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Publications (193)
Wave Energy Converters (WECs) enable renewable power extraction from ocean waves. The intermittent and dynamic behavior of wave energy requires the capture and storage of energy extracted by the WEC. This work investigates the use of Lithium-ion batteries (LIBs) in this application.
Helical anchors have been widely used by the onshore industry and are now being considered as anchors for offshore renewable energy infrastructure. As a step towards better understanding of helical anchor behaviour, this paper presents an investigation of the deformation mechanisms observed in centrifuge model tests of a single plate subjected to d...
Helical piles have been widely used onshore which can withstand compressive and tensile loads. As a promising foundation for offshore wind developments in deep water, helical pile has advantages of quiet installation and significant uplift capacity. In this paper, numerical analyses are conducted to investigate the load bearing mechanism considerin...
This paper presents finite element simulations to re-interpret a series of full model and PIV centrifuge tests to study the uplift of skirted foundations. The focus is on the influence of uplift rate on the uplift capacity and the mechanism of “breakaway” (i.e., the phenomenon of sudden loss of uplift resistance). A backbone curve, quantifying the...
Due to the mechanical properties of the seabed exhibiting horizontal and vertical spatial variability, an important challenge in offshore geotechnical design lies in the selection of the relevant soil strength profile for foundation sizing, called hereafter the “design line.” Design values are most often selected depth-wise using existing field dat...
Interpreting seabed properties for future offshore wind farm development appears challenging given the requirement to investigate very large areas. Current approaches, where significant numbers of geotechnical boreholes and cone penetration tests (CPTs) are conducted-often at the location of each foundation or anchor-may prove prohibitive given the...
The offshore wind industry continues to expand rapidly around the world in response to demand for clean energy. Research to investigate monopile performance under cyclic lateral loading needs to replicate the installation process as well as the cyclic loading regimes. This has provided the impetus for the development of model pile driving hammers f...
A key step on the pathway to demonstrating wave energy converter (WEC) technology is ocean trials at a reduced scale. The Blue Economy Cooperative Research Centre and the Government of Western Australia (through the Department of Primary Industries and Regional Development) are funding the deployment of an M4 wave energy converter in King George So...
The undrained shear strength of fine-grained soils changes with time, reducing due to pore pressure generation, and increasing during consolidation. This paper describes an effective stress framework, implemented within a two-dimensional computational domain, that relates generation of pore pressure to accumulated plastic shear strain, allowing und...
A number of incidents of pile tip damage and extrusion buckling have been reported within the offshore industry, generally arising during driving of relatively thin-walled tubular pile foundations through hard layers or potentially heterogeneous sediments. The issue has become of particular concern with modern trends toward larger diameter piles, w...
The potential for pile tip damage and extrusion buckling has become an increasing concern for the offshore wind industry following the trend toward the use of large diameter thin-walled pile foundations, either as monopiles or as part of a jacket structure. Extrusion buckling may be triggered by an initial pile tip fabrication imperfection or pile...
In recent years, floating wind has been attracting increasing attention due to its ability to be deployed in greater water depths, which are usually associated with higher wind energy. At present, floating wind technology is more expensive than fixed offshore wind, with higher cost being driven by challenges such as the extended length of mooring l...
This paper presents the detailed formulation of a coupled hydro‐mechanical structure‐soil interface and demonstrates its application in simulating uplifting problems. This interface features real‐time prediction of the pore pressure generation and structure‐soil separation, and thus rate dependency and ‘breakaway’ can be modeled without user interv...
The number of incidents worldwide where pile tip damage has occurred during driving has accelerated following the growth of the offshore wind sector, and the expansion into areas with increased risk of embedded boulders or partially weathered soft rocks. The process involving pile–boulder–soil contact can be simulated with advanced three-dimensiona...
The touchdown zones of steel catenary risers and lazy wave risers are fatigue hotspots, where the risers interact continuously with the seabed due to hydrodynamic loading exerted on the host vessel. The whole-life interactions can range from small-amplitude daily motion cycles to motions that involve large-amplitude cyclic interaction with the seab...
The effect of soil spatial variability on the undrained vertical uplift capacity of plate anchors has been examined using the three-dimensional random finite-element approach. Multiple direct Monte Carlo simulations (MCS) were performed to quantify statistically how the anchor uplift capacity varied for variable soil conditions. This allowed examin...
Offshore infrastructure often interacts cyclically with the seabed over the operational life of a project. Previous research on the evolution of soil’s undrained strength under long-term, large-amplitude cyclic loading has focused on contractile clays and demonstrated that this cyclic interaction can lead to the initial generation and later dissipa...
Each pile in an offshore wind farm may be designed solely on the results of a single cone penetration test (CPT) positioned at its center or based on sample statistics calculated from multiple investigated locations in the same geotechnical unit. This study investigates quantitatively the effects of spatial variability of soil on the efficacy of th...
The use of plate anchors on permanent offshore facilities with taut or semi-taut moorings requires a thorough understanding of their long-term capacity under sustained loading. In this paper, a programme of centrifuge tests and numerical simulations is reported to investigate the capacity of a plate anchor deeply embedded in normally consolidated c...
Monopile foundations supporting offshore wind turbines are exposed to cyclic lateral loading, which can cause accumulated pile displacement or rotation and evolution of the dynamic response. To inform the development of improved design methods, the monopile's response to cyclic lateral loading has been explored through small-scale physical modeling...
This paper describes a series of experiments to investigate the effects of water entrainment in soil around and beneath oscillating cylinders at the seabed. This knowledge is important in order to predict the as-laid embedment of pipelines laid on the seabed, and to model how risers and chains interact with the seabed during their design life. The...
Seabed in regions, such as the Gulf of Guinea and North West Shelf of Australia, may exhibit a crust layer where the undrained shear strength can be an order of magnitude higher than that of the immediately underlying sediment. This can complicate design of steel catenary risers, where fatigue depends on the cyclic vertical stiffness of the pipe-so...
This paper describes a centrifuge investigation on drained monotonic and cyclic capacity of a plate anchor in dry loose sand. The model rectangular plate anchor was pre-embedded vertically at an embedment depth of 5 times the plate width, and was loaded horizontally at the mudline with monotonic or irregular cyclic loading to failure. The anchor wa...
The design of a large diameter monopile depends heavily on soil strength and so certainty of knowledge of this property is critical to cost-effective design. Monopiles are often designed based solely on the measurements of a single CPT positioned at its center, and the soil property within the zone of influence of the pile is normally assumed to be...
There have been a number of incidents worldwide where pile tip damage has occurred during pile driving, generally requiring costly remedial actions. The number of such occurrences has increased recently, consistent with the trend of increasing diameter tubular piles, which are increasingly thin-walled relative to the diameter, used to support offsh...
There have been a number of incidents worldwide where pile tip damage has occurred during pile driving, generally requiring costly remedial actions. The number of such occurrences has increased recently, consistent with the trend of increasing diameter tubular piles, which are increasingly thin-walled relative to the diameter, used to support offsh...
This paper presents centrifuge tests undertaken to investigate the combined VH capacities of suction caisson in sand under multidirectional loadings following series of low magnitude horizontal cyclic loading. These loading paths are relevant to foundations of array of floating renewables such as wave energy converters or wind turbines. The centrif...
This paper presents the development of an improved plasticity model to define the combined vertical and horizontal capacity of suction caisson in sand under low vertical loads, conditions relevant for foundations of offshore wind turbines. Model tests following a variety of load paths were used to demonstrate the change of the shape of the yield su...
This study investigated the change in monotonic and cyclic capacity of a plate anchor across different degrees of consolidation in dense sand. To quantify the effect of consolidation on anchor capacity, a framework is introduced and validated using centrifuge model anchor test data. The centrifuge tests considered a rectangular plate loaded at vary...
The response of rigid piles in sand to an inclined tensile load is poorly documented and understood, particularly when the load is cyclic. This is becoming relevant for floating marine renewable energy devices such as wave energy converters and floating wind turbines. This paper considers centrifuge data for rigid piles in dense sand subjected to d...
This paper investigates submarine slide-pipe interaction through centrifuge tests and computational fluid dynamics (CFD), with particular focus on the soil flow mechanisms that occur around a suspended pipe at non-Newtonian Reynolds numbers (Renon-Newtonian) between 0.5 and 40. The centrifuge tests involve horizontal translation of a model pipe in...
This paper reports on a series of centrifuge tests to investigate the feasibility and performance of a novel spudcan foundation design featuring a peripheral skirt with side openings. The ‘skirted spudcan’, designed and patented by Keppel, is particularly beneficial in layered seabeds with a clay layer overlaying sand. The purpose of the side openi...
In the search for enhanced alternatives to the conventional footings of jack-up platforms, the offshore industry has turned to novel types of shallow foundations. A recent hybrid foundation concept was proposed that merges a skirted footing with a deeper caisson, with the motivation to mobilise higher bearing capacities and increase the foundation...
This paper presents an improved plasticity force-resultant model for anchors deeply embedded in clays, developed from large deformation finite element analyses. The current available force-resultant models for anchors are mainly developed from small strain finite element analysis while experimental approach has not been used due to technical challe...
Suction caissons have recently been considered as potential anchoring solutions for floating renewable devices (wind turbines and wave energy converters) in shallow waters, where-unlike for floating oil and gas applications in deep water-sandy seabeds are to be expected. This paper presents a simple framework to calculate the maximum drained capaci...
Site investigation data have shown that a crust layer may occur at the surface of many seabeds, with the crust exhibiting undrained strengths up to an order of magnitude higher than that of underlying normally consolidated sediments. This may affect the fatigue life assessment of steel catenary riser (SCR) as a result of riser-soil interaction. The...
This note examines the interaction between the helices of a multi-helix anchor in terms of the mobilized drained capacity response in tension. Assessments are made on the basis of centrifuge tests in dense silica sand, supplemented with data from existing studies. The centrifuge tests were designed to isolate potential anchor installation effects f...
Preloaded foundation capacity has recently been a topic of major interest in offshore foundation engineering. The increase in undrained shear strength due to preloading and consolidation enables the foundation to resist a larger environmental load, thereby reducing the size of the footprint. This paper investigates the shape and size of the VHM (i....
This paper presents a geotechnical engineering perspective on the design of anchoring systems for floating wind turbines and floating wave energy converters. It explores several transformational research directions in anchor technology and anchor design, moving away from standards established for floating oil and gas structures, and acknowledging t...
This paper presents a geotechnical engineering perspective on the design of anchoring systems for floating wind turbines and floating wave energy converters. It explores several transformational research directions in anchor technology and anchor design, moving away from standards established for floating oil and gas structures, and acknowledging t...
Monopile supports are to this day the preferred foundation solution for offshore wind turbines. There is still an empirical gap, however, between the in-situ conditions for these monopiles and the test conditions the current design methods are based on.This relates to both pile geometry and load conditions.The gap introduces uncertainties and in or...
A common challenge in experimental research is making measurements without unintentionally omitting data at key locations or altering the mechanical properties of the object of interest. In recent years fi-bre optic sensing systems have been used to overcome these challenges in both geotechnical field monitoring and full scale geotechnical laborato...
Offshore foundations are typically designed to resist mooring loads coming from a single direction. This paper provides some insights into the geotechnical challenges associated with anchor sharing (i.e. where mooring loads are coming from multiple directions to one anchor) for Offshore Renewable Energy (ORE) applications. Firstly, the multidirecti...
This paper reports numerical modeling results investigating the diving potential and optimization of offshore anchors. A simplified two-dimensional plate anchor model and a complex three-dimensional anchor model were investigated in the finite element analyses. Good agreement with established analytical predictions provided validation of the numeri...
Station keeping of floating facilities requires mooring lines that terminate at anchors located on or within the seabed. This article provides an overview of currently available anchoring technology, including guidance on the types of seabed and mooring configurations that each are suited to, and the considerations that need to be made in the desig...
The emergence of commercial offshore floating renewable energy devices that are expected to be deployed in large integrated arrays in relatively shallow water requires anchor types that are suited to sandy seabeds. This paper considers centrifuge test data that quantify the capacity of a novel dynamically installed plate anchor in sand under draine...
Improvement of the undrained capacities of foundation as a result of preloading, has received attention in offshore engineering only recently. It offers the benefit of optimising foundation design and reducing footprint and cost. This paper investigates the preloading performance of skirted circular foundations in clay using 3D coupled finite-eleme...
This paper presents a novel dynamically installed anchor concept suitable for sand. The anchor, referred to as the DPAIII, uses a thin ‘blade-like’ design to reduce bearing resistance during penetration, and comprises a lower plate attached to an upper removable follower. The anchor is installed through the kinetic energy it gains during free-fall...
Dynamically installed anchors are torpedo-shaped anchors that are installed by dropping them through the ocean such that they self-bury in the soft seabeds typically encountered in deep water. This paper presents and considers field data from reduced scale anchor tests at two sites to validate a new release-to-rest model for dynamically installed a...
Australia's National Geotechnical Centrifuge Facility (NGCF) was launched in 2016 following some 30 years of developing a world-leading capability for conducting appropriately scaled centrifuge model tests in the field of geotechnical engineering. The first centrifuge was installed at the University of Western Australia in 1989, funded partly on th...
This article presents the fundamental principles associated with the physical modeling of geotechnical problems, with an emphasis on the performance and design of offshore foundations systems. The similitude principles necessary for reduced scale modeling of an offshore foundation to exhibit an identical behavior to the full-scale structure it repr...
Results of finite-element analyses calculating the undrained capacities of skirted circular foundations under uniaxial vertical, horizontal, and moment loading are presented. Parallel finite-element analyses using both the Tresca failure criterion and the modified cam clay (MCC) model are reported. The variations in capacity are presented as functi...
This paper describes advances in offshore anchoring technology made possible through research undertaken recently at the Centre for Offshore Foundation Systems at the University of Western Australia. The paper focuses on the behavior and performance of statically and dynamically installed anchors for floating structures, addressing issues associate...
The process of remolding and subsequent recovery of soil shear strength is a common geotechnical problem, especially in the offshore environment, where foundations and pipelines are subjected to intermittent operational and environmental loads. A novel vertically oriented penetrometer (VOP) was used in a centrifuge testing program to study the chan...
Finite element analysis and geotechnical centrifuge tests were carried out to investigate the multi-directional load distribution acting on shared anchors for arrays of floating structures, and to understand its consequences on the anchor behaviour and performance in order to inform geotechnical engineering design. The results show that the capacit...
Predicting the final embedment depth of a dynamically installed anchor is a key prerequisite for reliable calculation of anchor capacity. This paper investigates the embedment characteristics of dynamically installed anchors in normally consolidated and overconsolidated clay through a series of centrifuge tests involving a model anchor instrumented...
Anchors are widely used offshore as foundation systems to moor floating platforms and renewable energy devices to provide uplift resistance in vertical or resistance in inclined direction. Most of the available research work has concentrated on in-plane loading. However, any failure of a single mooring line in a storm can cause out-of-plane loading...
This paper presents key outcomes of a 3-year Joint Industry Project funded by 6 Operators on the impact of submarine slides on pipelines. This JIP developed new techniques to simulate slide runout, and assess the resulting loading and deformation of seabed pipelines. The work was distilled into guidance for practical application, which has found ad...
Dynamically embedded plate anchors (DEPLAs) are a promising option for anchoring floating facilities in deep water, as relative to current technology such as suction caissons, the anchor will be much smaller and less expensive to install. This paper considers data from the final stage of an experimental campaign that has been undertaken as a prelim...
Dynamically embedded plate anchors (DEPLAs) are a promising option for anchoring floating facilities in deep water, as relative to current technology such as suction caissons, the anchor will be much smaller and less expensive to install. This paper considers data from the final stage of an experimental campaign that has been undertaken as a prelim...
The use of plate anchors in permanent moorings for deep-water floating structures requires a thorough understanding of their performance under sustained and cyclic loading. This paper addresses the former aspect through a series of centrifuge tests on vertically loaded plate anchors in normally consolidated kaolin clay, supported by large-deformati...
Six degree-of-freedom motion data from projectiles free-falling through water and embedding in soft soil are measured using a low-cost inertial measurement unit, consisting of a tri-axis accelerometer and a three-component gyroscope. A comprehensive framework for interpreting the measured data is described and the merit of this framework is demonst...
Self-elevating mobile jack-up units have been employed in offshore exploration and development in shallow waters at depths of up to approximately 150 m. Jack-ups are designed to move to a new site after operations are completed. The spudcan footings, which can be embedded up to three diameters deep in soft soil, must therefore be extracted by jacki...
Centrifuge tests investigating the effect of compressive preloading and consolidation on the subsequent uplift capacity of shallow skirted foundations that rest on lightly over-consolidated kaolin clay are reported. The uplift resistance, total and pore pressures at the foundation invert were monitored during the installation, consolidation and upl...
Helical anchors are used widely onshore and have recently been mooted as an innovative foundation
method for lightweight offshore structures. From structural considerations, as the load requirement for
each plate on a helical anchor increases, it becomes necessary to increase the diameter ratio of the
central shaft to the plate, and even to replace...
This paper presents a pioneering real-time hybrid testing method for geotechnical centrifuges. The method was used to investigate the behaviour of a jack-up leg reinstalled near an existing footprint, a problem that is highly non-linear, stress dependent and involves complex soil-structure interactions. By physically modelling only the footprint-le...
The soil response in the wake of dynamically installed (free-fall) projectiles is poorly understood, notably with respect to the potential for the hole the projectile creates during dynamic penetration to remain open. The work reported in this paper considered this problem through centrifuge tests in which the impact of free-falling projectiles on...
Current site investigation practice for offshore pipeline design relies on soil parameters gathered from boreholes or in situ test soundings to depths of 1–2 m below the mudline. At these depths, the fine-grained seabed is very soft and possesses low undrained strength, which can be difficult to measure. This paper describes a centrifuge test progr...
This paper provides experimental evidence that shows that the drained cyclic capacity of a plate anchor in dry dense sand may be higher than the equivalent monotonic capacity. The experimental data show that when cyclic loading is low relative to the monotonic capacity, increases in the eventual capacity are observed; when the magnitudes of the cyc...