scholarly journals Representative Environmental Condition for Fatigue Analysis of Offshore Jacket Substructure

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5494
Author(s):  
Tsung-Yueh Lin ◽  
Yi-Qing Zhao ◽  
Hsin-Haou Huang
Keyword(s):  
Fatigue Damage ◽  
Environmental Conditions ◽  
Element Model ◽  
Computational Time ◽  
Wave Load ◽  
Sea State ◽  
Stress Signals ◽  
Cumulative Fatigue Damage ◽  
The Taiwan Strait

The 20-year cumulative fatigue damage of an offshore jacket substructure was estimated under the long-term local environmental conditions in the Taiwan Strait. Because of the nonlinearity of wave load for slender members of the structure, time-domain simulations of the dynamic finite element model were conducted for each sea state. By utilizing the Dirlik method to process the stress signals, the fatigue damages of joints were computed. Concerning the computational time, we propose a probability-based method of using a representative combination of environmental conditions in this study, which can considerably reduce the required number of evaluations prior to determining fatigue damage, thereby improving the process of preliminary design. The results show that only three sea states among 120 can represent 28% of the average damage ratio, and up to 17 sea states fully resolved the fatigue life.

Comparative Study on Fatigue Damage Assessment of a Structure Member in a Bulk Carrier Using Various Environmental Conditions

2019 ◽  
Author(s):  
Fredhi Agung Prasetyo ◽  
Naoki Osawa ◽  
Mohammad Arif Kurniawan ◽  
Siti Komariyah
Keyword(s):  
Fatigue Damage ◽  
Environmental Conditions ◽  
Damage Assessment ◽  
North Atlantic Ocean ◽  
Environmental Condition ◽  
Scatter Diagram ◽  
Sea State ◽  
Fatigue Design ◽  
Design Life

Abstract Specific design life could be identified by using fatigue damage assessment in the structure engineering field as well as in the maritime sector. Fatigue assessment is one of the assessments to be conducted during review of ship structure design. Fatigue assessment of ship structural member is mainly conducted based on specific environmental condition. In general, specific environmental condition, which is provided by Classification Society rules, is a long term sea-state data of North Atlantic Ocean. The wave scatter diagram presents the tabulation of a long term data of sea state history in the specific ocean. Therefore, a realistic encounter of wave scatter diagram is essential to simulate the variation of wave loadings applied on the ship structure in determination of fatigue design life. Since the application of North Atlantic ocean environmental condition is commonly used by major Classification societies, this condition might give the substantial deterioration on the fatigue design life of the ship that specially operate only in specific ocean area, i.e. South East Asia area. In this work, the wave scatter diagram of various environmental conditions is chosen and the statistical characteristic is compared. The wave load sequence that is used on the fatigue damage assessment are generated by using the concept of storm model, so that the changing nature of sea state could be emulated as in real ocean. Fatigue damage of a structure member of 220 meter Bulk Carriers is calculated based on various environmental conditions.

Analysis of the Fatigue Damage on the Offshore Wind Turbines Exposed to Wind and Wave Loads Within the Typhoon Area

2004 ◽  
Author(s):  
Atsushi Yamashita ◽  
Kinji Sekita
Keyword(s):  
Fatigue Damage ◽  
Wind Turbines ◽  
Offshore Wind ◽  
Wave Loads ◽  
Wave Load ◽  
Offshore Wind Turbines ◽  
Simple Addition ◽  
Recorded Data ◽  
Term Data

For the design of offshore wind turbines exposed to wind and wave loads, the method of combining the wind load and the wave load is significantly important to properly calculate the maximum stresses and deflections of the towers and the foundations1). Similarly, for the analysis of the fatigue damage critical to the structural life, the influences of combined wind and wave loads have not been clearly verified. In this paper fatigue damage at the time of typhoon passing is analyzed using actually recorded data, though intrinsically long-term data more than 10years should be used to properly evaluate the fatigue damage. This paper concludes that the fatigue damage of the tower caused by the wave load is not substantial and, thus, the fatigue damage by the combined wind and wave load is only 2–3% larger than the simple addition of the independent fatigue damages by the wind and the wave loads. The fatigue damage of the tower top, which is required to reduce the diameter in order to minimize the aerodynamic confliction with blades, is larger than that of the tower bottom. The fatigue damage at the foundation by the combined wind and wave load is 25% larger than the simple addition of the wind and wave damages, as the foundation is directly exposed to the wave load. For the foundation, the proper structural section can be designed in order to improve the structural performance against fatigue.

Closed-Form Spectral Fatigue Analysis for Compliant Offshore Structures

1988 ◽  
Vol 32 (04) ◽  
pp. 297-304
Author(s):  
Y. N. Chen ◽  
S. A. Mavrakis
Keyword(s):  
Closed Form ◽  
Fatigue Damage ◽  
Computational Cost ◽  
Power Spectra ◽  
Offshore Structures ◽  
Fatigue Analysis ◽  
Cumulative Fatigue Damage ◽  
High Computational Cost

Spectral fatigue analysis frequently has been applied to welded joints in steel offshore structures. Although, on the theoretical basis, the spectral formulation holds certain advantages over other formulations such as the discrete, design wave type of analysis, numerical methods developed on that basis generally suffer from the shortcomings of lack of precision and high computational cost. This paper synthesizes the uncertainties resulting from modeling errors that are regarded heretofore as unavoidable in an analysis. Such errors are traced to the approximations introduced in handling of wave data, in numerical integration of the response power spectra, and in the integration that leads to the determination of cumulative fatigue damage. To each of these sources of modeling error, a transparent, closed-form method is proposed which not only eliminates the potential errors but, surprisingly, improves the computational efficiency many times. The sensitivity of fatigue damage upon the variability of the shape parameter due to variability of wave environment for the so-called simplified analysis utilizing an idealized mathematical long-term probability density function (for example, the Weibull distribution) is also discussed.

A Fatigue Design for Large Container Ship Taking Long-Term Environmental Condition Into Account

2011 ◽  
Author(s):  
Masayoshi Oka ◽  
Yoshitaka Ogawa ◽  
Ken Takagi
Keyword(s):  
Fatigue Damage ◽  
Element Model ◽  
Full Scale ◽  
Elastic Model ◽  
Direct Computation ◽  
Wave Condition ◽  
Irregular Wave ◽  
Fatigue Design ◽  
Tank Test

In order to promote the reliable evaluation for the fatigue strength of ships, the validation of a direct load and strength computation was performed based on the tank test and the full scale measurement. The fatigue damage in short term sea state under various operation parameters was indicated quantitatively by the tank test in irregular wave utilizing the elastic model. The long term fatigue damage was evaluated based on the full scale measurement [1]. The fatigue damage inferred from the measured stress on deck structure is quite small compared with the direct computation utilizing a full ship finite element model. That is mainly caused by the difference of environmental wave condition. Moreover, the effect of operational condition through whole life was indicated by the direct computation quantitatively. To make more rational fatigue design, it is important to take the long-term wave condition into account.

Wave and Current Induced Cumulative Fatigue Damage Assessment for Offshore Pipeline on Free-Span

2008 ◽  
Author(s):  
Ali Valipour ◽  
Mehrdad Zoroufi ◽  
Abbas Yeganeh Bakhtiary ◽  
Reza Valipour
Keyword(s):  
Fatigue Damage ◽  
Element Model ◽  
Major Influence ◽  
Spectral Amplitude ◽  
Linear Wave ◽  
Offshore Pipelines ◽  
Drag Forces ◽  
Waves And Currents ◽  
Cumulative Fatigue Damage ◽  
Wave Induced

Suspending pipelines between two points over an uneven seafloor is called free-spanning which induces more vortices behind the pipe especially when the pipelines are exposed to the hydrodynamic effects of waves and currents. These influences cause a significant increase in the dynamic acting drag forces. In fact, the oscillatory acting drag forces, as a result of changes in the net pressure and velocity filed around the pipeline, increase the probability of fatigue damage. Since the fatigue life of offshore pipelines has a major influence on the useful life of a project, studying it for offshore pipelines laid on uneven sea beds has become very important. Both the consequence of vortex shedding as a result of wave and current interaction with the pipeline, and the selected suitable approach in assessing fatigue damage has made the design process sophisticated. In the present study, it is attempted to employ a proper finite element model with the capability of coupling the dynamic drag forces induced by wave and current conditions with estimating cumulative fatigue damage methods. The wave profile is simulated using Non-deterministic Spectral Amplitude in Gaussian sea state and using linear wave formulation to calculate wave -induced forces. Moreover, the current force is estimated by using the conventional Morison Equation as well as employing a new approach of estimating current -induced dynamic drag forces obtained by a numerical model that includes the VIV effects. Finally cumulative fatigue damage as a result of acting those forces is investigated for various conditions of laying pipeline on the seabed.

S-N Curve Model for Assessing Cumulative Fatigue Damage of Deep-Water Composite Riser

2020 ◽  
Author(s):  
Manander Singh ◽  
Suhail Ahmad ◽  
A. K. Jain
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Deep Water ◽  
Deterministic Model ◽  
Flexural Stress ◽  
Stress History ◽  
Bending Stresses ◽  
Stress Signals ◽  
Cumulative Fatigue Damage ◽  
Related Stress

Abstract Random stress produces fatigue damage due to fluctuation in the presence of high bending stresses gets enhanced and leads to the primary failure of the production composite riser. The main problems with the fatigue deterministic model are related to the fact that not all waves have the same period. The second problem is due to the assumption that all waves are regular and do not into account the stochastic nature of the marine environment. The wave data is provided on a statistical basis. Work attributed to damage related stress distribution and interaction of composite along with integral difficulties in fatigue is challenging task. Resulting flexural stress history is random in nature. The purpose of this study is to present a methodology for assessing cumulative fatigue damage using MATLAB of the deep-water composite riser. The simulation of 12 random sea states is examined for the purpose of estimation of accumulated damage. Using the recommended method by DNV-OS-C501, fatigue life of composite riser is determined for different conditions. Damage induced by stress signals of varying amplitudes is calculated using Palmgren-Miner’s rule. Total fatigue life for stress history is estimated by the summation of damage fractions. Estimation of fatigue damage over riser’s entire service life is done taking into consideration the entire expected sea area. Extreme flexural stress random fluctuations are estimated with and without currents.

scholarly journals Fatigue Analysis of Deepwater Hybrid Mooring Line Under Corrosion Effect

2014 ◽  
Vol 21 (3) ◽  
pp. 68-76 ◽  
Author(s):  
Dongsheng Qiao ◽  
Jun Yan ◽  
Jinping Ou
Keyword(s):  
Fatigue Damage ◽  
Oil And Gas ◽  
Line Tension ◽  
Chain Structure ◽  
Mooring Line ◽  
Mooring System ◽  
Load Spectrum ◽  
Sea State ◽  
Mooring Lines

Abstract In the deepwater exploitation of oil and gas, replacing the polyester rope by a wire in the chain-wire-chain mooring line is proved to be fairly economic, but this may provoke some corresponding problems. Te aim of this paper is to compare the fatigue damage of two mooring system types, taking into account corrosion effects. Using a semi-submersible platform as the research object, two types of mooring systems of the similar static restoring stiffness were employed. Te mooring lines had the chain-wire-chain and chain-polyester-chain structure, respectively. Firstly, the numerical simulation model between the semi-submersible platform and its mooring system was built. Te time series of mooring line tension generated by each short-term sea state of South China Sea S4 area were calculated. Secondly, the rain flow counting method was employed to obtain the fatigue load spectrum. Thirdly, the Miner linear cumulative law model was used to compare the fatigue damage of the two mooring system types in long-term sea state. Finally, the corrosion effects from zero to twenty years were considered, and the comparison between the fatigue damage of the two mooring system types was recalculated.

How to Account for Short-Term and Long-Term Variability in the Prediction of the 100 Years Response?

2017 ◽  
Author(s):  
Quentin Derbanne ◽  
Guillaume de Hauteclocque ◽  
Martin Dumont
Keyword(s):  
Return Period ◽  
Environmental Conditions ◽  
Gumbel Distribution ◽  
Accurate Method ◽  
Design Methods ◽  
Short Term ◽  
Sea State ◽  
Reliability Method ◽  
Unit Design

Current practices in offshore unit design are based on the prediction of the 100 years response (tension, offset, stress...). The methodologies described in various standards (ISO, API...) are all very similar: several design environments are described with a combination of sea state, wind and current. Usually envelope contours are used, describing a set of environmental conditions corresponding to a 100 years return period. These design conditions are supposed to produce the highest responses. A time domain (or sometimes frequency domain) simulation is done on each of these short-term conditions, and the 3h most probable maximum (MPM) is computed for each. The highest MPM over all the design conditions is taken as the 100 years response. This approach completely neglects the short-term variability of the response. This paper compares several design methods with the exact 100 years response. The exact 100 years response is computed by integrating the conditional short-term distributions with respect to the probability density function of the environmental conditions. The various design methods are all based on a simplification of an Inverse First Order Reliability Method (IFORM) approach, which requires computing one or several design conditions corresponding to one or several return periods, each of these conditions being associated with a given short-term quantile. Computations are done using two datasets. At first realistic line tensions of 7 offshore units are used, based on a large number of simulations with a mooring software. On a second stage a more general parametric model using a Weibull distribution to describe the long-term variability and a Gumbel distribution to describe the short-term distribution of the 3h maximum is used. It is shown that the current methods are unconservative with respect to the exact 100 years response. A more accurate method is proposed, based on a 40 years return period associated with the quantile 90% and a correction factor of 1.04.

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