Fatigue Analysis of Risers

2002 ◽  
Author(s):  
Rommel Burbano Bolan˜os ◽  
Javier Espinosa Rivera ◽  
Dante Campos
Keyword(s):  
Fatigue Analysis ◽  
Ground Movement ◽  
Present Condition ◽  
Structural Safety ◽  
Lateral Stiffness ◽  
Wave Loads ◽  
Fatigue Reliability ◽  
Stress Concentrations ◽  
Study Zone ◽  
Different Diameters

This paper studies the fatigue problem of risers in marine platforms located in the Bay of Campeche, Mexico. Considering the future wave loads on these systems, the lifetime of these structures is obtained. Possibly, these systems have problems of fatigue in the zones where large stress concentrations appear. The risers fatigue analysis with a regular pipeline section is carried out taking into account operational and environmental load conditions. Due to operation, among others, the risers are subject to internal pressure, thermal expansion, and the type of fluid that transports. In order to take into account the environmental conditions one it is considered that the riser is subject to waves, current and ground movement, which were suitably modeled in the analysis. The supports on the platform, in the riser zone, were considered. They take into account the movements and their corresponding lateral stiffness. To evaluate the load cycles to which the risers are subject, for the study zone, the annual rates of occurrence and all the sea states have been considered. In addition, all the possible heights and directions of the wave that might be present in the Bay of Campeche have been considered the accumulated damage caused by the diverse cycles of stresses by means of the Palmgren Miner rule are assessed. This study includes the analysis of representative number of risers with different diameters and recent inspections. This allows us to know, in an approximated way, the present condition of the risers; it an give us suitable information for the calculation of the fatigue reliability and therefore define the present levels of structural safety of these facilities.

Structural Safety Assessment of a 1100 TEU Container Ship, Based on a Enhanced Long Term Fatigue Analysis

2014 ◽  
Vol 1036 ◽  
pp. 935-940
Author(s):  
Leonard Domnisoru ◽  
Ionica Rubanenco ◽  
Mihaela Amoraritei
Keyword(s):  
Safety Assessment ◽  
Safety Evaluation ◽  
Irregular Waves ◽  
Structural Safety ◽  
Random Wave ◽  
Wave Loads ◽  
Strength Assessment ◽  
Integrated Method ◽  
Hydroelastic Response

This paper is focused on an enhanced integrated method for structural safety assessment of maritime ships under extreme random wave loads. In this study is considered an 1100 TEU container test ship, with speed range 0 to 18 knots. The most comprehensive criteria for ships structural safety evaluation over the whole exploitation life is based on the long term ship structures analysis, that includes: stress hot-spots evaluation by 3D/1D-FEM hull models, computation of short term ship dynamic response induced by irregular waves, long term fatigue structure assessment. The analysis is enhanced by taking into account the ships speed influence on hydroelastic response. The study includes a comparative analysis on two scenarios for the correlation between the ships speed and waves intensity. The standard constant ship speed scenario and CENTEC scenario, with total speed loss at extreme waves condition, are considered. Instead of 20 years ship exploitation life estimated by classification societies rules from the long term structural safety criteria, the enhanced method has predicted more restrictive values of 14.4-15.7 years. The numerical analyses are based on own software and user subroutines. The study made possible to have a more realistic approach of ships structural strength assessment, for elastic and faster ships as container carriers, in compare to the standard one based only on naval rules, delivering a method with higher confidence in the designed structural safety.

Fatigue Damage Accumulation under the Complex Varying Loading

2014 ◽  
Vol 617 ◽  
pp. 187-192 ◽  
Author(s):  
Boris Melnikov ◽  
Artem Semenov
Keyword(s):  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Damage Model ◽  
Hysteresis Loops ◽  
Fatigue Analysis ◽  
Wave Loads ◽  
Fatigue Damage Accumulation ◽  
History Of ◽  
Strain Stress ◽  
Irregular Loading

Fatigue analysis of steel parts of structures, which are subjected to complex irregular loading programs caused by wind, thermal, wave loads, earthquakes and combined imposed actions, requires in some cases using special methods of stress-strain evaluation. The model of the low cycle fatigue nonlinear damage accumulation is developed with taking into account the history of the deformation process. The damage is defined on the base of considering the quasi-static accumulation of maximal strain (stress) and hysteresis loops. The identification of material constants of the model is discussed. Application of the damage model for fatigue analysis of the antennas, pipelines, basements and fasteners units is considered and a comparison with experiments is given.

Fatigue Analysis for Mooring System of a Spar-Type Floating Offshore Wind Turbine

2020 ◽  
Author(s):  
Xutian Xue ◽  
Xiaoyong Liu ◽  
Nian-Zhong Chen ◽  
Xifeng Gao
Keyword(s):  
Wind Turbine ◽  
Fatigue Analysis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Safety Factors ◽  
Mooring Lines ◽  
Hydrodynamic Analysis ◽  
Floating Offshore Wind Turbine ◽  
Different Diameters ◽  
Rainflow Counting

Abstract This paper aims to perform a time-domain mooring fatigue analysis for a Spar-type floating offshore wind turbine operated in the South China Sea. Tension ranges of mooring lines are achieved from a hydrodynamic analysis where the effects of wind, wave and current are considered. A rainflow counting method is used to calculate the number of mooring tension cycles with corresponding ranges. The fatigue lives of mooring lines are then predicted by Palmgren-Miner’s rule according to T-N & S-N curves. A comparison of fatigue lives predicted by T-N & S-N curves-based approaches with/without considering safety factors is made. The results show that the T-N curves-based approach is more conservative than the S-N curves-based approach if safety factors are not considered in the two approaches, while the fatigue lives predicted by both approaches are in general comparable when the safety factors suggested by API and DNVGL are applied in the two approaches. A comparative study of three kinds of R4 grade studless mooring chains with different diameters (2.5-inch, 4-inch, 5-inch) is also conducted and the results show that the design with the 2.5-inch chain does not meet the fatigue requirements.

Structural Safety Assessment Based on the Fatigue Analysis of the Ice-Resistant Jacket Platforms

2010 ◽  
Author(s):  
Xiaofei Che ◽  
Dayong Zhang ◽  
Qianjin Yue
Keyword(s):  
Risk Assessment ◽  
Fatigue Failure ◽  
Safety Assessment ◽  
Design Method ◽  
Hot Spot ◽  
Cyclic Stress ◽  
Fatigue Analysis ◽  
Structural Safety ◽  
Bohai Bay ◽  
General Process

Most of the ice-resistant jacket platforms in Bohai Sea have been close to or reached their service life. In order to keep the platforms perform safely, a reasonable risk assessment of the existing platforms should be considered. The hazard of the structural fatigue failure under the ice-induced vibrations is so serious, which plays an important role in the safety of the platforms. In this paper, the general process of the structural safety assessment based on the fatigue analysis is established. Firstly, risk assessment of fatigue failure needs to determine whether the cyclic stress of hot-spot induced by ice-vibrations under normal ice condition is so significant. Then, the method of estimating ice-induced fatigue life of existing platforms is developed based on the field data and the safe life design method. Finally, as an application example, the safety assessment of one old jacket platform in Bohai Bay is carried on, which can provide a warrant for owners to repair or reject platforms.

Effect of Shut-Down Procedures on the Dynamic Responses of a Spar-Type Floating Wind Turbine

2013 ◽  
Author(s):  
Zhiyu Jiang ◽  
Torgeir Moan ◽  
Zhen Gao ◽  
Madjid Karimirad
Keyword(s):  
Wind Turbine ◽  
Effective Means ◽  
Bending Moment ◽  
Dynamic Responses ◽  
Structural Safety ◽  
Wave Loads ◽  
Main Shaft ◽  
Rotor Speed ◽  
Design Standards ◽  
Floating Wind Turbine

The design standards (IEC, DNV and GL) define a minimum set of combinations of external conditions and design situations as load cases. Like other design load conditions, the design situations relating to fault and shut-down events shall be addressed. Emergency shut down occurs in the presence of severe faults to prevent turbine damage. For pitch-regulated turbines, blade pitching to feather provides an effective means of aerodynamic braking. The blades are pitched to feather at the maximum pitch rate. This action exerts huge loading on the turbine and may challenge the structural safety. In this paper a 5-MW spar-type wind turbine is used as a case study. By using the HAWC2 code, the turbine pitch actuator fault and shut-down scenarios are simulated through external Dynamic Link Libraries. The shut-down scenarios are: normal shut down with blade pitching, emergency shut down with blade pitching, and emergency shut down with blade pitching and mechanical brake. Due to the occurrence of fault, the pitch angle of one blade is fixed from a specific occurrence time. The supervisory controller reacts by pitching the remaining two blades to the maximum pitch set. The maximum yaw motion value is observed after the first revolution of the rotor during which the tower-top torsion experiences a change of direction. Negative platform pitch motion as well as tower-bottom bending moment are induced due to the pitching activity of the two blades. The response extremes of the main shaft bending moment and the yaw motion exhibit clear variation with the blade azimuth when emergency shut down is initiated. The tower-bottom bending moment and nacelle acceleration are relatively more affected by the wave loads. For a given blade azimuth, larger response variation is observed under harsher environmental conditions. Under the fault scenario, the effects of different shut-down procedures on the response extremes are investigated. It is found that the response extremes are affected significantly by the rotor speed. Among the three procedures, normal shut down, which is associated with the slowest decaying aerodynamic excitations and the highest rotor speed, usually leads to the largest response extremes near the rated wind speed. The employment of mechanical brake reduces rotor speed, motion responses and structural responses effectively. During shut down, the responses of yaw motion, nacelle fore-aft acceleration, main shaft bending moment, and tower-bottom side-to-side moment may be of concern for the floating wind turbine studied.

A Three-Dimensional FE Approach for the Fatigue Analysis of Flexible Pipes Tensile Armors Inside End Fittings

2020 ◽  
Author(s):  
Marcelo N. R. Miyazaki ◽  
José Renato M. de Sousa ◽  
Gilberto B. Ellwanger ◽  
Vinicius R. da Silva
Keyword(s):  
Fatigue Resistance ◽  
Three Dimensional ◽  
Local Stress ◽  
Fatigue Analysis ◽  
Acceptance Test ◽  
Stress Concentrations ◽  
Flexible Pipes ◽  
Dimensional Finite Element ◽  
Operational Tests ◽  
Three Dimensional Finite Element

Abstract During the end fitting (EF) assembly, the tensile armors of flexible pipes are folded and then unfolded to allow the assessment to the inner sheath and the activation of the inner sealing system. This procedure leaves residual stresses and plastic deformations on these armors, which affect their fatigue resistance and, consequently, the overall performance of the pipe. Hence, in this work, a methodology to predict the fatigue resistance of tensile armors inside an EF is proposed. This methodology relies on stresses calculated with a previously presented three-dimensional finite element (FE) approach and is employed to analyze the fatigue response of a 6” production riser in catenary configuration. This fatigue analysis not only addresses the effects from several irregular sea states but also the local stress concentrations associated with the EF assembly and pre-operational tests (e. g., Factory Acceptance Test, FAT). The results obtained indicate that the EF entrance may be a critical point for fatigue failure and, moreover, the lower fatigue resistance is related to a region where higher alternate stresses occur despite the very high mean stresses are observed in other regions along the tensile armors.

Structural Safety Review of a Building Damaged by Explosion in Mexico City

2016 ◽  
Vol 713 ◽  
pp. 111-114
Author(s):  
Jorge A. Avila ◽  
Jorge Arturo Avila-Haro
Keyword(s):  
Reinforced Concrete ◽  
Mexico City ◽  
Longitudinal Direction ◽  
Present Condition ◽  
Structural Safety ◽  
Seismic Zone ◽  
Joint Work ◽  
Lateral Capacity ◽  
Capacity Curves ◽  
Reinforced Concrete Slabs

The structural assessment of a building damaged by the effects of an explosion located in Mexico City is presented. The structure consists in 12 complete levels, a thirteenth partially completed level for elevators, and a basement. The building is mainly conformed of steel frames with box columns, I-beams and trusses; peripherally reinforced concrete slabs attached to girders through shear connectors; its reinforced concrete box foundation (basement slab, grade beams and floor slab) is supported on control piles at a depth of 5.9 m. The building did not present any damage in the 1985 Mexico City earthquake; the original structural design is from the 1960’s (RCDF-66) [1], for a reduced seismic coefficient cs= 0.06. A review of the present condition of the structure against the requirements of the current RCDF-04 (transition seismic zone: Ts~1.0 s and cs=0.32; Q=2) was performed in this work [2]. Based on the three-dimensional structural behavior, spectral modal dynamic analyses were performed, including the joint work of the super-structure and the foundation. The structure does not present any lack of lateral stiffness and/or resistance problems, even after the explosion. According to the non-linear static (Push-over) analyses (with and without over-strenghts effects), the lateral capacity curves prove that the building has a slightly higher lateral capacity in the longitudinal direction and, to a lesser extent, in the short direction, than the one required in the current regulation. No corrective structural actions were needed, except for the rehabilitation of the structural elements affected by the explosion.

scholarly journals Fatigue Strength Assessment of Trimaran Cross-Deck Structure Based on Spectral and Simplified Fatigue Method

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Chunbo Zhen ◽  
Tianlin Wang ◽  
Pengyao Yu ◽  
Liang Feng
Keyword(s):  
Transfer Functions ◽  
Three Dimensional ◽  
Stress Transfer ◽  
Direct Calculation ◽  
Fatigue Behaviour ◽  
Fatigue Analysis ◽  
Fe Analysis ◽  
Linear Potential ◽  
Wave Loads ◽  
Strength Assessment

In order to investigate the fatigue behaviour of trimaran cross-deck structural details, the spectral and simplified fatigue analysis approaches are proposed. In spectral fatigue approach, three-dimensional (3D) linear potential flow theory and global FE analysis are used for wave loads and stress transfer functions calculation; the stochastic spectral fatigue analysis is carried out considering the weighted wave headings factors. In simplified fatigue approach, based on the direct calculation procedure of LR rules, the evaluation of simplified fatigue loads and loading conditions are presented, and the stress ranges are obtained by global finite element (FE) analysis. Then the fatigue lives of a few hot spots are computed to demonstrate the application of the proposed method. The result shows that the method given in this paper has a good applicability. This study offers methodology for the fatigue analysis of trimaran cross-deck structure, which may be regarded as helpful references for structural design of these types of ships.

Engineering Establishment of Living Quarters for Jack-Up Rig Structures

2016 ◽  
Author(s):  
Yeong Su Ha ◽  
Joo Shin Park ◽  
Jeong Bon Koo ◽  
Byung Jin Cho ◽  
Kuk Yeol Ma ◽  
...  
Keyword(s):  
Structural Engineering ◽  
Three Dimensional ◽  
Technical Specification ◽  
International Standards ◽  
Structural Safety ◽  
Fe Model ◽  
Wave Loads ◽  
Offshore Structure ◽  
Local Loads ◽  
Jack Up

The Living-Quarters (hereafter referred to as ‘LQ’) is one of the major structures for ship and offshore structure. The LQ gives safe living conditions to crews on board. Until now the structural design of LQ structure is based on simplistic beam calculation to determine the initial scantling under design load. These days, safety for people is a raising issue. It is needed to meet the high oil company’s needs as well as technical specification throughout offshore project. But, the engineering procedure for LQ structure is not clearly defined by classification of society rules and international standards. In this paper, the newly engineering procedure for LQ design is established considering LQ global loads with local loads for large equipment such as helideck structure, telecom mast and life saving appliances, and so on. To consider LQ global loads with local loads, the integrated three dimensional FE model and high technology engineering should be needed to require many kind of rules for equipment. Recently, the damage of LQ structure is occasionally reported during towing condition for jack-up rig structure. The LQ of jack-up rig is encountered such as slamming pressure and greenwater produced by harsh wave loads during towing condition because of small height of freeboard comparing to the wave height. To verify the structural safety under towing condition, the detailed non-liner analysis is performed to verify the load-carrying capacity against greenwater pressure. We newly propose a structural engineering procedure to improve the reliability of the LQ design in the jack-up rigs. From basis of this procedure, a more reasonable and optimized results are proposed as a practical manner as well as scientific approach.

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