驯“辐”黑色幽灵——电磁辐射的成因、影响和应对策略

科学将电磁波称为“幽灵电波”，它看不见、闻不到、摸不着，却叉无时无刻不影响着我们的身体健康，干扰着我们PC的正常工作。倡导健康使用电脑，是我们现代计算机的一贯态度。本文将带领大家一步一步的揭开电磁辐射的神秘面纱，告诉大家如何驯化这个恐怖的幽灵。     

Unsteady RANS modelling of flow past a rectangular cylinder: Investigation of Reynolds number effects

The unsteady flow field around a two-dimensional rectangular prism with a fineness ratio (chord-to-thickness) of 5.0, is studied using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. A noncommercial unstructured flow solver is used in the simulations at various Reynolds numbers (from 26,000 to 1,850,000 based on the chord length), two different angles of attack (0° and 4°) and low Mach number (0.1). A grid-convergence study is presented in order to investigate the dependence of the flow solution on the spatial and temporal discretization. Results obtained with one- and two-equation turbulence models are compared, including models based on the Explicit Algebraic Reynolds Stress (EARSM) approach. The aim of this work is to assess the capability of the computationally efficient two-dimensional URANS calculations to predict the features of complex massively separated flow around this type of geometry. A further goal is to use numerical simulations to investigate the strong Reynolds number effects observed in wind-tunnel experiments. Satisfactory agreement with the wind-tunnel data is obtained for several test cases, but only the turbulence model based on the EARSM approach captured the significant lift increase at non-zero angles of attack due to variation of Reynolds number. This phenomenon is shown to be related to the progressive upstream migration of the time-averaged shear-layer reattachment location on one side of the rectangular cylinder. The effects of the Reynolds number on the mechanism of vortex shedding are also explored in the simulations.     

Unsteady RANS simulations of flow around a bridge section

This paper presents the results of unsteady Reynolds-averaged Navier-Stokes (URANS) simulations of flow around a common bridge deck geometry. Computations are performed with a noncommercial unstructured flow solver using two-dimensional hybrid meshes with fine near-wall resolution. The influence of different simulation parameters (grid refinement, time-step size, turbulence modelling) is analyzed, in particular in order to obtain flow solutions independent of spatial and temporal discretization. Results given by a one-equation eddy-viscosity turbulence model and a two-equation explicit algebraic Reynolds stress model are compared. Despite the limits imposed by the URANS approach and the relatively inexpensive two-dimensional computations, satisfactory agreement is found with the experimentally measured forces and pressures. These simulations help to explain the discrepancy between the results of two wind-tunnel test campaigns and show the dramatic influence of non-perfectly sharp edges on the global flow field development. The capability of the numerical approach to capture complex Reynolds number effects is also discussed.     

Heat treatment and magnetic properties of Fe-23Cr-16Co-X alloys

Fe-23Cr-16Co alloys containing titanium and titanium and niobium simultaneously were investigated. A dependence was noted between the parameters of TMA and low-temperature ageing influencing the level ofB _r,H _c and (BH)_max and alleviating the action of niobium on alloy sensibility on fluctuations of these parameters was noticed. TEM investigations revealed the existence of the phase connected with the presence of niobium in the alloy. The results confirm -creative action of niobium and titanium and point to a substantial influence of the temperature of annealing, preceeding solutioning on the final magnetic properties.