Journal of Central South University

When the bi-stable stochastic resonance method was applied to enhance weak thruster fault for autonomous underwater vehicle (AUV), the enhancement performance could not satisfy the detection requirement of weak thruster fault. As for this problem, a fault feature enhancement method based on mono-stable stochastic resonance was proposed. In the method, in order to improve the enhancement performance of weak thruster fault feature, the conventional bi-stable potential function was changed to mono-stable potential function which was more suitable for aperiodic signals. Furthermore, when particle swarm optimization was adopted to adjust the parameters of mono-stable stochastic resonance system, the global convergent time would be long. An improved particle swarm optimization method was developed by changing the linear inertial weighted function as nonlinear function with cosine function, so as to reduce the global convergent time. In addition, when the conventional wavelet reconstruction method was adopted to detect the weak thruster fault, undetected fault or false alarm may occur. In order to successfully detect the weak thruster fault, a weak thruster detection method was proposed based on the integration of stochastic resonance and wavelet reconstruction. In the method, the optimal reconstruction scale was determined by comparing wavelet entropies corresponding to each decomposition scale. Finally, pool-experiments were performed on AUV with thruster fault. The effectiveness of the proposed mono-stable stochastic resonance method in enhancing fault feature and reducing the global convergent time was demonstrated in comparison with particle swarm optimization based bi-stochastic resonance method. Furthermore, the effectiveness of the proposed fault detection method was illustrated in comparison with the conventional wavelet reconstruction.

The effect of yield-to-tensile strength ratio (Y/T) on failure pressure of X70 pipeline without and with corrosion defects was investigated. The stress-strain response of materials was characterized by a power-law hardening curve. Two formulas to estimate the strain hardening exponent n for a special Y/T were obtained by least squared regression method and the influence of Y/T on n was analyzed. As an application of n-Y/T expression, the analytical solutions of burst pressure for X70 pipeline without and with corrosion defects were also obtained. The results indicate that the burst pressure of defect-free X70 pipe without corrosion defects is a function of the Y/T, pipe geometry t 0/D 0 and engineering tensile strength, and increases as Y/T or t 0/D 0 increases; whilst the burst pressure of corroded X70 pipe decreases with the increase of defect depths, d/t. Comparisons indicate that the present analytical solutions closely match available experimental and numerical data.

Due to the advantages of low cost, fast response and pollution resistance, digital hydraulic pump/motor can replace conventional variable hydraulic pump/motor in many application fields. However, digital hydraulic components produce large hydraulic impact at variable moments, which will shorten the service life of mechanical components. Through the simulation analysis of the variable process of digital pump/motor, it is found that the discontinuous flow caused by displacement step changes is the fundamental cause of hydraulic impact. The data analysis results of experimental tests are in good agreement with the simulation analysis results. In view of hydraulic secondary components, a variable control method based on dual-mode operating characteristics is proposed. The TOPSIS algorithm is used to give comprehensive evaluation of the displacement control results after this method. The results show that the control quality of digital pump/motor after adopting the control method has been effectively improved, with an average improvement of about 40%.

CIFER software is used to identify steering and roll dynamics of a container ship. In this software, advanced features such as the Chirp-Z transform (CZT) and composite window optimization are applied to the time history of steering and roll dynamics to extract high quality frequency responses. From the extracted frequency responses, two linear transfer functions of Nomoto model are fitted for yaw and roll dynamics of the vessel. Based on the identified Nomoto model, a PID heading controller and a Kalman filter observer are constructed. The simulation results of heading controller for line of sight (LOS) waypoint guidance show excellent tracking of pilot inputs in the presence of wave induced motions and forces.

Để giải quyết vấn đề axit hóa của quặng bauxite chứa lưu huỳnh cao trong quá trình lưu trữ, bằng cách mô phỏng môi trường lưu trữ khoáng sản trong phòng thí nghiệm, cơ chế axit hóa và các yếu tố ảnh hưởng đến quặng bauxite chứa lưu huỳnh cao đã được nghiên cứu và xác nhận bằng phương pháp biến số đơn. Kết quả cho thấy axit hóa chủ yếu do sự oxy hóa của quặng bauxite chứa lưu huỳnh, chủ yếu là oxy hóa tự nhiên của Pyrite (FeS2), sau đó các khoáng chất kiềm hòa tan trong sự hiện diện của nước, dẫn đến hiện tượng axit hóa, chịu ảnh hưởng bởi độ ẩm và lưu lượng không khí. Cuối cùng, nhiều chất tạo axit hơn được hình thành, dẫn đến việc axit hóa quặng bauxite chứa lưu huỳnh cao. Việc axit hóa quặng bauxite chứa lưu huỳnh cao là do tác động kết hợp của oxy trong không khí và nước, có thể được giảm thiểu đáng kể bằng cách kiểm soát sự khuếch tán của oxy trong không khí.

A simple, reliable and rapid isocratic liquid chromatography (LC)-mass spectrometric detection (MS) coupled with electrospray ionization (ESI) method for simultaneous separation and determination of calycosin-7-O-β-D-glucoside, ononin, calycosin and formonometin in Astragali Radix was developed. After the samples were extracted with ethanol, the optimum separation conditions for these analytes were achieved using water and acetonitrile (70:30, v/v) containing 0.2% (v/v) acetic acid as a mobile phase and a 2.0 mm×150 mm Hypersil-Keystone C18 column. Selective ion monitoring (SIM) mode and [M+H]+ ions at m/z 447, 431, 285 and 269 were used for quantitative analysis of four main active components above mentioned. The calibration curves were linear in the range of 0.4−175.0 μg/mL for calycosin-7-O-β-D-glucoside, 0.2−146.0 μg/mL for ononin, 0.4−210.0 μg/mL for calycosin and 0.5−217.0 μg/mL for formonetion, respectively. The limits of quantification (LOQ) and detection (LOD) were 0.4 μg/mL and 0.08 μg/mL for calycosin-7-O-β-D-glucoside, 0.2 μg/mL and 0.06 μg/mL for ononin, 0.4 μg/mL and 0.1 μg/mL for calycosin, 0.5 μg/mL and 0.1 μg/mL formonetion, respectively. The standard recoveries were in the range of 96.5%−104.7%. The developed method has successfully been used for the determination of four main flavonoids in Astragali Radix from various sources and can be used for identification, differentiation and quality evaluation of Astragali Radix.

The exploration of stable and highly efficient alkaline hydrogen evolution reaction (HER) electrocatalysts is imperative for alkaline water splitting. Herein, Se-doped NiCoP with hierarchical nanoarray structures directly grown on carbon cloth (Se-NiCoP/CC) was prepared by hydrothermal reaction and phosphorization/selenization process. The experimental results reveal that Se doping could increase the electrochemical active sites and alter the electronic structure of NiCoP. The optimized Se-NiCoP/CC electrode exhibits outstanding HER activity in alkaline electrolyte, which only needs a low overpotential of 79 mV at the current density of 10 mA/cm2. When serving as anode and cathode electrode simultaneously, the Se-NiCoP/CC electrodes achieve current density of 50 mA/cm2 at a low voltage of only 1.62 V. This work provides a feasible way to rationally design high active HER electrocatalysts.

B4C/6061Al composites reinforced with nano- to micrometer-sized B4C particles were fabricated via powder metallurgy route consisting of spark plasma sintering (SPS) and hot extrusion and rolling (HER), followed by T6 treatment. The microstructural evolution and mechanical properties were investigated. Results showed that the status of B4C particles changed from a network after SPS to a dispersion distribution after HER. The substructured grains reached 66.5% owing to the pinning effect of nano-sized B4C, and the grain size was refined from 3.12 μm to 1.56 μm after HER. After T6 treatment, dispersed Mg2Si precipitated phases formed, and the grain size increased to 1.87 μm. Fine recrystallized grains around micro-sized B4C were smaller than those in the areas with uniform distribution of nano-sized B4C and Mg2Si. The stress distributions of as-rolled and heated composites were similar, considering that the T6 heat treatment was only effective in eliminating the first internal stress. The Vickers, microhardness, and tensile strength of as-SPSed composites were greatly improved from HV 55.45, 0.86 GPa, and 180 MPa to HV 77.51, 1.08 GPa, and 310 MPa, respectively. Despite the precipitation strengthening, the corresponding values of as-heated composites decreased to HV 70.82, 0.85 GPa, and 230 MPa owing to grain coarsening.

Electrolytic manganese residue leachate (EMRL) contains plenty of Mn2+ and NH4+−N, and phosphogypsum leachate (PGL) contains large amounts of PO43−−P and F−. Traditional methods of EMRL and PGL discharge could seriously damage the ecological environment. In this study, an innovative method for cooperative removal Mn2+, NH4+−N, PO43−−P, F− from PG and POFT was studied. The result showed that Mn2+, PO43−−P and F− were mainly removed in forms of Mg3Si4O10(OH)2, Mn3O4, Mn3(PO4)2, Mg3(PO4)2, CaSO4·2H2O, MnF2, MnOOH and Ca2P2O7·2H2O, when LG−MgO was used to adjust the pH value of the system to 9.5, and the volume ratio of EMRL and PGL was 1:4, as well as reaction for 1 h at 25 °c. NH4+−N was mainly removed by struvite precipitate, when the molar ratio of N:Mg:P was 1:3:2.4. The concentrations of Mn2+, NH4+−N and F− were lower than the integrated wastewater discharge standard. The concentration of PO43−−P decreased from 254.20 mg/L to 3.21 mg/L. This study provided a new method for EMRL and PGL cooperative harmless treatment.