可溶性汞化苯乙烯－丙烯酸甲酯共聚物的合成

用自由基溶液降合方法制备一系列苯乙烯－丙烯酸甲酯线型共聚物，用核磁共振测定了苯基在共聚物中的百分比，在该共聚物的四氢呋喃溶液中，用三氟乙酸汞在共聚物的苯环上进行亲电取代反应，得到可溶性汞化共聚物，由于这类泵化共的可溶于四氢呋喃，二氯甲烷等溶剂，用重沉淀法多次提纯，得到了纯度很高，溶解性较好的含重金属二价汞的共聚物，用红外光谱仪测定共聚物上的汞基团，用原子吸收定量测试共聚中的汞的百分聚代率，结果表明     

On the Shear Number Effect in Stratified Shear Flow

The influence of the shear number on the turbulence evolution in a stably stratified fluid is investigated using direct numerical simulations on grids with up to 512 × 256 × 256 points. The shear number SK/ε is the ratio of a turbulence time scale K/ε to the shear time scale 1/S. Simulations are performed at two initial values of the Reynolds number Re _Λ= 44.72 and Re _Λ= 89.44. When the shear number is increased from small to moderate values, the nondimensional growth rate γ= (1/SK)dK/dt of the turbulent kinetic energy K increases since the shear forcing and its associated turbulence production is larger. However, a further increase of the shear number from moderate to large values results in a reduction of the growth rate γ and the turbulent kinetic energy K shows long-time decay for sufficiently large values of the shear number. The inhibition of turbulence growth at large shear numbers occurs for both initial values of the Reynolds number and can be explained with the predominance of linear effects over nonlinear effects when the shear number is sufficiently high. It is found that, at the higher initial value of the Reynolds number, the reduction of the growth rate occurs at a higher value of the shear number. The shear number is found to affect spectral space dynamics. Turbulent transport coefficients decrease with increasing shear number. Received 23 June 1998 and accepted 25 February 1999     

Axisymmetric trawl cod-ends made from netting of a generalized mesh shape

The equations governing the geometry of axisymmetric trawl cod-endsmade from netting of meshes of a particular generalized structureare derived. From this, by suitable setting of the initial meshbar lengths, the equations governing the geometry of cod-endsthat are of importance to the fishing industry can be readilydeduced. It is assumed that arbitrary membrane forces act normalto the edges of the mesh elements, that there is no shear forceacting on the edge of a mesh element and that the twine thatmakes up the netting is extensible. The case where there isslackness in the mesh bars in the circumferential directionis dealt with and it is demonstrated how the finite structureof a knot can be taken into account. The case where the membraneforces arise solely as a result of and can be expressed by theappropriate components of the tensions in the mesh bars is alsoexamined and numerical solutions are found for a range of examples.     

Large eddy simulation of homogeneous shear flows with several subgrid‐scale models

In this article, large eddy simulation is used to simulate homogeneous shear flows. The spatial discretization is accomplished by the spectral collocation method and a third‐order Runge–Kutta method is used to integrate the time‐dependent terms. For the estimation of the subgrid‐scale stress tensor, the Smagorinsky model, the dynamic model, the scale‐similarity model and the mixed model are used. Their predicting performance for homogeneous shear flow is compared accordingly. The initial Reynolds number varies from 33 to 99 and the initial shear number is 2. Evolution of the turbulent kinetic energy, the growth rate, the anisotropy component and the subgrid‐scale dissipation rate is presented. In addition, the performance of several filters is examined. Copyright © 2005 John Wiley & Sons, Ltd.     

A Direct Numerical Study of Transport and Anisotropy in a Stably Stratified Turbulent Flow with Uniform Horizontal Shear

Direct numerical simulations of homogeneous turbulence in stably stratified shear flow have been performed to aid the understanding of turbulence and turbulent mixing in geophysical flow. Two cases are compared. In the first case, which has been studied in the past, the mean velocity has vertical shear and the mean density is vertically stably stratified. In the second case, which has not been studied systematically before, the mean velocity has horizontal shear and the mean density is again vertically stably stratified. The critical value of the gradient Richardson number, for which a constant turbulence level is obtained, is found to be an order of magnitude larger in the horizontal shear case. The turbulent transport coefficients of momentum and vertical mass transfer are also an order of magnitude larger in the horizontal shear case. The anisotropy of the turbulence intensities are found to be in the range expected of flows with mean shear with no major qualitative change in the range of Richardson numbers studied here. However, the anisotropy of the turbulent dissipation rate is strongly affected by stratification with the vertical component dominating the others. This revised version was published online in July 2006 with corrections to the Cover Date.