【作者】 黄文峰；

【导师】 李志军；

【作者基本信息】 大连理工大学 ， 港口、海岸及近海工程， 2013， 博士

【摘要】 季节性冰盖的生消是我国北方地表水体的重要现象之一,如江河、湖泊、水库等。静态水体生长的湖泊冰盖对水体环境和工程设施可产生以下影响：一是冰盖几乎切断了大气-水体物质交换和削弱了其间的能量交换,改变了水体生态环境。例如,冰层切断了气-水气体交换可引起水体缺氧；冰层的透光性质和热传导性质控制着冰下水体的光、热结构,影响到水生生物和微生物的活动强度。二是受岸坡和水工结构物的限制,冰层温度改变而伴生的热胀冷缩效应,可对水库坝体、护坡、水工建筑物等施加挤压、剪切等荷载,甚至造成破坏。所以,研究冰自身的基本物理性质和热学、力学参数对于冰区环境和工程都具有重要意义。本文连续多个冬季对湖冰开展了现场调查和室内试验,来揭示湖冰生消过程和物理微结构特征,测定湖冰导热系数、剪切和弯曲强度,并探索湖冰微结构对冰热学、力学参数的影响规律和机理。首先,湖冰生消过程和微结构观测结果表明,(1)东北高纬度和青藏高原高海拔热融湖湖冰过程是当地气象过程的结果,融化期的东北平原湖冰和整个冰期高原湖冰存在明显的冰面升华和融化现象。(2)天然湖冰基本由表层颗粒晶体冰(P1或P3型)和中下部柱状晶体冰(S1或S2型)构成,颗粒冰厚度一般不多于最大冰厚的40%。湖冰内气泡特征较为复杂,基本形态可分为圆球型、细圆柱型、线粒型和脊椎型,区域差异显著。青藏高原湖冰内气泡尺寸和含量明显高于前人报告的关于淡水湖冰气泡含量。(3)湖冰晶体类型、尺寸不随冻结时间变化,冰内气泡随冰厚的增加先后出现圆球状气泡区、“洁净的冰”区、细圆柱气泡区,融化期开始后冰内气泡扩张、贯通,含量和尺寸增大；湖冰晶体构成和气泡特征存在年差异,主要受当年水文、气象条件控制。(4)建立了湖冰晶体和气泡参数与生长速率的关系。(5)对比分析淡水湖冰、渤海海冰、夏季北极海冰微结构异同,证实冰内孔隙的形成位置与冰晶体边界分布并不存在明显关系。其次,开展高纬度和高海拔湖冰导热系数测定工作,分析湖冰微结构对导热系数的影响规律。(1)湖冰晶体类型和尺寸对导热系数影响较弱,柱状冰水平向导热系数比竖直向略低(约5%)。东北高纬度湖冰气泡含量低(<3%)对导热系数影响不明显。(2)对比分析以往多孔介质导热系数理论计算模型的优劣,提出综合考虑冰内气泡含量、尺寸和分布形式的联合计算模型来计算湖冰导热系数。(3)尝试测定“高温”湖冰的导热系数,当冰温接近于融点且随着冰温的升高,湖冰导热系数迅速减小,并给出估算高温湖冰导热系数的曲线。再次,大量开展高纬度湖冰单剪强度和三点简支梁抗弯强度试验,测定天然湖冰剪切和弯曲强度,并探索湖冰微结构对其影响规律。(1)率先开展天然淡水湖冰剪切强度测试,在不同加载方向下颗粒冰剪切强度呈现各向同性,柱状冰表现出各向异性；本文从切断晶体比例、晶体边界和裂纹扩展机理等方面探讨冰晶体对湖冰剪切破坏形式和各向同异性的影响机理。(2)大批次开展湖冰弯曲强度测试工作,其中独立测定颗粒冰抗弯强度尚属首次,颗粒、柱状冰抗弯强度的各向同异性特征与抗剪强度相同,并从拉、压裂纹形成和扩展机理分析了冰晶体的影响。(3)冰内气泡含量虽小,但却造成湖冰抗弯强度约15%的降低,主要归因于气泡含量、结构以及其提供了拉伸破坏的原生裂纹。(4)综合评价了加载应变速率和冰温对剪切和弯曲强度的影响,随着温度降低,湖冰强度增大；湖冰峰值强度(或韧-脆转换区)对应的应变速率在2×10-5～5×104/s范围内。本文充分地揭示了湖冰晶体、气泡结构特征,及其年内、年际变化特征,发现湖冰生长过程对微结构的影响关系,并从本质上讨论了湖冰物理微结构对导热系数、剪切和弯曲强度的影响规律和机理。这些成果可为冬季湖泊、水库的运行、管理,水工建筑物的抗冰设计提供科学依据,对评价冰区工程行为和水体环境对气候变化的响应具有重要意义。更多还原

【Abstract】 In norhern China, surface water bodies, such as rivers, lakes and reserviors, are usually characterized by the seasonal growth and decay of ice covers. Static grown ice covers take signifficant impacts on the aquatic environment and engineering infrastructures. On one hand, ice cover obstructs the mass exchange and weakens the heat exchange between air and water, changing the aquatic ecology. For instance, ice cover cut off the gas exchange between atmosphere and water, which can cause a hypoxia. The irradiance tranmissivity and heat conductivity of ice cover takes the charge of the thermal structure of under-ice water, which can influence the activities of hydrobios. On the other hand, constraited by the banks and hydrostructures, thermal forces can be produced in form of compression and shear due to ice temperature variation, and be exerted on or even destroy the infrastructures, such as dams, revetments and water intakes. Therefore, the knowledge of basic physical properties, thermal and mechanical parameters of ice has many implications on ice-infested environment and engineering. The present paper conducted the continuous filed investigations and lab tests of static lake ice during several winters. Its purpose is to reveal the growth and decay process and physical structure of lake ice, to determine the thermal conductivity, shear and flexural strengths, and to discuss the effects of microstructure on the thermal and mechanical properties.Firstly, the investigations of lake ice processes and microstructure indicated that,(1) lake ice covers are the results of local meteorological processes in high-latitude Northeastern plain (NEP) and in high-altitude Qinghai-Tibet Plateau (QTP). The surface ice sublimation and thaw is rigorous after the beginning of melt period in NEP and during the whole ice period of QTP.(2) Lake ice is mainly consituted of the upper granular-grained ice layer (P1or P3ice) and the middle and bottom columnar-grained ice layer (S1or S2ice). The granular layer accounts for less than40%of the maximum thickness. Gas inclussion within lake ice is complicated, with the shape of sphere, slim cylinder, dotted-line and rachis. The gas inclussion is also characterized by site-specitic. QTP lake ice trapped much larger gas content than those reported previously.(3) Lake ice crystal type and size do not alter temporally. However, as the ice cover grows, the spheric bubble band, clear ice and slim cylinder bubble band emerge subsequently. As the ice starts to melt, the expanding and connecting of gas bubbles increases the bubbles sizes and contents. Annual variations of ice crystalline and gas structure are controlled by the changing local hydrology and meteorology.(4) The relationships of lake ice growth rate with ice crystal size and gas content were developed.(5) The microstructural intercomparisons of freshwater lake ice, Bohai Sea sea ice and summer Arctic sea ice were evaluated, and it is proved that the position of voids incorporated in ice is not related signifficantly to ice crystal boundaries.Secondly, the thermal conductivities of lake ice in high latitude and altitude were measured several times, and the effects of microstructure on conductivity were analyzed. The results showed that,(1) the size and orientation of ice crystal have minor effects on the thermal conductivity. Horizontal thermal conductivity of columnar ice is slightly smaller than vertical one by～5%. Gas inclusion does not take effective impacts on the conductivity of NEP high-latitude lake ice, due to its too minor gas content (<3%).(2) Previous porous medium models for thermal conductivity calculation were validated. Considering the effects of gas content, size and structure, a new synthetical model was formulated to determine the lake ice thermal conductivity.(3) A tempt to measure thermal conductivity of "warm" ice was conducted. For warm ice, as the ice temperature increases near the melt point, the thermal conductivity decreases drastically. A new curve was proposed to estimate the thermal conductivity of warm lake ice.Thirdly, a great number of single-plane shear tests and three-point singly supported beam tests were carried out to determine the shear and flexural strengths of NEP high latitude lake ice. The effects of microstructure were also analyzed on lake ice strengths. The findings are as follows:(1) a large quantities of shear tests were precursively done for natural lake ice. The granular-and columnar-grained ice have an isotropic and anisotropic shear behavior. The cross-crystal force, cohesion friction of crystal boundary and crack propagation were introduced to account for the failure modes and anisotorpy of ice specimens.(2) A large group of simple beam tests were conducted. The flexural strength of columnar ice has not been reported previously. The directional differences of flexural strengths is similar to those of shear tests for granular and columnar ice. The crystal effects were discussed from the aspects of the compression and tension crack formation and propagation.(3) Although the gas content difference is quite small, it seems to cause15%depress in flexural strength of bubbly ice specimen. This is largely attributed to gas structure that acts as the original crack in tension stress field.(4) The effects of the strain rate and ice temperature were estimated synthetically. Lake ice strengths increase with the decreasing temperature. The peak strengths takes up at strain rate of2×10-5～5×10-4/s (i.e. ductile-brittle transition section).Generally, the present thesis thoroughly revealed the features, and the inter-and intra-annual variations of lake ice crystal and gas pore structure, and formulated the relationship between the ice growth rate and microstructure. The effects of microstructure on the thermal conductivity, shear and flexural strengths were also discussed essentially. The findings of this thesis would provide good grounds for the running and management of wintertime lakes and reservoirs, and for the anti-ice design of hydro-infrastructures, and also have important implications for assessing the responses of the ice-infested engineerings and equatic environment to the climate change.更多还原