Floating body external acceleration behavior

circles · July 2022

Hello all,

Hope all is well. Lately I have been working on modeling floating objects, I have observed something and I would really appreciate your input on this.

I started with the falling sphere example, specifically ....\examples\main\11_Floating, in that example the gravitational acceleration g=-9.81, when I set it to zero, g=0 and instead use an external file to define a constant acceleration of -9.81m/s^2, I get different results. The option "global gravity" does not seem to affect the solution.

I then tried spheres of different radius, and different problem configurations as well such as a body fully submerged in water etc. It always seem to be the case.

How can I use an external file which acts as a global acceleration both on fluid and solid bodies?

Regards

circles · August 2022

Can we define both fluid and solid mk 's when using acceleration input?

Alex · August 2022

You can impose external acceleration to fluid volumes and you can also impose external acceleration to floating objects.

Regards

Alex

Asalih3d · August 2022

You can even do something as this, see CaseTemplate.xml

circles · August 2022

Thank you for your replies, I have tried something like what's shown below with or without gravity definition (constant gravity=0,0,0).

        <accinput mkfluid="0">
          <acccentre x="0.0027" y="0.004" z="0.004" comment="Center of acceleration" units_comment="metres (m)" />
          <globalgravity value="0" comment="Global gravity enabled (1) or disabled (0)" />
          <acctimesfile value="CaseForcesData.csv" comment="File with linear and angular acceleration data" />
        </accinput>
			  <accinput mkbound="51">
          <acccentre x="0.0027" y="0.004" z="0.004" comment="Center of acceleration" units_comment="metres (m)" />
          <globalgravity value="0" comment="Global gravity enabled (1) or disabled (0)" />
          <acctimesfile value="CaseForcesData.csv" comment="File with linear and angular acceleration data" />
        </accinput>
      </accinputs>

However, as I said even if the acceleration is constant in the external file (so that it would let's say act like g=0,0,-9.81 on both the fluid and floating body), it does not give me the expected results.

Alex · August 2022

Note that if you define initial gravity definition to 0, then you have to impose the value of cte B (equation of state), which defines the compressibility.

circles · August 2022

Thank you @Alex!

The simulation proceeds without throwing error even if I don't define cte B, I actually haven't tried explicitly defining B when initial gravity is 0.

I will try a series of test cases and share my updates.

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Floating body external acceleration behavior

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