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Nonlinear interactions between large waves and freely floating bodies are investigated by a 2D fully nonlinear numerical wave tank (NWT). The fully nonlinear 2D NWT is developed based on the potential theory, MEL/material-node time-marching approach, and boundary element method (BEM). A robust and stable 4th-order Runge–Kutta fully updated time-integration scheme is used with regriding (every time step) and smoothing (every five steps). A special φn-η type numerical beach on the free surface is developed to minimize wave reflection from end-wall and wave maker. The acceleration-potential formulation and direct mode-decomposition method are used for calculating the time derivative of velocity potential. The indirect mode-decomposition method is also independently developed for cross-checking. The present fully nonlinear simulations for a 2D freely floating barge are compared with the corresponding linear results, Nojiri and Murayama’s (Trans. West-Jpn. Soc. Nav. Archit. 51 (1975)) experimental results, and Tanizawa and Minami’s (Abstract for the 6th Symposium on Nonlinear and Free-surface Flow, 1998) fully nonlinear simulation results. It is shown that the fully nonlinear results converge to the corresponding linear results as incident wave heights decrease. A noticeable discrepancy between linear and fully nonlinear simulations is observed near the resonance area, where the second and third harmonic sway forces are even bigger than the first harmonic component causing highly nonlinear features in sway time series. The surprisingly large second harmonic heave forces in short waves are also successfully reproduced. The fully updated time-marching scheme is found to be much more robust than the frozen-coefficient method in fully nonlinear simulations with floating bodies. To compare the role of free-surface and body-surface nonlinearities, the body-nonlinear-only case with linearized free-surface condition was separately developed and simulated. 相似文献
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1 .IntroductionTheappraisalofagooddesignforaverylargefloatingstructure(VLFS)thatwillserveinaspeci fiedoceanarearequiresthatthestructuralsystembeeconomicallydesigned ,therequirementsforitsfunctionbesatisfiedandthestructurekeepsstableinitswholeserviceperio… 相似文献
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Ten exposed sandy sites covering a range from reflective to dissipative beaches were sampled in south-central Chile to evaluate: (1) spatial changes in species richness, abundance and biomass of the intertidal macroinfauna in response to changes in mean grain size, beach face slope and beach type, and (2) spatial changes in abundance, biomass and body sizes of the most abundant species in response to changes in the physical factors. The number of species, abundance and biomass per beach in general decreased with increasing particle size and beach face slope (steeper beaches) and increased from reflective to dissipative conditions. The best fit for number of species was with Dean's parameter, a measure of beach type, whereas for abundance and biomass the best fits were found with particle size. The isopod Excirolana braziliensis and the anomuran Emerita analoga increased in abundance and biomass towards dissipative conditions, whereas Excirolana hirsuticauda showed the opposite trend in biomass and was significantly larger in beaches with steeper profiles. It is concluded that responses to changes in beach type are more pronounced at community level than within species populations. 相似文献
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Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations. 相似文献
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Descriptive Analysis and Classification of Benthic Communities in Some Mediterranean Coastal Lagoons (Central Italy) 总被引:3,自引:0,他引:3
Abstract. Benthic samples were taken seasonally at 32 stations in five coastal lagoons of Central Italy (Fogliano, Monaci, Caprolace, Fondi, and Lungo) during a two-year period (1982–1984). Composition and distribution of benthic populations in each lagoon as well as seasonal trends of species richness, density, diversity, and redundancy are presented and discussed.
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
The faunal differentiation appeared to be mainly due to the different degree of water exchange, both with marine and continental systems. 相似文献
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The annual cycle of Synechococcus (cyanobacteria) in the northern Levantine Basin shelf waters (Eastern Mediterranean) 总被引:1,自引:0,他引:1
Abundance of picoplanktonic chroococcoid marine cyanobacteria Synechococcus was monitored weekly over the year 1998 in shallow coastal waters of the northern Levantine Basin. The ambient physical, chemical and biological variables (temperature, salinity, Secchi disk depth, total suspended sediment, nitrate, phosphate, Chl a and phytoplankton) were also measured. Synechococcus was found to be more abundant during summer and early autumn and less during winter and early spring. At the surface and 15 m depth, cell concentrations were in the range 6.4 × 103–1.5 × 105 and 3.2 × 103–1.6 × 105 cells·ml−1, respectively. Based on the Pearson product–moment correlation analysis, a highly significant correlation between Synechococcus abundance and ambient temperature was observed (n = 40, r = 0.558, P < 0.01). As Synechococcus forms blooms that usually do not last more than a week, the short time‐scale survey achieved in this study was appropriate to reveal its abundance dynamics. Several factors such as rapid changes in nutrient concentration (especially nitrate), phytoplankton, light availability, temperature, salinity, freshwater input and vertical mixing played a relevant role on the abundance of Synechococcus over the year in the highly dynamic shallow coastal waters of the Levantine Basin. 相似文献