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71.
Quadrant front face pile supported breakwater is a combination of semicircular and closely spaced pile breakwaters which couples the advantages of these two types. This type of structure consists of two parts. The bottom portion consists of closely spaced piles and the top portion consists of a quadrant solid front face on the seaside. The leeward side of the top portion with a vertical face would facilitate the berthing of vessels. An experimental investigation on this breakwater model in a wave flume is carried out for three water depths. For each water depth, three different spacings between the piles were adopted for the investigation. The dynamic pressures exerted along the quadrant front face due to regular waves were measured. The variation of dimensionless pressures with respect to scattering parameter for different gap ratio (spacing between the piles/diameter of pile) and for relative pile depth (water depth/pile height) are presented and discussed. In addition, the dimensionless total forces exerted on the breakwater model as well as its reflection characteristics as a function of scattering parameter are reported. 相似文献
72.
To plan for proper mitigation measures, one should have an advanced knowledge of the phenomenon of tsunami propagation from the deep ocean to coastal waters. There are a few methods to predict tsunamis in the ocean waters; one method is the effective use of data buoy measurements. Although data buoys have been used along the Indian waters there has been a tremendous growth in the number of buoy deployment recently. Under the National Data Buoy Programme (NDBP) of India, the 2.2 m diameter discus data buoys were deployed along the east and west coasts of India for measuring meteorological and ocean parameters. It would be advantageous if these buoys could be efficiently used to measure rare events such as tsunamis. Understanding the dynamic behavior of the buoy is of prime importance if a tsunami warning system is to be successful. This may be accomplished through experimental or numerical studies. A comprehensive experimental study has been conducted to understand the dynamic behavior of a wave rider buoy exposed to a variety of waves. It is common that tsunami waves are represented in terms of shallow water waves, namely solitary and cnoidal waves. Hence, in the present study, the discus type data buoy is scale modeled and tested under the action of solitary and cnoidal waves in the laboratory. The time histories of wave elevations, as well as heave and pitch motions of the buoy model, were analyzed through a spectral approach as well as through wavelet transformations. The wavelet approach gives more detailed insight into the spectral characteristics of the buoy motion in the time scale. The harmonic analyses were performed for the cnoidal wave elevations and subsequent motion characteristics that give an insight into the energy variations. The details of the model, instrumentation, testing conditions and the results are presented in this paper. 相似文献
73.
We present meterwave maps showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in He i
l10830 spectroheliograms.Using the model of coronal holes by Dulk et al. (1977) we derive the electron density from the radio observations of the brightness temperature. The discrepancy between the density value derived from the Skylab EUV data and that computed from our radio data is even larger than in Dulk et al. 's comparison at similar and higher frequencies. 相似文献
74.
We compare simultaneous high resolution soft X-ray and 6 cm images of the decay phase of an M3 X-ray flare in Hale Region 16413. The photographic X-ray images were obtained on an AS & E sounding rocket flown 7 November, 1979, and the 6 cm observations were made with the VLA. The X-ray images were converted to arrays of line-of-sight emission integrals and average temperature throughout the region. The X-ray flare structure consisted of a large loop system of length 1.3 arc min and average temperature 8 × 106 K. The peak 6 cm emission appeared to come from a region below the X-ray loop. The predicted 6 cm flux due to thermal bremsstrahlung calculated on the basis of the X-ray parameters along the loop was about an order of magnitude less than observed. We model the loop geometry to examine the expected gyroresonance absorption along the loop. We find that thermal gyroresonance emission requiring rather large azimuthal or radial field components, or nonthermal gyrosynchrotron emission involving continual acceleration of electrons can explain the observations. However, we cannot choose between these possibilities because of our poor knowledge of the loop magnetic field. 相似文献
75.
76.
Saha Sourita Sharma Som Chhabra Abha Kumar Kondapalli Niranjan Kumar Prashant Kamat Dharmendra Lal Shyam 《Natural Hazards》2022,113(1):143-155
Natural Hazards - The present study focuses on investigating the impacts of a sudden dust storm on the atmospheric boundary layer (ABL) over Ahmedabad (23.02°N, 72.57°E), an urban site... 相似文献
77.
Natural Hazards - The agricultural land of the whole world is deteriorating due to the loss of top fertile soil reducing agricultural productivity and groundwater availability. Mainly, natural... 相似文献
78.
79.
Yuling Wu Udaysankar S. Nair Roger A. PielkeSr. Richard T. McNider Sundar A. Christopher Valentine G. Anantharaj 《Boundary-Layer Meteorology》2009,133(3):367-389
Prior numerical modelling studies show that atmospheric dispersion is sensitive to surface heterogeneities, but past studies
do not consider the impact of a realistic distribution of surface heterogeneities on mesoscale atmospheric dispersion. While
these focussed on dispersion in the convective boundary layer, the present work also considers dispersion in the nocturnal
boundary layer and above. Using a Lagrangian particle dispersion model (LPDM) coupled to the Eulerian Regional Atmospheric
Modeling System (RAMS), the impact of topographic, vegetation, and soil moisture heterogeneities on daytime and nighttime
atmospheric dispersion is examined. In addition, the sensitivity to the use of Moderate Resolution Imaging Spectroradiometer
(MODIS)-derived spatial distributions of vegetation characteristics on atmospheric dispersion is also studied. The impact
of vegetation and terrain heterogeneities on atmospheric dispersion is strongly modulated by soil moisture, with the nature
of dispersion switching from non-Gaussian to near-Gaussian behaviour for wetter soils (fraction of saturation soil moisture
content exceeding 40%). For drier soil moisture conditions, vegetation heterogeneity produces differential heating and the
formation of mesoscale circulation patterns that are primarily responsible for non-Gaussian dispersion patterns. Nighttime
dispersion is very sensitive to topographic, vegetation, soil moisture, and soil type heterogeneity and is distinctly non-Gaussian
for heterogeneous land-surface conditions. Sensitivity studies show that soil type and vegetation heterogeneities have the
most dramatic impact on atmospheric dispersion. To provide more skilful dispersion calculations, we recommend the utilisation
of satellite-derived vegetation characteristics coupled with data assimilation techniques that constrain soil-vegetation-atmosphere
transfer (SVAT) models to generate realistic spatial distributions of surface energy fluxes. 相似文献
80.
Ilvaite, Ca(Fe2+, Fe3+)Fe2+Si2O8(OH), a black mixed valence iron silicate shows considerable Fe2+?Fe3+ electron delocalization above 400 K, reminiscent of magnetite. A crystallographic phase transition from orthorhombic (Pnam) to monoclinic (P2 1/a) symmetry takes place on cooling at 343 K induced by electron ordering. In both phases, Fe2+ and Fe3+ occur in double octahedral chains parallel to the c axis. The thermal characteristics of the magnetic susceptibilities and their anisotropies in different crystallographic planes have been measured in the temperature range 400?21 K. Below 343±1K, a continuous rotation of the molar susceptibility K ∥ in the ab plane down to 90±2 K is observed, where the symmetry of the magnetic ellipsoid remains unchanged. X a, X b and X c increase abruptly below 123±0.5 K, although antiferromagnetic ordering of Fe2+ and Fe3+ spins on A sites was suggested in previous Mössbauer and neutron powder diffraction studies. In addition, 1/X a shows an antiferromagnetic maximum at 50±3 K, whereas 1/X b and 1/X c at first increase sharply below 123 K, followed by antiferromagnetic curvatures in the lowest temperature region. This behavior is consistent with the antiferromagnetic ordering of Fe2+ spins in the B sites. The observed magnetic phenomena suggest charge delocatization effects between adjacent Fe2+(A)-Fe3+(A) pairs not only along c, but also along a and b directions. The negative sign of the molar anisotropy (K ∥-K⊥) suggests a singlet ground State 5A1 for the Fe2+ ions, in agreement with previous Mössbauer studies. 相似文献