Browsing by Author "Zhou, Ning"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Active control of sound transmission through plates in a reverberant environment
    Zhou, Ning (Virginia Tech, 1992)
    Active control of sound transmission through an elastic plate placed between two reverberation chambers is studied experimentally. Active acoustic control is performed using piezoelectric sensors and actuators bonded to the plate. The control technique uses an adaptive control algorithm. Results are presented for harmonic excitation provided by a speaker in the source chamber at two resonant frequencies of the plate. Influence of different types of error sensors, varied actuator locations, and varied speaker locations are studied. Compared to microphone sensors in the receiving chamber, piezoelectric sensors are shown to be effective in reducing sound transmission through the plate. Average reduction of sound pressure level (SPL) on the order of 20 dB or 13 dB are achieved when the plate vibrates at mode (3,1) or (3,3). Microphone sensor locations are shown to influence the controlled sound field, those located where the direct sound field is dominant result in larger SPL reductions. SPL reductions are caused by two mechanisms: modal reduction and modal restructuring, and the dominance of either is shown to depend on actuator locations. When the sound field is non-diffuse, speaker locations influence the SPL and the SPL reduction by changing the plate's structural response. Also included in this work, previously developed one-dimensional (I-D) modal sensor theory for beams is used to develop modal sensors for a clamped plate. Two I-D modal sensors are applied to a fully clamped plate and each shown to observe a particular subset of plate vibration modes. Previous work developed the theory for two-dimensional (2-D) modal sensors for simply-supported plates. A necessary and sufficient condition for the spatial functions of 2-D modal sensors are developed for plates with arbitrary boundary conditions.
  • Thumbnail Image
    A New Multi-Scale State Estimation Framework for the Next Generation of Power Grid EMS
    Zhao, Junbo; Wang, Shaobu; Zhou, Ning; Huang, Renke; Mili, Lamine M.; Huang, Zhenyu (IEEE, 2019-08-01)
    Accurate system state information under various operation conditions is a prerequisite for power grid monitoring and efficient control. To achieve that goal, a new multi-scale state estimation framework is proposed, paving the way for the development of next generation of energy management system (EMS). The developed framework consists of three key components, namely the static state estimation (SSE) module, the dynamic state estimation (DSE) module, the interfaces and switching logics between the two modules. Specifically, the singular spectrum analysis (SSA)-based change point detection approach is developed to monitor the system continuously. If no event is detected by the SSA, the robust SSE using both SCADA and PMU measurements is executed. Otherwise, the event is declared and the results from SSE are used to derive the initial condition for DSE. During the transient process, only PMU-based DSE is executed for system monitoring and it will be terminated when SSA does not detect any change point of the system. After that, the DSE results are forwarded for SSE initialization and bus voltage magnitude and angle estimations. Simulation results carried out on the IEEE 39-bus system demonstrate the effectiveness and benefits of the proposed framework.