Advanced Materials Research Vols. 718-720

Abstract: This paper studied the concentration distribution of gas extinguishing agent numerically in high velocity flow field. Civil aircraft power plant compartment has been a difficult area for its high velocity flow field formed after fire happens. Focusing on this issue, certain results, such as mass flow rate of agent gas, total mass of agent and extinguishing efficiency were presented. A typical apparatus of fire extinguishing system was set up, and its fire-fighting efficiency was evaluated. Critical ratio of mass flow rate and flow velocity, gas discharge time and locations of gas sample tubes were recommended. The results and data can provide a practical way in fire extinguishing system evaluation in civil aircraft power plant compartment.

Abstract: A non-contact testing method is proposed for encapsulation treated or insulation coated switching power supplies, which is implemented by reconstructing the pulse width modulation (PWM) signal of switching converters from the near field radiation of magnetic components. The radiation pattern of a buck converter is investigated, and the magnetic field sensing probe and PWM signal reconstruction circuit are also illustrated. The reconstruction testing is carried out on a buck converter; the duty cycle error of the reconstructed PWM signal is less than 0.2%, which validates the proposed method.

Abstract: Optical freeform surfaces are complex surfaces with non-rotational symmetry that break through the limitations of conventional optical element, and are widely used in advanced optics application for system configuration simplifying and performance enhancing. Interferometric test with computer generated holograms (CGH) has been widely used in the aspherical surfaces testing for their unique wavefront transformation, as well as the freeform surfaces testing with high precision. As an important parameter, it is different at the definition of asphericity in freeform surfaces manufacture and test. Asphericity for interferometric test which verifies the testing ability of the CGH and determines testing system initial configuration was calculated with minimum maximum angle deviation. Reverse ray tracing could get the optimal solution of CGH local phase at certain location in the CGH design. For the non-rotational symmetry of freeform surfaces, the phase of sample point in CGH surface should be calculated in three-dimensional coordinate system. The calculation method of discrete phase was deduced by ray tracing, as well as the phase distribution on freeform surface were proven by calculating in such way. The results were compared with simulation by optical design software. It shows that the method is right and high accuracy to be used in the CGH design for the freeform surfaces.

Abstract: To execute stall active control technology effectively and make clear of stall inception induced by modal disturbance, this paper carries out the correlative research on modal disturbance and rotating stall on the two-stage low-speed axial compressor. The results indicate that the stall inception of the compressor is modal style and the modal oscillation propagates at 38% rotor speed while the stall cell propagation speed is 42% rotor speed. The phase angles of modal oscillation and rotating stall along the axial direction are different, but their trajectories are both similar to the blade passage shape. The stall mechanisms of modal-type and spike-type inceptions are different. It doesnt appear that leading-edge tip clearance flow spillage blow the blade tip while the modal-type stall formation.

Abstract: A three-dimensional horizontal axis wind turbine model was experimentally studied. The experiment was carried out in a laboratory wind tunnel. With PIV measurement, details about flow fields in the near wakeof the turbine blade were obtained. The result shows vortices generateon the tailing edge of the blade, and propagatedownstream then dissipate into small vortices. Vortices also generate at the tip of the blade, propagate downstream and along the radial direction then dissipate. The dissipation of the tip vortex is slower than the former. We also find that the wake of turbine blade rotates in the opposite direction of the blade.

Abstract: The elastic tube bundle is a new-style heat exchange element that can enhance heat transfer efficiency and reduce energy consumption. It is difficult to obtain exact analytical solutions because of the complex shape and constraint condition. An experimental modal testing technique is applied to get the dynamic properties. Some issues to which one should pay attention during the experiment are emphasized. Natural frequencies and mode shapes are identified from the test and compared to numerical results. Agreement is found for most frequencies of interest. But, some discrepancies exist for the vibration in-plane due to the inevitable operation error.

Abstract: In some cases, combined use of a few centrifugal pumps can be seen frequently. In some working conditions, some of them may work under abnormal mode (take turbine mode for example). So it is needed to know the characteristics of pumps under the modes. One way to obtain the characteristics is test. In this paper, a nonlinear mathematical model is presented to describe the characteristics. The solution to the model is performed by a specialized particle swarm algorithm. A numerical example shows good agreement between model curves and pump test data.

Abstract: Refuse truck accounted for 70% of the sanitation vehicle, which was the major heavy duty vehicle type in city. Therefore its fuel economy and emission characteristics were under higher requirements. This research did the emission test on the chassis dynamometer by using compressed truck, testing C-WTCV and CCBC circle emission, and fuel consumption respectively. The research showed the Km fuel consumption of CCBC circle was about 1.3 times of the C-WTVC from the analysis of fuel consumption and the emission of CO2.From the analysis of emission factor, the emission of NOX and CO of the CCBC circle was both higher than the C-WTVC, respectively 1.9 times and 1.4 times. However, the emission of HC was only 36% of the C-WTVC. C-WTVC was very similar to the motor of the CCBC circle in city, however the motorway cycle and emission both had significant difference from CCBC circle.

Abstract: A nonlinear modeling of magnetic inductor with hysteresis using PSpice is presented. The describing functions are used to model the high frequency hysteresis to make up the defect of Jile-Atherton static hysteresis mathematical model. The subcircuits which include the nonlinear magnetic inductor are used to the circuit of filter by PSpice. The hysteresis-related characteristic of intermodulation distortion and corner frequency can be predicted by the improved inductor subcircuit models have been verified experimentally.

Abstract: The problem of output feedback stabilization for networked control system with time-varying delay is discussed. By constructing a novel LyapunovKrasovskii functional,the output feedback controller is obtained in terms of LMIs. The dynamics information of the time-varying delay is taken into account in the structured controller, and the obtained result is less conservative. A numerical example is given to illustrate the effectiveness of the presented method.