Improved transient simulation of salient-pole synchronous generators with internal and ground faults in the stator winding

An improved model for simulating the transient behavior of salient-pole synchronous generators with internal and ground faults in the stator winding is established using the multi-loop circuit method. The model caters for faults under different ground conditions for the neutral, and accounts for the distributed capacitances of the windings to ground. Predictions from the model are validated by experiments, and it is shown that the model accurately predicts the voltage and current waveforms under fault conditions. Hence, it can be used to analyze important features of faults and to design appropriate protection schemes

Space-time Characteristics and Experimental Analysis of Broadening First-order Sea Clutter in HF Hybrid Sky-surface Wave Radar

In high frequency (HF) hybrid sky-surface wave radar, the first-order sea clutter broadening is very complex and serious under the influence of ionosphere and bistatic angle, which affects the detection of ship target. This paper analyzes the space-time characteristics based on the HF sky-surface wave experimental system. We first introduce the basic structure, working principle and position principle based on our experimental system. Also analyzed is the influence of ionosphere and bistatic angle on the space-time coupling characteristics of broadening first-order sea clutter and the performance of space-time adaptive processing (STAP). Finally, the results of theoretic analysis are examined with the experimental data. Simulation results show that the results of experiment consist with that of theoretic analysis

An efficient method to detect mutual overlap of a large set of unordered images for structure-from-motion

Recently, low-cost 3D reconstruction based on images has become a popular focus of photogrammetry and computer vision research. Methods which can handle an arbitrary geometric setup of a large number of unordered and convergent images are of particular interest. However, determining the mutual overlap poses a considerable challenge. We propose a new method which was inspired by and improves upon methods employing random k-d forests for this task. Specifically, we first derive features from the images and then a random k-d forest is used to find the nearest neighbours in feature space. Subsequently, the degree of similarity between individual images, the image overlaps and thus images belonging to a common block are calculated as input to a structure-from-motion (sfm) pipeline. In our experiments we show the general applicability of the new method and compare it with other methods by analyzing the time efficiency. Orientations and 3D reconstructions were successfully conducted with our overlap graphs by sfm. The results show a speed-up of a factor of 80 compared to conventional pairwise matching, and of 8 and 2 compared to the VocMatch approach using 1 and 4 CPU, respectively

Gossip-Based Indexing Ring Topology for 2-Dimension Spatial Data in Overlay Networks

AbstractOverlay networks are used widely in the Internet, such as retrieval and share of files, multimedia games and so on. However, in distributed system, the retrieval and share of 2-dimension spatial data still have some difficult problems and can not solve the complex retrieval of 2-dimension spatial data efficiently. This article presents a new indexing overlay networks, named 2D-Ring, which is the ring topology based on gossip for 2-dimension spatial data. The peers in our overlay networks exchange the information periodically and update each local view by constructing algorithm. 2-dimension spatial data is divided by quad-tree and mapped into control points, which are hashed into 2D-Ring by SHA-1 hash function. In such way, the problem of 2-dimension spatial data indexing is converted to the problem of searching peers in the 2D-Ring. A large of extensive experiments show that the time complexity of constructing algorithm of 2D-Ring can reach convergence logarithmically as a function of the network size and hold higher hit rate and lower query delay

Effects of chitosan addition on growth performance, diarrhoea, anti-oxidative function and serum immune parameters of weaned piglets

The present experiment was designed to determine the efficacy of a commercial source of chitosan (CS) to enhance performance, anti-oxidative function, and immune response in weaned pigs. A total of 60 crossbreed piglets (Duroc × Landrace × Yorkshire), with average live bodyweight of 8.85 ± 1.52 kg, were weaned at 28 ± 2 days and randomly assigned to five treatment groups, which were fed maize-soybean meal diets containing 0 (basal diet, control) and 250, 500, 1000, and 2000 mg/kg CS. The experiment lasted for two weeks. Body weight was recorded and daily feed intake was calculated. Faecal consistency was monitored for the overall period. After two weeks, blood samples were collected and anti-oxidative and immune parameters were determined. The results showed that CS improved average daily gain and daily gain: daily feed intake during the experiment. Mean faecal score values for the second week were improved by CS, which showed decreased values compared with the control diet. The CS increased the total antioxidant capacity and the activities of superoxide dismutase, catalase and glutathione peroxidase and the content of reduced glutathione in serum, and decreased the malondialdehyde and cortisol contents of serum. Furthermore, CS increased the levels of serum IL-1β，IL-2 and IgG. These findings suggested that the use of CS improved performance and anti-oxidative function, and regulated the immune response of weaned pigs.Keywords: Anti-oxidative capability, chitosan, immunity, performance, piglet

Friction and Wear Behavior of Wear-Resistant Belts in Drill Joints for Deep and Ultra-Deep Wells

The friction and wear of an new material for the drill joint were compared with those of traditional wear-resistant belt materials using an SD-1 test rig against a 42Mn2V steel counterface under deep and ultra-deep well conditions. This provides recommendations as to the tribological application of the wear-resistant belt. The results obtained strongly indicate that the friction and wear of a polycrystalline diamond (PCD) composite are much lower than those of the traditional wear-resistant belt materials. Among those materials, the friction and wear behavior of a FeNiNb alloy are higher than those of a FeCrMnMo alloy. Of the three wear-resistant belt materials, the bilateral protection performance of a PCD composite is the best one. It is feasible to use this composite as the wear-resistant belt material in the drill joint for deep and ultra-deep wells. The dominant wear mechanism of the wear-resistant belt materials is the microcutting wear, accompanied by the adhesive one. In addition, the wear degree of the PCD composite is the least one.Трение и износ традиционных износостойких материалов для поясов сравнивали с этими же характеристиками нового материала для бурового разреза. Использован испытательный стенд SD-1 с контртелом из стали 42Mn2V, моделирующий режим глубоких и сверхглубоких скважин, с целью разработки рекомендацией по использованию износостойкого пояса в условиях трения. Показано, что трение и износ поликристаллического алмазного композита гораздо ниже, чем традиционных износостойких материалов, например, трение и износ сплава FeNiNb выше, чем сплава FeCrMnMo. Из трех износостойких материалов наилучшую двухстороннюю защиту обеспечивает алмазный композит, что подтверждает эффективность его использования для поясов буровых разрезов в глубоких и сверхглубоких скважинах. Преобладающим механизмом является микроабразивный износ, сопровождаемый абразивным, при этом степень износа композита наименьшая

Influence of casting temperature on the thermal stability of Cu- and Zr-based metallic glasses: theoretical analysis and experiments

Influence of casting temperature on the thermal stability of Cu- and Zr-based metallic glasses (MGs) was analyzed based on the monomer-cluster structural model using the Johnson-Mehl-Avrami (JMA) equation. The result indicates that increasing the casting temperature can enhance the thermal stability of MGs. It is suggested that it be attributed to the decrease in the amount of the local ordering clusters induced by the elevating casting temperature. The prediction is confirmed by continuous heating transformation diagrams constructed for the Cu- and Zr-amorphous samples obtained under different casting temperatures

Analysis and reduction of on-load DC winding induced voltage in wound field switched flux machines

DC winding induced voltage pulsation in wound field switched flux (WFSF) machines causes DC winding current ripple and field excitation fluctuation, challenges the DC power source and deteriorates the control performance. Hence, reducing this pulsation is important in the design of a WFSF machine. In this paper, based on the analytical models, rotor skewing and rotor iron piece pairing are proposed and comparatively investigated by the finite element (FE) method to reduce the on-load DC winding induced voltage in WFSF machines having partitioned stators and concentrated AC windings. FE results show that peak to peak value of the on-load DC winding induced voltage in the analysed 12/10-pole partitioned stator WFSF (PS-WFSF) machines can be reduced by 78.42% or 77.16% by using rotor skewing or rotor pairing, respectively, whilst the torque density can be maintained by >90%. As for the 12/11-, 12/13- and 12/14-pole PS-WFSF machines, by using rotor iron piece inner arc pairing, the on-load DC winding induced voltage can be reduced by 64.11%, 52.12% and 76.49%, respectively, whilst the torque density can also be maintained by more than 90%. Prototypes are built and tested to verify the analytical and FE results

Mechanical Properties of GF/pCBT Composites and Their Fusion-Bonded Joints: Influence of Process Parameters

High melting viscosity of thermoplastic composites gives no way of using substantial volume fractions of reinforcing agents. This problem can be solved by in-situ polymerization of an extremely low-viscosity cyclic butylene terephthalate (CBT) resin. Continuous glass fiber-reinforced poly(cyclic butylene terephthalate) (GF/ðCBT) composites with high fiber fractions were manufactured, and the mechanical properties as a function of the catalyst mass fraction and fiber filling ratio were studied. The longitudinal tensile strength of the composites was enhanced by increasing the fiber volume fraction, and the influence of the fiber fraction on the bending strength of high fiber filling-ratio composites was evaluated. Furthermore, the mechanical properties and failure modes of GF/ðCBT fusion-bonded joints with different number of bonding areas of different lengths were investigated. It was found that high-strength composite materials can be obtained, which are applicable for fusion-bonded structures.Высокая вязкость плавления термопластических композиционных материалов не позволяет использовать значительные объемные долевые концентрации армирующих наполнителей. Эта проблема может быть решена путем in-situ полимеризации циклобутилентерефталатной смолы с чрезвычайно низкой вязкостью. Были изготовлены поли(циклобутилентерефталатные) композиционные материалы, армированные непрерывным стекловолокном (CF/pCBT) с высоким его содержанием, изучены механические свойства с учетом весовой доли катализатора и степени наполнения волокном. Предел прочности композиционных материалов при растяжении в продольном направлении возрос за счет увеличения объемной доли концентрации волокна, изучено влияние объемной доли волокна на прочность при изгибе для композиционных материалов с высокой степенью наполнения волокном. Кроме того, исследованы механические свойства и режимы разрушения GF/pCBT сваренных плавлением соединений с различным количеством зон связывания разной длины. Установлено, что можно получать высокопрочные композиционные материалы, пригодные для сваренных плавлением конструкций

Study of f_0(980) and f_0(1500) from B_s \to f_0(980)\pi, f_0(1500)\pi Decays

In this paper, we analyze the scalar mesons $f_0(980)$ and $f_0(1500)$ from the decays $\bar B^0_s \to f_0(980)\pi^0, f_0(1500)\pi^0$ within Perturbative QCD approach. From the leading order calculations, we find that (a) in the allowed mixing angle ranges, the branching ratio of $\bar B^0_s\to f_0(980)\pi^0$ is about $(1.0\sim1.6)\times 10^{-7}$, which is smaller than that of $\bar B^0_s\to f_0(980)K^0$ (the difference is a few times even one order); (b) the decay $\bar B^0_s \to f_0(1500)\pi^0$ is better to distinguish between the lowest lying state or the first excited state for $f_0(1500)$, because the branching ratios for two scenarios have about one-order difference in most of the mixing angle ranges; and (c) the direct CP asymmetries of $\bar B^0_s \to f_0(1500)\pi^0$ for two scenarios also exists great difference. In scenario II, the variation range of the value ${\cal A} ^{dir}_{CP}(\bar B^0_s \to f_0(1500)\pi^0)$ according to the mixing angle is very small, except for the values corresponding to the mixing angles being near $90^\circ$ or $270^\circ$, while the variation range of ${\cal A} ^{dir}_{CP}(\bar B^0_s \to f_0(1500)\pi^0)$ in scenario I is very large. Compared with the future data for the decay $\bar B^0_s \to f_0(1500)\pi^0$, it is ease to determine the nature of the scalar meson $f_0(1500)$.Comment: 16 pages, 3 figures, Revte