Environmental load estimation for offshore structures considering parametric dependencies

2021 ◽  
Author(s):  
Adhitya Ramadhani ◽  
Faisal Khan ◽  
Bruce Colbourne ◽  
Salim Ahmed ◽  
Mohammed Taleb-Berrouane
Keyword(s):  
Offshore Structures ◽  
Load Estimation ◽  
Environmental Load ◽  
Parametric Dependencies

EXTREME ENVIRONMENTAL LOAD MODELS FOR WAVE AND CURRENT RESPONSE SURFACE METHOD

2016 ◽  
Vol 3 (2) ◽  
Author(s):  
Zafarullah Nizamani ◽  
Yap Eng Ching ◽  
Mohamed Mubarak Bin Abdul Wahab ◽  
Abdullateef Olanrewaju
Keyword(s):  
Response Surface ◽  
Wave Height ◽  
Limit State ◽  
Offshore Structures ◽  
State Function ◽  
Current Response ◽  
Environmental Load ◽  
Local Conditions ◽  
Load Model ◽  
Load Models

The three most uncertain environmental design loads acting on offshore structures are wave height, current and wind velocity. If the reliability of structure is to be determined, then we need to have limit state function for load which requires that we should transform the environmental loads into load model. Load model, which predicts the load, will ultimately affect the design resistance and thus its final impact on cost could be large. Since, there are many offshore structures located in different offshore regions in Malaysia, the calibration of the environmental load model, should be evaluated to determine which model fits best. To obtain the environmental load model, response surface technique is generally applied. Load models suggested by DNV and ISO code are analysed to determine the best model fit for local conditions of Malaysia. Base shear, wave height and current velocity are used in a linear fit to determine polynomial response surface. The results showed that due to the geography of Malaysia different regions might have to use specific load models instead of a general load model for all regions.

Environmental Load Factors for Offshore Structures

1999 ◽  
Vol 121 (4) ◽  
pp. 261-267
Author(s):  
H. P. Hong ◽  
M. A. Nessim ◽  
I. J. Jordaan
Keyword(s):  
Model Uncertainty ◽  
Offshore Structures ◽  
Specific Model ◽  
Load Factor ◽  
Environmental Load ◽  
Load Effect ◽  
Environmental Loads ◽  
Load Factors ◽  
Environmental Process ◽  
The Impact

An analysis of the impact of model uncertainties on the design factors for environmental loads on offshore structures was carried out. Considering uncertainties in environmental processes, the load effect models and the member resistance, an approach was developed that gives explicit consideration to model uncertainty in codified design. For frequent environmental load effects, a two-factor approach was developed that defines the overall load factor as the product of two components: a basic factor accounting for uncertainty in the environmental process and a separate factor accounting for model uncertainty. The overall load factor is to be applied to the specified load, which is defined as the load corresponding to the environmental process value associated with a specified return period. This load can be calculated from the environmental process without considering model uncertainty. The model uncertainty factor was defined as a linear function of the mean and the standard deviation of the model uncertainty parameter. It can be estimated based on a specific model and reliability analysis. This two-factor approach has two advantages: (a) it allows for reductions in the load factor if conservative or more accurate models are used; and (b) it eliminates the need for the designer to consider model uncertainty in estimating the specified load. The approach was used to develop a set of load factors for environmental loads on offshore structures. These factors were calibrated to produce reliability levels consistent with those implied by the load factors in CSA-S471.

Cost-Effective Load Monitoring Methods for Fatigue Life Estimation of Offshore Platform

2014 ◽  
Author(s):  
Nevena Perišić ◽  
Ulf T. Tygesen
Keyword(s):  
Kalman Filter ◽  
Expansion Method ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Special Importance ◽  
Load Estimation ◽  
Wave Load ◽  
Modal Expansion ◽  
Modal Expansion Method ◽  
Load Monitoring

The lifetime of offshore structures are ruled by accumulated fatigue damage so structural load monitoring is of special importance for re-assessment of offshore platforms. However, direct measuring of the actual loading is usually not feasible due to sensor limitations. An alternative approach to direct load measuring is load estimation from the limited number of measurements of dynamic responses of the structure. This paper presents two, conceptually different, model based, methods for load estimation in time domain: modal expansion method and Kalman filter based method. The Kalman filter based method uses the reduced FEM and provides estimations of limited number of signals, where the modal expansion method expands the mode shape vectors to estimate the displacements and stresses at all unmeasured locations. This paper is a part of ongoing development of methods for linear and nonlinear system identification, FEM updating, wave load calibration and lifetime prediction of offshore structures.

Environmental Contour Lines: A Method for Estimating Long Term Extremes by a Short Term Analysis

2008 ◽  
Author(s):  
S. Haver ◽  
S. R. Winterstein
Keyword(s):  
Major Part ◽  
Offshore Structures ◽  
Environmental Load ◽  
Short Term ◽  
Sea State ◽  
Contour Lines ◽  
Linear Problems ◽  
Term Analysis ◽  
Do So

Design of offshore structures involves the calculation of reliable estimates for loads and responses corresponding to annual exceedance probabilities of 10-2 and 10-4. In order to do so, all sources of inherent randomness must be accounted for, i.e. the short term variability of say the 3-hour extreme value in a given sea state should be combined with the long term variability of the sea state characteristics. This calls for some sort of a long term analysis. For linear or nearly linear problems this can easily be done, while such an analysis becomes more complicated and time consuming for strongly non-linear response problems. The difficulties are greater if a major part of the environmental load is of an on-off nature. This paper illustrates an approximate approach, the environmental contour line method, for obtaining proper estimates of long term extremes utilizing a short term analysis. Examples are also included.

Effects of Waves and Currents on Extreme Loads on a Jacket

2015 ◽  
Author(s):  
Kjersti Bruserud ◽  
Sverre Haver
Keyword(s):  
Wind Waves ◽  
Offshore Structures ◽  
Load Estimation ◽  
Extreme Wave ◽  
Load Model ◽  
Extreme Loads ◽  
Extreme Load ◽  
Peak Over Threshold ◽  
Waves And Currents ◽  
Threshold Approach

In lack of simultaneous data of metocean parameters such as wind, waves and currents, Norwegian design regulations presently recommend a conservative combination of metocean parameters for estimation of characteristic metocean loads on offshore structures. A simplified parametric load model for a jacket, based on waves and currents, is assumed. Several approaches to load estimation are investigated and the following are considered; different averaging length of extreme currents, the effect of peak-over-threshold approach for estimation of extreme wave and currents compared to all-sea states approach and extreme load estimation directly from a load time series. When compared to the recommended approach, all other approaches yield a reduced estimated characteristic metocean load. The results are intended be illustrative and not suitable for use in design.

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