混凝土海工结构的实践与发展

在海况条件下,钢筋混凝土(R.C.)和预应力混凝土(P.C.)的耐久性和经济性比钢优越;轻质混凝土和钢纤维混凝土抗冲击和抗疲劳等性能也比较好,因此,自七十年代初期起,在海洋工程中的应用日益广泛,发展迅速。 (一)石油平台 1973年在挪威建造的Ekofish储油罐是世界上第一个大型混凝土重力式海工结构,标志着混凝土海工结构迅速发展的一个起点。迄今为止,在北海油田已建造安装了15个重力     

添加牡蛎壳粉对混凝土鱼礁性能的影响

探究牡蛎壳粉可替代混凝土中河砂的可行性及其最佳掺量,将牡蛎壳加工成粒径为1～2 mm的牡蛎壳粉后,按不同梯度替代C45混凝土配合比中的河砂,并与普通混凝土试块进行比较,在实验室条件下进行了力学性能实验和溶出物实验,测试其抗压强度、抗渗性能、pH、营养盐。研究表明:(1)牡蛎壳粉可用作混凝土人工鱼礁材料,在抗压强度、抗渗性能不发生显著变化(P0.05)的前提下,牡蛎壳粉最多可替代40%的河砂;(2)牡蛎壳粉部分替代混凝土中河砂后,溶出物的pH显著(P0.05)优于普通混凝土试块中溶出物的pH,并且牡蛎壳粉替代30%的河砂时,其溶出物效果是最优的;(3)牡蛎壳粉礁块组在人工海水中会比普通混凝土礁块组更快地溶出藻类生长所需要的硅酸盐,同时溶出无机氮、磷酸盐的量比普通混凝土组要低。     

基于LabVIEW的自升沉式潜标模拟测试系统设计

自升沉式潜标正式布放使用前应进行大量的测试试验工作。为了能够在岸边或实验室对潜标的各项性能进行验证和调试工作,开发了基于LabVIEW的潜标模拟测试系统。该系统充分利用虚拟仪器的特点,采用模块化编程技术,利用软件模拟潜标在水下的各种运动状态及传感器感应的测量参数变化,或通过对现场测量数据的回放查找分析潜标系统本身存在的缺陷,实现潜标不下水或少下水就可以进行全面测试的目的。实验结果表明,利用模拟测试系统可以进行固定值、极值和连续变化值模拟,能够缩短设备开发周期,优化系统控制方案,对提高产品质量具有非常重要的作用。     

不同含沙量细粒沉积物浑水体流变特性研究

强烈波浪作用在河口海岸区域引发海底沉积物的剧烈扰动,所形成的近底高浓度浑水体可汇集成海底浊流,在污染物和含碳物质自近海向远海输运方面起着重要作用,是陆海相互作用的重要驱动力。而近底高浓度含沙层因含沙量及其中组分的不同,其流动性亦不同。针对海底可能存在的高浓度含沙层,采用流变试验,通过剪切速率-剪切应力间的流变关系对不同含沙量下的粉土浑水体进行流变特性分析,并结合前人所做的不同粉粒黏粒比例、不同含量的浑水体流变测试结果,将粉土浑水体在100～1 350kg/m³含沙量范围内划分为牛顿流体、过渡流体和宾汉流体三种流体类型,给出了以粉粒与黏粒组分为主的含沙浑水体的流变性质变化界限图,为近底高浓度含沙层运动研究提供流体性质分类参照。     

东太平洋粘土沉积物的增白实验研究和结构分析

为了有效开发利用深海粘土，必须针对东太平洋粘土的特点提高其自度和活性。对东太平洋中国大洋调查区粘土沉积物进行湿法提纯后，采用酸溶氢气法以锌做还原剂对其进行了增白处理，并在不同温度下焙烧；分析了酸的类型、浓度、还原剂用量、反直时间及焙烧温度等对粘土增自效果的影响，得出了最佳工艺条件；测定增白前后粘土的物理化学性能和粘土矿物的结构，发现增自的同时还可以提高粘土的比表面积和其在有机溶剂中的分散性；增白后粘土矿物总体上保持了层状结构，但局部结构有一定的破坏，因而提高了粘土矿物的结构活性。     

中国东部陆架海区粒度分析研究进展

沉积物的粒度受到物源区性质、沉积动力条件和搬运方式等因素的控制。自第四纪以来,我国东部陆架区由于海陆变迁、气候突变等古环境演化而沉积了巨厚的沉积物,这些成因特点都在沉积物的粒度特征中得到反映。沉积物粒度分析的经典方法是对粒度测试得到的数据进行计算和整理得到粒度参数和粒度图解,进而分析包括水动力、物源等在内的沉积环境特征。近年来随着计算机技术和数学模型的发展,沉积物粒度的应用也更加多元,如通过陆架区表层沉积物的粒度趋势研究现代沉积输运特征;通过敏感粒度研究高分辨率古气候演化;通过分离钻孔沉积物粒度数据重建古水深变化等。     

软弱砂岩骨料碾压混凝土的配制及其特性研究

在东南亚和我国西南地区由于缺乏合适的原材料,必须采用软弱骨料配制混凝土。以东南亚某工程现场的软弱砂岩为原材料,开展碾压混凝土配制和性能试验工作,探讨了该骨料配制碾压混凝土的可行性。采用软化系数为0.71的软弱砂岩,配制强度等级分别为C18020的二级配碾压混凝土和C1807.5的三级配碾压混凝土。结果表明,采用该砂岩骨料可以配制出满足强度要求的碾压混凝土,其用水量比常规骨料高15~20 kg/m3,拌和物密度和抗压弹模较低。其中,二级配碾压混凝土采用50%粉煤灰掺量、0.55水胶比;三级配碾压混凝土采用60%粉煤灰掺量、0.65水胶比。骨料抗碾压破碎模拟试验表明该骨料在碾压过程中破坏程度很低,说明采用该软弱骨料配制碾压混凝土具有可行性。     

测量船水声换能器透声板防腐涂料测试

针对测量船声学换能器透声板表面腐蚀问题,分析了发生原因和防腐措施的技术途径。提出了兼顾防腐、透声和化学兼容等性能的技术路线,对选择的三种涂料进行声学测试,确定采用在防海生物性能、透声性能和材料间结合性能等方面达到适用的技术方法和涂料。     

基于总有机碳法的超滤膜截留性能测定研究

随着超滤技术在海水淡化预处理的应用推广,其性能检测和质量控制已引起广泛关注。截留性能是判断超滤膜质量优劣的主要指标,科学、准确测量截留性能对超滤膜研发、生产及应用具有重要意义。本文以葡聚糖为超滤膜截留性能测试基准物,研究了总有机碳法测定水溶液中的葡聚糖浓度,并计算超滤膜对葡聚糖的截留率。结果表明,水溶液中的葡聚糖浓度与总有机碳测试峰面积呈良好线性关系,相关系数R达到0.999以上,回收率为89.1%～108%,相对标准偏差为0.3%～2.7%,超滤膜截留率测试结果与现行标准中规定的浊度法一致。方法具有操作简便、重现性好、灵敏度高、稳定可靠等优点,适用于超滤膜截留性能测试。     

山东省龙口煤码头粉煤灰混凝土试验小结

本文介绍了掺粉煤灰混凝土在北方港口工程中的应用试验,主要对粉煤灰混凝土的强度、耐久性等性能进行了试验和研究,取得了较理想的结论,为粉煤灰混凝土的推广和应用积累了经验。     

Traction rheological properties of simulative soil for deep-sea sediment

The traction capacity of the mining machine is greatly in?uenced by the traction rheological properties of the deep-sea sediments. The best simulative soil was prepared for substituting the deep-sea sediment based on the deep-sea sediment collected from the Paci?c C-C mining area. Traction rheological properties of the simulative soil were studied by a home-made test apparatus. In order to accurately describe the traction rheological properties and determine traction rheological parameters, the Newtonian dashpot in Maxwell body of Burgers model was replaced by a self-similarity spring-dashpot fractance and a new rheological constitutive model was deduced by fractional derivative theory. The results show the simulative soil has obvious non-attenuate rheological properties. The transient creep and stable creep rate increase with the traction, but they decrease with ground pressure. The fractional derivative Burgers model are better in describing non-attenuate rheological properties of the simulative soil than the classical Burgers model. For the new traction rheological constitutive equation of the simulative soil, the traction rheological parameters can be obtained by ?tting the tested traction creep data with the traction creep constitutive equation. The ground contact length of track and walking velocity of the mining machine predicted by the traction rheological constitutive equation can be used to take full advantages of the maximum traction provided by the soil and safely improve mining effciency.     

青岛海水拌和混凝土力学性能试验研究

海水拌和的水泥净浆在标准稠度用水量和体积安定性方面与淡水拌和的水泥净浆没有明显差别,但凝结时间提前。水泥胶砂和混凝土的抗压、抗折强度与淡水拌和的相当。海水拌和的混凝土配合比可以采用淡水混凝土的配合比。     

Numerical investigation of the uplift performance of prestressed fiber-reinforced polymer floating piles

Finite element analyses of prestressed fiber-reinforced polymer floating piles subjected to uplift force have been conducted in this paper. First, parameters of the modified BPE model (bond–slip model at the fiber-reinforced polymer–concrete interface) were calibrated using existing pullout testing data on fiber-reinforced polymer rebars embedded in concrete. Nonlinear spring elements were used in numerical modeling to characterize the bond–slip behavior at the fiber-reinforced polymer–concrete interface. A parametric study was performed to assess the influence of rebar diameter, fiber-reinforced polymer material, embedment length, and concrete strength on the mobilized bond stress. Upon the successful modeling of the pullout performance of fiber-reinforced polymer rebars in concrete, numerical models were developed to investigate the dependence of the uplift performance of floating piles on the prestress level, uplift force, fiber-reinforced polymer type, and compressive strength of concrete.     

Compression–shear coupling rheological constitutive model of the deep-sea sediment

In deep-sea mining engineering, the compression–shear coupling effect of the sediment on the moving tracked mining vehicle must be considered, since it is proved to be existing in compression–shear creep test of the sediment simulant. Based on the endochronic theory, the compression–shear coupling rheological model is established by the definition of intrinsic time and calculation of deviatoric tensor, where the coupling rheological parameters can be obtained by the compression–shear creep test. For simulating sinkage and traction force of the moving tracked mining vehicle, the compression–shear coupling rheological model as well as compressive rheological model and direct shear rheological model (regardless of coupling rheological effect) is programmed and introduced into RecurDyn software (with only traditional elastic–plastic constitutive model) for comparison. Research results show that the sinkage is the largest, and the traction force is the smallest under the compression–shear coupling rheological model, which could better reflect the worse working situation. The compression–shear coupling rheological model could provide theoretical basis for optimal design and safety assessment of the tracked mining vehicle.     

海砂颗粒形态评价与海拌混凝土性能研究

为初步评估海洋资源用作混凝土原材料的可行性,先通过数字图像技术求取海砂与河砂颗粒样本的椭圆率、圆度及坚固性参数,对两者颗粒形态特征做出综合评价,然后采用RCT法检测海拌混凝土游离氯离子含量,并测定混凝土不同龄期的抗压强度及碳化深度。结果表明,海砂与河砂颗粒细长程度、棱角及内凹曲面显著程度均非常接近,颗粒形态不存在本质差异;天然海水有助于混凝土早期强度的提升,对后期强度及碳化深度的影响则较为微弱;商品海砂会对混凝土力学性能产生轻微负面影响,并使抗碳化性能大幅下降。     

海洋钢筋混凝土结构牺牲阳极保护系统电极行为的研究

于１９８９－１９９０年在室内条件下，用牺牲阳极保护浸泡于海水中的多种钢筋凝土试件测试不同试件中钢筋极化与阳极布局、涂层质量，涂层厚度及试件浸水情况的关系。结果表明，牺牲阳极能有效地保护全浸海水中的混凝土试件，对间断浸淋海水的试件也有一定的保护作用，通过改善阳极安装工艺，保护作用可望提高；电偶电流在各阴阳极上的分布将随涂层质量，涂层厚度和试件浸水情况不同而异，回路中电阻和电极极化情况是影响电流分布的     

Planar flow model identification for improved navigation of small AUVs

Motivated by the desire to improve the navigation performance of small autonomous underwater vehicles, we seek simple methods for modeling the local flow that affects the vehicle's trajectory. We propose a low-complexity, planar flow field model that consists of a uniform flow component and a singular flow component. Assuming this simplified flow field model, we develop identification algorithms that can be performed quickly using small, sparse data sets collected by a platoon of vehicles. The basic approach involves estimating the uniform flow component, localizing an assumed flow singularity, and identifying the parameters which characterize the singular flow. In order to identify the singular flow component, we propose a least squares and a constrained least squares approach. In the latter case, the minimization is constrained to preserve the average divergence and circulation of the measured flow. Preserving divergence and circulation predictably results in a larger overall error because it eliminates two free model parameters, but it produces a flow model which more realistically captures the flow in the larger region of the measurement points. Numerical simulations and an initial experiment illustrate the parameter identification process as well as the benefits of incorporating a flow field model for vehicle navigation.     

Pulsatile vortex generators for low-speed maneuvering of small underwater vehicles

Compact zero-mass pulsatile jet actuators are proposed for low-speed maneuvering and station keeping of small underwater vehicles.¹ The flow field of such jets are initially dominated by vortex ring formation. Pinched-off vortices characterize the extremum impulse accumulated by the leading vortex ring in a vortex ring formation process. Relevant parameters in this process are identified in order to design simple and low cost zero-mass pulsatile jet actuators. Thrust optimization of synthetic jets for maximal thrust generation is achieved by enforcing the jet formation number to be around 4. Prototypes of such actuators are built and tested for underwater maneuvering and propulsion. The actuators could be used in two ways: (i) to improve the low-speed maneuvering and station keeping capabilities of traditional propeller driven underwater vehicles, and (ii) as a synthetic jet for flow control and drag reduction at higher cruising speeds. A model for calculating the rotation rate of the underwater vehicle is also proposed and verified.     

混凝土联锁排应用于海底电缆防护稳定性研究

海底电缆穿越底质坚硬海床时,覆盖混凝土联锁排可以有效保护海缆。根据国网舟山500 kV海底输电电缆所在海域实测水文数据,采用力学平衡公式和数值模拟两种计算方法,研究混凝土块在极端水流作用下的在位稳定性。基于推导出的力学平衡公式,对其进行函数分析后发现,当混凝土块底边固定时,存在一个极值高度,此时铺设在海床的混凝土块最为稳定,可以抵挡的水流流速最大。通过数值模拟,研究了混凝土联锁排在水流作用下的三维流态特征,对不同形状混凝土块的受力情况进行比较后发现,当混凝土块边缘为圆角时,可以改变边缘周边的水流结构,总体上加强混凝土块的稳定性。经计算,尽管国网舟山500 kV海底输电电缆所在的灰鳖洋海域潮流流速较大,但常规长、宽、高为0.4 m×0.4 m×0.3 m的块体组成的混凝土联锁排可以抵抗水流的冲击,保护海底电缆。     

海底滑坡对海洋单桩冲击力试验研究

为了研究海底滑坡对海洋单桩的冲击力大小,首先通过调整高岭土、粉砂的不同含量,得到不同流变特性、不同密度的碎屑流,采用Herschel-Bulkley模型和幂率模型对流体流变性质进行描述;随后利用自制海底滑坡模型槽,模拟碎屑流在不同流速和黏度下对模型桩的冲击;并结合流体力学理论,建立阻力系数与非牛顿流体雷诺数之间关系表达式。试验数据表明:碎屑流黏度和流速是影响海底滑坡冲击力的主要因素,海底滑坡冲击力随着泥浆黏度和流速的增加而增大。同时,考虑碎屑流剪切稀释特性,得到管桩阻力系数随雷诺数变化的拟合公式,为海洋桩基础设计提供参考。