Experimental Study of Pipeline Stability on Sandy Seabed under the Influence of Ocean Currents

Ocean-current-induced pipeline stability on sandy seabed was simulated physically in a flow flume. The process of pipeline losing onbottom stability in currents was recorded and analyzed. Experimental data show that, for a pipeline directly laid on sandy seabed, there exists a linear relationship between the dimensionless submerged weight of pipeline and Froude number, in which the current-pipe-soil coupling effects are reflected. The sand-particle size effects on pipeline onbottom stability are further discussed. The new established empirical relationship may provide a guide for the engineering practice of current-induced on-bottom stability design of a submarine pipeline.

谈镐生文集

本文集收入了著名力学家、应用数学家、中国科学院院士谈镐生先生在流体力学、稀薄气体动力学和应用数学研究领域的论文和研究报告26篇，谈镐生先生倡导和支持力学基础研究的有关文章和论述21篇，谈先生的学术活动和生活图片多幅，以及谈镐生先生生平，最后附有谈先生生平年表。

 

 

星载激光对水下目标通信可行性研究

The characteristics of media in communication channel are analyzed briefly and the reasonable optical parameters of media are adopted. With certain communication system parameters the temporal and spatial distributions of the received signal from submerged platform are simulated using Monte Carlo method. The upper limit of the ratio of Monte Carlo estimated error to averaged value is about 0.3%. From the simulated results, the optimized sampling timing of receiver and field of view of telescope are obtained. Also the signal-to-noise ratio of the receiver is calculated. Based on this, the error probability of the communication system is deduced from laser pulse position modulation and maximum likelihood detection. The results show that under severe environment robust laser communication from a satellite to a submerged platform can be achieved.

Habitat degradation of Rhinopithecus bieti in Yunnan, China

Black-and-white snub-nosed monkeys (Rhinopithecus bieti) are endemic to the Trans-Himalayas in Northwest Yunnan and Southeast Tibet between the upper Yangtze and Mekong Rivers. Based on field surveys and previous reports, we identified the dark-coniferous forest, the mixed coniferous and broadleaf forest, and oak patches as suitable habitats (SH) for the monkeys. Summer grazing lands (SGL), which were made by local people cutting and burning the dark-coniferous forest at the high altitude belt, replaced SH. To have a general view of the status of the SH in Yunnan, we estimated the areas of SH and SGL from satellite images in 1997, and compared with areas estimated from aerial photo-based maps (ca. 1958). The work resulted in: 1) the area of SH was 4,169 km(2) in 1997; 2) SGL was 1,923 km(2); 3) during the past 40 years, the area of SH decreased by 31% (1,887 km(2)), and SGL increased by 204% (1,291 km(2)); and 4) the mean size of forest patches decreased from 15.6 to 5.4 km(2). In addition, the area of SGL is positively correlated to local human population (R-2 greater than or equal to0.53), implying that the reduction and fragmentation of habitat for Rhinopithecus bieti is a result of population growth of humans, who mostly employ traditional modes of production. Only 11 monkey groups remained in the changing habitat. Considering that forests at lower elevation were also encroached upon by farmlands in a similar way, the forest ecosystem is highly threatened. The destruction will continue unless there is a change in the mode of production in the region.

Allelopathic interactions between the Potamogeton spp and toxic cyanobacteria (Microcystis aeruginosa)

This study aimed to investigate the allelopathic activities between 3 Potamogeton spp. (Potamogeton maackianus, Potamogeton malaianus and Potamogeton pectinatus) and the toxic cyanobacteria (Microcystis aeruginosa). All Potamogeton spp inhibited the growth of M. aeruginosa in both coexistence and exudates experiments. Inhibition of M. aeruginosa growth by plant exudates depended strongly on the biomass of P malaianus. Initial pH (6.5-9.8) did not influence the inhibitory effects of P. malaianus exudates. However, the M. aeruginosa inhibited the net photosynthesis and respiration of all three pondweed test spp.. The decreases in photosynthesis and respiration were probably caused by the toxic compounds released by M. aeruginosa, rather than its shading effects. The M. aeruginosa also decreased the nutrients (phosphorus and nitrogen) uptake rates of macrophytes. The absorption rates of phosphorus and nitrogen and net photosynthesis were decreased sharply. These results will help to restore submerged plants in eutrophic waters.

Influence of Potamogeton crispus growth on nutrients in the sediment and water of Lake Tangxunhu

An incubation experiment was performed on Potamogeton crispus (P. crispus) using sediment collected from Lake Tangxunhu in the center of China, in order to determine the effects of plant growth on Fe, Si, Cu, Zn, Mn, Mg, P, and Ca concentrations in the sediments and overlying waters. After 3 months of incubation, Ca, Mg, and Si concentrations in the water column were significantly lower, and P and Cu concentrations were significantly higher than in unplanted controls. The effect of P. crispus growth on sediment pore waters and water-extractable elements varied. Concentrations of Ca, Mg, Si, Fe, Cu, and Zn were significantly higher, and P was significantly lower, than in pore waters of the control. Water-extracted concentrations of Fe, Mg, and Si in the sediments were lower, and P was higher, than in the control. Presence of P. crispus generally enhanced concentration gradients of elements between pore waters and overlying waters but not for P. The growth of P. crispus was associated with an increase in water pH and formation of root plaques, resulting in complex effects on the sediment nutritional status.

Effects of ammonium on growth, nitrogen and carbohydrate metabolism of Potamogeton maackianus A. Benn

Growth, nitrogen and carbohydrate metabolism in relation to eutrophication were studied for a submerged plant Potamogeton maackianus, a species common in East Asian shallow lakes. The plants were grown in six NH4+-N concentrations (0.05, 0.50, 1.00, 3.50, 5.00 and 10.00 mg/L) for six days. NH4+-N levels in excess of 0.50 mg/L inhibited the plant growth. The relationships between external NH4+-N availability and total nitrogen (TN), protein-N, free amino acid-N (FAA-N) and NH4+-N in plant tissues, respectively, conformed to a logarithmic model suggesting that a feedback inhibition mechanism may exist for ammonium uptake. The response of starch to NH4+-N was fitted with a negative, logarithmic curve. Detailed analysis revealed that the influx NH4+-N had been efficiently incorporated into organic-N and eventually stored as protein at the expense of starch accumulation. These data suggest that this species may be able to tolerate high levels of ammonium when dissolved oxygen is sufficient.

Nonylphenol and octylphenol in urban eutrophic lakes of the subtropical China

The paper studied two estrogenic pollutants, 4-nonylphenol (NP) and 4-tert-octylphenol (OP) in water, suspended particle (SP) and sediments in urban eutrophic lakes. The concentrations of NP ranged from 1.94 to 32.85 mu g/l, 0.876 to 31.13 mu g/l and 3.54 to 32.43 mu g/g dry weight (dw) in water, suspended particle (SP) and sediments, respectively, and that of OP from 0.027 to 1.44 mu g/l, 0.008 to 1.777 mu g/l and 0.058 to 1.245 mu g/g dw in water, suspended particle (SP) and sediments, respectively. An increasing trend in the concentration was noticed in all matrices close to the sewage inlets, which was found to be the major factor affecting the spatial distribution of alkylphenols (APs) in the lakes. Due to restoration of submerged macrophytes, which might accumulate APs, the contaminations of APs in the Little Moon Lake (LML) and the Little Lotus Lake (LLL) were lower than those in the Big, Moon Lake (BML) and the Bier Lotus Lake (BLL). A reasonable correlation of NP and OP was obtained among water, suspended particle and sediment. The possible environmental stress of APs concentration on aquatic organisms in Wuhan urban lakes was also discussed.

The restoration of aquatic macrophytes for improving water quality in a hypertrophic shallow lake in Hubei Province, China

This paper deals with a case study of the restoration of submerged macrophytes for improving water quality in a hypertrophic shallow lake, Lake Donghu of Wuhan, Hubei Province, China. Macrophyte restoration experiments were conducted in large-scale enclosures established in three sublakes of different trophic status, and the effectiveness for water quality improvement was tested by using the enclosure experiment in the hypertrophic sublake. Water quality was remarkably improved after the reestablishment of aquatic macrophytes. It is suggested that the submerged vegetation of less polluted sublakes could be capable of recovering spontaneously once the stocking of herbivorous fishes has been ceased, and the K-selected plants such as Potamogeton maackianus should be introduced into these sublakes to enhance the stability of aquatic vegetation. However, it may not be possible and economical to restore the submerged macrophytes in severely polluted basins unless external pollution has been cut off and internal nutrient loadings considerably reduced. In this case, the r-selected submerged plants should be used as the pioneer species for macrophyte recovery. (C) 2001 Elsevier Science B.V. All rights reserved.

Photosynthetic bicarbonate utilization by a terrestrial cyanobacterium, Nostoc flagelliforme (Cyanophyceae)

The photosynthetic characteristics of the terrestrial cyanobacterium, Nostoc flagelliforme, after complete recovery by rewetting, was investigated to see whether it could use bicarbonate as the external inorganic carbon source when submerged. The photosynthesis-pH relationship and high pH compensation point suggested that the terrestrial alga could use bicarbonate to photosynthesize when submerged. The photosynthetic oxygen evolution rates were significantly inhibited in Na+-free and Na+ + Li+ media but were not affected by the absence of Cl-, implying that the bicarbonate uptake was associated with Na+/HCO3- symport rather than Cl-/HCO3- exchange system.

Macrozoobenthos in 2 shallow mesotrophic Chinese lakes with contrasting sources of primary production

Comparative studies on macrozoobenthos were done in 2 shallow mesotrophic lakes in the middle basins of the Yangtze River, China: Lake Biandantang where macrophytes were abundant, and Lake Houhu where macrophytes were scarce Samples were taken monthly at 4 stations in each lake from April 1997 to March 1999, and a total of 67 and 31 tara of macrozoobenthos were recorded in Lake Biandantang and Lake Houhu, respectively. Both annual mean density and biomass of macrozoobenthos were higher in Lake Biandantang than in Lake Houhu: 780 vs 532 indivials/m(2) and 37.1 vs 25.9 g wet mass/m(2), respectively. Abundance of functional feeding groups followed the order: scraper > collector > predator > shredder in Lake Biandantang, and collector > predator > scraper > shredder in Lake Houhu. Only 1 density peak occurred from winter to early spring in Lake Houhu; however, in Lake Biandantang, there were 2 peaks, the winter peak and spring peak. K-dominance curves and Shannon-Wiener, Simpson, and Margelef indices indicated that macrozoobenthos were more diverse in Lake Biandantang than in Lake Houhu Our study suggests that, in shallow lakes, submerged macrophytes are essential for the maintenance of biodiversity of macrozoobenthos mainly because the macrophytes increase habit heterogeneity and availability of suitable food, and may also decrease predation by fish on the macrozoobenthos.

A comparative study of benthic nematodes in two Chinese lakes with contrasting sources of primary production

Ecological studies on benthic nematodes were conducted in two small, shallow lakes in the middle Yangtze basin, China; Lake Houhu, where the main source of primary production is phytoplankton and Lake Biandantang where it is predominantly macrophytic in origin. Monthly sampling was carried out from April 1996 to March 1997. A total of 36 species of nematodes was found in Lake Houhu and 51 species in Lake Biandantang. The dominant trophic groups of nematodes were algophages in Lake Houhu and bacteriophages associated with omniphages and phytophages in Lake Biandantang. Community analyses based on K-dominance curves, Shannon-Wiener and Simpson diversity indices, demonstrate that the benthic nematodes are more diverse in Lake Biandantang than in Lake Houhu. The results suggest that the abundance of submerged vegetation is essential for maintenance of habitat heterogeneity and biodiversity of nematodes in shallow lakes.

CONTRIBUTION OF BACTERIOPLANKTON, PHYTOPLANKTON, ZOOPLANKTON AND DETRITUS TO ORGANIC SESTON CARBON LOAD IN A CHANGJIANG FLOODPLAIN LAKE (CHINA)

The relative compositions of bacterioplankton, phytoplankton, zooplankton and detritus of seston were studied during the course of inundation in a floodplain lake of central Changjiang (China). Peaks in bacterial biomass developed shortly after flooding, coinciding with the initial leaching of organic nutrients from vegetation submerged under floodwater, and again at high water, shortly before the climax of phytoplankton biomass. Rods predominated the bacterial carbon biomass. Phytoplankton developed a postflood bloom at initial falling, corresponding to the drainage of the lake water into the river. While minimal biomass occurred during the advent of flooding, most likely due to disturbance and dilution. Algal biomass was usually dominated by Chlorophyta. Highest biomass of zooplankton was recorded at the end of the flooding in connection with the decline in turbidity, and once again at early drainage, closely associated with high phytoplankton biomass. Copepods (mainly nauplii) always constituted the majority of zooplankton carbon biomass. Peaks in detrital carbon concentrations were recorded at rising and falling water phases, corresponding respectively to the riverine discharge and decomposition of macrophyte mats. At rising water phase, CPOC was abundant. While during other water phases, this predominance was shifted to FPOC alone. Taken together, average contribution of bacterioplankton, phytoplankton, zooplankton and detritus to total seston carbon was 3.29, 21.21, 6.83 and 68.67 %, respectively.

Interaction of linear waves with an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth

The linear water wave scattering and radiation by an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth is investigated by use of the multipole expansion method. The diffracted and radiated potentials are expressed as a linear combination of infinite multipoles placed at the centre of each cylinder with unknown coefficients to be determined by the cylinder boundary conditions. Analytical expressions for wave forces, hydrodynamic coefficients, reflection and transmission coefficients and energies are derived. Comparisons are made between the present analytical results and those obtained by the boundary element method, and some examples are presented to illustrate the hydrodynamic behavior of multiple horizontal circular cylinders in a two-layer fluid. It is found that for two submerged circular cylinders the influence of the fluid density ratio on internal-mode wave forces is more appreciable than surface-mode wave forces, and the periodic oscillations of hydrodynamic results occur with the increase of the distance between two cylinders; for four submerged circular cylinders the influence of adding two cylinders on the wave forces of the former cylinders is small in low and high wave frequencies, but the influence is appreciable in intermediate wave frequencies.

Response amplitude and hydrodynamic force for a buoy over a convex

A buoy as an offshore structure is often placed over a convex such as a caisson or a submerged island. The hydrodynamic fluid/solid interaction becomes more complex due to the convex compared with that on the flat. Both the buoy and the convex are idealized as vertical cylinders. Linear potential theory is used to investigate the response amplitude and the hydrodynamic force for a buoy over a convex due to diffraction and radiation in water of finite depth. These are derived from the total velocity potential. A set of theoretical added mass, damping coefficient, and exciting force expressions have been proposed. Analytical results of the response amplitude and hydrodynamic force are given. Finally, the numerical results show that the effect of the convex on the response amplitude and hydrodynamic force for the buoy is ignored if the size of the convex is relatively smaller.