Abstract:On the basis of a brief introduction to the relevant theories of the superhydrophobic surfaces, this review focuses on the development of key technologies in the fabrication process of metal-based superhydrophobic surfaces, attaching particular importance to the analysis of the current status of different fabrication methods, including the core points of surface preparation process, design and construction of micro-/nano-topography, modification with low-surface-energy materials, improvement of surface property, etc. The application status of metal-based superhydrophobic surfaces in various engineering fields, including self-cleaning, metal anti-corrosion, underwater drag reduction, etc., has been summarized systematically, and the key factors affecting the mechanical stability of superhydrophobic surfaces have been pointed out. Moreover, the challenges and issues need to be faced during the development of fabrication process are also discussed. This work is expected to present reference background for advancing the practically engineering application of large-area metal-based superhydrophobic surfaces.

Abstract:The existing parameter identification method of biped robot that uses the joint torque has low identification precision. The identification method based on full contact force and motion capture data requires additional equipment, which limits the application in a large range. Regarding this problem, a method for inertial parameter identification of biped robot based on ZMP data is proposed. The objective function is defined as the position deviation of the theoretical ZMP and the actual ZMP. The range of the parameters and the total weight of robot are considered as two constraint conditions. Then the optimization model of inertial parameter identification of biped robot is established, which only needs sample data acquired from the robot itself. Because the built model cannot be split into linear form, the gradient vector and Hessian matrix of the objective function are derived with respect to the parameter vector. Also, the optimization algorithm is given based on steepest descent method and Newton method. Using the biped part of the GoRoBoT-II robot, the inertial parameter identification experiment of the leg links is carried out. The proposed method is compared with the traditional identification method based on joint torque. It is found that the result of the proposed ZMP-based identification method is closer to the nominal value of the parameters obtained by 3D geometric modeling. Also, the deviation between theoretical ZMP and actual ZMP is 4.6 mm, which is smaller than the deviation (12.4 mm) of traditional method, indicating that the proposed ZMP-based parameter identification method can obtain better results than traditional methods.

Abstract:To improve the consistency and flexibility of master manipulator in minimally invasive surgery, an 8-joint series force feedback master manipulator was designed. From the perspective of position-posture decoupling, this design realized position-posture decoupling through a double parallelogram structure, which improved the consistency of operation in different positions and postures. Using the modified D-H parameter method and inverse transformation method, the forward and inverse kinematics of the master manipulator were solved respectively, and the position-posture decoupling strategy was verified from the perspective of kinematics. Based on Monte Carlo method, the minimum working space of the master manipulator was analyzed by MATLAB programming. Then the Jacobi matrix of the master manipulator was solved. Based on the global conditioning index and global conditioning mean square error index, the comprehensive motion performance index of the master manipulator was defined. Taking the minimum working space as a constraint, the motion performance and structure size of the master manipulator were analyzed and optimized through genetic algorithm. The optimization results show that, compared with the initial design, the comprehensive performance index of the master manipulator is improved by 15.32%, and especially the workspace volume with good motion performance is increased to 3 times of the original, which basically includes the operation required work area. On the basis of ensuring the consistency of operation and enough working space, the master manipulator has good and stable motion performance.

Abstract:To unveil the effect of canard’s vertical position (g/c_w=-0.15, -0.5,0, 0.05 and 0.15) on longitudinal aerodynamic characteristics of a dynamic canard configuration, both water-tunnel force measurements and CFD numerical simulations are conducted to research the unsteady pitching oscillations (k=0.037 5 and 0.600 0) of canard configurations. It has been found that the variations of canard’s vertical position bring more influences on the lift coefficients of the canard than the ones of wing. During the low-frequency pitching-up process, the canard vortex of the lower deployed case becomes more sensitive to the interaction from the downstream wing, which brings an earlier double-spiral breakdown of canard vortex. When undergoing the low-frequency pitching-down process, the canard vortex of the lower deployed case is harder to rebuild than the higher deployed one. During the high-frequency upstroke process, due to the large reduction of canard leading-edge effective attack angle, the canard vortex initially develops on the lower surface of the canard for both lower and higher deployed cases. When undergoing the high-frequency downstroke process, the convection flow of canard vortex for the lower deployed case is faster than the higher deployed one, thus the canard lift coefficients of the former case become smaller. In addition, compared to the canard configuration with a lower deployed canard, the higher deployed case can own a larger maximum lift coefficient of wing during the low frequency pitching oscillations. When undergoing a high-frequency downstroke stage, due to the breakdown of wing vortex and canard’s vertical position, the wing lift coefficients of the higher deployed case become smaller.

Abstract:Aiming at the high-temperature rotating blade with composite cooling structure of a gas turbine, the high temperature flow field on outer gas side and the inner cooling flow fields in the double cambers with serpentine baffling passages and composite cooling structures were simulated using the gas-thermal coupling numerical simulation method. The influence of the presence or absence of ventilating hole on the cold air flow resistance characteristic and the heat transfer performance were investigated. It is found that the air film/impingement/turbulence composite cooling structures used in the serpentine passages inside the blade without ventilating hole design have a better heat transfer performance, and both the internal and external surface temperature distribution are in a reasonable range under the given cold air flow flux. However, the total pressure supplied by the inlet of the cooling air is too large, which is resulted from the higher flow resistance of the entire inner cooling channel. By the design of local ventilating hole, the internal flow resistance is effectively reduced. Under the condition that the heat exchange effect is only slightly influenced, the required cold air supply pressure and the cold air volume are both significantly reduced, and the air volumes for the double cambers get a better match. The prototype blade has a better engineering application by the redesign.

Abstract:To study the wave-making characteristics of a shallow navigation submarine in the stratified fluid caused by density difference, a multiphase-flow CFD model for evaluating the wave-making characteristics is established by using the RANS equation, Realizable k-ε turbulence model and UDF method. Thereafter, the process of a full-appendage submarine navigating at different positions with low, medium, and high forward speeds in the shallow layer of density-stratified fluid is simulated, and the effects of the forward speed, the distance from interfaces and density-stratified fluid on the wave-making and velocity characteristics of the submarine in the interfaces are investigated. The result shows that the higher the forward speed and the closer to the interface are, the more intense the submarine wave-making in the interfaces will be. Especially in the mid-speed stage, there will be a large wave excited by submarine, and a big difference of wakes between the free surface and internal wave surface is obviously seen, of which the main performance is that the front of wave on free surface is a peak and the front of wave on internal surface is a trough. The response of the wave-making on the internal interface to the changes of various navigation parameters is insensitive than that on the water-free surface. The present numerical model has high accuracy, which can provide an effective method for analyzing the wave-making characteristics of submarine navigating in density stratified fluid.

Abstract:To solve the problem that the empirical modeling for thermal error of machine tool spindle lacks physical significance, and the modeling accuracy and robustness are greatly affected by pseudo-hysteresis effect of thermal deformation, a modeling method for thermal error of machine tool spindle which has clear physical meaning and is not affected by pseudo-hysteresis effect is derived from theoretical perspective. Firstly, the spindle is simplified as a one-dimensional rod. Taking into account the convection between cylinder surface and air, the analytical solutions of temperature field and thermal deformation of the rod under the condition of single-end heat source are obtained by using heat transfer theory. Then the thermal deformation expression is transformed, and the first-order autoregressive model for the rod under the condition of single-end fixed heat source is derived. After that, the validity of the first-order autoregressive model for the thermal deformation of the rod under the condition of variable heat source is verified, and the relationship between the coefficients of the autoregressive model and the physical characteristics of the spindle, the time interval of the autoregressive model and the heat source is pointed out. Finally, finite element simulation is carried out, and the experimental verification is performed on Headman T65 lathe. The simulation results show that the first-order autoregressive model can effectively estimate the thermal deformation of the one-dimensional rod under the condition of variable heat source and is not affected by the pseudo-hysteresis effect. The experimental results on the T65 lathe show that, compared with multiple linear regression model, the first-order autoregressive model is more robust and has clear physical significance.

Abstract:To solve these two problems that it is difficult to extract the characteristics of weak periodic impact caused by the strong background noise of the signal generated during the rolling bearing fault, and the general diagnosis model does not have a strong recognition effect on the timing characteristics of the fault vibration signal during the intelligent diagnosis of the bearing fault mode, this paper put forward a fault diagnosis method based on the maximum correlation kurtosis deconvolution(MCKD)algorithm, Teager energy operator and long short-term memory(LSTM). Firstly, the rolling bearing vibration signal is denoised by MCKD algorithm, the periodic impact characteristics of the signal which are covered by noise are extracted, the Teager energy operator is used to detect the transient impact of the signal and the Teager energy sequence is obtained. The results are then divided into training sets and test sets, the training set is input into the established LSTM fault diagnosis model for learning. Finally, the LSTM model with appropriate parameters is applied to the test set to output fault diagnosis results. The experimental results show that the proposed method can diagnose faults of various types and sizes at one time and has high identification accuracy. It is a fault diagnosis method that can effectively utilize the timing characteristics of strong background noise signals.

Abstract:To effectively improve the fuel cell vehicle economy, it is necessary to systematically explore how to carry out deep energy saving. First, the impact of configuration on fuel economy is analyzed by simulation, and then based on the theoretical hydrogen consumption model, the influencing factors of hydrogen consumption are determined and the microeconomic analysis of each influencing factor is carried out in turn. Finally, the hydrogen consumption limit of the vehicle is determined by ergodic weight coefficient dynamic programming method to explore the influence of control strategy factors on vehicle energy consumption. In addition, the method to determine the cost function in terminal constrained dynamic programming is studied, and the deep global optimization is realized based on this method. The results show that, from the configuration point of view, the presence or absence of super capacitors has little effect on the economy of the vehicle, but FC+B configuration has better economy than FC+B+C configuration. From the microeconomic point of view, quantitative analysis of different factors affecting hydrogen consumption reveals the importance of each factor on vehicle economy. From the control strategy optimization point of view, the power following control strategy can better play the vehicle economy. The deep energy-saving analysis of fuel cell vehicles from different perspectives reveals an effective way to improve the vehicle economy, and also provides an effective theoretical basis for the selection of configuration and components and the formulation of control strategy.

Abstract:To accurately estimate the junction temperature and solve the over-temperature problem, a junction temperature state observer is designed to predict the junction temperature of IGBT in real time considering the mutual influence of electrical and thermal parameters. First, the effects of conduction current, bus voltage and junction temperature on IGBT loss are studied on the offline test platform of IGBT. The mathematical model of IGBT loss was derived by linear interpolation method. Second, a thermal network model is built up based on the IGBT transient thermal resistance test platform. Last, the state equations of each temperature node are derived and a full-order state observer is designed to compensate the drawback of open-loop state equation. The error between output shell temperature and the measured shell temperature is corrected in real time on full-order junction temperature observer. To verify the effectiveness of the designed method, simulations carried out on Matlab\\Simulink and experiment setup are established. The simulation and experimental results show that the predicted junction temperature can track the target value, and the designed method is validated.

Abstract:To more accurately estimate the state of charge of the power source of EVs, Thevenin equivalent circuit model is optimized, and the charge of state is estimated by adaptive extended Kalman filter. Firstly, the external characteristic data of the experimental battery and the open circuit voltage curves under charge and discharge state are obtained. The factors of charge and discharge state change are added to the corresponding curve of open circuit voltage-charge of state. Secondly, in the aspect of parameter identification, the off-line identification is optimized. The charge-discharge state and charge of state are considered on the basis of the off-line identification of fixed parameters. The estimation of terminal voltage is compared with on-line identification. Finally, based on the optimized battery model, the charge of state is estimated by adaptive extended Kalman filter and its comparison algorithm. And the estimation accuracy of terminal voltage and charge of state is compared under complex pulse current conditions. Experimental results show that the accuracy of terminal voltage estimation for off-line identification of optimized battery model is less than 0.01 V, which is higher than that for on-line identification. Based on the optimization model and off-line identification, adaptive extended Kalman and extended Kalman and interactive multi-model algorithm are constructed to estimate the charged state of the battery. The experimental results show that the estimation accuracy of charged state based on optimization model adaptive algorithm is 0.05, which is higher than that of the two contrast algorithms. The accuracy of adaptive extended Kalman filter based on optimization model is higher than that of interactive multi-model extended Kalman filter and extended Kalman filter.

Abstract:A variable gain sliding mode control algorithm is proposed for a space robot to track the path aimed at capturing a target. MATLAB/Simscape is used to verify the dynamic model of the space robot and the control algorithm. First, Lagrange method is adopted to establish the dynamic model, and subsequently a model considering the uncertainty of the system is developed. A sliding mode controller which introduces a variable gain is developed. The gain can adapt to the uncertainty of the system and its motion thereby facilitating the controller to be robust. Further, the theoretical model of the space robot is verified using Simscape Multibody. In addition, for the scenarios of single joint motion, multiple joints motion and uncertain system, the proposed control method is applied to the robot for tracking a desired path. Numerical results have demonstrated that in comparison with computed control method, the new method presents higher control accuracy and faster convergence speed.

Abstract:Aiming at the problem of low flow control accuracy of the dynamic flow balance valve, based on the orifice flow and concentric annular gap flow equations, the spool opening profile was initially designed, and the pressure difference compensation coefficient factor correction method was proposed to optimize and modify the existing profile formula. Based on the large eddy simulation (LES) turbulence model, the flow control accuracy and flow accuracy error of the dynamic flow balance valve before and after optimization were studied by numerical simulation, the influence of the valve core opening profile on the pressure pulsation intensity was compared and analyzed, and a flow test bench was built to verify the proposed optimization method. The results show that the pressure difference compensation factor correction method to optimize the spool opening profile can effectively reduce the pressure pulsation intensity of the spool end face, and improve the flow control accuracy of the dynamic flow balance valve to 3.7%. The flow field simulation calculation and the experimental results basically coincide with the trend.

Abstract:To improve the fuel economy of engineering transportation vehicles and reduce the mining costs of coal enterprises, taking the mining truck cargo box as the research object, a comprehensive lightweight design method for two working conditions is proposed. Firstly, the finite element model of the cargo box is established, and the strength performance of the cargo box under two typical working conditions, the state of running at a uniform speed with a full load and unloading are analyzed. Then, a parameterized model is established under two typical working conditions, and five design variables are defined. The sample points are selected by using the optimal Latin hypercube sampling and the corresponding response values are obtained in the established two-condition comprehensive analysis model. By comparing and verifying different approximate models, the radial basis function (RBF) approximate model is selected to establish the relationship between variables and responses. Based on the approximate model, NSGA-II algorithm is used for multi-objective optimization to obtain different optimal design schemes. The target scheme is selected for static strength and fatigue strength verification. The results show that the optimal design parameter values can be obtained by using this method and the optimized cargo box of the mine car can meet the requirements of strength under two different working conditions, as well as the weight is reduced by 7.47%.

Abstract:To avoid the performance degradation of vehicle fuel cells due to start-stop changes, power fluctuations and other states, in the development process of energy management strategy, it is necessary to consider the durability of fuel cells while ensuring the economy. In this paper, the start-stop state of fuel cell is set as the state variable, and the idle transition stage is added between the start-up and shutdown states of the fuel cell, so as to achieve the adaptive start stop interval control of the fuel cell. The joint cost function of economy and durability is constructed by using fuel cell performance degradation index as durability cost and vehicle energy consumption as economic cost. Based on the improved dynamic programming algorithm, a joint optimization energy management strategy for the economy and durability of extended range fuel cell vehicles is established. The simulation results show that the vehicle energy consumption of the proposed strategy is 5.3% higher than that of the classical dynamic programming strategy, the output power of the fuel cell is stable, the start-stop changes are less, and the performance degradation degree is improved by 65.5%, which effectively ensures the vehicle economy and fuel cell durability.

Abstract:A simple and economical upper-limb exoskeleton robot actuated by the pneumatic muscle is developed. Aiming at the problem of large tracking error, poor robustness, and chatter in single pneumatic muscle joint motion control, a backstepping method based adaptive robust controller is developed. This controller presents a two-layer cascade structure, and each layer includes a robust feedback part, a recursive least squares estimation based parameter adaptive part, and a gradient-based fast dynamic compensation term. The controller stability is proven by the Lyapunov theory, and the effects of the parameter adaptive and fast dynamic compensation term are analyzed further in terms of the comparative experiments. The results validate the excellent transient and steady performance of the developed controller, especially the transient absolute tracking error is less than 0.94 mm and the steady-state root-mean-square tracking error is less than 0.21 mm during tracking sinusoidal signal with an amplitude of 15 mm. Furthermore, disturbance experiments validate the developed adaptive robust controller inherits the disturbance objection ability from the deterministic robust controller.

Abstract:To quantify and identify the crucial geometric errors which constrain machine accuracy in the process of manufacturing and fabricating parts, we introduced Jacobian-torsor model to study the geometric error of dual-drive z-axis assembly in horizontal machine center. Combined the tolerance zone of parallelism and straightness, we determined the variation range and constraint equation of torsors based on dimension and geometric tolerance, and then we established the error model. We compared the simulation results and the measured error data of similar conditions, and used Sobol sensitivity analysis method to identify crucial geometric errors. The results show the availability of the Jacobian-torsor model in geometric error analysis quantificationally. The lead error of ball screw, flatness of base, straightness of guide and parallelism between sliders in Y direction were identified as the crucial errors, and the intercoupling of some errors is obvious.

Abstract:To reduce the vibration of the opening spherical shell, this paper proposes a kind of spherical shell with local active constrained layer damping (ACLD). Based on the first-order shear deformation theory and the Donnell shell theory, the strain is expressed as a function of displacement. The spherical shell deformation is represented by the expansions of Jacobian polynomials in latitude direction and Fourier functions in the longitude direction. The system dynamics model is established by use of the energy method and Lagrange equation. The effects of the structure parameters of ACLD, damping layer duty ratio and excitation voltage of piezoelectric layer on modal frequency and damping ratio are studied and the frequency response of the mid-point of the spherical shell is compared under different excitation voltages. The results show that the proper viscoelastic thickness and duty ratio can dissipate the vibration energy of spherical shell effectively. The large size of the piezoelectric layer in the latitude and longitude direction can generate big damping ratio of the system but it will make the mass and modal frequency grow so fast that the performance of the spherical shell is destroyed. The application of excitation voltage can promote the dissipation of vibration energy almost without changing the modal frequency. However, a certain excitation voltage can be effectively only for reduction of the modal amplitude in a specific direction.

Abstract:Aiming at the objective evaluation of shift quality of DCT (dual clutch transmission) vehicles, 10 parameters are selected as the evaluation indexes of shifting quality from two evaluation dimensions of smoothness and power performance. In order to solve the problems of redundancy between indicators and the lack of rationality of the existing weighting methods, based on the primary evaluation indicators, the evaluation indicators are reduced by using the rough set knowledge reduction method optimized by genetic algorithm, and the effectiveness of the reduction is verified by using the classification model of support vector machine. Then, based on the concept of attribute importance, the reduced evaluation index is weighted. The test results show that the method can effectively delete redundant indicators, and reasonably weight the evaluation indexes, which provides a basis for objective evaluation of shift quality of DCT vehicles.