Design and Feasibility Assessment of a Jack-Up Offshore Platform for Small Launch Vehicles

With the development of the ocean resources, the design of the offshore platform attracts increasing attention. The wave load computation is an important part for the design of the offshore platform. Currently, model experiments are mainly used to get the wave load of the offshore platform, which is complex, inefficient, and error-prone. To improve the efficiency of calculation, more simplified formulas for the wave load computation were deduced based on the wave diffraction theory. Moreover, a simple method was proposed based on the Matlab and software was developed to calculate the wave load. Experiments were conducted by a designed cylinder floater model to obtain the values of the wave load. Some simulations were made to calculate the wave load under the condition that water depth, wave frequency and other relevant parameters were same with the experiments. The wave load values calculated by the software had similar change trends with that of the experiment data, which proved the feasibility of the formulas for the wave load computation based on diffraction theory and the accuracy of the numerical algorithm in the computation of wave load based on Matlab. Compared with the model experiments, the software based on the diffraction theory was a cheaper and convenient way to obtain the values of wave load when the platform in the ocean is designed. So the new method will improve the efficiency in the wave load computation and is in favour of the design of offshore platform.

Station-keeping is one of the important factors in the design of offshore platforms. Some offshore platforms, such as Spar, Semi-submersible and FPSO, use mooring lines as a mean for station-keeping. Tensions in the mooring lines are one of the key factors in station-keeping. The design of an offshore platform and its mooring lines is based on computed motions of the platform and associated mooring line tensions from numerical simulations using a software code on the basis of metocean criteria. This paper presents an Artificial Neural Network (ANN) model for the prediction of mooring line tensions based on the motions of the platform. This ANN model is trained with time histories of vessel motions and corresponding mooring line tensions for a range of sea states from the results of numerical simulations. After the model is trained, it can reproduce with great fidelity and very fast the mooring line tensions. In addition, it can generate accurate mooring line tensions for sea states that were not included in the training, and this demonstrates that the model has captured the knowledge for the underlying physics between vessel motions and mooring line tensions. The paper presents an example of the training and the validation of the model for a semi-submersible offshore platform for a range of sea states. The training of the ANN model employed a back-propagation learning algorithm. In this algorithm the computed output error is back-propagated through the neural network to modify the connection weights between neurons. The training started with a small number of hidden neurons, and the model grew adaptively by adding hidden neurons until either the target output convergence is achieved or a maximum number of additional hidden neurons is reached. The ANN model discovers nonlinear relationships between the input and output variables during training. The paper presents comparison of time series of mooring line tensions for sea states that were and were not included in the training between those from the numerical simulations and those computed by the trained ANN model. Fatigue assessment is also used to quantitatively measure the accuracy of the ANN model prediction of the time series of mooring line tensions. The paper presents the results of fatigue assessment using various stages of the ANN models with different number of hidden neurons. This shows that the additional hidden neurons improve the prediction of the ANN model of the mooring line tensions for sea states that were and were not included in the training. This approach of prediction of mooring line tensions based on vessel motions using ANN model paves the way to the development of an ANN-based monitoring system. Also, this ANN study demonstrates a great potential for the use of a more general and comprehensive ANN model to help monitor the dynamic behavior of floating systems and forecast problems before they occur by detecting deviations in historic patterns.

Analysis of wind load effect on key components in a jack-up offshore platform

Soil-response considerations in areas of potential seismic activity can be important to the design of an offshore platform and its foundations. Many of these considerations are similar to those for onshore structures. Here, the geotechnical aspects of seismic design of offshore platforms are reviewed, with special attention to template-type structures supported on piles. Introduction Fixed offshore platforms are being designed and constructed in many parts of the world, including areas of potential seismic activity. Soil-response considerations in these areas can be an important part of the seismic design of the platform and its part of the seismic design of the platform and its foundations. Very little observational data are available regarding the behavior of such platforms during strong earthquakes. However, many of the considerations are similar to those for structures located on land. Important factors that influence soil response for offshore or onshore structures include the regional seismicity and the distance of the structure to faults, and the type, physical characteristics, and geometric distribution of the foundation soils. A factor that is specific to the offshore environment is the presence of a body of water above the soil deposit. The effects of ocean waves deserve special consideration because of the importance they may have in determining soil properties, and also because of the general similarities between wave and earthquake motions. This paper presents a review of geotechnical aspects related to the seismic design of offshore platforms. Only template-type structures supported on piles are considered, but most aspects discussed in the paper also would be applicable to gravity-type structures placed directly on the sea floor. Examples are presented at the end of the paper for illustration. Geotechnical Aspects The occurrence of an earthquake results in energy propagating away from the earthquake source in the form of propagating away from the earthquake source in the form of seismic waves traveling in the earth's crust. Part of this energy is transmitted to the soil materials at a site, from the soil, the energy is transmitted to structures through their foundations. In many cases, only horizontal motions need to be considered because (1) horizontal ground accelerations during earthquakes are usually larger than vertical accelerations, and (2) horizontal seismic forces are often more critical for the design than vertical forces. In some cases, however, vertical motions are equally as important and should be considered. For the typical situation sketched in Fig. 1, in which all soil and rock layers are horizontal, it is reasonable to assume that horizontal motions are caused mainly by vertically propagating shear waves. The rock acceleration time history can be considered as the input to the system. For free-field conditions (that is, far from the platform structure), the soil motions will be determined only by the input and the characteristics of the soil. The presence and depth of water above the sea floor will not influence ground response; water cannot transmit shear and, therefore, the sea floor will behave essentially as a free surface. Therefore, the analysis reduces to that of a shear beam of soil subjected to a base excitation. Waves other than vertically propagating shear waves may be contributing to horizontal ground motions. These include shear waves propagating at an angle to the vertical and surface waves propagating in a horizontal direction. JPT P. 244

Design And Construction Of Deep Water Platforms

Tubular-joint ultimate-strength equations that are helpful for offshore platform design are presented. The formulas are based on data from 346 platform design are presented. The formulas are based on data from 346 joint tests. They are easy to use and cover more joint configurations than do present design formulas. Introduction The sizing of tubular joints for ultimate strength is an important step in the design of offshore platforms. This process is performed once platform members have been designed to withstand operational and severe environmental loading conditions. Even though nominal member stresses may be at reasonable levels, the complex behavior of tubular intersections can result in highstress amplification that can lead to failure. In many cases, the walls of joint cans must be thickened or member diameters must be increased to provide adequate strength. The procedure for designing tubular joints must be simple and should lend itself to automation to handle the large number of joints in most platforms. Considerable computer output must be screened to determine maximum applied loads at each joint. Predicted joint strength must be calculated for each member intersection and compared with the applied loads. Joints with deficient capacity are then sized again. At present, empirical expressions represent the state of the art for predicting the ultimate strength of tubular joints. They are based on axially loaded laboratory joint tests. Very little ultimate-strength data exist for bending or combined axial and bending loads. Consequently, bending and combined loading effects are usually accounted for in an heuristic manner. Analytical methods have not been successful because of the geometric, computational, and analytical complexities involved. The finite-element method probably could be applied but would be too costly, time-consuming, and complicated for practical joint design. To be acceptable, a finite-element model would have to include nonlinear material behavior, a fracture criterion, and, possibly, nonlinear geometric terms to account for local buckling. Thus, for the short term, the empirical approach seems most practical. practical.This paper presents a new set of joint-strength equations that are helpful for platform design. The expressions are based on more data and cover more joint configurations than present procedures. The formulas are presented along with some comparisons of the new presented along with some comparisons of the new predictions with those of current methods. An example predictions with those of current methods. An example problem is also given to illustrate how the equations are problem is also given to illustrate how the equations are used in joint design. Tubular-Joint Failure Behavior Part of the problem in analytically predicting Part of the problem in analytically predicting tubular-joint strength is that many competing failure modes are possible in even the simplest of joints. Thus, it is possible in even the simplest of joints. Thus, it is helpful for designers to have some insight into failure mechanisms to produce both safe and efficient designs. In the following sections we review a number of potential failure modes for simple T-, X-, and K-joints to point out trends in joint behavior and important design considerations. For purposes of this discussion, the chord and branch members are as defined in Fig. 1 (Type 1). The chord generally has a large diameter and larger wall thickness than the branches. The branch members are coped and welded to the chord wall to form the joint. JPT P. 449

The growth of the offshore industry into newer regions - including seismic regions - requires a detailed understanding of the earthquake design of offshore platforms. Guidance is provided in ISO 19901-2, " Petroleum and natural gas industries, Specific requirements for offshore structures, Seismic design procedures and criteria." This was adopted almost in it's entirely by API in 2013 in the form of API RP2EQ, " Seismic Design Procedures and Criteria for Offshore Structures." This paper provides supplemental information to these ISO and API standards with the intent to provide additional guidance to engineers analyzing and designing platforms in earthquake regions. The guidance is based on practical application of these standards over the past few years on platforms located in different worldwide regions. Issues discussed include: historical development of seismic guidelines; the importance of ductility in a platform design; Pushover and Time History analysis procedures; definitions of platform collapse; and, pre-planning for post-earthquake actions. Historical Development of Offshore Platform Seismic Guidelines Offshore platforms have been designed and installed in seismic regions since the 1960s when the first platforms were installed offshore California. These early structures used the onshore seismic design practice contained in the Uniform Building Code (UBC) of the time. The first specific guidance for seismic design for offshore platforms appeared in the API RP 2A (RP2A)" Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms," 1st Edition published in October 1969 and contained specific reference to the UBC including the calculation of an equivalent lateral seismic design load using a special structure design factor for offshore platforms. However, the guidance was limited to only a half page of the sixteen page document. The API RP 2A 3rd Edition issued in January 1972 maintained the UBC guidance but was the first to specifically also mention dynamic analysis as an option, although the guidance was limited to a small paragraph.

Nowadays, there are a lot of oil and gas exploration activities all over the world, especially offshore. Oil and gas production itself has many supporting factors in the production process, of which one of them is the offshore platform. Over time, the offshore platform will experience a degradation in strength from the initial design, therefore offshore platforms need to carry out appropriate inspection, maintenance and repair (IMR) programs so that the offshore platform does not reach critical conditions and disrupt the oil and gas production process, resulting in significant losses and not achieving the planned production rates. The offshore platform design is a combination of steel structure and other materials, methods, and loads that are initially worked at the port, such as wave loads, currents, and several other parameters such as gravity, wind, and earthquake. Most of the offshore platforms that currently exist (worldwide) were made in the period of oil investment that developed between 1970 and 1980, thus, the platform's age has now reached 40 to 50 years (El-Reedy, 2012). This research data based on a platform in the Makassar strait between the islands of Kalimantan and Sulawesi. The method used in this research is the platform's design, data observation, data analysis, data processing, and statistical multilinear regression analysis. This research is investigating the degradation trend of the offshore platform and predicting the future of potential failure because of corrosion and marine growth. After the platform encounters degradation over several years, it will decrease the service life before the degradation starts to matter. The results show after data processing that, offshore platforms encounter degradation over several years, and it is presented by a graph containing the condition trend over a multi-year condition because of corrosion and marine growth, and its effect towards unity check (UC) that define structure health. Unity check value produced from allowable stress versus capacity. In this research, structural health monitoring is predicting the potential failure of the platform towards its UC effect of corrosion and marine growth, with a max of the UC value is 0.8 because its a critical value. The failure of the structure possibly would have an affect on the cost-effectiveness. Therefore it is necessary to predict when the structure will fail so that the costs used are effective. Unfortunately, there is no core data for the environmental changes every year at the platform, so the model's equation does not include environmental conditions.

Experimental research on ventilation characteristics of a main engine room in a jack-up offshore platform

Tubular joint ultimate strength equations that are helpful for offshore platform design are presented. The formulae are based on data from 346 joint tests. They are easy to use and cover more joint configurations than present design procedures. The ultimate strength behavior of platform tubular joints is highlighted by reviewing potential failure mechanisms and pointing out salient trends in available data. A brief review of the development is presented which extends the work of Washio (1) and Gibstein (2). Some comparisons are made between the new predictions and those of available methods. These give some indications of where conservatism may exist and show the range of parameters over which current practice may overestimate the lower bound to available experimental data. An example problem is included to illustrate how the new formulae can be used to design a typical K-joint. A final section discusses the needs for future research. INTRODUCTION The sizing of tubular joints for ultimate strength is an important step in the design of offshore platforms. This process is accomplished once platform members have been designed to withstand operational and severe environmental loading conditions. Even though nominal member stresses may be at reasonable levels the complex behavior of tubular intersections can result in high stress amplification that can lead to failure. In many cases the walls of joint cans must be thickened or member diameters must be increased to provide adequate strength. The procedure for designing tubular joints must be simple and should lend itself to automation in order to handle the large number of joints in most platforms. Considerable computer output must be screened to determine maximum applied loads at each joint. Predicted joint strength must be calculated for each member intersection and compared with the applied loads. Joints with deficient capacity are then re-sized. At present, empirical expressions represent the state-of-the-art for predicting the ultimate strength of tubular joints. They are based on axially loaded laboratory joint tests. Very little ultimate strength data exists for bending or combined axial and bending loads. Consequently, bending and combined loading effects are usually taken into account in an heuristic manner. Analytical methods have not been successful because of the geometric, computational, and analytical complexities involved. The finite element method could probably be applied but would be too costly, time consuming and complicated for practical joint design. A finite element model, to be acceptable, would have to - include nonlinear material behavior, a fracture criterion and possibly nonlinear geometric terms to account for local buckling. Thus for the short term, the empirical approach seems most practical. This-paper presents a new set of joint strength equations that are helpful for platform design. The expressions are based on more data and cover more joint configurations than present procedures. The formulas are presented along with some comparisons between the new predictions and those of current methods. An example problem is also given to illustrate how the equations are used in joint design.

This paper summarizes the work product and activities of anInternational Standards Organization (1S0) panel (committee) formed to create a set design standards for steel offshore platforms to be located in earthquake prone areas. This work product is a draft set of earthquake design standards which have been submitted for review and eventual incorporation, along with the products of other panels, into a comprehensive set of fixed steel offshore platform design provisions for worldwide use. The 1S0 committee heirarchy, the basic charge to the panel, the mix of necessary talents, liaisons, references, the code development process and the challenges to produce this draft are described. The basic earthquake design process is outlined. Future improvements to this draft are identified, as are the challenges that lie ahead. Background An industry initiative to forge a common set of sustainable engineering specifications for oil and gas industry use on a worldwide basis was started in 1993. The drivers behind this are potential cost savings through uniformity, consistency and better communication. These factors can reduce costs through less expensive fabrication and improved safety. The intent is to create global standards that reflect the use of 'Product Service Level' (PSL) philosophy, making maximum use of existing standards and minimum use of manpower. As in the other petroleum-related technical arenas, the global offshore platform design community had to decide how to best organize to meet this challenge, and what base document should be used, since there exist several professional society and national versions of platform design codes. This paper outlines the evolution of one part of this effort, relating to the design of offshore platforms against earthquake effects. ISO Heirarchy & Panel 5 Charge The various standing, advisory, oversight and ad-hoc 1S0 committees and technical panels formed to develop theseinternational design standards are by default numerous. The author's understanding of the offshore platforms ISO heirarchy is Standing Committee 7 on Offshore Structures (SC7) is responsible for the work products of three Work Groups (WG3 - Fixed Steel Structures, WG4 - Fixed Concrete Structures and WG5 - Floating Systems). These Work Groups direct the work of specialized technical resource panels, which work for one or more of these three Work Groups. This organization is depicted in Figure 1. Panel 5 on 'Seismic Loadings and Response' presently works for WG3/Steel and WG4/Concrete, and is charged with developing a comprehensive set of seismic design criteria for sizing fit-for-purpose platforms to be located in earthquake prone areas, while utilizing existing standards as much as possible, and incorporating PSL philosophy. Such areas include the Cook Inlet, Alaska, and offshore Southern California, Mexico, Venezuela, Peru, Australia, New Zealand, Indonesia, Japan, China, eastern Russia, india and in the Caspian Sea.

American Institute of Mining, Metallurgical and Petroleum Engineers Inc. Abstract Model testing of offshore mobile platforms and related marine equipment, as a means for improving designs and increasing operating profits, is currently receiving considerable attention. Model testing presents the best method for investigating the dynamic characteristics of mobile platforms, thereby predicting the force and motion platforms, thereby predicting the force and motion response in waves and wind. The validity of scaling model results to fullscale proportions is predicated upon the application of appropriate engineering factors which have been derived from experiments in fluid mechanics. For most platform parameters, scaling accuracies to within 5 per cent - 6 per cent are obtainable. Improved scaling accuracies may be anticipated in the future as a result of improved modeling techniques and additional correlation between model data and prototype performance. Development of computer-implemented mathematical simulations promises additional assistance. Although design of offshore platforms and related equipment is influenced by a number of factors in addition to hydrodynamic considerations, new and improved model test data, correlated with prototype results, may be expected to accelerate technical advancement. These factors, combined with the potential for new concept development, will influence future industry planning. Introduction Model testing of offshore mobile platforms and related marine equipment is currently receiving greater attention than ever before. The reason for this increase in model testing activity stems primarily from the progressive movement to deeper water and the attendant requirements for floating structures.

Spectral fatigue analysis approach is highly recommended for fixed offshore platform design and reassessment by API. This method is a computationally efficient method, being able to handle the random nature of environmental ocean wave conditions during calculating wave loads on the offshore platforms and subsequent structural responses. However, its fundamental theory is based on the assumption of linearity of both structural system and wave loading mechanism. Although this method is critically appropriate to be applied in offshore platform design and fatigue assessment for deep water scenarios where wave and force nonlinearities are not very severe, it has still been widely utilized for the design and assessment of shallow water platforms in offshore industry without carefully considering possible errors caused by strong nonlinear factors between ocean waves and forces. The source giving rise to the errors is because of the difficulties in choosing suitably correct wave heights for a series of wave periods required for producing transfer functions between sea state spectra and structural response spectra. Therefore, the studies to justify the possible errors of the spectral fatigue analysis method for shallow water platforms have been provoked. This paper presents the results of the studies of investigating the errors from currently existing spectral fatigue analysis method. A new technical approach that can reduce the errors in the spectral fatigue analysis of shallow water platforms is introduced. The proposed technical approach is mainly focused on producing realistic transfer functions between sea state spectra and structural response spectra, which can reasonably reflect the individually local sea state data by using wave height-period joint probability density function. Hence the fatigue damage and life at the tubular joints of offshore platforms can be more precisely predicted. The spectral fatigue analysis of a practical shallow water jacket platform in the recent platform design project has been performed using the proposed approach and the results are discussed.

In June of 2012, a 25-day field program was carried out off the east coast of Newfoundland and Labrador with the objective of obtaining high quality 3D profiles of both grounded and freely floating icebergs. The motivation for collecting the data was to provide valuable information relating to the design of offshore platforms in iceberg-prone environments. Specifically, the data was originally acquired to provide insight regarding contact area growth as a function of penetration during a simulated impact with an offshore structure, and to assist in assessing the risk of topsides impact. The above water portion (sail) of the icebergs were profiled using photogrammetry while the below water portion of the icebergs (keel) were profiled using a multibeam system mounted on a remotely operated vehicle (ROV). The drift and rotation of the iceberg during the profiling process was derived using the above water photogrammetry, and was used to correct the below water multibeam data to account for the motion of freely floating icebergs. The drift and rotation was also used to merge the above and below water portions of the iceberg. An overview of the program and resulting data set is presented in this paper. Ultimately, twenty nine three dimensional iceberg profiles were obtained as a result of this work, providing significant improvements in the iceberg shape data available for input in the design of offshore platforms in regions where icebergs present a risk to these structures.

Accurate prediction on the behaviour of the largest waves in an ocean environment is vital to the safe design and performance of offshore platforms. This paper is concerned with the description of extreme waves, and includes both linear and nonlinear modelling of the largest water waves arising within directionally spread sea-state. The statistical description of the most probable temporal shape of the free surface in the vicinity of a large crest, for a given wave period and wave direction is found to correspond to the statistics of an extreme wave event. A variety of time-frequency analysis techniques is used to demonstrate that the free surface elevation time histories of focused wave groups are in close agreement with linear theory. A deterministic nonlinear correction is proposed for isolated extreme storm events. The NewWave formulation associated with this proposed nonlinear correction coefficient is employed to simulate the interactions between an extreme wave event and an idealized platform loading column. Statistics of the predicted maximum crest elevation are obtained using an exact linear interaction formulation of the scattering of water waves by a vertical circular cylinder in conjunction with a unidirectional Bretschneider spectrum. The results show that the second-order coefficient of the Stokes-type wave component is affected by directional spreading. Statistical analyses suggest that second-order wave theory describes the wave field very accurately even for extreme events. The present study provides a critical insight into the free surface elevation maxima of random seas containing waves of different frequencies and various energies, thus safeguarding the air-gap design of the offshore platform.