Random Waves and Capsize Probability Based on Large Amplitude Motion Analysis

2002 ◽  
Author(s):  
Jan O. de Kat ◽  
Dirk-Jan Pinkster ◽  
Kevin A. McTaggart
Keyword(s):  
Time Domain ◽  
Random Waves ◽  
Extreme Wave ◽  
Small Probability ◽  
Safe Operation ◽  
Short Term ◽  
Physical Behavior ◽  
Wind Climate ◽  
Large Amplitude Motion

The objective of this paper is to apply a methodology aimed at the probabilistic capsize assessment of two naval ships: a frigate and a corvette. Use is made of combined knowledge of the wave and wind climate a ship will be exposed to during its lifetime and of the physical behavior of that ship in the various sea states it is likely to encounter. This includes the behavior in extreme wave conditions that have a small probability of occurrence, but which may be critical to the safe operation of a ship. Time domain simulations provide the basis for deriving short-term and long-term statistics for extreme roll angles. The numerical model is capable of predicting the 6 DOF behavior of a steered vessel in wind and waves, including conditions that may lead to broaching and capsizing.

Long Term Analysis for Estimation of Wave Slamming Pressures for Spar Design

2015 ◽  
Author(s):  
Ho-Joon Lim ◽  
Gunnar Lian ◽  
Sverre Haver ◽  
Oddgeir Dalane ◽  
Bonjun Koo ◽  
...  
Keyword(s):  
Model Tests ◽  
Design Parameters ◽  
Exceedance Probability ◽  
Extreme Wave ◽  
Short Term ◽  
Sea State ◽  
Norwegian Sea ◽  
Wave Slamming ◽  
Term Analysis

A long term analysis was performed to determine extreme wave slamming loads on the Aasta Hansteen Spar, the first production and storage Spar to be installed in the Norwegian Sea. The Spar will experience high slamming pressures on the hull due to harsh environments in the field. Extensive model tests were performed to measure the wave slamming pressure which is one of challenging design parameters. The slamming loads were measured with a 3×3 array of force transducer panels attached to the Spar hull. The extreme slamming loads were estimated from 3-hour simulations of the 100-yr and 10000-yr wave environments at the Aasta Hansteen field in the Norwegian Sea. The wave simulations included fourteen sea states, and each sea state was represented by as many as 20 realizations. Based on model test data, short term analysis of 3-hour extreme pressure at each tested sea state was performed using the Gumbel distribution. Due to high variability of 3-hour maximum pressures, a long term analysis was required to investigate the proper percentile level to be used in the design. The paper presents a long term statistical methodology for extreme wave slamming loads that is used to calculate long term slamming pressures corresponding to a specified annual exceedance probability of q (e.g., q = 10−2 and q = 10−4). The paper also derives the appropriate non-exceedance probability for a short term wave environment that reproduces the long term pressures of a specified annual exceedance probability, q. Various sensitivity analyses (e.g., on the two Gumbel parameters, number of realizations, etc.) were performed to validate the short term target percentiles and associated extreme pressures derived from this approach. Details of the model tests and methodology to define the design pressure profile above mean water level (MWL) are presented in a companion paper of this Conference.

Analysis of Short-Term and Long-Term Wave Statistics by Time Domain Simulations Statistics

2017 ◽  
Author(s):  
Øistein Hagen ◽  
Ida Håøy Grue ◽  
Jørn Birknes-Berg ◽  
Gunnar Lian ◽  
Kjersti Bruserud
Keyword(s):  
Wave Height ◽  
Time Domain ◽  
Statistical Distributions ◽  
Short Term ◽  
Sea State ◽  
Wave Statistics ◽  
Individual Wave ◽  
Wave Heights ◽  
Crest Height

In the design of new structures and assessment of existing structures, short- and long term statistical distributions of wave height, crest height and wave periods, as well as joint distributions, are important for structural integrity assessment. It is important to model the statistical distributions accurately to calculate wave design criteria and to assess fatigue life. A detailed study of the wave statistics for an offshore location at the Norwegian Continental Shelf field is carried out. Extensive time domain simulations for the complete scatter diagram of possible sea states are carried out by a second order wave model. Time series of the surface elevation are generated for JONSWAP and Torsethaugen wave spectra, and for several wave spreading models. Statistics for individual wave heights, crest heights and wave periods are established. The simulated results for the short-term statistics are compared with existing short term models that are commonly used, viz. the Forristal, Næss and Rayleigh wave height distributions, and the Forristall 2nd order crest height distribution. Also, parameterized distributions for wave height and for crest height are fitted to the simulated data. The long-term distributions F(H) and F(C) of all simulated individual wave heights H and crest heights C are determined by weighting the simulations with the long-term probability of occurrence of the sea state. Likewise, the long-term distributions F(Hmax) and F(Cmax) of the maximum simulated individual wave heights Hmax and crest heights Cmax in the sea states are determined. The design criteria for return periods R = 1, 10, 100 and 10 000 years are determined from the appropriate quantile levels. The effect of statistical uncertainty is investigated by comparing the confidence intervals for the estimated extreme values results as function of the number N of 3-hour time domain simulations per sea state for 10<N<500.

Long-Term Analysis Applied to Mooring Systems Design

2020 ◽  
Author(s):  
Pedro Seabra ◽  
Luis Volnei Sudati Sagrilo ◽  
Paulo Esperança
Keyword(s):  
Time Domain ◽  
Environmental Conditions ◽  
Systems Design ◽  
Environmental Data ◽  
Coupled Analysis ◽  
Offshore Structure ◽  
Short Term ◽  
Extreme Response ◽  
Term Analysis

Abstract Nowadays, the most used methodology to predict line tensions is the short-term coupled analysis, where the mooring system responses are obtained by a time-domain analysis for only some specific design combinations of extreme environmental conditions. This mooring analysis demands certain considerations and it is not the best way to obtain the offshore structure responses. The advances in both quantity and quality of collected environmental data and the increase of the computers processing power has enabled to consider the approach of more accurate long-term methodologies for mooring systems design. This paper proposes a numerical/computational procedure to obtain the extreme loads (ULS) acting on offshore platforms’ mooring lines. The work is based on the methodology of long-term analysis, employing a 10-yr long short-term environmental dataset of 3-h sea-states, where each short-term environmental condition is composed of the simultaneously observed environmental parameters of wave (sea and swell), wind and current. The methodology is applied to the analysis of three different mooring systems: a) spread-moored FPSO, b) Semi-Submersible platform and c) turret-moored FPSO. The Bootstrap approach is employed in order to take into account the statistical uncertainty associated to the estimated long-term most probable extreme response due to the limited number of short-term environmental conditions. The work was carried out using Dynasim software [1] to generate the time domain tension time series, which were later post-processed by using computational codes developed with Python software. Longer short-term numerical simulations lengths than the short-term period (3-h) have been investigated in order to understand the influence of this parameter on the final extreme long-term top tensions.

Environmental Contour Lines for Design Purposes: Why and When?

2004 ◽  
Author(s):  
Sverre Haver ◽  
Gudmund Kleiven
Keyword(s):  
Time Domain ◽  
Exceedance Probability ◽  
Response Analysis ◽  
Short Term ◽  
Structural Problems ◽  
Contour Lines ◽  
Convenient Approach ◽  
Probabilistic Structure ◽  
Term Response

Methods of prediction of structural loads corresponding to a required target annual exceedance probability are reviewed. Particular attention is given to utilization of environmental contour lines for such a purpose. This approach is based on using short term methods for predicting adequate estimates of the q-probability response. The environmental contour line approach is a very convenient approach if complicated structural problems are considered. For such problems one will often have to involve numerical time domain analyses or model tests to reveal the short term probabilistic structure of the response maxima, making a full long term response analysis impossible for most practical problems.

scholarly journals EFFECTS OF MEASUREMENT ERROR ON LONG-TERM WAVE STATISTICS

1984 ◽  
Vol 1 (19) ◽  
pp. 24
Author(s):  
Bernard Le Mahaute ◽  
Shen Wang
Keyword(s):  
Measurement Errors ◽  
Extreme Event ◽  
Definite Descriptions ◽  
Extreme Wave ◽  
Short Term ◽  
Wave Statistics ◽  
Record Length ◽  
Long Run

The effect of sample size on confidence band in predicting the extreme wave height is related to the return period and the duration of the sample record length. An estimate of errors resulting from various methods of data acquisition is given. The uncertainties corresponding to various number of years of observation and various measurement errors are analyzed for various return intervals. It is shown that data accuracy and record length are equally important in long term wave predictions. At the present time, the determination of extreme event benefits more from relatively less accurate long-term hindcast calculation rather than short-term high quality measurements. In the long run, a long-term accurate measurement program is imperative if more definite descriptions of extreme events are sought.

Long-term monitoring of a progressively deteriorating bridge to support safe operation

2021 ◽  
Author(s):  
Darby Johannessen ◽  
Tim Heldt ◽  
Neal Lake ◽  
Hanson Ngo ◽  
Joshua Frew
Keyword(s):  
Structural Performance ◽  
Safe Operation ◽  
Short Term ◽  
Strain Monitoring ◽  
Structural Capacity ◽  
Conventional Instrumentation ◽  
Term Monitoring ◽  
Initial Results ◽  
Selection Of

<p>Gradual deterioration of concrete structures due to alkali-silica reaction (ASR) and other mechanisms is a worldwide issue which is especially concerning for bridges. Currently, the point at which such deterioration begins to significantly impact structural capacity is not clearly defined. In this study, long-term continuous strain monitoring instrumentation was installed on a deteriorating Queensland bridge in order to monitor structural performance and support ongoing management. Short-term conventional instrumentation was also installed, and a grillage model was developed in order to facilitate benchmarking and validation of the long-term system. This paper describes the rationale, selection of instrumentation and presents initial results.</p>

Estimation of Short-and Long-Term Probability Distributions of Wave-Induced Loads Acting on a Cruise Vessel in Extreme Seas

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Suresh Rajendran ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Time Domain ◽  
International Association ◽  
Probability Distributions ◽  
Bending Moment ◽  
Green Water ◽  
Cruise Ship ◽  
Short Term ◽  
Strip Theory ◽  
Radiation Forces

A time domain code based on strip theory is applied to calculate the probability distributions of relative motions and bending moments of a cruise ship in a set of extreme seas. The code includes two levels of complexity. The simpler one combines linear radiation and diffraction forces with nonlinear Froude–Krylov forces, hydrostatic forces, and shipping of green water on the bow. Cummins formulation is used to represent the radiation forces. The second approach is a generalization of the first one and, although the formulation is based on the linear assumption (of the radiation forces), the effects of body nonlinearity are considered by a simplified method: the memory functions, infinite frequency added masses, and the radiation restoring coefficients are assessed at each time instant as function of the instantaneous wetted surface. A similar procedure is used to calculate the diffraction forces. The code is used to analyze the responses of a cruise ship in a set of extreme sea conditions. The short-term nonlinear responses are represented by empirical probability distributions, obtained from the nonlinear time domain simulations, and the quality of the predictions is assessed by comparing with model tests experimental data. Finally, the long-term value of the bending moment is calculated from the short-term distribution of the nonlinear loads in a few extreme sea states selected based on coefficient of contribution method, and the results are compared with the International Association of Classification Societies (IACS) rule bending moment.

scholarly journals Removing Ocular Movement Artefacts by a Joint Smoothened Subspace Estimator

2007 ◽  
Vol 2007 ◽  
pp. 1-13 ◽  
Author(s):  
Ronald Phlypo ◽  
Paul Boon ◽  
Yves D'Asseler ◽  
Ignace Lemahieu
Keyword(s):  
Time Domain ◽  
Lower Order ◽  
Statistical Models ◽  
Predictive Power ◽  
Simulated Data ◽  
Short Term ◽  
Ocular Movement ◽  
The Time Domain ◽  
Electroencephalogram Eeg

To cope with the severe masking of background cerebral activity in the electroencephalogram (EEG) by ocular movement artefacts, we present a method which combines lower-order, short-term and higher-order, long-term statistics. The joint smoothened subspace estimator (JSSE) calculates the joint information in both statistical models, subject to the constraint that the resulting estimated source should be sufficiently smooth in the time domain (i.e., has a large autocorrelation or self predictive power). It is shown that the JSSE is able to estimate a component from simulated data that is superior with respect to methodological artefact suppression to those of FastICA, SOBI, pSVD, or JADE/COM1 algorithms used for blind source separation (BSS). Interference and distortion suppression are of comparable order when compared with the above-mentioned methods. Results on patient data demonstrate that the method is able to suppress blinking and saccade artefacts in a fully automated way.

Conceptual short-term memory (CSTM) supports core claims of Christiansen and Chater

2016 ◽  
Vol 39 ◽  
Author(s):  
Mary C. Potter
Keyword(s):  
Working Memory ◽  
Rapid Serial Visual Presentation ◽  
Language Comprehension ◽  
Short Term Memory ◽  
Visual Presentation ◽  
Long Term Memory ◽  
Short Term ◽  
Term Memory ◽  
Use Of Knowledge

AbstractRapid serial visual presentation (RSVP) of words or pictured scenes provides evidence for a large-capacity conceptual short-term memory (CSTM) that momentarily provides rich associated material from long-term memory, permitting rapid chunking (Potter 1993; 2009; 2012). In perception of scenes as well as language comprehension, we make use of knowledge that briefly exceeds the supposed limits of working memory.

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