Deterministic-Spectral Fatigue Analysis of a Typical Jacket Platform (SPD1) Using Directional Wave Spectrum

2007 ◽  
Author(s):  
M. Azimirad ◽  
A. R. M. Gharabaghi ◽  
M. R. Chenaghlou
Keyword(s):  
Fatigue Life ◽  
Shallow Water ◽  
Spectral Method ◽  
Frequency Spectrum ◽  
Persian Gulf ◽  
Wave Spectrum ◽  
Fatigue Analysis ◽  
Sea Waves ◽  
Directional Wave ◽  
Random Nature

Fixed offshore platforms or Jacket type platforms are the most common offshore structures used for oil & gas Exploration & Production industry in Persian Gulf, because water depth is such that the shallow water condition is dominant. Sea waves as dominant environmental loading are cyclic and have random nature. The applied cyclic sea wave forces will lead to fatigue damages in jacket’s joints. There are different methods to investigate the fatigue life of jackets such as deterministic method, simplified method, spectral method and transient method. Spectral method is a suitable method, which can consider the random nature of sea waves in fatigue analysis. Deterministic-spectral method developed by Bishop et al. is used to estimate the fatigue life of shallow water jacket platforms. However, in this method the frequency spectrum of waves is used in the analysis, but generally sea waves are propagating in different directions with different frequencies, so directional wave spectrum can consider wave randomness more properly. In this paper, frequency domain spectral method using Deterministic-Spectral approach has been used to estimate the fatigue life of a typical jacket platform (SPD1 at South Pars Field - Persian Gulf). Base wave cases were chosen from joint histogram of height & period that is calculated based on scatter diagrams of South Pars Field. First the jacket was modeled by ANSYS software, then by applying base wave cases to it and analyzing the critical TT joint under internal cyclic forces, hot spot stress transfer functions at 8 nodes around the intersection of joint were obtained. Using JONSWAP standard spectrum and the spreading function proposed by Goda, sea state’s Power Spectral Densities (PSD) and directional spectrums are multiplied to obtain stress spectra. The fatigue damage and fatigue life then are calculated. Results indicate that the fatigue life based on frequency spectrum is less than the fatigue life based on directional spectrum.

Spectral Fatigue Analysis of Shallow Water Jacket Platforms

1996 ◽  
Vol 118 (3) ◽  
pp. 190-197 ◽  
Author(s):  
N. W. M. Bishop ◽  
Q. Feng ◽  
P. Schofield ◽  
M. G. Kirkwood ◽  
T. Turner
Keyword(s):  
Fatigue Life ◽  
Shallow Water ◽  
Spectral Method ◽  
Transfer Functions ◽  
Time History ◽  
Sea Surface ◽  
Wave Loading ◽  
Time Step ◽  
Design Work ◽  
New Approach

The spectral analysis approach is a very elegant and computationally efficient method of analyzing the fatigue life of offshore jacket platforms. The primary limitation of the approach is that it assumes linearity of both the structural system and the wave-loading mechanism. The approach is now widely used for the analysis of deepwater, dynamically responsive platforms where nonlinearities are usually not serious. There are also advantages associated with using the approach for shallow water platforms although nonlinearities then become significant, particularly the wave-loading mechanism. Various methods have been proposed to enable the spectral method to be used for some nonlinear situations, including a new approach which uses the Longuet-Higgins wave height-period joint probability density function in order to obtain a better linearization technique. This linearization process is associated with the particular wave heights chosen for producing the transfer functions. The new approach provides a better method for choosing the appropriate height of each so-called base wave case. In order to verify the new approach, a time series analysis, including wave-loading nonlinearities, has been adopted to obtain a reference fatigue life. The sea surface elevation spectrum has been decomposed into a set of equivalent harmonic components. The water particle velocities and accelerations were then individually evaluated and the appropriate (Morison’s) wave loading was computed for each time step in the sea surface time history. The structural stress response time history was then calculated, from which a fatigue life estimate was obtained. This paper presents the results obtained using this new approach, as well as comparative results obtained using the deterministic, spectral, and time domain approaches applied with a representative sea state. The results show that the deterministic-spectral method has a considerable amount of potential, especially for new design work where weight savings and/or increased confidence levels may be achieved.

DIRECTIONAL WAVE SPECTRUM IN SHALLOW WATER WAVES USING AN ARRAY OF PIXEL BRIGTHNESS ON VIDEO IMAGES

2011 ◽  
pp. 433-441
Author(s):  
MUHAMMAD ZIKRA ◽  
NORIAKI HASHIMOTO ◽  
MASAKI YOKOTA ◽  
MASARU YAMASHIRO ◽  
KOJIRO SUZUKI
Keyword(s):  
Shallow Water ◽  
Water Waves ◽  
Wave Spectrum ◽  
Shallow Water Waves ◽  
Directional Wave Spectrum ◽  
Video Images ◽  
Directional Wave

Hybrid Fatigue Analysis Method for Railway Carbody Structure

2008 ◽  
Vol 44-46 ◽  
pp. 733-738 ◽  
Author(s):  
Bing Rong Miao ◽  
Wei Hua Zhang ◽  
Shou Ne Xiao ◽  
Ding Chang Jin ◽  
Yong Xiang Zhao
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Hybrid Method ◽  
Dynamic Stress ◽  
Stress Test ◽  
Fatigue Analysis ◽  
Railway Vehicle ◽  
Analysis Method ◽  
Structure Dynamic ◽  
Multi Body

Railway vehicle structure fatigue life consumption monitoring can be used to determine fatigue damage by directly or indirectly monitoring the loads placed on critical vehicle components susceptible to failure from fatigue damage. The sample locomotive carbody structure was used for this study. Firstly, the hybrid fatigue analysis method was used with Multi-Body System (MBS) simulation and Finite Element Method (FEM) for evaluating the carbody structure dynamic stress histories. Secondly, the standard fatigue time domain method was used in fatigue analysis software FE-FATIGUE and MATLAB WAFO (Wave Analysis for Fatigue and Oceanography) tools. And carbody structure fatigue life and fatigue damage were predicted. Finally, and carbody structure dynamic stress experimental data was taken from this locomotive running between Kunming-Weishe for this analysis. The data was used to validate the simulation results based on hybrid method. The analysis results show that the hybrid method prediction error is approximately 30.7%. It also illustrates that the fatigue life and durability of the locomotive can be predicted with this hybrid method. The results of this study can be modified to be representative of the railway vehicle dynamic stress test.

Fatigue Life Prediction of Drill-String Subjected to Random Loadings

2014 ◽  
Author(s):  
Jiahao Zheng ◽  
Hongyuan Qiu ◽  
Jianming Yang ◽  
Stephen Butt
Keyword(s):  
Fatigue Life ◽  
Time History ◽  
Beam Theory ◽  
Drill String ◽  
Finite Element Models ◽  
Bernoulli Beam ◽  
Stress Cycles ◽  
Rainflow Counting ◽  
Euler Bernoulli Beam ◽  
Random Nature

Based on linear damage accumulation law, this paper investigates the fatigue problem of drill-strings in time domain. Rainflow algorithms are developed to count the stress cycles. The stress within the drill-string is calculated with finite element models which is developed using Euler-Bernoulli beam theory. Both deterministic and random excitations to the drill-string system are taken into account. With this model, the stress time history in random nature at any location of the drill-string can be obtained by solving the random dynamic model of the drill-string. Then the random time history is analyzed using rainflow counting method. The fatigue life of the drill-string under both deterministic and random excitations can therefore be predicted.

scholarly journals Fatigue life prediction of upper arm suspension using strain life approach

2019 ◽  
Vol 17 (1) ◽  
pp. 25-40 ◽  
Author(s):  
Hafida Kahoul ◽  
Samira Belhour ◽  
Ahmed Bellaouar ◽  
Jean Paul Dron
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Fatigue Life ◽  
Aluminium Alloys ◽  
Fatigue Analysis ◽  
Vertical Force ◽  
Upper Arm ◽  
Element Analysis ◽  
Content Type ◽  
Critical Location

Purpose This paper aims to present the fatigue life behaviour of upper arm suspension. The main objectives are to predict the fatigue life of the component and to identify the critical location. In this analysis, three aluminium alloys were used for the suspension, and their fatigue life was compared to select the suitable material for the suspension arm. Design/methodology/approach CAD model was prepared using Solid Works software, and finite element analysis was done using ANSYS 14.0 software by importing the Parasolid file to ANSYS. The model is subjected to loading and boundary conditions; the authors consider a vertical force with constant amplitude applied at the bushing that connected to the tire, the others two bushing that connected to the body of the car are constraint. Tetrahedral elements given enhanced results as compared to other types of elements; therefore, the elements (TET 10) are used. The maximum principal stress was considered in the linear static analysis, and fatigue analysis was done using strain life approach. Findings Life and damage are evaluated and the critical location was considered at node 63,754. From the fatigue analysis, aluminium alloys 7175-T73 (Al 90%-Zn 5.6%-Mg 2.5% -… …) and 2014-T6 (Al 93.5%-Cu 4.4%-Mg 0.5%… …) present a similar behaviour as compared to 6061-T6 (Al 97.9%-Mg 1.0%-Si 0.6%… … .); in this case of study, these lather are considered to be the materials of choice to manufacture the suspension arms; but 7175-T73 aluminium alloys remain the material with a better resistance to fatigue. Originality/value By the finite element analysis method and assistance of ANSYS software, it is able to analyse the different car components from varied aspects such as fatigue, and consequently save time and cost. For further research, the experimental works under controlled laboratory conditions should be done to determine the validation of the result from the software analysis.

A Method for Fatigue Analysis of Pipelines on Topsides of FPSO Systems

2005 ◽  
Author(s):  
Pol Spanos ◽  
Alba Sofi ◽  
Juan Wang ◽  
Berry Peng
Keyword(s):  
Fatigue Life ◽  
Random Vibration ◽  
Equations Of Motion ◽  
Plug Flow ◽  
Fatigue Curve ◽  
Sea Waves ◽  
Random Loading ◽  
Euler Beam ◽  
Stress Spectrum ◽  
The Galerkin Method

Pipelines located on the decks of FPSO systems are exposed to damage due to sea waves induced random loading. In this context, a methodology for estimating the fatigue life of conveying-fluid pipelines is presented. The pipeline is subjected to a random support motion which simulates the effect of the FPSO heaving. The equation of motion of the fluid-carrying pipeline is derived by assuming small amplitude displacements, modeling the empty pipeline as a Bernoulli-Euler beam, and adopting the so-called “plug-flow” approximation for the fluid (Pai¨doussis, 1998). Random vibration analysis is carried out by the Galerkin method selecting as basis functions the natural modes of a beam with the same boundary conditions as the pipeline. The discretized equations of motion are used in conjunction with linear random vibration theory to compute the stress spectrum for a generic section of the pipeline. For this purpose, the power spectrum of the acceleration at the deck level is determined by using the Response Amplitude Operator of the FPSO hull. Finally, the computed stress spectrum is used to estimate the pipeline fatigue life employing an appropriate S-N fatigue curve of the material. An illustrative example concerning a pipeline simply-supported at both ends is included in the paper.

Sign in / Sign up

Export Citation Format

Share Document