Simulation experiments are performed in order to study processes which could lead to a better understanding of cometary nuclei. During the KOSI (Kometensimulation) experiments decimeter-sized samples of porous H2O and CO2 ice-dust mixtures are irradiated with light. Phenomena like heat transport into the sample, compositional and structural modifications of the sample and release of dust and gas are studied which occur within centimeter to decimeter distance from the sample surface. Techniques to handle and analyse low temperature ice samples are developed. So far, six KOSI experiments have been performed and about six more are expected to be carried out within the next three years. This paper describes the approach taken and techniques used in the KOSI experiments. We discuss the relevance of some initial results obtained for cometary research.