The present investigation examines the effectiveness of a composite cushion charging structure, placed at the bottom of underwater boreholes, to mitigate bedrock damage induced by blasting excavation during cross-sea engineering. With reference to the embedded open caisson blasting project for a major cross-sea bridge, this research adopted a combined methodology of field sampling and controlled underwater explosion model tests. A piezoelectric ceramic detection system was employed to quantitatively analyze how the composite cushion, composed of iron-sand concrete layers with varying wave impedances, affects rock sample damage. Piezoelectric signals were processed via wavelet packet analysis to calculate the axial damage factor (DI) of the blast hole. Furthermore, by integrating fractal dimension theory with damage mechanics, a quantitative assessment was performed on the propagation behavior of cracks formed on the top surfaces of rock specimens under different test conditions. Results demonstrate that the implemented composite bottom cushion effectively mitigates blast-induced damage by significantly inhibiting macroscopic crack propagation, reducing surface crack density, and decreasing the axial penetration depth of cracks into the rock mass. Detailed analysis of axial damage reveals a clear trend, showing that the reduction in DI becomes more pronounced as the wave impedance of the cushion material increases. Specifically, within the borehole-affected zone (0–12 cm), the maximum achievable reduction in DI reaches 10.70%. At the bottom measurement point, reductions exceeding 90% are observed for the higher-impedance cushion configurations. In conclusion, this work confirms that employing a composite cushion charging structure in underwater drilling and blasting operations can significantly alleviate blast-induced damage to foundational bedrock. The findings also establish that axial damage to the rock mass can be effectively controlled by adjusting the wave impedance of the iron-sand concrete in the cushion layer. These outcomes offer valuable insights for optimizing blasting design and enhancing damage control in marine engineering projects.
To address the challenges of rapid deployment for heavy-duty unmanned platforms and impact protection during drop-landing, a buffer airbag system was designed to ensure the safe landing of the unmanned platform. First, theoretical modeling was used to preliminarily determine the geometric parameters of the buffer airbag and the size of the vent holes. A finite element simulation model that included the buffer airbag, the unmanned platform and the ground was established using the control volume method (CVM) to simulate the cushioning process of the airbag. The impact dynamics response during the landing attenuation process was analyzed, and the specific energy absorption (SEA) of the buffer airbag system was introduced to evaluate its cushioning performance. The analysis results indicate that during the landing buffer process, the unmanned platform reached a maximum overload value of 16.8g at 0.06 s, and the platform velocity reached a post-rebound maximum of 0.79 m/s at 0.1 s. At 0.18 s, the platform shifted laterally due to the center of gravity, and one side of the platform first contacted the ground. This led to fluctuations in overload value and velocity, but the overall landing process remained stable. The calculated SEA of the buffer airbag system was 1527 J/kg. Using the control variable method, the influence of key parameters on the buffer performance of the airbag was analyzed, revealing the effects of vent hole size, critical exhaust pressure, airbag base area and airbag height on the performance of the buffer. The study found that the influence of airbag height on the two key indicators (maximum overload and SEA) was consistent, presenting no optimization conflict. However, after the height exceeded 0.37 m, a diminishing returns effect appeared. When the other three variables were changed individually, they caused a conflict between the goals of minimizing maximum overload and maximizing SEA, making it impossible to improve both simultaneously through independent optimization. To resolve this issue, an optimal latin hypercube design was used for sampling, and a three-layer neural network was employed to construct proxy models for the objective functions. The root mean square error (RMSE) and coefficient of determination (R2) of these two types of proxy models were calculated to evaluate their regression performance. The NSGA-Ⅱ genetic algorithm was integrated for multi-objective optimization. The results showed that for the proxy models predicting maximum overload and SEA, the RMSEs were 0.4895 and 0.7262, and the R2 values were 0.9833 and 0.9364, respectively. All R2 values were greater than the industry benchmark of 0.9, indicating high reliability of the proxy models. When the vent hole area was 3952 mm2, the critical exhaust pressure, the airbag base area were 158 kPa and 1.08 m2, respectively. Meanwhile, the maximum overload was reduced from 16.8g to 14.5g, and the SEA remained stable at 1529 J/kg. Based on the characteristics of the airbag's buffer process, a gantry crane-based simulation test method for unmanned platform airdrop and lifting was designed. A piezoelectric IEPE acceleration sensor was used to measure the overload value of the unmanned platform. Experimental verification showed that the measured maximum overload value was 15.2g, with a mere 4.8% error compared to the simulation result, confirming the correctness of the optimization scheme. This research provides efficient and low-cost design technical support for the soft landing systems of unmanned platforms, enhancing the safety and efficiency of operational deployment.
In complex and sensitive environments, minimizing the disturbance of blasting vibration to surrounding residents is the primary concern during blasting construction. To explore a quantitative evaluation method for human dynamic response to blasting vibration, this study conducted single-subject in-situ blasting tests under strictly controlled safety conditions. By integrating digital image correlation (DIC) with a synchronous electrocardiogram (ECG) measurement system, the dynamic response characteristics of the human body surface under varying blasting vibration intensities were preliminarily analyzed. A height-dependent fitting relationship for peak particle velocity (PPV) was established under the present test conditions, with the body divided into two regions: below the waist and above the waist. Given the safety constraints of in-situ blasting tests, laboratory shake-table tests were also conducted. A comparative analysis using heart rate variability (HRV) evaluation indices was performed to preliminarily demonstrate the feasibility of using a shake table to simulate blasting vibration for human perception studies. The preliminary results indicate that under the present test conditions, the vertical vibration velocity of the human body is significantly higher than the horizontal velocity, with the vertical direction identified as the dominant vibration direction. The vertical vibration velocity exhibits a characteristic pattern of “attenuation below the waist and amplification above the waist”. Compared with the ground surface velocity, the attenuation rate in the lower body region ranges from 55.7% to 65.9%. The vibration velocity in the upper body region is amplified by a factor of 1.25 to 1.74. The horizontal vibration velocity decreases from the feet to the head, with an attenuation rate of 52.6% to 60%. The error in HRV indices obtained from the in-situ and shake-table tests is less than 10%, preliminarily confirming the feasibility of employing a shake table to simulate blasting vibration for human perception research. These exploratory in-situ tests provide a methodological reference for quantifying human vibration response and studying perceived ECG changes due to blasting vibrations.
Efficiently achieving plane wave loading on the test specimen is a key technical issue in the design of blast wave simulators. Based on the existing device, testing data of large-scale shock tubes, and LS-DYNA software, numerical models of blast wave propagation in simulators were established. Numerical simulations were conducted to develop a safe, economical, and reusable blast wave simulator. A quantitative method for assessing the uniformity of overpressure load on the loading area was proposed. Numerical analyses were performed to investigate the influence of the shape and length of the expansion section and the length of the conditioning section on the uniformity of overpressure load on the loading area. Key structural parameters, including the wall thickness of the expansion and conditioning sections, as well as the spacing and height of the stiffeners, were numerically optimized. Validation tests were conducted on the blast wave simulator. It is found that the established numerical model can accurately reproduce the blast wave propagation, and the prediction results show good agreement with the testing data. Taking the errors of overpressure peak value and arrival time as indicators, the quantitative evaluation of overpressure load uniformity on the loading area is achieved. Considering the balance between technical and economic factors, the developed blast wave simulator is designed with a symmetrically configured expansion section 3 m in length. The length of the conditioning section can be extended as much as the actual investment allows. Based on the numerical results, the wall thickness of both the expansion and conditioning sections is determined to be 30 mm. The height and spacing of the stiffeners are both recommended to be 150 mm. The results of validation tests confirm that the geometric and structural design meets the requirements of blast loads and structural resistance, and the developed simulator is suitable for component-level tests.
Addressing the high probability of injury and fatality associated with traditional anti-riot kinetic energy projectiles represented by rubber bullets, a novel low-kinetic-energy frangible projectile with the characteristics of reliable shell fragmentation and the energy release of powder dispersion was designed based on the existing launch platforms of non-lethal weapons, aimed to improve the application safety of anti-riot kinetic energy projectiles. Through shooting tests on anthropomorphic dummy targets and ballistic gelatin targets, the dynamic impact responses of the two targets under the blunt impacts of frangible projectiles were obtained. In the dummy target tests, the frangible projectile achieved reliable fragmentation and exhibited a significant kinetic energy slow-release effect; the calculated injury assessment indicators for different parts of the dummy were all within the safety threshold. Comparative analyses with the blunt impact test results of rubber bullets show that this type of frangible projectile has significantly higher safety than rubber bullets while maintaining effective pain-inducing performance. In the ballistic gelatin target shooting tests, under the same projectile mass and impact velocity, the peak pressure generated in the gelatin measured by the internal sensor differed by approximately one order of magnitude between the frangible projectile and the rubber bullet. The test results show that the novel low-kinetic-energy frangible projectile can effectively attenuate the peak impact pressure of the projectile and greatly reduce its injury potential through the fragmentation of the projectile shell and the dispersion of the powder filled inside the projectile, which provides technical support for improving the application safety of anti-riot kinetic energy ammunition.
