Special collection of 12 issues of "Journal of Shanghai Jiaotong University" in 2021
Numerical wave simulation is a significant research topic. In this paper, the open source computational fluid dynamics (CFD) platform, OpenFOAM, is utilized to simulate Stokes fifth-order waves. Since geometrical volume-of-fluid (VOF) could better capture free surface due to its geometrical reconstruction step, the free surface simulations are accomplished by applying OpenFOAM built-in geometrical VOF method-isoAdvector, and the relaxation zone scheme is introduced through secondary development for wave absorption. The mesh density and Courant number convergence analyses with geometrical VOF are conducted. The simulation shows that satisfactory results could be obtained with a large Courant number. The algebraic and geometrical VOF simulated data with respect to wave elevation and phase at varied wave steepnesses and frequencies are recorded and compared with the theoretical value of Stokes fifth-order waves, which demonstrates that geometrical VOF is better than algebraic VOF in the prediction of wave elevation. Finally, the lengths and weights of the wave absorption zone are discussed, and the results imply that the best practice for the wave absorption is assigning the wave absorption zone length at least two times of the wave length along with applying exponential weight distribution.
In the initial design stage of a semi-submersible platform, the main particulars of the platform are the key factor affecting the hydrodynamic performance and construction cost. Therefore, multi-objective optimization of the main particulars of the semi-submersible platform is of great engineering significance. First, the design variables of each platform and sample database are determined by design of experiments. Then, the hydrodynamic performances of the semi-submersible platform are analyzed by using the panel method and Morison’s equation. The distribution of probes for estimating the wave elevations on the calm water surface is arranged, and the airgap can be computed. Based on the database obtained by numerical simulation, the surrogate models based on radial basis function (RBF) are established. Next, the formal parameters in RBF are obtained by using the leave-one-out cross validation method. The surrogate model can greatly improve the optimization efficiency. Finally, by using the multi-objective particle swarm optimization (MOPSO) method, taking safety and economy of offshore platforms as two optimization objectives, and taking platform stability, airgap and horizontal motion performance as constraints, the optimization program for the semi-submersible platform can be obtained. Through the detailed analyses of the optimization program for the semi-submersible platform, the most efficient design strategy for the three-column semi-submersible platform is proposed.
To realize the practical scale application of the spar-type floating offshore wind turbine (FOWT) in the medium depth sea areas, a novel 6 MW spar-type floating offshore wind turbine is analyzed by model test and numerical simulation under extreme conditions. The response of main freedom degrees, the mooring tense and the stress at the danger point are explored by a 1∶65.3 scale model at the State Key Laboratory of Ocean Engineering in Shanghai JiaoTong University. Coupled motion response of the spar-type floating wind turbine is calculated by using numerical simulation software in time domain. The results of the numerical simulation and model test are compared and analyzed in time and frequency domain. The maximum deviation between numerical simulation and model test is less than 12%, which shows that the numerical simulation results are in good agreement with the model test results. The dynamic response energy of the FOWT is mainly concentrated at low frequency and wave frequency. Moreover, the whole FOWT system has an excellent survivability under extreme conditions. Finally, the ultimate load of the wind turbine is predicted, which provides the necessary theoretical basis and calculation parameters for the structural strength calculation.
To improve the safety and operating efficiency of underwater slender bodies, the hanging underwater slender body is divided into several micro segments for analysis. The equilibrium equations of each segment are listed according to the mechanical equilibrium and deformation coordination conditions. Then, the equilibrium equations are solved with MATLAB programming. When the upper end moves horizontally and periodically, the upper end motion amplitude, upper end motion period, and lower end weight are changed separately to obtain the amplitude envelope of hanging underwater slender bodies. Based on the results of numerical calculations, the response envelope characteristics of hanging underwater slender bodies are analyzed. The maximum amplitude point on the amplitude envelope of the slender body is generally at the upper end. As the parameters change, it can be converted to the lower end. Changing the amplitude and period of upper end motion has a greater impact on the minimum amplitude point. The lower end weight has a small influence on the minimum amplitude point. By adjusting the ranges of these parameters, the positions of maximum amplitude point and minimum amplitude point on the amplitude envelope of slender body can be controlled.
In order to explain and control the unexpected yawing phenomenon of large oil tankers, a pilot model is used to replace the original proportional model and is combined with the nonlinear ship responding model to construct a model of the whole closed-loop maneuvering system, which is found to be similar to the chaotic Duffing equation, and to be able to have a positive Lyapunov exponent after parameter adjustment, indicating that the chaotic theory can be used to explain this unexpected yawing phenomenon. In order to realize course keeping control with robustness to parameter uncertainty, based on the model built and the backstepping method, a sliding mode control scheme is proposed. The simulation illustrates that the static state rudder angle is smaller than 5° and course deviation is smaller than 0.07° when the chaotic yawing is at the theoretical maximum. Chaotic yawing is eliminated. The idea of establishing man-in-the-loop chaotic system is novel, and the method of solving backstepping parameter uncertainty through sliding mode is easy and effective.
In order to improve the force condition of ballasted railway subgrade structure and reduce maintenance cost, it is necessary to study the influence of subgrade structure parameters on subgrade dynamic response under train load. Orthogonal test was designed and used to analyze the sensitive relationship between dynamic response of railway subgrade structure and parameters of each structural layer, and the optimal parameter combination of subgrade structure of ballasted railway was determined by combining analytic hierarchy process (AHP) and linear evaluation index. The parameters include elastic modulus of ballast bed, elastic modulus of surface and bottom layer of subgrade bed, thickness of ballast bed, thickness of surface and bottom layer of subgrade bed, and elastic modulus of foundation. The results show that the thickness of track bed is the main factor that affects dynamic stress of ballast bed, dynamic stress and vibration acceleration of surface layer of subgrade bed. The elastic modulus of foundation is the main factor that affects the vertical displacement of the sleeper. The mechanical optimum parameter combination of ballast track structure parameters is determined as the elastic modulus ballast bed is 250 MPa, elastic moduli of surface and bottom layer of subgrade bed are 120 MPa and 115 MPa, the thickness of ballast bed is 0.35 m, the thickness of surface and bottom layer of subgrade bed are 1.1 m and 2.3 m, and the elastic modulus of foundation is 70 MPa.
In order to overcome the disadvantage of vehicle ride comfort caused by large vibration and torque excitation of vehicle engine in start/stop mode, a flow mode magneto-rheological (MR) mount is designed for low frequency working conditions. Based on the analysis on the influence of exciting current on the viscosity of the MR fluid (MRF) and the relationship between the fluid resistance effect and the flow rate in the damping channel, the magnetic circuit and the damping performance of the MR mount model are analyzed. According to the mathematical model of the MR mount damping force, the multi-objective optimization function of the magnetic circuit is established. The co-simulation optimal platform is developed by using the Isight and ANSYS software. The non-dominated sorting genetic algorithm II (NSGA-II) is used to optimize magnetic circuit design. The dynamic performance test of the MR mount monomer and the vibration isolation performance test of the whole vehicle in start/stop mode are conducted respectively. The results show that the controllable damping force of the optimized MR mount increases by 111.71% and the restoring force increases by 21.99% compared with those before. When the vehicle is in start/stop mode and the excitation current is 1.0A, the peak vibration acceleration of the passive side (the side connected to the body) with the optimized MR mount decreases by 33.3% compared with that before. Besides, the peak vibration acceleration of driver’s seat rail decreases by 21.6%, which significantly improves the ride comfort of the vehicle.
Experiments of vertical water entry for a cylinder with different inclined angles are performed at a low Froude number to investigate the cavity evolution and hydrodynamics. Unique phenomena of double cavities and separated cavity are observed. The accurate trajectories and attitude angles for the inclined cylinders are proposed, which are extracted by utilizing the method of digital image correlation from the image sequence recorded by a high-speed camera. The raw data of trajectory and attitude angle are fitted using the method of quintic smoothing spline, with which, the velocity and acceleration of the cylinders during water entry are estimated, and the cylinder characteristics of motion and hydrodynamic force are studied. The experimental results demonstrate that the unique cavity phenomena are observed for the inclined cylinder during water entry, such as cavity separation and double cavities. The acceleration increases quickly after the cylinder penetrates into water and achieves the maximum value after cavity separation occurs. After that, the acceleration decreases quickly and tends to zero. The vertical velocity of the cylinder with a large initial inclined angle decreases faster than that with a small inclined angle, while the corresponding horizontal velocity increases rapidly. The trajectories of the cylinder with different initial inclined angles generally present the characteristics of first moving in the upstream direction and then in the downstream direction. With respect to the properties of inclined angle, the angular acceleration responds very quickly to the hydrodynamic force, and it generally first increases and then decreases. In addition, the angular speed of cylinder for a large initial inclined angle increases faster than that for a small inclined angle. The inclined angle shows the same trend as well. The cylinder drag and lift coefficients rapidly increase after the cylinder enters the water, and then slowly increase after the cavity pinches off. Moreover, the force coefficients increase more quickly for the cylinder with a large initial inclined angle.
In both the natural environment and hydraulic engineering, there widely exists the phenomenon of gravity current. In practical conditions, most beds are covered with gravel and sediment particles of different sizes, which can be regarded as rough bed conditions. Therefore, it is of practical scientific significance and engineering application value to study the dynamic characteristics of gravity current flowing over rough beds. By conducting flume experiments for continuous-flux gravity current, and considering the bed roughness and the current initial mass fraction comprehensively, the propagation characteristics such as head position, head velocity, and entrainment coefficient of gravity current are analyzed, the turbulence characteristics such as the turbulence intensity and Reynolds stress at different cross-sections are studied, and the bed shear stress is calculated by using the Reynolds stress method and the turbulent kinetic energy method. The results show that the velocity of the gravity current head is negatively correlated with the bed roughness, but positively correlated with the current initial mass fraction. In the experimental runs of conspicuous roughness and high initial mass fraction, the former is the dominant factor for the kinematic characteristics of gravity currents. When the bed roughness increases to a certain extent, the "lifting phenomenon" of the averaged longitudinal velocity profiles occurs in the gravity current body. One minimum and two maximun values are presented in the turbulence intensity profile of gravity current, and the longitudinal turbulence intensity is the main controlling factor for the current turbulent structure. Besides, the vertical turbulence intensity over rough beds increases significantly compared with that of smooth beds. Near the bed, the Reynolds shear stress is positive, whereas far away from the bed, the Reynolds shear stress is negative. The bed shear stress calculated by using the Reynolds stress method is higher than that by using the turbulent kinetic energy method at identical bed roughness. At the same bulk Richardson number, the entrainment coefficient of gravity current is positively correlated with the bed roughness. It can be concluded that the influence of rough beds on gravity current is mainly as follows: increasing friction resistance, reinforcing mixing effect, redistributing current density near the bed, thickening turbulent boundary layer, and "lifting phenomenon" of the averaged longitudinal velocity profiles.
In this paper, the prediction of the energy transmission spectrum for layered periodic structures is studied. By considering three cases of geometric parameters and physical parameters changing individually or simultaneously, a deep back propagation (BP) neural network is constructed to realize accurate prediction of the energy transmission spectrum of layered periodic structure. A comparison of the predicted results with those obtained by the radial basis function (RBF) neural network verifies the effectiveness of the proposed method.
The preparation technology of micro-nano structure on copper surface is studied and optimized. Aqueous solution containing sodium carbonate and sodium molybdate is used as electrolyte, and the copper sample is anodized at a constant voltage to form a layer of oxidation on the copper surface. Then, the copper surface is treated with aqueous solution containing phosphate and sodium dihydrogen phosphate as corrosion solution to obtain a micro-nano structure on the copper. The surface is observed by using a scanning electron microscope. Finally, the analysis software is used to analyze the scanning electron microscope image to calculate the micro-nano structure pores on the copper surface. The results show that when the anodizing voltage is 15 V, the anodizing time is 20 min, the phosphoric acid mass fraction is 20%, and the corrosion time is 30 min, the copper surface is relatively smooth, and the porosity reaches 25.77%. Orthogonal experiments demonstrate that the type, concentration of the corrosive solution, and etching time have a great effect, while the anodizing electrolyte, voltage and electrolysis have no significant effect on the porosity. Using a combination of anodic oxidation and chemical corrosion, micro and nano junctions with uniform and high porosity can be prepared on the copper surface.
The study described in this paper is derived from a real rotor production workshop where low reliability leads to poor quality of workpieces. A single machine scheduling problem considering machine availability constraints is addressed. The availability is defined by the machine reliability, which can be restored by preventive maintenance. Preventive maintenance with different improvement factors is defined in the mathematical model to minimize the total tardiness. A genetic algorithm is designed to solve the problem. Numerical results show that the proposed approach can effectively deal with the impact of machine availability constraints on production scheduling. Sensitivity analyses provide valuable managerial insights for real workshop scheduling.
A lattice self-reconfigurable modular soft robot based on the expansion-contraction motion rule is designed, which is composed of several soft modules, each of which is composed of a silica gel main body with positive hexahedron configuration and a master-slave docking surface. The internal bulged design makes it have a good expansion performance. The master-slave docking surface is composed of an iron disk and a suction disk type electromagnet connected with the silica gel main body by thread composition. Based on the relationship between the volume change of the soft module and the internal pressure, the expansion of the soft module is analyzed. The mapping relationship between the inflation pressure and the expansion of soft module is established. Besides, the inflation pressure required for the connection of adjacent two soft modules is obtained. Each soft module can expand 1.5 times under the working pressure of 30 kPa, and the docking and separation of two adjacent soft modules are realized by using the electromagnet connection and the expansion-contraction motion rules of soft modules. The self-reconfiguration of the modular soft robot can be realized by the sequential docking and separation of multiple adjacent modules. The feasibility of self-reconfiguration of soft robot is verified by the self-reconfiguration experiment.
Automatically extracting key data from annual reports is an important means of business assessments. Aimed at the characteristics of complex entities, strong contextual semantics, and small scale of key entities in the field of corporate annual reports, a BERT-BiGRU-Attention-CRF model was proposed to automatically identify and extract entities in the annual reports of enterprises. Based on the BiGRU-CRF model, the BERT pre-trained language model was used to enhance the generalization ability of the word vector model to capture long-range contextual information. Furthermore, the attention mechanism was used to fully mine the global and local features of the text. The experiment was performed on a self-constructed corporate annual report corpus, and the model was compared with multiple sets of models. The results show that the value of F1 (harmonic mean of precision and recall) of the BERT-BiGRU-Attention-CRF model is 93.69%. The model has a better performance than other traditional models in annual reports, and is expected to provide an automatic means for enterprise assessments.
When using the convolutional neural network (CNN) model to predict short-term traffic congestion, due to the convolution pooling operation of the model, part of the data for the information of the target position will be lost, resulting in the decline of the resolution of the output features and the decrease in the predictive ability of the model. To solve this problem, this paper proposes a dilated-dense neural network model. First, it uses dilated convolution to obtain the characteristics of a larger receptive field with fewer network parameters, and fully extracts complex and variable data spatio-temporal characteristics. Then, through down-sampling and equivalent mapping of dense network, it solves the problem of parameter degradation in the process of increasing layers of neural network. Finally, it uses the actual urban road average speed data blocks to verify the validity of the model. The results show that compared with the convolutional neural network model, the average absolute error of the network structure prediction is reduced by 3% to 23%.
Aimed at the problem of instability and deviation of multiple training model in limited samples, this paper proposes a method of distance metric learning based on the Gaussian mixture model, which can solve this problem more reasonably by dividing the dataset. Distance metric learning relies on the excellent feature extraction capabilities of deep neural networks to embed the original data into the new metric space. Then, based on the deep features, the Gaussian mixture model is used to cluster the analyzer and estimate the sample distribution in this new metric space. Finally, according to the characteristics of sample distribution, stratified sampling is used to reasonably divide the data. The research shows that the method proposed can better understand the characteristics of data distribution and obtain a more reasonable data division, thereby improving the accuracy and generalization of the model.
In order to improve the aerodynamic performance and stability of the floating platform of an isolated vertical axis wind turbine, a novel structure design concept of the wind turbine with a coaxial counter-rotating vertical axis was proposed. Based on the computational fluid dynamics theory, a numerical simulation was conducted with the application of the Reynolds-averaged Navier-Stokes (RANS) shear stress transfer (SST) k-ω turbulence model, and combined with the eddy current theory, the aerodynamic performance and stability with different tip speed ratios (TSR) were further compared. The results show that in the same flow field, the floating platform of the counter-rotating wind turbine is more stable. When TSR<1.3, the long-time stall makes the de-vortex of the counter-rotating wind turbine more serious, and the wind energy utilization efficiency is lower. When TSR>1.3, the wind energy in outflow field is more absorbed by the rotor of the counter-rotating wind turbine. In addition, the length of remote vortex is shorter and the intensity is lower. Therefore, the wind energy utilization efficiency is higher. Coaxial counter-rotating has a certain reference value for the performance optimization of the vertical axis wind turbine.
It is a challenging problem to efficiently calculate and systematically analyze the motion laws and working gait of the inchworm-like soft robot. A simple mechanical model consisting of a rigid slider and a curved beam is established under quasi-static conditions, in order to realize quasi-static modeling and simulation analysis of the inchworm-like soft robot. First, based on the Euler-Bernoulli beam theory, the total potential energy expression of the beam is obtained. Next, combining the boundary conditions and the governing equation derived from the total potential energy based on the variational principle, a set of ordinary differential equations are established. Then, through discretization and dimensionlessness of those equations, a class of nonlinear algebraic equations for numerical solution is proposed. Finally, in the light of the contact situation between curved beam and ground as well as the viscous and slip condition of the system, the motion of the robot is divided into three stages. Through numerical calculations, the different configurations of the curved beam in different stages with the change of the initial curvature amplitude are obtained, which makes it possible to describe the law, the gait, and the net displacement of the soft robot in a motion cycle and solve the problem of movement connection of soft robots at different stages. The quasi-static method is characterized by high computational efficiency, which is more suitable for analyzing the motion configuration of soft robots.
To predict the resonance frequency of the real liquefied natural gas (LNG) tank, a Cartesian grid based three-dimensional (3D) multiphase flow model is used to simulate violent sloshing in a prismatic tank at different filling levels and excitation frequencies. In this model, a semi-implicit finite difference method is adopted to solve the incompressible two-phase flow Navier-Stokes (N-S) equations on a staggered Cartesian grid. Besides, a radial basis function ghost cell method (RBFGCM) is used to treat the irregular tank walls and a 3D gradient-augmented level set (GALS) method is used to capture highly nonlinear free surfaces. Based on the present model, the violent sloshing induced by rolling excitations in the 3D prismatic tank is simulated. Satisfactory convergences of grid sizes and time steps demonstrate the high accuracy and reliability of the present method. Moreover, the present results of the impulsive pressure and wave elevation agree well with the experimental data for different filling water depths. In addition, violent sloshing phenomena are captured such as wave rolling. Furthermore, the relationship between the pressure amplitude on the tank wall and the excitation frequency at four filling levels are investigated to identify the resonance frequency of the prismatic tank, to provide theorical guides for structrual design of the tanks.
In order to improve the stress shielding effect caused by excessive elastic modulus of metal plates during fracture healing, a kind of 3D printing oriented lattice structure plate is designed based on topology optimization and the finite element modeling technology. A simplified finite element model of the titanium alloy tibial plate is established by using the finite element method. Combined with the finite element method and the data sampling method, the solid plate system and the lattice plate system are simulated, and the similarities and differences between their performances are compared. Based on the analysis of mechanical properties of lattice plate system, the lightweight design of the plate is realized and the stress shielding effect of the bone is improved. The results show that the weight of the lattice plate can be reduced by about 40% under the condition of guaranteed strength. The lattice plate is sensitive to the thickness. By reducing the thickness of the plate in a small range, the stiffness of the plate can be significantly reduced. The application of the lattice plate can effectively increase the average stress of the skeleton by about 4% and reduce the stress shielding effect of the skeleton. The simulated analysis results can provide references for the optimization design of low stress shielded plates.
A carbon dioxide(CO2) ejector expansion air conditioning system for vehicles is developed in a calorimeter laboratory. In experimental tests on a standard mobile air conditioning bench, the effects of different operating parameters on the performance of the CO2 refrigeration system for vehicles are studied, and the performance advantages of the CO2 ejector expansion refrigeration system are comparatively analyzed. The research results show that the cooling capacity of the CO2 ejector expansion refrigeration system for vehicles is almost equal to that of the CO2 conventional cooling system. Both increasing the indoor air flow rate and increasing the compressor speed can effectively increase the cooling capacity of the CO2 ejector expansion refrigeration system, and the ejector can increase the coefficient of performance (COP) of the system by 1.65% to 12.60% under different working conditions. The outdoor temperature has a great impact on the CO2 ejector expansion refrigeration system performance, and the performance of CO2 ejector expansion refrigeration system for vehicles decays obviously at a high ambient temperature.
Aimed at the problem of the compressors of the low temperature air source heat pump system, this paper analyzes the impact of volume ratio on performance and proposes a novel three-cylinder two-stage variable volume ratio rotary compressor. The performance of the proposed compression system is compared with that of the traditional two-stage compression system of the same terminal in the experiments. The results show that the three-cylinder two-stage system operates in a stable manner with a coefficient of performance (COP) of 1.52 at a ambient temperature of -30 ℃,while the traditional two-stage system does not work. The COP of the three-cylinder two-stage system is always 1.25% to 12.41% higher than that of the traditional two-stage systems at any ambient temperature. When the ambient temperature is stable and the water supply temperature increases, the amount of dissipated heat at the terminal increases. At the same time, the maximum heat of external machine decreases, as well as the COP. When the ambient temperature is 7 ℃ and -25 ℃ respectively, and the water supply temperature changes from 40 ℃ to 55 ℃,the COP of the three-cylinder two-stage system is 1.15% to 8.86% and 4.32% to 7.33% higher than that of the traditional two-stage system, respectively. The power consumption of the three-cylinder two-stage system is always 3.78% to 16.67% lower than that of the traditional two-stage system.
A wireless transcutaneous energy transfer (TET) system is researched. The characteristic functions of system voltage gain and transmission efficiency are obtained by circuit analysis. Meanwhile, according to the typical technical parameters of the TET system, a characteristic analysis is conducted. Therefore, based on the energy injection technique, a variable frequency constant voltage control method is proposed which enables the TET system to operate at a high efficiency all time when both the load and the transfer distance change. The experimental set of the TET system is arranged. The experimental results have verified the correctness of the theoretical analysis and design scheme. When the transfer distance is fixed, the overall efficiency remains constant in the whole load variation range. The overall efficiency of the TET system is above 83% within typical transfer distances. The multi-physics simulation software is used to simulate the human tissue safety. The simulation results show that the maximum electric field strength, the specific absorption rate, and the maximum temperature are lower than their corresponding limitations.
Based on a hybrid excitation generator, a novel electric vehicle range-extender was proposed and the control system structure and the working principle were described. The multi-speed point working area was determined, according to the overall efficiency characteristics of the hybrid excitation range-extender. Based on the flexible adjustable characteristics of the air-gap magnetic field of the hybrid excitation generator, a double-closed-loop generation control algorithm was designed by decoupling the speed-power around the working area of the range-extender. The control strategy model was built by using MATLAB/Simulink and verified based on the prototype of the self-developed hybrid excitation range-extender. The test results show that the hybrid excitation range-extender has fast-dynamic response of output power and small steady-state error of speed and power control. Further, the steady-state and transient operating conditions are both located in the set working area. Therefore the power generation control strategy is feasible.
Tian Xinliang’s group proposed a novel flow control method called "Flexible coating reduces drag" (FCRD) with a flexible enclosure constructed behind the bluff body to adjust the fluid forces received and the flow pattern around it. Compared with the traditional flow control methods, FCRD does not change the structure of the control object and thus has a positive engineering application prospect. Besides, FCRD brings out a new "fluid-structure-fluid" interaction problem, which needs further investigation.
Aimed at the problems of unmanned marine exploration vessels, such as the short voyage time and the limited sensing ability caused by sensor failure under complex marine environments, a long-range unmanned ocean-air stereo exploration vessel driven by wind and solar energy is developed. An elevating ducted wind turbine is designed for high efficiency and low starting wind speed, and a deployable solar photovoltaic power generation system is developed. Therefore, wind power and solar energy can be utilized to realize a hybrid system, which overcomes the instability of single energy power supply, and effectively ensures the endurance of unmanned exploration vessel. Then, a ship-borne tethered ummanned aerial vehicle (UAV) system is developed with an autonomous takeoff and landing control section. Finally, the information fusion technology of ship borne and airborne sensors is adopted to greatly improve the perception ability of the unmanned ship to the surrounding environment and the function of three-dimension detection of sea and air. The unmanned surface vessel (USV) proposed in this paper is permitted to perform the assigned task with different types of loading equipment according to the scenarios.
A method for online detection and compensation of grinding wheel wear based on machine vision is proposed in this paper. The principle of workpiece-contour-image (WCI) based online wheel wear detection is presented, and the online compensation of wheel-wear-induced contour error is analyzed, based on which, studies are conducted on the developed complex contour grinding platform. The results reveal that the proposed method can effectively detect the wheel wear in real-time and compensate the contour error caused by wheel wear to improve the machining accuracy. The research provides a new method for online detection of wheel wear and prediction of wheel dressing.
Aimed at the uncertainty of equipment quantity and input, the defective products and its rework in the manufacturing process are investigated. Considering the influence of the number or input of the devices on system reliability, a manufacturing system reliability evaluation model is established based on stochastic flow network. The homogeneous Markov process is used to analyze the state of system degradation and maintenance. Considering the constraint of system reliability, a systematic maintenance model is proposed to minimize maintenance cost. The results of the numerical experiment demonstrate that the proposed model is effective and advanced.
The double cantilever beam flexible pin structure with interference fit is usually adopted by the planetary gear shaft of large gear gearbox, and the interference fit structure at this location is prone to fretting fatigue. The maximum and minimum values of effective interference are theoretically calculated. Besides, the bending load process of flexible pin is simulated by using the finite element software Abaqus. In addition, the influences of bending load, interference and the depth of carburized layer on contact stress, frictional shear traction and slip amplitude are analyzed. Moreover, the influence degrees of various factors on fretting fatigue damage are investigated, and the S-N curve of flexible pin fatigue life is predicted by utilizing the SWT (Smith-Watson-Topper)critical plane theory method. Furthermore, the bending load fatigue loading test is conducted on several groups of specimens, the S-N curve of the flexible pin test is obtained, and the fretting fatigue damage morphology of the component surface is analyzed after the test. The results show that the influence of bending load on fatigue life is greater than that of the interference, and the depth of the carburized layer. The fatigue life of SWT prediction is in good agreement with the test data. Therefore, numerical simulation analysis can be used to help check the fatigue life of the flexible pin in engineering design.
Alloy elements can influence the microstructure evolution of aluminum alloys in the state of solid solute atoms or nano-precipitated silicon particles, but it is still a controversial subject which form has a more significant effect on the microstructure of aluminum alloys. Therefore, taking the Al-1%Si alloy as the research object, the ratio of precipitation state and the solid solution state of the silicon atoms was changed before deformation and a multi-pass accumulative roll-bonding method was used to achieve large deformation. In order to compare the influence of solid solute atoms and nano-precipitated silicon particles on the structure and properties of aluminum alloy during deformation, a comparative study was conducted on the evolution of nano-precipitated silicon particles, grain size, and dislocation density in the process of reaching the saturation state of the microstructure and mechanical properties. The results show that the initial samples with less nano-precipitated silicon particles and more solute silicon atoms have a higher saturated dislocation density and a smaller saturated grain size after deformation, corresponding to a higher saturated yield strength. Solid solute silicon atoms dispersed in the Al-1%Si alloy have a better overall effect than nano-precipitated silicon particles of the same volume in preventing the dynamic recovery of dislocations, which is consistent with the theoretical analysis of dislocations. The dislocation recovery ability in the material affects its saturated grain size. The stronger the dislocation recovery capacity, the larger the saturated grain size.
A self-developed strip-type high-temperature friction and wear test device was used to simulate the high-temperature friction process of uncoated 22MnB5 boron steel under actual hot stamping conditions. The mold was preheated to simulate the temperature increase of the die in the hot stamping process. The effects of mold temperature on the friction behavior and mechanism of uncoated boron steel were studied by using the friction coefficient test, surface wear morphology observation, and cross-section and matrix structure chart of hot stamping boron steel. The results show that the friction coefficient between the uncoated boron steel and the H13 steel is basically stable at 0.5 when the temperature of the mold is low, and the wear mechanism is mainly classified to abrasive wear and adhesive wear. Besides, when the mold temperature exceeds 100 ℃,the friction coefficient of the uncoated boron steel decreases from 0.474 to 0.414 with an increase of temperature from 150 ℃ to 200 ℃,inferring that the adhesive wear is weakened. The Vickers hardness of the boron steel matrix is approximately close to 430 from room temperature to 100 ℃. Moreover, with the temperature further rising to 150 ℃ and 200 ℃,the hardness decreases to 413.5 and 399.7 respectively, which indicates that the mold temperature has a significant effect on the mechanical behavior of formed parts.
In connection with the elastic-plastic failure problem of offshore jacket platform subjected to a powerful earthquake, an improved modal pushover method based on performance design is proposed. The elastic-plastic seismic performance and failure modes of the jacket platform are obtained to solve the problem of elastic-plastic performance evaluation of the offshore jacket platform in strong earthquakes. The elastic-plastic seismic responses of the platform in 8-degree seismic fortification and rare intensity are calculated by using different methods, and the differences between these responses are compared. Besides, the influences of combined modes, mode shape vectors, and uncertainties of seismic are discussed. The results show that the high-order vibration modes and mode shape vectors have a great influence on the elastic-plastic seismic performance of the platform. The first 9 or higher order modes and mode shape vectors should be adopted. The seismic-resistant weak links are located at the top of the platform in 8-degree seismic fortification and rare intensity, which should be paid more attention to. The seismic responses of the platform show significant differences and discreteness in different seismic activities, which have the same peak seismic acceleration. The improved modal pushover method is suggested to be used to evaluate the elastic-plastic seismic performance of jacket platform.
To solve the problem that the natural frequency of deck arch bridges would decrease rapidly when the span increases, a novel arch bridge structure named deck V-arch bridge is proposed. The V-shaped members are added between the main girders and the arch ribs to increase the stiffness of the arch bridge, thereby increasing the natural frequency of the structure. Through the timely conversion of the structural system, the first-phase dead load is carried by the arch ribs, while the second-phase dead load and live load are carried by the variable height truss with main girders as upper chords, arch ribs as lower chords, and V-shaped members as webs, with multi-point elastic constraints. The entire structure has the advantages of arch and truss. In order to verify the correctness of the research and calculation of the dynamic characteristics of the deck V-arch bridge, a test bridge with a span of 10 m is built. The first natural frequency of the vertical bending in the plane of the bridge is tested by utilzing the pulsation test. The stiffness and dynamic characteristics are calculated by utilizing the finite element software. The influence of V-shaped member stiffness on the natural frequency and that of the number of V-shaped members on the temperature stress of the structure are analyzed. The necessity of system transformation is studied. The results show that the difference between test value and calculated value of the first natural frequency of vertical bending in the plane is small. The mode shape is in good agreement with the finite element analysis. With little or no additional material, the natural frequency of the structure is significantly increased, especially the in-plane frequency. The stiffness of the V-shaped members has a reasonable setting range. When the inner angles of the triangle formed by the main girders or the arch ribs are between 45 ℃ and 60 ℃,the number of V-shaped web members is suitable. The structural stiffness of deck arch bridge with V-shaped members is greatly improved, and at the position of L/4 (L is the span of the bridge), the upward deflection generated by the static live load of the train is approximately zero. After the transformation of the structural system, the deck V-arch bridge can fully exert the superiority of the arch force.
It is necessary to predict accurately the maneuverability of autonomous underwater vehicle (AUV) diving by self-propulsion to improve its safety and stability. A method was presented to predict the vehicle’s forces and flow details in real time during forced diving motion. A full appended model was built, the propeller’s rotating motion was simulated, and coupled with user defined function (UDF), the Reynolds-averaged Navier-Stokes (RANS) equations were solved. This method can improve the accuracy and computation efficiency of the dynamic mesh method by using multi-block mesh with the moving zone method. The numerical method was validated by comparison of the computational and experimental results of AUV’s velocity in AUV self-propulsion test. The numerical results of AUV forced diving by self-propulsion showed that, at the initial time, the AUV had a large acceleration which resulted in a large resistance. When the pitch changed, the vertical force oscillated. The wake of the propeller twisted and the thrust of the propeller varied. In steady diving, the thrust and resistance became steady.
In order to improve the cargo owner’s satisfaction and obtain better economic benefits for shipping companies, the ship deployment along routes and speed optimization of tramp ships are studied, considering the influencing factors of ship scheduling with the configuration and speed of self-owned ships and chartered ships. A goal is developed by minimizing sailing cost, fuel, and waiting cost at ports, penalty cost for late arrival at ports, time cost, and voyage ship chartering cost by applying fuzzy time window to characterize the cargo owner’s satisfaction. The model of scheduling and speed optimization with fuzzy time window for heterogeneous tramp ships is established. A variable neighborhood genetic simulated annealing (VNGSA) algorithm is presented to solve the problem. First, the ship type is matched with the cargo. Then the route is generated according to the time constraint. Finally, the neighborhood search strategy is adopted to improve the solution quality. Computational results indicate that integrated planning for ship scheduling and speed can reduce sailing cost; considering time requirement of cargo owners can increase their satisfaction. This paper can enrich tramp ship routing and speed optimization problems and provide a theoretical tool for shipping companies to make related decisions.
The non-rigid airship is a low-rigidity and inflatable aircraft which has obvious fluid-structure interaction characteristics. In this paper, the unsteady explicit dynamic fluid-structure interaction analysis framework of non-rigid airship is constructed based on the parametric section (PARSEC) method, the radial basis function (RBF), and the Delaunay mapping method. The reliability and accuracy of the numerical method are verified by the cases of plate impact and the aeroelasticity of NACA0014 wing. The calculation framework is also suitable for unsteady bidirectional fluid-structure interaction analysis of thin-envelope aerostats such as high-altitude balloon. Finally, the time domain and frequency domain responses of one non-rigid airship are simulated by the above framework. The research results show that there is an approximately linear relationship between the dominant frequency of vibration and the pressure difference of the airship.
Aimed at the problem of avoidance strategy of formation satellites when facing the threat of space debris, a non-dominated sorting genetic algorithm (NSGA-II) is improved and used to code satellites. Besides, the improved differential evolution algorithm is used as the orbital generation model, while Pareto dominance is used to select the optimal solution set. By introducing maneuver consumption, collision probability, work efficiency, and other indicators of formation satellites, the avoidance orbits of satellite are screened to ensure that all the indicators of formation satellites are taken into account. Taking the 3-satellite formation of ocean reconnaissance satellite as an example, the phase adjustment, probability calculation, and horizontal dilution of precision (HDOP) calculation models are introduced. The optimal solution of avoiding orbits is obtained by utilzing the multi-objective optimization algorithm. The simulation results show that this method can formulate a more targeted formation satellite avoidance strategy with different objectives.
Aimed at the nonlinearity and uncertainty of building energy consumption, a forecasting approach based on the support vector machine is proposed in this paper for the prediction of hourly energy consumption of an office building. The univariate model test is used to determine the input parameters. Superior model hyper-parameters are found by grid search optimization. The confidence interval of the model fitting error is applied to describe the uncertainty of building energy consumption. A case study is conducted using the data collected from an actual office building to verify the proposed approach. The results show that the overall mean absolute percentage error (MAPE) of the model after grid search optimization is reduced by 31.3%, and a higher model precision is achieved. After combining the prediction with the confidence interval, MAPE is found to be lower than 1.5% in different seasons and the building operation fluctuations are embodied. This approach can be used in the diagnosis and optimization of building operation.
Uniform current effects on the characteristic of irregular waves along with its uncertainty are presented considering wave-current interaction in the actual ocean environment. First, relative tests of interaction of irregular wave and uniform current are conducted in the circulating water channel at Shanghai Jiao Tong University. Then, the wave elevations are measured to validate the numerical results obtained from the numerical simulation of wave-current interaction based on Reynolds-Averaged Navier-Stokes (RANS) equations. Finally, significant wave height and average period of irregular wave are selected to conduct the uncertainty analysis including both grid-convergence and time-step-size convergence studies. The results show that wave height probability distribution agrees well with Rayleigh distribution in the co-current and no-current cases. The spectral peak of irregular wave moves to the low frequency in the co-current conditions. Besides, significant wave height of irregular wave is more sensitive to grid size, while the average period is more affected by time step size. Moreover, uniform co-current can reduce the degree of dependence of significant wave height on time step size, while the influence on the average period is on the contrary.
Aimed at the wind-induced response and vibration reduction of an H-rotor type three-bladed vertical axis wind turbine (VAWT), and based on computational fluid dynamics (CFD) method, a numerical simulation is conducted to obtain the blade wind pressure distribution during the rotation period. Then, the wind pressure obtained is applied to the surface of the blades to analyze the wind vibration response of the VAWT. Dampers are arranged at different positions of the VAWT to simulate the vibration reduction capacity. The results show that applying the damper at the connection between the main shaft and the support rod of VAWT could reduce the displacement response of the structure to a certain extent and the maximum drop would reach 44%. Furthermore, the displacement reduction rate of the structure is related to the position of the damper. If a damper is arranged near the top end of the blade, the maximum displacement of the structure would occur at the bottom of the blade. However, if a damper is arranged near the bottom end of the blade, the maximum displacement of the structure would occur at the top of the blade and the maximum drop would reach 40.7%. The results would provide technical reference for research on the vibration reduction of VAWT structures.
Special collection of 12 issues of "Journal of Shanghai Jiaotong University" in 2021 
