Our research centre mainly focuses on the following research areas by using some of the state-of-the-art techniques including peridynamics and inverse finite element method (iFEM).
The peridynamic theory provides the capability for improved modeling of progressive failure in materials and structures. Further, it paves the way for addressing multi-physics and multi scale problems. Even though numerous journal articles and conference papers exist in the literature on the evolution and application of the peridynamic theory, it is still new to the technical community. Please see below for numerous application areas of peridynamics performed by PDRC researchers.
INVERSE finite element method
Inverse Finite Element Method (iFEM) is a new approach for real-time monitoring of structures. iFEM basically allows prediction of full-field displacements, strains and stresses by collecting strain data from discrete locations. iFEM does not require loading information to make predictions. Using full-field displacement information, shape sensing analysis can be done. Using full-field strain and stress information, structural health monitoring can be done. Please see below for various areas of iFEM that PDRC researchers are working on.
Damage initiation and its subsequent propagation in fiber-reinforced composites are not understood as clearly as they are, for example, for metals because of the presence of stiff fibers embedded into the soft matrix material, causing inhomogeneity. Under the assumption of homogeneity, a lamina has orthotropic elastic properties. Even though this assumption is suitable for stress analysis, it becomes questionable when predicting failure. Most composite structures include notches and cutouts, not only reducing the strength of the composites but also serving as potential failure sites for damage initiation. They also promote common failure modes of delamination, matrix cracking, and fiber breakage. These failure modes are inherent to the inhomogeneous nature of the composite, thus the homogeneous material assumption taints failure analyses.
Researchers: Dr. Cagan Diyaroglu, Ms. Yan Gao, Mr. Yakubu Galadima, Ms. Jeeyeon Heo
CORROSION DAMAGE MODELLING
Due to their unpredictability, rapid growth and difficulty of detection, localised forms of corrosion represent a threat to human life and the environment. The current empirical and semi-empirical approaches used by engineers to hinder corrosion damage have several disadvantages and limitations. In this regard, numerical approaches can be a valuable complement. However, the majority of the numerical techniques currently available in the literature are based on partial differential equations, which become invalid in the presence of field’s discontinuities such as cracks and sharp concentration gradients. In order to overcome these limitations, a recently introduced continuum theory of mechanics based on integro-differential equations, peridynamics, is used modelling of polycrystalline fracture, stress-corrosion cracking, pitting corrosion and crack propagation from corrosion pits in materials exposed to different corrosive environments.
Researchers: Dr. Dennj De Meo, Mr. Andrzej Czerwonka, Mr. Mingyang Li, Mr. Zhenghao Yang, Mr. Ademolu Richard, Ms. Olena Karpenko
The Arctic is considered as the Middle East of the future. Around 30% of the world’s undiscovered gas and 13% of the world’s undiscovered oil are expected to be stored in the North Arctic Circle. Despite of its advantages, utilization of the Arctic region for sailing brings new challenges due to its harsh environment. Therefore, ship structures must be designed to withstand ice loads in case of a collision between a ship and ice takes place. Such incidents can cause significant damage on the structure which can yield flooding and sinking of the ship. In order to capture the macro-scale behaviour of ice, well-known Finite Element Method (FEM) has been used in various previous studies. The effectiveness of computational techniques such as finite elements in modelling material failure has lagged far behind their capabilities in traditional stress analysis. This difficulty arises because the mathematical foundation on which all such methods are based assumes that the body remains continuous as it deforms. By taking into account all these challenging issues, a state-of-the-art technique, peridynamics can be utilized for ice-structure interaction modelling.
Researchers: Mr. Bozo Vazic, Mr. Xu Ji, Ms. Wei Lu
The components of Integrated Circuit (IC) devices are susceptible to moisture absorption at different stages of the production environment which can lead to hygrothermal stresses during the surface mounting process. The moisture concentration in electronic packages can be determined based on the wetness approach. If the saturated concentration value is dependent on temperature or time, the analogy between the wetness equation and the standard diffusion equation is not valid and requires special treatment. Peridynamics is utilized for the solution of wetness field equation in the case of saturated concentration varying with time.
Researchers: Dr Cagan Diyaroglu
EXTREME LOADING ON STRUCTURES
Efficient quantitative assessment of damage to structures is an active need that hasn’t been satisfactorily addressed. From a defense perspective, damages to structures stem from two main modes of loading: explosions leading to airblast loading on a structure, and direct strikes causing damage through penetration. In some cases both modes coexist. Both of these loading modes have the potential to cause extensive damage on both the external and internal structure. Detection of damage in structures may be straight-forward through visual inspection (cracks, holes, etc.). However, quantification of damage is a daunting task. In addition to the damage that is visible, there exists further damage internal to components and at joints of components. On-site evaluation of damage that is not visible involves expensive specialized equipment, and may not be fully satisfactory in visualization of internal damage. Therefore, damage assessment process stands to benefit from its augmentation by computational modelling and analysis.
Researchers: Dr. Cagan Diyaroglu, Ms. Yan Gao, Ms Jeeyeon Heo
STRUCTURAL HEALTH MONITORING
Structural health monitoring (SHM) is a procedure that obtains precise real-time information from a structure regarding its global or local structural state. The main objective of SHM is the detection of unusual structural behaviors, which pinpoint failure or an unhealthy structural condition. Detection of an unhealthy condition not only contributes to the detailed inspection plan of the structure, but also reduces uncertainty concerning the structure that is being monitored. The exercise of SHM serves to both increase human and environmental safety while at the same time reducing maintenance costs. As a consequence, it is necessary to develop a SHM system that uses the measured data obtained from the on-board sensors for any type of practical engineering applications such as bridges, ships, aerospace vehicles etc.
Researchers: Dr. Adnan Kefal, Mr. Mingyang Li, Mr. Yildirim Dirik, Mr. Jimmy Mayang
STRUCTURAL analysis of renewable energy devices
Renewable energy is energy that is collected from renewable resources, which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat. Offshore Wind Turbines are becoming a very popular renewable energy source for electricity generation. However, marine environment is a harsh environment and can cause fatigue and corrosion damages which should be taken into accound for the safety and durability of offshore renewable energy devices.
Researchers: Dr. Adnan Kefal, Mr. Mingyang Li
fire damage modeling
Composite materials are increasingly used in marine industry as in many other sectors including aerospace and automotive. For instance fiberglass reinforced plastic (FRP) materials have many advantages over other traditional metallic materials such as (i) resistance to the marine environment, (ii) lightweight, (iii) high strength, (iv) seamless construction, (v) low maintenance and (vi) durability. Moreover, composite materials can provide a step change in vessel efficiency both in terms of energy use and maintenance costs. Although these materials have many advantages, one of the biggest disadvantages of composites is their poor fire performance. Composite materials are usually composed of glass or carbon fibre and polymer matrix material and they are flammable. Therefore, understanding the damage and failure in fire condition is a crucial issue for safety since the damage induced by fire may result in collapse of the marine structure which may cause injuries and deaths.
Researcher: Ms. Yan Gao
Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly.
Researcher: Mr. William Lee Dickie
Fatigue is the weakening of a material caused by repeatedly applied loads. It is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values that cause such damage may be much less than the strength of the material typically quoted as the ultimate tensile stress limit, or the yield stress limit. Fatigue occurs when a material is subjected to repeated loading and unloading. If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators.
Researchers: Mr. Ning Zhu, Dr. Cemal Kochan, Mr. Kyutack Hong, Ms. Olena Karpenko
fracture in lithium-ion batteries and fuel cells
Hybrid propulsion system has become popular in marine industry due to increasingly strict emission control standards. Hence, as one component in the system, marine batteries become attractive in marine design. Solid Oxide Fuel Cells (SOFCs) and lithium ion battery are the most promising energy storage devices in the electric propulsion system or HPS. Since silicon particles expands around 400% in volume during lithation, the battery electrodes will experience large volumetric change during normal battery cycling. As a result, misdistribution of stress may form inside the battery electrode. Therefore, degradation and delamination may happens in the battery electrode after many cycling process of marine battery.
Researcher: Dr. Hanlin Wang
Fluid–structure interaction (FSI) is the interaction of some movable or deformable structure with an internal or surrounding fluid flow. Fluid–structure interactions are a crucial consideration in the design of many engineering systems, e.g. aircraft, spacecraft, engines and bridges. Aircraft wings and turbine blades can break due to FSI oscillations. Fluid–structure interactions also occur in moving containers, where liquid oscillations due to the container motion impose substantial magnitudes of forces and moments to the container structure that affect the stability of the container transport system in a highly adverse manner.
Researchers: Dr. Cagan Diyaroglu, Dr. Adnan Kefal, Mr. Yildirim Dirik, Mr. Cong Nguyen, Mr. Mingyang Li
Metal-based additive manufacturing, or three-dimensional (3D) printing, is an emerging technology across various industries including the marine industry. Manufacturing metal components layer by layer increases design freedom and manufacturing flexibility. Therefore, complex geometries can be easily created, product customisation can be enhanced and time to market can be shortened. However, currently only a few number of alloys can be reliably printed. Metal-based additive manufacturing often involves the deposition of layers of an alloy feedstock in the form of powders or wires, which are melted together by a rapidly moving heat source to form a solid mass. The rate of solidification is often an order of magnitude higher than that is seen during conventional casting techniques, and the process of building up layers causes non-uniform cooling. This leads to thermal stresses in the alloy which can generate cracks known as hot tears.
Researchers: Ms. Olena Karpenko, Mr. Bingquan Wang
NONLOCAL CONTINUUM MECHANICS
Nonlocal continuum mechanics is becoming increasingly popular with the development of new materials and systems such as carbon nanotubes and graphene. Nonlocal continuum mechanics has a length scale parameter which doesn’t exist in classical techniques. Therefore, it can represent non-classical physical phenomena. Moreover, it is computational more adventageous with respect to atomistic techniques since it is a continuum approach.
Researchers: Mr. Bingquan Wang
Soft materials are important in a wide range of technological applications. They may appear as structural and packaging materials, foams and adhesives, detergents and cosmetics, paints, food additives, lubricants and fuel additives, rubber in tires, etc. In addition, a number of biological materials (blood, muscle, milk, yogurt, jello) are classifiable as soft matter. Liquid crystals, another category of soft matter, exhibit a responsivity to electric fields that make them very important as materials in display devices (LCDs).
Researcher: Ms. Yunke Huang
artificial intelligence/machine learning
Artificial intelligence (AI), sometimes called machine intelligence, is intelligence demonstrated by machines, in contrast to the natural intelligence displayed by humans and other animals. AI is “a system’s ability to correctly interpret external data, to learn from such data, and to use those learnings to achieve specific goals and tasks through flexible adaptation”.
Structural inspection is a critical part of the ship structural integrity assessment. Corrosion, as a very pervasive type of structural degradation, can potentially lead to catastrophic failure or unanticipated out of service time. In order to mitigate the unfavourable consequences of age-related structural failure, a wisely planned inspection is needed. The current practice of calendar-based inspection of ship structures may cause either an unexpected stoppage during normal routine due to unpredicted structural failures or yield higher costs for unnecessary inspections. Therefore, a strategy to determine timely and effective inspection plans is highly desirable. This is why there is recently a growing interest in the reliability-based inspection planning of ship structures. Reliability procedures are believed to have substantial potential to provide the ship owners and operators with a tool for rationalizing the determination of the inspection interval in order to maximize the efficiency of inspections and minimize cost of inspection by avoiding unnecessary gauging surveys.
Researchers: Mr. Luigi Russo, Mr. Akmal Azizan
Desalination is a process that takes away mineral components from saline water. Saltwater is desalinated to produce water suitable for human consumption or irrigation. Most of the modern interest in desalination is focused on cost-effective provision of fresh water for human use. Due to its energy consumption, desalinating sea water is generally more costly than fresh water from rivers or groundwater, water recycling and water conservation. However, these alternatives are not always available and depletion of reserves is a critical problem worldwide. Currently, approximately 1% of the world's population is dependent on desalinated water to meet daily needs, but the UN expects that 14% of the world's population will encounter water scarcity by 2025.
Researchers: Dr. Islam Amin, Mr. Bozo Vazic, Mr. Wenxuan Xia
With the advancement of manufacturing techniques including 3-D printing, designing new materials with superior properties are now possible. Computational techniques can play a crucial role in the design process.
Researchers: Mr. Wenxuan Xia, Mr. Zhenghao Yang, Mr. Yakubu Galadima
oxidation damage in composites
Surface oxidation degrades the durability of polymer marix composites operating at high temperatures due to the presence of strong coupling between the thermal oxidation and structural damage evolution. The mechanism of oxidation in polymer matrix composites leads to shrinkage and damage growth. The thermo-oxidative behavior of composites introduces changes in diffusion behavior and mechanical response of the material.
Ships and offshore structures are complex structures. Due to harsh marine environment, these structures may suffer from fatigue and corrosion damages.
Researchers: Dr. Cagan Diyaroglu, Dr. Adnan Kefal, Mr. Cong Nguyen, Mr. Yildirim Dirik, Mr. Jimmy Mayang
Subsea structures are essential part of ocean structures including pipelines, cables and risers which are especially important for oil&gas field.
Researchers: Mr. Michael Ogbeifun, Mr. Daniel Mancini
Nuclear fuel pellets are used to generate heat for power generation as a result of fission process. Therefore, it is essential to understand its thermal transport for enhancing power output and preventing potential accidents. Uranium dioxide (UO2) is the main component of the fuel pellet. Its composition can have both an excess and deficiency of oxygen relative to stoichiometric UO2. Studies by show that in hyper-stoichiometric Urania (UO2 + x), the oxygen ions tend to accumulate in the regions of high temperature gradient or the Soret effect (the transport of oxygen atoms due to a temperature gradient). It is experimentally found that the thermal conductivity of UO2 decreases with temperature and with increasing non-stoichiometry. The fuel pellets are placed in a cladding and there exists a gap between fuel pellet and the cladding. The cooling water passing through the fuel elements extracts heat from the nuclear fuels. However, significant microstructural changes and deterioration of the fuel pellet occur due to the fission process. As a result, the degraded physical state of the fuel becomes the limiting factor for long term and transient reactor performance.
SHIP COLLISIONS & GROUNDING
Accidents can happen at any time due to human error, technical problems or harsh environmental conditions. For the ships, accidents may occur in several forms such as collision of two ships, collision of ship with a flexible offshore structure or grounding phenomenon. All of these may result in undesirable and catastrophic consequences including human life loses, environmental problems due to oil spill, etc. Hence, it is important to take into account the possibility of any form of accidents during the design process in order to reduce the unexpected outcome of these accidents.
Researchers: Dr. Cagan Diyaroglu, Mr. Cong Nguyen
structural control of offshore wind turbines
High flexibility of new offshore wind turbines (OWT) makes them vulnerable since they are subjected to large environmental loadings, wind turbine excitations and seismic loadings. A control system capable of mitigating undesired vibrations with the potential of modifying its structural properties depending on time-variant loadings and damage development can effectively enhance serviceability and fatigue lifetime of turbine systems.
Researcher: Mr. Arash Hemmati
nanomechanics: graphene fracture & nanoindentation
Traditionally, there exist two main approaches to simulate the mechanical behavior of materials at the nano-scale. The first approach is based on Classical Continuum Mechanics (CCM) when the continuum assumption is valid. When nano-scale effects become significant, it is no longer applicable since it does not have a length-scale parameter. Furthermore, its equation of motion is not suitable for problems including discontinuities since the spatial derivatives are not defined in such cases. The second approach is based on Molecular Dynamics (MD). It is a powerful tool as long as the interactions between atoms and molecules are well defined. However, even with current powerful supercomputers, the total simulation time and size of the models are still limited. Therefore, it is necessary to use a methodology that is based on continuum mechanics and have a length scale parameter to capture the nano-scale effects. Furthermore, it should be applicable for problems with discontinuities. Peridynamics is a suitable approach for this since it is a continuum mechanics formulation with a length scale parameter.
Researcher: Dr. Cagan Diyaroglu, Mr. Ning Zhu
The hydraulic fracturing process creates and propagates cracks in a porous medium by injecting fluid pressure. It has gained significant attention as a result of its use in oil and gas extraction from unconventional shale resources. In this particular application, a mixture of hydraulic fluid, sand, and chemicals is pumped into a well to create cracks in low-permeable shale, and keep them open after the removal of the fluid. Once the process is complete, the permeability of the shale increases significantly; thus, oil and/or gas starts to flow through the well. Another application of hydraulic fracturing concerns heat extraction from geothermal resources. Similar to the technique used in oil and gas extraction, the permeability of hot rocks is enhanced by pumping cold water into the rock. Cold water can be pumped from one well (injection well), and hot water can be extracted from the other well (production well). This technique, known as Hot Dry Rock (HDR), is used in the production of electricity.
vortex particle method
Vortex Particle Method is a technique for fluid flow simulations.