STRUCTURAL INTEGRITY

Peridynamics

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.

composite materials

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.

Damage in a composite lamina subjected to underwater shock loading

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.

ICE-STRUCTURE INTERACTIONS

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.

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.

Impact damage assessment of reinforced concrete

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.

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.

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.

fatigue

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.

Hydrodynamic pressure distribution acting on a containership.

FLUID-STRUCTURE INTERACTION

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.

SOFT MATERIALS

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).

STRUCTURAL RELIABILITY

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.

MATERIAL DESIGN

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.

Variation of oxidation state in a rectangular G30/PMR-15 lamina with a pre-existing crack

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.

Parallel mid-body of the Panamax containership

ships&offshore structures

Ships and offshore structures are complex structures. Due to harsh marine environment, these structures may suffer from fatigue and corrosion damages.

subsea structures

Subsea structures are essential part of ocean structures including pipelines, cables and risers which are especially important for oil&gas field.

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.

Schematic layout of tuned mass dampers (TMD) and tuned liquid column dampers (TLCD) in the nacelle

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.

hydraulic fracturing

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.