Projects completed and being carried out by the Hydrodynamic Group

Dynamics of Spilled Oil

Two research students will start to work on this topic. One will look at how the behaviors of oil after just spilled, such as from an oil-tanker, are affected by water waves and/or motions of the oil-tanker; the other will study on the behaviors of oil in breaking waves near coastlines.

Nanofluid Dynamics

Nanofluid is formed by adding nano scale particles to normal fluid to produce a new homogeneous, stable, and high-performance fluid medium. Some research in recent years showed that a majority of nanofluids have a higher thermal conductive coefficient and some other have better characteristics than normal fluids. The main aim of this research is to study the motion features of nano particles in fluid and to better understand the behaviors of nanofluid properties. This project is financially supported by the school QR fund for three years.

New generation tool for estimating wave/current loads on marine structures comprising slender members

Structures with slender members are widely used in marine engineering, and include jack-ups and jacket platforms for oil-gas production and offshore wind energy platforms. Current methods used to model the effects of wave and current kinematics on these structures are too simplistic and not adequate for extreme conditions in harsh weather. The proposed tool will overcome these problems by developing a new computational tool. This work is supported by EPSRC – Finance South East Collaboration Fund.

Marine Renewable Energy

One PhD student is working on real time simulation of floating offshore wind energy systems. In this project, we are looking at interaction between turbines and floating platform and the role plaid by nonlinearity. The final aim of the project is to develop software which can perform real time simulation of a floating offshore wind energy system.

Effect of number of mooring lines on the responses of the FOWT system

In addition to this project, the Hydrodynamic Research group is also collaborating with researchers in Harbin Engineering University, China, on offshore wind energy system and wave energy system.

Apart from the above, Qingwei Ma carried out research on hydrodynamics associated with tidal turbine and wave energy device in 1980s and 1990s. Some reference papers are given below:

Ma, Q.W., 1995, "Nonlinear analysis on hydrodynamic performance of oscillating water column wave energy device with a lateral opening", Proceedings 14th Int. Conf. OMAE, Copenhagen, Vol.1, pp. 131-137.

Chen, Y.Y. and Ma, Q.W., 1990, "Study on a turbine based on Magnu's effect", Proceedings of International Conference of New and Renewable Energy, Beijing, China.

Ma, Q.W. and Zhu D.M., 1986, "Computation on hydrodynamic characteristics of cycloid propeller under turbine condition", Proceedings of International Symposium on Propeller and Cavitation, Wuxi, China, pp 51-57.

Nonlinear interactions between violent waves and elastic structures

This project is supported jointly by the Royal Society, the Royal Academy of Engineering, and the British Academy through the prestigious Newton International Fellowship.

The aim of the research is to improve understanding of fully nonlinear interaction between violent waves and 3D elastic structures and to provide knowledge that can help achieve safe and cost-effective design of structures. This will be achieved by extending the existing numerical methods proposed and developed by the research group.

Floating Bodies with Liquid Tanks in Steep Waves

This project is supported by the Leverhulme Trust, UK and lasts for two years from Jan 2009. The project is summarised as follows.

To make use of ocean resources, various types of floating structures with internal liquid tanks, such as FPSO (Floating Production Storage and Offloading) vessels, oil ships, LNG/LPG (Liquefied Natural/Petroleum Gas) carriers and cruise ships with swimming pool (e.g. Queen Mary 2), have been or will be designed and utilized. They are commonly exposed to water waves. The external water waves excite the motion of the floating structures, which could initiate so-called sloshing waves in the internal liquid tanks when they are partially filled. Such sloshing motions may be very violent, resulting in instantaneous large loads on the tank walls and causing damage. In addition, those loads also affect the response of the whole structures in waves and thus influence the manoeuvrability and safety of the structures. Therefore, the responses of such floating structures, considering both external wave effects and the motions of the liquid inside their internal tanks, have to be carefully investigated in order to ensure safety. Although a large volume of work has been dons in this area, the investigation on the fully coupling fully nonlinear interaction is rare. This project aims to make some contribution to fill the gap.

Numerically Modelling and Investigating Wind Effects on Freak waves

This project is supported by the Leverhulme Trust, UK and lasts for two years from 2007. The project is summarised as follows.

Freak waves (also called rogue waves) are extraordinarily large water waves in ocean. Although the occurrence of freak waves is considered as rare, they potentially pose severe hazards for mariners and man-made structures. Many incidents involving loss of many lives have been considered to be caused by freak waves and thus freak waves are a real threat to all human activities in the ocean.

Evidence has shown that the freak wave phenomenon must be affected by winds in many cases. Although various mechanisms and corresponding models have been suggested, wind effects are not satisfactorily taken into account. One may envisage that wind effects on freak waves may fall into two aspects. The first aspect is about whether wind itself can initiate the formation of freak waves while the second aspect is about how wind can influence the properties of freak waves that are generated mainly by other mechanisms. No paper dealing with the first aspect has been found. Only a few papers considering the second aspect are available in the open literature so far. The issues addressed in this proposal also fall into the second aspect but are well beyond the scope of the published papers in the sense that more general and complex cases are considered and the wind effects on waves are modelled by numerically solving for the air flow rather than by approximating the air pressure based on empirical models.

The originality of the proposed research is reflected by (a) addressing issues associated with wind effects on freak waves, which are important but have not yet been investigated; (b) performing extensive numerical simulations, rather than expensive physical experiments and (c) using a novel approach that has not yet been used elsewhere for wind effects on freak waves.

Comparison of freaks with (upper) and without (lower) wind effects (simulated by the QALE-FEM)

Interaction between Breaking Waves and Three-Dimensional Surface-Piercing Structures

This project is supported by the Leverhulme Trust, UK and lasts for three years from 2006. The project is summarised as follows.

Wave breaking has remained a great challenge in offshore/coastal engineering and scientific communities since it plays a vital role in air–sea interactions, bed-sea interactions and wave-structure interactions. Experimental studies can provide very useful and reliable results for some cases but are generally very expensive. Thus, researchers have made great efforts to study the phenomenon using numerical simulations. Most of them, however, have so far focused on two-dimensional (2D) problems. Only few attempts have been made to numerically investigate three-dimensional (3D) problems, such as those concerned with wave breaking over submerged bodies fixed on sea bed, but none with the interaction between breaking waves and 3D moving surface structures, as indicated by publications. It seems that two main barriers exist which deter researchers from performing thorough investigations on 3D problems of this kind. One is the plunging/splash coupled with the motion of structures, which is very difficult to deal with by using conventional numerical methods. The other is the requirement for a large amount of computational time as very fine grids (or mesh) and many small time steps are needed to model the flow after wave breaking.

The proposed research will pioneer a new way to numerically model the interaction between the breaking waves and structures (in particular, the cylindrical ones). The results obtained will lead to better understanding of the phenomenon, which is very important for securing and improving the safety of structures used in several engineering disciplines, but are rarely available now. Although this research targets the interaction between the breaking waves and structures, the method and computer codes developed may be extended to problems in other areas, such as coastal protection, waste/pollutant (such as oil) transportation due to breaking waves, breaking of internal waves in ocean and so on, which are of great interest to environmental and oceanographic communities.

Water impact on a wall

Hydrodynamic behaviours of Gliding Hydrofoil Crafts

This is a joint project with Jiangsu University of Science and Technology, China, supported by the Royal Society, UK and lasting for two years from 2006.

The general purpose of this research is to numerically and experimentally study unsteady hydrodynamic behaviours of a new developed high-speed watercraft – Gliding Hydrofoil Crafts (GHCs). The specific objectives include 1) extending the existing computer code for nonlinear water waves to being able to deal with unsteady hydrodynamic problems associated with Gliding Hydrofoil Crafts; 2) carrying out model tests to measure the total forces acting on the craft and pressure at some points on the craft hull; 3) investigating the interaction between the hydrofoil and gliding under-surface to help designers to find better combination of these two components; 4) investigating the unsteady behaviours in transitional modes; and 5) investigate the unsteady behaviours during craft turning at different speed.

The waves generated by a moving ship with a hydrofoil underneath

(Froude number is about 0.5 and without incoming waves) and simulated by the QALE-FEM

Non-linear Response of Moored Floating Structures to Steep Waves

This project is awarded by EPSRC, UK and lasts for three years to March 2006. The project can be summarised as follows.

Use of moored floating structures, such as SPARs and FPSOs, as production and/or storage systems is now ever-increasing practice in offshore oil and gas industry, particularly with the operation moving to deep sea in the new century. Operating in such an environment, the structures are likely to expose to very hash seas and extremely steep waves because they have to remain on sites even when encountering severe weather. Such a situation implies that the vessels of this kind may not avoid undergoing large motions and large loading, which will result in many undesired consequences, such as disturbing the operation of facilities on board, increasing the risk for the system to be damaged and so on. Much previous work has suggested that the interaction between moored floating structures and extremely steep waves need to be addressed with great care and has identified that fully nonlinear analysis is necessary to deal with it. However, there are many challenges associated with the analysis in the framework of fully nonlinear theory.

Free response of 2D body in water waves

Response of a 3D Wigley Hull to steep waves with a incident angle of 15^o

(please click here to download the movies of the free-response case or here for fixed cases)

2D Overturning waves (slope of bed: 1:15) (Please click here to download the movie)

3D Overturning waves on 3D bed

Tank length: 19d; Width: 8d; Initial wave height: 0.6d; slope of bed 1:15; total CPU time: 54 minutes on a normal PC (Pentium Ⅳ 2.53GHz processor, 1G RAM) for the computing period from to

(Please click here to download the movie)

Coupled Nonlinear Motion of Moored Floating Structures with Water Columns in Open-Bottom Tanks

This work examines the behaviour in ocean waves of moored floating structures that incorporate open-bottom tanks on their submerged hull geometry. These tanks contain water columns that can flow in or out through their open bottoms, and may also include a volume of trapped air on the top of such water columns, which acts as a spring. The motion of the floating structure is influenced by interactions between the vessel, the air springs and the water columns underneath them. During operations, the volume of air above the water columns can be trapped or allowed to flow freely to and from the atmosphere.

The complete nonlinear equations of motion for the whole system are derived. These equations include nonlinearities not only due to the products of the motions of the floating structure and water columns but also due to coupled products of the motions of the rigid body and the water columns. Numerical results show that the effects of such nonlinearities may be important for many cases.

Interaction of Steep Waves with Offshore Structures

In this work, a new methodology and corresponding computing code for simulating three-dimensional interaction between steep waves and structures were developed based on a fully nonlinear wave theory. The associated boundary value problem was solved using a finite element method. A recovery technique was implemented to improve the FEM solution. The velocity was calculated by a numerical differentiation technique. The corresponding algebraic equations were solved by the conjugate gradient method with an SSOR preconditioner. The radiation condition at a truncated boundary was imposed based on the combination of a damping zone and the Sommerfeld condition. The numerical results had been compared by other researchers and by the investigators with the some analytical solutions and experimental data, which showed very good agreements. This was a piece of innovative work in this area. To investigator’s knowledge, there had been no similar work published at that time.

Numerical Investigation on moored SPAR platforms in ocean waves

Its aim was to numerically simulate the performance of SPAR platforms subjected to the ocean waves and current. The forces acting on the SPAR were calculated based on a slender body theory. The coupling between the SPAR and mooring lines were modelled by assuming the mooring lines to be nonlinear springs or by matching the motion equation of the mooring lines with the dynamic response of the SPAR. The vessel's motion was simulated in time domain using fully nonlinear motion equations. The adaptive Runge-Kutta method was employed for numerical solution of the differential equations. The most important contribution in this work was that some nonlinear effects ignored in previous work were identified to be considerably important in many cases.

Modelling Marine Structures Subjected to Underwater Explosions

This project was supported by a big company. It aimed to numerically investigate the critical issues associated with the use of finite element methods in modelling the interaction between structures and shock waves induced by underwater explosions. This work was carried out using commercial packages - LS-DYNA, ABAQUS and RADIOSS. The important results of this work were a set of guidance on how to modelling the structural responses under the condition of underwater explosions, which could be used by engineers in the company to solve critical problems they were concerned with.

Second Order Solution of Transient Waves

Although the second order theory had been widely used in frequency domain, the rare solution had been published about non-linear transient waves in time domain. In this work, an analytical solution in time domain based on the perturbation method was derived. An important application of the solution is to be used as check tool for numerical models.

Drift Force Calculation on Moored Offshore Structures

This project was financially supported by British Council. The work was associated with the numerical calculation of the wave drift (second order) forces on moored floating structures. A computer code was developed based on a boundary element method, which was combined with linear analysis code of UCL. This code has been used to evaluate second order wave forces and moments on the mooring vessels of mono-hulls and tandem hulls.

Drift Force on a Submerged Sphere

An analytical solution to calculate the nonlinear wave drift force on a sphere based on perturbation theory in this work. It can be used to analyse the performance of the sphere-like mooring structures.

Numerical Modelling the Performance of Wave Energy Device

A numerical method based on a boundary element method to analyse the hydrodynamic performance of a wave energy device was suggested. In this method, some nonlinear effects were considered. It can also be used for the analysis of the other problems associated with water column motions, e.g., in a moon pool of some offshore structures.

Numerical and Experimental Investigation on cycloidal propellers and turbines

This was a special type of propeller used in naval architecture. The propeller has vertical axes and several blades whose attack angles are adjustable to achieve a higher efficiency. The device could also be used as a turbine for extracting energy from tidal current and wind. Extensive experimental investigation was carried out and a numerical method was suggested based on lifting-line theory to modelling its performance.

Study on a turbine based on Magnu's effect

This project was to develop a numerical method to model the performance of a turbine based on Magnu's effect and to carry out the investigations on feasibility to use it for extracting energy from tidal current.