不同边界条件下非饱和土地基中的Rayleigh波传播

地球表面绝大部分土层并非处于完全饱和状态,故采用传统的饱和土两相介质理论进行动力学分析时,计算结果往往与实际情况不符。针对这一客观问题,以非饱和土为研究对象,在三相孔隙介质波动理论的基础上开展了非饱和土体半空间中Rayleigh波的弥散特性研究。分别考虑了两种不同的边界条件:(a)不透水不透气地基边界;(b)透水透气地基边界。根据边界条件及相关的本构关系式,推导出相应Rayleigh波的弥散方程,再通过Newton-Raphson法进行数值求解。最后讨论了在不同边界条件下,非饱和土地基表面附近Rayleigh波的弥散特性受到地基土饱和度、频率以及土体固有渗透系数的影响。计算结果表明:在两种边界条件下Rayleigh波的传播均受到地基土饱和度变化的影响。并且,频率及渗透系数在不同边界条件下对Rayleigh波特性的影响明显不同。     

动态大气散射系数的颜色衰减先验图像去雾

针对颜色衰减先验图像去雾算法存在对较浓的有雾图像去雾效果不佳的问题,提出基于动态大气散射系数的颜色衰减先验图像去雾算法.用动态大气散射系数取代颜色衰减先验去雾算法中恒定大气散射系数的假设,定义大气散射系数为关于图像景深的指数函数.利用Middlebury stereo datasets中无雾图像和相应的景深图像得到合成有雾图像.采用均方误差(MSE)和结构相似度(SSIM)的综合评价参数MSE-SSIM确定上述指数函数的两个参数的最佳取值.实验结果表明与颜色衰减先验算法、He、Meng算法相比,该算法的去雾图像清晰颜色自然,有效地提高了去雾效果.     

Time diversity evaluation for attenuation mitigation method using attenuation data in Thailand and Japan

In order to support future satellite broadcasting and communication in the Ka band and above, the time diversity method provides a novel attenuation mitigation technique for maintaining satellite service availability at levels between 99.9 and 99.99%. In this paper, the time diversity method is analyzed using various time delays from between 1 min and 1 h in an effort to mitigate convective rain attenuation by using various beacon signal transmission delays. For comparison purposes, receiver beacon data from Japan and Thailand are presented to highlight tropical and non‐tropical zone regional differences, and the International Telecommunications Union (ITU) R P.618‐12 standard is used for scaling up the Thaicom beacon frequencies from 12.57 and 12.59 GHz in the Ku band to 19.45 GHz, which is the Ka band frequency used by Japan's communication satellite (CS) beacon. We found that the time diversity method is very useful for mitigating the effects of rain attenuation. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal cycling behavior of nanostructured 8YSZ，SZ/8YSZ and 8CSZ/8YSZ thermal barrier coatings fabricated by atmospheric plasma spraying

The nanostructured single-ceramic-layer (SCL) 8YSZ thermal barrier coatings (TBCs), double-ceramic-layer (DCL) Sm₂Zr₂O₇ (SZ)/8YSZ and SZ doped with 8 wt% CeO₂ nanoscale particles (8CSZ)/8YSZ TBCs were fabricated by atmospheric plasma spraying (APS) on nickel-based superalloy substrates with NiCoCrAlY as the bond coating. The thermal cycling behavior of the three as-sprayed TBCs was investigated systematically at 1000 ℃ and 1200 ℃. The results reveal that the thermal cycling lifetime of the nanostructured DCL 8CSZ/8YSZ TBCs is the longest among them, which is largely due to the fact that the intermediate layer buffer effect of the DCL structure, more porosity and improvement of thermal expansion coefficient from doping CeO₂ nanoparticles can relieve thermal stress to a great extent at elevated temperature. The failure mechanism of the nanostructured TBCs has been discussed in detail.     

聚脲弹性体复合夹层结构的防爆性能

应用LS–DYNA有限元软件,对聚脲弹性体复合夹层结构在0.5 kg炸药(TNT)爆炸载荷作用下的动态响应过程进行数值模拟。研究了复合夹层结构厚度和质量固定条件下聚脲弹性体夹层厚度对复合夹层结构抗爆性能的影响。分析了不同聚脲弹性体夹层厚度对复合夹层结构变形的影响,并分析了聚脲弹性体夹层的吸波和吸能特性。结果表明,在爆炸载荷作用下,当复合夹层结构总厚度固定时,随着聚脲弹性体夹层厚度的减小,复合夹层结构的抗爆性能先增大后减小,当钢板与聚脲弹性体夹层厚度比为1.4∶1.2∶1.4时,变形的整体性最好,其抗爆的潜力最大,其冲击波衰减率最大为85.6%,能量吸收效果也最好,其综合抗爆能力较好;在质量固定条件下,随着聚脲弹性体夹层厚度的增加,其抗爆能力先增大后减小,当钢板与聚脲弹性体夹层厚度比为0.903∶3.5∶0.903时,其变形和能量吸收效果最好,冲击波衰减率最大为81.87%,其综合抗爆能力较好。     

On the investigation into the kinetics of the ultrasound-assisted atmospheric freeze drying of eggplant

Atmospheric freeze drying is a highly attractive process for the dehydration of thermosensitive products, like food, due to the fact that water is removed at low temperature by sublimation. Unfortunately, drying times can be very long because of the internal resistance of the product to vapor diffusion: power ultrasound can be an effective means of accelerating the process, thus reducing the operating cost. The aim of this study was to assess the effect of air temperature and velocity, ultrasound power and sample size on the drying kinetics of eggplant (Solanum melongena L.) samples and, afterward, to analyze in silico an industrial process. Experiments were performed under various conditions regarding air temperature (?5, ?7.5, ?10°C), velocity (2 and 5?m?s^?1), power ultrasound (0, 10.3, 20.5?kW?m^?3, 21.9?kHz), and sample size. Drying rate was measured experimentally. The air velocity showed no relevant effects on the drying kinetics, and the effect of air temperature was slight when compared to the marked reduction in the drying time obtained when ultrasound was applied. The uniformly retreating interface model was modified to account for the cubic shape of the samples and used to establish the kinetic parameters, in particular to evaluate water diffusivity in the dried product, searching for the best fit between measured and calculated moisture content. The model was finally used to optimize the process in silico, considering an industrial unit as test case. In this case, it appeared that power ultrasound can increase the productivity of a tunnel dryer up to four or five times, and it allows the operational and fixed costs of the plant to be reduced significantly.     

Real-time monitoring of peanut drying parameters in semitrailers

Knowledge of peanut drying parameters, such as temperature and relative humidity of the ambient air, temperature and relative humidity of the air being blown into the peanuts, and kernel moisture content, is essential in managing the dryer for optimal drying rate. The optimal drying rate is required to preserve quality and desired flavor. In the current peanut-drying process, such parameters are elusive in real time and are either not measured or only measured periodically by an operator. A peanut-drying monitoring system, controlled by an embedded microcontroller and consisting of relative humidity and temperature sensors and a microwave peanut moisture sensor, was developed to monitor drying parameters in real time. It was deployed during the 2014 peanut harvest season at a peanut buying point in central Georgia, USA. It was placed in 45-ft (13.7-m) drying semitrailers to monitor in-shell kernel moisture content, temperature of the drying peanuts, temperature, and relative humidity of the exhaust air from the peanuts and relative humidity of the air being blown into the peanuts in real time. In-shell kernel moisture content was determined with a standard error of performance of 0.55% moisture content when compared to the reference oven-drying method. Data from drying parameters were time-stamped and stored on a CompactFlash card every 12?s and were used to assess the efficiency of dryer control settings. Ambient air conditions were measured by an on-site weather station. Results of the study support the value of such a monitoring system and show that implementation of the system for dryer control has the potential for saving a buying point, in the current economical context, as much as $22,000 annually in costs of electric energy and propane.     

设定地震场地相关设计反应谱的研究

我国现行国家标准《水工建筑物抗震设计标准》（GB 51247—2018）规定,场地相关设计反应谱宜釆用与基于《工程场地地震安全性评价》（GB 17741—2005）的设计地震动峰值加速度相应的“设定地震”确定。为便于工程技术人员理解和应用,本文进行了确定设定地震内涵和步骤的高级科普性阐述,将按《〈水电工程水工建筑物抗震设计规范〉（NB 35047—2015）设定地震确定场地相关设计反应谱补充说明》,以“最大发生概率原则”的确定方法加以说明。我国缺乏直接由强震记录统计的加速度反应谱衰减关系,权且采用美国“下一代衰减关系（NGA）”,其中涉及到震中距和断层距的转换,本文对转换过程进行了进一步论述,以期形成共识。此外,考虑到不同“NGA”衰减关系给出的加速度反应谱差异较大,提出确定设定地震反应谱的新思路。建议汇集已有岩基上较近距离的实测强震记录的反应谱资料,对其按震级和距离进行适当分档,然后插值确定设定地震的场地相关设计反应谱,这样既可以免除当前我国缺乏反应谱衰减关系的困难,还能使确定场地相关设计反应谱的过程大为简化和合理。     

大通河降雨径流关系演变与水资源衰减初步研究

大通河位于祁连山区,开发利用程度低,实测径流基本为天然径流,1956—2000年平均径流量28.95亿m~3。在全球气候变暖的背景下,降雨-径流关系发生了明显的改变,以水文气象要素明显的分界点1997年进行分时段比较,汛前径流明显衰减,汛后上游径流明显增加,中下游径流有一定减少,年均水资源减少1.72亿m~3。选择受冰川融水和冻土释水影响较小的中下游区间来水分析,得到蒸发增加减少径流深38 mm。基于上中游分阶段径流比较认为,枯季径流的增加来自冻结层下水的稳定释水,春季径流的减少由季节性冻土释水疏干和陆面蒸发增加导致,夏秋季径流的增加主要是冰川融水和冻结层上水转化成冻结层下水减少沼泽消耗所致。综合分析认为,随着气温的继续升高,冰川融水消失,冻结层上水进一步转化,伴随着源头沼泽的消失,冻结层下水的增加对蒸发增加引起的水资源衰减有所缓减。     

溅射时间对Ni/SiO_2玻璃光衰减片衰减性能的影响

为了提高光衰减片整体的光衰减效果,采用真空磁控溅射法,利用真空磁控溅射仪制备纳米级厚度的Ni/SiO2玻璃光衰减片.利用X-射线衍射(XRD)、原子能谱、扫描电镜和722分光光度计等表征手段,研究溅射时间(5、10、15、20、25 min)对透光率、微观结构的影响.实验结果表明:当溅射工作压力为0.4Pa,溅射时间为25 min时,金属Ni在SiO2玻璃基片上形成(111)和(200)晶面取向的镀Ni薄膜;SiO2玻璃基片上沉积的薄膜平整,颗粒分布均匀、排列紧密;试样的透光率达到0.41,采用磁控溅射法制备金属Ni/SiO2玻璃复合薄膜式光衰减片满足光纤通信需求.