海洋工程试验池中风场模拟

在考虑海洋工程装备在极端海况和运行海况下的载荷与受力,风载荷也是一个不可忽视的因素.目前物理模型试验仍是研究海洋工程结构物载荷与运动性能的重要手段,而深海结构物在水平漂移运动较大,如何在较大范围内得到满足试验要求的风场,是提高试验能力的重要问题.应用数值计算方法对大范围的风场模拟进行了分析,并进行了相应的物理实验,在此基础上对海洋工程试验的风场模拟提出了若干建议.     

A numerical modeling of hydrodynamic characteristics of various planing hull forms

A numerical algorithm based on the boundary element method (BEM) is presented for predicting the hydrodynamic characteristics of the various planing hull forms. The boundary integral equation is derived using Green's theorem on the wetted body surface and the free surface. The ventilation function at the transom is estimated with Doctor's empirical formula. This function is defined as the transom zone free surface boundary condition. The combined boundary integral equation and modified free surface boundary condition are simultaneously solved to determine the dipole on the wetted hull surface and the source on the free surface. The method is applied to investigate three examples of planing hulls, which include flat-plates, as well as wedge-shaped and variable deadrise planing hulls. Their hydrodynamic characteristics are calculated for different speeds. Computational results are presented and compared with existing theories and experiments. On the whole, the agreement between the present method and the selected experimental and numerical data is satisfactory.     

Ontological Engineering for Interpreting Geospatial Queries

Despite advancements in geographic information system (GIS) technology, the efficient and effective utilization of GIS to solve geospatial problems is a daunting process requiring specialized knowledge and skills. Two of the most important and burdensome tasks in this process are interpretation of geospatial queries and mapping the interpreted results into geospatial data models and geoprocessing operations. With the current state of GIS, there exists a gap between the knowledge user's possess and the knowledge and skills they need to utilize GIS for solving problems. Currently, users resort to training and practice on GIS technology or involving GIS experts. Neither of these options is optimal and there is a need for a new approach that automates geoprocessing tasks using GIS technology. This paper presents an ontological engineering methodology that uses multiple ontologies and the mappings among them to automate certain tasks related to interpretation of geospatial queries and mapping the interpreted results into geospatial data models and geoprocessing operations. The presented methodology includes conceptualization of geospatial queries, knowledge representation for queries, techniques for relating elements in different ontologies, and an algorithm that uses ontologies to map queries to geoprocessing operations.     

Un exemple de volcanisme calco-alcalin de type orogénique mis en place en contexte de rifting (Cambrien de l'oued Rhebar,Meseta occidentale,Maroc)

The Middle Cambrian calc-alkaline Oued Rhebar volcanic complex (western Meseta, Morocco) compares with rocks originated in orogenic contexts. The La/Nb ratios are relatively high (5.2), suggesting a lithospheric mantle origin. The La/Ta ratios, higher than 26, and the negative Nb anomaly indicate a lithospheric source contaminated by the continental crust. These rocks were generated in the Mesetian Mid-Cambrian rift and would have inherited their orogenic signature from the partial melting of a previously metasomatized mantle. To cite this article: H. El Hadi et al., C. R. Geoscience 338 (2006).     

Comparative studies on analytical methods for the assessment of petroleum contamination in the marine environment II. Gas chromatographic analyses

Although determinations of hydrocarbons in the marine environment are usually based on the same analytical steps, i.e. organic solvent extraction, column chromatographic purification, and hydrocarbon detection and identification; variations in equipment and solvent systems used in the extraction step, and also in the columns for purification and analysis, seriously impaired the development of a consistent data base concerning oil pollution on a global scale.Many authors and conferences emphasized the need, in this field, for a comparative study on the efficiency of various published analytical techniques.Fifteen techniques with 24 applications were chosen and applied to a fixed weight of uniform samples of sediments, mussels, fish, shrimps and green algae. The final hydrocarbon extracts were analyzed individually on a 2 m stainless-steel packed column (SE 30).The results obtained from this work showed considerable variations in the efficiency of different techniques from identical samples. The hydrocarbon yields varied from 94 to 1.4 ppm in sediments, from 40 to 9 ppm in mussels; from 216 to 1.3 ppm in fish; from 8.3 to 3.1 ppm in shrimps; and from 343 to 273 ppm in algae, all relative to wet weight of the samples. The gas chromatograms of the hydrocarbons obtained were found to be quite different with regard to peak intensities and distributions. This means that hydrocarbons obtained by the application of different techniques varied in their compositions and relative concentrations of their constituents. These results confirm what was already obtained and discussed previously using spectrofluorometric analyses.It can be concluded that it is necessary to establish a standard technique for the preparation of marine samples, for extraction and purification of the hydrocarbon extracts which should be applied by all laboratories specializing in this field.     

An efficient tool for accelerating the numerical solution of the stochastic subsurface flow problem using neural networks

 An efficient numerical solution for the two-dimensional groundwater flow problem using artificial neural networks (ANNs) is presented. Under stationary velocity conditions with unidirectional mean flow, the conductivity realizations and the head gradients, obtained by a traditional finite difference solution to the flow equation, are given as input-output pairs to train a neural network. The ANN is trained successfully and a certain level of recognition of the relationship between input conductivity patterns and output head gradients is achieved. The trained network produced velocity realizations that are physically plausible without solving the flow equation for each of the conductivity realizations. This is achieved in a small fraction of the time necessary for solving the flow equations. The prediction accuracy of the ANN reaches 97.5% for the longitudinal head gradient and 94.7% for the transverse gradient. Head-gradient and velocity statistics in terms of the first two moments are obtained with a very high accuracy. The cross covariances between head gradients and the fluctuating log-conductivity (log-K) and between velocity and log-K obtained with the ANN approach match very closely those obtained by a traditional numerical solution. The same is true for the velocity components auto-covariances. The results are also extended to transport simulations with very good accuracy. Spatial moments (up to the fourth) of mean-concentration plumes obtained using ANNs are in very good agreement with the traditional Monte Carlo simulations. Furthermore, the concentration second moment (concentration variance) is very close between the two approaches. Considering the fact that higher moments of concentration need more computational effort in numerical simulations, the advantage of the presented approach in saving long computational times is evident. Another advantage of the ANNs approach is the ability to generalize a trained network to conductivity distributions different from those used in training. However, the accuracy of the approach in cases with higher conductivity variances is being investigated.     

Forest fire susceptibility modeling using hybrid approaches

Forest fires are considered one of the most highly damaging and devastating of natural disasters, causing considerable casualties and financial losses every year. Hence, it is important to produce susceptibility maps for the management of forest fires so as to reduce their harmful effects. The purpose of this study is to map the susceptibility to forest fires over Nowshahr County in Iran, using an integrated approach of index of entropy (IOE) with fuzzy membership value (FMV), frequency ratio (FR), and information value (IV) with a comparison of their precision. The spatial database incorporated the inventory of forest fire and conditioning factors. As a whole, 41 forest fire locations were identified. Out of these, 29 locations (≈70%) were randomly chosen for the forest fire susceptibility modeling (FFSM), and the remaining 12 locations (≈30%) were utilized for the validation of the models. Subsequently, utilizing FMV‐IOE, FR‐IOE, and IV‐IOE models, forest fire susceptibility maps were acquired. Finally, the modeling ability of the models for FFSM was assessed using an area under the receiver operating characteristic (AUROC) curve. The results manifested that the prediction accuracy of the FMV‐IOE model is slightly higher than that of the FR‐IOE and IV‐IOE models. The incorporation of IOE with FMV, FR, and IV models had AUROC values of 0.890, 0.887, and 0.878, respectively. The resulting FFSM can be effective in fire repression resource planning, sustainable development, and primary warning in regions with similar conditions.     

Structural styles,hydrocarbon prospects,and potential in the Salt Range and Potwar Plateau,north Pakistan

The Salt Range/Potwar Plateau (SRPP) is part of the Himalayan foreland and an important petroleum province in north Pakistan. The hydrocarbons are commonly produced from stacked Cambrian to Eocene clastic and carbonate reservoirs which have an average thickness of 1 km. These strata are overlain by at least 5 km of Miocene and younger continental molasse sedimentation in the deepest part of the foreland basin. Surface and subsurface (seismic interpretations and borehole data) geology combined with the timing and the patterns of sedimentation has allowed to interpret the deformation as thin skinned, with a detachment in weak Eocambrian evaporates and the development of ramp-and-flat structures, since about 8 Ma. We have reviewed the structural interpretations with new borehole logs, field geology, and reserve estimates in this paper to precisely define oil-field structures with a view on future exploration. As a result of this work, 12 oil fields are classified as three detachment folds, four fault-propagation folds, four pop-ups, and one triangle zone structure. The latter two are identified as better prospects with the last one as the best with estimated reserves of 51 million barrels of oil (MMBO). Hence, the triangle zones along with other ramp-and-flat structures from the North Potwar Deformed Zone (NPDZ) are recognized to provide potential future prospects. Finally, a 40-km-long structural cross section from NPDZ is used to discuss complex deformation of the triangle zone and duplex structures as future potential prospects. About 55 km of shortening across the NPDZ during Plio-Pleistocene time is calculated, which has important bearing on the geometry of prospects, reserve calculations, and the future exploration.