Abstract:In view of the problems of highly redundant degree-of-freedoms, strongly dynamic coupling between manipulator(s) and mobile platform of the Ground mobile manipulators (GMM), some challenging puzzles in GMMs are still being open, including equivalent dynamics modelling of action chain and its simplification method, the high-dimensional dynamic manipulate planning under strong environmental interaction, dynamic stability, as well as real-time manipulator control, and so forth. Focusing on dynamic modelling and coupling analysis, motion planning, dynamic stability, and manipulator control of the GMMs, current literatures are investigated and a review on the state-of-the-art of whole-body motion planning and control of the GMMs is presented. Some key problems and technical challenges are summarized, and the future direction is prospected.

Abstract:To improve the machining efficiency of robot milling of large aluminum alloy components without reducing the machining quality, a comparative experimental study of applying planetary compound milling method was conducted. A robotic planetary compound milling system was proposed first, while its basic structure and operation principle were introduced. The tool nose trajectories of robotic planetary compound milling (RPCM) and robot end milling (REM) were compared by establishing the models of the tool nose trajectories. Then, a series of single-factor robot milling experiments about Al-2024 were carried out, and the machining efficiency, cutting force and surface roughness of RPCM and REM feeding along X or Y directions were investigated. The results showed that compared with REM, the machining efficiency of RPCM has been improved at least 21.34% and surface roughness has been reduced by at least 33.33%. At the same time, the maximum cutting force component and the axial cutting force of RPCM were superior to REM. The RPCM is equivalent to an ordered combination of multiple trochoidal milling with spaced fixed phase angles. Under the conditions of the same robot system configuration and processing parameter combination, the machining performance of RPCM is better than REM.

Abstract:Rolling bearing noise environment is complex, low signal-to-noise ratio and the vibration signal is nonstationary and nonlinear, the accuracy of traditional diagnostic methods is low in noisy environment, thus an improved capsule network feature extraction structure and the calculation method of back propagation loss value is proposed. The Inception structure of multi-scale convolutional kernel and spatial attention mechanism are applied to extract features instead of the single convolutional layer of capsule network, so as to obtain prominent feature data in key areas under different scales. Vector neurons are constructed with capsule structure, and digital capsules of classification structure are obtained through dynamic routing, so as to realize fault diagnosis. The loss calculation of training process adopts the method of combining interval loss and reconstruction loss, and a more reasonable calculation process of back propagation is constructed by adjusting the proportional coefficient of the two. To verify the actual diagnostic effect of the model, the experiment was carried out by adding gaussian white noise of different amplitude energy and adjusting the signal-to-noise ratio by using the experimental data of four rotating speeds and corresponding four load conditions in the bearing data set of Caesar western reserve university. The double convolutional layer capsule network was compared with the traditional convolutional neural network. The results show that the method can get good diagnostic results in noisy environment and has obvious advantages over other diagnostic methods in noise resistance.

Abstract:Aiming at automatically detecting the slight scratch of smooth surface of mobile phone screen, a method for small target segmentation and insignificant defects detection based on “Classification net + Attention U-Net” is presented. The necessary components of smooth surface defect detection system based on the classic U-Net are proposed, including preparation of data set, semantic segmentation network, definition of evaluation standards and loss function, appropriate regularization methods and special initialization method. The reason for failing to detect and false detection of insignificant defects by the constructed classic U-Net are analyzed. An improved scheme of adding segmentation network to classification network and adding the Attention mechanism to the classic U-Net is presented. A network consists of “Classification network + Attention U-Net” is constructed to improve the effects of small target segmentation and insignificant defects detection. The results show that the pixel accuracy rate of defects detection of mobile phone screen arrives 0.997 by the presented improved net. The presented method can meet the actual requirements on detecting the slight scratch defects of the mobile phone screen. It can also provide valuable reference for similar scratch and crack detection of smooth surface of ceramic tiles.

Abstract:To reveal the soot formation characteristics of lignite and the role of Na in coal-derived soot formation, inductively coupled plasma emission spectrometer, X-ray photoelectron spectroscopy, fourier transform infrared absorption spectrometer and other methods were used to study the yield, surface and overall chemical properties of soot produced by the pyrolysis of acid-washed Yimin lignite loaded with blank, physically adsorbed Na (ANa) and ion-exchangeable Na (INa) under different residence time in a drop-tube reactor. The results show that during the surface growth stage of lignite derived soot, the increase of soot yield is far more than the decrease of tar yield. When the residence time is long enough, soot yield decreases and oxygen-containing functional groups content increases. Loading Na can reduce soot yield, but INa has much stronger inhibitory effect on soot than ANa, and INa also can increase ether and sulfone content in pyrolysis aerosol. These phenomena indicate that during lignite secondary pyrolysis, small molecular aromatic compounds, aliphatic substances and light gases would also increase soot yield through surface growth. Oxygen-containing substances in lignite pyrolysis gas can exhibit oxidation of soot when the residence time is long enough. INa can maintain the organic binding state with char or volatiles, reduce primary tar release in primary pyrolysis, and promote the combination of volatiles and oxygen-containing substances in secondary pyrolysis. But ANa has no obvious effect in primary pyrolysis. In the second pyrolysis, gasified ANa and INa have the same mechanism of inhibiting soot formation.

Abstract:To explore a NO reduction technology of coal-fired industrial boilers with high efficiency and low cost, the applewood pyrolysis char and pyrolytic semi-char which are suitable for industrial applications were used as reducing agents, and the effect of microwave on the two samples reducing NO was studied in a microwave reaction system. For explaining the NO reduction experiment results, the infrared temperature measurement experiment, and the physical and chemical properties such as pore structure and TG reactivity was studied. The results show that, compared with the pyrolytic semi-char, the pore structure of applewood pyrolysis char is more developed with higher BET specific surface area and pore volume, it also ignites earlier, the combustion reaction rate reaches its maximum earlier and burns out first. However, its combustion intensity, reaction ability of earlier stage, flammability and combustion performance are weak. When the microwave is not applied, the NO reduction ability of applewood pyrolysis char is stronger than that of pyrolytic semi-char. Both the two samples have better NO reduction ability with microwave applying, and with the increase of microwave power, the NO reduction rate increases. The effect of microwave on pyrolytic semi-char reducing NO is stronger than that of applewood pyrolysis char. Meanwhile, infrared temperature measurement that the surface temperature of two samples both increases confirms that the microwave has an obvious thermal effect which could promote the NO reduction by char.

Abstract:To solve the problem that the state of health(SOH) of lithium-ion batteries is difficult to be estimated accurately under dynamic working conditions and full life cycle, a method based on fixed charging voltage segment was proposed. Firstly, the charging capacity in a fixed voltage segment during the charging process was treated as the equivalent health factor of battery capacity estimation. Secondly, the optimal charging voltage segment was selected by using genetic algorithm. Finally, eight verification numerical examples based on the aging experiment data of two types of lithium battery were designed, which were different in discharging current and SOH interval. Experimental results show that the value of MAE and RMSE that comes from the estimated SOH of training set batteries and testing set batteries in eight numerical examples were less than 1.55%. The proposed method can accurately estimate the SOH of lithium batteries under full lifetime(SOH between 100% and 60%) for different discharging rates and materials, which means this method is good applicable in practice.

Abstract:To study the ductile fracture mechanical properties of DP590 high-strength steel sheet, based on the DF2012 ductile fracture criterion, six types of tensile specimens under different stress states were designed to obtain the plastic flow and fracture parameters of the materials. In this study, an experiment-simulation hybrid method was used to calibrate the parameters of the ductile fracture criterion, for which accurately describing the plastic behavior before fracture is the key to calibrate the parameters of ductile fracture criterion. A newly proposed anisotropic Drucker yield criterion and a modified Voce hardening criterion were used to characterize the plastic behavior of DP590, and the constitutive model was compiled into a VUMAT subroutine by Fortran language and embedded into ABAQUS simulation software for tensile simulation of specimens. The experimental and simulation results show that the constitutive model can accurately predict the force curves of different specimens at different angles along the rolling direction. Based on the tensile experiments and the calibrated constitutive model, the parameters of DF2012 ductile fracture criterion were calibrated and the fracture locus of DP590 in two-dimensional space of stress triaxiality and fracture strain was constructed. And three typical ductile fracture criteria (Cockcroft-Latham, Clift and Rice-Tracey) were used for comparison. The results show that DF2012 ductile fracture criterion calibrated based on experiment-simulation hybrid method can reasonably construct the fracture locus of DP590 and accurately predict the fracture occurrence of tensile specimens under different stress states.

Abstract:To reduce the micro upsetting force, extend the life of the mold and improve the plasticity and the forming quality of material, the ultrasonic vibration assisted micro upsetting was studied. Modeling and simulation of ultrasonic vibration assisted micro upsetting on copper was carried out to study the effect of ultrasonic parameters on forming force and deformation, and the results showed that the ultrasonic vibration could reduce the micro upsetting force and increase the deformation, the force reduction and deformation increase had a positive linear relationship with the ultrasonic amplitude and a non-linear positive correlation with the ultrasonic frequency. Ultrasonic vibration assisted micro forming platform was built up and the micro upsetting force curves, the surface topography and size of the specimen under different ultrasonic powers were obtained. Experimental results showed that the micro upsetting force reduction increased with the increasing of ultrasonic power. The surface topography was improved with the increasing of ultrasonic power when the power was lower than 1.50 kW. But the surface topography was worse with the increasing of ultrasonic power when the power was higher than 1.50 kW. Simulation and experiment study showed that the ultrasonic vibration could effectively reduce the micro upsetting force, increase plastic deformation, reduce the drum shape and improve the surface topography and forming uniformity.

Abstract:To accurately analyze the strength characteristics of hydraulic support considering the canopy torsional loading condition, by taking ZY6800/08/18D hydraulic support as the research object, the three-dimensional solid finite element model is established. According to the results of hydraulic support test, selecting the location of measuring points on the simulation model, the stress distributions of the hydraulic support are compared under eight boundary conditions for the canopy and base. In addition, the contact stress and status are analyzed under the frictional contact boundary condition between the base and worktable. It is pointed out that the phenomenon of incomplete contact of the base is caused by the load asymmetry during the canopy torsional loading. The influence of four simplified methods for pin joint on the stress distribution is also analyzed under the constant constraint boundary condition. Finally, the stress distribution obtained from the experiment evaluates the accuracy and efficiency of various boundary and pin joint simplification methods. When the canopy boundary selects fixed support, the base boundary selects friction contact with the working table, and retaining the pin joint and bonding the pin joint to the axle hole, the simulation results are the closest to the test results, and the simulation has high-efficiency. The research results can provide the basis and reference for the accurate estimation of the hydraulic support stress distribution.

Abstract:To enhance the knowledge of non-uniform heat flux distribution of receiver in a solar power tower plant, an optical simulation software, SolTrace, was used to model the Gemasolar plant system geometrically and optically, and the wall heat flux distribution of the receiver was obtained. According to the convergence judgment, 5 000 000 rays were used for follow-up study. The accuracy of the model was verified by comparison with results from the litearture. Under the standard condition at the design point on Summer Solstice, the incident radiation of sunlight was adopted. From the simulation results, it is found that the variation of the solar radiation heat flux received on the wall of different receiver tubes is related to the annular distribution of the heliostat field. For a single absorber, the wall heat flux distribution is non-uniform, and the comparison with the Gaussian approximation distribution proves that this distribution is quite different from the design condition. Then, the heat flux distribution of the receiver at noon of Winter Solstice was obtained by using the model. Overall, it is concluded that SolTrace simulation is more practical than the simplified Gaussian approximation distribution for the treatment of wall heat flux distribution of external cylindrical absorber.

Abstract:To explore the influence of lubricant viscosity on the lubrication condition and performance of bearings under high speed condition, the temperature rise and vibration characteristics of 7014C angular contact ball bearings made of Si₃N₄ ceramic and GCr15 steel under different lubricant viscosities were studied. The results show that the temperature rise and vibration of bearings decrease firstly and then increase with the increasing of lubricant viscosity, and the effect increases with the increasing of rotating speed. At the same time, ceramic bearings show better performance than steel bearings under different lubricant viscosities. By combining the test results with the analysis of lubrication condition, the relationship among lubricant viscosity, lubrication condition and performance of bearing is discussed, which provides important basis for selection of the applicable lubricant viscosity of high speed angular contact ball bearings. In addition, the rolling surface damage under different lubrication conditions was analyzed. The results show that the rolling surface damage of both ceramic bearing and steel bearing is small and with little difference under full oil-film EHL. Under partial oil-film EHL, the surface damage of bearing is serious, with a large number of micro peaks and pits. The surface damage on bearing balls and outer raceway is more serious than that of inner raceway, and the surface scratch on steel balls is denser and deeper than that of ceramic balls.

Abstract:To improve the efficiency of port berth scheduling, and aiming at the shortages of grey wolf optimization with slow convergence speed and easy to fall into local optimum, an improved grey wolf optimization is proposed. The improved grey wolf optimization allocates the initial positions of individuals by sin chaotic sequence, enhancing the population uniformity and ergodicity. The head wolf leading strategy is introduced to accelerate the convergence of the algorithm and improve the efficiency of the algorithm. The cooperative competition mechanism is introduced to enhance the local search ability of the algorithm. When the gray wolf population is updated, the adaptive weight is introduced to meet the optimization requirements of different periods. Finally, the performance of the algorithm is analyzed and compared with six algorithms. Experiments show that the algorithm has obvious advantages in convergence speed and convergence accuracy. And the standard deviation of the solution obtained by running the algorithm 20 times independently is 0, which shows that the algorithm has good immunity to solving problems of different dimensions. Besides, satisfactory results have been achieved in the application of port berth scheduling, after the optimization of the algorithm, the total stay time of all ships was reduced by 14.7% compared with before. So the algorithm can obtain relatively better scheduling schemes and provides a new strategy for port berth scheduling optimization.

Abstract:To improve the robustness of position control of tank ammunition transfer manipulator under external disturbance such as road excitation, a fixed-time terminal sliding mode controller (FTSMC) was designed. Firstly, the dynamic model of the ammunition transfer manipulator with basic vibration was established, and the basic vibration of the system was processed into the model uncertain disturbance term. Then a new fixed-time convergence disturbance observer was designed to compensate the uncertainties of the system model and enhance the robustness of the controller, and a fixed-time terminal sliding mode controller was designed based on the fixed-time convergence double power reaching law and the fixed-time non-singular fast terminal sliding mode control surface. Finally, the fixed time convergence stability of closed-loop systems was proved by Lyapunov method. The comparison experimental results under three working conditions show that the designed composite controller is robust to model uncertain disturbance, and the accurate positioning of the ammunition transfer manipulator is realized. The experimental results verify the correctness and effectiveness of the algorithm in practical engineering applications.

Abstract:To improve the accuracy of gas turbine pull-rod rotor modeling, a virtual material layer was introduced at the contact surface of the wheel to characterize the contact effect. By the mathematical statistical model and gaussian distribution function, the mechanical model of the normal contact stiffness of contact surface was obtained, and the contact characteristics under different parameters were analyzed. Based on the constitutive relation of the deformation of material mechanics, the elastic modulus and poisson′s ratio of the virtual material layer were derived, and the contact layer was modeled. The results of dynamic calculation show that, under rigid support, the contact effect caused by the change of preload has a significant influence on the fourth-order critical speed, and the speed deviation can reach 2.31%. The results of introducing nonlinear oil film force show that the increase of preloading force leads to the advance of all motion states, and the dynamic results of solid rotor and rotor considering the contact of preloading force are quite different. The introduction of virtual material layer simplifies the modeling process of gas turbine rotor considering the contact effect and reflects the weakening effect of the contact effect on the transverse vibration stiffness of the rotor.

Abstract:Panoptic power is one of the economic and effective ways to improve urban safety. This paper takes panopticism as the theoretical basis and aims to promote the safety of building clusters, and summarizes the two types of panoptic power: site panoptic power and faade panoptic power. By using the research methods of visibility analysis and viewshed analysis, the panoptic power model of building clusters is constructed for quantification, thereby providing a new perspective for the scientific evaluation of the public safety in the panoptic aspect and further offering new ways to identify weak safety area in building clusters.

Abstract:To explore the service behavior of thermal protection materials in hypersonic environments, wind tunnel experiments and numerical simulation methods are used to investigate the failure of D6AC steel structure under multi-physics coupling. Based on the basic theory of hypersonic aerodynamics and structural mechanics, the multi-physics coupling theory model of hypersonic D6AC steel structure is established. The aerodynamic heating and structural response in different flight environments are obtained by N-S equation simulation, and the results of numerical simulation are verified in wind tunnel test. The aerodynamic heat is the main factor leading to the failure of D6AC steel structure. Under three different flow conditions, the ablation phenomenon occurs in the steel structure, and the starting time of the structure ablation depends on the total temperature of the incoming flow.

Abstract:In order to overcome the shortcomings of the traditional Back Electromotive Force(BEMF) Detection Algorithm, such as filtering delay and error of phase compensation, the morphological filtering is applied to two-dimensional signal to design a digital filter with fixed delay, which makes the filtering delay not to change with the speed and no additional sampling circuit is needed. At the same time, the digital phase-locked loop algorithm is used to improve the delay algorithm of back EMF zero crossing. According to the above methods, a simulation model is built and a controller of brushless DC motor is designed. The simulation and experimental results show that this new BEMF detection algorithm can improve the rotor position detection accuracy of brushless DC motors effectively, and make the control accuracy of speed fluctuations reach the level of one ten thousandth.

Abstract:In this paper, a semi-coke with a particle size of 5-8 mm was used as a carrier to prepare a semi-coke loaded Fe₃O₄ composite material (Fe₃O₄@MSCe). The physicochemical properties and valence bond structure of the sample were characterized by SEM, XPS, XRD and FTIR, and the decomposition performance and heat release law of Fe₃O₄@MSCe/H₂O₂ multiphase Fenton system were studied. The results show that Fe₃O₄@MSCe retains the porous morphology of the semi-coke, and Fe₃O₄ is uniformly and firmly supported on the surface of the semi-coke particles. Under the alkaline conditions of pH=7.8～11.2, both maintain good decomposition activity. In the case of [H₂O₂] =0.25 mol/L, Fe3O4@MSCe dosage is 533 g·L^-1, pH=7.8, T₀=30 ℃, 300 mL o-phenylenediamine solution with a concentration of 0.04 mol·L^-1 decomposition, the rate is 90.9%, and the temperature rise value of the solution is 7.1 ℃. It shows good decomposition performance and exothermic characteristics, which provides technical support for solving the problems of the existing Fenton technology and the energy utilization of sewage treatment.

Abstract:Granular matters have the biphasic characteristics of transmitting pressure while flowing and stiffening while jamming, which makes them the ideal driving medium of the soft robots. Yet with the complex mechanical properties of the granular matters, it is extremely challenging to predict the motion of granular matters-driven soft robots. Considering the discreteness of granular matters and the continuity of hyperelastic soft cavities, a motion analysis method of the soft actuator based on the coupling simulation of FEM-DEM is proposed in this paper. The structure of the soft cavity of bending actuator that has constraints of radial enhancement is optimized on basis of previous researches. Rules of the actuator’s deformation are analyzed using the coupling calculation method of FEM-DEM and the contrast calculation is conducted with the FEM simplifying granular matters to continuous medium using Mohr-Coulomb model. The actuator prototype is manufactured using technologies of 3D printing and silicone casting, and the kinetic characteristic and capacity of variable stiffness are tested. The experimental and simulation data show that, compared with the FEM based on the Mohr-Coulomb model, the coupling calculation method of FEM-DEM proposed in this paper is expected to increase the accuracy of predicting the actuator’s bending angle by about 14.3%. Using granular matters with smaller diameters can improve the deformation capacity. At the same time, compared with the original scheme in previous researches, the maximum bending angle of the actuator that has constraints of radial enhancement increases from 48.9°to 72.7° without weakening the capacity of stiffness tuning.

Abstract:In this study, the direct numerical simulations of turbulent channel flow combined with Parallel Direct Method of DNS (PDM-DNS) are performed, and high parallel efficiency is obtained. A parallel efficiency of over 95% can be achieved on 256 cores of the Tianhe-2 supercomputer. Statistics of four cases with Re_τ=6,4, 960 and 2000 have been compared with the Lee&Moser’s results and the reliability is verified. Further, based on the advantage of finite-difference with immersed boundary condition easy to deal with wall boundary condition, a simulation added local burr band at Re_τ=176 has been performed to realize research of complex boundary condition. The proposed method provides a new tool for the study of turbulent channel flow with complex boundary condition.

Abstract:The active vibration isolation control problem under multi-frequency fluctuant line spectrum excitation was studied, and an improved wavelet packet adaptive control algorithm was proposed. It was difficult for traditional adaptive algorithms to control multi-frequency line spectra at the same time. Narrowband filtering algorithms also could not achieve good effect under fluctuant frequency excitation. Therefore, the wavelet packet decomposition algorithm was introduced to the control algorithm to divide the signal into equally spaced frequency bands. And then, a parallel control strategy was adopted to control multi-frequency line spectrum. The influence of different wavelet basis functions on signal decomposition was analyzed, and the optimal wavelet basis was determined. Aimed at the problems caused by the virtual line spectrum and too many sub-bands, the wavelet packet decomposition algorithm was improved to reduce the calculation amount and eliminate the virtual line spectrum in the sub-band. An independent step size was set for each sub-band, and modified according to the tongue-line function. The control system was build to carry out experiment. The results showed that the improved wavelet packet adaptive algorithm proposed in this paper can achieve good control effect under multi-frequency fluctuant line spectrum excitation, and the vibration energy of line spectrum was significantly reduced.

Abstract:To study the micro pore characteristics of cement stabilized macadam and the change process of pore space structure under load, through the establishment of three-dimensional pore model to quantify the cross section pore and three-dimensional pore, and the conversion of three-dimensional pore network structure, the parameters such as pore coordination number, pore volume and throat length were extracted. The changing process of pore space structure was deduced by studying the changing rule of parameters with the step-by-step load. Results show that the quantitative porosity of cross section and three-dimensional porosity could characterize the pore change of materials. The peaks in m and n regions extended from 12.10% and 10.29% to 13.89% and 13.41%, the peak distribution region in n region spanned 11 layers. The waveforms in the m and n regions changed drastically and the micro structure of the pores changed significantly. The mean value of coordination number changed from less than 0.45 to 0.505 and the small pores in the pore volume occupied 80% of the pore space structure, but the pore volume changed with increasing load. During the gradual loading process of throat, the maximum throat length increased by nearly 2mm, the throat changed from negative to positive and the load changed the pore space structure. The change of pore microstructure and pore space structure resulted in the change of internal structure of materials and the macro failure of materials. Therefore, the macro failure of materials was essentially related to the change of pore structure.

Abstract:Traction system of mountainous track carrier mainly includes driving drum, wire rope, and cargo trolley, but the wire rope is the core component. At present, there is no clear spatial mathematical model for the wire rope of mountainous track carrier. To further study the mechanical model and failure behavior of the wire rope, it is necessary to derive the spatial geometric mathematical model and three-dimensional model, so as to avoid large-scale tests to explore the service life and damage rules of the wire rope. The spatial spiral equation of the traction wire rope in the upright and curved state are derived by using differential geometry and the principle of spatial coordinate transformation, and the software of MATLAB and Solidworks are utilized to parameterize design and establish entity array. The results show that the curvature and deflection of the straight section and the bending section of the wire rope are periodically changing. The space spiral equation provides a basis for the establishment of mechanical model of mountainous track carrier wire rope and the study of damage mechanism.

Abstract:Establishing a solar radiation model which employs pertinent meteorological parameters for the estimation of solar radiation is essential for enhancing solar radiation data. The statistical duration used by the radiation model influences the model’s coefficients and further affects its estimation errors. To select a proper statistics duration and minimize the radiation model estimation error, this paper proposes a kind of method that chooses an appropriate statistical duration based on the climate abrupt change year. By analyzing the meteorological and radiation data records of more than 25 years from 90 observatories and meteorological stations in China, three meteorological elements that are closely related to solar radiation, namely, sunshine duration, temperature and humidity, are used for abrupt change inspection. The coefficient of variation method is used to determine the climate abrupt change year. Daily global radiation model and daily diffuse radiation model are established respectively by choosing the statistics duration of observation data for over 25 years and the statistics duration after climate abrupt change year. The estimation errors of different models using different statistics duration are compared. According to the error results, the Root Mean Square Error percentage can be reduced by above 2% if data record years after the climate abrupt change year, which serves as the time node, are used as the modeling statistics duration. It demonstrates that the method of choosing radiation modeling duration using climate abrupt change year can reduce the modeling estimation error effectively. The method provides a reference to select the statistical duration in radiation models.