Extreme Response And Fatigue Damage In A Deepwater Platform Exposed To Nonlinear Wave Loading

1986 ◽  
Author(s):  
K. Syvertsen ◽  
K.A. Farnes ◽  
D.N. Karunakaran ◽  
T. Overvik
Keyword(s):  
Fatigue Damage ◽  
Nonlinear Wave ◽  
Wave Loading ◽  
Extreme Response

Research on Ship Structural Fatigue Damage Under Nonlinear Wave Bending Moment

2017 ◽  
Author(s):  
Jingxia Yue ◽  
Lihua Peng ◽  
Wengang Mao ◽  
Chi Zhang ◽  
Wei Dong ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
Frequency Response ◽  
Fatigue Damage ◽  
Nonlinear Wave ◽  
Model Test ◽  
Bending Moment ◽  
Irregular Waves ◽  
Wave Loading ◽  
Ship Structures ◽  
Structural Fatigue

Loads acting on ship structures are complex and randomly over time and the nonlinear effect caused by wave loading is one of the research focus. The linear and nonlinear vertical wave bending moment (VBM) in different speeds and sea states and their effects on ship structural fatigue strength were investigated for a flat container with high ratio of width to depth. The VBM under the linear regular waves and irregular waves were calculated based on the three dimension (3D) potential theory. The considered nonlinear wave loading was caused by sea pressure near the mean free surface as well as the geometric nonlinearity. Hydrodynamic calculations in regular wave were presented to figure out the frequency response function (FRF) of VBM in the mid-ship section. Irregular waves were verified to obtain the VBM history in 4 sea states. What’s more, VBMs from a segmented elastic model test were obtained to investigate the influence of nonlinearity. On the basis of the wave loadings obtained from simulation and test, the hotspot stress histories under irregular waves were deduced in time domain by using the beam theory. Fatigue cumulative damage per hour under several random sea states were obtained on the basis of the rain-flow counting and S-N curve. Based on the fatigue damage from the numerical analysis and model test, it is believed that speeds and significant wave height have a positive correlation with the fatigue damage of ship structures. A good agreement was obtained between the numerical analysis values and the low frequency part of the test and the nonlinear analysis in the simulation could offer reasonable prediction for the fatigue damage caused by the wave frequency response. Also shown as the test result, fully nonlinearities have a great contribution to the fatigue damage.

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.

Probabilistic Models Applicable to the Short-Term Extreme Response Analysis of Jack-Up Platforms

2003 ◽  
Vol 125 (4) ◽  
pp. 249-263 ◽  
Author(s):  
M. J. Cassidy ◽  
G. T. Houlsby ◽  
R. Eatock Taylor
Keyword(s):  
Probabilistic Models ◽  
Probability Distributions ◽  
Response Analysis ◽  
Wave Loading ◽  
Physical Processes ◽  
Short Term ◽  
Analysis Techniques ◽  
Extreme Response ◽  
Increasing Demand ◽  
Jack Up

There is a steadily increasing demand for the use of jack-up units in deeper water and harsher conditions. Confidence in their use in these environments requires jack-up analysis techniques to reflect accurately the physical processes occurring. However, nearly all analyses are deterministic in nature and do not account for the inherent variability in governing parameters and models. In this paper, probabilistic models are used to develop an understanding of the response behavior of jack-ups, with particular emphasis placed on the extreme deck displacement due to a short-term event. Variables within the structural, foundation and wave loading models are assigned probability distributions and their influence on the response statistics is quantified using a response surface methodology.

The Influence of Alternative Wave Loading and Support Modeling Assumptions on Jack-Up Rig Response Extremes

1996 ◽  
Vol 118 (2) ◽  
pp. 109-114 ◽  
Author(s):  
L. Manuel ◽  
C. A. Cornell
Keyword(s):  
Nonlinear Models ◽  
Random Wave ◽  
Force Model ◽  
Wave Loading ◽  
Force Modeling ◽  
Hydrodynamic Damping ◽  
Extreme Response ◽  
The Absolute ◽  
Non Gaussian ◽  
Jack Up

A study is conducted of the response of a jack-up rig to random wave loading. Steady current and wind load effects are also included. The effects of varying the relative motion assumption (in the Morison equation) and of varying the bottom fixity assumptions are investigated. One “fixity” model employs nonlinear soil springs. Time domain simulations are performed using linearized as well as fully nonlinear models for the jack-up rig. Comparisons of response statistics are made for two seastates. Hydrodynamic damping causes the rms response to be lower in the relative Morison case. The absence of this source of damping in the absolute Morison force model gives rise to larger resonance/dynamic effects—this tends to “Gaussianize” the response. Hence, the relative Morison model leads to stronger non-Gaussian behavior than the absolute Morison model. This is reflected in moments as well as extremes. The different support conditions studied are seen to significantly influence extreme response estimates. In general, stiffer models predict smaller rms response estimates, but also exhibit stronger non-Gaussian behavior. The choice of the Morison force modeling assumption (i.e., the relative versus the absolute motion formulation) is seen to have at least a secondary role in influencing response moments and extremes.

An Assessment of Response-Surfaces for Estimation of Fatigue Damage and Extreme Response Due to Environmental Loads

2003 ◽  
Author(s):  
Bernt J. Leira ◽  
Tore Holma˚s ◽  
Kjell Herfjord
Keyword(s):  
Fatigue Damage ◽  
Environmental Parameters ◽  
Response Surfaces ◽  
Specific Response ◽  
Statistical Distributions ◽  
Marine Structures ◽  
Environmental Loads ◽  
Response Characteristics ◽  
Polynomial Coefficients ◽  
Extreme Response

For marine structures subjected to environmental loads (i.e. waves, current, wind), the fatigue damage and long-term response characteristics can frequenlty expressed in terms of the environmental parameters by polynomial response surfaces. For both types of “response”, an integration across the range of variation for all the environmental parameters is required. The location of the intervals which give rise to the dominant contribution to these integrals is studied. Convergence studies are performed by applying response surfaces of increasing order, from linear to cubic expressions. In addition, response surfaces with lower cut-off limits at specific values for the environmental parameters are also investigated. Having obtained general expressions on non-dimensional form, various examples which correspond to specific response quantities for marine structures are considered. Typical values for the polynomial coefficients, and for the statistical distributions representing the environmental parameters, are applied. Convergence studies are subsequently performed for the particular example response quantities which are considered in order to make comparison with the general formulation. For the extreme response, the application of “extreme contours” obtained from the statistical distributions of the environmental parameters in combination with the response surface is explored.

The Effect of Whipping/Springing on Fatigue Damage and Extreme Response of Ship Structures

2010 ◽  
Author(s):  
Wengang Mao ◽  
Jonas W. Ringsberg ◽  
Igor Rychlik
Keyword(s):  
Fatigue Damage ◽  
North Atlantic Ocean ◽  
Gaussian Model ◽  
Container Ship ◽  
Level Crossing ◽  
Ship Structures ◽  
High Frequency Response ◽  
The North ◽  
Extreme Response ◽  
Wave Induced

Wave-induced vibrations, also known as whipping and springing, are defined as the high frequency response of ship structures. In this paper, the fatigue damage caused by whipping and springing is presented by investigating the amidships section of a 2800 TEU container ship that operates in the North Atlantic Ocean. A simplified fatigue model, originally from the generalized narrow-band approximation for Gaussian load, is employed to include the damage contribution from wave-induced vibrations. In this model, the significant response range hs and the mean stress up-crossing frequency fz are simplified using only the wave-induced loading and encountered wave frequency, respectively. The capacity and accuracy of the model is illustrated by application on the measurements of the 2800 TEU container ship for different voyages during 2008. The whipping-induced contribution to the extreme response is investigated by means of the level crossing approach. It shows that the level crossing model for Gaussian load cannot be used for the prediction of extreme responses, such as the 100-year stress, based on a half-year full-scale measurement. It is found that a more complicated non-Gaussian model is required to consider the contribution from whipping.

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