1,721,167 research outputs found
Successive 3D FE analysis technique for characterization of fatigue crack growth behavior in composite-repaired aluminum plate
No full textAn analytical approach using successive finite element analysis technique was conducted to characterize the fatigue crack growth behavior of pre-cracked aluminum plates reinforced with composite patches. For single-sided repairs, due to the asymmetry and the presence of out-of-plane bending, crack front shape would become skewed curvilinear started from a uniform through-crack profile, as observed from previous studies. As the stress intensity factor (SIF) calculated at the crack tip is much influenced by crack front shape, it is necessary to predict the actual crack front shape evolution and take it into account for the accurate analysis of fatigue behavior. Present procedure performed a three-dimensional geometrically nonlinear finite element analysis to determine the SIF distribution at a set of points along the crack front, and then estimated the crack growth increments at these points by invoking a fatigue crack growth rate relationship (power-law relationship). A new crack front was then established for the next step by using a relevant remeshing scheme. Through conducting this procedure successively, the crack path of the patched plate as well as the fatigue life was evaluated with sufficient accuracy. The analytical predictions of both the crack front shape evolution and the fatigue life were in good agreement with the experimental observations. (C) 2004 Elsevier Ltd. All rights reserved
MAXIMUM POWER-CONVERSION EFFICIENCY FOR THE UTILIZATION OF SOLAR-ENERGY
No full textThe overall efficiency of solar thermal power plants is investigated for estimating the upper limit of their practical performances. This study consists of the theoretical optimization of the heat engine and the optimization of the overall system efficiency, which is the product of the efficiency of the solar collector and the efficiency of the heat engine. In order to obtain a more realistic performance of the solar thermal power plant, the solar collector concentration ratio, the diffused solar radiation and the convective and radiative heat losses of the solar collector are taken into account. Instead of the classical Carnot efficiency, the efficiency at maximum power is used at the optimal conversion efficiency of a heat engine. By means of simple calculations, the optimal overall system efficiency and the corresponding operating conditions of the solar collector are obtained. The results of the present work provide an accurate guide to the performance estimation and the design of solar thermal power plants
THE MAXIMUM POWER FROM A FINITE RESERVOIR FOR A LORENTZ CYCLE
No full textThe production of power from a heat source with finite heat-capacity rates has been studied for the Carnot and Lorentz cycles. The maximum power for the Lorentz cycle is twice that of the Carnot cycle for a given pinch-temperature difference
FINITE-TIME OPTIMIZATION OF A RANKINE HEAT ENGINE
No full textWe study the power and efficiency of a low grade energy Rankine heat engine which is widely used for power generation from heat recovered or collected at low temperatures. We develop an analytical formula for estimating the finite time Rankine power cycle efficiency at maximum power from heat reservoirs with finite heat capacity rate to obtain a bound on the power conversion systems. This simple formula does not need any detailed thermodynamic data. The accuracy of the procedure is shown by comparisons between the analytical values and those calculated using detailed thermodynamic data. It is also seen that the observed efficiency data on well designed real power plants fall in the domain anticipated theoretically. The efficiency at maximum power provides a measure of the power available in a practical Rankine heat engine
New fluorene-acceptor random copolymers: Towards pure white light emission from a single polymer
No full textPortfolio rebalancing model using multiple criteria
No full text[[abstract]]In order to achieve greater flexibility in portfolio selection, transaction cost, short selling and higher moments should be considered, and actual transactions should be reflected. In this paper, five portfolio rebalancing models, with consideration of transaction cost and consisting of some or all criteria, including risk, return, short selling, skewness, and kurtosis, are compared to determine the important design criteria for a portfolio model. Two examples are used to perform simulated transactions, and the results indicate that the investment strategy of 'buy and hold' does not produce better returns for all the portfolios in the first example, and the models with higher moments or adopting short selling strategy perform better while rebalancing in the second example. (C) 2010 Elsevier B.V. All rights reserved.[[note]]SC
Effect of oxygen pressure on Tl2Ca2Ba2Cu3O10±δ formation
No full textWe investigated the formation of Tl2Ca2Ba2Cu3O10 +/- delta as a function of oxygen pressure and temperature. Our results explain some previous difficulties in forming single-phase T12Ca2Ba2Cu3O10 +/- delta and suggest new routes for making bulk and thin-film Tl-Ca-Ba-Cu-O superconductors. In particular, we find that the temperature needed to form T12Ca2Ba2Cu3O10 +/- delta can be greatly reduced by using low oxygen pressures during synthesis.We thank P. E. D. Morgan for enlightening discussions of the liquid droplet formation mechanism. In addition, we thank R. J. Savoy, J. E. Vazquez, and G. Gorman for their technical support. This work was conducted under the auspices of the Consortium for Superconducting Electronics with partial support by the Defense Advanced Research Projects Agency (Contract No. MDA972-90-C-0021)
- …
