Reliability Analysis of Offshore Wind Turbines Using Copula

2018 ◽  
Author(s):  
Weifei Hu ◽  
Zhiyu Jiang ◽  
Yeqing Wang
Keyword(s):  
Reliability Analysis ◽  
Environmental Conditions ◽  
Joint Distribution ◽  
Environmental Parameters ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Design Stage ◽  
Offshore Structure ◽  
Distribution Models ◽  
Restricted Form

Offshore structures are subject to severe environmental conditions and require high operating and maintenance costs. At the design stage of an offshore structure, it is necessary to perform load analysis and to consider representative environmental conditions characterized by statistical models. However, many available joint distribution models of the environmental parameters can only describe the correlation of these parameters in a very restricted form. The use of simple probabilistic models without correctly addressing their correlation may lead to significant bias in the reliability analysis. Here, the correlation between three offshore environmental parameters including the significant wave height, wave peak period, and mean wind speed is described by copula. The copula density functions and theoretical derivations of copula correlation parameters using actual sea state data are provided for general applications of reliability analysis of offshore structures. Hindcast data of two representative sites are used to fit the best copula. The developed copula-based joint distribution can be used for accurate reliability analysis of offshore structures considering long-term fatigue loads and extreme responses.

Assessment of the Reliability of the Moorings of a Floating Structure Against the Extreme Cyclone Hazard

2019 ◽  
Author(s):  
Mark Manzocchi ◽  
Vikas Kejriwal ◽  
Eric Hoo
Keyword(s):  
Environmental Conditions ◽  
Joint Distribution ◽  
Environmental Parameters ◽  
Exceedance Probability ◽  
Surface Model ◽  
Short Term ◽  
Floating Structure ◽  
Time Histories ◽  
Vessel Response

Abstract This paper describes the methodology adopted for an analysis performed to assess the reliability of the moorings of a free weathervaning FPSO against the cyclone hazard. A joint distribution characterizing the long-term cyclone metocean conditions was fitted to a database of environmental conditions at the site of interest. A series of archetype cyclone histories were selected from the cyclone database to capture the evolving relationships between key environmental parameters during a cyclone. A response-surface model for extreme tension in the vessel moorings was developed for the short-term extreme vessel response as a function of environmental conditions by fitting the surface to an extensive series of time-domain vessel response analyses. The reliability of the mooring system was evaluated using Monte Carlo simulation by sampling from the fitted joint distribution of long-term cyclone characteristic and generating simulated cyclone time histories by scaling the archetype cyclones. The response model for short-term exceedance probability is used to develop the probability of exceedance within each simulated cyclone, and the probability of exceeding a given response is derived from the simulation.

Reference Strength of Ice to be Used in Designing Offshore Structures

1988 ◽  
Vol 110 (4) ◽  
pp. 414-420
Author(s):  
A. L. Tunik
Keyword(s):  
Compressive Strength ◽  
Reference Value ◽  
Environmental Parameters ◽  
Offshore Structures ◽  
Observation Data ◽  
Offshore Structure ◽  
Site Specific ◽  
Acceptable Accuracy ◽  
Simplified Method ◽  
Ice Strength

The strength of ice depends on many factors. If they are known, the strength can be predicted with an acceptable accuracy. When designing an offshore structure, a designer usually has to select appropriate values of ice strength from incomplete, uncertain and random observation data for the site-specific ice environment. In this paper, a simplified method of selecting such values is described. A reference value of compressive strength is presented as an analytical function of averaged site-specific environmental parameters and offshore structure dimensions which are usually available to the designer.

Integrating Constrained Random Waves in Endurance Time Analysis of Offshore Structures Subjected to Sea Waves

2012 ◽  
Author(s):  
H. Matin Nikoo ◽  
M. Zeinoddini ◽  
H. Estekanchi ◽  
M. Golestani
Keyword(s):  
Time Domain ◽  
Offshore Structures ◽  
Design Stage ◽  
Offshore Platforms ◽  
Sea Waves ◽  
Base Shear ◽  
Time Analysis ◽  
Offshore Structure ◽  
Endurance Time ◽  
Damage Indices

This paper introduces a novel methodology for design and assessment of offshore structures exposed to irregular sea waves. For this, Constrained NewWave (CNW) is integrated with the Endurance Time Analysis (ETA) methodology, which is basically developed for the performance based analysis of onshore structures to earthquake loads. In this approach, the offshore structure is simulated in time-domain under a set of calibrated intensifying wave functions. They are devised to represent a gradually increasing roughness of the sea state by time. A performance index such as base shear, drift or stress in a critical structural members are monitored until they reach to a predefined maximum value. A higher endurance time (corresponding to a higher wave height) is to be interpreted as a better performance of structure. Ability to consider spectral features of waves, waves’ irregularity, the wave-in-deck impacts, utilizing a relatively simple approach, requiring relatively low computational times and capability to consider any desirable damage indices are the advantages of this novel method. The method can be used in the design stage, collapse analysis and for the assessment of existing offshore platforms. In this paper the effectiveness of this method has been examined on offshore jacket platforms. The results obviously have highlighted the potentials of this approach for the dynamic, time-domain, non-linear analysis and assessment of offshore platforms.

Design Point Effect Due to Severe Storm Conditions on the Reliability Assessment of Offshore Structures: Case Study

2005 ◽  
Author(s):  
Ahmed Mostafa Tawfik
Keyword(s):  
Wave Height ◽  
Environmental Conditions ◽  
Current Velocity ◽  
Offshore Structures ◽  
Structural Safety ◽  
Design Stage ◽  
Design Point ◽  
Reliability Method ◽  
Storm Wave

Structural reliability is of an intense significance for the evaluation of failure probability and safety levels of offshore structures in their structural design stage, especially when the variables are eminently random. Hence, the environmental conditions are considered among the most important parameters in the design of offshore structures whose effect of great contribution to structural safety. The 100 year storm wave height and current velocity constitute the majority of uncertainty in the environmental conditions. Eventually, these values are used as stochastic values i.e. mean values in addition to standard deviation. This paper uses the stochastic values of 100 year storm wave height and current velocity to estimate the probability of failure. These simulations had been encountered in the structural analysis and design on practical case study representing an offshore structure located in the Mediterranean Sea to predict the reliability level. The outcome of these simulations uses the Response Surface Method with design point technique for both stress and displacement limit states. The results of this Reliability method lead to an acceptable level for reliability analysis and risk assessments.

On the Structural Capacity of Grouted Connections in Offshore Structures

2011 ◽  
Author(s):  
Inge Lotsberg ◽  
Andrzej Serednicki ◽  
Espen Cramer ◽  
Ha˚kon Bertnes ◽  
Per Enggaard Haahr
Keyword(s):  
Large Diameter ◽  
Offshore Structures ◽  
Offshore Wind ◽  
Design Stage ◽  
Design Standards ◽  
Safety Level ◽  
Axial Capacity ◽  
Structural Capacity ◽  
Jacket Structures ◽  
Industry Practice

During the last year, the offshore wind tower structure industry experienced that the design of the grouted connections between the top tower and monopile structure did not necessarily result in an acceptable safety level. A number of wind towers were reported to settle on the monopile structure and the resulting force flow in the structures was different to that intended at the design stage. A joint industry project was therefore carried out to investigate the structural capacity of these connections. It was found that the axial capacity of the grouted connections is a larger function of the diameter and surface tolerances than that accounted for in existing design standards. This paper reviews the industry practice relating to the design of grouted connections in monopile structures. The physical behaviour of the connections is explained and some of the most critical issues related to the design of large diameter grouted connections are assessed. This knowledge is also considered to be of significance for the design of grouted connections in skirt piles in jacket structures subjected to alternating loading.

scholarly journals Failures and Reliability in Hawts Operating in Mountainous Areas, Open Sea and in Harsch Climate Sites

2021 ◽  
Vol 312 ◽  
pp. 11010
Author(s):  
Giovanni Maria De Pratti
Keyword(s):  
Data Collection ◽  
Reliability Analysis ◽  
Environmental Conditions ◽  
Energy Production ◽  
Offshore Wind ◽  
Mountainous Areas ◽  
Open Sea ◽  
Erosion Corrosion

Recently, offshore wind plants, as Horn’s Riv one, have reached a remarkable interest and development. In these sites, HAWT’s blades experiment corrosion, erosion and fouling and, at higher latitudes, icing conditions too, as in mountainous areas and in harsch climate sites. The operative conditions may influence the machine damages and they may occur as consequence of erosion, corrosion, fouling, icing, exfoliation caused by the above mentioned environmental conditions. The paper reports about data collection about failures occurred to HAWTS operating in offshore, mountainous and harsch climate sites in last ten years. Particularly, the damage occurred to blades, gears and bearings have been examined and the consequences analysed. The occurred failures are examined and the reliability of WTGs is assessed by appropriate models and analysis. The results are com pared to literature data and they may be very useful in programmable maintenance and in predictable one. Reliability analysis may be also useful to increase energy production.

scholarly journals Investigation on Applicability and Limitation of Cosine Similarity-Based Structural Condition Monitoring for Gageocho Offshore Structure

Sensors ◽  
2022 ◽  
Vol 22 (2) ◽  
pp. 663
Author(s):  
Byungmo Kim ◽  
Jaewon Oh ◽  
Cheonhong Min
Keyword(s):  
Initial Study ◽  
Offshore Structures ◽  
Cosine Similarity ◽  
Offshore Wind ◽  
Real Field ◽  
Research Station ◽  
Offshore Structure ◽  
Potential Threat ◽  
Damage Scenarios ◽  
Sustainable Resources

The key to coping with global warming is reconstructing energy governance from carbon-based to sustainable resources. Offshore energy sources, such as offshore wind turbines, are promising alternatives. However, the abnormal climate is a potential threat to the safety of offshore structures because construction guidelines cannot embrace climate outliers. A cosine similarity-based maintenance strategy may be a possible solution for managing and mitigating these risks. However, a study reporting its application to an actual field structure has not yet been reported. Thus, as an initial study, this study investigated whether the technique is applicable or whether it has limitations in the real field using an actual example, the Gageocho Ocean Research Station. Consequently, it was found that damage can only be detected correctly if the damage states are very similar to the comparison target database. Therefore, the high accuracy of natural frequencies, including environmental effects, should be ensured. Specifically, damage scenarios must be carefully designed, and an alternative is to devise more efficient techniques that can compensate for the present procedure.

Evaluation of the Ice Load Acting on an Arctic Offshore Structure With Different Ice Drifting Angle

2020 ◽  
Author(s):  
Young-Shik Kim ◽  
Yun-Ho Kim ◽  
Hyung-Do Song ◽  
Jin-Ho Jang ◽  
Solyoung Han ◽  
...  
Keyword(s):  
Evaluation Method ◽  
Offshore Structures ◽  
Mean Value ◽  
Experimental Methodology ◽  
The Arctic ◽  
Design Stage ◽  
Ocean Engineering ◽  
Offshore Structure ◽  
Ice Load ◽  
National University

Abstract In this study, an evaluation method and results for ice load acting on an Arctic offshore structure with various ice drifting angles are discussed. Korea Research Institute of Ships and Ocean Engineering (KRISO) has conducted a research project to develop a hull form design for year-round floating type offshore structures in the Arctic condition with dynamic positioning and mooring system. Six cooperating organizations participated in the project: Samsung Heavy Industry, Korean Register, Pusan National University, Korea Maritime & Ocean University, Dong-Eui University, and Inha Technical College. In the design stage of an Arctic offshore structure, ice load consideration is the key component for the safety and reliability analysis. However, there is no generally used tool for evaluation of ice load acting on an Arctic offshore structures. In this study, ice loads acting on an Arctic FPSO in managed ice conditions with various ice drifting angles are examined by experimental methodology. Dramatic mean value changes in ice load with different ice drifting angles are observed in the model test. This experimental ice load evaluation method can be applied to the other types of offshore structure which might operate in sea ice condition.

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