Development of Combined Load Spectra for Offshore Structures Subjected to Wind, Wave, and Ice Loading

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider the effects of ice loading and its stochastic nature on the fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action.

Design and Structural Testing of Blades for a 2MW Floating Tidal Energy Conversion Device

The floating tidal energy is increasingly recognised to have the potential of delivering a step-change cost reduction to the tidal energy sector, by extracting energy from deeper water sites through energy conversion devices. To ensure the normal operation of a tidal energy convertor within its service life, the device should be designed properly and evaluated through a series of strength and durability testing. The Large Structures Research Group at NUI Galway is working closely with, renewable energy company, Orbital Marine Power and, blade manufacture, ÉireComposites Teo, to design and test the next generation of SR2000 tidal turbine blade, with aims to increase the turbine power production rate and to refine the design for low cost. This paper presents a brief description of the structural design and testing of a blade for the O2-2000 tidal turbine, one of the largest tidal turbines in the world. NUI Galway will utilise their in-house software, BladeComp, to find a blade laminates design that balances both blade strength and material cost. The structural performance of the designed blade will be assessed by conducting static and fatigue testing. To achieve this objective, a support frame to fix the blade is designed, a load application device is introduced and the methodology for design tidal loading conversion is proposed in order to complete the testing at NUI Galway.

A Novel Prediction Perspective to the Bending Over Sheave Fatigue Lifetime of Steel Wire Ropes by Means of Artificial Neural Networks

Steel wire ropes are frequently subjected to dynamic reciprocal bending movement over sheaves or drums in cranes, elevators, mine hoists, and aerial ropeways. This kind of movement initiates fatigue damage on the ropes. It is a quite significant case to know bending cycles to failure of rope in service, which is also known as bending over sheave fatigue lifetime. It helps to take precautions in the plant in advance and eliminate catastrophic accidents due to the usage of rope when allowable bending cycles are exceeded. To determine the bending fatigue lifetime of ropes, experimental studies are conducted. However, bending over sheave fatigue testing in laboratory environments require high initial preparation cost and a long time to finalize the experiments. Due to those reasons, this chapter focuses on a novel prediction perspective to the bending over sheave fatigue lifetime of steel wire ropes by means of artificial neural networks.

Fatigue Characterization and Fractographic Analysis of Aluminium 6063 Alloy

Aluminium and its alloy are widely employed in various automobile and aircraft areas because of their unique specific strength and formability. Al alloys that have been employed in aerospace structural components will undergo dynamic loading, which leads to fatigue due to mechanical stress and thermal conditions. Considering studies toward the low cycle fatigue behaviour of Al alloys are significantly narrowed, this chapter sighted to the analysis of fatigue behaviour of Al 6063 alloy at the various total strain amplitude (TSA) of 0.4% and 0.8%, which performed through the low cycle fatigue testing machine at the frequency rate of 0.2 Hz. The test results show that for 0.4% TSA, the number of cycles to failure (N) is 1786, whereas as the TSA increases, N got reduced. For 0.8% TSA, the cycle to failure is 291 and samples undergone cyclic softening during the test. The rate of cyclic plastic strain raised up with the increase in the TSA. Crack propagation was observed along with the quasi-cleavage fracture for 0.4% TSA and cleavage fracture for 0.8% TSA.

Bayesian Fatigue Life Prediction of Corroded Steel Reinforcing Bars

This paper presents a general method for fatigue life prediction of corroded steel reinforcing bars. A fatigue testing on standard specimens with pitting corrosion is carried out to obtain corrosion fatigue data. The maximum corrosion degree (MCD), characterizing the most severe site of the corrosion pit, is identified to have a log-linear relationship with the fatigue life. A fatigue life model incorporating the MCD and the stress range for corroded steel reinforcing bars is proposed. The model parameters are identified using the testing data, and the model is considered as the baseline model. To utilize the proposed model for life prediction of corroded steel reinforcing bars with different geometries and working conditions, the Bayesian method is employed to update the baseline model. The effectiveness of the overall method is demonstrated using independent datasets of realistic steel reinforcing bars.

The Correlation Between Static Fatigue Testing and the Quantitative Myasthenia Gravis Score and Activities of Daily Living Profile

Fatigue is a common symptom in myasthenia gravis (MG), but both objective and subjective measures of fatigue are poorly studied in the disease. We conducted a pilot study of static fatigue testing (SFT) in a group of MG patients, using an isometric quantified muscle analysis computer system. Results from sustained isometric contraction of 5 muscle groups in 77 patients were correlated to the Quantitative MG Score (QMG) and the Activities of Daily Living Profile (MG-ADL), two commonly used outcome measures. Pearson correlation coefficients for the SFT were highest (0.33) for hand grip for both the QMG and MG-ADL. Correlations were quite poor for the proximal muscle groups and ankle dorsiflexion. More work is needed to develop objective and subjective measures of fatigue in MG.