Abstract:In order to solve the problem that the absolute vibration displacement is difficult to directly measure in many engineering practices, a novel quasi-zero-stiffness-based sensor system is proposed. Firstly, the static characteristics of the Euler beam and the sensor system are analyzed and the condition of the quasi-zero-stiffness characteristic of the sensor system at equilibrium position is obtained. Secondly, the dynamic model of sensor system is established and solved, and then the effects of equivalent damping, stiffness ratio of compressed Euler beam and spring, the amplitude of measured signal on the measurement accuracy are discussed. Thirdly, the time-domain responses under different excitation signals are studied. The results show that the sensor system can be used to measure the absolute micro-vibration displacement directly, accurately and real-timely. The novel quasi-zero-stiffness sensor system should be a feasible or better measurement scheme for various vibration control with full system states feedback.

Abstract:In the process of product reliability design, usually, the distribution of reliability index is not completed in one time. Different design stages have different reliability allocation methods. With the deepening of the design process, the results of the preliminary distribution may be unsatisfactory, so it's necessary to re-allocate the reliability index in middle and late stages. Prior to the index allocation, all the minimal cut sets are classified by a certain algorithm, and then the selected minimum cut sets to be allocated are distributed by using an artificial neural network (ANN). The ultimate goal is to allocate the reliability index to the minimal cut sets or elementary events of fault tree. By comparing the initial reliability before distribution and the reliability after distribution, we can find out the weak points in product design and then improve the design, which examines the results of FMECA (failure mode, effects and criticism analysis) to some extent.

Abstract:An adaptive Super-twisting control strategy is proposed to solve the problem that the wind turbine based on a doubly-fed induction generator (DFIG) is easy to be interfered with grid voltage fluctuation and external wind speed. The strategy realizes that control objectives vary with operation zones which depend on wind speed, that is, the active power is optimized in the partial load zone and the active power is limited in the full load zone. At the same time, the stator reactive power is adjusted according to the grid need to compensate the power factor in different regions. It has the advantages of easy implementation, strong robustness and adjustable gain of adaptive control, and is suitable for non-linear systems with external disturbances and time-varying parameters. The simulation results show that the controller designed by this strategy has good robustness in active power control and reactive power control in doubly-fed wind power generation system, the chattering is reduced and the sliding variables converge fast to the sliding manifolds in finite time.

Abstract:It's difficult to obtain the analytic solution of complicated optimization problems in engineering. To try to get numerical solution with numerical computation method is easy to get local optimal solution instead. In order to improve the speed and accuracy of numerical optimal solution to high-dimensional problems, the population is divided into intelligent population and common population on the basis of traditional culture algorithm, and they are initially optimized according to different evolving ways respectively. Furthermore, simulation of practical examples by MATLAB program is carried out. The results show that the speed is greatly improved after optimization and the cultural algorithm with initialized improvement can approximate the optimal solution faster and more accurately in high-dimensional optimization problems. The optimized cultural algorithm provides a new reference for practical engineering problem.

Abstract:Bi-directional DC/DC converter is the core of the hybrid electric vehicle's energy management system and plays a key role in its energy bi-directional flow control. According to the requirement of the hybrid electric vehicle to its converter, we select the bi-directional Buck/Boost converter as the main circuit topology, which reduces the weight and volume and improves the work efficiency. At the same time, we use semiconductor soft switch technology to reduce the switching loss effectively. Dynamic models of this bi-directional DC/DC converter under different operation modes are derived, controllers corresponding to different working modes are also designed, and thus both system stability and dynamic response ability are improved. The simulation and experimental results validate the correctness of theoretical analysis.

Abstract:To improve the calculation efficiency of reliability assessment for power system, a load shedding model of reverse equivalent pairing based on power flow sensitivity is proposed. Firstly, based on the sensitivity in the system's base state, an analytical formula of the sensitivity in fault state is deduced, and thus a fast solution to the trend sensitivity matrix is achieved. Secondly, according to the power flow sensitivity of nodes injection power with respect to overload branches, the selection rule of control nodes for both generation and load nodes is presented. Furthermore, a model of reverse equivalent pairing adjustment is constructed based on this selection rule. A modified formula of power adjustment amount of pairing nodes group is also presented and it eliminates the see-saw phenomenon of overload for normal transmission lines in adjusting process and avoids the power flow verification in traditional methods, which makes the system has a higher state analysis speed. Finally, the effectiveness and fastness are verified by evaluating RBTS, IEEE-RTS79 and IEEE-RTS96 test systems.

Abstract:Random forest algorithm has better classification performance as a combination of classification and is suitable for a variety of classification environments, but it also has some flaws. For example, it can not distinguish positive and negative class when dealing with unbalanced data. By setting conditions on sampling results, we improve the Bootstrap sampling method, reduce the influence of sampling on non-equilibrium and ensure the randomness of this algorithm. Then, we weight every decision tree according to the non-equilibrium coefficient of the generated data to enhance the discourse right of the decision tree which is sensitive to the non-equilibrium data and improve the classification performance of the whole algorithm dealing with unbalanced data. With these two above improvements, the new algorithm can significantly improve classification performance when the number of decision tree is insufficient.

Abstract:Flow stress usually does not decrease with the increase of the deformation temperature of steel deformed at high temperature in two-phase region, and the minimum value of the flow stress will be found in the two-phase region. In order to find out the effect of chemical compositions on the flow stress behavior in the two-phase region, the deformation behavior of studied steels near two-phase region is researched by thermal simulation test. Meanwhile, the microstructures after deformation and the change of flow stress near the two-phases region are analyzed. The ferrite phase transformation start temperatures and the decrease of flow stress in two-phases region are obtained. The influence of main alloying elements such as C, Si and Mn on the ferrite transformation start temperature Ar₃ and the decrease of flow stress are obtained by regression fitting.

Abstract:The anhydrite rock swells obviously when it's exposed to water, and the non-uniform dynamic distribution of groundwater leads to uneven expansion of surrounding rock.We take the anhydrite rock in Lirang tunnel, Liangzhong highway, as the research object,and set different initial water amount to carry out the anhydrite confined swelling experiment with using the consolidometer, which aims at figuring out the change rules of water absorption, swelling strain and confined swelling stress of the anhydrite rock. The results show that the water absorption rate of anhydrite increases rapidly at first and then slowly. The water absorbed by anhydrite in the process of rapid growth is mainly converted to crystal water, and in the slowly growth process,the free water inside the anhydrite gradually increases.The swelling strain and swelling stress of anhydrite increase with the increase of soaking water. When the soaking water volume is one-fourth of the theoretical water consumption of complete gypsification, it reaches the turning point where the growth rates of swelling strain and stress significantly decrease. The water absorption of anhydrite rock has a time effect, and there is a negative exponent relation between water absorption and time. Based on it, combined with the humidity stress field theory, the anhydrite time-dependent constitutive is obtained.

Abstract:For further optimizing the rock stacking structure of the dump in open-pit mines and decreasing dumping cost, we put forward a block stacking sequence optimization algorithm trying to solve the problem of material dumping among multiple dumps which hasn't been effectively solved. Firstly, the minimum transport work of the material flow is taken as the objective function and the design parameters and the relationship between spatial shape and location of dumps are taken as constraints to build a model of stacking sequence. Then, with taking the design of dumping planning as the basic space constraint to construct a priori condition, a dynamic generation algorithm for multiple dumps in decision-making stage is proposed. Finally, the 0-1 integer programming is used to solve the whole planning problem, the optimal stacking sequence of the block model in multiple dumps is obtained, and the detailed flow planning scheme of the soil rock flow in the dumping sites is given. To solve the problem that the transport distance of soil rock materials is increasingly large as the mining depth increases in the open-pit of Heishan in Xinjiang, we use the proposed algorithm to optimize the rock stacking structure of its dumps with the aim of minimizing transport work. The optimal stacking scheme for the internal structure of the dumps in south and north of the mine in the future 11 years is determined, and compared with the original design, the transportation energy consumption is effectively controlled, which can save 1-2 billion yuan of dumping transport costs.

Abstract:Aiming at loss and depletion of mineral resources caused by poor effect of selection and mining in the process of open pit mining, we research the influence of mining process, mining procedure and bench height on the effect of selection and mining through theoretical analysis and calculation. The selection and mining effect of different equipment is analyzed to select the optimal mining technology according to the characteristics of different types of coal and rock. Taking the mining model with a single bench as the research object, we analyze and calculate the selection and mining indexes of different advancing directions, and establish an optimization model of minimum thickness of coal seam with the goal of maximizing the economic benefits. By establishing mathematical model, the relationship between step height and coal loss rate, rock mixing ratio, minimum recoverable thickness and minimum thickness is deduced, and then the method to improve the effect of selection and mining by optimizing the bench height is found out. Baiyinhua No.2 open-pit mine is taken as an example and the results show that by choosing proper mining technology, advancing method and optimizing the height of the bench height, the selection and mining effect of the open pit mine can be effectively improved.

Abstract:When traditional gauss projection method is used to treat long-span lines in east-west direction, the frequent change belt can solve neither the reference ellipsoid projection to Gauss plane projection length deformation nor the influence of the height to the length of the deformation caused by the domestication. Therefore, some scholars have proposed a new method to establish an ellipsoid of engineering based on the theory of least squares, rotation of space coordinate system and ellipsoid transformation. Based on this theory, the authors verify and analyze the method through the specific examples of high-speed railway GPS control network. The experimental analysis shows that this method can greatly reduce the deformation component of the transverse axial direction after the projection, avoid the phenomenon of Gaussian projection zoning, and effectively reduce the projection distortion caused by elevation. It is especially suitable for long line engineering with long span, and the mathematical model is mature and the calculation process is clear, which can be used for reference in line engineering measurement.