A computer implemented method for conducting a fluid simulation of a porous medium, the method comprising: retrieving, by a computing system, a representation of a three-dimensional physical porous medium, the representation including pore space corresponding to the porous medium, with the representation including at least one portion of under-resolved pore structure (42a', 42b', 42c', 42d') in the porous medium; defining, by the computing system, a representative flow model for the under-resolved pore structure in the representation; constructing (58, 64), by the computing system fluid force curves that correspond to fluid forces in the under-resolved pore structure in the representation based on precomputed physical properties of the under-resolved pore structure corresponding to the defined representative flow model, wherein the constructing comprises if precomputed physical properties for the defined representative flow model are stored in a library, retrieving the precomputed physical properties, if precomputed physical properties for the defined representative flow model are not stored in the library, conducting a simulation in a fully-resolved representative subdomain of the under-resolved pore structure to calculate the physical properties, and determining fluid forces in the under-resolved pore structure based on the precomputed physical properties of the under-resolved pore structure; and conducting the fluid simulation of the porous medium, wherein conducting the fluid simulation of the porous medium comprises applying the determined fluid forces at the under-resolved pore structure. retrieving, by a computing system, a representation of a three-dimensional physical porous medium, the representation including pore space corresponding to the porous medium, with the representation including at least one portion of under-resolved pore structure (42a', 42b', 42c', 42d') in the porous medium; defining, by the computing system, a representative flow model for the under-resolved pore structure in the representation; constructing (58, 64), by the computing system fluid force curves that correspond to fluid forces in the under-resolved pore structure in the representation based on precomputed physical properties of the under-resolved pore structure corresponding to the defined representative flow model, wherein the constructing comprises if precomputed physical properties for the defined representative flow model are stored in a library, retrieving the precomputed physical properties, if precomputed physical properties for the defined representative flow model are not stored in the library, conducting a simulation in a fully-resolved representative subdomain of the under-resolved pore structure to calculate the physical properties, and determining fluid forces in the under-resolved pore structure based on the precomputed physical properties of the under-resolved pore structure; and if precomputed physical properties for the defined representative flow model are stored in a library, retrieving the precomputed physical properties, if precomputed physical properties for the defined representative flow model are not stored in the library, conducting a simulation in a fully-resolved representative subdomain of the under-resolved pore structure to calculate the physical properties, and determining fluid forces in the under-resolved pore structure based on the precomputed physical properties of the under-resolved pore structure; and conducting the fluid simulation of the porous medium, wherein conducting the fluid simulation of the porous medium comprises applying the determined fluid forces at the under-resolved pore structure.