Numerical Analysis on the Effects of Submerged Depth of the Grid and Direction of Incident Wave on Gravity Cage   总被引：1，自引：0，他引：1  

陈昌平  李玉成  赵云鹏  董国海  桂福坤 《中国海洋工程》2009,23(2):233-250

In this paper,the numerical model of the net cage with the grid mooring system in waves is set up by the lumped mass method and rigid kinematics theory,and then the motion equations of floating system,net system,mooring system,and floaters are solved by the Runge-Kutta fifth-order method.For the verification of the numerical model,a series of physical model tests have been carried out.According to the comparisons between the simulated and experimental results,it can be found that the simulated and experimental results agree well in each condition.Then,the effects of submerged depth of grid and direction of incident wave propagation on hydrodynamic behaviors of the net cage are analyzed.According to the simulated results,it can be found that with the increase of submerged depth of grid,the forces acting on mooring lines and bridle lines increase,while the forces on grid lines decrease;the horizontal motion amplitudes of floating collar decrease obviously,while the vertical motion amplitudes of floating collar change little.When the direction of incident wave propagation changes,forces on mooting lines and motion of net cage also change accordingly.When the propagation direction of incident wave changes from 0° to 45°,forces on the main ropes and bridle ropes increase,while the forces on the grid ropes decrease.With the increasing propagation direction of incident wave,the horizontal amplitude of the forces collar decreases,while the vertical amplitude of the floating collar has little variation.  相似文献   

Spectroscopic survey of the Galaxy with Gaia– II. The expected science yield from the Radial Velocity Spectrometer     

M. I. Wilkinson  A. Vallenari  C. Turon  U. Munari  D. Katz  G. Bono  M. Cropper  A. Helmi  N. Robichon  F. Thévenin  S. Vidrih  T. Zwitter  F. Arenou  M.-O. Baylac  G. Bertelli  A. Bijaoui  F. Boschi  F. Castelli  F. Crifo  M. David  A. Gomboc  A. Gómez  M. Haywood  U. Jauregi  P. de Laverny  Y. Lebreton  P. Marrese  T. Marsh  S. Mignot  D. Morin  S. Pasetto  M. Perryman  A. Pr&#;a  A. Recio-Blanco  F. Royer  A. Sellier  A. Siviero  R. Sordo  C. Soubiran  L. Tomasella  Y. Viala 《Monthly notices of the Royal Astronomical Society》2005,359(4):1306-1335

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Dynamics of perfect fluid unified dark energy models     

Luís M. G. Beça  Pedro P. Avelino 《Monthly notices of the Royal Astronomical Society》2007,376(3):1169-1172

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Comparison between Eulerian diagnostics and finite-size Lyapunov exponents computed from altimetry in the Algerian basin     

Francesco d’Ovidio  Jordi Isern-Fontanet  Cristóbal López  Emilio Hernández-García  Emilio García-Ladona 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):15-31

Transport and mixing properties of surface currents can be detected from altimetric data by both Eulerian and Lagrangian diagnostics. In contrast with Eulerian diagnostics, Lagrangian tools like the local Lyapunov exponents have the advantage of exploiting both spatial and temporal variability of the velocity field and are in principle able to unveil subgrid filaments generated by chaotic stirring. However, one may wonder whether this theoretical advantage is of practical interest in real-data, mesoscale and sub-mesoscale analysis, because of the uncertainties and resolution of altimetric products, and the non-passive nature of biogeochemical tracers. Here we compare the ability of standard Eulerian diagnostics and the finite-size Lyapunov exponent in detecting instantaneous and climatological transport and mixing properties in the south-western Mediterranean. By comparing with sea-surface temperature patterns, we find that the two approaches provide similar results for slowly evolving eddies like the first Alboran gyre. However, the Lyapunov exponent is also able to predict the (sub-)mesoscale filamentary processes occurring along the Algerian current and above the Balearic Abyssal Plain. Such filaments are also observed, with some mismatch, in sea-surface temperature patterns. Climatologies of Lyapunov exponents do not show any compact relation with other Eulerian diagnostics, unveiling a different structure even at the basin scale. We conclude that filamentation dynamics can be detected by reprocessing available altimetric data with Lagrangian tools, giving insight into (sub-)mesoscale stirring processes relevant to tracer observations and complementing traditional Eulerian diagnostics.  相似文献   

The Phobos gravitational field modeled on the basis of its topography     

Zdeněk Martinec  Karel Pěč  Milan Burša 《Earth, Moon, and Planets》1989,45(3):219-235

The parameters of the best-fitting ellipsoid have been derived using the latest spherical harmonics of the Phobos topography (Duxbury, 1989) by solution of non-linear overdetermined inverse problem. The lengths of the equatorial axes of the ellipsoid have been determined (a = 12.9 km, b = 11.4 km). They are nearly the same as established by Duxbury (ibid.) on the basis of the linearized relationship between the squared lengths of ellipsoidal axes and the topography coefficients C ₂₀ and C _22. The length of the polar axis (c = 9.1 km) differs of about 20% from Duxbury's value. Supposing mass homogeneity of Phobos, the Stokes parameters of the external gravitational field have been derived up to those of the sixth degree and order. The large irregularities in the Phobos figure cause the values of the Duxbury's potential coefficients be fairly inaccurate except the harmonics C ₂₀, C ₃₂, S ₄₃ and S ₅₁, i.e. linearized relationship between gravity and topography cannot be applied for Phobos. Finally, positions of the centre of figure and the directions of the principal axes of inertia have been established.  相似文献   

Angular momentum and tidal evolution of Saturn's system     

Milan Burša 《Earth, Moon, and Planets》1991,54(3):241-255

It has been demonstrated that dynamically the Saturnian system is analogous to the Jovian system; however, it is not an analogue of the Solar system as a whole. The departures in the figure parameters of the tri-axial Saturnian satellites orbiting in 1 : 1 resonance, from equilibrium figure parameters are not large in general, and the tidal and centrifugal distorting forces can be supposed to be responsible for the actual figures. The estimates for different dynamical parameters of the system support the hypothesis that the tri-axial satellites in 1 : 1 resonance were formed from the same protoplanetary nebula that gave rise to Saturn.  相似文献   

Are There Radio-quiet Solar Flares?     

Arnold O. Benz  Roman Brajša  Jasmina Magdalenić 《Solar physics》2007,240(2):263-270

Some 15% of solar flares having a soft X-ray flux above GOES class C5 are reported to lack coherent radio emission in the 100 – 4000 MHz range (type I – V and decimetric emissions). A detailed study of 29 such events reveals that 22 (76%) of them occurred at a radial distance of more than 800″ from the disk center, indicating that radio waves from the limb may be completely absorbed in some flares. The remaining seven events have statistically significant trends to be weak in GOES class and to have a softer non-thermal X-ray spectrum. All of the non-limb flares that were radio-quiet above 100 MHz were accompanied by metric type III emission below 100 MHz. Out of 201 hard X-ray flares, there was no flare except near the limb (R>800″) without coherent radio emission in the entire meter and decimeter range. We suggest that flares above GOES class C5 generally emit coherent radio waves when observed radially above the source.  相似文献   

Acceleration Phase of Coronal Mass Ejections: II. Synchronization of the Energy Release in the Associated Flare     

Darije Maričić  Bojan Vršnak  Andrew L. Stanger  Astrid M. Veronig  Manuela Temmer  Dragan Roša 《Solar physics》2007,241(1):99-112

We analyze the relationship between the acceleration of coronal mass ejections (CMEs) and the energy release in associated flares, employing a sample of 22 events in which the CME kinematics were measured from the pre-eruption stage up to the post-acceleration phase. The data show a distinct correlation between the duration of the acceleration phase and the duration of the associated soft X-ray (SXR) burst rise, whereas the CME peak acceleration and velocity are related to the SXR peak flux. In the majority of events the acceleration started earlier than the SXR burst, and it is usually prolonged after the SXR burst maximum. In about one half of the events the acceleration phase is very closely synchronized with the fastest growth of the SXR burst. An additional one quarter of the events may be still considered as relatively well-synchronized, whereas in the remaining quarter of the events there is a considerable mismatch. The results are interpreted in terms of the feedback relationship between the CME dynamics and the reconnection process in the wake of the CME.  相似文献   

Does the timing of the spawning migration change for the southern component of the Northeast Atlantic Mackerel (Scomber scombrus,L. 1758)? An approximation using fishery analyses     

Antonio Punzón  Begoña Villamor 《Continental Shelf Research》2009,29(8):1195-1204

Part of the Northeast Atlantic mackerel population migrates towards the southern spawning area (Cantábrian Sea) at the end of winter. In this seasonal handline fishery targeting mackerel, the most important in the study area that targets this species, the timing of the peak of catches has shifted forward (later) in recent years. This paper presents results pointing to the likelihood that this shift is due to a change in the timing of the spawning migration to the southern area of the Northeast Atlantic mackerel population. Three types of fleet have been identified within this fishery, and in all of them there is a forward shift in time in effort exerted. Moreover, a new model has been defined for the standardization of catch per unit effort (CPUE). The fishing season appears to have shifted forward by 29 days between 2000 and 2006. Nevertheless, changes have been detected neither in the exploitation pattern nor in the duration of the fishing season during the period studied. A shift on this scale has important consequences for the management of the resource, the fleets that exploit it and the resource assessment survey designs that will have to be adapted to this new scenario.  相似文献   

Evolution of active galactic nuclei broad-line region clouds: low- and high-ionization lines     

D.R. Gonçalves  A.C.S. Friaça  V. Jatenco-Pereira 《Monthly notices of the Royal Astronomical Society》2001,328(2):409-418

The formation of quasar broad-line region (BLR) clouds via thermal instability in the presence of Alfvén heating has been discussed by Gonçalves, Jatenco-Pereira & Opher. In particular, these studies showed the relevance of Alfvén heating in establishing the stability of BLR clouds in the intercloud medium. The present paper shows the results of time-dependent calculations (we use a time-dependent hydrodynamic code) following the evolution of BLR clouds, since their formation from the 10⁷-K intercloud medium. We also calculate the UV and optical line emission associated with the clouds in order to compare with observations. Our results are compared with those of UV and optical monitoring of well-studied AGN, which suggest that the BLR is most probably composed of at least two different regions, each one giving rise to a kind of line variability, since low- and high-ionization lines present different patterns of variability. We discuss the alternative scenario in which lines of different ionization could be formed at the same place but heated/excited by distinct mechanisms, considering the Alfvén heating as the non-radiative mechanism.  相似文献