  This work presents an intermediate resolution model of the hydrodynamics of
colloidal particles based on a mixed Eulerian-Lagrangian formulation. The
particle is constructed with a small set of overlapping Peskin's Immersed
Boundary kernels (blobs) which are held together by springs to build up a
particle impenetrable core. Here, we used 12 blobs placed in the vertexes of an
icosahedron with an extra one in its center. Although the particle surface is
not explicitly resolved, we show that the short-distance hydrodynamic responses
(flow profiles, translational and rotational mobilities, lubrication, etc)
agree with spherical colloids and provide consistent effective radii. A
remarkable property of the present multiblob model is that it naturally
presents a "divergent" lubrication force at finite inter-particle distance.
This permits to resolve the large viscosity increase at dense colloidal volume
fractions. The intermediate resolution model is able to recover highly
non-trivial (many-body) hydrodynamics using small particles whose radii are
similar to the grid size $h$ (in the range $[1.6-3.2]\,h$). Considering that
the cost of the embedding fluid phase scales like the cube of the particle
radius, this result brings about a significant computational speed-up. Our code
Fluam works in Graphics Processor Units (GPU's) and uses Fast Fourier Transform
for the Poisson solver, which further improves its efficiency.
