32 research outputs found
Ionic Conductivity in Laco<sub>1-X</sub>Mg<sub>X</sub>0<sub>3-δ</sub>: A Potential Cathode Material for Solid Oxide Fuel Cells
No full textABSTRACTA serious concern with present designs of solid oxide fuel cells is the requirement that “triple-point junctions” exist, sites at which the cathode, electrolyte and oxidizing gas are in simultaneous contact. Only at these junctions can the cathode catalyze the reduction of oxygen into 0= ions and initiate their subsequent transport through the electrolyte. Enhanced ionic conductivity in the cathode material may increase the surface area over which reduction can take place and relax the triple-point constraint. To this end, we have examined the electrical and structural properties of LaCo1-xMgx03-δ materials under various atmospheres. Oxygen ion transport in this and related ABO3 perovskites takes place via oxygen vacancy migration. We have opted to investigate the effect of Mg doping on the transition metal site in an effort to maintain a significant oxygen vacancy concentration in oxidizing atmospheres (as would be encountered during fuel cell operation) and to isolate the effects of A- and B-site doping.</jats:p
Effect of technetium-99 conjugated with methylene diphosphonate on IgM-RF, IgG-RF and IgA-RF
No full textFine flow field and unsteady hydrodynamic performance calculation for rudder cavitation
No full text[Objectives] In order to study the precise flow field of rudder cavitation and its related laws of unsteady hydrodynamic performance, [Methods] a propeller and rudder model of a certain ship is established, and a structure grid, SST k-ω turbulence model and VOF method are used to calculate the rudder cavitation. In order to understand the phenomenon of rudder cavitation, an observation experiment is carried out with a real ship. The calculated results are compared with the experimental results, proving the reliability of the numerical method. The periodic changes in rudder cavitation are then discussed and analyzed, and rudder cavitation is calculated on the basis of cavitation and non-cavitation under the two states of three kinds of rudder angles. [Results] The results show that when the cavitation range is small, it has little effect on average rudder force. As the cavitation range increases, its influence on average rudder force increases significantly while lateral rudder force decreases significantly. Once cavitation occurs, the amplitude of unsteady force increases greatly;the greater the cavitation range, the greater the amplitude of unsteady force. [Conclusions] The results of this study can provide technical support for assessing the hydrodynamic performance of rudders under cavitation conditions in the pursuit of optimal rudder design
Numerical simulation on bearing force of propeller for machining errors in non-uniform inflow
No full textIn order to study the bearing force caused by the machining errors of composite material propeller in non-uniform flow, the propeller was computed by changing the machining error of the propeller in six degrees of freedom, in which the main blade translates and rotates along the coordinate axis artificially by way of the statistical method. The bearing force of a DTMB P4119 propeller with a machining error was calculated according to the SST k-ω model and sliding meshing non-uniform flow to figure out the impact of various machining errors on the propeller, enabling a fundamental rule about the impact of various machining errors on a propeller's bearing force to be formed. The results show that vertical bearing force and horizontal bearing force increase linearly, and first-order blade frequency bearing force rarely changes with the increase of machining errors in each freedom; machining errors along the directions of diameter and pitch have a great impact on the propeller shaft's frequency bearing force. Therefore, we can put forward a more refined principle about the machining accuracy of propellers
Vibration Properties of Submerged Sandwich Cylindrical Shell Based on Wave Propagation Approach: Analytical and Experimental Investigation
No full textThe vibration properties of the submerged sandwich cylindrical shell with a viscoelastic core are investigated in this paper. Considering the acoustic-structure coupling, the analytical model of the submerged sandwich cylindrical shell that can handle three medium conditions including fluid-filled, fluid-loaded, and fluid-filled and -loaded is derived based on the wave propagation approach and the Flügge thin-shell theory. The vibration properties of the sandwich cylindrical shell under different medium and boundary conditions are analyzed, followed by a comparison of the damping effect of the constrained damping layer. Finally, an analysis is conducted on the influence of thicknesses of viscoelastic and constrained layers on vibration spectrum and natural frequency under fluid-filled and -loaded conditions. An experimental platform was established to conduct relevant experiments. Several important conclusions can be drawn
Structural Improvement of the ω-Type High-Speed Rail Clip Based on a Study of Its Failure Mechanism
No full textIn the circumstances of high-speed railways, the wheel-rail vibration is significantly aggravated by polygonal wheel wear and rail corrugation, which subsequently leads to the wheel-rail interaction at higher frequencies and potential failure of the rail fastening. In this paper, a ω-type clip of the fastening in the CRH high-speed rail was used to investigate the failure mechanism. First, a dynamic wheel-rail coupling model and a finite element analysis of the rail clip were developed, from which the rail vibration frequency and modal frequencies of the clip with different installation torques were obtained. The experimental tests and modal simulation results were mutually verified. In addition, the real-time vibration measurement and the wheel-rail wear monitoring were carried out at a CRH high-speed railway site. It was found that the resonant frequencies of the ω-type clip in the installation condition coincided with the excitation frequencies of the wheel-rail interaction induced by wheel-rail wear. The high-frequency dynamic failure mechanism of a typical ω-type clip, W300-1, is put forward for the first time. Moreover, a high-frequency rail clip fatigue test system was designed and developed specifically for this study. The loading excitation frequency of the clip test used was set as 590 Hz, and the loading amplitude was 0.05 mm. After 125-minute operation of the test system, the clip was broken at the expected location predicted by the FEA model. The high-frequency fatigue test result further verified that the failure mechanism of the ω-type clip was due to the resonance of the clip with its excitation force from the wheel-rail interaction. Finally, the clip was then structurally improved taking into account the stiffness and mass, which led to its resonant frequencies shifting away from the high-frequency excitation range, hence avoiding resonance failure of the subject clip
Study on the Coupling Frequency of Double-Sided Submerged Ring-Stiffened Cylindrical Shells
No full textBased on the Flügge theory and orthotropic theory, the acoustic vibration coupling model of ring-stiffened cylindrical shell is established by using the wave propagation method and virtual source method. And the effects of water immersion on both sides, free surface, and hydrostatic pressure on the cylindrical shell are considered in the coupling model. Muller three-point iterative method is used to solve the coupling frequency. The calculation results of degradation theory are compared with COMSOL’s calculation results and experimental results, respectively, which verifies the reliability of the theoretical method. Finally, the influence of fluid load, ring rib parameters, boundary conditions, hydrostatic pressure, and free surface on the coupled vibration of ring-stiffened cylindrical shell is analyzed by an example
Analysis on effect of shaft strut hydrofoil on anti-cavitation performance for surface ship
No full text[Objectives] In order to improve the anti-cavitation performance of shaft strut on a surface ship,[Methods] we study the front strut, compare the pressure distribution and anti-cavitation performance of the improved hydrofoil with those of the original hydrofoil at different attack angles of incident flows, and analyze the hydrodynamic performance of the improved hydrofoil at different flow rates and attack angles. We also predict the initial cavitation speeds of three types of hydrofoil according to the cavitation conditions,and verify the predicted values according to the calculation results.[Results] The results show that the hydrodynamic performance and initial cavitation speed of the improved hydrofoil-1 have been significantly improved when compared with those of the original hydrofoil at the incident flow attack angles of 0°,5° and 10°;the improved hydrofoil-2 has better anti-cavitation performance at the attack angles of 0° and 5°,while worse anti-cavitation performance at 10°;the initial cavitation speed predicted according to the pressure distribution is relatively close to the results based on the cavitation, which shows that it is feasible to predict the initial cavitation speed by this method when the accuracy requirement is not high.[Conclusions] This provides a technical approach for vibration and noise reduction of a surface ship
Damage Analysis of PR Type Fastener Clip for Vibration Reduction and Noise Suppression in Subway Circumstance
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