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.

A Method for Fatigue Analysis of Piping Systems on Topsides of FPSO Structures

2005 ◽  
Vol 128 (2) ◽  
pp. 162-168 ◽  
Author(s):  
P. D. Spanos ◽  
A. Sofi ◽  
J. Wang ◽  
B. Peng
Keyword(s):  
Fatigue Life ◽  
Random Vibration ◽  
Equations Of Motion ◽  
Plug Flow ◽  
Axial Flow ◽  
Fatigue Curve ◽  
Random Loading ◽  
Euler Beam ◽  
Stress Spectrum ◽  
The Galerkin Method

Pipelines located on the decks of FPSO systems are exposed to damage due to sea wave induced random loading. In this context, a methodology for estimating the fatigue life of fluid-conveying pipelines is presented. The pipeline is subjected to a random support motion that simulates the effect of the FPSO heaving. The equation of motion of the 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 (Fluid-Structure Interactions Slender Structures and Axial Flow, Academic Press, San Diego, Vol. 1). 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.

Fatigue life evaluation and failure analysis of light beam direction adjusting mechanism of an automobile headlight exposed to random loading

2017 ◽  
Vol 233 (2) ◽  
pp. 224-231
Author(s):  
Nana Wang ◽  
Jinxiang Liu ◽  
Qing Zhang ◽  
Hailin Yang ◽  
Mu Tang
Keyword(s):  
Fatigue Life ◽  
Failure Analysis ◽  
Light Beam ◽  
Random Vibration ◽  
Real Life ◽  
Bench Test ◽  
Beam Direction ◽  
Random Loading ◽  
Test Analysis ◽  
Road Surface Roughness

Failure of the light beam direction adjusting mechanism (LDAM) of an automotive headlight might occur after hundreds of driving hours, though the strength of components conforms to the requirement specified in the random vibration bench test standard. In order to determine the causes of the failure, fatigue life prediction and failure analysis based on numerical method of the LDAM exposed to random loading both in bench test and field experiment were carried out. In the bench test analysis, the Dirlik method was utilized to calculate the lifetime by taking the power spectrum density in the frequency domain. In the fatigue analysis for the field experimental loading, to consider the effect of nonuniform temperature distribution, a numerical process in time domain is developed to calculate the lifetime of the LDAM subjected to the random vibration caused by road surface roughness. As a result, the predicted life and failure locations are in good agreement with real life and actual failure regions, respectively.

scholarly journals Fatigue life estimation under multi-axial random loading in light poles

2015 ◽  
Vol 37 ◽  
pp. 183
Author(s):  
Kazem Reza Kashyzadeh
Keyword(s):  
Fatigue Life ◽  
Random Vibration ◽  
Equivalent Stress ◽  
Loading Conditions ◽  
Random Loading ◽  
Life Estimation ◽  
Fatigue Life Estimation ◽  
Light Pole ◽  
Variable Wind ◽  
Random Vibration Analysis

In the present paper, fatigue life of light poles under multi-axial random loading based on the variable wind direction and speed has been studied. To achieve these purposes, light pole is simulated with all loading conditions in ABAQUS Software. To consider to the three storm days as the critical loading conditions, Random vibration analysis has been performed to obtain stress histories and equivalent stress. Finally, Calculate fatigue life of light pole by using Dirlik Theory.

Stochastic Dynamic Analysis of U-OWC Wave Energy Converters

2017 ◽  
Author(s):  
Pol D. Spanos ◽  
Federica M. Strati ◽  
Giovanni Malara ◽  
Felice Arena
Keyword(s):  
Monte Carlo ◽  
Wave Energy ◽  
Random Vibration ◽  
Equations Of Motion ◽  
Statistical Linearization ◽  
Stochastic Dynamic ◽  
Sea Waves ◽  
Monte Carlo Data ◽  
Linear Differential ◽  
Stochastic Dynamic Analysis

The paper presents a random vibration analysis of a U-Oscillating Water Column wave energy harvester (U-OWC). The U-OWC comprises a vertical duct on the wave beaten side, in addition to the elements of conventional OWCs. From a mathematical perspective, the U-OWC dynamic response is governed by a set of coupled non-linear differential equations with asymmetric matrices of mass, damping, and stiffness. In this work, an approximate analytical solution of the U-OWC equations of motion is sought by using the technique of statistical linearization. This technique allows pursuing rapid random vibration analyses via classical linear input-output relationships. The analysis is conducted by considering the case of the full-scale prototype in the port of Civitavecchia (Rome, Italy). The reliability of the proposed approach is assessed versus relevant Monte Carlo data. For this, realizations of sea states compatible with typical power spectral density functions of sea waves are employed. The performed analyses prove that the statistical linearization technique based approach is an efficient and reliable tool which may both circumvent the use of time-consuming Monte Carlo simulations, and be used for a variety of design optimization related parameter studies.

Dynamic Stability of a Beam Carrying Moving Masses

1971 ◽  
Vol 38 (4) ◽  
pp. 1003-1006 ◽  
Author(s):  
H. D. Nelson ◽  
R. A. Conover
Keyword(s):  
Dynamic Stability ◽  
Floquet Theory ◽  
Equations Of Motion ◽  
Graphical Form ◽  
Continuous Series ◽  
Governing Equations ◽  
Euler Beam ◽  
Lateral Response ◽  
Regions Of Stability ◽  
The Galerkin Method

The dynamic stability of the lateral response of a simply supported Bernoulli-Euler beam carrying a continuous series of equally spaced mass particles is analyzed. The beam rests on a uniform elastic foundation and damping is considered by including a distributed viscous damping coefficient. The particles are restricted to constant speed. The Galerkin method is used to generate a set of approximate governing equations of motion possessing periodic coefficients. Floquet theory is utilized to study the parametric regions of stability which are displayed in graphical form.

scholarly journals Experimental Design and Validation of an Accelerated Random Vibration Fatigue Testing Methodology

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Yu Jiang ◽  
Gun Jin Yun ◽  
Li Zhao ◽  
Junyong Tao
Keyword(s):  
Fatigue Life ◽  
Stress Responses ◽  
Life Prediction ◽  
Random Vibration ◽  
Fatigue Testing ◽  
Fatigue Tests ◽  
Fatigue Life Prediction ◽  
Power Spectral ◽  
Vibration Fatigue ◽  
Non Gaussian

Novel accelerated random vibration fatigue test methodology and strategy are proposed, which can generate a design of the experimental test plan significantly reducing the test time and the sample size. Based on theoretical analysis and fatigue damage model, several groups of random vibration fatigue tests were designed and conducted with the aim of investigating effects of both Gaussian and non-Gaussian random excitation on the vibration fatigue. First, stress responses at a weak point of a notched specimen structure were measured under different base random excitations. According to the measured stress responses, the structural fatigue lives corresponding to the different vibrational excitations were predicted by using the WAFO simulation technique. Second, a couple of destructive vibration fatigue tests were carried out to validate the accuracy of the WAFO fatigue life prediction method. After applying the proposed experimental and numerical simulation methods, various factors that affect the vibration fatigue life of structures were systematically studied, including root mean squares of acceleration, power spectral density, power spectral bandwidth, and kurtosis. The feasibility of WAFO for non-Gaussian vibration fatigue life prediction and the use of non-Gaussian vibration excitation for accelerated fatigue testing were experimentally verified.

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