  Simplifying the geometry of a CAD model using defeaturing techniques enables
more efficient discretisation and subsequent simulation for engineering
analysis problems. Understanding the effect this simplification has on the
solution helps to decide whether the simplification is suitable for a specific
simulation problem. It can also help to understand the functional effect of a
geometry feature. The effect of the simplification is quantified by a
user-defined quantity of interest which is assumed to be (approximately) linear
in the solution. A bound on the difference between the quantity of interest of
the original and simplified solutions based on the energy norm is derived. The
approach is presented in the context of electrostatics problems, but can be
applied in general to a range of elliptic partial differential equations.
Numerical results on the efficiency of the bound are provided for
electrostatics problems with simplifications involving changes inside the
problem domain as well as changes to the boundaries.
