This work presents a fluid-particle interaction method for the simulation of three-dimensional incompressible fluids laden with particles. We follow an immersed-boundary approach to enable overlapping (nonmatching) fluid-particle interfaces, as an alternative to classical Arbitrary Lagrangian Eulerian (ALE) approaches. The fluid (governed by the Navier-Stokes equations) is described in an Eulerian way and resolved through the finite element method (FEM) with a fixed Cartesian mesh. The particles (assumed spherical) are described in a Lagrangean way and resolved through the discrete element method (DEM). The fluid-particle interfaces are treated through Nitsche’s method, whereby we impose the particles´ surface velocities and spins as boundary conditions to the fluid in a weak sense. To compute the stresses at the interfaces, we follow a simple methodology developed by the authors in [1] based on the fluid´s resolved pressure and velocity gradient fields in the vicinity of the interfaces. This avoids local disturbances on the pressure field around the fluid elements intersected by the particles, as typically observed when using weakly-based methods (such as Nitsche´s method) for coupling nonmatching meshes. Particle-to-particle and particle-to-wall contacts are fully permitted and resolved. To assess the accuracy and effectiveness of the developed scheme, numerical simulations of 3D fluid flows laden with particles are performed and compared against reference solutions. This work is an extension of a former work by the authors in [2], wherein only 2D flows were enabled at the time (and through a different fluid-particle interaction scheme, based on Lagrange multipliers instead of Nitsche´s method). References [1] A. S. Müller, E. M. B. Campello, Henrique C. Gomes, Gustavo C. Buscaglia. A methodology for evaluating fluid-dynamic forces on immersed bodies in 3D fluid flows with nonmatching fluid-body meshes. Computational Particle Mechanics (submitted), 2024. [2] A. C. S. Fernandes, H. C. Gomes, E. M. B. Campello, P. M. Pimenta. A coupled FEM–DEM method for the modeling of fluids laden with particles. Comp. Part. Mech. 8, 349–368 (2021). https://doi.org/10.1007/s40571-020-00336-3.