Numerical study of wave and longshore current interaction

Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induced longshore currents were modeled by shallow water equation.Water wave provided the radiation stress gradients to drive current.Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state.The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole（2001） and Reniers and Battjes（1997） were simulated.The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents,and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction,and the breaking wave induced longshore current effect on wave transformation is not obvious.     

Study on the Dynamic Process of the Onset of South China Sea Summer Monsoon

By using the NCEP/NCAR reanalysis data from 1958 to 1997, we first looked into the atmospheric flow conditions in the one month immediately prior to the onset of the South China Sea summer monsoon （SCSSM） each year. A monthly-averaged zonal basic flow of 40-yr composite was then calculated. The stability of Rossby wave in the basic flow was studied based on the spherical barotropic vorticity equation. Furthermore, the spectral function expansion method was adopted to define and compute the evolvement of a developing wave packet. The results indicate that there exists barotropic instability of spherical Rossby wave in the climatically-averaged flow field before the SCSSM onset. The instability is triggered by the westerly jet stream in the Southern Hemisphere, and the strongest instable perturbation lies to the south of the westerly jet stream. The peak of the developing spherical Rossby wave packet propagates from mid and high latitudes to low latitudes, though not crossing the equator, spurring the cumulus convection in the tropical zones. The eruption of the cumulus convection and its spread to monsoon regions help to speed up the adjustment of the general circulation and the SCSSM onset. It is concluded that elements that contribute to the SCSSM onset are on global scale, albeit the onset itself looks like a local phenomenon.     

Optimal Matching Analysis of Net Buoyancy and Pitching Angle for Underwater Gliders

Control parameter optimization is an efficient way to improve the endurance of underwater gliders(UGs), which influences their gliding efficiency and energy consumption. This paper analyzes the optimal matching between the net buoyancy and the pitching angle and proposes a segmented control strategy of Petrel-L. The optimization of this strategy is established based on the gliding range model of UG, which is solved based on the approximate model, and the variations of the optimal control paramet...     

Effects of separate and mutual application of Na and Si on drought resistance of Haloxylon ammodendron

We studied pot cultivated Haloxylon ammodendron’s growth, physiological changes and drought resistance under NaCl, H₂SiO₃, and NaCl+H₂SiO₃ treatments. Results show that 0.3 g/kg NaCl, 0.2 g/kg H₂SiO₃ or 0.3 g/kg NaCl+0.1 g/kg H₂SiO₃ treatments can effectively promote growth and improve the drought resistance of H. ammodendron. Compared with that without NaCl treatment, H. ammodendron’s height, crown diameter and fresh weight increased by 42%, 91% and 62% respectively under 0.3 g/kg NaCl treatment, and its main stem diameter, main root diameter and main root length increased by 40%, 39% and 23%, respectively. Compared with that without H₂SiO₃ treatments, H. ammodendron’s height, crown diameter and fresh weight increased by 36%, 45% and 27% respectively under 0.2 g/kg H₂SiO₃ treatment, and its main stem diameter, main root diameter and main root length increased by 23%, 23% and 20%, respectively. Compared with that under 0.3 g/kg NaCl treatment, H. ammodendron’s height, crown diameter and fresh weight and main root length increased by 9%, 10%, 17% and 12% respectively under 0.3 g/kg NaCl+0.1 g/kg H₂SiO₃ treatment. Compared with that under 0.1 g/kg H₂SiO₃ treatment, H. ammodendron’s height, crown diameter and fresh weight increased by 28%, 76% and 68% respectively under 0.3 g/kg NaCl+0.1 g/kg H₂SiO₃ treatment, and its main stem diameter, main root diameter and main root length increased by 30%, 32% and 27%, respectively. This suggests that moderate levels of NaCl+H₂SiO₃ interaction can effectively promote growth and improve drought resistance of H. ammodendron than separate applications of NaCl or H₂SiO₃.     

Astronomical Dating of the Middle Miocene Hanjiang Formation in the Pearl River Mouth Basin,South China Sea

The Hanjiang Formation of Langhian age(middle Miocene) in the Pearl River Mouth Basin (PRMB),South China Sea consists of deltaic siliciclastic and neritic shelf carbonate rhythmic alternations,which form one of the potential reservoirs of the basin.To improve stratigraphic resolutions for hydrocarbon prospecting and exploration in the basin,the present study undertakes spectral analysis of high-resolution natural gamma-ray(NCR) well-logging record to determine the dominant frequency components and test whether Milankovitch orbital signals are recorded in rhythmic successions.Analytical results indicate the orbital cycles of precession(～19 ka and～23 ka), obliquity(～41 ka),and eccentricity(～100 ka and～405 ka),which provide the strong evidence for astronomically driven climate changes in the rhythmic alternation successions.Within biochronological constraint,a high-resolution astronomical timescale was constructed through the astronomical tuning of the NGR record to recent astronomically calculated variation of Earth’s orbit. The astronomically tuned timescale can be applied to calculate astronomical ages for the geological events and bioevents recognized throughout the period.The first downhole occurrences of foraminifers Globorotalia peripheroronda and Globigerinoides sicanus are dated at 14.546 Ma and 14.919 Ma,respectively,which are slightly different from earlier estimates in the South China Sea. When compared with the global sea-level change chart,the astronomical estimate for the sequences recognized based on microfossil distributions have the same end time but the different initiation time. This is probably due to the local or regional tectonic activities superimposed on eustatic rise which postponed the effect of global sea-level rising.Astronomical timescale also resolves the depositional evolution history for the Langhian Stage(middle Miocene) with a variation that strongly resembles that of Earth’s orbital eccentricity predicted from 13.65 Ma to 15.97 Ma.We infer that the main factor controlling the variability of the sedimentation rate in the Hanjiang Formation is related to the～405-ka-period eccentricity.     

Concrete durability under different circumstances based on multi-factor effects

Concrete durability has become a hot research field in civil engineering. Concrete structures suffer salt-erosion damage to different degrees in the semi-arid region of North China. The environmental condition is one of the important factors affecting the durability of concrete constructions. To realize fully the interaction between various environmental factors, this paper researched concrete durability in the salt environment under combined actions(immersing, freeze–thaw cycles, and wet–dry cycles). According to the laboratory test data, the concrete-durability degradation law under coupling-effect factors was investigated. The results show that concrete's compressive strength decreases with the increase of salt concentration and immersion time. No matter what the environmental conditions were, the compressive strength-loss ratio increased with the test time. The compressive strength-test results indicate that sodium sulfate has the strongest corrosive effect on concrete durability, followed by calcium chloride, with sodium chloride having the weakest corrosion. Compared with the other two environmental factors, the wet–dry cycle is the key factor affecting concrete durability. Therefore, in engineering practice, the influence of environment conditions on the strength and durability of concrete should be taken into full consideration, especially in the wet–dry environment with salt conditions.     

A Numerical Study on Effects of Land-Surface Heterogeneity from “Combined Approach” on Atmospheric Process Part I: Principle and Method

1.IntroductionAnideallandsurfacemodelmustbothrealisticallydescribethelandsurfacecharacteristics(especiallytheuniversalheterogeneity)andbecomputationallyinexpensive.CurrentlyPOpularlandsurfacemodelsareallbasedon"bigfeartheory,inwhichamodelgridcellisdividedintomanypatches(e.g.,abaresoilpatchoravegetationpatch;manyregularpatchesdividedintoaccordingtogeographicallocations),andinwhichonlyinterpatchvariabilityistakenintoaccountwhileseldomintrapatchvariabilityis,whentheheterogeneityisconsidered.Even…     

中国湿地研究进展与展望

Wetland is one of the most important ecosystems in the world, possessing important functions such as hydrologic regulation, degrading pollutants, adjusting climate, preventing erosion, maintaining geochemical cycle and providing habitats for important species, etc. (Chen, 2001; Mitsch; 2000; Chen, 2003), and has enjoyed the reputation of "earth's kidney" and "biology supermarket".1ThecharacteristicsanddistributionofwetlandsinChinaChina has a wetland area of 65.94 million ha (not including riv…