返回舱垂直自由入水砰击过程的数值模拟

文章数值研究返回舱垂直自由入水砰击过程中水气流场与返回舱运动之间的动力学与运动学耦合问题。水气两相流的流动方程选为非定常雷诺平均Navier-Stokes(URANS）方程和Realizable k-ε湍流模型,返回舱的运动方程选为刚体的一维平动方程,水气交界面的追踪采用流体体积函数（VOF）方法,返回舱与水面之间的相对运动采用动网格技术实现。在计算方法得到试验验证的基础上,数值研究了返回舱的不同触水速度、质量对入水过程中砰击力、加速度等参数的影响规律;给出了入水过程中加速度峰值与触水速度及质量之间的定量关系式;发现了返回舱底部的入水砰击压强峰值发生在入水初期,且压强峰值始终位于喷溅射流的根部。     

Observation of aphelion cloud belt over Martian tropics,its evolution,and associated dust distribution from MCS data

The present study uses five Martian years of observations from Mars Climate Sounder onboard Mars Reconnaissance Orbiter for investigating the Aphelion Cloud Belt (ACB) over the tropics. Analysis of zonal mean water ice column opacity suggests that the spatial extension of the ACB is mainly confined over the tropics and mid-latitudes (-20 – 40°N) during L_S ~ 45 – 135° (L_S = 0° signifies northern spring equinox). The ACB is seen primarily in the nighttime only due to the truncation of the daytime profile observations at significantly higher altitudes (at ~30 km). Zonal mean ice extinction profiles show ACB’s altitudinal range within ~10 – 40 km, and the existence of a thin cloud band in the absence of a thick ACB during aphelion season. Three phases of the ACB could be identified as the formation phase during L_S = 45 – 75° (phase 1), the peak phase during L_S = 76 – 105° (phase 2), and the decaying phase during L_S = 106 – 135° (phase 3). Observation of the cloud latitude belt shows a northward movement starting from phase 2, prominent over regions nearby Lunae Planum and Xanthe Terra. During this phase, the top level of thick clouds within the ACB decreases to ~20 km in the southern hemisphere, while it increases a little over the northern hemisphere (NH). The decreasing tendency continues in phase 3 over the entire region ?10 – 10°N, and the thick cloud base moves higher over the NH, though the vertical depth of it becomes narrower than phase 2. Temperature profiles do not show any noticeable influence on the northward evolution of the ACB. However, the study at a regional level indicates a possible association of upper tropospheric dustiness with the ACB’s evolution. The mechanism is evident in the correlation analysis mostly at an altitude range of ~18 – 35 km. The migrating semidiurnal tide (SMD) as a proxy of dust or water ice forcing, and the calculated upper tropospheric dust radiative heating, shows an apparent northward movement of their peak amplitude within the three phases of the ACB. This match between the spatiotemporal variations of the SMD and the water ice was not observed previously. However, the correlating behavior seems to be prominent in the areas nearby Lunae Planum and Xanthe Terra and the upper-tropospheric region of the atmosphere.     

丙二醇改性水溶液的发汗冷却实验研究

针对液态水相变发汗冷却实验中的振荡、表面温度分布不均及结冰现象,对液体冷却剂进行调研,选取丙二醇添加剂对液态水改性,在主流温度573K,雷诺数1.2×10⁴的亚声速高温风洞中实验研究了不同丙二醇改性水溶液浓度和注入率下多孔平板的相变发汗冷却特性。结果表明：随丙二醇浓度增大,多孔平板对改性水溶液的渗透率增大,多孔平板表面温度的振荡幅度减小,同时振荡周期内温度波峰降低。因此,使用丙二醇改性水溶液作为冷却剂,发汗冷却结构表面温度分布更加均匀,热疲劳损伤减小,承温极限升高,进而烧蚀风险降低,这对有效且高效的热防护系统设计具有重要意义。另外,注入率越大平板表面冷却效果越好,表面温度的振荡幅度越小,因此增大注入率也是改善多孔板表面温度波动的有效方式。     

Estimation of vertically integrated water vapor in Hungary using MODIS imagery

Information about the amount and spatial structure of atmospheric water vapor is essential in understanding meteorology and the Earth environment. Space-borne remote sensing offers a relatively inexpensive method to estimate atmospheric water vapor in the form of integrated water vapor (IWV). The research activity reported in the present paper is based on the data acquired by the HRPT/MODIS (High Resolution Picture Transmission, MODerate resolution Imaging Spectroradiometer) receiving station established in Budapest (Hungary) by the Space Research Group of the Eötvös Loránd University. Integrated water vapor is estimated by the remotely sensed data of the MODIS instrument with different methods and also by the operational numerical weather prediction model of the European Centre for Medium-Range Weather Forecasts (ECMWF). Radiosonde data are used to evaluate the accuracy of the different IWV fields though it has been pointed out that the in situ data also suffers from uncertainties. It was found that both the MODIS and the ECMWF based fields are of good accuracy. The satellite data represent finer scale spatial structures while the ECMWF data have a relatively poor spatial resolution. The high quality IWV fields have proved to be useful for radiative transfer studies such as the atmospheric correction of other satellite data from times different than the overpass times of satellites Terra/Aqua and the forecast times of the model data. For this purpose the temporal variability of IWV is scrutinized both using ECMWF and MODIS data. Taking advantage of Terra and Aqua overpasses, the mean rate of change of IWV estimated by the near infrared method was found to be 0.47 ± 0.45 kg m⁻² h⁻¹, while it was 0.13 ± 0.65 kg m⁻² h⁻¹ based on the infrared method. The numerical weather prediction model’s analysis data estimated −0.01 ± 0.13 kg m⁻² h⁻¹ for the mean growth rate, while using forecast data it was 0.24 ± 0.18 kg m⁻² h⁻¹. MODIS data should be used when available for the estimation of the IWV in other studies. If no satellite data are available, or available data are only from one overpass, ECMWF based IWV can be used. In this case the analysis fields (or the satellite field) should be used for temporal extrapolation but the rate of change should be calculated from the forecast data due to its higher temporal resolution.     

Magnetic levitation of large water droplets and mice

We report successful levitation of large water droplets and mice using a newly built variable gravity simulator. The simulator consists mainly of a superconducting magnet with a room temperature accessible experimental levitating space. The superconducting magnet generates a field and field gradient product that is large enough to levitate water and many other common liquids. The warm bore of the magnet has a diameter of 66 mm, large enough to levitate small mammals. We demonstrate that water drops up to 50 mm in diameter and young mice can be levitated in the system. The capability of levitating large water drops and biological systems offers new opportunities for conducting detailed and in-depth study of properties of fluids and biological systems in reduced gravity environments.     

工程施工中深基坑高程放样的误差分析

论述了市政工程施工中深基坑高程放样方法,对放样过程中产生的误差及误差的大小进行了分析。本测量放样方法可以满足给排水工程施工,以及符合高程精度要求的验收规范。     

Global water vapour distribution in the upper troposphere and lower stratosphere during CRISTA 2

Water vapour measurements during the second mission of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument are presented in the altitude regime 8–20 km. Mixing ratios are shown on isentropic surfaces (300–500 K) as global zonal means and as averages in 60° longitude sectors. Transports are indicated to occur preferentially on isentropic surfaces in the northern hemisphere, but not in the tropics and in the south. The hygropause is found shifted away from the equator towards the winter hemisphere. The amount of shift is longitude dependent and can be as great as 20–30°. The water content of the hygropause area shows considerable zonal asymmetries.     

Four-month Moon and Mars crew water utilization study conducted at the Flashline Mars Arctic Research Station,Devon Island,Nunavut

A categorized water usage study was undertaken at the Flashline Mars Arctic Research Station on Devon Island, Nunavut in the High Canadian Arctic. This study was conducted as part of a long duration four-month Mars mission simulation during the summer of 2007. The study determined that the crew of seven averaged 82.07 L/day over the expedition (standard deviation 22.58 L/day). The study also incorporated a Mars Time Study phase which determined that an average of 12.12 L/sol of water was required for each crewmember. Drinking, food preparation, hand/face, oral, dish wash, clothes wash, shower, shaving, cleaning, engineering, science, plant growth and medical water were each individually monitored throughout the detailed study phases. It was determined that implementing the monitoring program itself resulted in an approximate water savings of 1.5 L/day per crewmember. The seven person crew averaged 202 distinct water draws a day (standard deviation 34) with high water use periods focusing around meal times. No statistically significant correlation was established between total water use and EVA or exercise duration. Study results suggest that current crew water utilization estimates for long duration planetary surface stays are more than two times greater than that required.     

CRISTA-NF measurements of water vapor during the SCOUT-O3 Tropical Aircraft Campaign

The new remote sensing experiment CRISTA-NF (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere – New Frontiers) successfully participated in the SCOUT-O3 Tropical Aircraft Campaign in November and December 2005. CRISTA-NF operated aboard the high-altitude research aircraft M-55 Geophysica. Mid-infrared spectra (4–15 μm) were measured in the limb sounding geometry with high spatial resolution (250 m vertical sampling, 5–15 km along track sampling). Measurements were carried out during transfer flights between Oberpfaffenhofen, Germany, and Darwin, Australia, as well as during several local flights near Darwin. Water vapor volume mixing ratios in the upper troposphere and lower stratosphere were derived from the CRISTA-NF radiance measurements by utilizing a rapid radiative transfer forward model and the optimal estimation retrieval approach. CRISTA-NF water vapor measurements below the hygropause have a total retrieval error of 15–40% (i.e. root mean square of accuracy and precision). The systematic terms are dominating in the retrieval error budget. The contributions of a priori information to the retrieval results are less than 5–10%. The vertical resolution of the observations is about 250–500 m when permitted by instrument sampling. In this paper we present first results for three transfer flights of the campaign. Being generally in good agreement with corresponding ECMWF operational analyzes, the CRISTA-NF measurements show significantly higher variability and local structures in the upper tropospheric water vapor distributions.