The method,in which a few carats of diamond grits are placed inside a capsule together with a steel ball,shaken for a number of times,and the unbroken ratio of the grits is then used to evaluate the quality of the diamond,has been well established for many years.However,the unbroken percentage,in an equivalent view,represents the impact toughness of the grits and cannot reflect the value of the crushing energy.Most of the previous empirical formulas obtained from experiments by scholars cannot be applied to practical tests.In this paper,a dimensional analysis was applied to investigate the impact toughness experiment,and the dimensionless relationship has been built among those variables such as the toughness index,the impact time,the impact frequency and the crushing energy per unit area.According to the results of a large number of experiments with synthetic diamond grits of mesh size 45/50,the percentage of the broken grits H is proportional to the impact time T1.14 when the impact frequency is 2400 r/min,and the impact frequency f2.576 when the number of impacts is 2000.
Based on a digital image correlation(DIC)method with the measurements of a high speed crack’s displacement and strain fields,a technique to accurately and automatically locate its crack tip has been developed.The crack tip is identified by finding the abrupt jump on the opening(or dislocation)curve of a point on the trace of the crack propagation,while the opening is measured through a virtual extensometer technique and the abrupt jump is identified by finding the peak on the curve.The method was verified using a specially designed experiment and applied to measure the critical crack tip opening angle of a rock sample.Because the involvement of analytical models has been avoided and then the good performance could be ensured for low resolution speckle images,this technique is expected to be very useful in the quantitative study of high speed cracks in experiments using high speed cameras.
An attitude controller using the second order sliding mode control methodology with a backstepping approach(SOSMCB)is designed and implemented for a spinning missile with two internal moving mass blocks.The system consists of a rigid body and two radial internal moving mass blocks and its mathematical model is established based on Newtonian mechanics.The control scheme integrates a second order sliding mode control algorithm into the last step of the backstepping approach,and its stability is proved by means of a Lyapunov function.The performance of the controller is demonstrated by numerical simulations,the results show that the attitude controller is stable and effective.
To analyze factors that affect the detection probability of six laser range-finders of rotating rocket,taking a missile as the target,the detection model was established according to a detection mechanism.Based on the model,the detection probability was calculated via Monte Carlo method under different conditions.With the calculation results,the relationship of detection probability with the rolling rate and the missile velocity was illustrated in figures,when the laser emitting frequency was 10 kHz,20 kHz,30 kHz respectively under the condition that rocket met the front of missile as well as the condition that rocket met the rear of missile.The figures show that the detection probability increases as laser emitting frequency increases or the rolling rate increases,while it decreases as the missile velocity increases.Detection probability is higher when rocket meets the front of missile than that when rocket meets the rear of missile.In order to maintain a track of approaching Mach 2 targets,rotation rate should be more than 100 r/s.
In recent years,a large number of small volume,low cost micro electro mechanical systems(MEMS)digital three-axis angular rate gyroscopes have been developed and widely used in civil and military fields.However,these kinds of gyroscopes have poor performances in initial zero-bias,temperature drift,In-Run bias stability,bias repeatability,etc.,their output errors need to be compensated before being used.Based on a lot of experiments,the temperature drift and the initial zero-bias are the major error sources in the MEMS gyroscopes output data.Due to the poor repeatability of temperature drift,the temperature compensation coefficients need to be recalculated every time before using.In order to recalculate parameters of the temperature compensation model quickly,a 1st-order polynomial model of temperature is established,then a forgetting factor recursive least squares estimator will be adopted to identify the model parameters in real time.Static and dynamic experimental data shows that this method removed/compensated the temperature drift and initial zero-bias from the output of the gyroscopes effectively.
Based on multidisciplinary design optimization(MDO),a new design method is put forward for hydraulic shift mechanism of heavy-duty vehicle automated manual transmission(AMT).Taking a shift cylinder for example,the collaborative optimization(CO)method for the design problem of a cylinder is devided into one system level design optimization problem and three subsystem level design optimization problems.The system level is an economic model and the subsystem level is mechanics,kinetics,and a reliability model.Application of the multidisciplinary design optimization software iSIGHT modeling and solving,optimal solution of the shifting cylinder CO model is obtained.According to the optimal solution,oil cylinders are machined out and installed on the gearbox of an AMT system for the bench cycle shift test.The results show that the output force and action speed of the optimized mechanism can meet requirements very well.In addition,the optimized mechanism has a better performance compared to the structure of the traditional design method,which indicates that the CO method can optimize the design of hydraulic transmission.
With an advanced foreign hydraulic automatic transmission as the objective,an analytical method for the gear-shifting schedule is proposed.First the demanded maximum gradient of test is estimated.Then a test scheme and analytical procedure is formulated by initial test and hypothetical shift parameters.Finally through gear-shifting tests under different road conditions,load,accelerator pedal position limitation,throttle opening and output shaft speed are found to be the gear-shifting parameters.Under a common road condition,the gear-shifting schedule is a double-parameter schedule.Based on the driver’s demands on braking and dynamic performance,different shift schedules are made under downhill,uphill and quick releasing acceleration pedal conditions.The operation criteria of down-shift schedule on abrupt grade are proposed.
In order to control the vehicle body position precisely,1/4 nonlinear mathematical model of hydro-pneumatic suspension is established,and the influence of the frictional force in a hydraulic cylinder is analyzed.The friction characteristics are described based on the LuGre model when the piston of a hydraulic actuator is operated at a low speed.Due to the fact parameters of the friction model are effected by the system condition,an adaptive friction compensation(AFC)controller is designed through the Backstepping method,and a dual-observer has been implemented to estimate the friction state.The global asymptotic convergence of a closed-loop system is proven by the Lyapunov theorem.The simulation results show that the positional accuracy of the adaptive friction compensation yiedls a significant improvement in the vehicle height adjustment as compared to the PID control,demonstrating the effectiveness of the adaptive fiction compensation method in the vehicle height adjustable system of the hydro-pneumatic suspension.
The effects of different flow forms on an opposed-piston two-stroke(OPTS)gasoline-directinjection(GDI)engine was studied by analyzing the mixture formation and combustion.Swirl was broken and dissipated gradually and the turbulence kinetic energy(TKE)was small in the compression process;however,tumble was strengthened and the TKE was strong in the compression process.For swirl around X axis(the axis of cylinder)and tumble around Y axis(the vertical direction of injector),droplets were attached to the cylinder liner by the centrifugal force and the mixture distribution was poor.For tumble around Zaxis(the direction of injector),the wall film in cylinder liner was thin and mixture distribution was homogeneous.Results showed that since the injector were installed on the wall of the cylinder liner in the OPTS-GDI engine,the spray angle was small and the mixture formation time was short.The 45° oblique axis tumble ratio of 1 was reasonable for the mixture formation and combustion for an OPTS-GDI engine.
In order to improve the shift decision strategy for an off-road vehicle with automated manual transmission(AMT),the generalized road resistance coefficient is defined based on the longitudinal dynamics analysis.Vehicle mass and generalized road resistance coefficient are estimated using the recursive least square(RLS)method with multiple forgetting factors.The improved shift schedule is designed based on the generalized road resistance coefficient under uphill road condition.The simulation and real vehicle test verify the effectiveness of improved shift strategy and the improvement of vehicle dynamic performance.
In order to overcome the shortcomings of the previous obstacle avoidance algorithms,an obstacle avoidance algorithm applicable to multiple mobile obstacles was proposed.The minimum prediction distance between obstacles and a manipulator was obtained according to the states of obstacles and transformed to escape velocity of the corresponding link of the manipulator.The escape velocity was introduced to the gradient projection method to obtain the joint velocity of the manipulator so as to complete the obstacle avoidance trajectory planning.A7-DOF manipulator was used in the simulation,and the results verified the effectiveness of the algorithm.
A new structure of the photonic crystal fiber(PCF)based Mach-Zednder interferometer(MZI)is fabricated and presented.The structure has microholes ablated by a femtosecond laser.The fringe visibility can be enhanced more than 10 dB compared with the interferometer without a microhole.The interferometer is characterized by sodium chloride solutions for refractive index(RI)sensing.The RI sensitivities are greatly increased by the hole fabrication since it directly changes the cladding modes of the PCF.For the interferometer sensor with two holes,the RI sensitivity is 157.74 nm/RIU,which is 5 times than that of the sensor without a microhole.Microholes ablation with a femtosecond laser on PCF can increase the sensor’s sensitivity dramatically.Femtosecond laser has a wide application prospect in the field of performance improvement of the sensors.
The 7-DOF model of a full vehicle with an active suspension is developed in this paper.The model is written into the state equation style.Actuator forces are treated as inputs in the state equations.Based on the basic optimal control theory,the optimal gains for the control system are figured out.So an optimal controller is developed and implemented using Matlab/Simulink,where the Riccati equation with coupling terms is deduced using the Hamilton equation.The all state feedback is chosen for the controller.The gains for all vehicle variables are traded off so that majority of indexes were up to optimal.The active suspension with optimal control is simulated in frequency domain and time domain separately,and compared with a passive suspension.Throughout all the simulation results,the optimal controller developed in this paper works well in the majority of instances.In all,the comfort and ride performance of the vehicle are improved under the active suspension with optimal control.
In order to solve kinematic redundancy problems of a hydraulic quadruped walking robot,which include leg dragging,sliding,impingement against the ground,an improved gait planning algorithm for this robot is proposed in this paper.First,the foot trajectory is designated as the improved composite cycloid foot trajectory.Second,the landing angle of each leg of the robot is controlled to satisfy friction cone to improve the stability performance of the robot.Then with the controllable landing angle of quadruped robot and a geometry method,the kinematic equation is derived in this paper.Finally,agait planning method of quadruped robot is proposed,a dynamic co-simulation is done with ADAMS and MATLAB,and practical experiments are conducted.The validity of the proposed algorithm is confirmed through the co-simulation and experimentation.The results show that the robot can avoid sliding,reduce impingement,and trot stably in trot gait.
In order to compromise the conflicts between control accuracy and system efficiency of conventional electro-hydraulic servo systems,a novel pump-valve coordinated electro-hydraulic servo system was designed and a corresponding control strategy was proposed.The system was constituted of a pumpcontrolled part and a valve-controlled part,the pump controlled part is used to adjust the flow rate of oil source and the valve controlled part is used to complete the position tracking control of the hydraulic cylinder.Based on the system characteristics,a load flow grey prediction method was adopted in the pump controlled part to reduce the system overflow losses,and an adaptive robust control method was adopted in the valve controlled part to eliminate the effect of system nonlinearity and parametric uncertainties due to variable hydraulic parameters and system loads on the control precision.The experimental results validated that the adopted control strategy increased the system efficiency obviously with guaranteed high control accuracy.
A robust finite-horizon Kalman filter is designed for linear discrete-time systems subject to norm-bounded uncertainties in the modeling parameters and missing measurements.The missing measurements were described by a binary switching sequence satisfying a conditional probability distribution,the commonest cases in engineering,such that the expectation of the measurements could be utilized during the iteration process.To consider the uncertainties in the system model,an upperbound for the estimation error covariance was obtained since its real value was unaccessible.Our filter scheme is on the basis of minimizing the obtained upper bound where we refer to the deduction of a classic Kalman filter thus calculation of the derivatives are avoided.Simulations are presented to illustrate the effectiveness of the proposed approach.
A strong and stable correlation in quantum information is of high quality for quantum information processing.We define two quantities,selective average correlation and ripple coefficient,to evaluate the quality of correlation in quantum information in a time interval.As a new communication channel,Heisenberg spin chains are widely investigated.We select a two-qubit Heisenberg XXZs pin chain with Dzyaloshinskii-Moriya interaction in an inhomogeneous magnetic field as an example,and use the two quantities to evaluate the qualities of the correlation in quantum information with different measures.The result shows that,if the time evolutions are similar,there needs only evaluating one of them to know when the correlation has high quality for quantum information processing.
A new method for recharging active medical implant(AMI)in vitro based on incoherent light source and results of the simulation experiments are proposed.Firstly,the models of the AMI recharging method based on incoherent light source in vitro are developed,which include the models of an incoherent light source and skin tissue.Secondly,simulation experiments of the incoherent light source of the AMI recharging process in vitro based on the Monte Carlo(MC)method are carried out.Finally,absorbed fractions of different layers and distributions of density along x axis of the tissue model and other important conclusions have been achieved.
A novel reference-driven method for MR image reconstruction based on wavelet sparsity and nonlocal total variation(NLTV)is proposed.Utilizing the sparsity of the difference image between the target image and the motion-compensated reference image in wavelet transform domain,the proposed method does not need to estimate contrast changes and therefore increases computational efficiency.Additionally,NLTV regularization is applied to preserve image details and features without blocky effects.An efficient alternating iterative algorithm is used to estimate motion effects and reconstruct the difference image.Experimental results demonstrate that the proposed method can significantly reduce sampling rate or improve the quality of the reconstructed image alternatively.
An improved preprocessed Yaroslavsky filter(IPYF)is proposed to avoid the nick effects and obtain a better denoising result when the noise variance is unknown.Different from its predecessors,the similarity between two pixels is calculated by shearlet features.The feature vector consists of initial denoised results by the non-subsampled shearlet transform hard thresholding(NSST-HT)and NSST coefficients,which can help allocate the averaging weights more reasonably.With the correct estimated noise variance,the NSST-HT can provide good denoised results as the initial estimation and high-frequency coefficients contribute large weights to preserve textures.In case of the incorrect estimated noise variance,the low-frequency coefficients will mitigate the nick effect in cartoon regions greatly,making the IPYF more robust than the original PYF.Detailed experimental results show that the IPYF is a very competitive method based on a comprehensive consideration involving peak signal to noise ratio(PSNR),computing time,visual quality and method noise.更多还原
A dynamic learning rate Gaussian mixture model(GMM)algorithm is proposed to deal with the problem of slow adaption of GMM in the case of moving object detection in the outdoor surveillance,especially in the presence of sudden illumination changes.The GMM is mostly used for detecting objects in complex scenes for intelligent monitoring systems.To solve this problem,a mixture Gaussian model has been built for each pixel in the video frame,and according to the scene change from the frame difference,the learning rate of GMM can be dynamically adjusted.The experiments show that the proposed method gives good results with an adaptive GMM learning rate when we compare it with GMM method with a fixed learning rate.The method was tested on a certain dataset,and tests in the case of sudden natural light changes show that our method has a better accuracy and lower false alarm rate.
To investigate effects of Dragon’s Blood(DB),a traditional Chinese medicine,on blood coagulation and NO/iNOS level in myocardium and serum of rats in simulated microgravity for the first time,Sprague Dawley(SD)rats were randomly divided into six groups:(a)5-day control group,(b)5-day model group,(c)5-day drug group,(d)21-day control group,(e)21-day model group,and(f)21-day drug group.Blood coagulation and NO/iNOS level in myocardium and serum were examined after 5 and 21 days of simulated microgravity respectively.The results showed that blood of tail-suspended rats was in a hypercoagulable state that could not be converted with time extending.Conversely,DB changed these parameters towards normal level and the curative effects became better when tail-suspension lasted till the 21 st day.NO concentration of both myocardium and serum for two periods all increased markedly and DB could effectively reduce these increases except that of 21-day myocardium NO.Activity of iNOS increased markedly as early as 5 days and became more serious on the 21 st day,while DB showed preventive effect on the 21 st day.Western Blot analysis illustrated that the expression of iNOS in the 5-day model group increased significantly over the 5-day control group and the expression in the 5-day drug group dramatically returned to the normal level.The similar trend was observed on the 21-day groups without notable variances.The findings of this study can serve for the further use of Dragon’s Blood in space diseases.