Abstract: This paper examines the effects of pile-soil-structure interaction on the dynamic response of offshore platforms under the action of near-fault earthquakes. Two offshore platforms models are investigated, one with completely fixed supports and one with piles which are clamped into deformable layered soil. The soil deformability for the second model is simulated using non-linear springs. These platform models are subjected to near-fault seismic ground motions. The role of fault mechanism on platforms’ response is additionally investigated, while the study also examines the effects of different angles of incidence of seismic records on the maximum response of each platform.
Abstract: Offshore platforms for ultra-deep waters are form-dominant by design; hybrid systems with large flexibility in horizontal plane and high rigidity in vertical plane are preferred due to functional complexities. Offshore triceratops is relatively a new-generation offshore platform, whose deck is partially isolated from the supporting buoyant legs by ball joints. They allow transfer of partial displacements of buoyant legs to the deck but restrain transfer of rotational response. Buoyant legs are in turn taut-moored to the sea bed using pre-tension tethers. Present study will discuss detailed dynamic analysis and preliminary design of the chosen geometric, which is necessary as a proof of validation for such design applications. A detailed numeric analysis of triceratops at 2400 m water depth under random waves is presented. Preliminary design confirms member-level design requirements under various modes of failure. Tether configuration, proposed in the study confirms no pull-out of tethers as stress variation is comparatively lesser than the yield value. Presented study shall aid offshore engineers and contractors to understand suitability of triceratops, in terms of design and dynamic response behaviour.
Abstract: Increasing demand for large-sized Floating, Storage and Regasification Units (FSRUs) for oil and gas industries led to the development of novel geometric form of Buoyant Leg Storage and Regasification Platform (BLSRP). BLSRP consists of a circular deck supported by six buoyant legs placed symmetrically with respect to wave direction. Circular deck is connected to buoyant legs using hinged joints, which restrain transfer of rotational response from the legs to deck and vice-versa. Buoyant legs are connected to seabed using taut moored system with high initial pretension, enabling rigid body motion in vertical plane. Encountered environmental loads induce dynamic tether tension variations, which in turn affect stability of the platform. The present study investigates Mathieu stability of BLSRP under the postulated tether pullout cases by inducing additional tension in the tethers. From the numerical studies carried out, it is seen that postulated tether pullout on any one of the buoyant legs does not result in Mathieu type instability even under excessive tether tension. This is due to the presence of hinged joints, which are capable of dissipating the unbalanced loads to other legs. However, under tether pullout of consecutive buoyant legs, Mathieu-type instability is observed.
Abstract: Superstructures like offshore platforms, tall buildings, transition towers, skyscrapers and bridges are normally designed to resist compression, uplift and lateral forces from wind waves, negative skin friction, ship impact and other applied loads. Better understanding and the precise simulation of the response of batter piles under the action of independent uplift loads is a vital topic and an area of active research in the field of geotechnical engineering. This paper investigates the use of finite element code (FEC) to examine the behaviour of model batter piles penetrated in dense sand, subjected to pull-out pressure by means of numerical modelling. The concept of the Winkler Model (beam on elastic foundation) has been used in which the interaction between the pile embedded depth and adjacent soil in the bearing zone is simulated by nonlinear p-y curves. The analysis was conducted on different pile slenderness ratios (lc⁄d) ranging from 7.5, 15.22 and 30 respectively. In addition, the optimum batter angle for a model steel pile penetrated in dense sand has been chosen to be 20° as this is the best angle for this simulation as demonstrated by other researcher published in literature. In this numerical analysis, the soil response is idealized as elasto-plastic and the model piles are described as elastic materials for the purpose of simulation. The results revealed that the applied loads affect the pullout pile capacity as well as the lateral pile response for dense sand together with varying shear strength parameters linked to the pile critical depth. Furthermore, the pile pull-out capacity increases with increasing the pile aspect ratios.
Abstract: Structure-borne noise is an important aspect of
offshore platform sound field. It can be generated either directly by
vibrating machineries induced mechanical force, indirectly by the
excitation of structure or excitation by incident airborne noise.
Therefore, limiting of the transmission of vibration energy
throughout the offshore platform is the key to control the structureborne
noise. This is usually done by introducing damping treatment
to the steel structures. Two types of damping treatment using onboard
are presented. By conducting a Statistical Energy Analysis
(SEA) simulation on a jack-up rig, the noise level in the source room,
the neighboring rooms, and remote living quarter cabins are
compared before and after the damping treatments been applied. The
results demonstrated that, in the source neighboring room and living
quarter area, there is a significant noise reduction with the damping
treatment applied, whereas in the source room where air-borne sound
predominates that of structure-borne sound, the impact is not
obvious. The conclusion on effective damping treatment in the
offshore platform is made which enable acoustic professionals to
implement noise control during the design stage for offshore crews’
hearing protection and habitant comfortability.
Abstract: To understand the seismic behavior of the offshore
structures, the dynamic interaction of the water-structure-soil should
be assessed. In this regard the role of the water dynamic properties in
magnifying or reducing of the effects of earthquake induced motions
on offshore structures haven't been investigated in precise manner in
available literature. In this paper the sea water level fluctuations
effects on the seismic behavior of a sample of offshore structures has
been investigated by emphasizing on the water-structure interaction
phenomenon. For this purpose a two dimensional finite element
model of offshore structures as well as surrounded water has been
developed using ANSYS software. The effect of soil interaction with
embedded pile foundation has been imposed by using a series of
nonlinear springs in horizontal and vertical directions in soil-piles
contact points. In the model, the earthquake induced motions have
been applied on springs and consequently the motions propagated
upward to the structure and surrounded water. As a result of
numerical study, the horizontal deformations of the offshore deck as
well as internal force and buckling coefficient in structural elements
have been recorded and controlled with and without water presence.
In part of study a parametric study has been accomplished on sea
water level fluctuations and effect of this parameter has been studied
on the aforementioned numerical results.
Abstract: Structural Integrity Management (SIM) is
important for the protection of offshore crew, environment, business assets and company and industry reputation. API RP 2A contained guidelines for assessment of existing platforms mostly for the Gulf
of Mexico (GOM). ISO 19902 SIM framework also does not
specifically cater for Malaysia. There are about 200 platforms in
Malaysia with 90 exceeding their design life. The Petronas Carigali
Sdn Bhd (PCSB) uses the Asset Integrity Management System and
the very subjective Risk based Inspection Program for these
platforms. Petronas currently doesn-t have a standalone Petronas
Technical Standard PTS-SIM. This study proposes a recommended
practice for the SIM process for offshore structures in Malaysia,
including studies by API and ISO and local elements such as the
number of platforms, types of facilities, age and risk ranking. Case
study on SMG-A platform in Sabah shows missing or scattered
platform data and a gap in inspection history. It is to undergo a level
3 underwater inspection in year 2015.
Abstract: To improve HSE standards, oil and gas industries are
interested in using remotely controlled and autonomous robots instead
of human workers on offshore platforms. In addition to earlier reason
this strategy would increase potential revenue, efficient usage of
work experts and even would allow operations in more remote areas.
This article is the presentation of a custom climbing robot, called
Walloid, designed for offshore platform topside automation. This 4
arms climbing robot with grippers is an ongoing project at University
of Oslo.
Abstract: The oil and gas industry has moved towards Load and
Resistance Factor Design through API RP2A - LRFD and the
recently published international standard, ISO-19902, for design of
fixed steel offshore structures. The ISO 19902 is intended to provide
a harmonized design practice that offers a balanced structural fitness
for the purpose, economy and safety. As part of an ongoing work, the
reliability analysis of tubular joints of the jacket structure has been
carried out to calibrate the load and resistance factors for the design
of offshore platforms in Malaysia, as proposed in the ISO.
Probabilistic models have been established for the load effects (wave,
wind and current) and the tubular joints strengths. In this study the
First Order Reliability Method (FORM), coded in MATLAB
Software has been employed to evaluate the reliability index of the
typical joints, designed using API RP2A - WSD and ISO 19902.