DEVELOPMENT OF HAZARD PREDICTION SYSTEM FOR INTENTIONAL ATTACKS IN URBAN AREAS

A hazard prediction system has been developed for chemical, biological and radiological (CBR) attacks in urban areas with the use of the mesoscale meteorological model, RAMS and its dispersion model HYPACT. The developed simulation system can predict 1) concentration of hazardous gases and 2) the number of casualties based on the population database of Japan. RAMS is equipped with an optional scheme to simulate airflow around buildings based on the volume fraction of the buildings within each grid cell. However, this scheme requires significant computational time if applied for fine meshes. Accordingly, we have developed a new computational scheme using the RAMS code with a mesh size of a few meters to simulate the effect of a building complex on the dispersion. This scheme requires computational time of as little as a few minutes on a conventional personal computer. The computational scheme first extracts the shapes of the buildings from a digital map database. Then, a set of steady flows is calculated for 16 wind directions using a fine mesh, and the results are saved as a database. Next, the scheme calculates an unsteady flow on a coarse mesh, which is nudged by a linear combination of the relevant data from the 16-wind direction steady airflow database. The nudging is performed at the boundaries of the fine mesh domain using the Least Mean Square Method (LMSM).The dispersion prediction scheme is currently being validated with the use of field and wind tunnel data.