Two simulation techniques that are used to approach two very different suspension problems - continuum scale 'active fluids' contain living cells that can respond to external stimuli such as light; and passive fluids contain anisotropic particles whose size is small enough that non-continuum effect caused by solvent needs to be accounted for. In the first part, instability caused by hydrodynamic interaction between the living cells is probed by Fluid Particle Dynamics (FPD). In the second part, Coarse-Grained Molecular Dynamics (CGMD) simulation is applied to investigate the relation between microstructure of the suspension, such as orientation distribution function, particle moments to its rheological behavior, such as shear viscosity.