Reference no: EM132886205

M22011 Structural Integrity - University of Portsmouth

Structural Integrity Assessment

Part 1: Fatigue analysis of an offshore wind turbine blade

Background:
A small-scale wind energy generation offers a significant potential for supplying small and isolated loads, households, or off-grid communities with no access to the electricity distribution network. Unlike the larger-scale counterparts (wind turbines), small wind systems generally operate unsupervised and operate at different power/rotor speed regulations. The latter could impact the variations of blade performances, particularly when conducting fatigue analysis. Fatigue loading is always a major factor for wind turbine life, particularly rotor blades. Excessive fatigue loads will lead to a reduction in the blade life and increase maintenance costs and financial losses. Figure 1.1 illustrates the external forces acting on a turbine blade. The design against fatigue is therefore an important part of the (small) wind turbine design process. The International Electrotechnical Commission (IEC) has published an International standard for wind turbines design, known as BS EN IEC 61400-1: Wind turbines- Part 1: Design requirements.

Task:
As part of a design consultancy work, your task is to estimate the fatigue life of a turbine blade in this case the NREL 5MW wind turbine (WT) blade. The WT will be operating in a location with an average wind speed of 13 m/s.

In your analysis and report, you should include the following:
1. Description of the relationship between the aerodynamic loads and the normal or axial and tangential forces as well as the pitching moment.
2. A flow chart illustrating the process of fatigue analysis.
3. Using Qblade (a free-to-download software: the determination of the lift and drag coefficients.
4. By choosing the worst-case condition, a work out evidence (Excel format is accepted) of the fatigue analysis. You could use the pre-determined FE modelling results (Table 1.3) for the analysis (FE modelling is not necessarily needed, but welcome).

The wind speed in such a long-time span cannot be considered constant at any site. It will be influenced by the weather conditions, the local land terrain and the height above the ground surface. A Weibull distribution can be adopted to describe the wind speeds for a long-term period, defined by two parameters, K which is the shape parameter and C which is the scale parameter of the distribution. In this case, the Weibull distribution of the wind speed of European offshore wind farms over the whole year is adopted, where the shape parameter K=2.0, and the scale parameter C =15m/s [1, 2]. The wind field simulations per minute for one hour could be randomised using MATLAB. The wind speed generated by Weibull distribution and the associated maximum stress over time during the time period are illustrated in Figure 1.2.

Part 2: Creep life assessment of a superheater header and nozzles

Background
A superheater header of a power generation plant (Figure 2.1) is subjected to a two-shifting operation mode, where it will be operating throughout the week starting from Monday at 8am, but will be turned off over the weekend from Friday at 6pm.

Referring to Figure 2.1, the header (position 2) is welded to the nozzles (position 1). On the other end of the nozzles, the tubes are welded to a plate by means of sealing weld (position 3).

The header and the nozzles are manufactured from 18Cr-9Ni-3Cu-Nb-N (according to ASME SA-213) or X10-Cr-Ni-Cu-Nb-18-9-3 (according to VdTUV 550), also known as S304H steel. The operating conditions and material properties of the S304H steel are summarised in Table 2.1.

Task:
After a continuous operation of 16,000 hours, the owner of the plant would like to perform creep life assessment on the header and nozzles, either in accordance to EN12952-4 [1] or the European Creep Collaborative Committee (ECCC) procedure and materials data sheet [2, 3]. The remaining life will need to be evaluated assuming when there is no temperature fluctuation and at the same time when there is a 5ºC fluctuation. The report to the owner shall be made to include the analysis and recommendations that can help preventing a creep failure.

Attachment:- Structural Integrity Assessment.rar