ABSTRACT This paper describes an original approach to reduce drastically the analysis time needed for fatigue design of structures by using machine learning techniques. The approach is applied to the spectral fatigue analysis of various structural details on a converted FPSO hull, where design iterations are usually time consuming. For the structural detail example used in the present study, numerical results show that by including the right inputs to the machine learning algorithm, the predicted fatigue life could compare well with the spectral fatigue analysis output with a score of up to 0.997. For the critical elements with high fatigue damage, the predicted fatigue life is found up to 2.5 times of the actual value. Overall an estimated 5.5 hours (out of 6 hours) are saved for one iteration of spectral fatigue analysis. INTRODUCTION Ocean developments for oil and gas and renewables involve site specific floaters designs. For such assets, it is required to perform detailed structural analysis at the design stage to consider all the specificities of the structure and the environments in the design and make sure the floater can operate safely throughout its design life. For fatigue design, the state of the art approach for such floaters is spectral fatigue analysis. The calculations of the fatigue damage using a full spectral direct calculation approach is labor intensive, especially when design iterations are needed. The complete assessment procedure comprises hydrodynamic analysis to compute wave-induced loads; structural analysis for both global coarse mesh and local fine mesh finite element models; statistical analysis to calculate the short-term stress response based on the environmental conditions on site; and lastly fatigue strength evaluation using the applicable fatigue S-N curve. This analysis approach can be rather time consuming in cases where many structural details are assessed or where multiple iterations are needed to reach a satisfactory design.

Abstract In the study, the results of a statistical modeling of global ice loads from drifting ice features on the "Molikpaq" (PA-A) ice-class platform for "Sakhalin-II" Project are investigated. The authors made a comparative analysis of ice loads on wide structure in the ice conditions of the Sea of Okhotsk according to the procedures and guidelines from different Codes. The cumulative distribution function and design ice loads on this platform is received, recommendations for future estimation of ice loads on Sakhalin offshore platforms are discussed.

ABSTRACT: The most reliable source of defining water resistance to the vessel's motion is testing models in a testing tank. In this case, a number of features associated with the realization of similarity streams coefficients and a small measured section are arisen in small test tanks. The Far East testing tank in KnASTU belongs to the category of a small one. It includes two towing systems with measure complexes, wave-maker, lifting bottom which simulating shallow water, model and bench areas. The problems associated with large-scale effect because of the limited length of the model up to 4 meters, turbulence of boundary layer and control of rate flow are under review. Methods related to exception of the instability of the test results (smoothing procedure) and the approximation of the results are proposed. Procedures of predicting the velocity of uniform motion of high-speed models are developed in the case when section of the uniform motion is absent. The method of receiving the accompanying test results - the definition of the apparent mass of water is pointed out. All this allows extending the small testing tank facilities. INTRODUCTION The testing tank in Komsomolsk-na-Amure State Technical University is an educational and scientific experimental complex. The testing tank belongs to the category of a small tank because its metal basin has dimensions L × B × H = 40 × 4 × 3 m and dock part has dimensions L × B × H = 4,5 × 1,6 × 3 m. Towing models in the tank can be carried out by two independent drives - towing carriage and gravitational towing system (GTS). At the end of the tank plate wave maker is installed, providing a sea-way of a given intensity with opposite direction according to the motion of model.

ABSTRACT: In the study, the problems of a statistical modeling of ice loads from drifting hummocky features and level ice fields on the reinforced gravity based structures in Piltun-Astohsky and Lunsky fields offshore Sakhalin are investigated. The authors made a comparative analysis of ice loads on various types of gravity based structures in conditions of the Sea of Okhotsk according to the standards, procedures and guidelines from various codes of design. And also the probabilistic model of ice loads, developed by the authors in the previous studies, was considered for comparative analysis. INTRODUCTION Practical realization of oil and gas projects in the Far East has started with "Sakhalin I" and "Sakhalin II" Projects under which four reinforced- concrete gravity producing platforms, like "Orlan" ("Sakhalin I"), "Piltun-Astohsky-A" (PA-A or "Molikpaq"), "Piltun-Astohsky-B" (PA-B) and "Lunsky-A" (LUN-A) ("Sakhalin II") were built on 30-50 m depths. Nevertheless, to provide reliability, safety and to decrease risk of operation of similar structures remain a problem till now. Durability and reliability of the ice-resistant structures depends on validity of calculation of the ice loads from ice features of a various age and nature (such as drifting level ice fields, the hummocky and rafting fields, separate hummocks of large size, grounded hummocks, etc.). Thereupon the problem of comprehensive study of ice impacts and development of methods of calculation of ice loads on the offshore hydroengineering structures remains urgent in world practice for more than one decade. The existing design codes from USA and Canada (API, 1995; CSA, 2004; ISO, 2007), and also some other countries, are grounded on experience of design and exploitation of fixed platforms for environmental conditions of Cook Inlet, the Beaufort Sea and Bohai Bay, where platforms of pile type and gravity-based concrete structures were applied.

ABSTRACT: The solution offered in the study is directed to taking into account joint operation of the spatial beam structures of offshore facilities and the pile foundations loaded by them. The content of this method is an application of a simple design beam model of piles which exactly describes behavior of a top part of actual piles affected by external loads in elastic setting. INTRODUCTION One of the most widespread structures of the marine oil-and-gas platform bases are spatial beam structures from steel. Similar structures, as a rule, are installed in nonfreezing water areas at maximum 500m depth to or at small depths in case of small thickness of an ice cover (Fig. 1). The piles of various types are applied as the base of such offshore structures most often (Fig. 2, a). Joint calculation of a spatial beam structure of a support with system of the piles transferring the load on the ground of the base is rather complicated and it requires application of the specialized program systems and the great deal of time. Therefore at a stage of a preliminary choice of a variant of the base (configuration of the piles, a way of their immersing, length and cross section) the simplified methods are applied, as a rule that consist in separate calculation of the top structure and the substructures. At the preliminary stages of calculation it is used to consider that the top structure should be separated from the substructure at the set-off level (Рис. 3, a). Thus top structure is calculated individually under condition of fastened supports of a spatial structure. Such method is rather simple and it allows to define the key parameters of the future foundation in order to go to more difficult testing calculation further.

ABSTRACT: Strength properties of ice fields in marine areas have high variability in space and time. That's why there appears an uncertainty in ice load analysis which may cause poor accuracy. Hence, it's necessary to consider parameters of both ice-structure interaction and ice structure inhomogeneity when assuming calculated ice strength. In the paper we show that it is necessary to take into consideration ice cover spatial inhomogeneity. A program of experimental investigation of ice cover spatial inhomogeneity is presented that allows taking this issue into account when considering ice strength distribution. Analysis of results is also presented. INTRODUCTION Ice loads on off-shore structures in the northern seas are often predominant and, as a rule, they affect main parameters of such structures. Oil and gas extracting platforms are very expensive and they need numerous maintenance staff. Failure of the structure may cause ecologic calamity and even human victims. Hence it's obvious how it is important to make proper distribution of ice loads calculated values. Ice loads on off-shore structures depend on numerous factors, such as geometric size of ice structures, ice structure, drift speed, ice weight, strength parameters of ice structures, combinations of various ice effects, weight of adjoining water, size of the off-shore structure, etc. Strength of sea ice varies in space and it varies with time. That's why proper estimation of ice strength is very important for more accurate analysis of ice loads. From this point of view the most effective way is to divide perennial process of ice-structure interaction into two processes made in different time scales, such as long-term and short-term periods (Bekker, 1990). Perennial field observations and defining of probable distribution of ice cover main parameters will allow explaining ice properties variations in space and time all-over the process of designed structure exploitation (long-term period).

ABSTRACT: After six years of negotiation the Antarctic Treaty Consultative Parties (ACTPs) reached agreement on a Convention for the Regulation of Antarctic Mineral Resource Activities (CRAMRA). The agreement is not a code of detailed regulations, but rather a set of standards and criteria upon which decisions about possible future Antarctic mineral resource activities must be based. Five institutions are established to administer the entire process. Activities must proceed in three distinct stages: prospecting, exploration and development. No activity can proceed beyond prospecting unless there is a unanimous decision by the Commission to open an area for exploration and possible development. Decisions for mineral resource activity cannot be made until there is adequate informat10n to make informed judgements on the possible environmental impacts. No activity can ta~e place unless the technology and procedures are available to: meet the strict standards of the treaty, to monitor the impact of the activity, and to respond effectively to accidents. The agreement contains many restraints and controls on mineral resource activities. Any operation that poses an environmental threat can be shut down. It 1S apparent from all the checks and balances in the convention that it is not an open invitation to develop the mineral resources of Antarctica. Although the future of the agreement is somewhat clouded, what is clear is that it will be many years before there is any significant mineral resource activity in Antarctica, if ever. NOMENCLATURE Antarctic Treaty: An international treaty for the preservation and protection of Antarctica. The Treaty dedicates Antarctica to peace and peaceful pursuits. The Treaty was brought into force in 1961 with 12 nations as the original signatories: Argentina, Australia, Belgium, Chile, France, Japan, Nell Zealand, Norway, South Africa, Soviet Union, Un1ted Kingdom and United States.

ABSTRACT: This work deals with the types of nonlinearities of the sea bed ground, those arising in offshore pile activities. The iteration methods of nonlinear ground computer calculation were proposed. The modification of Murzenko" s model (1966) was given with the account of plastic strenthening-disstrenthening and. dilatation. This nonlinear-elastic approach is an effective one in solving the problems when offshore platforms" and port facilities" design takes large pile displacements into an account. The results of calculations of test experiments showed a satisfactory convergence. INTRODUCTION Steel tube pile foundations are widely used for port hydro technical construction and for shelf platform erections for oil-gas extraction. The piles accept considerable horizontal loads from its upper part exerted by waves and ice. Calculation and pile foundation design techniques are highly requires because of the high costs and reliability of offshore structures. Lengthy piles and complex variable geological conditions give rise to a set of nonlinear factors affecting "the pile-ground" system interaction. It" s very important to take into account the pile disconnection and its sliding along the ground, pile spatial work along with formations of diverse stress states, pile group effect, in the ground. The paper presented describes the techniques of ground rigidity calculations required for pile evaluation accounting physical and geometrical nonlinearities. The techniques developed afford to combine the calculations of "the upper structure - pile group - ground". NONLINEAR ELASTIC APPROACH FOR MEDIA WITH LARGE DEFORMATION At large pile displacements an immence deformation is developing in the ground, and the hypothesis accepted small deformations becomes untrue. Here it is used the non-linearelastic approach based on nonlinear dependence between stresses and strains taken to be common in all points in the ground rook. Elastic and non-elastic deformations are not divided and empiric "stress - elastic-plastic deformation" relationship is used.

ABSTRACT: This paper is concerned with the optimum design of stringer-stiffened cylinder found in tension leg platforms based on the component reliability. In the context of structural design, a major goal is to achieve a balanced design between safety and cost, that is, the design should probably based on the structural reliability. The total cost is minimized, which is composed of the structural cost and failure cost, with constraint on the allowable reliability index and some design requirements drawn from various design codes. The numerical results with varying the number of design variables considered in the optimisation procedure are derived and optimum designs are compared with the minimum weight designs from the view point of safety. The present results provide a more efficient design than the rule-based design in use at present and it is drawn that the minimum weight design may lie on the unsafe side. The paper ends with a discussion of the present results and an extension of the concept toward a more economically efficient design of such kind of structures. INTRODUCTION In view of the inherent random nature of the loading and the strength as well as the imperfect structural analysis and load estimation, the structural optimization needs to be based on the structural reliability. the last two decades we have seen much work on the reliability- based optimum design linked with the classical deterministic optimisation formulations. It has been proposed for some times that a more rational criterion for structural design is that safety be represented by the reliability or alternatively at the failure probability of a structural, and hence the reliability constraint should likely be included in the re-design and the optimisation process to get a more efficient design (Kishi et al,1985, Frangopol,1985, Corotis and Soltani,1985).

ABSTRACT: This paper presents a method of static analysis of a marine cable spanning two fixed points. The top tension of the cable is given, while the total arc length, equilibrium configuration, and top and bottom angles are to be determined. In the analysis, a functional is Introduced in which the potential energy of stretching and virtual work done by other forces are included The stationary condition of the functional and one of two equilibrium equations are used to solve the problem. Application of the finite element method yields a system of nonlinear equations, which is solved using the Newton-Raphson iterative procedure. Accuracy of the method is demonstrated by a comparison of the numerical results obtained with those of a catenary and a neutrally-buoyant cable. INTRODUCTION In many designs, the top tension of a marine cable or mooring line spanning two fixed points is specified. The specified tension may be governed by the strength of the cable, the capacity of the Installation equipment, or the desired top force for operation. The problem of static analysis for the cable, therefore, is to find the cable configuration and the total arc length when the top tension is given. In contrast, an alternative problem is to find the configuration and maximum top tension with a given total arc length. This paper focuses on the former problem. Although the governing differential equations of a cable segment are simple, explicit solutions can be obtained only for simple cases due to the nonlinearity In the problem and, in general, solutions are obtained by numerical techniques. Literature of the analysis of mooring lines and cables can be found In several text books, for example Berteaux (1976), Irivne (1981), and Leonard (1988). Extensive reviews are given by Migliore (1979) and Webster (1982).

ABSTRACT: This paper presents a quasi-static mooring analysis model to assist the designer in predicting the performance of a jetty mooring system at exposed locations. The analytical model is based on the quasi-static method using the load incremental method and allows nonlinear elastic behavior of the multisegmented mooring lines. This model will aid the designer to provide quick optimal results of ship movements and mooring line and fender reactions for various alternative mooring arrangements. Results of computer programs were compared with the model test results of ballasted 250,000 DWT tanker moored to an offshore jetty. From the results it may be concluded that the quasi-static analysis model developed in this study could be used to determine the vessel excursions, mooring line forces and fender reactions. 1. INTRODUCTION For the design of the mooring system of a ship moored at locations exposed to wind, current and waves, it is essential to have the knowledge of the method to assist the designer in predicting the performance of the mooring system. This paper utilizes a quasi-static mooring analysis model (Chernjawski (1980)*) to find more suitable and safer mooring system by means of mooring lines and fenders under severe weather conditions. In general, the design of an appropriate mooring system depends on water depth, ship size, allowable motions of the moored ship and the external forces. Whatever type of mooring arrangement is selected, the size and number of mooring lines will depend on the external forces present such as wind, current and waves. The quasi-static method assumes the wind and current forces to be static and the wave induced forces to be dynamic. In addition, the wave induced force can be decomposed into two parts: the first order high frequency wave forces and the second order mean and slowly varying wave drift forces.

Abstract: In this paper a simple numerical procedure has been proposed to predict the probable extent of damage to tubular members due to collisions. In the procedure a tubular member is reduced to a spring-mass system having two degrees-of-freedom, one for local denting damage and the other for overall bending damage. Results of impact tests have been correlated with those of numerical analysis in order to achieve an empirical representation of the strain-rate sensitivity and other dynamic effects upon the spring coefficient for bending deformation. Reasonably good correlation between the theoretical estimates of damage by the proposed procedure and the test results is realized. A rigorous parametric study has been conducted to calculate local denting damage, overall bending damage, maximum spring forces and plastically dissipated energy for various values of geometric and material property parameters and speed and mass of the striker. Simple design equations are then derived based upon the parametric study results. 1. Introduction For more efficient design of offshore structures considering offshore collisions it is necessary to be able to predict the probability of occurrence of minor collisions, the consequential extent of damage and the residual strengths of the damaged structures. In this paper, however, only the extent of damage of offshore tubulars due to minor collisions will be considered. A question may be raised whether offshore minor collisions can be considered as quasi-static phenomena or need to be treated as dynamic ones. An experimental study was carried out by Arochiasamy et al.[l] on the response of a hydro-elastic semi-submersible to bergy-bit impacts. It was observed from the experiments that the rebound velocity of the bergy-bits after impact were approximately 70 to 75% of the impact velocity. A series of lateral impact tests on tubulars having simply supported roller conditions were conducted by the authors[2].

ABSTRACT: The paper discusses problems of the pipeline construction In severe environments and considers approaches to selection of materials and construction techniques for arctic pipelines. In particular, it covers such aspects as pipeline burying in frozen soils with the use of ditch bottom polymer foam paddling and pipeline anchoring in permafrost, with some anchor design configurations illustrated. Mention is made of the use of enameled pipes and their Joining methods. Useful application of brazing is reported. INTRODUCTION At present, high pace of construction and quality of pipelines laid under extreme climatic conditions such as those existing In the USSR arctic and subarctic areas, permafrost, bogged and flooded terrains of the West-Siberian region are feasible only through using new materials and procedures. The Arctic dry land is a terrain with widespread permafrost soils having a temperature down to -10 deg C, laced with bogs, lakes, numerous streams and creeks. Grounds of Arctic regions vary. The surface is composed of permafrost sands, loams, sand loams, peats, gravel, etc. The ground components are ice-consolidated with the ice contents factor being of 0.4 - 0.8. On the top, the grounds have the tundra moss-and grass cover. In summer, the grounds are subjected to intense thawing, with seasonal thaw penetration depth of 2 - 2.5 m. With thawing, they lose their load carrying capacity. The tundra topography is mostly level, and in summer, the terrain is flooded over vast areas. Accomplishment of construction jobs in these adverse environments involves extremely serious difficulties raised by the necessity to adhere to stringent ecological requirements. Basic requirements to be handled when laying pipelines in Arctic regions With very sensitive and easily destroyable tundra vegetation cover as follows: preserving moss-and-grass cover In its natural state, providing drainage facilities, and doing the job In winter on frozen ground, with using ground-or snow-built work pads. Special environment of construction jobs In Arctic conditions specify requirements for the pipes, procedures and facilities.