CAARC标准高层建筑模型表面风荷载的数值模拟研究

基于FLUENT软件平台,对长边迎风和短边迎风时,CAARC标准高层建筑模型表面风荷载进行了时均模拟和大涡模拟,并与风洞试验结果进行对比。结果表明,数值模拟所得迎风面平均风压与试验值较为接近;在背风面和侧风面,仅大涡模拟可较准确地反映平均风压分布趋势。数值模拟与风洞试验所得脉动风压的差异大于平均风压。长边迎风时,脉动风压模拟值与试验值的较大差异存在于背风面;短边迎风时,两者的较大差异存在于侧风面。CAARC模型周边流场运动形态将直接影响其表面风压分布特性。在背风面,顶部环流和尾流涡对控制风吸力大小;环流区域和涡对尺寸减小,则背风面风吸力降低。在侧风面,长边迎风时,旋涡脱落运动致使侧面风压分布趋于均匀;短边迎风时,较宽的侧风面尺寸促使分离剪切层发生稳定再附并形成有组织的旋涡结构,其将诱导产生梯度变化的平均风吸力和较为突出的风压脉动。

Movement of dispersed droplets of W/O emulsion in a uniform DC electrostatic field: Simulation on droplet coalescence

Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as well as its distribution,local concentration distribution and droplet size-velocity relation with the applied time of electric field. The simulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence.

Mean Residence Time of CO2 Molecules in Flexible ZIF-8 Cages Explored by Molecular Dynamics Simulations

The adsorption sites and diffusion mechanism of CO2 molecules in the flexible Zn（MeIM）2 （MeIM=2-methylimidazole） （ZIF-8） have been investigated by grand canonical Monte Carlo and molecular dynamics simulations. A reasonable time correlation function is for the first time constructed to explore the mean residence time of CO2 molecules in the ZIF-8 cages, suggesting that C02 molecules can remain in the same cage for up to several tens of picoseconds. Furthermore, we find that the mean residence time almost linearly increases with the increasing pressure （or loading） at 273 and 298 K.

Using Pipeline Instructions by Parallel Simulation of Mathematical Models

Simulation is an important and useful technique helping users understand and model real life systems. Once built, the models can run proving realistic results. This supports making decisions on a more logical and scientific basis. The paper introduces method of simulation, and describes various types of its application. The authors used the method of analysis of the creation and implementation of the programme code. The authors compared parallel instruction of computing defined to pipelined instructions. The power of simulation is that a common model can be used to design a large variety of systems. An important aspect of the simulation method is that a simulation model is designed to be repeated in actual computer systems, especially in multicore processors. For this reason, it is important to minimize average waiting time for fetch and decode stage instructions. The objective of the research is to prove that the parallel operation of programme code is faster than sequential operation code on the multi processor architecture. The system modeling uses methods and simulation on the parallel computer systems is very precise. The time benefit gained in simulation of mathematical model on the pipeline processor is higher than the one in simulation of mathematical model on the multi processors computer system.

Numerical analysis of periodic flow unsteadiness in a single-blade centrifugal pump

In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in detail by defining unsteady intensity and turbulence intensity in both rotor and volute domains under design condition Q=33 L s 1.The results show that the distributions of flow unsteadiness are the functions of impeller rotating angle and have complex unsteady characteristics.The obvious T u fluctuations can be also observed for different impeller positions.In addition,time-averaged unsteady intensity and time-averaged turbulence intensity were calculated by averaging the results of each mesh node for entire impeller revolution period to evaluate the strength distributions of flow unsteadiness directly and comprehensively.The accumulative results of an impeller revolution can directly show the positions and strength of the flow unsteadiness and turbulence intensity in both rotor and stator domains which can be an important aspect to be considered in the single-blade pump optimum design procedure for obtaining more stable inner flow of the pump and decreasing flow-induced vibration and noise.The flow unsteadiness in the side chamber cannot be neglected for an accurate prediction of the inner flow of the pump,and the optimizing design procedure for a single-blade pump impeller will not be accurate using CFD tool if the unsteady flow phenomenon in the side chamber is not considered.