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1.
This study investigates the possibility of applying the theory of fuzzy random variables through the fuzzy Monte Carlo simulation approach for the reliability-based risk analysis of a rubble-mound breakwater. The results are presented and compared with the traditional Monte Carlo calculation. This study indicates that the present theory may provide a useful tool for the joint handling of randomness and fuzziness in the computation of reliability and may have a good potential to be used for reliability assessment of coastal structures. 相似文献
2.
Comparison of Linear Level I Green-Naghdi Theory with Linear Wave Theory for Prediction of Hydroelastic Responses of VLFS 总被引：4，自引：0，他引：4
Very Large Floating Structures (VLFS) have drawn considerable attention recently due to their potential significance in the exploitation of ocean resources and in the utilization of ocean space. Efficient and accurate estimation of their hydroelastic responses to waves is very important for the design. Recently, an efficient numerical algorithm was developed by Ertekin and Kim (1999). However, in their analysis, the linear Level I Green-Naghdi (GN) theory is employed to describe fluid dynamics instead of the conventional linear wave (LW) theory of finite water depth. They claimed that this linear level I GN theory provided betler predictions of the hydroelastic responses of VLFS than the linear wave theory. In this paper, a detailed derivation is given in the conventional linear wave theory framework with the same quantity as used in the linear level I GN theory framework. This allows a critical comparison between the linear wave theory and the linear level I GN theory. it is found that the linear level 相似文献
3.
YAN Chenghua 《中国海洋工程》2001,(2):291-300
A two-dimensional nonlinear sloshing problem is analyzed by means of the fully nonlinear theory and time domain second order theory of water waves. Liquid sloshing in a rectangular container subjected to a horizontal excitation is sim-ulated by the finite element method. Comparisons between the two theories are made based on their numerical results, It is found that good agreement is obtained for the case of small amplitude oscillation and obvious differences occur for large amplitude excitation. Even though, the second order solution can still exhibit typical nonlinear features of nonlinear wave and can be used instead of the fully nonlinear theory. 相似文献
4.
We present a study on the emergence of spatial variability, or patchiness, in biophysical simulations of plankton ecosystems. Using a standard approach to modelling such ecosystems, we represent a distribution of plankton as a lattice of non-identical interacting oscillatory populations. Spatial variation is imposed in population parameters, such as maximum growth rate, leading to a spread in the natural (uncoupled) population properties. Using the methods of synchronisation theory, the emergent spatial structure of the coupled system is investigated as a function of the strength of interaction between populations. Surprisingly, a range of coupling strength is found to induce a tenfold increase in the spread in frequency of oscillation of populations in comparison with the uncoupled level of spatial variation. This apparent desynchronisation corresponds to the formation of temporally evolving clusters of local synchronisation: the interplay of grid-cell scale variability and dispersal between populations leads to patchiness at larger scales. However, the occurrence and length-scale of this patchiness is found to be sensitive to typical simulation parameters such as spatial resolution and strength of dispersal, with emergent spatial structure altering abruptly from patchy to homogeneous as these parameters are varied. These results indicate that whilst cluster synchronisation may be a genuine mechanism for the formation of spatial structure in plankton distributions, biophysical modellers should be aware of the possibility of artificial patchiness arising from the basic physical structure of their model. 相似文献
5.
This paper investigates the structural properties of a model fluid dictated by an effective inter-particle oscillatory potential by grand canonical ensemble Monte Carlo (GCEMC) simulation and classical liquid state theories. The chosen oscillatory potential incorporates basic interaction terms used in modeling of various complex fluids which is composed of mesoscopic particles dispersed in a solvent bath, the studied structural properties include radial distribution function in bulk and inhomogeneous density distribution profile due to influence of several external fields. The GCEMC results are employed to test the validity of two recently proposed theoretical approaches in the field of atomic fluids. One is an Ornstein--Zernike integral equation theory approach; the other is a third order + second order perturbation density functional theory. Satisfactory agreement between the GCEMC simulation and the pure theories fully indicates the ready adaptability of the atomic fluid theories to effective model potentials in complex fluids, and classifies the proposed theoretical approaches as convenient tools for the investigation of complex fluids under the single component macro-fluid approximation. 相似文献
6.
Regime shifts: Can ecological theory illuminate the mechanisms? 总被引：2，自引：0，他引：2
“Regime shifts” are considered here to be low-frequency, high-amplitude changes in oceanic conditions that may be especially pronounced in biological variables and propagate through several trophic levels. Three different types of regime shift (smooth, abrupt and discontinuous) are identified on the basis of different patterns in the relationship between the response of an ecosystem variable (usually biotic) and some external forcing or condition (control variable). The smooth regime shift is represented by a quasi-linear relationship between the response and control variables. The abrupt regime shift exhibits a nonlinear relationship between the response and control variables, and the discontinuous regime shift is characterized by the trajectory of the response variable differing when the forcing variable increases compared to when it decreases (i.e., the occurrence of alternative “stable” states). Most often, oceanic regime shifts are identified from time series of biotic variables (often commercial fish), but this approach does not allow the identification of discontinuous regime shifts. Recognizing discontinuous regime shifts is, however, particularly important as evidence from terrestrial and freshwater ecosystems suggests that such regime shifts may not be immediately reversible. Based on a review of various generic classes of mathematical models, we conclude that regime shifts arise from the interaction between population processes and external forcing variables. The shift between ecosystem states can be caused by gradual, cumulative changes in the forcing variable(s) or it can be triggered by acute disturbances, either anthropogenic or natural. A protocol for diagnosing the type of regime shift encountered is described and applied to a data set on Georges Bank haddock, from which it is concluded that a discontinuous regime shift in the abundance of haddock may have occurred. It is acknowledged that few, if any, marine data are available to confirm the occurrence of discontinuous regime shifts in the ocean. Nevertheless, we argue that there is good theoretical evidence for their occurrence as well as some anecdotal evidence from data collection campaigns and that the possibility of their occurrence should be recognized in the development of natural resource management strategies. 相似文献
7.
Relativistic Information Entropy on Uncertainty Analysis 总被引：1，自引：0，他引：1
Jin Weiliang Han Jie
Professor Dr. -Eng. Dept. of Civil Engineering Zhejiang University Hangzhou Lecturer. Dept. of Information Science Electronic Engineering Zhejiang University Hangzhou 《中国海洋工程》1996,(4)
- in this paper, a new approach to relativistic information entropy is used to assess some relative uncertainties in structural reliability assessment. This approach is composed of the information theory and the relativistic theory, and can be used to measure the relativity of parameter uncertainty and system uncertainty in structural reliability theory based on the same generalized relativistic reference system. Therefore, the structural reliability assessment can be assessed reasonably by the approach. 相似文献
8.
Diana Tingley Jóhann Ásmundsson Edward Borodzicz Alexis Conides Ben Drakeford Ingi Rúnar Eðvarðsson Dennis Holm Kostas Kapiris Sakari Kuikka Bogi Mortensen 《Marine Policy》2010
This paper presents the findings of risk identification and risk perception research conducted in relation to the fisheries systems of four distinct and diverse European countries: Faroes, Iceland, Greece and the UK. Risk research traditionally attempts to quantify the potential threat or consequences from a range of risk events or hazards. This research, however, adopted a social sciences perspective and so assumed that a risk event or hazard can mean different things to different people and that these perceptions are also context and culturally dependent. Risk perceptions were examined and risk registers developed in each country for a range of stakeholder groups. A ‘mental modelling’ approach was adopted in a series of qualitative interviews. Findings were examined in terms of a wide range of psychological, social and cultural risk theories. Differences in risk perceptions were noted between stakeholder groups and countries and contextual influences were examined such as the widely differing fisheries management systems used in each country. This research provides one of the first attempts to systematically evaluate risks and perceptions across a range of fisheries-systems. The findings support social science theories which argue that risk is a subjective, as opposed to objective, concept and that this subjectivity will therefore affect our attempts to assess and manage those hazards we think we can potentially influence or control. 相似文献
9.
10.
针对全国海域使用情况的监测需求,本文应用扩展的证据理论进行围填海区域检测,预设类别空间为{围填海,海水}。实验结果显示基于扩展的证据理论不仅能够较准确地检测出围填海区域,而且将浅海中的水下沙脊或小岛划分为不确定的未知类别。说明扩展的证据理论能够更好地完成围填海的检测,体现了扩展的证据理论解决实际问题的能力,同时,也为全海域的围填海监测提供了新的思路和扩展空间。 相似文献
11.
An investigation on internal solitary waves in a two-layer fluid: Propagation and reflection from steep slopes 总被引：2，自引：0，他引：2
Chen-Yuan Chen John Rong-Chung Hsu Min-Hung Cheng Hsin-Hsun Chen Ching-Feng Kuo 《Ocean Engineering》2007,34(1):171-184
Experimental investigations on internal solitary wave (ISW) propagation and their reflection from a smooth uniform slope were conducted in a two-layered fluid system with a free surface. A 12-meter-long wave flume was in use which incorporated with: (1) a movable vertical gate for generating ISW; (2) six ultrasonic probes for measuring the fluctuation of an ISW; and (3) a steep uniform slope (from one of θ=30°, 50°, 60°, 90°, 120° and 130°) much greater than those ever published in the literature. This paper presents the wave profile properties of the ISW recorded in the flume and their nonlinear features in comparison with the existing Korteweg de Vries (KdV) and modified Korteweg-de Vries (MKdV) theories. Experimental results show that the KdV theory is suitable for most small-amplituded ISWs and MKdV theory is appropriate for the reflected ISWs from various uniform slopes. In addition, both the amplitude-based reflection coefficient and reflected energy approach a constant value asymptotically when plotted against the slope and the characteristic length ratio, respectively. The reflected wave amplitudes calculated from experimental data agree well with those reported elsewhere. The optimum reflection coefficient is found within the limit of 0.85 for wave amplitude, among the test runs from steep normal slope of 30° to inverse angle of 130°, and around 0.75 for the reflected wave energy, produced by an ISW on a vertical wall. 相似文献
12.
Human presence, coastal erosion, and tourism activities are increasing the attention to coastal flooding risk. To perform risk assessments, long time series of observed or hindcast wave parameters and tide levels are then necessary. In some cases, only a few years of observation are available, so that observed extreme data are not always representative and reliable. A hindcast system aimed to reconstruct long time series of total tide levels may be of great help to perform robust extreme events analysis and then to protect human life, activities as well as to counteract coastal erosion by means of risk assessments. This work aims to propose a simplified method to hindcast storm surge levels time series in semi-enclosed basins with low computational costs. The method is an extension of a previous work of some of the authors and consists of a mixed approach in which the estimation of storm surge obtained by using the theory of linear dynamic system is corrected by using a statistical method. Both steps are characterized by low computational costs. Nevertheless, the results may be considered reliable enough also in view of the simplicity of the approach. The proposed method has been applied to the Manfredonia case study, a small village located in the Southern Adriatic Italian coast and often prone to coastal flooding events. The comparison of extreme events estimated on the basis of hindcast levels time series is satisfactorily similar to those estimated on the basis of observed tide series. 相似文献
13.
As the number of ships for marine transportation increases with the globalisation of the world economy, waterways are becoming more congested than before. This situation will raise the risk of collision of the ships; hence, an automatic collision avoidance system needs to be developed. In this paper, a novel approach based on deep reinforcement learning (DRL) is proposed for automatic collision avoidance of multiple ships particularly in restricted waters. A training method and algorithms for collision avoidance of ships, incorporating ship manoeuvrability, human experience and navigation rules, are presented in detail. The proposed approach is investigated not only by numerical simulations but also by model experiments using three self-propelled ships. Through the systematic numerical and experimental validation, it is demonstrated the developed approach based on the DRL has great possibility for realising automatic collision avoidance of ships in highly complicated navigational situations. 相似文献
14.
Unified Water Gravity Wave Theory and Improved Linear Wave 总被引：2，自引：0，他引：2
Fu Yuhua Senior Engineer Structural Engineering Department China Offshore Oil Development Engineering Corp. Beijing 《中国海洋工程》1992,(1)
- Based on Least Square Method, this paper presents variational principle for handling various water gravity wave theories and the unified water gravity wave theory was given. By using this variational principle of unified water wave theory, two kinds of improved linear waves were derived. The first one uses the same boundary conditions which were applied to derive 5-order Stokes wave. The second one uses the accurate boundary conditions (Eqs. 11 and 12). The two improved linear waves were compared with the existing linear wave. 相似文献
15.
基于AHP法和灰色模式识别理论的海底管道系统路由定量风险评估 总被引：3，自引：1，他引：3
根据海底管道路由潜在风险的特点及风险类型,提出了一种将层次分析法（AHP法）和灰色模式识别理论相结合的海底管道系统路由定量风险评估方法,该方法利用AHP确定风险评价指标体系,运用灰色模式识别理论,建立识别结果标准,并结合实际工程进行计算,计算结果表明该方法是可行的. 相似文献
16.
In this paper, by non-dimensional analysis, it is found that finite-depth theory is more appropriate to the study of internal solitary waves (ISWs) in the South China Sea (SCS) than shallow-water theory. The 1-degree grid data of monthly mean temperature and salinity data at standard levels in the SCS are used to solve the linearized vertical eigenvalue problem. The nonlinear parameter and the wave phase speed are computed, then the nonlinear phase speed and the characteristic half-width of ISWs are calculated respectively by two different theories to investigate the difference between these two parameters in the SCS. The nonlinearity is the strongest near the continental slope of the SCS or islands where the bottom topography changes sharply, it is stronger in summer than that in winter; it increases (decreases) as pycnocline depth deepens (shallows), stratification strengthens (weakens) and pycnocline thickness thins (thickens). The nonlinear wave phase speed and the characteristic half-width are the largest in deep sea area, they then reduce peripherally in shallower water. The nonlinear wave phase speed in the SCS changes slightly with time, but the characteristic half-width changes somewhat larger with time. In most of the SCS basin, the nonlinear wave phase speed derived from shallow-water theory is very close to that derived from finite-depth theory, but the characteristic half-width derived from shallow-water theory is about 0.2–0.6 times larger than that derived from finite-depth theory. The ISW induced horizontal current velocity derived from shallow-water theory is larger than that derived from finite-depth theory. Some observed and numerical modeled ISW characteristic half-widths are compared with those derived from shallow-water and finite-depth theories, respectively. It is shown that, the characteristic half-widths derived from finite-depth theory agree better with observational and numerical modeled results than those derived from shallow-water theory in most cases, finite-depth theory is more applicable to the estimation of ISW characteristic half-widths in the northern SCS. It is also suggested that, to derive the precise ISW parameters in further study, the physical non-dimensional ratios which are related with ISW characteristic half-width, amplitude, thermocline and water depths should be calculated, so that an appropriate theory can be chosen for estimation. 相似文献
17.
浅水区波浪非线性效应对砂质海床动力响应的影响 总被引：4，自引：2，他引：2
以广义Biot动力固结理论为基础,运用一阶椭圆余弦波和二阶Stokes波等非线性波浪理论考虑浅水区波浪荷载的非线性效应,在时域上采用有限元方法对非线性波浪力作用下饱和砂质海床的动力响应进行了数值求解,并与线性波浪作用下海床动力响应特性进行了对比分析。结果表明,随着波长与水深之比L／d及无量纲参数T(g/d)^1/2的增大,非线性波浪对海床动力响应的影响增大。与线性波浪理论相比,孔隙水压力与有效应力幅值的增大效应非常显著。因此在近海海洋建筑物设计与工程场地评价中,波浪力的非线性特性必须引起注意。 相似文献
18.
块体理论起源于大陆,通过与大洋板块学说从空间域、时间域、基本构造单元、驱动力等方面的对比分析认为,该理论也可以延伸并推广到全球范围,使得以大陆地壳为主要研究对象的块体学说,与以大洋地壳为主要研究对象的大洋板块学说遥相呼应并互为补充,使得全球构造理论体系趋于完善。块体理论对中国海陆构造格架演化的有效应用是勾画出了"块体构造理论"的最基本框架体系。由此得出块体的主要地学特征:首先是在块体内需要一个可以成为内核的生长中心(一般是年代古老的块体核心——元古代甚至是太古代),其后是在古老内核周边出现岩浆活动以及活化的造山带,两者逐渐依附于或是粘贴在块体核心部位的外围,使块体在后来的演化过程中体量不断增长,直到出现新的崩裂(形成新的块体)或是与其他块体一起汇聚于未来的超级大陆。其次是明确了块体的边界有3种基本类型:对区域构造有控制作用的深大断裂、主动型大陆边缘和被动型大陆边缘。块体的一般地质构造演化阶段也可以分为胚胎期、幼年时期、成长发育时期、衰亡期4个主要阶段,这4个阶段构成了块体地质演化的一个完整的生命周期。 相似文献
19.
When a bubble plume exists beneath a free surface, such as after a subsea gas well blowout, a generally horizontal flow occurs in the vicinity of the surface and this flow is influenced by the fact that the surface is free. Two very different theories for such surface flows have been developed in the past and the bases of these theories are reviewed here. The results of measurements of surface flows above plumes of relatively large scale are given. These are compared with both of the existing theories. One theory is found to be accurate at small radii from the plume centre and the other theory is found to be accurate at large radii. The needed boundary condition for the theory that is accurate at large radii is supplied by the results of the theory that is accurate at small radii. 相似文献
20.
Rethinking small-scale fisheries compliance 总被引：3，自引：1，他引：2
Fisheries compliance has been identified as key to sustainable fisheries management. However, it has been widely acknowledged that the approach by many governments worldwide to achieve compliance is largely through law enforcement efforts. Although theories of normative action have expanded compliance thinking from that of rationalist approaches, this paper takes the argument further. By drawing on criminology and security discourse, and on empirical research on small-scale fisheries in South Africa, this paper argues for a new approach to our understanding of compliance. Furthermore, it argues that rather than taking law as given, the formation of law and the power dynamics influencing such processes are critical aspects that need to be acknowledged and understood in fisheries compliance theory. 相似文献