新型黏弹性阻尼器足尺性能试验研究

黏弹性阻尼器是一种典型的被动控制装置,它可以通过黏弹性材料的剪切滞回耗能起到提高结构阻尼和减小结构地震或风振响应的作用.自主研发了损失系数不小于0.5的黏弹性材料,并基于此材料研发了新型国产黏弹性阻尼器.通过对黏弹性阻尼器足尺试件进行不同应变幅值、加载频率工况下的基本力学性能试验、以及低周疲劳性能试验,研究了不同工况下...     

Impact of different sampling rates on precise point positioning performance using online processing service

In this study, the effect of different sampling rates (i.e. observation recording interval) on the Precise Point Positioning (PPP) solutions in terms of accurac...     

Interaction of linear waves with an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth

The linear water wave scattering and radiation by an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth is investigated by use of the multipole expansion method. The diffracted and radiated potentials are expressed as a linear combination of infinite multipoles placed at the centre of each cylinder with unknown coefficients to be determined by the cylinder boundary conditions. Analytical expressions for wave forces, hydrodynamic coefficients, reflection and transmission coefficients and energies are derived. Comparisons are made between the present analytical results and those obtained by the boundary element method, and some examples are presented to illustrate the hydrodynamic behavior of multiple horizontal circular cylinders in a two-layer fluid. It is found that for two submerged circular cylinders the influence of the fluid density ratio on internal-mode wave forces is more appreciable than surface-mode wave forces, and the periodic oscillations of hydrodynamic results occur with the increase of the distance between two cylinders; for four submerged circular cylinders the influence of adding two cylinders on the wave forces of the former cylinders is small in low and high wave frequencies, but the influence is appreciable in intermediate wave frequencies.     

URANS investigation of the interaction between the free surface and a shallowly submerged underwater vehicle at steady drift

An axisymmetric underwater vehicle (UV) at a steady drift angle experiences the complex three-dimensional crossflow separation. This separation arises from the unfavorable circumferential pressure gradient developed from the windward side toward the leeward side. As is well known, the separated flow in the leeward side gives rise to the formation of a pair of vortices, which affects considerably the forces and moments acting on the UV. In this regard, the main purpose of the present study is to evaluate the role of the leeward vortical flow structure in the hydrodynamic behavior of a shallowly submerged UV at a moderate drift angle traveling beneath the free surface. Accordingly, the static drift tests are performed on the SUBOFF UV model using URANS equations coupled with a Reynolds stress turbulence model. The simulations are carried out in the commercial code STARCCM+ at a constant advance velocity based on Froude number equal to F_n = 0.512 over submergence depths and drift angles ranging from h = 1.1D to h = ∞ and from β = 0 to β = 18.11°, respectively. The validation of the numerical model is partially conducted by using the existing experimental data of the forces and moment acting on the totally submerged bare hull model. Significant interaction between the low-pressure region created by the leeward vortical flow structure and the free surface is observed. As a result of this interaction, the leeward vortical flow structure appears to be largely responsible for the behavior of the forces and moments exerted on a shallowly submerged UV at steady drift.     

Experimental study on wide-shallow composite bucket foundation for offshore wind turbine under cyclic loading

As an appropriate type of foundation for offshore wind turbines (OWTs), wide-shallow composite bucket foundation (WSCBF) is cost-competitive, and it has a unique and special substructure that comprises seven internal rooms arranged in a honeycomb-like structure. In this study, the cyclic behavior of WSCBF for OWTs embedded in saturated clay was investigated using a large-scale model subjected to lateral cyclic loading. The responses of foundation under constant- and various-amplitude cyclic loadings were recorded in terms of displacements, rotations, and bending moments. The variations in stiffness and damping were obtained, and a collaborative bearing mechanical model between the bucket and soil was considered, which was beneficial for improving the stiffness of the whole structure. Accumulative deformation was found to have little effect on the bearing capacity of the foundation. Dynamic analysis in frequency domain was further performed on both moment and rotation data, and the complex, frequency-dependent impedance was also studied.     

双酚A及其类似物对哺乳动物和鱼类神经毒性效应及机制研究进展

双酚A及其类似物双酚S、双酚F、双酚AF和卤代双酚A等双酚类化合物广泛用于生产聚碳酸酯塑料和环氧树脂,生产量大且目前在各种环境介质、食品及人体内均有检出。近年来,研究发现很多神经疾病的发生与双酚类化合物的暴露密切相关,有关双酚A及其类似物的神经毒性日益受到国内外研究者关注。本研究从对动物行为、神经发育、神经递质含量及神经递质代谢等方面综述了双酚类化合物的神经毒性效应及作用机制,为今后进一步探究双酚A类似物的神经毒性作用及其安全性评价提供更多的理论参考。     

海洋自主航行器多海湾区域完全遍历路径规划

海洋自主航行器在对海底地形测绘和水文信息搜集过程中,简单锯齿形完全遍历路径规划算法对多海湾海底地形探测易出现重复区域和遗漏区域的问题。本文提出了遗漏海湾和重复海湾及其进入点、退出点和门户的路径规划环境表达概念,并将其应用在基于行为的锯齿形完全遍历路径规划改进算法中,有效地减少了海洋自主航行器全覆盖地形测绘的重复区域和遗漏区域。在网格化定常流场海域内,对某一阻力特性已知的自主水下机器人进行了完全遍历路径规划仿真,验证了基于重复和遗漏海湾搜索行为的完全遍历路径规划算法的遍历性和不重复性,并降低了区域全覆盖地形测绘任务的耗能。最终,通过小型无人艇湖试验证了算法在完全遍历路径规划中的节能性和实用性。     

乘车软件应用前后出租车寻客路径偏好分析

本文尝试通过模拟出租车的路径选择探索乘车软件推广对出租车寻客路径偏好造成的影响。基于出租车的历史寻客轨迹,提取起终点对之间的出租车寻客路径集,选取路径的行程距离、历史乘客数目、历史载客行程距离等六个指标,对出租车的寻客路径选择行为进行多项Logit模型建模。通过分析模型的系数大小,得到各因子对出租车寻客路径选择的影响以及出租车在起终点对间寻客的偏好因子;通过统计出租车在各行政区内或跨行政区寻客时以各因子为偏好因子的起终点对数目,得到偏好因子的空间分布差异;此外,通过对比乘车软件推广前后的建模结果,得到出租车寻客路径选择偏好的变化规律。     

钢板混凝土联肢剪力墙抗震性能试验研究

以轴压比和钢连梁弯剪比为主要参数,设计并制作了3个1/4缩尺的钢板混凝土联肢剪力墙子结构,对试件施加恒定轴压力和水平往复加载.观察了各试件破坏特征,对比了顶层水平荷载-侧移曲线和骨架曲线以及延性系数和等效黏滞阻尼系数等抗震性能指标.结果表明:高轴压比会使整个试件的延性变差;弯剪比越大试件耗能能力越好,弯剪比越小试件刚度...     

珠江口硒的形态分布特征

硒属于硫族元素,在化学和生物化学性质上,硒与硫、碲相似.它和砷一样也是一种类金属物质.硒广泛存在于自然界中,岩石、土壤、沉积物、水体、生物体以及大气环境都含有不同程度的硒.硒是生物必需的一种微量元素,一方面表现出重要的生物功能,另一方面在较高浓度下也表现出毒性,摄入过多可导致动物和人硒中毒[1].在陆源硒向海洋的输送中河流占重要贡献,河流可能是溶解硒输入海洋的主要来源[2,3].河口区是陆地径流与海水相互混合的地带,其中发生的反应直接影响元素的入海通量,因此研究河口化学元素的行为对估计河流向海洋的输入及建立全球生物地球化学循环模型有十分重要的意义.