Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
Offshore platform with large deck area may provide great possibilities to develop ocean spaces which may be used as resident areas, airports, power stations, etc. Since these structures have very heavy dead loads, reaction forces on the base foundation become severe and necessitate very firm foundation system. If these reaction forces can be reduced by some method such as large diameter members of buoyancy-type, the concept of large offshore platforms with the buoyancy type large diameter member may become popular in the offshore industry. This paper investigates the dynamic response of such a structure under the action of sea waves, currents and earthquakes. The equation of motion of the structure is obtained by the substructure method. The response analysis is carried out using frequency domain random-vibration approach and the results are expressed using root-mean-square (rms) displacements and stresses. The long-term behavior of the offshore structure is examined with first passage probabilities of level crossing of extreme responses. It is suggested that reliable evaluation of the dynamic response can be carried out using the reliability method based on the second moment approach. INTRODUCTION One of the possibilities for developing the ocean space effectively may be the construction of large-scale offshore structures. These structures with wide deck areas may be used as residential or commercial areas, airports, waste disposal sites and so on. Since large offshore structures have heavy dead loads, reaction forces on the foundation become severe and require very firm foundations(Kawano et al(l996)). If the reaction forces can be reduced by some method such as buoyancy-type large members, then large-scale offshore structures may become popular. In this study, the dynamic response analyses of offshore platform with buoyancy-type large members subjected to wave loads, current loads and earthquake loads are examined using random vibration approach.
Referring to a real case located in the lower Adriatic Sea (involving the floating exploitation of an oil reservoir in deepwater conditions), the paper presents the first results of new hazard analyses focused upon the role of the components of the production system which are located between the subsea wellheads and the FPSO unit. Therefore, the main concern of the study is the validation of a risk assessment methodology and its application to a real and peculiar study case. The analysis leads to start drawing significant conclusions concerning the most serious accidental events, together with the possible implications related to the occurence frequency and to the dimension of the outcoming consequences. The results of the study outcome in a project-oriented way, as far as project review and editing (e. g.) could be concerned, with particular reference to the impact prevention toward the environment, within a global project overview. INTRODUCTION AGIP Aquila oil field lies in 850 m of water about 45 km offshore Brindisi, mid-Otranto channel, Adriatic Sea, having proved recoverable oil reserves of 20 MM bbl, as far as today's Reservoir Engineering know how can state, with a foreseen peak production of 17000 BOPD;4 oilwells already exist, drilled by SONAT and R.&B. contractors. The heavy environmental conditions and the limited amount of reserves do combine altogether to make the field development extremely complex from many different points of view. The conditions found in deepwater impose the use of absolutely new technologies, where - moreover - the fundamentally economic pressure proper of any small oil field exploitation project requires to strongly drive down the development and operating costs, as already extensively documented in the recent past by careful studies such as: Giannesini et al., 1995.
Abstract A probabilistic framework is presented for determining design global iceberg impact loads for offshore structures, with example calculations provided for a cylindrical GBS (gravity based structure) and an FPSO (floating production, storage, and offloading system). Emphasis is given to the development of efficient simulation techniques, the effect of iceberg rotation on loads, modelling local shape of the iceberg at contact point, and sensitivity analysis to evaluate areas of uncertainty which cannot be treated probabilistically. 1. INTRODUCTION A number of offshore oil production systems have been proposed for the Grand Banks region off Canada's east coast, the two main systems at present being a GBS and a ship shaped FPSO. For both systems the possibility of iceberg impacts must be included in the structural design requirements. For the GBS, consideration must be given to possible impacts with large icebergs that cannot be towed. For the FPSO, design requirements are reduced as larger icebergs can be detected and avoided by towing or moving the system off location. While considerable experience has been acquired in designing for wave loads, experience in designing for iceberg impact loads is limited. As a consequence, it is necessary to place a higher degree of reliance on analytic and physical modelling. Using probabilistic methods, variations in iceberg size and shape, ice strength, detection capability, waveinduced velocity, and impact eccentricity can be accounted for, to the extent that the models and parameter distributions used are accurate. Where data is limited and processes are not fully understood, calculated design loads should be considered as conditional on the particular assumptions used. Sensitivity analysis is an important tool in evaluating the importance of different assumptions, determining if adequate information is available, and choosing a final design value. In Section 4, the development of distributions for the required shape parameters is presented.
ABSTRACT In this study, a trial calculation of design ice loads on a candidate arctic structure for offshore Sakhalin is conducted. Estimation of the design ice loads is performed using a probability based method proposed by the author. This method calculates a probability density of ice loads by the Monte Carlo simulation and produces a return period - ice loads relation from the simulated probability density. The method proposed is briefly explained. Two important elements of the method. the ice load models for possible ice - structure interactions which are specified in interaction scenarios associated with offshore Sakhalin are determined and probability density functions for variables associated with ice and sea condition at offshore Sakhalin are also determined. Some trial calculations are done. And some necessities to apply the method are discussed. INTRODUCTION Japan Oil Industries Association (hereafter, JOIA) has been organizing a research program. The first phase of the program mainly concentrates to establish methods for calculating ice load on arctic structures which have rather simple geometric shapes such as conical and vertical structures. The first phase seems to be successful, then JOIA has decided to proceed his research activity toward more practical aspects. One of new tasks to be dealt with the JOIA research program is an application of obtained knowledge to design a structure in offshore Sakhalin. Ishikawajima -Harima Heavy Industries Co., Ltd. (hereafter, IHI) is assigned to develop a method to set a design ice load. un has developed a method for setting a design ice load to be applicable to a structure in Beaufort Sea. This method is named IDIFES and reported in ISOPE"92 conference(Kato, 1992a). These modifications are mostly made on probability density functions (hereafter P.D.F.) for variable defining the ice and sea conditions at the region in question.
INTRODUCTION The total area of the Sakhalin offshore which is the more investigated and oil and gas perspective part of the Russian territory in the Far - East region constitutes about twenty thousand square kilometers. Exploratory drilling on the Sakhalin offshore has been conducted since 1975. As a result of many exploration several oil and gas as well as gas condensate fields are discovered the largest of which are located on the offshore of the north- eastern Sakhalin coast. The total hydrocarbon resources of the north- eastern part of Sakhalin island are estimated at about 1 billion tons for oil and condensate and 1.2 trillion of cubic meters for gas (Bogdanchikov, Astafiev, 1997). High level of procedure and reliability when estimating these reserves should be noted moreover, the fact that the reliable base of resources on the Sakhalin offshore has been prepared for development should also be stated. The potential oil and gas consumers in domestic market are the Russian regions in the Far East which at present are acute short of fuel (about 10 M tons of reference fuel in volume) (Bogdanchikov, Astafiev, 1997). fu foreign market the main hydrocarbon consumers are first of all the parties of the Asia-Pacific ocean region. As to the "Sakhalin-2" project the first crude delivery from the block of offshore fields is planned in 1999 and under the "Sakhalin-I" project it is planned in 2001. Under the "Sakhalin-I" and "Sakhalin-2" projects fields will be developed in accordance with the Federal law of the Sharing Production Agreements (Federalโฆ. 1995). fu this case each partner of the particular project will have a right for independent using its share of the produced resources. At present several alternatives of produced production unloading to consumers are being discussed.
- Asia > Russia > Far Eastern Federal District > Sakhalin Oblast (1.00)
- Asia > Russia > Far Eastern Federal District > Sakhalin Island > Sea of Okhotsk (1.00)
A copper alloy occurs a slip line, when it receives a deformation of tensile. So as to accompany a micro phenomenon for a slip line, it is difficult to observe 3 dimensional measurement. For Atomic Force Microscopic (AFM), however, it is possible to observe on very micro shape. In this research, it is considered initiation phenomenon of the slip line that is a closely relevant to a fracture for ductility materials. A fracture begins with corroding new surface that occurs by slip in copper alloys. Several test specimens gave a tensile urn-axis loading with various stationary speeds. At that time, several test specimens with various strains were examined surface roughness measurement and were observed by an atomic force microscope. An occurrence frequency of the slip line are investigated from the results. INTRODUCTION Generally, it is said that pure copper is excellent about the ductility. Moreover, it is one of materials with high utility value as an industrial material. When slips were accompanied to pressure, the copper improved malleability and ductility. However, when the new phase according to a slip are corroded the occurrence of the crack might be caused even if it is excellent copper in an environmental strength[1]. In the process concerning a ductility destruction of the metal, the examination concerning the generation of the slip line which is the first change on the surface of metal is indispensable to elucidate valuable information about the destruction mechanism or the destruction cause. The shape of cross section and the size about the slip line generated by tensile test are clarified by the observation of the scanning electron microscope (SEM) which uses the replica method[2]. In the viewpoint of the formation mechanism of the slip lines and the generation frequency concerning the shape of the slip lines, the generation behavior of the slip line is hardly researched.
For more than twelve years the port of Rotterdam has operated a probabilistic admittance policy for tidal-bound vessels. When introducing this method, no decrease in safety was allowed. The chance of touching the channel bottom is therefore limited by safety criteria. The risk taken during the channel trip includes not only the chance of touching the bottom but also the outcome of this event. This resulted in politically and scientifically acceptable criteria. Introduction The port of Rotterdam is one of the biggest in the world. Both the amount of iron ore and the number of containers transhipped increased again last year. Vessels with a draught of up to 22.55m are able to use the approach channel. 350 channel-bound vessels (draught more than 117.40m) arrive at Rotterdam each year. Looking at these figures, one can understand that the Port of Rotterdam has a very high economical value for the Netherlands. To safeguard the port's position, many investigations are carried out to increase accessibility. Vessels with a draught of over 20.00m are tidal-bound. For these vessels (250 each year), the water level is not sufficient. Only at high tide can they reach the port. This results in a restricted period of time during which tidal-bound vessels can transit the approach channel. Specially developed calculation methods have optimised the usage of the restricted time for entering the channel. Another way to increase accessibility is more dredging. However this is extremely expensive. The economic reason for increasing the accessibility of the port of Rotterdam without dredging is however contrary to a safe channel transit. The number of vessels can be increased. Also, the required keel clearance can be lowered. However, both will result in a higher chance of touching the channel bottom, or worse, an accident. The final design is always a compromise between safety and accessibility.
Inspections of tankers and VLCCs are difficult and costly due to the size of the area to be inspected. Still, many inspectors rely on their own experience to perform inspection, instead of using a systematic approach. Trying to develop a more effective inspection strategy, this paper first reviews the current practice of tanker inspection. Past experience with fatigue and corrosion is discussed. Particularly, three fatigue-cracking trend analyses are summarized. The framework of a risk-based inspection strategy is then developed. The risk-based approach used two parameters, criticality and susceptibility, to rate the inspection priority so that structural details with higher risk receive more attention. This approach, named priority assessment, should provide the basis for developing inspection strategies which could enhance the current practice. INTRODUCTION When a tanker or a very large crude carrier (VLCC) starts servicing, its hull structure will be monitored by a series of in-service inspections to assess the integrity of the hull structure. These inspections provide a means to evaluate the current condition of steel and coatings, to detect unexpected flaws and damages, and permit appropriate maintenance and repair measures to be taken to preserve the integrity of the hull structure. Corrosion and fatigue cracking are the most pervasive types of structural problems experienced by tankers. Each of the problems, if not properly repaired or rectified, can potentially lead to catastrophic failures or unanticipated out-of-service time. A way to mitigate these problems is through a proper structural assessment and maintenance process. Inspection is obviously a critical part of this process. A primary function of inspection is to verify the existing condition, identify, record and document defects/damage and monitor the structural performance. One difficulty associated with inspections is its cost. It is well known that the costs of inspection for these damage categories represent an enormous financial burden for ship owners and operators.
- Research Report (0.68)
- Overview (0.66)
- Transportation > Marine (1.00)
- Law Enforcement & Public Safety (1.00)
- Law (1.00)
- (3 more...)
- Health, Safety, Environment & Sustainability (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.68)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.68)
Abstract Fatigue testing under simulated service conditions has advantages over constant amplitude tests. For example the variability in both amplitude and frequency content of service loading can he reproduced by carrying nut tests under simulated service conditions. This means that the complex interactions between environment and loading which govern fatigue crack growth mechanisms in offshore structures are taken into account. Existing fracture mechanics models and fatigue crack growth prediction methods generally rely on using the overall equivalent stress range with a suitable crack growth law for fatigue crack growth prediction under variable amplitude loading. For S-N type analysis this method is by far the hest when dealing with variable amplitude sequences. However. for fracture mechanics (PM) crack growth prediction employed after an in-service inspection schedule. the use of the overall sequence equivalent stress range will not allow for sequence effects to the accounted for. These effects can he significant under service loading conditions as crack growth is largely dependent on the stress intensity fader range-which is a function of stress range and crack size. It is possible that the use of the overall sequence equivalent stress concept in a fracture mechanics analysis procedure may not he robust enough to handle the high degree of variability observed in service as crack growth acceleration and retardation can not account for. A different and mo]'e realistic fracture mechanics hazed approach is required. This paper presents a new fracture mechanics based model for predicting fatigue crack growth in offshore structures. The model relies on the use of measurable sea state properties to determine crack growth associated with each sea state over its duration. INTRODUCTION Fatigue is the main source of structural degradation of structures in the North Sea and has been the focus of many major research programmers.
ABSTRACT The object of this paper is to describe a practical methodology to continuously monitor the safety of complex structures such as offshore platforms. A Level IV nondestructive damage evaluation methodology is one in which damage is not only detected and sized but the impact of the damage on the performance of the structure is also evaluated. The methodology of interest here is a Level IV nondestructive damage evaluation (NDE) method which can nondestructively assess the condition of the existing structure and simultaneously evaluate the safety of that same structure utilizing structural reliability concepts. The methodology proposed in this paper deals with two broad activities:periodic nondestructive damage localization and severity estimation; and the assessment of structural safety based on the results of the nondestructive damage detection. To meet this objective, an established methodology which yields information on the changes ill sectional stiffness properties (e.g., axial, bending, and torsion) from changes in dynamic properties (i.e., mode shapes and frequencies) of the pre-damaged and post-damaged structures is reviewed. Next, an efficient technique to directly assess the reliability of a complex structural system (such as an offshore platform) from the reliabilities of the components of the structure is developed. The efficacy of the combination of these two activities (Le., the nondestructive damage detection and the structural reliability evaluation) is demonstrated using pre-damage and post-damage modal data obtained from numerical simulations of the dynamic responses of a frame. INTRODUCTION During the past two decades, a significant amount of research has been conducted in the area of nondestructive damage evaluation (NDE) utilizing the changes in the dynamic response of a structure. The relative safety of a structure is then quantified as a probability of failure (i.e., the complement of the reliability of the structure).