The paper presents the results of the determination from vibration tests of impedance functions for a concrete basemat of a one-quarter scale model of a nuclear power-plant containment building. The tests were designed to excite all rigid-body modes of the foundation. In addition to the impedance functions for all the rigid-body degrees of freedom, natural frequencies and damping for the fundamental modes were estimated. Comparison of the test-determined modal characteristics with corresponding analytical ones based on the Lysmer analog shows that though the latter gives natural-frequency estimates of the right order of magnitude, it does not give acceptable estimates of the damping coefficient. Analytical impedance functions based on a model of a rigid-plate on an elastic half-space were found to have the sam trend as the test-determined ones at lower frequencies, but not at higher frequencies. The utility of test data for verification of analysis is discussed. 相似文献
The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (u, w) and temperature (T) are more planar homogeneous than their vertical flux of momentum (u*2) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (>15 %), this unique data set confirmed that single tower measurements represent the canonical structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the moving-equilibrium hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u*, especially when u* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (Iw) and the arrival frequency of organized structures (/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed. 相似文献
Observations indicated that for the El Niño/Southern Oscillation (ENSO) there have been eastward displacements of the zonal wind stress (WS) anomalies and surface heat flux (short wave heat flux and latent heat flux) anomalies during El Niño episodes in the 1981–1995 regime relative to the earlier regime of 1961–1975 (without corresponding displacements during La Niña episodes). Our numerical experiments with the Zebiak–Cane coupled model generally reproduced such displacements when the model climatological fields were replaced by the observed climatologies [of sea surface temperature (SST), surface WS and surface wind atmospheric divergence] and simulated climatologies (of oceanic surface layer currents and associated upwelling) for the 1981–1995 regime. Sensitivity tests indicated that the background atmospheric state played a much more important role than the background ocean state in producing the displacements, which enhanced the asymmetry between El Niño and La Niña in the later regime. The later regime climatology state resulted in the eastward shifts in the ENSO system (WS and SST) only during El Niño, through the eastward shift of the atmosphere convergence heating rate in the coupled model. The ENSO period and ENSO predictability were also enhanced in the coupled model under the later regime climatology. That the change in the mean state of the tropical Pacific atmosphere and ocean after the mid 1970s could have produced the observed changes in ENSO properties is consistent with our findings. 相似文献
A series of three-dimensional finite element analyses of deep excavations with the integrated system between buttress walls and diaphragm walls was conducted to investigate the effect of the buttress wall intervals, treatments, locations, height, and thickness on limiting deformations induced by deep excavation. The integrated retaining system was formed by maintaining buttress walls when soil was excavated. The wall deflection control mechanism of the integrated retaining system mainly came from the combined stiffness between the buttress wall and the diaphragm wall. In addition, the ground settlement control mechanism came from the combined stiffness between the buttress wall and the diaphragm wall, and the frictional resistance between the buttress wall and the surrounding soil. For achieving 50% reduction in the wall deflection and the ground surface settlement, the length and intervals of buttress walls that were applied to the integrated retaining system were at least 4 and 8 m, respectively. When the deflection at the diaphragm wall head was well restrained, for example, by the floor slab, the position of the buttress wall head could be located at a depth the diaphragm wall starts to bulge out. In such a case, the performance between the full height and limited height of buttress walls was quite close. Furthermore, a new well-documented excavation project was analyzed to verify the performance of the integrated retaining system. Results showed that the integrated retaining system worked excellently if the joints between buttress walls and diaphragm walls were constructed properly. 相似文献
The boron isotopic ratio of 11B/10B (δ11BSRM951) and trace element composition of marine carbonates are key proxies for understanding carbon cycling (pH) and palaeoceanographic change. However, method validation and comparability of results between laboratories requires carbonate reference materials. Here, we report results of an inter‐laboratory comparison study to both assign δ11BSRM951 and trace element compositions to new synthetic marine carbonate reference materials (RMs), NIST RM 8301 (Coral) and NIST RM 8301 (Foram) and to assess the variance of data among laboratories. Non‐certified reference values and expanded 95% uncertainties for δ11BSRM951 in NIST RM 8301 (Coral) (+24.17‰ ± 0.18‰) and NIST RM 8301 (Foram) (+14.51‰ ± 0.17‰) solutions were assigned by consensus approach using inter‐laboratory data. Differences reported among laboratories were considerably smaller than some previous inter‐laboratory comparisons, yet discrepancies could still lead to large differences in calculated seawater pH. Similarly, variability in reported trace element information among laboratories (e.g., Mg/Ca ± 5% RSD) was often greater than within a single laboratory (e.g., Mg/Ca < 2%). Such differences potentially alter proxy‐reconstructed seawater temperature by more than 2 °C. These now well‐characterised solutions are useful reference materials to help the palaeoceanographic community build a comprehensive view of past ocean changes. 相似文献
This paper presents a novel strut-free earth retaining wall system for excavation in soft clay, referred to as the rigid and fixed diaphragm (RFD) wall retaining system. The RFD system is comprised of four main structures—diaphragm walls, rib-walls, cross walls, and buttress walls—and a complementary structure—the cap-slab. The characteristics of the RFD system are: (1) the formation of a continuous earth retaining wall by constructing diaphragm walls along the circumference of the excavated zone; (2) the formation of a rigid and fixed retaining wall system by a series of rib-walls and cross walls; and (3) the formation of a rigid retaining wall by buttress walls and the cap-slab. Furthermore, the performance and mechanisms of the RFD system were investigated carefully through three-dimensional finite element analyses. The results demonstrated that the system stiffness of the RFD system was a major factor controlling deformations induced by excavation. Moreover, the excavation geometry determined the dimension of each component of the RFD system.