Abstract:

Abstract: Halloysite nanotubes (HNTs), a tubular natural mineral material, have potential applications in many fields. Based on the research status at home and abroad, the existing surface modification methods (physical modification and chemical modification) of HNTs were introduced based on the structural characteristics and surface properties of HNTs. The unique hollow tubular structure, large cavity, surface hydrophilicity and surface chargeability of HNTs were elaborated. These influence on physicochemical properties (mechanical properties, thermal stability, hydrophilicity, Zeta potential) and antibacterial and antifouling properties of membranes were discussed and the mechanism of action was analyzed. At the same time, the important roles of the hollow tubular structure and hydrophilicity of HNTs in the hybrid membranes in the solution and diffusion of gas molecules, water molecules, etc., were described in detail. In addition, based on the excellent properties of HNTs, this paper focused on the applications of HNTs in the field of membrane separation: antibacterial, antifouling, oil-water separation, desalination, dye separation, gas separation, etc. Finally, the possible future application fields of HNTs-based membrane materials were prospected, in order to provide some help in improving the understanding of HNTs and the design and preparation of new HNTs-based hybrid membranes.

Abstract: Due to the trade-off limit between membrane flux and selectivity, the development and application of traditional polymer membranes in liquid separation are further impeded. Covalent organic frameworks (COF) are a newly emerging class of porous materials, which hold great promise for developing high-performance membranes with rapid molecule/ion transport and high-efficient liquid separations. In this review, the effects of pore size, stability, hydrophilicity/hydrophobicity and surface charge on the physicochemical properties, pore structures, and separation properties of COF structure-function relationship of COF membranes was discussed. The strategies of regulating the COF properties to optimize membrane performance were briefly described, mainly including selection/pre-design of monomers to synthesize COF membranes and post-modification of COF membranes. In addition, the fabrication strategies of advanced COF membranes were highlighted: blending, in-situ growth, vacuum-assisted filtration and interfacial polymerization. Also, the latest research advances of COF membranes in seawater desalination, sewage treatment, organic solvent nanofiltration and osmotic energy conversion were outlined. Finally, in view of membrane material preparation and commercialization requirements, the current challenges and future development trends of COF membranes were proposed, providing inspiration for the “on-demand design” of new functional COF membranes and useful guideline for the development and practical application of COF membranes for liquid separation.

Abstract: In practical environment, chaotic time series often contain a lot of noise and outliers. Because of these interference factors, the prediction performance of the kernel adaptive filter based on the second-order similarity measure could decrease significantly in chaotic time series prediction. Based on the above problems, a robust kernel adaptive filter prediction algorithm for chaotic time series was proposed. The proposed algorithm based on the nonlinear similarity measure of the generalized logarithmic kernel loss function, could improve the robustness of the kernel adaptive filter in impulsive noise environment effectively. At the same time, the algorithm adopted adaptive K-Means sampling sparse Nyström nonlinear mapping method, which could fix the network size of the algorithm in advance, and thus reduce the computational complexity of the kernel adaptive filter algorithm. Through the recursive updating method, the proposed algorithm had faster convergence speed. Finally, the Mackey-Glass chaotic time series prediction simulation was carried out for the adaptive filter algorithms. The simulation results showed that, as a new robust K-Means sampling Nyström recursive minimum generalized logarithmic kernel loss prediction method, compared with sparse kernel adaptive filter algorithm, this algorithm had better robustness in impulsive noise. Compared with other typical robust kernel adaptive filter prediction algorithms, this algorithm had faster convergence rate and higher filtering accuracy.

Abstract: At present, the vector math functions on the PuDianNao chip of the domestic artificial intelligence processor can only be implemented by calling scalar functions cyclically, and the performance of this method is relatively low. Based on the PuDianNao chip, three optimization methods were proposed. The first two were interpolation method and SIMD masking method. Thirdly, based on a hardware array structure on PuDianNao, VLIW instructions were used to operate each processing unit in the array, and the SIMT programming model was encapsulated programmatically. The accuracy and performance of the above three methods were tested, and the experimental results showed that the third method had the best accuracy and performance. The third method was used to implement the vector mathematical function library PuDianNao-VecMath based on the domestic PuDianNao chip, which solved the problem that the multi-branch structure of mathematical functions was difficult to vectorize. The function library had good precision performance, stable functions and correct operation. The provided interfaces included rounding functions, transcendental functions, comparison functions, activation functions and other common basic math library functions. In terms of precision, the entire data of the function definition domain interval was used as input, and the operation result was compared with the result of the scalar function running on the CPU i7. The results showed that the maximum ULP value was 2, and the maximum ULP value of the half-precision version was 1. Compared with the use of scalar loop, the performance was greatly improved. Compared with the scalar loop, the single-precision version had an average speed-up ratio of 18. 26 and a maximum speed-up ratio of 35. 90. The halfprecision version had an average speed-up ratio of 15. 65 and a maximum speed-up ratio of 30. 11.

Abstract: In order to improve the efficiency of urban travel and parking supply-demand matching, an integrated model of parking mode selection and berth allocation for optimal configuration of travel system was explored. Firstly, a parking choice equilibrium model considering the travel cost of shared parking users and non-shared parking users was constructed. A descent algorithm was designed to solve the parking choice equilibrium model. Secondly, for shared parking users, the integrated berth allocation integer programming model of shared parking platform operators, berth suppliers and berth demanders was established. The travel choice model and the berth allocation model were linked through the decision variables of shared parking allocation. The example showed that the reception rate of the proposed berth allocation model to the user reservation request reached 83%, and the model could be effectively applied to the actual parking problem. Travel users prefered to choose parking lots with short driving distance and walking distance. When the growth gap between shared parking and non-shared parking traffic was the largest, the scale of parking requests could not only enable operators to obtain higher profits, but also improve the balance between shared parking and non-shared parking traffic.

Abstract: To solve the problems of slow convergence speed, high average delay, and low bandwidth utilization of existing intelligent routing algorithms, in this study, a multi-path intelligent routing algorithm RDPG-Route based on deep reinforcement learning (DRL) was proposed. In the algorithm, the recurrent determi-nistic policy gradient (RDPG) was used as the training framework, the long short-term memory (LSTM) was introduced as the neural network. The algorithm advantages of RDPG were used to handle high-latitude problems and the storage capacity of the memory in the LSTM loop core, the dynamically changing network state could be input to the neural network for training. After the algorithm training converged, the action value output by the neural network was used as the network link weight, and the traffic was divided based on the multi-path routing strategy to realize the intelligent dynamic adjustment of the network routing. Finally, RDPG-Route routing algorithm was compared with ECMP, DRL-TE, and DRL-R-DDPG routing algorithms respectively. The results indicated that RDPG-Route had better convergence and effectiveness. Compared with other optimal intelligent routing algorithm, RDPG-Route could reduce the average end-to-end delay by at least 7.2%, improve the throughput by 6.5%, and reduce the packet loss rate by 8.9% and the maximum link utilization rate by 6.3%.

Abstract: Aiming at the problem of longitudinal low-frequency vibration isolation of ship propulsion shafting, a high-load quasi-zero stiffness isolator was designed based on disc spring with negative stiffness characteristics and positive-stiffness coil spring in parallel. The dynamic equation of the shafting-quasi-zero stiffness vibration isolation system was established. Through the harmonic balance method, the steady-state response of the system was solved, and the validity of the solution was verified by numerical calculation. For the problem of system response stability, firstly, the influence of nonlinear stiffness of quasi-zero stiffness isolator and external excitation force amplitude on response stability were studied，and combined with the longitudinal static deformation of the shafting, the nonlinear stiffness was determined. Then the specific structural and mechanical parameters of the disc spring and the coil spring were obtained through static analysis. Finally, the influence of damping ratio of quasi-zero stiffness isolator and external excitation force amplitude on the response stability of the system were analyzed, the damping ratio was determined. The results showed that when the nonlinear stiffness and damping ratio were taken as 1×1012 N/m3 and 0.05, respectively, the main resonance of the system no longer jumps, and the solution of the steady-state response of the system was stable within 200 Hz. In the meantime, even with a load of 10 000 N, the quasi-zero stiffness isolator could still effectively isolate the vibration in the range of 10 Hz to 200 Hz.

Abstract: Based on the response spectrum analysis method, ANSYS finite element software and its APDL programming, the three-dimensional finite element model that could fully reflect the structural characteristics was established by using the spatial beam element, 3D longitudinal spring damping element and solid element. And the seismic calculation of support and hanger of an air conditioning unit in suspension installation mode was carried out. Considering the static load and OBE seismic load, the static analysis was carried out firstly, and then the modal analysis and multi-point response spectrum analysis of OBE seismic load were carried out. Finally, according to the calculation results of static analysis and spectrum analysis by the square root of sum square method (SRSS method) of the modal combination, based on ASME AG-1 codes, the strength and stiffness of support and hanger were subjected to seismic evaluation. The results showed that with the combination of static load and OBE seismic load, the tensile stress, shear stress, bending stress and tensile-bending combination of the support and hanger were less than the stress limit, and had a wide margin of safety. Most of the displacement of the support and hanger come from the rigid displacement of the whole system caused by the shrinkage of spring dampers, and the rest came from the relative displacement of the channel steel bottom frame, both of which could meet the requirements and have a large safety margin. Expansion bolts at the root of the support and hanger were mainly affected by the tension, and their strength could meet the requirements and the safety margin was large. The evaluation showed that the support and hanger of the suspended air conditioning unit had sufficient seismic strength and stiffness.

Abstract: Organic Rankine Cycle (ORC), a reliable way in recovering waste heat efficiently was examined in this study. Firstly, considering the heat exchange area of the evaporator and the thermodynamic performance of the system, the performance evaluation index F(·) was defined. When the heat source temperature was 105-165 ℃ and the evaporator pinch point temperature difference(PPTD) was 3-30 ℃, the influence of the evaporator PPTD on the system performance was simulated and analyzed from the aspects of working fluid flow rate and evaporation temperature, respectively. The results showed that the net output work and thermal efficiency of the system increased with the decrease of PPTD, and respectively reached the maximum value of 53.53 kW and 12.21% when the heat source temperature was 165 ℃ and the PPTD was 3 ℃. At a certain working fluid flow rate and the heat source temperature was 165 ℃, the F(·) was the minimum, where the optimal PPTD was 15 ℃. At a certain evaporation temperature, the F(·) decreased with the increase of PPTD. Then, on the self-built small-scale ORC low-temperature waste heat power generation test platform, the influence of the evaporator PPTD on the performance of ORC system at different heat source flow rate, cooling water flow rate and working fluid flow rate was studied. It is found that when the heat source flow rate was 4 m3/h, the system performed better with a lower PPTD, meanwhile the working fluid flow rate of 700 kg/h and cooling water flow rate of 3 m3/h made the system performance the best.

Abstract: In this study, three series of mechanical tests were carried out on 18CrNiMo7-6 alloy steel materials to determine the damage parameters of the Johnson-Cook (J-C) damage model, which could be widely used in numerical simulations such as high-speed impact and mechanical forming. Through the quasi-static tensile test and finite element simulation of notched specimens, the calculation method of stress triaxiality considering both spatial distribution effect and strain accumulation effect was determined. The results showed that the failure strain decreased with the increase of stress triaxiality. Through the tensile test at 10-3 s-1, 10 s-1 and 103 s-1 strain rates and the impact test of SHTB, it was found that the yield strength of the material increased with the increase of strain rate, indicating that the material had obvious strain rate strengthening effect, and the failure strain increased with the increase of strain rate. In the tensile tests at 25 ℃, 200 ℃, 300 ℃ and 400 ℃, it was found that the yield strength of the material decreased gradually with the increase of temperature, but the tensile strength of the material at 300 ℃ was higher than that at 200 ℃, and the failure strain decreased gradually with the increase of temperature. According to the above experimental results, the parameters of J-C damage model were fitted, and the reliability of the fitted parameters could be seen from the goodness of fit. Finally, experimental results and finite element results of Taylor test were compared. The results showed that when the impact speed was 430 m/s, the impact samples obtained from the experiment and simulation were damaged, and the maximum error between the failure mode of the samples obtained by finite element simulation and the experimental results was 6.3%. The rationality of the J-C damage model selected in this study and the effectiveness of the experimental parameters were verified.

Abstract: In order to test the vertical accuracy of the vertical level plane about the rotating laser, the vertical level error of the laser level was analyzed. Using the sine and cosine theorems of spherical triangles, the calculation formula of total deviation of the rotating axis from the axis of the rotating laser was deduced. The mathematical model of the deflective deviation with the total deviation of the rotating axis from the axis was established. A special test device with double light pipes based on horizontal axis symmetry was built, and a scheme was designed to first measure the error component separately and then synthesize the vertical error, and experiments were carried out to verify it. The results showed that the maximum difference was no more than 6.3" obtained in our scheme in different instrument poses, which was better than the maximum difference of 16.5" in the traditional scheme, which proved that the designed scheme was technically feasible, and the mathematical model was accurate and reliable.

Abstract: To provide a reference for manual cutter inspection in shield tunneling, in this study the wear of disc cutters was simplified as a multivariate nonlinear regression problem, and constructs a data analysis framework was constructed to predict the cutter wear quantitatively by combining the effect of three kinds of factors, which were machinery, geology and management. The shield tunnel section from Panyu Square Station to Nancun Wanbo Station of Guangzhou Metro Line 18 was taken as the engineering background, 4 parameters were selected and 2 386 labeled data derived from 34 face cutters and 81 manual inspections were obtained. The training of BPNN was expedited by using the LM algorithm and SMBO method, which fully exploitd the regression ability of the neural network. The prediction got coefficients of determination (R2) over 0.86 for 83.3% of the test samples, and the accuracy was greatly improved compared with the reference formula used for data labeling. It showed that the model trained by this method had higher accuracy in the prediction of disc cutter wear.

Abstract: Considering the problem that the comprehensive evaluation value of the catastrophe theory evaluation method was too high and the evaluation values were relatively close, an improved method for regression analysis using a three-parameter exponential curve was proposed and verified by two examples. Not only the calculated improved evaluation value and the conventional evaluation value were the same in size order, but also the range was significantly increased, and the distribution of the data on [0,1] was more scattered. Considering the natural and social attributes of the Yellow River ice flood disaster, established a four-level risk evaluation index system was established, and the improved method was applied to the ice flood disaster risk assessment of 4 counties on both sides of the Yellow River from Toudaoguai to Wanjiazhai in Inner Mongolia. The results showed that Pianguan County was in a very low-risk area; Zhungeer Banner was in a high-risk area; Qingshuihe County and Tuoketuo County were in the medium-risk area. The comprehensive evaluation values obtained by the conventional catastrophe theory evaluation method were very close, except for Pianguan, the rest are concentrated in the interval [0.912, 0.941], which was not conducive to intuitively and effectively distinguishing the degree of risk. The improved method could effectively expand the distribution range of the adjusted comprehensive evaluation value, and the range reached 0.446, which had a higher level of resolution, and the level of risk was more comparable. The evaluation results were basically consistent with the analysis of actual ice conditions in various regions.

Abstract: In order to study the seismic fragility of multi-span continuous girder-rigid frame bridges, based on OpenSEES platform, a non-linear seismic response analysis model of the actual bridge was established. Through incremental dynamic analysis, fragility curves of bridge components such as piers, supports, and abutments were established. Time-varying seismic fragility of piers of key anti-seismic components of bridges in the whole life cycle was analyzed. The failure probability of bridge structure system was estimated by boundary method, and system fragility of bridges was studied as an example. The analysis results showed that in the same damage state, 1# and 4# piers were more likely to be damaged, followed by 5# piers, and 2# and 3# piers had the least probability, as to the pier height, material strength and restraint of pier crest all affected its fragility. The bearing at abutment was more likely to cause damage than the bearing at pier; the slope of the fragility curves of the two abutments was larger, and there was no significant difference in their probability of the same damage. The probability of slight, medium and serious damage of pier increased significantly after endurance damage in the whole life cycle, moderate damage state beyond the probability increased by 3.1%, 11.3%, 20.9%, 29.1%, 34.1%, respectively, and severe damage state increased by 3.9%, 13.5%, 25.1%, 33.4%, 35.4%, respectively. Bridge systems were more fragile than individual components, and using the fragility of a single component to evaluate the fragility of the bridge could overestimate the seismic performance of the bridge.

Abstract: When a new station crosses the existing station in the water-rich strata, MJS and freezing method will be used to reinforce it. The cement soil constructed by MJS construction method will produce a lot of hydration heat, which can increase the temperature of added solids, and the horizontal freezing effect. This paper is based on the background that some single-layer sections of the platform layer of the newly-built Metro Line 7 of Nanjing Metro need to pass through the upper existing station at a short distance,the variation law of MJS reinforced soil temperature is studied by numerical simulation, and the correctness of numerical simulation is verified by actual measurement. The results show that the maximum temperature of MJS pile reaches 80.07 ℃ within 3~8 days after completion of construction, and the more intensive MJS pile layout and the larger the reinforcement area, the higher the temperature generated in the solid center of pile group, and the slower the initial cooling rate under natural cooling condition. After the hydration heat release of MJS pile reaches the maximum temperature, the temperature decreases in the form of negative exponential power function, and the cooling rate is fast first and then slow. The influence range of MJS on the temperature of surrounding soil expands gradually with time, and the larger the reinforcement range is, the larger the influence range of surrounding soil temperature is, and the influence range can be up to 4.5 m beyond the boundary of MJS reinforced soil. The closer it is to the cement-soil reinforcement area, the higher soil temperature is. Combined with the existing MJS hydration heat release law, strength research and numerical simulation results, considering the temperature field distribution and temperature value of hydration heat at different times, it is suggested that the best opening time should be the 60th day after the completion of MJS reinforcement in similar projects in the future.