Abstract:In order to distribute the geometric errors of parts economically and reasonably, a method for the analysis and design of geometric accuracy was proposed. According to the specific structure of a three-axis CNC surface grinding machine, a geometric error propagation model including 21 parameters was established on the basis of multi-body system theory and homogeneous coordinate transformation method. The model was verified and it had ideal prediction accuracy. Key geometric errors were analyzed by using orthogonal design and parameter test of DOE methods. After cost analysis and error tracing, a cost-quality model for key geometric error variables was established on the basis of robust design theory. At last, the tolerances of key geometric error variables were distributed according to this model. The results have shown that the methods mentioned above are effective in the distribution of the geometric accuracy of grinding machine.

Abstract:In practical application, when the test weight is insufficient, it is urgent to solve the safety and reliability problems of crane structure. The deflection value is one of the key inspection indices of crane girder under rated loading in overall test. Therefore, it is very important that the influence of structure parameters on the mid-span deflection is quantified. For large-span and heavy-duty gantry cranes, the effect of rigid-soft legs on mid-span deflection was not considered in the past. So a mathematical model was established for universal large-span and heavy-duty gantry cranes. Considering the coupling effect of the bending moment of girder and legs, the analytical solution was derived and obtained on the basis of the variational principle. Then, the experimental model was designed and experiments were performed on the WEW-600B type testing machine. The experiment data show that the analytical solution of the gantry-frame structure deflection is more accurate than the pre-existing calculation method, which provides an analytical tool for the design and inspection of gantry structures.

Abstract:Taking cylindrical hole shaft joint surface as the research object, the actual error model of hole shaft joint surface with coupled tolerance was studied based on the new generation of GPS standard system. Taking cylindricity for instance, combining with the cylindrical form error evaluation method in the GPS standard, the external associated size actual change interval solving model of the cylindrical hole shaft surface was established, and the effect of actual error on fitting property was analyzed by using Monte Carlo method to simulate the random error. The formation mechanism of hole shaft joint surface error under the coupling effect of three kinds of tolerance, including direction tolerance and position tolerance, was analyzed, the actual error models of cylindrical hole shaft joint surface under different fitting properties were established, and the actual change interval of each error component of the joint surface and actual fitting property were obtained. Hole shaft actual assembly accuracy prediction in the design phase was achieved by taking the tolerance optimization design of the hole and shaft parts with the actual hole shaft joint surface accuracy and fitting property requirements as the constraints, and hole shaft processing cost as the objective. Finally, the feasibility and practicability of this method were verified with an example of hole shaft assembly accuracy analysis and tolerance optimization.

Abstract:In order to improve the speed ratio control accuracy and stability of Continuously Variable Transmissions (CVTs), the thrust balance impact factors were studied and the relationship between the primary pulley thrust and the secondary pulley thrust was analyzed. Theoretical analysis and experiment verification methods were utilized. A math model for thrust ratio was developed. The impact on balance thrust ratio from speed ratio, torque ratio, input torque and primary speed was investigated in test bench experiment. The results are as follows: 1) the balance thrust is proportional to the ratio between the primary and secondary working wrap angles; 2) The thrust ratio becomes smaller when the input torque is larger under the same speed ratio condition; 3) The thrust ratio increases when the input torque ratio becomes larger; 4) The thrust becomes smaller when the maximum input torque becomes larger under the same torque ratio condition; 5) The impact from primary speed can be ignored. This paper explains the balance mechanism of thrust ratio and provides a theoretical and experimental basis for controlling speed ratio accurately.

Abstract:Traditional magnetic abrasive polishing process is only suitable for processing one side of the workpiece, but it cannot polish double-surface at the same time. To overcome the shortcomings of current methods, this paper presented a new magnetic polishing process based on annular magnetic field, which can polish both sides of the workpiece simultaneously. Electromagnet with annular magnetic field was designed, and then finite element simulation analysis was carried on. In order to further explore the effect of current intensity, the clearance between the magnetic pole and the workpiece, the spindle speed and polishing time on surface roughness, double-surface polishing experiments were carried out on the material of stainless steel. It was concluded that the surface roughness Ra decreased with the increase of polishing time, working gap and spindle speed. Orthogonal test scheme was designed to obtain the reasonable process parameters and experimental verification was made. Finally, a good surface roughness on both sides was obtained. The experiment has proved that the method can polish both sides of the workpiece surface at the same time, and the surface roughness Ra of two surfaces decreases from the original 0.2 μm to Ra (S) = 0.094μm and Ra (N) = 0.068μm respectively.

Abstract:The Poincaré map of periodic motion was established, and the bifurcation diagram of two parameters was obtained by using an explicit critical criterion without using eigen values when the difficulties caused by the classical Neimark-Sacker bifurcation critical criterion described by the properties of eigenvalues were considered. The bifurcation diagram helps to proactively design the quasi-periodic impact motion of the system. Then, the stability of the quasi-periodic impact motion was further analyzed by utilizing the center manifold and normal formal theory. Finally, numerical experiments verify that the stable quasi-periodic impact motion can be generated at chosen parameters points.

Abstract:This paper discussed the nonlinear torque of the engagement of selectable one-way clutch, which causes shift impact in the transmission. Firstly, dynamic models including steady states and transient state were built on the basis of the second Newton's law. Secondly, the nonlinear torque of the engagement of the one-way clutch was calculated by explicit FEM method. Thirdly, the torque of the output shaft and rotational velocities of both the input and the output shaft were calculated under the excitation of the torque of the input shaft and impact generated by the quick engagement of the one-way clutch, which was obtained by explicit FEM method. Finally, tests on the engagement of the one-way clutch during shifts were carried out. The test results have shown that the torque peaks and the vibration frequencies on the output shaft are similar in different situations when the speed of input shaft is different. The simulation results are similar to the test results. This proves the method proposed is appropriate in the research of the dynamic characters of the transmission shifting by one-way clutches.

Abstract:This paper studied the transient flow-field response of a simplified vehicle pitching around its front axle. The transient numerical solver employed is based on the large-eddy simulation. The sinusoidal -pitching motion was imposed on the model, and the Strouhal number was 0.13. The numerical method was validated with wind-tunnel experiments. The change rule of the results between transient simulation and quasi-steady simulation is quite large. It has been found that the quasi-steady simulation cannot reproduce the aerodynamics performance of vehicle driving on road. It has also been found that, from the transient simulation results, there is a time lag at the extreme position, which suggests that the flow-field has hysteresis effects. The complex flow-field of transient flow around the road vehicle was thoroughly understood from the space and time through the Q-criterion to identify the coherent structures of the flow.

Abstract:FE models of different oblique crash cases between passenger car and SUV in different crash overlaps and impact severities were developed to investigate the injury responses of the driver in oblique crashes. The method combining the FE and multi-body software was used to analyze the injury response of driver in different cases. It is shown that the impact severity and the crash overlap have great influence on the injury response of the head and the lower limb. It is also indicated that the driver injury response in 30% crash overlap case is more sensitive to the impact severity and the driver injury response in 70% crash overlap case is the lowest in three crash overlap cases.

Abstract:In order to reduce the thermal deformation and improve the accuracy of the grinding wheel spindle in high speed & precision grinder, the heat insulation coating was applied to the hybrid bearing with deep-shallow oil recesses. Using FLUENT and ANSYS two softwares, the thermal characteristics of the heat insulation coatings on the bearing with different thickness and different thermal conductivity were analyzed by some oil supply pressures of the bearing and the spindle speeds. The results show that temperature and thermal deformation of the hybrid bearing and their uniform distribution are gradually decreased with the increase of the thickness of the heat insulating coating and with the decrease of the thermal insulation coating's thermal conductivity and with the increase of the oil supply pressure and with the decrease of the spindle speed; Heat insulation coating can be the average bearing temperature distribution. High performance heat insulation coating will greatly reduce the thermal deformation of the bearing spindle and improve the accuracy of the spindle, the machining precision of the grinding machine with the spindle will be improved.

Abstract:In order to address the redundancy of image in the detection process of rail surface defects, an algorithm of matching for the redundancies of rail surface images was proposed. At the beginning, the rail surface area was extracted by using the vertical projection method. And then, the location information of defects was obtained through the image preprocess and binarization on the rail surface. Next, the morphological information of the rail surface defects was achieved in the horizontal projection method. At last, the defect location information and morphological information were matched on the basis of the improved fuzzy matching algorithm. The experiment results verify that this algorithm can effectively identify the redundancy information of image, and the accuracy rate is as high as 97.5%.

Abstract:Aiming at the probe shortcomings in terms of solder joint detection efficiency and accuracy rate in the rough location, this paper proposed a new method to precisely acquire spot coordinates. The method takes advantage of morphological characteristics of solder joints, and utilizes polar Hough transform algorithm and the improved edge detection operator. This method reduces the storage parameters through the morphological structure of decision, and greatly improves the speed of computation by using polar coordinates to construct 2D parameters. Combined with the algorithm of filtering, least square and double threshold method, it can detect and calibrate the solder joint in high-noise background to improve the efficiency of the robot for the detection efficiency and accuracy rate of the solder joint quality. It has important practical significance in industrial processing. The experiment results show that the accuracy of this method reaches 99.2%, and the speed has been greatly improved.

Abstract:With wide application of AC drive electric locomotives in railway networks, the negative sequence current and neutral section increase significantly, and the co-phase power supply system with Railway Power Conditioner (RPC) is an effective solution. In order to increase its cost performance, a new Hybrid Railway Power Conditioner(HRPC) for co-phase was proposed. Compared with the traditional RPC, HRPC is much lower than RPC in operation voltage, so its capacity of active part decreases significantly. This paper analyzed its topology, compensation principle and operation voltage of its active part. The design of its key parameter was given. The results prove that HRPC is lower by 46%~50% than that of RPC in completing similar compensational tasks through simulation.

Abstract:Compared with the traditional power, many different kinds of micro sources and control modes are used in distributed generation (DG) , which makes the small signal electromechanical transient analysis of the power grid difficult. This study established a reduced order model of photovoltaic (PV) power generation considering the behavior of battery and inverter, and presented a power source model of solid-oxide fuel cell (SOFC) by analyzing the characteristic patterns of the full-order state-space model and the time constant of SOFC and PV. Then, the model was used to study the effect of grid-connected DC distributed generation on power system small signal stability through simulation examples. The research shows that SOFC or PV affects the system damping characteristics by changing the power flow and the system equilibrium point. When the output increases, due to the increasing spinning reserve of the conventional unit, the damping characteristics are strongly related to the conventional unit, in which working in the operation mode of reducing output will show a tendency to increase.

Abstract:Aiming at the deficiency of energy saving technology in enterprise distribution network, an energy saving management system of distribution network based on multi-agent genetic algorithm was proposed. Combined with genetic algorithm and multi-agent system, a GA-MAS algorithm was proposed. Each multi-agent was equivalent to an individual of genetic algorithm, and the adjacent multi-agent was in interaction. The GA-MAS algorithm was combined with the evolutionary mechanism of the genetic algorithm for global optimal solution. The agent structure model of the energy saving equipment and the intelligent architecture model of high / low voltage system were presented. Using the proposed GA-MAS algorithm, the optimal regulation of energy-saving equipment was obtained, so the least cost of the energy-saving equipment had the biggest energy saving profit. The simulation and practical application have shown that the proposed energy saving management system of distribution network can reduce the total active power loss and the total number of capacitors, and achieve the best regulation of energy-saving device. It has also been shown that the proposed GA-MAS algorithm has faster convergence speed.

Abstract:This paper presented a single current active damping method based on two- degrees-of-freedom proportional integral derivative (2DOF-PID) control for LCL-type grid-connected inverter, which consists of proportional integral (PI) links and incomplete differential link. PI part is used to control the grid-connected current to inject the grid with high-quality. Incomplete differential part enhances the damping coefficient of LCL inverter, effectively suppresses the resonance peak caused between the inverter and the grid to improve the system reliability and stability, and speeds up the dynamic response. This method does not require additional voltage / current sensor, thus reducing the inverter cost. By establishing the transfer function of the 2DOF-PID controller, the system stability margin and dynamic characteristics were analyzed, and the proper control parameters were selected. The simulation and experiment platforms were built. The simulation and experiment results have shown that, in LCL-type grid-connected inverter under 2DOF-PID controller, the total harmonic distortion (THD) of grid-connected current is only 2.2% at full load, which is far below the national standard (GB/T 30427-2013). When the loads change from a half to all, the system overshoot reduces to 9 %, and the system response is faster than other methods.

Abstract:This paper proposed a two-phase network-aware virtual machine allocation algorithm (NWTP). Firstly, based on the randomness (the mixing of tree topology, servers and fiber) of modern data center network topology, the bandwidth requests of virtual machines were divided into two types of inner-bandwidth and outer-bandwidth according to the difference of interactive objects. Secondly, the virtual machine allocation requests were decomposed into two successive phases, and the corresponding network-aware model was established. Thirdly, pipelining technology was developed to regard the bandwidth region partitioning and physical host allocation as two consecutive steps, and to conduct parallel processing. For bandwidth region partitioning phase, the stability of physical host was dynamically perceived by using node betweenness and clustering coefficient, addressing differential allocation strategy to select the appropriate physical host set for the virtual machines subset. For the physical host allocation phase, more virtual machines were allocated to physical host resources with the largest load variance, which saved inner-bandwidth of data center and balanced physical hosts load. Finally, by comparing with the genetic algorithm GA, the annealing algorithm SA and greedy algorithm GR were simulated. Numerical results have shown the performance of NWTP in allocation time, network delay, network throughput rate, CPU utilization, bandwidth utilization and physical host usage.

Abstract:Aiming at the inaccuracy of clustering numbers and the slow speed of ordinary consensus clustering algorithms, Newman greedy algorithms of complex networks theory and spectral clustering algorithms were combined to propose a novel consensus clustering algorithm based on Minkowski distance. The algorithm depicts the similarity between samples in terms of Minkowski distance and adopts the strategy of random walk. By adjusting the parameters of the Laplacian distance, the accurate information of the clustering number is automatically obtained. The simulation results show that the proposed consensus clustering algorithm based on Minkowski distance has the superiority of the running time and accuracy of the clustering number. This method was applied to actual copper froth flotation process, and the results further illustrated its effectiveness.

Abstract:N-Gram, Nave Bayes, K nearest neighbors and TF-IDF are classical text classification models with a wide range of applications. People are often puzzled about which classification model should be used in a certain Chinese text classification task. This paper collected more than ten thousand Chinese news texts, and designed a series of experiments to analyze the performance of these models in varied situations from classification parameters, training data scale, text length and skewed data sets. The characteristics of these models were summarized, which provides a practical guide for the model selection in Chinese text classification tasks.

Abstract:In order to improve the efficiency of online diagnose of faults in discrete event system, from the viewpoint of the observable events judging occurrence of faults, this paper proposed a method called minimal observation sequences of faults. The finite state automaton was selected to model the discrete event system. First, a fault model of system was established in the offline, which was used to exclude the path independent of the system failure. Then, a minimal observation sequence model of faults was established according to the fault model. When the discrete event system is diagnosed online, it is necessary to compare the observations received by sensors with the model of minimal observation sequences. If any path in the model is found to satisfy the online observations, the fault in the termination state of the path will be described. Otherwise, no fault occurs. By comparing with the experiment results, the model of minimal observation sequences of faults can be used to determine the occurrence of faults as soon as possible. That is to say, the model for the system can find the faults timely and save the cost of online diagnosis.

Abstract:The methods using spectral information alone are often ineffective due to the spectral similarity between roads and other artificial structures with impervious surface. This paper proposed a knowledge-based method for urban road extraction by including spatial texture information. The spatial texture feature was firstly extracted by the local Moran's I and the derived texture was added to the spectral bands of images for image segmentation. Then, features like brightness, standard deviation, rectangularity, aspect ratio and area were selected to form the hypothesis and verification model. Finally, roads were extracted by applying the models and were post-processed on the basis of mathematical morphology. This new method was evaluated by a 0.1m aerial image. The results show that the extraction accuracy reaches about 88% by using the proposed method, 5% higher than the corresponding images without the spatial texture information.