  Three dimensional (3D) topology optimization problems always involve huge
numbers of Degrees of Freedom (DOFs) in finite element analysis (FEA) and
design variables in numerical optimization, respectively. This will inevitably
lead to large computational efforts in the solution process. In the present
paper, an efficient and explicit topology optimization approach which can
reduce not only the number of design variables but also the number of degrees
of freedom in FEA is proposed based on the Moving Morphable Voids (MMVs)
solution framework. This is achieved by introducing a set of geometry
parameters (e.g., control points of B-spline surfaces) to describe the boundary
of a structure explicitly and removing the unnecessary DOFs from the FE model
at every step of numerical optimization. Numerical examples demonstrate that
the proposed approach does can overcome the bottleneck problems associated with
a 3D topology optimization problem in a straightforward way and enhance the
solution efficiency significantly.
