查看更多>>摘要：In this paper,the influence of the limited-tension interface between lid and soil on the undrained bearing capacity of the wide-shallow bucket foundation is examined by finite element(FE)analysis.The interface between the lid and the soil is modeled using a simplified approach called the surface-based cohesive behavior,with the aim of simulating the limited-tension interface.Ini-tially,the interaction between the lid and the soil is explored under the zero-and unlimited-tension conditions by small-scale experi-ments.Afterward,the effects of the embedment ratio,soil strength heterogeneity,and lid-soil interface on the bearing capacity are outlined,and the failure mechanisms are explained by FE analysis.A modified closed-form formula is given to compute the moment bearing capacity with the limited-tension interface between the lid and the soil for different embedment ratios and soil strength het-erogeneities.The numerical results reveal that the existing approximating solutions,which assume fully bonded interaction,accu-rately exhibit the shape of the normalized failure envelopes in hm and vh load space for the limited-tension interface.However,the shape of the vm envelopes differs,requiring a novel solution to estimate the combined bearing capacity of the bucket foundation based on the embedment ratio and soil strength heterogeneity with a zero-tension interface between the lid and the soil.
查看更多>>摘要：In this paper,a new quasi-zero-stiffness(QZS)nonlinear isolation system using a double-curved beam(DCB)as a nega-tive stiffness structure is proposed,and its performance is investigated.The negative stiffness provided by the DCB to the isolator in the equilibrium position reduces the isolator's overall dynamic stiffness.Static and dynamic characteristics of the system are investi-gated.The amplitude-frequency characteristics and force transmissibility equation of the system were derived via the harmonic bal-ance method.The effects of damping ratio and excitation force amplitude on amplitude-frequency and force transmissibility curves are examined,and the isolation performance is compared with that of an equivalent linear isolator supporting the same mass with the same static deflection as nonlinear isolators.Furthermore,MATLAB numerical simulation software is used to perform dynamic time analysis of the nonlinear isolation system.The results indicate that the amplitude-frequency curves of the nonlinear isolation system exhibit bending,accompanied by discontinuous jumps in frequency.The appropriate increase in the damping ratio or reduction in the excitation amplitude benefits the vibration isolation performance of the nonlinear vibration isolation system.Compared with the equivalent linear isolation system,the QZS isolation system exhibits a better low-frequency vibration isolation performance,which provides a theoretical basis for the design of low-frequency nonlinear isolators.
LE ConghuanSUN QingyuanZHANG PuyangDING Hongyan...
1423-1435页
查看更多>>摘要：The horizontal bearing capacity of the screw pile and monopile was analyzed by model tests.Results showed that the horizontal bearing capacity of the screw pile was significantly greater than that of the monopile under the same loading conditions.With the increase in horizontal loading speed,the ultimate horizontal bearing capacity of the two piles also increases,and the difference decreases gradually.Moreover,the influence of vertical loading on the horizontal bearing capacity of screw pile and monopile is studied at the horizontal loading speed of 2 mm s-1.The findings indicate that vertical load evidently affects the horizontal bearing capacity of common piles,but slightly influences the horizontal bearing capacity of screw piles.
查看更多>>摘要：Since the 1980s,the robust economic growth of China has prompted extensive land reclamation projects along its coast-line,notably affecting local hydrodynamics and resulting in ecological repercussions.Using a nearshore finite volume ocean model,we constructed a hydrodynamic model for Shacheng Bay,a southeastern coastal region with a winding and narrow entrance.We exam-ined the hydrodynamic changes and mangrove dynamics over the past 36 years and the relationship between hydrodynamic altera-tions and mangrove degradation.Simulation results reveal that extensive reclamation projects between 1984 and 2000 weakened the current in Shacheng Bay,leading to decreased water exchange capacity and a significant reduction in mangrove area from 0.3 to 0.06 km2.During this period,over 37%of mangrove degradation was ascribed to time-changing hydrodynamic variables without the di-rect influence of land reclamation.The results also highlight the changes in local hydrodynamics and water exchange patterns that adversely influenced mangrove growth.From 2000 to 2020,there were minimal coastline changes in Shacheng Bay,demonstrating reduced land reclamation activities.This stopped the further weakening trend of the currents,with a slight increase during ebb tides,while the residual current continued to weaken due to the decreasing tidal prism and water exchange capacity.The mangrove area partially recovered during this period,expanding from 0.06 to 0.11 km2,predominantly in new areas instead of where mangroves disap-peared from 1984 to 2000.This work underlines the intricate relationship between land reclamation,hydrodynamics,and mangrove ecosystems,underscoring the need for sustainable coastal development strategies.
查看更多>>摘要：Seed movement is a key hub for the management of Spartina alterniflora.Seed transport patterns under varying domi-nant wind directions and initiation rates were evaluated by tidal model combined with ecological model.Before the simulation,S.alterniflora distribution in the research area was determined and seed deposition rate was measured experimentally.Research find-ings indicated that:1)Wind direction affected the primary direction of seed dispersal for S.alterniflora.2)A positive correlation was discovered between wind speed and the distance traveled by S.alterniflora seeds,such that seeds showed the longest displacement under prevailing summer winds,with maximum displacement of up to 25 m.3)Starting velocity played a key role in the determina-tion of the extent of S.alterniflora seed dispersal.Specifically,when initiation flow velocity reached 0.1 m s-1,seed transport range was maximized.Furthermore,as time progressed,seed transport range continued to expand.
查看更多>>摘要：The active sensor often uses the convergence zone mode to detect a distant target in the deep ocean.However,convergence zones are regions with limited widths that only appear at some discrete distances.Thus,widening the width by adjusting the transmit-ting array depth facilitates target observation and detection.Traversal search is an effective method for determining the optimal depth,but the heavy computation burden resulting from the calculation of the transmission losses at all source depths impedes its application.To solve the problem,a fast method based on ray cluster theory is proposed.Due to the coherent sound field structure in the deep ocean,several ray clusters with different departure angles radiate from the source,where ray clusters with small departure angles reverse in the water and form a convergence zone.When the source is set to a depth that only the first ray cluster inverts in water,the maximum width of the convergence zone is obtained.Based on this,an optimal transmitting array depth selection method utilizing the reversion condition of the first ray cluster is formulated.Simulation results show that the active sensor can achieve a large con-vergence zone width with real-time performance using the proposed method.
查看更多>>摘要：Dissolved carbon(dissolved organic carbon and dissolved inorganic carbon)is the major component of the ocean carbon cycle,representing one of the largest carbon pools on Earth.Cold seeps and hydrothermal systems serve as the two main windows for the material and energy recycling exchange between the lithosphere and outer spheres(biosphere,hydrosphere and atmosphere).How-ever,recent studies have found that the dynamic activities of fluids in these two extreme systems are a crucial source of'new'carbon in the deep ocean.These carbon sources may become vital contributors to carbon and energy in marine ecosystems,which affect the global deep-sea carbon budget,and the marine ecosystems as well.In this review,we summarize the sources and formation mechanisms of dissolved carbon in the seep fluids from the cold seeps and hydrothermal vents,the contribution of methane oxidation to dissolved carbon,and the characteristics of the carbon isotope composition in the fluid.Furthermore,we analyze and discuss the influence of car-bon discharged from seabed on the seawater carbon cycle by comparing and contrasting these two extreme environments.The research may assist in promoting a deeper understanding of the carbon cycle and material interaction in the ocean,particularly further carbon cycle research in the back-arc basin where cold seeps and hydrothermal vents commonly prevail.
查看更多>>摘要：The strength parameters of hydrate-bearing sediments(HBS)are vital to geological risk assessment and control during drill-ing and production operations.However,current publications mainly focus on the laboratory evaluation of strength parameters through triaxial compression,generating results intrinsically deviating from those obtained through petrophysical modeling.In this study,we developed an integrated apparatus that can simultaneously measure wave velocity and the mechanical behaviors of HBS under triaxial compression conditions.A series of experiments were conducted to analyze correlations between wave velocities and strength parameters.Results reveal that the P-and S-wave velocities considerably increase with hydrate saturation and are affected by effective confining pressure.Failure strength and elastic modulus are correlated with P-wave velocity.Finally,semi-empirical models are developed to predict strength parameters based on P-wave velocity and extended to establish longitudinal profiles for strength parameters of hydrate reservoirs in the Nankai Trough.This study offers insights into the acoustic properties of HBS under stress states for the prediction of mechanical parameters during natural gas hydrate development.
查看更多>>摘要：Bioturbation is one of the important processes that affect the structure and function of sedimentary environments.The parti-cle mixing and element migration processes caused by bioturbation can interfere with the circulation of matter and the explanation of sedimentary records.Therefore,the quantitative characterization of bioturbation structures in the sedimentary sequence is of great sig-nificance in the field of sedimentology.Estuaries,where fresh and saltwater mix,exhibit high ecological heterogeneity and biodiversity,making them ideal places to explore bioturbation.This paper targets the subaqueous Yellow River Delta to quantitatively characterize bioturbation structures and their spatial distribution patterns using computed tomography(CT)scanning and three-dimensional recon-struction technology.By combining sediment characteristics and sedimentary environment analysis,the main factors affecting bioturba-tion structures are elucidated.The results show that bioturbation structures in the subaqueous Yellow River Delta can be divided into four types based on their morphology:uniaxial type,biaxial type,triaxial type,and multiaxial type.Skolithos,Palaeophycus in the uni-axial type,and Thalassinoides in the multiaxial type are the most developed structures.Different types of bioturbation may be con-structed by trace-making organisms belonging to the same category or functional group.The intensity of bioturbation in this area ranges from 0 to 4%,with a decreasing trend from nearshore to offshore.There is a downward decreasing trend in the intensity of bioturbation overall in the sedimentary cores,with three vertical distribution patterns:exponential decay pattern,fluctuating decay pattern,and impul-sive pattern.The impulsive pattern of bioturbation in a core may indicate the abrupt change in sedimentary environment induced by the Yellow River channel shift in 1996.These results suggest that factors affecting the development of bioturbation include grain size,porosity,consolidation,organic matter content of sediments,and sedimentation rate that is mainly influenced by local hydrodynamic conditions.The environment with clayey silt(average grain size 10 μm)and moderate sedimentation rate(around 0.5 cm yr-1)is the most suitable area for the development of bioturbation in the Yellow River subaqueous delta.
查看更多>>摘要：Inductively coupled mooring chain transmission technology plays a crucial role in the long-distance online monitoring of marine hydrographic information.However,the impedance characteristics of the seawater medium pose a limitation on its capability to achieve high-speed real-time transmission of underwater images.In this paper,based on the principle of inductively coupled transmis-sion for marine applications,the selected 1920×1080 pixel images are segmented,packaged,and then transmitted to the sending node using the user datagram protocol(UDP),and the modulation and demodulation of the transmitted images are realized using the orthogo-nal frequency division multiplexing(OFDM)algorithm of least squares(LS)estimation,and eight combinations with different mapping modes and coding rates are tested in the bandwidth of 200-800 kHz and the quality of the transmitted images is evaluated using three criteria:mean squared error(MSE),peak signal to noise ratio(PSNR),and structural similarity index(SSIM).The results indicate that the image transmission quality is optimal when the mapping method is 16-quadrature amplitude modulation(16QAM),the coding rate is 1/2,and the center frequency is 800 kHz.Under these conditions,the maximum transmission rate is 0.84 Mbit s-1,the SSIM crite-rion exceeds 0.91690 dB,and the learned perceptual image patch similarity(LPIPS)is less than 0.06000.This paper provides a solution for the underwater image transmission of inductively coupled mooring chains for marine applications.
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