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101.
Claudio Chiaruttini Stefano Grimaz Enrico Priolo 《Soil Dynamics and Earthquake Engineering》1996,15(2):75
A two-dimensional elastic Chebyshev spectral element method (SPEM) is used to model the seismic wavefield within a massive structure and in its vicinity. We consider 2-D models where a linear elastic structure, with quadrangular cross-section, resting on an elastic homogeneous half-space, is impinged upon by the waves generated by a surface impulse at some distance. The scattering of Rayleigh waves and the response of the structure are extensively analysed in a parametric way, varying size, mechanical parameters and shape of the load. Some of the models considered are representative of embankments and earth dams. The simulation shows that some models resonate, storing part of the incoming energy. With realistic parameters, the lowest resonance frequency is due to pure shear deformation and is controlled by the shear velocity and height of the load. Flexural modes are excited only at higher frequencies. The acceleration at the top of the structure may be five/seven times higher than at the base, depending on the mass of the structure. The gradual release of trapped energy produces a ground roll lasting several seconds after the wave front has passed. The ground-roll amplitude depends on the sturcture's mass and can be as large as 30% of the peak acceleration. Outside resonance conditions, the ground motion is almost unaffected by the presence of the artefact; the horizontal motion on top of it is nearly twice the motion at ground level. Similar results should be expected when the incident field is an upcoming shear wave. A qualitative discussion shows that the presence of anelastic attenuation in the embankment does not significantly alter the preceding conclusions, unless it is of very low values (e.g. Q < 15).The modelling results that we discuss indicate that the soil-structure interaction may substantially alter the ‘free-field’ ground motion. From a practical point of view, the main conclusions are: (1) careful analysis is necessary when interpreting seismic records collected in the vicinity of large artefacts; (2) seismic hazard at a site may depend on the presence of man-made structures such as embankments, dams, tall and massive buildings. 相似文献
102.
港池的布局会改变其周边海域水动力条件及其泥沙冲淤状况,为了进一步了解其影响程度,本文以山东日照豪迈重工临港厂区运输码头的改造工程为研究对象,利用平面二维数值模型MIKE21/3 Integrated Models,建立了潮流和波浪耦合作用下的泥沙输移数值模型,对该工程附近海域进行了波浪、潮流和泥沙输移的数值模拟。同时采用实测数据对数值模型进行了验证,数值模拟结果与实测资料拟合较好,表明MIKE21能有效地模拟运输码头及其周围海域潮流的变化过程。以日照豪迈重工临港厂区运输码头为依托,基于数值模拟结果,分析不同改造方案下的水动力条件和泥沙冲淤状况。结果表明:港池布局对水动力条件影响甚微,对地形地貌冲淤影响较大;模拟结果确定港池南向开口为最佳改造方案,为工程的规划和设计提供科学依据。 相似文献
103.
Abstract Canada has increased the number of tsunami warning stations on the Pacific Coast from two to three. The last gauge was installed at the north end of Vancouver Island, thereby filling a large gap previously existing and providing full coverage along the coast. The record of gauges at two of the three locations is accessible either by telephone or by means of meteor burst communication, alleviating the difficulties experienced during the tsunami threat of May 6, 1986, when telephone communications were disrupted by heavy use. The gauge at Langara Island will be relocated in a more accessible and also a more tsunami‐responsive location at Rennell Sound in the Queen Charlotte Islands. All tsunami gauges also serve as tide gauges, recording the water level every 15 min. In the event of a tsunami, the recording interval can be altered to every 60 s. Suggestions have been made that Canada attempt deep‐sea recording of tsunamis off its Pacific Coast. Although this would be of great scientific value, no such program is contemplated at this time. 相似文献
104.
Ice Sheet-Thermohaline Circulation Interactions in a Climate Model of Intermediate Complexity 总被引:3,自引:0,他引:3
A vertically integrated dynamic ice sheet model is coupled to the atmosphere-ocean-sea ice-land surface climate model recently
developed by Wang and Mysak (2000). The background lateral (east-west) ice sheet discharge rate used by Gallee et al. (1992) is reduced and the planetary emissivity is increased (to parameterize the cooling effect of a decrease of the atmospheric
CO2 concentration), in order to build up substantial ice sheets during a glacial period and hence set the stage for ice sheet-thermohaline
circulation (THC) interactions. The following iceberg calving scheme is then introduced: when the maximum model height of
the North American ice sheet reaches a critical value (2400 m), a prescribed lateral discharged rate is imposed on top of
the background discharge rate for a finite time. Per a small prescribed discharge rate, repeated small iceberg calving events
occur, which lead to millennial-scale climate cycles with small amplitudes. These are a crude representation of Dansgaard-Oeschger
oscillations. Over one such cycle, the zonally averaged January surface air temperature (SAT) drops about 1.5°C at 72.5°N.
However, a large prescribed lateral discharge rate leads to the shut down of the THC. In this case, the January SAT drops
about 5°C at 72.5°N, the sea ice extent advances equatorward from 57.5° to 47.5°N and the net ice accumulation rate at the
grid of maximum ice sheet height is reduced from 0.24 to 0.15 m/y. Since data strongly suggest that a collapsed THC was not
a steady state during the last glacial, we restore the THC by increasing the vertical diffusivity in the North Atlantic Ocean
for a finite time. The resulting climate cycles associated with conveyor-on and conveyor-off phases have much larger amplitudes;
furthermore, the strong iceberg calving events lead to a larger loss of ice sheet mass and hence the period of the oscillations
is longer (several thousand years).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
105.
G. T. Csanady 《Journal of Oceanography》1997,53(1):67-80
A “slip law” connects the excess velocity or “slip” of a wind-blown water surface, relative to the motion in the middle of
the mixed layer, to the wind stress, the wind-wave field, and buoyancy flux. An inner layer-outer layer model of the turbulent
shear flow in the mixed layer is appropriate, as for a turbulent boundary layer or Ekman layer over a solid surface, allowing,
however, for turbulent kinetic energy transfer from the air-side via breaking waves, and for Stokes drift. Asymptotic matching
of the velocity distributions in inner and outer portions of the mixed layer yields a slip law of logarithmic form, akin to
the drag law of a turbulent boundary layer. The dominant independent variable is the ratio of water-side roughness length
to mixed layer depth or turbulent Ekman depth. Convection due to surface cooling is also an important influence, reducing
surface slip. Water-side roughness length is a wind-wave property, varying with wind speed similarly to air-side roughness.
Slip velocity is typically 20 times water-side friction velocity or 3% of wind speed, varying within a range of about 2 to
4.5%. A linearized model of turbulent kinetic energy distribution shows much higher values near the surface than in a wall
layer. Nondimensional dissipation peaks at a value of about eight, a short distance below the surface. 相似文献
106.
Experiments were conducted in a wave flume to study the differences between harmonic evolution of monochromatic waves as they propagate over a submerged impermeable or porous step under non-breaking conditions. Results are used as a preliminary analysis to establish some engineering design criteria on harmonic generation on submerged porous structures. The root-mean-squared wave height evolution is also studied and compared to linear models as a first approximation. It is shown that porous structure increases the effective relative depth and decreases the relative wave height, resulting in a lower Ursell number and a lower chance to generate harmonics. The effective water depth over a step as defined in the paper, provides information to evaluate the potential harmonic generation. 相似文献
107.
108.
地下水-地表水相互作用是水资源管理和地表水生态系统保护中重要的一个环节,氡同位素(222Rn)由于其在地下水与地表水中含量差异显著、性质保守、检测难度低,广泛运用于地下水-地表水相互作用的研究当中。本文通过总结分析222Rn在不同地表水体(海水、河水、湖水等)中的应用,指出刻画地下水氡浓度的异质性是估算地下水排泄的重点和难点。在估算海底地下水排泄(SGD)时,氡的混合损失项估算不确定、海水氡浓度时空变异性、SGD的多组分特征等可能给估算结果带来较大不确定性;在估算河流地下水排泄时难以确定氡的大气逃逸量;研究人员对氡在示踪地表水补给地下水方面的研究程度相对不足。本文从科学研究和实际生产方面,对222Rn的研究应用提出以下潜在方向:(1)降低地下水氡空间变异性对估算地下水排泄量的影响;(2)针对不同水体、不同水文条件,准确刻画氡的大气逃逸量;(3)拓展222Rn示踪能够解决的科学问题;(4)将氡质量平衡模型计算与不确定分析相结合,实现软件化。 相似文献
109.
110.