Assessment of Full-Scale Measurements With Regard to Extreme Hogging and Sagging Condition of Container Ships

2011 ◽  
Author(s):  
Wengang Mao ◽  
Jonas W. Ringsberg ◽  
Zhiyuan Li ◽  
Igor Rychlik
Keyword(s):  
Ultimate Strength ◽  
Full Scale ◽  
Practical Applications ◽  
Atlantic Trade ◽  
The North ◽  
Rice's Formula ◽  
Extreme Response ◽  
Hermite Transformation ◽  
Rice’S Formula ◽  
Non Gaussian

In the design of a vessel’s ultimate strength the extreme hogging condition is of great concern. Due to special properties of container ship structures, such as large bow flare and overhanging stern, wave-induced slamming makes the ship responses more skewed to sagging conditions. In particular in large sea states, the ratio between maximum sagging and hogging can be quite high. Hence, the sagging condition might be very crucial with respect to a ship’s ultimate strength. In this study, the extreme response caused by hogging and sagging is derived from upcrossing spectrums of ship responses. The Weibull fitting method and Rice’s formula for the computation of the upcrossing spectrum are discussed using full-scale measurements from a container vessel on the North Atlantic trade. The extreme ship responses are therefore predicted using the long-term upcrossing spectrum. In the case where the ship response can be approximately treated as a series of stationary Gaussian processes, the corresponding upcrossings are computed by the explicit Rice’s formula. For the non-Gaussian ship response, it is shown that the 4-moment Hermite transformation is an efficient approach to compute the corresponding upcrossing spectrums. The parameters in the transformation mainly depend on the wave environments and operation profiles. The relations between these parameters and the wave environments are needed if no measurement is available. However, according to the full-scale measurements, it is not possible to find general formulas to estimate the parameters in terms of wave environments or operation profiles for the practical applications.

Extreme Response Prediction of Steel Risers Using a Four Parameter Distribution

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Miguel Alfonso Calderon Ibarra ◽  
Fernando Jorge Mendes de Sousa ◽  
Luís Volnei Sudati Sagrilo ◽  
Ying Min Low
Keyword(s):  
Water Depth ◽  
Extreme Values ◽  
Extreme Value Distribution ◽  
Response Prediction ◽  
Parameter Distribution ◽  
New Approach ◽  
Offshore Engineering ◽  
Extreme Response ◽  
Hermite Transformation ◽  
Non Gaussian

Short-term extreme response estimates are required in many areas of ocean and offshore engineering, such as steel risers design. As in many cases, the response in non-Gaussian, a theoretical solution, is usually not readily available for this purpose. Hermite transformation and Weibull-based models, among others, are some alternatives that have been used in connection with sampled response time series. In this work, a new approach is investigated. Recently, a four-parameter distribution known as the shifted generalized lognormal distribution (SGLD) has been presented in the literature. One of its main advantages is that it covers regions of skewness–kurtosis not covered by other distributions of common use in engineering. In this paper, the performance of this distribution is evaluated in the extreme values' estimation of the utilization ratios of steel riser sections. Three alternatives for using SGLD are investigated in two case studies of different dynamic behavior. The first one is a steel-lazy wave riser (SLWR) connected to a turret-moored FPSO (floating, production, storage and offloading unit) in 914 m water depth, and the second is a SLWR connected to a spread-mooring FPSO in a water depth of 1400 m. The results obtained by the SGLD-based analysis, which considered several simulation lengths, are compared to those obtained by means of an extreme value distribution fitted to episodical extremes obtained from many distinct realizations. The results of a traditional Weibull-fitting approach to the response peaks and those obtained with a Hermite transformation-based model are also presented for comparison.

Notes on the Prediction of Extreme Ship Response

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Wengang Mao ◽  
Igor Rychlik
Keyword(s):  
Full Scale ◽  
Container Ship ◽  
Expected Number ◽  
Practical Applications ◽  
Local Maxima ◽  
Non Gaussian

In this note the relation between two simple approaches to estimate the extreme ship response used when no, or a limited, amount of data are available is discussed. The first one employs the long term distribution of the local maxima of ship response while the second one uses the expected number of upcrossings of a level by the response. It is mathematically demonstrated that the two approaches are equivalent. However, the upcrossing method is more straightforward and convenient for practical applications, particularly for non-Gaussian responses. The full-scale measurements of a 2800 TEU container ship during the first six months of 2008 are used in the comparisons.

scholarly journals Editorial: Special issue on marine safety and Rice’s formula

Extremes ◽  
2011 ◽  
Vol 14 (2) ◽  
pp. 153-155
Author(s):  
Holger Rootzén ◽  
Ross Leadbetter
Keyword(s):  
Special Issue ◽  
Rice's Formula ◽  
Editorial Special Issue ◽  
Rice’S Formula ◽  
Marine Safety

Behaviour of cold-formed steel built-up I-section columns composed of four U-profiles

2018 ◽  
Vol 22 (3) ◽  
pp. 613-625 ◽  
Author(s):  
M Anbarasu ◽  
M Venkatesan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Ultimate Strength ◽  
Element Model ◽  
Cross Sectional ◽  
Direct Strength Method ◽  
The North ◽  
Compression Members ◽  
Cross Sectional Dimension ◽  
Cold Formed Steel

This work reports numerical results concerning the cold-formed steel built-up I-section columns composed of four U-profiles under axial compression. A finite element model is developed by using the software program ABAQUS. The developed model includes geometric, material nonlinearities and geometric imperfections. The finite element model was verified against the experimental results reported in the cold-formed steel built-up open section columns. In the parametric study, the sections are analysed with several cross-sectional dimension ratios and lengths, in order to assess their influence on the buckling behaviour and ultimate strength of cold-formed steel built-up I-section columns. After presenting and discussing the numerical parametric results, the article shows that the current direct strength method in the North American Specification for cold-formed steel compression members design curve fails to predict adequately the ultimate strength of some of the columns analysed and addresses the modification proposed on current direct strength method curves, providing improved predictions of all the numerical ultimate strength available. The proposed method is also assessed by reliability analysis.

The Shipping of the North Atlantic Cotton Trade in the Mid-Nineteenth Century

2000 ◽  
Author(s):  
Lars U. Scholl ◽  
Lars U. Scholl ◽  
Lars U. Scholl
Keyword(s):  
United States ◽  
North Atlantic ◽  
The United States ◽  
Southern States ◽  
Atlantic Trade ◽  
The North ◽  
Seasonal Characteristics ◽  
Arrival Dates ◽  
The North Atlantic ◽  
Cotton Trade

This essay analyses the North Atlantic Cotton Trade through records of cotton arrivals at Liverpool, using two sets of data from 1830-1832 and 1853-1855. Using Customs Bills of Entry, Williams presents data of cotton receipts from the United States to Liverpool; quantities of bales exported; numbers of vessels; origin ports of vessels; distinguishes between regular and occasional cotton traders; arrivals at Liverpool by nationality; and vessel tonnage. He determines that the majority of vessels participated in the cotton trade seasonally, and suggests that the cotton trade was not self-contained, but part of a complex interrelationship within the North Atlantic trade system, encompassing commodity dealings, shipping employment levels, and the seasonal characteristics of cargo. The conclusion requests further scholarly research into the pattern of ship movements in the Atlantic. Two appendices provide more data, concerning arrival dates of regular traders in Liverpool, and the month of departure of cotton vessels from Southern states.

Full-Scale Measurements of Welding-Induced Initial Deflections and Residual Stresses in Steel-Stiffened Plate Structures

2018 ◽  
Vol Vol 160 (A4) ◽  
Author(s):  
M S Yi ◽  
C M Hyun ◽  
J K Paik
Keyword(s):  
Residual Stresses ◽  
Ultimate Strength ◽  
Computational Models ◽  
Plate Thickness ◽  
Offshore Structures ◽  
Full Scale ◽  
Stiffened Plate ◽  
Plate Structures ◽  
Initial Imperfections ◽  
Numerical Predictions

Plated structures such as ships and offshore structures are constructed using welding techniques that attach support members (or stiffeners) to the plating. During this process, initial imperfections develop in the form of initial deformations (deflections or distortions) and residual stresses. These initial imperfections significantly affect the buckling and ultimate strength of these structures. Therefore, to assess the strength of welded plate structures, it is very important to predict the magnitude and pattern of welding-induced initial imperfections and their effects on buckling and ultimate strength. To determine the reliability of the prediction methods, it is desirable to validate the theoretical or numerical predictions of welding-induced initial imperfections through comparison with full-scale actual measurements. However, full-scale measurement databases are lacking, as they are costly to obtain. This study contributes to the development of a full-scale measurement database of welding-induced initial imperfections in steel-stiffened plate structures. The target structures are parts of real (full-scale) deckhouses in very large crude oil carrier class floating, production, storage and offloading unit structures. For parametric study purposes, four test structures by varying plate thickness are measured while the stiffener types and weld bead length are fixed. Modern technologies for measuring initial deformations and residual stresses are applied. The details of the measurement methods are documented for the use of other researchers and practicing engineers who want to validate their computational models for predicting welding-induced initial imperfections.

Determination of Short Term Extreme Response Values for Temporary Riser Systems: A Practical Approach

2016 ◽  
Author(s):  
Ali Cetin ◽  
Trond Pytte ◽  
Sveinung Eriksrud
Keyword(s):  
Time Series ◽  
Extreme Values ◽  
Classical Method ◽  
Practical Method ◽  
Rayleigh Distribution ◽  
Relevant Variable ◽  
Extreme Response ◽  
Non Gaussian ◽  
Probability Modelling

Operation limits for temporary riser system are determined according to some probability of exceedance of a relevant variable. Accordingly, consistent statistical analysis and probability modelling of the data is required. The common industry approach is to rely on the classical narrow-banded Gaussian process assumption when considering time series of variables of interest. Thus, the time series peaks are characterized by means of the Rayleigh distribution and the relevant extreme values are estimated based on this. However, non-linearities present in riser systems may yield non-Gaussian (wide-banded) processes, rendering the classical approach inappropriate. In the present work, an approximate and practical method is presented to address above issue. It is demonstrated that the approximate method is capable of consistently estimating the relevant extreme values, even where the classical method comes short.

scholarly journals Need for Caution in Interpreting Extreme Weather Statistics

2015 ◽  
Vol 28 (23) ◽  
pp. 9166-9187 ◽  
Author(s):  
Prashant D. Sardeshmukh ◽  
Gilbert P. Compo ◽  
Cécile Penland
Keyword(s):  
Process Model ◽  
Large Scale ◽  
Probability Distributions ◽  
Extreme Weather ◽  
Recent Change ◽  
Atmospheric Variability ◽  
Tail Probabilities ◽  
The North ◽  
Special Cases ◽  
Non Gaussian

Abstract Given the reality of anthropogenic global warming, it is tempting to seek an anthropogenic component in any recent change in the statistics of extreme weather. This paper cautions that such efforts may, however, lead to wrong conclusions if the distinctively skewed and heavy-tailed aspects of the probability distributions of daily weather anomalies are ignored or misrepresented. Departures of several standard deviations from the mean, although rare, are far more common in such a distinctively non-Gaussian world than they are in a Gaussian world. This further complicates the problem of detecting changes in tail probabilities from historical records of limited length and accuracy. A possible solution is to exploit the fact that the salient non-Gaussian features of the observed distributions are captured by so-called stochastically generated skewed (SGS) distributions that include Gaussian distributions as special cases. SGS distributions are associated with damped linear Markov processes perturbed by asymmetric stochastic noise and as such represent the simplest physically based prototypes of the observed distributions. The tails of SGS distributions can also be directly linked to generalized extreme value (GEV) and generalized Pareto (GP) distributions. The Markov process model can be used to provide rigorous confidence intervals and to investigate temporal persistence statistics. The procedure is illustrated for assessing changes in the observed distributions of daily wintertime indices of large-scale atmospheric variability in the North Atlantic and North Pacific sectors over the period 1872–2011. No significant changes in these indices are found from the first to the second half of the period.

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