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1.
海洋生态系统动力学模型的可预测性是模型应用的重要限制因子之一,而模型稳定性则是模型可预测性的前提。本文提出了一个基于降维理论的方法,用于研究质量守恒的营养盐-浮游植物-浮游动物-碎屑(NPZD)这类海洋生态系统动力学模型的稳定性和Hopf分岔。研究结果显示,NPZD模型的非奇异平衡点是稳定的,而当模型参数在临界值附近变动时可能会发生Hopf分岔。同时,本文采用数值模拟的方法对该理论分析结果进行了实例验证。本文提出的基于降维理论的方法能够从理论上有效分析质量守恒系统的稳定性问题和Hopf分岔。 相似文献
2.
Analytical expressions of the bifurcation boundaries for symmetric spread mooring systems 总被引：4，自引：0，他引：4
For a general symmetric Spread Mooring System .(SMS), the five necessary and sufficient conditions for stability are derived analytically. It is shown that only two conditions are dominant in symmetric ship moorings. The equations derived in this paper provide analytical means for determining static and dynamic loss of stability, as well as elementary singularities and roots to chaos, of symmetric SMS configurations, such as those recommended by the American Petroleum Institute. Thus, first it becomes easy to identify the morphogenesis occurring when a bifurcation boundary is crossed; and second, it is possible to determine the dependence of a symmetric SMS on any design parameter—such as mooring line length, orientation, pretension, etc. Theoretical results are verified by comparison to numerical results generated with nonlinear dynamics and codimension one and two bifurcation theory. The mathematical model of the SMS consists of the nonlinear third order manoeuvring equations without memory of the horizontal plane slow motion dynamics—surge, sway, and yaw—of a vessel moored to several terminals. Mooring lines are modeled as synthetic nylon ropes, chains, or steel cables. External excitation consists of time independent current, wind, and mean wave drift forces. 相似文献
3.
He Guangne Yang Bin Wen Nai
Professor Dalian University of Technology Dalian Engineer Design Research Institute of Shanghai Harbour Engineering Shanghai . Lecturer Dalian Fisheries College Dalian 《中国海洋工程》1996,(1)
The stability of slope is affected by a number of factors, some of which have not only random property but also fuzzy characteristic. Therefore, the analysis of slope stability is really an uncertain problem. The customary safety factor does not in reality reflect stability scientifically, quantitatively and practically. In order to obtain more practical results, the slope stability is treated as a fuzzy random event for the evaluation of its fuzzy probability. Finally, the seismic stability of an existing coastal embankment is analyzed by means of the suggested fuzzy probabilistic method. It may be seen that the results of analysis can more fully represent the numerical assessment of the degree of slope seismic stability. 相似文献
4.
《Oceanic Engineering, IEEE Journal of》1979,4(2):52-59
Estimation of ship rotational motions induced by ocean waves plays a central role in many navigation and fire control applications. Inertial-type instruments are available which give good measurements of the attitude, but some form of signal processing is necessary to obtain angular rates or predict attitudes. Using optimal moving-average (or transversal) filters, we can obtain very good estimates of attitude rates as well as predictions of these values. Filter parameters can be changed adaptively to maintain good performance as the ship changes heading or velocity. The problem of designing these optimal filters is examined in detail and numerical results are given for a particular set of conditions. Two implementations of the adaptive filter are discussed. One is based on a recursive estimation of the process autocorrelations with the filter coefficients being recomputed at periodic intervals or whenever nonstationary conditions are detected. The second implementation is based on Widrow's LMS algorithm. Both alternatives for the adaptive filter implementation are quite reasonable in terms of their computational requirements. The steady-state performance analysis can be considered to be a lower bound on the errors incurred by an adaptive filter. 相似文献
5.
The primary objective of this study is to introduce a stochastic framework based on generalized polynomial chaos (gPC) for uncertainty quantification in numerical ocean wave simulations. The techniques we present can be easily extended to other numerical ocean simulation applications. We perform stochastic simulations using a relatively new numerical method to simulate the HISWA (Hindcasting Shallow Water Waves) laboratory experiment for directional near-shore wave propagation and induced currents in a shallow-water wave basin. We solve the phased-averaged equation with hybrid discretization based on discontinuous Galerkin projections, spectral elements, and Fourier expansions. We first validate the deterministic solver by comparing our simulation results against the HISWA experimental data as well as against the numerical model SWAN (Simulating Waves Nearshore). We then perform sensitivity analysis to assess the effects of the parametrized source terms, current field, and boundary conditions. We employ an efficient sparse-grid stochastic collocation method that can treat many uncertain parameters simultaneously. We find that the depth-induced wave-breaking coefficient is the most important parameter compared to other tunable parameters in the source terms. The current field is modeled as random process with large variation but it does not seem to have a significant effect. Uncertainty in the source terms does not influence significantly the region before the submerged breaker whereas uncertainty in the incoming boundary conditions does. Considering simultaneously the uncertainties from the source terms and boundary conditions, we obtain numerical error bars that contain almost all experimental data, hence identifying the proper range of parameters in the action balance equation. 相似文献
6.
基于极限分析上限方法的海底斜坡稳定性评价 总被引：2，自引：1，他引：1
极限平衡法仍是当前海底斜坡稳定性的主要工程评价方法,但该法只能给出稳定性分析的近似解答。基于极限分析运动学定理,假定海底斜坡发生对数螺线型滑移破坏模式,将滑体有效自重和简化波浪力等以外荷载形式叠加引入到虚功率方程中,与潜在滑动面上由黏聚力产生的内能耗散率相平衡,建立考虑一阶简化波浪效应的海底斜坡上限解法;利用多变量无导数求极值的逐级迭代方法与最优化技术,结合抗剪强度折减思想,求解波浪加载下不同时刻的海底斜坡稳定性与相应的临界破坏机构,并针对典型算例开展有限元数值解的验证。进而联合采用数值法与上限解,探讨波高、波长、水深等波浪参数对海底斜坡稳定性与滑动机制的影响。结果表明,本文提出的上限解与数值解吻合较好,获得的安全系数与破坏模式等符合一般规律,为波浪作用下海底斜坡的稳定性评价提供了新的途径。 相似文献
7.
针对源自位场等效源理论和点质量方法的似大地水准面计算模型适用性问题,重点围绕虚拟点质量反演和似大地水准面计算两个解算阶段,分别提出了3种实用化的积分模型改化方法,同时设计了3个阶段改化模型试验检验方案,使用超高阶位EGM2008作为数值模拟标准场,对两个解算阶段不同改化模型的计算效果进行了数值精度检核,并开展了数据观测噪声影响评估检验,得出了一些有参考和实际应用价值的研究结论。在一定条件下,使用改化点质量方法计算似大地水准面可获得1 cm的内符合度。 相似文献
8.
针对源自现代Bjerhammar边值理论的似大地水准面计算模型适用性问题,重点围绕地面重力异常向下延拓和似大地水准面计算两个解算阶段,分别提出了3种实用化的积分模型改化方法,同时设计了三阶段改化模型实验检验方案,使用超高阶位模型EGM2008作为数值模拟标准场,对两个解算阶段不同改化模型的计算效果进行了数值精度检核,并开展了数据观测噪声影响评估检验,得出了一些有参考和实际应用价值的研究结论。在一定条件下,使用改化Bjerhammar方法计算似大地水准面可获得1～2 cm的内符合度。 相似文献
9.
针对源自Stokes-Helmert边值理论的大地水准面计算模型适用性问题,首先详细解析了Stokes-Helmert方法的基本原理和计算模型,研究探讨了该方法与其他现有方法的关联性和差异性,分析比较了Stokes-Helmert计算模型和相同类型模型的技术特点,提出了Stokes-Helmert计算模型的实用改化方法,同时设计了4种分步改化模型的实验验证方案,使用超高阶位模型EGM2008作为数值模拟标准场,对分步改化模型的计算效果进行了数值精度检核,并开展了数据观测噪声影响评估检验,得出了一些有参考和实际应用价值的研究结论。在一定条件下,使用改化Stokes-Helmert方法计算(似)大地水准面可获得优于2cm的内符合度。 相似文献
10.
It has been known that the axisymmetric Cauchy–Poisson problem for dispersive water waves is well posed in the sense of stability. Thereby time evolution solutions of wave propagation depend continuously on initial conditions. However, in this paper, it is demonstrated that the axisymmetric Cauchy–Poisson problem is ill posed in the sense of stability for a certain class of initial conditions, so that the propagating solutions do not depend continuously on the initial conditions. In order to overcome the difficulty of the discontinuity, Landweber–Fridman's regularization, famous and well known in applied mathematics, are introduced and investigated to learn whether it is applicable to the present axisymmetric wave propagation problem. From the numerical experiments, it is shown that stable and accurate solutions are realized by the regularization, so that it can be applicable to the determination of the ill-posed Cauchy–Poisson problem. 相似文献
11.
Shandong province is located on the east coast of China and has a coastline of about 3100 km. There are only a few tsunami events recorded in the history of Shandong Province, but the tsunami hazard assessment is still necessary as the rapid economic development and increasing population of this area. The objective of this study was to evaluate the potential danger posed by tsunamis for Shandong Province. The numerical simulation method was adopted to assess the tsunami hazard for coastal areas of Shandong Province. The Cornell multi-grid coupled tsunami numerical model (COMCOT) was used and its efficacy was verified by comparison with three historical tsunami events. The simulated maximum tsunami wave height agreed well with the observational data. Based on previous studies and statistical analyses, multiple earthquake scenarios in eight seismic zones were designed, the magnitudes of which were set as the potential maximum values. Then, the tsunamis they induced were simulated using the COMCOT model to investigate their impact on the coastal areas of Shandong Province. The numerical results showed that the maximum tsunami wave height, which was caused by the earthquake scenario located in the sea area of the Mariana Islands, could reach up to 1.39 m off the eastern coast of Weihai city. The tsunamis from the seismic zones of the Bohai Sea, Okinawa Trough, and Manila Trench could also reach heights of >1 m in some areas, meaning that earthquakes in these zones should not be ignored. The inundation hazard was distributed primarily in some northern coastal areas near Yantai and southeastern coastal areas of Shandong Peninsula. When considering both the magnitude and arrival time of tsunamis, it is suggested that greater attention be paid to earthquakes that occur in the Bohai Sea. In conclusion, the tsunami hazard facing the coastal area of Shandong Province is not very serious; however, disasters could occur if such events coincided with spring tides or other extreme oceanic conditions. The results of this study will be useful for the design of coastal engineering projects and the establishment of a tsunami warning system for Shandong Province. 相似文献
12.
讨论Goupilaud层模型的反演算法的数值不稳定性问题、误差传播及其同入射波形的关系，提出了一种不稳定性控制方法。通过对实际实验数据的数值计算表明：该方法可以使任意波形反演算法的稳定性得以明显改善，避免了至今任意波形反演算对实际信号不可直接运行的难题，实现了任意入射波形的实时反演。 相似文献
13.
Time-Variant Reliability Analysis of FPSO Hull Girder Considering Corrosion Based on Statistics 总被引：1，自引：0，他引：1
FPSO is a kind of important exploitation platform used in ocean oil and gas industry, which has the unique character of mooring at outsea for a long time. Since it can not be inspected and maintained thoroughly at dock like other kinds of ships, the reliability of FPSO hull girder during the whole service should be focused. Based on latest corrosion database and rational corrosion model, the ultimate strength of one FPSO is calculated under the conditions of slight, moderate and severe corrosion. The results not only provide the reliability under different corrosion conditions, but also do well for further inspection and maintenance research. The results provide necessary foundation for deciding inspection intervals and maintenance measures, which has practical sense to improve the general safety level of ocean engineering. 相似文献
14.
A numerical assessment study of tsunami attack on the rubble mound breakwater of Haydarpasa Port, located at the southern entrance of the Istanbul Bosphorus Strait in the Sea of Marmara, Turkey, is carried out in this study using a Volume-Averaged Reynolds-Averaged Navier-Stokes solver, IHFOAM, developed in OpenFOAM® environment. The numerical model is calibrated with and validated against the data from solitary wave and tsunami overflow experiments representing tsunami attack. Furthermore, attack of a potential tsunami near Haydarpasa Port is simulated to investigate effects of a more realistic tsunami that cannot be generated in a wave flume with the present state of the art technology. Discussions on practical engineering applications of this type of numerical modeling studies are given focusing on pressure distributions around the crown-wall of the rubble mound breakwater, and the forces acting on the single stone located behind the crown-wall at the rear side of the breakwater. Numerical modeling of stability/failure mechanism of the overall cross-section is studied throughout the paper.The present study shows that hydrodynamics along the wave flume and over the breakwater can be simulated properly for both solitary wave and tsunami overflow experiments. Stability of the overall cross-section can only be simulated qualitatively for solitary wave cases; on the other hand, the effect of the time elapsed during tsunami overflow cannot be reflected in the simulations using the present numerical tool. However, the stability of the overall cross-section under tsunami overflow is assessed by evaluating forces acting on the rear side armor unit supporting the crown-wall of the rubble mound breakwater as a practical engineering application in the present paper. Furthermore, two non-dimensional parameters are derived to discuss the stability of this armor unit; and thus, the stability condition of the overall cross-section. Approximate threshold values for these non-dimensional parameters are presented comparing experimental and numerical results as a starting point for engineers in practice. Finally, investigations on the solitary wave and tsunami overflow experiments/simulations are extended to the potential tsunami simulation in the scope of both representation of a realistic tsunami in a wave flume and stability of the rubble mound breakwater. 相似文献
15.
This paper aims to investigate the effects of the porous baffles on the suppression of sloshing for the tanks with axisymmetric geometries under lateral excitation. Based on the assumptions of inviscid, irrotational, incompressible liquid and small amplitude sloshing, an axisymmetric boundary element method (BEM) for 3D Laplace equation is derived by using the Green's theorem together with the weighted residual method. And a zoning method is employed to model fluid domain in the tanks with complex porous baffles. Meanwhile, the porous baffles are treated motioning together with the tanks, and the velocity across the porous baffle is assumed to be linearly proportional to the pressure gradient between each side of the porous baffle. And the mechanism of suppressing the sloshing response is mainly the energy dissipation of the fluid passing through the porous baffle. Moreover, the linear free surface boundary conditions are also used to solve the governing equations. Compared with other numerical methods, the most prominent advantage of the BEM in solving axisymmetric potential problem is that only the boundaries of half the cross-section instead of the entire problem domain should be discretized, which can cut down large amount of memory and time costs. The present method is verified by comparing the numerical results with the existing literatures, and excellent agreements are obtained. Meanwhile, the proposed models are applied to investigate the effects of the porous baffles on sloshing response in circular cylindrical, annular cylindrical and conical tanks. The effects of the porous baffle length, porous-effect parameter, installation angle and baffle height on the sloshing force, natural frequency and surface elevation are studied. Additionally, some typical sloshing pressure distributions, velocity potential contours and velocity fields are plotted. The results show that swirls at the tips of the baffles can be observed in many cases, and the top-mounted porous baffle makes more significant suppression effects on sloshing response than that of bottom-mounted porous baffle, while increasing the number of ring porous baffles can achieve better restraint effects on sloshing response. And increasing the baffle length of the horizontal wall-mounted ring porous baffle can significantly decrease the sloshing frequencies, as well as the first non-dimensional natural frequency decreases with decrease in porous-effect parameter of the coaxial porous baffle. In addition, remarkable effects on sloshing can be obtained when reasonable designed by selecting the optimal porous-effect parameter, installation angle and baffle height. And this paper can be a useful guide for the seismic design and analysis of many actual liquid storage tanks (such as the Advanced Passive PWR, large water cooling tower, etc.). 相似文献
16.
A new set of approximations to the standard TEOS-10 equation of state are presented. These follow a polynomial form, making it computationally efficient for use in numerical ocean models. Two versions are provided, the first being a fit of density for Boussinesq ocean models, and the second fitting specific volume which is more suitable for compressible models. Both versions are given as the sum of a vertical reference profile (6th-order polynomial) and an anomaly (52-term polynomial, cubic in pressure), with relative errors of ∼0.1% on the thermal expansion coefficients. A 75-term polynomial expression is also presented for computing specific volume, with a better accuracy than the existing TEOS-10 48-term rational approximation, especially regarding the sound speed, and it is suggested that this expression represents a valuable approximation of the TEOS-10 equation of state for hydrographic data analysis. In the last section, practical aspects about the implementation of TEOS-10 in ocean models are discussed. 相似文献
17.
海洋油气平台在达到作业寿命后必须进行废弃处置,将海上退役平台改作人工鱼礁投放,对优化渔业资源、促进海洋经济持续发展具有重要意义。基于平台拆卸结构,共制作了箱状、管状、柱状、网状4种典型鱼礁实物模型,通过室内模拟试验和数值模拟研究,分析了不同鱼礁类型单体的稳定性和流场效应。结果表明：开口率0.1至0.8的箱状礁的稳定性均能满足要求,但开口率高于0.6的箱状礁难以形成连续的背涡流区域,设计时应使开口率低于0.6;管状礁应选择堆叠放置方式投放,且堆叠层数与稳定性和流场造成能力均呈正相关,在设计时尽量提高管状礁的堆叠层数;柱状礁设计时应尽量降低其重心,并减小迎流投影面的中空面积投放;基于平台的钻井架、火炬臂、栈桥设计的3种网状礁,均满足礁体稳定条件,且均能形成大范围的背涡流区域,可作为人工鱼礁投放。研究成果为平台造礁礁体结构设计提供了理论依据与实践基础,对海上退役平台的废弃处置具有一定的参考价值。 相似文献
18.
此文应用Fourier方法和能量不等式研究了常系数和变系数的对流扩散方程在迎风差分格式的情形下数值解的稳定性,所得结果对实际计算有着重要的意义。 相似文献
19.
This work aims to demonstrate the dynamical properties of the free interface separating two bounded layers of electrified Newtonian fluids inside a parametrically excited boxed basin. The mathematical model of the investigated problem is contacted with the linearized Navier–Stokes equation of viscous fluids and Maxwell equations together with the boundary conditions that are solved utilizing Laplace transform. Solutions of the governing equations in time domain are then numerically calculated by using Durbin's numerical inverse Laplace transform scheme. Graphical illustrations of the accomplished numerical results are provided to examine the influence of some selected parameters on the stability picture of the interfacial waves as well as the electric surface charge distribution. The numerical results proposed that the electric Euler number Eu, promotes the instability of the wave motion whatever the values of the frequency of oscillation and the destabilizing effect of Eu becomes weaker at larger values of the frequency; while a dual effect (in) stabilizing of the frequency of oscillations is reported whether the electric effects exist or not. This irregular influence of the frequency oscillation has also been monitored regarding to the forces exerted on the side wall of the container. 相似文献
20.
In this work, sloshing flows were successfully simulated by using a coupled numerical scheme between smoothed particle hydrodynamics (SPH) and smoothed point interpolation method (S-PIM) (SPH-SPIM coupled method). SPH is a Lagrangian particle method to solve flow fields while S-PIM is developed to deal with the structure dynamics. A coupling scheme is proposed, the key of which is that the fluid and solid fields are not necessary to be discretized by the same resolution. The stability, accuracy, convergence and conservation of the SPH-SPIM coupled method were validated by the case of hydrostatic water column on an elastic plate. Then, a wave impact problem was simulated to verify that the present SPH method worked well for sloshing flows. Finally, two sloshing problems with an elastic baffle were simulated, which validated the accuracy and stability of the method in predicting the fluid-structure interaction (FSI) features during the process of sloshing. It has been found that both the shape of the free surface and the large deformation of the elastic baffle can be well captured by the present method, which shows the potential of the present method to be a good candidate for simulating sloshing problems. 相似文献