshore Pipelines ◽  
Soil Response ◽  
Significant Difference ◽  
Wave Induced ◽  
Soil Responses

The evaluation of the wave-induced soil response is particularly important for many coastal engineering installations such as offshore pipelines, platforms and breakwaters. Most previous investigations have been limited to the linear regular wave loading, even though the real situation is under random waves. In this study, we propose a semi-analytical solution for the random wave-induced pore pressure and effective stresses in marine sediments. Based on the new analytical solutions, different soil responses under the random wave loading are investigated and compared with the corresponding results under the linear regular waves. Numerical examples demonstrate the significant difference on wave-induced seabed response between these two wave loadings due to the irregularity introduced by the random waves. Finally, the influence of several soil parameters on the soil response under random wave loading is also examined.

Extreme Response Prediction for Fixed Offshore Structures by Monte Carlo Time Simulation Technique

2016 ◽  
Author(s):  
M. K. Abu Husain ◽  
N. I. Mohd Zaki ◽  
M. B. Johari ◽  
G. Najafian
Keyword(s):  
Monte Carlo ◽  
Statistical Properties ◽  
Simulation Technique ◽  
Random Wave ◽  
Wave Loading ◽  
Offshore Structure ◽  
Sampling Variability ◽  
Time Simulation ◽  
Wide Range ◽  
Extreme Response

For an offshore structure, wind, wave, current, tide, ice and gravitational forces are all important sources of loading which exhibit a high degree of statistical uncertainty. The capability to predict the probability distribution of the response extreme values during the service life of the structure is essential for safe and economical design of these structures. Many different techniques have been introduced for evaluation of statistical properties of response. In each case, sea-states are characterised by an appropriate water surface elevation spectrum, covering a wide range of frequencies. In reality, the most versatile and reliable technique for predicting the statistical properties of the response of an offshore structure to random wave loading is the time domain simulation technique. To this end, conventional time simulation (CTS) procedure or commonly called Monte Carlo time simulation method is the best known technique for predicting the short-term and long-term statistical properties of the response of an offshore structure to random wave loading due to its capability of accounting for various nonlinearities. However, this technique requires very long simulations in order to reduce the sampling variability to acceptable levels. In this paper, the effect of sampling variability of a Monte Carlo technique is investigated.

Transformation of Random Wave Spectrum on Beaches

1979 ◽  
Vol 105 (4) ◽  
pp. 711-717
Author(s):  
Cheng Y. Yang ◽  
Yun Hai Chen
Keyword(s):  
Wave Spectrum ◽  
Random Wave

Installation of Long Span Boat Landing on Float Over Platforms - A Case Study

2021 ◽  
Author(s):  
Charles John George ◽  
Cibu Varghese ◽  
Faris Ragheb Kamal
Keyword(s):  
Production Process ◽  
Energy Absorption ◽  
Arabian Gulf ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Long Span ◽  
Heavy Lift

Abstract Fixed offshore platforms are normally provided with landing platforms that enable berthing of supply vessels, crew boats etc. These landing platforms or ‘Boat landings’ are energy absorption structures provided on substructures (jackets) of offshore platforms. Their purpose is to facilitate personnel access from vessel to platforms for performing various tasks including manning the platform, its maintenance etc. Vessel also approach the platforms for providing supplies in case of a manned platform and for providing bunkers, spares etc. As such, boat landing is an integral part of offshore platform and its design and installation becomes equally important. They are preferably located at leeward direction as far as practical, to avoid accidental vessel drift into the platform. For smaller standalone offshore platforms installed with Heavy Lift Crane Vessels, boat landing is installed after the jacket is piled to seabed. Since sequence of installation of boat landing is prior to that of Topside, such installations are straightforward and without obstructions from the Topside. For the bigger accommodation, production, process platforms located in super-complex (or standalone) with topsides installed by float over method, boat landings sometimes are in the wide float over barge slots. In such cases, installation of boat landing becomes very critical due to the post installation after the Topside and associated obstructions from the Topside. This is similar or more critical than a boat landing removal / refurbishment activity carried for a brownfield project. This paper explores the challenges and associated steps adopted to execute the safe installation of these critical structures underneath a newly installed Topside. This case study details the installation of ∼300mt boat landings onto recently installed Greenfield platforms in Arabian Gulf using efficient rigging, suiting the EPC Contractors’ crane assets.

scholarly journals Investigating Vapour Cloud Explosion Dynamic Fatality Risk on Offshore Platforms by Using a Grid-Based Framework

Processes ◽  
2020 ◽  
Vol 8 (6) ◽  
pp. 685
Author(s):  
Usama Muhammad Niazi ◽  
Mohammad Shakir Nasif ◽  
Masdi Muhammad ◽  
Faisal Khan
Keyword(s):  
Risk Analysis ◽  
Well Being ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Plant Design ◽  
Maximum Increase ◽  
Fatality Risk ◽  
Dynamic Risk ◽  
Vapour Cloud ◽  
Grid Based

The reliability of petroleum offshore platform systems affects human safety and well-being; hence, it should be considered in plant design and operation in order to determine its effect on human fatality risk. Methane Vapour Cloud Explosions (VCE) in offshore platforms are known to be one of the fatal potential accidents that can be attributed to failure in plant safety systems. Traditional Quantitative Risk Analysis (QRA) lacks in providing microlevel risk assessment studies and are unable to update risk with the passage of time. This study proposes a grid-based dynamic risk analysis framework for analysing the effect of VCEs on the risk of human fatality in an offshore platform. Flame Acceleration Simulator (FLACS), which is a Computational Fluid Dynamics (CFD) software, is used to model VCEs, taking into account different wind and leakage conditions. To estimate the dynamic risk, Bayesian Inference (BI) is utilised using Accident Sequence Precursor (ASP) data. The proposed framework offers the advantage of facilitating microlevel risk analysis by utilising a grid-based approach and providing grid-by-grid risk mapping. Increasing the wind speed (from 3 to 7 m/s) resulted in maximum increase of 21% in risk values. Furthermore, the integration of BI with FLACS in the grid-based framework effectively estimates risk as a function of time and space; the dynamic risk analysis revealed up to 68% increase in human fatality risk recorded from year one to year five.

Dynamic Analysis of an Offshore Platform With Excessive Vibration Under Wave Loading

2003 ◽  
Author(s):  
Chunyan Ji ◽  
Huajun Li ◽  
Shuqing Wang
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Dynamic Characteristics ◽  
Model Experiment ◽  
Offshore Platform ◽  
Normal Operation ◽  
Bohai Bay ◽  
Fe Modeling ◽  
Wave Loading ◽  
Relative Movement

An offshore platform of jacket type in Bohai Bay vibrates excessively under design environmental conditions, which has affected the normal operation of the platform. In order to mitigate the vibration of the platform, it is essential important to explore the cause of the vibration. So the objective of this study is to investigate the cause of the excessive vibration. In this paper, dynamic characteristics of the offshore platform are analyzed by numerical simulation using finite element (FE) modeling. To further verify the numerical results, a model experiment is conducted. Numerical and experimental results demonstrate that there are relative movement and impact between the piles and the jacket, i.e. the piles and the jacket didn’t connect well to an entity. It is this cause that the stiffness of the platform deceases and impact between piles and the jacket legs induce excessive vibration. And also the grouting measure is advised to reduce the vibration of the offshore platform according to the analysis results.

Optimal Vibration Control Strategy for Offshore Platforms Accounting for AMD Constraints

2004 ◽  
Author(s):  
Chunyan Ji ◽  
Qingmin Meng
Keyword(s):  
Control Algorithm ◽  
Feedback Gain ◽  
Offshore Platforms ◽  
Control Force ◽  
Wave Loading ◽  
Offshore Structure ◽  
H2 Control ◽  
Input Control ◽  
The Mathematical Model ◽  
H2 Optimization

In order to control the excessive vibration of offshore platforms under wave excitations, an H2 control algorithm was presented in this paper. In the present study, noise terms for generating filtered wave loading and accounting for model uncertainty are separated. In addition, in H2 optimization problem, AMD’s capacities are considered by setting the limits of AMD stroke and maximum input control force. And the formulations of such algorithm are described. In order to investigate the feasibility and effectiveness of the proposed method, a numerical example applied to an offshore platform is presented in this paper. The numerical results demonstrate that the proposed algorithm is effective in reducing the vibration of offshore structure when there are some uncertainties in building the mathematical model of the structure. In addition, AMD designed by the proposed method can keep its operation by choosing appropriate feedback gain among several gain candidates based on the AMD limits.

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