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811.
812.
Design and projected performance of a flapping foil AUV 总被引:1,自引:0,他引:1
Licht S. Polidoro V. Flores M. Hover F.S. Triantafyllou M.S. 《Oceanic Engineering, IEEE Journal of》2004,29(3):786-794
The design and construction of a biomimetic flapping foil autonomous underwater vehicle is detailed. The vehicle was designed as a proof of concept for the use of oscillating foils as the sole source of motive power for a cruising and hovering underwater vehicle. Primary vehicle design requirements included scalability and flexibility in terms of the number and placement of foils, so as to maximize experimental functionality. This goal was met by designing an independent self-contained module to house each foil, requiring only direct current power and a connection to the vehicle's Ethernet local area network for operation. The results of tests on the foil modules in the Massachusetts Institute of Technology (MIT) Marine Hydrodynamics Water Tunnel and the MIT Ship Model Testing Tank are both used to demonstrate fundamental properties of flapping foils and to predict the performance of the specific vehicle design based on the limits of the actuators. The maximum speed of the vehicle is estimated based on the limitations of the specific actuator and is shown to be a strong function of the vehicle drag coefficient. When using four foils, the maximum speed increases from 1 m/s with a vehicle C/sub D/ of 1.4 to 2 m/s when C/sub D/=0.1, where C/sub D/ is based on vehicle frontal area. Finally, issues of vehicle control are considered, including the decoupling of speed and pitch control using pitch-biased maneuvering and the tradeoff between actuator bandwidth and authority during both the cruising and hovering operation. 相似文献
813.
V. A. Dulov S. I. Klyushnikov V. N. Kudryavtsev O. V. Shulgin O. G. Shcherbak 《Physical Oceanography》1991,2(4):269-282
An overview of experiments is given on the observation of the dependence of the intensity of wind wave breaking on large-scale
currents' inhomogeneities and atmospheric boundary layer stratification. The data were interpreted using a model in which
the variance of the wind wave breaking intensity reflects fluctuations in the influx of energy to wind waves due to various
factors.
Translated by V. Puchkin. 相似文献
814.
The effects of varying intensities of off-road vehicle and pedestrian traffic on vegetation height and percent-cover were investigated at two sites representing pioneer and climax dune shrubland communities in South African dune systems. In all cases, a decreasing trend in vegetation height and percentage cover subsequent to application of the treatments was evident, although this was more clear in the shrub than in the pioneer community. The impact on vegetation variables increased with increasing intensity of vehicle and pedestrian treatments. Vehicles driven along a curved path resulted in greater vegetation destruction than those driven along a straight path. High intensity (single application) treatments resulted in an initial decrease in vegetation height and cover immediately after the impact, which was followed by a further decline over the next 3 months. This two-step response was attributed to the subsequent gradual death of the vegetation which was not evident immediately following the impact. Due to their faster growth rate, pioneer dune communities appear to have the capacity to recover following impacts, while dune shrub communities tend to be more vulnerable, exhibiting signs of damage for longer periods. The results of this study have value for managers of coastal dune systems, particularly those impacted by human recreational activities. 相似文献
815.
The proposed numerical model simulates the short-term temporal changes in shoreline position due to a structure interrupting the longshore sediment flux. The impacts of both the groin-type construction and underwater trench of arbitrary orientation relative to the shore are discussed. In order to estimate the sediment mass trapped by the structure, a submodel of the longshore sediment transport induced by a random wave field is developed. The contribution of the surface roller in momentum balance as well as in sediment suspension is included. The shoreline changes are computed from the equation deduced from the mass conservation. The perturbations in the longshore sediment discharge caused by a structure are assumed to concentrate within some boundary area of which the spatial scale is proportional to the structure's length until the latter is exceeded by the width of the sediment flux. It is shown in particular that the total effect of a long trench (channel) and a pier in its nearshore part results in general shoreline recession except for the vicinity of a pier. The model is tested against the laboratory data of Baidei et al. (1994) and applied to the Baidara Bay coast (Kara Sea) where a pipeline would be designed. 相似文献
816.
V. D. Posdinin 《Physical Oceanography》1987,1(1):47-53
A functional connection between probability of turbulence generation by shear instability in current velocity and Väisälä-Brunt frequency is obtained. Examples are cited of sections with isoclines of probable turbulence generation in the 30–500-m layer in the Antarctic circumpolar current north of Kergelen island.UDK [551.465.15+551.46.08] (269) 相似文献
817.
Abstract. The reproductive cycle of the comatulid crinoid Nemaster rubiginosa from Discovery Bay, Jamaica is described histologically. The cycle is annual and may be divided into (1) a "resting" phase (summer) in which most adults possess immature, unsexable gonads, (2) a recovery phase (early fall) marked by the re-initiation of gametogenesis and rapid gonadal growth, (3) a breeding phase (late fall and winter) during which the gonads are mature and repeated spawning likely takes place, and (4) a post-spawning phase (spring) during which relict gametes are removed from the shrinking gonads. Although unsexable individuals predominate during the "resting" phase, a small proportion of the adult population is unsexable at all times of the year. The reproductive condition of animals in the same month in two successive years was very similar, suggesting that the timing of reproduction is quite predictable from year to year. The re-initiation of gametogenesis in the early fall is correlated with both rising sea temperature and shortening daylength, and the October to March breeding season corresponds to the period of short daylengths at the study site. The well-defined and synchronized annual reproductive cycle of Nemaster rubiginosa contrasts with the more prolonged and variable reproductive cycles reported for other tropical crinoids and points to a diversity of breeding patterns among tropical crinoids. 相似文献
818.
We present the results of experimental investigations of the characteristics of turbulence in the layer of wave-induced mixing.
The data on the fluctuations of velocity, temperature, and conductivity are obtained with the help of a Sigma-1 measuring complex. The computed values of the dissipation rate of turbulent energy are compared with different models proposed
for the subsurface layer. It is shown that the available models fail to guarantee satisfactory agreement of the numerical
results with the experimental data for the layer of active wave action and, in particular, in the presence of swell. This
leads us to the conclusion concerning the necessity of parametrization and assimilation of more complete data on the state
of the sea surface, the structure of currents, and the surface layer of the atmosphere in the models.
__________
Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 15–28, March–April, 2007. 相似文献
819.
The structure, evolution, and breaking of a tidal internal wave on a steep shelf are discussed on the basis of the data of temperature measurements. The bottom slope at the measurement site is close to the critical slope for a tidal wave. The tidal wave and other waves are inclined coastward. The tidal-wave amplitude increases monotonically with increasing horizon depth. The tidal wave is nonlinear in amplitude and turns over on the outer shelf. On the inner shelf, the internal wave is close in shape to rectangular and generates harmonics of its own. The harmonics make the tidal wave steeper and form solitary rises similar to bilateral bores. All these features ensure a more rapid sink for the internal-tide energy. 相似文献
820.