J Murphy & Sons: Anchorsholme Outfall – Combined CFD & Orcaflex Reduce Risk and Cost



Accurate prediction of pipeline load

Reduced risk of pipes being damaged

SUMMARY

We provided analysis of the installation process and the transportation of a 3.7km long Polyethylene outfall, the largest ever installed in the UK. Leveraging our cross-capability expertise we proposed the application of a combined CFD and Global Dynamic Analysis to provide the most accurate representation of the loading on the pipeline and its behaviour during transportation and installation. This allowed for the most appropriate towing vessel to be selected and ultimately a successful installation.

SITUATION

We were selected by J Murphy & Son’s, a global multi-disciplined engineering and construction company to support them in the £20 million Anchorsholme project. We provided analysis of the installation process and the transportation of the 3.7km long Polyethylene outfall, the largest ever installed in the UK. The outfall was transported from the North coast of Northern Ireland across the Irish Sea to Blackpool in the North West of England.

CHALLENGE

With this project being a first of a kind, our client needed an accurate way to effectively de-risk the project and gain insight into the loading on the pipeline and its behaviour during transportation and installation. The analysis was necessary to output tow forces for a range of tow speeds and environmental conditions, loads/moments acting on the flanged connections between pipe strings and the forces, at regular intervals along the pipeline, required to hold it on-station while floating near shore in preparation for installation. Our client had limited experience in this area and therefore needed a level of guidance on the approach to the problem to ensure the most representative analysis.

SOLUTION

Leveraging our cross-capability expertise, we proposed the application of a combined CFD and Global Dynamic Analysis to provide the most accurate representation. We lead the project from the very first contact with J Murphy to the presentation of results, ensuring the approach was well understood and accepted by all stakeholders. Global Dynamic Analysis was used to carry out the dynamic tow analysis and the floating simulation (for installation).  To obtain appropriate drag coefficients, a steady-state CFD analysis, assessing four flow directions (0deg, +15deg, +30deg and 90deg), was carried out. The CFD model included the detail of the pipeline’s concrete collars to generate more accurate lateral and axial drag coefficients. The CFD adjusted the conservative drag coefficients typically applied in traditional methods. To remove further conservatism, JONSWAP (Joint North Sea Wave Project) irregular waves were considered in preference to regular waves in the tow analysis. The output of our analysis allowed for the most appropriate towing vessel to be selected and for the operation procedures to be well understood ensuring no damage to the pipeline and ultimately a successful installation. 

BENEFITS
  • We improved the understanding of the behaviour of the pipeline during towing under a variety of environmental conditions which reduced the risk of the pipes being damaged
  • We improved the understanding of the towing vessel requirements and the vessel requirements for installation, reducing the cost through more accurate prediction of pipeline loads (preventing unnecessary over-specifying of the towing vessel thrust requirements).
  • The CFD drag coefficients were significantly lower than those used in traditional hand calculations (as specified in the offshore design codes).


We provided analysis of the installation process and the transportation of a 3.7km long Polyethylene outfall, the largest ever installed in the UK. Leveraging our cross-capability expertise we proposed the application of a combined CFD and Global Dynamic Analysis to provide the most accurate representation of the loading on the pipeline and its behaviour during transportation and installation. This allowed for the most appropriate towing vessel to be selected and ultimately a successful installation.



We were selected by J Murphy & Son’s, a global multi-disciplined engineering and construction company to support them in the £20 million Anchorsholme project. We provided analysis of the installation process and the transportation of the 3.7km long Polyethylene outfall, the largest ever installed in the UK. The outfall was transported from the North coast of Northern Ireland across the Irish Sea to Blackpool in the North West of England.



With this project being a first of a kind, our client needed an accurate way to effectively de-risk the project and gain insight into the loading on the pipeline and its behaviour during transportation and installation. The analysis was necessary to output tow forces for a range of tow speeds and environmental conditions, loads/moments acting on the flanged connections between pipe strings and the forces, at regular intervals along the pipeline, required to hold it on-station while floating near shore in preparation for installation. Our client had limited experience in this area and therefore needed a level of guidance on the approach to the problem to ensure the most representative analysis.



Leveraging our cross-capability expertise, we proposed the application of a combined CFD and Global Dynamic Analysis to provide the most accurate representation. We lead the project from the very first contact with J Murphy to the presentation of results, ensuring the approach was well understood and accepted by all stakeholders. Global Dynamic Analysis was used to carry out the dynamic tow analysis and the floating simulation (for installation).  To obtain appropriate drag coefficients, a steady-state CFD analysis, assessing four flow directions (0deg, +15deg, +30deg and 90deg), was carried out. The CFD model included the detail of the pipeline’s concrete collars to generate more accurate lateral and axial drag coefficients. The CFD adjusted the conservative drag coefficients typically applied in traditional methods. To remove further conservatism, JONSWAP (Joint North Sea Wave Project) irregular waves were considered in preference to regular waves in the tow analysis. The output of our analysis allowed for the most appropriate towing vessel to be selected and for the operation procedures to be well understood ensuring no damage to the pipeline and ultimately a successful installation. 



  • We improved the understanding of the behaviour of the pipeline during towing under a variety of environmental conditions which reduced the risk of the pipes being damaged
  • We improved the understanding of the towing vessel requirements and the vessel requirements for installation, reducing the cost through more accurate prediction of pipeline loads (preventing unnecessary over-specifying of the towing vessel thrust requirements).
  • The CFD drag coefficients were significantly lower than those used in traditional hand calculations (as specified in the offshore design codes).
CFD Drag Analysis Sub Model
CFD drag analysis velocity contour at 157.5 degrees environmental direction
Orcaflex Dynamic Tow Base Model
Installed Outfall Pipeline
Orcaflex Onshore Floating Pipeline Base Model

SECTOR

PROJECT ATTRIBUTES

ANSYS CFD

Orcaflex V10.1c

Flexible Pipeline (PE Material)

JONSWAP (Joint North Sea Wave Project)


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The CFD drag coefficients were significantly lower than those used in traditional hand calculations

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