Intended or not intended resonance phenomena are well known to everyone out of daily life, even if it’s not obvious to us that natural frequencies play a roll – for example a mother pushing her child on a swing exactly at the peak, giving more energy to the resonance system “swing-child” this way.

With a technical system the transmission of more energy leads during resonance – i. e. the externally forced excitation frequency equals one of the eigen frequencies – leads to an overly high amplitude and therefore to an unavoidable destruction of the system, the so-called resonance catastrophe. Especially in civil engineering this is the worst case scenario and is to be avoided under every circumstance. Therefore, one has to determine every eigen frequency of the system, at which accelerating and restraining forces, induced by mass inertia or restoring forces from stiffness properties, balance each other. This can be done via finite element based natural frequency calculation (modal analysis). These frequencies are characteristic for every object and have a corresponding shape which would assume the shape of the displacements of the object when rocking with this specific natural frequency. With the help of the physical property obtained by simulation, the designer can draw his conclusions to unmatch practical relevant loadcases with the structure’s natural frequencies.

In Z88Aurora® you can use a Lanczos solver for natural frequency calculation. Features include:

• Supported elements:
  • Hexahedron No. 1 (linear) & No. 10 (quadratic)
  • Tetrahedron No. 16 (quadratic) & No. 17 (linear)
• Lanczos solver to calculate eigenvalues and modal form vectors
• Incremental display of natural frequencies via the postprocessor
• Individually selectable number of calculated eigenmodes

Unfortunately, Z88V14OS does not offer modal analyses.