A methodology for Response Gap Analysis in offshore oil spill emergency management.

In case of offshore oil spills, the success of emergency response largely depends on the meteorological and oceanographic conditions during and after the spill, which are expressed by a set of different environmental factors. A "gap" in the response may be caused by unfavourable environmental factors that could limit its effectiveness or even impede it. In this context, Response Gap Analysis (RGA) studies identify the environmental factors negatively influencing the emergency response in a given sea area and aim at assessing the percentage of time during which the response would be without success or impossible to deploy. In the present study, a new RGA methodology is described, based on 11 environmental factors. Different oil spill response strategies are considered: mechanical recovery, application of dispersants by vessel and by aircraft, and in-situ burning. A case-study is presented to demonstrate the methodology and discuss the outcomes obtained by its application.

Testing and Modelling of Elastomeric Element for an Embedded Rail System.

Modelling of elastomeric elements of railway components, able to represent stiffness and damping characteristics in a wide frequency range, is fundamental for simulating the train-track dynamic interaction, covering issues such as rail deflection as well as transmitted forces and higher frequency phenomena such as short pitch corrugation. In this paper, a modified non-linear Zener model is adopted to represent the dependences of stiffness and damping of the rail fastening, made of elastomeric material, of a reference Embedded Rail System (ERS) on the static preload and frequency of its deformation. In order to obtain a reliable model, a proper laboratory test set-up is built, considering sensitivity and frequency response issues. The equivalent stiffness and damping of the elastomeric element are experimentally characterised with force-controlled mono-harmonic tests at different frequencies and under various static preloads. The parameters of the non-linear Zener model are identified by the experimental equivalent stiffness and damping. The identified model correctly reproduces the frequency- and preload-dependent dynamic properties of the elastomeric material. The model is verified to be able to predict the dynamic behaviour of the elastomeric element through the comparison between the numerically simulated and the experimentally measured reaction force to a given deformation time history. Time domain simulations with the model of the reference ERS demonstrate that the modelled frequency- and preload-dependent stiffness and damping of the elastomeric material make a clear difference in the transient and steady-state response of the system when distant frequency contributions are involved.