Modelling Wave Forces on a Buoy

Hi all,

I'm still very, very new to the Simulink/Simscape side of the MATLAB/Mathworks suite. I have been trying for the last few hours to find a method of converting the heave wave forces on a buoy into a functional method for finding its position at a certain time. Effectively, this involves an external force of oscillating magnitude acting as given by the attached function. Despite my best efforts, however, my system appears to create a constant upwards load (which is greatly overshadowed by the force of gravity. Am I missing something? Please let me know.

[Yifeng Tang]

You attached model is complaining about missing "D" in the Heave Wave Force Signal. Could you please update that, in the mask probably?

[Ben Hauben]

Done.

[Yifeng Tang]

Same error. Did you save :p

[Ben Hauben]

Oops, fixed it. Not looking like I'll get a reply for it but you know it happens

Answer 1

[Yifeng Tang]

Thanks for sharing the model.

Looks like the main issue is caused by the source term inside the Heave Wave Force Signal. It was set as a "repeating sequence stair", so it stays as a constant for a duration of 5*T you set, and then move on to the next value of the function. For the 60 sec you simulated, the output from this source remains constant until the last step, when 5*T=60. If you run the model for longer, you will see the multiple steps, each with the value of one element in the array produced by the HeaveFK function. I don't think this is what you want it to do.

Using the "Repeating Sequence" block instead. See the attached example. And the position is now oscillating.

[Ben Hauben]

Thanks so much! This makes life so much easier.