Abstract:Given the uncertainty of the severity of stray current on the corrosion area of buried pipelines along the subway line, a three-dimensional finite element analysis model of stray current is established to study the distribution of stray current under the operation mode of subway upward and downward trains and the dynamic changing process of the cathode and anode area on the buried pipeline. Considering only the influence of anode stray current, the interference area and degree of the buried pipeline during train operation are judged by comparing different models. The results show that when the two trains are running in opposite directions at the same time, the interference area of the buried pipeline is mainly distributed on both sides, and the interference area is symmetrical concerning the central position of the pipeline. When the upward train starts 18，37 s and 55 s earlier than the downward train, the areas with strong interference degrees on the buried pipeline are mainly distributed on the right side of the pipeline. Among them, when the upward train starts 55 s earlier than the downward train, there is a large interference current density on the buried pipeline, up to 18 A/m² . In the later protection of subway stray current, corresponding measures can be taken for the serious interference area of pipeline in combination with finite element model.

Abstract:To study the eccentric mechanical properties of concrete filled steel tube reinforced concrete column (CFSTRC) under fire, a finite element model is developed. The failure mode, deformation, internal force, strain and stress, interaction between steel and concrete under fire are analyzed, and the results with different parameters are discussed. The results show that under fire, the CFSTRC column shows good plasticity with overall instability failure mode, and the eccentric mechanical response of the column can be roughly divided into three stages. There is a phenomenon of internal force redistribution in each part of the column. With the tensile area of the column section gradually expanding, the interaction force between steel tube and concrete also increases gradually under fire. The section size and slenderness ratio of column have great influence on the bearing capacity of square steel tube-reinforced concrete column under fire.

Abstract:Prefabrication and assembly construction technology is more and more widely used in bridge construction because of its advantages of environmental protection, convenient construction and controllable quality. Based on the project of national highway 329 smart expressway, this paper puts forward a new construction method of front supporting and rear anchoring based on the original prefabricated and assembled bent cap construction method, and studies the internal force of the whole construction process of the two methods through numerical analysis and comparison. The research shows that: in the construction of front support and rear anchor, the internal force distribution of the capping beam is similar to that of a simply supported beam under the conditions of lifting the capping beam and front support, while the internal force distribution is similar to that of a cantilever beam under the conditions of removing the crane; the structural internal force of the capping beam during the whole construction process of the front supported and rear anchored construction method is significantly less than the rear anchored construction method due to the synergistic effect of the front supported and the rear anchored. Especially when the crane is removed, the maximum bending moment of the capping beam is reduced by 73%, indicating that the front supported and rear anchored construction method have greater safety; the maximum tensile stress of the bent cap in the whole construction process is only 1.2 MPa, which is less than the design value of the axial tensile strength of the concrete of 1.83 MPa, indicating that the bent cap is always safe and reliable in the installation process. The proposal of front supported and rear anchored construction has important guiding significance for the innovation and development of construction technology of spliced bridge substructure.

Abstract:Traditional text encryption algorithm is not applicable to image encryption, so classical Logistic map has limited range of system parameters and unequal distribution of chaotic sequences. In this paper, an image encryption algorithm based on cyclic shift combined with improved Logistic and Tent map is proposed. The initial values and control parameters of improved Logistic and Tent map were set, and the bitt retake technology was applied to improve the chaos effect in the transition state, so as to improve the effect of image encryption algorithm. When the plaintext image was processed, Arnold transform and XOR pre-encryption were carried out first, and the image was partitioned. Then, the sequence generated by Tent map was used for sorting index and circular shift. In the process of encryption, the plaintext image underwent pixel replacement and pixel diffusion, so that the value and position of the plaintext pixel were changed. Experimental results show that this algorithm has good encryption performance and security.

Abstract:In order to study the impact of operating trains on the operating performance of the bridge erecting machine in the construction of adjacent new railways, taking the newly-built Nanchang-Jingdezhen-Huangshan railway passenger dedicated project as the background, through the establishment of a numerical analysis model, the paper analyzes the lateral aerodynamic force generated during the train running near the operating line on the stress state of the whole process of bridge erecting machine in the bridge construction. The results show that the deformation state of the main beam 2 is obviously affected by the lateral aerodynamic force when the No. 1 trolley of the bridge erecting machine prepares to take the beam(Stage 1), and the maximum deformation is 4.5 mm. The stress of main beam 1 and main beam 2 are approximately symmetrically distributed in the area of 30-65 m. When the No. 1 trolley and No. 2 trolley of the bridge erecting machine are preparing to drop the beam (Stage 2), they are affected by the lifting of the concrete beam, and the lateral aerodynamic force has a certain influence on the deformation state of the two main beams of the bridge erecting machine, and the maximum difference is 2.5 mm and 3.6 mm respectively. Due to the large dead weight of the concrete beam, the lateral aerodynamic force has little effect on the main girders of the bridge erecting machine at Stage 2. However, since the maximum stress of the main girders of the bridge erecting machine is as high as 263.93 MPa, the safety factor of the structure in this state is relatively small. In order to ensure the safety during the construction process, real-time monitoring of the whole construction process of the girder is required.

Abstract:The planning of railway logistics park is mostly upgraded from the existing railway freight facilities. Following the analysis of the main functions and the requirements of the railway logistics parks layout planning, an optimization functional areas layout model is proposed to minimize transshipment costs and maximize relevance, considering the constraints of existing railway freight facilities, functional area length, shape, direction requirements, and entrance and exit settings. Route-based distance is adopted in the model. Based on the NSGA- Ⅱ algorithm, the continuous penalty factor is designed according to the satisfaction of the layout result for the constraint condition, and the constraint condition is converted into the objective function penalty value. On this basis, the slice tree coding sequence and multiple mutation methods are introduced, and the algorithm can effectively avoid falling into the local optimum. Case analysis demonstrates that the algorithm is effective and has high solution accuracy, and the layout scheme is reasonable.

Abstract:As environmental pollution and energy crisis become more and more serious, electric vehicles have attracted widespread attention due to their advantages of low emission and low noise. But a flood of electric vehicles plugged into the grid will have a huge impact on the power system. Especially in the living area, EV users are generally used to enter the community to charge their cars immediately after work, which makes this period the peak period of household electricity consumption. Large-scale uncontrolled charging behavior will cause security risks to the power grid and affect the normal operation of the power grid. On account of this phenomenon, a two-level programming model aiming at “peak cut” for time-of-use price of electric vehicles in residential areas was established. The lower was minimization model of charging cost for lower users, getting the charging load. The upper was load time distribution equilibrium model of upper power grid, obtaining time-of-use price of fast and slow charging power. It could change the charging behavior of residents by time-of-use price. Finally, the calculation example showed that the power supply stability of the grid was improved by 57.66%.

Abstract:Mountain city trunk line undertakes the main traffic volume of the city, which has the characteristics of large differences in traffic flow characteristics and uneven traffic distribution, creating new requirements for traffic control. In order to improve the traffic efficiency of urban trunk line, this paper takes the mountain city trunk line system as the research object and establishes the optimization method of coordinated control of mountain city trunk line based on swarm algorithm. At the level of coordinated control, a coordinated control method for tracing the source of congestion based on the minimum delay in the sub area is established. At the single point control level, the optimal control based on hierarchical feedback is built up. Finally, the coordinated control scheme is generated by combining the regulation rate at the coordination level and the single point level. The example verification shows that for the trunk multi-lane merging system, the average delay and average parking times of swarm optimization algorithm scene are reduced by 22.06% and 28.42% respectively compared with the uncontrolled scene. Compared with the current control scheme scenario, the average delay, average parking times and average travel time of trunk multi-lane merging system have been reduced by 23.04%, 24.08% and 19.38% respectively. It can be proved that the swarm optimization algorithm has a good control effect on the multi-lane merging system of trunk lines in mountainous cities.

Abstract:For the input coupling and output coupling issues of compliant mechanisms with multiple degrees of freedom, a method for topological design of fully decoupled compliant mechanisms with multiple materials is presented. The multiple materials interpolation model based on the element stacking method is adopted. The maximization of the weighted sum of multiple output displacements is applied as the objective function. Both input coupling and output coupling constraints are proposed to suppress the coupling issues. The coupling constraints and the structural volume for each material are used as the constraints. The model for topological design of fully decoupled compliant mechanisms with multiple degrees of freedom using multiple materials is established. The method of moving asymptotes is adopted to solve the topology optimization problem. The obtained compliant mechanisms considering the coupling issue is different from those without considering the coupling issue. Both input coupling and output coupling of compliant mechanisms with multiple degrees of freedom can be suppressed effectively. The input and output motions of the compliant mechanisms can be completely decoupled. The influence of different coupling coefficients on the results is analyzed.

Abstract:The head loss in pipe flow when fluid goes through bend flow channel is one of the main factors leading to serial mechanism fire-monitors’ pressure drop and short-distance jet. The design of a fire-monitor with 2 degrees of freedom compound mechanism, which realizes the substitution of the traditional bend flow channel (BFC) with a straight one(SFC) based on the analysis of fluid dynamics theory, is presented in this paper. The expected results of the work were achieved based on the experimental results, which has guidance for the redevelopment of novel fire-monitor with longer distance, higher efficiency and lower energy consumption than traditional one.

Abstract:The change trend of exhaust gas temperature margin (EGTM) of civil aviation engine reflects its performance degradation. In order to employ the change trend of EGTM to map the performance degradation of the engine, an deep integrated neural network prediction method based on empirical mode decomposition (EMD) al gorithm and convolution short-term memory network (CNN-LSTM) is proposed in this study. EMD was used to decompose the original EGTM sequence into multiple natural mode components and residual components, and all the resulting components were used as model input. The convolution long-term and short-term memory network was used to capture the nonlinear correlation of each component and extract the long-term dependence to construct the framework of deep learning model. In order to verify the effectiveness of the proposed method, the actual test data of EGTM of an airline for 10 years were used for experimental analysis, and 5 kinds of neural networks were designed as competitive models for comparative study. The experimental results show that the proposed EMD-CNN-LSTM fusion neural network model can reduce the mean absolute error and the root mean square error by 37.82% and 33.01%, and increase the goodness for fitting by 1.02%, compared with competitive models. Furthermore, when EGTM is in the sensitive area, EGTM single-point prediction accuracy of the proposed model is significantly higher than that of other competitive models. Therefore, the proposed fusion neural network model has good accuracy and stability in EGTM prediction of civil aviation engine.

Abstract:Large-scale three-dimensional(3D)hierarchical Ag nanosheet-assembled films on the indium tin oxide(ITO)glass substrates were fabricated via two-step electrochemical deposition method, and its surface-enhanced Raman scattering effect(SERS)was studied. As a large number of hot spots were located at the edges of Ag nanosheets and the cross-linking gaps between the neighboring nanosheets across the whole substrate, using 3,3′-diethylthiatricarbocyanine iodide(DTTCI)as probing molecules, the Ag nanosheet-assembled film exhibited strong SERS effect. The SERS experiments showed that the Ag film assembled by nanosheets with high pack density exhibited excellent detecting performance, which could be used as effective low-cost SERS substrate for ultrasensitive detecting of substances.

Abstract:The fence height and incoming wind velocity are the main factors affecting the spatial dispersion of construction dust. Taking a construction site in Beijing as an example, the construction dust data of a certain period was selected for CFD simulation, and the results were compared with the actual measured dust concentration data of the site for verification. By analyzing the meteorological wind velocity data during the construction period of the site, 6 kinds of incoming wind velocities of 2，3，4，5，7 m/s and 9 m/s with exponential law were selected, and 6 kinds of fence heights of 1.8, 2.0, 2.2, 2.5, 2.8 m and 3.0 m were chosen. The CFD simulations were conducted to compare and analyze the spatial distribution and dispersion characteristics of construction dust under different fence heights and incoming wind velocities. In order to comprehensively evaluate the impact of construction dust on the human body and external environment, the averaged dust emission rate in the range of breathing height 0.5~1.5 m and the dust fugitive ratio were proposed as evaluation indexes. The results show that the averaged dust emission rate of 3.0 m fence height has the lowest overall index at the six incoming wind velocities, indicating that dust pollution has the least harm to the human body. The dust fugitive ratios of the six fence heights under the same incoming wind velocity are almost the same, which indicates that the impacts on the external environment are almost the same. The impacts of the construction dust on the human body and the external environment are the most serious when the incoming wind velocity is 3 m/s and 5 m/s, respectively.

Abstract:With the rapid development of domination theory, the problem of edge domatic set partition of graphs has attracted much attention. As G=(V，E), a nonempty graph, D⊆E is said to be an edge domination set of G. If ∀e∈E-D， there exists an edge e′∈D，so that e is adjacent to e′ and E(G) is the set of all the edges of G. The maximum number of nonintersecting edge domination sets that can be partitioned into is the edge domatic number d′(G) of graph G. The partition of edge domination set of Wheel graph W_n+1 with strong symmetry is the main research content, and the set edge domination number of Wheel graph W_n+1 is obtained by deductive reduction method. Accordingly, the application of deductive reduction method in edge domatic set partition of special graph is realized.