1. Getting Started

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In this step by step guide only 2D axiysymmetric models will be considered. This allows for all the main principles to be demonstrated while keeping analysis times and model complexity to a minimum in order to ensure new users can follow the guidelines satisfactorily. 

Note: It is strongly advised that all CMUT models be run in the Double Precision

There are two important distinctions that have to be made between traditional OnScale models and Electrostatic CMUT models. They can be grouped into two categories. 

Linearity

As we know, most OnScale applications are linear in nature

  • Output scales linearly with Input
  • Double the Input; double the Output
  • Output can be 'corrected' during post-processing
  • Basis for linear systems analyses - using Convolution to extract output from input and impulse response

However, Electrostatic problems are inherently nonlinear

  • Coupling efficiency changes with displacement
  • Mechanical Nonlinearities exist
  • Mechanical 'restoring forces' increase with displacement

Therefore, to accurately analyze a nonlinear problem, all input values must be correct during simulation

  • No 'correction' during post-processing
  • Many additional places to make mistakes
  • Requires greater knowledge of system being modelled
  • Requires greater care during simulation

Large Deformation

Standard OnScale models are considered as small deformation, which is effectively anything less that 1% strain and therefore is fantastically well-suited to the vast majority of piezoelectric and wave-propagation applications.

  • Displacements are small compared to structure size
  • Nanometer sized motions on millimeter sized structures
    • 6 orders of magnitude difference
  • Assumption that nodal positions never change

Electrostatic models, however, are very much large deformation in nature

  • Displacements are large compared to structure size
  • Micron sized displacements on micron sized structures
  • Positions are updated every timestep
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