Structural integrity assignment

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: σe!"!#$%#&!'()!*

Where N=number of cycles, σe = 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)

𝐷 = # 𝑛! 𝑁!!

Goodman diagram

(see Lecture 1 note on HCF for character’s

definition)

Table 1.2: Aerodynamic properties of NREL 5MW wind turbine blades

1=+ u

m

a

a

SS ss

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Fig. 1.2: Wind speed generated by Weibull distribution and the associated maximum stress over time during the time period.

Fig. 1.3: FE model results showing the maximum stress as a function of wind speed.

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Table 1.3: Pre-determined FE modelling results – derived from the Fast Fourier Transform (FFT)

analysis to determine the number of cycle (frequency) in one service hour

Peak Cycle, n σmax (MPa) σmin (MPa)

1 5

44.62 10.98

43.42 11.51

37.28 11.44

42.50 10.94

42.50 10.94

References:

1. IEC 61400-3:2009 Design requirements for offshore wind turbines

2. G. Bedon, M. Raciti Castelli, E. Benini, Optimization of a Darrieus vertical-axis wind turbine using blade element - momentum theory and evolutionary algorithm, Renew. Energy 59 (2013) 184– 192, https://doi.org/10.1016/j.renene.2013.03.023.

3. C. Zhang, H.P. Chen, Fatigue damage model of wind turbine composite blades under uncertain

wind speed, in: G.S.M. Papadrakakis, V. Papadopoulos (Ed.), 2nd International Conference on Uncertainty Quantification in Computational Sciences and Engineering (UNCECOMP 2017), Rhodes Island, Greece, 2017, pp. 616–626.

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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.

Fig. 2.1: Superheater header of a power generation plant sketch

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.

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Table 2.1: Superheater header material properties and operating conditions

Operating conditions Value Internal Pressure 24 MPa

Operating temperature 650ºC

Material properties Yield Strength at 20ºC 270 MPa

Yield Strength at 650ºC 160 MPa

Ultimate Tensile Strength at 20ºC 590 MPa

Ultimate Tensile Strength at 650ºC 370 MPa

Modulus of elasticity, E at 20ºC 189,000 MPa

Modulus of elasticity, E at 650ºC 137,500 MPa

Stress rupture (in association with the materials’s

Creep resistance) for 100,000 hour,

116 MPa

------------------- End of Assignments ------------------ References:

1. EN12952 Water-tube boilers and auxiliary installation – Part 4: In-service boiler life expectancy

calculations, 2011, n.d.

2. ECCC Recommendations – Volume 9 Part II (Issue 1): High temperature component analysis

overview of assessment and design procedures, 2014, n.d.

3. ECCC Data Sheets 2005

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Marking Scheme Only one report will be submitted (online submission through Moodle), but it will comprise 2 parts of the assignment detailed as follows:

Part 1: Fatigue analysis of an offshore wind turbine blade Brief report: containing no more than 600 words

Structure, clarity and layout of the report/presentation 5 Marks Explanation or rationale of the approaches/methodologies (a flow chart of a process), including referencing 15 Marks

Results presentation, and interpretation (analysis), summary of the findings 30 Marks

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

Short report – containing 800 words Structure, clarity and layout of the report/presentation 5 Marks Results presentation, discussion and interpretation (analysis) 25 Marks Summary of the findings and recommendations, including referencing 20 Marks Total 100 Marks