In the present paper, the profiles of incipient spilling breaking waves with wavelengths ranging from 10 to 120cm were studied experimentally in clean water. Short-wavelength breakers were generated by wind, while longer-wavelength breakers were generated by a mechanical wavemaker, using either a dispersive focusing or a sideband instability mechanism. The crest profiles of these waves were measured with a high-speed cinematic laser-induced fluorescence technique. For all the wave conditions reported herein, wave breaking was initiated with a capillary-ripple pattern as described in Duncan et al . ( J. Fluid Mech ., vol. 379, 1999, pp. 191–222). In the present paper, it is shown that at incipient breaking the crest shape is self-similar with two geometrical parameters that depend only on the slope of a particular point on the front face of the gravity wave. The scaling relationships appear to be universal for the range of wavelengths studied herein and hold for waves generated by mechanical wavemakers and by wind. The slope measure is found to be dependent on the wave phase speed and the rate of growth of the crest height prior to incipient breaking.
Low-frequency waves induced by the shoaling of random gravity waves (the primary waves) on sloping beaches were studied experimentally. Incident primary waves with a Pierson-Moskowitz (PM) spectrum were mechanically generated at a water depth of 0.7 m and propagated toward beaches with three different slopes (1/20, 1/30, and 1/40) in separate experiments. Four wave conditions with significant wave heights ranging from 0.078 to 0.125 m were used. The time series of surface elevations were simultaneously recorded at various water depths along the beach. Low-frequency waves were obtained from the data with a low-pass filter. Our results show that the spectra of low-frequency waves on beaches are dramatically changed by the beach slope and the wave height of incident primary waves. The cross-correlation of low-frequency waves with the surface-elevation envelope of the primary waves shows that the incident bound long waves are dominant. Free low-frequency waves propagate in the offshore direction with very low amplitudes due to high energy dissipation on the beach. The energy ratio between the low-frequency and the primary waves in the shoaling region outside the surf zone strongly correlates to the local surface skewness. For a given water depth, the low-frequency wave energy is proportional to m03/2, where m0 is the primary wave energy, in agreement with the field observations.
The error and precision of the total radiation and PAR calculational methods used constantly in China are tested and comparatively studied using radiation data form 9 stations (1961～1980) in Northeast China. Employed the universal formula of calculating total radiation upon the multi-factors synthesis, the main findings can be conclude: the relative error of the month and the year are 4.0% and 3 0%, respectively; the multiple correction coefficient are 0 990 and 0 787; the radiation calculational methods adapted to Liaoning province are erected. The experiential formula of PAR coefficient of total radiation, which is created by Zhou Yunhua etc. well reflects the seasonal changes and influential factors of the coefficient. Selecting above-mentioned methods that adapt to Liaoning province, the total radiation and PAR of Liaoning province are calculated and the distributive characters are analyzed using the data of related climatic elements during 1961～1990.
Mechanically generated weakly breaking waves were studied experimentally in clean water and water with a soluble surfactant whose bulk concentration was above the critical micelle concentration (CMC). For the surfactant case, the breaker, which forms a surface-tension-dominated spilling breaker in clean water [wave frequencies 1.42 to 1.15Hz , see Duncan, J. Fluid Mech. 379, 191 (1999)], ranges from a spiller at the highest frequency to an overturning wave with a plunging microjet at the lowest frequency. It is shown that this behavior is consistent with that of a wave in a pure liquid with a lower surface tension than water rather than water with a surfactant monolayer. The analysis of the geometrical characteristics of the breaking surface generated by the jet impact on the front face of the wave crest indicates a patch of more violent turbulence suggesting an increase of air-sea transfer compared to the clean water case.
The dynamics of longitudinal surface waves in surfactant films in a large wave tank (14.8 m long, 1.2 m wide, and 1.0 m deep) were studied experimentally. Three soluble surfactants (Triton X‐100, sodium dodecyl sulfate, and hemicyanine) were added to the tank water in separated experiments; however, other naturally occurring surfactants were present as well. Since it is exceedingly difficult to control surfactants in large water tanks, these mixed surfactant conditions are probably typical of laboratory‐scale experiments on the effects of surfactants on gravity‐capillary wave phenomena. In the present experiments, longitudinal waves were generated with a Teflon bar that barely touched the water surface and oscillated horizontally in a direction perpendicular to its length. The longitudinal waves were measured with a technique that is based on the phase shift of capillary waves that were generated mechanically with a propagation direction perpendicular to that of the longitudinal waves. The wave number ( α L ), the phase speed, and the damping coefficient ( β L ) of the longitudinal waves were obtained for wave frequencies ranging from 0.2 to 1.5 Hz in the various surfactant films. The experimental data agree well with the theoretical dispersion relationship of longitudinal waves, and the fitting of this equation to the experimental data yielded the equilibrium surface elasticity, the surface viscosity, and the surface‐to‐bulk diffusion parameter. For nearly all experimental conditions, β L / α L was greater than 0.414, its value based on theory with the surface viscosity set to zero. It was found that the longitudinal wave dispersion curves intersect the capillary‐gravity wave dispersion curves at frequencies ranging from 2.53 to 3.55 Hz. This intersection point is known to be the frequency of the maximum damping of capillary‐gravity waves.
From the blue-green algae species a representative algae, namely, ChloreUlla vulgaris (CV)to belong to Chlorophyta is selected as one of algae species studied in order to investigate the effect of TN, TP on the growth behavior of CV with the Monod equation, and calculate the semi-saturation constants of CV to TP(K(SP)) and TN(K(SN)). K(SN) >> K(SP) showed that the effect of TP on growth of CV is obvious significant than that of TN. The growth rate of Chlorella vulgaris is very sensitive to the concentration of phosphorus: Compares with the blank value, the special growth rate (mu) has been enhanced under the low concentration of 0.002 mg x L(-1), then the concentration turned to 0.2 mg x L(-1) the special growth rate (mu) has been enhanced obviously; but there was hardly any change under the concentration of nitrogen from 0.000 to 0.050 mg x L(-1). At the same time, in order to reveal whether there was a generalized character associating the growth dynamics of CV with that of dominant blue-green algae species, the dynamic models including CV constructed from our experimental data, dominant blue-green algae and sea algae from literature information have been compared and analyzed systemically, and the results showed that their growth dynamics behavior and ecological characteristic were extremely similar and common. According to extrapolation of the intercommunity of all growth dynamics we could describe and show availably there is a common behavior to the growth of dominant blue-green algae in the Three Gorges reservoir region. This conclusion would have some important theoretical and applied significance.
This paper describes the results of radar scattering experiments carried out at the wavetank facility at the University of Maryland, College Park. Spilling and plunging breakers with a water wavelength of approximately 80 cm were generated through dispersive focusing of a chirped wave packet, and were then imaged with a high‐speed camera in conjunction with a laser sheet. Simultaneously, the radar backscatter generated by the breakers when viewed with an “up‐wave” look direction was measured by an ultrawideband, dual‐polarized, X‐band radar with a range resolution of approximately 4 cm. The nominal grazing angle of the radar was 12°. In addition to providing both quantitative profiles of the evolving water surface and the corresponding ultrahigh resolution radar backscatter, this experimental setup also included a moving instrument carriage that allowed the sensors to follow the breakers throughout their entire evolution. Numerical scattering simulations that use the measured surface profiles as inputs were also conducted in order to further dissect the scattering mechanism. An analysis of the results shows that for the spilling breaker, over 90% of the horizontally (HH) polarized radar backscatter is generated during the initial stage of breaking by the small bulge near the wave crest. For vertical (VV) polarization, the crest bulge produces about 60% of the total backscattered energy. For both polarizations, the Doppler velocity associated with this energy is very close to that of the phase speed of the dominant wave in the water wave packet. For VV, the remainder of the backscattered energy is generated by the turbulent, postbreaking surface, and in fact a close correlation is observed between increases in the VV backscatter amplitude and the shedding of vortex ripples after the wave breaks. For the plunging breaker, the initial feature on the crest (an overturning jet) generates a lower percentage of the total backscattered energy. For the spilling breaker, agreement between the experimental and numerical results is good, particularly in the Doppler domain. The simulations also indicate uncertainty in the polarization ratio measurements that is related to multipath scattering. To the extent that they can be applied to the open ocean, these results can serve as a guide for the development of future breaker models.
In this paper, the regression effects, accuracies and figures of three mathematical models for simulating light vertical distribution in rice canopy were compared. The model Sz=Soea+bLAI (z) was the best. The quantitative relationships between a, b and LAI (z) accumulated to a height above the ground, solar altitudes were discussed. A universal available model for light distribution in crop canopy was proposed, and the error in utilizing the model was analysed. Meanwhile, daily changes in light intensity in representative layers of the canopy were described by harmonic analysis.
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