An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distribution...An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distributions of flow velocities and suspended sediment concentrations along water depth, it significantly enhanced the applicability of 2D models in simulating open channel flows, especially in channel bends. Preliminary numerical experiments in a U-shaped and a sine-generated experimental channel indicate that the proposed method performs quite well in predicting the change of bed-deformation in channel bends due to suspended sediment transport. This method provides an effective alternative for the simulations of channel morphodynamic changes.展开更多
In order to quantify the losses of nanoparticles in a bend of circular cross-section, the penetration efficiency of nanoparti- cles of sizes ranging from 5.6 nm to 560 nm in diameter is determined as a function of the...In order to quantify the losses of nanoparticles in a bend of circular cross-section, the penetration efficiency of nanoparti- cles of sizes ranging from 5.6 nm to 560 nm in diameter is determined as a function of the Dean number, the Schmidt number and the bend angle. It is shown that the effect of the Dean number on the penetration efficiency depends on the particle size. The Dean number has a stronger effect on the penetration efficiency for small particles than for large particles. There exists a critical value of the Dean number beyond which the penetration efficiency turns from increasing to decreasing with the increase of the Dean number, and this critical value is dependent on the particle size and the bend length. The penetration efficiency increases abruptly when the Schmidt number changes from 7 500 to 25 000. Finally, a theoretical relation between the penetration efficiency and the Dean number, the Schmidt number and the bend length is derived.展开更多
We present fabrication and experimental measurement of a series of photonic crystal waveguides. The complete devices consist of an injector taper down from 3 μm into a triangular-lattice air-hole single-line-defect w...We present fabrication and experimental measurement of a series of photonic crystal waveguides. The complete devices consist of an injector taper down from 3 μm into a triangular-lattice air-hole single-line-defect waveguide with lattice constant from 410nm to 470nm and normalized radius 0.31. We fabricate these devices on a silicon- on-insulator substrate and characterize them using a t unable laser source over a wavelength range from 1510 nm to 1640nm. A sharp attenuation at photonic crystal waveguide mode edge is observed for most structures. The edge of guided band is shifted about 30nm with the 10nm increase of the lattice constant, We obtain high-efficiency light propagation and broad flat spectrum response of the photonic crystal waveguides.展开更多
Straight single-line defect optical waveguides in photonic crystal slabs are designed by the plane wave expansion method and fabricated into silicon-on-insulator （SOI） wafer by 248-nm deep UV lithography. We present...Straight single-line defect optical waveguides in photonic crystal slabs are designed by the plane wave expansion method and fabricated into silicon-on-insulator （SOI） wafer by 248-nm deep UV lithography. We present an emcient way to measure the light transmission spectrum of the photonic crystal waveguide （PhC WG） at given polarization states. By employing the Mueller/Stokes method, we measure and analyse the light propagation properties of the PhC WG at different polarized states. It is shown that experimental results are in agreement with the simulation results of the three-dimensional finite-difference-time-domain method.展开更多
Standard reducer bends have structural functions of both bend and reducer pipe at the same time. However, there is a lack of strength design method in the current codes. In order to develop the strength design method ...Standard reducer bends have structural functions of both bend and reducer pipe at the same time. However, there is a lack of strength design method in the current codes. In order to develop the strength design method of the reducer bends subjected to internal pressure, analytical formulas are re-examined. Finite element analysis and stress measurements of the reducer bend are carried out. It is found that it is not appropriate to analyze the reducer bends by using thin membrane theory. The formula derived directly from circumferential stress formula of reducer bends under internal pressure is conservative, which is further verified by the finite element analysis results and it can thus be applied to piping design.展开更多
Nanoparticle transport and deposition in bends with circular cross-section are solved for different Reynolds numbers and Schmidt numbers. The perturbation method is used in solving the equations. The results show that...Nanoparticle transport and deposition in bends with circular cross-section are solved for different Reynolds numbers and Schmidt numbers. The perturbation method is used in solving the equations. The results show that the particle transport patterns are similar and independent of the particle size and other parameters when suspended nanoparticles flow in a straight tube. At the outside edge, particle deposition is the most intensive, while deposition at the inside edge is the weakest. In the upper and lower parts of the tube, depositions are approximately the same for different Schmidt numbers. Curvatures of tube, Reynolds number, and Schmidt number have second-order, forth-order, and first-order effects on the relative deposition efficiency, respectively.展开更多
A numerical study of fluid flow and heat transfer of turbulent developing flow in 90°circular bends is presented using a finite-difference method bond CFD code. Results show an appreciable fluid redistribution pr...A numerical study of fluid flow and heat transfer of turbulent developing flow in 90°circular bends is presented using a finite-difference method bond CFD code. Results show an appreciable fluid redistribution process in large radius bend that brings about an overall heat transfer augmentation, especially at the outer side of the bend, and the significant deterioration at the inner side. The influence of two major parameters, namely, the bend-to-tube radius ratio and the bulk Reynolds number on the flow structure as well as on the local heat transfer is investigated.展开更多
In this paper, the computational results of a gas-particle two phase flow in a bend with a rectangular cross-section is presented. The movement of the particles in a curved pipe is numerically analyzed by using random...In this paper, the computational results of a gas-particle two phase flow in a bend with a rectangular cross-section is presented. The movement of the particles in a curved pipe is numerically analyzed by using random statistical method. The zones and rate of erosion on the wall in a bend are determined. The results are in accordance with the experiment, which indicate that the erosion is influenced by gas velocity, particle size and bend curvature.展开更多
基金Project support by the National Natural Science Foundation of China (Grant No: 50479034), the Natural Science Foundation of Tianjin (Grant No: 05YFSZSF02100).
文摘An algorithm to compute three-dimensional sediment transport effect was proposed in this paper to enhance the capability of depth-averaged numerical models. This algorithm took into account of non-uniform distributions of flow velocities and suspended sediment concentrations along water depth, it significantly enhanced the applicability of 2D models in simulating open channel flows, especially in channel bends. Preliminary numerical experiments in a U-shaped and a sine-generated experimental channel indicate that the proposed method performs quite well in predicting the change of bed-deformation in channel bends due to suspended sediment transport. This method provides an effective alternative for the simulations of channel morphodynamic changes.
基金supported by the Major Program of the National Natural Science Foundation of China(Grant No.11132008)
文摘In order to quantify the losses of nanoparticles in a bend of circular cross-section, the penetration efficiency of nanoparti- cles of sizes ranging from 5.6 nm to 560 nm in diameter is determined as a function of the Dean number, the Schmidt number and the bend angle. It is shown that the effect of the Dean number on the penetration efficiency depends on the particle size. The Dean number has a stronger effect on the penetration efficiency for small particles than for large particles. There exists a critical value of the Dean number beyond which the penetration efficiency turns from increasing to decreasing with the increase of the Dean number, and this critical value is dependent on the particle size and the bend length. The penetration efficiency increases abruptly when the Schmidt number changes from 7 500 to 25 000. Finally, a theoretical relation between the penetration efficiency and the Dean number, the Schmidt number and the bend length is derived.
文摘We present fabrication and experimental measurement of a series of photonic crystal waveguides. The complete devices consist of an injector taper down from 3 μm into a triangular-lattice air-hole single-line-defect waveguide with lattice constant from 410nm to 470nm and normalized radius 0.31. We fabricate these devices on a silicon- on-insulator substrate and characterize them using a t unable laser source over a wavelength range from 1510 nm to 1640nm. A sharp attenuation at photonic crystal waveguide mode edge is observed for most structures. The edge of guided band is shifted about 30nm with the 10nm increase of the lattice constant, We obtain high-efficiency light propagation and broad flat spectrum response of the photonic crystal waveguides.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60345008, 60537010, 60536030, and the National High Technology Research and Development Programme of China under Grant No 2005AA311030.
文摘Straight single-line defect optical waveguides in photonic crystal slabs are designed by the plane wave expansion method and fabricated into silicon-on-insulator （SOI） wafer by 248-nm deep UV lithography. We present an emcient way to measure the light transmission spectrum of the photonic crystal waveguide （PhC WG） at given polarization states. By employing the Mueller/Stokes method, we measure and analyse the light propagation properties of the PhC WG at different polarized states. It is shown that experimental results are in agreement with the simulation results of the three-dimensional finite-difference-time-domain method.
文摘Standard reducer bends have structural functions of both bend and reducer pipe at the same time. However, there is a lack of strength design method in the current codes. In order to develop the strength design method of the reducer bends subjected to internal pressure, analytical formulas are re-examined. Finite element analysis and stress measurements of the reducer bend are carried out. It is found that it is not appropriate to analyze the reducer bends by using thin membrane theory. The formula derived directly from circumferential stress formula of reducer bends under internal pressure is conservative, which is further verified by the finite element analysis results and it can thus be applied to piping design.
基金supported by the National Natural Science Foundation of China (No. 10632070)
文摘Nanoparticle transport and deposition in bends with circular cross-section are solved for different Reynolds numbers and Schmidt numbers. The perturbation method is used in solving the equations. The results show that the particle transport patterns are similar and independent of the particle size and other parameters when suspended nanoparticles flow in a straight tube. At the outside edge, particle deposition is the most intensive, while deposition at the inside edge is the weakest. In the upper and lower parts of the tube, depositions are approximately the same for different Schmidt numbers. Curvatures of tube, Reynolds number, and Schmidt number have second-order, forth-order, and first-order effects on the relative deposition efficiency, respectively.
文摘A numerical study of fluid flow and heat transfer of turbulent developing flow in 90°circular bends is presented using a finite-difference method bond CFD code. Results show an appreciable fluid redistribution process in large radius bend that brings about an overall heat transfer augmentation, especially at the outer side of the bend, and the significant deterioration at the inner side. The influence of two major parameters, namely, the bend-to-tube radius ratio and the bulk Reynolds number on the flow structure as well as on the local heat transfer is investigated.
文摘In this paper, the computational results of a gas-particle two phase flow in a bend with a rectangular cross-section is presented. The movement of the particles in a curved pipe is numerically analyzed by using random statistical method. The zones and rate of erosion on the wall in a bend are determined. The results are in accordance with the experiment, which indicate that the erosion is influenced by gas velocity, particle size and bend curvature.
