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1.
The nonlinear dynamic analysis of a multipoint slack moored buoy is performed under the action of first and second order wave forces. The nonlinearity of the system is caused by the geometric nonlinearity of the mooring lines. The resulting nonlinear equation of motion is solved by an incremental time marching scheme. The nonlinear responses of the system are analysed to investigate different kinds of dynamic instability phenomena that may arise due to the nonlinearity of the system. As an illustrative example, a hollow cylindrical buoy anchored to the sea bed by means of six slack mooring lines is considered. The responses of the system are obtained and analysed for three regular waves namely, 5 m/5 s, 12 m/10 s and 18 m/15 s. The results of the study show that different kinds of instability phenomena like nT subharmonic oscillations, symmetry breaking bifurcation and aperiodic responses may occur in slack mooring systems. Further, a second order wave force may considerably influence the dynamic stability of such systems. 相似文献
2.
Abandonment and recovery solution of submarine pipelines 总被引:1,自引:0,他引:1
T.K. Datta 《Applied Ocean Research》1982,4(4):247-252
3.
- In order to employ cost effective frequency domain analysis for off-shore structures treatment of hydrodynamic loading is essential. Drag and inertia dominated, resonating and antiresonating cases under random sea states are analyzed to highlight the implications and relative merits of four salient linearization techniques. 相似文献
4.
The Bengal basin, Bangladesh, represents one of the most densely populated recent floodplains of the world. The sediment
flux through the basin is one of the highest on a global scale. A significant portion of this sediment load find its sink
in the basin itself because of its lower elevation and frequent flooding. The textural, mineralogical and chemical nature
of the sediments thus have an important bearing on the environmental quality of the basin as well as for the Bay of Bengal.
The sediment load of the Ganges-Brahmaputra-Meghna (GBM) river system consists exclusively of fine sand, silt and clay at
their lower reaches within the Bengal basin, Bangladesh, and is deposited under uniformly fluctuating, unidirectional energy
conditions. The sediments have a close simitarity in grain size with the sediments of the surrounding floodplain. The mineral
assemblage is dominated by quartz and feldspars. Illite and kaolinite are the major clay minerals, and occur in almost equal
proportion in bed sediments. The heavy mineral assemblage is dominated by unstable minerals which are mostly derived from
high-rank metamorphic rocks. The characteristic smaller grain-size, i.e. having large surface-to-mass ratios, and the mineralogy
of sediments suggests that they are susceptible to large chemical adsorptive reactions and thus could serve as a potential
trap for contaminants. However, the sediments of the GBM river system in the Bengal basin, Bangladesh, shows lower concentration
of Pb, Hg and As, and a marginally higher value for Cd as compared to that of standard shale. Considering population density
and extensive agricultural practice in the basin, the sediments can in the long run become contaminated.
Received: 9 November 1994 · Accepted: 18 June 1996 相似文献
5.
A Markov method of analysis is presented for obtaining the seismic response of cable‐stayed bridges to non‐stationary random ground motion. A uniformly modulated non‐stationary model of the random ground motion is assumed which is specified by the evolutionary r.m.s. ground acceleration. Both vertical and horizontal components of the motion are considered to act simultaneously at the bridge supports. The analysis duly takes into account the angle of incidence of the earthquake, the spatial correlation of ground motion and the quasi‐static excitation. A cable‐stayed bridge is analysed under a set of parametric variations in order to study the non‐stationary response of the bridge. The results of the numerical study indicate that (i) frequency domain spectral analysis with peak r.m.s. acceleration as input could provide more r.m.s. response than the peak r.m.s. response obtained by the non‐stationary analysis; (ii) the longitudinal component of the ground motion significantly influences the vertical vibration of the bridge; and (iii) the angle of incidence of the earthquake has considerable influence on the deck response. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
Stability of fluorite and titanite in a calc-silicate rock from the Vizianagaram area, Eastern Ghats Belt, India 总被引:1,自引:0,他引:1
In the Vizianagaram area (E 83°29.442′; N 18°5.418′) of the Eastern Ghats Belt, India, a suite of graphite‐bearing calc‐silicate granulites, veined by syenitic rocks, developed wollastonite‐rich veins at 6–7 kbar and > 850 °C. During subsequent near‐isobaric cooling wollastonite was replaced by calcite + quartz and a graphic intergrowth of fluorite + quartz ± clinopyroxene. Titanite with variable Al and F contents is present throughout the rock. Combining the compositional variation of titanite and recent experimental data, it is demonstrated that the mineral assemblage, the composition of coexisting fluids and the mobility of Al exert a far greater control on the composition of titanite than pressure, temperature or the whole rock composition. Thermodynamically computed isothermal–isobaric logfO2– logfCO2 and logfF2– logfO2 grids in the systems Ca–Fe–Si–O–F (CISOF; calcite‐free) and Ca–Fe–Si–O–F–C–H (CISOFV; calcite‐present) demonstrate the influence of bulk rock and fluid compositions on the stability of the fluorite‐bearing assemblages in diverse geological environments and resolve the problem of the stability of titanite in fayalite + fluorite‐bearing rocks in the Adirondacks. The mineralogy of the studied rocks and the topological constraints tightly fix the logfO2, logfF2 and logfCO2 at ?15.8, ?30.6 and 4.1, respectively, at 6.5 kbar and c. 730 °C. Because of the similarity in the P–T conditions, the compositions of pore fluids in the fluorite‐bearing assemblages of the Adirondacks and the Eastern Ghats Belt have been compared. 相似文献
7.
Reid E. Buskirk Peter S. K. Knappett M. Bayani Cardenas Saugata Datta Walter S. Borowski Itza Mendoza-Sanchez 《Ground water》2024,62(3):459-468
This note describes the development and testing of a novel, programmable reversing flow 1D (R1D) experimental column apparatus designed to investigate reaction, sorption, and transport of solutes in aquifers within dynamic reversing flow zones where waters with different chemistries mix. The motivation for constructing this apparatus was to understand the roles of mixing and reaction on arsenic discharging through a tidally fluctuating riverbank. The apparatus can simulate complex transient flux schedules similar to natural flow regimes The apparatus uses an Arduino microcontroller to control flux magnitude through two peristaltic pumps. Solenoid valves control flow direction from two separate reservoirs. In-line probes continually measure effluent electrical conductance, pH, oxidation–reduction potential, and temperature. To understand how sensitive physical solute transport is to deviations from the real hydrograph of the tidally fluctuating river, two experiments were performed using: (1) a simpler constant magnitude, reversing flux direction schedule (RCF); and (2) a more environmentally relevant variable magnitude, reversing flux direction schedule (RVF). Wherein, flux magnitude was ramped up and down according to a sine wave. Modeled breakthrough curves of chloride yielded nearly identical dispersivities under both flow regimes. For the RVF experiment, Peclet numbers captured the transition between diffusion and dispersion dominated transport in the intertidal interval. Therefore, the apparatus accurately simulated conservative, environmentally relevant mixing under transient, variable flux flow regimes. Accurately generating variable flux reversing flow regimes is important to simulate the interaction between flow velocity and chemical reactions where Brownian diffusion of solutes to solid-phase reaction sites is kinetically limited. 相似文献
8.
9.
A comparative study is made of the stepped structure of atmospherics during sunrise and sunset hours at three harmonically related frequencies in the VLF band, observed at the coast of the Bay of Bengal. The occurrences of the steps, their duration, time sequence and amplitudes are critically examined. Our analysis reveals that the start times of the third and second steps of the sunrise effect are always before ground sunrise, while the start of the main step is distributed on both sides of it. During sunset hours, the onset time of the main step is before the local ground sunset, but for the second and third steps, the onset times are after that. The results are interpreted by considering the multi-hop propagation as well as the distributed noise sources surrounding the observing site. 相似文献
10.
Scattering of antiplane shear waves (SH) in two dimensions by surface and near-surface defects in a homogeneous, isotropic elastic semi-infinite medium has been studied. Attention has been focused here in the range of medium to long wavelengths. A combined finite element and analytical technique has been used to study the problems of scattering by semi-circular and triangular canyons. The results for the former case are compared with the known exact solution and those for the latter case are compared with some available approximate solutions. Finally a problem of multiple scattering by a triangular canyon and a nearby circular tunnel is studied. Numerical results are presented showing the effects of multiple scattering and different angles of incidence. These results are of interest in earthquake engineering. 相似文献