Academic literature on the topic 'Riserva Naturale Marina'

Marine risers are key apparatus in connecting the subsea wells to the oil production platform. When the ocean current flow past a riser, the vortex shedding behind riser may induce vibration. If the frequency of vortex shedding is approaching or equal to the natural frequency of riser, the resonance will be generated. Such phenomenon leads to the potential fatigue damage of riser. Therefore, the safety and assurance of marine risers are widely arousing the interest of offshore engineering. In present paper, previous apparatus or methods in suppressing vortex-induced vibration (VIV) of risers used in marine engineering are firstly analyzed, and correspondingly the conditions in design of VIV suppressors are proposed. Based on the Bernoulli equation, the disturbance in flow around a bluff body and the relationship of vortex shedding in span-wise direction, a new method of VIV suppression is proposed. The numerical results have shown that the vibration of risers could be reduced by such disturbance.

Marine risers, and offshore structures in general, may have undesirable natural frequencies and/or mode shapes. Structural redesign is mandatory in such cases. An Inverse Perturbation Redesign (IPR) method, which uses only the finite element analysis of the baseline system and was developed in previous work for general structures, is extended in this work to handle systems with geometric stiffness matrices like marine risers. The IPR method is currently applicable to undamped structural systems or systems with Rayleigh damping and is valid for large or small changes which are frequently required to change modal characteristics of offshore structures. The vibratory characteristics of risers can be altered by modifying among others, the riser top tension, the drilling mud density and the geometry of the riser tubes. The effects of their change on the riser frequencies and modes are derived and applied to two typical riser redesign problems using the IPR method.

Natural frequencies, mode shapes and critical buckling loads of marine risers simply supported at both ends are given in closed form by using the WKB method. These solutions allow variable cross section, bending rigidity, tension and mass distribution along the riser length. Furthermore, a simple procedure to predict natural frequencies for other boundary conditions is described. Some special forms of these closed-form solutions are compared with existing solutions in the literature.

Vibrations induced by flow, generally referred to as vortex induced vibrations, are of great importance in the design of marine risers. These flexible cylindrical risers undergo vibrations of very high amplitude when the vortex shedding frequency matches the natural frequency of the riser. Such vibrations are capable of putting the safety of crew working on offshore platforms in question. Hence the prediction of response of such structures is considered very important. Although a lot of numerical work has been done in this field treating the problem as a two-way fluid structure interaction, the fact that these works demand very high computational efforts has not made it pertinent where high end computing resources are not readily available. A quick prediction of the structural response of such slender structures needs to be handy to the engineers at times of need. This paper addresses a solution technique for such a problem through an economical method for quick and reliable prediction of riser response under vortex induced vibration utilizing minimum computational effort for moderate Reynolds number (Re = 3 x 105). Two dimensional flow simulations are carried out using RANSE based CFD followed by the uniform mapping of hydrodynamic forces on to the three dimensional riser. The grid used for the numerical simulation has been well validated against wind-tunnel experimental results for Re= 5.3 x 104. Hydrodynamic forces corresponding to the first three harmonics of natural frequency of the riser have been used as input in the structural solver to analyse the response using finite element method. Trajectories of the cylinder in the first three modes of vibration have been obtained, a typical eight figure pattern which is characteristic for lock-in vibration. It is found that the method is quite effective in the quick computation of flow induced vibration problems for low and moderate Reynolds numbers.

This paper presents a direct method for determining natural frequencies of lateral modes of vibration for marine risers in deep water. This method applies to marine risers that are vertical, relatively straight, and attached at both ends. The method is particularly useful for determining natural frequencies of higher modes that are sometimes difficult to obtain analytically or numerically. Comparisons of numerical results with published data show that even though the method of solution is approximate, the calculation procedure gives useful engineering results. The algorithm is based on classical vibration theory and can easily be programmed on portable computers for direct use on offshore oil rigs.

The marine riser has transfer dynamic cyclic load to the top of casing string when deepwater drilling operating. Considering with the nonlinear characteristics of seabed soil, the variable string cross section, and the axial load on the top of string, a dynamic differential equation of casing string below mud line and its numerical solution were established. Results illustrate that, the lateral displacement, the bending moment, and the shear of the casing string are not equal when lateral dynamic cyclic loading achieves amplitude due to the soil hysteresis effect. The diameter and wall thickness of conductor have less affect to string vibration frequency, cannot adjust the string natural frequency by adjusting these parameters. The natural frequency of casing string in sand is bigger than it in clay. The undrained shear strength of soil has great effect on the natural frequency of casing string in clay. The lateral displacement amplitude is highest when the vibration frequency of casing string at its natural frequency.

2006/2007
L’obiettivo di tale studio è stato quello di implementare un Sistema di Informazione Geografica (GIS) per il monitoraggio dell’attività di pesca e delle risorse alieutiche, considerando le marinerie delle Isole Egadi, a rappresentanza di alcune tipologie di base dell’attività di pesca artigianale e per i diversi vincoli ambientali che in quest’area insistono quali la Riserva Naturale Marina e i Siti Natura 2000, al fine di suggerire opportune strategie di protezione sia per le risorse pescabili che per l’ambiente. Quindi un sistema esperto a supporto delle decisioni, che consenta di visualizzare i complessi scenari nell’ambito della valutazione delle risorse alieutiche nella dimensione spazio-temporale (Spatial Decision Support System), orientato alla pianificazione territoriale per un uso sostenibile delle risorse naturali, sinergica e coordinata tra i vari enti territoriali preposti. Nel corso di tale studio è stato messo a punto un data-warehouse, orientato alla pianificazione territoriale contenente differenti tipologie di dati ambientali, un database relazionale (RDBMS) contenente i dati riguardanti la pesca e la flotta, e un GIS in grado di gestire, analizzare, integrare dati eterogenei, riferendoli alle rispettive posizioni geografiche, finalizzato nello specifico ai seguenti obiettivi: - Studio delle caratteristiche ambientali dell’area di interesse; - Caratterizzazione della struttura della flotta per ciascun porto; - Variabilità degli attrezzi utilizzati nel tempo e nello spazio in ciascun porto; - Indagine delle specie catturate, qualitativamente e quantitativamente; - Indagine dello sforzo di pesca e cattura per unità di sforzo (CPUE), nello spazio e nel tempo; - Analisi dei principali parametri chimico-fisici ambientali (temperatura, salinità, ossigeno, etc); - Rilevazione delle condizioni climatiche e meteo-marine; - Individuazione di specie e habitat di elevato valore ecologico; - Valutazioni ambientali e indicazioni gestionali. In particolare, è stata indagata l’area di studio, gli aspetti geologici, biologici, con particolare rilievo ad habitat e specie di interesse scientifico e/o ecologico, mediante ricerche bibliografiche e campagne sperimentali in mare. Sono state realizzate le indagini inerenti la pesca e la flotta mediante i seguenti metodi: metodo indiretto e metodo diretto. Il metodo indiretto ha compreso la raccolta dei dati settimanalmente mediante rilevazione allo sbarco, per un intero anno. Il metodo diretto ha compreso la realizzazione di campagne sperimentali opportunamente pianificate, utilizzando come campionatore diverse tipologie di imbarcazioni e attrezzi delle marinerie dell’area, per la raccolta diretta di dati, sempre nell’arco di un anno. Durante le pescate sperimentali si è fatto uso di strumentazione GPS (Global Positioning System) per registrare le coordinate geografiche del punto iniziale, medio e finale dell’attrezzo in pesca. La profondità, a cui sono state effettuate le pescate, è stata registrata mediante ecoscandaglio. I dati oceanografici sono stati prelevati in situ, mediante sonde multiparametriche. Sono state rilevate informazioni riguardo le condizioni climatiche e meteo-marine. E’ stato realizzato un GIS facendo uso del software ArcGIS 9.1 della ESRI. Per la definizione dei temi e per uniformare le informazioni raccolte e catalogate nel datawarehouse, questo è stato strutturato in accordo ad un Thesaurus di Riferimento per Applicazioni ambientali (Environmental Applications Reference Thesaurus, EARTh). I dati riguardanti la pesca e la flotta sono stati elaborati e organizzati in un Database relazionale (RDBMS), che ha permesso la gestione dell’informazione geografica assicurando caratteristiche quali efficienza nelle prestazioni, controllo degli accessi, controllo delle ridondanze, conferendo una formidabile elasticità alla struttura e quindi di analisi spaziale, permettendo così di analizzare i diversi aspetti dei fenomeni. Questo è stato arricchito con collegamenti (hyperlink) a documenti utili (leggi, direttive, vincoli territoriali), immagini (foto di barche, coste, specie, attrezzi), pagine web. Infine, il sistema è stato organizzato in modo che, effettuando differenti interrogazioni ed operazioni quali analisi di dati spaziali (interpolazioni, operazioni di overlay, raster calculator), analisi degli attributi (query o funzioni di ricerca, SQL, summarize, statistics) e analisi integrata (spaziali e attributi), ha permesso di ottenere differenti informazioni nella dimensione spazio-temporale. In conclusione, il sistema è stato predisposto per analizzare e visualizzare i complessi scenari esistenti nell’ambito della valutazione delle risorse alieutiche nella dimensione spazio-temporale (monitoraggio), considerando le caratteristiche ambientali e le diverse problematiche dell’area, in modo da prevedere i possibili scenari futuri (forecasting) creando una modellizzazione della realtà, al fine di: fornire indicazioni nel pianificare una gestione ottimale delle risorse, razionale, integrata e sostenibile, quindi fornire spazialmente una scelta di soluzioni al decisore (Spatial Decision Support System) per la conservazione degli stock ma anche per preservare gli ecosistemi marini; avviare in caso di un’area sottoposta a più vincoli (Riserva Marina, Sito Natura 2000, IBA) una pianificazione concertata e sinergica tra i diversi livelli istituzionali preposti (governance multilivello e interscalare) ed evitare quindi una pianificazione conflittuale o ridondante. Il sistema realizzato potrebbe vedere applicazione nell’ambito delle seguenti pianificazioni: per la realizzazione dei piani di gestione pesca regionali, inerenti il Programma Operativo Pesca - FEP nazionale (Fondo Europeo per la Pesca); per l’elaborazione dei piani di gestione dei Siti Natura 2000; per la predisposizione delle varie fasi della Valutazione Ambientale Strategica (VAS); per la predisposizione di piani territoriali di Gestione Integrata della Fascia Costiera GIZC; nell’istituzione di Aree Marine Protette o Riserve Naturali Marine, Parchi, ed in particolare risulterebbe utile nella pianificazione della zonazione, soprattutto quando in tali aree è presente come forte componente l’attività di pesca, ricoprendo un elevato valore in termini di occupazione, commercio, attività ricreative e quindi di benessere economico.
The objective of this study was to implement a Geographic Information System (GIS) for the monitoring of fishing activities and alieutic resources in the Egadi Islands, as being representative of a few fundamental kinds of small-scale fishing and for various existing environmental restrictions such as the Marine Reserve and Natura 2000 sites. The purpose was to suggest appropriate conservation strategies for both alieutic resources and the environment. In other words, an expert system to decision support, making it possible to visualize complex scenarios in the assessment of alieutic resources in a space-time dimension (Spatial Decision Support System), geared towards spatial planning -for a sustainable use of natural resources- in synergy and coordination among the various authorities in charge. In the study a data-warehouse was set up, geared towards spatial planning and containing various categories of environmental data, a relational database (RDBMS) containing data on fishing and fleets, and a GIS capable of processing, analyzing and integrating heterogeneous data in reference to their respective geographical locations, with the following specific objectives: - Study of the environmental characteristics of the area of focus; - Characterization of the structure of the fleet for each port; - Investigating fishing gear changes in time and space in each port; - Quantitative and qualitative investigation of the species caught; - Analysis of fishing effort and catch per unit effort (CPUE), in time and space; - Analysis of the main environmental -physical and chemical- parameters (temperature, salinity, oxygen, etc.); - Survey of climatic and sea weather conditions; - Identification of species and habitats of high ecological value; - Environmental assessment and management guidelines. In particular, the investigation was carried out on the area of focus, its geological and biological aspects, with special attention to habitats and species of scientific/ecological interest, through bibliographic research and experimental sampling at sea. The investigation on fishing and fleets has been carried out with the following methods: indirect method and direct method. The indirect method has involved weekly collection of data from interviews at landing, over a whole year. The direct method has involved carefully planned sampling trips, using various types of boats and gear of the local fisheries for direct collection of data, also over a whole year. In the sampling process, a GPS (Global Positioning System) was used to record the initial, middle and final geographical coordinates of the fishing gear. Depths of experimental fishing were recorded with an echo sounder. Oceanographical data were obtained on site, with the use of multiparametric probes. Information has been recorded on climatic and sea weather conditions. The GIS was set up using ArcGIS 9.1 software by ESRI. For definitions of topics and to standardize the information collected and filed in the data-warehouse, this has been structured in accordance to the Environmental Applications Reference Thesaurus (EARTh). Data regarding fishing and fleets have been processed and organized in a relational database (RDBMS), which has made it possible to manage geographical information as well as assuring characteristics such as efficiency of performance, access control, redundancy control, thus giving the structure remarkable flexibility also in terms of spatial analysis and the possibility of looking at the various aspects of events. The database has also been enriched with hyperlinks to useful documents (laws, directives, planning restrictions), images (photos of boats, coastlines, species, gear), and web pages. Finally, the system has been organized so as to be able to obtain various kinds of information in a space-time dimension through operations and procedures such as spatial data analysis (interpolation, overlay, raster calculator), analysis of attributes (query or search functions, SQL, summarize, statistics) and integrated analysis (spatial data and attributes). In conclusion, the system has been set to analyze and visualize complex scenarios in the assessment of fishable resources in a space-time dimension (monitoring), taking into consideration the environmental characteristics and various critical factors of the area, so as to forecast possible scenarios and create models of reality with the purpose of: providing indications for optimal, rational, integrated and sustainable resource management, as well as a range of spatial options for decision-makers (Spatial Decision Support System) for the conservation of stock and marine ecosystems; in the case of areas subjected to multiple restrictions [Marine Reserve, Natura 2000 site, IBA (Important Bird Areas)], giving way to a concerted, synergic planning activity among the various authorities in charge (multi-level and inter-scalar governance) and thus avoiding any conflictual, redundant planning. Such system could be applied in the following planning situations: implementation of regional fishing management plans within the national Operational Programme – EFF (European Fisheries Fund); preparing of management plans for Natura 2000 sites; preparation of the various phases of Strategic Environmental Assessment (SEA); preparing of plans for the Integrated Coastal Zone Management (ICZM); institution of Marine Protected Areas or Marine Reserves, Parks, in particular, it would be useful to plan the zoning of this areas protected, especially when fishing activity is strong and of high value for occupation, trade, recreational activities and hence economic welfare.
XX Ciclo
1971

L’esperienza è al giorno d’oggi l’essenza della vacanza, i turisti sono sempre più attivi, alla ricerca di attività che permettano loro di conoscere al meglio il luogo nel quale si trovano. L’interazione con le persone, la conoscenza della storia e la scoperta delle tradizioni che caratterizzano i differenti luoghi divengono l’elemento fondamentale della vacanza. Il presente elaborato si propone di analizzare i principali sviluppi del turismo nel XXI secolo ed ideare una proposta di offerta in grado di soddisfare una domanda di turismo sostenibile e a carattere esperienziale. L’obiettivo è la proposta di un nuovo itinerario e quindi di una nuova offerta turistica nella quale la componente esperienziale diviene l’elemento caratterizzante. L’idea è la creazione di un itinerario completo che colleghi due realtà: Il Parco della biosfera dei Nockebrge e la Riserva naturale marina di Miramare. Questi due luoghi, seppur distanti tra loro (uno in Italia, nella provincia di Trieste e l’altro in Austria, nella regione della Carinzia) presentano caratteristiche comuni: entrambi rientrano all’interno del Programma UNESCO Man and Biosphere ed offrono progetti ed iniziative che sposano la forma del turismo sostenibile e responsabile. Fondamentale è il collegamento tra le due realtà, la mobilità è una delle componenti chiave nell’ideazione di una nuova offerta. In questo caso si parla di mobilità lenta: è infatti attraverso l’Alpe Adria Trail e la Ciclovia Alpe Adria che le due Riserve saranno tra loro collegate. Questi luoghi possono quindi costituire un asset primario per la creazione di una vacanza esperienziale che permetta ai turisti di scoprire il “Genius Loci” del Friuli Venezia Giulia e di una parte della Regione della Carinzia.

Il lavoro di tesi consiste nel primo commento scientifico a 44 liriche scelte dello Splendido violino verde, la quinta raccolta poetica di Angelo Maria Ripellino (1923-1978), pubblicata nel 1976. L’apparato esegetico di ciascuna poesia è suddiviso in un cappello introduttivo, in cui, accanto all’analisi tematica, sono sciolti i riferimenti eruditi, storici e biografici ed è fornito il prospetto metrico, e nelle note esplicative in calce al testo, riservate all’analisi puntale degli aspetti retorici e linguistici e alla creazione di un tessuto di rimandi intertestuali ed extratestuali. Di particolare interesse ai fini del lavoro è stata l’analisi, mai effettuata prima, della agende manoscritte dell’autore, conservate nel fondo ripelliniano dell’Archivio del Novecento dell’Università La Sapienza di Roma. Queste hanno permesso di indirizzare lo studio sul versante della critica genetica, poiché contengono appunti di liriche e stralci di versi che costituiscono gli unici avantesti superstiti della raccolta. La loro consultazione ha, inoltre, svelato in molti casi l’origine e la natura di alcuni riferimenti culti celati nelle poesie, confermando il profondo legame tra la scrittura poetica e quella saggistica e critica dell’autore. Ampio spazio è stato quindi dedicato all’intertestualità e alla ricerca delle numerose e variegate fonti, che spaziano dalla letteratura italiana medievale, moderna e contemporanea alle letterature straniere. Spicca inoltre la presenza di fonti relative ad altre arti (teatro, cinema, pittura e musica) che rendono particolarmente densa la scrittura lirica ripelliniana. Nel saggio introduttivo si è tentato di raccogliere i risultati dell’analisi puntuale dei testi, facendo emergere le costanti tematiche e stilistiche, con particolare riguardo per la facies linguistica della raccolta, caratterizzata da molteplici prestiti lessicali dalla tradizione letteraria, fusi insieme a lessico tecnico, termini quotidiani e numerosi vocaboli stranieri col raggiungimento di uno stridente espressionismo.

A well-established empirical procedure, which we refer to as Weighted Waveform Analysis (WWA), is employed to reconstruct a model riser’s response over its entire length using a limited number of strain measurements. The quality of the response reconstruction is controlled largely by identification of the participating riser response modes (waveforms); hence, mode selection is vital in WWA application. Instead of selecting a set of consecutive riser vibratory modes, we propose a procedure that automatically identifies a set of non-consecutive riser modes that can thus account for higher harmonics in the riser response (at multiplies of the Strouhal frequency). Using temporal data analysis of the discrete time-stamped samples, significant response frequencies are identified on the basis of power spectrum peaks; similarly using spatial data analysis of the sparse non-uniformly sampled data, significant wavenumbers are identified using Lomb-Scargle periodograms. Knowing the riser length, the most important wavenumber is related to a specific mode number; this dominant mode is in turn related to the dominant peak in power spectra based on the temporal data analysis. The riser’s fundamental frequency is estimated as the ratio of the empirically estimated dominant spectral frequency to the dominant mode number. Additional mode numbers are also identified as spectral peak frequencies divided by the fundamental frequency. This mode selection technique is an improvement over similar WWA procedures that rely on a priori knowledge of the risers fundamental frequency or on knowledge of physical properties and assumptions on added mass contributions. At selected target locations, we compare fatigue damage rates, estimated based on the riser response reconstructed using the WWA method with the proposed automated mode selection technique (we refer to this as “improved” WWA) and those based on the “original” WWA method (that relies on a theoretically computed fundamental natural frequency of the riser). In both cases, predicted fatigue damage rates based on the empirical methods and data at various locations (other than the target) are cross-validated against damage rates based directly on measurements at the target location. Results show that the improved WWA method, which empirically estimates the riser’s fundamental natural frequency and automatically selects significant modes of vibration, may be employed to estimate fatigue damage rates quite well from limited strain measurements.

It is said that nature attempts to solve the ‘problem of life’ through evolution. ‘Solutions’ are proposed which are then tested in the world around us. Natural selection ensures that the best characteristics are inherited by subsequent generations. This paper gives details of a new method of automated riser design and optimization using techniques based on evolutionary theory. Genetic algorithms are a subset of evolutionary computation which rely on natural selection to evolve good designs. A given design (e.g. riser system) is represented by a ‘genome’ in which the design variables are encoded in the form of ‘genes’. The optimization software interfaces with an industry standard marine simulation package for design evaluation which gives rise to a great deal of flexibility and few limitations on model complexity. The software can be used for whole system design including multiple risers or as an assistant for the optimization of specific design variables. The software is capable of evaluating systems using both static and dynamic simulations for any number of loadcase scenarios. The design of a titanium catenary gas export riser intended for Statoil’s Kristin semi-submersible platform in the North Sea is used to illustrate the method. The design created by the evolutionary software is a significant improvement on the design created using a traditional approach. The results demonstrate improvements in dynamic response together with a reduction in the riser bill of materials cost of approximately one-third, whilst the time spent on design was reduced by nearly an order of magnitude.

Depleting oil reserves in shallow waters, off-shore oil fields are opening the avenues of new ventures in deep sea conditions. A marine riser is a major component of an offshore drilling and production system that are either fixed or floating in nature. Deepwater risers are quite long and significant currents usually excite natural bending mode that is much higher than the fundamental bending mode. In ultra deep environment currents usually change in magnitude and direction with depth, thereby inducing possibility of exciting multiple modes of the riser vibration due to VIV. Vortex induced vibration analysis has been carried out of a long marine riser in a probable deep sea location. To improve the understanding under deepwater harsh environments, the behavior of the riser under these forces is thoroughly investigated. 3D Nonlinear dynamic analysis of riser is obtained in the time domain using finite element software package ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability analyses of riser. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken using bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo Simulation. The bi-linear crack growth models are found to lead to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.

Marine riser is a major component of offshore drilling and productions systems that are either fixed or floating. Since, a marine riser is intended to remain in station for the productive life of an oil field; it will be exposed to wide variety of hazards, with the potential for environmental damage, structural failure or damage to the material. As part of the design process, there are requirements of structural strength based on criteria referring to failure modes, such as rupture by over loading, fatigue failures, buckling or unstable fracture. 3D Nonlinear dynamic analysis of riser is carried out in the time domain using finite element solver ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue and fracture reliability analysis of riser under random waves and random waves together-with vessel motion. In the present study application of structural concepts for the evaluation of the fatigue resistance of marine risers, including reliability techniques has been presented. The limit state function has been established for cumulative fatigue damage using S-N curve approach and fracture mechanics approaches considering number of parameters, random in nature. Reliability methods deal with the uncertain nature of loads, resistance etc. and lead to prediction of the failure and a rational measure of the safety coefficient. Response surface method (RSM) in conjunction with First Order Reliability Method (FORM) has been used for reliability estimation. The results are compared with Monte Carlo simulation method. The design point important for the probabilistic design is located on the failure surface. The effects of the uncertainties in various random variables on riser fatigue reliability are highlighted.

Risers are fluid conduits from subsea equipment to surface floating production platforms. The integrity of a riser system plays a very important role in deepwater developments. Riser dynamic analysis is an important part to the system design. This paper investigates riser dynamic analysis using the WKB-Based dynamic stiffness method. This paper first presents a theoretical formulation of the dynamic stiffness method. It then combines the dynamic stiffness method with the WKB theory, which assumes that the coefficients in the differential equation of motion are slowly varying. The WKB-based dynamic stiffness method is derived and a frequency dependent shape function is expressed implicitly. The Wittrick and Williams (W-W) algorithm is further extended to solve eigen value problem for a general non-uniform marine riser. Examples of non-uniform riser are analyzed and the results show the efficiency of this method. In addition, a pipe-in-pipe riser system is analyzed for natural frequencies and mode shapes using the WKB-based dynamic stiffness method with the W-W algorithm. The characteristic of the mode shapes is described for such a riser system.

With the development of the offshore oil and gas fields, multiphase transportation technology is becoming more and more important because it’s a cost-effective way for marginal and offshore fields. However, the complexity characteristics of the gas-oil-water multiphase flow, the hard offshore environmental conditions bring huge challenges to offshore platforms, subsea production systems, subsea pipelines and risers. Severe slugs in offshore risers, hydrate and wax block in subsea pipelines and flowlines will appear when the production system is shut down. In this paper, an experimental facility to simulate the riser slug flow is built, and the flow pattern of severe slug is given, the effects of the incline angles and viscosities on the formation of severe slugs in the riser is experimentally studied and analyzed using water-air, oil-air and water-oil and air. On this base, a cost effective real-time recognition technology of severe slug in the riser is present and its related automatic throttle control method has been validated by natural gas and crude oil with the 25m high riser system, which devotes to the future deepwater riser slug control system.

Vortex-Induced Vibrations (VIV) are three-dimensional (3D) oscillations of slender structures that are induced by fluid vortices shedding off the moving structure. VIV is intriguing because the largest magnitude of the oscillations is generally perpendicular to the incident fluid flow. Much of the historical research in VIV has focused on the inducing hydraulics of this fluid/structure interaction. We instead focus on the structural mechanics for valuable insights as to why and how VIV physically occurs. We first review the basic mechanics of a suspended pipeline that is horizontally-oriented and then explore the same for a marine riser that is vertically-oriented. In particular, we will investigate the following: • How gravity and fluid drag curves the slender structures • How this global curvature locally promotes VIV • How period doubling is a natural consequence of geometry • How changes in boundary conditions, shedding periodicity, fluid drag, and fluid velocity affect VIV

Abstract Analytical, experimental and computational models have historically been heavily simplified, linearized, and otherwise reduced. This paper shows how such model reductions eliminate the fundamental geometric changes that determine real behavior in cables, strings, moorings, guys, pipelines, riser, plates, skins, subsea hulls, and other such slender and thin structures. The paper details each physical quantity that we must add back into our overly reduced models to improve the basic nature, evolution, and accuracy of the resulting motions and vibrations. For example, even slight changes in local rotation anywhere along a cable can create large nonlinear changes in the dynamic nature of its behavior. The evolved complexity of the resulting global motions and vibrations in space and time often defy what we normally expect from such a simple structure. Although this paper focuses on the modeling of deep-water moorings and risers of an ocean platform, the same geometric effect is fundamental to most science and engineering models. Understanding how small changes in geometry can nonlinearly affect any structured behavior will help demystify much of the poorly-understood motions and vibrations in a large diversity of applications, including induced vibrations, sound, structural acoustics, aero-elasticity, sound, light and atomic radiation.

The transverse vibratory response of a long, slender vertical top-tension riser, subject to an ocean current, is studied. The problem is treated as a coupled fluid-flow/vibration problem which is solved numerically. The fluid flow part is represented by the 2-D Navier-Stokes equations, with LES and strip theory, which are solved numerically to obtain the flow field and determine the vortex-shedding behavior in the flow. The approach flow is a shear flow ranging in Reynolds number from 8000 to 10,000. Given the flow field and vortex-shedding behavior, the transverse fluid forcing function can be determined at a given instant, which becomes the input to the Euler-Bernoulli beam equation to calculate the displacement of the riser, using a technique that involves the WKB method and modal decomposition. The boundary conditions for the fluid-flow equations are updated each time step as the cylinder moves. The natural frequency of the riser is tension-dominated, not bending stiffness-dominated. With the decrease in tension with increasing depth, the natural frequency is affected. Therefore, the solution will be influenced by the depth-dependent tension. This study has indicated some interesting features regarding the VIV of a variable-tension riser. The vibrational response is greater for a variable-tension riser than for a constant-tension riser, when the variable-tension riser is assumed to have the same top tension as the constant-tension riser. Therefore, it is important to take into account the variable tension when estimating fatigue failures of marine risers.