Journal of Central South University

In order to solve fretting instability problem of gear shaft shoulder due to torsional vibration in mechanical system, the mathematical model of fretting instability vibration of gear shaft shoulder was established by adopting the method of combining kinematics and tribology, and the numerical analysis was applied to the fretting instability mechanism of gear shaft shoulder by introducing the friction instability damping ratio. The numerical results show that the main factors causing the unstable and vibrating gear shaft shoulder are the large tightening torque and too large static friction coefficient. The reasonable values of the static friction coefficient, the amount of interference and tightening torque can effectively mitigate the fretting instability phenomenon of gear shaft shoulder. The experimental results verify that damping plays a significant role in eliminating the vibration of gear shaft control system.

Oxygen fuels have broad application prospects and great potential for realizing efficient and clean combustion, and hence this study applies diesel/n-butanol blends to explore the influence of split-injection strategy on combustion and emission characteristics. Simultaneously, changing the way of exhaust gas recirculation (EGR) gas introduction forms uneven in-cylinder components distribution, and utilizing EGR stratification optimizes the combustion process and allows better emission results. The results show that the split-injection strategy can reduce the NOx emissions and keep smoke opacity low compared with the single injection, but the rise in accumulation mode particles is noticeable. NOx emissions show an upward trend as the injection interval expands, while soot emissions are significantly reduced. The increase in pre-injection proportion causes the apparent low-temperature heat release, and the two-stage heat release can be observed during the process of main combustion heat release. More pre-injection mass makes NOx gradually increase, but smoke opacity reaches the lowest point at 15% pre-injection proportion. EGR stratification can optimize the emission results under the split injection strategy, especially the considerable suppression of accumulation mode particulate emissions. Above all, fuel stratification coupled with EGR stratification is beneficial for further realizing the in-cylinder purification of pollutants.

Flatness pattern recognition is the key of the flatness control. The accuracy of the present flatness pattern recognition is limited and the shape defects cannot be reflected intuitively. In order to improve it, a novel method via T-S cloud inference network optimized by genetic algorithm (GA) is proposed. T-S cloud inference network is constructed with T-S fuzzy neural network and the cloud model. So, the rapid of fuzzy logic and the uncertainty of cloud model for processing data are both taken into account. What’s more, GA possesses good parallel design structure and global optimization characteristics. Compared with the simulation recognition results of traditional BP Algorithm, GA is more accurate and effective. Moreover, virtual reality technology is introduced into the field of shape control by LabVIEW, MATLAB mixed programming. And virtual flatness pattern recognition interface is designed. Therefore, the data of engineering analysis and the actual model are combined with each other, and the shape defects could be seen more lively and intuitively.

Deformation prediction and the analysis of underground goaf are important to the safe and efficient recovery of residual ore when shifting from open-pit mining to underground mining. To address the comprehensive problem of stability in the double mined-out area of the Tong-Lv-Shan (TLS) mine, which employed the dry stacked gangue technology, this paper applies the function fitting theory and a regression analysis method to screen the sensitive interval of four influencing factors based on single-factor experiments and the numerical simulation software FLAC3D. The influencing factors of the TLS mine consist of the column thickness (d), gob area span (D), boundary pillar thickness (h) and height of tailing gangue (H). The fitting degree between the four factors and the displacement of the gob roof (W) is reasonable because the correlation coefficient (R2) is greater than 0.9701. After establishing 29 groups that satisfy the principles of Box-Behnken design (BBD), the dry gangue tailings process was re-simulated for the selected sensitive interval. Using a combination of an analysis of variance (ANOVA), regression equations and a significance analysis, the prediction results of the response surface methodology (RSM) show that the significant degree for the stability of the mined-out area for the factors satisfies the relationship of h>D>d>H. The importance of the four factors cannot be disregarded in a comparison of the prediction results of the engineering test stope in the TLS mine. By comparing the data of monitoring points and function prediction, the proposed method has shown promising results, and the prediction accuracy of RSM model is acceptable. The relative errors of the two test stopes are 1.67% and 3.85%, respectively, which yield satisfactory reliability and reference values for the mines.

The bottleneck of strontium compounds preparing from celestite is the promotion of Sr/S isolation efficiency. Low energy consumption and zero release method for isolating Sr/S in preparing Sr(OH)2 process from celestite in mild condition was described. Sr element remained in precipitation with formation of Sr(OH)2, while S element entered into leachate with formation of Na2SO4. The effects of initial concentration of NaOH, conversion temperature, liquid-to-solid (L/S) ratio and conversion time on Sr/S ratio of samples for celestite conversion were systematically investigated by experiments. The results demonstrated that the efficiency of Sr/S isolation increased with the initial concentration of NaOH, L/S ratio and conversion time, and decreased with conversion temperature. The maximum conversion ratio of Sr(OH)2 was 93.88% under the optimum condition, whose Sr/S ratio of sample could reach to 41.16. It illustrated that better isolation efficiency of celestite could be achieved in alkaline treatment. The results of SEM-EDS analyses demonstrated that the conversion reaction was a dissolution-precipitation process.

Springback of a SUS321 complex geometry part formed by the multi-stage rigid-flexible compound process was studied through numerical simulations and laboratory experiments in this work. The sensitivity analysis was provided to have an insight in the effect of the evaluated process parameters. Furthermore, in order to minimize the springback problem, an accurate springback simulation model of the part was established and validated. The effects of the element size and timesteps on springback model were further investigated. Results indicate that the custom mesh size is beneficial for the springback simulation, and the four timesteps are found suited for the springback analysis for the complex geometry part. Finally, a strategy for reducing the springback by changing the geometry of the blank is proposed. The optimal blank geometry is obtained and used for manufacturing the part.