Academic Year 2020/21

M22011 – Structural Integrity Coursework Deadline For Submission: End of May 2021 at 23:59 (TBD)

Submission Instructions A report in pdf uploaded to a Turnitin dropbox on Moodle

Instructions for completing the assessment:

See next page

Examiners: Dr Sarinova Simandjuntak

M22011 – Structural Integrity 2020-2021 Page | 1

Coursework – Structural Integrity Assessment (M22011) Summary This unit is assessed by one report containing two pieces of coursework of equal weighting (50%). The coursework draws on experience from industrial/consulting work on the application of creep and fatigue analysis, and is aimed at providing a realistic opportunity for work experience at engineering consulting in some of the key areas of structural integrity assessment. Instructions: You should do the 2-part assignments stated in this coursework. Both requires a separate brief write- up or report, but join the two reports to form only 1 document (PDF) submission. There is a maximum number of words that you can include in the report (see marking criteria). This implies that your report should be clear but concise and adopting a technical reporting style. Read and understand the problem before you attempt to solve the problems. Each problem is defined in the description of the part’s assignment. Please refer to the specific requirements and marking criteria in each assignment. Although discussion and team work are encouraged, your report must be a piece of an independent and individual work. Submissions will be through a Moodle drop-box where Turnitin facility will be used to monitor and detect similarity in all submissions. Students are warned of the risk of failing the unit, or a significant loss of marks, if a high similarity is reported by Turnitin indicating plagiarism.

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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: https://sourceforge.net/projects/qblade/), 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).

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Fig. 1.1: Illustration of external forces acting on a wind turbine blade

Overview on Method, General Properties, Operating Conditions, Data for Fatigue Analysis The general properties of the NREL 5MW WT blades are outlined in Table 1.1. Whilst the

aerodynamic properties of the NREL 5MW WT blade are listed in Table 1.2.

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.

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Table 1.1: The general properties of the NREL 5MW WT blades and fatigue solutions

Parameters Values/Solutions Rating 5 MW

Number of blades. 3

Rotor diameter, hub diameters and height 126m, 3m, 90 m

Cut-in, designed, and cut-out wind speed 3 m/s, 11.4 m/s, 25 m/s

Cut-in and rotor speed 6.9 rpm, 12.1 rpm

Pitch angle 0 degree

Blade’s material: Glass fibre reinforced

composite (DD16)

UTS = 100 MPa

Typical S-N curve model: ?e!”!#$%#&!'()!*

Where N=number of cycles, ?e = corrected

stress (MPa)

a1 = 1.3, and a2=0.16 (for composite material)

where A1=a1sUTS

A2 = a2. sUTS

Miner’s rule:

(see Lecture 1 note on HCF for character’s

definition)

?? = # ??! ??!!

Goodman diagram

(see Lecture 1 note on HCF for character’s

definition)