In order to improve the stress shielding effect caused by excessive elastic modulus of metal plates during fracture healing, a kind of 3D printing oriented lattice structure plate is designed based on topology optimization and the finite element modeling technology. A simplified finite element model of the titanium alloy tibial plate is established by using the finite element method. Combined with the finite element method and the data sampling method, the solid plate system and the lattice plate system are simulated, and the similarities and differences between their performances are compared. Based on the analysis of mechanical properties of lattice plate system, the lightweight design of the plate is realized and the stress shielding effect of the bone is improved. The results show that the weight of the lattice plate can be reduced by about 40% under the condition of guaranteed strength. The lattice plate is sensitive to the thickness. By reducing the thickness of the plate in a small range, the stiffness of the plate can be significantly reduced. The application of the lattice plate can effectively increase the average stress of the skeleton by about 4% and reduce the stress shielding effect of the skeleton. The simulated analysis results can provide references for the optimization design of low stress shielded plates.
A carbon dioxide(CO2) ejector expansion air conditioning system for vehicles is developed in a calorimeter laboratory. In experimental tests on a standard mobile air conditioning bench, the effects of different operating parameters on the performance of the CO2 refrigeration system for vehicles are studied, and the performance advantages of the CO2 ejector expansion refrigeration system are comparatively analyzed. The research results show that the cooling capacity of the CO2 ejector expansion refrigeration system for vehicles is almost equal to that of the CO2 conventional cooling system. Both increasing the indoor air flow rate and increasing the compressor speed can effectively increase the cooling capacity of the CO2 ejector expansion refrigeration system, and the ejector can increase the coefficient of performance (COP) of the system by 1.65% to 12.60% under different working conditions. The outdoor temperature has a great impact on the CO2 ejector expansion refrigeration system performance, and the performance of CO2 ejector expansion refrigeration system for vehicles decays obviously at a high ambient temperature.
Aimed at the problem of the compressors of the low temperature air source heat pump system, this paper analyzes the impact of volume ratio on performance and proposes a novel three-cylinder two-stage variable volume ratio rotary compressor. The performance of the proposed compression system is compared with that of the traditional two-stage compression system of the same terminal in the experiments. The results show that the three-cylinder two-stage system operates in a stable manner with a coefficient of performance (COP) of 1.52 at a ambient temperature of -30 ℃,while the traditional two-stage system does not work. The COP of the three-cylinder two-stage system is always 1.25% to 12.41% higher than that of the traditional two-stage systems at any ambient temperature. When the ambient temperature is stable and the water supply temperature increases, the amount of dissipated heat at the terminal increases. At the same time, the maximum heat of external machine decreases, as well as the COP. When the ambient temperature is 7 ℃ and -25 ℃ respectively, and the water supply temperature changes from 40 ℃ to 55 ℃,the COP of the three-cylinder two-stage system is 1.15% to 8.86% and 4.32% to 7.33% higher than that of the traditional two-stage system, respectively. The power consumption of the three-cylinder two-stage system is always 3.78% to 16.67% lower than that of the traditional two-stage system.
A method for online detection and compensation of grinding wheel wear based on machine vision is proposed in this paper. The principle of workpiece-contour-image (WCI) based online wheel wear detection is presented, and the online compensation of wheel-wear-induced contour error is analyzed, based on which, studies are conducted on the developed complex contour grinding platform. The results reveal that the proposed method can effectively detect the wheel wear in real-time and compensate the contour error caused by wheel wear to improve the machining accuracy. The research provides a new method for online detection of wheel wear and prediction of wheel dressing.
Aimed at the uncertainty of equipment quantity and input, the defective products and its rework in the manufacturing process are investigated. Considering the influence of the number or input of the devices on system reliability, a manufacturing system reliability evaluation model is established based on stochastic flow network. The homogeneous Markov process is used to analyze the state of system degradation and maintenance. Considering the constraint of system reliability, a systematic maintenance model is proposed to minimize maintenance cost. The results of the numerical experiment demonstrate that the proposed model is effective and advanced.
The double cantilever beam flexible pin structure with interference fit is usually adopted by the planetary gear shaft of large gear gearbox, and the interference fit structure at this location is prone to fretting fatigue. The maximum and minimum values of effective interference are theoretically calculated. Besides, the bending load process of flexible pin is simulated by using the finite element software Abaqus. In addition, the influences of bending load, interference and the depth of carburized layer on contact stress, frictional shear traction and slip amplitude are analyzed. Moreover, the influence degrees of various factors on fretting fatigue damage are investigated, and the S-N curve of flexible pin fatigue life is predicted by utilizing the SWT (Smith-Watson-Topper)critical plane theory method. Furthermore, the bending load fatigue loading test is conducted on several groups of specimens, the S-N curve of the flexible pin test is obtained, and the fretting fatigue damage morphology of the component surface is analyzed after the test. The results show that the influence of bending load on fatigue life is greater than that of the interference, and the depth of the carburized layer. The fatigue life of SWT prediction is in good agreement with the test data. Therefore, numerical simulation analysis can be used to help check the fatigue life of the flexible pin in engineering design.
To solve the problem of machine maintenance optimization of degraded systems, the preventive maintenance policy of a two-machine one-buffer production system is studied. First, random degradations of both machines are considered. For imperfect minimal repair and preventive maintenance, a Markov process is used to describe the system state. Then, a profit model for the production system is established based on cost and income. Finally, preventive maintenance decisions in different system states are determined by maximizing long-term expected profits. The model is solved by value iteration, and numerical analysis results show that the maintenance decision of the machine depends not only on its own state, but also on the state of other machines and the amount of the buffer.
Based on the hardware of the new artificial anal sphincter system, this paper analyzes the power consumption of each module. After low-power consumption design and reasonable setting of the sampling period, the system power consumption is significantly reduced. At the same time, the area under the rectal pressure waveform is used as the standard for judging defecation willingness. Instead of the single-point pressure threshold method, it provides a basis for anal incontinence patients to go to the toilet, and thus improves the accuracy of the rectal perception function. Combining in vitro and in vivo experiments, the low-power consumption of the artificial anal sphincter designed in this paper can extend the working time of the system to 16 d after a single charge. It increases the working time by 230% with a rectal perception accuracy of 96%.
Based on the McCabe-Thiele (M-T) method and the conservation of mass and energy, the PandaX-4T collaboration group designs an efficient cryogenic distillation system to reduce the mole fraction of krypton in commercial xenon from 5×10-7 to 1×10-14. Since the ultra-high purity xenon cryogenic distillation system has completed the offline purification operation, it is necessary to conduct the corresponding operation analysis. Therefore, the stability and purification performance of the ultra-high purity xenon cryogenic distillation system are studied by analyzing the parameters such as temperature, pressure, flowrate, and mole faction of the product xenon in each operating stage. The PandaX-4T cryogenic distillation system has been operating stably for 1.5 m at a collection efficiency of 99% and a purification rate of 10 kg/h, and has purified 5.75 t of xenon. The experimental data show that the system is stable, safe, and reliable in all stages of operation, and the krypton concentration in product xenon is less than 7.99×10-12. The operation analysis of the PandaX-4T ultra-high purity xenon cryogenic distillation system has a theoretical research value and practical engineering significance, providing very important reference for optimization of distillation operation of the next stage.
In structural strength topology optimization based on the variable density method, there are gray cells in the optimization result, making it difficult to accurately predict the structural stress which changes greatly before and after post-processing. This paper uses a filter-projection-based structural parameterization method to achieve a continuous decrease in the proportion of structural intermediate density units during the iterative optimization process. By studying the influence of the main optimization parameters of the structural ratio strength problem on the optimization process and structural strength optimization, a novel optimization strategy of structural topology optimization followed by approximate shape optimization is proposed, which realizes the accurate control of the change of structural stress during the optimization process, achieveing structural strength optimization while improving the stability of the optimization process. Typical optimization examples verify the rationality and practicability of the proposed optimization method.
In order to realize the stable application of microfluidic inertial switch in the intelligent ammunition fuze system, a bidirectional anti-high overload microfluidic inertial switch is proposed to solve the problem of switch contact instability caused by the mercury droplet separation under high impact. The structures of snake-shaped buffer channel and three-stage capillary valve are designed based on the principle of capillary force applied to the mercury droplet in microchannel. The force state of the mercury droplets in the contraction type and the expansion type of capillary valves is analyzed. The static threshold model of the mercury droplet in the rectangular channel is established. The user defined function (UDF) is used to apply acceleration load to the finite element simulation of the switch. The simulation analysis suggests that under the action of typical forward service drop load and typical reverse service drop load, the mercury droplets can be restored to its initial state without droplet separation, indicating that the switch has a reliable anti-high overload ability. Two centrifugal experiments are conducted to complete the preparation and injection of tiny mercury droplets. The microfluidic switch prototype is used in the impact test of the Machete drop hammer. The results show that the mercury droplet separation does not occur in the switch under the action of typical forward impact load and typical reverse impact load, which are consistent with the simulation results.
To meet the requirements of the low background and high sensitivity of the large-scale dark-matter detector PandaX-4T, nKr/nXe≤1×10 -13 (n is the amount of substance) is required. The ultra-high purity krypton/xenon cryogenic distillation tower was used as an example in this paper. First, the distillation tower and the construction design of the distillation system were briefly introduced. Then, the operation parameters of the distillation tower were simulated and optimized by using HYSYS, and the distributions of the pressure, temperature and Kr concentration in the distillation tower were obtained. After that, the influences of those operational conditions including the feeding point position, the reflux ratio, the feeding flowrate, the heat of the reboiler, the flowrate of the off-gas, and the feeding pressure to the xenon purity of the distillation system were studied, and the optimized operation parameters were proposed. When the column pressure is set at 221 kPa and the reflux radio is set at 145, the krypton content in xenon can be purified from 5×10-7 to 4.1×10-14, which has an important guiding significance for further improvement of the purity of the xenon product of the xenon/krypton cryogenic distillation system.
The biosafety and biocompatibility after implantation of the transcutaneous energy transfer system of artificial anal sphincter is verified by combining simulation and experiment in this paper. The biosafety study is based on the simulation of bioelectromagnetic radiation experiment and the thermal rise during the charging period while the biocompatibility study is based on the coloration experiment of the tissue around the energy supply system during the in vivo experiment. The results of biosafety indicate that the transcutaneous energy transfer system performs excellently in bioelectromagnetic safety in the experimental environment with a resonance frequency of 110 kHz and an output power of 10 W. In addition, the local specific absorption rate is far below the international human electromagnetic safety standard. After 30 minutes of fast charging, the system temperature increases by 2.81 ℃, which is lower than the temperature threshold of 4.8 ℃, demonstrating the outstanding biothermal safety of the system. The section staining experiment of the wireless energy supply system indicates that the poly-ether-ether-ketone (PEEK) shell can significantly reduce immune rejection and improve the biocompatibility of the system.
To develop an intelligent process design system, a process knowledge modeling approach is proposed to help engineers determine the values of parameters. First, various models are introduced to represent different kinds of process information. Then, a binary tree-based approach is proposed for representing formula-based process knowledge, together with an ordered tree-based approach for representing table-based process knowledge. Thereafter, an aggregate model of process knowledge is established, which can effectively integrate process template with route selection knowledge, formula-based process knowledge, and table-based process knowledge. Finally, a knowledge-based prototype system for intelligent process design is developed. The process design of a complex cable product is taken as an example to verify the modeling method. The result demonstrates that the proposed approach can enhance the decision-making capability of an intelligent process design system, which can thus improve the efficiency and quality of process design.
Flexible flanging is a novel forming process by local continuous loading, but its process law and planning method are not perfect. Based on the characteristics of aviation sheet metal parts, the feature flanging parts were designed. Simulation of flexible flanging was conducted on the Abaqus platform, and the influence of key process parameters such as rolling pass numbers, the angle distribution of each pass, roller diameter, and rolling speed on forming quality were obtained. Considering the forming efficiency, the process parameters were optimized and verified by experiments. The results show that the forming quality of flexible flanging can be significantly improved with low cost by optimizing key process parameters, and the forming efficiency can be improved to a certain extent.
For the fault diagnosis needs of the full life cycle (light degradation, moderate degradation, and severe degradation) of rolling bearing under the environment of high background noise, a genetic algorithm-output input hidden feedback (GA-OIHF ) Elman neural network model is proposed to achieve precise diagnosis of the degradation faults of rolling bearing. Ensemble empirical mode decomposition (EEMD) is selected to effectively reduce the noise and extract fault features of the vibration signal. An OIHF Elman neural network is designed by increasing the feedbacks from the output layer to the hidden layer and the input layer based on the Elman neural network, thus further improves its ability to process full life cycle data of rolling bearing. Then, a novel GA-OIHF Elman neural network model is developed by combining the genetic algorithm (GA) and the OIHF Elman neural network. The novel GA-OIHF Elman neural network model combines the global optimization of GA and the local optimization ability of the OIHF Elman neural network to achieve an accurate fault diagnosis of the entire life cycle of rolling bearing. The experimental results show that the GA-OIHF Elman algorithm model can not only accurately diagnose the fault in the full life cycle of rolling bearing, but also ensure the stability of the diagnosis model for different faults including different fault components and stages.
To study the dynamic performance of the V-shaped electrothermal actuator, electrothermal and thermoelastic coupling models are established based on the heat transfer theory and the forced vibration equation, respectively. A one dimensional multi-physical field coupling theoretical model of the V-shaped electrothermal actuator is proposed. The electrothermal coupling model is solved by the method in which the sine transformation and the implicit difference are combined together. Then, a convergence test is performed. The number of discrete points in the sine transformation has less influence on the temperature stability. The transient and static temperature distributions of the model coincide with that of the finite element method (FEM) at different voltages. The static displacements gained by the experiment and the edge detection algorithm also match well with that gained by the thermoelastic coupling model at different voltages. Based on the proposed model, the dynamic performances of the actuator at step and sine voltages are analyzed. The research results indicate that changes of temperature and displacement in the middle of the V-shaped electrothermal actuator are larger with the amplitude of sine voltage increasing. When the loading time of sine voltage is larger than 5 periods (50 ms), the average temperature and displacement in the middle of the actuator are equal to those with equivalent direct voltage. When applied to a periodic voltage, the motion of the actuator is also gradually cyclical and has the same time period with the voltage cycle.
Aimed at the problem of degradation assessment of shore bridge hoisting gearbox, an online evaluation method of degradation state based on improved symbol sequence entropy (O_ISSE) and logistic regression is proposed. First, a threshold factor is introduced to retain the “coarse-grained” information of the signal change direction and amplitude, reduce the “sensitivity” of original algorithm to the impact component, and propose an improved symbol sequence entropy (ISSE).Then, the sliding window Weibull fitting method is used to effectively filter out the influence of fluctuations in the ISSE characteristic sequence to form O_ISSE. Finally, a logistic regression model is trained and established, and the H value of health factor of the unknown sample are calculated to realize its status recognition online.The example analysis of the life data of the hoisting gearbox of a dock in Shanghai is conducted. The results show that the ISSE and logistic regression model can describe the complexity of signal, track and identify performance degradation status accurately.
To solve the problems of alignment for launch container loading in field-artillery rocket, a novel end-effector, i.e., a swing-compliant hook, is proposed, whose structural parameters are optimized. First, the theoretical model describing the performance of the swing-compliant hook is established based on the node displacement method. The static displacement, static stress, and swing curve of the swing-compliant hook are analyzed by MATLAB, which verifies the rationality of the model. Then, the main structure parameters on the performance of the swing-compliant hook are obtained by using the experimental design method. Additionally, a response surface model characterizing the comprehensive performance of the swing-compliant hook is established. The optimization results show that when the length and the installation height of the compliant mechanism are 90 mm and 23 mm, and the end height of the lifting hook is 110 mm, the swing-compliant hook has an excellent performance in docking, lifting, transferring, and locating.
