Current projects

• Lifting objects off seabed

  PhD student

  Mason (Sen) Mei

  Supervisors

  Assoc Prof Yinghui Tian, Prof Mark Cassidy

  Most of us have experienced the difficulty of lifting our shoes up from muddy ground (the quintessential ‘stuck in the mud’). This tells us that uplifting an object off the seabed requires much greater than its own submerged weight. This is termed as breakout phenomenon. The most significant component of the resistance force emanates from the ‘suction’ generated. During uplifting the ‘suction’ will dissipate and an abrupt and significant reduction in uplift resistance may occur.

  The research aims to improve the understanding of breakout process to enable offshore engineering operations, where a wide variety of applications, such as decommissioning of offshore infrastructures and securing offshore foundations, would require the knowledge of this problem.

• Behaviour of embedded anchor chains

  PhD student

  Wenlong Liu

  Supervisors

  Assoc Prof Yinghui Tian, Prof Mark Cassidy

  Offshore floating facilities are required to be secured through a mooring system, which comprises anchors and mooring lines. The segment of the mooring line, predominately using metallic chain, is embedded in the soil to connect the embedded anchor and takes a reversed catenary shape. The friction capacity of the anchor line itself can take up a major component of the overall anchor capacity. The bearing capacity of embedded anchors is controlled by the chain inclination and depth at the padeye. Most of existing research and current design practices consider the anchor line profile in a two-dimensional vertical plane. The friction and normal soil resistance to the anchor chain are not coupled in the existing analytical design method of embedded anchor line.

  The aim of this research is to gain in-depth knowledge about the soil resistance to the chain links and advance the fundamental understanding of three-dimensional performance of the embedded anchor line. This research mainly uses numerical simulation method to investigate the bearing capacity and combined yield surface of the chain link. A new numerical approach based on a force-resultant macroelement plasticity model will be developed to implement three-dimensional analysis of the anchor line.

• Securing submerged floating tunnels

  PhD student

  Wei Lin

  Supervisors

  Assoc Prof Yinghui Tian, Prof Mark Cassidy

  A submerged floating tunnel is a conceptual design of a tunnel that floats in water, supported by its buoyancy (specifically, by employing the hydrostatic thrust, or Archimedes' principle). Although the idea can be stemmed back to the late 19th century, none submerged floating tunnel has been built yet. One of the key barriers for this promising new infrastructure is how the tunnel can be securely moored to the seabed. This project aims to provide an efficient geotechnical solution through a loop of conceptual development, numerical modeling, centrifuge modelling and final verification using large scale model tests. Expected outcomes include a rigorously verified mooring system, quality first-hand observations and scientific knowledge advance, which are expected to pave the way for constructing the first submerged floating tunnel.

• Cyclic capacity of horizontal plate anchors in sand

  PhD student

  Rene Kurniadi

  Supervisors

  Dr Shiaohuey Chow, Prof Mark Cassidy, Dr Anamitra Roy (co-supervisor)

  The emergence of offshore floating renewable energy devices requires economic anchor solutions for sand. Plate anchors could represent such a solution due to their high efficiency in resisting tensile uplift loading. The monotonic capacity of plate anchors is relatively well investigated in sand. However their performance under realistic and long term offshore environmental or cyclic loading is not well understood. This project aims to investigate the performance of horizontal plate anchors under cyclic loading in sand. The project will involve numerical modelling using advanced constitutive model and model anchor tests using state-of-the-art centrifuge modelling. The outcomes of the project will be integrated into an accessible design tool to enable better predictability of the anchor cyclic capacity in practice.

• Effect of partial drainage on plate anchor capacity in sand

  PhD student

  Zhenyu Liu

  Supervisors

  Dr Shiaohuey Chow (The University of Melbourne), Assistant Professor, Dr Mason Ghafghazi (University of Toronto), Associate Professor Yinghui Tian (University of Melbourne)

  Plate anchors could be a cost-effective solution for mooring offshore renewable energy devices, although their response to realistic loading under offshore conditions still requires a more robust understanding, particularly under partially drained conditions imposed by rapid loading rates (e.g. under severe storm condition). Partial drainage (or the worst case scenario of undrained condition) occurs when the water in the porous sand skeleton is unable to drain away upon loading, resulting in a rapid increase of pore water pressure or generation of excess pore water pressures. The reduced drainage has a significant effect on the sand strength, which, in turn, affects the capacity of plate anchors. To date, there is limited numerical capability in simulating partially drained capacity of plate anchors in sand. This joint University of Melbourne (UoM) – University of Toronto (UoT) project aims to investigate effect of partial drainage on plate anchor capacity in sand using numerical and experimental approaches. The outcomes of the project will be integrated into an accessible design tool to enable better predictability of anchors capacity under partial drainage in sand in engineering practice.

• Assessment of offshore geo-hazard and failure prediction using AI-ML

  PhD student

  Farid Fazel Mojtahedi

  Supervisors

  Dr Negin Yousefpour, Dr Shiaohuey Chow, Professor Mark Cassidy

  Offshore systems and subsea infrastructures are vulnerable to different natural geo-hazards, including turbidity currents, submarine landslides (and events that trigger tsunami), scour (seabed sediment mobility), and fluid flow. Such geo-hazards are the features that are commonly found in deep-marine settings. It is essential to early characterize, predict, and assess the risk and impacts of geo-hazards, particularly in deep remote fields, for operation maintenance of these systems and minimizing the failure, damage, and environmental risks. Assessment of geo-hazards is traditionally based on site investigation data that are exposed to considerable uncertainties for such factors as variable ground and water (current) conditions, dynamic nature of seafloor condition, lack of resolution, and gaps in survey data. Our understanding of Mass-transport complexes (MTCs) in the submarine and offshore environments have been improved nowadays as a result of emerging technologies. Nevertheless, there are still uncertainties about the way of evolution of the flow and volume behavior of MTCs during their translation, the factors controlling these changes, the relationship with their internal geometry and architecture, and the implications of MTC emplacement processes for the assessment of geo-hazard risk in sedimentary basins. Innovative predictive modelling and probabilistic approaches allow maximizing the interpretations, decreasing the required frequency of seafloor data acquisitions, and capturing the uncertainties. The purpose of the current research is providing innovative solutions for better understanding the offshore geo-hazards triggers and signs and assessing the risk of future geo-hazard events according to real-time, dynamic data obtained from the seafloor.

• Development of a Soil-Specific CPT Interpretation Method for Partially Drained Penetration

  PhD student

  Xingyi Wu

  Supervisors

  Assistant Professor, Dr Mason Ghafghazi (University of Toronto), Associate Professor Yinghui Tian (University of Melbourne), Dr Shiaohuey Chow (The University of Melbourne)

  The Cone Penetration Test (CPT) is a predominant site characterization tool since it provides a wealth of information on soils (e.g. pore water pressure, bearing capacity, and so on) with the fast and inexpensive application. The cone penetration process has a complicated interaction with the pore water in soils because of the generation of excess pore water pressures due to the penetration. This makes interpretation of CPT results particularly challenging. The joint research topic focuses on producing soil-specific CPT interpretation methods by accounting for the complicated nature of the soil, and the interaction of soil, water and the advancing cone. This project will involve the numerical modelling of the interaction between the cone and the soil during the penetration by employing the advanced soil constitutive model under different drainage conditions. The results from the numerical modelling will be used to propose a new interpretation method of CPT results. The outcome of this project will assist engineers to get more precise soil properties from CPT results.

• Engineering screw piles to secure offshore wind energy turbines

  PhD student

  Zeliang Li

  Supervisors

  Professor Mark Cassidy, Associate Professor Yinghui Tian

  Project start date: Feb 2022

  Screw piles or so-called helical anchors have been routinely used as foundations for land use to withstand relatively large tension load. Due to its relatively quiet installation process and strong capability to provide significant uplift resistance, its application on offshore wind industry is considered as a potential solution for larger scale turbines in deep water where the tension on the upwind footing could become a critical issue. This project will use innovative geotechnical methods to develop verified designs, guidelines and numerical tools for predicting the forces required to install screw piles into the seabed and their capacity to resist extreme wind and wave forces relevant to these structures. As foundations cost up to 35% of construction, screw piles will provide significant economic and environmental benefits in reducing costs and unlocking substantial renewable energy from our oceans.

• Developing a novel foundation to secure floating renewable energy turbines

  PhD student

  Behnam Norouzi

  Supervisors

  Professor Mark Cassidy, Associate Professor Yinghui Tian, Prof Guanlin Ye (SJTU), Dr Yifa Wang

  Project start date: May 2022

  Energy production based on fossil fuel reserves is largely responsible for carbon emissions, and hence global warming. The planet needs concerted action to reduce fossil fuel usage and to implement carbon mitigation measures. Offshore wind farms, as one of the best solutions, are becoming increasingly popular in the quest for renewable sources of energy, and different offshore wind turbines are being installed in different parts of the world.

  Despite the advantages, offshore wind farms are costly. Wind speeds increase with distance from the shore, producing higher loads on the turbines, requiring more robust structural design and higher transmission costs. In order to make offshore wind farms cost-effective, the turbines must be large and located in deep waters. These requirements increase the cost of the foundation structures, which can be a significant percentage of the total cost. Over 40% of the expenditure of wind turbines lies in the foundation solutions to secure the turbines. Various criteria and factors are considered in the design of these foundations, including: Water depth, soil conditions, and applied loads. Developing more economic as well as efficient foundations in marine environmental conditions is the key scientific challenge to tap the immense renewable energies, especially in deep waters. This research aims to develop such a geotechnical solution by methodically examining a novel foundation system to secure the game-changing floating turbines.

• Pipeline Walking and Lateral Buckling Problem

  PhD student

  Soumyajyoti Ghosh

  Supervisors

  Associate Professor Yinghui Tian, Professor Mark Cassidy,

  Project start date: Feb 2022

  Subsea pipelines for oil and gas transportation are laid at ambient sea temperature, but operated at high temperature and high pressure conditions.  Under these repeated cycles of start-ups and shut-downs a pipeline may move axially (Short Pipeline) or buckle laterally ( Long Pipeline); depending upon whether fully constrained effective axial force can be mobilized or not. An interaction between lateral buckling and walking is also a possibility.

  The aim of the research is to understand the pipeline walking and lateral buckling phenomenon individually, along with their interaction. The study will mostly focus on numerical and analytical Modelling. The expected outcomes will be beneficial for safe design of subsea pipelines against lateral buckling and walking.

• Soil-structure interaction framework for monopiles in sand under cyclic loading

  PhD student

  Olgu Orakci

  Supervisors

  Dr Shiaohuey Chow (University of Melbourne), Associate Professor Yinghui Tian ( University of Melbourne),  Assistant Professor Dr George Anoyatis (KU Leuven), Assistant Professor Dr Stijn Francois (KU Leuven)

  Project start date: June 2022

  Recent developments in the offshore renewable energy sector have resulted in bigger wind turbines and thus an increase in the most commonly used monopile foundation’s diameter to guarantee their performance, especially under higher lateral cyclic loads due to waves and wind. Taking into account the effects of the cyclic loading, especially on the long-term foundations’ capacity highlights the monopiles’ ability to control the response as well as the life span of such energy infrastructure. Despite the diverse group of available approaches to estimate cyclic soil-structure response, an alternative that can consider strain accumulation by means of a thermodynamically consistent, multi-surface plasticity framework to generate more accurate predictions of cyclic long-term displacements, remains still unexplored. In this regard, this joint KU Leuven (KUL) - University of Melbourne (UoM) project aims to develop a novel three-dimensional (3D) soil-structure interaction model for monopiles subjected to lateral cyclic loading in sand by means of a finite element solution using advanced soil constitutive modeling and laboratory testing. Theoretical development will include model calibration via a laboratory cyclic testing program and application to monopile-soil interaction problems including comparisons with predictions from existing models and available test data. The outcomes of the project will be integrated into an accessible design tool to enable better predictability of monopiles cyclic capacity in engineering practice.