Theory and approach to reactive power flow tracing

Based on an analysis of the characteristics of reactive power supplies and reactive loads, this paper presents a method for forming a lossless reactive network using an equivalent technique of modeling the branch admittance as a reactive power supply and the branch power loss as a virtual load. A downstream distribution matrix for a power system is constructed based on its reactive lossless network, and the analytical model and its algorithm for tracing reactive power flow (TRPF) is proposed. A method dealing with the abnormal downstream distribution matrix of active power flow also is discussed. The main advantage of the proposed method is that the matrix theory is used to analyze the TRPF model directly and no assumption on the flow distribution is needed. Case studies of the IEEE14 Bus and IEEE30 Bus systems demonstrate the accuracy and the validity of the proposed method.     

Dynamic analysis and optimization of gear trains in a megawatt level wind turbine

Through coupling vibration analysis of the transmission system of a 1.5 MW wind turbine gearbox, a torsional vibration model of a gear drive system in wind turbines is established. The fourth order Runge Kutta integration method is applied to calculate the dynamic response of a gear system caused by wind loads, time varying meshing stiffness, and system damping. The harmonic balance method is used to find the analytic solution. Based on the solution, a mathematical model for optimum gear system design is established. The model aims at minimizing the vibration acceleration of the planet gear and the total mass of the gear transmission system. The optimization toolbox in MATLAB program is adopted to obtain the optimal solution. A calculated example shows that the primary natural frequency of the gear system has been raised, the dynamic properties of the gear train have been improved remarkably, and the total mass of the gear train has been decreased.     

Contact analysis of a new style planetary reducer with a double crank and internal gear board

To address the problems of low carrying capacity and short life of bearings in current ring reducers, a new type of ring reducer is proposed which consists of a two stepped transmission. One is a planetary transmission, and the other is an N type planetary transmission with a low tooth number difference. Based on the analysis of structural features, the transmission principle, and a transmission load situation, a contact finite element model of the new type of ring reducer is set up, and the stress value and the actual pairs of meshing teeth are derived by calculation. Based on gear modification research theory, the second stage transmission gear pairs of the new reducer are modified on its teeth profiles. Results demonstrate that the load capacity of transmission gear pairs have been enhanced greatly.     

The optimal energy efficiency of wireless networks nodes based on solar cells

To improve the energy efficiency of solar cells in wireless sensor networks nodes, the energy relationship between solar cells and the wireless sensor networks nodes is studied. An adaptive algorithm is adopted to ensure the wireless sensor networks work normally at different sunlight intensities. An energy model is designed that reveals the energy relationship between the output power of the solar cells and the power of nodes working normally at a standard sunlight intensity. The experimental results show that the model represents the adaptive energy relationship between the solar cells and the nodes, ensures that the nodes work stably in a long term, and extends the life cycle of the sensor networks as long as possible. The model has important guiding significance for wireless sensor networks designation.     

Key rock strata effecting analysis on surface boreholeshear deformation fracture

A good method for creating a surface borehole for withdrawing coal strata methane is to build before excavation and use during the whole process. But the excavation greatly affects the overlying rock strata, and when the excavation face passes through the     

Numerical analysis on the performance of spiral antennas

The surfaces of the Planar Spiral Antennas and Conical Spiral Antennas are analyzed with planar triangle. The surface currents of the antennas are solved by using the Method of Moment (MoM) based on the RWG basis function. The input impedance, directivity, gain, radiated power and radiation field of the antenna can be found. The results indicate that, in very wide frequency band, the value of the input impedance equals to the theoretical value of Self-Compensated antennas (in agreement with Babinet-booker' principle), which is,188.5 ohm , the half of the wave impedance of free space, while the directivity, gain and radiated power are stable within the frequency band. When the antenna is driven by the signal of derivative Gaussian pulse, the radiating electric field waveform is obtained by the Fourier transform. When the spiral antenna is used as the pulse radiation antenna, the waveform of the radiation electric field shows the characteristics of the Gaussian quadratic differential.     

Numerical analysis of noise radiation from motorcycle engine shell

FEM/BEM (Finite Element Method/Boundary Element Method) mode analysis of the noise radiation from motorcycle engine shell is conducted. The natural frequency is compared between FEM/BEM analysis and experimental analysis. The FEM/BEM results are agreed with the experiment results, which proves that the finite element model is correct. The frequency response is analyzed and the structure’s noise radiation is simulated by means of FEM/BEM, in order to predict the noise radiation from the motorcycle engine shell and gain the sound field characteristic outside the structure. The calculation data is compared with the experiment data in different frequency bands. The result shows high accordance, which indicates that this method is effective.     

Simplifying and validating the model of wet flue gas desulphurization spray tower for 660MW units

The wet limestone gypsum flue gas desulphurization system for 660 MW units of a thermal power plant is taken as the object, based on the study of the mass transfer between the gas phase and the liquid phase、chemical reaction mechanism in desulphurization tower and reasonable simplified hypothesis, the turbulent mathematical model of the spray type tower is developed by the methods of concentration of parameters and module modeling. The model is validated by the test of stable state and the turbulent experiments, which can be used as the basis for developing the real training simulation model of the desulphurization system.     

Maximum tree method based aspect mining method

By means of discovering crosscutting concerns from legacy systems, aspect mining intends to help migrate the systems to an aspect oriented design. An improved method based on maximum tree method for aspect mining is presented. The method uses aspect ideas to capture the runtime method call information by mining crosscutting concerns from dynamic behaviors, and then constructs a method call relationship data matrix. Based on fuzzy similarity relation theory, by introducing the similarity, an object similarity matrix is constructed, and the maximum tree method is used to identify the crosscutting concerns in the system. The method can provide a basis for system’s software reconstruction and reusability. An experiment is conducted to verify the validity of the method. Compared with the existing typical mining methods, the method shows the virtue of clear implementation and high efficiency.     

The Effect of Slabs on the Failure Mode of Reinforced Concrete Frame Structures

A majority of reinforced concrete frame structure failure patterns resulting from the May 12, 2008 earthquake in Wenchuan County, P. R. China were analyzed. It was found that the main failure mode of frame works was “strong beam, weak column”, which conflicts with the design criteria of “strong column, weak beam”. The cause of this failure pattern was analyzed. A new concept is put forward that should be considered in design work. The over strength caused by slabs connected monolithically to the beams is analyzed. The joint types, transverse beam stiffness and lateral drift influence the reinforcing effect of the sla, Moreover, a reinforced concrete frame model was simulated using the program ABAQUS. The slab reinforcement stress distributions at different lateral drifts were analyzed and the effective flange width value proposed.