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981.
982.
On the basis of the Helmholtz decomposition, a grid‐free numerical scheme is provided for the solution of unsteady flow in hydraulic turbines. The Lagrangian vortex method is utilized to evaluate the convection and stretch of the vorticity, and the BEM is used to solve the Neumann problem to define the potential flow. The no‐slip boundary condition is satisfied by generating vortex sticks at the solid surface. A semi‐analytical regularization technique is applied to evaluate the singular boundary surface integrals of the potential velocity and its gradients accurately. The fast multipole method was extended to evaluate the velocity and velocity gradients induced by the discretized vortex blobs in the Lagrangian vortex method. The successful simulation for the unsteady flow through a hydraulic turbine's runner has manifested the effectiveness of the proposed method. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
983.
This paper presents some applications of the canonical dual theory in optimal control problems. The analytic solutions of several nonlinear and nonconvex problems are investigated by global optimizations. It turns out that the backward differential flow defined by the KKT equation may reach the globally optimal solution. The analytic solution to an optimal control problem is obtained via the expression of the co-state. Some examples are illustrated. 相似文献
984.
In this paper, a model is built to explore how the parameters (amplified spontaneous emission (ASE), temperature and round-trip loss) influence the output power in a thin-disk laser. It is found that optical efficiency of the disk laser is reduced with the increase of ASE, temperature or round-trip loss. The parameters are optimized to maximize the output power based on our model. We find that it is necessary to balance the need to lower the temperature with the need to control ASE during the optimization process. But the balance becomes more difficult to achieve with the increase of round-trip loss. We conclude that output power of more than 2.6 MW with a single disk can be achieved, but the necessary disk size (more than 0.5 m) is far beyond the actual technical limits. But it is possible to achieve output power of over a hundred kilowatts using a 10 cm disk in the near future. 相似文献
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Gangxian Zhu Dichen Li Anfeng Zhang Gang Pi Yiping Tang 《Optics & Laser Technology》2012,44(2):349-356
To investigate the influencing rules of the variations of powder and laser defocusing distance on surface quality and obtain the smooth surface of parts in laser direct metal deposition, the thin-walled metal parts were fabricated under three different powder defocusing distances and three different laser defocusing distances conditions. The experimental results show that a high surface quality can be obtained with the powder focussed below the substrate and laser focussed above the substrate process, and the variation in which the powder focus moves from above to below the melt pool plays a leading role and the variation in which the laser focus moves from above to below the melt pool plays a supplementary role in the influence on the surface quality. To explain the experimental results, a simple model of the track height is established. 相似文献
990.
Yan Sun Nianchen Zhou Wei Zhang Yaowen Li Zhenping Cheng Jian Zhu Zhengbiao Zhang Xiulin Zhu 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3788-3796
Two novel and well‐defined polymers, poly[6‐(5‐(diphenylamino)‐2‐((4‐methoxyphenyl)diazenyl)phenoxy)hexyl methacrylate] (PDMMA) and poly[6‐(4‐((3‐ethynylphenyl)diazenyl) phenoxy)hexyl methacrylate] (PDPMMA), which bear triphenylamine (TPA) incorporated to azobenzene either directly (PDMMA) or with an interval (PDPMMA) as pendant groups were successfully prepared via reversible addition‐fragmentation chain transfer polymerization technique. The electrochemical behaviors of PDPMMA and PDMMA were investigated by cyclic voltammograms (CV) measurement. The hole mobilities of the polymer films were determined by fitting the J‐V (current‐voltage) curve into the space‐charge‐limited current method. The influence of photoisomerization of the azobenzene moiety on the behaviors of fluorescence emission, CV and hole mobilities of these two polymers were studied. The fluorescent emission intensities of these two polymers in CH2Cl2 were increased by about 100 times after UV irradiation. The oxidation peak currents (IOX) of the PDMMA and PDPMMA in CH2Cl2 were increased after UV irradiation. The photoisomerization of the azobenzene moiety in PDMMA had significant effect on the electrochemical behavior, compared with that in PDPMMA. The changes of the hole mobility before and after UV irradiation were very small for both polymers. The HOMO energies (EHOMO, HOMO: the highest occupied molecular orbital) of side chain moieties of TPA incorporated with cis‐isomer and trans‐isomer of azobenzene in PDMMA and PDPMMA were obtained by theoretical calculation, which are basically consistent with the experimental results. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献