SPI-based Regional Drought Prediction Using Weighted Markov Chain Model

Abstract: Drought is one of the most serious natural disasters in China. Drought disasters occur frequently and caused huge economic loss in recently. In this paper, a drought prediction model based on weighted Markov Chain is put forward. An application is demonstrated by Anhui province of Huaihe River in China. Based on the precipitation data during 1958-2006 at monthly scale, the different time scales Standardized Precipitation Index (SPI) is computed and the occurrence frequency of extreme drought, severe drought, moderate drought, slight drought and non-drought is obtained. The prediction of SPI is conducted by weighted Markov Chain model and the prediction accuracy is computed for the SPI of different time scales. The results show that weighted Markov Chain model is an effective tool for drought prediction and can provide decision-making for regional drought management

Influence of support stiffness on aero-engine coupling vibration quantitative analysis

This paper investigates the whole aero-engine coupling vibration, as a rotor tester to be the research object. The rotor tester system is composed of two mountings, stator system, support structures and the rotor system. The modal experiment of the whole tester under the condition of mounting in the test room is carried out. The finite element (FE) model of the rotor tester is built, and the model was modified and validated according to the modal test results. A rotor-stator coupling factor and a section rotor-stator rubbing risk coefficient are proposed, the influence of the support stiffness values on the engine vibration characteristics, such as natural frequencies, modal shapes, rotor-stator coupling degree, and stator-rotor rubbing risk degree at compressor and turbine section is quantitative studied. Results show that the support stiffness contributes to the rigid body modal shapes greatly and to the rotor bending ones slightly. The factor and coefficient defined in this study are both reasonable, and they can reflect the corresponding characteristics exactly. Moreover, the effect of the supports stiffness values on the rotor-stator coupling degree and the rotor-stator rubbing risk degree is nonlinear. The rotor-stator coupling factor and the section stator-rotor rubbing risk coefficient proposed in this study provide a new way to quantitatively research the whole engine coupling vibration

Three-dimensional shape measurement with dual reference phase maps

Single reference-phase-based methods have been extensively utilized in digital fringe projection systems, yet they might not provide the maximum sensitivity given a hardware system configuration. This paper presents an innovative method to improve the measurement quality by utilizing two orthogonal phase maps. Specifically, two reference phase maps generated from horizontal and vertical (i.e., orthogonal) fringe patterns projected are combined into a vector reference phase map through a linear combination for depth extraction. The experiments have been conducted to verify the superiority of the proposed method over a conventional single reference-phase-based approach

Acoustic tweezer with complex boundary-free trapping and transport channel controlled by shadow waveguides.

Acoustic tweezers use ultrasound for contact-free, bio-compatible, and precise manipulation of particles from millimeter to submicrometer scale. In microfluidics, acoustic tweezers typically use an array of sources to create standing wave patterns that can trap and move objects in ways constrained by the limited complexity of the acoustic wave field. Here, we demonstrate spatially complex particle trapping and manipulation inside a boundary-free chamber using a single pair of sources and an engineered structure outside the chamber that we call a shadow waveguide. The shadow waveguide creates a tightly confined, spatially complex acoustic field inside the chamber without requiring any interior structure that would interfere with net flow or transport. Altering the input signals to the two sources creates trapped particle motion along an arbitrary path defined by the shadow waveguide. Particle trapping, particle manipulation and transport, and Thouless pumping are experimentally demonstrated

Observations of Field Current and Field Winding Temperature in Electrically Excited Synchronous Machines with Brushless Excitation

Electrically excited synchronous machines have become an alternative in electrification of transportations and renewable power generations. To reduce the extra effort in the maintenance of sliprings and brushes for field excitation, brushless excitation has been developed. However, when brushless excitation is adopted, the field winding becomes physically inaccessible when the machine is rotating. To solve this problem, an algorithm is proposed in this study to observe the field current and field winding temperature of an EESM with brushless excitation. The stator currents are measured and then used to correct the machine state predictor. The correction of the state prediction is interpreted to adjust the field winding resistance and temperature value. The algorithm is evaluated in simulations. The estimations of field current and field winding temperature track the measurements successfully