bulkbevegelse

Bulkbevegelse is the motion of matter as a whole within a region, in which a large part of the material moves with a coherent, average velocity. It is a concept used across disciplines to describe macroscopic transport, in contrast to microscopic or random motions such as diffusion or thermal agitation. In fluid dynamics, bulk movement refers to the advective transport of mass and momentum: the velocity field of the fluid averaged over a control volume defines the bulk velocity. The mass flow rate through a cross-section is the product of density, area and bulk velocity (m_dot = rho A v_bulk). The evolution of bulk motion is governed by the Navier–Stokes equations in continuum mechanics, with additional terms for sources or forces. Bulk movement can be steady or unsteady, laminar or turbulent, with fluctuations around the mean profile.

In practical contexts, bulk movement is used to describe wind over a region, ocean currents, pipeline flow, or the transport of granular materials. In meteorology and oceanography, bulk wind or bulk transport models estimate the large-scale movement of air or water masses by averaging over spatial scales. In geology, bulk movement can describe landslides or avalanches where large volumes of material move coherently. In crowd and cell dynamics, bulk movement denotes collective motion of many individuals or cells, often studied with models that include alignment and interaction forces.

Overall, bulkbevegelse emphasizes the macroscopic, coherent component of motion, and is analyzed with concepts from continuum mechanics and advection, distinct from diffusion or micro-scale dynamics.