It’s hard for me to say what a third party means by “relative chain diameter”. Is it possible that you could ask the third party in question.

However, as Sarah stated in an earlier response, if you can find from your test data, the actual value of “relative chain diameter” assumed in the test then you can enter that value as the “normal drag area” in OrcaFlex and use your Cd = 2.2-2.6 directly.

Please let us know if this doesn’t help you solve your problem.

Sorry to re-open this thread but I have a similar question as Ika.
I also have test data where the drag coëfficiënt equals 2.2-2.6, the drag area it was based on was calculated by the ‘relative chain diameter’ times the length. Here lies my problem, I can’t seem to find what they mean by ‘relative chain diameter’. Is this the diameter of a rod of metal in the link or rather the width of the entire link?

Could anyone help me with this please?

Thank you,
Bruno

As far as I can tell Google SketchUp uses an un-documented proprietary file format. This means we have no way of working out how to import such a file other than reverse engineering it – and I doubt we’d be very successful at that.

This is symptomatic of a wider issue which is that, as far as I know, there is no standard for 3D modelling files. Every package/technology uses its own proprietary file format. Even worse, these files change from one version of a package to the next.

We have taken the simplest approach possible which is to use the native format of DirectX which is the .x file.

Perhaps the best route for you, if you want to use SketchUp is to export from SketchUp to something like .3ds and then convert that into .x with PolyTrans. However, I think you’d need the Pro version of SketchUp.

I’m sorry we can’t be more helpful but I really don’t think we can do much more without there being a published standard for 3D modelling files.

I’ve sent you an e-mail that gives a more detailed response to your question and includes some background information on the different line type diameters that are used in OrcaFlex.

However, the short answer to your question is that you need to find out what drag area your drag coefficient of 2.6 was based on. OrcaFlex defines the normal drag area per segment from the product of the normal drag diameter (which is set on the line type data) and the segment length. Note that I’m assuming here that your drag coefficient is for the normal direction. Once you have established what drag area you should be using with your model test drag coefficient, you can simply set the normal drag diameter appropriately to ensure that you get the same area. Then you can simply directly enter your drag coefficient directly.

Sarah Ellwood

Thanks in advance.

-Ika-