A finite element approach for predicting the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay     

《Applied Ocean Research》2019

This paper presents a finite element approach to calculate the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay, in which a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure exists. A modified Mohr-Coulomb model characterized by incorporating a four-phase variation of the mobilized strength and dilation parameters with an equivalent accumulated plastic strain is developed and tested for the overlying dense silica sand. An extended Tresca model is used for the strain softening of the underlying clay. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength and dilation parameters as well as the spudcan geometries. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data, allowing the numerical study to be extended parametrically. The four-phase variation of the mobilized strength and dilation parameters involved in the progressive failure of the upper dense sand is parametrically studied and extended to cover the range of sand relative densities that are of practical interest. Additionally, comparisons with the typical existing LDFE analyses using both simple and sophisticated constitutive models are carried out. It shows that the present approach performs fairly well to calculate the full resistance profile of a spudcan deeply penetration in both thin and thick dense sand overlying clay, especially the peak and post-peak resistance, within around 5% of the corresponding centrifuge tests results.  相似文献   

Quick Phase Identification for Dense Seismic Array with Aid from Long Term Phase Records of Co-located Sparse Permanent Stations     

CHEN Yini  LI Jun  WANG Zhenjie  ZHAO Mengqi  YU Tiehong  LI Danning  YU Junyi  WANG Weitao 《中国地震研究》2020,34(3):328-342

The phase identification and travel time picking are critical for seismic tomography, yet it will be challenging when the numbers of stations and earthquakes are huge. We here present a method to quickly obtain P and S travel times of pre-determined earthquakes from mobile dense array with the aid from long term phase records from co-located permanent stations. The records for 1 768 M ≥ 2.0 events from 2011 to 2013 recorded by 350 ChinArray stations deployed in Yunnan Province are processed with an improved AR-AIC method utilizing cumulative envelope and rectilinearity. The reference arrivals are predicted based on phase records from 88 permanent stations with similar spatial coverage, which are further refined with AR-AIC. Totally, 718 573 P picks and 512 035 S picks are obtained from mobile stations, which are 28 and 22 times of those from permanent stations, respectively. By comparing the automatic picks with manual picks from 88 permanent stations, for M ≥ 3.0 events, 81.5% of the P-pick errors are smaller than 0.5 second and 70.5% of S-pick errors are smaller than 1 second. For events with a lower magnitude, 76.5% P-pick errors fall into 0.5 second and 69.5% S-pick errors are smaller than 1 second. Moreover, the Pn and Sn phases are easily discriminated from directly P/S, indicating the necessity of combining traditional auto picking and integrating machine learning method.  相似文献   

Remnants of the amalgamation of the east and west Cathaysia blocks revealed by a short-period dense nodal array     

《地学前缘(英文版)》2023,14(1):101482

The Cathaysia block located at the southeast South China block (SCB) is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao–Huilai and Zhenghe–Dapu deep faults (here referred as GHF and ZDF, respectively). Although the extension of the ZDF to the northeast, which represents the amalgamation of the two sub-blocks has been confirmed, the development of the GHF to the southwest remains to be verified. To better constrain the detailed deep structure beneath the southwest Cathaysia, which hold great significance for revealing the evolution of the SCB, a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin (SSB). Combining with the regional 10 permanent stations (PA), we obtained two profiles with teleseismic P-wave receiver function stacking. The most obvious feature in our results is the ascending Moho towards the coastal area, which is consistent with the passive margin continental and extensional tectonic setting. The stacking profile from the dense nodal array (DNA) shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB. We deduce that this offset may be casued by the deep extension of the GHF, which represents the remnants of the amalgamation of the Cathaysia block. From the other evidences, we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface. The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB. The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF, which serves as a channel for upwelling hot materials.  相似文献   

Experiments on Exploration of Shallow Fine Structures and the Construction of the 1-D Velocity Model in the Pingtan Island, Fujian     

GUO Yang  XU Jiajun  LIN Chen  JIN Xing  YAO Huajian  YANG Hongfeng  CAI Huiteng 《中国地震研究》2019,33(2):265-275

112 short-period seismographs were set up in the 400km² area of Pingtan Island and its surrounding areas in Fujian. The combined observations of the airgun source and ambient noise source were carried out using a dense array to receive the 387 airgun signals excited around the island and one month of continuous ambient noise recording. The 1-D P-wave and S-wave shallow velocity model of Pingtan Island is obtained by the inversion of the airgun body wave''s first arrival time data, and the reliability of the velocity model is verified by using the surface wave phase velocity dispersion curve, which can provide initial model for subsequent 3-D imaging. The experimental results show that this experiment is a successful demonstration of local scale green non-destructive detection, which can provide basic data for shallow surface structure research and strong vibration simulation of the Pingtan Island.  相似文献   

Storm-driven shelf-to-canyon suspended sediment transport at the southwestern Gulf of Lions     

A. Palanques  J. Guillén  P. Puig  X. Durrieu de Madron 《Continental Shelf Research》2008

Shelf-to-canyon suspended sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300 m depth from November 2003 to March 2004. Two major storm events producing waves H_s>6 m coming from the E–SE sector took place, the first on 3–4 December 2003 (max H_s: 8.4 m) and the second on 20–22 February 2004 (max H_s: 7 m). During these events, shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended sediment on the canyon head and the adjacent outer shelf causing the first downcanyon sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of shelf water stratification. This event was too short to allow the sediment resuspended on the shallow shelf to reach the canyon head. In contrast, the February event, reinforced by dense shelf water cascading, was long enough to transfer resuspended sediment from shallow shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of shelf-to-canyon sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-shelf sediment transport during these events.  相似文献   

He Conductivity in Cool White Dwarf Atmospheres     

S. Mazevet  M. Challacombe  P. M. Kowalski  D. Saumon 《Astrophysics and Space Science》2007,307(1-3):273-277

We investigate the conductivity of warm dense helium under conditions found in the atmospheres of cool white dwarfs using ab initio simulations. The calculations performed consist of quantum molecular dynamics simulations where the electronic wavefunction at each time step is obtained using density functional theory, while the ion trajectories are calculated using the resulting quantum mechanical forces. We use both conventional DFT (PW91) and hybrid (PBE0) functionals to calculate the conductivities that provide an estimate of the ionization fraction. While the calculations are in good agreement with the measurements for the equation of state, a significant discrepancy exists with the recently measured conductivity.  相似文献   

江苏连续三次区域性浓雾形成过程的机理分析   总被引：2，自引：1，他引：1  

濮梅娟  马明明  张雪蓉  王博妮  邵禹晨 《气象科学》2018,38(2):139-148

本文利用常规观气象测资料、NCEP/NCAR再分析资料及风廓线雷达资料和能见度自动观测资料等对2013年12月上旬江苏省连续三次区域性浓雾的特征和发生发展机理进行了详细分析,重点对锋面冷却雾的形成过程进行了研究。结果表明:三次浓雾过程都发生在有利的环流形势下,但成因却显著不同。辐射雾主要由夜间地面辐射冷却配合高湿静风形成,边界层低空急流有利于逆温的形成,为浓雾发展、维持提供条件;平流雾是由海上暖湿平流流经江苏冷的下垫面而形成,东南气流输送充足的水汽、加上稳定的逆温层是平流雾形成的必要条件;锋面雾由冷锋前部的冷平流冷却效应而形成,浓雾主要发生在锋前,但冷锋入侵后,前期充分的水汽积累和动力辐合使锋后能见度依然较低,浓雾继续存在。  相似文献   

Fast rotation of neutron stars and equation of state of dense matter     

Pawe&#x; Haensel  Julian L. Zdunik  Micha&#x; Bejger 《New Astronomy Reviews》2008,51(10-12):785

Fast rotation of compact stars (at sub-millisecond period) and, in particular, their stability, are sensitive to the equation of state (EOS) of dense matter. Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. At such rotational frequency the effects of rotation on star’s structure are significant. We study the interplay of fast rotation, EOS, and gravitational mass of a sub-millisecond pulsar. We discuss the EOS dependence of spin-up to a sub-millisecond period, via mass accretion from a disk in a low-mass X-ray binary.  相似文献   

南京冬季雾爆发性增强的物理特征研究   总被引：22，自引：4，他引：18  

濮梅娟  严文莲  商兆堂  杨军  李子华 《高原气象》2008,27(5)

根据2006年12月在南京市郊观测的3次浓雾过程(12月12日、14日和24~27日)资料,分析了雾的发展过程及爆发性增强特征,探讨了雾体爆发性增强的原因。结果表明:南京冬季雾爆发性增强的物理特征是在很短时间内(30 min以内),能见度急剧下降,雾滴数密度和含水量明显增加、尺度明显增大、雾滴谱变宽。究其原因,发现夜晚长波辐射增强或近地层出现冷平流造成的气温急剧下降,日出后地表水分蒸发或西南湿平流增强造成的湿度明显增大以及湍流混合作用,都能导致雾体爆发性增强。  相似文献   

Measuring the k–S–p relations on DNAPLs migration     

Masashi Kamon  Kazuto Endo  Takeshi Katsumi 《Engineering Geology》2003,70(3-4):351-363

Migration characteristics of dense non-aqueous phase liquids (DNAPLs) in the subsurface can be expressed as a water–DNAPL two-phase system based on mainly the k–S–p relations, which describe the relations among relative permeability (k), degree of water saturation (S), and capillary pressure head (p). The aims of this research are to develop an experimental system with new type of probes, such as the electrical conductivity probe for measuring the degree of water saturation and the hydrophilic and hydrophobic tensiometer for measuring the pore water and DNAPL pressures, and also to estimate the results obtained from the developed experimental system. From these tests, the excellent k–S–p relations were obtained and the efficiency and validity of this developed experimental system have been confirmed in terms of the concept of the scaling coefficient calculated by interfacial tensions.  相似文献