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Consider a ship vibrating in the fundamental/principal/first symmetric mode shape (similar to that of a Bernoulli-Euler beam), induced by the main engine (similar to that of a vibration shaker).

I wish to balance out - not to dampen - the vibrations.

Should one balance out at the source, i.e. at the main engine, or at one of the structures' antinodes?

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  • $\begingroup$ What do you mean to "balance out" a vibration? $\endgroup$ – DanielSank Jun 17 '16 at 7:25
  • $\begingroup$ It means that the resulting steady-state vibration amplitude equals zero (at least that is what we are aiming for) $\endgroup$ – Ole Jun 17 '16 at 8:09
  • $\begingroup$ So, you're trying to do something so that the modes at frequencies which the engine can drive have nodes at the engine's location? $\endgroup$ – DanielSank Jun 17 '16 at 8:11
  • $\begingroup$ No. As I state, one should either balance out at the source, i.e. at the main engine, or at one of the structures' antinodes. Fundamentally this question is about modal balancing, but I cannot find the answer / figure it out as of now... $\endgroup$ – Ole Jun 17 '16 at 10:59
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Your question is possibly too specialised for Physics SE. It might be better in Engineering SE. You might also try an Internet Search.

The reasons for choosing one over the other might be specific to naval architecture, which I know very little about.

Intuition tells me to balance at source. This introduces a compensating force in the same plane, which nullifies the vibration force without creating any torque. Balancing in a different plane creates an oscillating torque.

Attempting to balance at an anti-node, eg by attaching a mass to increase inertia, alters the modal frequencies of vibration of the ship. The vibration source still exists, so other modes might be amplified, or new modes excited.

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