Contribution of Ergonomics to Workspace Sesign in the Offshore Accommodations Module

Tubular joints are integral components of offshore structures and as such, many codes and standards address their design. The fatigue damage process of tubular joints in offshore structures is inherently variable and uncertain. In addition, potentially, there are important bias and uncertainties introduced by the analytical models used in design codes and standards. Therefore, in the development of reliability based fatigue design and requalification criteria, it is important to recognize these differences and to develop the best estimates of joint fatigue durability. This paper summarizes a study to identify the primary sources of bias and uncertainty associated with assessment of fatigue lives of tubular joints in offshore platforms. Based on the extensive screened test data, the important uncertainty sources of tubular joint fatigue durability has been examined, and the uncertainty models are developed to facilitate development of reliability based fatigue design and requalification criteria and fatigue inspection guidelines for tubular joints in offshore platforms. Introduction The development of the reliability based offshore platform design and requalification guidelines involves defining the scope (class of structure, load cases, etc.) and code format - including definition of characteristics values; selecting reliability measures; assessing uncertainties in loads and resistance; establishing target reliability levels; and determination of factors of safety, and load and resistance factors. Tubular joints are one of the main technical problems and high cost areas in the design, construction and maintenance of steel, template-type offshore structures. The uncertainty assessment of the tubular joints is therefore one of the most important components in the development of the reliability based design and requalification criteria for offshore platforms. The nature of uncertainties of the joint capacity and durability and methods for their modeling and analysis is a key in reliability based structural design of offshore platforms. Similarly, it is a key in development of realistic inspection and maintenance programs for these structures. In the context of development of criteria for design and requalification of platforms1 and floating facilities2 in the Bay of Campeche and development of inspection and maintenance programs for these facilities3,4, this study was intended to address a paradox that had developed from inspections of platforms in the Bay of Campeche.5 This paradox was that when inspections were made of joints in older platforms that were evaluated using detailed fatigue analysis methods6 to have fatigue lives that were in the range of months to years, no cracking could be detected. However, damage was found at other joints where it was not predicted or expected.5 This raised the question of: what was the confidence with the fatigue analyses? The objective of this paper is to summarize development of uncertainty models of the fatigue strength of tubular joints. Following a brief review of uncertainty of tubular joint fatigue durability, the sources of uncertainties in tubular joint fatigue durability are logically organized and quantitatively and qualitatively evaluated. Based on this evaluation, the uncertainty models are developed to facilitate development of reliability based fatigue design and requalification criteria, and guidelines for the inspection and maintenance of template-type offshore platforms.

The purpose of this paper is to analyze teamwork performance in offshore platform design, discussing the contribution of design intermediary also called objects, to establish a connection between collective and individual approaches in design activities. These boundary allow participants to conceive and maintain a shared conception of a problem in which knowledge is structured in applied situations during the decision making process. The nature of the design process is presented stressing the two complementary dimensions - individual and collective - that participants need to integrate to find a feasible solution to a problem. The role played by graphical representations in the design process is discussed, and the association to the concept of objects is also presented. An application to a real situation on offshore platform design is described, showing how a specific boundary object - the electronic mock-up - strongly influence how participants relate, identify the tasks to be accomplished, and make decisions accordingly. The conclusion emphasizes some objects features and suggests some issues for future development.

With the rapid development of offshore oil drilling equipment industry, PDMS (Plant Design Management System) software has been widely used in offshore platform Design. Firstly, this paper combines the application of PDMS in designing the drilling system for deepwater semi-submersible offshore platform, systematically introducing the digital prototype design process based on PDMS software for the design of supporting platform (ship) drilling system. Secondly, we get the application effect of Marine engineering design based on PDMS. Finally, it is concluded that the overall layout of the platform with tight design space and high design density can be better optimized by using PDMS software, which enable multiple professionals to jointly complete the complex design process and explore an efficient Marine production mode.

This paper presents a radically different approach to investigating the upending of an offshore platform structure from a horizontal floating position to a vertical position. Upending motion is caused by selectively ballasting the structure, by hoisting with a barge crane, or by altering any other controllable physical parameter that can affect structure position. A man-computer system is described in which an engineer engages in a graphical dialogue with an interactive computer to perform an heuristic investigation of structure upending motion. Through an experimental process relying more on discovery than proof, the engineer formulates and tests hypotheses about structure responses to physical parameter alterations that are not amenable to rigorous analysis. The system in this way represents an extension of the analytical abilities of an experienced and intuitively motivated engineer, providing the engineer a means for attaining insight into the upending phenomenon through free interaction with the computing system. Used frequently during the overall platform design process, the system can be an invaluable tool for developing upending procedures as part of overall design. A Newtonian analysis of upending motion is discussed, and an analytical model based on hydrostatics is proposed as an alternative approach for simulating structure response as a slow-motion phenomenon. The system structure and command language are described. Guidelines are offered on how the hydrostatic model is used to predict total upending motion by a process of synthesizing the engineer's understanding of incremental structure motions. The man-computer system has been implemented with a simple graphics configuration providing limited graphics capability. A brief example session demonstrates that an heuristic approach to studying upending motion with a hydrostatic modeling technique can be supported. Experiments with a sophisticated interactive graphics system, however, suggest that a far more powerful man computer system can be developed. The expanded range of graphics capability indicate enhanced interactive potential between the engineer and the computer, and represent a desirable and reasonable extension to the system implemented. 1. AN INTRODUCTION 1.1 Nature of the Problem The offshore industry has long been familiar with stationary (or fixed) offshore platforms that are supported by the sea floor with their decks above the sea level. Fixed platforms have served the petroleum industry for more than thirty years as facilities for drilling rigs, production facilities, well protectors and housing for on-site personnel. Non-petroleum applications of offshore platforms range from oceanographic research and weather gathering stations, ship loading facilities for mining operations and offshore terminals, dolphins for berthing complexes in harbors and deep water terminals, and even as stations for harvesting fish. Offshore platform designs vary considerably according to specific environmental conditions and service requirements, and as new requirements arise in unfamiliar environments, designs and construction methods will necessarily change. The platforms of interest in this study, however, consist of a deck structure supported by a tower. The tower is a rigid space frame of long slender tubular shapes, whose legs (column members) are fixed to the sea floor by piles.

The measured static and dynamic response characteristics of four jacket-type platforms in water depths up to 373 feet are described. Fundamental periods and damping were determined both by free vibration tests and spectral analysis of random response data. For each platform, measured end-on and broadside natural periods were nearly equal with values ranging from 1.5 to 1.9 seconds; the theoretically predicted natural period for one of these platforms was close to the measured value. Damping estimates range from approximately 1.0 to 5.0 percent of critical depending on the methods of testing and data analysis. For one platform spectra of both deck motions and wave heights are presented; measured amplitudes of response are compared to theoretical predictions. Motions predicted using regular Airy wave theory overestimate the measured motions for the tested platforms and the low sea states considered. INTRODUCTION Importance of Dynamics. In the design of offshore platforms, the possibility of dynamic response must be considered in the member force analysis. For platforms installed in active earthquake regions dynamic response analysis is mandatory. For regions where extreme waves and high cycle fatigue control the design, the need to consider dynamic response is not as clear. Estimates of dynamic response should first be made with simple models to determine if costly detailed analyses are required. Simple models are also quite powerful for examining a range of dynamic response conditions thus fostering a better understanding of dynamic platform behavior and allowing a more appropriate and efficient use of detailed analysis. In addition, with reference to the subject of this paper, the simple models indicate which parameters are important enough to be considered for experimental investigation. As a first approximation wave forces are often assumed to vary sinusoidally and the familiar steady-state response spectrum for single degree freedom (SDF) systems is used to estimate the importance of considering dynamic response (Figure 1). For this model and idealized force, dynamic amplification factor, AF, is dependent only on the perio9 ratio, R, and the system damping, S. Clearly, AF is large and very sensitive to damping for values of R near one (resonance). Using these curves to estimate the dynamic effect of a 12 second force on a four second structure (R =3.0), AF is seen to be about 1.12, i.e., maximum dynamic response is 1.12 times the maximum static response. For this period ratio AF is nearly independent of damping. Thus dynamic response to extreme waves is predicted to be small and insensitive to damping on the basis of this model. On the other hand, for the fatigue life calculation the waves of interest are much smaller with periods ranging from three to six seconds. For the same example four second platform, corresponding R values range from 0.75 to 1.5. In this region of the response spectrum AF is large and strongly dependent on damping. In fact, when damping is small, the AF at resonance can be expressed approximately as(Equation available in full paper)

A state-of-the-art review of the needs and problems involved in developing improved methods of inelastic dynamic analysis of offshore soi1-pi1estructure systems subjected to extreme earthquake shaking has been completed. It is concluded that dev.e10pment of a design-oriented computer code for three-dimensional, nonlinear dynamic analysis of fully coupled offshore soil-pi1e-structure systems is warranted. Complementary studies of several components of the system model are also required in order to develop user guidelines for parameter selection. The results of this review and a proposed course of action in terms of superstructure and substructure modeling strategy, computer code structure, and parameter selection are described. INTRODUCTION Recent years have seen an increase in the opportunities to pursue development of oil and gas resources in frontier areas which lie within seismically active regions of the world. Renewal of development activity in the Santa Barbara Channel and the recently held lease sales in the Gulf of Alaska and offshore Southern California and the 'East Coast of the United States have quickened the pace. These opportunities bring with them the need to consider earthquake ground motions in the process of criteria selection and design of offshore platforms. The overall philosophy which has developed in recent years to guide the selection of earthquake design criteria for many onshore structures involves a bi1eve1 approach. In principle, this philosophy prescribes a lower level of ground shaking which the structure should be designed to resist without significant damage. Although not always defined quantitatively, this lower level design requirement is intended to represent a condition of strong ground shaking that has a reasonable likelihood of occurring once during the life of the structure. A second higher level of ground shaking is prescribed, which the structure is to be designed to resist without catastrophic failure or loss of life. This higher level of ground motion is intended to represent a condition which has a low probability off being exceeded the life of the structure. As reflected by the current edition of the API-RP2A Guidelines, this bi1eve1 philosophy for defining earthquake design criteria has been adopted by the oil industry for use in offshore platform design. In the terminology used in RPZA, these two design requirements are referred to as "strength" and "ductility" levels, respectively. The implication of the "strength" level requirement is that this base or lower level of ground motion must be resisted in the elastic range. The use of the term "ductility" level underscores the desire to allow, and specifically provide for, controlled inelastic behavior in platform and foundation elements under the unlikely occurrence of severe shaking which is associated with the upper level design event. Although this desire to provide for inelastic behavior under severe levels of earthquake shaking is strongly motivated by the desire to combine cost efficiency with safety in design, there is also good engineering justification.

This paper presents a procedure a coupling of the finite element method and normal mode technique for obtaining the elastic dynamic response of offshore platforms subjected to arbitrary time and space-dependent forces. The finite element method deals with the complexities of the actual problem by reducing it to an assembly of structural elements, with known elastic and inertial properties, connected together at a discrete number of points on their boundaries. The normal mode technique is then used to reduce the resulting matrix equation of order N to the solution of N single degree-of-freedom equations with certain constraints on the assumed form of damping. An example analysis, utilizing this procedure and an actual offshore platform under the action of two different types of dynamic forces, is presented. These forcing functions are: wave forces as determined through the use of a fifth-order gravity-wave theory and seismic forces as generated by the north-south component of the May 18, 1940, El Centro, California, accelerogram. The platform is assumed to respond according to the assumptions associated with the Bernoulli-Euler beam and bar theory. INTRODUCTION In the field of offshore platform analysis and design, as in many other fields, the tools of analysis are derived through an evolutionary process. As knowledge and ability increase for more accurate prediction of the environmental forces on platforms, the methods of analysis must improve to maintain consistent accuracy. The American Petroleum Institute(l) in its Recommended Practice for Planning, Designing, and Constructing Fixed Offshore Platforms recognizes this evolutionary process and encourages designers of offshore platforms to use "all research advances available to them" The advent of high-capacity, high-speed digital computers has revolutionized the field of structural dynamic analysis. In the past the approach was to reduce the structural model to the simplest form, usually an "equivalent"single-or dual-degree-of-freedom system or "equivalent" beam or bar model for which known closed-form solutions to the dynamic equations were available. While this approach gave valuable insights into the nature of the dynamic response problem, it did not give the detailed elastic response information that is possible today. This paper presents a method which the authors believe is the next step in the evolutionary process of offshore-platform dynamic analysis. It is a combination of the finite element method and the normal mode technique. The finite element method more accurately takes into account the geometry of the system than the so-called "equivalent" methods. Although the finite element method and the normal 'mode technique have been known for a number of years, it is only with advanced computer technology that these approaches have been economically feasible for the analysis of large complex structures. This economic feasibility, the increased accuracy of predictions of dynamic forces on platforms in the operating environment, and the desire of operators to construct offshore platforms in deeper water and use them under more hostile operating conditions, will force designers to use more advanced methods of dynamic analysis.

This paper presents the design and analysis of an improved lightweight, bottom-founded, offshore platform for multi-purpose use in support of field development operations in water depths to 500 feet and possibly greater, and in severe as well as in mild marine environments. The concept, an innovation based on current tripod-type structures, utilizes a novel framing support system which results in an extremely efficient design with a broad range of applicability. The development of diverse applications for the concept and an assessment of its limits of applicability are discussed. This paper is of interest to the designer, the engineer, or others wh O are seeking an alternative, straightforward and cost effective approach to the design and installation of offshore platforms. The data presented is useful to those assessing the economic feasibility of an offshore field development. The paper discusses platform performance data, including member stresses, deflections, and natural periods of vibration, and offers criteria related to the environment, payload, and water depth for which the concept is best suited. Estimated platform weight and cost data versus water depth for various environments and development scenarios are presented and compared with data from more conventional platform concepts. It is demonstrated that the improved concept offers significant advantages over current designs. OBJECTIVE OF THE DESIGN This design concept was developed in response to the ever growing need for more cost effective solutions to the development of our offshore hydrocarbons reserves. The objective of the design was to develop an offshore structure that 1) is very lightweight, 2) has a relatively high deck load capacity, 3) is suitable for use in a large range of water depths, 4) is adaptable for the pre-drilling and completion of wells, 5) can be fabricated in a relatively short period of time, 6) can be installed with conventional lifting and/or drilling equipment, and 7) can be easily relocated for reuse at another offshore site where the water depth differs greatly from the first site. GENERAL DESCRIPTION The basic concept is a tripod structure as illustrated in Figures 1 to 3. The configuration shown in these figures is called a "Right Angle" configuration because it appears, when viewed from the side, as a 90° right angle. The right angle configuration offers greater access for the drilling of wells. In a "symmetrical" configuration the apex of the tripod is placed at the centroid of the triangular base. The symmetrical configuration is suitable for those applications that do not have wells. The principal component of the structure is the column. The column is designed as a separately installed element which is lifted or floated into place offshore in a single piece. It may contain risers, umbilicals, sumps, caissons, and other facilities as needed for offshore operations. The column is designed to support a cantilevered equipment deck.

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures. The structural integrity of platform components under the maximum and minimum operating loads of environmental conditions is required for risk assessment and inspection plan development. In-place analyses have been executed to check that the structural member with all appurtenances robustness and capability to support the applied loads in either storm condition or operating condition. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The analysis includes interpretation of dynamic design parameters based on the available site-specific data, together with foundation design recommendations for in-place loading conditions. The SACS software is utilized to calculate the natural frequencies of the model and to obtain the response of platform joints according to in-place analysis then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have important effects on the results of the in-place analysis behavior. The result shows that the in-place analysis is quite crucial for safe design and operation of offshore platform and assessment for existing offshore structures.

The VSC-HVDC technology has emerged as the preferred solution for large-scale transmission of offshore wind power generation due to its flexibility, controllability, adaptability, and environmental friendliness. As a core component of VSC-HVDC, the lightweight design of the offshore converter platform plays a crucial role in determining the economic viability of VSC-HVDC. However, high-voltage and large-capacity offshore converter platforms involve numerous internal components and complex spatial distributions of multiphysical fields, posing significant challenges to achieving compact and lightweight designs. This paper aims to deeply explore the distribution laws of multi-physical fields and their influencing factors of the offshore converter platform through multi-physical field simulation technology, provide theoretical support for research in related fields, and offer references for the future design of offshore converter platforms.

The influence of mooring system in rogue wave impact on an offshore platform

As the result of safety factors considered in load and resistant values for the design of new offshore platforms, a higher resistance compared to the 100 year return period environmental loading, is achieved in the structure. This type of design is usually performed using linear methods of structural analysis. In this case the structure practically has a high reserve capacity which is disregarded in the design phase but may be considered in special cases. One of these important cases is when an existing structure is assessed and evaluated after elapse of its structural life. In this case using the platforms reserve capacity, through a non-linear analysis such as push-over, would be logical and economic. In this paper initially the factors affecting a platform non-linear analysis and methods for considering non-linear characteristics of structures will be discussed. Then the results of an investigation on the behavior of three Persian Gulf platforms due to wave loading using the non-linear push over analysis method of USFOS software are presented. Finally, the results of these analyses are compared with the API RP2A’s assessment criteria [1].

The paper presents a systematic study of the structural loads induced by abnormal waves on a FPSO. This work is a follow-up of a previous investigation that explored the possibility of using freak, abnormal or episodic waves as additional wave load conditions to be considered in the design of ships and offshore platforms. In the previous work, a procedure was developed and implemented to adopt deterministic time series of wave elevation, which may include abnormal waves, as reference design conditions to calculate the wave induced structural loads on ships. An application example was presented for a FPSO subjected to the well known New Year Wave trace that was measured during a severe storm in Central North Sea. In the present paper, the same procedure is applied to obtain the wave induced structural loads on a FPSO, but a systematic investigation is carried out by using a large set of wave traces. These wave traces have been measured at different occasions in the North Sea, additionally at one location in the Central Gulf of Mexico, and they all include episodic freak waves. In this way it is possible to assess the influence of realistic rogue wave characteristics on the wave induced structural loads. Finally, and based on the platform responses to all wave traces, some statistics are produced, regarding the platform responses and structural loads induced by rogue waves.

Safety in the design of offshore platforms: Integrated safety versus safety as an add-on characteristic

Using floating platforms to support offshore wind turbines will be necessary for many countries to reach their Net-Zero targets, since much of the wind resource is located at water depths at which fixed offshore wind turbines are uneconomic or technologically unfeasible. However, floating platforms for wind turbines are still at an early stage of development, and there are a wide range of platform designs. This paper reviews the current state-of-the-art of floating offshore wind turbine platform designs which currently have or have previously had a prototype, demonstration, or farm scale project at sea. The most common design goals for the platforms and the corresponding design features of platforms used to achieve those goals are reviewed. Past, current and projected future levelized cost of energy values for floating offshore wind are reviewed and discussed. The development of each platform design is described, including evolving design goals and resulting changes in platform features. Finally, overall trends in platform designs are discussed and divided into three phases, defined by changing goals: (i) influences from the offshore oil and gas industry, (ii) specialization to floating offshore wind, and (iii) further specialization to local environment.