Damage response of hull structure subjected to contact underwater explosion

A high-pressure shock wave was produced during a process near-field underwater explosion, which led to serious damage into structures. A Smooth Particle Hydrodynamic (SPH) method is suitable for solving problems with large deformations. Hence, it is used to investigate pressure characteristics and dynamic response of hull structures subjected to near-field underwater explosion. Effect of free surface was taken into consideration. Propagation of shock wave in multi medium and its dynamic response to hull structures were analyzed

Damage response of steel plate to underwater explosion: Effect of shaped charge liner

© 2017 Elsevier LtdA shape of charge liners has a great effect on formation of a metal jet and its penetration into a target. In this paper, three different shapes of a charge liner, namely, conical, hemispherical and spherical-segment, are chosen to investigate their effect on damage response of a plate to underwater explosion. A Smooth Particle Hydrodynamic (SPH) method based on mesh-free Lagrange formulation is applied to simulate an entire process of a shaped-charge detonation, formation of a metal jet as well as penetration on a steel plate. Initially, a SPH model of the shaped charge with a spherical-segment liner is developed, and its results are compared with experimental data to verify the effectiveness of this method. Then, numerical simulations of shaped charges with different liners are performed to study the damage characteristics of a steel plate subjected to underwater-explosion shock loading and the metal jet. It was found that for the shock wave the peak value of the radial pressure is larger than that of the axial pressure during the detonation process; the level of pressure in the spherical-segment case was higher than that of the other two cases. After the detonation, the metal jet was gradually produced under the effect of the detonation wave. Three types of the metal jet - a shaped charge jet (SCJ), a jetting projectile charge (JPC) and an explosive formed projectile (EFP) – were formed corresponding to three cases with conical, hemispherical and spherical-segment liners. The obtained results show that the velocity and length of the SCJ in the conical case are greater than that of the other cases, and it therefore may lead to a larger penetration depth. In addition, the EFP has a better motion stability for a velocity difference in the spherical case is lower than that of the other two cases. Subsequently, the shock wave arrives at the plate earlier than the metal jet, which will cause deformation of the plate. Due to higher pressure, the shock wave in the spherical-segment case has a stronger damaging effect on the plate than that in the other two cases. Finally, the metal jet reaches the plate causing a hole. Because of a wider jet head, the EFP results in a more serious damage to the plate. The suggested analysis and its results provide a reference for structural design of shaped charge warheads

SPH-FEM simulation of shaped-charge jet penetration into double hull: a comparison study for steel and SPS

A high-speed metal jet capable to cause severe damage to a double-hull structure can be produced after detonation of a shaped charge. A Smoothed Particle Hydrodynamics (SPH) method with a mesh-free and Lagrange formulations has natural advantages in solving extremely dynamic problems. Hence, it was used to simulate the formation process of a shaped-charge jet. A Finite Element Method (FEM) is suitable for a structural analysis and is highly efficient for simulations of a complex impact process in a relatively short time; therefore, it was applied to develop a double-hull model. In this paper, a hybrid algorithm fully utilizing advantages of both SPH and FEM is proposed to simulate a metal-jet penetration into a double hull made of different materials – steel and SPS (Sandwich Plate System). First, a SPH-FEM model of a sphere impacting a plate was developed, and its results were compared with experimental data to validate the suggested algorithm. Second, numerical models of steel/SPS double-hull subjected to a shaped-charge jet were developed and their results for jet formation, a penetration process and a damage response were analysed and compared. The obtained results show that the velocity of the metal jet tended to decrease from its tip to the tail during its formation process. The jet broke into separate fragments after the first steel shell was penetrated, causing the damage zone of the second shell that grew as a result of continuous impact by fragments. As for the SPS structure, its damage zone was smaller, and the jet trended to bend becoming thinner due to the resistance of the composite layer. It was found that the polyurethane layer could have a protective effect for the second shell

SPH-BEM simulation of underwater explosion and bubble dynamics near rigid wall

A process of underwater explosion of a charge near a rigid wall includes three main stages: charge detonation, bubble pulsation and jet formation. A smoothed particle hydrodynamics (SPH) method has natural advantages in solving problems with large deformations and is suitable for simulation of processes of charge detonation and jet formation. On the other hand, a boundary element method (BEM) is highly efficient for modelling of the bubble pulsation process. In this paper, a hybrid algorithm, fully utilizing advantages of both SPH and BEM, was applied to simulate the entire process of free and near-field underwater explosions. First, a numerical model of the free-field underwater explosion was developed, and the entire explosion process– from the charge detonation to the jet formation–was analysed. Second, the obtained numerical results were compared with the original experimental data in order to verify the validity of the presented method. Third, a SPH model of underwater explosion for a column charge near a rigid wall was developed to simulate the detonation process. The results for propagation of a shock wave are in good accordance with the physical observations. After that, the SPH results were employed as initial conditions for the BEM to simulate the bubble pulsation. The obtained numerical results show that the bubble expanded at first and then shrunk due to a differences of pressure levels inside and outside it. Here, a good agreement between the numerical and experimental results for the shapes, the maximum radius and the movement of the bubble proved the effectiveness of the developed numerical model. Finally, the BEM results for a stage when an initial jet was formed were used as initial conditions for the SPH method to simulate the process of jet formation and its impact on the rigid wall. The numerical results agreed well with the experimental data, verifying the feasibility and suitability of the hybrid algorithm. Besides, the results show that, due to the effect of the Bjerknes force, a jet with a high speed was formed that may cause local damage to underwater structures

Application of smoothed particle hydrodynamics in analysis of shaped-charge jet penetration caused by underwater explosion

© 2017 Elsevier Ltd A process of target pen etration by a shaped-charge jet includes three main stages: charge detonation, formation of a metallic jet and its penetration of the target. With continuously increasing computational power, a numerical approach gradually becomes more prominent (combined with experimental and theoretical methods) in investigations of performance of a shaped-charge jet and its target penetration. This paper presents a meshfree methodology - Smoothed Particle Hydrodynamics (SPH) - for a shaped charge penetrating underwater structures. First, a SPH model of a sphere impacting a plate is developed; its numerical results agree well with the experimental data, verifying the validity of the mentioned developed method. Then, results obtained for different cases - for various materials of explosives and liners - are discussed and compared, and as a result, more suitable parameters of the shaped charge in order to increase the penetration depth are obtained - HMX and copper were chosen respectively as the explosive and the liner material. It follows by validation of a model of a free-field underwater explosion, developed to verify the effectiveness of the modified SPH method in solving problems of underwater explosion; its numerical results are compared with an empirical formula. Finally, the SPH method is applied to simulate the entire process ranging from the detonation of the shaped charge to the target penetration employing the optimal parameters. A fluid around the shaped charge is included into analysis, and damage characteristics of the plate exposed to air and water on its back side are compared

SPH-FEM simulation of shaped-charge jet penetration into double hull: A comparison study for steel and SPS

This paper was accepted for publication in the journal Composite Structures and the definitive published version is available at http://dx.doi.org/10.1016/j.compstruct.2016.08.002A high-speed metal jet capable to cause severe damage to a double-hull structure can be produced after detonation of a shaped charge. A Smoothed Particle Hydrodynamics (SPH) method with a mesh-free and Lagrange formulations has natural advantages in solving extremely dynamic problems. Hence, it was used to simulate the formation process of a shaped-charge jet. A Finite Element Method (FEM) is suitable for a structural analysis and is highly efficient for simulations of a complex impact process in a relatively short time; therefore, it was applied to develop a double-hull model. In this paper, a hybrid algorithm fully utilizing advantages of both SPH and FEM is proposed to simulate a metal-jet penetration into a double hull made of different materials – steel and SPS (Sandwich Plate System). First, a SPH-FEM model of a sphere impacting a plate was developed, and its results were compared with experimental data to validate the suggested algorithm. Second, numerical models of steel/SPS double-hull subjected to a shaped-charge jet were developed and their results for jet formation, a penetration process and a damage response were analysed and compared. The obtained results show that the velocity of the metal jet tended to decrease from its tip to the tail during its formation process. The jet broke into separate fragments after the first steel shell was penetrated, causing the damage zone of the second shell that grew as a result of continuous impact by fragments. As for the SPS structure, its damage zone was smaller, and the jet trended to bend becoming thinner due to the resistance of the composite layer. It was found that the polyurethane layer could have a protective effect for the second shell

Damage response of hull structure subjected to contact underwater explosion

A high-pressure shock wave was produced during a process near-field underwater explosion, which led to serious damage into structures. A Smooth Particle Hydrodynamic (SPH) method is suitable for solving problems with large deformations. Hence, it is used to investigate pressure characteristics and dynamic response of hull structures subjected to near-field underwater explosion. Effect of free surface was taken into consideration. Propagation of shock wave in multi medium and its dynamic response to hull structures were analyzed

Study on Load Characteristics of Underwater Explosion Using RKDG-LS-DGF and BEM

This study numerically investigates the underwater explosion bubble dynamics during the process from detonation to bubble jet with a hybrid algorithm based on Runge Kutta Discontinuous Galerkin-Level Set-Direct Ghost Fluid method (RKDG-LS-DGF) and boundary element method (BEM). RKDG-LS-DGF method is used to simulate the physical process from the detonation of a column charge at one end to the formation of a nonspherical initial bubble and the process of bubble jet. And BEM is adopted to simulate bubble pulsing characteristics. In addition, the numerical results are compared with the experimental results to verify the feasibility of the numerical method. It is found that, during the detonation process of a column charge, the detonation product experiences a shape change from an initial ellipsoid into a sphere during expansion. After the detonation, the bubble experiences expansion and contraction and develops a jet. The jet threads through the bubble in the opposite direction to gravity and induces a high-pressure region. Subsequently, the pressure of this region decreases when the bubble reexpands after being penetrated by the jet. The numerical results agree well with the experimental data, which proves that axisymmetric RKDG-LS-DGF method and BEM are successfully combined to simulate the whole process of underwater explosion

Formation of Shaped Charge Projectile in Air and Water

With the improvement of the antiknock performance of warships, shaped charge warheads have been focused on and widely used to design underwater weapons. In order to cause efficient damage to warships, it is of great significance to study the formation of shaped charge projectiles in air and water. This paper uses Euler governing equations to establish numerical models of shaped charges subjected to air and underwater explosions. The formation and the movement of Explosively Formed Projectiles (EFPs) in different media for three cases: air explosion and underwater explosions with and without air cavities are discussed. First, the velocity distributions of EFPs in the formation process are discussed. Then, the empirical coefficient of the maximum head velocity of EFPs in air is obtained by simulations of air explosions of shaped charges with different types of explosives. The obtained results agree well with the practical solution, which validates the numerical model. Further, this empirical coefficient in water is deduced. After that, the evolutions of the head velocity of EFPs in different media for the above three cases are further compared and analyzed. The fitting formulas of velocity attenuation of EFPs, which form and move in different media, are gained. The obtained results can provide a theoretical basis and numerical support for the design of underwater weapons