Simulations of fluid-particle systems are of great interest for a wide variety of fields in both science and engineering. Therefor, simulation techniques and tools are needed that are able to both accurately and efficiently simulate such systems. When resolved simulations are needed, a coupling between the lattice Boltzmann method (LBM) for the fluid flow and the discrete element method (DEM) for the particle dynamics is among the best choices, and such a coupling is presented in this work: LBDEM coupling creates a bridge between two well-established open-source codes, Palabos for the LBM and LIGGGHTS for the DEM. After a short introduction, the theoretical foundations are discussed: the theory of the LBM and the DEM, as well as coupling methodologies, are outlined with emphasis on the mathematical and algorithmic aspects. For the coupling, a set of validation cases is presented in a 2D implementation and the 3D simulation code. Good agreement with experiments and numerical results obtained by other methods is found for several cases. Further, parallel performance of the 3D implementation is discussed, and tests show that LBDEM coupling scales well for up to 256 cores. The application part of this thesis starts with a literature review on the behaviour of particulate suspensions in narrow channels. Starting from the Fåhræus-Lindkvist effect and the Segré-Silberberg effect, experimental and numerical results are summarized along with theoretical models for lateral forces on particles in narrow channels. The two following chapters present numerical simulations of particle motion in narrow channels follow. In the first of these two chapters, 2D simulations of a single circular particle of varying diameter in Poiseuille flow are presented. It is found that the focusing time of this particle scales like 1/Re, and that there are at least four different modes of migration towards the equilibrium position: monotonous, oscillating, overshooting, and channel crossing. In the second chapter on channel flow, the behaviour of a suspension of varying solid fraction in a square channel is investigated by means of 3D simulations. In such systems, equilibrium positions exist close to the channel faces and corners, and their stability depends on Reynolds number and solid fraction. At least two new patterns are found: At Re =60, 190, at a solid fraction of fs = 0.3% a secondary equilibrium position closer to the channel center appears at the channel faces. At Re = 310, 500, for single particles both face and corner positions are stable, however around fs = 0.1% the face equilibrium positions become unfavorable for the particles. Both these effects can be attributed to particle interactions. In a second application of LBDEM coupling, the behaviour of particle beds under turbulent shear flow, similar to what occurs in river beds, is investigated. Three different beds are considered: monodisperse (d = 1mm), bidisperse (d = 1, 2mm) and prolate ellipsoids with aspect ratio of 2 and the same volume as the smaller spheres. It was found that the monodisperse and ellipsoid beds behaved similarly, while in the bidisperse bed first the smaller particles were picked up by the flow, clearly before the larger particles start to move. In this work, LBDEM coupling has been proven to be an efficient and accurate simulation tool for the detailed simulation of fluid-particle systems.