Structural Integrity Of Semisubmersibles And Gravity Platforms To Bergy-Bit/Iceberg Impact

The JCSM concept (short for Jackup Combined Semisubmersible Multifunction Platform) is a new type of semisubmersible platform presented by the first author, which overcomes the shortcomings of the available semisubmersible platforms, and combines the advantages of the traditional semisubmersible platform, the Jackup platform and the new FPSO concept - IQFP. Due to the complicated interaction between stability and hydrodynamic performance, it is necessary to explore the effect of geometrical parameters of the main body on the stability and hydrodynamic performance in order to obtain the optimal design plan of a JCSM platform. Firstly, the structure components and innovations of the JCSM were briefly reviewed in order to facilitate readers to understand its full picture. Then, six independent geometric parameters were selected by carefully studying the shape characteristics of the initial design plan of a JCSM study case. Furthermore, the stability heights and motion responses of various floating bodies of the JCSM case with different geometric parameters in wave were calculated using boundary element method based on potential flow theory. Lastly, effect of the shape parameters on stability and hydrodynamic performance of the JCSM was qualitatively evaluated. The research would shed lights on the shape design of the JCSM main body.

The purpose of this research was to experimentally characterize the flexural and tensile characteristics of fiber-reinforced Very High-Strength Concrete (VHSC) panels. The panels were made with a unique mix of cementitous materials achieving compressive strength of 26,000 psi (180 MPa) or greater. VHSC panels were reinforced with polypropylene fibers of 1 inch (25.4 mm) in length and Polyvinyl alcohol (PVA) micro-fibers of ½ inch length, incorporated at 1.5% by volume. For the flexural behavior, 17×2×½ inch flat panels were tested under third-point loading tests, while the direct tension experiments were tested on 10×3×½ inch tension panels under a direct tensile load. Flexural tests were conducted on three panels of plain VHSC, three panels of VHSC reinforced with polypropylene fibers and three panels of VHSC reinforced with ½ inch micro-fibers. Similar testing program was used to conduct the direct tension tests. Also, compression test conducted on 2×2×2 inch cubes and compressive test conducted on 4 inch by 8 inch cylinders test were used to establish compressive strength and modulus of elasticity respectively. Results show that the compressive strength, tensile strength and fracture toughness of the VHSC panels were much greater than those normally obtained by typical concrete material. The presence of fibers increases the toughness of VHSC specimens between 80 and 190% and increases the tensile strength by 23 to 47%. The modulus of elasticity and Poisson’s ratio recorded herein were determined according to ASTM C 469-02. Laboratory experiments on flexural and tensile properties of thin, very high-strength, fiber reinforced concrete panels, were used to study the material and characterize the panels’ reaction to load. Parameters such as compressive strength, tensile strength, toughness, elastic modulus, Poisson’s ratio and first-crack strength were determined and may be considered for potential use as design parameters in future material improvements.

Finite element (FE) studies are undertaken to investigate the accuracy of currently available concrete constitutive models in predicting the behavior of steel fiber-reinforced concrete (SFRC) panels tested in pure shear. The tension-stiffening, tension-softening, and compression-softening behaviors of the panels are evaluated and compared with predictions made using the disturbed stress field model and currently available concrete constitutive models. In addition, the effects of crack slip and crack spacing parameters on the modeling accuracy are assessed. The FE analysis results indicate that although current constitutive models are able to simulate the behavior of conventionally reinforced concrete panels accurately, the models overestimate the strength and deformation capacity of SFRC elements. Three factors are found to significantly influence the calculation accuracy: the tension stiffening/softening model, the consideration of shear slip on crack surfaces, and the crack spacing parameters.

The depletion of mineral resources on land, the increasingly bad environmental problems, and the beginning of the marine blue encirclement movement in the early 21st century mean that ocean energy has gradually become the focus of human resources development. To better develop and utilize marine green energy, we study the sea level according to specific sea conditions. A semi-submersible offshore platform is designed to collect and use offshore wind and solar power. In this paper, the semi-submersible platform is introduced from the design concept, initial stability calculation, load calculation and cost calculation. Through the measure of wind load, wave load and stability, the offshore platform can normally work under specific sea conditions. In this paper, it is calculated that the unballast center of gravity of the whole structure is 41.31 meters, the floating center of the system is 9.23 meters, and the center of gravity is under the steady center. The result of the wind load calculation is 21990110.4 N, the total cost of the whole semi-submersible platform is 170340458.14 RMB, and the unit cost is 14195.0381784 RMB/kW. This paper looks forward to designing a semi-submersible platform with solid stability and high efficiency in the collection of wind energy and light energy, and hopes to alleviate the environmental problems and make people pay more attention to the use of marine green energy.

In this study, ultra-high-strength fiber-reinforced concrete (UFC) panels were used as a quick and effective measure for seismic strengthening of damaged reinforced concrete (RC) columns. Four 1/3-scale specimens, which replicated RC columns of the soft-first-story of a 10-story condominium building that was heavily damaged in the 2016 Kumamoto Earthquake, were constructed and tested. The specimens were strengthened using UFC panels after being preloaded to the drift ratio, at which the maximum load capacity of the target column was measured, and then subjected to the main loading until the ultimate state was reached. The UFC panels were installed on the two faces of the column in a direction parallel to the assumed loading direction. Two of the specimens had a UFC or RC wing wall attached to one side of the column, which was also aligned with the assumed loading direction. During the preloading and main loading, the specimens were subjected to a cyclic lateral load and varying axial load that simulated an earthquake load. The proposed method improved the maximum strength and ultimate drift ratio, and helped restore the initial stiffness of specimens with UFC panels and a wing wall to that of a column specimen during preloading. The test results of a previous study, wherein the target column, loading method, and strengthening method were the same but the specimens were not damaged before strengthening, were compared to study the impact of the damage on the RC column before strengthening.

This paper proposes a new shear strengthening method for reinforced concrete (RC) beams, in which ultra-high-strength fibre-reinforced concrete (UFC) panels are bonded to existing structural members, and studies the strengthening effects of the method. The experimental design and results showing the shear resisting capacity and bond-slip properties are presented. To apply the proposed strengthening method to existing RC structures, the size effect on the strengthening performance is also studied. In the experiments, two sizes of RC beams (one-quarter and half the depth of real bridge girders) are used. The proposed shear strengthening method achieves great strengthening effects on both sizes of beams and beneficial effects on shear strength and failure mode. In order to propose a proper design for the shear strengthening method, numerical methods are also used to estimate the shear force carried by UFC panels. The estimated shear force carried by the UFC panels agrees well with the experimental results.

The paper presents experimental data generated for calibrating finite element models to predict the performance of reinforced concrete panels with a wide range of construction details under blast loading. The specimens were 1.2 m square panels constructed using Normal Weight Concrete (NWC) or Fiber Reinforced Concrete (FRC). FRC consisted of macro-synthetic fibers dispersed in NWC. Five types of panels were tested: NWC panels with steel bars; FRC panels without additional reinforcement; FRC panels with steel bars; NWC panels with glass fiber reinforced polymer (GFRP) bars; and NWC panels reinforced with steel bars and external GFRP laminates on both faces. Each panel type was constructed with three thicknesses: 152 mm, 254 mm, and 356 mm. FRC panels with steel bars had the best performance for new construction. NWC panels reinforced with steel bars and external GFRP laminates on both faces had the best performance for strengthening or rehabilitation of existing structures. The performance of NWC panels with GFRP bars was strongly influenced by the bar spacing. The behavior of the panels is classified in terms of damage using immediate occupancy, life safety, and near collapse performance levels. Preliminary dynamic simulations are compared to the experimental results.

1. ABSTRACT The paper describes the basic principles followed for the dynamic analysis of the behaviors of floating framed structures. The main theoretical results calculated by a computer program system based on a non linear dynamic method of analysis for two self floating, gravity type, drilling and production platforms (200 meter and 90 meter water depth platforms of original Kenmare design), are presented together with experimental results performed on models of said platforms at the Netherlands Ship Model Basin. From the analysis and tests comparison made on the above models, the requirement to adopt a non linear method of analysis, which is not normally used for such type of calculations, is demonstrated. 2. INTRODUCTION One of the most important problems in the design of floating offshore structures is the dynamic behavior in floating condition. This is obvious for semi submersible drilling platforms, where structural damages and operational delays can be minimized by means of analytical studies in the design stage, but it is significant also for fixed offshore platforms of the type designed by Kenmare, due to the method of installation. In fact for gravity platforms /18/, sometimes subject to long oceanic trips from the construction to the installation site, the floating condition loads are not less significant for the design than those m the standing on bottom condition. Of course, for this type of platform the floating condition is limited in time, and some problems, e. g. fatigue while floating, are not involved. However an incorrect design may cause great difficulties during towing and lead, in extreme conditions, to the loss of the unit. It should be remembered that the great eight above the sea level of this type of platform, towed in upright position, coupled to bad dynamic performance, may cause dynamic stresses, in the upper portion, higher than the maximum stress level reached after installation. Tecnomare S. p.A. has faced these problems during the design of its 200 m W. D. gravity type platform /18/ and, more recently, in the development of four 90 m W.D. gravity type platforms to be constructed in Northern France and installed offshore Congo, after an ocean voyage of about 6000 miles, during a period of 3 months. For this reason, being there involved non linear phenomena very significant for such structures, the non linear computer system DISMAR, presented in the following pages, has been developed. The main applications of the system together with model tests comparison are presented and discussed. 3. CRITICAL ANALYSIS OF CURRENTLY EMPLOYED TECHNIQUES 3. 1. Quasi-static Method Quasi-static method of analysis, widely employed in the past, may be schematized in the following main steps, shown in fig. 3:Structure is assumed to have no motion.Sea state is simulated as a regular, long crested sine wave system; wave height and period are selected on a given probability level.Forces on the restrained structure, due to this wave system and to the associated current and wind speeds, are calculated.

This paper studies the current available options for floating production platforms in developing deepwater oil fields and the potential development models of future oil and gas exploration in the South China Sea. A detailed review of current deepwater platforms worldwide was performed through the examples of industry projects, and the pros and cons of each platform are discussed. Four types of platforms are currently used for the deepwater development: tension leg platform, Spar, semi-submersible platform, and the floating production system offloading. Among these, the TLP and Spar can be used for dry tree applications, and have gained popularity in recent years. The dry tree application enables the extension of the drilling application for fixed platforms into floating systems, and greatly reduces the cost and complexity of the subsea operation. Newly built wet tree semi-submersible production platforms for ultra deepwater are also getting their application, mainly due to the much needed payload for deepwater making the conversion of the old drilling semi-submersible platforms impossible. These platforms have been used in different fields around the world for different environments; each has its own advantages and disadvantages. There are many challenges with the successful use of these floating platforms. A lot of lessons have been learned and extensive experience accumulated through the many project applications. Key technologies are being reviewed for the successful use of floating platforms for field development, and potential future development needs are being discussed. Some of the technologies and experience of platform applications can be well used for the development of the South China Sea oil and gas field.

Abstract: Offshore platforms are divided into many types which are mainly categorized according to waterdepth in the installation location. However, the design differs for each type to accomplish the target of the operation. But for some case of sea waterdepths and an aggressive environment such as the North Sea, steel ones are not suitable, so the heaviest type called gravity platform having enormous mass is used. This type of platform has its special requirements and procedures for construction and needs special types of construction materials in order to resist the climate factors applied due to the aggressive environment. The paper carefully illustrates how the principal Environmental loads (wind and wave), current forces, loads from ice and loads from earth-quake for (earth-quake prone zones) are deployed to archive the design and construction of offshore concrete gravity platforms. Two design methods (Analysis and Design of Shell structures) and the Tangent Modulus Methods of design of Offshore Concrete Gravity platforms are discussed

This paper discusses the operation of three different types of gravity platforms in the North Sea. When the Brent, Cormorant, and Dunlin fields platforms in the North Sea. When the Brent, Cormorant, and Dunlin fields were discovered, drilling required the use of a completely untried type of platform. Various design problems and their solutions are described. platform. Various design problems and their solutions are described. Introduction When oil exploration rigs first drilled in the northern North Sea, many companies knew that if oil was found, no established production method existed in such hostile waters. The announcement in Aug. 1972 by Shell U.K. Exploration and Production Ltd. of the discovery of the Brent Field heralded one of the most expensive and innovative oilfield development programs ever seen. In the following year, Shell announced the discovery of two more fields in the far north, Cormorant and Dunlin. For these three fields, six platforms were ordered (summarized in Table 1). Five of these were of a type completely untried for drilling operations: gravity platforms. Unlike a conventional steel jacket, which platforms. Unlike a conventional steel jacket, which relies on piles driven deep into the seabed to keep it secure, a gravity platform relies mainly on its own weight contacting a large area of the seabed to prevent it from moving. This paper discusses Shell's experience in operating three different types of gravity platforms (Fig. 1). (Shell Expro operates in the North Sea on behalf of Shell and Esso in a 50/50 partnership covering all areas where joint acreage is held). Because economic incentives to start exploiting the oil as soon as possible were great, there was no time to think out every detail of platform design before construction began. Simultaneous design and construction became the order of the day. When drilling engineers began to look at the problems of drilling from a gravity structure, it soon was apparent that disturbing the platform foundation (the seabed) by drilling through it would weaken the structure itself. Avoiding undue disturbance of the seabed and near-surface sediments was a major concern. These gravity platforms were larger than any used before. The high derrick-floor elevation along with the great water depth could lead to difficulties in getting mud returns while drilling tophole - the second major concern. A third problem was to design the conductor and subsequent pipe strings to take wind and wave loads, either applied directly or through the platform. Fourth, each individual platform had its own individual problems resulting from differences in general layout and design. Conductor String Design The main criteria for the conductor strings wereto be strong enough to absorb environmental loads,to be strong enough to take vertical loads imposed by platform settlement,to be strong enough to be driven to refusal using the largest diesel hammer that could be used in a derrick (Delmag D-55, 144,000 ft-lbf),if possible, to be driven so deep that mud returns could be obtained at derrick-floor level without fracturing the formation at the conductor shoe when drilling out of the conductor, andto be large enough for a 20-, 13 3/8-, 9 5/8-, and 7-in. casing scheme. P. 926

E&P Notes (May 2022)

An experimental study on electrokinetic improvement of the load-carrying capacity of offshore foundations embedded in soft clays is conducted. The paper presents a summary of method and results of two series of electrokinetic tests conducted on natural and simulated marine clays in small-scale and large-scale laboratory testing facilities. The results demonstrated that the load-carrying capacity of the foundation models increased up to three times after electrokinetic treatment. Introduction Recent developments in the offshore oil and gas industry have resulted in an increasing number of offshore construction projects that include different types of offshore platforms. If the seabed in the construction areas consists of soft marine clay deposits, these structures may encounter serious geotechnical problems. These soil deposits are widespread in the oceans throughout the world and are often characterized by the low shear strength and high compressibility that usually result in extensive settlement under structural loading. The construction and installation costs of the structures are enormous, and the consequences of failure can be catastrophic. To overcome the foundation problems caused by difficult soil conditions, there are two alternatives, i.e., increasing the size of the foundation or improving the soil. Electrokinetics (EK) may be used to strengthen the soil when the latter alternative is considered in design and construction. This study investigates the feasibility of electrokinetic strengthening of soft marine clays, and consequently increasing the load-carrying capacities of foundations embedded in such soils. Over the last decade, skirted foundations have been increasingly used to support large offshore structures such as gravity platform jackets, jackup rigs, semi-submersible platforms, floaters, tension leg platforms, sub-sea systems and other structures. Skirted foundations are used to resist both compressive forces from fixed jacket structures (e.g. Sleipner T platform) (Sparrevik, 1998) and tensile forces from floating or tension-lag platforms (Snorre TLP platform) (Fines et al., 1991). They have been used in the past in water depths that range from 70 m (e.g. Draupner E heavy jacket in the North Sea) (Tjelta, 1995) to about 1000 m (e.g. semi-submersible platform at Marlim Field offshore Brazil) (Mello et al., 1998). Skirted foundations are large, hollow, cylindrical foundation elements that are usually made of steel. Their capacity to carry loads depends on factors such as depth of skirt penetration, cylinder diameter, soil strength and the combination of horizontal, vertical and moment loads. When soft soils are encountered in a site, however, the load-carrying capacity is governed by an undrained shear failure in the soil. Therefore, the undrained strength of the soil becomes one of the major concerns in the design of skirted foundations. Skirted foundations are installed by penetrating the skirts into the seabed, first partially under self-weight, and then by creating an underpressure inside the cylinder (Andersen and Jostad, 1999). A thin zone of soil along the skirts will be remoulded during installation.

In this paper, the fluid–structure interaction of floating offshore wind turbine (FOWT) platforms under complex ocean conditions is investigated using OpenFOAM and in-house developed models. Two types of FOWT platform, i.e., a semi-submersible platform and a barge platform, are studied for their dynamic responses to either wave or current. The results reveal that a semi-submersible platform exhibits larger cross-flow motion and lock-in phenomenon, while a barge platform experiences smaller motion with no significant lock-in within the velocity range examined. The combined wave–current conditions are further studied for the semi-submersible platform, with different angles between wave and current, the current speeds, and wave parameters. Unlike other investigations focusing on colinear wave–current interaction, in which the waves usually mitigate vortex-induced motion (VIM); here, we find that waves might lead to an enhanced VIM with a large angle between current and wave. The evaluation on the interaction effect factor shows that the largest wave height in the lock-in region does not lead to the most dangerous scenario, herein, the largest platform motion. Instead, a smaller wave height with a large wave period can induce even larger motion.

An experimental investigation has been conducted to study the impact resistance and ductility of simply-supported steel fibre reinforced (SFR) concrete square panels. Two series of panels, 50mm and 75mm thick, were manufactured with three distinct types of steel fibres. Within each series, two relatively low-volume fibre concentrations (0.5% and 1.0%) were adopted in the concrete mix. Repeated impact was provided by a freefalling hemispherical shaped steel projectile at the centre of the panels. For a given panel thickness, an empirical formula was used to calculate the critical height that would cause perforation. However, in order to study the influence of repeated impact, only 50% of the calculated critical height of each series of panels was used. After each impact, the deflections of the SFR concrete panels were measured and plotted. The nominal increase in thickness does not significantly improve the damage resistance and ductility of SFR concrete panels as tested. However, the fibre concentration a...