Parametric study for underwater blast-induced pipeline response embedded in marine sediments

Abstract

Blast response of submerged pipelines has been a research focus in recent years. In this article, a three-dimensional numerical model is established to investigate dynamic response of pipelines due to underwater explosion. The u–p approximation is integrated into finite element method (FEM) to simulate pore water effect in the seabed. Numerical continuity between hydraulic pressure in the flow field and pore pressure in the marine sediment is guaranteed to realize the blast response of submerged pipelines in ocean environment. Both fluid–structure interaction (FSI) and pipeline–seabed interaction (PSI) have been considered in the proposed model simultaneously. A comprehensive parametric study is carried out after validation of the present model with test data from underground explosion and underwater explosion, respectively. The effect of embedment depth, TNT equivalent, stand-off distance, pipeline diameter, and pipeline thickness to blast response of the submerged pipelines is investigated based on numerical results. Variation of deformation patterns and stress distribution of the pipeline with various installation and structure parameters has been illustrated and discussed to facilitate engineering practice.     

Population connectivity of an overexploited coastal fish,Argyrosomus coronus (Sciaenidae), in an ocean-warming hotspot

The West Coast dusky kob Argyrosomus coronus is a commercially exploited fish with a distribution confined to the Angola–Benguela Frontal Zone (ABFZ) of the southeastern Atlantic Ocean. A previous study revealed that during a recent period of local warming the species extended its distribution into Namibian waters, where it hybridised with the resident and congeneric Argyrosomus inodorus. Environmental changes are a major threat to marine biodiversity and when combined with overfishing have the potential to accelerate the decline of species. However, little is known regarding the evolutionary history and population structure of A. coronus across the ABFZ. We investigated genetic diversity, population structure and historical demographic changes using mtDNA control region sequences and genotypes at six nuclear microsatellite loci, from 180 individuals. A single, genetically homogeneous population was indicated across the distributional range of A. coronus (φ_ST = 0.041, F_ST = 0.000, D = 0.000; p > 0.05). These findings imply that the oceanographic features within the ABFZ do not appear to significantly influence population connectivity in A. coronus, which simplifies management of the species. However, reconstruction of the demographic history points to a close link between the evolutionary history of A. coronus and the environmental characteristics of the ABFZ. This outcome suggests the species’ vulnerability to the rapid environmental changes being observed across this region, and highlights a pressing need for transboundary management to mitigate the impacts of climate change in this global hotspot of seawater temperature changes.     

Development of the cyclic p–y curve for a single pile in sandy soil

Pile foundations that support transmission towers or offshore structures are dominantly subjected to cyclic lateral load induced by wind and waves. For a successful design, it is crucial to investigate the effect of cyclic lateral loads on the pile behavior that is loaded laterally. Although the p–y curve method is generally utilized to design the cyclic laterally loaded pile foundations, the effect of cyclic lateral loads on the pile has not been properly implemented with the p–y curve. This reflects a lack of consideration of the overall stiffness change in soil–pile interaction. To address this, a series of model pile tests were conducted in this study on a preinstalled aluminum flexible pile under various sandy soil conditions. The test results were used to investigate the effect of cyclic lateral loads on the p–y behavior. The cyclic p–y curve, which properly takes into account this effect, was developed as a hyperbolic function. Pseudo-static analysis was also conducted with the proposed cyclic p–y curve, which showed that it was able to properly simulate cyclic laterally loaded pile behavior in sandy soil.     

南海东北部新构造运动及其动力学机制

南海东北部地处欧亚板块与菲律宾海板块的交汇区,新构造运动活跃。根据地震活动性、震源机制解和GPS资料对该区的新构造活动特征进行分析,在此基础上讨论该区新构造运动的动力学机制。分析发现,菲律宾海板块NW向俯冲对该区的影响最为显著,导致了该区较强的地震活动性以及与俯冲方向一致的构造应力场。而印藏碰撞产生的侧向应力传递也影响到该区,控制华南地块向SE方向运动,并与菲律宾海板块的NW向俯冲共同作用,使华南地块在SE向运动的同时伴有逆时针旋转。印藏碰撞的SE向应力传递对俯冲产生的NW向水平挤压的抵消作用,使得地震活动性自东向西减弱以及构造应力场P轴方位角顺时针旋转。在这一背景下,区内滨海断裂带的活动控制了该区的地震、海岸带构造升降等新构造运动。     

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燕山水库的主要环境工程地质问题

本文在简要介绍燕山水库工程地质环境的基础上,分析论述了可能产生的环境工程地质问题。指出水库淹没及浸没、水库诱发地震、坝基渗透变形及膨胀土体稳定问题是该水库的主要环境工程地质问题,并提出了进一步研究的途径。     

华北定点形变的小波分析与地震活动研究

利用小波分析方法对华北地区１９９０ 年到１９９８ 年的多台定点形变观测资料进行了分析计算,并将计算结果与该地区的地震活动进行了对比分析,同时讨论了不同阶的小波分解结果的物理意义及其与地震之间的对应关系。认为小波分解本质是窗口加权滑动平均,能有效地对各种不同频率成分的形变按不同的频段分离,为识别地震形变异常提供一种新的手段。在空间分布上,地形变的变化幅度与地震活动强度相对应,即在华北西北部地震活动性较强的包头、张家口一带,台站形变的强度明显高于华北东南部地震活动性较弱的泰安、营口等地区。在时间分布上,张北ＭＬ６ ．２ 级地震前大约两年东西方向的形变振幅随时间变化明显加大。     

Impacts of Aerosol-Radiation Interactions on the Wintertime Particulate Pollution under Different Synoptic Patterns in the Guanzhong Basin,China

The effects of aerosol–radiation interactions(ARI) are not only important for regional and global climate, but they can also drive particulate matter(PM) pollution. In this study, the ARI contribution to the near-surface fine PM(PM2.5)concentrations in the Guanzhong Basin(GZB) is evaluated under four unfavorable synoptic patterns, including "northlow", "transition", "southeast-trough", and "inland-high", based on WRF-Chem model simulations of a persistent heavy PM pollution episode in January 2019. Simulations show that ARI consistently decreases both solar radiation reaching down to the surface(SWDOWN) and surface temperature(TSFC), which then reduces wind speed, induces sinking motion,and influences cloud formation in the GZB. However, large differences under the four synoptic patterns still exist. The average reductions of SWDOWN and daytime TSFC in the GZB range from 15.2% and 1.04°C in the case of the"transition" pattern to 26.7% and 1.69°C in the case of the "north-low" pattern, respectively. Furthermore, ARI suppresses the development of the planetary boundary layer(PBL), with the decrease of PBL height(PBLH) varying from 18.7% in the case of the "transition" pattern to 32.0% in the case of the "north-low" pattern. The increase of daytime near-surface PM2.5 in the GZB due to ARI is 12.0%, 8.1%, 9.5%, and 9.7% under the four synoptic patterns, respectively. Ensemble analyses also reveal that when near-surface PM2.5 concentrations are low, ARI tends to lower PM2.5 concentrations with decreased PBLH, which is caused by enhanced divergence or a transition from divergence to convergence in an area. ARI contributes 15%–25% toward the near-surface PM2.5 concentrations during the severe PM pollution period under the four synoptic patterns.     

In situ stress field of eastern Australia

New in situ data based on hydraulic fracturing and overcoring have been compiled for eastern Australia, increasing from 23 to 110 the number of in situ stress analyses available for the area between and including the Bowen and Sydney Basins. The Bowen Basin displays a consistent north‐northeast maximum horizontal stress (σ_H) orientation over some 500 km. Stress orientations in the Sydney Basin are more variable than in the Bowen Basin, with areas of the Sydney Basin exhibiting north‐northeast, northeast, east‐west and bimodal σ_H orientations. Most new data indicate that the overburden stress (σ_V) is the minimum principal stress in both the Bowen and Sydney Basins. The Sydney Basin is relatively seismically active, whereas the Bowen Basin is relatively aseismic. Despite the fact that in situ stress measurements sample the stress field at shallower depth than the seismogenic zone, there is a correlation between the stress measurements and seismicity in the two areas. Mohr‐Coulomb analysis of the propensity for failure in the Sydney Basin suggests 41% of the new in situ stress data are indicative of failure, as opposed to 13% in the Bowen Basin. The multiple pre‐existing structural grains in the Sydney Basin further emphasise the difference between propensity for failure in the two areas. Previous modelling of intraplate stresses due to plate boundary forces has been less successful at predicting stress orientations in eastern than in western and central Australia. Nonetheless, stress orientation in the Bowen Basin is consistent with that predicted by modelling of stresses due to plate boundary forces. Variable stress orientations in the Sydney Basin suggest that more local sources of stress, such as those associated with the continental margin and with local structure, significantly influence stress orientation. The effect of local sources of stress may be relatively pronounced because stresses due to plate boundary forces result in low horizontal stress anisotropy in the Sydney Basin.     

Preliminary 3–D geological model of the Kalgoorlie region,Yilgarn Craton,Western Australia,based on deep seismic‐reflection and potential‐field data

The granite‐greenstone terranes of the Eastern Goldfields Province, Yilgarn Craton, Western Australia, are a major Australian and world gold and nickel source. The Kalgoorlie region, in particular, hosts several world‐class gold deposits. To attempt to understand why these deposits occur where they do, it is important to understand the crustal architecture in the region and how the major mineral systems operate in this architecture. One way to understand these relationships is to develop a detailed 3–D geological model for the region. The best method to map the 3–D geometry of major geological structures is by acquisition and interpretation of seismic‐reflection profiles. To contribute to this aim, a grid of deep seismic‐reflection traverses was acquired in 1999 to examine the 3–D geometry of the region in an area including the Kalgoorlie mineral region and mineral fields to the north and west. This grid was tied to the 1991 regional deep seismic traverse and 1997 high‐resolution seismic profiles in the same region. The grid covers an area measuring approximately 50 km wide by 50 km long and extended to a depth of approximately 50 km (below the base of the crust in this region). The resulting 3–D geological model was further constrained by both surface geological data and geophysical interpretations, with the seismic interpretations themselves also constrained by gravity and magnetic modelling. The 3–D model was used to investigate the geometric relationships between the major faults and shear zones in the area, the relationship between the granite‐greenstone succession and the basement, and the spatial relationships between the greenstones and the granites. Interpretation of the grid of seismic lines and construction of the 3–D geological model confirmed the existence of the detachment surface and led to the recognition that the granite‐greenstone contact usually occurs at a much shallower level than the detachment. Also, west‐dipping faults in the vicinity of the Golden Mile, including the Abattoir Shear through to Boulder‐Lefroy Fault, appear to be more important than previously thought in controlling the structure of that area. An antiformal thrust stack occurs beneath a triangle zone centred on the Golden Mile. The Black Flag Group was deposited in a probable extensional setting, and late extension was also probably more important than previously thought. The granite‐gneiss domes were uplifted by the formation of antiformal thrust stacks at depth beneath them.