Efficient analysis of pile-group effect on seismic stiffness and strength design of buildings     

Izuru Takewaki  Akiko Kishida 《Soil Dynamics and Earthquake Engineering》2005,25(5):355-367

A new efficient method is developed for the analysis of pile-group effects on the seismic stiffness and strength design of buildings with pile foundations. An efficient continuum model consisting of a dynamic Winkler-type soil element and a pile is used to express the dynamic behavior of the structure-pile-soil system with only a small numerical error. The pile-group effect is taken into account through the influence coefficients among piles which are defined for interstory drifts and pile-head bending moments. It is shown that, while the pile-group effect reduces the interstory drift of buildings in general, it may increase the bending moment of piles at the head. This means that the treatment without the pile-group effect results in the conservative design for super-structures and requires a revised member design for piles.  相似文献   

Desert vegetation and timing of solar radiation     

J.C. Walton  F. Martinez-Gonzalez  R. Worthington 《Journal of Arid Environments》2005,60(4):697-707

Timing and amount of solar radiation were examined as factors influencing the distribution of seven perennial plants on a small mountain located in the Chihuahuan Desert. Average direct beam solar radiation fluxes at differing times throughout the day and year were estimated with computer calculations. Principal components analysis was used to reduce the number of solar radiation parameters and include the maximum available information with a manageable number of variables. The remaining solar radiation parameters were compared to plant distributions using redundancy analysis and generalized additive models. Unimodal, bimodal, and monotonic responses were all found depending upon the species and solar radiation parameter. Niche separation at this location depends upon the timing as well as the amount of solar radiation.  相似文献   

Polymorphic phase transition in Superhydrous Phase B     

M. Koch-Müller  P. Dera  Y. Fei  H. Hellwig  Z. Liu  J. Van Orman  R. Wirth 《Physics and Chemistry of Minerals》2005,32(5-6):349-361

We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200°C (LT) and 1400°C (HT) using a multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction, Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures (down to −180°C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT polymorph crystallizes in a lower symmetry space group (Pnn2), whereas the HT polymorph assumes a higher symmetry space group (Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering occurs not only at the Mg sites but also at the hydrogen sites.  相似文献   

Three dimensional numerical simulation of residential building on shrink–swell soils in response to climatic conditions          下载免费PDF全文

Xiong Zhang  Jean‐Louis Briaud 《国际地质力学数值与分析法杂志》2015,39(13):1369-1409

Shrink–swell soils can cause distresses in buildings, and every year, the economic loss associated with this problem is huge. This paper presents a comprehensive system for simulating the soil–foundation–building system and its response to daily weather conditions. Weather data include rainfall, solar radiation, air temperature, relative humidity, and wind speed, all of which are readily available from a local weather station or the Internet. These data are used to determine simulation flux boundary conditions. Different methods are proposed to simulate different boundary conditions: bare soil, trees, and vegetation. A coupled hydro‐mechanical stress analysis is used to simulate the volume change of shrink–swell soils due to both mechanical stress and water content variations. Coupled hydro‐mechanical stress‐jointed elements are used to simulate the interaction between the soil and the slab, and general shell elements are used to simulate structural behavior. All the models are combined into one finite element program to predict the entire system's behavior. This paper first described the theory for the simulations. A site in Arlington, Texas, is then selected to demonstrate the application of the proposed system. Simulation results are shown, and a comparison between measured and predicted movements for four footings in Arlington, Texas, over a 2‐year period is presented. Finally, a three‐dimensional simulation is made for a virtual residential building on shrink–swell soils to identify the influence of various factors. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Scaling-laws of Radio Spike Bursts and Their Constraints on New Solar Radio Telescopestwo     

Tan Bao-lin  Cheng Jun  Tan Cheng-ming  Kou Hong-xiang 《Chinese Astronomy and Astrophysics》2019,43(1):59-74

Radio observation is one of important methods in solar physics and space science. Sometimes, it is almost the sole approach to observe the physical processes such as the acceleration, emission, and propagation of non-thermal energetic particles, etc. So far, more than 100 solar radio telescopes have been built in the world, including solar radiometers, dynamic spectrometers, and radioheliographs. Some of them have been closed after the fulfillment of their primary scientific objectives, or for their malfunctions, and thus replaced by other advanced instruments. At the same time, based on some new technologies and scientific ideas, various kinds of new and much more complicated solar radio telescopes are being constructed by solar radio astronomers and space scientists, such as the American E-OVSA and the solar radio observing system under the framework of Chinese Meridian Project II, etc. When we plan to develop a new solar radio telescope, it is crucial to design the most suitable technical parameters, e.g., the observing frequency range and bandwidth, temporal resolution, frequency resolution, spatial resolution, polarization degree, and dynamic range. Then, how do we select a rational set of these parameters? The long-term observation and study revealed that a large strong solar radio burst is frequently composed of a series of small bursts with different time scales. Among them, the radio spike burst is the smallest one with the shortest lifetime, the narrowest bandwidth, and the smallest source region. Solar radio spikes are considered to be related to a single magnetic energy release process, and can be regarded as an elementary burst in solar flares. It is a basic requirement for the new solar radio telescope to observe and discriminate these solar radio spike bursts, even though the temporal and spatial scales of radio spike bursts actually vary with the observing frequency. This paper presents the scaling laws of the lifetime and bandwidth of solar radio spike bursts with respect to the observing frequency, which provide some constraints for the new solar radio telescopes, and help us to select the rational telescope parameters. Besides, we propose a spectrum-image combination mode as the best observation mode for the next-generation solar radio telescopes with high temporal, spectral, and spatial resolutions, which may have an important significance for revealing the physical essence of the various non-thermal processes in violent solar eruptions.  相似文献   

Are peatlands in different states with respect to their thermodynamic behaviour? A simple test of peatland energy and entropy budgets     

Fred Worrall  Ross Morrison  Chris Evans  Joerg Kaduk  Susan Page  Alex Cumming  Mark Rayment  Nicholas Kettridge 《水文研究》2021,35(12):e14431

Whilst all ecosystems must obey the second law of thermodynamics, these physical bounds and controls on ecosystem evolution and development are largely ignored across the ecohydrological literature. To unravel the importance of these underlying restraints on ecosystem form and function, and their power to inform our scientific understanding, we have calculated the entropy budget of a range of peat ecosystems. We hypothesize that less disturbed peatlands are ‘near equilibrium’ with respect to the second law of thermodynamics and thus respond to change by minimizing entropy production. This ‘near equilibrium’ state is best achieved by limiting evaporative losses. Alternatively, peatlands ‘far-from-equilibrium’ respond to a change in energy inputs by maximizing entropy production which is best achieved by increasing evapotranspiration. To test these alternatives this study examined the energy balance time series from seven peatlands across a disturbance gradient. We estimate the entropy budgets for each and determine how a change in net radiation (ΔR_n) was transferred to a change in latent heat flux (ΔλE). The study showed that: (i) The transfer of net radiation to latent heat differed significantly between peatlands. One group transferred up to 64% of the change in net radiation to a change in latent heat flux, while the second transferred as little as 27%. (ii) Sites that transferred the most energy to latent heat flux were those that produced the greatest entropy. The study shows that an ecosystem could be ‘near equilibrium’ rather than ‘far from equilibrium’.  相似文献   

黄海海雾WRF数值模拟中垂直分辨率的敏感性研究   总被引：9，自引：1，他引：8       下载免费PDF全文

杨悦  高山红 《Acta Meteorologica Sinica》2016,74(6):974-988

基于WRF模式探究不同垂直分辨率下模式对黄海海雾的模拟表现。将3种垂直分层方案（35η、44η与63η）和2种边界层方案（YSU、MYNN）组合,对10次海雾做模拟研究。统计分析了水平雾区与雾顶高度对垂直分辨率的敏感性,并利用1次典型个例剖析了雾顶长波辐射与雾体湍流的作用。统计结果显示,提高垂直分辨率能显著改进水平雾区的模拟效果,改善明显的个例在不同垂直分辨率试验下的雾顶高度差异也较大;YSU方案相比于MYNN方案更敏感,从35η层增至44η层其试验个例的击中率（POD）和公正预兆得分（ETS）的平均改进率分别提高了13.29%和10.22%。典型个例研究结果揭示,模式对雾顶长波辐射和雾体湍流作用的模拟程度强烈依赖垂直分辨率：粗垂直分辨率给出的湍流强度很弱,导致模拟失败;雾顶存在“云水含量增多→长波辐射增强→降温加大→云水含量增多”的正反馈过程,细垂直分辨率比粗垂直分辨率更容易维持与增强此反馈;只有细垂直分辨率才能模拟出雾顶长波辐射冷却产生的贯穿雾体直抵海面、强度不弱于近海面机械湍流的浮力湍流,它导致雾体降温而出现符合观测事实的海温高于气温的现象。  相似文献   

贵州辐射雾的时空变化特征及其气象要素分析     

谢清霞  唐延婧  庞庆兵 《气象与环境科学》2016,39(2):119-125

选取2008—2012年贵州省3646站次的辐射雾天气过程,根据08时能见度大小将其划分为4级雾、3级雾、2级雾和1级雾四个等级,利用常规地面观测资料分析其时空变化特征,并根据辐射雾多发生区选取出修文、三穗和凤冈3个分布在贵州省高速干道上的站点,利用相应地面气象观测台站的逐日逐时实测气象要素资料,分析其不同等级的气象要素特征。结果表明:各等级辐射雾在10月—次年1月发生较多;空间分布呈"东多西少"格局,4级雾主要分布中心为修文和岑巩,其余等级辐射雾主要分布中心为三穗、凤冈、平塘、正安、松桃和锦屏;修文站的4级雾偏多与其平均相对湿度明显偏高、风速小于3 m/s和风向主要为偏东风相关性较高;三穗站和凤冈站的平均相对湿度与当日08时和前一日20时的气温差相对利于雾的生成,但其风速较小,垂直混合较弱,故其主要为较低等级雾。  相似文献   

非匀一冠层热辐射方向性3维模型构建——以玉米冠层为例     

马红章  刘素美  孙根云  杜永明  孙林  柳钦火 《遥感学报》2016,20(3):374-381

建立适用于多类型植被场景的热辐射方向性模型是进行地表热辐射方向性研究的一种手段。利用真实植株几何及生理参数的统计平均值来刻画理念植株,并给定其空间分布特征,进行不同生长期植被冠层的描述。基于冠层双向孔隙率思想构建了冠层热辐射方向性3维模型,模型继承了孔隙率模型在计算冠层热辐射方向性上的简洁优势同时以几何光学的思想考虑了冠层空间异质性对冠层热辐射方向性的影响。以玉米冠层为例,进行了不同生长期玉米冠层热辐射方向亮温的模拟,通过与实地测量数据的比对表明,本文发展的模型能够较准确地模拟不同生长期玉米植被场景的方向亮温变化规律,模拟误差主要来自理念株的刻画误差、玉米叶片形状的近似以及忽略了多次散射贡献等3个方面。模型的构建方法对稀疏植被场景、浓密植被场景、多类型植被的混合场景均可适用,不同观测几何下的植被场景4组份面积比计算结果有望应用于复杂地表条件下地表返照率的研究。  相似文献   

气溶胶大气辐射校正区域性分析     

刘小力  王琪洁  张勇  梁忠壮 《测绘科学》2016,41(4):55-60,82

针对使用6S模型中标准气溶胶模型进行大气辐射校正时结果较差的问题,该文提出使用实测气溶胶模型代替其进行计算。利用AERONET数据产品分析了香河、榆中等部分站点的气溶胶成分及其区域性分布特点,证明了中国气溶胶的成分具有明显的区域特性;并对6S模型中标准气溶胶模型与香河地基观测气溶胶光学参数进行比较,结果表明,两者具有较大的差异;最后使用不同的气溶胶模型校正Landsat5TM影像,结果表明,采用实测气溶胶数据进行大气辐射校正结果较优。  相似文献