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1.
Introduction The southeast coastal margin of Chinese mainland is important to understand the mutual movement, matter exchange and energy transfer between ocean and land lithospheres, as well as their effects. The coastal area in Fujian Province is advanced in economy development but it has frequent earthquakes, or even strong earthquakes. Therefore, the current study on in-situ stress state measurement is of great significance for studying continental dynamics, marginal sea dy- namics, seismo… 相似文献
2.
Stefano Pierini 《地球物理与天体物理流体动力学》2013,107(1-4):97-108
Abstract In the context of ageostrophic theory in a homogeneous ocean, a nondimensional number is determined which corresponds to the Ursell number for long gravity waves. It is defined as Q = NL 2/h 3, where N is the amplitude of the wave travelling along the long length-scale direction, L is its length and h (which for gravity waves is the water depth) is given by h=(l 4 f 2/g)1/3. where l is the short length-scale, f the Coriolis parameter and g the acceleration due to gravity. The physical meaning of Q is as follows: if Q? O(1) the free evolution of the wave is linear and weakly dispersive, if Q = O(1) nonlinear and dispersive effects balance out and finally if Q ?O(1) the evolution is nonlinear and non-dispersive. Expressions for the time scales for the development of dispersive and nonlinear effects are also determined. These results apply to topographically trapped waves, namely barotropic continental shelf and double Kelvin waves travelling along a rectilinear topographic variation. 相似文献
3.
An eigenfunction solution is presented for the dynamic response of vertical circular cylinders to earthquake excitation in a compressible fluid of finite depth. This single eigenseries expansion eliminates the need for a double summation over both the eigenfunctions and the trial functions as required by Rayleigh-Ritz methods. Revised definitions for the added mass and hydrodynamic radiation damping coefficients per unit length are derived from the hydrodynamic fluid pressures. Based on comparisons between these newly defined coefficients, the compressibility of the fluid is found to be relatively more important at dimensionless frequencies greater than unity (ω > 1.0) when analysing both rigid and flexible cylinders having relatively large diameter to water depth ratios,r0/h > 0.25 (squatty type). This conclusion regarding the relative importance of the fluid compressibility is derived from a comparison between the relative magnitudes and the vertical distributions over depth of both the added mass and radiation damping coefficients per unit length for both rigid and flexible squatty cylinders. From additional comparisons with Rayleigh-Ritz solutions that require trial functions, the results for totally immersed flexible slender cylinders (r0/h< 0.10) are shown to be equivalent; but the results for totally immersed flexible squatty cylinders (r0/h > 0.25) are not. The reason for this difference appears to be in the truncation of the trial function series in the Rayleigh-Ritz methods, which excludes the higher mode shapes, and in the definitions of the added mass coefficients. Comparisons with laboratory data for both rigid and flexible cylinders confirm the accuracy of the solutions obtained by the eigenseries in the limited frequency interval above the highest frequency for surface gravity waves (f > 1.0 Hz) and below the first dimensionless cut-off frequency for acoustic waves (ω< 1.0). 相似文献
4.
A non-hydrostatic model in cross-sectional form with an idealized sill is used to examine the influence of sill depth (h
s) and aspect ratio upon internal motion. The model is forced with a barotropic tide and internal waves and mixing occurs at
the sill. Calculations using a wide sill and quantifying the response using power spectra show that for a given tidal forcing
namely Froude number F
r as the sill depth (h
s) increases the lee wave response and vertical mixing decrease. This is because of a reduction in across sill velocity U
s due to increased depth. Calculations show that the sill Froude number F
s based on sill depth and across sill velocity is one parameter that controls the response at the sill. At low F
s (namely F
s ≪ 1) in the wide sill case, there is little lee wave production, and the response is in terms of internal tides. At high
F
s, calculations with a narrow sill show that for a given F
s value, the lee wave response and internal mixing increase with increasing aspect ratio. Calculations using a narrow sill
with constant U
s show that for small values of h
s, a near surface mixed layer can occur on the downstream side of the sill. For large values of h
s, a thick well-mixed bottom boundary layer occurs due to turbulence produced by the lee waves at the seabed. For intermediate
values of h
s, “internal mixing” dominates the solution and controls across thermocline mixing. 相似文献
5.
Utilizing an eigenfunction decomposition, we study the growth and spectra of energy in the vortical (geostrophic) and wave (ageostrophic) modes of a three-dimensional (3D) rotating stratified fluid as a function of ε = f/N, where f is the Coriolis parameter and N is the Brunt–Vaisala frequency. Throughout, we employ a random large-scale forcing in a unit aspect ratio domain and set these parameters such that the Froude and Rossby numbers are roughly comparable and much less than unity. Working in regimes characterized by moderate Burger numbers, i.e. Bu = 1/ε2 < 1 or Bu ≥ 1, our results indicate profound change in the character of vortical and wave mode interactions with respect to Bu = 1. Indeed, previous analytical work concerning the qualitatively different nature of these interactions has been in limiting conditions of rotation or stratification domination (i.e. when Bu ? 1 or Bu ? 1, respectively). As with the reference state of ε = 1, for ε < 1 the wave mode energy saturates quite quickly and the ensuing forward cascade continues to act as an efficient means of dissipating ageostrophic energy. Further, these saturated spectra steepen as ε decreases: we see a shift from k ?1 to k ?5/3 scaling for k f < k < k d (where k f and k d are the forcing and dissipation scales, respectively). On the other hand, when ε > 1 the wave mode energy never saturates and comes to dominate the total energy in the system. In fact, in a sense the wave modes behave in an asymmetric manner about ε = 1. With regard to the vortical modes, for ε ≤ 1, the signatures of 3D quasigeostrophy are clearly evident. Specifically, we see a k ?3 scaling for k f < k < k d and, in accord with an inverse transfer of energy, the vortical mode energy never saturates but rather increases for all k < k f . In contrast, for ε > 1 and increasing, the vortical modes contain a progressively smaller fraction of the total energy indicating that the 3D quasigeostrophic subsystem, though always present, plays an energetically smaller role in the overall dynamics. Combining the vortical and wave modes, the total energy for k > k f and ε ≤ 1 shows a transition as k increases wherein the vortical modes contain a large portion of the energy at large scales, while the wave modes dominate at smaller scales. There is no such transition when ε > 1 and the wave modes dominate the total energy for all k > k f . 相似文献
6.
Abstract In the presence of a magnetic field, convection may set in at a stationary or an oscillatory bifurcation, giving rise to branches of steady, standing wave and travelling wave solutions. Numerical experiments provide examples of nonlinear solutions with a variety of different spatiotemporal symmetries, which can be classified by establishing an appropriate group structure. For the idealized problem of two-dimensional convection in a stratified layer the system has left-right spatial symmetry and a continuous symmetry with respect to translations in time. For solutions of period P the latter can be reduced to Z 2 symmetry by sampling solutions at intervals of ½P. Then the fundamental steady solution has the spatiotemporal symmetry D 2 = Z 2 ? Z 2 and symmetry-breaking yields solutions with Z 2 symmetry corresponding to travelling waves, standing waves and pulsating waves. A further loss of symmetry leads to modulated waves. Interactions between the fundamental and its first harmonic are described by the group D 2h = D 2 ? Z 2 and its invariant subgroups, which describe solutions that are either steady or periodic in a uniformly moving frame. For a Boussinesq fluid in a layer with identical top and bottom boundary conditions there is also an up-down symmetry. With fixed lateral boundaries the spatiotemporal symmetries, again described by D 2h and its invariant subgroups, can be related to results obtained in numerical experiments and analysed by Nagata et al. (1990). With periodic boundary conditions, the full symmetry group, D 2h ?Z 2, is of order 16. Its invariant subgroups describe pure and mixed-mode solutions, which may be steady states, standing waves, travelling waves, pulsating waves or modulated waves. 相似文献
7.
A theory which describes the constant f-plane flow of a steady inviscid baroclinic boundary current over a continental margin with a bathymetry that varies slowly in the alongshore but rapidly in the offshore directions is developed in the parameter regime (LD/L)2 ≤ Ro 1, where LD is the internal deformation radius, L the horizontal length scale, and Ro the Rossby number. To lowest order in the Rossby number the flow is along isobaths with speed qo = Vu(h,z)|Vh|/α, where Vu(h,z) is the upstream speed, α the upstream bottom slope at depth h, and Vh the bottom slope downstream at depth h. The lowest order flow produces a variation in the vertical component of relative vorticity along the isobath as the magnitude and direction of Vh vary in the downstream direction. The variation of vorticity requires a vertical as well as a cross-isobath flow at first order in the Rossby number. The first order vertical velocity is computed from the vorticity equation in terms of upstream conditions and downstream variations of the bathymetry. The density, pressure, and cross-isobath flow at first order in the Rossby number are then calculated. It is shown that in the cyclonic region of current (d/dh(Vu/α) > 0), if the isobaths diverge in the downstream direction ((∂/∂s)|Vh| < 0), then upwelling and onshore flow occur. The theory is applied to the northeastern Florida shelf to explain bottom temperature observations. 相似文献
8.
Abstract The variational lower bound v > 0.39π2 determined by Ivers (1984) for the infimum decay rate v of axisymmetric poloidal magnetic fields is corroborated numerically and an upper bound v < 0.66°2 established. This is achieved by correcting and extending results for certain flows considered by Chandrasekhar (1956). 相似文献
9.
The effects of variable speeds of spreading of submarine slides and slumps on near-field tsunami amplitudes are illustrated. It is shown that kinematic models of submarine slides and slumps must consider time variations in the spreading velocities, when these velocities are less than about 2cT, where
is the long period tsunami velocity in ocean of constant depth h. For average spreading velocities greater than 2cT, kinematic models with assumed constant spreading velocities provide good approximation for the tsunami amplitudes above the source. 相似文献
10.
11.
—?Modal summation technique is used to generate 5000, three-component theoretical seismograms of Love and Rayleigh waves, assuming modified PREM (PREM-C) and AK135F global earth models. The focal depth h and the geometrical fault parameters are randomly chosen so as to uniformly cover possible source mechanisms and obtain uniform distribution of log h in the interval 1?h?h?M s of the form:¶ΔM s (h)=0 forh< 20km, ΔM s (h)=0.314log(h)-0.409 for 20≠h< 60km, ΔM s (h)=1.351log(h)-2.253 for 60≠h< 100km, ΔM s (h)=0.400log(h)-0.350 for 100≠h< 600km .¶After applying the above correction, the relationship between the surface wave magnitude and the scalar seismic moment for the observational data set significantly improves, and becomes independent of the source depth. In relation to CTBT, no depth correction is needed for M S when the m b ???M S discriminant is computed, because the proposed correction is zero for earthquakes with foci above 20?km. 相似文献
12.
The kinematic‐wave and diffusive‐wave approximations were investigated for unsteady overland flow resulting from spatially varying rainfall excess. Three types of boundary conditions were adopted: zero flow at the upstream end, and critical flow and zero depth‐gradient at the downstream end. Errors were derived by comparing the dimensionless profiles of the flow depth over the plane with those computed from the dynamic‐wave solution. It was found that the mean errors for both the approximations were independent of the type of rainfall excess distribution for KF02 > 5, where K is the kinematic‐wave number and F0 is the Froude number. Therefore, the regions (KF02, F0) where the kinematic‐wave and diffusive‐wave solutions would be fairly accurate and for any distribution of spatially varying rainfall, were characterized. The kinematic‐wave approximation was reasonably accurate, with a mean error of less than 5% and for the critical depth at the downstream end, for KF02 ≥ 20 with F0 ≤ 1; if the rainfall excess was concentrated in a portion of the plane, the field where the kinematic‐wave solution was found accurate, it was more limited and characterized for KF02 > 35 with F0 ≤ 1. The diffusive‐wave solution was in good agreement with the dynamic‐wave solution with a mean error of less than 5%, in the flow depth, for KF02 ≥ 15 with F0 ≤ 1; for rainfall excess concentrated in a portion of the plane, the accuracy of the diffusion wave solution was in a region more restricted and defined for KF02 ≥ 30 with F0 ≤ 1. For zero‐depth gradient at the downstream end, the accuracy field of the kinematic‐wave was found to be greater and characterized for KF02 > 10 with F0 ≤ 1; for rainfall excess concentrated in a portion of the plane, the region was smaller and defined for KF02 > 15 with F0 ≤ 1. The diffusive‐wave solution was found accurate in the region defined for KF02 > 7·5, whereas for rainfall excess concentrated in a portion of the plane, the field of accuracy was for KF02 > 12·5 with F0 ≤ 1. The lower limits of the regions, defined on KF02, can be considered generally valid for both approximations, but for F0 < 1 smaller lower limits were also characterized. Finally, the accuracy of these approximations was influenced significantly by the downstream boundary condition. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
13.
Using the data set of about 1 Hz Lg amplitudes from 80 stations in the six eastern provinces of China, the ratios of horizontal
to vertical amplitude of Lg waves,H/Z are determined. The mean lg(H/Z)-value is equal to 0.13. For the station bases of soft deposit,granite and sedimentary rock, lg(H/Z)-values average 0.55, 0.04 and 0.10, respectively. For the three kinds of station bases, the station terms of horizontal
amplitude,C
h
average 0.65, −0.09 and 0.00; that of vertical amplitude,C
z
average 0.32, −0.04 and 0.00, respectively. There are the relations betweenC
h
,C
z
and lg(H/Z):C
h
=0.01+2.10C
z
andC
h
=−0.15+1.46 lg(H/Z).
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 281–286, 1991.
Project sponsored by the Chinese Joint Seismological Science Foundation. 相似文献
14.
James A. Yoder Larry P. Atkinson S. Stephen Bishop Jackson O. Blanton Thomas N. Lee Leonard J. Pietrafesa 《Continental Shelf Research》1985,4(6):611-635
During July and August 1981 subsurface intrusion of upwelled nutrient-rich Gulf Stream water was the dominant process affecting temporal and spatial changes in phytoplankton biomass and productivity of the southeastern United States continental shelf between 29 and 32°N latitude. Intruded waters in the study area covered as much as 101 km including virtually all of the middle and outer shelf and approximately 50% of the inner shelf area.Within 2 weeks following a large intrusion event in late July, middle shelf primary production and Chl a reached 3 to 4 gC m− d−1 and 75 mg m−, respectively. At the peak of the bloom 80% of the water column primary production occurred below the surface mixed-layer, and new primary production (i.e., NO3-supported) exceeded 90% of the total. Chl a-normalized photosynthetic rates were very high as evidenced by high mean assimilation number (15.5 mg C mg Chl a−1 h−1), high mean α (14 mg C mg Chl a−1 Ein−1 m), and no photoinhibition. As a result of the high photosynthetic rates, mean light-utilization index (Ψ) was 2 to 3 times higher than reported for temperature sub-arctic and arctic waters.The results imply a seasonal (June to August) middle shelf production of 150 g C m−1, about 15% higher than previous estimates of annual production on the middle shelf. Intrusions of the scale we observed in 1981 may not occur every summer. However, when such events do occur, they are by far the most important processes controlling summer phytoplankton dynamics of the middle and outer shelf and of the inner shelf in the southern half of the study area. 相似文献
15.
Wave tank experiments with long internal waves of elevation, of different initial length l, moving in a two-fluid system, interacting with a weak slope of 0.045 rad, show an onshore flow of the dense water, at the undisturbed pycnocline-slope intersection, of duration $11.3\sqrt{l/g'}Wave tank experiments with long internal waves of elevation, of different initial length l, moving in a two-fluid system, interacting with a weak slope of 0.045 rad, show an onshore flow of the dense water, at the
undisturbed pycnocline-slope intersection, of duration 11.3?{l/g￠}11.3\sqrt{l/g'} (g′ reduced gravity). This period corresponds to that of a strong bottom current event measured in the stratified ocean at the
Ormen Lange gas field, at 850 m depth, lasting for 24 hrs, corresponding to 11.2?{l/g￠}11.2\sqrt{l/g'}, using the width l = 300 km of the Norwegian Atlantic Current (NAC) at the site as length scale, suggesting a lateral sloshing motion of the
NAC causing the event. The onshore velocity of the dense fluid has a maximal velocity of 0.4?{g￠h2}0.4\sqrt{g'h_2} in laboratory and 0.5 ms-1=0.3?{g￠h2}^{-1}=0.3\sqrt{g'h_2} in the field (h
2 mixed upper layer thickness). Run-up of the dense fluid, beyond the undisturbed pycnocline-slope intersection, has initially
a front velocity of 0.35?{g￠h2}0.35\sqrt{g'h_2}, corresponding to the velocity of the head of a density current on a flat bottom. Due to disintegration, an initially depressed
pycnocline results in comparatively smaller run-up and velocity. While moving past the turning point, a dispersive wave train
is formed in the back part of the depression wave, developing by breaking into a sequence of up to eight boluses moving by
the undisturbed pycnocline-slope intersection. 相似文献
16.
Tsunami created by spreading submarine slides and slumps with spatially variable final uplift are investigated in the near-field using a kinematic model. It is shown that for velocities of spreading comparable to and smaller than the long period tsunami velocity
(g is the acceleration due to gravity and h is the ocean depth), the models with spatially uniform final uplift of the accumulation and depletion zones provide good approximation for the tsunami amplitudes in the near-field. For spreading velocities 2–5 times greater than cT, and for applications that use wavelengths of the order of the source dimensions, the spatial variability of the final uplift has to be considered in estimation of the high-frequency tsunami amplitudes in the near-field. 相似文献
17.
Shelf-to-canyon suspended sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300 m depth from November 2003 to March 2004. Two major storm events producing waves Hs>6 m coming from the E–SE sector took place, the first on 3–4 December 2003 (max Hs: 8.4 m) and the second on 20–22 February 2004 (max Hs: 7 m). During these events, shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended sediment on the canyon head and the adjacent outer shelf causing the first downcanyon sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of shelf water stratification. This event was too short to allow the sediment resuspended on the shallow shelf to reach the canyon head. In contrast, the February event, reinforced by dense shelf water cascading, was long enough to transfer resuspended sediment from shallow shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of shelf-to-canyon sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-shelf sediment transport during these events. 相似文献
18.
Atsushi Kubokawa 《地球物理与天体物理流体动力学》2013,107(2):119-137
Although the study of topographic effects on the Rossby waves in a stratified ocean has a long history, the wave property over a periodic bottom topography whose lateral scale is comparable to the wavelength is still not clear. The present paper treats this problem in a two-layer ocean with one-dimensional periodic bottom topography by a simple numerical method, in which no restriction on the wavelength and/or the horizontal scale of the topography is required. The dispersion diagram is obtained for a wavenumber range of [?π/L b , π/L b ], where L b is the periodic length of the topography. When the topographic?β?is not negligible compared to the planetary β, the Rossby wave solutions around the wavenumbers which satisfy the resonant condition among the waves and topography disappear and separate into an infinite number of discrete modes. For convenience, each mode is numbered in order of frequency. As topographic height is increased, the high frequency barotropic Rossby wave (mode 1) becomes a topographic mode which can exist even on the f plane, and the highfrequency baroclinic mode (mode 2) becomes a surface intensified mode. Behaviors of low frequency modes are somewhat complicated. When the topographic amplitude is small, the low frequency baroclinic modes tend to be bottom trapped and the low frequency barotropic modes tend to be surface intensified. As topographic amplitude further increases, the relation between the mode number and vertical structure changes. This change can be attributed to the increase of the frequency of the topographic mode with the topographic amplitude. 相似文献
19.
Derege Tsegaye Meshesha Atsushi Tsunekawa Mitsuru Tsubo Nigussie Haregeweyn Enyew Adgo 《水文科学杂志》2013,58(12):2203-2215
AbstractKnowledge of rainfall characteristics is important for estimating soil erosion in arid areas. We determined basic rainfall characteristics (raindrop size distribution, intensity and kinetic energy), evaluated the erosivity of rainfall events, and established a relationship between rainfall intensity I and volume-specific kinetic energy KEvol for the Central Rift Valley area of the Ethiopian highlands. We collected raindrops on dyed filter paper and calculated KEvol and erosivity values for each rainfall event. For most rainfall intensities the median volume drop diameter (D50) was higher than expected, or reported in most studies. Rainfall intensity in the region was not high, with 8% of rain events exceeding 30 mm h-1. We calculated soil erosion from storm energy and maximum 30-min intensity for soils of different erodibility under conditions of fallow (unprotected soil), steep slope (about 9%) and no cover and management practice on the surface, and determined that 3 MJ mm ha-1 h-1 is the threshold erosivity, while erosivity of >7 MJ mm ha-1 h-1 could cause substantial erosion in all soil types in the area.
Editor Z.W. Kundzewicz; Associate Editor Q. Zhang 相似文献
20.
Summary The waves generated by a steadily moving two-dimensional pressure distribution are examined using non-linear shallow water theory. The applied pressure is zero ahead of the disturbance, that is in the downstream direction, and is a constantP
0 in the upstream direction, these regions being joined smoothly by a cubic function.We consider here only the case of supercritical flow in both regions, the solution representing an asymmetric solitary wave travelling with the disturbance. The wave profiles are determined by an iterative method previously employed for non-linear waves. Wave amplitudes and profiles, and the wave drag, associated with each system are computed for various values ofP
0/Q g h, whereh is the undisturbed depth of water ahead of the wave.The solution obtained reduces to the classical solitary wave of finite amplitude when the applied pressure is everywhere zero.
Division of Numerical and Applied Mathematics, National Physical Laboratory. 相似文献
Résumé Nous avons calculé les expressions des profils d'ondes solitaires produites par une pression, qui se propagent sur la surface d'une couche d'eau peu profonde avec une vitesseU plus grande que (g h)1/2. La pression appliquée est nulle en avant de l'onde, elle est une constanteP 0 en arrière, et entre ces deux régions elle est representée par une fonction cubique. Les profils sont calculés par une methode iterative déjà employée pour des ondes non-linéaires. L'amplitude, le profil et la force ont été evalués pour diverses valeurs deP 0/Q g h, ouh est la profondeur en avant de l'onde.
Division of Numerical and Applied Mathematics, National Physical Laboratory. 相似文献