Estimating Long-Term Extreme Slamming From Breaking Waves

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Gunnar Lian ◽  
Sverre K. Haver
Keyword(s):  
Limit State ◽  
Gumbel Distribution ◽  
Nonlinear Problems ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Exceedance Probability ◽  
Ultimate Limit State ◽  
Breaking Wave ◽  
Large Variability

Characteristic loads for design of offshore structures are defined in terms of their annual exceedance probability, q. In the Norwegian Petroleum Regulations, q = 10−2 is required for the ultimate limit state (ULS), while q = 10−4 is required for the accidental limit state (ALS). In principle, a full long-term analysis (LTA) is required in order to obtain consistent estimates. This is straightforward for linear response problems, while it is a challenge for nonlinear problems, in particular if they additionally are of an on–off nature. The latter will typically be the case for loads due to breaking wave impacts. In this paper, the challenges related to estimation of characteristic slamming loads are discussed. Measured slamming loads from a model test are presented, and the observed large variability is discussed. The stochastic nature of slamming loads is studied using a simplified linear relation between the sea states and the Gumbel distribution parameter surfaces. The characteristic slamming loads with q-annual probability of exceedance are estimated from an LTA using the short-term distribution of the slamming loads and the long-term distribution of the sea states. The effect of integrating over a smaller area of the scatter diagram of the sea states is studied. The uncertainties in response from slamming loads are compared to a more common response process, and the relation between variability and the number of realizations in each sea state is looked into.

Efficient Evaluation of Long-Term Response for Design of Components of Offshore Structures

2017 ◽  
Author(s):  
Paulo Mauricio Videiro ◽  
Luis Volnei Sudati Sagrilo
Keyword(s):  
Limit State ◽  
Offshore Structures ◽  
Ultimate Limit State ◽  
Wave Load ◽  
Wave Effects ◽  
Load Effects ◽  
Bracing System ◽  
Term Response ◽  
Tubular Component

This paper compares two approaches for the estimation of long-term response of wave load effects on offshore structures. These approaches are applied to estimate the extreme value of the cross section interaction ratio of a tubular component of the bracing system of a semisubmersible platform. The tubular component is subjected to axial loads and bending moments due to static loads and wave effects. The iteration ratio in the ultimate limit state is defined by applying design criteria derived from API RP-2A LRFD [6]. The approaches are also applied to estimate the long-term response of a single degree of freedom system due to wave actions. The first approach is based on the proposals of Videiro and Moan [3]. The results of the first approach are compared with a new model of long-term response estimation, based on the up-crossing rate distribution of the response process.

Implementation of a Method for Free-Spanning Pipeline Analysis

2021 ◽  
Author(s):  
Joannes Gullaksen
Keyword(s):  
Dynamic Response ◽  
Flow Direction ◽  
Limit State ◽  
Cross Flow ◽  
Ultimate Limit State ◽  
Force Model ◽  
Short Term ◽  
Direct Wave ◽  
Current Loading

Abstract The scope of this paper is to provide a method implemented in an application for assessment of dynamic response of free spanning pipelines subjected to combined wave and current loading. The premises for the paper are based on application development within pipeline free span evaluation in a software development project. A brief introduction is provided to the basic hydrodynamic phenomena, principles and parameters for dynamic response of pipeline free spans. The choice of method for static and dynamic span modelling has an influence on calculated modal frequencies and associated stresses. Due to the importance of frequencies and stresses for fatigue and environmental loading calculations, the choice of analysis approach influences the partial safety factor format. The aim of the structural analysis is to provide the necessary input to the calculations of VIV and force model response, and to provide realistic estimations of static loading from functional loads. Environmental flow conditions are implemented in the application, such as steady flow due to current, oscillatory flow due to waves and combined flow due to current and waves. Combined wave and current loading include the long-term current velocity distribution, short-term and long-term description of wave-induced flow velocity amplitude and period of oscillating flow at the pipe level and return period values. Inline and cross-flow vibrations are considered in separate response models. For pipelines and risers, modes are categorized in in-line or cross-flow direction. A force model is also considered for the short-term fatigue damage due to combined current and direct wave actions. Design criteria can be specified for ultimate limit state (ULS) and fatigue limit state (FLS) due to in-line and cross-flow vortex induced vibrations (VIV) and direct wave loading.

A First Step Towards the Development of a Pipeline Wrinkle Material Ultimate Limit State

2006 ◽  
Author(s):  
Aaron Dinovitzer ◽  
Sanjay Tiku ◽  
Vlado Semiga ◽  
Abdelfettah Fredj ◽  
Joe Zhou ◽  
...  
Keyword(s):  
Limit State ◽  
Low Frequency ◽  
Failure Criteria ◽  
Ultimate Limit State ◽  
Ongoing Research ◽  
Undesirable Event ◽  
Load Effects ◽  
Line Pressure ◽  
Fault Displacement

While the formation of a wrinkle in an onshore pipeline is an undesirable event, in many instances this event does not have immediate pipeline integrity implications. The magnitude or severity of a wrinkle formed due to displacement controlled loading processes (e.g. slope movement, fault displacement, frost heave and thaw settlement) may increase with time, eventually causing serviceability concerns (e.g. fluid flow or inspection restrictions). Pipe wall damage leading to cracking and eventually a loss of containment involves contributions from the wrinkle formation and growth processes, as well as, wrinkle deformations promoted by in-service line pressure, temperature and seasonal soil displacements. The objective of this paper is to provide an overview of the ongoing research efforts, sponsored by TransCanada PipeLines Ltd. and Tokyo Gas Co. Ltd., towards the development of a mechanics based wrinkle ultimate limits state that may be used in future to evaluate the long term integrity of wrinkled pipeline segments. The research efforts include non-linear finite element modeling to demonstrate the ability of experimentally derived material properties to predict the formation of through wall cracking induced by high and low frequency load effects. This paper outlines the material testing program used to support the development of failure criteria capable of considering the contributions of monotonic deformation, as well as, high and low cycle cyclic loading.

An Assessment of Load and Response for Horizontal Slamming Loads From Model Scale Experiments

2018 ◽  
Author(s):  
Martin Storheim ◽  
Gunnar Lian
Keyword(s):  
Structural Response ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Load Level ◽  
Material Behavior ◽  
Wave Impact ◽  
Large Variability ◽  
Slamming Load ◽  
Reasonable Approach ◽  
Wave Slamming

Steep breaking waves can result in high impact loads on offshore structures, and several model test campaigns have been conducted to assess the effect of horizontal wave slamming. High loads have been measured, and they can be challenging to withstand without significant deformation. For wave slamming problems it is common to estimate the characteristic slamming load and assume that this will give an equivalent characteristic response. One challenge related to the slamming load is that it has a large variability in load level, the duration of the load and the shape of the overall load pulse. This variability can have a large impact on the estimated response to the characteristic load, causing a similar or larger variability in response. Due to the sensitivity to the structural response, it may be difficult to interpret large amounts of such data to arrive at a relevant design load without making overly conservative assumptions. This paper investigates the sensitivity of the structural response to assumptions made in the material modelling and how the short term variability is affected if we instead of load use response indicators such as plastic strain and max deformation to arrive at a characteristic load. For this purpose, a simplified dynamic response model is created, and the recorded wave impact events can then be evaluated based on the predicted structural response from the simplified model. It was found that the structural response is sensitive to the structural configuration. The assumed material behavior and hydro-elastoplastic effects were identified to greatly affect the structural response. A reasonable approach to arrive at the q-annual response seems to be to first estimate the q-annual extreme slamming load, and then run the structural analysis on several of the measured slamming time series with the estimated q-annual extreme pressure.

Reliability of TLP Tendons Under Storm Sea States

2005 ◽  
Author(s):  
Federico Barranco Cicilia ◽  
Edison Castro Prates de Lima ◽  
Lui´s Volnei Sudati Sagrilo
Keyword(s):  
Reliability Analysis ◽  
Limit State ◽  
Nonlinear Dynamic Analysis ◽  
Analytical Models ◽  
Cumulative Probability ◽  
Wave Forces ◽  
Ultimate Limit State ◽  
Sea State ◽  
Extreme Response

This paper presents a methodology for reliability analysis of Tension Leg Platform (TLP) tendons subjected to extraordinary sea state conditions like hurricanes or winter storms. A coupled approach in time domain is used to carry out TLP random nonlinear dynamic analysis including wind, current and first and second order wave forces. The tendons Ultimate Limit State (ULS) condition is evaluated by an Interaction Ratio (IR) taking into account dynamic combination among tension, bending and hydrostatic pressure. Expected long-term extreme IR is obtained through the integration of cumulative probability functions (CPFs) fitted to response maxima associated to individual short term sea states. The reliability analysis is performed using a time-integrated scheme including uncertainties in loads, tendon strength, and analytical models. Failure probabilities for the most loaded tendon of a TLP in Campeche Bay, Mexico, considering a 100-yr design sea state and the 100-yr extreme response generated by long-term observed storms are compared.

scholarly journals ON DESIGN FEATURES OF PROPPED AND UNPROPPED HYPERSTATIC STRUCTURES

2007 ◽  
Vol 13 (2) ◽  
pp. 123-129 ◽  
Author(s):  
Algirdas Kudzys ◽  
Romualdas Kliukas ◽  
Antanas Kudzys
Keyword(s):  
Reinforced Concrete ◽  
Design Methodology ◽  
Extreme Values ◽  
Limit State ◽  
Ultimate Limit State ◽  
Term Survival ◽  
Partial Factor ◽  
Ultimate Limit ◽  
Composite Steel

An effect of structural and technological features on the design methodology of hyperstatic precast reinforced concrete and composite steel‐concrete structures is discussed. Permanent and variable service, snow and wind loads of buildings and their extreme values are analysed. Two loading cases of precast reinforced concrete and composite steel‐concrete continuous and sway frame beams as propped and unpropped members are considered. A redistribution of bending moments for the ultimate limit state of beams is investigated. A limit state verification of hyperstatic beams by the partial factor and probability‐based methods is presented. It is recommended to calculate a long‐term survival probability of beams by the analytical method of transformed conditional probabilities.

scholarly journals Reliability Updating of Offshore Structures Subjected to Marine Growth

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 414
Author(s):  
Franck Schoefs ◽  
Thanh-Binh Tran
Keyword(s):  
Limit State ◽  
Dynamic Bayesian Network ◽  
Offshore Structures ◽  
Drag Forces ◽  
The North ◽  
The North Sea ◽  
Inspection And Maintenance ◽  
Inspection Data ◽  
Atlantic Area

Marine growth is a known problem for oceanic infrastructure and has been shown to negatively impact the reliability of bottom-fixed or floating offshore structures submitted to fatigue or extreme loading. Among other effects, it has been shown to change drag forces by increasing member diameters and modifying the roughness. Bio-colonization being highly random, the objective of this paper is to show how one-site inspection data increases reliability by decreasing uncertainties. This can be introduced in a reliability-based inspection framework for optimizing inspection and maintenance (here, cleaning). The modeling and computation are illustrated through the reliability analysis of a monopile in the European Atlantic area subjected to marine growth and according to the plastic collapse limit state. Based on surveys of structures in the North Sea, long-term stochastic modeling (space and time) of the marine growth thickness is first suggested. A Dynamic Bayesian Network is then developed for reliability updating from the inspection data. Finally, several realistic (10–20 measurements) inspection strategies are compared in terms of reliability improvement and the accuracy of reliability assessment.

Characteristic Levels of Strongly Nonlinear Extreme Wave Load Effects

2016 ◽  
Author(s):  
Thomas B. Johannessen ◽  
Øistein Hagen
Keyword(s):  
Wave Breaking ◽  
Nonlinear Problems ◽  
Offshore Structures ◽  
Short Term ◽  
Nonlinear Load ◽  
Load Effect ◽  
Strongly Nonlinear ◽  
Load Effects ◽  
Term Analysis

Offshore structures are typically required to withstand extreme and abnormal load effects with annual probabilities of occurrence of 10−2 and 10−4 respectively. For linear or weakly nonlinear problems, the load effects with the prescribed annual probabilities of occurrence are typically estimated as a relatively rare occurrence in the short term distribution of 100 year and 10 000 year seastates. For strongly nonlinear load effects, it is not given that an extreme seastate can be used reliably to estimate the characteristic load effect. The governing load may occur as an extremely rare event in a much lower seastate. In attempting to model the load effect in an extreme seastate, the short term probability level is not known nor is it known whether the physics of the wave loading is captured correctly in an extreme seastate. Examples of such strongly nonlinear load effects are slamming loads on large volume offshore structures or wave in deck loads on jacket structures subject to seabed subsidence. Similarly, for structures which are unmanned in extreme weather, the governing load effects for the manned structure will occur as extremely rare events in a relatively frequent seastate. The present paper is concerned with the long term distribution of strongly nonlinear load effects. Using a simple point estimate of the wave elevation correct to second order and a crest kinematics model which takes into account the possibility of wave breaking, the long term distribution of drag load on a column above the still water level is studied and compared with a similar loading model based on second order kinematics which does not include the effect of wave breaking. The findings illustrate the challenges listed above. Model tests are useful in quantifying strongly nonlinear load effects which cannot be calculated accurately. But only a relatively small number of seastates can be run in a model test campaign and it is not feasible to estimate short term responses far beyond the three hour 90% fractile level. Similarly, Computational Fluid Dynamics (CFD) is increasingly useful in investigating complex wave induced load effects. But only a relatively small number of wave events can be run using CFD, a long term analysis of load effects cannot in general be carried out. It appears that there is a class of nonlinear problems which require a long term analysis of the load effect in order for the annual probability of occurrence to be estimated accurately. For problems which cannot be estimated by simple analytical means, the governing wave events can be identified by long term analysis of a simple model which capture the essential physics of the problem and then analysed in detail by use of CFD or model tests.

Characteristics of the Wave Slamming Forces on Jacket Structures Under Plunging Breaking Waves Based on Experimental Data

2017 ◽  
Author(s):  
Jithin Jose ◽  
Olga Podrażka ◽  
Ove Tobias Gudmestad ◽  
Witold Cieślikiewicz
Keyword(s):  
Energy Demand ◽  
Clean Energy ◽  
Breaking Waves ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Wave Forces ◽  
Breaking Wave ◽  
Jacket Structures ◽  
Wave Slamming ◽  
Wave Properties

Due to increased energy demand and thrive for clean energy, offshore wind energy has become popular these days. A large number of offshore wind turbines supported by fixed type substructures have been installed, among which jacket structures are getting popular in recent times. The forces from breaking waves are a major concern in the design of offshore structures installed in shallow waters. However, there are only limited studies available regarding breaking wave forces on jacket structures and still there exist many uncertainties in this area. During the WaveSlam experiment carried out in 2013, a jacket structure of 1:8 scale was tested on a large number of breaking wave conditions. Wave properties and the forces on the structure were measured during the experiment. The total wave slamming forces are being filtered from the experimental measured force using the Empirical Mode Decomposition method and local slamming forces are obtained by the Frequency Response Function method. Based on these results, the peak slamming force and slamming coefficients on the jacket members are estimated. The wave parameters (wave height and period) and wave front asymmetry are obtained from measured wave properties. The variation of slamming forces and slamming coefficients with respect to these parameters are also investigated.

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