Time Domain Fatigue Analysis of the Pin for Offshore Bridges Considering the Nonlinear Effect of Sliding Connections

2017 ◽  
Author(s):  
Wenbin Dong ◽  
Ingar Scherf ◽  
Gudfinnur Sigurdsson
Keyword(s):  
Fatigue Life ◽  
Friction Coefficient ◽  
Frequency Domain ◽  
Time Domain ◽  
Stochastic Analysis ◽  
Fatigue Analysis ◽  
Fatigue Assessment ◽  
Nonlinear Spring ◽  
Linear Frequency ◽  
Nonlinear Time Domain

A bridge between platforms needs to operate safely and continuously over its lifecycle. This paper focuses on the fatigue assessment of the bridge pin connection due to relative movements between platforms. A nonlinear time domain stochastic fatigue analysis of the pin connection in a bridge in the North Sea using a combined model of the jacket platforms and the interconnecting bridge is presented. The fatigue life is compared to the fatigue life from a linear frequency domain stochastic analysis. The facility has been in operation for more than 40 years and the operator requested an update of the inspection plans for the bridge. An RBI analysis has been done according to [1] based on fatigue results from wind gusts and relative movements. Regarding the fatigue assessment due to relative movements there are uncertainties related to selection of the friction coefficient. It was assessed that a friction coefficient of 0.4 is slightly conservative in this case. The fatigue life of the pin was calculated based on a linear frequency domain stochastic analysis, assuming that the bridge was fixed at both ends and this was considered reasonable conservative for fatigue estimation. Efforts have been made in the study presented here to assess the conservatism through a nonlinear time domain stochastic fatigue analysis. The sliding connections of the bridge are simulated by nonlinear springs. The effects of assuming different friction coefficients and different nonlinear spring models for a certain friction coefficient on the fatigue damage of the pin are investigated by a sensitivity study. The fatigue lives of the pin thus computed for a series of short-term sea states for the different assumptions for the friction coefficient and the nonlinear spring model are then compared to the result from a corresponding frequency domain approach.

Non-Linear Time and Frequency Domain Methods for Multi-Row Aeromechanical Analysis

2012 ◽  
Author(s):  
M. T. Rahmati ◽  
L. He ◽  
D. X. Wang ◽  
Y. S. Li ◽  
R. G. Wells ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Computational Models ◽  
Linear Time ◽  
Navier Stokes ◽  
Frequency Domain Method ◽  
Domain Method ◽  
Frequency Domain Methods ◽  
Blade Row ◽  
Nonlinear Time Domain

An unsteady Navier-Stokes solution system for aeromechanical analysis of multiple blade row configurations is presented. A distinctive feature of the solver is that unified numerical methods and boundary condition treatments are consistently used for both a nonlinear time-domain solution mode and a frequency-domain one. This not only enables a wider range of physical aeromechanical problems to be tackled, but also provides a consistent basis for validating different computational models, identifying and understanding their relative merits and adequate working ranges. An emphasis of the present work is on a highly efficient frequency-domain method for multi-row aeromechanic analysis. With a new interface treatment, propagations and reflections of pressure waves between adjacent blade rows are modeled within a domain consisting of only a single passage in each blade row. The computational model and methods are firstly described. Then, extensive validations of the frequency-domain method against both experimental data and the nonlinear time-domain solutions are described. Finally the computational analysis and demonstration of the intra-row reflection effects on the rotor aerodynamic damping are presented.

Structural Fatigue Assessment of Offshore Platform Considering the Effect of Nonlinear Drag Force

2016 ◽  
Author(s):  
Weichen Ding ◽  
Liang Pang
Keyword(s):  
Fatigue Life ◽  
Frequency Domain ◽  
Drag Force ◽  
Time Domain ◽  
Nonlinear Effect ◽  
Nonlinear Term ◽  
Wave Force ◽  
Morison Equation ◽  
Nonlinear Form ◽  
Wave Induced

Fatigue assessment for jacket platforms is an indispensable practical issue. Because of the small-scale leg diameter, these structures are often drag dominated and wave-induced force in these structures can be tackled by using either linear or nonlinear form of Spectral Morison Equation. However, it is really complicated and difficult to incorporate nonlinear form of the Morison Equation to acquire the spectral density of the wave force, which is an important step of fatigue estimation. In this paper, in order to estimate the influence of nonlinear effect in wave force, fatigue assessments containing nonlinear effect for the fixed offshore structure are presented. Firstly, shallow-water jacket model locating at a water depth of 20 m is established and involved in calculation. Besides, for the sake of validating the effectiveness of the nonlinear term, the linear and nonlinear form of wave-induced force spectral densities are calculated by the Morison Equation in frequency domain. Secondly, the fatigue life of the jacket platform is assessed in time domain, where time-history of wave force can be obtained by transforming the linear or nonlinear wave force spectral densities from frequency domain to time domain. After the contrast of acquired fatigue life, the comparative results can indicate that the nonlinear drag force contributes a 14% fatigue damage to the total and the influences of the nonlinear term cannot be ignored for the jacket model.

scholarly journals Durability Analysis for Coil Spring Suspension Based on Strain Signal Characterisation

2018 ◽  
Vol 7 (3.17) ◽  
pp. 104
Author(s):  
Chin Chuin Hao ◽  
Shahrum Abdullah ◽  
Ahmad Kamal Ariffin ◽  
Salvinder Singh Karam Singh
Keyword(s):  
Fourier Transform ◽  
Fatigue Life ◽  
Frequency Domain ◽  
Time Domain ◽  
Life Prediction ◽  
Energy Content ◽  
Fatigue Life Prediction ◽  
Coil Spring ◽  
Time Frequency ◽  
Strain Signal

This paper aims to predict the durability of an automobile coil spring by characterising the captured strain data. The load histories collected at coil spring are often presented in time domain but time domain cannot provide sufficient information for fatigue life prediction. The objective of this study was to characterise the strain signal in time domain, frequency domain and time-frequency domain for fatigue life prediction. The signal obtained in time domain was used to predict the fatigue life of the coil spring through Rainflow cycle counting technique and models of strain-life relationships. In frequency domain, fast Fourier transform revealed that the frequency components in the strain signal ranged between 0-5 Hz. The frequencies can be further categorised into two ranges: 0-0.3 Hz and 1-2 Hz. Power spectral density confirmed that the frequencies with high energy content were 0-5 Hz and the total energy content in the signal is 4.0872x103 µɛ2. Short time Fourier transform can identify the local time and frequency properties of the signal but it has a limitation in time-frequency resolutions. Wavelet transform can provide a better time-frequency resolutions and it confirmed that the transients in the time domain had frequency range of 1-2 Hz. In summary, this study revealed different possible approaches of signal processing in fatigue life assessment of automotive components as guidance for the selection of suitable approach based on the type of information needed for the analysis.  

Optimization of Frequency Domain Fatigue Analysis for Unbonded Flexible Risers

2021 ◽  
Author(s):  
Jiabei Yuan ◽  
Yucheng Hou ◽  
Zhimin Tan
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Transfer Functions ◽  
Hybrid Approach ◽  
Fatigue Analysis ◽  
System Response ◽  
Similar Response ◽  
Potential Cost ◽  
Spectrum Prediction ◽  
Flexible Risers

Abstract Fatigue analysis of flexible risers is a demanding task in terms of time and computational resources. The traditional time domain approach may take weeks of time in global simulation, local modelling and post-processing of riser responses to get fatigue results. Baker Hughes developed a fast hybrid approach, which is based on a frequency domain technique. The new approach was first implemented at the end fitting region and then to all other regions of the riser. Studies showed that the hybrid approach achieved convenient and conservative results in a significant shorter period of time. To improve the accuracy and reduce conservatism of the method, Baker Hughes has further optimized the analysis procedure to seek better results approaching true solutions. Several methods were proposed and studied. The duration of representative cases and noncritical cases have been extended. The steps to predict stress spectrum based on transfer functions have also been updated. From previous studies, only one transfer function was built for fatigue load cases with similar response spectra. This assumption linearizes the system response and produces certain level of discrepancy against true time domain solution. In this study, multiple ways of spectrum prediction are evaluated and compared. The paper summarizes several techniques to further optimize the hybrid frequency domain approach. The updated fatigue results are found to be more accurate. The optimized approach therefore gives more flexibility to engineers to approach the true solutions, which were originally acquired from full 3-hr time domain simulations. The approach requires less analysis time and reduces iterations in pipe structure and riser configuration design, which leads to faster project execution and potential cost reduction.

Mating Analysis and a Typical Floatover Design

2012 ◽  
Author(s):  
Alan M. Wang ◽  
Ruhua Yuan ◽  
Shaohua Zhu ◽  
Min He ◽  
Ju Fan ◽  
...  
Keyword(s):  
Diffraction Analysis ◽  
Shallow Water ◽  
Frequency Domain ◽  
Time Domain ◽  
Bohai Bay ◽  
Hydrodynamic Properties ◽  
Nonlinear Time Domain ◽  
Offshore Operations

This paper presents a typical floatover design in the shallow water and benign environment of Bohai Bay, China and the major floatover installation devices, as well as the nonlinear time-domain mating analysis. The nonlinear mating simulations are performed using SIMO based on the hydrodynamic properties of the floatover barge, obtained by WADAM, from the linear diffraction analysis in frequency domain. The mating analysis yields numerical findings in selecting and designing floatover devices critical to the success of the floatover operations, thus minimizing any potential operation risks and enabling the offshore operations as smoothly and efficiently as possible.

An efficient time domain fatigue analysis and its comparison to spectral fatigue assessment for an offshore jacket structure

2016 ◽  
Vol 49 ◽  
pp. 97-115 ◽  
Author(s):  
Said Fawad Mohammadi ◽  
Nelson Szilard Galgoul ◽  
Uwe Starossek ◽  
Paulo Mauricio Videiro
Keyword(s):  
Time Domain ◽  
Fatigue Analysis ◽  
Fatigue Assessment
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