Non-contact Underwater Explosion Research Articles

A Design Approach to Assess Effects of Non-Contact Underwater Explosions on Naval Composite Vessels

A Design Approach to Assess Effects of Non-Contact Underwater Explosions on Naval Composite Vessels

Characterization of underwater shock transient effects on naval E-glass biaxial fiberglass laminates: An experimental and numerical method

Non-contact underwater explosions (UNDEX) can cause extremely large deformations on naval composite structures related to heavily nonlinear phenomena. For this reason, for military purposes, used materials must have excellent shock resistance properties. Historically, the underwater shock transient effects on fiberglass laminates are predicted using quasi-static approaches. In this paper, the composite materials are characterized by experimental modal analysis as well as by a comprehensive series of shock tests, whose results are compared with numerical models. Namely, the MIL S 901 D Medium Weight Shock Machine (MWSM) was used to perform dedicated shock tests, in which composite specimens are supported on a special constraining structure designed to create large deflections and providing reproducible results. A dynamic implicit finite element model has been set, validated by modal analysis at first, and then applied to simulate the MWSM test behavior and to predict the structural response of different E-Glass polyester resin laminates. In the end, the complete comparison of numerical results and experimental data is reviewed to validate the modeling strategies for shock design of navy ships.

Failure analysis for concrete gravity dam subjected to underwater explosion: A comparative study

The failure analysis of concrete gravity dams subjected to noncontact underwater explosions (UNDEXs) plays a significant role in evaluating the safety of dams. In this paper, two types of numerical models were developed to predict the failure behavior of a typical concrete gravity dam, i.e., the fully-coupled and semi-coupled model, which can provide a cross validation of the analysis results. The two models were verified by the experimental data and then adopted for the failure analysis. The results show that the shock wave can produce peak value in the blast responses and concentrated damage directly opposite to the explosive source. Even after the energy transmission at the fluid–structure interface, the UNDEX load still had influence on the failure behavior of the dam and can induce a total swelling in the velocity response.

A Study on Shock Test Design Method Using Linear Dynamic Model of Light Weight Vertical Shock Test Machine

Naval surface ships and submarines could be exposed to non-contact underwater explosion(UNDEX) environment. Equipment installed on the ships and submarines could be damaged by shock load generated by UNDEX environment. Therefore, shock survivability of equipment generally evaluated by shock tests. Ground based shock test machine such as Light weight shock test machine(LVSM) is developed to simulate shock load caused by UNDEX environment. In this study, linear dynamic model of LVSM is proposed and evaluated to improve shock test design procedure. Parameters of the model are decided by optimizing time domain response compared to zero payload experiment. Proposed model is verified by comparing simulation results and test results of maximum payload experiment. Finally, shock test design using the model is described for various test equipment weight. Keywords: 수중 폭발, 충격 시험, 충격 시험 장비 Keywords: UNDEX, Shock Test, Shock Test Machine

Research on Response Characteristics of Hydraulic Gate Subjected to Non-contact Underwater Explosion Load

In this paper, the response characteristics of deep-hole planar steel gates under the separate induction of bubble pulsating load are studied. Through the large-scale finite element simulation software ABAQUS, using the explicit dynamic finite element analysis method, the contact surface of the gate and the water is taken into account by the fluid-solid coupling algorithm. When the water level is constant, the gate is subjected to explosion and the impact of the generated bubble impact on the gate structure and its anti-explosion ability are analyzed. The equivalent stress, displacement, and equivalent plastic strain of the gate under six different cases were simulated. Then, the effect of bubble pulsating load on the stress characteristics of the gate and the anti-explosion ability of the gate were summarized.

PERFORMANCE STUDY OF HYBRID BOLTED-BONDED VERTICAL T- AND L-JOINTS WITH COMPOSITE ADHERENDS SUBJECTED TO UNDERWATER SHOCK PRESSURE

Three-dimensional explicit dynamic simulations are carried out to study the failure of hybrid bolted-bonded vertical T- and L-joints under noncontact underwater explosion shock pressure. In this modelling, adherends are fibrous laminated composites having an orthotropic behavior, while bolts and adhesive layers exhibit an isotropic behavior. It is found that hybrid vertical T- and L-joints display appreciably higher joint resistance to underwater explosion shock pressure than adhesive T- and L-joints.

Experimental and Numerical Investigation of Reinforced Concrete Pile Subjected to Near-Field Non-Contact Underwater Explosion

High-pile wharf is an important port structure and may suffer from accidental explosions or terrorist bombing attack during the service life. The reinforced concrete (RC) pile is one of the popular vertical load-bearing piles of high-pile wharf structure. As a main load-bearing member of the high-pile wharf structure, the damage of RC pile due to underwater explosive may cause subsequently progressive collapse of the whole structure. In this paper, the dynamic response and failure mode of RC pile in high-pile wharf structure under the near-field non-contact underwater explosion are investigated using a combined experimental and numerical study. First, a typical RC pile was designed and tested for the near-field non-contact underwater explosion. The failure mode and damage of the RC pile specimen were obtained and analyzed. Second, the numerical model of the RC pile under near-field non-contact underwater explosion was established by adopting the commercial software AUTODYN, and then validated based on experimental results. It was shown that the results from numerical model and experimental test compared very well in terms of the damage pattern and lateral displacement. Furthermore, the full-scale numerical model of the RC pile for the near-field non-contact underwater explosion was developed based on the validated numerical model to investigate the damage pattern and failure mode of RC pile under varied underwater explosives. Lastly, the safety distance for the RC pile for the underwater explosion loading with consideration of different explosive mass, the explosive depth and the concrete strength was suggested. The outcome of this study presented reference for analysis, assessment and design of the type of RC pile for high-pile wharf structure subjected to near-field non-contact underwater explosion.

Pressure Wave Caused by Trinitrotoluene (TNT) Underwater Explosion—Short Review

The development of computational techniques and computer hardware has an impact the analysis of short-term (fast-changing) processes, such as the impact of a non-contact underwater explosion pressure waves. A theory of underwater explosions, gas bubble formation and pressure waves are presented. The course of the pressure wave in time, and its propagation in the acoustic medium are presented. The study presents empirical descriptions of non-contact pressure explosion waves. We propose to use them in simulations of ship hull strength and other objects immersed in liquids that are exposed to the effects of non-contact trinitrotoluene (TNT)-charge explosions. Pressure distributions and their time courses given by authors such as R.H. Cole, J.S. Nawagin, W. Stiepanow, T.E. Farley and H.G. Snay, T.L. Geers and K.S. Hunter are compared. A method of pressure wave modeling using acoustic media implemented in Computer Aided Engineering (CAE) programs is presented. The results of the values and the time course of the pressure acting on the underwater object are given. The influence of FEM (Finite Element Method) mesh density on the obtained results is examined and presented. The aim of the article is to expand our knowledge of underwater explosions, compare mathematical descriptions of the pressure waves developed by different authors and show the differences between them. In addition, we present the distinction between contact and non-contact explosions and analyze how changes in the mesh density of acoustic elements affects the reflection of the incident wave caused by an underwater explosion.

Effects of sacrificial coatings on stiffened double cylindrical shells subjected to underwater blasts

Underwater explosion shock loadings can seriously damage the vitality and fighting capacity of warships. Plastering a layer of sacrificial coating on the ship hull is one of effective strategies to isolate shock impulses and absorb shock energy. In this paper, the shock mitigation effects of sacrificial coatings plastered on a stiffened double cylindrical shell are analyzed numerically. The numerical models are validated by conducting a series of physical experiments of a stiffened double cylindrical shell under noncontact underwater explosion. Three different configurations are considered: both the pressure and thin hulls are plastered with sacrificial coatings; only the thin hull is plastered with sacrificial coatings; and only the pressure hull is plastered with sacrificial coatings. The total pressure field in water and the dynamic response of the stiffened double cylindrical shell are obtained. The results indicate that the deformation and motion of the sacrificial coatings can more easily generate rarefaction wave, which can decrease the total shock impulse acting on the structure. Among three configurations, the configuration of the coating plastered on the thin hull has a better capability of isolating the shock impulse and reducing the shock loadings transmitted to the pressure hull. The dynamic stress and velocity responses of the shell are effectively decreased. Comparisons between different configurations suggest that the coating on the thin hull plays a key role in mitigating shock loadings, while the coating on the pressure hull has limited effects. Moreover, comparison results between the bare hull and the equivalent model which increases the thickness of the thin or pressure hulls under the same mass conditions indicate that the method of using a sacrificial coating is more effective in improving the blast resistance of the structure. The research results are useful in guiding the shock resistance design of stiffened double cylindrical shells.

Numerical Investigation on Damage of Concrete Gravity Dam during Noncontact Underwater Explosion

AbstractA three-dimensional (3D) numerical model was developed in this paper to investigate the damage and failure of a concrete gravity dam under attack from a noncontact underwater explosion base...

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.

Взрывосопротивляемость полимерных композиционных материалов при неконтактном подводном взрыве

Взрывосопротивляемость полимерных композиционных материалов при неконтактном подводном взрыве

Resistance of GPS samples to non-contact underwater explosion

Test data obtained from experiments on GRP test samples in the explosion chamber of Krylov State Research Centre are given. Characteristic features of material damage accumulation and failure processes are discussed based on the experimental data. The sample material damage is assessed versus three indicative effects (criteria): binder failure, fiber rupture, through-thickness penetration (hole). Finite element modelling of the experiments is used for a more detailed analysis of stress-strain state of material samples.

Research on the shock resistance optimal design of small-sized submerged vehicle subjected to non-contact underwater explosion

How to improve the strength of submerged structures for undertaking the underwater explosion loading is an important problem confronted by the designers of surface ships and submarines. In this art...

Shock Analysis of Water Backed Perforated Plate Subjected to Underwater Explosion

Perforated plates are essential structural components of sonar acoustic domes of the submarines and underwater platforms. The sonar acoustic domes are considered as ‘water backed condition’ for structural analysis. It is of utmost importance to study the structural response of sonar acoustic domes subjected to noncontact underwater explosion since it has wide scope in defence application. It is intended to investigate the free field pressure due to the underwater explosion and structural response of perforated plate using ANSYS LS-DYNA software for plastic explosive kirkee (PEK), Tri Nitro Toluene (TNT) and Composition 4 explosives. The free field pressure from TNT explosion is validated with the Cole’s expression available for this explosive. The time history plots for free field pressure, displacement and principal stress are plotted for all the three explosives. The free field pressure is validated with Cole’s formula and found 18 % variation for TNT and 14 % for PEK explosive.

Numerical investigation of the dynamic response of optimized composite elliptical submersible pressure hull subjected to non-contact underwater explosion

Predicting the dynamic response of a floating and submerged structure subjected to underwater explosion is greatly complicated by the explosion of a high explosive, propagation of shock wave, bubble-pulse and complex fluid–structure interaction (FSI) phenomena. A numerical simulation has been carried out to examine the behavior of optimized composite elliptical submersible pressure hull to non-contact underwater explosion (UNDEX) and take the effect of bubble-pulse. Various explosive weights and explosion distances were explored to determine the critical weights and safe distance. The optimization process is performed using ANSYS parametric design language (APDL). After that the finite element package ABAQUS was used to model the UNDEX and the FSI phenomena. Time histories of the wet-surface displacement, velocity and Tsai–Hill failure index are presented for different composite plies. All of these results can be a valuable reference for designing underwater vehicles to resist UNDEX.

Modeling of the Minehunters Hull Strenght

The paper presents problems of modeling the ship’s hull subjected to the load of shock wave associated with non-contact underwater explosion. The article presents equations for describing the parameters of shock wave subjected to an impulse load. The paper presents a proposal of identification of a degree of hazard the ship’s hull forced from underwater explosion. A theoretical analysis was made of influence of changes of hull structure in vicinity of hull. Modeled signals and hull structure were recognized within sensitive symptoms of three sub models: model of hull structure, model of impact and model of propulsion system. All sub models allow testing forces and their responses in vibration spectrum using SIMULINK software and FEM models. The results of testing allowed performing simulations of a similar nature to the actual loads of underwater explosions. Virtual model of the hull of the ship responds in a similar manner to the real impacts.

Finite Element Analysis of Deep Elliptical Submersible Pressure Hull Subjected to a Side-On Non-Contact Underwater Explosion

Predicting the dynamic response of a floating and submerged structure subjected to underwater explosion is greatly complicated by the explosion of a high explosive, propagation of shock wave, bubble-pulse, complex fluid-structure interaction phenomena and the dynamic behavior of the floating structures. A numerical simulation has been carried out to examine the behavior of elliptical submersible pressure hull to non-contact underwater explosion (UNDEX) and take the effect of bubble-pulse. The finite element package ABAQUS was used to model the UNDEX and the fluid-structure interaction (FSI) phenomena. The pressure wave resulting from an UNDEX was assumed to be a spherical wave. Plastic strain and the time histories of the wet-surface displacement, velocity and von Mises stress are presented. The analytical results are valuable for designing underwater vehicles to resist UNDEX.

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 a surface ship structure subjected to an underwater explosion bubble

Bubble load in a noncontact underwater explosion can cause the ship hull global response and local response. In current literature, the ship hull is usually simplified as a hull girder to analyze its global response. However, literature dealt with the local response of a 3-D surface ship hull subjected to an underwater bubble were limited. This investigation develops a procedure which couples the finite element method with doubly asymptotic approximation (DAA) method to study the problem of transient responses of a ship hull structure subjected to an underwater explosion bubble. Using a 3-D ship model as examples, the global and local responses of the ship model in vertical, transverse and longitudinal directions are performed in detail. The acceleration, velocity and displacement time histories are presented. The characteristics of both the global and local responses of the ship model are discussed. The numerical results show that besides global whipping response, the ship hull also sustains severe local responses in different directions subjected to underwater explosion bubble jetting, which should be taken into consideration.