# Bluerov2 hydrodynamics

Hello there,

I want to develop a control system for the Bluerov2,

I need then to derive the nonlinear mathematical model of the Bluerov2 behaviour. The idea is to put it into Simulink or Matlab to analyse the system dynamics.

To do that, I need the Bluerov2 hydrodynamic coefficients, that (according to some literature I read) are calculated using Computational Fluid Dynamics.

I’m not really familiar with fluid dynamics, so I’m writing you to ask if someone already have those coefficients, or any experience in how to obtain them.

Maybe it is possible with the uuv_simulator in gazebo, mentioned in this topic?
I also found an open source tool for that, the OpenFOAM. But I’m not sure if it works for this task.

Any help in this topic is welcome!

Thank you

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Are you talking about the drag coefficient? If so, you I would suggest to do this by testing the drag force in a pool as the behavior of the fluid around cables and propeller will be different when set into a congested cluster inside the frame compared to the individual drag based on their shape alone or even based on testing parts one by one. I know I would go for the water test method.

Hi @olaya,

Thanks for the post! Depending on the level of detail and accuracy that you are looking for, there’s a few ways to do this. For a first order approximation I would recommend considering a flat plate equivalent approach. Basically, you can figure out the rough “flat plate” area of the ROV in each direction and use a drag coefficient of `C_d = 1.0` for that area.

If you’re looking to get an accurate non-linear model then it will be a lot more complicated and I won’t be much help!

-Rusty

Hi @olaya,

in the UUV simulator parameter identification cannot be done, but there is this source material on the experimental identification of parameters for the BlueROV1 that can maybe helpful to you

https://brage.bibsys.no/xmlui/handle/11250/2409503

It is a thesis from a student at NTNU.
I think that maybe the best option to start working on your model.

Best,

Musa

Hi, @rjehangir
I have calculated the hyrodyanmic parameter. During the sitl simulation, how could I configure these parameters.
Thank you.

Hi,

we did some simple approximations for the SITL model, you can check it here.

As you can see, the buoyancy force/volume is calculated with our knowledge of the net buoyancy from the original vehicle, and `equivalent_sphere_area` is calculated with a sphere radius that is empiric.

Be free to improve it and send some patchs

Do you happen to still have these values? I’m currently modelling the BlueROV2 dynamics in MATLAB and I’ve been looking for some reliable values for the hydrodynamic parameters.

I am also interested in modelling the BlueROV2 dynamics if anyone has done the CFD/experiments to find the 6-DOF hydrodynamic coefficients.