OrcaFlex validation

We publish a number of documents describing the validation of OrcaFlex. Links to these can be found below. For more information please get in touch with our software team who would be happy to help.

The principal validation document for OrcaFlex is 99/005 OrcaFlex QA, Testing and Validation which describes the overall software QA process we use for developing OrcaFlex. The document also presents some comparisons of OrcaFlex with both real world data and other programs. We recommend that you read this document first.

Detailed validation cases

We also publish a number of more detailed validation cases:

99/101 A comparison with Flexcom for a typical deepwater SCR. The comparison covered statics, regular
wave dynamics and irregular wave dynamics.
99/102 A comparison with published results from a paper published at OMAE 2006. The paper compares
OrcaFlex to a code written as part of the author’s PhD study. Static and dynamic comparisons
are considered.
99/103 A comparison with published results from a paper published at OMAE 2005. The paper compares
OrcaFlex to a solution of the governing set of continuous equations for a cable with bending stiffness
for a static case.This comparison is a particularly strong validation of OrcaFlex since the authors use
the continuous equations rather than the discretised finite element approach of OrcaFlex.
99/104 A comparison with published work by Reismann, in the International Journal of Non-Linear Mechanics.
This paper considers numerical analysis of the large-deflection due to coupled torsion/bending of a weightless
99/105 Three separate comparisons with standard theoretical results: (1) the catenary equations, extended to allow for
axial stretch; (2) natural frequencies of a beam; (3) deflection of a cantilever beam.
99/106 A validation of OrcaFlex’s implementation of frequency dependent added mass and damping for vessels. This compares
results from the BMT frequency domain program NMIWAVE with OrcaFlex time domain results. The comparison also provides
validation of OrcaFlex’s handling of wave load RAOs.
99/107 A validation of the way OrcaFlex handles buoyancy forces and pipe internal contents pressure effects, and the
resulting effective tension and wall tension that OrcaFlex reports. OrcaFlex is compared against results presented
in Nigel Barltrop’s book Dynamics of Floating Structures: Volume 2.
99/108 A comparison of statistical properties of maxima from OrcaFlex generated wave elevation time series with theoretical values
based on the Rayleigh distribution.

Turbine validation

We have performed two separate validation studies, comparing the response of the OrcaFlex turbine object against that predicted by other analysis codes. The validation studies are documented by the following:

  • R1405#01#01 Wind Turbine Validation Report considers the National Renewable Energy Laboratory (NREL) offshore 5-MW reference wind turbine (RWT). The study considers two separate turbine systems: (i) land-based and (ii) floating, based on the OC3 Hywind system. A range of select OrcaFlex results are compared against equivalent results from FAST (running ElastoDyn), HAWC2 and Bladed; gathered as part of the OC3 study.
  • R1512#01#01 Comparison of loads from OrcaFlex and OpenFAST for the IEA 15MW RWT summarises a validation study which considers version 1.1.3 of the IEA 15MW RWT. Presented is an overview comparing select results, calculated by OrcaFlex, against equivalent results predicted by OpenFAST (running BeamDyn). The study considers the structural dynamics of the turbine blade oscillating freely under gravity and the aeroelastic response of the rotor-nacelle assembly (RNA) and tower to steady, stepped, skewed & turbulent wind.

OrcaWave validation

OrcaWave is a diffraction analysis program which calculates loading and response for wet bodies due to surface water waves via potential flow theory. This major new area of functionality was introduced to OrcaFlex version 11.0 in November 2019. We have validated OrcaWave by comparing its results to theoretical predictions where possible, and also by comparing results from OrcaWave to results from Wamit.

R1429#01#01 OrcaWave validation report summarises the validation work, and includes all input data files and meshes used in the validation report.

VIV validation

We have been involved with several studies that compared the various OrcaFlex time domain VIV models against real-world measurements of VIV. We have documented these comparisons in the following documents:

We would like to thank BP, the Norwegian Deepwater Programme, the DeepStar Project and Southampton University for access to the VIV measurements used in these comparison studies.