Narrow Results

A scaled model of a concrete gravity dam was designed, and nine tests were conducted to investigate the dynamic response characteristics of the dam subjected to underwater explosions. The pressure time histories in the water, and the velocity and acceleration time histories of the dam during various explosions were recorded. The acceleration signal was processed by the Fast Fourier Transform (FFT) to perform time–frequency conversion. The energy migration law of the acceleration signal along the dam elevation was explored based on the theory of wavelet packets. Furthermore, the effects of charge weight, explosion distance, and explosion depth on the dynamic response of the dam were comprehensively investigated. The results show that the distribution of peak acceleration along the dam elevation closely relates to the explosion distance, but the global response of the dam tends to weaken as the explosion distance increases. Increasing the charge weight causes an enhancement in the dam response. Compared with an explosion suspended in water, the bottom explosion causes a weaker response to the dam. With the increase of the dam elevation, the energy of the acceleration signal gradually shifts from low frequency to high frequency. The bubble curtain has a significant mitigation effect against underwater explosions.

Orifices designed into an arch dam for flood discharge significantly reduce the ability of the dam to resist an explosion, especially when an explosive charge is detonated close to an orifice, and the dam may suffer considerable damage in consequence. We created a fully coupled model to represent the dynamic interactions between reservoir water, explosive, arch dam and abutments. Shock wave propagation and damage initiation and propagation were compared between arch dams with and without orifices. The effects of orifices on damage modes and the spatial distribution of damage were investigated. Damage characteristics of the top and middle orifices subjected to explosive loads were also analyzed. Results showed that the top and middle orifices designed into an arch dam have an important effect on the impact resistance of arch dams, especially when an explosive is detonated at an orifice inlet. At a certain mass of explosive, complete failure of the dam wall at the adjacent sluice piers of the top orifices can occur, and penetration failure may also occur at the middle orifice.

The response of the side shell to non-contact underwater explosion is of major concern in ship design. While extensive research is carried out on air-backed plates, relatively less attention is paid to water-backed plates. Nevertheless, the response of the water-backed plates becomes relevant when the water filled side shells are exposed to an underwater shock loading. Availability of scant information on the experimental results of water-backed plates is the primary motivating factor to make analytical estimates. These estimates are provided in comparison with an air-backed plate for identical attack geometry and target parameters. This work aims to bring out a comparative procedure for the damage assessment between air- and water-backed plates so that the response of the latter can be presented in terms of that of the former.

The response of monolithic steel plates subjected to blast was extensively studied, and dozens of dimensionless numbers were proposed to predict the response. While the existing dimensionless numbers are not convenient to use in some scenarios with relatively complicated conditions, the dimensionless number proposed for blast loaded steel plates based on dimensional analysis extends the range of application. Different from other dimensionless numbers, the properties of medium with which the blast load transmits are incorporated to extend the application range to more general scenarios. The responses of the plate subjected to both near-field blast with non-uniform load and far-field blast with uniform load, i.e. both the external and internal blasts (for steel boxes), are reasonably predicted. The physical implication of the proposed dimensionless number is clear in that the media properties, geometrical features, characteristics of material, and loading are incorporated, which are readily available in test. A variety of test data are used to validate the applicability and versatility of the proposed dimensionless number.

Concrete gravity dams are a common form of dams. The dynamic response analysis of concrete gravity dams under the action of underwater explosions is indispensable for survivability assessments. Due to the constraints of the environment and other conditions, an underwater explosion test of a prototype concrete gravity dam is difficult to achieve. The centrifuge scaled-down test that satisfies similarity theory provides a new way to study the dynamic response of underwater explosions on concrete gravity dams. In a near-field explosion, the shock wave of an underwater explosion will cause direct damage to the gravity dam, and the detonation products after the shock wave will aggravate the damage. Under the premise of verifying the concrete dynamic response material parameters and the fluid–solid coupling model of the underwater explosion, numerical calculations of the scaled underwater explosion model of the centrifuge and the prototype underwater explosion were carried out, and the similarity between the scaled dam response model of the underwater explosion centrifuge and the prototype was discussed. The analysis shows that the scaled-down centrifuge model can better reflect the local damage of the prototype dam subjected to shock waves. The difference between the scaled centrifuge model and the prototype model of underwater explosion damage to the dam is concentrated on the overall damage. The damage effect of detonation products on the prototype dam body is mainly concentrated in the middle and lower parts of the dam body, while the damage effect of detonation products on the dam body in the scaled-down model is mainly concentrated in the middle and upper parts of the dam body.

This paper presents some experimental data on roll compaction concrete cofferdam vibration induced by underwater explosion. A formula for the bubble pulse period of underwater explosion is proposed via dimension analysis and compared with Cole formula. An experiential formula is summarized on the relation among the structure vibration velocity, explosive charge and the distance from charge to structure. The formula indicates that the structure vibration velocity is directly proportional to square root of the charge when the charge package was near the structure. When the distance is farther between the charge and the cofferdam, the peak particle velocity (PPV) is smaller.