Abstract:A hierarchical trajectory planning method with path and speed co-search and decoupling optimization is proposed to address the multi-constraint trajectory planning problem in structured road scenarios. To ensure the quality of the initial trajectory solution, the upper initial trajectory planner constructs the Spatio-temporal cost map by taking into account the risk field and spatio-temporal information of dynamic obstacles, and searches for the safe and feasible initial trajectory using a three-dimensional A* algorithm. The lower trajectory planner implements decoupling for the trajectory planning as path planning and velocity planning with the minimum curvature, maximum speed, and comfort as the goal. A numerical optimization algorithm is used to construct a spline optimization model for the path and speed, in order that in the process of obstacle avoidance it can give full play to the dynamic performance of the vehicle and at the same time improve the ride comfort, simplify the constraint conditions on local space-time tunnel thought, and improve solving efficiency. The experiment results show that the proposed method has better driving efficiency, comfort, and real-time performance.

Abstract:The universal design method of the Fourier series follower cam has a narrow application range to solve the near-rest interval and poor iterative convergence. In this work, an improved extensible near-rest angle high-speed Fourier cam design method is proposed. With the introduction of the function of angles in the near-rest interval, the general near-rest displacement equation of Fourier cam is solved. The velocity, acceleration equation, jerk, and jump of the follower are solved by successive derivation. Based on the cam feature parameters and profile curve data, the Fourier cam 3D model was established. The improved Fourier cam design method is verified by comparing it with the universal algorithm. The camshaft speed and push rod lift affecting the kinematic characteristic of the cam are investigated. The results indicate that the proposed model has a wide range of applications, excellent iterative convergence to solve the cam profile，and a small impact force. As the near-rest interval, camshaft speed, and push rod lift increase, the maximal velocity and acceleration of the follower increase. The proposed model is of guiding significance to reduce the vibration of the high-speed cam mechanism and improve the working precision of transmission.

Abstract:Aiming at the low classification accuracy and efficiency of the original hyperdisk classifier, a Robust Hyperdisk Model (RHD) is proposed, where the relaxation variable is introduced based on the original hyperdisk model, and the constraints of current class samples and heterogeneous samples are considered at the same time to avoid the intersection of hyperdisks, so as to obtain a more reasonable category region estimation. Then, a Robust Nearest Neighbor Hyperdisk Classifier (RNNHDC) is proposed，which combines the RHD model with the nearest neighbor classification method. The RNNHDC only needs to calculate the distance from unknown sample points to each category RHD. And the RNNHDC has high computational efficiency and can be directly applied to multi-classification tasks. The RNNHDC has good classification efficiency. Finally, RNNHDC is applied to gearbox fault diagnosis. Experimental verification is carried out on two different gearbox datasets. The experimental results show that RNNHDC has better classification accuracy, robustness, and efficiency. The RNNHDC can be effectively used for gearbox intelligent fault diagnosis.

Abstract:In order to improve the combustion and emission performance of the ethanol-gasoline engine, the tests on an ethanol-gasoline engine were carried out with different injection strategies under typical working conditions. The effects of injection strategies and ethanol proportions on engine combustion and emissions were compared and analyzed. The results showed that the Brake Specific Fuel Consumption（BSFC） decreased first and then became stable with TCOI in advance, and decreased with the increase of the number of injections. Compared with a single injection, multiple injections reduced BSFC by up to 7%, and carbon monoxide and hydrocarbon emissions were obviously reduced, but it led to a slight increase in nitrogen oxide emissions (much less than the impact of TCOI）. After gasoline was mixed with ethanol, the combustion duration became longer, but the thermal efficiency of the engine was significantly improved due to ignition timing and early combustion center. Increasing the proportion of ethanol and TCOI can reduce the carbon monoxide concentration by up to 15%. The effect of ethanol proportion on hydrocarbon and nitrogen oxide depended on the TCOI. TCOI was a good parameter of the injection characteristics, and the impact on emissions was greater than that of ethanol proportion and number of injections. Selecting the appropriate number of injections, ethanol proportion, and TCOI can significantly improve engine thermal efficiency and reduce emissions.

Abstract:Aiming at the thermal safety problem caused by insufficient heat dissipation of the power battery module at a high discharge rate, taking a prismatic lithium-ion battery as the research object, a cooling structure of battery thermal management system embedded with aluminum heat pipe-aluminum plate is designed. An orthogonal test scheme with four factors and three levels is established. The analysis method combining the Range method and the Hierarchy method is adopted to study the heat dissipation performance of the battery module under natural convection. The effect of multi-parameter coupling with fin number, fin position, fin pitch, and fin size of the condensing section of heat pipe on the maximum temperature of battery module coupling is analyzed at the 3C discharge rate. The results indicate that the order of influence weights of various parameters on the maximum temperature of the battery module is as that: fin number fin size > fin position > fin pitch. The optimum parameter combination of the fin is A3B2C3D3. Under the environment of natural convection, appropriately reducing the fin pitch can not only ensure the heat dissipation efficiency but also benefit the compactness of the battery heat dissipation system. Furthermore, different convective heat transfer conditions are compared and analyzed. When the convective coefficient of a fin is 55 W·m-2·K-1，and the fin pitch is 9 mm，the maximum temperature of the battery module is 40.57 ℃, and the maximum temperature difference is 3.89 ℃，with the optimal parameter combination of the fin even discharged under 3C accelerated working condition.

Abstract:To study the influence of muscle activation on human neck injury under a specific braking condition, a mixed finite element dummy model was developed with detailed neck geometry and active and passive response capabilities of muscles. The kinematics and biomechanical responses of the occupant’s head and neck at relaxing and pre-tension states with a specific helmet under a specific braking condition were studied, respectively. The results indicated that pre-tensioning of the neck muscles before the start of braking reduced the peak values of the three kinematic parameters of head centroid horizontal acceleration, head relative to T1 thoracic spine horizontal displacement, and rotation angle by more than 20%, resulting in better stability of the neck during the entire moving process. From a biomechanical point of view, pre-tensioning the neck muscles reduced the maximum Von-Mises Stress of the vertebrae and intervertebral discs by 36.95% and 48.20%, respectively; the Nij value was reduced by 25.06%, which reduced the risk of neck injury in this braking condition.

Abstract:As the evaluation of passengers’ comfort is not comprehensively considering the effect of the odor of Volatile Organic Compounds (VOCs) or health hazard of VOCs in a car in the present work, automobiles were taken as a kind of indoor micro-environmental system. The Weber-Fechner law was applied to establish an evaluation method of passengers’ comfort by comprehensively considering both the odor and health hazard of VOCs in a car based on the natural background concentration of typical VOCs compositions, national standards, and the olfactory threshold data. It was also the first time to quantitatively determine the influence weights of the typical VOCs compositions on passengers’ comfort and passengers’ comfort levels combined with the coefficient of variation method and triangular fuzzy theory. In addition, this paper proposed a method of quantitatively comparing passengers’ comfort in different cars based on the comment set and carried out a case study using the above proposed evaluation method. The case study indicated that，among the four types of cars，the fourth car presented the highest passengers comfort level.

Abstract:To synchronize the material transfer and adsorption process of the packaging machine, a combined channel of main and secondary wall panels with multiple negative-pressure suction cups is proposed. The flow field model of the negative-pressure channel is established based on computational fluid dynamics technology. Combined with the RNG k-ε turbulence model and enhanced wall treatment, the effects of channel structural parameters and fan flow on the pressure and velocity distribution are discussed. The results show that the airflow is influenced by expanding pipe, deflector, and fan position. The secondary flow at the expanding pipe intensifies the pressure loss, the deflector near the negative- pressure suction cups reduces the turbulence, and the fan located in the channel center improves the average airflow velocity. Based on the analytic hierarchy process, a quantitative model for the comprehensive performance of flow characteristics is established. When the fan velocity is at 13 m/s, the flow performance of the main and the secondary wall panels increases by 53% and 21%, respectively. However, the effect of the fan is higher than that of the structure when the fan velocity increases to 18 m/s.

Abstract:To improve the aerodynamic performance of a small forward curved centrifugal fan, the centrifugal fan used for car seat ventilation was taken as the research object in this paper. The effects of the number of blades, the blade outlet angle, the blade inlet angle, and the blade thickness on the aerodynamic performance of the centrifugal fan were studied by means of combining numerical simulation and an orthogonal experiment. The experiment used a small air volume fan performance test bench to validate the numerical simulation results. Three-level orthogonal table L9（34） was selected to arrange the test, and impeller models with nine different parameter combinations were established. The optimal centrifugal fan parameter combinations were obtained by using the computational fluid dynamics method with maximum static pressure as the optimization objective. In addition, the pressure and velocity distribution in the centrifugal fan before and after optimization were compared and analyzed. According to the direct analysis of the orthogonal test results, it can be seen that the influence of each parameter on the maximum static pressure of the centrifugal fan is in the order of the blade outlet angle, the blade inlet angle, the number of blades and the blade thickness. In addition, the maximum static pressure can be achieved by the following parameters: the number of blades of 55, the blade inlet angle of 95°, the blade outlet angle of 125°, and the blade thickness of 0.8 mm. The dimensionless characteristic curve of the optimized fan is better than that of the original fan, and the static pressure can be increased by 3.78%~10.67% in a high-efficiency area. Compared with the pressure and velocity distribution of the flow field inside the centrifugal fan before and after optimization, the distribution of the flow field inside the optimized centrifugal fan is more uniform, the pressure in the low-pressure area at the impeller inlet is lower, and the velocity is higher, which is more conducive to the flow into the centrifugal fan.

Abstract:In order to accurately obtain the temperature field distribution characteristics of double-pulse metal inert gas (MIG) welding of aluminum alloy plates, a dynamic combined welding heat source model based on the heat distribution and weld formation characteristics of full penetration welding was proposed. Through the preparation of subroutines and the secondary development of finite element software, the spatial distribution loading of the dynamic heat source model was realized, and the weld bead morphology and temperature field distribution characteristics in the simulation process were obtained. According to the simulation process parameters, the butt-welding experiment of 2 mm-thick 6061-T6 aluminum alloy plates was carried out by double-pulse MIG welding. The weld bead morphology characteristics were obtained, the temperature data of temperature measurement points were recorded, and the thermal cycle curves of temperature measurement points were drawn. By comparing the simulation and experimental results，it is found that，for the full penetration welding of aluminum alloy sheet, the weld morphology obtained by the dynamic combined heat source model is in good agreement with the actual weld bead morphology, and the simulation error of temperature field is within the allowable range. The maximum error point appears at 20 mm away from the weld, and the maximum error is 12.25%.

Abstract:To obtain high volume fraction low angle grain boundary（LAGBs） and low volume fraction recrystallization microstructure so as to improve the comprehensive properties of aluminum alloy, the effects of High Strain Rate Rolling (HSRR) processing parameters on microstructures and mechanical properties of 7050 aluminum alloy were explored. Electron backscatter diffraction（EBSD），Transmission Electron Microscopy（TEM） were used to characterize the volume fraction of low angle-grain boundarys（LAGBs） and dynamic precipitates. The results show that a high fraction of LAGBs can be obtained by HSRR, and the fraction of LAGBs increases with the increasing strain rate but decreases with the temperature. The fraction of LAGBs is 95.6% with the rolling parameter of 370 ℃/20 s-1. The alloy rolled at 400 ℃/20 s-1 exhibits good comprehensive mechanical properties after 470 ℃/0.5 h short-term solution treatment and 120 ℃/24 h aging treatment, with the ultimate tensile strength of 530 MPa，the yield strength of 442 MPa，the elongation at fracture of 19.1%. The mechanical properties of the plates rolled with the strain rate of 20 s-1 are better than that with the strain rate of 10 s-1 at the same rolling temperature.

Abstract:The two-stage aging process can increase the corrosion resistance of the alloy while ensuring the high strength of the Al-Zn-Mg-Cu aluminum alloy material. The mechanical properties and microstructure change of 7A85 aluminum alloy panel under different two-stage aging conditions were studied by a tensile test at room temperature, conductivity measurement, and scanning electron microscopy (SEM). The results show that the influencing order of factors on the strength and conductivity of materials is as follows: final aging time > final aging temperature > initial aging temperature > initial aging time; the influencing order of factors on elongation is as follows：final aging temperature > initial aging temperature > final aging time > initial aging time. The orthogonal results show that the suitable two-stage aging system is 110 ℃ / 6h + 155 ℃ / 8h, the tensile strength is 617.0 MPa，and the elongation is 12.6%. This study provides a reference for the application of 7A85 aluminum alloy sheet in the aerospace field.

Abstract:The in-situ TiB2/2219 aluminum matrix composite ingots were prepared by using the high-temperature-mixed molten salt method. The effect of TiB2 content on microstructure and properties of in-situ TiB2/2219 aluminum matrix composites is investigated by optical microscopy, scanning electron microscopy, X-Ray diffraction, combined with elastic modulus, room temperature tensile and Charpy impact test methods. The results showed that the TiB2 mass fraction increased from 0 to 5%, and the TiB2 particle size and the average grain size of TiB2/2219 aluminum composite ingots decreased. The elastic modulus, tensile strength, and yield strength of TiB2/2219 aluminum matrix composite increased significantly as TiB2 content increased, but the ductility and impact toughness decreased. The elastic modulus, tensile strength, yield strength, and ductility of 5% TiB2/2219 aluminum matrix composites plate were 88.7 GPa, (474.2±2) MPa, (400.6±1) MPa and (4.7±0.1) %, respectively.

Abstract:Using medium-temperature coal pitch particles with a softening point of 85 ℃ and a particle size of 0.30～0.45 mm as raw materials, pitch balls were prepared by the suspension method and stabilized by the mixed oxidation method（HNO3 oxidation and O2 oxidation). Pitch-based Spherical Activated Carbon is prepared from non-melting pitch balls through carbonization and CO2 activation. The pitch balls were characterized by SEM, TG/DTG, and FT-IR. The results show that the pitch balls prepared by the suspension method have a smooth surface, an average sphericity of 0.981, and a concentrated particle size distribution. The weight of the pitch ball of 0.30～0.45 mm accounts for more than 93%. After the activation temperature of 940 ℃ and 6 h of heat preservation, the BET specific surface area of Pitch-based Spherical Activated Carbon is 1 545.20 m2/g and the microporosity is 75.30%.

Abstract:The influence of secondary damage caused by freeze-thaw cycles on recycled concrete after the Alkali-Silica Reaction (ASR) was studied. The specimens were immersed in 1 mol/L NaOH solution at 80 ℃ for alkali silicic acid reaction for 28 days and then subjected to 20 and 40 freeze-thaw cycles to measure the expansion rate and relative dynamic elastic modulus of the specimen. The analysis shows that the promotion effect of early ASR on the secondary expansion of recycled concrete after freezing reaches the maximum when the content of recycled aggregate is 30%. As for the relative dynamic elastic modulus, whether early ASR can promote secondary damage after freezing and thawing depends on the alkali activity of the aggregate. The higher the alkali activity of aggregate, the weaker the promotion effect.

Abstract:Using diamond abrasive and Ni-Cr-P pre-alloyed powder as grinding material and solder alloy, the Ni-Cr-P/ composite sintered body was prepared by brazing process. The effects of different brazing temperatures on the interfacial and grinding properties of the Ni-Cr-P/diamond sintered body were explored. The melting characteristics of Ni-Cr-P alloy were characterized by differential thermal analysis（DTA），the wetting effects and interface structure of Ni-Cr-P alloy on the diamond were observed by scanning electron microscope（SEM），and the bonding between diamond surface and the alloy was analyzed by X-ray photoelectron spectroscopy（XPS）. The results show that at the optimal brazing temperature of 940 ℃, some carbon elements on the diamond surface migrate into the liquid solder so as to form Cr—C bonds in the dense layer of Cr3C2，which effectively improves the wettability between Ni-Cr-P alloy and the diamond surface. Thus, the interface structure endows the compressive strength of single diamond particles and grinding ratio of the brazing grinding head with the maximum values（i.e., 36.83 N and 64.2）， which are significantly improved by 18.27% and 72.58% when compared to 850 ℃, respectively.

Abstract:This work aims to study the effect of pulse power supply on the formation of TiO2 nanotubes and their photocatalytic properties under different voltage and duty cycles in the pulse mechanism. A pulsed power supply was used to prepare TiO2 nanotubes on the surface of pure titanium substrates with different pulse voltages and duty cycles. The surface morphology and composition of the nanotube were analyzed by SEM and EDS. By optimizing the voltage and duty cycle parameters, we obtained TiO2 nanotubes with good shapes, which were used to explore their photocatalytic degradation of methyl orange. When the pulse voltage was increased from 50 V to 80 V with a duty cycle of 15%, TiO2 nanotubes showed high quality, and the tube diameter was increased with the increasing voltage. The methyl orange solution was degraded by 21.2% after 6 h xenon lamp irradiation. The results show that TiO2 nanotubes prepared by pulse voltage anodic oxidation can degrade methyl orange by photocatalysis.

Abstract:Aiming at the problem of poor damping performance of di-phenylmethane diisocyanate (TDI) polyurethane (PU) elastomer prepared by chain extension of pure 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), MOCA/polytetrahydrofuran ether glycol (PTMG) mixed chain extender was used to prepare PTMG-TDI PU elastomer with different chain extender ratios by prepolymer method. FTIR, DSC, and DMA tests showed that with the increase of PTMG1000 (Mn=1 000) in the mixed chain extender, the hydrogen bonding index of PU reduced, and the microphase separation degree of soft and hard segments decreased leading to the melting temperature and melting enthalpy of hard segment microcrystalline decreased, and the loss factor tan δ increased. When the MOCA/PTMG1000 (molar ratio) is 85 15，the PU hardness, tensile strength，and tear strength are 85 A，33.1 MPa, and 70.5 kN/m, respectively. Compared with the PU prepared by pure MOCA，the hardness is reduced by 5 A, the mechanical strength is maintained at a higher value and the tan δ is increased. Finally, the prepared metal hub/PU roller meets the durability test standard, and the operating noise is reduced by 3 dB.

Abstract:A model of the single droplet evaporation of nano-fuel was conducted based on ANSYS FLUENT software with reference to the visualized evaporation experiments. The effects of nanoparticle mass concentration and size on the temperature distribution and fuel-vapor mass concentration during droplet evaporation were discussed. It was revealed by the simulation results that the evaporation equilibrium temperature of droplets tended to rise up with the increasing nanoparticle mass concentration or the size of the diminishing nanoparticle, and the vapor volume fraction was higher during the same evaporation period. At the ambient temperature of 573 K, the temperature inside the nano-fuel droplet was raised by absorbing heat from the external environment. And within the computational domain, the temperature boundary layer and mass concentration boundary layer were formed along the outward droplet surface, which promoted the conversion of liquid to gas. At the initial evaporation of nano-fuel droplet, the vapor volume fraction, as well as the evaporation rate was relatively low, while during the proceeding of evaporation, with the assistance of nanoparticles in enhancing heat and mass transfer, the liquids were evaporated to vapors with increasing rate.

Abstract:Aiming at the problem of degradation of system frequency modulation performance caused by uncertain transmission delays, system parameters and load disturbance, communication bandwidth constraint and calculation burden, and the intermittent generation of wind power, in this paper, a Sampling PI Load Frequency Control（SPI-LFC） scheme is proposed considering the signal sampling period and transmission delay. And the exponential decay rate is introduced to evaluate the rapidity of the system. Firstly, a sampled-data-based delay-dependent SPI-LFC model of a time-delay power system with wind power is constructed. Then, by constructing a new two-sided closed-loop Lyapunov functional and applying linear matrix inequalities technology, the sampling period of system, the stability margin of communication delays, and the stability criterion and SPI control design method related to exponential convergence rate are derived. The simulation results show that the proposed scheme has a larger sampling period, communication delay stability margin, and large exponential decay rate. And it also has strong robustness against uncertain system parameters, load disturbance, and the intermittent generation of wind power.

Abstract:In order to study the corona aging characteristics of silicone rubber materials with different proportions under haze conditions, three types of silicone rubber materials with different proportions were selected, and the aging characteristics were tested by the static contact angle, scanning electron microscope, and Fourier transform infrared spectrum. The results show that the corona aging characteristics of the three types of silicone rubber materials with different ratios under haze conditions are quite different. Among them, the corona aging characteristics of the A-type materials with low silica gel content and high aluminum hydroxide content is relatively excellent, which are manifested in better surface morphology and fewer attachments. The hydrophilic groups can migrate to the interior of the material at a faster speed, so the recovery rate is the fastest, but the hydrophobicity loss of such materials is relatively serious. At the same time, the characteristic peak areas of the Si—O—Si group and Si—CH3 group in such materials after aging are relatively large, the main chain and side chain are more complete, and the chemical structure damage is the smallest.

Abstract:In order to solve the problem that the performance of impedance matching deteriorates due to the insufficient precision of the inductor in miniaturized antenna impedance matching, a complementary metal-oxide-semiconductor（CMOS） circuit for automatic antenna impedance matching is proposed. Firstly, a new impedance-matching method is proposed, which realizes impedance matching by adding capacitors to the input and end of the antenna. Then by integrating the matched capacitors, an automatic impedance matching circuit is proposed. The main principle is to judge the input power of the antenna through the power detection circuit and the peak detection circuit and to change the input impedance of the antenna through the capacitor scanning circuit and the capacitor controlled by the program. The innovation of the circuit is also reflected in removing the step of adjusting impedance matching using a network analyzer, so as to reduce the influence of test environment change on impedance matching. The design requirements of the output impedance of the RF power amplifier are reduced. The precision of impedance matching can be changed by designing the precision of matching capacitors.

Abstract:In order to improve the safety and stability of the power system and solve the defect that traditional time-frequency transform methods cannot accurately separate and extract disturbance signals in power quality analysis, a new approach was proposed for power quality analysis based on synchronous compression conversion based on Multiple Matching Synchronous Transform (MMSST). Firstly, the method uses MMSST to decompose power signals into a series of Intrinsic Mode Functions (IMF), and then the instantaneous frequencies and amplitudes can be achieved by applying the Hilbert transform (HT) to the intrinsic mode functions. The results of simulation and measured experiments show that, compared with the Empirical Mode Decomposition (EMD) algorithm, MMSST can accurately separate and extract each disturbance component in the voltage disturbance signal, realize the accurate extraction of the instantaneous frequency and amplitude of each disturbance component, and has strong robustness.