1. A simulation method comprising: storing a geometric model representing a shape of an organ as a collection of elements formed from a plurality of nodes and a plurality of connections among the nodes; storing a first vessel network model representing a network of first vessels whose diameters are larger than or equal to a specified threshold; storing a plurality of second vessel networks each representing a network of second vessels whose diameters are smaller than the specified threshold, wherein one or more of the second vessel networks are connected to each of the nodes; first analyzing, by a processor, hemodynamics in the first vessels belonging to the first vessel network model, based on the geometric model of the organ and reflecting motion of the organ; and second analyzing, by the processor, hemodynamics in the second vessels belonging to the second vessel network models connected to the plurality of nodes, by using result data of the first analyzing which indicates the hemodynamics in the first vessels at each of the nodes.