A Parametric Study on Effects of Environmental Loadings on Fatigue Life of Steel Catenary Risers (Using a Nonlinear Cyclic Riser-Soil Interaction Model)

2010 ◽  
Author(s):  
Mehrdad Kimiaei ◽  
Mark Randolph ◽  
Ivan Ting
Keyword(s):  
Fatigue Damage ◽  
Deep Water ◽  
Interaction Model ◽  
Fatigue Assessment ◽  
Wide Range ◽  
Non Linear ◽  
Wave Heights ◽  
Steel Catenary Risers ◽  
Vessel Motion ◽  
Floating Platforms

Steel catenary risers (SCRs) are often the preferred option for subsea tie-back to floating platforms in deep water due to their conceptual simplicity, ease of construction and installation and simple interface with the flowlines. Fatigue design of SCRs, particularly in the touch down area (TDA), has always been one of the major engineering challenges. Traditionally, fatigue assessment of SCRs has usually been highly conservative, because of lack of precise understanding of the non-linear soil-riser-interaction in the TDA. Most fatigue studies are based on assumed linear stiffness for the seabed, partly because of the lack of robust non-linear riser-seabed interaction models and partly because the linear response simplifies the fatigue study. The recent availability of non-linear seabed response models provides an opportunity to improve fatigue assessment, but it is first necessary to evaluate how best to conduct fatigue studies for such nonlinear systems which can be sensitive to wide range of input parameters. This paper outlines a new advanced numerical model, considering nonlinear cyclic riser-soil interaction behavior, used to determine the contribution of different loading parameters on fatigue damage of SCRs in the TDA in deep water soft sediments. The main loading parameters considered are: different motions of floating vessels, wave heights, wave periods and wave packs ordering. Numerical modeling has shown that over 95% of the fatigue damage corresponds to floating vessel motion parallel to the riser axis at the connection point to the vessel. It is also shown that riser response at TDA is highly influenced with amplitude and period of the environmental loadings.

Seabed Interaction Modelling Effects on the Global Response of Catenary Pipeline: A Case Study

2013 ◽  
Author(s):  
Hany Elosta ◽  
Shan Huang ◽  
Atilla Incecik
Keyword(s):  
Fatigue Damage ◽  
Linear Time ◽  
Interaction Model ◽  
Fatigue Performance ◽  
Random Waves ◽  
Floating Platform ◽  
Geotechnical Parameters ◽  
Non Linear ◽  
Interaction Modelling ◽  
Seabed Interaction

A steel catenary riser (SCR) attached to a floating platform at its upper end encounters oscillations in and near its touchdown zone (TDZ), which results in interaction with the seabed. Field observations and design analysis of SCRs show that the highest stress and greatest fatigue damage occurred near the touchdown point where the SCR first touches the seabed soil. The challenges regarding the fatigue damage assessment of an SCR in the TDZ are primarily because of the non-linear behaviour of SCR–seabed interaction and considerable uncertainty in seabed interaction modelling and geotechnical parameters. Analysis techniques have been developed in the two main areas: SCR–seabed interaction modelling and the influence of the uncertainty in the geotechnical parameters on the dynamic response and fatigue performance of SCRs in the TDZ. Initially, this study discusses the significance of SCR–seabed interaction on the response of an SCR for deepwater applications when subjected to random waves on soft clay using the commercial code OrcaFlex for non-linear time domain simulation. In the next step, this study investigates the sensitivity of fatigue performance to geotechnical parameters through a parametric study. It is proven that employing the improved lateral SCR-seabed interaction model with accurate prediction of soil stiffness and riser penetration with cyclic loading enables us to obtain dynamic global riser performance in the TDZ with better accuracy. The fatigue analyses results prove that the confounding results indicated by the previous research studies on the SCR in the TDZ are due to different geotechnical parameters imposed with the seabed interaction model. The main benefit of employing non-linear seabed approach is to capture the entity of realistic soil interaction behaviour in modelling and analysis and to predict the likelihood of the fatigue damage of the SCR with seabed interaction, thereby minimising the risk of the loss of the containment with the associated environmental impact.

Methodology for Time Domain Fatigue Life Assessment of Risers and Umbilicals

2010 ◽  
Author(s):  
Oddrun Steinkjer ◽  
Nils So̸dahl ◽  
Guttorm Gryto̸yr
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Time Domain ◽  
Life Assessment ◽  
Statistical Uncertainty ◽  
Short Term ◽  
Fatigue Assessment ◽  
Fatigue Life Assessment ◽  
Non Linear ◽  
Selection Of

Risers and umbilicals are exposed to dynamic loading from waves and floater motions. These structures are known to have a pronounced non-linear response characteristic. Non-linear time-domain finite element analyses is in general required to give an adequate description of the non-linearities involved. Analyses of a large number of short-term environmental conditions considering stochastic wave loading are required to give a representative description of the long-term fatigue loading on the structure. Short term fatigue damage is established by means of rain-flow cycle (RFC) counting in each stationary short-term condition. It is has been experienced that significant statistical uncertainties can be present in the short-term fatigue damage estimates. This is because the accumulated fatigue damage in a stationary condition normally has significant contribution from the largest stress cycles in the realisation. Selection of proper simulation length is hence essential to obtain reliable fatigue life estimates. Applicable codes and standards for risers and umbilicals provide Design Fatigue Factors (DFF) to secure adequate safety against failure due to wave induced fatigue. The total uncertainty in the calculated fatigue damage comes from various sources and the DFFs in e.g. DNV-OS-F201 “Dynamic Risers” and API-RP-2RD corresponds to a certain uncertainty level in the fatigue damage estimate. A recommended target value for the statistical uncertainty of the fatigue damage estimates is given with basis in these design codes. The objective of this paper is to give a description of a methodology recommended for time domain fatigue assessment. Special focus will be on the importance of adequate simulation time for predicting the short-term fatigue damage and selection of the short-term seastates in the scatter diagram. Statistical uncertainty is one source that the analyst actually can influence by selecting proper analysis methodology. A statistical uncertainty meassure can be used to evaluate the robustness in the estimated fatigue life. Assessment of statistical uncertainty in fatigue damage estimate is demonstrated by case studies. The fatigue assessment methodology discussed in this paper, will be described in an update of DNV-RP-F204 “Riser Fatigue” 2010.

2D and 3D CFD Investigations of Seabed Shear Stresses Around Subsea Pipelines

2013 ◽  
Author(s):  
Wenwen Shen ◽  
Terry Griffiths ◽  
Mengmeng Xu ◽  
Jeremy Leggoe
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Interaction Model ◽  
Suspended Sediment Transport ◽  
Shear Stresses ◽  
Parametric Function ◽  
Ample Evidence ◽  
North West ◽  
Wide Range ◽  
Subsea Pipelines

For well over a decade it has been widely recognised that existing models and tools for subsea pipeline stability design fail to account for the fact that seabed soils tend to become mobile well before the onset of pipeline instability. Despite ample evidence obtained from both laboratory and field observations that sediment mobility has a key role to play in understanding pipeline/soil interaction, no models have been presented previously which account for the tripartite interaction between the fluid and the pipe, the fluid and the soil, and the pipe and the soil. There are numerous well developed and widely used theories available to model pipe-fluid and pipe-soil interactions. A challenge lies in the way to develop a satisfactory fluid-soil interaction algorithm that has the potential for broad implementation under both ambient and extreme sea conditions due to the complexity of flow in the vicinity of a seabed pipeline or cable. A widely used relationship by Shields [1] links the bedload and suspended sediment transport to the seabed shear stresses. This paper presents details of computational fluid dynamics (CFD) research which has been undertaken to investigate the variation of seabed shear stresses around subsea pipelines as a parametric function of pipeline spanning/embedment, trench configuration and wave/current properties using the commercial RANS-based software ANSYS Fluent. The modelling work has been undertaken for a wide range of seabed geometries, including cases in 3D to evaluate the effects of finite span length, span depth and flow attack angle on shear stresses. These seabed shear stresses have been analysed and used as the basis for predicting sediment transport within the Pipe-Soil-Fluid (PSF) Interaction Model [2] in determining the suspended sediment concentration and the advection velocity in the vicinity of pipelines. The model has significant potential to be of use to operators who struggle with conventional stabilisation techniques for the pipelines, such as those which cross Australia’s North West Shelf, where shallow water depths, highly variable calcareous soils and extreme metocean conditions driven by frequent tropical cyclones result in the requirement for expensive and logistically challenging secondary stabilisation measures.

scholarly journals In Vitro Synergistic Interactions of Isavuconazole and Echinocandins against Candida auris

Antibiotics ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 355
Author(s):  
Unai Caballero ◽  
Sarah Kim ◽  
Elena Eraso ◽  
Guillermo Quindós ◽  
Valvanera Vozmediano ◽  
...  
Keyword(s):  
Interaction Model ◽  
Antifungal Drugs ◽  
Health Concern ◽  
Candida Auris ◽  
Fungistatic Activity ◽  
Drug Concentrations ◽  
Low Concentrations ◽  
Wide Range ◽  
Time Kill

Candida auris is an emergent fungal pathogen that causes severe infectious outbreaks globally. The public health concern when dealing with this pathogen is mainly due to reduced susceptibility to current antifungal drugs. A valuable alternative to overcome this problem is to investigate the efficacy of combination therapy. The aim of this study was to determine the in vitro interactions of isavuconazole with echinocandins against C. auris. Interactions were determined using a checkerboard method, and absorbance data were analyzed with different approaches: the fractional inhibitory concentration index (FICI), Greco universal response surface approach, and Bliss interaction model. All models were in accordance and showed that combinations of isavuconazole with echinocandins resulted in an overall synergistic interaction. A wide range of concentrations within the therapeutic range were selected to perform time-kill curves. These confirmed that isavuconazole–echinocandin combinations were more effective than monotherapy regimens. Synergism and fungistatic activity were achieved with combinations that included isavuconazole in low concentrations (≥0.125 mg/L) and ≥1 mg/L of echinocandin. Time-kill curves revealed that once synergy was achieved, combinations of higher drug concentrations did not improve the antifungal activity. This work launches promising results regarding the combination of isavuconazole with echinocandins for the treatment of C. auris infections.

ECA Methodology for Fatigue Design of Risers and Flowlines

2007 ◽  
Author(s):  
C. H. Luk ◽  
T. J. Wang
Keyword(s):  
Fracture Mechanics ◽  
Design Method ◽  
Steel Catenary Riser ◽  
Fatigue Design ◽  
Wide Range ◽  
Fatigue And Fracture ◽  
Level 3 ◽  
Fatigue Loads ◽  
Vessel Motion ◽  
Level 2

Engineering Criticality Assessment (ECA) is a procedure based on fracture mechanics that may be used to supplement the traditional S-N approach and determine the flaw acceptance and inspection criteria in fatigue and fracture design of risers and flowlines. A number of design codes provide guidance for this procedure, e.g. BS-7910:2005 [1]. However, more investigations and example studies are still needed to address the design implications for riser and flowline applications. This paper provides a review of the existing ECA methodology, presents a fracture mechanics design method for a wide range of riser and flowline fatigue problems, and shows flaw size results from steel catenary riser (SCR) and flowline (FL) examples. The first example is a deepwater SCR subjected to fatigue loads due to vessel motion and riser VIV. The second example is a subsea flowline subjected to thermal fatigue loads. The effects of crack re-characterization and material plasticity on the Level-2 and Level-3 ECA results of the SCR and flowline examples are illustrated.

Probabilistic Fatigue Assessment of a Mooring Line Based on Station-Keeping Trials in Ice

2021 ◽  
Author(s):  
Chana Sinsabvarodom ◽  
Bernt J. Leira ◽  
Wei Chai ◽  
Arvid Naess
Keyword(s):  
Fatigue Damage ◽  
Probabilistic Models ◽  
Full Scale ◽  
Mooring Line ◽  
Stress Range ◽  
Station Keeping ◽  
Probability Models ◽  
Line System ◽  
Fatigue Assessment ◽  
Rainflow Counting

Abstract The intention of this work is to perform a probabilistic fatigue assessment of a mooring line due to loads associated with the station-keeping of a ship in ice. In March 2017, the company Equinor (Statoil) conducted full-scale tests by means of station-keeping trials (SKT) in drifting ice in the Bay of Bothnia. The vessel Magne Viking was employed in order to represent a supply vessel equipped with a mooring line system, and the realtime loading during the full-scale measurement was recorded. The second vessel Tor Viking was serving as an ice breaker in order to maintain the physical ice management activities with different ice-breaking schemes, i.e. square updrift pattern, round circle pattern, circular updrift pattern and linear updrift pattern. The fatigue degradation corresponding to these different patterns were investigated. The peaks and valleys of the mooring tension are determined using the min peak prominence method. For the purpose of probabilistic fatigue assessment, the Rainflow-counting algorithm is applied to estimate the mooring stress range. Fatigue assessment based both on Rainflow counting and fitted probabilistic models were performed. For the latter, the stress range distributions from the observed data of mooring loads are fitted to various probability models in order to estimate the fatigue damage. It is found that the stress ranges represented by application of the Weibull distribution for the probabilistic fatigue approach provides results of the fatigue damage most similar to the Rainflow counting approach. Among the different scenarios of Ice management schemes, the circular updrift pattern provides the lowest magnitude of the fatigue degradation.

Management of Complex Loading Histories for Use in Probabilistic Creep-Fatigue Damage Assessments

2018 ◽  
Author(s):  
N. A. Zentuti ◽  
J. D. Booker ◽  
R. A. W. Bradford ◽  
C. E. Truman
Keyword(s):  
Fatigue Damage ◽  
Input Parameter ◽  
Three Dimensional ◽  
Complex Loading ◽  
Fe Model ◽  
Plant Component ◽  
Fatigue Lifetime ◽  
Wide Range ◽  
Stress Components ◽  
Creep Fatigue

An approach is outlined for the treatment of stresses in complex three-dimensional components for the purpose of conducting probabilistic creep-fatigue lifetime assessments. For conventional deterministic assessments, the stress state in a plant component is found using thermal and mechanical (elastic) finite element (FE) models. Key inputs are typically steam temperatures and pressures, with the three principal stress components (PSCs) at the assessment location(s) being the outputs. This paper presents an approach which was developed based on application experience with a tube-plate ligament (TPL) component, for which historical data was available. Though both transient as well as steady-state conditions can have large contributions towards the creep-fatigue damage, this work is mainly concerned with the latter. In a probabilistic assessment, the aim of this approach is to replace time intensive FE runs with a predictive model to approximate stresses at various assessment locations. This is achieved by firstly modelling a wide range of typical loading conditions using FE models to obtain the desire stresses. Based on the results from these FE runs, a probability map is produced and input(s)-output(s) functions are fitted (either using a Response Surface Method or Linear Regression). These models are thereafter used to predict stresses as functions of the input parameter(s) directly. This mitigates running an FE model for every probabilistic trial (of which there typically may be more than 104), an approach which would be computationally prohibitive.

Fatigue Assessment of Concrete Members Strengthened by FRP Materials

2014 ◽  
Vol 617 ◽  
pp. 221-224 ◽  
Author(s):  
Alena Čavojcová ◽  
Martin Moravcik
Keyword(s):  
Fatigue Damage ◽  
Cross Section ◽  
Theoretical Approach ◽  
Material Properties ◽  
Beam Cross Section ◽  
European Standard ◽  
Fatigue Assessment ◽  
Concrete Members ◽  
Damage Structure ◽  
T Beam

Fatigue and fatigue damage leads to a change in material properties that can lead to the element failures. Generally, it is necessary to verify the influence of the fatigue effects on the concrete members according to European standard EC2, [1]. FRP materials have been possibly used for the fatigue damage structure rehabilitation. There we can apply the condition of the limit boundaries stress on concrete and limit force in FRP material theoretical approach. Fatigue assessment will be analyzed for T-beam cross section with reinforcement and strengthened FPR material in this paper.

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