共查询到20条相似文献,搜索用时 15 毫秒
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This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal. In experiments, semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated. The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements. The modification of the spontaneous emission rate, which is reflected in the change of spectral shape and PL lifetime, is clearly observed. While an obvious increase in the PL lifetime is found at most wavelengths in the band gap, a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge. Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal. It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously. This finding provides a simple and effective way for improving the performance of light emitting devices. 相似文献
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一类非线性系统次优控制的灵敏度法 总被引:1,自引:0,他引:1
本文研究一类非线性定常系统的次优控制问题。通过在系统中引入 1个灵敏度参数并将系统变量关于灵敏度参数展开 Maclaurin级数 ,使求解最优控制的非线性两点边值问题化为一族线性两点边值问题。利用截取最优控制级数的有限项求得系统的次优控制律。仿真实例表明 ,该方法对非线性系统次优控制律的设计是有效的 相似文献
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The rotary ring flume is used to study the silty sand movement in a periodic alternating current.Characteristics of sediment movement of different coasts in the tidal current are summarized.More detailed analysis of erosion-sedimentation function in a numerical simulation is made.The equilibrium sediment concentration is advanced.Based on the equilibrium sediment concentration,the seabed erosion-sedimentation index is derived and the seabed erosion-sedimentation calculation is analyzed.The seabed erosion-sedimentation index is used to calculate the seabed evolution of Yangshan sea area and a good agreement with field measurements is obtained. 相似文献
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The dynamic stability of the heave motion of marine cable-body systems operating in alternating taut–slack conditions is considered, based upon a single-degree-of-freedom model. In this model the fluid damping is linearised and the cable is replaced by a spring of bi-linear stiffness. The period-one Poincare map is derived, and its stability is analysed by examining its Jacobian matrix. Numerical simulations are also carried out to show the transition from a periodic response to a chaotic one through period doubling. 相似文献
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In many engineering problems one deals with quantities that must be considered to be of a stochastic or random nature. This is true for the natural environment such as wind, waves, and earthquakes, which are the driving mechanism behind the loadings on a wide variety of land-based and offshore structures. From a design perspective it is important to determine the expected highest value of a stochastic process, and structural fatigue life. The relevant procedures are reasonably well established for processes that have narrow band spectra, but it is much less clear how to deal with non-narrow band cases. In this paper it is shown that the extremes of a Gaussian, non-narrow band process are asymptotically equal to the extremes calculated according to the narrow band formula. Also demonstrated is that fatigue estimates may, with good accuracy, be based on the narrow band formula unless the bandwidth becomes extremely large. These statements are illustrated by examples of a process with (1) a low pass box spectrum, and (2) a Pierson–Moskowitz wave amplitude spectrum. It is also shown that the bandwidth parameter may in some cases be counter-intuitive, as the Pierson–Moskowitz spectrum has a larger bandwidth parameter than the box spectrum, even when both cover the same frequency range. 相似文献
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S. A. Ermakov I. A. Kapustin O. V. Shomina 《Izvestiya Atmospheric and Oceanic Physics》2014,50(2):204-212
Investigation of damping of gravity-capillary waves (GCWs) in the presence of turbulence is a classical hydrodynamic problem which has important geophysical applications, one of which is related with the problem of forming a radar and optical image of a ship wake on wavy water surface. In this work a new method for the laboratory study of surface wave damping in turbulized liquid is described and the results are presented. The damping of standing GCWs by turbulence on the water surface in a tank mounted on a vibration table is studied. GCWs and turbulence are excited using a two-frequency mode of vibration table oscillations. A high-frequency small amplitude signal is used for parametric GCW excitation; a low-frequency large amplitude signal is used for generating turbulence due to water flowing through a fixed perforated grid submerged into the tank. The coefficient of GCW damping is determined by measured threshold of parametric excitation of the waves; turbulence characteristics are determined by the PIV and PTV techniques. Dependences of GCW damping coefficients on their frequency at different turbulence intensities are obtained, estimates for turbulent viscosity are presented, and a comparison with empirical models proposed earlier is performed. 相似文献
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三体船的水动力性能是目前水动力学研究的热门。对于中高速三体船来说,其静水阻力的很大一部分由兴波阻力构成,而对于兴波最大的影响因素就是片体位置的布局。以一艘圆舭型三体船为研究对象,运用黏流计算流体力学(CFD)方法模拟分析4种不同片体位置对三体船静水阻力和兴波干扰的影响。数值计算采用自主研发的黏流CFD求解器naoe-FOAM-SJTU。数值预报得到三体船静水阻力结果与模型试验结果吻合较好,验证了当前CFD方法预报三体船阻力的可靠性。通过不同片体位置三体船阻力计算发现,方案4的船型方案阻力最优,且通过细节的主片体间兴波干扰流场的结果给出了不同片体布置方案对三体船阻力和兴波的影响。 相似文献
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O. S. Ermakova S. A. Ermakov Yu. I. Troitskaya 《Izvestiya Atmospheric and Oceanic Physics》2007,43(1):86-94
The evolution of a turbulent layer excited by standing surface parametric waves is studied experimentally. The time dependence of the depth of the turbulized region is obtained. It is found that the thikness of the layer is described by a nonlinear dependence as distinguished from the previously obtained theoretical results. The dynamics of turbulent-layer embedding is described on the basis of a semiempirical theory and the assumption that the outer scale of turbulence is constant. Satisfactory agreement with experimental data is obtained. In the context of the proposed model, a relationship is found between the quantities characterizing the turbulence and surface waves. The dependence of the steepness of surface waves on the acceleration of the bottom is obtained experimentally. The data obtained in this study can be used for estimation of turbulence generation during a submarine earthquake. 相似文献
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讨论了一类离散非线性系统降维观测器的存在性。对给定的Lyapunov函数,在保证观测误差渐近稳定的条件下,给出了该离散非线性系统降维观测器的设计方法。用数值例子说明了该设计方法的有效性。 相似文献
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J.M. Huthnance 《Estuarine, Coastal and Shelf Science》1982,15(3):277-299
We consider a model where the fluid depth depends on both horizontal coordinates, quasi-steady depth-uniform non-divergent fluid flow is governed by inertial, pressure and bottom-frictional forces, sand transport is proportional to the cube of the instantaneous current but augmented by a down-slope component and by wind-wave action, and sand is conserved.It is found that low parallel banks grow fastest, so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate. The inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump. A small bump can evolve to an equilibrium bank (typically after an initial rapid extension across the tidal currents) provided that sand is sufficiently restricted and particularly if some wind-wave action prevents growth up to the sea surface. Sand banks are likely to be in a late stage of evolution, when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition. The equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents, or when sand is abundant. 相似文献
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A numerical model is developed by use of the boundary integral equation method to investigate the responses of a two-dimensional floating structure.The structure under consideration consisting of two pontoons,is connected by a rigid framework,and linked to the sea floor by a mooring system.The theoretical conception is based on potential theory with linear external forces,and applied to an arbitrarily shaped body and water depth.The discussion includes the influence of draft and space between pontoons on the responses of the floating structure.Finally,the validity of the method is adequately verified by experimental results. 相似文献
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传感器优化配置的修正逐步累积法 总被引:1,自引:0,他引:1
讨论了模态实验中传感器的配置问题。利用结构振型矩阵转置的 QR分解得到传感器的初始配置。以模态置信度 MAC矩阵的最大非对角元为目标函数 ,利用本文提出的修正逐步累积法得到传感器的配置 ,并提出传感器配置必须结合优化效果和经济性 2方面综合考虑 相似文献
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The problem of propagation of obliquely incident surface water waves over a pair of asymmetrical rectangular trenches in a channel of finite depth is examined for its solution. The mathematical problem is handled for its numerical solution with the aid of a system of singular integral equations of first kind. The resulting integral equations are solved numerically by using suitably designed polynomial approximations of the unknown functions. System of linear algebraic equations is obtained by utilizing the zeros of Chebyshev polynomial of first kind as collocation points and hence the occurrence of ill-conditioned matrix is avoided. The effectiveness of the pair of trenches is studied by analyzing the physical quantities namely the reflection and transmission coefficients. As a special limiting case, the results for a single trench problem are derived and are found to be in excellent agreement with the results available in the literature. The effect of various parameters are analyzed through different graphs for a pair of asymmetrical trenches. The energy balance relation is derived and used to check the accuracy of numerical results. 相似文献
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Applicationofone-linemodeltothepredictionofshorelinechangeQinChongrenandHeJiangcheng(RecivedJuly20,1995;acceptedJanuary15,199... 相似文献
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In this article, two full-scale pile loading tests were conducted to observe the field performance of the super-long bored piles, and a simplified approach for nonlinear analysis of the load-displacement behavior of a single pile was presented. The field tests on piles indicates that, under the maximum test load, more than 70% of the pile top settlement is caused by the compression of pile shaft. For practical purposes, the pile top settlement can be reduced through improving the pile shaft strength. When the load reaches the maximum test load, the proportion of the load carried by the pile tip is approximately 30%. The super-long pile is functioning as an end-bearing friction pile. The skin friction at shallow depth is fully mobilized and decreases from a peak value with increasing load. However, the skin friction of deeper soil is not fully developed due to less relative displacement. Furthermore, a BoxLucas1 model is used to capture the relationship between unit skin friction and pile-soil relative displacement, whereas a hyperbolic model is used to describe the relationship between toe stress and pile base displacement. Based on the BoxLucas1 model and the hyperbolic model, a load transfer method is used to clarify the response of a single pile, and a computational flow chart is developed. The efficiency and accuracy of the present method is verified using the field tests on piles. The proposed simple analytical approach is economical and efficient, resulting in savings in time and cost. 相似文献