A piezoelectric composite vibrator with a bilaminated structure is designed and fabricated, in this work by applying bending vibration to increase vibration displacement and reduce resonance frequency. The finite element software ANSYS (ANSYS, Inc. USA) is used to simulate the 2-2 and 1-3 piezoelectric composite bilaminated vibrators under free boundary condition and optimize their design. Simulation results show that the vibration displacement of the 2-2 vibrator is higher than that of the 1-3 vibrator, and the resonance frequency of the former is lower than the latter. Five pieces each of the 2-2 and piezoelectric ceramic vibrators are prepared. In addition, simulation and experimental results indicate that the vibration displacement of the 2-2 vibrator increases by 2.3 times, whereas its resonance frequency decreases by nearly 100 Hz, in comparison with those of the piezoelectric ceramic bilaminated vibrator.
In engineering practice, the initial support system is commonly installed in the vicinity of the tunnel face after excavation, whereas the self-capacity of rock mass will fail to be utilized and the cost of the initial support system will be expensive. In this study, a methodology is proposed to determine the appropriate timing of initial support installation to find out the balance of tunnel safety and construction cost. Firstly, the global safety factor is introduced as the critical indicator to evaluate tunnel stability. Then, the comprehensive graphic relationship between the global safety factor and the distance to the tunnel face is established. Once the global safety factor decreases to an admissible value, the stability of the surrounding rock is in a critical state and the corresponding distance is the recommended location for installing the initial support. In these procedures, the installation time of the initial support at the typical tunnel section can be quickly designed and fed back by a direct indicator during construction. Meanwhile, several cases with different conditions have been carried out to discuss the regularity of the method.
The voltage stability is substantially a dynamic stability, but the primary method which is more mature and engineering practical to analyze the stability of voltage is still static analysis. The time-domain simulation is an important measure in research of complex power grid. With the development of full dynamic simulation technology, the research of dynamic voltage stability by using full dynamic simulation program which is based on time-domain simulation can be carried out. This paper uses full dynamic simulation program in dynamic voltage stability research, lays special stress on research in how generator over-excitation limiter functioned and influence in dynamic voltage stability research, and raise 2 methods and steps to figure out dynamic stable voltage in both over-excitation counted and not counted. The simulation results of examples indicate the correctness and effectiveness of these methods, and also fully verify the function and influence of generator over-excitation limiter in full dynamic voltage stability research.
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