Martin Larcher

Explosions in complex geometries - a comparison of several approaches

For the design and calculation of structures loaded by air blast waves, especially from inside the structure, assumptions on the applied load are needed. This paper presents several simulation methods for the air blast loading of structures and their ability to be used for complex geometries. Experimental-analytical pressure-time functions of spherical load conditions applied to the structure by disregarding the air are not applicable in such cases because they do not account for reflections, shadowing and channelling effects. Fluid calculations, which model also the solid explosive, are very expensive due to the extremely small elements for the explosive and the air nearby. This paper therefore presents a review of a well-known simulation method, which uses a balloon with compressed air instead of the explosive. A procedure is developed which makes it possible to determine the overpressure of such a balloon for a given size of the explosive more accurately than before. The pressure-time function and the impulse-distance function of calculations using this method show good correspondence with experimental-analytical data. The functioning of the method is verified against experimental results.

Influence of venting areas on the air blast pressure inside tubular structures like railway carriages

In case of a terrorist bomb attack the influence and efficiency of venting areas in tubular structures like train carriages is of interest. The pressure-time function of an air blast wave resulting from a solid charge is first compared to that of a gas or dust explosion and the capability of a venting structure to fly away is assessed. Several calculations using fluid-structure interaction are performed, which show that after a certain distance from the explosion, the air blast wave inside a tubular structure becomes one-dimensional, and that the influence of venting areas parallel to the wave propagation direction is small. The pressure peak and the impulse at certain points in a tubular structure are compared for several opening sizes. The overall influence of realistic size venting devices remains moderate and their usefulness in mitigating internal explosion effects in trains is discussed.

Effectiveness of finite-element modelling of damage and injuries for explosions inside trains

ABSTRACT The rail-bound sector has become a preferred target of terrorist attacks because of its vulnerability, and the most frequent way to carry out these attacks has been the use of explosive devices. The aim of this study is to investigate the effectiveness of modelling detonation effects inside train carriages using explicit finite element techniques. The numerical simulations consider fluid-structure interaction phenomena and several parametric studies are conducted. Carriage damage and injuries to the passengers are examined. Displacements in the model of the carriage structure do not vary greatly for small changes of the charge size, its location, or by open doors. Changing charge size, the location of the detonation, and door setting, however, had significant impact on the risk of eardrum rupture and fatality. Comparison of the simulation and real life data demonstrate a good agreement between the real and calculated displacements of the carriage, whereas the risk of death and eardrum rupture is slightly higher in the calculations. The model presented can reproduce a reliable actual situation if more parameters that influence injuries of blast waves were considered.

Safety and Security of Urban Areas through Innovative Architectural and Structural Concepts

In the past terrorist attacks were increasingly directed against so-called soft targets. Thus, it is necessary to analyze the threats and to protect “public spaces” in urban areas that are primarily not considered permanent critical infrastructure. Specific threats e.g. explosions, vehicle impact and impact of flying debris, arise from various scenarios. Public spaces are to be protected by structural, architectural and land shaping elements that are not recognized as protective elements by the public. This paper describes architectural attractive, art work, and constructional protective measures as well as intelligent design in landscape architecture for the protection of public spaces in urban areas. Overall, the paper deals with a non-standard development and use of physical protective measures.