Interaction mechanisms among waves,currents and a submerged plate     

《Applied Ocean Research》2019

Wave-induced loads on a submerged plate, representative of submerged breakwater, coastal-bridge deck and a certain type of wave energy converter, in a uniform current are investigated in this study using fully nonlinear numerical wave tanks (NWTs) based on potential flow theory. The coupling effect of wave and current is explored, and the underlying interaction mechanisms of the hydrodynamic forces are described. The presence of a background current modifies the frequency dispersion. It produces changes of the water-surface elevation, and also has an effect on wave-induced loads. Depending on the nonlinearity, higher harmonic wave components are generated above the submerged plate. These contribute to the wave forces. It is found that the horizontal and the vertical force, hence the moment, are affected in the opposite way by the currents. The Doppler shifted effect dominates the vertical force and the moment on the plate. Whereas, the Doppler shifted effect and the generation of higher wave harmonics play opposite roles on the horizontal forces. The contribution of 2^nd order harmonics is found to be up to 30% of the linear component. The current-induced drag force, represented by the advection term ρU∂φ/∂x in the pressure equation, is found to lead to a decrease in the moment for the most range of wavelengths considered, and an increase in the moment for a small range of longer waves.  相似文献   

基于模糊自整定PID的直升机飞行控制律设计     

苏延旭  王庆领 《南京气象学院学报》2018,10(2):131-137

在经典PID控制律基础上,引入模糊控制的概念设计模糊自整定PID控制律改进无人直升机姿态回路控制器,实现了PID控制器的参数在线自整定,并改善了控制器性能.通过Matlab对闭环系统进行算法仿真,表明模糊自整定PID控制器能够发挥优于传统PID控制器的控制性能.最后对所设计的控制器进行半物理仿真验证,通过对比典型输入指令下经典PID和模糊自整定PID两种控制器的控制效果,验证了模糊自整定PID对系统性能的优化.  相似文献   

Study of physical and chemical properties of vitrinites. Inferences on depositional and coalification controls     

A. Jimnez  M. J. Iglesias  F. Laggoun-Dfarge  I. Surez-Ruiz 《Chemical Geology》1998,150(3-4):197-221

A detailed study of petrological, geochemical, textural and coking properties was carried out on vitrains from the Puertollano, Blanzy–Montçeau, Asturias and Teruel. The objective was to determine in depth the physical and chemical properties of a series of natural and pure vitrinites of different rank, and the influence that the sedimentary and post-sedimentary conditions had on them. It is demonstrated that although vitrains are almost entirely made up of the huminite/vitrinite maceral group they have a different composition, thermal behaviour and physical properties. Thus, geochemical and textural properties of Blanzy–Montçeau vitrains can be considered to be representative of the telinite, the major component in both samples (75% vol.) at the beginning of the bituminization stage (subbituminous/high volatile C bituminous coals). The characteristics of the Puertollano vitrains described here can also be attributed to the telocollinite (>80% vol.) for the high volatile C bituminous coal. Variations in physico-chemical properties between Puertollano and Blanzy–Montçeau vitrains are due to the differences in the initial composition of organic matter. Slight differences (i.e., bed moisture content or porosity) between vitrains from the two coal seams in the same basin can be attributed to their stratigraphic position. Several parameters such as S₂, HI, oil and extraction yield and fluorescent properties suggest that the Puertollano and Blanzy–Montçeau vitrains have a lower hydrocarbon potential. The relationships between geochemical and textural properties make it possible to distinguish between ‘normal' and perhydrous vitrains. The two different hydrogen-enrichment processes that occur in vitrains from the Teruel and Asturias basins can be distinguished from the extraction yield data.  相似文献   

Participation in higher education: A geodemographic perspective on the potential for further expansion in student numbers     

Peter Batey  Peter Brown  Mark Corver 《Journal of Geographical Systems》1999,1(3):277-303

Higher education in England has expanded rapidly in the last ten years with the result that currently more than 30% of young people go on to university. Expansion is likely to continue following the recommendations of a national committee of inquiry (the Dearing Committee). The participation rate is known to vary substantially among social groups and between geographical areas. In this paper the participation rate is calculated using a new measure, the Young Entrants Index (YEI), and the extent of variation by region, gender and residential neighbourhood type established. The Super Profiles geodemographic system is used to facilitate the latter. This is shown to be a powerful discriminator and to offer great potential as an alternative analytical approach to the conventional social class categories, based on parental occupation, that have formed the basis of most participation studies to date. Received: 20 October 1998/Accepted: 5 May 1999  相似文献   

FT-IR Spectroscopic Investigation of Hydrous Components in Sillimanite from Eastern Ghat Granulite Belt, India     

R.V. Karanth  George Mathew  T.K. Gundu Rao 《Gondwana Research》1999,2(1):89

FT-IR spectra of sillimanite samples from high grade regionally metamorphosed rocks belonging to the granulite terrain (amphibolite to pyroxene granulite facies) deciphers prominent OH features. Heating experiments indicate growth of prominent band at 3161cm⁻¹. Heating above 1000°C all OH features disappear in intensity into broad features with slight shift of bands towards lower energies. Complete dehydration requires temperatures above 1000°C. Coexistence of boron and OH features are also observed in all sillimanite samples. The high temperature behaviour of sillimanite from the granulite terrain discerns that the hydrous species in sillimanite were incorporated much below 700°C, however, secondary hydration due to pegmatite activity, retrograde metamorphism and migmatisation is not ruled out. Thus a near anhydrous condition were probably not achieved during the granulite facies metamorphism in Eastern ghat granulite terrain.  相似文献   

硼及硼同位素地球化学在地质研究中的应用   总被引：17，自引：0，他引：17  

肖荣阁  大井隆夫  蔡克勤 《地学前缘》1999,6(2):361-368

总结了硼及硼同位素的地球化学特征：（１）硼是易溶元素,主要赋存在地球表层,尤其是海水、海相沉积物及海水交代岩石中。其同位素组成δ１１Ｂ值按顺序变化,封闭盐湖卤水（＞４０‰）＞海水（３９５‰）＞海相硼矿物（１８２‰～３１７３‰）＞海相沉积物（１３９‰～２５２‰）＞海水交代岩石（４５１‰～１０８５‰）。大陆水及陆相沉积物硼含量及硼同位素组成变化极大,并多以负值为主。海陆过渡构造带则具有过渡的硼丰度值和硼同位素组成。（２）１１Ｂ较１０Ｂ具有更活跃的地球化学性质,因此在水岩作用中具有明显的同位素交换。硅化交代作用中,岩石被硅化交代,释放硼,并优先释放重硼,同位素组成变轻;在脱硅反应中,岩石释放硅吸收硼,并优先吸收重硼,同位素组成变重。在封闭体系中,水溶液淋滤岩石中部分的硼,即可大量富集,并富集１１Ｂ;在开放体系中,岩石硼被大量淋滤流失,δ１１Ｂ值明显降低。由于水岩作用的结果,从新鲜海底玄武岩到正常海水,硼同位素值从－２９５‰到３９５‰逐渐升高。（３）变质脱水反应中硼被大量排出,并优先排出重硼同位素,进入流体相,因此随着变质程度由低到高,岩石中硼含量及同位素组成δ１１Ｂ值由高变低。（４）在成矿研究中?  相似文献   

Surfactant components of marine organic matter as agents for biogeochemical fractionation and pollutant transport via marine aerosols     

C. Oppo  S. Bellandi  N. Degli Innocenti  A. M. Stortini  G. Loglio  E. Schiavuta  R. Cini   《Marine Chemistry》1999,63(3-4)

The role of surfactant organic matter in marine aerosol production has been studied under conditions in which there is a large coverage of whitecaps on the sea surface. To improve the knowledge of matter exchange and pollutant recycling from the sea surface into the atmosphere, a spray drop adsorption model (SDAM) was developed and the validity of the proposed model verified by the following experimental results: (1) an increase of surfactant matter on the sea surface during rough sea conditions (‘surface wave concentration'); (2) an (hyperbolic-like) increase of the enrichment ratio (ER) of surfactant fluorescent organic matter (SFOM), made up predominantly by humic substances (HS), as the particle size decrease; (3) a similar behaviour for elements with pollutant properties, and which are known to interact with HS and other surfactant materials, considered pollution tracers. An additional laboratory experiment, based on the adsorption model conditions, gives enrichment ratio greater than unity for K and Ca. The first results on marine aerosols trapped in marine clouds (at 1000 m above sea level and at 100 km from the coast) seem to further support the proposed model and its ability to predict the transition from saline to almost entirely organic particles for the smaller fractions of marine aerosols. The possible contribution of these particles to the recycling and to the long range transport of pollutants via marine aerosols has been considered.  相似文献   

Peptide decomposition by extracellular hydrolysis in coastal seawater and salt marsh sediment     

Silvio Pantoja  Cindy Lee 《Marine Chemistry》1999,63(3-4)

Extracellular peptide hydrolysis rates were measured in seawater and sediment from Flax Pond salt marsh using peptide analogs (LYA-peptides) as substrates. This technique allows the direct measurement of specific hydrolysis products and thus provides insights into enzymatic hydrolysis pathways. In sediments, hydrolysis rate constants of LYA-peptides varied seasonally and with depth. Highest activity was found in spring and summer, and most cores exhibited a subsurface maximum. Calculations using the concentrations of chemically-measured peptides suggested that extracellular hydrolysis of peptides is faster than the rate of free amino acids uptake. However, not all peptides may be available for enzymatic hydrolysis. In both seawater and sediment, extracellular hydrolysis of peptides of up to 8 amino acids yielded smaller peptides and free amino acids. Hydrolysis rates depended on size of the peptide substrate, although a clear relationship with number of amino acid constituents was not evident. Peptides containing >2 amino acids were hydrolyzed 10–400 times faster than dipeptides or the fluorogenic substrate Leucine-MCA. Thus, dipeptidases are either uncommon in nature, or hydrolysis is carried out by nonspecific hydrolases that with a low affinity for dipeptides. This is also suggested by the presence of a lag time before dipeptide hydrolysis begins, and the absence of dipeptide hydrolysis in 0.2-μm-filtered. One implication of this finding is that measurements of hydrolysis rates using substrates like Leu-MCA may not accurately predict the magnitude of hydrolysis rates of macromolecules in the marine environment. Even though dipeptide hydrolysis is slow compared to that of larger peptides, LYA-dipeptides are preferentially produced from the hydrolysis of larger substrates. LYA-dipeptides do not penetrate cell membranes of microorganisms because of their size, but natural dipeptides are smaller and can be transported across the cell membrane. Since dipeptides do not appear to accumulate in natural waters, they must be rapidly removed by microorganisms.  相似文献   

Heavy metals in particulate matter and sediments in the southern Barcelona sedimentation system (North-western Mediterranean)     

Pere Puig  Albert Palanques  Joan A. Sanchez-Cabeza  Pere Masqu 《Marine Chemistry》1999,63(3-4)

Concentrations of selected heavy metals (Cr, Cu, Ni, Pb and Zn) from surface sediments, suspended particulate matter and settling particles in the southern Barcelona continental margin were studied in order to evaluate the environmental impact of the anthropogenic metals discharged by the Llobregat River in this Mediterranean area. The temporal variation of heavy metals discharged by this river onto the continental shelf is clearly related to the river water flow. Part of the fine sediment and associated heavy metals transported by the Llobregat River during periods of low river flow accumulate on the river bed, and they are totally removed and discharged onto the Barcelona continental shelf during sporadic river water flow increases. Metals produce significant anomalies of chromium (×2.5), copper (×3.4) and zinc (×3.7) in the surface sediments of the Llobregat prodelta and tend to be transported along the continental shelf following the mean flow. Metals associated with the finest suspended flocs transferred to the slope are controlled by the shelf-slope density front and are transported along slope by the general geostrophic current, instead of accumulating and becoming concentrated in the slope bottom sediments. Settling particulate matter collected in sediment traps on the Barcelona continental slope offshore of the shelf-slope front shows low heavy metal concentrations except in a few sediment trap samples that are significantly metal-enriched in chromium (×4.5) and zinc (×6.8). This enrichment is associated with very short and sporadic river flow increases and is only recorded inside the Foix submarine canyon, which acts as a preferential conduit for the shelf-slope sediment transfer.  相似文献   

Development and Re‐Evaluation of Tourmaline Reference Materials for In Situ Measurement of Boron δ Values by Secondary Ion Mass Spectrometry     

Katharina Marger  Matthieu Harlaux  Andrea Rielli  Lukas P. Baumgartner  Andrea Dini  Barbara L. Dutrow  Anne‐Sophie Bouvier 《Geostandards and Geoanalytical Research》2020,44(3):593-615

Six tourmaline samples were investigated as potential reference materials (RMs) for boron isotope measurement by secondary ion mass spectrometry (SIMS). The tourmaline samples are chemically homogeneous and cover a compositional range of tourmaline supergroup minerals (primarily Fe, Mg and Li end‐members). Additionally, they have homogeneous boron delta values with intermediate precision values during SIMS analyses of less than 0.6‰ (2s). These samples were compared with four established tourmaline RMs, that is, schorl IAEA‐B‐4 and three Harvard tourmalines (schorl HS#112566, dravite HS#108796 and elbaite HS#98144). They were re‐evaluated for their major element and boron delta values using the same measurement procedure as the new tourmaline samples investigated. A discrepancy of about 1.5‰ in δ¹¹B was found between the previously published reference values for established RMs and the values determined in this study. Significant instrumental mass fractionation (IMF) of up to 8‰ in δ¹¹B was observed for schorl–dravite–elbaite solid solutions during SIMS analysis. Using the new reference values determined in this study, the IMF of the ten tourmaline samples can be modelled by a linear combination of the chemical parameters FeO + MnO, SiO₂ and F. The new tourmaline RMs, together with the four established RMs, extend the boron isotope analysis of tourmaline towards the Mg‐ and Al‐rich compositional range. Consequently, the in situ boron isotope ratio of many natural tourmalines can now be determined with an uncertainty of less than 0.8‰ (2s).  相似文献