Applied Mechanics and Materials Vols. 670-671

Abstract: High-speed crashworthiness characteristics of aluminum alloy bumper were investigated both experimentally and numerically, and then lightweight deign was performed based on these studies. After the simulation results were analyzed, chose plate thickness matching as an optimization direction and got crashworthiness indicators: cross-sectional force, energy absorption, and specific energy absorption (SEA). Design of experiment (DOE) for initial 25 sampling points, which provide input data for approximation, is implemented using the optimal Latin hypercube design (OLHD) method. Polynomial response surface (PRS) models, which are used to approximate LS-DYNA simulation models, are built using the moving least square (MVS), whose all coefficients of determination are over 0.97, indicated high accuracy. The simulation results of optimal designs, which are obtained after 52 iterations of genetic algorithms (GA), show that the mass loss of 30.8%, while energy absorption increase of 4% , SEA increase of 50.3%, and crushing forces decline.

Abstract: The difficulties in oil mining is increasing and the quality of the remaining oil reduced gradually after Daqing oil field came into the late high water contamination stage. There are several factors that prevent the convention from single layer fracturing technology to multilayer fracturing technology. Firstly, about 20% of fracturing rate could be achieved by elevating the K Series packer 3 times in the 5 fracturing techniques, but the performance of the plastic tube cannot be guaranteed. Secondly, the fracturing success rate is not guaranteed if Y series are elevated 4 times to complete the 5 layer fracturing, besides consistent intervals between the five layers must be maintained, which is very difficult. To further enhance the vertical well fracturing multilayer capability, we carry out multi-layered vertical well fracturing technology research, and have achieved good results in the field application.

Abstract: To solve the problem that thermal control design of the combination of star sensor is high requirement and difficult to implement, the thermal control design of the combination of star sensor using C-C graphite material was proposed in this paper. By taking some combination of star sensor requiring difference in temperature on bracket of star sensor less than 4.5°C and temperature of flange of star sensor in 8.5±2°C as an example. Thermal analysis was achieved to validate the thermal control design scheme proposed in the paper. Analysis results show that the thermal control design scheme can make difference in temperature of bracket of star sensor in orbit less than 2.73°C, and flange of star sensor in orbit between 7.47°C and 8.93°C,which meet the temperature requirement very well. The design scheme is reasonable.

Abstract: The experiments of static and dynamic characteristics of rubber bushing for rear suspension telescopic shock absorber were carried out at four directions such as axial, radial, torsion and yaw, by MTS831 and SAGINOMIYA test system. The tests prove that: rubber bushing has great damping, and rubber bushing has obvious nonlinear characteristic; the dynamic stiffness under low frequency and large amplitude excitation is smaller, while the dynamic stiffness under high frequency and small amplitude excitation is greater; at the same amplitude, the dynamic stiffness increases with the increasing excitation frequency. The test results can provide support for the optimization design of rubber bushing.

Abstract: A argon Pseudospark discharge is studied and modelled with our developed simulation program. The structure of our code is flexible and transparent. The modular structure is divided into three main parts: electromagnetics module which forms the heart of the model, the neutral gas module, and the chemical reaction module. The above three parts with the plasma module are controlled by the user. The strong modularity makes the code easy to handle and easy to adjust or expand. This project will do in-depth numerical simulation for the study of the inception of breakdown characteristics via a electrostatic particle-in-cell plus Monte-Carlo collision method. The model tracks the trajectories of both electrons and ions, including ionizing collisions in the gas phase by electrons and ions, and secondary electron emission by ions on surfaces. The result indicated the pseudospark discharge breakdown process mainly induced by field emission.The peak discharge current is found to be dependent on gas pressure,electrode borehole diameter. The effect of these design parameters on the peak anode current has been analysed. Simulate the discharge breakdown physical processes for the Pseudospark in order to lay the theoretical foundation for the optimize and improve the pulse power electron beam.

Abstract: Groundwater heat pump (GWHP) systems in three different hydrogeological fields, Beijing were selected, and their effects on temperature of groundwater in recharged aquifer were researched for three years. Results showed that the degree of thermal breakthrough was controlled by the distance between pumping wells and injection wells, and the temperature of groundwater with high flow rate can recover to normal faster than those with low flow rate. When distance between pumping wells and injection wells were shorter than 30m, thermal breakthrough may happen and the variation range of groundwater temperature during one heating or cooling period was 8~12°C.However, thermal breakthrough can be negligible and the temperature of groundwater may be steady when the distance between those wells was longer than 50m. Furthermore, GWHP in two different hydrogeological fields were selected to observe their effects on groundwater quality for one year. One GWHP was situated on the northwest piedmont alluvial fan of Beijing and the other was located in the southeast plain area of Beijing. Groundwater was sampled from those fields and thirty-two inorganic components were analyzed. Heavy metals were not detected, and calcium, magnesium, chloride, sulfate, fluoride and other ten inorganic components were studied. Groundwater quality in the northwest of Beijing was relatively steady because that aquifer was in relative oxidation environment. However, groundwater quality in the southeast of Beijing was subject to change because that aquifer was in relative reduction environment. Nitration reaction happened in the plain area, and ammonia, nitrite converted into nitrite nitrogen and nitrate nitrogen, respectively. Simultaneously, pH, concentrations of iron and manganese decreased, and total hardness increased.

Abstract: The main objective of this study is to select the reasonable parameters for the ten-needle inline nozzle structure. Its internal flow fields were simulated by using FLUENT software. Quadrature calculations are conducted according to different inlet flow, different diameters and different lengths of the needles. The partial flow and drift rates under different inlet fluxes were analyzed. Through curve fitting method, the size ranges of the optimal structure under different conditions are obtained.

Abstract: The random factor method (RFM), an effective numerical simulation method, is employed to analyze the probabilistic characteristics and reliability sensitivity of uncertain structure system. The natural frequencies of the system can be expressed as the function of the random factors. By using the random variable’s algebra synthesis method, the expressions for the mean value and standard deviation of natural frequencies are derived from Rayleigh quotient. The reliability mode and the safety probability of random systems are defined, and then the frequency reliability sensitivity analysis method is presented. The formulas of failure probability sensitivity are derived when random variables are normally distributed. The reliability index is evaluated, and its sensitivity to mean values and variances are mathematically expressed, then the efficiency and accuracy of the proposed method are demonstrated by a numerical example.

Abstract: In order to ensure that the wind turbines are reliable in stable condition and economical in maintenance cost, the most effective way is to estimate and monitor the performance and operation of the wind turbine. Traditional fault diagnosis methods using multivariate statistical process usually assume the unit only has a single operating condition, so it’s not suitable for multi-regimes. Aiming at this problem, this paper proposed a global performance estimation method of multi-regimes condition based on Gaussian mixture model (GMM). First establish GMM to train the baseline model, cluster the sample data using the similar GMM method, and then calculate the distance between the baseline model and the GMM of sample data by two different methods. The result shows that this method can identify the characteristics of the turbine productivity well, and can detect the abnormality of power curve that is related to incipient fault.

Abstract: The accuracy reliability problems have long been studied. In order to research ball screw’s accuracy reliability under radical force, some work have done. By using mechanical vibration theory, the dynamic response equation of the beams under external excitation has been derived out. Then by using Matlab, the dynamic response of screw rod under working circumstance is studied, and the dynamic response equation is obtained. At last some calculation examples have given. Results showed that screw’s polar moment of inertia section errors have decisive influences on precision and reliability. By using vibration theory and second moment theory, a new meathod have been proposed in evaluating the ball screw accuracy reliability. Key Words: Screw Transmission; Dynamic Response; Accuracy and Reliability