Sensitivity Analysis of Monopiles’ Fatigue Stresses to Site Conditions Using Monte Carlo Simulation

The design of support structures of offshore wind turbines contains high number of design variables that influence load characteristics and structural responses. These variables are stochastic and cause many uncertainties. Some of them are examined in this study. It is investigated how scattering of site conditions and load parameters affect the structural response. It is exemplified in terms of stresses that contribute to the accumulated fatigue damage within a monopile substructure. Random sampling of combinations of site conditions and load parameters is performed in order to classify the effects of parameter scattering on the stress variability by means of Sobol’ indices. Analysis shows that the highest influence on stress outputs have the variations in the load parameters. The reason is the sensitivity of the structural dynamical response to the wave height increase and decrease of distance between the wave peak frequency and the structural eigenfrequencies. © 2017 ISOPEEC/Horizon202

Sensitivity Analysis of Material and Load Parameters to Fatigue Stresses of an Offshore Wind Turbine Monopile Substructure

Steel monopiles are support structures mostly applied for offshore wind turbines. Their installation is straightforward, in particular, in shallow and medium waters. While the wind turbine tower is primarily affected by wind, the wave loads are dominant for the monopile, as it is submerged to a large extent. This study deals with the influence of uncertainties in material and load parameters on the behaviour of those structures. It is investigated how the scattering of material properties (namely Young's modulus of elasticity) affect the structural response. In addition, loads with different characteristics are applied, and it is examined how the changes in loads influence the structural response. The analysed output data of interest are the extreme stresses leading to the accumulation of fatigue damage. In order for a realistic modelling, wave loads are considered with irregular sea states with different wave characteristics (significant wave heights and wave peak periods). The final aim of the analysis is to classify the effects of specific wave characteristics on the stresses by means of a sensitivity analysis. The analysis shows that variations in the wave peak period have the strongest influence on stress outputs. This effect results from the strong sensitivity of the structural dynamical response to the decrease of the difference between the values of the wave peak frequency and the natural frequencies of the structure. © 2017 The Authors. Published by Elsevier Ltd

Uporedna Analiza Osetljivosti Konstrukcija “Jacket” I Monopil Na Parametre Opterećenja

Nowadays, much attention is payed to the development of renewable energy resources. Wind energy plays a major role in this issue. That is why there is a growing interest for improving the design process of wind turbines at many aspects. This study deals with offshore wind turbines (OWT) from the reliability aspect. Estimating the uncertainties, a deeper understanding of behavior of the structure is obtained. As waves are the dominant load on OWT support structures, this paper addresses how specific wave characteristics affect the structure. Two structural types of support structures are studied, with the aim to evaluate pros and cons of both

Stochastic variables in modelling of the wave loads on offshore wind turbine structures

Nowadays, with respect to trend of Kyoto protocol, many producers turn to renewable energy resources. That leads to a fact that more than 75% of new power capacity installations in EU in the year 2015 are renewables. The leading among the new renewable energy resources is wind energy. In the last decades, even more wind energy is accommodated by moving offshore. That brings up a problem of more complicated design, which includes new loads to be investigated and modelled. For offshore wind turbines, dominant loads are wave and wind loads. For the substructure itself, the highest impacts have wave-induced loads, as it is submerged at most of its height. As the waves are stochastic and irregular loads, this paper investigates appropriate methods for modelling of the wave loads, in order to achieve a very realistic load model and results. This is only some of the numerous challenges in this area of expertise, which are more accurately investigated in a research plan within the framework of the Innovative Training Network (ITN) AEOLUS4FUTURE, related to reliability of offshore wind energy structures

A review on experimental fatigue analysis of tubular joints for offshore wind turbine substructures

The scientific community is devoting more attention to the wide scope of offshore wind turbine structures. Since such structures are subjected to high level of fatigue loads as well as a large number of load cycles caused by wind, waves and turbine operation, the fatigue performance of welded connections is usually a design driving criteria. In this paper, a brief review on experimental fatigue analysis of circular hollow section joints for jacket structures is presented. Special emphasis is given to full-scale experimental testing. In order to face some of the challenges in this area of expertise, an experimental research plan within the framework of the Innovative Training Network (ITN) AEOLUS4FUTURE is introduced, aiming to understand and validate the fatigue performance of circular hollow section joints produced by an automated process, using Tandem MIG/MAG welding

A state-of-the-art review on local fatigue design of support structures for offshore wind turbines

The scientific community is devoting more attention to the wide scope of offshore wind turbine structures. Since such structures are subjected to high level of fatigue loads as well as a large number of load cycles caused by wind, waves and turbine operation, the fatigue performance of welded connections is usually a design driving criteria. In this paper, a brief revision on load simulation and strength analysis procedures as well as local fatigue design methods of support structures for offshore wind turbines is presented. In order to face some of the challenges in this area of expertise, a research project is introduced, aiming to exploit residual capacities in the fatigue design of tubular joints of support structures for offshore wind turbines

Influence of wave load variations on offshore wind turbine structures

Nowadays, much attention is payed to the development of renewable energy resources. Wind energy plays a major role in this issue. That is why there is a growing interest for improving the design process of wind turbines at many aspects. This study compares two types of offshore wind turbines structures, the monopile and the jacket structure, in their dependency on wave load characteristics’ variations. The examined wave characteristics are significant wave height and wave peak period. The jacket structure showed lower influence of increase of wave height to stresses in the cross section at the bottom of the structure compared to the monopile structure. The monopile structure showed slight dependency of stresses on increasing wave frequency, while the jacket structure showed nearly no dependency, due to its more complex geometry and higher stiffness

Fatigue Analysis on Innovative 10 Mw Offshore Jacket Structure Using Integrated Design Approach

The fatigue limit state (FLS) of fixed offshore wind turbine structures is critical and difficult to handle. As it is the most common design driving criteria for offshore structures, the simulation and calculation of this phenomenon must be as accurate as possible. Research is needed to improve the current design. There are mainly two design approaches available: Integrated design approach (IDA) and Sequential design approach (SDA). The IDA, described in this paper, considers the coupled structural analysis of a whole wind turbine system exposed to wind- and wave-induced loads in an aero-hydro-elastic solver. The results given by solver are loads series, which are afterwards used for obtaining the stress series with stress concentration factors (SCF) included. The stresses are processed in terms of rainflow counting and finally, fatigue damage of a critical K-joint is obtained externally, to avoid the use of damage equivalent loads (DEL) as by default in the solver, but to calculate it by means of the Efthymiou principle. The whole procedure with methods is explained in this paper

The New Therapeutic Approaches in the Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease which is characterized by extremely complex pathogenetic mechanisms and multifactorial etiology. Some of the many pathophysiological mechanisms involved in the development of NAFLD include oxidative stress, impaired mitochondrial metabolism, inflammation, gut microbiota, and interaction between the brain-liver-axis and the regulation of hepatic lipid metabolism. The new therapeutic approaches in the treatment of NAFLD are targeting some of these milestones along the pathophysiological pathway and include drugs like agonists of peroxisome proliferator-activated receptors (PPARs), glucagon-like peptide-1 (GLP-1) agonists, sodium/glucose transport protein 2 (SGLT2) inhibitors, farnesoid X receptor (FXR) agonists, probiotics, and symbiotics. Further efforts in biomedical sciences should focus on the investigation of the relationship between the microbiome, liver metabolism, and response to inflammation, systemic consequences of metabolic syndrome

Optimization of ultrasound assisted extraction of antioxidant compounds from marjoram (Origanum majorana L.) using response surface methodology

The present study optimized the ultrasound assisted extraction (UAE) conditions to maximize the antioxidant activity [Ferric ion Reducing Antioxidant Power (FRAP)], total phenol content (TP) and content of individual polyphenols of extracts from marjoram. Optimal conditions with regard to amplitude of sonication (24.4–61.0 μm) and extraction temperature (15–35 °C) and extraction time (5–15 min) were identified using response surface methodology (RSM). The results showed that the combined treatment conditions of 61 μm, 35 °C and 15 min were optimal for maximizing TP, FRAP, rosmarinic acid, luteolin-7-O-glucoside, apigenin-7-O-glucoside, caffeic acid, carnosic acid and carnosol values of the extracts. The predicted values from the developed quadratic polynomial equation were in close agreement with the actual experimental values with low average mean deviations (E%) ranging from 0.45% to 1.55%. The extraction yields of the optimal UAE were significantly (p < 0.05) higher than solid/liquid extracts. Predicted models were highly significant (p < 0.05) for all the parameters studied with high regression coefficients (R2) ranging from 0.58 to 0.98