Direct Time Domain Life Cycle Loading Analysis on a Floating Platform

2018 ◽  
Author(s):  
Ho-Joon Lim ◽  
Manoj Jegannathan ◽  
Bonjun Koo ◽  
Johyun Kyoung ◽  
Eleni Beyko
Keyword(s):  
Life Cycle ◽  
Fatigue Life ◽  
Time Domain ◽  
Simulation Analysis ◽  
Fatigue Analysis ◽  
Mooring Line ◽  
Direct Simulation ◽  
Floating Platform ◽  
Cycle Loading ◽  
Simulation Results

Time domain numerical simulations with TechnipFMC’s in-house program were performed to estimate life cycle loading on a floating platform using High Performance Computing (HPC). Direct Simulation Analysis (DSA) were conducted to estimate fatigue life of mooring lines of two Spar platforms and the results were compared with fatigue life estimated from the condensed bin approach. In the Direct Simulation Analysis, 35-year hindcast wave and wind data with 3-hour interval for Gulf of Mexico was used. The wind and wave data covers from January 1979 to December 2013 for every 3-hours. The current data was not available so associated current information was approximately estimated. The time domain direct simulation results include nonlinear loads, nonlinear responses and seasonal effects such as hurricane events. The life cycle loading analysis tool developed will reduce uncertainties and increase the accuracy and reliability of the estimation of the mooring fatigue life during the service life of platform. Fatigue life of a mooring line from condensed bin analysis is highly variable with more than 20% depending on the selected wave seed number. In addition, the fatigue life from condensed bin analysis is about 20% less than the fatigue life from the Direct Simulation Analysis. This paper presents the systematic comparisons between the conventional approach and the direct time domain simulation results and also provides some major findings. In addition to the mooring line fatigue analysis, the structural fatigue analysis is also being performed and the results will be presented in the near future.

Analysis of Cornering Strength of Steel Wheels Including the Effects of Disc and Rim Interference Assembly

2019 ◽  
Author(s):  
Bin Dang ◽  
Yingchun Shan ◽  
Xiandong Liu ◽  
Xiaoran Wang ◽  
Yue Zhang ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Commercial Vehicle ◽  
Simulation Analysis ◽  
Cyclic Stress ◽  
Stress Variation ◽  
Steel Wheel ◽  
Bending Load ◽  
Simulation Results ◽  
Stress Simulation

Abstract The cornering fatigue test of commercial vehicle steel wheel is modeled and simulated by finite element method in this paper. The influence of interference stress between wheel disc and rim on the simulation results is analyzed. The interference stress is taken as predefined fields to superimpose with the stress generated by the bending load. Then the influence of two different superposition methods defining the interference stress as the average stress and the predefined fields on the stress in dangerous area of the wheel is compared. The results show that the interference stress has a significant effect on the stress state of the wheel and increases the amplitude of symmetric cyclic stress, which directly affects the prediction of fatigue life of the wheel. Therefore, the interference stress must be taken into consideration in the simulation analysis of cornering fatigue test. The influence of different interference stress superposition methods on the stress variation in the dangerous area is obviously different. The method which superimposes interference stress as predefined fields with the stress generated by the bending load is more consistent with the actual assembling and loading process of the wheel. Therefore, this paper provides a reasonable method for the simulation of cornering fatigue test, which can provide more accurate stress simulation results for the prediction of cornering fatigue life of the wheel.

The Effect of Mooring Line Pre-Tension on FDPSO’s Motion

2016 ◽  
Author(s):  
Yanlong Sun ◽  
Huilong Ren ◽  
Zhendong Liu ◽  
Liu Yan ◽  
Zepeng Guo
Keyword(s):  
Time Series ◽  
Model Test ◽  
Time Domain ◽  
Prediction Method ◽  
Line Tension ◽  
Mooring Line ◽  
Floating Platform ◽  
Motion Response ◽  
Drilling Unit ◽  
Environment Condition

As a multifunction floating platform, Floating Drilling, Production, Storage and Offloading (FDPSO) combining the well-known Floating Production, Storage and Offloading (FPSO) with a drilling unit. For the environment condition of deep-water oilfield is very severe, the motion response and mooring line tension of FDPSO is a worthy topic of studying. In this study, the numerical time-domain coupled prediction method for the mooring line tension and motion response of FDPSO system is constructed by ANSYS AQWA software. Furthermore, the results of a model test conducted in Harbin Engimeering University are used to investigate the feasibility and validity of the commercial simulation. The effect of mooring line pre-tension on the response of FDPSO is studied by varying the pre-tension of mooring line during the calculation. The time series curve of the mooring line tension and motion response, and the comparison of motion spectrum and mooring line tension spectrum are provided in this article.

Research on Modeling and Simulation Analysis of Direct Drive System in Simulink and Simscape Environment

2013 ◽  
Vol 579-580 ◽  
pp. 699-705
Author(s):  
Hong Bo Liao ◽  
Shi Xun Fan ◽  
Mo Hei ◽  
Da Peng Fan
Keyword(s):  
Modeling And Simulation ◽  
Relative Error ◽  
Time Domain ◽  
Simulation Analysis ◽  
Theory Model ◽  
Drive System ◽  
Direct Drive ◽  
Simulation Results ◽  
Time Domain Response ◽  
Frequency Domain Response

In order to verify and analysis the theory model of direct drive system, the methods of computer-aided modeling and simulation analysis in Simulink and Simscape environment were presented. Based on the theory model of direct drive system, simulation models were constructed in two kinds of different environment, the model building and analysis process were detail introduced, the simulation results were compared and experiment verification. The simulation and experiment results showed that the relative error of time domain response of simulation results under two kinds of environment is within 4%, the relative error of frequency domain response is within 4.5%. Comparing simulation results under Simulink environment with the real test results, the relative error of time domain response is within 20%, and the relative error of frequency domain response is within 15%. The consistence and correctness of the two methods are verified, the proposed methods can also be applied to modeling and simulation analysis of others Mechatronic servo system.

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.

Mooring Line Damping Estimation by a Simplified Dynamic Model

2007 ◽  
Author(s):  
Halvor Lie ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Dynamic Model ◽  
Time Domain ◽  
Low Frequency ◽  
Line Tension ◽  
Mooring Line ◽  
Short Term ◽  
Simplified Method ◽  
On Line ◽  
Simulation Results ◽  
Frequency Domain Approach

When predicting slowly varying resonant vessel motions, a realistic estimate of the motion damping is crucial. Mooring line damping, which is mainly induced by the drag force on line, can dominate the total damping of catenary moored systems and methods for predicting mooring line damping are therefore required. Based on a simplified dynamic model of mooring line tension, an approach to estimate the corresponding damping is presented in this paper. Short-term time domain simulations of dynamic line tension are carried out to verify the accuracy of the simplified frequency domain approach. Compared with the simulation results, the practical simplified method proposed herein gives a maximum 30% lower prediction of the damping coefficient of each mooring line and an about 20% smaller estimate of the total line damping and therefore yields conservative estimates of the low frequency vessel motions.

A Conjoint Analysis of the Stability and Time-Domain Analysis on Floating Platform During Mooring Line Breaking

2019 ◽  
Author(s):  
Jiaguo Feng ◽  
Yi Yu ◽  
Yan Qu ◽  
Wenhui Xie ◽  
Min Wu ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Time Domain ◽  
Stability Problem ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Mooring Line ◽  
Floating Platform ◽  
The Stability ◽  
The Time Domain ◽  
Floating Platforms

Abstract The stability of platform is important to ensure the platforms are safe, especially during the mooring line breaking process in typhoon condition. The paper presents a stability analysis method for floating platforms of the mooring line breaking process based on the time-domain analysis. The time-domain simulation during the mooring line breaking is provided. The time of the mooring line break, the max tilt angle of platform and the amended equivalent overturning moment are calculated for the stability analysis. The results show that the platform would have a serious tilt when the mooring line breaks, this increases the overturning moments and may cause the platform not meets the stability requirements during this process. It is necessary to pay attention to the stability problem during the mooring line breaking process in typhoon condition. And properly locating the down-flooding points is recommended to avoide the stability problem.

scholarly journals Numerical Study of the Influence of Fishnet Mesh Size on a Floating Platform

2020 ◽  
Vol 8 (5) ◽  
pp. 343
Author(s):  
Hung-Jie Tang ◽  
Chai-Cheng Huang ◽  
Ray-Yeng Yang
Keyword(s):  
Resonant Frequency ◽  
Time Domain ◽  
Numerical Study ◽  
Mesh Size ◽  
Nonlinear Effects ◽  
Line Tension ◽  
Body Motion ◽  
Mooring Line ◽  
Floating Platform ◽  
The Time Domain

This study aims to investigate the influence of fishnet mesh size on a floating platform. A self-developed, time-domain numerical model was used for the evaluation. This model is based on potential flow theory, uses the boundary element method (BEM) to solve nonlinear wave-body interactions, and applies the Morison equation to calculate the hydrodynamic forces exerted on fishnets. The mooring system is treated as a linear and symmetric spring. The results near the resonant frequency of the platform indicate that the smaller the fishnet mesh size, the lower the heave, pitch, and sea-side tension response amplitude operators (RAOs), but the higher the reflection coefficient. The results in the lower frequency region reveal that the smaller the fishnet mesh size, the lower the surge and heave RAOs, but the higher the pitch and tension RAOs. Meanwhile, the time-domain results at the resonant frequency of heave motion are shown to indicate the influences of a platform with various fishnets mesh sizes on the rigid body motion, mooring line tension, and transmitted wave heights. In addition, a comparison of nonlinear effects indicates that, after reducing the fishnet mesh size, the second-order RAOs of heave, pitch, and sea-side tension decrease, but the changes are minor against the first-order results.

Comparison of Different Approaches for Fatigue Damage Accumulation in Steel Risers

2011 ◽  
Author(s):  
Fernanda C. M. Takafuji ◽  
Clo´vis A. Martins
Keyword(s):  
Fatigue Life ◽  
Dynamic Analysis ◽  
Fatigue Damage ◽  
Time Domain ◽  
Damage Accumulation ◽  
Maximum Stress ◽  
Fatigue Analysis ◽  
Fatigue Damage Accumulation ◽  
Stress Point ◽  
Offshore Industry

Fatigue is one of the main concerns of the offshore industry nowadays, since the failure of equipments could put not only the environment but also some people’s lives in danger. As described in DNV-RP-C203 and in DNV-RP-F204, the aim of fatigue analysis is to verify if a certain structure — in this case, a riser — will be able to operate adequately during a desired period of time, as well as to obtain information to program inspections. In a riser, the efforts vary along its length and also around its circumference. If one considers the stress around the circumference, the maximum stress point may change. To be realistic, one approach is to calculate the stress and fatigue life around the circumference. To be more conservative and also simplify the calculation, one could consider that the maximum stress always occurs at the same point. The purpose of this paper is to compare the fatigue life obtained with both approaches in order to verify the differences between them and verify how conservative that simplification can be. To perform the task, a steel riser is considered and the dynamic analysis is executed in time domain using Orcaflex 9.4. The fatigue is analyzed through the S-N Curve approach and the Miner’s rule is used to accumulate the damage.

scholarly journals Transient Responses Evaluation of FPSO with Different Failure Scenarios of Mooring Lines

2021 ◽  
Vol 9 (2) ◽  
pp. 103
Author(s):  
Dongsheng Qiao ◽  
Binbin Li ◽  
Jun Yan ◽  
Yu Qin ◽  
Haizhi Liang ◽  
...  
Keyword(s):  
Service Condition ◽  
Mooring Line ◽  
Mooring System ◽  
Transient Effects ◽  
Floating Platform ◽  
Transient Responses ◽  
Mooring Lines ◽  
Performance Deterioration ◽  
Steady State Responses ◽  
Influence Process

During the long-term service condition, the mooring line of the deep-water floating platform may fail due to various reasons, such as overloading caused by an accidental condition or performance deterioration. Therefore, the safety performance under the transient responses process should be evaluated in advance, during the design phase. A series of time-domain numerical simulations for evaluating the performance changes of a Floating Production Storage and Offloading (FPSO) with different broken modes of mooring lines was carried out. The broken conditions include the single mooring line or two mooring lines failure under ipsilateral, opposite, and adjacent sides. The resulting transient and following steady-state responses of the vessel and the mooring line tensions were analyzed, and the corresponding influence mechanism was investigated. The accidental failure of a single or two mooring lines changes the watch circle of the vessel and the tension redistribution of the remaining mooring lines. The results indicated that the failure of mooring lines mainly influences the responses of sway, surge, and yaw, and the change rule is closely related to the stiffness and symmetry of the mooring system. The simulation results could give a profound understanding of the transient-effects influence process of mooring line failure, and the suggestions are given to account for the transient effects in the design of the mooring system.

Study of HVDC System and Subsynchronous Oscillation

2015 ◽  
Vol 1092-1093 ◽  
pp. 356-361
Author(s):  
Peng Fei Zhang ◽  
Lian Guang Liu
Keyword(s):  
Power Plant ◽  
Time Domain ◽  
Simulation Method ◽  
Time Domain Simulation ◽  
Stable Convergence ◽  
Turbine Generator ◽  
Plant Model ◽  
Subsynchronous Oscillation ◽  
Hvdc System ◽  
Simulation Results

With the application and development of Power Electronics, HVDC is applied more widely China. However, HVDC system has the possibilities to cause subsynchronous torsional vibration interaction with turbine generator shaft mechanical system. This paper simply introduces the mechanism, analytical methods and suppression measures of subsynchronous oscillation. Then it establishes a power plant model in islanding model using PSCAD, and analyzes the effects of the number and output of generators to SSO, and verifies the effect of SEDC and SSDC using time-domain simulation method. Simulation results show that the more number and output of generators is detrimental to the stable convergence of subsynchronous oscillation, and SEDC、SSDC can restrain unstable SSO, avoid divergence of SSO, ensure the generators and system operate safely and stably

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