  In various applications, design problems involving structures and compliant
mechanisms experience fluidic pressure loads. During topology optimization of
such design problems, these loads adapt their direction and location with the
evolution of the design, which poses various challenges. A new density-based
topology optimization approach using Darcy's law in conjunction with a drainage
term is presented to provide a continuous and consistent treatment of
design-dependent fluidic pressure loads. The porosity of each finite element
and its drainage term are related to its density variable using a Heaviside
function, yielding a smooth transition between the solid and void phases. A
design-dependent pressure field is established using Darcy's law and the
associated PDE is solved using the finite element method. Further, the obtained
pressure field is used to determine the consistent nodal loads. The approach
provides a computationally inexpensive evaluation of load sensitivities using
the adjoint-variable method. To show the efficacy and robustness of the
proposed method, numerical examples related to fluidic pressure loaded stiff
structures and small-deformation compliant mechanisms are solved. For the
structures, compliance is minimized, whereas for the mechanisms a
multi-criteria objective is minimized with given resource constraints.
