Underwater Contact Explosion Research Articles

Experimental and numerical investigation of arch concrete slabs subjected to underwater contact explosions with the inner arch side facing air

Arch structures with their inner arch side exposed to air and outer arch side exposed to water are often encountered in practical projects, and these engineering structures may be subjected to various explosive attacks during operation. This paper investigates the damage mechanism and dynamic response of arch concrete slabs with the inner arch side facing air against underwater contact explosions (UWCEs). The explosion tests of the arch concrete slab with the inner arch side facing air were carried out. The accuracy and applicability of the numerical model were verified by comparing with the explosion results. After that, the failure evolution and energy transition of the arch concrete slab with the inner arch side facing air were studied. The effects of different explosion masses, explosion distances, and reinforcement schemes on the antiknock performance of arch concrete slabs are further explored. The results show that as the explosive mass of UWCEs increases, the damage mode of the arch concrete slab with the inner arch side facing air changes from cracking along the longitudinal direction and local failure to spalling on the inner arch side and fragmentation of the contact specimens. The existence of curvature of the arch slab will cause the damage of the arch slab to intensify. The failure mode of the arch concrete slab changes from local failure to slight failure with cracks as the explosion distance increases. Increasing the longitudinal steel bars on the outer arch side can effectively inhibit the generation and development of cracks.

Experimental and numerical study on damage behavior of air-backed steel-concrete-steel composite panels subjected to underwater contact explosion

The damage behavior and explosion resistance of air-backed steel-concrete-steel (SCS) composite panels subjected to underwater contact explosions were investigated experimentally and numerically. Firstly, the underwater explosion experiments of the SCS panels were conducted using the novel test setup, and the final damage morphology and residual deflection of these panels were obtained. Secondly, the corresponding finite element model was established in LS-DYNA and validated against the test results, based on the refined numerical modelling, the damage process of the SCS composite panel under 200 g underwater contact explosion was reproduced. After that, the damage mechanism of the SCS panels was revealed through the analysis of internal energy absorption and stress wave propagation inside the SCS panels. Subsequently, the damage behavior of the SCS panels when subjected to underwater and air contact explosions was compared. Finally, a series of parametric analysis were performed to explore the effects of the material strength and structural form on the explosion resistance of SCS panels. Both the experimental and numerical results indicate that the SCS panels suffered global damage. The core concrete absorbed more than 80 % of the explosion energy and the restraint of the steel plates effectively reduced the spalling damage of the core concrete. The SCS composite panel makes full use of the advantages of concrete and steel panels, resulting in superior underwater explosion resistance.

Blast resistance performance and failure modes of prestressed thin-walled aqueducts subjected to underwater contact explosion

To solve the problem of regional water resource shortage, water diversion projects have been built around the world. As an essential lifeline project, the prestressed aqueduct is commonly used in cross-regional water transfer and diversion projects. However, the prestressed aqueduct is inclined to damage and collapse under explosion loading due to its thin structure. The main purpose of this paper is to investigate the nonlinear dynamic performance and failure modes of the large prestressed U-shaped thin shell aqueduct to underwater contact explosion. The prestress application approach is validated by theoretical calculations. The reliability of the analysis method of underwater contact explosion for reinforced concrete structures is verified by the underwater contact explosion test. Damage cracking process and nonlinear dynamic response characteristics of prestressed aqueducts to the underwater contact explosion with different explosive weights are performed. Blast resistance performances of prestressed aqueducts are discussed in terms of the crack length, residual displacement, and prestressing force loss. The influence of prestress level on the damage modes of the prestressed aqueduct under the blast loading is discussed. The results indicate that thin-walled U-shaped structures are extremely vulnerable to localized damage from underwater contact explosions. The blast-resistance performance of the U-shaped thin shell aqueduct can be significantly improved by applying prestress.

Study on the protection mechanism and damage grade prediction of different corrugated steel‒concrete composite structures under underwater contact explosion

Considering that corrugated steel has a certain anti-explosion protective effect, the influences of corrugated steel shape parameters on the protective effect of corrugated steel–concrete composite structures have not been considered. In this paper, the FEM–SPH coupling method is used to establish a simulation model of an underwater contact explosion wall panel. The numerical results are compared with the experimental results to verify the effectiveness of the simulation method. Furthermore, the underwater energy absorption effect, protection effect and influences of the wall panel of different composite structure protective layers on the damage process and failure mode are explored, the underwater explosion-proof mechanism is revealed, and the prediction curve of the damage grade of the wall panel is constructed. The results show that simulation results of the concrete slab front and back explosion surfaces are basically consistent with the experimental results. Under different composite structure protection schemes, the peak pressures of the composite structure protection schemes with 12-mm-thick corrugated steel and with 75° corrugated steel are reduce by 63.2% and 60%, respectively, relative to the noncomposite protection scheme, while the total energies of the corresponding composite structure are increased by 50.6% and 61.4%, respectively; the damage ranges of the wall panel are reduced by 83% and 81.6%, respectively. This finding shows that changing the corrugated steel shape parameters in the composite structure can effectively improve the energy absorption effect and reduce damage to the wall panel. The blast wave first propagates to the corrugated steel in the form of an incident wave and then propagates in the form of transmitted and reflected waves. Part of the wave propagates to the wall panel when the transmitted wave arrives at the corrugated steel lower surface, while the rest of the wave forms a reflected longitudinal wave and reflected transverse wave through reflection. Then, the transmitted wave acting on the wall panel attenuates. Under the protection schemes of the corrugated steel composite structure with a 12-mm thickness and corrugated steel composite structure with a 75° angle, the maximum protection rates are 63.2% and 60.0%, respectively, the energy consumption sharing rates are 69.48% and 66.26%, respectively, and the damage levels are moderate. The multiangle comparative analyses of different protection schemes suggest that the corrugated steel composite structure with a 12-mm thickness should be selected. The prediction curve can intuitively evaluate the influences of the quantity of explosive loads and the thickness/angle of corrugated steel changes of the composite structure on the damage to the wall panel. The research results can serve as a reference for the adhibition of underwater explosion protective engineering projects.

Dynamic stability of concrete structures with varying sections to underwater contact explosion: A case study of gravity dams

Concrete structures with varying sections are widely used in the fields of ocean engineering, hydraulic engineering and civil engineering. And the damage mechanism of variable-section structures to underwater contact explosion, which involves localized damage by explosion impact and instability by overall structural vibration, is very complex. The gravity dam is taken as an example, the coupled analysis model for gravity dams under underwater contact blast is established, a prototype test on the dynamic response of a gravity dam under underwater explosion is conducted to verify the reliability of the fluid-solid interaction method, and the reliability of the concrete dynamic damage model adopted in this paper is validated by a small-scale field test on the internal blast damage of a gravity dam. The damage mechanism of gravity dams subjected to underwater contact explosion is analyzed. A stability analysis method for gravity dams to underwater contact explosion is proposed, which allows simultaneous consideration of the dam stability in the blast-induced vibration phase and the static phase after damage. The dynamic stability performance of gravity dams to underwater contact explosion is analyzed. And a stability assessment criterion that could be used to assess the safety level of dams at various stages is presented.

Damage behavior of concrete members subjected to underwater contact explosion

In order to investigate the damage mechanism of dams subjected to underwater contact explosion, firstly, an experimental program was conducted with six concrete slabs and two explosive quantities. The test results showed that the diameter and depth of the crater on the front and back surface of the concrete slab increased with increasing explosive quantity with radial and circular cracks generated. Three different concrete material models were tested and it was found the CDP model was most suitable in simulating concrete subjected to underwater explosion. The calibrated models were used to conduct parametric studies to study the effect of explosive quantity, slab thickness, and transferring medium (water or air). Numerical analysis results showed that the diameter and depth of the crater on both the front and back surface of the concrete slab decreased with increasing slab thickness and decreasing explosive quantity. In addition, the damage caused by the air contact explosion was smaller and more concentrated in the detonation center compared with underwater contact explosion. Finally, a gravity dam and an arch dam were modeled to study the effect of detonation depth and water level on the damage distribution pattern of the dams. Based on the results, recommendations were provided for the anti-explosion protection design of hydraulic structures.

Failure modes and dynamic responses of roller compacted concrete gravity dams subjected to underwater contact explosion based on the cohesive model

Considering the construction technology of roller compacted concrete (RCC) gravity dams, there are layers in dams inevitably, which may affect the blast responses of dams. This paper is aimed to investigate the effects of RCC layers on the failure modes and dynamic responses of RCC gravity dams bearing underwater contact explosion loading. Initially, the zero-thickness cohesive element model is presented to simulate the crack behavior of the RCC layers. An impact test of a concrete beam is selected to verify its reliability. The concrete damage plasticity model considering strain rate effects is utilized to simulate the various responses of concrete under blast load. The dam–reservoir–foundation interactions are described using the coupled Eulerian-Lagrangian method. The numerical methods are validated by a field blast test of a concrete structure. Subsequently, numerical models were established for gravity dam-reservoir-foundation systems, with and without considering RCC layers respectively. Based on validated algorithms, these models were utilized to explore the effects of RCC layers on the blast performance of the dam. Finally, the influence of the parameters of RCC layers on the nonlinear responses and failure modes of the dam is further investigated, including the maximum traction, the fracture energy, and the layer thickness. The results reveal that the layers significantly change the failure modes. The RCC layers are the weak link of the dam and they will lower the anti-explosion performance of the dam. Therefore, it is crucial to take the layers into account when conducting anti-explosion research, and RCC dams cannot be simply simplified as normal concrete dams. To guarantee the safety of the dam, it is important to ensure the layers with sufficient strength and fracture energy, as well as an appropriate thickness.

Experimental investigation of steel fiber reinforced concrete slabs subjected to underwater contact explosions

Fiber reinforced concrete has gained significant attention due to its higher ductility and flexural behavior, making it a promising material for resisting extreme loads such as those caused by blast and impact. In this study, we present experimental results from static tests conducted on steel fiber reinforced concrete with different content of hooked end steel fibers and concrete strength. Underwater contact explosion tests were performed for 6 pieces of 50 cm × 50 cm x 6 cm steel fiber reinforced concrete slabs. The damage patterns observed in the slabs were analyzed, and shock pressure data was measured and compared with empirical formula calculations. Test results demonstrate that the addition of steel fiber effectively enhances the compressive and tensile strength of concrete while also significantly improving its anti-explosion capacity. In contrast, the plain concrete slab (control group) displayed an overall state of failure during underwater contact explosions. Steel fiber reinforced concrete slabs primarily experienced bending failure and “Y" crack damage, accompanied by local collapse failure on the back surface. Overall, these findings suggest that steel fiber reinforced concrete holds great promise as a superior material for resisting extreme loads, particularly in marine environments.

Experimental and numerical investigation on saturated concrete subjected to underwater contact explosion

The hydraulic concrete structures were partially or fully in direct contact with water during the service life. The mechanical properties of saturated concrete are different from dry concrete because of the presence of water. To investigate the underwater blast resistance mechanism of saturated concrete, saturated concrete slabs were first tested in underwater explosion experiments with different TNT masses of 2.5 g, 5 g, and 10 g. The experimental results showed that the crater on the front of the concrete slab was smaller than those on the back and the size of the crater increased with increasing mass of TNT. Numerical simulations were conducted and material parameters were determined based on additional tests: The damage model under different stress states was proposed by repeated loading and unloading tests in tension and compression under different confining pressures. The damage model was then embedded into the Holmquist-Johnson-Cook (HJC) model. Quasi-static and dynamic compression experiments were conducted to determine the material parameters of the saturated concrete. A three-dimensional fluid-solid coupling numerical model in ABAQUS was proposed for simulating the underwater explosion and its interaction with the saturated concrete slab. Finally, the mechanisms that produce differences in the damage pattern of concrete slabs at different explosive masses are revealed.

Experimental and Numerical Investigation on Saturated Concrete Subjected to Underwater Contact Explosion

Experimental and Numerical Investigation on Saturated Concrete Subjected to Underwater Contact Explosion

Mitigation effects of air-backed RC slabs retrofitted with CFRP subjected to underwater contact explosions

Reinforced concrete (RC) structures are commonly used in ocean engineering, and can be subjected to various blast scenarios. To evaluate the strengthening effects of the carbon fiber reinforced polymer (CFRP) on the blast resistance of air-backed RC slabs to underwater contact explosions, a numerical approach based on the coupled Lagrange-Euler (CLE) method is proposed. First, two blast tests with available experimental results are utilized to verify the numerical method. Then, numerical investigations are conducted on air-backed slabs retrofitted with CFRP subjected to underwater contact explosions using the verified analytical method. The retrofitting effectiveness of CFRP on air-backed RC slabs against underwater contact explosions are analyzed contrastively. In addition, the effects of various factors, namely, the retrofitted scheme, retrofitted thickness, retrofitted material, and charge weight, on the blast resistance of FRP retrofitted air-backed slabs are investigated. The results demonstrate that the CFRP retrofitting can significantly improve the blast resistance of air-backed slabs against underwater contact explosions by reducing deformation and catching flying debris.

Blast resistance of air-backed RC slab against underwater contact explosion

Reinforced concrete (RC) structures are common in engineering, and usually exposed to air or water, may be subjected to various blast scenarios. This paper aims to investigate the blast resistance of an air-backed RC slab against underwater contact explosions (UWCEs). A detailed numerical model based on CLE method considering explosive, water, air, and RC slab is developed to examine the structural behavior of the air-backed RC slab due to UWCEs. At first, the reliability of the numerical method is validated by comparing the numerical results of an UWCE test with experimental data. Then, the difference in dynamic behavior of air-backed and water-backed RC slabs due to UWCEs is explored with the calibrated model. The results indicate that the blast response of the air-backed slab induced by UWCE is fiercer than that of water-backed slab with equal charge mass. In addition, parametric studies are also conducted to explore the effects of the charge mass, standoff distance, reinforcement spacing, concrete compression strength, and boundary condition on the blast performance of the air-backed RC slab.

A study on damage characteristics of double-layer cylindrical shells subjected to underwater contact explosion

In this study, the damage characteristics of double-layer cylindrical shells with interlayer water subjected to small charge underwater contact explosion were investigated through experimental and numerical methods. At the same time, the distribution characteristics of the field pressure near the double-layer cylindrical shells and detailed bubble dynamics were revealed. The experimental results showed that there were crevasse and non-crevasse areas in the outer shell of the double-layer cylindrical shells, which form “inrushing bubbles” and “induced bubbles” in the interlayer water, respectively. Their subsequent bubble collapse behavior continued to impact the inner shell. Based on the traced analysis of the field pressure and deformation duration characteristics of the double-layer cylindrical shells, the load characteristics of the shock wave, interlayer bubble (inrushing bubble and induced bubble), and outboard bubble load sequence response to double-layer cylindrical shells were obtained.

Damage prediction of stiffened plates subjected to underwater contact explosion using the machine learning-based method

A machine learning-based method is used to predict damage responses of stiffened plates subjected to underwater contact explosion. The data set of damage responses of a stiffened plate with different thicknesses under different charge masses and standoff distances is collected from a detailed finite element model established by the LS-DYNA program. In order to efficiently obtain the optimal machine learning model, influences of the number of hidden layers, the number and distribution of hidden layer neurons on the network performance are investigated. Due to fluid-structure interaction, material and geometric nonlinearities, it is found that the three hidden layers network is required to predict damage responses of the stiffened plates, even for the prediction of the dimension of the damaged domain which has only one target parameter. Meanwhile, the number of multi-hidden layer neurons can be determined by the empirical formulas coupled with the trial-and-error method, and the rarely studied hidden neuron distribution can be further selected based on the quantitative relationship between input features and target parameters. The damage border, the dimension of the damaged domain, and plastic deformations of the undamaged domain predicted by the optimal networks are in good agreement with the LS-DYNA results.

Investigation on influence factors about damage characteristics of ice sheet subjected to explosion loads: Underwater explosion and air contact explosion

Ice blasting efficiency is greatly influenced by many factors of explosives. This study aims to investigate the laws of the damage characteristics of the ice sheet influenced by explosive factors. Fully-coupled numerical models of underwater explosions for ice-breaking were established based on the experimental test, and the numerical results were in good agreement with the experimental results. The damage characteristics of ice sheets subjected to underwater and air contact explosion loads were thoroughly investigated by changing explosive types, explosive shapes, and the length to diameter ratios of cylinder charge. The results demonstrate that high-energy explosives, such as HMX and OCTOL explosives, can result in more serious damage to the ice sheets than the explosion of TNT, FEFO, PBX9010, and TETRYL explosives. A cylinder charge can be suggested to improve the efficiency of ice-breaking owing to its adjustable length to diameter ratios. The underwater explosion type is preferable to the air contact explosion for ice-breaking owing to the combined action of shock wave and bubble loads. The prediction formulas for the failure diameters of the ice sheets are proposed based on dimensional analysis, which provides a reference for ice-blasting engineering.

Safety Evaluation of Arch Dam Subjected to Underwater Contact Explosion

The stability of an arch dam can be significantly damaged by an extreme underwater explosion. This study proposed a damage index for assessing the degree of local damage of an arch dam after the dam was subjected to an underwater explosion. The damage index was applied to assess local damage at the middle part of the dam, surcharge holes, and abutment. A model was developed to evaluate the stability of the entire dam based on the spatial distribution of damage and the damage on the base interface. Results showed that local explosion damage at flood discharge holes or abutments might cause instability of the arch dam. When the contact explosion action location is on the abutment, it only needs 310 kg to cause the overall damage of the arch dam, while when the action location is on the middle part of the dam, the quantity of explosive required is 2800 kg.

Research on Contact Explosion Response of Reinforced Concrete Slab

In order to compare the contact explosion response of reinforced concrete in the air to that under the water, a FEM model based on multi-material fluid-structure coupling method is constructed to simulate the responses and failure process of two-way reinforced concrete slabs under contact explosion. The model is verified by fellow tests, then used to calculate dynamic responses and damage conditions of two-way reinforced concrete slabs subjected to underwater contact explosion and air contact explosion. It is found that the local destruction area of the slab subjected to underwater contact explosion roughly turned into a circle, while it turned into a rhombus for air contact explosion. Nonetheless, the damage of the reinforced concrete slab subjected to underwater explosion is more serious.

Numerical study on ice damage characteristics under single explosive and combination explosives

Explosives are considered an effective method of breaking an ice jam or clearing an ice barrier. As underwater explosions can have a severely destructive impact on ice sheets, investigating the damage mechanism and dynamic characteristics of the ice sheet is significant. This paper presents a study on the ice damage characteristics subjected to single and combination explosives utilizing the Arbitrary-Lagrangian-Eulerian (ALE) technique to solve the Fluid-Structure interaction (FSI) processes between the fluid and ice structures. The numerical model is validated by reference results and experimental data. The damage evolution and mechanism of the ice sheet are analysed. The different responses of the ice sheet subjected to underwater contact and underwater explosions are discussed. In addition, the critical explosion charge just sufficient to break the ice is investigated. Moreover, the ice damage characteristics from two explosives in combination are analysed. The results demonstrate that the damage to the ice sheet induced by the underwater explosion is significantly larger than an underwater contact explosion with an equal charge mass; The blast efficiency of the two combination explosives with a suitable spacing distance in the horizontal direction is higher than that of a single explosive with an equal charge mass. The analyses and results provide a reference for the ice-breaking engineering.

Damage Characteristics of Polymer Plates under the Impact of the Near‐Field and Contact Underwater Explosion

In order to study the damage characteristics of polymer plates under the impact of the underwater explosion, the underwater contact and near‐field explosion tests of polymer plates were conducted using different explosive quantities. In this paper, eight polymer plates with the size of 500 mm × 500 mm × 60 mm were made, and eight groups of explosion tests were carried out by using the rock emulsion explosive and nonconductive detonators. The damage modes and spatial distribution characteristics of the polymer plate generated by the underwater contact and near‐field explosion impact with different explosive quantities are compared and analyzed. In addition, the characteristics of the shock wave propagation in the plates are investigated. It can be observed that the main damage mode of polymer plate is overall damage under the contact underwater explosion. For the near‐field explosion, the main damage mode changes to overall failure, and the damage of contact explosion to polymer plate is greater than that of underwater near‐field explosion. The polymer plate can reduce and delay the shock wave effectively, but the effect decreases with the increase of explosive quantity in the underwater contact explosion.

Experimental and numerical study of damage characteristics of RC slabs subjected to air and underwater contact explosions

Reinforced concrete (RC) is one of the most commonly used construction materials. However, impact and blast loads could completely destroy RC structures, causing tremendous casualties and property losses. Therefore, analyzing the damage mechanism and dynamic behaviour of RC structures under blast loading is significant. This paper presents a study on the behaviour of RC slabs subjected to air and underwater contact detonation. Two RC slabs were tested under real blast loads. One was tested under air contact explosion of 210 g TNT, the other was tested subjected to underwater contact explosion of 6 g TNT. Damage evolution and damage mechanism of the RC slabs subjected to the air and underwater contact explosions are investigated by using high-fidelity numerical models. The damage patterns obtained from the numerical models match well with those of the tests. The effect of experimental environments on the structural behaviour of the slabs subjected to the underwater explosions is also discussed. The different response of the RC slabs subjected air and underwater explosions with identical charge mass are analyzed contrastively by employing the validated coupled method. The results show that the present model can give a reliable prediction of damage characteristics for RC structures under various blast scenarios. The experimental environments have important influence on the structural response and bubble development. The damage of the RC slabs induced by underwater contact explosion is significantly larger than that caused by air contact blast with equal charge mass.