Structural Response of Ice-Going Ships Using a Probabilistic Design Load Method

2015 ◽  
Author(s):  
Boris Erceg ◽  
Freeman Ralph ◽  
Sören Ehlers ◽  
Ian Jordaan
Keyword(s):  
Scale Effects ◽  
Probabilistic Approach ◽  
Structural Response ◽  
Probabilistic Methods ◽  
Stiffened Panel ◽  
Safety Level ◽  
Design Load ◽  
Northern Sea Route ◽  
Ice Conditions ◽  
Probabilistic Nature

Ships operating in ice-covered waters experience intense loads from ice features, particularly multiyear ice. Therefore, their structures have to be able to withstand these loads, making structural design paramount. Current formulations of ice class rules do not fully account for the probabilistic nature of ice loads, i.e. scale effects for local ice pressures captured in full-scale measurements. Furthermore, ice class rules do not consider route-specific ice conditions when calculating the design load, i.e. the exposure of the vessel to ice crushing determined by the number and duration of rams. An approach to arctic ship design based on probabilistic methods was developed by Jordaan and co-workers in 1993 and is described in this paper. The approach is used to estimate extreme design loads based on the annual interaction events and the design strategy (target exceedence criteria). The objective of this paper is to select an appropriate ice class for a vessel navigating along the northern sea route, and to compare the design requirements with those determined using the probabilistic approach based on measured data and expected exposure. Local hull pressures have been measured using the USCGC Polar Sea for a range of ice conditions including first year and multi-year ice. Impact conditions similar to those expected along the Northern Sea route were selected and corresponding pressurearea parameters used for input into the probabilistic approach discussed above. This paper will compare the design and response of an exemplary stiffened panel using the described approach to requirements given in Finnish Swedish Ice Class Rules. A case study structure will be analyzed using Finite Element Method for a chosen exposure scenario and target safety level.

Probabilistic Design Load Method for the Northern Sea Route

2015 ◽  
Author(s):  
Tõnis Tõns ◽  
Freeman Ralph ◽  
Sören Ehlers ◽  
Ian J. Jordaan
Keyword(s):  
Statistical Design ◽  
Full Scale ◽  
Probabilistic Methods ◽  
The Arctic ◽  
Probabilistic Design ◽  
Load Prediction ◽  
Safety Level ◽  
Northern Sea Route ◽  
Extreme Load ◽  
Ice Conditions

A probabilistic design method allows us to link statistical data from the operational area of the vessel with design loads providing the availability for more precise safety level assessment, which is important to ensure safe and sustainable ship transit in ice covered waters. Statistical design methods are well used for open water using spectral analysis. Wave induced loads are estimated by linking statistical load parameters to the sea state parameters. Statistical methods to estimate ice-induced loads are also available, however, current Polar Class rules are not considering probabilistic methods for determining ice-induced loads. This paper shows how developed probabilistic methods can be used for the design of ice going ships, especially for ships operating along the Northern Sea Route (NSR). The method presented in this paper will combine available data from full-scale measurements performed in the Arctic with ice conditions defined using historical data from satellite sources. The full-scale measurements are used to develop the parent distribution, which forms the basis for the extreme load prediction based on the number of excepted interactions along the NSR. Satellite data from history will be used to model ice conditions, e.g. ice type and ice concentration, along the route.

Methodology to Evaluate Sea Ice Loads for Seasonal Operations

2015 ◽  
Author(s):  
Jan Thijssen ◽  
Mark Fuglem
Keyword(s):  
Sea Ice ◽  
Offshore Structures ◽  
Ice Thickness ◽  
Safety Level ◽  
Site Specific ◽  
Design Load ◽  
Ice Load ◽  
Ice Conditions ◽  
Design Loads ◽  
Ice Loads

Offshore structures designed for operation in regions where sea ice is present will include a sea ice load component in their environmental loading assessment. Typically ice loads of interest are for 10−2, 10−3 or 10−4 annual probability of exceedance (APE) levels, with appropriate factoring to the required safety level. The ISO 19906 standard recommends methods to determine global sea ice loads on vertical structures, where crushing is the predominant failure mode. Fitted coefficients are proposed for both Arctic and Sub-Arctic (e.g. Baltic) conditions. With the extreme ice thickness expected at the site of interest, an annual global sea ice load can be derived deterministically. Although the simplicity of the proposed relation provides quick design load estimates, it lacks accuracy because the only dependencies are structure width, ice thickness and provided coefficients; no consideration is given to site-specific sea ice conditions and the corresponding exposure. Additionally, no term is provided for including ice management in the design load basis. This paper presents a probabilistic methodology to modify the deterministic ISO 19906 relations for determining global and local first-year sea ice loads on vertical structures. The presented methodology is based on the same ice pressure data as presented in ISO 19906, but accounts better for the influence of ice exposure, ice management and site-specific sea ice data. This is especially beneficial for ice load analyses of seasonal operations where exposure to sea ice is limited, and only thinner ice is encountered. Sea ice chart data can provide site-specific model inputs such as ice thickness estimates and partial concentrations, from which corresponding global load exceedance curves are generated. Example scenarios show dependencies of design loads on season length, structural geometry and sea ice conditions. Example results are also provided, showing dependency of design loads on the number of operation days after freeze-up, providing useful information for extending the drilling season of MODUs after freeze-up occurs.

scholarly journals Sensitivity and Uncertainty Studies for the Modelling of Marine Growth Effect on Offshore Structures Loading

2002 ◽  
Author(s):  
Franck Schoefs
Keyword(s):  
Extreme Events ◽  
Structural Integrity ◽  
Scale Effects ◽  
Structural Response ◽  
Fatigue Loading ◽  
Offshore Structures ◽  
Growth Effect ◽  
Sensitivity Analyses ◽  
Physical Analysis ◽  
Safety Level

Structural response to extreme events or fatigue loadings and structural integrity are major criteria to be quantified in a rational process of reassessment. It is now well established that the probabilistic mechanics approach gives an efficient means for measuring the relative changing in safety level compared to a predefined requirement. To this aim, effects of marine growth have been largely studied during the last two decades. This natural process of structural colonization is particularly hard to embrace because it leads to various consequences as over-loading effect coming from screen and drag effects, bio-chemical attacks of materials and mask effects for inspections methods. Only effects on loading are studied here. These effects are particularly hard to quantify because of the bio-variety of marine growth, season conditioning, natural cleaning or death of species, severe competition leading to replacement of some species and of course local hydrodynamic conditions. As in situ data collection through inspections is hard to practice and very expensive, lot of works propose experiments respecting scale effects and numerical modelling. Both are needed to perform uncertainty and sensitivity analyses. This paper proposes a numerical analysis of marine growth effects based on Response Surface Methodology. This method is here suggested to provide explicit approximations of load variables acting on offshore structures submitted to extreme events or fatigue loading as Jacket platforms. Then, from a sensitivity analysis, main factors conditioning load effects are pointed out. From a physical analysis of hydrodynamics parameters affecting these dominant variables, their probabilistic modelling is then suggested using available published experiments for several probabilistic characteristics.

scholarly journals Conception and Evolution of the Probabilistic Methods for Ship Damage Stability and Flooding Risk Assessment

2021 ◽  
Vol 9 (6) ◽  
pp. 667
Author(s):  
Dracos Vassalos ◽  
M. P. Mujeeb-Ahmed
Keyword(s):  
Risk Assessment ◽  
Probabilistic Method ◽  
Probabilistic Methods ◽  
Full Description ◽  
Safety Level ◽  
Probability Of Survival ◽  
Damage Stability ◽  
Passenger Ships ◽  
Flooding Hazards ◽  
Flooding Risk

The paper provides a full description and explanation of the probabilistic method for ship damage stability assessment from its conception to date with focus on the probability of survival (s-factor), explaining pertinent assumptions and limitations and describing its evolution for specific application to passenger ships, using contemporary numerical and experimental tools and data. It also provides comparisons in results between statistical and direct approaches and makes recommendations on how these can be reconciled with better understanding of the implicit assumptions in the approach for use in ship design and operation. Evolution over the latter years to support pertinent regulatory developments relating to flooding risk (safety level) assessment as well as research in this direction with a focus on passenger ships, have created a new focus that combines all flooding hazards (collision, bottom and side groundings) to assess potential loss of life as a means of guiding further research and developments on damage stability for this ship type. The paper concludes by providing recommendations on the way forward for ship damage stability and flooding risk assessment.

Assessment of Residual Ultimate Strength of VLCC According to Damage Extents and Average Compressive Strength of Stiffened Panel

2014 ◽  
Author(s):  
Ji-Myung Nam ◽  
Joonmo Choung ◽  
Se-Yung Park ◽  
Sung-Won Yoon
Keyword(s):  
Compressive Strength ◽  
Ultimate Strength ◽  
Probabilistic Approach ◽  
Stiffened Panel ◽  
Moment Capacity ◽  
Hull Girder ◽  
Damage Area ◽  
Damage Indices ◽  
Smith Method ◽  
Average Compressive Strength

This paper presents the prediction of residual ultimate strength of a very large crude oil carrier considering damage extents due to collision and grounding accidents. In order to determine extents of damage, two types of probabilistic approaches are employed: deterministic approach based on regulations based on ABS [1], DNV [2], and MARPOL [3] and probabilistic approach based on IMO probability density functions (PDFs) (IMO guidelines [4]). Hull girder ultimate strength is calculated using Smith method which is dependent on how much average compressive strength of stiffened panel is accurate. For this reason, this paper uses two different methods to predict average compressive strength of stiffened panel composing hull girder section: CSR formulas and nonlinear FEA. Calculated average compressive strength curves using CSR formulas (IACS [5, 6]) and nonlinear FEA are imported by an in-house software UMADS. Residual ultimate moment capacities are presented for various heeling angles from 0° (sagging) to 180° (hogging) by 15° increments considering possible flooding scenarios. Three regulations and IMO guidelines yield minimum of reduction ratios of hull girder moment capacity (minimum of damage indices) approximately at heeling angles 90° (angle of horizontal moment) and 180° (angle of hogging moment), respectively, because damage area is located farthest from neutral axis.

scholarly journals Probabilistic Methods for the Incompressible Navier–Stokes Equations With Space Periodic Conditions

2013 ◽  
Vol 45 (3) ◽  
pp. 742-772
Author(s):  
G. N. Milstein ◽  
M. V. Tretyakov
Keyword(s):  
Boundary Conditions ◽  
Numerical Integration ◽  
Periodic Boundary ◽  
Stokes Equations ◽  
Weak Sense ◽  
Periodic Boundary Conditions ◽  
Probabilistic Methods ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Probabilistic Nature

We propose and study a number of layer methods for Navier‒Stokes equations (NSEs) with spatial periodic boundary conditions. The methods are constructed using probabilistic representations of solutions to NSEs and exploiting ideas of the weak sense numerical integration of stochastic differential equations. Despite their probabilistic nature, the layer methods are nevertheless deterministic.

scholarly journals Probabilistic Assessment of Innovative Mitigating Measures for Buried Steel Pipeline–Fault Crossing

2015 ◽  
Author(s):  
Vasileios E. Melissianos ◽  
Dimitrios Vamvatsikos ◽  
Charis J. Gantes
Keyword(s):  
Hazard Analysis ◽  
Structural Response ◽  
Comprehensive Analysis ◽  
Effectiveness Evaluation ◽  
Second Step ◽  
Flexible Joints ◽  
Intensity Measure ◽  
Seismological Data ◽  
Fault Displacement ◽  
Probabilistic Nature

A methodology is presented on assessing the effectiveness of flexible joints in mitigating the consequences of faulting on buried steel pipelines through a comprehensive analysis that incorporates the uncertainty of fault displacement magnitude and the response of the pipeline itself. The proposed methodology is a two-step process. In the first step the probabilistic nature of the fault displacement magnitude is evaluated by applying the Probabilistic Fault Displacement Hazard Analysis, considering also all pertinent uncertainties. The second step is the “transition” from seismological data to the pipeline structural response through the fault displacement components as the adopted vector intensity measure. To mitigate the consequences of faulting on pipelines, flexible joints between pipeline parts are proposed as innovative measure for reducing the deformation of pipeline walls. Thus, the mechanical behavior of continuous pipelines and pipelines with flexible joints is numerically assessed and strains are extracted in order to develop the corresponding strain hazard curves. The latter are a useful engineering tool for pipeline – fault crossing risk assessment and for the effectiveness evaluation of flexible joints as innovative mitigating measures against the consequences of faulting on pipelines.

A Probabilistic Approach to Fatigue Safety and Integrity of TTRs

2014 ◽  
Author(s):  
Mir Emad Mousavi ◽  
Sanjeev Upadhye ◽  
Vishnu Vijayaraghavan ◽  
Kevin Haverty
Keyword(s):  
Fatigue Damage ◽  
Probabilistic Method ◽  
Probabilistic Approach ◽  
Probabilistic Methods ◽  
Fatigue Reliability ◽  
Fatigue Design ◽  
Integrity Index ◽  
Biased Estimators ◽  
Integrity Analysis

Probabilistic methods can improve the reliability of fatigue damage evaluation in top tensioned (production) risers because they tend to provide less biased estimators on their safety, which can be used for more reliable decision making concerning their design. Such methods consider the collective impact of uncertainties in the riser system, which is not accurately assessed in conventional fatigue analysis. The large factors of safety that are commonly used in deterministic-based fatigue damage assessment tend to assure the high safety of the design, still they are generic factors that do not take advantage of available data for accurate quantification of system safety. This paper presents a probabilistic method toward fatigue reliability and integrity analysis of TTR systems. By using rules of probability, a simplified method is developed to estimate the probability of failure of the TTR system in its lifetime, considering the uncertainties with the Palmgren-Miner rule, the cyclic loads, and the fatigue strength of the components, and other analysis approximations. The method is then used for a comparative assessment on the fatigue reliability of the TTR components and calculating its fatigue Integrity Index. The method is illustrated in a case study and is used to provide recommendations that could possibly improve the TTR fatigue design by reducing its cost, increasing its safety, and maximizing its integrity.

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