Abstract:For the levitation system of medium-low speed maglev train， an elevated rail beam model with variable stiffness based on vector form intrinsic finite element method and a vehicle system model based on Newtonian mechanics equations were established. The two models were coupled by controllable levitation electromagnetic force. Then， the mid-span displacement of rail beam， the angle of beam end， the vibration acceleration and the deviation of suspended airgap were taken as the important indexes. The vibration response and the displacement deformation response of the corresponding structural component of maglev train and track line were obtained through numerical simulation based on the proposed coupled model of vehicle-bridge magnetic force. Finally， the effectiveness of the proposed magnetic coupling model was verified through the field experiment of full-size maglev train preliminarily.

Abstract:In order to ensure the suspension stability of maglev train， the active control of suspension system is studied. Firstly， based on the minimum suspension unit of single electromagnet of maglev train， the corresponding control mathematical model of current is established. Combined with the simulation， it is shown that the proportion-integration-differentiation（PID）control algorithm is very sensitive to time-varying disturbances such as nonlinear load. Then， a sliding mode control method based on the stability proof of bifurcation theory is proposed. Combined with the parameter self-adjusting function of radial basis function （RBF） neural network， a suspension control module with vibration suppression is constructed to effectively suppress the vibration of electromagnet. Finally， the Simulink control model is constructed and the single electromagnet suspension experimental platform is built for relevant simulation and experiments. The results show that the effect of electromagnet vibration on the suspension performance is particularly obvious. The proposed control algorithm can effectively suppress the electromagnet vibration in the presence of complex disturbances and improve the dynamic performance of the suspension system.

Abstract:By analyzing the principle of eddy current effect and adopting the finite element method to simulate the suspension electromagnetic field， the key factors of eddy current effect on electromagnetic force are obtained， and the front magnetic levitation system model considering eddy current effect is established. According to the dynamic characteristics of magnetic levitation system during train operation， a parameter optimization algorithm without changing the existing nominal controller structure is proposed. The optimized controller has already been implemented and applied to Changsha Maglev Express Line successfully. The actual operation data indicate that the robustness and the anti-interference ability of front magnetic levitation system have been significantly improved.

Abstract:In this paper， the framework of control loop performance evaluation based on the cloud theory is introduced to the electromagnetic levitation system. With the measured data of a commercial maglev train in commissioning phase， the feasibility of the proposed evaluation method is tested. In addition， by means of the multiple variable system， evaluation results of the control loop performance are visualized in an intuitive fashion.

Abstract:Based on the quasi one-dimensional theory， the mathematical model of air-gap magnetic field was established with the actual motor parameters of medium-low speed maglev train to analyze the relationship between the running speed and the air-gap magnetic field of the motor. Then the mathematical model is verified from three aspects of air-gap magnetic field， secondary eddy current and traction by using finite element simulation. It is shown that the train speed affects the longitudinal dynamic end effect（LDEE） of the motor to distort the air-gap magnetic field. And the eddy current is generated at the entrance and exit regions of the motor on the secondary induction plate， which reduces the thrust and efficiency of the motor. By comparing the longitudinal dynamic end effect of half-filled slot structure and full-filled slot structure， the traction force of the half-filled slot structure is more seriously affected by the speed.

Abstract:In order to evaluate the applicability of U-type girder for medium-low speed maglev transport， a dynamic model of maglev train was established， which involves the proportional-integral-derivative （PID） levitation control system. Meanwhile， a finite element model of the 25 m-span U-type girder with the height of 1.7 m was also built. Then， by using a distributed co-simulation platform for maglev transport system， the dynamic response of maglev vehicle-track-girder system was calculated when the vehicles ran at the speed of 20 to 100 km·h^-1. Numerical results show that the vertical deformation of the U-type girder at the mid-span， the levitation gap fluctuation， the vertical acceleration of the carbody and the U-type girder have little change with the increase of the running speed. The mid-span vertical deformation of the U-type girder does not exceed 3.00 mm， the maximum vertical displacement of the F-type rail is about 3.81 mm， the levitation gap fluctuation is less than 1.00 mm， and the maximum vertical acceleration of the carbody mass center is 0.13 m·s^-2. In particular， the vertical acceleration of the rail adjacent to the rail joints at the mid-span or the beam end of the girder decreases at first and then increases with the increase of the running speed， and the maximum acceleration reaches 5.0g. In sum， the medium-low speed maglev train can run over the U-type girder safely and smoothly.

Abstract:The output of food waste in China is large， with high moisture content and extremely perishable， difficult to collect and treat， and low utilization rate. How to treat and resource-utilize food waste in an environmentally friendly， efficient and economical manner has become the focus of attention. As an important organic acid， the lactic acid (LA) is widely used in food， chemical and other fields. Based on the introduction of the mechanism of lactic acid production by microbial fermentation and the development of lactic acid production technology by food waste fermentation， we summarize the effects of bacterial species， carbon and nitrogen sources， pH value and other important factors on lactic acid production by food waste fermentation， and analyze the development status of lactic acid separation and purification technology in fermentation liquid. Finally， the key points and difficulties in the future research and application of lactic acid production technology by food waste fermentation are prospected.

Abstract:Anaerobic digestion is one of the most important strategies for organic wastes disposal. Firstly， the potential impacts of carbonaceous materials on the anaerobic digestion of organic wastes for volatile fatty acids and biogas production as well as the main influencing factors were demonstrated. Then， the main functional mechanisms were revealed from the perspectives of microbial community structure and abundance， microbial activities improvement （i.e. metabolic enzymes and the abundance of genes）， electron transfer acceleration among microorganisms， pollutants toxicity reduction （i.e. ammonia and organic acids）， and the synergistic effects with other substances （i.e. iron）. Finally， the potentiality and necessity of utilizing carbonaceous materials for the built-up of high-efficient and economic combined processes for anaerobic digestion were prospected.

Abstract:The effect of environmental estrogen nonylphenol （NP） on the anaerobic fermentation of waste activated sludge for short-chain fatty acids （SCFAs） production was investigated， and the mechanism was revealed by means of metagenomic sequencing. It was found that NP promoted the SCFAs production during the anaerobic fermentation of the sludge， and the acceleration increased firstly and then decreased with the increase of NP concentration. The yield of SCFAs reached the maximum when the content of NP was 200 mg·kg^-1 dry sludge， which was 2-fold of that in the control. The production of acetic acid was increased by almost three times due to the presence of NP. Mechanism exploration based on metagenomic analysis exhibited that the reduction of acid-consuming and the improvements of acidogenic microorganisms was advantageous to the accumulation of SCFAs with NP. In addition， the relative abundance of functional genes in glycolysis， deamination and β-oxidation of glucose， amino acid and fatty acid was improved obviously. Also， the abundance of genes in adenosine triphosphate binding box transporters （ABC transporters） which control the transport of organic substrates into cells， two-component system for the SCFAs metabolism， and ABC transporters on SCFAs efflux increased remarkably. Furthermore， the abundance of genes related to biofilm formation regulated by quorum sensing in the presence of NP was increased， which was beneficial to cell growth and defense.

Abstract:Polystyrene （PS） microplastics （MPs） were taken as an example to analyze its aging pattern in leachate， as well as the enrichment effect of aging process on antibiotic resistance genes （ARGs） and the enrichment mechanism. The results show that the specific surface area and oxygen-containing groups of PS microplastics increase after 90 d of aging. ARGs can be selectively enriched on the surface of PS microplastics in leachate， and the degree of enrichment increases with the aging time. Furthermore， the genus-ARGs co-correlation network and the gene expression prediction were used to reveal the mechanism of ARGs enrichment. It is found that the niche formed on the surface of PS microplastics has closer ARGs-microbe correlation， and the expression level of genes involved in ARGs spread is higher.

Abstract:A pilot-scale denitrification biofilter system was constructed to investigate the deep denitrification performance when the actual secondary effluent was adopted， and the effects of key parameters （i.e. hydraulic load， C/N ratio and temperature） on the operation were carried out. The pilot-scale system mainly used external carbon source for denitrification rather than organic matter existed in the secondary effluent. The recommended hydraulic loading and C/N ratio was 5 m·h^-1 and 4， and under the conditions the average removal efficiencies of COD and TN were 62.8% and 67.3%， respectively. When the temperature was 15~27 ^oC， TN in the effluent was steady below 10.0 mg·L^-1. The relative abundances of conventional denitrifiers such as Hyphomicrobium and Methyloversatilis （accounted for 25.12%） were higher in the pilot-scale denitrification biofilter system， and the relative abundances of simultaneous nitrification-denitrification bacteria such as Methylotenera and Paracoccus were also much higher （accounted for 33.29%）. These bacteria guaranteed the good denitrification performance in the system.

Abstract:To explore the mechanical properties of seawater sea sand recycled aggregate concrete （SSRAC）， SSRAC prisms were designed with different mix proportions. The complete stress-strain curves were tested under uniaxial compression with the strain rates of 10^-5 s^-1 and 10^-2 s^-1. Failure modes of specimens and the peak stress， strain at peak stress and elastic modulus were analyzed. And the effects of the strain rate， replacement ratio of recycled coarse aggregate （RCA） and shell particle contents on the above indices as well as the dynamic increase factor （DIF） were discussed. Meanwhile， the pore distribution of SSRAC from computed tomography （CT） tests was used to explain the development of characteristic indices of stress-strain curves. Finally， based on the existing uniaxial compression constitutive models of RAC， the predicted complete stress-strain curve was obtained by taking the DIF of characteristic indices and the modified shape factor of descending branch into account.

Abstract:Based on an experimental apparatus for downburst simulation， a 1∶300 downburst wind field suitable for the wind pressure distribution test of a long-span flat roof structure was simulated in the atmospheric boundary layer wind tunnel. On this basis， the wind pressure distribution characteristics of the long-span flat roof structure under downburst were studied， and were compared with the corresponding test results in exposure category B. The results show that in the model area， the relative position of downburst has little effect on the wind pressure coefficients； the average wind pressure distribution under downburst is basically the same as that in exposure category B， but the maximum absolute value of minimum wind pressure coefficient reaches 9.85， and is 77.8% higher than 5.54 in exposure category B； the corresponding power spectrum of fluctuating wind pressure is significantly higher than that in exposure category B； the maximum wind pressure coefficients of flat roof in exposure category B are close to or less than 0. However， in different wind directions under downburst， the ratios of the roof area with the maximum wind pressure coefficients over 0.15 are between 51% and 75%， and the local maximum wind pressure coefficient reaches 0.35； the high positive pressure in a large area will further affect the bearing capacity of the structure.

Abstract:Experimental study on the axial compression capacity of four Q420 steel U-rib stiffened plates with the scale ratio of 1∶2 is carried out to analyze the ultimate bearing capacity， failure mode and failure mechanism. The results show that the ultimate bearing capacities of the four plates all reach the full-section yield capacity. There are three failure modes including local buckling failure， global buckling failure and combined buckling failure. Under the ultimate compression state， the local buckling occurs before the plates reach the ultimate bearing capacity， and the global buckling finally leads to the failure of the plates. The failure positions predicted by the element slenderness are same as the experimental results， indicating that the element slenderness can be applied to the failure position prediction of the plates under the ultimate compression state.

Abstract:A resource constrained project takt transition scheduling problem based on project splitting was proposed under the background of aircraft pulsating assembly line takt transition process， and a mathematical model was established with the objective function of minimizing total transition time. According to the feature of the problem， a two-level iterative algorithm was developed. It is shown that the algorithm can decrease the transition time effectively and the degree of optimization for different project portfolios is 1.1%~23.4%.

Abstract:A theoretical analysis of hydrogen leakage through small holes was carried out， and the simulation of hydrogen leakage through small holes was conducted with Simulink and Fluent respectively. It is shown that the temperature has no significant effect on the hydrogen leakage， while the hydrogen pressure and the size of hydrogen storage space have a greater effect on hydrogen leakage process. Active ventilation is helpful to reduce hydrogen leakage inside the car. In addition， the hydrogen leakage in the confined space has the characteristics of leakage point accumulation， and the hydrogen accumulates at high places because of gravity.

Abstract:Heat transfer numerical model of a corrugated plate condenser was established. The plate condenser was used in organic Rankine cycle （ORC） power generation system and R245fa was chosen as working medium for 90 ℃ flushing water of blast furnace slag. Then the experimental platform was built to verify the correctness of the numerical model. With the help of the numerical model， the effects of the overheat degree， wall supercooling and vapour dryness on heat transfer coefficient， pressure drop and comprehensive heat transfer performance were discussed. And the heat transfer correlation formula for the plate condenser with R245fa as working medium was fitted. According to the volume fraction of condensate phase along the plate length， the possibility of intermediate drain of the condenser was discussed， and the suitable intermediate drain range along the plate length was given for the volume fraction of condensate phase.