Abstract:To explore the overall structural reliability of hypersonic vehicles and its influencing factors, and ensure the structural safety of the vehicles when performing missions, a new subdomain subinterval method for analyzing the structural strength reliability of hypersonic vehicles is proposed by combining the stress-strength interference model with the interval number. Firstly, the moment of each force surface of a hypersonic vehicle under different flight conditions is analyzed. Secondly, the vehicles structure is approximated as an equivalent cantilever beam, considering the uncertainties of its moment, width and height, which are expressed as interval numbers. Then, considering the degradation of the structural strength over time, a non-probabilistic reliability analysis is carried out based on the stress-strength interference model, and a dynamic reliability model of the vehicles structure is established. Finally, a new sub-domain sub-interval method is proposed to analyze the exponential degradation characteristics of the structural strength and the impacts of the flight dynamics on the structural reliability. The simulation results show that the subdomain subinterval method is more accurate than the traditional Monte Carlo method with the same number of sampling points, which verifies the feasibility and validity of the proposed method. The reliability of the vehicle decreases gradually with the exponential degradation of the structural strength of the vehicle. In addition, the flight dynamics of the vehicle has a major impact on the structural reliability, in which the reliability of the vehicle increases with the increase of the height of flight, and decreases with the increase of the velocity as well as the angle of attack.

Abstract:Grasping is mainly divided into grasping detection, trajectory planning, and execution. Accurate grasping detection is the key to completing grasping tasks. In order to achieve more accurate grasping detection and improve the performance of robot grasping, this paper proposes a grasping detection algorithm that integrates attention and multi-task learning based on key point detection algorithm. Firstly, a coordinate attention (CA) attention module is introduced in the feature extraction process to explicitly learn channel and spatial features and make full use of feature information. Secondly, a multi-task weight learning algorithm is added to the loss function to learn the optimal weights of the grasp center coordinates, gripper opening width, and rotation angle information. Finally, experiments are conducted on the Cornell dataset and the larger-scale Jacquard dataset. The results show that the proposed method has a significant improvement in detection speed compared to classical methods such as sliding windows and anchor box types, and has higher accuracy compared to simple key point detection methods. The proposed model achieves accuracy rates of 98.8% and 95.7% on the two datasets, respectively. Grasping examples show that the proposed model also has good grasping results for unconventional objects, and the model has excellent performance in accurate grasping under different Jaccard coefficient conditions. Moreover, the experiments with different initial values of the weight learning algorithm show that the proposed model has good robustness. In addition, the impact of different modules on the performance of the model is analyzed through ablation experiments.

Abstract:To improve the target capture speed of the guided projectile under the condition of large landing angle and reduce the angle deviation of the starting point of the terminal guidance, considering the terminal guidance section, a trajectory programming method considering multiple constraints of the seeker (TPM-CS) is proposed based on the traditional guided projectile trajectory programming method (TPM). The starting point constraint of the terminal guidance is established according to the maximum detection distance of the seeker, and the attack path constraint is established according to the geometric relationship between the projectile and the target as well as the angle of view of the seeker. Additionally, an objective function of minimizing the amplitude of leading angle and the amplitude of control variables is established. In order to achieve the best matching of parameters such as the initial trajectory inclination angle, deflection angle, rocket ignition time, gliding start-up time and seeker opening time of the guided projectile, a five-phases trajectory programming model is established, and the multi-phases Radau pseudo-spectrum method is used to transform the trajectory programming problem into a nonlinear programming problem. Finally, the nonlinear programming solver SNOPT is used to solve the problem. The seeker with different constrains parameters is selected for simulation, and the effect of the maximum detection range of the seeker and the angle of view of the seeker on the trajectory of the scheme are analyzed. The method proposed in this paper is compared with the traditional trajectory programming method for simulation. The simulation results show that compared with the traditional method, the initial angle deviation of the terminal guidance of the proposed trajectory programming scheme is reduced by 71.590%, and the time for the seeker to keep the target illuminated is prolonged by 6.120 times, which verifies the effectiveness and superiority of the proposed trajectory programming method.

Abstract:To solve the problem of poor communication performance of traditional multi-user dual-function radar communication system due to carrier allocation and improve the resource utilization rate of dual-function radar communication system, a multi-user power allocation scheme based on the communication user carrier sharing model is proposed, and the system has better communication performance by constructing a reasonable resource allocation problem. Firstly, the model of communication user carrier sharing signal in dual-function radar communication system is established. Secondly, in order to ensure the performance of the dual-function radar communication system, an optimization problem is constructed to maximize the system communication and rate and satisfy the constraints of radar signal-to-noise ratio lower bound, total power and user power. The feasibility of the optimization problem is strictly proved through theoretical analysis. Finally, in order to solve the convex optimization problem, a multi-user power allocation algorithm is proposed, which firstly introduces auxiliary variables to convert the objective function twice, decomposes it into two optimization sub-problems, which are then solved by alternate iteration. The results show that compared with the traditional user carrier allocation model, the communication rate of the optimized user carrier sharing model are increased by about 40%, which verifies that the proposed scheme has better communication performance and effectively improves the utilization rate of system resources. The research results of this paper provide a new idea and means for improving the communication performance of multi-user dual-function radar communication system.

Abstract:In order to improve the problems of strong subjectivity and weak logic correlation in current evaluation research, taking a certain type of launch platform as the object, this research constructed an evaluation system of invulnerability from three aspects: evaluation index system, evaluation method and evaluation grade criterion. PSR framework theory is adopted to construct an evaluation index system with causal logical correlation. In view of the large number of indicators, a screening method of evaluation index system was proposed based on the theoretical node number of complex heterogeneous network and k-means algorithm. Based on the mutual information theory and limit damage quantification, the index weighting method and index quantification method are proposed. In addition, the PSR framework theory is improved through the dimensional analysis, and the invulnerability evaluation method of DA-PSR is constructed. Furthermore the evaluation grade criterion method is proposed based on operational mission requirement. The results show that by selecting a simplified evaluation index system with the median value of the remaining nodes accounting for 52.990% of the total median value and the center value of the remaining cluster accounting for 90.550% of the total cluster center value, the invulnerability value of the launch platform can be evaluated to be 0.737, and the evaluation grades of the launch platform under different combat missions show the difference of "excellent, medium and medium" respectively. The evaluation method of invulnerability DA-PSR has low subjectivity and strong logical relevance, which is helpful to improve the credibility of evaluation results.

Abstract:To overcome the characteristic of “backhoe”, reduce the burden of pilots control, and improve the accuracy and safety of carrier landing, the direct lift control method with the characteristics of quick response and high accuracy, is introduced into the carrier landing control law. A two-level integrated landing controller is designed with the combination of prescribed performance nonlinear dynamic inversion and control allocation algorithm, which considers the decoupling not only between longitudinal trajectory control and attitude control but (also) between horizontal control and longitudinal motion. Firstly, the 6-DoF nonlinear model of aircraft is established. Then the dynamic inverse loop is connected with the control allocation loop organically by setting the intermediate virtual control vector. Meanwhile, the control performance of the dynamic inverse control loop is improved by prescribing the error vector constraint equation. Finally, the simulation results show that the designed direct lift controller can adjust the vertical path while keeping the angle of attack and flight speed stable, and allow the aircraft keep the altitude while aligning with the center line. This study indicates that the designed direct lift control system can achieve a one-by-one correspondence between pilot maneuvers and control variables, improve the efficiency of trajectory control in carrier landing, and greatly reduce the burden of pilot.

Abstract:To solve the problem that the adaptive adjustment ability of robotic compliant constant force grinding is insufficient due to the complex time-varying nonlinear coupling and uncertainty disturbance in the industrial robot grinding process, a robotic force-controlled end-effector is presented, which can decouple the translational and rotational motions about the axial direction and the axis of the end-effector. An active disturbance rejection controller and a variable impedance controller with particle swarm optimization and BP neural network are designed as the inner loop control and the outer loop control respectively. Moreover, a robotic active compliance constant force control method with the adaptive variable impedance is proposed to obtain the online adaptive optimization of impedance parameters and the dynamic adjustment of grinding force correction, and to realize the adaptive and active compliance constant force control for robotic grinding. The closed-loop stability of the proposed method is guaranteed by the Lyapunov stability theory. The effectiveness of the proposed method is verified by the co-simulation experiments on the virtual prototype platform of robotic grinding system and the physical experiment on the robotic experimental platform. The experimental results show that the proposed method can better realize the static and dynamic desired force tracking of the robotic grinding, reduce the grinding force fluctuation, force overshoot and the impact force of the grinding tool in the early stage of robotic grinding, improve the anti-disturbance stability, the constant force tracking performance and dynamic response ability of the robotic grinding force control system, and provide strong adaptability and robustness to handle the impact for the complicated and various working conditions of the robotic grinding.

Abstract:The purpose of this study is to analyze the dynamic characteristics of cracked blades of aero-engines, improve the reliability of aero-engines and minimize the occurance of catastrophic accidents. This study is based on the strain energy release rate and Castiglianos theorem, combined with Timoshenko beam theory, a new stress intensity factor and flexibility matrix of the cracked beam element is derived, considering the effect of the angles of the slant crack. According to the stress change of the cracked surface during vibration, a method is proposed for calculating time-varying stiffness of the cracked beam element based on the contact area of the cracked surface. A dynamic model of the slant cracked twisted blade with breathing effect is established. By comparing the natural frequencies and vibration responses obtained by the proposed model and the finite element model of the ANSYS Solid186 element, the validity of the proposed model is verified. The results show that as the crack angle increases from 0° to 80°, the natural frequency increases by approximate 3%, that is, as the crack angle increases (the crack front is closer to the blade tip), the natural frequency of the cracked blade increases. Additionally, as the crack angle increases, the vibration displacement amplitude of the rotating cracked blade decreases. The amplitudes of the constant component and the multi-frequency in the spectrum also decreases. Furthermore, the amplitude of the 1.0f_e under the first order resonance state is reduced by about 40%. The calculation speed of the dynamics response of the proposed model is faster than that of ANSYS model, with an improvement of about 22 times.

Abstract:The claw compressor is the most promising hydrogen circulating pump type due to its remarkable advantages of compact structure, dry oil-free and high reliability. However, conventional claw hydrogen circulating pumps suffer from severe gas leakage between two claw rotors due to point to point meshing, resulting in reduced volumetric efficiency of the pump and limiting the development of the hydrogen circulation pump. In order to minimize gas leakage between two claw rotors and improve the volumetric efficiency of pumps, this study proposed a novel twisting meshing structure adopting the circular arcs, high-order curves and their conjugate curves to instead of pitch circular arcs of conventional claw rotors. This leads to the development of a novel gear-claw rotor, effectively solving the issue of gas leakage between two claw rotors. Simultaneously, a geometric model of the novel gear-claw rotor was established, and the equations of rotor profiles were deduced. The transient flow of the internal gas in the hydrogen circulating pump with complex geometric boundaries was simulated in the working process. A comparative analysis was conducted between the pressure distributions and transient flow characteristics inside the working chamber of the conventional pump and the proposed gear-claw pumps. Additionally, a performance test bench for the claw hydrogen circulating pump was built to validate the accuracy of the numerical simulation results. The results indicated that compared with conventional claw rotors, the gas leakage velocity between the gear-claw rotors was reduced by 31.42% and 33.09% during the compression and discharge process, respectively, and its volumetric efficiency was increased by 10.92%.

Abstract:To study the deformation capacity of tensegrity structures with redundant cables, this paper proposed a method to select the optimal driving mode to achieve structural deformation based on the cable-driven concept with minimal energy dissipation. Firstly, the structural parameters of the tensegrity basic unit and the connection relationship between the member and the node were set, and the mechanical properties analysis was conducted on the structure in the new stable state after the contraction of the cable. This analysis yielded a new calculation formula of the node coordinates. Secondly, the structural parameters and material parameters were assigned to analyze the deformation process of the structure. The passive cables was firstly shrunk to prestress the tensegrity structure, and the additional dissipated elastic potential energy of the structure except for the active cables was calculated. Then, the active cables was shrunk to induce the deformation of the tensegrity structure. The energy dissipation work of the active cables and the final deformation of the structure were calculated. Moreover, the evaluation criteria of the optimal driving mode of the structural deformation were proposed. Finally, taking the double-layer axial splice structure with redundant cables as an example, the active and passive cables of the structure were differentiated and the optimal driving mode was studied. The results show that for the single axial deformation of the structure, when the diagonal cables are active and the middle horizontal cable is passive, the axial change of the structure is maximized while the energy dissipation is minimized. For the composite deformation involving axial deformation and torsional deformation, the composite deformation of the structure is maximized and the energy dissipation is minimized when the diagonal cables opposite to the rod member are active while the remaining diagonal cables are passive.

Abstract:To improve the objectivity and accuracy of energy efficiency evaluation of power users and meet the needs of userss demand for timely feedback and adjustment of energy efficiency, a real-time dynamic energy efficiency evaluation method for power users under edge architecture is proposed. On the basis of constructing the edge side evaluation framework, the dynamic logical relationship between the indicators is firstly analyzed based on the “Pressure-State-Response” conceptual model. The dynamic evaluation indicators are selected from multiple dimensions to construct the user energy efficiency evaluation index set. Considering the limited storage resources of edge nodes, the three attributes of importance, balance and independence of indicators are abstracted from the set to quantify. The quantified values of the three attributes are fused by the influence degree and optimization degree model, and the cooperative game theory is used to optimize the edge side to simplify the indicator set, so as to effectively remove the redundancy of the edge side data. Secondly, based on the CRITIC (criteria importance though intercrieria correlation) weight calculation method, the data information of the index is fully utilized, and a more objective weight coefficient is given to the index proposed in this method. Finally, the absolute ideal solution is constructed by improving the grey TOPSIS (technique for order preference by similarity to an ideal solution) evaluation method to effectively avoid the reverse ranking problem caused by the dynamic change of the number of users. The introduced grey correlation degree can make up for the defect that the European criterion cannot accurately measure the advantages and disadvantages of users in the traditional method. The experimental results show that the proposed edge energy efficiency evaluation method not only greatly reduces the demand for data storage, but also fully guarantees the reliability and robustness of the evaluation results, which has obvious advantages in reducing the scale of data upload and quickly completing user energy efficiency evaluation.

Abstract:To solve the problems of small size of metal bipolar plate surface defects in hydrogen fuel cells, indistinct defect contrast and various types of defects that make it difficult to detect, easily cause false and leaky detection and large size of the complexity of defect detection model that makes it difficult to deploy, an improved metal bipolar plate defect detection algorithm DN-YOLOv5 is proposed to explore the feasibility of rapid and accurate defect detection in the scene of metal bipolar plate visual detection workbench formed by stamping, so as to realize intelligent detection and improve detection efficiency. This research focuses on modifying the Backbone part of YOLOv5 backbone network, adding the number of modules in the network and the NAM attention mechanism, using the deeply separable convolution module to replace the original CSP/CBS backbone network convolution module and introducing SIoU to redefine the loss function, which greatly improves the lightweight degree of the backbone network. The experimental results show that the algorithm map@0.5 can reach 0.988, the detection transmission frame rate per second is 9.98, the number of model parameters is reduced by 52.13% and the true detection rate of 75 defect images in the test set reaches 99.74%. This method not only ensures the high detection rate of the model, but also significantly reduces the complexity of the model and the amount of parameter calculation. In addition, the algorithm combines the new detection scale to design a feature fusion network, which improves the small target and multi-target detection capabilities of the network. It has good stability, good robustness and good comprehensive performance, meeting the lightweight requirements of deploying mobile end scenarios for defect detection.

Abstract:To investigate the aerodynamic characteristics of the free-rotating wraparound fins projectile, the time-precise unsteady numerical simulation of wraparound fins projectile was carried out by using computational fluid dynamics method and slip grid technique. The literature review was compared and synthesized in order to verfiy the validity of the simulation; the appropriate number of grids and time steps were determined using grid-independent and time-step-independent tests, respectively. The difference in aerodynamic characteristics bewteen free-rotating wraparound fins projectile and fixed wraparound fins projectile were compared and analyzed at different Mach numbers; considering different wing and body differential roll conditions, the effects of differential roll angular velocity on the aerodynamic moment characteristics of free-rotating wraparound fins projectile were studied. The results show that the roll moment coefficient and the Magnus moment coefficient of the free-rotating wraparound fins projectile are significantly smaller than those of the fixed wraparound fins projectile due to the different strengths of the viscous vortices at the connection between the wing and the body; at Mach numbers 0.8 and 1.1, the Magnus moment coefficient of the free-rotating wraparound fins projectile is close to 0, and its roll moment coefficient is basically linearly related to the differential roll angular velocity, while the Magnus moment coefficient is significantly non-linearly related to the differential roll angular velocity. The roll moment coefficient of the free-rotating wraparound fins projectile is sharply reduced with the increase of Mach number and the Magnus moment coefficient is sharply increased with the increase of Mach number due to the influence of the viscous vortex at the wing and body joint. The above-mentioned factors have a great influence on the aerodynamic characteristics of the wraparound fins projectile, and should be taken into account in the aerodynamic and ballistic design.

Abstract:To solve the key technical problems of the laborious process and difficulty in achieving rapid structural optimization design using the traditional computational fluid dynamics (CFD) method to obtain the wind coefficient of the main beam section of port crane, a rapid prediction model for wind coefficient of crane main beam section based on convolutional neural network is proposed. The wind coefficient rapid prediction model proposed in this paper uses the free geometric deformation method to process the basic section shape to obtain the cross-section pattern set of crane main beam with rich geometric characteristics, CFD method is then used to calculate the wind coefficient corresponding to the cross-section pattern of each main girder to generate the dataset. On this basis, the prediction model is trained based on the dataset and its network structure is optimized, and the nonlinear mapping relationship between the main beam section and the wind coefficient is established. In addition, this paper further combines the prediction model with the genetic algorithm to establish an optimization design method for main beam cross-section. Taking the F₁₁ section in the dataset as an example, the accuracy and efficiency of the optimization method are tested by using the windproof performance as the optimization objective. The test results show that the wind coefficient rapid prediction model proposed in this paper achieves the average relative error of 1.87% when predicting the wind coefficient of each main beam section. The prediction time is in the order of milliseconds, which is significantly faster compared to the traditional CFD method, showcasing a significant improvement in efficiency. The optimized F₁₁ section of crane main beam section developed by applying the optimization design method developed in this paper is reduced by 15.89% compared with the wind coefficient before optimization. This significant reduction greatly improves the windproof performance of the main beam section, which proves the reliability of the optimization method proposed in this paper. It can be used as a new method for the optimization design and rapid selection of crane main beam section structure.

Abstract:The dynamic response of conventional hydraulic priority valve will lag when there is a sudden change in load flow. The response of spools opening and closing is slow because it is limited by ensuring that the pressure stability and the opening response speed are within the designed range. Consequently, the size of the fixed orifice is small so that when working conditions are switched, the closing speed of valves is slow, resulting in a small flow of oil through the orifice, which cannot meet the needs of the system for rapid oil supplementation. In order to solve the above problems, we designed and integrated a speed regulating microvalve in the main spool of the hydraulic priority valve. This microvalve uses the principle of different orifices in different oil flow directions to adjust the opening and closing response speed of the main valve, and achieve slow opening and quick closing of the valve core. According to the dynamic equations of the valve, the designed microvalve is modeled and optimized by simulation. The best matching parameters are determined and the effectiveness of the design is demonstrated. The experimental results show that by reasonably matching the flow area of the fixed orifice, the microvalve can speed up the closing speed of the main valve and replenish the auxiliary circuit oil to the main circuit in a timely manner. Moreover, compared with the traditional main spool with fixed orifice, the closing speed of the microvalve is doubled. When the steering or shifting operation is completed, the speed regulating microvalve can realize that the opening speed of the main valve is slower than the closing speed and reduce the impact of the pressure. This design solves the problem of slow closing speed of the main valve core when switching the priority valve. In addition, it helps the auxiliary pump to quickly supply oil to the main pump and meet large flow demands under different working conditions as well as improve the response speed of the system.

Abstract:This article aims to explore the flow field and sound field characteristics of the cavity structure of the dry ultrasonic cleaning head. According to the ultrasonic sounding mechanism of the dry ultrasonic cleaning head, a 3 mm cavity (small cavity) structure that generates sound through the hydrodynamic interaction between fluids and a 10 mm cavity (large cavity) structure that generates sound through the resonant interaction between fluid and acoustic mode are designed. The designed square cavity is numerically studied by the computational fluid dynamics (computational fluid dynamics, CFD) method. The results show that the two structures have similar flow field characteristics, and the flow-induced oscillation of the small cavity is more intense under the same pressure. As the pressure increases, the maximum velocity in the cavity increases and the growth rate of the maximum velocity decreases. The growth rates of the maximum velocity and the maximum velocity are similar for different cavities under the same pressure. Both structures can produce ultrasonic waves. The ultrasonic sound generation mechanism is related to the size of the cavity, and the occurrence mechanism is consistent with the predicted value. The research shows that the design of the channel structure of the dry ultrasonic cleaning head is not limited to the small cavity where the hydrodynamics interaction between fluids makes the sound, and the large cavity can also produce strong high-frequency ultrasound, which provides a reference for the structural design of the dry ultrasonic cleaning head.