Applied Mechanics and Materials Vols. 138-139

Abstract: This paper addresses the motion control of the parallel mechanism of virtual axis machine tool, which has a complex system model, the nonlinear and strong coupling characteristics and has strong external disturbances in high-speed machining. To further enhance its motion control performances, a novel adaptive dynamic sliding mode control method is proposed. The designed control system stability is proved theoretically. By building a new switching function, the second-order dynamic sliding mode control algorithm is designed to reduce the chattering of the conventional sliding mode control effectively and overcome the adverse effects of the fast changing dynamics of the actuators. By introducing the adaptive control, unknown external disturbances can be estimated online, which can improve the ability of resisting strong disturbances and the control precision of virtual axis machine tool. The simulation results for the virtual axis machine tool show that the designed control system has the good performances in tracking and resisting strong disturbances and can achieve the high precision motion control of the parallel mechanism of virtual axis machine tool.

Abstract: On the basis of the differential equation governing small flexure of thin elastic vibrating plate, the formula for calculating the phase velocity and group velocity of ice sheet wave propagation under the air cushion load is induced. The minimum of the phase velocity is the critical speed about ice breaking by air cushion vehicle (ACV). If ACV moves at the critical speed, the energy causing the deformation of ice sheet is concentrated constantly, thus the amplitude of the wave is enlarged enough to break the ice by resonance.

Abstract: Genetic algorithm (GA) is improved with fast non-dominated sort approach and crowded comparison operator. A new algorithm called parallel multi-objective genetic algorithm (PMGA) is developed with the support of Massage Passing Interface (MPI). Then, PMGA is combined with Artificial Neural Network (ANN) to improve the optimization efficiency. Training samples of the ANN are evaluated based on the two-dimensional Navier-Stokes equation solver of cascade. To demonstrate the feasibility of the hybrid algorithm, an optimization of a controllable diffusion cascade is performed. The optimization results show that the present method is efficient and trustiness.

Abstract: For aero-engines, high-altitude valve is a key component, which is important to the high-altitude performance of ventilation system. However, theoretical researches or experimental tests of high-altitude valve are rare. To define whether the high-altitude valve can work normally during the whole flight envelope and to offer relational information for the improve design, this article focuses on the operation process and characteristic computation of high-altitude valve. Based on operational principle and structural analysis, using mechanics method, the high-altitude characteristic computation of high-altitude valve was done and the flight height where the valve closes was identified. In the same way, we analysed the static characteristic, getting the inner-cavity pressure in high-altitude flying state. Compared with the experimental results, the analytical methods and calculated values are validated to be accurate. The characteristic curves obtained can be directly used in the check and acceptance or further design of high-altitude valve.

Abstract: Resistance strain gauge is common used in strain measurement, particularly in small elastic strain measurement, it has many advantages. However when the measured strain increases, the output nonlinearity of the Wheatstone bridge will become obvious; in this paper the nonlinearity error of the output in large-strain measurement is analyzed, and based on this a mathematical algorithm for nonlinearity compensation is proposed; finally the effect of the algorithm for nonlinearity compensation is proved by theoretical research and experimental treatment.

Abstract: Although functional near-infrared spectroscopy (fNIRS) has been developing as a useful tool for monitoring functional brain activity since the early 1990s, the quantification of hemoglobin concentration changes is still controversial and there are few detailed reports especially for continuous-wave (CW) instruments. By means of a two-layer model experiment mimicking hemodynamic changes in brain and mathematical analysis based on the modified Beer-Lambert law, we established an algorithm for a CW functional near-infrared spectroscopy (CW-fNIRS). The accuracy of this algorithm was validated both in comparison with direct measurements on brain tissue model and in vivo measurement upon human valsalva maneuver. This described method can also be utilized for other CW-fNIRS instruments to establish measuring algorithm.

Abstract: Objective: To counteract the organ motion caused by respiratory movement through controlling the positioning bed’s synchronous motion with the organ with the breathing sensor in body gamma knife treatment. Methods: The displacement curve of relationship between lung volume and organs in the lung was obtained by acquiring respiratory signals with the piezoelectric film respiratory sensor. Used single chip microcomputer to control stepper motor which spurts the positioning bed through the transmitter to make it move simultaneously in real time according to the law of organ motion, so as to counteract the organ motion caused by respiratory movement and thus to improve the precision of radiotherapy. Results: The experiment indicates that this method can make the steeper motor move according to the displacement curve. Conclusion: It is feasible to counteract the organ and tissue motions caused by respiratory movement by making the positioning bed reversely move in real time in accordance with the law of organ motion during radiotherapy treatment.

Abstract: This paper gives a non-destructive and non-contact inspection way based on image processing which is introduced to detect bridge cracks. System architecture is also introduced and key algorithms in crack image processing is studied. These key algorithms are: image gray scaling, image enhancement, image strengthing, gap survey and so on. In the end such method is used to measure actual gap and the reliability of such method on bridge inspection has been verified with the results.

Abstract: This article focuses on the temperature dependent dynamic properties of rubber isolator. First, a set of experimental device was designed to conduct the experimental investigation. Then, a polynomial model of hysteretic used as an isolator restoring force model was proposed and the model parameters were identified using the displacement-restoring force loop from experiment by the optimal least-squares arithmetic. Finally, the Hermite interpolation method was utilized to add the number of identified parameters, such that curvatures that represent the first order stiffness, the third order stiffness and damping varied with frequency, amplitude under different temperature were obtained. The analysis results indicated that the first order stiffness varies weakly with the temperature increasing, and there is an area of the first order stiffness varied drastically. The third order stiffness have a strong nonlinear area within the low frequency and little amplitude, the third order stiffness magnitude increases with the temperature increasing firstly, then decreases while the temperature over 50°C. There is a sensitive area as the amplitude less than 1.5mm, the damping decreases rapidly with the augmenting of vibration amplitude, and the rate of decreasing is less gradually with the temperature rising.

Abstract: Cotton stalk is a by-product of cotton planting process, and a great resource as a raw biomass material for manufacturing value-added composite products. The fine structure and fiber size of the cortex, xylem of the cotton stalk were studied in this paper. In addition, a new method for the processing of cotton stalk filament was developed. Composites consisting of polypropylene (PP) and cotton stalk filament were prepared by hot pressing. The effects of PP content and compressing temperature on the mechanical properties of cotton stalk filament /PP composites were studied. The results show that elevated temperatures, all of the composites are substantially stiffer and stronger than that at lower temperature. PP content improves the intensity and adhesion of composites. Simultaneous optimization of composites properties indicates that the composites with PP content of 40% and the compressing temperature of 195°C would sufficient meet the requirements of the GB/T 4897.1-2003 standard. Bio-renewable materials such as cotton stalk can be used as reinforcing materials for plastic composites.