Fiber simulation is a branch of mechanics that deals with modeling the dynamics and rheology of particles of large aspect ratio, or fibers with the goal of predicting the properties of fiber suspensions and networks based on first principles. Simulation of fiber suspensions have applications in paper industry and also in composites, including composites made of carbon nanotubes. Many of the models used to simulate fibers were developed by researchers in the field of rheology. Rheologically speaking fiber suspensions are non newtonian fluids, and can display normal stress differences.

Early fiber simulations employed particles which were rigid rods or prolate spheroids, whose equations of motion have analytical solutions. More recent models are able to represent flexible fibers. The models rely heavily on continuum mechanics concepts and the numerical methods employed have some similarities to those employed in molecular dynamics, or in dynamics of multi body systems.

The use of computers facilitates greatly the solution of fiber simulation problems. The complexity of the simulations arise from the system having a large number of degrees of freedom, and from the numerous possible interparticle interactions having place, such as friction, hydrodynamic interactions, and other kinds of interparticle forces such as colloidal forces that exert attractive or repulsive forces.