A GPU-based Transient Stability Simulation using Runge-Kutta Integration Algorithm

Graphics processing units (GPU) have been investigated to release the computational capability in various scientific applications. Recent research shows that prudential consideration needs to be given to take the advantages of GPUs while avoiding the deficiency. In this paper, the impact of GPU acceleration to implicit integrators and explicit integrators in transient stability is investigated. It is illustrated that implicit integrators, although more numerical stable than explicit ones, are not suitable for GPU acceleration. As a tradeoff between numerical stability and efficiency, an explicit 4th order Runge-Kutta integration algorithm is implemented for transient stability simulation based on hybrid CPU-GPU architecture. The differential equations of dynamic components are evaluated in GPU, while the linear network equations are solved in CPU using sparse direct solver. Simulation on IEEE 22-bus power system with 6 generators is reported to validate the feasibility of the proposed method.published_or_final_versio

Application of non-linear programming for large-scale AC-DC power flow analysis

This paper proposes a robust, non-divergent model for large-scale AC-DC power flow analysis. By introducing relaxation variables into power flow equations, the conventional power flow model is turned into a non-linear programming model to minimize the L2 norm of the relaxation variables subject to operation constraints and DC station control modes. The interior point method (IPM) is used to solve the model. Due to the special structure of the proposed model, the size of coefficient of correction equations in the IPM can be reduced to the same as Jacobian in the conventional Newton method. Further, the coefficient is symmetrical positive-definite with a diagonal perturbation, which leads to a better convergence than Newton direction. The model and algorithm proposed also have the following features: (1) no special initial value is needed; (2) strong robustness for power grids with plenty of small/negative impedance; (3) applicable for searching a desirable operation point by appropriate settings of inequality constraints; (4) striving for ultimate close to power flow solution avoiding to stop too early at a local minimizer. Numerical simulations on a 6527 buses power grid in China with 8 HVDC lines show that the proposed model has robust convergent property in the feasible region, around the boundary of the feasible region and even beyond the feasible region of power flow. © 2012 IEEE.published_or_final_versio

Lack of Prosodic Focus in Chongqing Dialect and Possible Historical Sources

This study investigates Chongqing Dialect, a language largely used in Southwest China which is mutually intelligible to Beijing Mandarin speakers. Phonetic variations triggered by focus in Chongqing Dialect, especially in the form of post-focus compression (PFC), are investigated in terms of max F0, mean F0, duration and intensity. A follow-up perception test is also conducted. The production experiment shows that there are no significant changes from no focus condition to focus condition in the factors analysed, and no PFC is observed in Chongqing Dialect. The perception test shows a rather low identification rate at around 40%. The results of this study support the hypothesis that there is a typological divide within the Chinese languages, and the reason is explored by an analysis of the historical roots of Chongqing Dialect. As a representative of Southwest Mandarin, the lack of PFC in Chongqing Dialect suggests that many other Southwest Mandarin dialects also may not have PFC

Large-time Behavior of Solutions to the Inflow Problem of Full Compressible Navier-Stokes Equations

Large-time behavior of solutions to the inflow problem of full compressible Navier-Stokes equations is investigated on the half line $R^+ =(0,+\infty)$. The wave structure which contains four waves: the transonic(or degenerate) boundary layer solution, 1-rarefaction wave, viscous 2-contact wave and 3-rarefaction wave to the inflow problem is described and the asymptotic stability of the superposition of the above four wave patterns to the inflow problem of full compressible Navier-Stokes equations is proven under some smallness conditions. The proof is given by the elementary energy analysis based on the underlying wave structure. The main points in the proof are the degeneracies of the transonic boundary layer solution and the wave interactions in the superposition wave.Comment: 27 page

A test of the power law relationship between gamma-ray burst pulse width ratio and energy expected in fireballs or uniform jets

Recently, under the assumption that the Doppler effect of the relativistically expanding fireball surface is important, Qin et al. showed that in most cases the power law relationship between the pulse width and energy of gamma-ray bursts (GRBs)would exist in a certain energy range. We check this prediction with two GRB samples which contain well identified pulses. A power law anti-correlation between the full pulse width and energy and a power law correlation between the pulse width ratio and energy are seen in the light curves of the majority (around 65%) of bursts of the two samples within the energy range of BATSE, suggesting that these bursts are likely to arise from the emission associated with the shocks occurred on a relativistically expanding fireball surface. For the rest of the bursts, the relationships between these quantities were not predicted previously. We propose to consider other spectral evolutionary patterns or other radiation mechanisms such as a varying synchrotron or Comptonized spectrum to check if the observed relationships for these rest bursts can also be accounted for by the Doppler model. In addition, we find that the upper limits of the width ratio for the two samples do not exceed 0.9, in agrement with what predicted previously by the Doppler model. The plateau/power law/plateau and the peaked features predicted and detected previously by Qin et al. are generally observed, with the exceptions being noticed only in a few cases. According to the distinct values of two power law indices of FWHM and ratio and energy, we divide the bursts into three subsets which are located in different areas of the two indices plane. We suspect that different locations of the two indices might correspond to different mechanisms.Comment: 16 pages, 7 figures, MNRAS accepte