强温变环境干扰下传感网络稳定控制模型仿真

在无线传感器网络性能的研究中,强温变环境下的传感器采集性能研究一直是相关领域的重点。在强温变环境下,传感节点会频繁切换工作模式,使得传感节点能量消耗出现强烈的波动,波动会破坏传感网络拓扑结构的整体稳定性。传统的传感通信方法在强温度环境下,以减少波动节点参与通信为代价控制稳定性,大幅降低了通信效率。提出自适应选择蚁群能效稳定性控制模型,分析强温变环境干扰下传感网络通信原理,得到传感网络节点能量特征,根据节点的能量特征,自适应完成强温变环境干扰下传感网络簇首的选择,采用蚁群智能的能效稳定性控制方案,通过重复迭代后,得到各簇头节点中对应信息素最浓的控制任务数量组合,形成最终传感网络整体控制模型,实现强温变环境下传感网络稳定性的有效控制。仿真结果说明,改进算法很好地解决了强温变环境干扰下传感网络稳定性控制的问题,提高了控制精度和稳定性。

基于MEMS陀螺的高温随钻定向测斜仪研究

针对油气井测量时所面临的小孔径、超深井、温度范围广、温度变化率高、工作时间长等挑战,研究了基于MEMS陀螺仪的定向测斜仪,设计了MEMS陀螺定向测斜仪软硬件系统.为确保该环境下的测量精度提出了一种动态温度补偿方案,并采用基于小波滤波多尺度分析的方法对动态温变环境下陀螺输出信号进行去噪滤波处理,以实现定向测斜仪系统的测量精度.论文给出了定向测斜仪硬件系统方案、定向测斜算法、小波多尺度滤波算法.测试结果表明:该系统在常温和动态温变环境下井斜方位角精度优于±2°,井斜角精度优于±0.1°,工作温度最高150℃,可适应我国深层油气井勘探开发的应用场景需求.

连续刚构桥长悬臂挂篮施工现浇段、合龙段结构行为分析

高墩大跨连续刚构桥边跨现浇段施工难度大,安全风险高。为解决这一问题,大跨径连续刚构桥边跨现浇段及合龙段施工时,拟采用接长挂篮来进行边跨现浇段及合龙段的施工。该文针对该工法开展了有限元仿真分析,研究了悬浇挂篮施工现浇段时的力学行为、环境温变对结构体系受力的影响,并进一步提出了解决措施。

温变环境中测试信号传输的仿真及试验

信号传输理论应用于电路网络中,由基尔霍夫定律推导了离散的温度-时间信号传输模型.给出了一种基于电压和电流的迭代算法,分别实现了导线升温、降温过程的信号传输仿真分析.研究表明:测试信号幅值随温度升高而逐渐衰减,在300℃时,幅值衰减了10%左右,而在升、降温并存环境中幅值衰减更加明显.在此基础上,设计了温变环境下的振动测试试验,所得结果与仿真分析结果一致.该研究为提高振动测试信号的精度提供了一种新方法.

非对称环形天线型面稳定性的参数匹配设计方法

为解决非对称环形索网天线在空间温变环境下型面稳定性较差的问题,推导了环形天线索网结构热载荷下的两个平衡方程.为实现索网在空间温变环境下的水平方向稳定,主副索网进行了等张力设计.给出了索网结构进行等张力设计的求解算法,该算法求解时采用最速下降法,比采用直接法具有更好的收敛性.为实现索网结构在空间温变环境下的垂直方向稳定,对主副索网的张力索截面参数进行了匹配设计.利用有限元法对设计进行了验证,结果表明,采用所述方法设计的非对称环形天线索网结构,在极端温度工况下具有很好的型面稳定性.

气压高度表温变环境下的误差建模研究

经过理论分析和反复试验,提出了气压高度表压力误差与温度电压变化率的线性回归模型.通过模型试验获取气压高度表误差模型参数.实时跟踪温度电压变化率,实时自动修正气压高度表在温变环境下的测量误差.经过多次验证,气压高度表补偿后的精度提高约60%,提高了气压表在温变环境条件下的适应能力,进一步拓宽了气压表的应用领域.该误差补偿技术在气压高度表领域具有通用性,而且简单易于实现,适于工程应用.

基于恒温控制的角度传感器设计

为了解决航天航空中角度传感器达到恒温较慢、适应温变环境能力差的问题,设计并制作了一种可以实现快速测量的小型恒温控制系统。本文通过对恒温室结构要求的介绍以及结构模型的建立,且经过设计分析、计算,选定了制作恒温室所需的材料并得到了角度传感器工作在不同温度时快速达到恒温所需的时间。实验结果表明,本系统可以实现快速测量的恒温,也可以达到较好的控温效果,并且具有功率小、体积小、结构简单、操作和控制方法简便、成本低、可靠性强等特点。

Health monitoring and comparative analysis of time-dependent effect using different prediction models for self-anchored suspension bridge with extra-wide concrete girder

The structural health status of Hunan Road Bridge during its two-year service period from April 2015 to April 2017 was studied based on monitored data.The Hunan Road Bridge is the widest concrete self-anchored suspension bridge in China at present.Its structural changes and safety were evaluated using the health monitoring data,which included deformations,detailed stresses,and vibration characteristics.The influences of the single and dual effects comprising the ambient temperature changes and concrete shrinkage and creep(S&C)were analyzed based on the measured data.The ANSYS beam finite element model was established and validated by the measured bridge completion state.The comparative analyses of the prediction results of long-term concrete S&C effects were conducted using CEB-FIP 90 and B3 prediction models.The age-adjusted effective modulus method was adopted to simulate the aging behavior of concrete.Prestress relaxation was considered in the stepwise calculation.The results show that the transverse deviations of the towers are noteworthy.The spatial effect of the extra-wide girder is significant,as the compressive stress variations at the girder were uneven along the transverse direction.General increase and decrease in the girder compressive stresses were caused by seasonal ambient warming and cooling,respectively.The temperature gradient effects in the main girder were significant.Comparisons with the measured data showed that more accurate prediction results were obtained with the B3 prediction model,which can consider the concrete material parameters,than with the CEB-FIP 90 model.Significant deflection of the midspan girder in the middle region will be caused by the deviations of the cable anchoring positions at the girder ends and tower tops toward the midspan due to concrete S&C.The increase in the compressive stresses at the top plate and decrease in the stresses at the bottom plate at the middle midspan will be significant.The pre-deviations of the towers toward the sidespan and pre-lift of the midspan girder can reduce the adverse influences of concrete S&C on the structural health of the self-anchored suspension bridge with extra-wide concrete girder.

Transaction Costs in Global Ecology Policy-Making

Global environmental meeting, legislating a reduction in the emission of greenhouse gases for planet earth, is what mankind now hopes for, having realized the enormous dangers in the process of climate change. Global warming is no longer denied by the so-called cornucopians （e.g. Lomberg）, but global policy-making originating in reunions of 190 governments or more stumble on collective action difficulties, spelled out in game theory. Paris will not succeed where Copenhagen failed, namely to arrive at a binding and enforceable global environment policy that will be implemented before it is too late. Instead, there will be massive transaction costs from negotiating and re-negotiating, endless voting, the making of promises exante and reneging ex post, as well as the futile attempts at any enforcement action, given state sovereignty. Mankind will have to learn how to cope with the outcomes of global warming, as resilience is the only hope.

基于PLECS的小型风力发电系统热分析

针对偏远山区极端温变环境对小型风力发电机工作性能产生的影响,分析了小型风力发电机的工作原理。从功率损耗衡量工作性能的角度出发,利用PLECS软件平台,以小型风电系统为对象,对开关管进行热分析,得到电路工作失效温度以及对应的阻值。同时分析了温度、负载阻值以及占空比对整体系统功率损耗的影响(低于5%),为提高温变环境下小型风力发电系统工作性能以及相关设计提供参考。

Application of different clustering approaches to hydroclimatological catchment regionalization in mountainous regions, a case study in Utah State

With respect to the different hydrological responses of catchments, even the adjacent ones, in mountainous regions, there are a great number of motivations for classifying them into homogeneous clusters. These motivations include prediction in ungauged basins(PUB), model parameterization, understanding the potential impact of environmental changes, transferring information from gauged catchments to the ungauged ones. The present study investigated the similarity of catchments through the hydro-climatological pure time-series of a 14-year period from 2001 to 2015. Data sets encompass more than 13,000 month-station streamflow, rainfall, and temperature data obtained from 27 catchments in Utah State as one of the eight mountainous states of the USA. The identification, analysis, and interpretation of homogeneous catchments were investigated by applying the four approaches ofclustering, K-means, Ward, and SOM(Self-Organized Map) and a newly proposed Wavelet-Entropy-based(WE-SOM) clustering method. By using two clustering evaluation criteria, 3, 5, and 6 clusters were determined as the best numbers of clusters, depending on the method employed, where each cluster represents different hydro-climatological behaviors. Despite the absence of geographic characteristics in input data matrix, the results indicated a regionalization in agreement with topographic characteristics. Considering the dependency of the hydrological behavior of catchments on the physiographic field aspects and characteristics, WE-SOM method demonstrated a more acceptable performance, compared to the other three conventional clustering methods, by providing more clusters. WE-SOM appears to be a promising approach in catchment clustering. It preserves the topological structure of data which can, as a result, be proofed in a greater number of clusters by dividing data into higher numbers of distinct clusters withsimilar altitudes of catchments in each cluster. The results showed the aptitude of wavelets to quantify the time-based variability of temperature, rainfall and streamflow, in the way contributing to the regionalization of diverse catchments.

Effect of Air Velocity on Thermal Comfort under Thermal Environment Ramp Changing

Set points of the indoor air temperature and relative humidity in short-term staying location were studied. In this condition, the thermal reaction of human body varied with the ramp changes of the environmental thermal parameters.The change rules of about 60 subjects′ thermal reaction to the ramp change of environment were surveyed, and the effect of air movement on the thermal reaction during transient condition was considered by using a questionnaire. With the experimental results and research findings under stable condition, a way to set environmental parameters of short-time staying location was recommended.

Changes in permafrost environments caused by construction and maintenance of Qinghai-Tibet Highway

The sideward permafrost along the Qinghai-Tibet Highway (QTH) contains massive ground-ice and is at a relatively high temperature.Under the influence of the steady increase of human activities,the permafrost environment has been changed greatly for a long time.At present,the permafrost becomes warm and rapidly degenerates,including the decline of the permafrost table,rising of the ground temperature,shortening of the length of frozen section,and extension of range of melting region.Some thaw hazards (e.g.thaw slumping and thermokarst pond) have widely occurred along both sides of the roadbed.In addition,due to the incomplete construction management,the vegetation adjacent to the highway is seriously damaged or eradicated,resulting in the land desertification and ecosystem out of balance.The dust,waste and garbage brought by drivers,passengers,maintenance workers,and transportations may also pollute the permafrost environment.

Entropy Analyses of Droplet Combustion in Convective Environment with Small Reynolds Number

This paper analyzes the entropy generation rate of simple pure droplet combustion in a tempera-ture-elevated air convective environment based on the solutions of flow, and heat and mass transfer between the two phases. The flow-field calculations are carried out by solving the respective conservation equations for each phase, accounting for the droplet deformation with the axisymmetric model. The effects of the temperature, velocity and oxygen fraction of the free stream air on the total entropy generation rate in the process of the droplet combustion are investigated. Special attention is given to analyze the quantitative effects of droplet deformation. The results re-veal that the entropy generation rate due to chemical reaction occupies a large fraction of the total entropy generated, as a result of the large areas covered by the flame. Although, the magnitude of the entropy generation rate per volume due to heat transfer and combined mass and heat transfer has a magnitude of one order greater than that due to chemical reaction, they cover a very limited area, leading to a small fraction of the total entropy generated. The en-tropy generation rate due to mass transfer is negligible. High temperature and high velocity of the free stream are advantageous to increase the exergy efficiency in the range of small Reynolds number (<1) from the viewpoint of the second-law analysis over the droplet lifetime. The effect of droplet deformation on the total entropy generation is the modest.

Interannual and Seasonal Changes in the Ice Cover of Glacial Lakes in the Snowy Mountains of Australia

Seasonal ice cover is uncommon on Australian lakes. In the Snowy Mountains, there are five natural, seasonally ice-covered lakes including Lake Cootapatamba, the highest lake in Australia. Blue Lake is the only one of the five lakes with sufficient volume to be relatively independent of short-term changes in ambient temperature, and therefore is the lake most likely to be of use in tracking long-term regional climate change. Ice forms on Blue Lake near the winter solstice and ice-breakup occurs from late September to November. Timing of breakup is related to spring temperature and, as such, mirrors the timing of general snow thaw in the mountains. The existence of historic photographs taken of the lake at about the time of ice breakup allows for the possibility of reconstructing a history of alpine climate and in 1905 ice breakup was probably as late as mid-December.

The Microclimatic Influence of a Water Body on an Urban Environment

The paper aims to investigate the potential of a water body to influence in lowering the warmth in the city of Sao Jose do Rio Preto, Brazil, due to the evaporative cooling effects. In order to verify its potential, three collecting points of temperature and humidity were placed in an urban area close to the municipal dam. The first one was placed on the dam margin, the second one, 50 m distant of the margin and, the third one, 100 m distant. The data were taken during December 2010 and then compared to the climate data of the Climate Station of CIIAGRO-Integrated Center of Agro Meteorological. The results show that the closer the collection point is to the water body, and the lower is the temperature variation. The humidity taxes verified at the closest point to the water body indicate values higher than those ones collected at the most distant point. The insertion of moisture through the water bodies in an urban environment demonstrated to be a strategy that improved the thermal conditions and has to be considered for urban planners to establish strategies of urban occupation.

Verification of the stomatal conductance of Nebbiolo grapevine

Wine is one of the most important Italian export products,and Nebbiolo is one of the most respected Italian grapes. In the summer of 2007,a measurement campaign was carried out in a Nebbiolo vineyard located in Vezza d’Alba,near Cuneo,Italy. Using a gauge of trade gases and some other instruments,we recorded the stomatal conductance and also some physiological parameters useful for estimating the dependence of stomatal conductance on environmental variables. The goal of this experiment was improving the parameterization of grapevine evapotranspiration through the assessment of the stomatal conductance and,in particular,of the functional dependence of the stomatal conductance on the following variables:the photosynthetically active radiation,the atmospheric temperature,the atmospheric moisture deficit,and the carbon dioxide concentration. The observations allowed us to check and,in some cases,to adapt the existing general parameterizations found in literature. The results showed some significant differences with the existing parameterizations concerning the atmospheric temperature,the atmospheric moisture deficit,and the carbon dioxide concentration. The parameterizations obtained in this experiment,although referring to a specific plant and site(namely the Nebbiolo at Vezza d’Alba),could allow assessment of the best environmental conditions under which the Nebbiolo grapevine production is the best,and in future could be tested for other grapevines or climates.

Analysis method of thermal dam deformation

Based on the internal temperature variation of a dam lagging behind the ambient temperature variation,the ambient temperature of continuous variation is disctetized,and the functional expression of the thermal displacement component of the dam caused by single instantaneous temperature variation is obtained.Considering the temporal and spatial distribution law of the ambient temperature and its relation with air and water temperature,the function is expanded into a Taylor series.As a result,the improved thermal displacement component expression for a dam monitoring model is obtained.

Excellent ductility and serration feature of metastable CoCrFeNi high-entropy alloy at extremely low temperatures

Seldom could metals and alloys maintain excellent properties in cryogenic condition, such as the ductility, owing to the restrained dislocation motion.However, a face-centered-cubic(FCC) CoCrFeNi highentropy alloy(HEA) with great ductility is investigated under the cryogenic environment. The tensile strength of this alloy can reach a maximum at 1,251±10 MPa, and the strain to failure can stay at as large as 62% at the liquid helium temperature. We ascribe the high strength and ductility to the low stacking fault energy at extremely low temperatures,which facilitates the activation of deformation twinning.Moreover, the FCC→HCP(hexagonal close-packed) transition and serration lead to the sudden decline of ductility below 77 K. The dynamical modeling and analysis of serrations at 4.2 and 20 K verify the unstable state due to the FCC→HCP transition. The deformation twinning together with phase transformation at liquid helium temperature produces an adequate strain-hardening rate that sustains the stable plastic flow at high stresses, resulting in the serration feature.

Improving the thermal shock resistance of ceramics by crack arrest blocks

Ceramics used in the high temperature environment are inevitably subjected to sudden temperature change, which may lead to catastrophic thermal shock failure due to the intrinsic brittleness of ceramics. In this paper, an experimental platform is designed to realize the in-situ observation during the thermal shock experiments. Experimental results show that all the cracks initiate from one of the edge midpoints and propagate to another one for square specimens. Such experimental observation is consistent with the maximum tensile stress zone with the maximum temperature gradient given by the finite element method(FEM). The different crack modes resulting from different heating rates after thermal shock experiments are observed and analyzed. Comparison between different clamping methods is conducted to study the effects of boundary conditions on the thermal shock experiments. Furthermore, in order to improve the thermal shock performance of alumina ceramics, crack arrest blocks are added near the edge midpoint. The thickness, shape and arrangement of the blocks are systematically investigated to understand the mechanism of improvement of thermal shock resistance.