Jack-up Offshore Platform Research Articles

Experimental Study of a Puncture Warning System for a Jack-Up Offshore Platform

Abstract During the operation of jack-up offshore platforms, the complex and variable seabed geological conditions involved can lead to serious accidents, such as pile leg punctures and platform tilt. The aim of this study is to introduce an early warning method for punctures that ensures the operational safety of these platforms. To accomplish this, a real-time monitoring and controlling system is designed using a programmable logic controller that shares data from sensors measuring displacement, tilt, and pressure. In addition, an experimental device is constructed to simulate a jack-up offshore platform in order to assess the safety response of the control system. The working state of the platform under different working conditions (puncture of one independent pile, same side or diagonal piles, and three-pile linkage) is evaluated by analysing the structural motion response, including platform tilt and foundation pressure. The findings reveal that the system developed in this study accurately detects the tilt condition of the offshore platform, and can ensure the operational safety of jack-up offshore platforms.

The collision performance of jack-up marine platforms based on pile-soil coupling technology

The truss jack-up offshore platform has become the main force of offshore oil and gas development with its stable operation ability and environmental adaptability. Meanwhile, along with the development of the offshore shipping industry, collisions between ships and offshore platforms have become more and more frequent. Therefore, it is important to study the collision performance of truss jack-up offshore platforms. Based on the “pile-soil” coupling technology, the non-linear finite element software ABAQUS is used to establish the pile-leg collision calculation model. The key parameters, such as damage deformation, collision force, and energy absorption, are analyzed through the analysis. The collision performance of the trussed offshore platform is analyzed through the calculated damage deformation, collision force, energy absorption, and other key parameters. The research results show that the collision between the ship and the marine platform has obvious local characteristics. In addition, the strength of the spar in the collision area can be increased appropriately to improve the collision performance of the platform effectively.

Experimental Investigation of the Coupling Effect of Jackup Offshore Platforms, Towers, and Seabed Foundations under Waves of Large Wave Height

A large number of jackup offshore platforms with towers are widely applied in ocean engineering. The dynamic response of the platforms to waves of large wave height is critical, as such waves may cause platform accidents, property damage, and casualties. Therefore, it is important to investigate the coupling effect of jackup offshore platform, towers and seabed foundations under waves of large wave height. In this study, the coupling effect of offshore platforms, tower structures, and seabed foundations under the impact of waves of large wave height was studied via a physical flume model test. The experimental results show that the impact of waves of large wave height on the platforms is significant when the wave is blocked by the platform surface as the water body gathers under the platform surface, causing a pile group effect that results in the onshore piles being subjected to larger pressures than the front ones. The combined action of wave impact and pile leg squeezing force leads to an increase in the pore pressure of the foundation bed near the pile leg, and the soil near the pile leg becomes soft, revealing the mechanism of instability of the offshore platform’s pile foundation under waves of large wave height. The acceleration of the longitudinal movement of the platform increases under waves of large wave height, and the vortex-induced vibration of the platform includes the vibration along the direction of the wave and perpendicular to it. A coupled vibration effect between the tower structure and the platform occurs under waves of large wave height, reducing the vibration of the platform itself. Furthermore, damping members are installed on the tower structure, greatly reducing the natural vibration period and the motion response of the tower structure. This study provides significant enlightenment for the design of offshore platforms with towers to protect against waves of large wave height.

Numerical Analysis of Dynamics of Jack-Up Offshore Platform and Its Seabed Foundation under Ocean Wave

Jack-up offshore platform is a type of important marine structure, which is mainly used for satellite launch, oil exploitation, and other engineering tasks in the offshore area. The offshore platform is bound to be subjected to wave loading in the course of use. Whether it can withstand the wave impact is an important engineering problem. To solve this engineering problem, the self-developed fluid–structure–foundation interaction coupling model OlaFlow-ABAQUS is used to explore the dynamic response characteristics of a jack-up offshore platform and its seabed foundation under three conventional wave conditions (wave height is 3, 5, and 7 m, respectively) in a coupled way. The numerical results show that only a small amplitude of periodic sloshing occurs for the jack-up offshore platform under the three conventional wave conditions. The maximum sloshing amplitude is up to 8 cm, and there is no visible residual displacement. It is indicated that there is no plastic deformation zone in the seabed foundation near the pile legs of the jack-up platform. It can thus be concluded that the jack-up platform has excellent stability under conventional wave conditions. Under conventional wave loading, momentary liquefaction occurs in the seabed foundation around the pile legs of the platform, and the maximum liquefaction depth is about 1 m. This study indicates that the coupling model OlaFlow-ABAQUS for the fluid–structure–foundation interaction is feasible, and has some advantages to study the dynamic response and to evaluate the stability of large-scale marine structures and their seabed foundations under ocean waves.

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

This paper aims to investigate the ventilation characteristics of a main cabin in a JU2000E jack-up offshore platform. A scaled model of the ventilation system was built based on the similarity theory, and the factors (such as the engine shutdown choice, the layout of the air outlets, and the supply air volume) that affect the ventilation characteristics were analyzed. The results showed that the reasonable choice of engine shutdown is able to reduce average temperature in certain locations of the engine room as well as decreasing the maximum temperature of the engine room. Suitable layout of the air outlets can accelerate the heat dissipation and reduce the temperature variance. When the air supply volume is 600 m3/h, it is the most economic to meet the heat dissipation requirement of the engine room. As a result, the findings provide important guidance for the ventilation system design of jack-up offshore platforms.

Experimental study on hydrodynamic characteristics of three truss-type legs of jack-up offshore platform

The research came from the project for 400-foot jack-up offshore platform's adaptation to environment. The empirical value of load coefficient is often selected by each Classification Society and the influence of other complex factors on hydrodynamic characteristics is ignored, which may make the result too conservative. Therefore, this paper took the jack-up offshore platform truss pile leg as research object, and the model experiments of single pile leg and three pile legs were conducted respectively, and the hydrodynamic coefficient under experimental conditions were studied. Based on the single-legged, the effects of three-legged model under different working conditions were quantitatively analyzed by defining the force component coefficient and the total force coefficients of group piles. This research may provide data support for structural optimization design and strength check analysis of jack-up offshore platform truss legs, which plays an important role in the fatigue detection and life evaluation of offshore platform.

Effect of sitting time on the breakout force of mat foundation on soft marine clay seabed

Jack-up offshore platform mat foundation has lower requirements on the bearing capacity on clay seabed than spudcan foundation, which is more suitable for the soft clay seabed. It is of great significance to reveal the mechanism of breakout force of mat foundation to ensure the safety and stability of offshore platform. In this study, field tests with different consolidation times were conducted to investigate the breakout force of mat foundation on soft marine clay seabed. Field results show that the suction generated by negative pore pressure in the seabed soil accounted for most of the breakout force, generally up to 90%. Then, the effects of consolidation time, preloading and uplift rate on the effective stress and breakout force were numerically studied. Numerical results show that the breakout force has a linear relationship with the consolidation degree of seabed soil. Under the same degree of consolidation, the breakout force per unit area increases with the increase of preloading. The uplift process changes from drained to undrained as the uplift rate increases.

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

In the complex Ocean environment, wind load is the most important factor that should be addressed in the design of jack-up platforms. Although many efforts have been made to analyze the dynamics of jack-up platforms considering wind load effect, literature review shows that very limited work has been done to address the calculation of the wind load coefficient of each individual key component in a platform. Moreover, the influence of different wind speeds and directions under different working conditions of the platforms is not discussed clearly. To this avail, this paper investigates the wind load effect on the key components in a 400 ft jack-up offshore platform under three design conditions through normative calculation, numerical simulation and wind tunnel test. The wind force and torque of each key component (such as the crane, pile leg, and main hull) were obtained to calculate its wind load coefficient. The change rule of the wind load coefficient with different wind speeds and directions was discussed. The calculation results of the numerical simulation agreed well with these of the wind tunnel test, while the normative calculation results did not. The findings of this study may provide a basis for optimal design of jack-up offshore platforms.

Topology optimization of jack-up offshore platform leg structure

Jack-up platforms are commonly found in the costal or offshore environment for offshore oil and gas recovering. Pile legs are the main component of jack-up platform, which support the whole platform and suffer from the ocean environment load. Topology optimization method is proposed in this article to find an optimized shape for the leg by maximizing its structural stiffness, with the purpose of providing enough resistance for extreme environment load. The whole design space is chosen as design variables, and the maximum stiffness is selected as the optimum objective, with the volume and displacement constrained. An innovative leg structure is generated with lighter weight. Finally, the static and transient dynamic characteristics of the optimized structure leg are analyzed, compared with the original one. It is found that the optimization results not only produce better material distribution with less mass, but also enhance the stiffness and strength requirements of leg structure under the extreme environment load.

Analysis of a Main Cabin Ventilation System in a Jack-Up Offshore Platform Part I: Numerical Modelling

This work aims to measure the thermodynamics of a main cabin ventilation system in a JU-2000E jack-up offshore platform. A three-dimensional (3D) physical model of the ventilation system was established, and the computational fluid dynamics (CFD) software (ANSYS FLUENT) was used to calculate the model thermodynamics. Numerical analysis was performed to investigate the influence mechanisms of the ventilation factors such as ventilation temperature and volume on the ventilation performance. The analysis results demonstrate that (1) top-setting of the exhaust vents is more effective than the side-setting in terms of high temperature reduction, (2) small ventilation temperature and volume can improve the ventilation efficiency, and (3) proper shutdown selection of the backup diesel engine can enhance the ventilation performance. Furthermore, the effect of humidity for the ventilation air was investigated. Lastly, an experimental platform was developed based on the simulation model. Experimental tests were carried out to evaluate the shutdown selection of the backup engine and have shown consistent results to that of the simulation model. The findings of this study provide valuable guidance in designing the ventilation system in the JU-2000E jack-up offshore platform.

In Situ Observation of Austenite Grain Growth and Phase Transformation of A517GrQ Rack Steel for Jack-Up Offshore Platform

Austenite grain size plays an important role for quenched and tempered A517 GrQ rack steel. In order to investigate the austenite grain growth behavior, in-situ austenizing experiments were conducted at different temperatures with varied holding time. Austenite grain growth, and subsequent bainite and martensite transformation were observed by a confocal laser scanning microscope (CLSM). The average austenite grain size increased rapidly from 32.7 μm to 137.9 μm with increasing temperature from 1100 °C to 1250 °C, and abnormal grain growth occurred at 1250 °C for 15 min. While holding from 5 min to 20 min at 1200 °C, the grain size grew gradually from 70.2 μm to 84.8 μm. The grain size distributions under different conditions all obey lognormal function. After austenizing, the rate of subsequent cooling has an significant impact on transformation process. The transformation duration time decreased from over 142 s to 11 s with increasing cooling rate at 1 °C/s and 5 °C/s, which could be corresponding to bainite and martensite transformation respectively.

Construction and Application of Virtual Roaming System Based on Virtools

This paper introduced a virtual roaming system which can be effectively used in studying ocean scenes based on 3ds max modeling tools and virtools development software. Establishing this system needs the following steps: building geometric model, making texture mapping, light treatment, importing model and designing interactive function. Taking jack-up offshore platform as an example, the system has three roaming modes including manual roaming with character, manual roaming without character and automatic roaming. Users can roam in this platform freely. The collision detection technology and the immersive technology were integrated into the system to improve the reality of it. The system also has a good visual effect and interactive function.

K-Type, Inverse K-Type and X-Type Legs Stability Analysis of Jack-Up Offshore Platform

The force situation of truss legs has an important impact on the jack-up offshore platform. The finite element analysis on three types truss leg was made, and the stability of the three types truss leg under preload, operating and storm survival condition was discussed. The result showed that the maximum stress was in the chord; they met the design requirements; K type, inverse K type can save material, and they both met resonance requirements. The former had a better stability under preload condition, and the later had the best stability under operating, storm survival condition.

Lifting Platform in Jack-Up Offshore Platform Based on Virtual Prototyping

This paper put forward a systematic design method based on virtual prototyping technology to simulate lifting platform of jacking system in jack-up offshore platform. After the main parameters of lifting platform in jack-up offshore platform were introduced, the 800T offshore platform modeling techniques were put forward, such as rigid body modeling techniques, flexible body modeling techniques, modal analysis techniques and kinematics analysis. The dynamics analysis was present with the simulation results, which demonstrates that this method is obviously helpful to get more accurate simulation results to verify the rationality of lifting platform in jack-up offshore platform.