Comparison of performance between rescaled range analysis and rescaled variance analysis in detecting abrupt dynamic change

In the present paper, a comparison of the performance between moving cutting data-rescaled range analysis （MC- R/S） and moving cutting data-rescaled variance analysis （MC-V/S） is made. The results clearly indicate that the operating efficiency of the MC-R/S algorithm is higher than that of the MC-V/S algorithm. In our numerical test, the computer time consumed by MC-V/S is approximately 25 times that by MC-R/S for an identical window size in artificial data. Except for the difference in operating efficiency, there are no significant differences in performance between MC-R/S and MC-V/S for the abrupt dynamic change detection. Mc-R/s and MC-V/S both display some degree of anti-noise ability. However, it is important to consider the influences of strong noise on the detection results of MC-R/S and MC-V/S in practical application

Structural optimization design of semi-rigid base asphalt pavement using modulus matching criterion and multi-indicator range analysis

Damage to semi-rigid base asphalt pavement is related to improper matching of the pavement structure moduli.This study mainly focused on the modulus matching of structural layers and the development of a pavement structure optimization method.First,the modulus loss of existing pavement structures was analysed,and a three-dimensional finite element model was established based on the existing pavement.Second,the influence of the modulus of each structural layer on the mechanical response indicators and fatigue life was analysed.Based on the results,a pavement structure design method using the smoothness of the stress-strain curve as the modulus matching criterion of the structural layers was proposed.And it was found that a strain convex point was present and that the stress mutation between the structural layers was significant when the modulus matching of the pavement structure was reasonable.Further,the evaluation indicators were divided into two groups,namely,mechanical indicators and fatigue life indicators.And it was proposed an optimized pavement structure design method based on modulus matching and multi-indicator range analysis.Finally,the optimal modulus combination of pavement structure was determined by this method.The research systematically studied the influence of the modulus of each structural layer on the mechanical response and fatigue life of the pavement,and proposed the concept and specific executive criteria of modulus matching for the first time.Meanwhile,it also provided an effective optimization method for pavement structure design.

Cavitation Optimization for a Centrifugal Pump Impeller by Using Orthogonal Design of Experiment

Cavitation is one of the most important performance of centrifugal pumps. However, the current optimization works of centrifugal pump are mostly focusing on hydraulic efficiency only, which may result in poor cavitation performance. Therefore, it is necessary to find an appropriate solution to improve cavitation performance with acceptable efficiency. In this paper, to improve the cavitation performance of a centrifugal pump with a vaned diffuser, the influence of impeller geometric parameters on the cavitation of the pump is investigated using the orthogonal design of experiment （DOE） based on computational fluid dynamics. The impeller inlet diameter D1, inlet incidence angle Aft, and blade wrap angle ~0 are selected as the main impeller geometric parameters and the orthogonal experiment of L9（3＂3） is performed. Three-dimensional steady simulations for cavitation are conducted by using constant gas mass fraction model with second-order upwind, and the predicated cavitation performance is validated by laboratory experiment. The optimization results are obtained by the range analysis method to improve cavitation performance without obvious decreasing the efficiency of the centrifugal pump. The internal flow of the pump is analyzed in order to identify the flow behavior that can affect cavitation performance. The results show that D1 has the greatest influence on the pump cavitation and the final optimized impeller provides better flow distribution at blade leading edge. The final optimized impeller accomplishes better cavitation and hydraulic performance and the NPSHR decreases by 0.63m compared with the original one. The presented work supplies a feasible route in engineering practice to optimize a centrifugal pump impeller for better cavitation performance.

Neck-spinning quality analysis and optimization of process parameters for plunger components:Simulation and experimental study

The plunger component is a key part of the plunger pump in the aircraft hydraulic system.Neck-spinning process is commonly used to fabricate plunger components,of which the quality of the spinning process significantly affects the performance of plunger pumps.One of the bottlenecks faced by the industry in the spinning process is to choose a suitable neck-spinning process so as to ensure the quality of plunger components.It is necessary to propose a reliable method to optimize the process parameters which affect the neck-spinning quality of plunger components.In this study,a calculable finite element analysis(FEA)model is established to simulate the threeroller neck-spinning process of the plunger component,which includes six typical slipper structures,two roller structures,and two spinning parameters.The FEA model is then validated by comparing the simulated spinning forces with the corresponding experimental results.The influence of the process conditions on the neck-spinning quality is investigated.And the orthogonal simulation results are analyzed by a combination of range method and fuzzy mathematical analysis method to recommend a reasonable slipper structure,roller structure and neck-spinning parameters.This study provides a promising method to improve the manufacturing quality of the typical plunger components.

Performance analysis of source ranging by use of virtual receiver technique under different frequency bands

The traditional matched field processing localization need complicated computation to get the replica field and has high dependence on environment parameters and acoustic field model. To overcome the shortcoming, virtual receiver technique is used for source ranging. A virtual receiver is constructed by correlating the two signals of the guide source and the objective source received by a vertical line array. Then, the slope of the interference striation of the virtual field is estimated using relevant signal processing method. Combining with the waveguide invariant/3, the range of the objective source is determined. Through the numerical simulations and data processing collected from the experiment carried out in the South China Sea in 2004, the virtual receiver technique for broadband source ranging under the slope- bottom shallow water environment is discussed. As the frequency increases, the frequency bands should be broadened to obtain complete interference striation for good ranging results. In data processing, the receiving array spacing is too large to promise the orthogonality of the modes as the frequency increases and ranging results become worse.