Topology optimization methods:

• Continuum (density) approach

  Start with a bounding envelope full of material. Where the material is relatively un-stressed, reduce the density and gradually steer the solution towards one that is just black and white (so that there is material or there isn't).

• Ground structure approach

  Start with a lattice-grid of beams connecting nodes. Selectively turn beams on or off depending on how stressed they are until you converge on the optimal solution.

• Parametric variation

  Describe the geometry of your design with a small number of variables. Change the variables until the design converges to the optimal (determined by some optimality criteria.) In this case, the length of a tuning fork is adjusted until the natural frequency is exactly 440Hz.