OpenLB – Open Source Lattice Boltzmann Code › Forums › on OpenLB › General Topics › IndicatorCuboid2D : Need extra Explanation › Reply To: IndicatorCuboid2D : Need extra Explanation December 22, 2020 at 9:11 pm #5433 AdrianKeymaster Any external force has to be added manually in OpenLB using forced dynamics. So if you currently use e.g. a normal BGK collision you already model a “weightless” system.