[Objective] With the gradual improvement of requirements for motor energy efficiency grade, outer-rotor low-speed permanent magnet motors are widely used in the industrial field, due to their advantages of high torque density, high efficiency, and energy saving. To meet the working conditions of heavy-load start-up and long-term low-speed heavy-load operation of industrial sector, the design of outer-rotor low-speed permanent magnet motors is developing in the direction of improving motor torque density. Accordingly, the issue of high heat generation caused by the high torque density of motors is becoming a focus of research. [Methods] To address the problem of high temperature rise in outer-rotor low-speed permanent magnet motors under heavy-load operation conditions, this paper established the physical model of outer-rotor low-speed permanent magnet motors and calculated the distribution of motor losses. First, based on the basic theory of computational fluid dynamics, according to the heat source distribution and structural characteristics of outer-rotor low-speed permanent magnet motors, the study designed and installed axial and circumferential Z-shaped water-cooled structures in stator bracket near the inner surface of the stator core. The simulation model with water inlet and outlet at the motor bottom was also established. The flow field and temperature field of two water-cooled structures were simulated and analyzed using Fluent software. The circumferential Z-shape structure was determined as a more suitable water-cooled design structure. Second, by the calculation method coupling fluid flow and heat transfer, the temperature field of the motor equipped with a circumferential Z-shaped 9-channel water-cooled structure was analyzed using Fluent software. Whether the water-cooled structure meeting the heat dissipation requirements of the outer-rotor low-speed permanent magnet motors was verified with the maximum temperature of the permanent magnet and insulation. Finally, based on the theoretical analysis, this paper determined the factors influencing heat dissipation in water-cooled structures, including water channel number, cooling water flow rate, and radial width of water channel section. The influences of different factors on motor temperature rise were studied using Fluent software. [Results] The results indicate that the flow rate distribution of the circumferential Z-shaped water-cooled structure is more uniform with a smaller inlet and outlet pressure difference, which is more suitable for outer-rotor low-speed permanent magnet motors. As the number of water channels, cooling water flow rate, and radial width of water channel section increase, the heat dissipation is enhanced. However, after each factor reaches a certain value, the motor temperature tends to stabilize. According to the analysis results, the final design includes 7 water channels with a radial width of 17 mm and a cooling water flow rate of 0.5 m/s. [Conclusion] The research results can provide a theoretical basis for the application of water-cooled systems of outer-rotor low-speed permanent magnet motors in high-load working environments.

[Objective] With the increasing demands for flight safety of unmanned aerial vehicles (UAVs), the dynamic characteristics of landing gear systems have become a critical research focus in UAV design. This study focuses on the landing contact mechanical behavior of rubber footpads in six-link landing gears and investigates the problems of nonlinear mechanical characteristics in modeling. By constructing a precise dynamic contact model, this research aims to elucidate the mechanical response mechanisms of rubber buffers under impact loads and provide theoretical support for optimizing the structural design of cushioning systems at landing gear foot ends. [Methods] A nonlinear contact mechanics model for rubber materials was developed based on the theoretical framework of the continuous contact force method. Innovatively integrating Hertzian contact theory with the Mooney-Rivlin strain energy function, the model accurately characterized the hyperelastic characteristic of rubber materials and the dynamic coupling effects at contact interfaces through non-ideal elastic collision relationships. On the ABAQUS platform, a finite element model adopting the Mooney-Rivlin hyperelastic constitutive model was established, and the landing collision process was numerically simulated using an implicit dynamic solver. A drop impact test bench equipped with force sensors was constructed to obtain experimental data for model validation. This integrated methodology, combining theoretical modeling, numerical simulation, and experimental validation, effectively overcomes the limitations of traditional empirical formulas. [Results] Systematic analysis reveals the influence of multiple physical parameters on contact mechanical characteristics. When the drop height increases within the range of 50 mm to 200 mm, the peak contact force exhibits proportional growth, with an increment of 1.78 kN. Within the load mass range of 5 kg to 20 kg, the peak contact force demonstrates an approximately linear relationship with load mass, showing an increase of 1.02 kN. Notably, increasing footpad thickness has an insignificant effect on reduction in impact force, while optimizing the footpad shape can effectively mitigate impact-induced vibrations. Comparative studies on structural shapes demonstrate that conical footpads, compared to traditional cylindrical designs, exhibit more even force distribution and effectively mitigate impact-induced vibrations. Experimental validation confirms the effectiveness of the model, with the peak contact force error being merely 6％ and a phase shift of key parameters controlled within 3 ms under the condition of 100 mm drop height. [Conclusion] The contact force demonstrates approximately directly proportional relationships with both drop height and footpad thickness, though the effect of thickness is relatively weak. Footpad shape optimization significantly reduces impact-induced vibrations, with conical footpads exhibiting superior cushioning performance. This study achieves theoretical breakthroughs in two aspects. A dynamic contact prediction method for rubber buffers was proposed by combining the continuous contact force method with the hyperelastic constitutive model, resolving the technical bottleneck of traditional approaches in addressing nonlinear coupling effects. A quantitative evaluation framework for cushioning performance was established by investigating the influence of multiple physical parameters on contact force at landing gear foot ends, providing a reliable theoretical basis for foot-end parameter optimization.

[Objective]In response to the problems of large volume and small stroke of current micro-positioning platforms, a new displacement amplification mechanism of a lever-compound bridge type was proposed, and a three-degree-of-freedom piezoelectric micro-positioning platform that could achieve large-stroke motion was designed. [Methods]First, the structure of the piezoelectric micro-positioning platform was proposed, and its working principle was analyzed. The piezoelectric actuator generated initial displacement, which was first amplified by the compound bridge structure and then amplified again by the lever mechanism. The final amplified displacement was output to the moving platform. In addition, the lever and compound bridge mechanisms for displacement amplification were designed and optimized, and the stiffness model and displacement amplification ratio mathematical model of the lever and compound bridge mechanisms for displacement amplification were established with theories of statics, material mechanics, and elasticity. According to the theoretical model, the dimensions of the lever and compound bridge mechanisms as displacement amplifiers were optimized, and the overall amplification factor after optimization was 20.6. Then, the structure of the flexible hinge was optimized, and finite element simulation was conducted on four typical notch shapes. After the analysis of the relationship between the output displacement and input force for the four flexible hinges, the flexible hinge of the straight beam type was selected. Finite element simulation was performed on the overall piezoelectric micro-positioning platform to analyze the displacement output performance and rotational output performance around the x-axis and y-axis of the piezoelectric ceramic actuator after deformation amplification. Finally, output testing was conducted on the designed piezoelectric micro-positioning platform. Experimental verification was conducted on the z-axis direction displacement output performance of the displacement amplifier and its rotational output performance around the x-axis and y-axis. [Results]Finite element simulation shows that the maximum output displacement of the piezoelectric micro-positioning platform in the z-axis direction is 740 μm with a simulation magnification factor of 15. The maximum output rotation angles around the x-axis and y-axis are 0.83° and 0.86°, respectively. The output test of the piezoelectric micro-positioning platform shows that the boost curve does not coincide with the buck curve, and there is a hysteresis phenomenon. The maximum output displacement in the z-axis direction is 706 μm. When the voltage is 30 V, the hysteresis displacement is the largest, which is 65 μm. The maximum output angle around the x-axis is 0.8°, and that around the y-axis is 0.79°. When the voltage is 30 V, the maximum hysteresis angle around the x-axis is 0.062°. When the applied voltage is 45 V, the maximum hysteresis angle around the y-axis is 0.047°. Compared with the simulation results, the maximum errors in motion along the z-axis direction and in rotation around the x-and y-axes are 34 μm, 0.03°, and 0.07°, respectively, with corresponding maximum relative errors of 4.6％, 3.6％, and 8.1％. [Conclusion]The piezoelectric micro-positioning platform based on the lever and compound bridge mechanisms for displacement amplification effectively solves the problem of small output displacement of piezoelectric ceramics, achieving large-stroke motion.

[Objective]To produce high-quality generator guard rings with straight busbars, minimal machining allowance, and low residual stress, a new process was proposed to reinforce the guard rings through the linkage of a hydraulic press and an ultra-high-pressure pump. [Methods]The mold was pressed down on the guard ring by a hydraulic press. An ultra-high-pressure liquid was injected into the interior of the guard ring by using an ultra-high-pressure pump to cause plastic deformation. The deformation shape of the guard ring was controlled by precisely controlling the pressure of the hydraulic press and the ultra-high-pressure liquid injected by the ultra-high-pressure pump. When the guard ring deformed to a certain extent, due to the increase in deformation resistance, the mold needed to be replaced to continue expansion until the expected forming size was reached. Compared to the traditional hydraulic expansion process for generator guard rings, the new process used equipment with a lower cost and a higher efficiency. The material used in the manufacturing of the generator guard ring was 50Mn18Cr5. Using the analysis function of ANSYS Workbench, a finite element analysis was conducted on the changes of the outer diameter and stress of the guard ring during the expansion process. At the same time, according to the requirements of the automatic control system, the automatic control program and human-machine interface (HMI) configuration interface were designed, with a programmable logic controller (PLC)used to control the production process of the generator guard ring. Various parameters such as the diameter change, deformation speed, system pressure, and temperature of the guard ring during the expansion process were displayed on the HMI configuration interface. By detecting the diameter changes of the guard ring during the expansion process, the pressure of the hydraulic press and the ultra-high-pressure pump was precisely controlled to ensure the smooth progress of hydraulic expansion. At the same time, if both the hydraulic press and the ultra-high-pressure pump failed, the automatic control system would also issue an automatic alarm, which can protect the safety of workers and avoid major safety accidents. [Results]The finite element analysis shows that the maximum error between the change in the outer diameter of the guard ring during the hydraulic expansion process and the actual production result is only 2.312 mm, which proves the feasibility of the new process. The intuitive presentation of the working status and parameters of the equipment through the HMI configuration interface not only ensures the production quality and efficiency of the generator guard ring but also makes the operation more convenient. [Conclusion]The new process that utilizes the linkage between a hydraulic press and an ultra-high-pressure pump can effectively produce high-quality generator guard rings with straight busbars, minimal machining allowance, and low residual stress, providing an efficient and low-cost technical solution for guard ring manufacturing.

[Objective]Petrochemical products are prone to leakage during production, transportation, and use, causing serious harm to the marine environment, marine biological resources, and coastal city environment. Therefore, there is a need to optimize the oil-water separation technology, in order to recover marine oil spills and purify the marine environment, which has important application value for marine oil pollution control and other aspects. The adsorption method, as a kind of oil-water separation technology with a good development prospect, is suitable for the treatment of marine oil spills. Its ability to deal with pollution is related to the adsorption material and adsorption structure. At present, most of the research on the adsorption method focuses on the field of material optimization, while less on adsorption structure improvement. To optimize the oil-water separation technology of the adsorption method, a feasible optimization scheme for the adsorption method from the structural level was proposed by leveraging bionics, which provides ideas for reference in this field. [Methods]In this paper, the traditional adsorption structure consisting of a single oil adsorption material was optimized, and a novel adsorption structure was proposed based on bionic engineering. Firstly, the sparse and porous characteristics of the stems of aquatic plants were analyzed, and a similar porous material, copper foam, was chosen as the main material of the adsorption structure. Then, the theoretical reason for the higher oil-water separation capacity of the internal vascular structure of oil-bearing crops was analyzed. The structure of parallel rows of oil and water channels produced the Marangoni effect, which created a tensile force between oil and water. Based on this, a laminar structure was designed, and a novel oil-water separation structure formed by interlocking of oleophilic hydrophobic and hydrophilic oleophobic materials was proposed. The hydrophilic oleophobic material was prepared by immersing copper foam into a mixture of potassium persulfate and potassium hydroxide. The oleophilic hydrophobic material was prepared by immersing copper foam into a mixture of n-hexane and polydimethylsiloxane (PDMS). The adsorption capacity of the new combined stacked adsorption structure was experimentally compared with that of the conventional single oil adsorption structure. The two adsorption structures were placed in equal volumes of emulsified and unemulsified oil-water mixtures at volume fractions of 1％, 5％, and 10％, and the oil adsorption amounts of the two structures within the same time were determined. [Results]The results show that the adsorption rate and oil adsorption amount of the new structure are higher than those of the conventional single adsorption structure under most conditions. [Conclusion]The feasibility of the adsorption structure scheme with the staggered superposition of the oleophilic hydrophobic layer and the hydrophilic oleophobic layer is proved, and the addition of the hydrophilic layer can effectively improve the oil adsorption capacity of the adsorption structure. The research results provide ideas and technical guidance for the optimization of oil-water separation technology from the structural aspect.

[Objective] To address the problems of low overlap, unstable internal and external gear thickness coefficients, and easy breaking of gear teeth due to thin tooth thickness in the zero-tooth-difference internal gear mechanism of the coupling device in the oil extraction system of submersible screw pump, a method of optimizing the modification coefficient in the mechanism to improve the degree of overlap was proposed, and the corresponding optimization model was designed. [Methods] The design defect regarding the modification coefficient of zero-tooth-difference mechanism in the traditional design method was analyzed. The objective function and constraints were determined, the design variables were defined. The linearly decreasing inertia weight method in the particle swarm optimization (PSO) algorithm was adopted to improve the local and global optimization ability of the particles. The shrinkage factor was introduced, and the convergence time was shortened by updating the speed iteration formula. The degree of overlap and tooth thickness coefficients were taken as the optimized objective functions. The optimization model was designed by combining the gear constraints of the zero-tooth-difference internal gear mechanism. [Results] To ensure the stability of the algorithm, the user′s initial input parameters are used for optimization analysis:the internal and external gear module is 6; the tooth number is 12; the pressure angle of the reference circle is 20°; the width of the external gear tooth is 30 mm; the width of the internal gear tooth is 28 mm; the eccentricity range is 2.5-5 mm. The improved PSO algorithm achieves the optimal solutions of radial modification coefficient and tangential modification coefficient, namely that it significantly improves the optimization results of modification coefficients. By comparing with the original data and optimization results, it is found that the degree of overlap of the improved PSO algorithm is increased by up to 26.2％. In particular, the degrees of overlap at different eccentricities are significantly enhanced after optimization. [Conclusion] The improved PSO algorithm has both global convergence and precise search ability, and the obtained modification coefficients are more reasonable and effective. The optimized tooth thickness coefficients of the internal and external gears tend to be more stable, which can effectively alleviate the problem of tooth breakage caused by the thinning of the tooth thickness. The optimized modification coefficients not only meet the various constraints but also facilitate the post-processing and improve the computational efficiency. Consequently, good design results are achieved.

[Objective] Cavitation is a physical phenomenon that occurs in nature and can be observed across several fields, including materials science, geology, and biology. Early studies on cavitation primarily focused on mitigating its adverse effects, such as reduced cellular function, rock fracture, and cavitation-induced damage to materials and performance deterioration of hydraulic machinery. However, positive applications of cavitation have been identified gradually in various fields, such as enhancing material strength, facilitating chemical reactions, and removing refractory organic pollutants. The study of the collapse process of cavitation bubbles near solid surfaces provides a deeper understanding of the mechanisms underlying the action of cavitation bubble collapse on solid surfaces, which can lead to better utilization of cavitation in various applications. These surfaces may include concave, convex, conical, and irregular geometries, with the surface of spherical particles being a type of convex surface. Cavitation technology has shown great promise in the treatment of oily sludge, as it can significantly improve oil recovery rates and enable the resourceful treatment of the sludge. The mechanism of cavitation disintegration of oily sludge lies in the generation of extremely high temperature, pressure, and jet velocity during the collapse of cavitation bubbles on the surface of the sludge particles. This helps to separate the oil from the solid particles, enabling oil recovery and reuse. [Methods] The dynamic behavior of cavitation bubble collapse near spherical particles was investigated to probe into the evolutionary process of cavitation bubble collapse and then to analyze the influence mechanisms of the particle-cavitation bubble distance and particle size on particle-cavitation bubble interaction. The principles of conservation of mass, momentum, and energy were used to describe the dynamic behavior of cavitation bubbles, and the volume-of-fluid method was used to accurately capture the changes in the topology of the bubble walls at the interface. The collapse process of the cavitation bubbles in the vicinity of spherical particles was numerically simulated using ANSYS software. [Results] The cavitation bubble collapses gradually near the spherical particle over time, and its collapse morphology is influenced by the distance parameter and size parameter. At the moment of the collapse of the cavitation bubble, a microjet directed toward the particle, and an extreme environment of high temperature and pressure was formed. [Conclusion] When a spherical particle is close to a cavitation bubble, the bubble collapses in a pear-shaped form. As the distance between the particle and the bubble increases, the bubble collapse takes on a more spherical shape. When the distance parameter decreases or the size parameter increases, the maximum pressure on the side wall of the particle increases. In addition, when the distance parameter or the size parameter decreases, the maximum jet velocity and the maximum temperature of the side wall of the particle increase. The collapse time of the cavitation bubble near a larger particle is longer and is significantly influenced by the distance parameter. The farther the bubble distance is, the longer the collapse time is.

[Objective] To improve power generation efficiency and accelerate the development of green and low-carbon economy, supercritical or ultra-supercritical units have gradually become the main units for thermal power generation in China. As a key component of supercritical or ultra-supercritical units, boiler tubes are mostly made of austenitic stainless steel. After being used in an environment of high temperature, high pressure, and steam for a long time, a boiler tube will face an oxidized inner wall, on which oxide scales are produced. Due to the start and stop of the unit and other factors, the oxide scales are easy to fall off and accumulate in the tube. When the accumulation reaches a certain degree, local blockage of the tube occurs, resulting in tube burst. The on-site quantitative detection of oxide scales is generally carried out by magnetic nondestructive detection. However, boiler tubes exhibit weak ferromagnetism due to cold working and long-term aging, which makes the results of existing magnetic quantitative detection method for oxide scales inaccurate. [Methods] To realize the accurate detection of oxide scale blockage in austenitic stainless steel tubes with weak ferromagnetism, this paper proposed a new magnetic detection method based on the enlargement of the magnetic circuit. The present study compared the simulation results of the existing magnetic detection method and the new one by finite element simulation and probed into the reasons why the existing method failed to accurately detect oxide scales in boiler tubes with weak ferromagnetism. [Results] The simulation results show that the absolute error of the proportion of the oxide scales blockage area is 138％-474％ in boiler tubes with weak ferromagnetism when the existing magnetic detection method is employed, while that is 3.4％-6.7％ in the case of using the new magnetic detection method. In short, the new magnetic detection method has a much smaller absolute error than the existing one, able to be applied to the quantitative detection of oxide scales in boiler tubes with weak ferromagnetism since which is less affected by tube magnetism. Oxide scales with different blockage area proportions in standard specimens with different wall thicknesses were detected using the new magnetic detection method. On this basis, correspondence was established between the detected signal values and the blockage area proportions in standard specimens with different wall thicknesses, verifying the correctness of the simulation results. The correctness of the calibration formula is verified by an experiment on field tubes containing oxide scales giving rise to different blockage area proportions, and the detection error of the new magnetic detection method is calculated. The experimental results show that the maximum absolute error of the proportion of oxide scale blockage area in specimens with weak ferromagnetism ranges from 1.2％ to 5.6％, and the maximum absolute error is less than 5.6％ in the specimen calibration experiment. In the field tube experiment, the range of this maximum absolute error is 1.5％-6.4％, and the maximum absolute error is less than 6.4％. [Conclusion] This indicates that the new magnetic detection method is less affected by the magnetism of the tube wall, and its error is acceptable in practical engineering. The proposed technique enables the nondestructive detection and evaluation of oxide scale blockage in austenitic stainless steel tubes with weak ferromagnetism.

Aiming at the problem of poor riding experience in the use of power vehicle, a power vehicle training system with human-computer interaction function was proposed. The lower computer of this system was composed of power vehicle, Hall sensor, single chip microcomputer, servo motor and other modules. The resistance of power vehicle could be continuously adjusted by the newly designed magnetic resistance device. The riding path of the host computer was optimized by using Bezier curve, and the scene tracking effect was improved by combining with real-time interpolation, equidistant interpolation and non-equidistant interpolation algorithms. The experimental results show that the path generated by the real-time interpolation algorithm based on Bezier curve can satisfy the somatosensory consistency and warrant the fluency and stability of riding scene during the process of human-computer interaction.

To address the issues of high resource consumption, high failure rate and maintenance difficulty of the traditional modular design for product manufacture or application by enterprises, an improved atomic clustering module division method considering green attributes, such as resource utilization, lifespan compatibility and maintainability etc., was proposed. Multiple green constraint matrices, valence matrices and distance matrices were constructed, and the Coulomb force relationships between components were calculated, after which a module division scheme was proposed. An integrated evaluation system employing RAHP, CRITIC and VIKOR was established, and the module division schemes were optimized by considering the indicators, such as average aggregation degree, coupling degree and cost balance degree. The products of an industrial steam turbine enterprise were used as the research object for green module division, and the results were compared with the traditional module division method. The results show that the products′ green performance is effectively enhanced by the improved atomic clustering module division method, meeting the requirements of green design.

Full ceramic ball bearings have excellent properties such as light weight, wear resistance, high(low) temperature resistance, corrosion resistance and good accuracy retention, and have broad application prospects in equipment manufacturing, aerospace and other advanced technology fields. The high-performance manufacturing technology system of full ceramic ball bearings has not yet been formed, which seriously restricts its application and development in high-end equipment and has also become a technical problem for the further expansion of the application field of full ceramic ball bearings. Based on the industry's demand for high-end bearing products, this paper analyzes the characteristics and advantages of full ceramic ball bearings, discusses the design methods applicable to these products, summarizes the high-performance manufacturing processes of key components such as ceramic balls and ceramic rings, evaluates the service performance and test technology of full ceramic ball bearings, and forecasts the related technologies and applications.

Progressive cavity pumps for oil extraction exhibit outstanding advantages in the extraction of high viscosity, high sand content crude oil. The working principle and environment of pumps determine the service life of the rubber stator, which is the core component and pivotal to this equipment. Enhancing the wearing and swelling resistance of stator rubber material of the progressive cavity pump is of great significance. This paper first introduces the core components and the oil extraction principle of progressive cavity pumps. Secondly, focusing on the practical requirements for the stator rubber in progressive cavity pumps, the primary research findings of domestic and international scholars regarding key properties like aging, swelling and friction of stator rubber materials are reviewed. Furthermore, with reference to the emerging multiscale methods for material research in recent years, this paper provides an overview of concepts, principles, methodologies and their applications in mechanics and tribological properties of stator rubber. Finally, the prospects of future methods and research approaches aimed at continuously enhancing the wearing and swelling resistance of stator rubber in progressive cavity pumps for the extraction of crude oil are outlooked.

Laser directed energy deposition (LDED) technology, as a cutting-edge additive manufacturing technique, has demonstrated significant advantages in the fields of material processing and product manufacturing. This paper reviews the development history, fundamental principles, technical characteristics, and current applications of LDED technology across various industrial sectors. LDED technology can effectively enhance material utilization rates, reduce manufacturing cycles, and enable the direct fabrication of complex components, particularly in industries such as aerospace, automobile manufacturing and healthcare. Through simulation analysis, online monitoring and closed-loop control strategies, LDED technology has further improved the precision of part formation and product quality. With technological maturation and optimization, LDED technology is expected to play a more significant role in reducing costs, enhancing performance, and promoting the green transformation of manufacturing industry.

The mismatch between gas supply and demand of reciprocating compressor is the main cause of high energy consumption. The stepless capacity regulation technology for suction valve is an effective means to solve this problem. Its implementation methods include linear mesh partial-stroke pressing-off regulation system and rotary cup-shaped fully controllable regulation system. The linear mesh partial-stroke pressing-off system can realize the precise and continuous regulation of the compressed capacity. The essence is hydraulic transmission control, which has the defects of small flow area, large resistance loss, serious impact, complex execution system and more fault points. Rotary cup-shaped fully controllable regulation system is a new type of stepless capacity regulation technology. Its essence is mechatronics and its principle is to accurately regulate the cup valve through the servo motor. It has the advantages of large flow area, small resistance loss, no friction when opening the valve, small friction stroke when closing the valve, and no impact of moving parts. In this paper, the theory, structure, control system and energy efficiency of the two regulation systems are comprehensively reviewed. It is proposed that the rotary cup controllable regulation system is the future development direction, and further research should be carried out for the theoretical research, structure optimization, material development and intelligent system development of the rotary cup controllable regulation system.

With the development of digital technology, the industrial internet of things (IIoT) has brought manufacturing into the era of intelligent manufacturing with high efficiency, high reliability and low-cost. In recent years, as one of novel manufacturing methods, additive manufacturing has demonstrated broad application prospects in such fields of aerospace, process industries, mold manufacturing and automotive manufacturing. During the additive manufacturing process, high-performance computing and analytical processing based on big data are particularly crucial for balancing “quality, efficiency and cost”. Focused on digital intelligent manufacturing, this paper performs an in-depth analysis on cloud platform principles, industrial software system of additive manufacturing, and addresses the challenges and potentials of digital additive manufacturing.

A digital twin framework for complex equipment operation and maintenance systems, combined with deep learning technology, was proposed to address the urgent need for intelligent transformation in current complex equipment operation and maintenance systems. This article first established a digital twin theory and application framework for complex equipment operation and maintenance systems based on deep learning. At the theoretical level, a multi-level digital twin framework for operation and maintenance systems was constructed by combining deep learning. At the application level, a digital twin application framework for the entire life cycle of operation and maintenance system was constructed according to the parallel driving form of knowledge-data-model. From the data perspective, an application form combining the theoretical framework with the NST model was proposed and validated through experiments. The experimental results indicate that the NST model has better prediction performance for non-stationary time series data of high-speed trains.

In order to improve the ride comfort and safety of vehicles, a new magnetic energy harvesting active suspension was proposed and its stability was studied. BP neural network PID control algorithm (BP-PID) was used to build a magnetic energy harvesting active suspension control system, and theoretical simulation was conducted by using MATLAB/Simulink. B-level and C-level random pavements were established to simulate and analyze the stability of magnetic energy harvesting active suspension at different speeds and pavement levels. The result shows that BP-PID control significantly improves suspension stability, in comparison with the passive suspension and the magnetic energy harvesting active suspension under PID control. The vertical acceleration of the vehicle body gets improved by 45.90％ at 60 km/h on B-level random road surfaces, demonstrating the rationality of BP-PID control, thus effectively improve the suspension stability.

Aiming at the difficulty of hysteresis model characterization caused by the nonlinear stiffness and damping characteristics of spherical wire rope isolator, a normalized Bouc-Wen hysteresis model with the improved nonlinear elastic and correction factors was proposed. In addition, the as-proposed model was further enhanced in combination with Simulink simulation, and the least square method combined with genetic algorithm was used to identify the parameters. To verify the effectiveness of the as-proposed model, the hysteresis loops of GGQ25-62L spherical wire rope isolator were drawn by numerical simulation under different working conditions and compared with experimental data. The results show that the as-proposed parameter identification method is accurate and reliable, and the experimental data are in good agreement with the theoretical curve. The model can describe the dynamic characteristics of the isolator effectively.

A multi-degree-of-freedom magnetic levitation actuator was proposed to replace the conventional electrical discharge machining (EDM) spindle motion, on account of that the spindle cannot adjust the inter-pole gap in time, leading to low machining efficiency during conventional EDM. The structure and principle of the magnetic levitation actuator were analyzed, and the dynamics model of the magnetic levitation actuator was established. The electromagnetic force generated by the actuator was simulated and analyzed by finite element simulation software, and the control effect of the magnetic levitation actuator was simulated and experimentally verified by designing conventional proportional-integral-differentiation (PID) control system and fuzzy PID control system. The results show that the magnetic levitation actuator has good following character, fast response speed and sufficient electromagnetic force to meet the requirements of micro EDM.

In view of the loosening of bolt connection structure under the impact of ship explosion, an anti-loosening structure of toothed double nut was designed. The anti-loosening principle of toothed double nut was analysed by using local slip theory, its anti-loosening performance was analysed by the change amount of pre-load and micro-slip through finite element simulation method, and the influencing factors of anti-loosening performance of toothed double nut and its influence rule were studied. The results show that the pre-load of toothed double nut decreases slowly and the changes of micro-slip are small, under the transverse impact load, showing a better anti-loosening performance. When the wedge angle is the same as the lead angle, the anti-loosening effect is the worst; the larger the wedge angle, the more the teeth number; the anti-loosening effect of toothed double nut gets better.

Aiming at the problem of poor landing performance of helicopter skid and three-point landing gear on complex terrain or dynamic nonlinear moving platform, an adaptive landing gear based on STM32 with X-leg layout and cable drive was proposed. Combined with the adaptive landing gear structure characteristics and control hardware, the multi-dimensional sensing cooperative control system was built. The attitude control algorithm was illustrated and verified in the simulation environment. The experimental results show that the adaptive landing gear and the cooperative control system can achieve a stable and safe landing on slopes and rough roads under various working conditions.

Aiming at the problem in mechanical fault diagnosis based on single-channel acoustic signals that collected signals always have the intensive interference, from which fault features are difficult to be extracted, a method combining the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) and the fast independent component analysis (FastICA) were proposed. Setting an intrinsic mode function (IMF) selection coefficient according to both the kurtosis and the signal correlation as criterion, IMFs adaptively decomposed by ICEEMDAN were effectively screened to reduce the noise and roughly extract the signal features. FastICA was applied to the selected IMFs regarded as virtual channels, by which blind source separation could be successfully achieved. The as-proposed method was verified by experimental data of inner and outer bearing ring faults. The results show that the as-proposed method can greatly reduce the noise and interference, and is efficacious for extracting fault features.

Aiming at the problem of poor robustness of permanent magnetic levitation system with variable flux path, an improved linear active disturbance rejection control (LADRC) method based on auxiliary model was proposed. The working principle of the levitation system was introduced, the dynamic model was established, and an improved LADRC controller was designed. Finally, the control effects of improved LADRC, PID and traditional LADRC were analyzed and compared. The simulation results show that the improved LADRC has the fastest response speed and no overshoot compared with the traditional LADRC and PID when 0.1 mm step disturbance was input. Besides, the air gap variation and the adjustment time of the system with improved LADRC are minimized when 0.5 N disturbance force was input. Compared with PID, the LADRC can improve the anti-disturbance ability of permanent magnetic levitation system with variable flux path.

Aiming at the problem that the inverse kinematics solving process of 6R manipulator is complicated and the solving precision is not ideal, an analytical inversion optimization algorithm based on the separation of position and attitude was proposed. The kinematic model of manipulator was established by using the improved D-H parameter method, and the forward kinematic equation of manipulator was derived through the link transformation matrix. The idea of position and attitude separation was used to design the inverse solution optimization algorithm, and the Monte Carlo method was used to analyze the workspace of manipulator. Furthermore, Matlab Robotics toolbox was used to verify the effectiveness of the improved algorithm. The results show that the improved algorithm has higher solving accuracy, greatly simplifies the solving process, and improves the operation efficiency compared with the existing analytical optimization algorithm.

Aiming at the problem that the same fault of computer numerical control (CNC)machine tool may be caused by different factors, or even by multiple factors working together, an inducing factor analysis method for CNC machine tool was proposed to accurately judge and find the fault location and solve the faults of CNC machine tool. The sparrow search algorithm (SSA) was used to improve the performance of BP neural network for diagnosing the common faults of CNC machine tools in service. The fault signals of different states were collected as the samples of BP neural network, and the fault state of machine tool was identified by the BP algorithm optimized by SSA. The results show that the misdiagnosis probability of diagnosing results is only 2.29%, which indicates that the SSA optimized BP neural network can be widely used for the fault detection and diagnosis of CNC machine tool.

Aiming at the problem that the traditional passive suspension system cannot maintain good riding comfort under complex working conditions, a robust controller of electromagnetic active suspension was designed. The dynamic model of 7-DOF electromagnetic active suspension for whole vehicle was established, the robust control theory was used to weight the controlled output and input, and the H_∞robust controller was designed. The electromagnetic active suspension system was simulated and analyzed under the conditions of random road surface at the speed of 30 km/h and 60 km/h, as well as the sinusoidal pulse road surface at the speed of 20 km/h and 45 km/h, respectively. The results show that the main performance indexes of electromagnetic active suspension with robust control get improved compared with those of passive suspension. Under the random road surface, the vertical acceleration of vehicle body is improved by 28.03％, indicating that the designed robust controller is reasonable. The electromagnetic active suspension with robust control can effectively improve the riding comfort of the vehicle.

Aiming at the problem that conventional passive suspensions cannot utilize the energy of vibration, a linear motor type energy-harvesting suspension was proposed, and the energy-harvesting characteristics of the suspension were discussed. The quarter-vehicle dynamic model was established, and the suspension parameters influencing energy-harvesting characteristics were derived under sine excitation. Through taking the induction electromotive force as the index and based on the model for the linear motor type energy-harvesting suspension, the suspension parameters were simulated and analyzed with a control variate method. In addition, an experiment was conducted using by a quarter-vehicle suspension experimental platform. The results show that the sprung mass, unsprung mass and spring stiffness are negatively correlated with the induced electromotive force of the linear motor, and the tire stiffness is positively correlated with the induced electromotive force of the linear motor.

Aiming at the problem of low diagnosis rate for gear fault diagnosis when it is difficult to collect sufficient sample data, a method based on least square generative adversarial networks (LSGAN) and combined with long short-term memory networks (LSTM) was proposed. The original samples of gear were input into the LSGAN model, and the data were augmented, through the alternate training of the generator and the discriminator, to learn the sample data under different states. A LSTM diagnosis model was trained by the generated samples and the original samples to complete the fault diagnosis with small samples. The as-proposed method was validated by the experimental data on gears from the University of Connecticu. The results show that the diagnosis accuracy increases to 98.3％ compared with the traditional method. The visualization method shows the superiority of this diagnosis method and provides a reference for fault diagnosis under small sample conditions.

Non-standard power distribution cabinets cannot be assembled automatically and can only be assembled manually because of its individual characteristics. A mental workload model was established according to the energy changes in θ、α、β bands of the electroencephalogram (EEG) signals of assemblers. The key factors that causing large increases in the mental workload curve were determined by analyzing the energy change of each EEG wave band with time. A threshold value prone to cause assembly errors was determined according to the change curve of mental workload with time. The results show that the effectiveness of as-proposed method gets proved by the uniformity of experimental conclusions with actual test results of manual assembly, providing theoretical basis for the optimization of manual assembly work of non-standard electrical cabinet.

In order to understand the wake characteristics of a small wind turbine and realize its fast simulation, a small horizontal-axis wind turbine with four blades was selected as the object. Large eddy simulation (LES) was adopted to investigate the spacial-temporal distribution characteristics of its wake. Meanwhile, a fast simulation method based on the actuator disc (AD) model was proposed to simulate the wind turbine wake. The results show that the wake of wind turbine is considerably complicated, and there are many types of vortex structures existing in the wake. A severe velocity deficit and two peak values are also observed for the turbulence intensity profile. Besides, by employing the AD model, the wake velocity deficit of the wind turbine can be accurately calculated to realize the fast simulation of dynamic behavior for wake vortex.