Abstract Due to the viscous shear stress, there is an obvious error between the real flow rate and the rotameter indication for measuring viscous fluid medium. At 50 cSt the maximum error of DN40 orifice rotameter is up to 35 %. The fluid viscosity effects on the orifice rotameter are investigated using experimental and theoretical models. Wall jet and concentric annulus laminar theories were adapted to study the influence of viscosity. And a new formula is obtained for calculating the flow rate of viscous fluid. The experimental data were analyzed and compared with the calculated results. At high viscosity the maximum theoretical results error is 6.3 %, indicating that the proposed measurement model has very good applicability.
Resonant properties of a cylindrical microwave cavity with ceramic material for a new type of rubidium clock are studied by mode matching method. The microwave cavity works at a certain frequency such as 6·835 GHz by accommodating a glass bubble containing rubidium vapour. To make electromagnetism focus on the centre of the cavity and further miniaturise the cavity to a large extent, a ceramic dielectric ring is installed in the inner layer of the glass bubble. In order to study the main factors of influencing resonant characteristics, resonant frequencies of TE011 mode are calculated and compared with simulated results. The results show that theoretical computations are in good agreement with simulations. In addition, the effects of the ceramic material and rubidium vapour on resonant frequency are analysed. This work is of great significance for cavity design and theory perfection in atomic clock.
We propose a dual-wavelength intra-cavity absorption sensor based mode competition. The sensitivity of output power to relative cavity loss in different pump current is studied experimentally by defining a sensitivity enhancement factor (SEF). A measurement sensitivity of 158.5 times that of a single-pass absorption sensor is achieved.
In this paper, we report on the near-field distribution of multi-core photonic crystal fiber lasers. The supermodes of photonic crystal fibers with foursquarely and circularly distributed multi-cores are observed. The supermode properties are investigated by using full-vector finite-element method (FEM). The mode operations of our 16-core foursquare-array and 18-core circular-array photonic crystal fiber lasers are simulated by the COMSOL Multiphysics software. The near-field distribution patterns of in-phase supermode are presented.
The sampling speed is limited by CPU's running speed in usual data acquisition system.A method of high speed sampling is introduced in order to resolve the problem in this paper.USB and GPIF are used for transmission and handshake.The CPU resource is released to other applications as soon as the sampling and transmission are comple- ted.EZ-USB FX2's resources are fully used in this method.This method is analyzed and validated.And many debug- ging skills are described in the paper.
Abstract The high-temperature gas generated by the missile launch will cause serious ablation to the launcher. In order to study the thermal protection of the launch device, a scheme of arranging vertical upward water spray pipes in the deflector is proposed, which realizes the thermal protection of the launcher by the vaporization and heat absorption principle of liquid water and the impact effect. Based on the Mixture multiphase flow model, coupled with the vaporization equation of liquid water and the component transport model, the cooling mechanism and effect of the proposed scheme are analyzed. Meanwhile, the numerical simulation of gas flow field under different water injection speed conditions is carried out, and the change law between different water injection speed and cooling effect is obtained. The results show that after the water sprayed by the pipes laid in the deflector, a water film will be formed on the surface of the deflector and the wall of the launch vehicle, which plays a role in the isolation of the high-temperature gas. The temperature of the launch device drops significantly. With the increase of water injection speed, the thickness of the water film formed on the surface of the deflector and the wall of the launch vehicle becomes larger, and the isolation effect on the gas becomes more obvious. When the water injection speed increases to 55m/s, the vaporization rate of liquid water in the direct impact area of the gas jet reaches the maximum, the heat absorption is the most at the same time, and the temperature in this area reaches the lowest level. The cooling effect of the water spray speed of 55m/s on the flow field is the best. This conclusion can provide a theoretical reference for the thermal protection design of missile launcher.
Abstract “Neighborhood” as the principle of “the closer the distance, the more relevant the attributes”, is often used as a key driving factor for the urban dynamic modeling of cellular automata; however, the current implementation of the “neighborhood” idea is mostly adopted Mean probability method. This method affects the accuracy of urban dynamic simulation to a certain extent because it ignores the spatial heterogeneity of neighboring cells. Based on the random forest method to evaluate the suitability probability of land use, this study uses the intensity gradient change characteristics of the luminous data to endow the traditional neighborhood cell heterogeneity characteristics, and builds a random forest neighborhood heterogeneity CA model (Random forest Neighborhood Heterogeneity Cellular Automata, RF-NH-CA), and verified the effectiveness of the model by simulating the changes in urban land use in the 21 districts of Chongqing’s main city from 2010 to 2017 through a multi-scheme comparative experiment. The results showed that the overall simulation accuracy of the RF-NH-CA model reached 97.59%, and the Kappa coefficient reached 0.7434; compared with the traditional models RF-CA, ANN-CA and Logistic-CA, FoM increased by 0.0274,0.0383,0.0579, respectively. The Kappa coefficient increased by 0.0162,0.0229,0.0351 respectively. Studies have shown that giving the neighborhood cell heterogeneity through luminous data has played a role in improving the accuracy of land use simulation, which is more in line with the real urban expansion.
Resonant properties of HE111 mode of a complicated microwave cavity with ceramic material, used in rubidium clock, are studied by mode matching method. The microwave cavity works at a certain frequency such as 6835GHz by accommodating a glass bubble containing rubidium vapor. To make electromagnetism focus on the centre of the cavity for energy exchange and further miniaturize the cavity to a large extent, a ceramic dielectric ring is installed in the inner layer of the glass bubble. In order to study main factors in∞uencing resonant characteristics, resonant frequencies of HE111 mode are calculated through eigen equation and compared with simulated results. The results show that theoretical computations are in good agreement with flnite element simulations. In addition, the efiects of loaded dielectric and rubidium vapor on resonant frequency are also analyzed. This work is of great signiflcance for the miniaturizing of the cavity and theory perfection in atomic clock.
We propose a novel surface plasmon resonance sensor design based on a grapefruit photonic crystal fiber. In such a sensor, phase matching between plasmon and a core mode is achieved by introducing microstructure into the fiber core. Using the finite element method, the confinement loss of the fiber is calculated to measure the sensitivity of the sensor. Simulation results show that this kind of sensor has an excellent effect, with the amplitude resolution to be as low as 2.88×10−5 RIU and the spectral resolution to be 6.67 ×10−5 RIU.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)