Dimensional analysis of thermal stratification in a suppression pool

Due to complexity of direct contact condensation (DCC), it is difficult to predict the thermal hydraulic phenomenon in a suppression pool (SP) of LWRs. Especially, the momentum, induced at condensation interfaces, depends on several interrelated parameters such as the steam mass flux, subcooling, and the diameter of the injection nozzle. Complicated interaction of those parameters creates difficulties in developing a comprehensive analytical model, which applicable to various conditions. To investigate the criteria of thermal stratification created by DCC, experiments were performed using a downsized suppression pool. Time resolved temperatures were acquired by vertically aligned thermocouples. Additionally, steam bubbles were visualized by a high speed camera in order to examine bubble shapes according to the mass flux and subcooling. Both steam bubble frequency and amplitude were analyzed for different DCC regimes. Finally, Richardson number was chosen as a suitable parameter for the dimensional analysis of experimental results. Corresponding velocity at far field in synthetic jet theory was employed to calculate Richardson number. The criteria for the occurrence of the thermal stratification were clearly determined according to the Richardson number.     

Effect of Richardson number on entropy generation over backward facing step

The flow over a backward facing step (BFS) has been taken as a useful prototype to investigate intrinsic mechanisms of separated flow with heat transfer. However, to date, the open literature on the effect of Richardson number on entropy generation over the BFS is absent yet, although the flow pattern and heat transfer characteristic both will receive significant influence caused by the variation of Richardson number in many practical applications, such as in microelectromechanical systems and aerocrafts. The effect of Richardson number on entropy generation in the BFS flow is reported in this paper for the first time. The entropy generation analysis is conducted through numerically solving the entropy generation equation. The velocity and temperature, which are the inputs of the entropy generation equation, are evaluated by the lattice Boltzmann method. It is found that the distributions of local entropy generation number and Bejan number are significantly influenced by the variation of Richardson number. The total entropy generation number is a monotonic decreasing function of Richardson number, whereas the average Bejan number is a monotonic increasing function of Richardson number.     

Construction of explicit and implicit dynamic finite difference schemes and application to the large-eddy simulation of the Taylor–Green vortex

A general class of explicit and implicit dynamic finite difference schemes for large-eddy simulation is constructed, by combining Taylor series expansions on two different grid resolutions. After calibration for Re→∞, the dynamic finite difference schemes allow to minimize the dispersion errors during the calculation through the real-time adaption of a dynamic coefficient. In case of DNS resolution, these dynamic schemes reduce to Taylor-based finite difference schemes with formal asymptotic order of accuracy, whereas for LES resolution, the schemes adapt to Dispersion-Relation Preserving schemes. Both the explicit and implicit dynamic finite difference schemes are tested for the large-eddy simulation of the Taylor–Green vortex flow and numerical errors are investigated as well as their interaction with the dynamic Smagorinsky model and the multiscale Smagorinsky model. Very good results are obtained.     

Richardson外推及其推广

本文分别针对微分方程数值求解和数值积分两类问题,讨论了一种常见的加速收敛方法-R ichardson外推及其推广,同时给出了一定的理论分析,对之进行了对比数值实验,验证了理论的正确性.     

A Generalization of the Kostka–Foulkes Polynomials

Combinatorial objects called rigged configurations give rise to q-analogues of certain Littlewood–Richardson coefficients. The Kostka–Foulkes polynomials and two-column Macdonald–Kostka polynomials occur as special cases. Conjecturally these polynomials coincide with the Poincaré polynomials of isotypic components of certain graded GL(n)-modules supported in a nilpotent conjugacy class closure in gl(n).     

A high order finite difference method with Richardsonextrapolation for 3D convection diffusion equation

In this paper, we extend the Sun and Zhang’s [24] work on high order finite difference method, which is based on the Richardson extrapolation technique and an operator interpolation scheme for the one and two dimensional steady convection diffusion equations to the three dimensional case. Firstly, we employ a fourth order compact difference scheme to get the fourth order accurate solution on the fine and the coarse grids. Then, we use the Richardson extrapolation technique by combining the two approximate solutions to get a sixth order accurate solution on coarse grid. Finally, we apply an operator interpolation scheme to achieve the sixth order accurate solution on the fine grid. During this process, we use alternating direction implicit (ADI) method to solve the resulting linear systems. Numerical experiments are conducted to verify the accuracy and effectiveness of the present method.     

Sixth-Order Compact Extended Trapezoidal Rules for 2D Schrödinger Equation

Based on high-order linear multistep methods (LMMs), we use the class of extended trapezoidal rules (ETRs) to solve boundary value problems of ordinary differential equations (ODEs), whose numerical solutions can be approximated by boundary value methods (BVMs). Then we combine this technique with fourth-order Padé compact approximation to discrete 2D Schrödinger equation. We propose a scheme with sixth-order accuracy in time and fourth-order accuracy in space. It is unconditionally stable due to the favourable property of BVMs and ETRs. Furthermore, with Richardson extrapolation, we can increase the scheme to order 6 accuracy both in time and space. Numerical results are presented to illustrate the accuracy of our scheme.     

A NOTE ON RICHARDSON EXTRAPOLATION OF GALERKIN METHODS FOR EIGENVALUE PROBLEMS OF FREDHOLM INTEGRAL EQUATIONS

In this paper, we introduce a new extrapolation formula by combining Richardson extrapolation and Sloan iteration algorithms. Using this extrapolation formula, we obtain some asymptotic expansions of the Galerkin finite element method for semi-simple eigenvalue problems of Fredholm integral equations of the second kind and improve the accuracy of the numerical approximations of the corresponding eigenvalues. Some numerical experiments ave carried out to demonstrate the effectiveness of our new method and to confirm our theoretical results.     

大黄鱼精子冷冻复苏后活力和超微结构的变化

大黄鱼精子以甘油为冷冻保存剂,经冷冻-解冻复苏后观察精子的活力和超微结构变化,并进行人工授精,观察冻精的受精能力.实验结果表明,冷冻精子的活力较高(83.1±6.2)%.大部分冷冻精子结构完整,进行人工授精可以获得较高的受精率(71.5±11.6)%.与鲜精对照组比较,仍存在差异(P<0.05).部分冷冻-解冻后的精子结构出现异常,畸形率达到29.3%(P<0.01).较常见的异常是精子质膜膨胀或破损,核膜消失,染色质解体,线粒体嵴消失,轴丝断裂成许多段等.冷冻精子结构异常可能是冻精解冻复苏后精子活力和受精力下降的主要原因.     

豆粕粉、肉骨粉和玉米蛋白粉替代部分鱼粉对大黄鱼生长与经济效益的影响

在海区小网箱中开展了豆粕粉加肉骨粉加玉米蛋白粉替代鱼粉的配合饲料饲养大黄鱼试验,结果表明:用豆粕粉加肉骨粉加玉米蛋白粉替代60%和30%鱼粉时,与同形态标准日粮相比,大黄鱼的生产性能和经济效益差异不显著,但30%的替代饲料鱼体生长更接近标准日粮。30%替代饲料的饲料系数、特定生长率、成活率、公斤鱼饲料成本、生物学综合评定值分别为1.74、1.385%、97.5%、9.4元和106.6%,与鲜杂鱼组相比,干基饲料系数低0.67、公斤鱼饲料成本低2.4元、生物学综合评定值高出6.6个百分点。以30%的替代量更为合适,而且膨化饲料优于粉状饲料。