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Quality Assurance & Validation

Quality Assurance

AMOG ensure a high level of Quality Assurance for SHEAR7 by implementing best practices in code development. These aspects of Quality Assurance are performed by AMOG under the funding provided by the User Group fees and include:

  • Regression tests:

    • Robust regression testing program, for verifying the SHEAR7 installation on multilingual Windows OS installations.

  • Version Control:

    • SHEAR7 is version controlled using the Subversion software tool.

  • Coding structure:

    • Refactoring of the major parts of the source code has been carried out to improve readability and ease long term maintenance of the code base.

  • Steadily implementing SHEAR7 programming activities towards achieving compliance with International Standard for software integrity, IEC 61508-3.

Validation

Unlike Quality Assurance, Validation tasks are not automatically included as part of AMOG's code development activities. In the past AMOG has performed internal software validation for SHEAR7 versions, with the purpose of benchmarking performance and validating the software as acceptable for contractor use. This internal validation is not externally reported and validation conditions are presently determined upon AMOG sole judgements, rather than to an externally agreed standard. There have been significant changes and upgrades to the software since AMOG took over administration of SHEAR7 at v4.5.

During the last 10 years more data has become available to validate the latest versions of the Program. Validation has been performed against small scale long flexible riser data. In general there is only a sparse amount of full scale riser data to validate against. Validation of version 4.6c of the program, which had a particular emphasis on VIV suppression effects was conducted and is available in OMAE 2011-49817 (Resvanis and Vandiver).

Additional validation tasks have been undertaken during the development of the program since the validation of version 4.6c, please refer to DeepStar reference paper - OMAE2013-10984 "USING MODEL TEST DATA TO ASSESS VIV FACTOR OF SAFETY FOR SCR AND TTR IN GOM" for further details.

This validation provided the grounding for the default parameter guidelines provided to users as part of the SHEAR7 User Guide of the current version. Key Validation parameters are shown below for the latest version of SHEAR7:

Key validation parameters are shown below:

           Table A1: SHEAR7 Default Parameters

Property

Riser Region

Bare

Straked

Fairings

Added Mass

1.0

2.0

2.0

Strouhal Number

0.18

0.10

0.10

Bandwidth

0.40

0.25

0.00

CL Table

1

5

5

Beta Control Number

4

4

4

Damping Coefficient

Reynolds Number Still Water

1.00

1.00

1.00

A/D Still Water

0.20

0.40

0.40

Low VR Regions

0.18

0.50

0.50

High VR Regions

0.20

0.20

0.40

Axial Flow Regions

0.00

0.00

0.00

Power Ratio Cutoff

0.05

0.05

0.05

Primary Zone Amplitude Limit

0.3

0.3

0.3

Lift Coefficient Reduction Factor

1.0

1.0

1.0

Power Ratio Exponent

1

1

1

Higher Harmonics Threshold

0.4

0.4

0.4

Higher Harmonics Factor

3.33

3.33

3.33


However it should be noted:
  • The published experimental results have been obtained from mostly low Reynolds number testing.

  • For straked risers, the experiments have a specific geometry (strake height = 25% of diameter; Strake pitch = 17.5 diameters).

  • All the straked experiments considered the straked region clean (do not have marine fouling) and are undamaged.

  • Future research is still needed to improve the ability to model fairings.

  • Typical response of a riser with partial strake/fairings coverage, will be driven mostly by the unprotected region, with the straked region providing damping.

  • The default value for the beta control number is 4; however, if the response is not converging this value can be increased up to 10.

  • The beta function is generally only important for high mode numbers, therefore, for efficient run times, the beta control number should be set to zero if modelling the following structures:

    • Rigid subsea jumpers with low mode numbers,

    • Pipeline response with low mode number,

    • In-line response at low mode number. 

  • The Higher Harmonics amplification factor and threshold are important when modelling systems that result in Higher mode number excitation. The default threshold value is 0.4 and the default Higher Harmonics amplification factor is 3.33

  • It is noted that the axial flow damping capability now available in SHEAR7 v4.9 remains as an experimental feature and is yet to be fully verified. Further testing has been planned for calibration against other model teats and field data. Although Axial Damping Coefficients are available from regulations associated with offshore analysis, these have not been verified for VIV predictions in SHEAR7. It is recommended that users set this parameter to 0.0 for their analyses.

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