The traditional acceleration sensor detection method has the problems of signal oscillation aliasing, serious sticking and difficult accurately to count the layers when the penetrators penetrate multi-layer buildings. An accurate layer counting method for penetration based on the magnetic anomaly detection (MAD) is proposed. The steel bars in the buildings will influence the distribution of the surrounding geomagnetic field. When the fuze penetrates a target with the warhead, the magnetic sensor is used to detect the magnetic anomaly signal (MAS) generated by the geomagnetic field distortion around the floors, so as to complete the state identification of penetration. The magnetic field simulation models of a multi-layer reinforced concrete target and a projectile penetrating multi-layer target are established. The distribution characteristics of magnetic field around the floors and the variation law of magnetic field intensity of fuze during penetration are obtained. The effects of oblique penetration, steel bar density and projectile material on the magnetic signal changes during penetration are analyzed. It is found that there is a clear corresponding relationship between the amplitude of magnetic signal and the position of floors during penetration, and the signal characteristics are obvious. The lower relative permeability of projectile material and the higher density of steel bars in the target are more conducive to the signal processing of magnetic detection. Finally, a MAD experiment is designed and carried out in the laboratory. The experimentl results show that the MAS is clear and easy to be distinguished during penetration, and the principle is proved to be feasible.
In order to explore the dynamic response of a convex reinforced conical-cylindrical shell under the combined action of hydrostatic pressure and deep-underwater explosion load, the hydrostatic pressure load and cone angle factors are added on the plastic string model, and the problem is simplified to resolve the wave equation with initial value and boundary conditions. The radial displacement of the intercostal shell is expressed as an infinite series by using the expansion of eigenvalue, and the corresponding unloading time is calculated for each eigenvalue, so as to show the attenuation characteristics of shock wave load. The finite element program Abaqus is used to carry out a numerical simulation study of underwater explosion with a maximum depth of 500m and a maximum impact factor of 0.79kg^{0.5}/m for a convex stiffened cylindrical shell with a half-cone angle of 20°. The results of theoretical model calculation of cylindrical and cone intercostal shells adjacent to the joint are verified, compared and discussed. The results show that, compared with that without hydrostatic pressure, the hydrostatic pressure decreases the stiffness of intercostal shells, which delays the maximum displacement, and the final radial displacement increases with water depth. Under different impact factors, the ultimate radial displacement error between the theoretical model and the numerical simulation is 21.7% (cone section) and 2.0% (column section), respectively. At the same time, due to the presence of cone angle, the shell displacements are no longer symmetrically distributed about the center point, and the final displacement of the center point is reduced by more than 40% compared with the column segment.
In order to solve the problem of poor closure of liner mouth at the edge in the integrated multiple explosively formed projectile (MEFP) warhead, an eccentric liner with different wall thickness along the circumferential direction is designed. The liner is applied to a D-shaped charge structure warhead. The effects of the thick-side orientation and eccentricity of liner on liner forming are studied through theoretical analysis and numerical simulation. The soft recovery experiment of explosively formedprojectile(EFP) was carried out. The results show that the thick-side orientation and eccentricity of eccentric liner have little effect on the velocity of EFP in each direction, but have a great influence on the EFP forming effect. The forming effect is best when the thick-side of liner is oriented to the center of the warhead. The size of eccentricity can adjust the speed difference of the micro element around the liner to the center, and improve the wrapping situation of liner mouth. And the test result of EFP is in good agreement with the simulated result. The eccentric liner can optimize the formation of EFP under oblique detonation by adjusting the matching relationship between the thickness of liner and detonation intensity. It can effectively solve the problem of poor shape of liner when the MEFP warhead with D-shaped charge structure is located at the edge. It provides reference for the structure design of liner at the edge of the integrated MEFP warhead.
Ship gun is one of the main weapons for attacking the targetsat sea, air and shore, and the penetration ability of semi-armor-piercing projectile for ship gun is an important index of evaluating its damage ability. Carrying out live-ship firing test is costly and lack of opportunities. In order to study the penetration ability of naval gun semi-armor-piercing projectile, a semi-armor-piercing simulation projectile is designed by referring to OTO Melara 127mm ammunition used by US MK-45 naval gun. On the basis of experiment, numerical simulation and empirical formula, the damage mode and crevasse size of target plate are analyzed. The experimental results show that, under the two plate inclination angles of 45° and 60° and two target velocities of 385m/s and 500m/s, the semi-armor-piercing simulation projectile has sufficient penetration ability to 12mm thick E36 steel plate, and the damage mode of simulation projectile to target plate is a thrust destruction. The average size of the crevasse is 1.25times the diameter of the projectile. The simulated results show that the calculated results including the residual velocity and breach are reasonably agreed with the experimental results.The calculated results of Thor’s formula are relatively close to the experimental results.After parameter optimization, the residual velocity error obtained by the experiment, empirical formula and simulation does not exceed 10%.
The causes and manifestations of non-uniform spatial-temporal distribution of overpressure peak of explosion shock wave are discussed from the characteristics of non-ideal detonation wave and the formation mechanism of explosion shock wave, which are verified by experimental images and data. Four kinds of 2kg explosives and a 250kg aluminized explosive were detonated to investigate the non-uniform distribution characteristics of shock wave overpressure, and the deviation among the overpressure peaks with the same distance to charge were analyzed. The results show that the higher the non-ideal level of explosive componentsis, the greater the charge mass is, and the closer it is to the charge, the more obvious the non-even characteristics of the overpressure peak are. A method to define the number of test points to meet the accuracy demand for the overpressure is proposed based on the analysis of the experimental data. It is suggested that the blast field should be divided into four areas with scale distances of less than 1.5m/kg^{1/3}, 1.5~3.0m/kg^{1/3}, 3~5m/kg^{1/3} and more than 5m/kg^{1/3}. The corresponding optimal number of measuring points is 6, 5, 4 and 2,respectively.
The influence mechanism of ethylene on the detonation initiation characteristics of coal powder/oxygen mixture is studied to realize the reliable ignition of the coal powder continuous rotating detonation engine. At the initial pressure of 100kPa, an electric ignition with high energy is used to carry out the direct detonation initiation experiments on the coal powder/oxygen mixture with and without the ethylene. The ignition energy is calculated by measuring the pressure of explosive wave produced via a high-energy electric spark in air. The coal powder/oxygen mixture cannot detonate without ethylene under the action of effective ignition energy of 6.3J. In this energy, if the ethylene with the equivalence ratio of 0.5 is added, the coal powder/oxygen mixture can be successfully initiated. If the effective ignition energy is reduced to 3.6J to made it be lower thanthe critical initiation energy of ethylene/oxygen mixture with an equivalent ratio of 0.5. the detonationcould be onset after adding coal powder. The above studies show that a certain amount of detonable gas (such as ethylene) needs to be added for the dirct detonation initiation of coal powder/oxygen mixture. On the other hand, the addition of coal powder can also broaden the detonation limit of ethylene/oxygen mixture. The results of this study can provide theoretical basis and technical support for the ignition of coal continuous rotating detonation engine.
The pyrotechnic separation device may bring the risk of exposure to a target due to its excessive actuation noise in its application in underwater weapon. Combined with the finite element and boundary element method, a numerical model is established to predict the actuation noise of pyrotechnical separation nut, which realizes the visualization of transient radiated noise during the separation process. The validity of the numerical model is verified by experiments.The source and generation mechanism of actuation noise are analyzed, and the noise source is quantitatively decoupled by calculating the sound power based on the test and simulation model. The results show that, in the frequency band of 10~6000Hz, the contribution of the impact of inner sleeve is about 50%, and the contribution of the impact of nut flap is about 23%. The contribution of combustion noise is less than 1%, but in the low-frequency band below 400Hz, the contribution of combustion noise is more significant, about 22%.
Eddy current asymmetry and transonic aerodynamic transition usually occure at a large angle-of-attack during the cross-domain flight process of guided missile, which may cause control instability and further increase miss distance. To solve the problems above, a missile roll channel dyanamics model is established, in which the strong nonlinearity of aerodynamic model, strong parameter uncertainty and strong external disturbance, and then an “observer+controller” composite control framework is proposed. This roll stabilization control framework contains a novel sliding mode disturbance observer and nonsingular terminal sliding mode. Based on this framework, a backstepping controller is proposed to compensate actuator dynamics. The stability and finite-time convergence properties of closed-loop system are verified through Lyapunov theory. Finally,the numerically simulated results demonstrate the superiority and universality of the proposed control method.
An adaptive control scheme is proposed for the position tracking control of a chain rotary magazine with parameter uncertainties and external disturbances. Based on neuro-fuzzy system ( NFS), nonlinear disturbance observer (NDO), and barrier Lyapunov function (BLF), the proposed scheme achieves high precision control while satisfying the engineering conditions of output constraint and input saturation. The BLF design ensures that the position tracking error of magazine is constrained within a bounded range. The function approximation ability of neural network and the reasoning ability of fuzzy logic system are combined to estimate the uncertainties of the system and reduce the dependence on the model. The combined NFS is used as part of NDO to further compensate for estimation errors and external disturbances and improve the control performance. In addition, the actuator input saturation problem is considered in the design of the controller. The simulated results show that the designed controller can realize the high-precision position tracking control of the magazine under three typical working conditions and system parameter changes, and meet the constraints of the system.
The rapid cooperative trajectory planning problem of glide-guided projectiles under multiple constraint conditions, such as time-spatial coordination, in single-gun multi-shot application scenarios is investigated An improved SCP strategy is proposed to balance the conflict between rapidity and optimality in sequential convex programming (SCP) method. Considering the small feasible region and high sensitivity to initial values under multiple constraints, two fast and effective iterative initial value generation schemes are designed. Aiming to fully exploit the overall control capability of projectile group, a centralized cooperative planning strategy is employed to solve all equation sets simultaneously. Simulated results demonstrate that the proposed method can effectively address the cooperative planning problem under multiple constraints, exhibiting good convergence performance and high computational efficiency.
The damage evaluation of anti-tank missile is a process throughout the entire life cycle of a missile development including design, production, testing and operational use. Both developers and users are highly concerned about the scientificness of damage evaluation method and the accuracy of evaluated results. The traditional damage evaluation method of anti-tank missile is oversimplified and does not reflect the correct functional damage as a whole. A state space-ased damage evaluation method is propoced. This method generates a functional damage evaluation matrix by mathmatically analyzing the interaction between missile and target and studying firing sensitivity and damage lethality. It can be used accurately to evaluate the declination of multiple tank functionalities under various possible encounter conditions. Simulated results verify that the derived functional damage evaluation matrix based on the new method can be used precisely to evaluate the damage effectiveness of anti-tank missile. This state space-based method can also be used to support the damage study of other anti-armoured weapon.
The transition and flow separation dominated by vorticity will occur, which have a significant impact on the maneuverability and control ability of missile, when a missile launches an all-aspect attack. The particle image velocimetry (PIV) and fluorescent oil flow visualization experiments are carried out in the FD-12 wind tunnel for a slender body in order to explore the influences of angle of attack and Mach number on the flow pattern in the leeward region of slender body.The characteristics of the flow field in the leeward region of slender body were obtained at the angles of attack α from 0° from180° with Ma=0.4/0.6/0.8. The results show that the flow in the leeward region of the model changes from attached flow to separation flow, and the separation vortex vary from symmetry to asymmetry when the angle of attack is <90°. The unsteady vortex shedding phenomenon exists in the leeward region and the time-averaged flow field has an obvious asymmetry characteristic at 100° and 120° angles of attack. The separation zone of windward face begins to appear asymmetric offset for α=150°. The lower boundary of initial separation zone crosses the end face of the model, forming a separation line in the rear of the model. When the angle of attack changes to 180°, there is an obvious ring-shaped separation zone and re-attachment zone at the upwind face and no obvious separation zone at the rear of the model. The results indicate that the flow field presents complex unsteady and nonlinear flow states due to the influence of bottom. In addition, the increase of the Mach not only enlarge the influence range of separation vortex, but also promote the position of separation vortex at the same angle of attack.
The shape design of the supercavitating vehicle is related to its tail-slap motion characteristics. In order to obtain the influence of the cone part of supercavitating vehicle on its tail-slap motion, the dynamic grid technology combined with the VOF multiphase flow model,SST k-ω turbulence model and Schnerr-Sauer cavitation model are applied to simulate the tail-slap motion of supercavitating vehicle with the four different cone parts. The tail-slap motion and trajectory characteristics of supercavitating vehicle are analyzed. The results show that the influence of the cone geometry on the tail-slap stability of supercavitating vehicle is nonlinear under the condition of a certain pitch angle speed. If the cone section is too long or too short, the shoulder of supercavitating vehicle will get wet and form secondary cavitation. The development of secondary cavitation can inhibit the tail wet, which causes the turning moment failing to reduce the pitching angle and then the tail-slap motion and the trajectory showing instability.
In order to solve the problem of anti-damage protection of ships under attack by anti-ship weapons,the dynamic response process characteristics of Y-shaped sandwich panel structure under different blast distances are analyzed by means of small cabin model experiment and finite element numerical analysis. Seven deformation modes of Y-shaped sandwich panel structure are summarized. It is found that the deformation mode of the panel is related to the blast distance and the relative strength of the rigidity of the panel and its connecting core, When the explosion distance is small, the panel is prone to local bulge deformation. If the blasting distance is large, it is prone to overall dish deformation or plate lattice deformation. If the core layer is strong and the panel is weak, the panel is prone to plate lattice deformation. If the core layer is strong and the panel is weak, it is prone to overall dish deformation. If the rigidity of the blast facing panel and the V core layer is large, the overall dish deformation of the back blast face panel occurs. Three typical deformation conditions of the Y core layer under the explosion load in the cabin are summarized, namely V buckling I instability V buckling I is constant, V is constant and I is constant; The influence of the thickness of the panel on the blasting surface, the thickness of the v-core layer and the thickness of the I-core layer on the anti-explosion performance of the Y-shaped sandwich panel structure is investigated. It is found that increasing the thickness of the panel on the blasting surface and the thickness of the I-core layer can significantly reduce the deformation of the back plate, but increasing the thickness of the panel on the blasting surface will reduce the total energy absorption of the structure, while increasing the thickness of the I-core layer will basically keep the total energy absorption of the structure unchanged. Increasing the thickness of the v-core layer, the energy absorption of the v-core layer will sharply decrease, and the maximum deformation, The total energy absorption of the structure decreases.
The low-speed roll missile seeker has a serious blurring feature in image collection due to its motion characteristics such as dithering and rotating,which directly affects the accuracy of subsequent image algorithms for target recognition,thus affecting the guidance accuracy.To solve the above problems,a blind deblurring algorithm based on a generative adversarial network is proposed. The motion blurring simulation system is used to simulate the motion blurring such as jitter and rotation of missile-borne image,and a fuzzy dataset of missile-borne image is made.The convolution neural network is used as the basic architecture of generator and discriminator,and several loss functions are designed to optimize the network together to reduce the noise and keep the image smooth during image restoration.The de-blurring of missile-borne image is achieved,and a more stable and clear image sequence is obtained.The experimental results show that the proposed algorithm performs better in peak signal-to-noise ratio and structural similarity than other algorithms and achieves state-of-the-art performance,and accords with the subjective perception of human vision.It has practical application value.
As a high-energy density explosive, the blast damage effect and mechanism of thermobaric explosive are different from traditional explosives. First of all, the characteristics and propagation law of thermobaric explosive blast shock wave are studied through the open space thermobaric explosive blast shock wave and thermal effect test. High-speed camera technology and fiber optic multispectral line temperature measurement technology are used to analyze the evolution characteristics of explosive fireball and the fireball surface temperature change pattern. Secondly, in order to study the destructive effect of the blast loads of thermobaric explosives on reinforced concrete structures, two typical reinforced concrete beams were subjected to explosion tests with different proportional blast distances. The damage characteristics and laws of two kinds of reinforced concrete (RC) beams with different charges and distances were elucidated. The research results show that, compared to TNT, the blast shock wave of thermobaric explosive has a large overpressure peak, long positive pressure action time and slow decay of peak characteristics, the thermobaric explosive blast temperature reaches up to 2400K, more than 1000K high temperature duration is more than 160ms, and the high impulse blast impact and sustained high temperature action lead to a greater degree of damage to reinforced concrete structures. Combining the effect of charges on the pattern of destruction, a damage criterion based on the proportional scaled distance and the amount of charge is proposed for reinforced concrete beams under the close-in (0.2-0.75m) blast loading of thermobaric explosives.
In view of the serious potential safety problems of waste propellants, five microorganisms that can reduce the nitrogen content of nitrocellulose (NC) are obtained by sampling, enriching, domesticating, separating and purificating near and around the wastewater treatment tank of nitrocellulose production. The time optimization experiment was carried out on the chaetomium elatum which has the best denitrification effect among them. It is found that the nitrogen content of NC could be reduced from 13.06% to 10.83% over time, and the X-ray photoelectron spectroscopy(XPS) results show that the content of N element on the surface of NC gradually decreases. Fourier Transform infrared spectroscopy (FT-IR), inVia Raman microscope (Raman) and gel permeation chromatography (GPC) are used to characterize the structure and molecular weight of NC. The infrared spectrum shows that the —OH peak intensity of NC at about 3400cm^{-1} is gradually increased because the hydrolysis of chaetomium elatum and O—NO_{2} occurs and the Raman spectrum shows that the intensity of NC energetic groups (O—NO_{2}) decreases significantly. At the same time, it is found by GPC that the number-average molecular weight and weight-average molecular weight of NC could be reduced by 2.34% and 6.40%, respectively, due to chaetomium elatum. In order to further determine the biological enzymes acting on NC, the separation of extracellular enzymes and intracellular enzymes, and ammonium sulfate gradient precipitation experiments proved that the extracellular enzymes precipitated by 0-30% (NH_{4})_{2}SO_{4} could effectively reduce the nitrogen content of NC. The significant effect of chaetomium elatum on reducing the nitrogen content of NC makes it have broad application prospects in the reuse of waste military NC and the biological denitrification of propellants.
Thermal dispersion is an abnormal phenomenon of bullet dispersion after continuous firing of a small-caliber automatic rifle. It has an important influence on the shooting accuracy and combat effectiveness of the hot gun, but the formation mechanism of thermal disperison is not completely clear. Through the comparison experiment of hot and cold guns, it is found that, in the hot gun state, the barrel transfers heat to the copper bullet jacket, then the temperature of the jacket increases to soften the material, and the interaction between the bullet and the barrel greatly increases the deflection angle of bullet velocity and the swing angle of bullet axis, which is the main reason of thermal dispersion. A thermal dispersion analysis and calculation strategy for a typical small-caliber automatic rifle is proposed based on the thermal dispersion mechanism obtained from the experiment. Hot gun state barrel temperature field and stress field analysis model, bullet-barrel interaction thermos-mechanical coupling calculation model and random exterior ballistic and bullet dispersion calculation model are established by using the method of segmental modeling and parameter transfer, which realizes the quantitative analysis and calculation of the firing dispersion in hot gun state. The calculated results are basically consistent with the experimental results. The research in this paper provides an effective calculation method for the quantitative analysis of thermal dispersion problem of small-caliber automatic rifles.
In the battlefield environment, the perception system of unmanned vehicle is susceptible to the influence of weather such as smoke and dust. The ability to detect and track key objects is greatly reduced under harsh weather conditions, resulting in serious consequences, such as object miss-detection, object misdetection and object missing. To address this problem, a fusion system of MMW radar and infrared camera is developed. The object-level fusion method is adopted to establish simple and effective fusion rules, extract and combine the dominant information from each sensor, and finally output stable objective perception results. The objects of MMW radar are checked and extracted. And an improved DBSCAN clustering algorithm is proposed to reduce the noise of MMW radar. The MobileNetv2 backbone network is introduced based on the YOLOv4 network. In the process of network training, the transfer learning method is used to expand the infrared data samples, which solves the problem of fewer training samples of infrared images. The experimental results show that the fusion algorithm has significantly better accuracy and high real-time performance in the smoke environment compared with the algorithm based on infrared camera only, which realizes the object detection and tracking of the fusion of MMW radar and infrared camera in the smoke environment, and improves the anti-interference ability of the object detection and tracking system of unmanned vehicles.
A tracked vehicle driving cycle considering road features is established to effectively evaluate the fuel economy of the vehicle powertrain. The operating data of vehicle on paved road, gravel road and undulating dirt road are collected as original data, and the data are filtered by wavelet analysis. Based on the processed vehicle data, the typical driving cycles under the condition of the three road surfaces are constructed by using principal component analysis, K-means clustering and Markov chain, and the similarity analysis of the constructed driving cycle is carried out. The research results show that the proposed method can be used to effectively construct the driving cycle that resembles the operating characteristics of military tracked vehicles, and the characteristics of the driving cycles under the condition of the three road surfaces have high similarity with the original data, the root mean square errors of the joint vehicle speed-acceleration probability distribution with the original data for the three road surfaces are 0.0356, 0.0039 and 0.0196, respectively, so the driving cycle constructed in this paper can effectively reflect the real operation of tracked vehicles.
In order to improve the accuracy of the steering control system of electric tracked vehicle and the sensitivity of vehicle steering, a steering control strategy is studied, and a dynamic analysis is made on a dual-motor coupling drive electric tracked vehicle. A steering dynamics model of electric tracked vehicle is established based on Mathematical simulation software. Then a steering control strategy based on PID parameter optimization of particle swarm optimization algorithm is designed. The improved ITAE index is used as the objective function of particle swarm optimization algorithm to optimize the control parameters in the PID steering control strategy in real time, and the control parameters are dynamically adjusted to realize the optimal output of vehicle steering control system. Finally, the hardware-in-the-loop simulation platform and real vehicle test are used to verify the control strategy. The test results shows that the steering control strategy is effective.
The interaction between wheels and snow soil is the basis of vehicle safety in plateau, polar and other environments. In order to construct a dynamic wheel-snow interaction model accurately characterizing the contact characteristics between wheels and snow soil, a simulation model of plate sinkage was established to obtain the pressure sinkage relationship of typical snow soil. Based on hard snow soil, a numerical simulation model of wheel-snow interaction was established to simulate the interfacial force of wheels and snow. The results of plate sinkage test and vehicle test were used to verify the validity of the numerical model. Based on the average contact stress, an analytical model of the interfacial force between wheels and snow was established, and the simulation results were used to verify the analytical model. The results show that: 1) the numerical simulation model of plate sinkage in the semi-infinite region can reflect the pressure sinkage characteristics of snow soil, and the simulation results of wheel snow interaction have a good agreement with the actual wheel sinkage and motion resistance coefficient. 2) The simulation results show that when the wheel slip rate is positive, the relationship between wheel load and wheel sinkage and the interfacial force of wheel snow tend to be stable. When the wheel slip rate is negative, the wheel sinkage becomes larger, which leads to the increase of the normal stress part of vertical support force and motion resistance. 3) When the wheel slip rate is positive, the analytical model of wheely-snow interaction can accurately predict the interfacial force of wheely-snow.
Military target recognition technology used in complex battlefield environment is the basis and key to improve the battlefield intelligence acquisition capability. A PB-YOLO military target recognition algorithm based on the improved YOLOv5 model is proposed to solve the problems of high missed and false detection rates and poor real-time performance of current military target recognition technology in complex battlefield environments. The improved target recognition algorithm is re-clustered for the identification anchor boxes of military units in the land battlefield to improve the model’s fitness for target size and accelerate the convergence of model, and the channel-spatial parallel attention mechanism is used to increase the model’s attention to the feature information and location information of the targets in complex battlefield environments. BiFPN is used in the feature fusion network part to improve the fusion ability and speed of the model for features, and the Alpha_IoU loss function is used to accelerate the convergence of model, and solve the problem of IoU calculation degradation when the real frame and the predicted frame overlap. The experimental results show that,compared with the mainstream target recognition algorithm, the mAP value obtained by the improved algorithm reaches 90.17% while ensuring the model space complexity under the self-built military target data set., Through the comparison of ablation experiments, the results show that, compared with the original model, the accuracy of the improved network is improved by 11.57%, and it has better recognition performance, which can provide effective technical support for battlefield intelligence acquisition.
Mastering the magnetic field distribution of ship is an important prerequisite for implementing the ship magnetic protection technology. Using the integral equation method to calculate the three-dimensional static magnetic field of the ship is one of the effective means.The integral equation method usually establishes the equation sets with the magnetization or magnetic flux density in the discrete elements as quantity to be calculated, and therefore obtains the solution of entire field based on the source region values. To further improve the calculated accuracy of magnetic field, it is necessary to increase the grid density at the cost of a sharp increase in computer memory requirement and computation. An integral equation method with scalar magnetic potential as quantity to be solved is used to address this problem. The ferromagnetic source is divided into tetrahedral elements, the unknown function is expanded in pieces according to the variational principle, and the singular integrals are found based on the relative positions of elements and nodes. The singular integrals are transformed into non-singular integrals by parameter substitution. The spherical analytical model shows that the modeling method using scalar magnetic potential only needs to discretize the source region into coarse grid cells to obtain the high-accuracycalculation results ofmagnetic field. After grids encryption, the scalar modeling method can maintain the computational accuracy, while its memory requirement and CPU execution time are significantly lower than those of vector modeling method. A virtual verification experiment is made for the three-dimensional ship magnetic field. For ferromagnetic objects such as ship hulls that need to be finely divided into elements, the static magnetic field calculated by the integral equation method based on the scalar magnetic potential agrees well with the results calculated by the finite element commercial software, and the integral equation methodis more efficient and save memory compared with the vector modeling method.
The navies of all countries have been attached to the research on the shock characteristics of shipboard equipment’s supporting element. However, the implementation of the impact strength tests for large load supporting element become a problem because of the load requirement going beyond the capacity of the test devices. The test methods for the impact strength of large load FRP support element of a power equipment are presented based on the non-contact underwater explosion and the shock environmental parameters of standard floating shock platform(FSP). The test devices are designed by means of ensuring the shock load, reducing the test load mass and improving the system installatrion frequency under the low speed impact condition. The test conditions are designed by means of calculating the shock factors based on the shock spectrum and the shock load requirement. Furthermore, the reduction factor between the actual test and the design factors is obtained from the influence of the several joint surfaces in the testing system on the shock load transfer. The results show that the deviation between the test load and the required load is less than 5%. The method provides a reference for the similar test in the future.
Stab-proof clothing can effectively protect life safety in terrorist attacks, medical problems, breaking the law and committing crimes and other incidents, but the mechanical creases of tab-proof clothing are easily produced in production and wearing. Based on the demand for rapid detection of crease defects of protective materials, a small sample-driven feature segmented neural network structure is proposed innovatively in the image recognition method, and the rapid and accurate detection of crease defects is realized. By introducing the attention mechanism and the depth-separable convolution module and giving the loss function and the optimizer two typical parameters, the detection accuracy and efficiency of the feature segmented neural network are improved comprehensively. A geometric information annotation algorithm is proposed and a visual detection platform is built for defect detection of protective materials, realizing the automatic and accurate location of mechanical creases and the output of geometric information. The results show that the accuracy of the model can reach 96.19%, and the annotation error of geometric information is less than 2%. The excellent visual detection function can be extended to the field of large-scale engineering automatic detection. The research work lays a foundation for constructing a protective performance prediction model of the stab-proof equipment with crease defects.
A multi-feature-based composite model particle filter algorithm is proposed to improve the accuracy and robustness of sound source location in reverberation and noise environment. In this algorithm, the likelihood function of the particle filter is constructed based on the multiple features of signal received by a microphone, where the depth features of multiple hypothesis time-delay estimated image are extracted by convolutional neural network (CNN), and a time-delay estimation model based on support vector regression (SVR) is established. Furthermore, the deficiency that single feature can’t suppress noise and reverberation simultaneously is remedied by introducing the beam output energy fusion mechanism. For the randomness of speaker motion, a composite model for sound source tracking is established to improve the robustness of speaker tracking system. The simulated and experimental results show that, based on the composite model, the position average root mean square error (RMSE) of multi-feature algorithm is reduced by more than 83% compared with that of steered response power and time delay estimation (SRPTDE) algorithm, and under multi-feature observation, the position average RMSE of composite model is reduced by more than 46% compared with that of Langevin model and the random walking model. The proposed algorithm realizes the effective tracking of random moving sound sources in complex environment.
Analytical calculation method for the analysis of equipment availability has the advantage of direct deduction process and accurate prediction of results, but it has been rarely reported due to the complexity of modeling process. Current availability analysis is mostly based on stochastic process or simulation methods. Considering preventive maintenance and condition-based maintenance, an analytical calculation method is proposed to calculate the operational availability and instantaneous availability of equipment, of which life is assumed to follow normal distribution. A simulation method is also constructed to determine the operational availability and instantaneous availability by simulating the working and maintenance process of the equipment. The analytical and simulation methods agree well with each other by comparing the availabilities of equipment with several set of different life distribution parameters. The proposed analytical method could provide support for the evaluation and optimization of preventive maintenance and condition-based maintenance schemes for equipment with normal life distribution.
The fault diagnosability evaluation can quantify the difficulty of diagnosing faults. A temporal distance measurement method based on dynamic time warping (DTW) is proposed to solve the problems of unobjectivity and inappropriate selection of measurement methods in the fault diagnosability evaluation methods. A diagnosability evaluation model is defined, and four elements of system structure, signal, test and failure mode can be extracted from an actual system, which lays the foundation for the subsequent diagnosability evaluation work. The traditional method of extracting the features from signals for similarity measure is abandoned, and the signals are regarded as time series. Based on the DTW method, the degree of similarity between signals in different states is measured as the evaluation basis for fault diagnosability. Momentum wheel system is used to simulate the proposed method. The experimental results show that the proposed method is objective and effective in diagnostic evaluation.
The supply support of wartime maintenance equipment is highly complex, random and dynamic, which leads to the uncertainty and fuzziness in the evaluation of wartime maintenance equipment supply support. A support ability evaluation indicator system is constructed based on the supply support tasks and processes of wartime maintenance equipment. An analytic hierarchy process (AHP) and a fuzzy comprehensive evaluation (FCE) method based on cloud model (CM) are proposed to objectively evaluate the supply support ability of wartime maintenance equipment. An indicator weight is obtained by using the cloud model to scale and aggregate the judgment matrix, which reduces the subjectivity and randomness of weight calculation.A membership matrix is obtained by using the cloud model to describe the evaluation matrix. The evaluated results show that the indicator system can well reflect the effect of wartime maintenance equipment supply support, and the improved comprehensive evaluation method can effectively solve the high fuzziness and uncertainty in the evaluation of wartime maintenance equipment supply support ability, and improve the robustness and objectivity of the evaluated results.