Abstract:

Abstract: The robust H_∞filtering problem of Markov jump systems with partly unknown transition probabilities and packet dropouts was investigated. Assuming that the probability of packet dropouts would obey Bernoulli distribution, a discrete-time Markov jump system with uncertain parameters and mode-dependent full-order filter were constructed based on the Delta operator. The slack matrix variables were introduced to solve the cross coupling between the system matrices and the Lyapunov positive matrices. The Lyapunov function, Schur complement and linear matrix inequalities were used to obtain sufficient conditions for the system to be stochastically stable and satisfy H_∞ performance. The optimal H_∞ performance index of the Delta operator system and the shifting operator system were obtained respectively with the known probability of packet dropouts. When the probability of the packet dropouts were lower, the robust performance as well as the optimal H_∞ performance of Delta operator system were better than the shift operator system. Numerical simulation proved that the method proposed in this paper not only was effective and feasible, but also had certain advantages.

Abstract: Due to the small sample size of traditional neural networks, the error rate of the recognition of the scene was very high, and it could not continuously learn during the execution of the task. This would lead to poor adaptability of traditional neural networks to unfamiliar environments. In response to these problems, a bionic robot behavior decision-making cognitive computing model was proposed. The algorithm used semi-supervised and state transition learning methods. Firstly, a small number of training samples were used to train the developmental neural network, so that it could have some basic behavioral decision-making capabilities. When the robot was exploring in the actual environment, it could continuously learn new unlearned scene data. When the robot completed the task, the network model would recall the specific scene it had experienced according to a certain probability, and combined the state transfer mechanism to continuously adjusted its own decision-making effect. This method could make the network model quickly converge to a stable state, and had strong adaptability in unknown environments. In order to verify the feasibility of the model, a real robot operating environment was designed, and the RIKIROBOT was used for navigation testing. Experimental results showed that this developmental model could converge to a stable state after 3 to 5 decision-making adjustments in an unknown environment, and the decision-making effect was continuously improved. Robots could deal with various complex environments by continuously accumulating knowledge, and had strong adaptability in unknown environments.

Abstract: In order to solve the increasingly serious problem of phishing, a phishing URL detection method based on convolution neural network (CNN) and bi-directional long short termmemory (BiLSTM) was proposed.This method first classified the URL based on the sensitive word segmentation method; classified the URL according to the special characters and sensitive words; and classified the non-sensitive words in the character level, so as to obtain the effective information of the special characters and sensitive words, and improve the use of URL data information. Then the segmented URL was input into CNN and BiLSTM, to obtain the spatial local features of the URL through CNN, to obtain the bidirectional long-distance dependent features of the URL through BiLSTM, and to detect phishing webpages based on the automatically extracted features.Compared with traditional machine learning and blacklist detection methods. Experimental results showed that the phishing URL detection method based on CNN and BiLSTM could achieve better detection results, the accuracy rate was 98.84%, the precision rate was 99.71%, the recall rate was 98.04%, and the F1 value was 98.86%. This method did not require manual feature extraction and could identify newly emerging phishing webpages.

Abstract: Neighborhood search is an important step in the spatial interpolation algorithm. Whether the neighborhood range is properly selected has a great impact on the interpolation efficiency and accuracy. Aiming at the problem that there were few studies on neighborhood search of interpolation algorithm, a neighborhood search strategy based on octree considering the spatial distribution of discrete points was proposed in this paper. Firstly, the minimal enclosing box of the sampling points was constructed and divided with octree, and the sampling points were grouped into each divided box. Then, the spatial distribution of the interpolating points was constrained by defining the point density. Finally, the above neighborhood search strategy is applied to the ordinary Kriging interpolation model. In order to verify the feasibility of the proposed method, in true 3D geological modeling, the proposed algorithm of this paper, the conventional Kriging interpolation based on fixed distance and fixed number strategy, and the inverse distance weighted interpolation were all used to calculate respectively, and the geological model was constructed from the data obtained from the interpolation. By comparing the method of this paper with the traditional spatial interpolation methods, it was concluded that the proposed method was superior to the traditional method in interpolation accuracy and efficiency when the same number of points were obtained under the same conditions, except for the fixed number method of 30 sample points. Although the fixed number method of 30 sample points had a slight advantage in accuracy, its calculation time is 6.6 times longer than that of the proposed method. In addition, the proposed method improved the time by 20% compared with the traditional method under the same conditions. Compared with the traditional method, the proposed method reduced the redundancy by nearly 1/3 when using the interpolated data to construct the geological model at the same level, thus improving the efficiency of calculation.

Abstract: For differences in tone, pitch, speaking speed, etc. of social speech and information loss or redundancy during filling, a speech emotional recognition method was proposed based on spatial-temporal features. The method applied convolutional neural network (CNN) and bilateral recurrent neural network (BiGRU), including spatial feature extraction module, temporal feature extraction module and feature fusion module. Considering the different lengths of audio data content, the audio data was preprocessed first, and three zero-padded padding lengths were applied to obtain spectrograms of different scales. Then the spatial feature extraction module was designed to capture the local feature of the audio, and used the temporal feature extraction module to obtain the temporal feature and the semantic relationship of the audio data, thus obtained three spatial-temporal feature vectors. In addition, these temporal feature vectors were fused and input full connection layer for classification of speech emotion. With the numerical experiment using IFLYTEK speech emotion data sets, the experiment achieved better results in the accuracy, precision, recall, and F1 value than those of the experiment of traditional speech emotion recognition model.

Abstract: To solve the low running speed of the multi-traveling salesman problem (MTSP) using the heuristic method, a CUDA-based hybrid particle swarm clustering-ant colony algorithm (GPSO-AC) was proposed by integrating their parallel characteristics with programming techniques optimally. GPSO-AC used GPU′s instruction architecture with multiple stream processors (SM) and single instruction multithreading (SIMT) to parallel the search process of numerous independent individuals, so as to accelerate the execution speed of the hybrid iterative method. GPSO-AC was tested on 6 datasets compared with other methods, such as PSO-AC, TPHA and K-means-AC. Then the influence of cost equilibrium constraint on the convergence performance of the optimal solution of weighted MTSP problem was discussed. Furthermore, the cost standard deviations obtained from GPSO-AC on chn31 with different traveling salesmen, were 1 165.26, 54.97 and 6.74 in the three cases respectively. The experimental results showed that the proposed algorithm was much faster than other CPU based algorithms and the advantage becomed more obvious with the expansion of the model size, and the convergence precision of the algorithm was better than the similar algorithms for solving MTSP problems.

Abstract: Four mono-block-layer-built-type (MOLB-type) SOFCs with different flow channel angles of 105°, 120°, 135° and 150° were modeled on the premise of the same reaction area, the same thickness of electrodes and same electrolyte layer. The effects on flow distribution, maximum temperature difference and electrical performance of these models by the various flow channel angles were simulated. The simulation results showed that the increase of flow channel angle had a positive effect on the gas transfer and corner effect in the anode above fuel flow channel but an inhibitory effect in the anode that was in contact with the interconnect. When the flow channel angle increased from 105° to 135°, the maximum temperature difference could be reduced by 6.18% for per 15° increase with rarely changing the electrical performance. The hydrogen mole fraction of MOLB-type SOFC with the flow channel angle of 150° was 11.3% higher than that of 105° on average at the corner line. Through comprehensive comparison, it was better for the flow channel angle of MOLB-type SOFC to be 135°.

Abstract: In order to improve the wear resistance of 316L austenitic stainless steel, a gradient nanostructured (GNS) surface layer was formed by ultrasonic nanocrystal surface modification (UNSM) method. The microhardness, residual stress and microstructure of the sample surface were studied by microhardness tester, nanoindentation tester, X-ray residual stress analyzer and scanning electron microscopy. And the wear resistance of gradient nanostructured surface layers with different depth was studied. The results showed that grain refinement existed on the surface of 316L stainless steel after UNSM treatment and the thickness of gradient nanostructure layer increased with the increase of treatment times. Compared to the untreated samples, the surface residual compressive stress increased from -413 MPa to -1 193 MPa, the surface microhardness increased from 306 HV0.2 to 405 HV0.2, and the friction coefficient was the least when the UNSM was treated three times. The results showed that the surface properties of 316L stainless steel were significantly improved by ultrasonic nano-surface modification, and the friction coefficient was reduced.

Abstract: In order to improve the quality of sand product, the crushing process of the vertical shaft impact crusher was simulated. The transient crushing process of the vertical shaft impact crusher and the reason of particle breakage were analyzed; and the influence laws of different rotor diameters, rotor speeds, feed particle sizes and feed rates on the velocity of particle ejection, crushing rate and rotor power were investigated. In addition, the relationship between velocity of particle ejection and crushing rate was analyzed and the reliability of the simulation results was verified. The results show that particles could be accelerated by the rotor and thrown towards the wall of the crushing chamber, not only the violent collision between the high-speed particles and the wall of the crushing chamber, but also the violent collision between different particles make the particles broken up after being thrown out. With the increase of rotor speed and rotor diameter, the crushing rate increased; while with increase of the feed rate, the crushing rate decreased; with the increase of feed particle size, the crushing rate increased at first and then decreased. In addition, with the increase of rotor speed, rotor diameter and feed rate, the rotor power would increase greatly while the feeding particle size had no effect on rotor power; the simulation rotor power was basically consistent with the actual rotor power. Considering the crushing rate comprehensively, when rotor speed was 1 600 r/min, rotor diameter was 1 100 mm, feed particle was 30 mm and feed rate was 160 t/h, this set of parameters was optimal in this paper.

Abstract: The process model of ORC system was established with Aspen Plus software to investigate the impacts of zeotropic mixtures on system performance. The thermal performance and economic performance of mixtures were studied when 60～100 ℃ evaporation temperature, and the system performance was comprehensively analyzed based on the gray correlation method. The results showed that the performance of many mixtures was better than their pure working fluids, especially 3R600a/7R601a. When evaporation temperature was 100 ℃, the grey correlation grade of 3R600a/7R601a reached the maximum 0.994, and its net output power, thermal efficiency, LEC were 56.59 kW, 11.76%, and 0.1312 width=5,height=12,dpi=110/kWh, respectively. Compared with the pure working fluid R600a, the net output power and thermal efficiency were increased by 31.73% and 11.05% respectively, LEC was decreased by 11.06%. The result showed that the target pure working fluid was mixed with another new working fluid with similar output power to obtain a zeotropic mixture with a large temperature glide, and the zeotropic mixture could significantly improve the performance of ORC system.

Abstract: To explore the influence of channel structure on the heat dissipation effect of electric vehicle drive motor of four different powers, the three-dimensional model of fluid flow and heat transfer in the shell was established. Fluent simulation was employed to calculate the flow field and temperature field of two different channel structure drive motors of different power. The results showed that only the six-channel structure could supply the demand of the heat dissipation when the motor power was more than 100 kW. When the motor power was 80 kW and 90 kW, the maximum temperature of the inner wall surface of the four-channel structure was 12.05% and 12.48% higher than that of the six-channel structure, respectively. At this time, the two kinds of channel structure could meet the heat dissipation requirement, but the pressure loss of the four-channel structure was 61.87% and 61.38% lower than that of the six-channel structure under the two kinds of power, respectively. Therefore, considering the difficulty of processing and the pressure bearing capacity of the shell, the four-channel circumferential "Z" shape structure should be preferred at lower power.

Abstract: Silicon carbide (SiC) coatings were prepared on the surface of high-purity graphite substrates by chemical vapor deposition, and the effects of deposition pressure and substrate position on the morphologies and oxidation resistance of the coatings were studied. The results showed that as the distances between the substrates at first and the air distribution plate increased, the preference of the <111> growth direction of the grains strengthened and then weakened, and the gravel-like growth characteristics of the grains also showed a law of change of strengthening first and then weakening. When the distances between the substrates and the air distribution plate were relatively close, the coatings were prone to pores. As the distances increased, the pores gradually disappeared, and the oxidation resistance of the coatings increased. With the further increase of the distances, the phenomenon of demarcation began to appear, causing the oxidation resistance of the coatings to decrease. Due to the preference of the <111> growth direction of the grains was weakened with the increase of deposition pressure, the gravel-like growth characteristics of the grains were also weakened. When the deposition pressure was 2 kPa, the coating had no obvious defects, the coating had excellent oxidation resistance, and when the deposition pressure increased to 5 kPa and 20 kPa, the coatings had defects of demarcation and delamination, respectively, resulting in a decrease in the oxidation resistance of the coatings. It was concluded that when the substrate position was 450 mm and the deposition pressure was 2 kPa, a SiC coating with dense structure, better combination with the substrate and excellent oxidation resistance could be prepared.

Abstract: Monocomponent polyurethane is a reactive adhesive, and its mechanical properties are better than those of conventional asphalt binders, but the reaction process is easily affected by environmental factors such as temperature, air and water, etc. During the paving and rolling construction of polyurethane mixes, it is necessary to strictly control the construction time nodes of each process in combination with the site temperature and humidity working conditions.In order to popularize the application of single-component polyurethane in road, curing and adhesive characteristics of monocomponent polyurethane were studied in this paper. Curing and adhesion characteristics of two single-component polyurethane (PU) binders were studied from FTIR, pull-out and shear tests. With the increase of natural curing conditions, the results showed that the isocyanate index of PU-I and PU-II decreased, while the urea index had the opposite trend. Both the isocyanate index and urea index of PU were stable after 4 days natural curing,and the variation coefficients of isocyanate index and urea index of PU-I and PU-II were 10% and 2%, 2% and 2%, respectively in 4-7 days, which belong to small variations, indicating that PU had basically reached the fully cured state. With the increase of curing time, the pull-out strength and shear strength of polyurethane bonding system generally increased, and the pull-out and shear strength of stone-polyurethane-stone interface were better than those stone-polyurethane-rubber, rubber-polyurethane-rubber bonding system. The pull-out strength of rubber-polyurethane-rubber interface was the worst, and the shear strength of stone-polyurethane-rubber interface was the worst.

Abstract: In order to reduce the chance of cross infection caused by people not wearing masks during the epidemic, a mask wearing detection access control system based on improved SSD and Jetson Nano is designed to quickly detect whether pedestrians at the entrance and exit wear masks and control the opening and closing of the gate. Firstly, 6 000 training pictures suitable for the system are extracted from the two data sets of MAFA and WIDER FACE, which are used as the training set and 2 000 as the test set; Secondly, the pixel level transformations such as random rue and saturation and geometric level transformations such as random expansion and random clipping are used to enhance the small targets in the data set, so as to add more samples to the data set and enhance the generalization ability of the detection network; Thirdly, the VGG feature extraction network of the original SSD is replaced by MobileNet-V3, which makes use of its speed advantage of depth-wise separable convolution, as well as the optimization strategies such as H-Swish activation function with less computation and lightweight attention mechanism (squeeze and excite) to accelerate the detection and improve the accuracy. Finally, the detection network is transplanted to Jetson Nano, an artificial intelligence edge computing device with limited computing power, equipped with high-definition display, design a foldable parallelogram baffle, and select appropriate peripheral equipment to form a multi-functional access control system with epidemic prevention value to quickly detect whether pedestrians at the entrance and exit of public places wear masks. The test results on the embedded device are as follows: the target detection algorithm SSD with MobileNet-V3 as the feature extraction network obtains 78% MAP and FPS is 12. Compared with the original SSD algorithm with VGG as the feature extraction network (FPS is 2), the detection speed is increased five times. Facts have proved that the system not only ensures the real-time performance, but also takes into account the detection accuracy, so achieves the balance of accuracy and speed.

Abstract: In a high proportion wind power system, the evaluation of system flexibility is the basis of flexible resource allocation and planning. In order to take into account the temporal and periodic characteristics of data, the typical scene set of the system was obtained after clustering reduction and fusion of wind power and load. Then, the flexibility demand, flexibility supply and flexibility index of the system were modeled. Then, the economic scheduling model with flexibility constraints is solved by traversing the typical scenarios. According to the scheduling results, the probability and expectation of insufficient flexibility of each typical scenario are calculated. Finally, the flexibility index of the system was calculated according to the probability of typical scenarios, and the flexibility of the system was evaluated to guide the allocation of flexibility resources. Through the example analysis, it was found that in the high-proportion wind power system, the downward flexibility resource was only the thermal power unit in operation, and the downward flexibility index did not meet the threshold requirement. A certain downward flexibility resource should be configured in the system, otherwise, a large number of wind abandon would occur.

Abstract: In order to study the variation law of stress flow of bridge steel Q345 with strong acid corrosion, 18 Q345 bridge steel specimens were immersed in 36% industrial hydrochloric acid for 0, 1, 4, 12, 48 and 72 h, respectively. The engineering stress-strain curves were obtained by quasi-static tensile test.The true stress-strain curve before necking was fitted by Origin software, and the elastic-plastic constitutive relation of strong corrosion bridge steel Q345 based on J-C model was obtained.On this basis, ABAQUS finite element model was established and the damage evolution of flexible metal was added to simulate the stress flow law and necking failure of steel plate, and the influence of different strong acid corrosion time on the mechanical property degradation of bridge steel Q345 was analyzed.The results showed that the elastic modulus of bridge steel Q345 with corrosion rate of 0.53%, 1.22%, 2.47%, 4.12% and 4.98% decreased by 1.26%, 2.36%, 4.04%, 7.01% and 10.93%, respectively, and the yield strength decreased by 0.61%, 2.61%, 3.56%, 5.37% and 6.82%, respectively, the ultimate strength decreased by 0.42%, 2.31%, 3.57%, 4.58% and 6.42%, respectively.The results showed that the decline rate of mechanical properties of bridge steel plate was relatively slow when corrosion time exceeded 12 h. J-C constitutive model could well simulate the stress flow of bridge steel under strong corrosion. The ductile degradation behavior of strongly corroded steel could be accurately simulated by the flexible damage evolution.

Abstract: In order to explore the load lateral distribution of the new structure composite T-girder bridge with corrugated steel web, a 60-meter-span large-segment prefabricated composite T-girder bridge with corrugated steel web was used for engineering design. A finite element model was established based on ANSYS to study the influence of the structural form and spacing of the diaphragm on the lateral load distribution, and to determine the most optimal layout, the finite element method was compared with the traditional lateral distribution calculation methods. The results showed that the transverse diaphragms of the three structural forms could reduce the peak value of the vertical mark value of the influence line of the load lateral distribution to a certain extent, and make the influence line of the load lateral distribution more smooth. The stiffness difference between the X-shaped steel truss diaphragm and the V-shaped steel truss diaphragm was very small, and the former was slightly higher than the latter. The steel plate type diaphragm improved the lateral load distribution most obviously. For the side beam, the load lateral distribution factors under the three structural forms were all less than 1% lower than that without the diaphragm, and the load lateral distribution factors of the center beam was reduced by 3.2% at the maximum compared with the case without the diaphragm. The lateral load distribution factor of the side beam under the action of the X-shaped steel truss was slightly better than the lateral load distribution factor under the action of the V-shaped steel truss, while the center beam was the opposite. The change of the interval of the diaphragm under the same structure had little effect on the influence line of the load lateral distribution. It was recommended to choose V-shaped steel trusses with an interval of 10 meters as the diaphragm. The rigid connected beam method was suitable to calculate the composite T-beam with corrugated steel webs. The difference between the lateral distribution factor of the side girder and the finite element method was about 6.92%, and the difference between the middle girder and the finite element method was about 1.22%.