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The Single Degree of Freedom Simulation Model of Underwater Explosion Impact

Grządziela Andrzej, Załęska-Fornal Agata, Kluczyk Marcin

Archives of Acoustics

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2020

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Vol. 45, No. 2

341--348

EN

The hulls of naval ships are exposed to forces and moments coming from internal and external sources. Usually, these are interactions that can be described mathematically by harmonic and polyharmonic functions. The shock of UNDEX type (underwater explosion) works completely differently and its time waveform is difficult to describe with mathematical functions as pressure vs. time. The paper presents a simplification of physical and mathematical models of 1-D kickoff pressure whose aim is performance the simulation of the external force of the detonation wave. The proposed models were verified and tuned on naval, sea trials. The main goals of the proposed models are to perform simulation calculations of the detonation pressure for different explosion charge weights from different distances of the UNDEX epicentre for the design process of machine foundation. The effects of pressure are transformed as impulses exposed on shock absorber mounted at light shock machine.

2

Finite element-finite volume simulation of underwater explosion and its impact on a reinforced steel plate

Valdani Arman Jafari, Adamian Armen

Archive of Mechanical Engineering

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2020

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LXVII, nr 1

5--30

EN

Marine structures are one of the most important industrial and military equipment in each country that should be protected against external forces. The main aim of this paper is a detailed investigation of the underwater explosion (UNDEX) and its effects on marine structures. For this purpose, the UNDEX structure was studied qualitatively and quantitatively using numerical methods. Then, the effects of blast waves on a marine structure reinforced by perpendicular blades were investigated. Finite element and finite volume schemes were used for discretization of the governing equations in the solid and fluid media, respectively. Also, for fluid-structure interaction (FSI), results of fluid and solid media were mapped to each other using the two-way FSI coupling methods. A comparison of numerical results with the empirical formula revealed that the trend of pressure-time curves was reasonable, approving the validity of the numerical method. Moreover, the numerical results indicated that detonation of 1 kg trinitrotoluene (TNT) creates a pressure wave with maximum amplitude of 24 MPa at a distance of 2 m. Also, it was found that the reinforcement blades can be used to improve the resistance of structures against explosive charges, which also results in the reduction of structures deformation.

3

Underwater Explosion Performance of RDX/AP-based Aluminized Explosives

Xiang D., Rong J., He X., Feng Z.

Central European Journal of Energetic Materials

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2017

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Vol. 14, no. 1

60--76

EN

To understand the underwater explosion (UNDEX) performance of RDX/AP-based aluminized explosives, six formulations of the explosives were prepared, with Al content varying from 30% to 55% and ammonium perchlorate (AP) content from 45% to 20%. A series of UNDEX tests that used a 1 kg cylindrical charge was conducted underwater at a depth of 4.7 m. The pressure histories of the shock wave produced at different positions and the bubble periods were measured. The coefficients of the similarity law equation for the shock wave parameters were fitted with experimental data. The effect of the aluminum/oxygen (Al/O) ratio on the performance of the energy output structure for RDX/AP-based aluminized explosives is discussed. The bubble motion during UNDEX was simulated using MSC.DYTRAN software, and the radius-time curves of the bubbles were determined. The results show that AP influences the detonation reaction mechanism of RDX/AP-based aluminized explosives, which causes different UNDEX performances. The bubble energy of the RDX/AP-based aluminized explosive was higher than that of RDX-based and HMX-based aluminized explosives.

4

A study on the UNDEX cup forming

El Mokadem A. E., Wifi A. S., Salama I.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 37, nr 2

556-562

EN

Purpose: This work investigates the use of the underwater explosion (UNDEX) for the free and plug assisted cup forming processes. Design/methodology/approach: A 3D finite element model is built to simulate the process of the UNDEX cup forming using ABAQUS finite element code. Johnson-Cook (JC) material plasticity model is used to represent strain rate sensitivity of the used materials. Johnson- Cook damage criterion is employed to detect the onset of damage in the cup forming process. Findings: Both relatively hard and soft plugs are considered and the effects of using different plug materials on cup profile, strains and the limiting drawing ratios are given. The onset of damage in this process is also indicated. The results suggest that a relatively hard plug can enhance the control of the cup shape and the uniformity of strain distribution leading to increased limiting drawing ratio. Research limitations/implications: This work suggests a methodology for the prediction of shape, different strain distribution, the limiting drawing ratio and the energy required for UNDEX cup forming process. Practical implications: This study could be useful in non-conventional high energy rate forming industry. Originality/value: The study reveals the possibility of producing flat-bottomed cup by the relatively hard plug assisted UNDEX forming technique.