Advanced Defense Science and Technology
Year:2015 | Volume:6 | Issue:3|Papers Count:7

Seawalls are sheltering structures used for protecting the coastal regions against wave induced forces. Storm, movement of the ships, explosions caused by the attacks to the platforms and issues like these could result in the creation of random waves in significant areas of the port. Because of random nature of the wave behavior, the application of physical models for the study of wave-structure interaction can be quite efficient. In the present research, physical models of thin flexible walls were constructed and tested in a wave flume subject to generated random waves.The water surface variations and the strains at the base of the wall were recorded using sensors; and the relationship between the strain and the wave height was obtained using the zero up-crossing method. The results indicate that the strain-wave height relationship is linear. Since the behavior of the wall is within the elastic region, the relationship between the strain and the flexural moment at the base of the wall follows the Hook’s Law; and accordingly the relationship between the wave height and flexural moment at the base of the wall was obtained.

The manner by which the shock waves, generated by an explosion, propagate in the medium surrounding an underground structure is very complex. This complexity is due to the interaction between the structure and the surrounding soil and the attenuation of the shock waves in the soil layers. In this research, by simulating the shock waves equivalent to the explosion of 900 kg of TNT, the effects of different parameters such as soil type, concrete type, and buried depth on maximum strain at the top and on the mid-length of the structure is investigated. For simulating the loading due to explosion, the finite element software, ABAQUS, has been utilized. Also, to numerically simulate the nonlinear behavior of the medium surrounding the underground structure, the Mohr-Columb model has been used. In view of the results obtained from the numerical analysis of various models, it was found that the parameter of underground structure depth has the greatest effect on the amount of maximum strain produced in the structure, followed by soil and concrete type.

Today, Spy satellite play a major role in obtaining the military information, especially imaging. Then, one of the defencive essentials is to reduce the satellite ability in the data collection. It will be applicable only with the satellite tracking and orbit prediction. The related preventive measures fall into two categories, namely passive defence and active defence. For this purpose, the precise orbit determination is the key factor. From the passive perspective, it is possible to camouflage the strategic activities through determining the satellite tracking and passing time. Today, the digital cameras with relatively high geometric and radiometric accuracy has opened a new insight in the satellite attitude determination and tracking. In the automatic star detection, high precision and reliable in extraction of the star's centers from the captured images and corresponding them with the astronomical coordinates is the most important point. In this article, the star's centers are extracted by the advanced image processing technique with subpixel precision. Using the motion coherence theory, the corresponding stars are detected first, and the outliers are removed by MSAC algorithm afterwards. The suggested method was applied to the images taken by TZK2-D and Star-100 cameras and a standard deviation of 10-3 pixel for point matching was achieved.

There are major differences between the behavior of explosive and another loads due to the nature of the explosive charges and the small duration of shock loads. Study on underwater explosion effects is important for evaluation of damages caused by the terrorist activities such as hydraulic structures and marine docks, dams, transmission lines in the seabed and etc. The high cost of laboratory modeling and explosion risks due to blast loads and sudden and severe deformations caused by an explosive charges in a short time, justify the use of numerical methods. In this paper the experimental results were compared with grid base numerical modeling (Eulerian and Lagrangian nature) and a meshless method (smooth particles hydrodynamics, called SPH). The numerical simulations are carried out based on the Ls-Dyna software and the maximum distance from the center of the explosion pressure, pressure time history curves at different points, and changes in water level are compared in different numerical methods. The results show that, Lagrangian approach and meshless method presents higher explosion pressure than Eulerian approach. Also, using the meshless methods, the explosion pressure can be determined in closer distance to a charge center, compared to another grid base methods.

Explosive accidents within recent years resulted in vulnerability and reduction of life of plenty of structures including sensitive and crucial structures. Sensitivity of this problem resulted in laboratory and theoretical studies for utilization of absorbent layers as energy dissipater. In this paper, behavior of two types of sandwich absorbent layers including steel honeycomb and fragile concrete composite as concrete wall guard under explosive loading was analyzed aiding finite element software ABAQUS. Explosive pressure was simulated based on CONWEP method. Comparison of results obtained from analysis shows that function of said layers differs proportional to the objective and value of explosive samples so that although the both types of absorbent layers have a considerable effect on reduction of damage to the main structure, but in samples with low explosion intensity, fragile layer with higher energy absorption and reduction of deflection of concrete wall’s central point has better function than crushable layer and in severe explosions, due to emergence of plastic behavior, steel crumpled layers have better function.

Blast wave trap is one of the ways to deal with and reduce the effects of blast wave inside the secure underground structures. In this paper, the effect of blast wave trap on reducing the overpressure in the main route of the tunnel has been studied. Accordingly, the blast wave propagation of different explosives in various distances from the tunnel entrance including blast wave trap has been simulated. Autodyn software was employed for numerical simulation.Based on the ratio of the overpressure applied to blast wave trap to obtained overpressure of the main route after blast wave trap, the appropriate distance and optimum length of the blast wave trap were calculated. The results show that blast wave trap can significantly reduce the overpressure applied to the blast wave trap zone. Besides, higher values of overpressure before blast wave trap zone leads to an increase of optimum length of blast wave trap along with more pressure reduction.

Generating and modifying spatial data for strategic areas of the country, especially boundary areas, is one of the key challenges in the defense technical information community. In this regard, digital elevation model (DEM) can be utilized to remove every ground operations in a direct process between the earth and overlapping satellite images. In this process, rational polynomial function (RPCs) are only used. However, these coefficients due to some errors in their gathering have some errors that must be removed in a manner. In proposed method of this study, the effects of RPC errors on IRS-P5 satellite images are reduced using the 2.5D matching procedure between IRS-P5 derived DEM and ASTER global DEM. Experimental results obtained by comparison between the resulting DEM and few available check points shows that the proposed method can achieve vertical accuracy of about 7 meter.