Mutual interaction between a semi-cylindrical arch and the air medium in its neighborhood loaded by a blast or shock wave is the subject of the paper put forward. An impingement of blast wave against structures can cause a reflection of the wave off the surface of the structure followed by a substantial transient aerodynamic load, which can cause a significant deformation of the structure. This deformation can alter the overpressure, which is built behind the reflected shock. In addition, a complex aero-elastic interaction between the blast wave and the structure is developed that can induce a reverberation, which can also cause substantial overpressure through the multiple reflections of the wave. This problem is of particular importance in the new design of future civil, military and underground structures built up from composite materials, as well as of military vehicles.

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In big cities underground spaces are built up for subways, underground parking and tunnels, etc. These rooms are threatened by terrorist attacks and not only human lives can be lost but also extensive material damage can be expected. This is why it is of great importance to predict dynamic impacts of explosives, which can then be transformed to static statistically evaluated loading. In this paper the impact of explosion and air strike wave is formulated and solved. Gas dynamics and dynamic response of soil with process of dissipation of air-strike energy are considered. This means that some part of this energy is transferred into structures and soil mass. It appears that for contact explosions on the soil surface this part can be up to 30% of the total explosion energy (in soft soils). The variables to be calculated are mass density of gas, the velocity of movements and the internal energy. The latter covers the influence of the gas pressure, being given for the adiabatic state. The air is linearly related to the internal energy of a unit mass of the gas, and the density, while in the neighborhood of the source of explosion the pressure changes nonlinearly with respect to the gas density. Time dependent finite element solution is compared with results published in Lucy, L.B. (1977). A numerical approach to testing of the fission hypothesis. Astron. J. 82, 1013.

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The problem of modeling the process of functioning of redundant measuring instruments is considered. The determination of the frequency of verifi cation of complex duplicate measuring instruments is validated on the basis of a semi-Markov model of the process of functioning of the instruments. The importance of the use of the theory of semi-Markov processes for modeling the functioning of redundant technical systems, including measurement systems, is demonstrated. A semi-Markov model of the process of functioning of measuring instruments by means of which the infl uence of such factors as the frequency of verifi cation, support of measuring instruments with spare parts, level of failure-free performance, and degree of maintainability on the reliability of measuring instruments may be taken into account is developed. A method of specifying a semi-Markov process that correctly and adequately approximates the true process is found. The availability factor of the measuring instruments is selected as the indicator of the operating effi ciency of the functioning of a measuring instruments and of the corresponding model.