Danish Ph.D. School in Nonlinear Science

Sponsored by the Danish Research Agency


Coherent structures may form as a result of nonlinearity in integrable as well as non-integrable systems, being either stable or unstable solitary excitations. In the latter case they may disperse or collapse. Temperature fluctuations (noise) and disorder influences the properties of the nonlinear excitations postponing collapse (blow-up) and stabilizing dispersion excitations. Coherent vortical structures play an important role for the evolution of flows in liquids, gasses and plasmas. In systems where the dynamics is mainly 2-dimensional these structures are characterized by having long life times. The structures are easily excited by external perturbations and may also form as a result of self-organization. Once formed the structures dominate the large scale dynamics. In such cases low-dimensional models may provide an accurate description of the flow dynamics. Vortex structures may trap particles and convect them over large distances and are thus of essential importance in connection with transport and mixing of mass, heat and momentum in the flows. Persistent coherent vortical structures also appear in some (anisotropic) 3-dimensional flow systems. The investigations of vortical structures and their dynamics combine theoretical and numerical studies (based on accurate large scale computational solutions of the evolution equations for different flows and geometries) with experimental research employing advanced diagnostics. The main subjects included are:

The long-term objective of the research is to utilise the acquired knowledge to synthesise and optimise new devices and systems. Specifically, new flow diagnostics is being studied in collaboration with Dantec Measurement Technology and microflow with particles are under investigation with The Micloelectronic Center, DTU. Numerical simulation of turbulent airflow in livestock buildings and comparison to laboratory measurements is performed in collaboration with Danish Institute of Animal Science, Department of Agricultural Engineering Production Systems, Research Centre Bygholm, Horsens.