ABSTRACT
Torsional vibration of flexible drive chain is a historical issue. With the maximization development and the rotating machinery high-speed operation, the drive chain systems of large-scaled units become more and more complex, which makes the torsional vibration problems becoming increasingly prominent in recent years. This article deeply analyzed the small signal stability of large-scaled WECS based on CMT, elaborated the torsional vibration mechanism and reasons for the first time and pointed out torsional vibration is caused by the disturbance wind and the DPC strategy. The disturbance wind is an external stimulus and can produce a low-frequency torsional vibration at the same frequency as wind speed. The DPC could weaken the drive chain damping. If the total damping of drive chain is negative, the unstable torsion vibration will occur. And if the drive chain is still a under-damped dynamic, the high-frequency torsional vibration at natural frequency will be generated. Therefore, large-scaled WECS must have damping control. This study found that appropriate enhancing drive chain stiffness could reduce low-frequency torsional vibration caused by wind speed. Therefore, a damping and stiffness compensation control method was proposed to suppress the torsional vibration. Compared with the conventional damping control, the new method not only can suppress the high-frequency torsional vibration but also has a good restraining effect on the low-frequency torsional vibration. Furthermore, the detailed design procedures including the calculation of injection damping and stiffness were given in this paper. Finally, the correctness and effectiveness of our analysis were further verified by the simulation experiments.
ABSTRACT
In this study, water-n-BuOH mixed solvents were used to synthesize the ZnAl-layered double hydroxides (ZnAl-LDHs) via hydrothermal method. The XRD, FT-IR, SEM, ICP and CHN analyses revealed that the type of intercalated anions, the layer Zn/Al ratios, and morphologies of the LDHs depended on the ratio of V(water)/V(n-BuOH) in the mixed solvents. When the ratio of V(water)/V(n-BuOH) is 3 or 0.3, the as-prepared LDHs had 3D "silk flowers" (ZnAl-LDH-3) or "Sedimentary rock" morphology (ZnAl-LDH-0.3). Adsorption properties of dyes on calcined LDHs were studied. Compared with ZnAl-LDO-0.3 and ZnAl-LDO-w (calcined from the LDHs obtained in pure water), ZnAl-LDO-3 showed much better adsorption efficiency for anionic dyes thanks to its much larger BET-specific surface area. The sorption kinetics for dyes was appropriately described by the pseudo-second-order model and sorption isotherms can be fitted more satisfactorily by the Langmuir model. With the increasing concentrations of dyes from 10mg/L to 400mg/L, the maximum absorption capacities of ZnAl-LDO-3 were 1540mg/g (2.21mmol/g) for congo red, 1153mg/g (3.52mmol/g) for methyl orange and 390mg/g (0.63mmol/g) for active red (X-3B), respectively. The adsorption dyes onto the external surface is still the main mechanism for LDO adsorbents. The ZnAl-LDO-3 was a potential adsorbent for dyeing wastewater treatment.
