Reliability-based comparative study for mooring lines design criteria     

Alberto Omar Vazquez-Hernandez  Gilberto Bruno Ellwanger  Luís Volnei Sudati Sagrilo   《Applied Ocean Research》2006,28(6):398-406

The characteristic environmental load effect for the design of mooring systems of floating units can be defined by means of three procedures: (a) the one associated to an extreme sea state with a given return period, (b) the worst one from a set of sea states on a contour line associated to a return period or (c) the extreme one based on response statistics for a long-term period. This work presents the result of a reliability-based partial safety factor calibration study for a LRFD mooring line design criteria considering the three approaches mentioned above. The calibration exercise is applied to three FPSOs considering North Sea environmental conditions and different water depths: 200, 800 and 3000 m. The mooring systems investigated take into account mooring lines made up of chains and polyester ropes. It is shown that, among all cases investigated, the design procedure based on the long-term response is the one that presents less scattered reliability indices around the target level.  相似文献   

A methodology for assessing the reliability of taut and slack mooring systems against instability     

A.A. Shah  A. Umar  N.A. Siddiqui   《Ocean Engineering》2005,32(10):1216-1234

In the present study, a methodology for reliability assessment of slack and taut mooring systems against instability has been presented. For this purpose, first, stability analysis of slack and taut mooring systems has been carried out and instable regions are obtained using procedure available in the literature. Having known the instable region(s), methodology for reliability assessment has been proposed which is based on Monte Carlo Simulation technique. After using the proposed methodology, probabilities of failure and reliability indices has been obtained for the above systems. Some parametric studies, such as, effect of lower and upper limits of instability and effect of frequency range of generations are also included to obtain the results of practical interest.  相似文献   

Changes in soils and vegetation in a Mediterranean coastal salt marsh impacted by human activities   总被引：10，自引：0，他引：10  

J. lvarez-Rogel  F.J. Jimnez-Crceles  M.J. Roca  R. Ortiz 《Estuarine, Coastal and Shelf Science》2007,73(3-4):510-526

This paper reports changes in vegetation distribution and species cover in relation to soil factors and hydrology in a semiarid Mediterranean salt marsh adjacent to the Mar Menor saline lagoon. Species cover, soil salinity, and the groundwater level were monitored between 1991 and 1993 and between 2002 and 2004, and total organic carbon, total nitrogen, total phosphorus, nitrates, ammonium and exchangeable phosphorus were measured in the soils in both study periods. In addition, three soil profiles were described in August 1992 and August 2004. The results indicate an elevation of the water table throughout the 13-year period, which was attributable to water flowing from areas with intensive agriculture. Flooding increased and soil salinity dropped in the most saline sites and increased in the least saline ones. The morphology of the soil profiles reflected the increase in flooding periods, due to the appearance of a greyer matrix in the deeper horizons and a more diffuse pattern of Fe mottles. Following these environmental changes, Sarcocornia fruticosa, Phragmites australis and Juncus maritimus strongly expanded at the wettest sites, which led to the disappearance of the original zonation pattern. The cover of Limonium delicatulum, in turn, decreased with the increase in moisture but increased following the increase in salinity. Changes in soil nutrients were only very evident in the sandy soils of the beach, probably due to the influence of organic debris deposited on the shoreline by the storms and due to the strong increase in the colonisation of this habitat by perennial species. According to the results obtained, control measures are needed in order to preserve habitat diversity in this and other salt marshes of this area. Monitoring of the vegetation distribution could be a useful tool to identify environmental impacts, in order to implement remedial actions.  相似文献   

Structural monitoring of offshore platforms using impulse and relaxation response     

Lalu Mangal  V. G. Idichandy  C. Ganapathy 《Ocean Engineering》2001,28(6)

Monitoring offshore platforms, long span bridges, high rise buildings, TV towers and other similar structures is essential for ensuring their safety in service. Continuous monitoring assumes even greater significance in the case of offshore platforms, which are highly susceptible to damage due to the corrosive environment and the continuous action of waves. Also, since a major part of the structure is under water and covered by marine growth, even a trained diver cannot easily detect damage in the structure. In the present work, vibration criterion is adopted for structural monitoring of jacket platforms. Artificial excitation of these structures is not always practicable and ambient excitation due to wind and waves may not be sufficient for collecting the required vibration data. Alternate methods can be adopted for the same purpose, for example, the application of an impact or a sudden relaxation of an applied force for exciting the structure. For jacket platforms, impact can be applied by gently pushing the structure at the fender while relaxation can be accomplished by pulling the structure and then suddenly releasing it using a tug or a supply vessel in both cases. The present study is an experimental investigation on a laboratory model of a jacket platform, for exploring the feasibility of adapting vibration responses due to impulse and relaxation, for structural monitoring. Effects of damage in six members of the platform as well as changes in deck masses were studied. A finite element model of the structure was used to analyze all the cases for comparison of the results as well as system identification. A data acquisition and analysis procedure for obtaining the response signatures of the platform due to the impulse and relaxation procedure was also developed for possible adoption in on-line monitoring of offshore platforms. From the study, it has been concluded that both impulse and relaxation responses are useful tools for monitoring offshore jacket platforms. The present work forms the basis for the development of an automated, on-line monitoring system for offshore platforms, using neural networks.  相似文献   

Approaches for comparative evaluation of raster GIS-based landslide susceptibility zonation maps     

R.P. Gupta  D.P. Kanungo  M.K. Arora  S. Sarkar 《International Journal of Applied Earth Observation and Geoinformation》2008

Evaluation of maps generated from different conceptual models or data processing approaches at spatial level has importance in many geoenvironmental applications. This paper addresses the spatial comparison of different landslide susceptibility zonation (LSZ) raster maps of the same area derived from various procedures.  相似文献   

Dynamic data integration for structural modeling: model screening approach using a distance-based model parameterization   总被引：2，自引：0，他引：2  

Satomi Suzuki  Guillaume Caumon  Jef Caers 《Computational Geosciences》2008,12(1):105-119

This paper proposes a novel history-matching method where reservoir structure is inverted from dynamic fluid flow response. The proposed workflow consists of searching for models that match production history from a large set of prior structural model realizations. This prior set represents the reservoir structural uncertainty because of interpretation uncertainty on seismic sections. To make such a search effective, we introduce a parameter space defined with a “similarity distance” for accommodating this large set of realizations. The inverse solutions are found using a stochastic search method. Realistic reservoir examples are presented to prove the applicability of the proposed method.  相似文献   

Probabilistic seismic hazard zonation of Syria     

Abdallah I. Husein Malkawi  Robert Y. Liang  Jamal H. Nusairat  Azm S. Al-Homoud 《Natural Hazards》1995,12(2):139-151

Earthquake hazard maps for Syria are presented in this paper. The Peak Ground Acceleration (PGA) and the Modified Mercalli Intensity (MMI) on bedrock, both with 90% probability of not being exceeded during a life time of 50, 100 and 200 years, respectively are developed. The probabilistic PGA and MMI values are evaluated assuming linear sources (faults) as potential sources of future earthquakes. A new attenuation relationship for this region is developed. Ten distinctive faults of potential earthquakes are identified in and around Syria. The pertinent parameters of each fault, such as theb-parameter in the Gutenberg-Richter formula, the annual rate ₄ and the upper bound magnitudem ₁ are determined from two sets of seismic data: the historical earthquakes and the instrumentally recorded earthquake data (AD 1900–1992). The seismic hazard maps developed are intended for preliminary analysis of new designs and seismic check of existing civil engineering structures.  相似文献   

A north-south section across the Queyras Schistes lustrés (Piedmont zone, Western Alps): Syn-collision refolding of a subduction wedge     

Pierre Tricart  Stephane Schwartz 《Eclogae Geologicae Helvetiae》2006,99(3):429-442

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New Generation of Probabilistic Seismic Hazard Assessment for the Area Cologne/Aachen Considering the Uncertainties of the Input Data     

G. Grünthal  R. Wahlström 《Natural Hazards》2006,38(1-2):159-176

A new earthquake catalogue for central, northern and northwestern Europe with unified M_w magnitudes, in part derived from chi-square maximum likelihood regressions, forms the basis for seismic hazard calculations for the Lower Rhine Embayment. Uncertainties in the various input parameters are introduced, a detailed seismic zonation is performed and a recently developed technique for maximum expected magnitude estimation is adopted and quantified. Applying the logic tree algorithm, resulting hazard values with error estimates are obtained as fractile curves (median, 16% and 84% fractiles and mean) plotted for pga (peak ground acceleration; median values for Cologne 0.7 and 1.2 m/s² for probabilities of exceedence of 10% and 2%, respectively, in 50 years), 0.4 s (0.8 and 1.5 m/s²) and 1.0 s (0.3 and 0.5 m/s²) pseudoacclerations, and intensity (I₀ = 6.5 and 7.2). For the ground motion parameters, rock foundation is assumed. For the area near Cologne and Aachen, maps show the median and 84% fractile hazard for 2% probability of exceedence in 50 years based on pga (maximum median value about 1.5 m/s²), and 0.4 s (>2 m/s²) and 1.0 s (about 0.8 m/s²) pseudoaccelerations, all for rock. The pga 84% fractile map also has a maximum value above 2 m/s² and shows similarities with the median map for 0.4 s. In all maps, the maximum values fall within the area 6.2–6.3° E and 50.8–50.9° N, i.e., east of Aachen.  相似文献   

New data on Upper Kimmeridgian-Tithonian biostratigraphy and ammonites of the eastern Crimea     

V. V. Arkad’ev  M. A. Rogov 《Stratigraphy and Geological Correlation》2006,14(2):185-199

Based on ammonites, Upper Kimmeridgian sediments are first established in the Crimean Mountains. The Kimmeridgian-Tithonian boundary recognizable in a continuous section is placed inside the Dvuyakomaya Formation of uniform largely clayey sediments. Assemblages of Kimmeridgian ammonites Lingulaticeras cf. procurvum (Ziegler), Pseudowaagenia gemmellariana Oloriz, Euvirgalithacoceras cf. tantalus (Herbich), Subplanites sp.) and Tithonian forms (?Lingulaticeras efimovi (Rogov), Phylloceras consaguineum Gemmellaro, Oloriziceras cf. schneidi Tavera, and Paraulacosphinctes cf. transitorius (Oppel) are described. A new biostratigraphic scheme proposed for the upper Tithonian-Berriasian of the Crimean Mountains includes the following new biostratigraphic units: the Euvirgalithacoceras cf. tantalus Beds of the upper Kimmeridgian, ?Lingulaticeras efimovi Beds of the lower Tithonian, and Oloriziceras cf. schneidi and Paraulacosphinctes cf. transitorius beds of the upper Tithonian. The middle Tithonian is proposed to consist of the fallauxi and semiforme (presumably) zones. The ammonities found determine the early Kimmeridgian-Berriasian age of the Dvuyakornaya Formation that is most likely in tectonic contact with the underlying Khutoran Formation.  相似文献