Prestiction friction compensation in direct-drive mechatronics systems

LuGre model has been widely used in friction modeling and compensation. However, the new friction regime, named prestiction regime, cannot be accurately characterized by LuGre model in the latest research. With the extensive experimental observations of friction behaviors in the prestiction, some variables were abstracted to depict the rules in the prestiction regime. Based upon the knowledge of friction modeling, a novel friction model including the presliding regime, the gross sliding regime and the prestiction regime was then presented to overcome the shortcomings of the LuGre model. The reason that LuGre model cannot estimate the prestiction friction was analyzed in theory. Feasibility analysis of the proposed model in modeling the prestiction friction was also addressed. A parameter identification method for the proposed model based on multilevel coordinate search algorithm was presented. The proposed friction compensation strategy was composed of a nonlinear friction observer and a feedforward mechanism. The friction observer was designed to estimate the friction force in the presliding and the gross sliding regimes. And the friction force was estimated based on the model in the prestiction regime. The comparative trajectory tracking experiments were conducted on a simulator of inertially stabilization platforms among three control schemes： the single proportional-derivative （PD） control, the PD with LuGre model-based compensation and the PD with compensator based on the presented model. The experimental results reveal that the control scheme based on the proposed model has the best tracking performance. It reduces the peak-to-peak value （PPV） of tracking error to 0.2 mrad, which is improved almost 50% compared with the PD with LuGre model-based compensation. Compared to the single PD control, it reduces the PPV of error by 66.7%.     

Calculation of thermodynamic parameters of Mg-Al-Y alloy

By means of Miedema formation enthalpy model with Toop model, the excess free-energy, enthalpies of formation, excess entropies and activity values of all components of Mg-Al-Y ternary alloy were calculated with computer programming. The experimental results show that enthalpies of formation, excess freeenergy and excess entropies of the ternary alloy are negative in the whole content range, the minimum values at 1 123 K are all obtained at x Al=55%, x Y=45%, x Mg=0%, which are-37.969, –30.961 kJ/mol and-6.24 J/(mol·k) respectively. Activity curves show that the activity values of Al and Y in Mg-Al-Y ternary alloy rapidly decrease with the decrease of molar fraction, the values of which are very small when the molar fraction decreases to 0.4. It means that there is a strong interaction between Al and Y and stable compounds can be form in the Mg-Al-Y ternary alloy system.     

Pyrolysis characteristics of rubber compositions in medical waste

Thermogravimetric study of rubber compositions （operating glove and catheter） in medical waste was carried out using the thermogravimetric analyser （TGA）,at the heating rate of 20 ℃/min in a stream of N2.The results indicate that the decomposition process of operating glove appears an obvious mass loss stage at 250-485 ℃,while catheter has two obvious stages at 240-510 ℃ and 655-800 ℃,respectively; both samples present endothermic pyrolysis reaction; the decomposition of operating glove and the first mass loss stage of catheter are in agreement with natural rubber pyrolysis; the second mass loss stage of catheter corresponds to CaCO3 decomposition.Based on the experimental results,a novel two-step four-reaction model was established to simulate the whole continuous processes,which could more satisfactorily describe and predict the pyrolysis processes of rubber compositions,being more mechanistic and conveniently serving for the engineering.     

Mathematical model of slotting manufacture and simulation for cosine gears简

A slotting method for cosine gears was proposed by using the involute cutter based on the conjugate theories of digital surface and gear meshing. The slotting model between the cosine tooth surface represented by discrete points and the cutter figuration determined by analytic function was built for their geometrical relationship and conjugate motion during the machining process. Conjugate points in the cutter section corresponding to the discrete points on the cosine gear tooth surface and the conjugate movements were solved. By using the flexible control of the CNC procedure, the active control of the cutting trace of the slotting cutter was accomplished and the envelop forming of the cosine gear was obtained. Based on the software C＋＋ and Matlab, the computer aided manufacturing （C;AM） system of the cosine gear was developed, and the simulation of the slotting process was accomplished. Several examples were provided to illustrate the approach. The result of the simulation demonstrates that the proposed slotting method is feasible.     

Thermal-hydro-mechanical coupling damage model of brittle rock简

Based on fluid mechanics, thermodynamics and damage mechanics, thermal-hydro-mechanical （THM） coupling damage model of brittle rock is established by analyzing THM coupling mechanism, where THM coupling damage variable DTHM is dominated by TH coupling damage variable DTH, TM coupling damage variable DTM and HM coupling damage variable DHM, and DTH is firstly expressed in term of dimensionless total thermal conductivity of the water Nu. Permeability test, uni-axial compression test and THM coupling test are conducted to measure the permeability, elastic modulus and THM coupling stress-strain curves of brittle rock. The tested values of THM coupling elastic modulus E＇HM are in good agreement with the predicted values of THM coupling elastic modulus ETHM, which can verify the newly established THM coupling damage model.     

A genetic Gaussian process regression model based on memetic algorithm

Gaussian process （GP） has fewer parameters, simple model and output of probabilistic sense, when compared with the methods such as support vector machines. Selection of the hyper-parameters is critical to the performance of Gaussian process model However, the common-used algorithm has the disadvantages of difficult determination of iteration steps, over-dependence of optimization effect on initial values, and easily falling into local optimum. To solve this problem, a method combining the Gaussian process with memetic algorithm was proposed. Based on this method, memetic algorithm was used to search the optimal hyper parameters of Gaussian process regression （GPR） model in the training process and form MA-GPR algorithms, and then the model was used to predict and test the results. When used in the marine long-range precision strike system （LPSS） battle effectiveness evaluation, the proposed MA-GPR model significantly improved the prediction accuracy, compared with the conjugate gradient method and the genetic algorithm optimization process.     

Dynamic characteristic analysis of whole machine tools based on Kriging model

In order to study the variation of machine tools＇ dynamic characteristics in the manufacturing space, a Kriging approximate model is proposed. Finite element method （FEM） is employed on the platform of ANSYS to establish finite element （FE） model with the dynamic characteristic of combined interface for a milling machine, which is newly designed for producing aero engine blades by a certain enterprise group in China. The stiffness and damping of combined interfaces are adjusted by using adaptive simulated annealing algorithm with the optimizing software of iSIGHT in the process of FE model update according to experimental modal analysis （EMA） results. The Kriging approximate model is established according to the finite element analysis results utilizing orthogonal design samples by taking into account of the range of configuration parameters. On the basis of the Kriging approximate model, the response surfaces between key response parameter and configuration parameters are obtained. The results indicate that configuration parameters have great effects on dynamic characteristics of machine tools, and the Kriging approximate model is an effective and rapid method for estimating dynamic characteristics of machine tools in the manufacturing space.     

Practical elasto-plastic damage model for dynamic loading and nonlinear analysis of Koyna concrete dam

The elasto-plastic damage model for concrete under static loading,previously proposed,was extended to account for the concrete strain-rate through viscous regularization of the evolution of the damage variables.In order to describe the energy dissipation by the motion of the structure under dynamic loading,a damping model which only includes stiffness damp stress was proposed and incorporated into the proposed rate dependent model to consider the energy dissipation at the material scale.The proposed model was developed in ABAQUS via UMAT and was verified by the simulations of concrete specimens under both tension and compression uniaxial loading at different strain rates.The nonlinear analysis of Koyna concrete dam under earthquake motions indicates that adding stiffness damp into the constitutive model can significantly enhance the calculation efficiency of the dynamic implicit analysis for greatly improving the numerical stability of the model.Considering strain rate effect in the model can affect the displacement reflection of this structure for slightly enhancing the displacement of the top,and can improve the calculation efficiency for greatly reducing the cost time.     

Ribbon model based path tracking method for autonomous ground vehicles

To resolve the path tracking problem of autonomous ground vehicles, an analysis of existing path tracking methods was carried out and an important conclusion was got. The vehicle-road model is crucial for path following. Based on the conclusion, a new vehicle-road model named ＂ribbon model＂ was constructed with consideration of road width and vehicle geometry structure. A new vehicle-road evaluation algorithm was proposed based on this model, and a new path tracking controller including a steering controller and a speed controller was designed. The difficulties of preview distance selection and parameters tuning with speed in the pure following controller are avoided in this controller. To verify the performance of the novel method, simulation and real vehicle experiments were carried out. Experimental results show that the path tracking controller can keep the vehicle in the road running as fast as possible, so it can adjust the control strategy, such as safety, amenity, and rapidity criteria autonomously according to the road situation. This is important for the controller to adapt to different kinds of environments, and can improve the performance of autonomous ground vehicles significantly.     

Slope analysis based on local strength reduction method and variable-modulus elasto-plastic model

Employing an ideal elasto-plastic model, the typically used strength reduction method reduced the strength of all soil elements of a slope. Therefore, this method was called the global strength reduction method （GSRM）. However, the deformation field obtained by GSRM could not reflect the real deformation of a slope when the slope became unstable. For most slopes, failure occurs once the strength of some regional soil is sufficiently weakened; thus, the local strength reduction method （LSRM） was proposed to analyze slope stability. In contrast with GSRM, LSRM only reduces the strength of local soil, while the strength of other soil remains unchanged. Therefore, deformation by LSRM is more reasonable than that by GSRM. In addition, the accuracy of the slope＇s deformation depends on the constitutive model to a large degree, and the variable-modulus elasto-plastic model was thus adopted. This constitutive model was an improvement of the Duncan~Chang model, which modified soil＇s deformation modulus according to stress level, and it thus better reflected the plastic feature of soil. Most importantly, the parameters of the variable-modulus elasto-plastic model could be determined through in-situ tests, and parameters determination by plate loading test and pressuremeter test were introduced. Therefore, it is easy to put this model into practice. Finally, LSRM and the variable-modulus elasto-plastic model were used to analyze Egongdai ancient landslide. Safety factor, deformation field, and optimal reinforcement measures for Egongdai ancient landslide were obtained based on the proposed method.     

Fluid-solid coupling model based on endochronic damage for roller compacted concrete dam

According to the characteristics of thin-layer rolling and pouting construction technology and the complicated mechanical behavior of the roller compacted concrete dam （RCCD） construction interface, a constitutive model of endochronic damage was established based on the endochronic theory and damage mechanics. The proposed model abandons the traditional concept of elastic-plastic yield surface and can better reflect the real behavior of rolled control concrete. Basic equations were proposed for the fluid-solid coupling analysis, and the relationships among the corresponding key physical parameters were also put forward. One three-dimensional finite element method （FEM） program was obtained by studying the FEM type of the seepage-stress coupling intersection of the RCCD. The method was applied to an actual project, and the results show that the fluid-solid interaction influences dam deformation and dam abutment stability, which is in accordance with practice. Therefore, this model provides a new method for revealing the mechanical behavior of RCCD under the coupling field.     

Wind-induced responses of super-large cooling towers

Traditional gust load factor （GLF） method, inertial wind load （IWL） method and tri-component method （LRC＋IWL） cannot accurately analyze the wind-induced responses of super-large cooling towers, so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads （ESWLSs） were derived based on structural dynamics and random vibration theory. The consistent coupled method （CCM） was presented to compensate the coupled term between background and resonant response. Taking the super-large cooling tower （H=215 m） of nuclear power plant in Jiangxi Province, China, which is the highest and largest in China, as the example, based on modified equivalent beam-net design method, the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out. Then, combining wind tunnel test and CCM, the effects of self-excited force on the surface pressures and wind-induced responses are discussed, and the wind-induced response characteristics of background component, resonant component, coupled term between background and resonant response, fluctuating responses, and wind vibration coefficients are discussed. It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.     

Mathematic modeling on flexible cooling system in hot strip mill简

A novel cooling system combining ultra fast cooling rigs with laminar cooling devices was investigated. Based on the different cooling mechanisms, a serial of mathematic models were established to describe the relationship between water flow and spraying pressure and the relationship between water spraying heat flux and layout of nozzles installed on the top and bottom cooling headers. Model parameters were validated by measured data. Heat transfer models including air convection model, heat radiation model and water cooling capacity model were detailedly introduced. In addition, effects on cooling capacity by water temperature and different valve patterns were also presented. Finally, the comparison results from UFC used or not have been provided with respect to temperature evolution and mechanical properties of Q235B steel grade with thickness of 7.8 mm. Since online application of the sophisticated CTC process control system based on these models, run-out table cooling control system has been running stably and reliably to produce resource-saving, low-cost steels with smaller grain size.     

Numerical and experimental investigations of weld pool geometry in GTA welding of pure aluminum简

A 2-D numerical model was developed to predict the shape of weld pool in stationary GTA welding of commercial pure aluminium, without considering fluid flow in the weld pool. A Gaussian current density and heat input distribution on the surface of the workpiece were considered. The parameters of Gaussian distribution were modified by comparing calculated results with experimental ones. It was found that these distribution parameters are fimctions of applied current and arc length. Effects of arc length, applied current and welding time on the geometry of the weld pool were investigated. To check the validity of the model, a series of experiments were also conducted. In general, the agreement between calculated overall shape of the weld pool and the experimental one was acceptable, especially in low applied currents. Therefore, it can be concluded that in pure aluminium, the heat conduction is dominant mechanism of heat transfer in the weld pool.     

Triaxial creep tests of weak sandstone from fracture zone of high dam foundation

The lithology of fracture zone which was developed at the dam foundation ofa hydropower station is weak sandstone with poor integrity and pore cementation contact.Its creep properties have a significant impact on the deformation and stability of the dam.Based on the characteristics of loose organizational structure,high moisture content and poor mechanical properties,the triaxial compression tests and creep tests were carried out,respectively.The results show significant non-linear,low strength and no obvious strength peaks.Both axial and lateral strains are achieved more than 3％ when the tests are failed.The weak sandstone has a significant creep property,but only transient and steady state appear under low stress.Increased stress causes creep intensified and lateral strain gradually exceeds axial strain.In the failure stage,it has characteristics of large axial plastic deformation,obvious volumetric ductility dilation and large steady creep rate.The accelerated creep appears shortly after transient loading under confining of pressures 1.0 MPa and 1.5 MPa.Therefore,an improved Burgers creep model considering the non-linear characteristics of weak sandstone is built based on hyperbolic equation and the creep parameters are identified.This model can well describe the creep properties of weak sandstone.     

A new formant feature and its application in Mandarin vowel pronunciation quality assessment

In order to improve the Mandarin vowel pronunciation quality assessment, a nox/el formant feature was proposed and applied to formant classification for Chinese Mandarin vowel pronunciation quality evaluation. Formant candidates of each frame were plotted on the time-frequency plane to form a bitmap, and its Gabor feature was extracted to represent the formant trajectory. The feature was then classified by using GMM model and the classification posterior probability was mapped to pronunciation quality grade. The experiments of comparing the Gabor transformation based formant trajectory feature with several other kinds of traditionally used features show that with this method, a human-machine scoring correlation coefficient （CC） of 0.842 can be achieved, which is better than the result of 0.832 by traditional speech recognition techniques. At the same time, considering that the long-term information of formant classification and the short-term information of speech recognition technique are complementary to each other, it is investigated to combine their results with linear or nonlinear methods to further improve the evaluation performance. As a result, experiments on PSK show that the best CC of 0.913, which is very close to the correlation of inter-human rating of 0.94, is gotten by using neural network.     

Predication of plasma concentration of remifentanil based on Elman neural network

Due to the nature of ultra-short-acting opioid remifentanil of high time-varying, complex compartment model and low-accuracy of plasma concentration prediction, the traditional estimation method of population pharmacokinetics parameters, nonlinear mixed effects model （NONMEM）, has the abuses of tedious work and plenty of man-made jamming factors. The Elman feedback neural network was built. The relationships between the patients＇ plasma concentration of remifentanil and time, patient＇ age, gender, lean body mass, height, body surface area, sampling time, total dose, and injection rate through network training were obtained to predict the plasma concentration of remifentanil, and after that, it was compared with the results of NONMEM algorithm. In conclusion, the average error of Elman network is -6.34%, while that of NONMEM is 18.99%. The absolute average error of Elman network is 27.07%, while that of NONMEM is 38.09%. The experimental results indicate that Elman neural network could predict the plasma concentration of remifentanil rapidly and stably, with high accuracy and low error. For the characteristics of simple principle and fast computing speed, this method is suitable to data analysis of short-acting anesthesia drug population pharmacokinetic and pharmacodynamics.     

Simulation of automobile fuel consumption and emissions for various driver’s manual shifting habits简

The effects of different habits of the drivers on gear shifting strategies for manual powertrain were investigated. For the realization of simulation, the shifting habits of the drivers were conducted in the Advisor software to investigate and compare the emission rates. Simulation was developed based on the optimal gear shifting strategy and criteria and was validated both in fuel economy and emissions by analyzing the results in the various driving cycle and driving styles. To explore an optimal gear shifting strategy with best fuel economy and lowest emission for a manual transmission, a strategy was designed with a highest possible gear criterion as long as the torque requirement can be satisfied. Based on two different criteria, namely the engine working conditions and the driver＇s intention, the governing parameters in decision making for gear shifting of manual transmission in conventional engine were discussed. It is also shown that the optimum gear shifting strategy is based on that both the engine state and the driver＇s intention eliminates unnecessary shiftings that are present when the intention is overlooked. The optimum shifting habit and the best driving cycle in terms of minimum emissions and fuel consumption were proposed.     

Experimental and field study on dissipation coefficient of supersaturated total dissolved gas

The elevated supersaturation of total dissolved gas （TDG） downstream of a high-dam spill has deleterious effects on fish in a large range. A one-dimensional （l-D） longitudinal model is optimal for the prediction of supersaturated TDG dissipation over a long distance. The key issue of the model is to determine the dissipation coefficient accurately. In agreement with field observations and experiment data, dimensional analysis and regression were performed to propose a formula for estimating the dissipation coefficient of supersaturated TDG in various rivers and reservoirs, and it involves the effects of the turbulence intensity, the hydro-pressure and the solid-liquid interface. The friction velocity, water depth, hydraulic radius and Froude number are independent variables in the formula which are easy to determine in practical applications. The 1-D longitudinal model is implemented to calculate the dissipation of TDG in a reach of the Jinsha River. Good agreement is found between the calculated results and field data for both the dissipation coefficient and the dissipation process.     

Flow field simulation and establishment for mathematical models of flow area of spool valve with sloping U-shape notch machined by different methods简

Precise function expression of the flow area for the sloping U-shape notch orifice versus the spool stroke was derived. The computational fluid dynamics was used to analyze the flow features of the sloping U-shape notch on the spool, such as mass flow rates, flow coefficients, effiux angles and steady state flow forces under different operating conditions. At last, the reliability of the mathematical model of the flow area for the sloping U-shape notch orifice on the spool was demonstrated by the comparison between the orifice area curve derived and the corresponding experimental data provided by the test. It is presented that the bottom arc of sloping U-shape notch （ABU） should not be omitted when it is required to accurately calculate the orifice area of ABU. Although the theoretical flow area of plain bottom sloping U-shape notch （PBU） is larger than that of ABU at the same opening, the simulated mass flow and experimental flow area of ABU are both larger than these of PBU at the same opening, while the simulated flow force of PBU is larger than that of ABU at the same opening. Therefore, it should be prior to adapt the ABU when designing the spool with proportional character.