The filling rate of adhesive is defined based on the geometric dimensions of the hemming model, and the numerical simulation model of the hemming process with adhesive is established by using the finite element method-smoothed particle hydrodynamics (FEM-SPH) method. By comparing and verifying with the hemming experiment with adhesive, the quantitative study of the influences of the hemming adhesive diameter, the edge distance, and the hemming thickness on the filling rate is realized. The research results show that the flow state and the final filling state of the adhesive layer obtained in the experiment are similar to the numerical simulation results, and the filling rate of the adhesive layer obtained in the experiment is highly consistent with the numerical simulation result, which verifies the feasibility and accuracy of the numerical simulation model. Further analysis shows that the influences of the hemming adhesive diameter, the edge distance, and the hemming thickness on the filling rate decrease in order, and the relationship formulas between the filling rate and process parameters, such as the hemming adhesive diameter, the edge distance, and the hemming thickness, are obtained by fitting, which provides a basis for the optimization design of the hemming process with adhesive of the automobile body sheet.
Unlike the traditional seismic analysis on bridge engineering which mainly concerns the relative motion, the seismic analysis of vehicle-bridge system focuses more on the absolute motion of the vehicle system, where the pseudo-static components need to be considered. In order to study the effect of structural pseudo-static components on the seismic responses of low-medium speed maglev vehicle-bridge system, the discussion relying on a typical low-medium speed maglev line was implemented. Considering the vehicle-bridge coupling relationship based on the proportional integral derivative (PID) active suspension control, two dynamic models for the low-medium speed maglev vehicle-bridge system subjected to earthquake were relatively established in the relative coordinate and the absolute coordinate, and the seismic forces were correspondingly solved by employing the relative motion method and the direct solution method. A case study was subsequently conducted, where the effect of structural pseudo-static components on dynamic responses of the vehicle-bridge system, including the maglev gap, the vehicle system and the bridge was further analyzed. The results show that the influence of pseudo-static components on the dynamic responses of the vehicle system is quite significant. Ignoring the pseudo-static components could seriously undervalue the dynamic responses of the vehicle system, of which the difference could be as high as 447%. Compared to the vehicle system, the influence of pseudo-static components on the vertical and transversal displacement responses of the bridge is fairly limited. Therefore, it is suggested that the absolute displacement method which takes the pseudo-static components into account should be adopted to deal with the seismic excitation in the maglev vehicle-bridge system.
Ocean waves have adverse effects on the operation and safety of ships. Real-time and accurate onboard wave monitoring is essential for green smart ships and navigational safety. It is an important method to use ship motion to perform inversion of the information of encountering waves, which has many advantages such as low cost and high spatio-temporal resolution, and has attracted wide attention. An inversion model based on artificial neural network (ANN) is proposed to deal with the shortcomings of existing ship motion inversion ocean wave models. Taking the motion time history of the ship as the input and the wave elevation time history as the output, the artificial neural network is used to extract the motion features of the ship, and the linear function is input to perform wave surface time history inversion. To verify the feasibility and the accuracy of the inversion model, a ship model tank test is conducted. The results show that the proposed wave measurement method based on the artificial neural network can well achieve regular wave and irregular wave elevation time history inversion. Most of the statistical errors of regular wave inversion are less than 10% and the error of irregular wave inversion is about 10%. The method proposed provides an effective and feasible means for inversion of wave time information in ship motion.
In order to explore the influence of different turbulence models on the resistance and flow field of an advancing submarine, based on the STAR-CCM+platform, and taking Sub-off as the geometric model, this paper adopts the finite volume method, combing 10 turbulence models to conduct numerical research on hydrodynamic and flow field characteristics of Sub-off. First, the LES-Smagorinsky turbulence model is used for the convergence of grids and time steps. Then, the appropriate grid and time step are selected to calculate 10 kinds of turbulence models in specific cases. Finally, the selected turbulence model is used to analyze the hydrodynamic characteristics and flow fields of Sub-off. The results show that there are great differences among the 10 turbulence models in the prediction of submarine hydrodynamic performance and flow field characteristics. LES-Smagorinsky can not only predict the hydrodynamic performance and the average flow field of submarine, but also accurately predict secondary variables of flow fields.
In order to improve the prediction accuracy of rogue waves of the long short-term memory (LSTM) neural network, prediction methods of LSTM with convolution neural networks (CNN), empirical mode decomposition (EMD), auto-aggressive integrated moving averagel (ARIMA) model, and Kalman filtering (KF) were studied. Based on the experimental data of the rogue waves of two single-peak and one three combined peaks, prediction models were established and predicted by data normalization, model parameter optimization and error evaluation. The results show that the prediction accuracy of the four combined models is significantly improved in all the three studied conditions, and the combination with the convolutional neural network has the highest prediction accuracy. The combined models provide a feasible scheme for improving the prediction accuracy of freak waves.
In the roll-hemming forming process of door cover, the non-metallic flanging adhesive and the interaction between light metal and flanging adhesive will affect the manufacturing accuracy and performance of the door cover, and increase the difficulty of roll-hemming forming and quality control of automobile body sheet with adhesive. Therefore, a numerical analysis model for roll-hemming forming of aluminum alloy sheet with adhesive was proposed based on the finite element method and the smooth particle hydrodynamic (FEM-SPH) method. First, SPH was used to simulate the extrusion flow process of the flanging adhesive, and a roll-hemming simulation model of sheet metal with adhesive was established in combination with FEM. Then, an experimental platform for two-pass roll-hemming forming of aluminum alloy sheet with adhesive was built, and the roll-hemming loss and surface wave coefficient were taken as the roll-hemming forming quality index to analysis and verify the validity of the numerical model. After that, the quality change between the first pass and the last pass and the key process parameters affecting quality were studied based on the orthogonal test method. Finally, the fitting relationship between roll-hemming forming quality and process parameters was established. The results show that the roll-hemming loss and the surface wave coefficient of the last pass are reduced compared with the first pass. The process parameters that affect the surface wave coefficient in descending order are flanging height, fillet radius, TCP-RTP value, and roller diameter. The process parameters that affect the roll-hemming loss in descending order are TCP-RTP value, fillet radius, flanging height, and roller diameter. The fitting relationship can support the prediction of roll-hemming forming quality of aluminum alloy sheet with adhesive.
Surface surcharge has a significant impact on the safety and stability of existing underground tunnels, and relevant regulations in soft clay areas have very strict restrictions on the tunnel displacement caused by surface surcharge. In order to accurately assess the impact of surface surcharge on the tunnel displacement in soft clay areas, the influence of surface surcharge on tunnel displacement and soil deformation is studied by using the centrifugal model test, and a corresponding finite element model is established based on the centrifugal model test. The parameter values of the soil constitutive model are determined by indoor soil tests. From the aspects of soil strain and shear stiffness, the applicability of the HS model and the HSS model in the analysis of the soft clay surface surcharge problem is compared and analyzed. Based on the result, the influence of surface surcharge on the deformation of soft clay formation and tunnel displacement is further discussed while comprehensively considering the size of the surface surcharge and the location of the tunnel. The results can provide some reference for engineering design.
Taking a running tunnel of Shanghai Railway Airport connecting line as a demonstration application project, the synchronous technology combining shield tunneling with segment assembling is proposed based on the active control on the oil pressure of the shield thrust system, which can solve the problem of the long construction period produced by a single shield machine employed in a long-distance shield tunnel project. The principle is to make full use of the extra stroke of propulsion cylinders generated by the axial insertion of the key block to assemble segments, and the theoretical operation time of a single ring can be reduced by 31.6%. Then, a large model test platform for this synchronization technology is established to verify its feasibility and reliability, and the redistribution method of the missing thrust force is introduced during the synchronous process, which is verified by the model test. The test results show that the actuators of the shield machine respond quickly, and the errors of the cylinder pressures and total thrust force of the propulsion system are controlled within ±2%. The attitude deviation of the shield machine is controlled within ±6 mm, and the error range of the driving speed is -2 to 4 mm/min. The segments are safe with the designed overburden thickness of 33 m, and the compressive safety coefficient reaches 1.68.
In order to investigate the dynamic response law of subgrade of a special railway line in loess region under moving train loading, the field test data and 2.5D finite element results were adopted to assess the dynamic stress distribution and its influence depth, and the environmental vibration law in the office area along the line was also analyzed. The results show that the excessive abstraction of the track system might enlarge the amplitude and influence the range of dynamic stress. The entity modeling of the ‘ballast-sleeper-fastener’ system makes the distribution of the dynamic stress in the subgrade more reasonable. The influence of energy consumption caused by the dynamic creep of soil have a negligible influence when the subgrade is in a quasi-static state. The speed has a negligible effect on the distribution of the dynamic stress of the subgrade when a freight train is running at a low speed, and the influence depth of the dynamic stress is about 4.2 m. As the speed decreases, the influence of track irregularity on the environmental vibration increases. The environmental vibration can be effectively controlled by improving the short wave length irregularity.
The large cruise ship is a type of ship with large size and high added value, which has been increasingly studied and developed during the recent years. Since a large cruise ship often sails in the crowded waters such as harbor and coastal area, the study of the hydrodynamic interaction between the cruise ship and other ships is crucial to ensure the navigation safety. Taking a large cruise ship and a KCS container ship as the study object, the hydrodynamic characteristics of the two ships at different longitudinal positions, transverse positions, and ship speeds in both deep and shallow water are predicted in model scale by solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations, and the variations of the hydrodynamic interactions between the two ships are identified. It is shown that different relative positions and ship speeds have significant effects on the lateral force and yaw moment acting on the two ships. The hydrodynamic interaction between the two ships in shallow water is more remarkable, and the relatively smaller ship is more affected by the ship-to-ship interaction.
Stiffened panel is a typical strength member in ships. Considering the change of material properties under the action of fire and high temperature, according to the thermal elastic-plastic finite element theory, based on the nominal temperature-time curve, the protective effect of the passive fire protection layer on the high temperature response characteristics and the residual strength of the stiffened panel and the influence of coating positions on the failure mode of the stiffened panel are studied, which provides reference for structural performance evaluation and structural fire protection design. Numerical analyses indicate that passive fire protection layer can effectively slow down the increase of stress and deformation induced by temperature rise. Overall coating does not change the failure mode of the overall buckling of the structure accompanied by the tripping of the stiffener, but significantly delays the failure time and has an obvious effect on maintaining residual ultimate strength. Partial coating will change the failure characteristics of the structure. Overall failure occurs when only the plate is coated, and beam-column failure occurs when only the stiffener is coated, accompanied by local buckling of the web. Overall coating shows the best protective performance on the residual strength of the stiffened panel, followed by plate coating. Stiffener coating, however, has a weak protective effect. The protection performance mainly depends on the heating and failure mode of the structure.
In order to handle the problem of complex and time-consuming simulation calculation in hull form optimization, the approximate model based on adaptive sampling has been widely used. In this paper, a maximum entropy (ME) adaptive sampling method based on uniform design (UD) is developed based on the Kriging approximate model and the leave-one-out (LOO) error method. Compared with the incremental Latin hypercube design (LHD) method, the adaptive sample distribution obtained by the proposed method are more uniform, and the accuracy of the global approximation model is higher. The proposed method is applied to the S60 hull form optimization, and the effectiveness is verified.
To address the uneven seabed following control problem under the time delay constraint of the actuator for the autonomous underwater vehicle (AUV), a robust time-delay controller with prescribed performance guidance law is proposed in this paper, which can improve the safety of the AUV during navigation. First, the seabed following error conversion is firstly performed based on a navigational safety barrier function. Then, by integrating the time-varying line-of-sight guidance angle, the prescribed performance guidance law is designed at the kinematics level to provide reference state input for the AUV. After that, to tackle the time delay problem of actuators and reduce demand for accurate modeling, a robust time-delay dynamic controller is designed using the radial basis function (RBF) neural network. Finally, based on the Lyapunov theory, the stability of the closed-loop system is proved. The simulation results illustrate that the designed controller can achieve uneven seabed following control. Moreover, the following errors are always confined to the preset limits, which can also enhance the safety performance of the AUV when following the uneven terrain of the seabed.
This paper studies the joint optimization problem of vessel scheduling and refueling strategy for container liner shipping with cooperative agreements signed by the container terminal operators and the shipping company with multiple vessel arrival time windows, multiple start and end times, and multiple handling rates. A non-linear mixed integer programming model for vessel scheduling and refueling strategy problem of liner shipping is established considering fuel price difference and discount factors at different refueling ports, which aims to minimize the total cost of liner shipping service. A set of discretization and linearization technique is applied to the original model in accordance with the vessel navigation controlling practice. Taking the AEX1 route served by China COSCO Shipping Corporation Limited as an example, a large number of simulation verifications are conducted. The results of numerical examples show that the joint optimization of vessel scheduling and refueling strategy helps shipping companies to flexibly adjust vessel sailing speed. It can significantly reduce the total cost of liner shipping service. The sensitivity analysis indicates that the total cost of liner shipping service and the vessel refueling volume in a voyage will reduce with the expansion of time window of vessel arrival at port in the cooperative agreement. No matter how the fuel price changes, the joint optimization of vessel scheduling and refueling strategy can effectively reduce the total cost of liner shipping service.
Dissimilar material structure has the advantages of both cost and performance, and has become an important means of lightweight for the new generation of autobody closure panels. However, the difference between physical properties of sheets and the complex change of adhesive material properties are easy to lead to structural curing mismatch deformation. In order to eliminate the structure deformation, a method for deformation prediction and surface reconstruction pre-compensation was proposed. Then, considering the material property transformation effect of curing degree, chemical shrinkage, and stress relaxation, a thermal-chemical-structural field coupled model for high temperature curing of hemming adhesive was established. Taking the typical aluminum/steel sheet curved-edge hemming structure as the research object, the multi-physics field curing process was simulated and analyzed, and the deformation of aluminum alloy outer panel was predicted, which was verified by non-contact measurement experiment using digital image correlation (DIC) method. Finally, the geometric compensation of curing deformation was conducted, the compensation efficiency of constraint direction, connection direction, and normal direction was compared and analyzed, and the reliability of the method was verified by experiment. The results show that compared with the traditional viscoelastic model, the multi-physics field coupling model can more accurately reflect the high temperature curing deformation of hemming structures with dissimilar materials. The geometric compensation method based on non-uniform rational B-splines (NURBS) surface reconstruction can effectively reduce the curing deformation of structures, and the normal direction compensation method is more efficient. This paper provides an important reference for the improvement of manufacturing accuracy and process optimization of the new generation of autobody closure panels with dissimilar materials.
