High residuals in solid mechanics frequency domain simulations

Vivek Kande Aerodynamics

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I am relatively new to solid mechanics simulations. I am working on simple 2D frequency domain simulations of simple solid resonators, as shown below. (the blue part is silicone, the white part is steel with custom stiffness and density values). I apply a harmonic pressure load on the top surface(edge in 2D), and measure the surface response. The bottom surface(edge) is free, the side ones are fixed. The model works fine with relative tolerance of 1e-6 when the thickness of the model is large (ex: 5mm ). The width of the model is 5mm. Now when i reduce the thickness to say 0.5 to 1mm, the model is not able to converge to even a relative tolerance of 1e-3. 1)Could anyone guide me, how to debug this issue? I tried playing with the mesh, refining it further, but that doesn't work. 2)On a side note, is the aspect ratio of cells being close to 1 a stricter requirement in solid mechanics FEM than that in standard CFD problems?



2 Replies Last Post 2026/06/11 10:02 GMT-4
Henrik Sönnerlind COMSOL Employee

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Posted: 7 hours ago 2026/06/11 9:13 GMT-4

The most common cause for non-convergence in frequency domain is that you try to solve at (or near) an eigenfrequnecy when the structure has no or very little damping.

The undamped linear problem is singular at resonance, since it would lead to an infinite response.

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Henrik Sönnerlind
COMSOL
The most common cause for non-convergence in frequency domain is that you try to solve at (or near) an eigenfrequnecy when the structure has no or very little damping. The undamped linear problem is singular at resonance, since it would lead to an infinite response.

Vivek Kande Aerodynamics

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Posted: 6 hours ago 2026/06/11 10:02 GMT-4

Hi, Thanks for the response. I am indeed working close to resonance frequency, that is by requirement of my research problem. However, I did add a loss factor damping . I understand that the amplitudes would be higher close to resonance, even higher when I am working with lower thickness models. However, I am plotting the response during the run, the amplitudes don't seem to diverge to unphysically large values.

Hi, Thanks for the response. I am indeed working close to resonance frequency, that is by requirement of my research problem. However, I did add a loss factor damping \eta=0.1. I understand that the amplitudes would be higher close to resonance, even higher when I am working with lower thickness models. However, I am plotting the response during the run, the amplitudes don't seem to diverge to unphysically large values.

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