High Impedance Arc Fault Modelling in Offshore Oil Platform Power Grid

In offshore oil platform power grid, high impedance arc fault occurs frequently. The fault characteristics of high- impedance arc information are weak and difficult to detect, which may not cause the protection method to activate. Therefore, it is important to detect and clear the high impedance fault. In the high impedance case, usually, the arc fault occurs. In the research, the arc model was established using the typical Cassie model and the high impedance arc fault characteristics in offshore oil platform power grids were analysed. An improved arc fault detection method using the phase angle difference between zero sequence voltage and zero sequence current was proposed to extract fault characteristics. This method requires limited detection information and high accuracy to solve the problem of small current and voltage changes in high-resistance arc faults. The offshore oil platform power grid and the arc were modelled using electromagnetic transients software PSCAD/EMTDC. The simulation results show that the arc model and fault detection method work well

Path Planning for Automatic Guided Vehicles (AGVs) Fusing MH-RRT with Improved TEB

In this paper, an AGV path planning method fusing multiple heuristics rapidly exploring random tree (MH-RRT) with an improved two-step Timed Elastic Band (TEB) is proposed. The modified RRT integrating multiple heuristics can search a safer, optimal and faster converge global path within a short time, and the improved TEB can optimize both path smoothness and path length. The method is composed of a global path planning procedure and a local path planning procedure, and the Receding Horizon Planning (RHP) strategy is adopted to fuse these two modules. Firstly, the MH-RRT is utilized to generate a state tree structure as prior knowledge, as well as the global path. Then, a receding horizon window is established to select the local goal point. On this basis, an improved two-step TEB is designed to optimize the local path if the current global path is feasible. Various simulations both on static and dynamic environments are conducted to clarify the performance of the proposed MH-RRT and the improved two-step TEB. Furthermore, real applicative experiments verified the effectiveness of the proposed approach

Computing and Information THE OBLIQUE WATER ENTRY IMPACT OF A TORPEDO AND ITS BALLISTIC TRAJECTORY SIMULATION

Abstract. To study the water entry ballistic trajectory of a torpedo, the wind tunnel experiment has been done based on the similarity principle. Then the drag coefficient of the torpedo is got when it enters the water, which is amended by the introduction of continuous supercavitation factor and local cavity effect factor. The vertical plane motion equations are established to get the torpedo’s trajectory. The large scale nonlinear transient finite element commercial software MSC. dytran is also used to simulate the initial water entry impact of the Disk-Ogive-Head[1] torpedo, including four special high-speed water entry attitude angles. Then the kinematics parameters as the tail of torpedo submerges in water are input into the motion equation as the initial conditions. Finally, two parts of the data are combined to get the whole kinematic and kinetic parameters. During the calculation, the ballistic modeling uses the cavitation number to determine the torpedo’s moving status: in the supercavitation stage, in partial cavity stage or in full wet navigation stage. The simulation results will do reference use to the following trajectory design. In addition, the water impact load and over load calculation of high-speed oblique water entry impact will help to design the intensity of torpedo’s shell

Research on Full-polarization Bistatic Scattering Characteristics of Aircraft

Whole space polarimetric bistatic scattering data of full-size aircraft targets were calculated via the mature electromagnetic calculation software. The fluctuation statistics characteristic of the polarimetric bistatic Radar Cross-Section (RCS) was carried out. It was found that the statistical properties of the four polarimetric types (HH, HV, VH, VV) of polarimetric bistatic RCSs are nearly the same, while the monostatic main and cross polarization RCSs statistical properties were quite different from each other. The characteristics of the distribution statistic for the monostatic and bistatic polarization ratio were carried out. Moreover, it was found that the cross-main polarization ratios were quite different, while the main polarization ratios were similar. The statistical results provide a theoretical reference for fully polarimetric bistatic radar aircraft target detection experiments

Research on Continuous Injection Direct Rolling Process for PMMA Optical Plate

Continuous injection direct rolling (CIDR) combined intermittent injection and rolling process is a new technology for molding optical polymer plates with microstructured patterns; research on forming PMMA optical plates is an aspect of it in this paper. The equipment of CIDR process consists of plastic injection module, precision rolling module, and automatic coiling module. Based on the establishing mathematical CIDR models, numerical analysis was used to explode the distribution of velocity, temperature, and pressure in injection-rolling zone. The simulation results show that it is feasible to control the temperature, velocity, and injection-rolling force, so it can form polymer plate under certain process condition. CIDR experiment equipment has been designed and produced. PMMA optical plate was obtained by CIDR experiments, longitudinal thickness difference is 0.005 mm/200 mm, horizontal thickness difference is 0.02/200 mm, transmittance is 86.3%, Haze is 0.61%, and the difference is little compared with optical glasses. So it can be confirmed that CIDR process is practical to produce PMMA optical plates

Comparison between numerical analysis and the levitation mass method measurement test of a spherical structure early impacting water

In order to precisely measure water impact loads of a spherical structure vertically dropping onto a calm water surface, a new validity check of the analysis using the levitation mass method experiment is proposed. The main feature of levitation mass method experiment is to obtain a better estimation of early water impact loads through the application of Doppler effect. Experimental results of different heights are verified based on the Assessment Index and are in comparison with the classical experimental data for validation purpose. It shows that the levitation mass method measurement is useful and effective to obtain the water impact loads for the crashworthiness analysis. Besides, early water impact hydrodynamic behaviors are simulated based on the nonlinear explicit finite element method, together with application of a multi-material arbitrary Lagrangian–Eulerian solver. A penalty coupling algorithm is utilized to realize fluid–structure interaction between the spherical body and fluids. Convergence studies are performed to construct the proper finite element model by the comparison with experimental results, where mesh sensitivity, contact stiffness, and time-step size parametric studies are thoroughly investigated. The comparisons between experimental and numerical results show good consistency by the prediction of the water impact coefficients on the structure.Published versio

Quantitative Assessment of Dynamic Stability Characteristics for Jet Transport in Sudden Plunging Motion

In this paper, we present a monitoring program of loss control prevention for airlines to enhance aviation safety and operational efficiency. The assessments of dynamic stability characteristics based on the approaches of oscillatory motion and eigenvalue motion modes for jet transport aircraft response to sudden plunging motions are demonstrated. A twin-jet transport aircraft encountering severe clear-air turbulence in transonic flight during the descending phase was examined as the study case. The flight results in sudden plunging motions with abrupt changes in attitude and gravitational acceleration (i.e., the normal load factor) are provided. Development of the required thrust and aerodynamic models with the flight data mining and the fuzzy logic modeling techniques was carried out. The oscillatory derivatives extracted from these aerodynamic models were then used in the study of variations in stability characteristics during the sudden plunging motion. The fuzzy logic aerodynamic models were utilized to estimate the nonlinear unsteady aerodynamics while performing numerical integration of flight dynamic equations. The eigenvalues of all motion modes were obtained during time integration. The positive real part of the eigenvalues is to indicate unstable motion. The dynamic stability characteristics during sudden plunging motion are easily judged by the values in positive or negative. The present quantitative assessment method is an innovation to examine possible mitigation concepts of accident prevention and promote the understanding of aerodynamic responses of the jet transport aircraft

Study on Frequency Stability of an Independent System Based on Wind-Photovoltaic-Energy Storage-Diesel Generator

Wind and photovoltaic power generation connected to the independent power system can save fuel, reduce carbon emissions, and provide significant economic and environmental benefits. Influenced by the characteristics of light resources and wind resources, the wind and photovoltaic output active power is characterized by volatility and randomness, which affects the frequency stability of the independent power system. In order to evaluate the frequency stability, in this paper, the simulation model of an independent power system is established, and the simulation model of a diesel generator, wind and photovoltaic are connected. Through droop calculation and Simulink simulation, the frequency characteristics of an independent power system under different working conditions are analyzed, and the maximum absorption capacity of wind and photovoltaic is studied. In an independent power system, when the new energy output is 25% of the total output, all the new energy output is cut off, the frequency drops by 0.5 Hz, and the frequency fluctuation is within the specified range

Increased Low-Frequency Resting-State Brain Activity by High-Frequency Repetitive TMS on the Left Dorsolateral Prefrontal Cortex

Beneficial effects of repetitive transcranial magnetic stimulation (rTMS) on left dorsolateral prefrontal cortex (DLPFC) have been consistently shown for treating various neuropsychiatrical or neuropsychological disorders, but relatively little is known about its neural mechanisms. Here we conducted a randomized, double-blind, SHAM-controlled study to assess the effects of high-frequency left DLPFC rTMS on resting-state activity. Thirty-eight young healthy subjects received two sessions of either real rTMS (N = 18, 90% motor-threshold; left DLPFC at 20 Hz) or SHAM TMS (N = 20) and functional magnetic resonance imaging scan during rest in 2 days separated by 48 h. Resting-state bran activity was measured with the fractional amplitude of low-frequency fluctuation (fALFF) and functional connectivity (FC). Increased fALFF was found in rostral anterior cingulate cortex (rACC) after 20 Hz rTMS, while no changes were observed after SHAM stimulation. Using the suprathreshold rACC cluster as the seed, increased FC was found in left temporal cortex (stimulation vs. group interaction). These data suggest that high-frequency rTMS on left DLPFC enhances low-frequency resting-state brain activity in the target site and remote sites as reflected by fALFF and FC