珠江河口虎门的地貌动力学研究

以野外现场调查、数值模拟和前人研究成果综合分析虎门的地貌动力学特征。因峡口上、下游水域开阔,涨落潮过程中发育着强大的双向不对称射流系统;由于峡口区流速最大,发育着冲刷深槽,而峡口的上、下游因流速降低,泥沙有规律地沉积,形成了涨潮三角洲与落潮三角洲堆积体,出现纵向上“马鞍”形断面特征和横向上“槽-脊-滩”的地貌特征,与其动力特征相适应。     

多孔紊动射流的数值模拟与实验研究进展

多孔射流作为流体运动的一种重要类型,在工程中具有非常广泛的用途。由于多孔射流各股水流之间的卷吸和掺混的存在,增加了流场的复杂性。长期以来研究人员从理论分析、实验测量和数值模拟方面对多孔紊动射流进行了大量的研究工作,目前已经认识了流场中的许多流动特性和流动机理。从数值模拟和实验研究两个方面,比较分析了国内外多孔紊动射流的研究现状和研究结果,评述了不同湍流模型以及不同实验测量方法对紊动射流的预测能力,讨论了存在的问题并对该领域的研究方向进行了展望。     

The mass accommodation coefficient of ammonia on water

The mass accommodation coefficient of ammonia gas on water has been determined by measuring the absorption rate of 50–200 ppm NH₃ in one atm of air or helium into a liquid jet of 97 µm diameter as function of the exposed jet length, and comparing the results with numerical simulations which treat as the only free parameter. The model considers in detail transport of NH₃ by molecular diffusion, penetration of the gas/water interface, hydrolysis in the acidified water, and transport of the solutes from the surface into the jet. A correction is applied for the time evolution of the jet surface speed, using literature data on the fluid mechanics of liquid jets. The result of nine sets of independent measurements is

Trace gas exchange at the air/water interface: Measurements of mass accommodation coefficients

A liquid jet of 90 m diameter and variable length has been utilized to determine absorption rates and, hence, mass accommodation coefficients , of atmospheric trace gases. The compounds investigated are HCl (0.01), HNO₃ (0.01), N₂O₅ (0.005), peroxyacetyl nitrate (>0.001), and HONO (0.005). It is concluded that the absorption of these trace gases by liquid atmospheric water is not significantly retarded by interfacial mass transport. The strengths and limitations of the liquid jet technique for measuring mass accommodation coefficients are explored.     

台风活动对副热带高压位置和强度的影响

利用一个浅水模式，实施了6组时间积分为4－5个模式日的试验，研究了台风对副热带高压中心位置及强度的影响。结果表明：台风和副热带高压的相互作用可以使高压中心位置西移,强度增加。据此讨论了台风活动和西北地区东部干旱之间统计联系的可能机制。     

Observations And Modelling Of The On-Ice And Off-Ice Air Flow Over The Northern Baltic Sea

Two cases of on-ice and off-ice air flow characterizing the opposite weather situations over the ice-edge zone in the northern Baltic Sea are analysed on the basis of aircraft observations, and modelled using atwo-dimensional mesoscale model. The stable boundary layer (SBL) during theon-ice flow exhibited little thermal modification, but a low-level jet (LLJ) was generated at the 250-m high top of the SBL. In the model, the LLJ was associated with inertial oscillations in space, while the baroclinicity explained the shape of the wind profile well above the SBL. Although the observed LLJ was most pronounced over the ice, the modelling suggests that it was not generated by the ice edge but by the coastline some 400 km upwind of the ice edge, where a much more drastic change in the thermal stratification and surface roughness took place. The generation, maintenance, and strength of the LLJ were very sensitive to the parameterization of turbulent mixing in the SBL. In the case of the off-ice flow, the modification of the air mass and the development of a convective boundary layer (CBL) both over the ice and open sea were reasonably well modelled. Sensitivity runs suggested that it was essential to take into account the effects of subgrid-scale leads, a forest in the archipelago (which was crossed by the air flow), and water vapour condensationinto ice crystals. The heat flux from leads was particularly important for the heatbudget of the CBL, and the observed growth of the CBL was partly due to theeffective mixing over the rough and relatively warm forest.     

MTCLIM模型系列研究报告(4):辐射估算方法在我国南方亚热带山地的改进

以已有的数据、理论和模型为基础,在我国南方亚热带山地对MTCLIM模型的辐射估算方法进行了改进,对模型参数作了重新估计。经过改进后,辐射子模型中的参数B的变化不再用月平均温差表示,而是用月平均水汽压来表示。交互验证估计参数的方法能消除不良数据的影响,获得较好的模拟效果,最后估计的参数T0 nadir.dry、α、C、a和b分别为0 823、0 000039、1 7、0 0173和0 0000122。与用原来参数估计的结果相比,参数估计后预测的日总辐射结果有明显改善,相关系数R2从原来的0 55～0 73提高到0 65～0 82,总平均绝对误差从原来的3 81MJ/m·d-1降低为2 90MJ/m·d-1,减少了约1MJ/m·d-1。     

高压旋喷桩桩周土摩阻力的分析与探讨

通过对旋喷桩的单桩静载试验，探讨了桩周土摩阻力作用的情况，通过计算和分析，得出了两个结论，为旋喷桩基础的设计提供参考。     

Extracting flow structures from tracer data

A method of visualizing structures in closed chaotic flows out of homogenous particle distributions is presented in the example of models of a meandering jet. To this end, the system will be leaked or opened up by defining a region of the flow, so that a particle is considered to be escaped if it leaves this region. By applying this method to an ensemble of nonescaped tracers, we are able to characterize mixing processes by visualizing the converging and stretching filamentations (stable and unstable manifolds) in the flow without using additional mathematical tools. The possibility of applying the algorithm to analyze buoy data, and a comparison with the finite time manifolds are discussed.     

Characterisation of the 1997 Vulcanian explosions of Soufrière Hills Volcano,Montserrat, by video analysis

The activity of Convention at Montserrat Soufrière Hills Volcano, Montserrat, during the period 1995–1999 included numerous violent explosions. Two major cycles of Vulcanian explosions occurred in 1997: a first of 13 explosions between 4 and 12 August and a second of 75 between 22 September and 21 October. The explosions were short-lived events lasting a few tens of seconds during which partial fountain collapse generated pyroclastic surges and pyroclastic flows, and buoyant plumes ascended 3–15 km into the atmosphere. Each explosion discharged on average 3×10⁵ m³ (dense-rock equivalent, DRE) of magma, draining the conduit to depths of 1–2 km. The paper focuses on the first few seconds of three explosions of the 75 that occurred in September/October 1997: 6 October 1997 at 17:50, 7 October 1997 at 16:02 and 9 October 1997 at 12:32. Physical parameters such as exit velocities, magmatic water contents and magma pressures at fragmentation are estimated by following and modelling the ascent of individual momentum-dominated finger jets visible on videos during the initial stages of each explosion. The model treats each finger jet as an incompressible flow sustained by a steady flux of gas and particles during the few seconds of ascent, and produces results that compare favourably with those using a multiphase compressible code run using similar eruptive parameters. Each explosion reveals a progressive increase in eruptive intensity with time, jet exit velocities increasing from 40 m s^–1 at the beginning of the explosion up to 140 m s^–1 after a few seconds. Modelling suggests that the first magma to exit was largely degassed, whereas that discharged after a few seconds contained up to 2 wt% water. Magma overpressures up to ~10 MPa are estimated to have existed in the conduit immediately prior to each explosion. Progressive increases in jet exit velocity with time over the first few seconds of each explosion provide direct evidence for strong pre-eruptive gradients in water content and magma pressure in the upper reaches (probably 100–500 m) of the conduit. Fountain collapse occurred during the first 10–20 s of each explosion because the discharging jets had bulk densities up to 100 times that of the atmosphere and were unable to entrain enough air to become buoyant. Such high eruptive densities were due to the presence of partially degassed magma in the conduit.Editorial responsibility: A. Woods