Time-Domain Investigation of a Semisubmersible in Rogue Waves

2002 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Christian Schmittner ◽  
Katja Stutz
Keyword(s):  
Time Domain ◽  
Rogue Wave ◽  
Limit State ◽  
Rogue Waves ◽  
Ultimate Limit State ◽  
Peak Period ◽  
Large Wave ◽  
Safety Standards ◽  
Design Wave Height ◽  
Present Design

Heave, pitch and roll motions as well as airgap are key characteristics of semisubmersibles in extreme seas which are defined by Ultimate Limit State design conditions (ULS) with a specified 100-year design wave height Hs and peak period Tp. The increasing number of reported rogue waves with unexpected large wave heights (Hmax/Hs > 2), crest heights (ζmax//Hmax > 0.6), wave steepness and group patterns (e.g. Three Sisters) may suggest a reconsideration of design codes by implementing an Accidental Limit State (ALS) with a return period of 104 years. For investigating the consequences of specific extreme sea conditions this paper analyses the seakeeping behaviour of a semisubmersible in a reported rogue wave, the Draupner New Year Wave embedded in irregular sea states. The numerical time-domain invegstigation using a panel method and potential theory is compared to frequency-domain results. In particular, the characteristics of the embedded rogue wave is varied to analyse the dynamic response of the semisubmersible in extreme wave sequences For validation, the selected sea condition is generated in a physical wave tank, and the sea-keeping behaviour of the semisubmersible is evaluated at model scale. In conclusion, the results deomstrate the consequences of rogue wave impacts, with respect to the relevance of present design methods and safety standards.

Reliability Analysis of Pipelines During Laying, Considering Ultimate Strength Under Combined Loads

1999 ◽  
Vol 122 (1) ◽  
pp. 40-46 ◽  
Author(s):  
Ragnar T. Igland ◽  
Torgeir Moan
Keyword(s):  
Structural Reliability ◽  
Limit State ◽  
Wave Spectrum ◽  
Probability Of Failure ◽  
Ultimate Limit State ◽  
Minor Importance ◽  
Target Level ◽  
Peak Period ◽  
System Effect ◽  
Load Effect

Structural reliability methods are applied to establish a measure of safety for pipelines during laying, and especially to calibrate semi-probabilistic ultimate limit state criteria based on measures of uncertainty, method of reliability, and a given target level. Ultimate collapse of thick tubes under combined external pressure, tension, and bending loads are studied applying the finite element method. Nonlinear effects of large deformations, effects of initial ovality, residual stresses, strain-hardening, yield anisotropy, and loading paths were accounted for in the analysis. A set of interaction equations is proposed. Load effects in the pipelines during installation by the S-lay method are studied. The effects of uncertainties in yield stress, mass, stiffness of the stinger, response amplitude operator and peak period for the wave spectrum were accounted for in the analysis. The major factors affecting strain concentration due to concrete coating are taken into account. A combination of design point calculation and importance sampling procedure is used to calculate the probability of failure. The study includes calibration of partial safety factors for the design format selected. The most important random variable is the model uncertainty for bending capacity, while the uncertainty of the load effect has minor importance for the probability of failure. The system effect is taken into account considering the correlation along the pipeline. The probability of failure is referred both to the total laying period as well as a 3-h period demonstrating that the target level needs to be defined in view of the reference time period. [S0892-7219(00)01501-6]

Hunting for Rogue Waves in a Three-Dimensional Nonlinear Wavefield: A Direct Simulation-Based Approach

2009 ◽  
Author(s):  
Wenting Xiao ◽  
Yuming Liu ◽  
Dick K. P. Yue
Keyword(s):  
Nonlinear Wave ◽  
Rogue Wave ◽  
Wave Spectrum ◽  
Three Dimensional ◽  
Rogue Waves ◽  
High Order ◽  
Wave Steepness ◽  
Large Wave ◽  
Resonant Interactions ◽  
Wavefield Simulation

We describe an investigation of the occurrence, statistics, and generation mechanisms of rogue wave in the open sea using direct three-dimensional phase-resolved nonlinear wavefield simulations. To achieve this we develop an efficient nonlinear wavefield simulation capability based on the high-order spectrum method which solves the primitive phase-resolved Euler equations. The simulations account for nonlinear wave-wave interactions up to an arbitrary high order in the wave steepness and are capable of accounting for effects of bottom bathymetry, variable current, and direct physics-based models for wind input and wave breaking dissipation. We apply direct large-scale simulations to obtain a large number of phase-resolved nonlinear wavefields, initially specified by directional wave spectra. The typical spatial-temporal domain size of such numerical nonlinear wavefields is O(103 km2) over evolution time of O(hr). These spatial and temporal scales account for quartet resonant interactions and partially for quintet resonant interactions among wave components in the wavefield. From the simulated nonlinear wavefields, rogue wave events are identified and their occurrence statistics are studied. It is shown that the classic linear theory (i.e. Rayleigh distribution) significantly underestimates the rogue wave occurrence. Second-order theory improves the Rayleigh prediction, but still underestimates the rogue wave occurrence in wavefields with moderately large wave steepness and relatively narrow directional spreading and spectrum bandwidth. The influence of key wave spectrum parameters (such as significant wave height, directional spreading, effective steepness, and spectrum bandwidth) on the rogue wave occurrence is analyzed. The classification of rogue waves according to their configuration is also obtained. The key characteristics of a rogue wave or rogue wave group in terms of kinematics and surface structure are analyzed and quantified. The nonlinear wave simulations, which provide full three-dimensional kinematics and dynamics of rogue wave events, provide a powerful tool for understanding the underlying mechanisms of their generation. They are elucidated by specific examples.

Modelling and Analysis of a Semi-Submersible Wind Turbine With a Central Tower With Emphasis on the Brace System

2013 ◽  
Author(s):  
Chenyu Luan ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Elastic System ◽  
State Of The Art ◽  
Limit State ◽  
Modeling Method ◽  
Ultimate Limit State ◽  
The Novel ◽  
Floating Wind Turbine ◽  
The Time Domain

This paper deals with analysis of the OC4 DeepCWind semi-submersible wind turbine, which is provided by NREL through the OC4 project. This concept is a three-column semi-submersible supporting a 5 MW wind turbine on an additional central column. The fact that the semi-submersible floater needs a large water line restoring moment to achieve sufficient stability and the control of the cost based on the steel weight make the design of braces and pontoons very challenging. Effective methods are needed to check the strength of the brace system based on the response forces and moments in the braces under different design environmental conditions, while the floating wind turbine is needed to be considered as an aero-hydro-servo-elastic system. A novel modeling methodology based on the code Simo/Riflex is introduced in this paper. Simo/Riflex is a state-of-the-art code that can account for the coupling effect between rigid body motions and slender structures (e.g. mooring lines, braces and blades) in the time-domain. Simo/Riflex can be combined with Aerodyn, which is a state-of-the-art aerodynamic code, to model the floating wind turbine as an aero-hydro-servo-elastic system, as well as be combined with simplified aerodynamic codes (e.g.TDHMILL) to improve the efficiency of the numerical simulation. The novel modeling method can give the forces and moments in the brace system of the floater under hydrodynamic and aerodynamic loads in the time-domain. In order to get the structural response of the braces, the side columns and the central supporting column are modeled as independent rigid bodies in Simo while the braces are modeled by beam elements in Riflex. Master and slave relationship is applied at the joints in between of the columns and braces. As an application example, the novel modeling method based on the code Simo/Riflex+TDHMILL, which is capable of modeling the floating wind turbine as an aero-hydro-elastic system, has been used to carry out Ultimate Limit State (ULS) design check for the brace system of the OC4 DeepCWind semi-submersible wind turbine based on relevant standards, i.e. NORSOK N00-3, NORSOK N-004, IEC61400-1, IEC61400-3. The modeling method can also be used by other codes which have similar features as Simo/Riflex.

Bending Moments of an FPSO in Rogue Waves

2004 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Christian E. Schmittner ◽  
Janou Hennig ◽  
Carlos Guedes Soares ◽  
Nuno Fonseca ◽  
...  
Keyword(s):  
Time Domain ◽  
Rogue Wave ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Bending Moments ◽  
The North ◽  
Frequency Domain Methods ◽  
Local Wave ◽  
The Time Domain ◽  
Wave Induced

The increasing numbers of reported rogue waves with extreme crest and wave heights and unusual group pattern with the consequence of severe damages raise the question if such exceptional events have to be considered routinely for the design of ships and offshore structures. For the investigation of the effects of rogue wave impacts time domain simulation methods are required in addition to traditional frequency domain methods which may not be sufficient to consider these extreme events. In this paper the vertical bending moments at the midship section of an FPSO are investigated using state of the art numerical simulation tools in combination with experiments. For the seakeeping tests the extremely high New Year Wave (registered in the North Sea) is generated in the wave tank, and motions and structural forces are analyzed at model scale. For validation the results are evaluated deterministically and compared to numerical simulations. The time domain calculation allows to artificially change local wave characteristics. The steepness of the selected rogue wave is varied and the influence on wave induced loads is studied. A comparison with standard procedures of seakeeping analysis and classification rules closes the paper.

The twin properties of rogue waves and homoclinic solutions for some nonlinear wave equations

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Wei Tan ◽  
Zhao-Yang Yin
Keyword(s):  
Differential Equations ◽  
Wave Equations ◽  
Rogue Wave ◽  
Nonlinear Partial Differential Equations ◽  
Rogue Waves ◽  
Homoclinic Solutions ◽  
Nonlinear Wave Equations ◽  
Bilinear Method ◽  
Wave Solutions ◽  
Rogue Wave Solutions

Abstract The parameter limit method on the basis of Hirota’s bilinear method is proposed to construct the rogue wave solutions for nonlinear partial differential equations (NLPDEs). Some real and complex differential equations are used as concrete examples to illustrate the effectiveness and correctness of the described method. The rogue waves and homoclinic solutions of different structures are obtained and simulated by three-dimensional graphics, respectively. More importantly, we find that rogue wave solutions and homoclinic solutions appear in pairs. That is to say, for some NLPDEs, if there is a homoclinic solution, then there must be a rogue wave solution. The twin phenomenon of rogue wave solutions and homoclinic solutions of a class of NLPDEs is discussed.

scholarly journals Fragility curves for Italian URM buildings based on a hybrid method

2021 ◽  
Author(s):  
A. Sandoli ◽  
G. P. Lignola ◽  
B. Calderoni ◽  
A. Prota
Keyword(s):  
Seismic Vulnerability ◽  
Fragility Curves ◽  
Limit State ◽  
Ultimate Limit State ◽  
Masonry Building ◽  
Masonry Buildings ◽  
Seismic Behaviour ◽  
Building Stock ◽  
Ground Acceleration ◽  
Damage Scenario

AbstractA hybrid seismic fragility model for territorial-scale seismic vulnerability assessment of masonry buildings is developed and presented in this paper. The method combines expert-judgment and mechanical approaches to derive typological fragility curves for Italian residential masonry building stock. The first classifies Italian masonry buildings in five different typological classes as function of age of construction, structural typology, and seismic behaviour and damaging of buildings observed following the most severe earthquakes occurred in Italy. The second, based on numerical analyses results conducted on building prototypes, provides all the parameters necessary for developing fragility functions. Peak-Ground Acceleration (PGA) at Ultimate Limit State attainable by each building’s class has been chosen as an Intensity Measure to represent fragility curves: three types of curve have been developed, each referred to mean, maximum and minimum value of PGAs defined for each building class. To represent the expected damage scenario for increasing earthquake intensities, a correlation between PGAs and Mercalli-Cancani-Sieber macroseismic intensity scale has been used and the corresponding fragility curves developed. Results show that the proposed building’s classes are representative of the Italian masonry building stock and that fragility curves are effective for predicting both seismic vulnerability and expected damage scenarios for seismic-prone areas. Finally, the fragility curves have been compared with empirical curves obtained through a macroseismic approach on Italian masonry buildings available in literature, underlining the differences between the methods.

Abundant rogue wave solutions for the (2 + 1)-dimensional generalized Korteweg–de Vries equation

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Huanhuan Lu ◽  
Yufeng Zhang
Keyword(s):  
Vries Equation ◽  
Rogue Wave ◽  
Rogue Waves ◽  
Third Order ◽  
First Order ◽  
Wave Solutions ◽  
De Vries ◽  
Rogue Wave Solutions ◽  
Bilinear Formulation ◽  
Hirota Bilinear

AbstractIn this paper, we analyse two types of rogue wave solutions generated from two improved ansatzs, to the (2 + 1)-dimensional generalized Korteweg–de Vries equation. With symbolic computation, the first-order rogue waves, second-order rogue waves, third-order rogue waves are generated directly from the first ansatz. Based on the Hirota bilinear formulation, another type of one-rogue waves and two-rogue waves can be obtained from the second ansatz. In addition, the dynamic behaviours of obtained rogue wave solutions are illustrated graphically.

Concrete Modeling for Extreme Wave Slam Events

2017 ◽  
Author(s):  
Kasper Wåsjø ◽  
Terje P. Stavang ◽  
Tore H. Søreide
Keyword(s):  
Time Domain ◽  
Linear Time ◽  
Limit State ◽  
Material Model ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Capacity Control ◽  
Extreme Wave ◽  
Conventional Design ◽  
Non Linear

Experience from model tests has initiated a growing attention towards extreme wave slam as a critical load situation for offshore large volume structures. Most of the problem is related to the local slam pressure, which may go up to several MPa’s for 100-year and 10 000-year waves. The paper deals with modeling techniques for marine concrete structures under extreme slam loading from waves where dynamic effects together with material softening play a major role for the response. Different analysis approaches for ultimate limit state (ULS) and accidental limit state (ALS) controls are discussed in view of reliability philosophy as basis for conventional design approach. The present paper is devoted to the local impact scenario and the alternative approaches for response and capacity control involving non-linear time domain analyses. Conventional design schemes as based on linear elastic models for response calculation together with code specified capacity control often come out more conservative than non-linear approach. The paper demonstrates by case studies how softening of the structure in general reduces the response in terms of section forces. A key issue when going from conventional linear approaches into non-linear techniques is to still keep an acceptable reliability level on the capacity control. Load and material factors are normally based on structures with limited non-linearity where linear response modeling is representative. Implementing non-linear material model in time domain analysis has a major challenge in limiting the sensitivity in response and capacity calculation. The paper demonstrates the way material model of concrete affects the section forces to go into local capacity control, and concludes on needed sensitivity analyses. Practical approaches on the concrete slam problem together with resulting utilizations from the control are demonstrated. The full non-linear technique by response and capacity control in one analysis is also handled, using average material parameters and justifying safety factors for the effect of implementing characteristic lower strength of concrete in the capacity. The paper ends up in a recommendation on non-linear time domain analysis procedure for typically slam problems. A discussion is also given on applicable design codes with attention to non-linear analysis.

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