排序方式： 共有61条查询结果，搜索用时 15 毫秒
51.
Submarine debris flow impact on suspended (free-span) pipelines: Normal and longitudinal drag forces
Arash Zakeri 《Ocean Engineering》2009,36(6-7):489-499
Computational fluid dynamics (CFD) analysis was employed to numerically simulate impact of clay-rich submarine debris flows on a suspended (free-span) pipeline at various angles of attack. The resultant horizontal drag force can be decomposed into two components: normal and parallel to the pipe axis. A method is presented for estimating the normal and longitudinal drag forces on a suspended pipeline and is applicable to a wide of impact situations. The work presented here complements the results of an earlier investigation into the drag forces on suspended and laid-on-seafloor pipelines. The previous investigation consisted of both physical laboratory experiments and CFD numerical analyses, for an impact situation normal to the pipe axis. The impact Reynolds numbers presented in this paper range between about 2 and 320. This range is considered appropriate for practical design purposes. 相似文献
52.
Computational Fluid Dynamics (CFD) numerical analysis was employed to analyze the situations tested experimentally, as described in Part I. The methodology and results of the CFD analyses are discussed and compared with the observations made from the experiments. The numerical model performed satisfactorily with regard to obtaining the impact forces exerted on the model pipe as well as simulating the hydroplaning phenomenon and estimating slurry flow heights. The experimental results were combined with the results of the CFD analyses to develop a practical method to compute the drag force caused by a submarine debris flow impact on a pipeline. The CFD analyses provided some insight to the separated region characterization, but the attempt to analyze the vortex shedding phenomenon as observed in the experiments was unsuccessful. Additional studies are required for better understanding of both the separated region characteristics and vortex shedding. 相似文献
53.
A Bayesian chemical mass balance approach was used to estimate the contributions of potential sources into the suspended sediments in the Mill Stream, a tributary of Chesapeake Bay in Maryland, US. The Bayesian approach allows us to incorporate the uncertainties as a result of measurement errors in the elemental profiles of sources and suspended sediments in the stream and also the heterogeneities of the elemental profiles among samples into the analysis and provides us with probability densities representing the contribution of each source. Based on the obtained results, river bank erosion is the major source of sediments with a contribution estimated to range from 83% to 99% with a 95% credible interval. Also, a 95% credible interval in a range of 0.06% to 8% for cropland and 0.1% to 14% for forestland was provided. Hence, while the contribution of sediments from cropland or forestland cannot be ruled out, the model does not definitively demonstrate a significant contribution from either source. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
54.
A Field Study of How Wind Waves and Currents May Contribute to the Deterioration of Saltmarsh Fringe
Deltaic landscapes, such as the Mississippi River Delta, are sites of extensive conversion of wetlands to open water, where increased fetch may contribute to erosion of marsh edges, increasing wetland loss. A field experiment conducted during a storm passage tested this process through the observations of wave orbital and current velocities in the fringe zone of a deteriorating saltmarsh in Terrebonne Bay, Louisiana. Incident waves seaward of the marsh edge and wave orbital and current velocities immediate landward of the marsh edge were measured. Through a dimensional analysis, it shows that the current and orbital velocities in the marsh fringe were controlled by the incident waves, inundation depth, submergence ratio, and vegetation density. Similarly, it is shown that the longshore currents in the inundated saltmarsh fringe depended on the local wave-induced momentum flux, vegetation submergence, and vegetation density in the fringe zone. The cross-shore current showed the presence of a return flow in the lower region of the velocity profile. A high correlation between the current direction and the local flow-wave energy ratio as well as the vegetation submergence and density is found, indicating the important role of surface waves in the fringe flow landward of an inundated wetland under storm conditions. The field observations shed light on the potential ecological consequences of increased wave activities in coastal saltmarsh wetlands owing to subsidence, sea level rise, limited sediment supply, increases in wind fetch, and storm intensity. 相似文献
55.
Determination of the optimum sealing method for Azad pumped storage dam considering seepage analysis
Seepage analysis of the upper reservoir of the Kurdistan Azad pumped storage dam with a volume of 3.8E+5 m3 is a key step for selection of the optimized sealing method. More than 60% of the Lugeon test results show very permeable behavior for the pit and abutments of the reservoir. In this study, regarding the permeability value of the reservoir abutments and pit obtained by means of Lugeon tests, seepage rate was computed using various analytical and numerical methods. Reservoir total seepage discharge was computed in steady-state regime by means of analytical and numerical methods (SEEP/W finite element software) as 1.14E+05 and 1.15E+05 m3/day, respectively. Distinct element method (UDEC software) showed variable behavior for the seepage flow. In the reservoir initial impounding stages, the amount of seepage was very high (1.70E+06 m3/day). Then, the seepage rate decreased gradually and reached to a constant value (1.12E+05 m3/day). For the reservoir 3D modeling, Seep3D commercial software was used and has shown water seepage discharge of about 1.18E+05 m3/day, means 3% of total reservoir volume. Based on the above-mentioned results and regarding behavior of seepage in the initial impounding stages, sealing element is necessary to prevent from seepage phenomenon. Clay blanket, concrete lining, asphaltic concrete, and geosynthetic are the proposed methods in a large water reservoir. After a feasibility study on various sealing methods, geomembrane was suggested as the best sealing method with the reasonable implementation cost. 相似文献
56.
Mohsen Kamalian Mohammad Kazem Jafari Abdollah Sohrabi-bidar Arash Razmkhah Behrouz Gatmiri 《Soil Dynamics and Earthquake Engineering》2006,26(8):753-765
In this paper, an advanced formulation of the time-domain, two-dimensional hybrid finite element–boundary element method (FEM/BEM) is presented, and applied to carry out site response analysis of homogeneous and non-homogeneous topographic structures subjected to incident in-plane motions. Seismic responses of half-plane, horizontally layered site, alluvial valley and ridge sections subjected to incident P and SV waves are analyzed in order to demonstrate the applicability and efficiency of the presented method. The numerical results show that hybrid BE/FE methods require smaller time steps than those needed by BEM schemes. They also show that in case of surface irregularities with height to half-width ratio of up to one, the topography effect could be noticeable, if incident waves have wavelengths of less than approximately eight times the width. 相似文献
57.
The effect of mineralization on the ratio of normal to tangential compliance of fractures 总被引：1，自引：0，他引：1
The effect of a fracture on the propagation of seismic waves can be represented in terms of the normal compliance BN and tangential compliance BT of the fracture. If BN / BT = 1 for all fractures, the effective elastic stiffness tensor of an isotropic background containing an arbitrary orientation distribution of fractures is orthotropic (i.e., has three orthogonal planes of mirror symmetry) in the long-wave limit. However, deviations from orthotropy may occur if BN / BT differs significantly from unity and this can cause the principal axes of the P -wave NMO ellipse and of the variation in the PP -reflection amplitude as a function of azimuth, to deviate from the fast and slow polarization direction of a vertically propagating S -wave. Simple models of a fracture in terms of a planar distribution of cracks suggest that BN / BT ≈ 1 for dry fractures. However, naturally occurring fractures often exhibit mineralization in the form of bridges between opposing faces of the fracture. The presence of such bridges leads to significant departures of BN / BT from unity. 相似文献
58.
59.
Siavash?SoroushianEmail author E.?“Manos”?Maragakis Arash?E.?Zaghi Esmaeel?Rahmanishamsi Ahmad?M.?Itani Gokhan?Pekcan 《地震工程与工程振动(英文版)》2016,15(1):19-29
A full-scale, two-story, two-by-one bay, steel braced-frame was subjected to a number of unidirectional ground motions using three shake tables at the UNR-NEES site. The test-bed frame was designed to study the seismic performance of nonstructural systems including steel-framed gypsum partition walls, suspended ceilings and fire sprinkler systems. The frame can be configured to perform as an elastic or inelastic system to generate large floor accelerations or large inter story drift, respectively. In this study, the dynamic performance of the linear and nonlinear test-beds was comprehensively studied. The seismic performance of nonstructural systems installed in the linear and nonlinear test-beds were assessed during extreme excitations. In addition, the dynamic interactions of the test-bed and installed nonstructural systems are investigated. 相似文献
60.