Naval University of Engineering

About: Naval University of Engineering is a education organization based out in Wuhan, China. It is known for research contribution in the topics: Heat transfer & Fault (power engineering). The organization has 8895 authors who have published 6980 publications receiving 33460 citations. The organization is also known as: Zhōngguó Rénmín Jiěfàngjūn Haǐjūn Gōngchéng Dàxué.

Progress in study on constructal theory and its applications

Abstract: The emergence and development of constructal theory, which has been a new discipline branch to research sorts of structures in nature and engineering, are reviewed. The core of the constructal theory is that various shapes and structures of the matters in nature are generated from the tendency to obtain optimal performance. Constructal theory and its application are summarized, from disciplines such as heat, mechanism, fluid flow, electricity, magnetism and chemistry, to life and non-life systems in nature.

Flow and radiation heat transfer of a nanofluid over a stretching sheet with velocity slip and temperature jump in porous medium

Abstract: In this paper, we present an investigation for the flow and radiation heat transfer of a nanofluid over a stretching sheet with velocity slip and temperature jump in porous medium. The Brownian motion and thermophoresis are taken into account according to Rosseland’s approximation. The governing coupled partial differential equations are non-dimensionalized and solved both numerically and analytically by local similarity method. The effects of involved parameters (velocity slip, temperature jump, thermal radiation, Prandtl number, Lewis number, Brownian motion, thermophoresis) on velocity, temperature and concentration profiles are presented graphically and analyzed. Moreover, the numerical results are compared with the analytical solutions obtained by Homotopy analysis method with very good agreement to validate the present results.

Large Signal Synchronizing Instability of PLL-Based VSC Connected to Weak AC Grid

Abstract: Similar large signal synchronizing instability that is common in traditional power system also exists in voltage source converter (VSC) dominated power system, which is increasingly reported and investigated. In this paper, the large signal instability of phase locked loop (PLL) synchronized VSC connected to weak ac grid is investigated. First, the influence of high grid impedance on PLL's dynamics is explored and an additional feedback loop is found to be introduced, which deteriorates the performance of PLL. Then an analysis model that is similar as the rotor motion model of synchronous generator (SG) is developed. Based on the developed model, equal-area method is employed to carry out the large-signal stability analysis. The large signal instability is found to be mainly resulted by the following two factors. One is the nonexistence of equilibrium point, which is similar as that there does not exist intersection between the mechanical power input curve and electromagnetic restoring force curve in SG grid connected system. The other is related with the transition process resulted by insufficient decelerating area, which leads to that the system cannot stably go through the transition from initial point to the existing equilibrium point. The proposed analysis not only contributes to revealing the physical mechanism but also provides guidance for the future improvement measures.

Robust Kalman filtering based on Mahalanobis distance as outlier judging criterion

Abstract: A robust Kalman filter scheme is proposed to resist the influence of the outliers in the observations. Two kinds of observation error are studied, i.e., the outliers in the actual observations and the heavy-tailed distribution of the observation noise. Either of the two kinds of errors can seriously degrade the performance of the standard Kalman filter. In the proposed method, a judging index is defined as the square of the Mahalanobis distance from the observation to its prediction. By assuming that the observation is Gaussian distributed with the mean and covariance being the observation prediction and its associate covariance, the judging index should be Chi-square distributed with the dimension of the observation vector as the degree of freedom. Hypothesis test is performed to the actual observation by treating the above Gaussian distribution as the null hypothesis and the judging index as the test statistic. If the null hypothesis should be rejected, it is concluded that outliers exist in the observations. In the presence of outliers scaling factors can be introduced to rescale the covariance of the observation noise or of the innovation vector, both resulting in a decreased filter gain. And the scaling factors can be solved using the Newton’s iterative method or in an analytical manner. The harmful influence of either of the two kinds of errors can be effectively resisted in the proposed method, so robustness can be achieved. Moreover, as the number of iterations needed in the iterative method may be rather large, the analytically calculated scaling factor should be preferred.