共查询到20条相似文献，搜索用时 15 毫秒
1.
Anna Marson 《Ocean & Coastal Management》1996,30(2-3)
The process of eutrophication in the Adriatic Sea Basin has emerged over recent decades as a problem that demands special consideration and treatment; one of the most important reasons is the damage to the economy due to its undesired effects.Scientific knowledge concerning this process, while not exhaustive, is sufficient as a basis for directing action. But the experience acquired to date demonstrates that scientific knowledge alone cannot steer practical action, assuring the use of all existing (limited) knowledge to define the best practicable actions in a given time and place. In other terms, the institutional framework has not been able to use this knowledge for improving the environmental state of the Basin.To overcome this unsatisfactory situation, a different definition of the problem is proposed, as well as a different way for designing suitable solutions. 相似文献
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We generalize the problem of evaluation of currents caused by the action of breeze winds to the three-dimensional case. In
the “solid-lid” approximation, the problem is reduced to the numerical solution of a two-dimensional equation for the integral
current function (with complex-valued coefficients) with subsequent evaluation of the components of current velocity according
to analytic formulas. The breeze is specified as acting in a narrow coastal strip in the form of a zonal wind. The three-dimensional
structure and the variations of currents near the west boundary of the Kerch Strait as functions of time are studied in detail. 相似文献
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The three-dimensional problem of the dynamics of a moored floating object under the action of regular waves is solved numerically as a boundary value problem by use of the finite-infinite element method. The cross-sectional shape of the floating body and the mooring arrangements may all be arbitrary. The mathematical formulations of the problem and procedures of the numerical method are presented in this paper. A corresponding computer program WALOAD has been developed, which is capable of computing wave forces on fixed and floating structures. Numerical computations using this program could give very accurate results, even though rather coarse meshes were used. The program is easy to use and is readily applicable in many practical situations. 相似文献
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通过物理模型试验 ,研究了黄茅海内不同治导线对潮汐要素的影响 ,得出治导线对河口湾内的潮位变化随着上游径流量的增加而逐渐减弱的结论。中水大潮时 ,湾顶与湾腰处高潮位降低 ,低潮位抬高 ,其幅度与治导线进占的海域面积成正比。洪水大潮时 ,高潮位一般也降低。低潮位则有时降低 ,有时有所抬高。河口湾治导线实施后 ,涨潮最大流速、平均流速和落潮平均流速均有所减小 ,但落潮最大流速不减反增。涨、落潮潮量有不同程度的减少 ,其减幅与治导线的进占规模成正比。各站的高、低潮位发生时间都有前移趋势 ,治导线越往外推 ,潮时前移量就越大。本文对这些现象的成因进行了分析 ,并就潮位、潮流速及潮流量的变化对防洪水位和交通航运水深的影响作了阐述。 相似文献
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赵子丹 《海洋学报(英文版)》1984,3(1):137-142
Almost all concepts on shear stresses under wave action have been put forward on the basis of linear wave theory, thus it can not be used to evaluate the net sediment transport rate caused by wave action. Using other way to solve this problem, the author makes an advance in the idea that the non-linear effect is also considered. 相似文献
9.
《Marine Policy》2013
At the Rio+20 meeting in June 2012, governments of the world committed to rebuilding fish stock sizes by 2015 at least to levels that can produce the maximum sustainable yield (MSY), even if that would require the temporary closure of fisheries. This study explores the outcomes of such action for European stocks. In 2012, only 8 of 48 stocks (17%) were abundant enough to produce MSY and with a business as usual scenario, this number would not increase by 2015. In contrast, if fishing was reduced to levels consistent with rebuilding and if some fisheries were temporarily closed, 50–70% of the examined stocks would be able to reach the Rio+20 target by the end of 2015. In this scenario, after three years with reduced catches, fish supply from European stocks would reach and exceed the levels of 2011 already in 2016. The implications for fish, fishers and fish consumers are discussed. 相似文献
10.
In this work, a theoretical analysis of the dynamic response of a poro-elastic soil to the action of long water waves is conducted. For some combinations of the physical parameters of the soil and the water waves, the vertical stress tends towards zero at a certain unknown depth in the soil, as measured from the top of that medium. Under this condition, the liquefaction of the soil is imminent, at which time the excess pore pressure is essentially equal to the overburden soil pressure. Physical problems of this type have been widely studied in the specialized literature. However, most major studies have focused on solving the governing equations together with a liquefaction criterion. Here, the maximum momentary liquefaction depth induced by long water waves is considered as part of the problem, which is treated as an eigenvalue problem. To solve this problem, the governing equations are written in dimensionless form. The theoretical results show that for long waves, the horizontal displacements are smaller in magnitude than the vertical displacements, and when the wavelength or wave period increases, the maximum liquefaction also increases. Analytical solutions for the excess pore pressure and the horizontal and vertical displacements are obtained. The analytical results for the pore pressure are found to be very close to the analytical results reported in the specialized literature. 相似文献
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Within the framework of the linear theory of long waves, we study the evolution of a wave process caused by the action of
surface pressure periodically varying in time in a bounded basin of variable depth without vertical walls. We assume that
the basin is filled with a homogeneous liquid nonperturbed at the initial time and take into account the action of dissipative
forces. We obtain the analytic solution of the posed problem. It is used to perform the detailed analysis of the influence
of the dissipative forces and the frequency of perturbing pressure on the characteristics of the process of evolution of waves.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
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小尺度群桩应用广泛,一直是学者研究的重点,小尺度有别于大尺度桩柱,由于桩柱周围存在漩涡的脱落,使得受力特性复杂。以往的研究过程中,波浪主要采用单向不规则波浪,并且试验模型多以两桩或三桩组成的群桩结构为主,桩数相对较少。多向不规则波与群桩结构的作用特点有别于单向不规则波且研究较少。通过物理模型试验,针对多向不规则波对于9桩桩排群桩结构的作用进行了研究。首先综合考虑KC1/3数和相对桩径的影响,提出以参数KCLD 1/3数来衡量群桩的效应,并分析了正向力与横向力随着参数KCLD 1/3数和相对桩距的变化关系,研究了群桩中不同桩位桩柱波浪力的变化规律和方向分布宽度对于群桩波浪力的影响。研究结果表明,群桩中各桩的正向力随着方向分布标准差的增大而减小,而横向力在相对桩距较大时随着方向分布标准差的增大而增大,同时群桩中不同位置桩上的波浪力具有较大的差异。 相似文献
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D. V. Alekseev V. A. Ivanov E. V. Ivancha V. V. Fomin L. V. Cherkesov 《Physical Oceanography》2005,15(1):37-49
The wave fields generated by cyclonic atmospheric disturbances in the region of the northwest shelf of the Black Sea are studied by using a σ-coordinate model. The problem is solved in the hydrostatic approximation with regard for nonlinearity and turbulent viscosity. To improve the space resolution of the model, we realize the procedure of embedded grids. It is shown that the action of a cyclone results in the formation of domains of pronounced surges whose shapes and location reflect the changes in the wind situation. The vertical structure of wave currents first depends only on the location of the atmospheric disturbance over the water area but, in the course time, begins to reflect specific features of the bottom topography.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 42–54, January–February, 2005. 相似文献
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应用比例边界有限元法求解狭缝对双箱水动力的影响 总被引：1，自引：1，他引：0
比例边界有限元法(SBFEM)是一种半解析数值分析的新方法,既融合了有限元法和边界元法的优点,又有其特有的优点。用该方法可求解有限水深下狭缝对双箱水动力作用的影响,为波浪与多浮体超大型结构的相互作用探索一些规律。整个计算域划分成2个无限子域和4个有限子域,并利用加权余量法在各个子域上推导了SBFEM的积分方程;计算了4个数值算例并与边界元等其它数值方法进行了比较,验证了该方法是一种用很少单元便能得到精确结果的高效方法。应用SBFEM对不同箱体宽度、不同狭缝宽度、不同吃水深度条件的双箱作了计算,得出了狭缝对双箱水动力干涉影响的一些规律,对超大型浮体水动力分析和结构设计具有一定的参考价值。 相似文献
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The current reduction in commercial fish stocks is a problem of global concern. In response to this situation, administrations around the world are attempting to recover critical stocks by implementing new regulations based on catching restrictions and recovery plans. These restrictions have negative effects on local economies, but species recovery also brings important benefits to society in the long term. Given that the recovery of endangered species also results in considerable non-use economic value, this paper employs contingent valuation techniques to measure individual preferences for different recovery levels. We distinguish primarily between existence and option values linked to various levels of the desired stocks and discuss how these values influence willingness to pay (WTP) estimates. Our results show that recovered stocks for hake and Norwegian lobster increase local welfare, and show that the median household WTP is about 17.73€ for a recovery programme regulated by the European Union. 相似文献
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Zhiwei Xie Jun Wang Yuanqiang Cai Hu Xiuqing Yin Cai 《Marine Georesources & Geotechnology》2020,38(1):122-131
AbstractAir booster vacuum preloading method is a useful method for strengthening dredged slurry. Though this method is improved effectively with the rapidly developed technology, the problem of inadequate reinforcement in deep layers of soil is still in existence. In view of the fact that the pressurizing system can effectively enhance the reinforcement effect. Therefore, this paper discusses the reinforcement effect of a new pressurizing system that put the booster pipeline at the bottom of soil. Meanwhile, another problem is found that the booster pipeline type was single at present, the action effect of different kind of booster pipeline is still uncertain. In this paper, laboratory experiments are performed to investigate the influence of two kinds of pressurization position and two types of booster pipeline on the treatment of five dredged slurry samples. The test results showed that though the vertical pressurizing system can be good to reinforce the middle soil layers, but the bottom pressurizing system can make the whole soil layer more homogeneous. Furthermore, the difference of the two kinds of booster pipeline on the reinforcement effect of soil is not significant. These results provide good guidance for practical application of air booster vacuum preloading in land reclamation project. 相似文献
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《Marine Policy》2013
The large marine ecosystem (LME) governance framework was developed to address the complexity inherent within the Wider Caribbean Region with respect to the region's shared living marine resources. The framework is adaptable to all multi-scale living marine resource situations and provides a basis for incremental implementation of interventions. Parts of the overall governance framework can be targeted for sub-framework development and strengthening through institutional reforms and capacity building. Three examples, the Eastern Caribbean flyingfish fishery, marine protected area (MPA) management and the Eastern Caribbean tuna fishery, are used to illustrate the application of the framework in facilitating and assessing governance effectiveness in the Caribbean. In each case, the purpose is to show the different governance questions that must be addressed at policy, strategy and action levels to make up a complete governance arrangement and how these are distributed among several levels on the institutional scale that typically occur in regional marine resource governance. 相似文献
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Amphipod larvae, Gammarus oceanicus, were exposed for 8 weeks to bis(tributyltin) oxide (TBTO) or tributyltin fluoride (TBTF), or for 5 weeks to leachates from tributyltin-containing antibiofouling paints. No larvae survived 8 weeks' exposure to 3 μg/litre TBTO or TBTF. Differential larval survival occurred during exposure to 0·3 gmg/litre of these same compounds. Paint leachates were shown to cause similar toxicity responses at comparable aqueous tributyltin concentrations. An examination of sublethal responses showed slight decreases in growth for larvae exposed to TBTO and to paint leachates, although responses at tributyltin levels below 1 μg/litre were not marked. Whole-animal oxygen consumption rates were not affected by low tributyltin exposure levels. While these studies demonstrate low level toxicity of tributyltins, effects on oxygen consumption and growth do not indicate a mode of action for these compounds. 相似文献