不同外边界条件下冻结黏土冻胀力试验研究

在自行研制的一套温度、压力、位移、水分均可控的人工冻土多功能冻胀试验系统上,开展了不同外载荷,单、双向冻结模式,预留一定冻胀量等不同外边界条件下黏土冻胀力试验。得出外荷载对冻胀力发展有明显抑制作用,冻胀力变化曲线由上凸型逐渐向下凹型过渡;冻结模式对冻胀力影响很大,双向冻结模式条件下使冻胀力增长明显,但增幅随冷源温度降低呈二次曲线衰减;同一试样的冻胀力与冻胀量可用二次抛物线来拟合。试验获得了更接近工程现场实际冻结工况下黏土冻胀特性,为多排管冻结设计提供参考。     

封闭系统正冻土水流的一个计算模型

A computational model of water migration flux of fine porous soil in frost heave was investigated in a closed system. The model was established with the heat-mass conservation law and from some previous experimental results. Through defining an auxiliary function an empirical function in the water migration flux, which is difficult to get, was replaced. The data needed are about the water content along the soft colunm after test with enough long time. We adopt the test data of sample soil colunms in [1] to verify the model. The result shows it can reflect the real situation on the whole.     

保温层梯形渠道温度场数值模拟对比分析

结合相关规范,利用通用有限元软件 ADINA对季节性冻土区不设置保温层与铺设保温苯板下的渠道温度场进行了数值模拟对比分析。结果表面：铺设保温苯板后的渠道,不仅苯板下温度已为正温,而且冻胀量相对于未设置苯板的渠道明显减小,充分说明保温法对于渠道抗冻胀是一种有效的措施。     

人工冻土冻胀融沉问题研究现状与展望

介绍了冻胀融沉问题和人工冻土冻胀融沉问题的特殊性；冻胀融沉问题的研究现状，包括冻胀机理和冻胀预报模型；融沉机理和影响融沉的主要因素；与冻胀融沉有关的参数测试的进展情况；工程中控制冻胀量和融沉量的一般方法；分析了冻胀融沉问题研究目前存在的问题；并展望了今后的发展方向。     

1961—2015年贵州省中西部初霜、终霜及霜期的时空演变

基于1961—2015年贵州省中西部逐日气温观测资料,运用趋势分析法、空间插值法和小波分析法等研究了贵州省中西部地区初、终霜及霜期的时空演变。研究表明:贵州省中西部地区霜的变化大致呈初霜延迟、终霜提前、霜期缩短趋势。各站点初、终霜及霜期变化趋势空间分布存在明显差异性,各站点初霜日期变化与年平均温度变化均呈正相关,终霜日期变化与年平均温度变化均呈负相关,霜期变化与年平均温度变化均呈负相关,且部分地区相关性显著。初霜变化时间尺度存在周期震荡中心为28a,终霜变化无明显震荡周期,霜期变化时间周期震荡中心为13a。     

基于Monte Carlo模拟的软土基坑隆起风险评估研究

基于圆弧滑动模型确定的安全系数,将基坑隆起破坏的不利事件划分为5种情况,利用Monte Carlo模拟确定不利事件发生概率,提出了考虑基坑隆起破坏引起的不利事件发生概率及经济损失的风险评估模型。将所提方法应用于福州地铁2号线某基坑工程中,结果表明,当围护结构插入比小于1.2时,加固对基坑隆起破坏损失期望减小效果显著;当围护结构插入比大于1.2时,加固对基坑隆起破坏损失期望减小效果一般;当插入比小于0.8时,基坑隆起破坏的损失期望等级属于“严重”;当插入比介于0.8～1.2时,基坑隆起破坏的损失期望等级属于“需要考虑”;当插入比大于1.2时,基坑隆起破坏的损失期望等级属于“可忽略”。     

Multiphysics extension to physically based analyses of pipes with emphasis on frost actions

Pipes, especially buried pipes, in cold regions generally experience a rash of failures during cold weather snaps. However, the existing heuristic models are unable to explain the basic processes involving frost actions. This is because the frost action is not a direct load but one that causes variations in pipe-soil interactions resulting from the coupled thermohydro-mechanical process in soils. This paper developed and implemented a holistic multiphysics simulation model for freezing soils and extended it to the analysis of pipe-soil systems. The theoretical framework was implemented to analyze both static and dynamic responses of buried pipes subjected to frost actions. The multiphysics simulations reproduced phenomena commonly observed during frost actions, e.g., ice fringe advancement and an increase in the internal stress of pipes. The influences of important design factors, i.e., buried depth and overburden pressure, on pipe responses were simulated. A fatigue cracking criterion was utilized to predict the crack initialization under the joint effects of frost and dynamic traffic loads. The frost effects were found to have detrimental effects for accelerating fatigue crack initialization in pipes.     

Experimental study on the anti-jacking-up performance of a screw pile for photovoltaic stents in a seasonal frozen region

The soils in seasonal frozen regions freeze and thaw frequently, causing severe frost heave and thaw settlement problems, which bring challenges to piles of photovoltaic stents. In this paper, laboratory tests are conducted with different types of screw piles under freezing conditions, with also using smooth piles for contrast. The aim is to simulate the freezing process of screw piles according to practical working conditions based on the similarity principle. Internal thermal resistance is ignored. The change laws of temperature, displacement, as well as the influence factors of types of screw piles are analyzed. The results indicate that: with a freezing depth of 30 cm, which is half of the pile length, large-double-bladed screw piles perform the best in antijacking-up, while all-bladed screw piles perform the worst, independent of the types of soil samples tested. The fitting relationship between jacking-up displacement and freezing depth is also proposed for each type of pile. Results obtained can provide an important reference to site construction in seasonal frozen regions.     

深部回采巷道底臌锚杆支护研究

针对鸡西东海煤矿采深1160m条件下,巷道产生底臌现象的实际情况,对32号层五采区四段回风平巷,应用底板锚杆支护进行研究。结果表明,在原有巷道支护的基础上加打底锚能够有效地控制底臌和巷道两帮的移近量,减少巷道围岩的变形量,保证巷道的稳定性,从而保证生产的正常进行。     

升沉补偿系统实验平台设计

海上作业时母船或平台受到海浪影响会产生大幅升沉运动,影响作业安全与工作效率,升沉补偿装置可以极大地改善海上工作环境.针对升沉补偿装置的研究和学生实验的教学需要,该文设计了一种升沉补偿系统实验平台,采用六自南度平台模拟真实的海上船只升沉运动,采用液压系统模拟负载在海上的受力情况,从而可以真实地反映海上工作情况.将主动控制...     

冻融环境下补偿收缩混凝土抗冻性能试验研究

为了研究补偿收缩混凝土的抗冻性能,采用慢冻法对普通混凝土和补偿收缩混凝土进行冻融对比试验。通过对比研究普通混凝土和补偿收缩混凝土冻融后质量损失、强度损失和相对动弹性模量变化趋势,从而得出补偿收缩混凝土的抗冻性能。试验结果表明,普通混凝土冻融100次后,质量损失率为2.09%,抗压强度下降35.2%,相对动弹性模量下降到60.8%;补偿收缩混凝土质量损失率为1.62%,抗压强度下降30.3%,相对动弹性模量下降到64.8%;试验三个参数指标表明添加膨胀剂有助于提高混凝土抵抗冻融破坏的能力,改善混凝土结构的损伤程度,体现了膨胀剂对混凝土的增强机理。     

高寒地区隧道的冻害机理综述

简述衬砌混凝土的冰冻破坏、局部存水冻胀破坏、冻胀性围岩冻胀破坏以及既有裂缝裂隙水的冻胀破坏等因素对高寒地区隧道的冻害机理。     

巷道底臌的治理与研究

根据爆破卸压的原理，在巷道底板通过爆破进行局部松动破坏形成一个松动圈，从而达到减缓或消除底臌，并研究单面卸压技术参数，对施工关键环节加以论述，为现场应用提供指导。     

Modeling of growth stress gradient effect on the oxidation rate at high temperature

A new oxidation kinetics model is established for high-temperature oxidation. We assume that the interface reaction is fast enough and the oxidation rate is controlled by diffusion process at high temperature. By introducing the growth stress gradient we modify the classical oxidation parabolic law. The modified factor of the oxidation rate constant is a function of growth strain, environment oxygen concentration, and temperature. The modeling results show that the stress gradient effect on the oxidation rate cannot be ignored. Growth strain will dominate whether the stress gradient effect promotes or slows down the oxidation process. The stress gradient effect becomes weaker at higher temperature. This effect is amplified at higher concentrations of environmental oxygen. Applied mechanical loads do not affect the oxidation rate. This model is available for high temperature oxidation of metals and alloys.     

基于属性约简的混凝土抗冻性挖掘方法

粗糙集中的属性约简是在保持信息库分类能力不变的条件下,通过删除其中不相关或不重要的属性得到的条件属性集合。影响混凝土抗冻性的主要因素有外加济、含气量、骨料、水灰比和坍落度等。文章主要利用属性约简算法,对混凝土的抗冻性进行决策性挖掘。     

基于比例风险退化模型的产品可靠性评估

为了利用退化数据评估长寿命产品的可靠性,提出一种新的比例风险退化模型.利用时间退化数据与应力加速寿命之间的相似关系,并假定退化数据的失效概率函数是时间协变量的比例函数,从而实现基于比例风险退化模型的可靠性评估.采用最小二乘法估计模型参数.由已知时刻的退化量失效率及比例函数外推产品在特定时间、预定失效阈值下的失效率及可靠度函数.以一种长寿命GaAs激光器的退化数据为例,完成该产品的可靠性评估.结果表明：所提方法能准确描述退化过程,是长寿命产品可靠性评估的一种有效方法.     

Modeling of arc force in plasma arc welding

A three. dimensional mathematical model for the transferred-type argon arc was developed to describe arc force on the anode surface. The software ANSYS was employed to solve the model. The model includes a part of torch and tungsten electrode to achieve m ore reasonable results. The arc temperature and flow fields were derived. And the influences of welding parameters on arc force were also studied. The simulated results show that arc pressure at the anode are dependent on the welding current, plasma gas flow rate and electrode neck-in, while not sensitive to arc length.     

渠道衬砌防渗及抗冻技术在灌区的应用

防渗及抗冻是宝鸡峡灌区输水渠道修建维护和更新改造要解决的基本问题,土质渠道渗漏严重且易冻消垮塌,混凝土衬砌渠道防渗较好但常因受冻而鼓胀破损,严重影响正常有效使用,并存在安全隐患。笔者在实践中调查分析灌区输水渠道冻胀破坏和老化渗漏等情况及原因,提出了灌区渠道防渗及抗冻的一些技术措施,以供参考。     

Iterative learning control of SOFC based on ARX identification model

This paper presents an application of iterative learning control (ILC) technique to the voltage control of solid oxide fuel cell (SOFC) stack. To meet the demands of the control system design, an autoregressive model with exogenous input (ARX) is established. Firstly, by regulating the variation of the hydrogen flow rate proportional to that of the current, the fuel utilization of the SOFC is kept within its admissible range. Then, based on the ARX model, three kinds of ILC controllers, i.e. P-, PI- and PD-type are designed to keep the voltage at a desired level. Simulation results demonstrate the potential of the ARX model applied to the control of the SOFC, and prove the excellence of the ILC controllers for the voltage control of the SOFC.     

Theoretical and experimental studies of heat transfer with moving phase-change interface in freezing and thawing of porous potting soil

Soil in a cold region is subject to frequent freezing and thawing cycles. Soil frozen for a prolonged period may cause adverse freeze damage to the plants due to cell dehydration or root cell rupture. It is important to understand the detailed heat transfer behaviors of the freezing and thawing processes to prevent freeze damage, and to devise proper mitigation measures for effective pot planting in cold regions. A theoretical model was developed to analyze the transient moving phase-change interface heat transfer in the freezing and thawing of porous potting soil. The theoretical derivation is based on the assumption that the soil freezes completely at a single temperature. Microscopic poromechanic effects on heat transfer behavior were ignored. The spatial domain of the problem was simplified to a 1 D spherical coordinate system with variation in the radial direction. Green＇s function was applied to solve for the time-dependent body temperature. Experiments were conducted for validation of the theoretical model Reasonable agreement between the theoretical predictions and experimental measurements was obtained. The theoretical model developed can be easily used to determine the sensitivity of various parameters in the freezing/thawing processes, e.g., thermal properties of soil, ambient temperature, and planting pot size.