Nonlinear acoustic waves in a collisional self-gravitating dusty plasma

Using the reductive perturbation method, we investigate the small amplitude nonlinear acoustic wave in a collisional self-gravitating dusty plasma. The result shows that the small amplitude dust acoustic wave can be expressed by a modified Korteweg-de Vries equation, and the nonlinear wave is instable because of the collisions between the neutral gas molecules and the charged particles.     

The effect of mass-transport deposits on the younger slope morphology,offshore Brazil

The effect of Cenozoic mass-transport deposits (MTDs) on the morphology of the Late Neogene to Quaternary seafloor is investigated using a 3D seismic volume from offshore Brazil. The studied MTD shows large remnant blocks deforming the seafloor several Ma after a principal instability event marking the base of the investigated strata. Remnant blocks formed during this latter instability event were quickly buried, with differential compaction between individual blocks and adjacent debrites triggering: a) seafloor instability on the flanks of uncompacted (remnant) blocks, b) the incision of submarine channels between seafloor highs formed by buried remnant blocks, c) local uplifted areas on the seafloor that may form potential triggers for future slope instabilities. The interpreted data show that palaeo-seafloor scarps reached more than 120 m in height, with flanking strata to remnant blocks reaching angles of 15°. Angles of this magnitude caused local collapse of seafloor strata and, in some intervals, the confinement of younger MTDs sourced from the upper slope. The statistical data presented here indicate that differential compaction over heterogeneous MTDs continued well after early burial, still deforming the seafloor c. 15 Ma after the main instability event. In addition, significant structural traps are formed by forced folds on remnant blocks that not experienced substantial compaction. Therefore, we conclude that MTDs on passive margins can control seafloor topography after early burial, at the same time contributing to the formation of significant structural traps in post-MTD successions.     

Teleparallel equivalent theory of (1+1)-dimensional gravity

A theory of (1+1)-dimensional gravity is constructed on the basis of the teleparallel equivalent of general relativity. The fundamental field variables are the tetrad fields e_i^μ and the gravity is attributed to the torsion. A dilatonic spherically symmetric exact solution of the gravitational field equations characterized by two parameters M and Q is derived. The energy associated with this solution is calculated using the two-dimensional gravitational energy--momentum formula.     

Hydrodynamic Forces and Instability of Submarine Pipelines Under Waves and Currents： A Review

Stability design of submarine pipelines is a very important procedure in submarine pipeline engineering design. The calculation of hydrodynamic forces caused by waves and currents acting on marine pipelines is an essential step in pipeline design for stability. The hydrodynamic forces-induced instabilities of submarine pipelines should be regarded as a wave/ current-pipeline-seabed interaction problem. This paper presents a review on hydrodynamic forces and stability research of submarine pipelines under waves and currents. The representative progress including the improved design method and guideline has been made for the marine pipelines engineering design through experimental investigations, numerical simulations and analytical models. Finally, further studies on this issue are suggested.     

高山峡谷地区桥址区岩溶发育特征地球物理勘察

发育深度、充填物、展布方向等岩溶发育特征是在高山峡谷地区进行桥址区地球物理勘察时需要重点考虑的问题,受风化物、岩层、地下水和地形等因素影响,很难得到满意的地球物理勘察信息.某悬索桥建于岩溶发育的高山峡谷地区,为了提高勘察效率,采用浅层地震、音频大地电磁、对称四极测深3种地球物理勘察方法,勘察精度依次提高,勘察内容相互印...     

泥沙粒径组成的不均匀性对海岸地形演变的影响

海岸的泥沙输沙模式决定着海岸地形的演变特征,不同的输沙模式会导致形成横向和倾斜沙坝、裂流沟槽等不同的地貌特征。本研究提出了一种考虑泥沙分布不均匀性的新输沙率公式,该公式包含了反映泥沙粒径不均匀性的概率加权和考虑泥沙颗粒遮蔽效应的加权。该公式所给出的载沙量与传统输沙率公式的对比表明,相同中值粒径下,二者有明显差异。将该输沙率公式应用于地形线性不稳定分析,所得到的地形不稳定性增长率不同于假定泥沙为均匀的结果,对应的地形变形波长也有所差别。     

南海东北部亚中尺度过程时空分布特征

基于高分辨率模型2009-2012年的模拟结果,本文对南海东北部亚中尺度过程的时空分布特征进行了研究。模拟结果表明,南海东北部上层广泛存在着相对涡度接近于局地行星涡度的亚中尺度过程。统计结果发现,亚中尺度过程的相对涡度的分布具有着明显的非对称性,即正涡度明显强于负涡度。这意味着相比于负涡度,具有正涡度的亚中尺度过程要更为活跃,而这主要是由离心不稳定导致。同时,亚中尺度过程在时间分布上表现出明显的冬强夏弱的季节变化特征。通过对该海区亚中尺度过程可能生成机制的分析发现,该季节变化与流场拉伸和混合层的厚度有着密切关系,冬季更强的流场拉伸和更深的混合层有利于通过锋生过程和混合层不稳定为亚中尺度过程生成提供更多的能量。     

Parametric Resonance Analyses for Spar Platform in Irregular Waves

The parametric instability of a spar platform in irregular waves is analyzed. Parametric resonance is a phenomenon that may occur when a mechanical system parameter varies over time. When it occurs, a spar platform will have excessive pitch motion and may capsize. Therefore, avoiding parametric resonance is an important design requirement. The traditional methodology includes only a prediction of the Mathieu stability with harmonic excitation in regular waves. However, real sea conditions are irregular, and it has been observed that parametric resonance also occurs in non-harmonic excitations. Thus, it is imperative to predict the parametric resonance of a spar platform in irregular waves. A Hill equation is derived in this work, which can be used to analyze the parametric resonance under multi-frequency excitations. The derived Hill equation for predicting the instability of a spar can include non-harmonic excitation and random phases. The stability charts for multi-frequency excitation in irregular waves are given and compared with that for single frequency excitation in regular waves. Simulations of the pitch dynamic responses are carried out to check the stability. Three-dimensional stability charts with various damping coefficients for irregular waves are also investigated. The results show that the stability property in irregular waves has notable differences compared with that in case of regular waves. In addition, using the Hill equation to obtain the stability chart is an effective method to predict the parametric instability of spar platforms. Moreover, some suggestions for designing spar platforms to avoid parametric resonance are presented, such as increasing the damping coefficient, using an appropriate RAO and increasing the metacentric height.     

地震精密水准网平差的一种高效算法研究

传统的地震水准网平差计算方法因需要进行大量的“零乘积”运算而致使运算效率低下,不适用于数据量较大的地震水准网计算工作。针对地震水准网平差计算过程中法方程系数具有对称正定的特性,利用变量循环重新编号法进一步提升运算效率。利用新算法进行数据平差计算,对比验证结果表明,与传统算法相比,地震精密水准网型越复杂,新算法节省的时间越多。     

A multi-model study of the restratification phase in an idealized convection basin

The representation of baroclinic instability in numerical models depends strongly upon the model physics and significant differences may be found depending on the vertical discretization of the governing dynamical equations. This dependency is explored in the context of the restratification of an idealized convective basin with no external forcing. A comparison is made between an isopycnic model including a mixed layer (the Miami Isopycnic Coordinate Ocean Model, MICOM), its adiabatic version (MICOM-ADIAB) in which the mixed layer physics are removed and the convective layer is described by a deep adiabatic layer outcropping at the surface instead of a thick dense mixed layer, and a z-coordinate model (OPA model).In the absence of a buoyancy source at the surface, the mixed layer geometry in MICOM prevents almost any retreat of this layer. As a result, lateral heat exchanges in the upper layers are limited while mass transfers across the outer boundary of the deep convective mixed layer result in an unrealistic outward spreading of this layer. Such a widespread deep mixed layer maintains a low level of baroclinic instability, and therefore limits lateral heat exchanges in the upper layers over most of the model domain. The behavior of the adiabatic isopycnic model and z-coordinate model is by far more satisfactory although contrasted features can be observed between the two simulations. In MICOM-ADIAB, the more baroclinic dynamics introduce a stronger contrast between the surface and the dense waters in the eddy kinetic energy and heat flux distributions. Better preservation of the density contrasts around the dense water patch maintains more persistent baroclinic instability, essentially associated with the process of dense water spreading. The OPA simulation shows a faster growth of the eddy kinetic energy in the early stages of the restratification which is attributed to more efficient baroclinic instability and leads to the most rapid buoyancy restoring in the convective area among the three simulations. Dense water spreading and warm surface capping occur on fairly similar time scales in MICOM-ADIAB although the former is more persistent that the latter. In this model, heat is mainly transported by anticyclonic eddies in the dense layer while both cyclonic and anticyclonic eddies are involved in the upper layers. In OPA, heat is mainly brought into the convective zone through the export of cold water trapped in cyclonic eddies with a strong barotropic structure. Probably the most interesting difference between the z-coordinate and the adiabatic isopycnic model is found in the temperature distribution ultimately produced by the restratification process. OPA generates a spurious volume of intermediate water which is not seen in MICOM-ADIAB where the volume of the dense water is preserved.