الفهرس 
Literature ReviewOnly 14 pages are availabe for public view
 |  | from | 166 |  |  |
| | | from | 166 | | |
Abstract
The main objective of this thesis is to suggest a design of detonation chamber to contain against the blast hazards as well as ensure safely detonation for the surrounding area. Parametric studies were carried out to identify the optimum design for the proposed chamber by provide numerical models that would allow us to understand the internal explosion effects.
In this research, AUTODYN software was used to study the internal explosion effect on the MEC behavior under blast loads. The parametric studies include; explosive charge weight, boundary conditions of the MEC and ring thicknesses.
A previous work using a steel cylindrical blast chamber was carried out by (Snyman, Mostert et al. 2016). (Snyman, Mostert et al. 2016) models were conducted to present the verification of the numerical analysis results obtained from AUTODYN. The obtained results were compared to the theoretical as well as the experimental results with reasonable accuracy. Also, the predicted values for the quasi-static pressures from AUTODYN agree with empirical and experimental relationships as given in the literature.
This chapter summarizes the conclusion of this thesis and gives recommendation for future researches.
8.1 Conclusion
This research concludes the following:
• The obtained pressure-time history inside the chamber from AUTODYN coincides with the typical pressure-time history for a fully confined structure as given in the literature.
• The pressure-time history for a fully confined structure is different from the pressure-time history for the free air or vented structure.
• Prediction of (Pqs) from charts based on (W/V) ratio using empirical equations and experimental results as given in the literature agree with (Pqs) results obtained from AUTODYN.
The 1st stage of this research focuses on studying the effect of using different chamber wall thicknesses (10mm, 20mm, 30mm) on the dynamic response of the MEC using two various explosive charges mass of (2kg TNT, 5kg TNT). Fully restrained boundary condition was applied to the MEC, to study the effect of the chamber wall thickness regardless of any other parameter. The numerical study presented in this stage led to some important results summarized below:
• For the MECs models, it has been found that increasing the MEC thickness decreases the maximum displacement by a percentage that raises between 13% to 72%. In some cases increasing the thickness prevents the MEC from failure.
2kg of TNT detonation
• 10 mm, 20 mm and 30 mm MEC could contain 2kg of TNT detonation, and no failure occurred for all chambers. Increasing the MEC thickness from 10 mm to 20 mm decreases the maximum displacement by 68%. Increasing the MEC thickness from 10 mm to 30 mm decreases the maximum displacement by 72%.
• Increasing the MEC thickness from 20 mm to 30 mm is not significant in case of 2kg TNT detonation, as the maximum displacement is reduced by 13%.
5kg of TNT detonation
• 10MEC could not contain the detonation as it failed just after 0.58ms.
• The pressure-time history inside 10MEC after failure agrees with the pressure-time history for a vented structure as given in the literature, the recorded blow-down time was 2m.s.
• By increasing the MEC thickness to 20 mm, failure was prevented and the 20MEC and 30MEC were able to contain the 5kg of TNT detonation.
• Increasing the MEC thickness from 20 mm to 30 mm in this case reduces the maximum displacement by 57%. It has more significant effect in decreasing the maximum displacement value than the case of 2kg TNT.
• In case of the chamber failure (10MEC under 5kg of TNT detonation), 10MEC existence delays the arrival time of the shock wave by a percentage that raises between 64% to 73% and attenuates the peak incident pressure value by a percentage that raises between 39% to 56%.
• Finally, 20MEC yields to be the best design for a mobile explosive chamber to contain small explosive charges up to 5kg of TNT, as its weight is much lighter than the 30MEC which makes it easily transported compared to 30MEC. 20MEC has been selected for the 2nd and 3rd stages of this research.
The 2nd and 3rd stages of this research study the effect of attaching a ring to the MEC and restrain the points at bolts locations. Various parameters such as ring thickness, number of restrained points and the mass of explosive charge were studied to obtain the influence of changing the boundary conditions on the MEC response. In the 2nd stage, the number of restrained points was 12 points while in the 3rd stage it was 24 points. For both stages various ring thicknesses and explosive charge masses were applied. Both stages conclude the following:
2kg of TNT detonation
• In the 2nd stage, using 20 mm ring thickness is not significant. It failed approximately after 1.8m.s and wave vectors started to escape under the chamber after this time. At the end, the 20MEC20R-12 (20mm MEC, 20mm ring, 12 restrained points) moved away from the air domain.
• The pressure-time history inside 20MEC20R-12 after failure agrees with the pressure-time history for a vented structure as given in the literature, the recorded blow-down time was 5m.s.
• Increasing the ring thickness to 30 mm results in preventing the 20MECR-12 from failure. Increasing the ring thickness to 40, 50 and 60 mm decreasing the displacement of the ring by a percentage that raises between 48% to 90% as well as for the chamber by a percentage that raises between 24% to 79%.
• In the 3rd stage, by comparing MECR-24 to MECR-12 and fully restrained case results, it was found that the number of restrained points of MECR has a significant influence on the dynamic response of the MEC under blast loading. Using more restrained points with same ring thickness reduces the displacement of the ring by a percentage that raises between 52% to 62% and for the chamber by a percentage that raises between 41% to 48%.
• The comparison between MECR-12 and MECR-24 showed that almost there was no obvious difference between the maximum displacements of 20MEC30R-24 and 20MEC40R-12, also for 20MEC40R-24 and 20MEC50R-12, also for 20MEC50R-24 and 20MEC60R-12. The results indicates that not only increasing the ring thickness makes the displacement closer to fully restrained case, but also increasing the number of the restrained points results in a closer displacement to the fully restrained case.
5kg of TNT detonation
• In the 2nd stage, the 60 mm ring was the minimum thickness that could contain the blast load. In this case increasing ring thickness to 60 mm results in preventing the 20MECR-12 from failure. Increasing ring thickness to 70 and 80 mm reduced the ring displacements by a percentage that raises between 38% to 64% as well as for the chamber by a percentage that raises between 8% to 27%.
• The difference between maximum chamber displacements of 20MEC70R-12 and 20MEC80R-12 is 8%, which is not significant in this case.
• In the 3rd stage, it was found that the change between the maximum chamber displacements of 20MEC50R-24, 20MEC70R-12, 20MEC80R-12 and 20MEC60R-24 doesn’t exceed 20%.
• By increasing the number of restrained points from 12 to 24, the minimum ring thickness decreased from 60 mm to 40 mm, while in case of 2kg TNT the minimum ring thickness remains the same, 30 mm, in both stages.
• In case of 5kg TNT, increasing the number of the restrained points has more influence effect than the case of 2kg TNT.
8.2 Recommendation for future work
The results of the numerical investigation showed that the MEC can contain detonation of small charges up to 5kg of TNT.
• Field testing is recommended to verify the numerical results and to investigate the risks of MEC installation process. Also, field testing using lager explosive charge masses is required to obtain the ultimate strength of the designed MECs, and to determine their actual capacities.
• More research is required to study the influence of representing the ground in the numerical analysis on the dynamic response of the MECs.
• Studying other methods to support the MEC as the connected flat ring requires either excessive thickness or many restrained points which is not recommended in this study.
• Studying the connection between the ring and the ground including type and grade of bolts is required, taking into consideration ease of installation.
• Time and method of installation are very important parameters that require minimizing number of bolts, as a very close bolts spacing results in difficult installation and time consuming.