To accurately evaluate the damage degree of the cylindrical shell structure caused by underwater explosion shock wave, the factor of impulse transmission efficiency during the coupling process between the shock wave and the target is considered. The total impulse absorbed by the cylindrical shell under the action of a spherical shock wave is suggested as the power parameter in the damage criterion of the cylindrical shell structure, and an integral calculation method for it is provided. A simplified algorithm without integral is further developed to avoid the complexity of engineering calculation. The accuracy and applicability of the criterion are examined by literature data. The results show that, when compared to the peak pressure criterion, the specific impulse criterion and the energy flux criterion, the absorbed impulse criterion can more accurately compare the damage effects of cylindrical shell targets under different working conditions, it has a stronger correlation with the damage degree, and its corresponding mean square error is reduced by more than 76%. The simplified calculation method for the new criterion approximates the results of the integral calculation, and the relative errors are all within 0.9% for the working conditions. The proposed damage criterion with good accuracy and applicability provides new support for the accurate assessment of the damage effect of the underwater explosion on cylindrical shell structures.

Although the existing methods for surface extended target tracking have the improved estimation performance, they increase the communication costs of target tracking systems. Besides, they can't avoid the influences of intermittent measurements. In order to solve these problems, the components of measurement vectors are divided into different groups according to the measuring methods of extended target information, and a measuring model described by a random matrix is developed. And then a surface extended target tracking model with intermittent measurements is developed by combining the proposed measuring model with the target motion model. Based on the proposed target tracking model, a multi-channel decoupled event-triggered mechanism is proposed to schedule the data transmissions between the sensor and the estimation center. Lastly, an event-triggered surface extended target tracking method is provided based on the cubature Kalman filtering algorithm. Simulated results show that the proposed method can be used to significantly reduce the communication consumptions with preserving estimation performance, and avoid the influences of intermittent measurements.

Submarine hydrodynamic pressure field is an important information source in the ocean battlefield. A simplified modeling method of submarine hydrodynamic pressure field is studied with the potential flow theory, and a Rankine body-based analytic model and a rotary body-based numerical model are both established to estimate the characteristics of submarine hydrodynamic pressure field on the bottom.The influences of submarine shape, dive depth, and other factors on the key parameters, such as peaknegative pressure and negative pressure duration, are analyzed based on validation study. The findings show that, as the submarine advances closer to the seabottom, the influences of submarine shape, dive depth, and other factors on the key characteristics become stronger, the shape of negative pressure area changes from V-shape of single peak to U-shape, or even W-shape of double peaks; for the same dive depth, the duration of negative pressure increases sharply and then decreases slowly with the increase in the speed of submarine. Meanwhile, no matter howlarge or smallthe submarine body is, the key characteristics have decayed at the transverse distance of y≥L, that is, it is difficult for the mines outside this transverse distance to detect the submarine.

The tracking error of the traditional Kalman method is significantly increased or even divergent due to the influence of interference and noise. A neural network-based target tracking method is proposed. The proposed method uses the deep neural network to solve the nonlinear change of target azimuth with time in different motion modes. The neural network model of underwater target tracking can generate a large number of measurement data through the motion model for full training, which effectively solves the problems of insufficient underwater acoustic target data and insufficient labeled samples. A new loss function is proposed to enhance the robustness of target tracking model under the condition of measurement discontinuity. The unlearned simulation data and measured sea trial data were tested. The results show that the convolutional neural network (CNN) is applicable for a target in 3 different motion modes，and can stably track targets when the platform is stationary or moving. Compared with the traditional Kalman filtering method, the tracking error of the neural network model is reduced by 7.75° and 1.41°, respectively, for the unlearned simulation data and the measured sea trial data, which verifies the robustness and scalability of the model.

In order to meet the requirements of underwater launch technology in large deep environment, a new water-driven underwater launch device with two-stage piston is proposed. The launch device is driven by high-pressure water in large deep environment to launch projectiles rapidly. A dynamic model of projectile pulled out of launching tube is established, and the principle verification test using high-pressure water-driven scheme is carried out. And the test data are compared with those of the reference test using high-pressure gas-driven scheme. The results show that the interior trajectories of water- and gas-driven schemes are basically the same. The comparative advantage of the high-pressure water-driven scheme is very obvious in large depth environment. The peak acceleration appears mainly in two moving processes, namely the launching instant and interstage transition between two stage pistons. The acceleration of projectile motion changes sharply in the interstage transition. The trajectory predicted results show that the maximum velocity range is 7.4-15.3 m/s and the maximum acceleration is less than 100 m/s²under the condition of the underwater launching depth of 100-500 m. The results verify the feasibility of the underwater launch device of two-stage piston driven by water pressure, which provides the design basis for the further development of launch device.

The development of unmanned underwater vehicle cluster poses a great challenge to underwater target detection. Aiming at the detection problem of underwater multiple low detectable targets and the need for concealment detection, an underwater multi-target passive detection method based on Hough transform tracking before detection technique was proposed. Firstly, a passive detection model of unmanned underwater vehicle was constructed by using aviation passive sonar buoy array. Secondly, the adaptive correlation cross location technology of multiple passive sonar buoys was used to realize data preprocessing before concealment detection. Finally, the two-threshold randomized Hough transform track-before-detect algorithm was adopted to achieve effective detection of multi-targets with low detectability in high noise density conditions. Simulation results show that this method has good detection performance under the conditions of low signal-to-noise ratio with intersecting point traces of multiple targets.

To ensure robustness against model uncertainties and actuator faults while reducing control energy consumption, this paper proposes a robust adaptive fault-tolerant scheme using the event-triggered input technique for the pitch attitude control of underwater gliders. Based on the backstepping method, the dynamic surface control technique is employed to avoid calulating the derivation of the virtual control law. Model uncertainties, external disturbances, and actuator faults are compensated as a whole using a RBF-NN that takes advantage of historical input and output data. A relative-threshold event-triggered condition is designed to avoid continuous updating of the control law. Finally, the Lyapunov stability theory is used to ensure the SGUUB of the closed-loop signals. The simulation results confirm that the proposed scheme has robust control performance and can better reduce control energy consumption and communication resource occupation.

In order to study the influence of preset rudder angle on the tail-slapping characteristics of a trans-media vehicle during high-speed water entry, a high-speed water entry experiment platform is built. A experimental model with an internal measurement unit is designed, and the high-speed water entry experiment of the trans-media vehicle with different preset rudder angles at the water entry angle of 20° is carried out. A high-speed camera is used to record the cavity during water entry of the vehicle, and the internal measurement unit is used to measure the motion parameters and surface pressure of the vehicle. The influence of preset rudder angle on the characteristics of cavity development and water entry as well as the surface pressure of the trans-media vehicle during high-speed water entry is analyzed. The experimental results show that: during the process of water entry, the trans-media vehicle goes through the stages of planing movement and tail-slapping, and the normal overload formed by tail-slapping can be up to twice of that caused by the planing; when the water entry distance is about 5 times the length of the vehicle, the cavity closes, and the pressure in the cavity decreases first and then increases before and after the cavity closure; when the cavity is closed, the attached cavity is separated from the main cavity as the preset rudder angle increases; when the preset rudder angle is 10°, the wake flow of the cavity shows the phenomenon of double vortex tube; with the increase of the preset rudder angle, the turn-flat ability of the trans-media vehicle is enhanced, and the climbing efficiency of the vehicle is improved when single-sided tail-slapping occurs.

To solve the problem that the trans-media flight vehicle will be subjected to large impact load in the process of entering water, a topology optimization design method for anti-impact structure with of negative Poisson's ratio based on engineering requirements is proposed. A star-quadrangular honeycomb (SQH) structure with negative Poisson's ratio which meets the requirements of impact resistance is obtained by adding the elastic modulus and Poisson's ratio into the objective function of topology optimization design. Based on the theoretical analysis model of SQH structure, the analytical formula of plateau stress under impact load is deduced and verified by numerical simulation. Compared with the specific energy absorption of star-circle honeycomb (SCH) and other negative Poisson's ratio structures, the specific energy absorptions of SQH structure under low-speed, medium-speed and high-speed impact are 28.74%, 45.2% and 7.03% higher than that of SCH structure, respectively. Through the fluid-solid coupling simulation analysis, the designed SQH sandwich structure is studied for load reduction by water- entry impact, and the influence of the main size parameters of SQH sandwich structure on the impact characteristics of water entry is further discussed. The results show that, within the allowable range of size, the increase in the inclination angle and wall thickness of SQH unit will reduce the peak acceleration of the structure and the transformation of kinetic energy into the deformation energy of the structure, which verifies the effectiveness of the negative Poisson's ratio structure topology optimization design for engineering requirements.

Traditional coating layer for underwater vehicles mainly depend on material renewal and structure optimization, which is difficult to cope with low-frequency active sonar detection. A lightweight, thin and low-frequency broadband underwater acoustic emission unit with high pressure resistance is designed based on the giant magnetostrictive material. The design and optimization process of the core components are analyzed emphatically, and the finite element simulation results are verified by the PSV-400 laser vibriometer. The optimal boundary constraints of the active emitting element are determined through the modal analysis of a fixed radiation panel. Compared with the performance of the emission unit in the original configuration, it is found that, under the premise of maintaining good directivity of underwater acoustic emission, the highest resonance frequency below 2 000 Hz is reduced by more than 10% based on the finite element analysis. Based on the acoustic structure coupling analysis, the maximum radiation source level of active emission unit in the low frequency range is 147.48 dB, which is increased by 4.65%. The frequency bandwidth of transmitting unit exceeds 1 500 Hz when the sound source level is higher than 100 dB. This means that there is a higher sound power level in this frequency bandwidth range. The emission unit can provide technical support for the application of array in the large-scale acoustic cladding. It has certain academic research value and broad engineering application prospect.

In order to improve the stealth performance of underwater vehicles, the effects of different turbulence models on the numerical simulation of the underwater vehicle with a cylindrical structure are investigated. Numerical simulations have been carried out by using the open source computational fluid dynamics toolbox called OpenFOAM. Three hybrid turbulence models were developed and embedded in the OpenFOAM toolbox. The three models are the Scale Adaptive Simulation (SAS) method, the Partially Averaged Navier-Storks (PANS) equation method and the Improved Delayed Detach Eddy Simulation (IDDES) method. Based on the developed three models, numerical computations were performed to obtain the distribution of the flow field and force characteristics. The results showed that the turbulence model selection has a significant influence on the hydrodynamic simulation of the underwater vehicle, which may provide guidance for the subsequent research on the stealth technology of underwater vehicles.

As natioans are pursing the concept of “zero casualties”, the unmanned minefield has gradually become the trend of future mine warfare. As a new type of combat force, the development of unmanned systems in the anti-mine field has attracted much attention, which is worthy of further study. Based on the current situation of unmanned mine countermeasure development abroad, the technical characteristics and typical equipment indicators of UUVs, UAV,s and USVs are compared. The key techniques in unmanned mine countermeasure equipment in the fields of energy power, autonomous control, cooperative control, deployment recovery and stealth are described and summarized. The development trend of remote control, universal design, functional expansion and collaborative development are analyzed, and some references for the development of mine countermeasures in China are provided.

To study the damage characteristics of a ship’s double bottom structure subjected to underwater explosion. Experiments on the interaction between the electric spark bubble and the ship’s double bottom structure with a hole are carried out. The pulsation characteristics of the bubble are captured by a high-speed camera, and the experiment is simulated by LS-DYNA to verify the effectiveness of the numerical model. Then, the finite element model of the full-scale cabin is established. By changing the explosion distance and water level between the double bottoms and designing 15 simulation scenarios, the damage characteristics of the double bottom structure subjected to shock wave and bubble loads are analyzed. The results show that: when the explosion distance is small, the outer bottom is broken, and the expansion of the "inner bubble" intensifies the tearing of the outer bottom and causes the plastic deformation of the inner bottom; when the explosion distance is large, the outer bottom only deforms and contacts with the inner bottom, driving the deformation of the inner bottom at the same time; when the water level between the two bottoms is low, the shock wave load attenuation is large with a small damage to the inner bottom, and the expansion of the "inner bubble" plays a major role in the deformation of the inner bottom; when the water level between the two bottoms is high, the shock wave load attenuation is small, the shock wave and bubble pulsation loads propagate through the water medium and act on the inner bottom, whose combined action causes its deformation.

In order to study the characteristics of the shock wave loads induced damage to the gas turbine structure in an underwater explosion, the transfer law of the shock wave loads of the underwater explosion in the main structure of the gas turbine was investigated, and the load transfer prediction was made for the gas turbine through the equivalent mechanical model. For the finite element simulation acceleration signals measured on the transfer path in the gas turbine, the empirical mode decomposition method and the corresponding Hilbert Huang transform were used to analyze the time-frequency domain and energy distribution of the signals. The results showed that: for the underwater explosion induced shock wave loads, the frequency information and load intensity can be obtained by the Hilbert-Huang transform and empirical mode decomposition method; the shock wave energy along the transfer path in the gas turbine varies with the load; as the transfer distance increases, the proportion of high-frequency energy decreases, which corresponds to the stress response of the gas turbine; at the same time, the mechanical model of the gas turbine can predict the load transfer of the gas turbine. The findings of this study could provide insights into the protection of the gas turbine against impact.

To study the underwater blast injury modes and thresholds for human, beagle dogs are adopted for gram-and kilogram-level underwater blast tests. The response of beagles to shock wave and bubble pulsation loadings is observed. Air containing organs such as lung and auditory apparatus suffer the most from the shock wave, bubble pulsation, negative pressure and other loads. Whether the head is above the water or not, the brain will be injured to some extent. Under the same underwater blast loading, the damage radius for a beagle in diving position is approximately 2.5 times that of one in swimming position. From experiments, the injury modes and thresholds for beagles under underwater blast are concluded, which can be used to predict and treat underwater shock injuries.

To deal with the influence of strong nonlinearity, strong coupling, external disturbance and uncertain parameters of underwater vehicle, an attitude decoupling control method based on linear active disturbance rejection control is proposed. The mutual coupling of each control channel of the underwater vehicle and the internal and external disturbances are regarded as the total disturbance, which is estimated by the extended state observer and introduced into the feedback controller for compensation. The original nonlinear system is transformed into a linear system to realize decoupling control. The virtual control quantity is introduced to decouple the coupling caused by the rudder. Based on the control system and the nonlinear dynamic model of the underwater vehicle, the stability analysis is given. The simulation results show that the controller based on linear active disturbance rejection has the characteristics of fast response, small overshoot and steady-state error, and strong robustness. Compared with PID control, the dynamic performance and anti-disturbance ability are greatly improved.

To improve the navigational stability of high-speed amphibious vehicles and reduce the pitch of the amphibious vehicle when encountering waves, a single vector water jet thruster system that can keep heading and adjust attitude is designed and applied to a model amphibious vehicle, as opposed to a multi-thruster configuration. Based on the Moving Reference Frame method for rotational basins, the RNG k-ε model is used to calculate the output thrust of the vectored waterjet thruster. Combined with the thrust results from the CFD calculations, joint vortex simulations are used to calculate the sailing characteristics of the amphibious vehicle fitted with vector water jet thrusters. The free-running heading-keeping experiment and forced-running pitch-reduction experiment are carried out on the towing pool model vehicle to verify the functions of the thruster. The simulation and experiment results show that the thruster can, to a certain extent, reduce the amphibious vehicle's pitch amplitude when encountering longitudinal waves during navigation, and the standard deviation of the vehicle's pitch is reduced by 38% and 23%, respectively, in the two pitch-reduction experiments. The vector water jet thruster also allows the amphibious vehicle to maintain a stable heading during navigation, and the lateral displacement of the vehicle is less than 0.6 m in the heading-keeping experiment.

Laying magnetic sensors on the seabed of the magnetic deperming facility is one of the main ways to measure ships' magnetic field. The position deviation of underwater magnetic sensors directly affects the measurement accuracy and evaluation of protection ability of ships' magnetic field. To address the problem that the existing methods are difficult to accurately locate the underwater magnetic sensors of the deperming station, a position correction method of underwater magnetic sensors of the deperming station based on multi-population particle swarm optimization (PSO) using dynamic learning strategies is proposed. Firstly, the energized current-carrying coil is equivalent to a magnetic dipole magnetic source, and then the relative position between the magnetic source and the magnetic sensor is changed by the linear multi-measurement method to obtain the magnetic field measurement data of the multiple groups of magnetic sensors. Based on this, the position correction model of underwater magnetic sensors is established, and the position deviation vector is optimized by the multi-population PSO algorithm using dynamic learning strategies, thus realizing the high-precision correction of the position of the underwater magnetic sensors. Based on the comprehensive analysis of the main influencing factors such as the equivalent error of the magnetic dipole, the numerical simulation and physical scale model experiment are designed. The results show that: this method can effectively solve the problem of position correction of underwater magnetic sensors in the deperming station; after correction, the position errors in x,y and z directions are less than 0.1m; the magnetic field measurement accuracy of the deperming station after correction can meet the requirements of ships' magnetic field measurement. This method can complete the correction of the underwater magnetic sensors with a position deviation of no more than 0.3m, and has good practical value.

To deal with the problem of low accuracy of the elementary highlight model in forecasting the acoustic scattering characteristics of underwater vehicles, a highlight model which can reflect the real lines and fine acousitcscattering characteristics of underwater vehicles is established.The linear interpolation algorithm and object segmentation method are used to establish the parametric highlight model of the command station and stern, and the planar elements method is adopted to verify the results.On this basis, the acoustic scattering characteristics of the Benchmark submarine model including the command station and stern are studied and compared with the standard solution of the BASIS method.The target strength experiment results of the Benchmark submarine scale model are obtained through acoustic scattering experiments of the model on lake, and then compared with the method of highlight model.The results show that the proposed model is accurate.Considering the spatial phase information of each component, the highlight model can forecast the acoustic scattering characteristics of underwater vehicles well.The findings of this study can provide insights into the fast prediction of acoustic scattering of underwater targets and have broad application prospects in the fast time-domain echo forecasting.

To investigate the damage characteristics of the near-field explosion shock wave load and bubble load on the typical cylindrical shell structure of a scaled-down torpedo, the ALE method was conducted and the effects of explosion distance and charge position on the deformation and damage characteristics of the cylindrical shell structure were explored. The validity of the numerical simulation method was verified by comparing it with the experimental results of the evolution process of the explosion bubble near the wall. The interaction between the explosion bubble and the cylindrical shell was studied under different explosion distances and charge positions, and the damage mechanism of different forms of load such the shock wave, bubble pulsation, and water jet on the cylindrical shell structure was analyzed in detail. The results showed that the damage effect of the shock wave on the cylindrical shell structure is strongly influenced by explosion distance; the increase of explosion distance sharply weakens the damage caused by the shock wave on the cylindrical shell, while the charge position of the cylindrical shell has a weaker effect on the damage of the shock wave; the damage to the cylindrical shell is significantly influenced by charge position; when the charge is arranged below the cylindrical shell, the shell generated the maximum plastic strain under the combined effects of bubble pulsation and water jet.