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1.
All numerical models are imperfect. Weak constraint variational data assimilation ( VDA ), which provides a treatment of the modelling errors, is studied; building on the approach of Vidard et al. (Tellus, 56 A, pp. 177–188, 2004). The evolution of model error ( ME ) is modelled using ordinary differential equations, which involve a scalar parameter. These approaches were tested using different high-resolution advection schemes. The first set of experiments were constructed to see if it is possible to account for (numerical) discretization error within such a framework. In other set of experiments, a systematic source of modelling error was introduced by deliberately specifying an incorrect value for the Coriolis parameter in the model. Results with observational state at half of the model state resolution, are also presented. We also discuss a method of estimating the scalar parameter in the ME through VDA . In all cases, the inclusion of ME provides reduction in forecasting errors. Also, our experiments indicate that different settings of the model (e.g. using different high-resolution advection schemes) would need different ME formulation. Results presented in this paper could be used to formulate sophisticated ME forms to account for systematic errors in higher dimensional models with complex advection schemes. 相似文献
2.
Since 1987, twice weekly, hydrological variables have been monitored at a fixed station in the Ría de Vigo (NW Spain), aiming to examine the time scales of variability and the relationships to meteorological conditions. The present paper analyses: (1) the advantage of Box-Jenkins transfer function (TF) models (single output–multiple input), a type of linear stochastic model, to describe the dynamic behaviour of the system; and (2) the coupling between the Ría and meteorological events at the time scale of autonomy of this coastal inlet affected by the Iberian coastal upwelling, approximately a fortnightly period. In order to achieve these objectives, thermohaline properties have been used to characterize the estuarine ecosystem (output variables), while wind regime, runoff in the drainage basin and incoming solar radiation have been considered as the main forcing variables (input variables). The use of the amplitude time series, derived from principal component analysis (PCA) applied to the deseasonalized meteorological variables, is also explored as a different set of input variables.When compared with standard regression models, all TF models built to describe thermohaline behaviour had reduced residual variance. Similar TF models, as well as percentage of explained variance, were also obtained when meteorological variables or the amplitude time series were used as input variables. The fitted TF models provided an insight into the ‘ inertial ’ behaviour of the system and the time scales of coupling of the system with the forcing variables. The plausible physical mechanisms which link the response of the system with the observed meteorological variability are also discussed. As could be expected, bottom thermohaline properties show a stronger inertial behaviour than the surface ones, which is particularly marked for bottom temperature. Besides, the shelf domain, by means of upwelling-downwelling events, strongly influences surface and bottom temperature, as well as bottom salinity; by contrast, surface salinity is mainly influenced by the effect of wind along the main axis of the Ría and runoff. In relation to the time scales of coupling between the system and the forcing variables, thermohaline properties show a dependance with the meteorological conditions in, at least, the immediately preceding fortnight period. It was concluded that: (1) TF models that incorporate meteorological information described the dynamic behaviour of the system adequately; and (2) this type of model can be useful as a first approximation to develop more sophisticated (deterministic) models, since, with the purpose of modelling any state variable of the system, both the coupling between different domains and the time scales of the interactions must be taken into account. 相似文献
3.
Since 1987, twice weekly, hydrological variables have been monitored at a fixed station in the R?́a de Vigo (NW Spain), aiming to examine the time scales of variability and the relationships to meteorological conditions. The present paper analyses: (1) the advantage of Box-Jenkins transfer function (TF) models (single output–multiple input), a type of linear stochastic model, to describe the dynamic behaviour of the system; and (2) the coupling between the R?́a and meteorological events at the time scale of autonomy of this coastal inlet affected by the Iberian coastal upwelling, approximately a fortnightly period. In order to achieve these objectives, thermohaline properties have been used to characterize the estuarine ecosystem (output variables), while wind regime, runoff in the drainage basin and incoming solar radiation have been considered as the main forcing variables (input variables). The use of the amplitude time series, derived from principal component analysis (PCA) applied to the deseasonalized meteorological variables, is also explored as a different set of input variables.When compared with standard regression models, all TF models built to describe thermohaline behaviour had reduced residual variance. Similar TF models, as well as percentage of explained variance, were also obtained when meteorological variables or the amplitude time series were used as input variables. The fitted TF models provided an insight into the ‘ inertial ’ behaviour of the system and the time scales of coupling of the system with the forcing variables. The plausible physical mechanisms which link the response of the system with the observed meteorological variability are also discussed. As could be expected, bottom thermohaline properties show a stronger inertial behaviour than the surface ones, which is particularly marked for bottom temperature. Besides, the shelf domain, by means of upwelling-downwelling events, strongly influences surface and bottom temperature, as well as bottom salinity; by contrast, surface salinity is mainly influenced by the effect of wind along the main axis of the R?́a and runoff. In relation to the time scales of coupling between the system and the forcing variables, thermohaline properties show a dependance with the meteorological conditions in, at least, the immediately preceding fortnight period. It was concluded that: (1) TF models that incorporate meteorological information described the dynamic behaviour of the system adequately; and (2) this type of model can be useful as a first approximation to develop more sophisticated (deterministic) models, since, with the purpose of modelling any state variable of the system, both the coupling between different domains and the time scales of the interactions must be taken into account. 相似文献
4.
在循环载荷作用下,合成纤维系缆的应力应变关系表现出明显的非线性特性,直接影响系泊缆绳的动力响应。如何针对其在循环载荷作用下的应力应变关系进行准确的定量描述是有关绷紧式系泊系统设计的关键问题。国内外研究者之前的研究不能反映缆绳的载荷历史、蠕变特性以及刚度变化过程,因此提出一个粘弹性粘塑性模型来描述合成纤维系缆的应力应变关系。本模型能够反映合成纤维缆绳的时间变化特性以及在整个加载—卸载过程中的刚度变化。此外,提出了明确的参数确定方法及步骤,基于简单的蠕变实验可以确定模型的各个参数。将两种载荷条件下聚酯缆绳的实验结果与模型结果进行对比,二者吻合较好,证明了模型的有效性和可靠性。本研究对于绷紧式系泊系统的研发和工程应用具有重要意义。 相似文献
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利用NCEP/NCAR全球再分析格点资料（空间分辨率1°×1°）、台风实况资料及海南省气象台站观测资料,选取1321号台风＂蝴蝶＂为研究个例,从天气学原理高低空形势及动力、热力学物理量等多角度分析了＂蝴蝶＂强度演变特征及影响因素.研究结果表明,副热带高压与高空西风槽是影响此次台风的主要大尺度天气系统,弱冷空气南侵、南海海温偏高及越赤道气流强盛是＂蝴蝶＂迅速加强的重要原因.西风槽引导弱冷空气南侵使得台风外围环流气压梯度增加,斜压不稳定状态加剧;南海海温达到29℃,海温偏高使台风区域大气层结降低,深热对流发展;105°E越赤道气流强盛为台风提供了充沛水汽和能量.三者共同作用促使台风强度突然增强.另外,低层涡度、高层散度、湿位涡及水汽通量等物理量能够较好地表征＂蝴蝶＂强度变化特征.低层辐合流入、高层辐散流出为台风的加强提供了动力条件;湿位涡下负上正表明大气热力层结不稳定;水汽通量增加表明水汽条件充足.良好的动力条件、热力条件与水汽条件共同作用,使得＂蝴蝶＂在短时间内迅速加强为强台风. 相似文献
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We study the evolution of finite perturbations in the Lorenz '96 model, a meteorological toy model of the atmosphere. The initial perturbations are chosen to be aligned along different dynamic vectors: bred, Lyapunov, and singular vectors. Using a particular vector determines not only the amplification rate of the perturbation but also the spatial structure of the perturbation and its stability under the evolution of the flow. The evolution of perturbations is systematically studied by means of the so-called mean-variance of logarithms diagram that provides in a very compact way the basic information to analyse the spatial structure. We discuss the corresponding advantages of using those different vectors for preparing initial perturbations to be used in ensemble prediction systems, focusing on key properties: dynamic adaptation to the flow, robustness, equivalence between members of the ensemble, etc. Among all the vectors considered here, the so-called characteristic Lyapunov vectors are possibly optimal, in the sense that they are both perfectly adapted to the flow and extremely robust. 相似文献
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基于滨海核电站海上γ辐射剂量率的智能化自动监测系统是一种无人值守的辐射监测装备,可全天候、长时间、在线组网、连续自动测量水面和空气中的γ剂量率、获取水中γ能谱数据并进行核素识别和计算活度浓度,并实时地将监测数据通过无线通信链路和北斗短报文两种形式上传至地面数据服务中心。在非事故情况下,该系统是对核电厂监督性监测系统的重要补充和完善;在发生重大核安全事故或放射性物质泄漏的情况下,能够有效解决传统的派船巡测时方法不标准、数据不及时不连续、人员受照风险大、船只易受污染和行动代价高等问题;在恶劣的极端气象条件下,无人值守的自动监测系统能够为核电站提供实时有效的水体和空气中的γ剂量率、气象、海水温度等监测数据,有效地提升了核电站在极端气象条件下的监测能力,对滨海核电站整体的安全性和可靠性具有一定积极意义。 相似文献
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Numerical Modeling of Sediment Mass Sliding and Tsunami Generation: The Case of February 7, 1963, in Corinth Gulf, Greece 总被引：1，自引：0，他引：1
G. A. Papadopoulos L. I. Lobkovsky R. Kh. Mazova I. A. Garagash V. Karastathis L. Yu. Kataeva V. G. Kaz'min 《Marine Geodesy》2007,30(4):315-331
Numerical modeling of a landslide process at the continental slope by taking into account slope parameters is performed for the tsunami event of February 7, 1963, reported in the Corinth Gulf, central Greece. A layered sediment structure was considered, and an initial external dynamic action at the landslide process was introduced. The results obtained were quite consistent with the observational runup data as well as with the results arrived at by conventional rigid-body and viscous-fluid models. However, this approach permits to describe in detail the formation of several wave groups and particular tsunami characteristics that are strongly dependent on the landslide model. 相似文献
10.
G. A. Papadopoulos L. I. Lobkovsky R. Kh. Mazova I. A. Garagash V. Karastathis L. Yu. Kataeva 《Marine Geodesy》2013,36(4):315-331
Numerical modeling of a landslide process at the continental slope by taking into account slope parameters is performed for the tsunami event of February 7, 1963, reported in the Corinth Gulf, central Greece. A layered sediment structure was considered, and an initial external dynamic action at the landslide process was introduced. The results obtained were quite consistent with the observational runup data as well as with the results arrived at by conventional rigid-body and viscous-fluid models. However, this approach permits to describe in detail the formation of several wave groups and particular tsunami characteristics that are strongly dependent on the landslide model. 相似文献
11.
Jean-François Balmat Frédéric Lafont Robert Maifret Nathalie Pessel 《Ocean Engineering》2009,36(15-16):1278-1286
This paper presents a fuzzy approach for the MAritime RISk Assessment (MARISA) applied to safety at sea. The aim of this work is to define automatically an individual ship risk factor which could be used in a decision making system. To achieve this purpose, a modular and hierarchical structure using fuzzy logic has been developed. It allows us to obtain a fuzzy risk factor (FRF) composed of a static risk factor (SRF) and a dynamic risk factor (DRF). The static risk factor assessment takes into account several static data relative to the ship (age, flag, gross tonnage, number of companies, duration of detention and type). The dynamic risk factor is evaluated by considering the meteorological conditions (sea state, wind speed and visibility) and the moment of the day. Moreover, the MARISA graphic interface developed with the Labview software is presented. This interface allows several simulations to be carried out to validate the fuzzy method proposed. Simulation results are presented. 相似文献
12.
An integrated dynamic model of China’s deep ocean mining system is developed and the fast simulation analysis of its longitudinal reciprocating motion operation processes is achieved. The seafloor tracked miner is built as a three-dimensional single-body model with six-degree-of-freedom. The track-terrain interaction is modeled by partitioning the track-terrain interface into a certain number of mesh elements with three mutually perpendicular forces, including the normal force, the longitudinal shear force and the lateral shear force, acting on the center point of each mesh element. The hydrodynamic force of the miner is considered and applied. By considering the operational safety and collection efficiency, two new mining paths for the miner on the seafloor are proposed, which can be simulated with the established single-body dynamic model of the miner. The pipeline subsystem is built as a three-dimensional multi-body discrete element model, which is divided into rigid elements linked by flexible connectors. The flexible connector without mass is represented by six spring-damper elements. The external hydrodynamic forces of the ocean current from the longitudinal and lateral directions are both considered and modeled based on the Morison formula and applied to the mass center of each corresponding discrete rigid element. The mining ship is simplified and represented by a general kinematic point, whose heave motion induced by the ocean waves and the longitudinal and lateral towing motions are considered and applied. By integrating the single-body dynamic model of the miner and the multi-body discrete element dynamic model of the pipeline, and defining the kinematic equations of the mining ship, the integrated dynamic model of the total deep ocean mining system is formed. The longitudinal reciprocating motion operation modes of the total mining system, which combine the active straight-line and turning motions of the miner and the ship, and the passive towed motions of the pipeline, are proposed and simulated with the developed 3D dynamic model. Some critical simulation results are obtained and analyzed, such as the motion trajectories of key subsystems, the velocities of the buoyancy modules and the interaction forces between subsystems, which in a way can provide important theoretical basis and useful technical reference for the practical deep ocean mining system analysis, operation and control. 相似文献
13.
It is shown that by implementing certain mine avoidance techniques, an underwater vehicle equipped with an obstacle avoidance sonar (OAS) and a navigation system can safely navigate an unknown minefield. The mine avoidance techniques take into account the physical limitations of the sonar and the navigation system, the maneuverability constraints on the underwater vehicle, and the required safe standoff distance from all mines. Extensive computer simulations have verified the mine avoidance capability in more than 50 different minefields. In all 50 simulations the vehicle reached a predetermined end point and maintained at least the specified, minimum safe standoff distance from each mine. The simulation accurately models the major difficulties associated with the sonar, the navigation system, and the vehicle dynamics. The sonar model includes surface, bottom, and volume reverberation; thermal, ambient, and flow noises; actual receiver and projector beam patterns; and false alarms and missed detections. The navigation system model contains the effects of biases, random noises, and scale factor errors. The vehicle dynamic model simulates angular velocities and accelerations associated with underwater vehicles 相似文献
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Understanding the internal stratigraphic architecture of sand-dominated deltas is critical to assessing the extent and distribution of petroleum reservoirs. The stratigraphic architecture and evolution of a major Early–Middle Jurassic fluvio-deltaic system (Plover Formation) on the Australian North West Shelf has been established through integrated analysis of core, borehole image logs and wireline logs for the Calliance field in the Browse Basin. Six facies associations identified in cored intervals are interpreted as tidally influenced channel- and tidal channel-fill complexes (FA1–FA2), crevasse-splay deposits and interchannel marshes (FA3), heterolithic mouthbars and sandflats (FA4), sandy mouthbars (FA5) and offshore transition to offshore (FA6). Therefore, the overall depositional system in the study area is proposed to be a tidally influenced deltaic system, in which FA6 represents prodelta deposits, FA5 and FA4 constitute distributary mouthbar deposits of the delta front and tidally influenced channel and interchannel deposits represent the lower delta plain (FA2, FA1, FA3). Analysis of image lithology and fabric are used to extend interpretation to uncored intervals and to identify intrusive and extrusive igneous units and associated volcaniclastic facies within the formation. Five third-order stratigraphic sequences (S1–S5) record progradational (S1, S2 and S4) and retrogradational (S3 and S5) phases of delta evolution. Paleocurrent indicators derived from borehole image logs indicate common southerly directed sediment dispersal in S2 and S3 and increasingly complex with westerly directions in S4 and S5. Two rift-related depositional phases are recognised separated by a phase of uplift between S3 and S4. The stratigraphic succession of S2 is consistent with the depositional pattern expected in a synrift setting and deposition of the over-thickened sandy succession (FA5 in S4), which is also the major reservoir interval, was most likely controlled by syn-tectonic faulting. 相似文献
15.
Zonal recovery is a prompt escape towards the sea performed by sandhoppers under stressful environmental conditions. Differences in habitat features, meteorological conditions during the tests and morphological characteristics of the individuals are all factors affecting orientation. This paper deals with the temporal variation of the orientation of a sandhopper sample, taking into account the effect of some environmental and morphological variables on these changes. The directions chosen by single animals in repeated trials under natural conditions were analysed, using longitudinal circular data. The longitudinal analysis highlights several details about three different kinds of intrapopulation variation due to: sun, wind and eye left/right asymmetry. A clear link between the successive directional responses is demonstrated as well as modulation of behaviour with time: the animals stabilise orientation towards a certain direction in successive trials. The use of longitudinal sets of data in orientation studies produces a good synthesis of directional behaviour, due to several advantages of this kind of analysis. These include the fact that the association between successive behaviours and variability through repeated trials is taken into account; a progressive improvement, due to the integration of information from previous experiences, can be detected; the role of the main cues and factors affecting orientation is more accurately defined; and more parsimonious statistical models can be used to fit the data. 相似文献
16.
Christian Winter Ming Da Chiou Rolf Riethmüller Verner B. Ernstsen Dierk Hebbeln Burg W. Flemming 《Geo-Marine Letters》2006,26(3):125-132
Process-based numerical modelling of coastal morphodynamics involves model and data reduction schemes in order to cope with computational limitations. Model reduction, on the one hand, may involve the discretisation of an interactive multidimensional, diverse natural system into a reduced set of coupled process-simulation modules. Data reduction schemes, on the other hand, are used to parameterise processes. The use of schematised open-boundary conditions, which are considered as representative in terms of their cumulative morphological effect, is based on the concept of “morphological” or “representative” boundary conditions. Recent model applications show realistic tendencies in terms of depositional and erosional areas. By contrast, the reproduction of characteristic changes in morphology such as the migration of bars, banks and channels is only occasionally achieved. Using field data on observed morphological impact of a single storm event and numerical model data, it is demonstrated that the concept of representative tides may lead to simulations of morphological development lacking natural dynamics. It is proposed that rather than being based on “representative” single tides, morphodynamic models should be applied with open-boundary conditions which take variations in longer-term tidal and meteorological forcing into account. 相似文献
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This paper presents an analytical solution for the dynamic behavior of both the platform and tethers in the tension leg platform system when the platform system is subjected to the wave-induced surge motion and the flow-induced drag motion. Along with the analysis the coupling problem of a two dimensional tension leg platform interacting with a monochromatic linear wave train in an inviscid and incompressible fluid is being considered. The scattering problem and radiation problem are first solved independently and then combined together to resolve for all unknowns. The dynamic behavior of the platform and tethers was further solved based on these solutions. The material property and the dimensional effect for the tether incorporated in the tension leg platform system are both taken into account in the analytical analysis. Corresponding to the variation of material properties and tether dimensions, it was found that the dynamic behavior of both the tether of tension leg platform and the platform itself is closely related to the material property and the dimension of the tether. 相似文献
20.
French meteorological data provide some information on wind direction since 1890. Since 1951, wind speed and direction have been digitised every three hours in many stations. The Brest tide gauge has recorded hourly sea levels since 1860, thus enabling hourly surges to be calculated and studied. This set of data has been organised into a data base and analysed in order to recognize evolution and trends. Strong winds are increasing in frequency in the western part of Brittany and decreasing in Normandy and Pays de Loire. Surges associated with these winds do present a slight decreasing trend. A more precise analysis allows to distinguish between southerly winds, which are slightly decreasing, and strong winds from other directions, which display a more or less important increase in frequency. The analysis shows trends that may be linked to the global circulation pattern, and that result in a new spatial distribution of winds on western France. 相似文献