水下无人系统学报

2024, 32(3): 383-383.

[Abstract](47) [FullText HTML] (40) [PDF 213KB](28)

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Research Progress of Cutting-Edge Technologies of Trans-Medium Vehicle Dynamics

WANG Cong, XU Haiyu, MA Guihui, SUN Longquan

2024, 32(3): 384-395. doi: 10.11993/j.issn.2096-3920.2024-0060

[Abstract](735) [FullText HTML] (137) [PDF 2436KB](203)

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In recent years, trans-medium equipment has received wide attention in the fields of ship and ocean, aerospace, and weapons. The overall scheme, key technologies, research methods, and operational efficiency related to trans-medium vehicles have become research hotspots. This paper briefly elaborated on the research background of trans-medium vehicle dynamics and reviewed the latest research achievements and progress in terms of water-entry slamming of vehicles, fluid-structure coupling during water entry and exit, trans-medium biomimetics, trans-medium power and propulsion, new trans-medium equipment, and trans-medium dynamics tests and simulation technologies. Finally, the key cutting-edge technologies that needed to be solved in the development of trans-medium vehicles were pointed out, so as to provide a reference for promoting the research on sea-air interface dynamics and unmanned systems.

Research of Trans-Medium Strategy for Unmanned Aerial-Undersea Vehicles

LIU Kun, LIU Yongqiang, LIN Hao, XIAO Junhao, PENG Hui, LU Xingju, LU Huimin

2024, 32(3): 396-410. doi: 10.11993/j.issn.2096-3920.2024-0038

[Abstract](772) [FullText HTML] (96) [PDF 6517KB](179)

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Unmanned aerial-undersea vehicles(UAUVs), with broad application prospects in both military and civilian fields, have gradually become a research hotspot in the field of robotics in recent years. UAUVs were taken as the research object in this study, and the development status of the bionic, multirotor, fixed-wing, and hybrid UAUV prototypes were discussed. In addition, the water-entry/exit strategies of the prototypes were reviewed. The important issues faced in the research on UAUVs were summarized, including the optimal design of bionic configuration, stability control during the trans-medium process, and propulsion selection, providing a reference for the subsequent research and development of trans-medium vehicles.

Review of the Development on Load Reduction Methods for Water Entry of High-Speed Vehicles

ZHENG Wei, LI Qiang, FAN Xudong, LÜ Xujian

2024, 32(3): 411-425. doi: 10.11993/j.issn.2096-3920.2024-0029

[Abstract](641) [FullText HTML] (96) [PDF 10625KB](139)

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The water entry process of high-speed vehicles involves complex fluid-structure interaction between multiple phase flows and vehicles, which can result in transient impact loads and potential structural damage. In this paper, a brief description of the high-speed water entry impact problem for vehicles is provided, with a focus on the current development of active and passive load reduction methods for vehicles. Additionally, the paper provides a summary of the advantages and disadvantages of common methods for reducing water entry loads, and elucidates the key research directions for reducing water entry loads of vehicles, aiming to provide a reference for further study on the characteristics of water entry loads and the load reduction methods of vehicles at high speeds.

Impact Load Characteristics of Large-Scale Trans-Medium Vehicles during High-Speed Oblique Water Entry

ZHANG Tongyun, WANG Cong, XU Haiyu, XIA Weixue, MA Xiaojian, ZHAO Jing

2024, 32(3): 426-433. doi: 10.11993/j.issn.2096-3920.2024-0021

[Abstract](411) [FullText HTML] (38) [PDF 1841KB](63)

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To investigate the impact load characteristics of large-scale trans-medium vehicles during high-speed oblique water entry, a three-dimensional unsteady numerical calculation model of high-speed oblique water entry of the trans-medium vehicles was established based on the volume of fluid (VOF) multiphase flow model and the S-DOF rigid body motion mode. The calculation accuracy of the numerical calculation model was checked and verified by using the free motion test data of the slender objects during high-speed water entry, and the impact load characteristics of the vehicles with flat heads and conical heads during high-speed oblique water entry were compared. The results show that the occurrence time of the maximum axial and longitudinal impact loads of the vehicle with a conical head is almost synchronous, while the maximum axial impact load of the vehicle with a flat head is significantly delayed compared with the longitudinal load. For the maximum impact load, the axial impact load of the vehicle with a flat head is greater than its longitudinal impact load, while the axial and longitudinal impact loads of the vehicle with a conical head are almost the same. Compared to that of the vehicle with a flat head, the axial impact load of the vehicle with a conical head is significantly reduced, and the maximum peak value is about 1/3 of that of the vehicle with a flat head when the water entry angle is 45°.

Flow Field and Motion Characteristics of Trans-Medium Submersible during Take-off and Landing on Water Surface

LU Deshun, ZHANG Shaoqian, WANG Haoyu, SUN Tiezhi

2024, 32(3): 434-450. doi: 10.11993/j.issn.2096-3920.2024-0042

[Abstract](386) [FullText HTML] (54) [PDF 7328KB](76)

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In order to explore the evolution of the flow field structure and motion characteristics of the trans-medium submersible during the take-off and landing on water surface, the volume of fluid(VOF) multiphase flow model, the shear stress transfer(SST) k-ω turbulence model, the Schnerr-Sauer cavitation model, and the Stokes fifth-order nonlinear wave theory were coupled to construct a numerical calculation method for the submersible during take-off and landing on water surface based on the numerical simulation technology of computational fluid dynamic(CFD). The take-off of the submersible on water surface in the static water environment, as well as its landing on water surface in the presence or absence of the wave was numerically simulated. The dynamic response, load change of the submersible, and the evolution of the flow field on free liquid surface in each process were analyzed. The results show that the submersible can maintain a stable attitude during the whole take-off process on water surface in a static water environment, and the flow field structure and free liquid surface evolution around it have strong symmetry. In the process of landing on water surface, the bottom of the submersible and the fairing are subjected to a large reverse attack force, making the submersible fluctuate to a certain extent, but it can quickly restore the steady state after several attenuation fluctuations. The existence of the wave will increase the attack load applied to the submersible at the moment of touching the water, aggravate the attitude fluctuation of the submersible, and delay the final recovery time of the attitude.

Comparison of High-Speed Water Entry Movement Process of Axisymmetric Bodies with Different Head Shapes

WANG Yu, XIONG Yongliang, TIAN Xuanhui, ZHOU Fuchang, LIU Ao, SUN Guocang

2024, 32(3): 451-462. doi: 10.11993/j.issn.2096-3920.2024-0028

[Abstract](339) [FullText HTML] (87) [PDF 7106KB](62)

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High-speed water entry of the trans-medium axisymmetric body is an instantaneous flow process, involving the complex multiphase flow of the axisymmetric body with the gas and liquid phases. In this paper, a numerical model of cavity dynamics after water entry was established based on Reynolds-averaged Navier-Stokes equations and a multiphase flow model of natural cavitation. The movement characteristics and hydrodynamic force effects of axisymmetric bodies with different head shapes during vertical water entry were studied. The effectiveness of the model and the numerical method was verified by comparing the numerical simulation results with the experimental results in related literature. The results show that the cavity characteristics and the movement speed laws of axisymmetric bodies with different head shapes after water entry are highly different. The corresponding transient drag coefficients also show great differences. The re-entrant jet effect is evident before the cavity is closed, and it affects the cavity shape and resistance of the axisymmetric body. The water entry speed of the axisymmetric body has a direct impact on the cavity size and impact load. When the water entry speed is small, the speed of the axisymmetric body decays relatively faster, and its drag coefficient is relatively larger.

Numerical Simulation of Water Entry Process of Trans-Medium Vehicles

LIU Pingan, GAO Hongtao, YANG Yanxi, HUANG Xi, GAO Song, JI Zhentao

2024, 32(3): 463-473. doi: 10.11993/j.issn.2096-3920.2024-0023

[Abstract](395) [FullText HTML] (56) [PDF 4018KB](88)

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The trans-medium water entry process of vehicles is often accompanied by multiphase flow, cavitation, phase change, and turbulence instability, which not only heighten the complexity of the flow field, but also render the forces highly unsteady and nonlinear. A numerical model for the water entry process of vehicles was developed. The volume of fluid(VOF) model was employed to capture the gas-liquid interface, and the Schnerr-Sauer model was utilized to describe the cavitation that occurred during the trans-medium process. The simulation of the water entry process of the trans-medium vehicle under different ventilation flows and deflection angles of the cavitator was carried out to investigate the flow field and cavity evolution laws during the trans-medium process. In addition, the fluid dynamics characteristics, as well as the kinematic characteristics of the vehicle during trans-medium process were analyzed. The simulation results show that the vehicle will present two different attitude change modes with the change of the ventilation flow during the water entry process: the increasing angular velocity leveling mode and the periodical pitching-type leveling mode. The water entry leveling process of the vehicle in different modes will show different motion characteristics. Moreover, an increase in the deflection angle of the cavitator and a decrease in the ventilation flow can improve the attitude change rate of the vehicle during the trans-medium water entry process.

Influence of Water Entry Speed on Oblique Water Entry Process of a Cylinder under Ice Hole Constraint

LU Lin, YANG Zhe, CHEN Kaimin, CHENG Yongdong, YANG Shuai

2024, 32(3): 474-481. doi: 10.11993/j.issn.2096-3920.2024-0027

[Abstract](338) [FullText HTML] (66) [PDF 4432KB](58)

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For the water entry problem of supercavitating cylinders in polar environments, a numerical simulation method for the water entry of the cylinder under ice hole constraint was established based on the Reynolds time-averaged Navier-Stokes equations, volume of fluid model, and overlapping mesh technique. On this basis, the simulation of the water entry process of the cylinder through the ice hole at different water entry speeds was carried out, and the cavity evolution and load characteristics of the cylinder in the water entry process were analyzed. The results show that ice hole constraint restricts the flow of water inside the ice hole, which in turn alters the surface splashing and the shape of the cavity wall, thus delaying the surface closing of the cavity. The limiting effect of the ice hole constraint on the cavity shape is essentially the same as the water entry speed increases. The cylinder head appears to have a larger area of high pressure, showing an asymmetric distribution. In addition, the ice hole constraint increases the water entry impact load of the cylinder, which accelerates the underwater speed decay of the cylinder and contributes to a larger deflection angle of the cylinder than in the ice-free condition. The research results can provide some reference for the water entry stability of polar supercavitating weapons.

Simulation of Water Entry Jet and Cavitation Characteristics of Hollow Projectiles

XIANG Junbang, WANG Xiaoguang, KANG Huifeng, XUAN Jialin, YANG Liu

2024, 32(3): 482-488. doi: 10.11993/j.issn.2096-3920.2023-0163

[Abstract](362) [FullText HTML] (83) [PDF 1525KB](61)

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In the water entry process of hollow projectiles, the formation of high-speed water jets is a crucial factor influencing their water entry. In order to study the influence of the through-hole aperture of hollow projectiles on jet and water entry characteristics, a vertical water entry simulation model for hollow projectiles with different apertures was established, and the intra-hole pressure characteristics and the difference in cavity development among projectiles with different apertures were compared. The results show that the aperture ratio is related to the intensity of intra-hole pressure at the moment of initial collision. The height and velocity of the jet decrease with an increase in the aperture ratio, which is related to the intra-hole pressure gradient. Additionally, the intensity of the pressure gradient diminishes as the aperture ratio increases. This study briefly describes the development of the cavitation phenomenon in hollow projectiles and analyzes the influence of the aperture ratio on the cavitation phenomenon. The results indicate that as the aperture ratio increases, the amount of vapor produced by the projectile decreases, leading to an earlier closing of the cavity.

Experimental Investigation on Cavity Characteristics during Water Entry of Disc-Headed Vehicle Assisted by Gas Jet Flow

ZHEN Zikun, ZOU Zhihui, JIANG Yunhua

2024, 32(3): 489-495. doi: 10.11993/j.issn.2096-3920.2024-0041

[Abstract](307) [FullText HTML] (61) [PDF 1656KB](47)

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The trans-medium vehicle is expected to quickly and stably break the free liquid surface. In addition, there are some problems in the trans-medium process, such as the damage to structures and instruments caused by the high impact load, cavity collapse, and ballistic trajectory instability caused by complex unsteady multiphase flow. To address these issues, a forward jet flow was provided at the head of the vehicle to make the vehicle quickly and stably break the free liquid surface. The jet flow penetrated and changed the flow field structure of the free liquid surface to reduce the high impact load. To investigate the multiphase flow characteristics of the cavity during water entry of the disc-headed vehicle assisted by gas jet, the water entry experiment of the disc-headed vehicle assisted by forward jet flow was carried out. The cavity morphology formed during water entry was analyzed, as well as the formation and evolution process of the broken cavity in the case of a gas jet flow impinging on the liquid surface. The effects of different ventilation nozzle diameters and ventilation flow rates on the cavity diameter and jet flow length were discussed. The experimental results indicate that the formation process of the broken cavity includes four stages, namely liquid surface depression, liquid surface oscillation, liquid flow, and cavity formation. The diameter and depth of the broken cavity decrease with the increase in ventilation nozzle diameter and increase with the increase in ventilation flow rate.

Numerical Calculation of Water Exit Process of Supercavitating Vehicles under Different Sailing Conditions

CHU Yue, LIU Pingan, HUANG Xi, GAO Song, JI Zhentao, ZHOU Xiaohu

2024, 32(3): 496-506. doi: 10.11993/j.issn.2096-3920.2024-0017

[Abstract](339) [FullText HTML] (68) [PDF 2464KB](56)

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The water exit process of vehicles is very complicated, accompanied by multiphase flow, cavitation, phase transition, and turbulence instability, and the applied force is highly unsteady and nonlinear. At present, studies on the water exit problem of the vehicle with cavitation focus on the vertical or oblique water exit, emphasizing the trajectory and attitude of the vehicle. There are few studies on the water exit process of the supercavitating vehicle. In this paper, based on STAR-CCM+ software, overlapping grid technology was used for meshing, and the volume of fluid(VOF) model was used to capture the gas-liquid interface. The Schnerr-Sauer model described the cavitation process around the vehicle, and a numerical calculation model of the water exit process of the vehicle was established. The water exit process of the vehicle under different sailing conditions(initial velocity, initial water depth, and ventilation) was simulated and calculated, and the flow field and cavity evolution laws under different conditions were obtained. The hydrodynamic and kinematic characteristics of the supercavitating vehicle were analyzed. The simulation results show that the underwater motion of the vehicle with different initial velocities presents two different modes. Under different water depths, the initial cavity number is different. Cavity around the vehicle is more likely to rupture in deeper waters. The cavity morphology can be improved effectively by increasing the ventilation.

Numerical Research on Evolution of Vertical Water-Exit Cavity of Vehicle under Ice Hole Constraint

WANG Hao, HUANG Zhengui, CHEN Zhihua, GUO Zeqing, WANG Yihang, LIU Xiangyan, NA Xiaodong

2024, 32(3): 507-515. doi: 10.11993/j.issn.2096-3920.2024-0020

[Abstract](244) [FullText HTML] (42) [PDF 2353KB](42)

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In high-latitude areas, the icing period is inevitable during winter. In view of the special mechanical environment of ice cracks faced during underwater launching in low-temperature ice zones, it is of great engineering value to expand the application of submarine-launched marine equipment in a low-temperature ice zone. The presence of floating ice inevitably enhances the nonlinearity of submarine-launched vehicles during high-speed water exit. A 6-degree-of-freedom(DOF) motion model of the vehicle was built by using the dynamic fluid interaction module(DFBI). Through comparative analysis of the underwater and cross-water motion stages of the submarine-launched vehicle under different ice hole sizes and shapes, the influence of ice holes on the evolution of the water-exit cavity was explored. The findings indicate that the ice hole has an obvious binding effect on the cavity during the process of water exit, and the binding effect increases with the decrease in ice hole size. For the same shape of the ice hole, a smaller ice hole size is accompanied by a greater impact on the pitching motion characteristics of the vehicle. For the same ice hole size, the circular ice hole has a greater impact on the pitching motion characteristics of the vehicle than square and triangular ice holes.

Numerical Simulation of Flow Field Characteristics of Supersonic Jet in Natural Cavitating Tail Cavity

CAO Yue, YU Jianyang, WANG Sihang, LÜ Lingyun, CHEN Fu

2024, 32(3): 516-524. doi: 10.11993/j.issn.2096-3920.2024-0059

[Abstract](233) [FullText HTML] (26) [PDF 3968KB](36)

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In order to reveal the evolution law of the supersonic flow field in the natural cavitating tail cavity and the flow field structure in the cavity, this paper simulated the flow field of the supersonic jet in the natural cavitating tail cavity based on the volume of fluid (VOF) multiphase flow model. The paper compared the distribution of the flow field parameters in the cavity under different cavitation number and different angles of attack of incident flow, and drew the following conclusions: The cavity shape of the natural cavitating tail cavity is relatively stable after the incident flow of the supersonic jet, and its evolution is mainly concentrated in the closure of the cavity tail. The development of the flow field of the supersonic jet in the cavity is mainly affected by the re-entrant jet. When there is no angle of attack of incident flow, the flow field is impacted by the re-entrant jet, and the axial development of the jet is suppressed. The axial jet appears retracted phenomenon. When there is an angle of attack of the incident flow, the position of the re-entrant jet has shifted, and the shear and suction effect is dominant. The axial development of the jet is rapid, and the stability of the attitude of the vehicle is mainly affected by the impact of the incident flow and the distribution of the surface high-pressure area. When the cavitation number is small, increasing the angle of attack of the incident flow can greatly increase the pitching moment of the vehicle.

Characteristics of Underwater Trajectory of Trans-Medium Vehicles

SHI Zelin, CHU Yue, HUANG Xi, GAO Song, JI Zhentao, LIU Pingan

2024, 32(3): 525-534. doi: 10.11993/j.issn.2096-3920.2024-0022

[Abstract](233) [FullText HTML] (55) [PDF 2139KB](59)

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In order to study the underwater trajectory and related dynamics characteristics of trans-medium vehicles, a trans-medium vehicle was used as the research object. The dynamics equations were established based on the momentum theorem and the moment of momentum theorem, and the dynamics characteristics of the trans-medium vehicle at different velocities and cavitator’s angles were analyzed. The results show that increasing the initial velocity will slightly reduce the horizontal navigation distance and navigation depth of the vehicle, and the velocity will decrease faster; increasing the cavitator’s angle will also lead to a slight decrease in the horizontal navigation distance and navigation depth of the vehicle. Reducing the initial angle has a significant impact on the horizontal navigation distance of the vehicle and the angle at the end of the calculation, but it almost does not affect the acceleration and force characteristics.

Comparative Analysis of Power Propulsion System Configurations of Air-Water Trans-Medium Torpedoes

LUO Kai, QIN Kan, HUANG Chuang, FENG Qixi, LI Daijin, DANG Jianjun

2024, 32(3): 535-541. doi: 10.11993/j.issn.2096-3920.2024-0018

[Abstract](322) [FullText HTML] (51) [PDF 895KB](82)

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At present, the trans-medium torpedoes equipped by foreign military forces are all composed of booster carriers and torpedo warheads. The air-water reusable power propulsion system can integrate the carrier and torpedo into one, which can achieve larger effective underwater attack payloads, long range, and lower life cycle costs, and it has the potential to develop multiple water-entry and exit functions. The air-water reusable power propulsion system is modified based on the conventional torpedo power system, making it capable of air propulsion and multi-mode switching. In this paper, three possible configurations of air-water reusable power propulsion systems were discussed in terms of operating principles, system performance, fuel selection, system control, research and development difficulties, and development potential. It is believed that for light trans-medium torpedoes, the configuration with the single OTTO-II fuel can be used, while for heavy torpedoes, the configuration with kerosene and OTTO-II dual-fuel and dual-combustion chamber system is preferred.

Influence of Different Water Depths on Gas Jet of Underwater Scarfed Nozzle

QI Ziyu, LI Haokun, ZHANG Yigan, LIU Huaping, YE Yonghao

2024, 32(3): 542-551. doi: 10.11993/j.issn.2096-3920.2024-0030

[Abstract](314) [FullText HTML] (55) [PDF 3961KB](40)

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Thrust vector control by scarfed nozzle jet can realize attitude control and trajectory adjustment of the undersea vehicle and improve the maneuvering performance and stability of the undersea vehicle. In order to investigate the working state of the underwater scarfed nozzle, the Reynolds time-averaged Navier-Stokes(RANS) method and the volume of fluid(VOF) model were used, and simulation of the flow field characteristics and thrust characteristics of the gas jet of the scarfed nozzle under different water depth conditions was carried out. The interaction between the gas jet and the water, as well as the change in the thrust characteristics of the nozzle were analyzed. The results show that the gas bubble forms a gas pocket at the top and a conical gas channel in the near field of the nozzle after four stages of development. The edges of the gas pocket detach under the action of the shear vortex to form a gas cluster. The shape and position of the nozzle wave system vary with the water depth, and the jet boundary is limited by the gas bubble boundary. They interact with each other, leading to the unstable evolution of the jet. The influence of the jet on the wall of the flat plate is asymmetric, with the long side being more affected than the short side. At the same moment, greater water depth indicates a smaller value of the nozzle thrust and more violent fluctuation along the thrust direction. The conclusions can provide a reference for the application of underwater thrust vector nozzles.

Underwater Target Recognition Based on Dynamic Ensemble of Random Forest

CAO Tao, DENG Jianjing, YUE Ling, LI Yongsheng

2024, 32(3): 552-557. doi: 10.11993/j.issn.2096-3920.2024-0054

[Abstract](167) [FullText HTML] (29) [PDF 1180KB](48)

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Accurate recognition of the target is the key to attacking enemy for underwater acoustic homing weapon. A real-time target recognition method for underwater acoustic homing weapon was proposed based on dynamic ensemble selection technology. The statistical features of energy distribution and spatial distribution were extracted from the output of target wideband correlation detection by using the different reflection characteristics of the target irradiated by the active wideband detection waveform of the underwater acoustic homing weapon. In addition, a dynamic ensemble model based on a random forest was constructed, and it was trained and tested on the marine dataset. The simulation analysis shows that the dynamic ensemble model proposed in this paper has better recognition effects than other classification models and can be applied to target recognition by underwater acoustic homing weapon.

Study on Reaction Kinetics Parameters and Combustion Phenomena of Li/SF₆

WU Haoqi, LUO Zhengyuan, BAI Bofeng

2024, 32(3): 558-564. doi: 10.11993/j.issn.2096-3920.2023-0108

[Abstract](182) [FullText HTML] (79) [PDF 2435KB](39)

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In order to investigate the combustion phenomenon and reaction kinetics parameters of Li/SF₆ under different temperature and pressure conditions, the Li/SF₆ combustion test platform with shock wave-induced high pressure thermal load excitation was used to measure the ignition delay period at the temperature of 830~1 400 K and the pressure range of 0.8~11 atm. The laws of Li/SF₆ combustion process and basic luminescence phenomena were investigated by the visual experiment section. Based on the typical Arrhenius dependence between ignition delay period and temperature and pressure, the reaction kinetics parameters were obtained by multiple linear regression method. The results show that the ignition delay period of Li/SF₆ combustion decreases with the increase in temperature and pressure, and the luminescence phenomenon gradually changes from a red isolated fire nucleus to a white bright flame with the increase in pressure. The pre-index factor A, exponential factor N, and activation energy E_a are obtained based on the experimentally measured ignition delay period, which provides an important basis for the identification of combustion characteristics and the construction of numerical simulation.

Research on Temperature Adaptability of Special Buffer Oil Cylinders

DAI Shaoyuan, LI Kaifu, CHEN Junfeng, DUAN Hao

2024, 32(3): 565-571. doi: 10.11993/j.issn.2096-3920.2023-0105

[Abstract](133) [FullText HTML] (39) [PDF 2926KB](17)

Abstract:
During the research on vibration and noise reduction of underwater weapons, it was found that the special buffer oil cylinder, as an important transmission component, is one of the main sources of noise. Therefore, the design of the buffer device for the special buffer oil cylinder is important, and the prediction of the buffer effect is the core of the buffer design. Due to the special working conditions, special buffer oil cylinders are mostly in standby mode. When a startup is started after a long interval, the hydraulic oil temperature in the buffer chamber is equal to the installation environment temperature. There will be a large temperature difference in the hydraulic oil in the buffer chamber between the first startup and subsequent startups. In order to ensure that the working requirements can be met even under extreme temperature conditions, temperature adaptability research needs to be conducted on the special buffer oil cylinders. Firstly, a mathematical model of the motion process of a special oil cylinder was established. Under extreme oil temperatures of 10±2 °C and 40±2 °C and oil supply pressure of 7.5±0.2 MPa, the flow field was numerically simulated using Fluent. Then, temperature adaptability tests were conducted in a large temperature box, and the full stroke motion time, vibration acceleration level, and other parameters of the special buffer oil cylinders were tested under two extreme temperature conditions. Finally, it was found through comparison that the experimental results were similar to the theoretical analysis and met the corresponding indicator requirements, which can provide a reference for the design and vibration and noise reduction of special buffer oil cylinders in the future.

Development Characteristics of Underwater Detonation Gas Jets in Confined Space

XU Zhiqian, KANG Yang, LI Ning, HUANG Xiaolong, LI Can, WENG Chunsheng

2024, 32(3): 572-581. doi: 10.11993/j.issn.2096-3920.2023-0104

[Abstract](231) [FullText HTML] (73) [PDF 2976KB](33)

Abstract:
To explore the development characteristics of gas jets generated by pulsed detonation water ramjet engines working underwater in water deflectors, numerical simulations and experimental validations were conducted on underwater detonation gas jets generated by detonation tube within a cylindrical confined space by utilizing the detonation of combustible gases to generate pulsating bubbles in the underwater confined space. A flow field model of a single gas jet in an underwater confined space was established based on the Reynolds-averaged equations, the k-ε two-equation model, and the gas-liquid interface tracking method of the volume of fluid(VOF) coupled with the phase transportation equation. The Compressible Inter Foam solver in OpenFOAM was employed for numerically solving pulsed detonation gas jets in the confined space. The results show that the influence of confined space on the leading shock wave of underwater detonation is slight, and the amplitude of the leading shock wave changes insignificantly compared to that in free underwater space. However, the pressure disturbance caused by the detonation gas jet significantly increases, and its duration is prolonged. Additionally, it leads to a noticeable increase in pressure within the confined space compared to that outside the confined space. The pulsation period of bubbles in the confined space is extended to approximately 60 ms, and the radial dimension of the confined space has little effect on the fluctuation period of the bubbles. Therefore, it can be seen that confined space can increase the near-field pressure at the outlet of the underwater detonation tube and extend the action time of the gas jet. The research results are of important guiding significance for the study of thrust performance improvement methods for pulsed detonation water ramjet engines.

Application of Fault Diagnosis and Prediction Techniques in Unmanned Undersea Systems

CHENG Wenxin, XIAO Ankang

2024, 32(3): 582-590. doi: 10.11993/j.issn.2096-3920.2024-0064

[Abstract](197) [FullText HTML] (66) [PDF 789KB](63)

Abstract:
As an integrated organic entity, unmanned undersea systems become more prone to faults as their level of integration increases and their structures get more complex. Consequently, the associated risks and potential losses escalate. In view of this, this paper reviewed the research status of fault diagnosis and prediction methods in China and abroad, providing an overview of their application in the field of unmanned undersea systems. At the same time, the future development trend of fault diagnosis and prediction technologies was analyzed, so as to provide a reference for improving the reliability and safety of unmanned undersea systems.

2024 Vol. 32, No. 3

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