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11.
Many investigations about the direct measurements of velocities to clarify the internal mechanism of the breaker have been carried out as a result of recent progress in the measuring techniques.This research attempts to clarify the breaking wave transformation system on a slope by an experiment and numerical analysis. In an experiment, the velocities in the surf zone were measured directly using an electromagnetic current meter, and the space distribution characteristic of the vorticity ω = (∂u/∂y − ∂u/∂x) and the skewness γ = (∂u/∂y + ∂u/∂x) were examined. Also, occurrence situations of the vortices at the time of water mass inrush were measured by video tape recorder (VTR) image processing. However, because the breaker is a violent phenomenon that is entrained with plentiful bubbles, the extent to which we can clarify breaker transformation in experiments is limited. Numerical simulations are substituted for experiments as a method to clarify breaker transformation.In numerical analysis, finite amplitude wave analysis based on the potential theory (non-viscous fluid) is possible before wave breaking; however, the analysis must take into account the viscous fluid after breaking. So, we use the Reynolds equations to develop a numerical simulation system of the breaker transformation on a sloping bottom. The numerical energy dissipation model of the breaker was compared to the experimental results, and a modified Simplified Marker and Cell (SMAC) method is presented. The internal characteristics of the breaker transformation are described using application examples. 相似文献
12.
Wavenumber spectra of the martian atmosphere covering zonal wavenumbers s=1-6 were obtained as a function of latitude and season for the first time from the temperatures measured by the Thermal Emission Spectrometer onboard the Mars Global Surveyor. The stationary component tends to peak at s=2, where the martian topography has large amplitude, and drops rapidly at higher wavenumbers. The transient component in the middle and high latitudes tends to peak at s=1, which is lower than the most unstable wavenumber based on linear theories, and exhibits spectral slopes much flatter than the stationary component. In the equatorial region, the spectra of the transient component are almost flat, indicating that the organization of large-scale structures is less efficient in this region. The spectral shapes are similar between the 0.5 and 2.2 hPa surfaces, except that the slopes are slightly steeper at 0.5 than at 2.2 hPa, probably due to selective vertical transmission at low wavenumbers. The seasonal variation is relatively large in the middle and high latitudes, where the maximum power occurs in winter and the minimum occurs in summer, with an exception that the transient component is maximum in spring in the southern hemisphere. Intensification of s=1 transient waves is observed around the period of the initiation of global dust storms. 相似文献
13.
European Venus Explorer (EVE): an in-situ mission to Venus 总被引：1，自引：0，他引：1
E. Chassefière O. Korablev T. Imamura K. H. Baines C. F. Wilson D. V. Titov K. L. Aplin T. Balint J. E. Blamont C. G. Cochrane Cs. Ferencz F. Ferri M. Gerasimov J. J. Leitner J. Lopez-Moreno B. Marty M. Martynov S. V. Pogrebenko A. Rodin J. A. Whiteway L. V. Zasova J. Michaud R. Bertrand J.-M. Charbonnier D. Carbonne P. Raizonville 《Experimental Astronomy》2009,23(3):741-760
The European Venus Explorer (EVE) mission was proposed to the European Space Agency in 2007, as an M-class mission under the
Cosmic Vision Programme. Although it has not been chosen in the 2007 selection round for programmatic reasons, the EVE mission
may serve as a useful reference point for future missions, so it is described here. It consists of one balloon platform floating
at an altitude of 50–60 km, one descent probe provided by Russia, and an orbiter with a polar orbit which will relay data
from the balloon and descent probe, and perform science observations. The balloon type preferred for scientific goals is one
which oscillates in altitude through the cloud deck. To achieve this flight profile, the balloon envelope contains a phase
change fluid, which results in a flight profile which oscillates in height. The nominal balloon lifetime is 7 days—enough
for one full circumnavigation of the planet. The descent probe’s fall through the atmosphere takes 60 min, followed by 30 min
of operation on the surface. The key measurement objectives of EVE are: (1) in situ measurement from the balloon of noble
gas abundances and stable isotope ratios, to study the record of the evolution of Venus; (2) in situ balloon-borne measurement
of cloud particle and gas composition, and their spatial variation, to understand the complex cloud-level chemistry; (3) in
situ measurements of environmental parameters and winds (from tracking of the balloon) for one rotation around the planet,
to understand atmospheric dynamics and radiative balance in this crucial region. The portfolio of key measurements is complemented
by the Russian descent probe, which enables the investigation of the deep atmosphere and surface. 相似文献
14.
Runup data in Biak Island and itsnearby islets are described with discussions oftsunami magnitude and a few characteristics such aswitnessed arrival times, wave periods and wavenumbers. From an engineering viewpoint, a relationbetween inundation depth and current velocity on landis also described with relations between inundationdepth and degree of damage to houses and between sanderosion depth and current velocity in backshoreregion, based on data collected from the present andpast tsunamis. 相似文献
15.
Numerical simulation of the 1992 Flores tsunami: Interpretation of tsunami phenomena in northeastern Flores Island and damage at Babi Island 总被引：2，自引：0，他引：2
Fumihiko Imamura Edison Gica Tomoyuki Takahashi Nobuo Shuto 《Pure and Applied Geophysics》1995,144(3-4):555-568
Numerical analysis of the 1992 Flores Island, Indonesia earthquake tsunami is carried out with the composite fault model consisting of two different slip values. Computed results show good agreement with the measured runup heights in the northeastern part of Flores Island, except for those in the southern shore of Hading Bay and at Riangkroko. The landslides in the southern part of Hading Bay could generate local tsunamis of more than 10 m. The circular-arc slip model proposed in this study for wave generation due to landslides shows better results than the subsidence model, It is, however, difficult to reproduce the tsunami runup height of 26.2 m at Riangkroko, which was extraordinarily high compared to other places. The wave propagation process on a sea bottom with a steep slope, as well as landslides, may be the cause of the amplification of tsunami at Riangkroko. The simulation model demonstrates that the reflected wave along the northeastern shore of Flores Island, accompanying a high hydraulic pressure, could be the main cause of severe damage in the southern coast of Babi Island. 相似文献
16.
Cosmic-ray-produced40K in the metal phase of six chondrites and50V in that of one chondrite were determined using a surface ionization mass spectrometer. The22Netotal/40Kmetal ratios of the chondrites are explained in part by shielding effects during cosmic-ray irradiation. The wide variation of this ratio in some groups of meteorites is explained in terms of partial loss of rare-gas nuclides. Radiation ages for the chondrites were determined using40K measurements and production-rate estimates from thick target calculations. 相似文献
17.
An improved resonant fluorescence instrument for measuring atomic oxygen concentration was developed to avoid the Doppler effect and the aerodynamic shock effect due to the supersonic motion of a rocket. The shock effect is reduced by adopting a sharp wedge-shaped housing and by scanning of the detector field of view to change the distance between the scattering volume and the surface of the housing. The scanning enables us to determine absolute values of atomic oxygen concentration from relative variation of the scattered light signal due to the self-absorption. The instrument was calibrated in the laboratory, and the numerical simulation reproduced the calibration result. Using the instrument, the altitude profile of atomic oxygen concentration was observed by a rocket experiment at Uchinoura (31°N) on 28 January 1992. The data obtained from the rocket experiment were not perfectly free from the shock effect, but errors due to the effect were reduced by the data analysis procedure. The observed maximum concentration was 3.8× 1011 cm−3 at altitudes around 94 km. The systematic error is estimated to be less than ±0.7×1011 cm−3 and the relative random error is less than±0.07× 1011 cm−3at the same altitudes. The altitude profile of the OI 557.7-nm airglow was also observed in the same rocket experiment. The maximum volume emission rate was found to be 150 photons cm−3 s−1 at 94 km. The observed altitude profiles are compared with the MSIS model and other in situ observations. 相似文献
18.
J.-P. Bardet C. E. Synolakis H. L. Davies F. Imamura E. A. Okal 《Pure and Applied Geophysics》2003,160(10-11):1793-1809
— Underwater landslides can trigger local tsunamis with high runup, endangering human life and devastating coastal cities, offshore structures, communication cables, and port facilities. Unfortunately, hazards from underwater landslides are not well understood and the extents of their potential damage remain difficult to ascertain at present. There is immediate need for multidisciplinary research to improve our understanding and plan countermeasures for mitigating their hazards. Conceived in the wake of the Papua New Guinea earthquake landslide and tsunami of 1998, this volume summarizes the state-of-the-art knowledge on underwater landslides and their potential to generate tsunamis from the multidisciplinary perspectives of observational and engineering seismology, geotechnical engineering, marine geology, and hydrodynamics. These various fields of engineering and science offer new synergetic opportunities to examine landslide tsunamis. This paper makes recommendations on future research directions, and will hopefully advance scientists' and engineers' understanding of these natural hazards and assist planners in mitigating their risks. 相似文献
19.
Far-Field Tsunami Potential and a Real-Time Forecast System for the Pacific Using the Inversion Method 总被引：1，自引：0，他引：1
Estimating tsunami potential is anessential part of mitigating tsunami disasters. Weproposed a new method to estimate the far-fieldtsunami potential by assuming faultmodels on the Pacific Rim. We find thata tsunami that generates in the areas wherethere is no tsunami in the history can damagethe Japanese coast. This shows that it isimportant to estimate tsunami potential byassuming fault models other than the pastearthquake data.Another important activity to mitigate tsunamidisasters is to provide appropriatewarnings to coastal communities when dangerfrom a tsunami is imminent. We applied anew inversion method using wavelet transformto a part of the real-time tsunami forecastsystem for the Pacific. Because this inversionmethod does not require fault location, it ispossible to analyze a tsunami in real timewithout all seismic information. In order tocheck the usability of the system, anumerical simulation was executed assuming anearthquake at sea off Taiwan. The correlationcoefficient for the estimated initialwaveform to the assumed one was calculatedto be 0.78. It takes 90 min to capturetime-series waveform data from tsunamigauges and 5 sec to estimate the 2-D initialwaveform using the inversion method. After that,it takes 2 minutes to forecast thetsunami heights at the Japanese coast. Since thesum of these times is less than the 105minutes transit time of the tsunami fromTaiwan to Japan, it is possible to give a warningto the residents before the tsunami attacksthe Japanese coast. Comparing the tsunamiheights forecasted by this system with thosecalculated by the fault model, the averageerror was 0.39 m. The average error ofthe arrival time was 0.007 min. 相似文献
20.
Ken Yanagisawa Fumihiko Imamura Tsutomu Sakakiyama Tadashi Annaka Tomoyoshi Takeda Nobuo Shuto 《Pure and Applied Geophysics》2007,164(2-3):565-576
The present study focuses on evaluation of the maximum and minimum water levels caused by tsunamis as risk factors for operation
and management at nuclear power facilities along the coastal area of Japan. Tsunamis generated by submarine earthquakes are
examined, basing literature reviews and databases of information on historical tsunami events and run-up heights. For simulation
of water level along the coast, a numerical calculation system should be designed with computational regions covering a particular
site. Also the calculation system should be verified by comparison of historical and calculated tsunami heights. At the beginning
of the tsunami assessment, the standard faults, their locations, mechanisms and maximum magnitudes should be carefully estimated
by considering historical earthquake-induced tsunamis and seismo-tectonics at each area. Secondly, the range of errors in
the model parameters should be considered since earthquakes and tsunamis are natural phenomena that involve natural variability
as well as errors in estimating parameters. For these reasons, uncertainty-induced errors should be taken into account in
the process of tsunami assessment with parametric study of the tsunami source model. The element tsunamis calculated by the
standard fault models with the errors would be given for the design. Then, the design tsunami can be selected among the element
tsunamis with the most significant impact, maximum and minimum water levels, on the site, bearing in mind the possible errors
in the numerical calculation system. Finally, the design tsunami is verified by comparison with the run-up heights of historical
tsunamis, ensuring that the design tsunami is selected as the highest of all historical and possible future tsunamis at the
site. 相似文献