Abstract:The fundamental principle and the structure of dielectric elastomer actuators, together with their applications in robotic systems were reviewed briefly, and the special stress was mainly laid on analyzing the progress in theoretical investigations on the properties of dielectric elastomer, including material characteristics, constitutive theory, failure mode and stability, etc. The actuator's specific requirements and the technique characteristics of the flexible electrodes were also summarized in detail. The application of dielectric elastomer actuators in robotic system was prospected on the basis of a profound discussion of the challenges that the dielectric elastomer actuators still have now.

Abstract:This article introduced the research status of the physics of coupling zone in Hall thrusters. The coupling zone is the area that links hollow cathode and Hall thruster channel. It determines the electron parameters on the inlet of the channel and the discharge characteristics of the hollow cathode. With negative-gradient weak magnetic field in this area, the local physics are highly complicated. The article chose four different facets to discuss the parameter distribution and influencing factors of this area:the transport of seed electrons towards the anode, the process of ion beam neutralization, the E×B drift of plasma bridge electrons and the hollow cathode discharge in coupling environment. By summarizing the characteristics of this area, the difficulties and shortcomings of current studies were analyzed and suggestions for further studies were given.

Abstract:Turbofan engine nozzle ejector technology was used for the design of a new turbine for efficient utilization of low-grade wind energy and ocean current energy. The turbine was composed of a low-rotation-speed single-stage and a lobed ejector. A parameterized method for building the lobed ejector structure was given. Reynolds-averaged NS equations and k-ε turbulence model were chosen for numerical study on the aerodynamic performance and ejection ability of the turbine using commercial software CFX. Simulation results indicated the lobed ejector could bring the wind/oceans currents energy into the back of turbine, the stream-wise vortices and normal vortices behind the lobes were produced to pump the low speed fluid behind the turbine. The effect could make the pressure reduced, the effective velocity almost increased 1.4 times, and the energy grade was improved. In the condition of wind speed ranges from 2 to 6 m/s and ocean current speed ranges from 2 to 4 m/s, the power output of the turbine exponentially increased as the flow velocity increased, and flow capacity was increased by 32.70% -35.33% than single-stage turbine. The energy utilization efficiency of the turbine went up to 66%-77%.

Abstract:Severe impact is detected in the application of deployable hinges in aerospace mechanisms such as solar array. The impact may result in failure of accessories connected to the hinges. To tackle this problem, this paper firstly proposes an approach to calculate magnitude of angular velocity and impact torque, based on which the key factor affecting the impact is concluded. Two schemes are devised based on intermittent mechanism and energy-storage mechanism. The effectiveness of the schemes to decrease the impact is discussed from the view of energy. Two structure models are built for each scheme and simulated to verify their feasibility. The simulation results indicate that the impact torque can be reduced by approximately 90% and 31%, respectively. In addition, two prototypes are manufactured, on which experiments of angular acceleration measurement are conducted, and the results demonstrate that the impact can be diminished by 95% and 40%, respectively.

Abstract:Calculation of the acoustics noise is divided into calculation of flow field and acoustic field based on the acoustic analogy theory. Numerical simulation of aeroacoustics noise caused by a kind of SUV vehicle rear-view mirror is finished by combining calculation of flow field step by step in complete domain & subdomain with calculation of acoustics field by ACTRAN. The simulation results of aeroacoustics noise caused by the rear-view mirror are well consistent with the experimental results. The accuracy and reliability of numerical simulation method is verified. The aeroacoustics noises caused by the optimized rear-view mirrors are simulated with this method. The contours of external flow field, internal & external acoustics field and the curves of sound pressure level spectrum of the vehicle are obtained. The outflow field turbulent fluctuation pressure, the vortex and the distribution location of the sound source are improved in the scheme Ⅲ of the rear-view mirror by analyzing the variation rule of flow field contour and the spectrum curve of acoustics field. The aeroacoustics noise propagated into cabin through the side window is weakened. The distribution of internal acoustics field in cabin is optimized and the comfortability of driver and passengers is improved.

Abstract:Intermittent demand is characterized by infrequent demand arrivals and variable demand sizes, which results in the difficult of demand forecasting. To solve this problem, a new approach was developed to forecast spare parts demand. The methodology provided mechanism to forecast the demand arrivals couple with the demand values when demand occurs. It firstly used the method of modulation to transform the 0-1 demand arrival time series into the continuous time series, and then adopted the neural network model to forecast the processed time series. Next, it applied the method of time aggregation to forecast the real demand time series, and took the rolling forecasting method into disaggregating, then got the predictive demand values. Applying this approach in forecasting the spare parts of the nuclear power equipment, the experimental results showed that the prediction accuracy was superior to Croston's method, exponential smoothing and BP neural network, which proved the methodology to be effective and accurate.

Abstract:To enhance the systematization and universality of solar wing panels' design theories and methods, a geometric model is proposed to describe the relationships between developable surface and panels' configuration. Using the analogy method, the straight generatrix of developable surface is regarded as revolute joint between two panels while the developable surface between straight generatrices as the panel. The unfolding principles of solar wing panels are expounded from the perspectives of geometry and mechanical configuration, the constraint equations of geometric features in the different panels' configurations are established. The concept of basic component of developable solar wing panels is elaborated and the basic components are found, which is helpful for its innovative design. The existing solar wing panels' configurations are classified and analyzed to demonstrate the relationships between developable surfaces and panels, the geometric model of a new panels' configuration is built by configuration analysis at last.

Abstract:A new method is proposed to solve the problem of NURBS curve separation. Firstly, both of the equal chord length and the equal error separation algorithms are simulated to verify the advantages and disadvantages. Given the relationships among chord length, error and deflection angle, the separation of the NURBS curve is proposed. The algorithm guarantees the chord length and error remaining unchanged, and the deflection angle stays in a feasible range. Then some simulations are carried out to test the correctness of the algorithm. At last, the plane grating is used to make an experience to verify the algorithm. Experimental results indicate that the continuous line segments can approach the NURBS curve with the proposed algorithm accurately and the fitting location is smooth. The proposed approach can discrete the NURBS curve into the continuous line segments effectively.

Abstract:To improve the accuracy and efficiency of classic AABB collide detection, An algorithm of the virtual sensors which is applied to the domain of Rover manipulator collide detection is proposes. At first, the inverse kinematics model of rover manipulator is established. Secondly, lunar terrain point cloud data is triangulated by Delaunay triangulation method, the triangulation face set is then stored in the leaf nodes of a multiple tree (AABB tree). In the end, the rover manipulator model is simplified by virtual sensors. By utilizing the virtual sensors to traverse the face set stored in the multiple tree, manipulator/lunar terrain collision are detected and avoided. The inner-yard experiment of lunar rover in-situ exploration task show that the accuracy of the collide detection increased to within 1mm and the time of collide detection decreased to 10 s by the algorithm proposed. The feasibility and efficiency of the collide detection algorithm is justified.

Abstract:To solve the problem of line path control when the 2-DOF articulated vehicle surmounting obstacle, the dynamical model is developed, the angle velocity φ_r of the rear body rotates about z axis, the velocity y_r along y axis and yaw velocity θ₁ of the front body relative to the rear body are chosen as controlled variables, and the error kinematic model of the vehicle is developed, the stability and controllability of system are analyzed. Because the net moment provided by the hydraulic steering mechanism has the amplitude, an anti saturation controller is designed by backstepping method to suppress the output saturation of the hydraulic steering mechanism in the yawing control. After putting the anti-saturation algorithm in the error control system, it is shown that the error in y direction i converges to 0 in 5 seconds, also the angle θ₁ and φ_r converge to 0. The tracking path of vehicle is beeline. The anti-saturation algorithm is verified to eliminate the yawing error effectively by the simulation. And the curve of net moment provided by the hydraulic steering mechanism is calculated in the process of the yawing control.

Abstract:The relative slow responding speed of system Electro-mechanical system, which is caused by the inertia and response lag of the engine and motors, results that the target points optimized through the upper control strategy cannot be tracked quickly and precisely. A coordinate strategy for electro-mechanical system based on dynamic response models of power sources and the mechanical system is present. The expert PID control and Model compensation control are used on Motor A and Motor B respectively, besides the engine adapts the virtual speed difference control. Furthermore, the dynamic response of state parameters can follow the optimized-state points well. The simulation results indicate that the desired control characteristic of coordinate control strategy is validated and the torque and rotation speed fluctuations of the motors and engine decrease significantly.

Abstract:To meet the needs of comfort and take the vehicle safety into account at the same time of car following model of the adaptive cruise control (ACC) system, a multi-objective robust control algorithm of car following model is designed based on model predictive control (MPC) theory. A mutually longitudinal kinematics model considering the pre-car acceleration noise is presented to fully reflect the dynamic evolution of ACC system and improve the model's accuracy and reliability. The target of the requirement of ACC system is analyzed and a multi-objective MPC algorithm considering comfort and safety is proposed. By introducing a correction term feedback, the robustness of the control system is improved for the reason of the MPC algorithm's sensitive to disturbance. By adopting vector management method, the problem is solved which the MPC algorithm can't find the optimum solution caused by hard constraints. The simulation shows that the designed control algorithm ensures that the acceleration and jerk of the ACC system is kept in the comfort range, while the distance between the pre-vehicle and host-vehicle is always greater than the minimum safe distance.

Abstract:To effectively describe stochastic deteriorations and environment effects on a system deterioration process, a two-stage deterioration model was proposed for a two-stage deteriorating system. Deterioration pit was used to denote a deterioration region where is going to suffer a deterioration process. The deterioration process is divided into two stages:the deterioration pit initiation process and the deterioration pit growth process. A non-stationary Gamma process and a non-homogeneous Poison process were introduced to model the deterioration pit initiation process and the deterioration pit growth process respectively. By regarding environment changes as random changes and introducing environment effect factor, a two-stage deterioration model with random changes was developed. Based on the deterioration model, a condition-based maintenance model was presented finally. The optimal inspection intervals of the system can be found by minimizing the expected maintenance cost under single stage deterioration model and two-stage deterioration model as different environment effect factors. Finally simulation experiments were designed. Results show that the proposed model is valid and practical for stochastic deterioration systems of decision-making maintenance actions.

Abstract:The thermodynamic analysis of the integrated system was conducted and the indexes of the power recovery efficiency and the exergy efficiency were chosen for system performance evaluation. The impact of inlet temperatures of both the heat resource and cooling water on the power recovery efficiency and the exergy efficiency of the system were analyzed under certain initial conditions. The exergy loss and exergy efficiency of each component of the system were demonstrated which could direct the improvement target of the system for better heat transfer performance. When the heat resource inlet temperature t_h1=300℃, the power recovery efficiencies of the Kalina cycle (cooling water t_c1=25℃) and Rankine cycle (t_c1=15℃) are respectively 18.2% and 14.6%, the exergy efficiencies are respectively 41.1% and 33.1%, while the composite power recovery efficiency and composite exergy efficiency of the ammonia-water Rankine cycle are respectively 19. 6% and 46. 5%. Moreover, when the temperature of heating water is set as 70℃ or 90℃, while the temperature of back water keeps 40℃, the Rankine cycle can get additional 55.3% or 65.6% heating recovery efficiency or 8. 7% or 13. 4% heating water exergy efficiency.

Abstract:Due to the frequent fluctuations of generation and consumption of blast furnace gas and difficulties to be predicted effectively in iron and steel works, the dynamic Lssvm prediction model with a timing update and self-correction function is established. The model is based on decomposed volatility and trend data of the generation and consumption after excluding the data "noise" by wavelet analysis, which combined with the actual blast furnace operating conditions. The amount of blast furnace gas generation of 3 200 m³ blast furnace and the consumption of the hot blast stove are taken as sample data to predict the future data in eight hours. The results show that the mean absolute error of the Lssvm prediction model with wavelet analysis has declined to 2.77%, the Update_Lssvm model is established to predict the accuracy of blast furnace gas generation date is 1. 55%, and blast furnace gas consumption of hot stove is 4.23%. The predict randomness problem of generation and consumption of blast furnace gas under the variable condition has been settled. Compared with other forecasting models, the prediction accuracy of the Update Lssvm model has been enhanced. The model not only has the generalization ability, but also provides a theoretical basis for optimal operation of blast furnace gas.

Abstract:The coupled thermal error between the spindle and feed shaft could actrually reduce the accuracy of workpieces in prcessing. For the problem, we developed the conprehensive thermal error model of spindle and feed shaft, with the expansion of workpieces, and verified it. The mutual effection among spindle, feed shaft and workpiece were comprehensively analyzed, and the multivariable linear regression model was developed among them. The results show that the comprehensive model could be consistent with lathe's processing situation and increase the processing accuracy effectively. The prediction accuracy for the spindle is more than 85%, and 70% for feed shaft. The error rang in processing is declined from 15 μm to 5 μm.

Abstract:In order to reduce design parameters and shorten design cycle, Joukowksky profile was utilized to construct torque converter stator blade. By simplifying the Joukowksky equation and adding a thickness term to its end, the Joukowksky stator blade model was given. According to fitting results, Joukowksky is able to present the existing stator blades and hence is suitable for stator blade design. Afterwards, the archive-based micro genetic algorithm was employed to optimize the Joukowksky stator blade based on an integrated 3D blade design system. The results indicated that the Joukowksky profile could be used in stator blade design with less parameters and the performances were improved after the optimization.

Abstract:To reduce the mass of tensegrity structure, this paper provides a minimal-mass optimization method and self-similar iterative design method for further reducing the mass. Taking a cylindrical tensegrity structure as the research object which is under the action of external load, and based on the relationship of component quality and the material failure mode, the force density and cross-section area are used to minimize the structural mass subjected to an equilibrium condition, and the answer is provided by a linear program. In this process, the selection method of minimal mass is provided under two failure modes, compression bar buckling and yield. For further reducing the quality, 3D T bar self-similar iterative structure is applied to the cylindrical tensegrity structurea, and a self-similar iterative design method to design a lighter tensegrity structure is proposed, in which the conception of effective alternative space is presented and a method is given for calculating the effective space. Examples show that the minimum quality optimization method and the design method of self-similar iteration can design a lighter tensegrity structure.

Abstract:In the wave energy converter, the performance of buoy motion can affect the energy absorption of the device directly. A three-dimensional numerical wave tank was built, which was based on CFD method using N-S equation. By simulating the time-domain motion of buoy and comparing with the experimental results, the feasibility of the CFD method was verified. Based on this, the effect of buoy motion on the surrounding fluid was analyzed using the flow field and the energy absorption regular of single and double DOFs was studied. It is shown that the buoy makes heave or pitch motion, the capture width ratio appears the maximum value with the increase of the PTO damping coefficient, the capture width ratio has the best PTO damping, the capture width ratio of double DOF buoy is higher than that of the single DOF buoy, the two DOF can affect each other in the energy absorption by comparing the different DOFs of the buoy.

Abstract:A new formula of normal contact damping for flexible joint interface was given by the revision fractal geometry theory and Hertz normal contact mechanics equation. Considering the changeable curvature radius at the tip of the summit and continuous load, the attaining way of differentiable function not partial differential function was induced to get two summits' interacting normal contact stiffness formula. The numeral curves imply that the normal contact damping decreases firstly and afterwards increases with the augment of fractal dimension of the surface raspy profile. When the fractal dimension of the coarse surface profile is smaller than the first inflection point, the normal contact damping enhances with the increase of fractal roughness. If the fractal dimension is larger than the first inflexion point, the normal contact damping reduces with the increase of fractal roughness. As the normal contact load improves, the normal contact damping firstly diminishes whereafter gains. Two inflection points and one extreme small point in the simulation curves might provide the reference for the optimization design of these contact parameters in dry tribological joint interface.

Abstract:To forecast the fatigue life of spline couplings accurately, taking the interaction of fretting wear and fretting fatigue into account, the fretting damage mechanism of a spline coupling was investigated, the prediction methods of fretting fatigue were analyzed, and by ignoring the position and direction of fatigue occurring, a new damage accumulation method based on SWT method for spline was provided, and the fretting fatigue life of this spline coupling under the given conditions was predicted. The results show that in the fretting process of spline coupling fretting wear and fretting fatigue competes and restrains with each other and leads to the spline coupling fatigue failure under the effect of two fretting modes eventually, the fatigue life of the spline coupling decreases with the SWT increasing. The damage accumulation method can reflect the effect of fretting wear on the fretting fatigue accurately, it gives a numerical reference for the designing and repairing of spline coupling, and at the same time, it also provides a basis for the further study of prediction fretting fatigue life in spline couplings which have clearance between the teeth.

Abstract:For an edge wave problem of electrical steel in SFR (schedule-free rolling) process, the CCT curves and the Gleeble thermal stress-stain simulator are analyzed for electrical steel. The deformation resistance decreases as temperature is lowered in the austenite-ferrite region (975-875℃). The significant roll wear contours and thermal behaviors characteristics of SFR are obtained by the measured data of industrial mills. Considering the difference of deformation resistance with double phases and the actual roll contours, a 3D elastic-plastic finite element coupling model of roll stacks and strip is established for the effect of roll force, roll bending and shifting system on the loaded roll gap profile, and the influence of friction coefficient, strip thickness and rolling speed on strip internal stress distribution. The change path of ratio crown difference by Shohet criteria are attained to explain the formation process of irregular edge wave in upstream stands of hot rolling mills with larger flatness dead zones, which provides evidences for flatness control of electrical strip in hot rolling.

Abstract:Aiming at the great hardship and low efficiency of deburring on the inner intersecting holes, using electrolytic machining theory and applying fixed inserting cathode pole layout, an automatic electrolytic deburring method based on detection of electric current is proposed, and a mathematic model is set up. Simulation and experiment are adopted to find out the effect of gab, voltage and time in the electrolytic deburring process. The result shows that the electric current density changes over time. Under the present pole layout condition, the average electric current goes down and the slope nearly reaches zero when deburring is completed. Taking this as the judgement of end of deburring, an automatic electrolysis deburring control system is developed. The experiment shows that the method can control the machining time according to the size of burr and remove it accurately. Besides the method has low cost and high quality.

Abstract:To reveal the effects of surface texture on the performances of journal bearings, the three-dimensional models of journal bearing with circular, squared and triangular texture are built. The models are simulated with CFD method based on the Navier-Stokes equation considering the cavitation effect and turbulence effect, and the performances of journal bearings with different texture shape, location, density and geometry are analyzed. The results show that, when the surface texture is distributed in load carrying region, the load carrying capacity of journal bearing can be improved, the fluid flow and friction coefficient can be reduced and the bearing with squared texture has a better load carrying capacity. There is an optimal combination of density, width and width-depth ratio of texture for the journal bearing to reach the largest load carrying capacity.

Abstract:To study the effects of stiffness characteristics on the working behavior of bolted joint with curvic coupling of heavy duty gas turbine, a stiffness analytical model was established with parametric modeling method. The curvic contact pressure, rotation stiffness, compression deformation have been derived by the proposed method, the deformation and stiffness change of all parts of the curvic coupling are investigated during the bolt tightening by finite element analysis and experimental method. The validity of the method is proved by experiments and finite element simulation. The results show that the bending behavior on the curvic and the cylinder part of the disc in bolt tightening, the curvic compression stiffness increases sharply and the stiffness data of other parts decreases slightly during bolt tightening process. The change laws including deformation, stiffness, contact stress, contact status of contact surfaces in curvic coupling are different from those in usual couplings.

Abstract:To plan a reasonable placement pattern, this paper analyzes the influence of component surface shape, deformation of preimpregnated fiber tows and mechanics direction of placement layers on planning placement routes on the meshed surface, and presents a practical engineering approach for pattern planning. The deflection angles between geodesic direction and mechanical direction and allowable placement direction are calculated, respectively. Then, the multi-constraint placement directions are determined by proportional control coefficient of the deflection angles, and a new route point is obtained in turn. The placement route planning is implemented on the surface. In addition, to achieve a uniform covering surface, the overlap coefficient to the coverage analysis of placement pattern is introduced and the reasonable positions of increasing or decreasing fiber tows are calculated. Thus, the placement pattern planning is completed on the component surface. A placement pattern planning on a free form surface, for example, is used to verify the validity of these methods.

Abstract:To solve the problem existing in the measuring and prediction of transverse thickness distribution of finish hot rolling, the adaptive neural network trained by hybrid algorithms of particle swarm optimization (PSO) and back propagation (BP) neural network is introduced. Based on the BP network, the network structure, weights and threshold are optimized by PSO algorithm for improving the network convergence speed and prediction accuracy. By the data of two high reversible hot rolling mill, the average error of thickness is 3.6 μm and the error absolute value is less than 4 μm accounted for 87.1%. The absolute error frequency of strip thickness within 30 μm is 90% by statistical analysis of the steady state rolling, excepting the head and tail of the strip. The research results show that the network model can replace crown instrument to predict the transverse thickness distribution in the actual production. And the control means of strip shape are precisely controlled. It illustrates that the network model can meet the requirement of high precision flatness control.

Abstract:A valveless synthetic jet-based micropump structure was designed for transporting liquid and a critical structure parameter determination method was developed for the largest flow rate and steady outflow of the micropump. The critical structure parameters included the chamber height and outlet diameter of the micropump. The chamber height could be set at the position where the axial instantaneous velocity in the center axis was invariable. And the outlet diameter could be obtained by the jet boundary on the outlet cross section. A three-dimensional numerical simulation was carried out to obtain the performance of the micropump. The velocity boundary condition and the SST turbulence model were utilized in the numerical simulation. The simulation results of a synthetic jet actuator fit the previous experimental results well. The results suggest that the optimal chamber height and outlet diameter are 7 mm and 1.78 mm respectively. And the flow rate can achieve 32.1 mL/min at the 0 back pressure and Reynolds number of 225. It's effective to design the chamber height and the outlet diameter of the micropump by this method to achieve the maximum flow rate and steady outflow.