Underwater Explosion Phenomena Research Articles

An open benchmark to assess the effects of underwater explosions on steel panels using the volume of fluid approach

Despite the underwater explosion phenomena (UNDEX) have been studied for decades and several numerical methods have been proposed in literature, the simulation of the whole phenomenon in issue is even nowadays a matter of research. In this paper, a Volume of Fluid (VOF) approach, which allows the simulation of Fluid-Structure Interaction (FSI), including the effects of seawater and vapor of cavitation on structures, is calibrated according to theory and experimental data. As a benchmark, a parallelepiped of fluid is built, verifying the effectiveness of the method with reference to some close-in explosions available in literature. In addition, VOF results are compared with the ones achieved from other researchers using the acoustic approximation. Strengths and limits of VOF coupling method are pointed out. In the end, the modelling strategy proposed and validated can be considered a suitable tool for the design of naval structures subject to underwater explosions.

Numerical modeling and simulation of underwater explosions interacting with discrete rigid bodies

The smoothed particle hydrodynamics (SPH) method is widely used to simulate underwater explosion phenomena. However, previous studies have focused on the interaction between the underwater explosion and continuous structures (e.g., steel plates and dams), while studies on the interaction between the explosion and discrete objects (e.g., debris) have not been reported. In this study, a multi-media coupled model containing water, explosion gas, discrete objects, and steel plates is developed based on the SPH method. The discrete object is modeled as a rigid body with a certain shape, which is discretized by SPH particles. The interaction between the discrete object and the adjacent fluid particles is realized by the kernel approximation, while the collision between different objects is realized by the contact algorithm. To improve the numerical stability, an artificial viscous term containing a threshold switch is added to the SPH momentum equation, while a density dissipation term is introduced into the continuity equation to reduce the noise of the pressure field. Subsequently, the established SPH model is used to simulate the underwater explosion process containing discrete rigid bodies, and the effects of the distribution, stacking form, and number of rigid bodies on the propagation of shock waves, bubble expansion, and deformation of steel plates and the effect of damage are analyzed. The results show that the rigid body will hinder the propagation of shock waves, help reduce the peak pressure of the shock wave behind, and then affect the direction of the diffusion of the explosion energy. Shock waves would produce diffraction, reflection, and transmission when passing through the rigid bodies, and the superposition of various waves would make the pressure distribution near the liquid–gas interface irregular. The rigid bodies stacked above the explosives would enhance the damage effect of the explosion on the steel plates below, and the damage effect is affected by the stacking form. The established model can simulate the multi-medium coupling process in a unified framework without coupling other methods and can effectively restore the complex interaction process between underwater explosion, discrete object, and structure.

Experimental and numerical investigations of near-field underwater explosions

Near-field underwater explosion (UNDEX) phenomena were investigated by experiments and numerical simulations. The UNDEX experiments were performed in a water tank using a ship-like model. One kilogram of TNT, one of the most widely used military high explosives, was used for the experiments. Numerical simulations were performed under the same conditions as in the experiments using the commercial software LS-DYNA. Underwater pressures, accelerations, velocities, and strains by shock waves were measured at multiple locations. Further, the bubble pulsation period and the whipping deformations of the ship-like model were explored. The experimental results are presented and examined through comparison with the results obtained from widely used empirical equations and numerical simulations.

Numerical study of the postcombustion effects on the underwater explosion of an aluminized explosive by a novel nonisentropic model for the detonation products

ABSTRACTAn aluminized explosive detonating in the water is distinguished by the nonideal effects caused by the postcombustion of the aluminum additives. These effects play a big role in the noncontact underwater explosion phenomena, but they are usually ignored or smoothed in the conventional experimental tests, as well as in the numerical simulations with empirical models fitting to those test data. Here we propose a nonisovolumic and nonisentropic slow reaction model and then utilize the method of characteristics to analyze how and how much the postcombustion effects the entire flow field. Numerical examples show the near-field flow properties are appropriately obtained, the geometric dissimilarity of the product expansion is embodied and the enforcement of the additional energy release is tracked. These results imply the proposed methods can be used to reveal the mechanism of the postcombustion effects and shock wave enforcement.

Structure Analysis of Marine Pipes under the Effect of Water Explosion Force (Wave)

Underwater explosion is a subject that has been paid attention to by many researchers. In this study the underwater explosion phenomena under shockwave loading is explored by numerical method. For this purpose, by modeling a marine pipe buried in the water by ABAQUS software, the effect of the shock wave and the damages were assessed. Then using the laboratorial results, the fluid-structure interaction and shock wave loading and its results were analysed. Finally, it was concluded from numerical modeling that the highest levels of strain on the pipe buried in the water under underwater explosion and shock wave loading occur in the ending parts of the pipe in both sides and away from explosion field.

Numerical simulation of underwater explosion near air–water free surface using a five-equation reduced model

Underwater explosion phenomena is a complicated problem, however, it has different and important applications. This type of explosion includes strong shock waves with generation of low pressure cavitation׳s zone and deformable interfaces. The main objective of this article is simulation of interaction of shock wave with interface of two-phase gas–liquid flow and capturing the complicated interface generated from explosion. For this reason, a five equations reduced model is considered with using a new cavitation model including gravity force effect. From the numerical point of view, a Godunov method was applied using HLLC solver. By using MUSCL-Hancock strategy, second order accuracy is achieved. To verify the developed computer code, a one dimensional shock tube test case and two test cases including one dimensional cavitation in open tube and a two dimensional underwater explosion where its experimental results can be found in the related literature are used for comparison to justify the obtained results. The comparison of the results confirms an excellent accuracy of the numerical results. The proposed new cavitation model, on the other hand, is capable of calculating low pressures and simulating the dynamic creation and evolution of the bulk cavitation below the free surface.

Dynamic behavior of stiffened plates under underwater shock loading

Abstract A numerical investigation has been carried out to examine the behavior of stiffened steel plates subjected to different shock loads resulting from an underwater explosion (UNDEX). The aim of this work is to enhance the dynamic response to resist UNDEX and obtain the optimal configuration for stiffened plates to resist underwater shock loading. A non-linear dynamic numerical analysis of the underwater explosion phenomena associated with different geometrical stiffened steel plates is performed using the ABAQUS/Explicit finite element code. Special emphasis is focused on the evolution of mid-point displacements and velocity. Further investigations have been performed to study the effects of including material damping and the rate-dependent material properties at different shock loads. The results indicate that stiffeners configurations and shock loads affect greatly the overall performance of steel plates and are sensitive to the materials data. Also, the numerical results can be used to obtain design guidelines of floating structures to enhance resistance of underwater shock damage, since explosive tests are costly and dangerous.

Optimal Configuration for Stiffened Plates under the Effect of Underwater Explosion

The dynamic response of a floating structure subjected to underwater explosion is greatly complicated by the explosion of a high explosive, propagation of shock wave, complex fluid–structure interaction phenomena, and the dynamic behavior of the floating structures. A numerical investigation has been carried out to examine the behavior of stiffened steel plates subjected to shock loads resulting from an Underwater Explosion (UNDEX). The aim of this work is to obtain the optimal configuration to resist underwater shock loading. A non-linear dynamic numerical analysis of the underwater explosion phenomena associated with different geometrical stiffened steel plates is performed using the ABAQUS/Explicit finite element program. Special emphasis is focused on the evolution of mid-point displacements. Further investigations have been performed to study the effect of including material damping and the rate-dependant material properties at different shock loads. The results indicate that stiffener configurations and shock loads affect greatly the overall performance of steel plates and sensitive to the material data.

수중폭발을 이용한 충격신관 작동 계측

In this paper, This study shows the content on the impact fuze test and the measurement using underwater explosion phenomena. The impact fuze has both a delay function and a super quick. Up to now, nothing but the naked eye of the observer has been used to verify performance of the impact fuze. The observer has determined the performance by the shape of the plume created from the explosion phenomenon. However, it is extremely difficult to use that method at a long range. In order to solve the problem, the measurement using the underwater explosion phenomena was tried.

Numerical Simulation and Response of Stiffened Plates Subjected to Noncontact Underwater Explosion

A numerical simulation has been carried out to examine the response of steel plates with different arrangement of stiffeners and subjected to noncontact underwater explosion (UNDEX) with different shock loads. Numerical analysis of the underwater explosion phenomena is implemented in the nonlinear finite element code ABAQUS/Explicit. The aim of this work is to enhance the dynamic response to resist UNDEX. Special emphasis is focused on the evolution of mid-point displacements. Further investigations have been performed to study the effects of including material damping and the rate-dependant material properties at different shock loads. The results indicate that stiffeners configurations and shock loads affect greatly the overall performance of steel plates and sensitive to the materials data. Also, the numerical results can be used to obtain design guidelines of floating structures to enhance resistance of underwater shock damage, since explosive tests are costly and dangerous.

Dynamic Response of Stiffened Plates Subjected to Underwater Shock Loading

The dynamic response of a floating structure subjected to underwater explosion is greatly complicated by the explosion of a high explosive, propagation of shock wave, complex fluid–structure interaction phenomena, and the dynamic behavior of the floating structures. A numerical investigation has been carried out to examine the behavior of stiffened steel plates subjected to shock loads resulting from an Underwater Explosion (UNDEX). The aim of this study is to enhance the dynamic response of stiffened plates to resist underwater shock loading. A non-linear dynamic numerical analysis of the underwater explosion phenomena associated with different geometrical stiffened steel plates is performed using theABAQUS/Explicit finite element program which provides an important analysis tool that can help engineers and designers to design and construct better structures to resist shock loads. Special emphasis is focused on the evolution of mid-point displacements and the maximum displacements. Further investigations have been performed to study the effects of including material damping and the rate-dependent material properties. The results obtained show that the inclusion of a damping material can absorb energy under blast load. It helps to reduce the force transmitted to the main structure. The inclusion of damping material helps to reduce the displacement of the plates. The results indicate that stiffener configurations affect greatly the overall performance of tested steel plates. The displacement–time histories are presentedwhich will be used in designing stiffened panels so as to enhance resistance to under water shock damage. The obtained numerical results can help in proposing design guidelines for floating structures in order to enhance the resistance to underwater shock damage, since explosive tests are considered costly and dangerous.

Numerical Evaluation of Composite Plates Performance under the Effect of Underwater Explosion

This paper examines the performance of composite plates with PVC foam cores and T700/epoxy composites face sheets, and steel plate have the same areal mass when subjected to Underwater Explosion (UNDEX). The objective of this study is to evaluate the dynamic response of those plates. A non-linear dynamic numerical analysis of the underwater explosion phenomena is performed using the ABAQUS/Explicit finite element code, which provides an important analysis tool that can help engineers and designers to design and construct better structures to resist shock loads. The temporal evolutions of plate deflection and central deflection histories were obtained. Further investigations have been performed to study the behavior of failure. The results indicate that the behavior of composite plate with PVC foam core to resist shock loads resulting from an UNDEX is better than steel plate, and the core thickness has a great effect on the plate`s response. The obtained numerical results can help to suggest design guidelines of floating structures to enhance resistance tounderwater shock damage, since explosive tests are costly and dangerous.

Numerical Modeling of Underwater Explosion by One-Dimensional ANSYS-AUTODYN

This article presents numerical simulation of underwater explosions using a one-dimensional “wedge” model of ANSYS-AUTODYN explicit software for nonlinear dynamics, provided by ANSYS Century Dynamics, Inc. (Canonsburg, PA, USA). Through numerical analysis of a typical underwater TNT explosion problems, the effects of the quadratic and linear viscosity on the key phenomenon of this complicated energetic physical process are conducted. The results show that appropriate values exist for these two viscosities to model the process in given mesh sizes. Based on these preliminary simulations, values of quadratic and linear viscosity, 1 and 0.034, 1 and 0.068 are determined for the ranges of scaled distance from 3 to 10 and 1.5 to 3, respectively. Effects of charge depth, charge mass, and mesh density on the shock wave and bubble pulse parameters are performed for four different explosives, 2,4,5-trinitrotoluene (TNT), H-6, pentolite, and pentaerythritol tetranitrate (PETN). All of the results are compared with empirical equations and show that the ANSYS-AUTODYN software can be used to model and capture the major features of underwater explosion phenomena at acceptable accuracy and timesaving.

Advances in ship survivability against underwater explosions

Mines, torpedoes and improvised explosive devices (IED) pose a serious threat to the survivability of naval combatants. Inasmuch, a major goal in the design of modern combatant ships has been to eliminate or at least reduce the devastating damage caused by underwater explosion events. Even though there has been extensive research performed on the various underwater explosion phenomena and their associated effects, effective shock testing and shock proofing strategies for naval ship systems have proven to be illusive. Through the use of modeling and simulation (M&S), live fire test and evaluation (LFT&E) and laboratory testing, general guidelines for the shock hardening of shipboard equipment and systems have been developed. In this paper, current aspect of ship survivability has been addressed and future direction is discussed.

An adaptive ALE method for underwater explosion simulations including cavitation

The aim of this paper is to develop a numerical procedure for simulating a simplified mathematical model of underwater explosion phenomena. The Euler set of equations is selected as the governing equations and the ideal gas and Tammann equations of state (EOS) are used to obtain pressure in the gas bubble and the surrounding water zone, respectively. The modified Schmidt EOS is used to simulate the cavitation regions. An arbitrary Lagrangian–Eulerian method is used to integrate the governing equations over an unstructured moving grid. A mesh adapting technique is applied to increase the accuracy as well as for better capturing of flow physics. Moreover, a least-square smoother is employed to moderate the undesirable effects of gas–water interface irregularities. The numerical results verify that the proposed method is capable of predicting complex physics involved in a spherical underwater explosion. The method also shows a very good performance in smoothing the interface while minimizing the loss of mass and momentum in two-dimensional problems.

Smoothed particle hydrodynamics for numerical simulation of underwater explosion

Underwater explosion arising from high explosive detonation consists of a complicated sequence of energetic processes. It is generally very difficult to simulate underwater explosion phenomena by using traditional grid-based numerical methods due to the inherent features such as large deformations, large inhomogeneities, moving interface and so on. In this paper, a meshless, Lagrangian particle method, smoothed particle hydrodynamics (SPH) is applied to simulate underwater explosion problems. As a free Lagrangian method, SPH can track the moving interface between the gas produced by the explosion and the surrounding water effectively. The meshless nature of SPH overcomes the difficulty resulted from large deformations. Some modifications are made in the SPH code to suit the needs of underwater explosion simulation in evolving the smoothing length, treating solid boundary and material interface. The work is mainly focused on the detonation of the high explosive, the interaction of the explosive gas with the surrounding water, and the propagation of the underwater shock. Comparisons of the numerical results for three examples with those from other sources are quite good. Major features of underwater explosion such as the magnitude and location of the underwater explosion shock can be well captured.

Precise measurements of underwater explosion phenomena by pressure sensor using fluoropolymer

Abstract To study underwater explosion phenomena, it is necessary to precisely measure underwater shock wave and bubble pulse. Currently, underwater shock wave is measured by pressure sensor, using tourmaline. However, this method cannot sustain underwater shock pressure higher than 20 MPa. To realize a pressure sensor which can sustain underwater shock pressure higher than 100 MPa, we developed a pressure sensor using fluoropolymer as the sensing element. Measurements of underwater shock wave profiles were performed by pressure sensor using fluoropolymer and the results were compared with those obtained using tourmaline. The experimental results show that the sensor using fluoropolymer can precisely measure underwater shock wave profiles in pressure ranges above 100 MPa. To understand the destructive effects of underwater explosion phenomena, it is necessary to accurately measure bubble pulse, as well as underwater shock waves. Precise measurements of peak pressure and impulse of bubble pulse, as well as underwater shock waves, were performed by pressure sensor using fluoropolymer. The experimental results show that the peak pressure of bubble pulse is about 15–30% of the peak pressure of the shock wave, but the impulse of bubble pulse is about 1.5–2.5 times bigger than that of shock wave, within the measured scaled distance range. This is due to the fact that the duration of bubble pulse is about ten times longer than that of shock wave.

Non-ideal detonation of emulsion explosives

Abstract In order to obtain a better understanding of the underwater explosion phenomena related to emulsion explosives, optical measurements using the water tank technique and cylinder expansion test were carried out. Streak photographs were taken using an image converter camera with a usual shadow graph system. Four kinds of emulsion explosives differing in aluminium contents were used in the experiments. These emulsion explosives were placed into copper and PMMA pipes. From the results obtained with the water tank technique, it is recognized that the maximum velocity of underwater shock wave in the case of a copper pipe is about 10% faster than that in the case of a PMMA pipe. From the cylinder expansion test, it is found that the degree of radial displacement of a copper case (Uexp) increases with increased aluminium content and that in the range of more than 10 wt.%, Uexp decreases with increased aluminium content.

The design and instrumentation of a simple system for demonstrating underwater explosive effects

AbstractThe design and testing of a system for studying underwater explosions is described together with the design of a suitable charge for use in the facility. From the results obtained it is concluded that the system offers a relatively simple method of demonstrating underwater explosion phenomena.