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Finite element analysis of spherically voided biaxial slabs subject to static and seismic loading
No full textSpherically voided biaxial slabs (SVBS) present structural advantages for static loading which can lead to economic solutions. There exist however lacunae, in the knowledge on the behaviour of SVBS diaphragm systems when subject to seismic induced ground motion which, if overlooked, would restrict their future advancement and proliferation into seismic regions. The assertion, of lower floor seismic accelerations due to the 25-30% SVBS mass reduction, should factor the response uncertainty due to the diaphragm stiffness, higher natural frequency and floor acceleration magnification. The present research presents an innovative structural modellisation approach to facilitate the nonlinear transient dynamic analysis (NLTDA) of SVBS diaphragms by the transmutation of their in-plane diaphragm bending behaviour into 3D Kirchhoff beam finite elements. The SVBS diaphragm in-plane flexural response is captured using a novel adaptation of the 2D static-nonlinear moment-curvature analysis (2D-SNLMCA) procedure on partially-perforated RC diaphragms. A method is proposed for the 2D-plane stress (2D-PS) models to directly emulate the 3D-SVBS diaphragm behaviour by converting their 3D morphology into a 2D-PS diaphragm configuration without the need of using 3D-solid-continuum nonlinear finite element analysis. The numerical tools adopted were validated using available experimental data and verified using the closed-form differential equation of motion for a dynamic system and RUAUMOKO dynamic finite element suite. The 3D-NLTDA model accurately captured the global diaphragm demands in terms of force, deformation, floor acceleration magnification and ductility levels which are compared to the diaphragm 2D-SNLMCA capacity levels. Diaphragm energy dissipation optimisation is possible through an iterative matching approach of the seismic demands using the 3D-NLTDA with the diaphragm designed moment-curvature response from the 2D-SNLMCA. This shows that the proposed methodology could be adopted in the design towards increasing energy absorption and therefore reducing structural damage. The 3D-NLTDA shows that the better performance of SVBS diaphragms during a seismic event, compared to a solid diaphragm, is not by default due to their lighter mass, as sometimes claimed in the literature, but is conditional on the diaphragm stiffness, floor acceleration magnification and reinforcement levels which can be assessed using the proposed methods
The limits of energy sufficiency: A review of the evidence for rebound effects and negative spillovers from behavioural change
No full text‘Energy sufficiency’ involves reducing consumption of energy services in order to minimise the associated environmental impacts. This may either be through individual actions, such as reducing car travel, or through reducing working time, income and aggregate consumption (‘downshifting’). However, the environmental benefits of both strategies may be less than anticipated. First, people may save money that they can spend on other goods and services that also require energy to provide (rebounds). Second, people may feel they have ‘done her bit’ for the environment and can spend time and money on more energy-intensive goods and activities (spillovers). Third, people may save time that they can spend on other activities that also require energy to participate in (time-use rebounds). This paper reviews the current state of knowledge on rebounds and spillovers from sufficiency actions, and on time-use rebounds from downshifting. It concludes that: first, rebound effects can erode a significant proportion of the anticipated energy and emission savings from sufficiency actions; second, that such actions appear to have a very limited influence on aggregate energy use and emissions; and third, that downshifting should reduce energy use and emissions, but by proportionately less than the reduction in working hours and income
Voting with their Money: Brexit and Outward Investment by UK Firms
No full textWe study the impact of the 2016 Brexit referendum on UK foreign direct investment.
Using the synthetic control method to construct appropriate counterfactuals, we show
that by March 2019 the Leave vote had led to a 17% increase in the number of UK
outward investment transactions in the remaining EU27 member states, whereas transactions in non-EU OECD countries were unaffected. These results support the hypothesis that UK companies have been setting up European subsidiaries to retain access
to the EU market after Brexit. At the same time, we �nd that the number of EU27
investment projects in the UK has declined by around 9%, illustrating that being a smaller economy than the EU leaves the UK more exposed to the costs of economic
disintegration
Aspects of bonded composite assemblies for aerospace applications
No full textComposite airframes are designed to be lightweight and robust. In order to avoid the regions of enhanced stress around mechanical fasteners, composite airframes also make use of adhesives to bond components. In doing so, the stress concentrations arising from joining are distributed over a larger area. When joining composites with adhesives, it is important to consider the surface condition prior to bonding; any contaminant present at the surface may result in a reduction in performance. If contaminants are present, they must be appropriately removed before the adhesive is applied and this is one major area of interest in this work. A second major area relates to understanding how bonded composite structures perform under loading. Advancing up the design tree, mechanical testing becomes more expensive due to the costs of specimens and testing, and thus there is an onus to produce finite element (FE) models that can accurately predict how these structures may perform. FE models require experimental testing to be undertaken for model validation, and the mechanical testing of such a structural element and its behaviour in relation to an FE model of the test specimen is the second major area of this work.
With regard to the characterisation of surfaces to be bonded, two aspects were considered. The first aspect considered a limited investigation into two surface inspection techniques for pre-bond qualification that were considered to show potential for automation. Whilst both techniques were able to detect a release agent contaminant on all surfaces tested, both techniques were unable to discern a hydraulic oil or barrier cream contaminant on peel-ply finished surfaces; it was therefore concluded that further development, beyond the scope of this thesis, was required before they could be integrated into a production line.
The second aspect of work on surfaces to be bonded considered the atmospheric plasma treatment (APT) of a carbon fibre/epoxy resin composite surface. The removal of a silicone-based release agent using APT, characterised using surface analytical techniques, was coupled with adhesive bond strength measurements. Failure surfaces of adhesively bonded lap-shear joints that had been bonded at various intervals in time after treatment were also investigated. It was concluded that the contaminant was not removed, but rather converted to a more stable silica form.
The work on the bonded composite structure investigated the mechanical testing to failure of adhesively bonded composite T-Joint structural elements. The full-field strain contours exhibited by the T-Joints during the load cycle were obtained through digital image correlation and compared to the predictions of an existing finite element model. Good agreement was found between the model predictions and the measured strains. Regions of high strain indicated by both the digital image correlation results and the finite element analysis were indicative of potential failure initiation sites in the fractured specimens and there was some evidence of these initiation sites on the specimen fracture surfaces
Three-Dimensional Physico-chemical Characterization 1 of Coarse Atmospheric Particles from Urban and Arid Environment of India: An Insight into Particle Optics
No full textAerosol particles scatter and absorb solar radiation and affects earth's radiation budget. The aerosol particles are usually non-spherical in shape and inhomogeneous in chemical composition. For simplicity, these particles are approximated as homogeneous spheres/spheroids in radiative models and in retrieval algorithms of the ground and spaceborne observations. The lack of information on particle morphology (especially shape), chemical composition (that govern their spectral refractive indices) and most importantly internal structure (three Dimensional, 3D spatial distribution of chemical species) lead to uncertainty in the numerical estimation of their optical and radiative properties. Here, we present a comprehensive assessment of the particles' volumetric composition. The particles were collected from typical arid and urban environments of India and subjected to Focused Ion-Beam (FIB) coupled with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscope (EDS). Particles from the arid environment were observed to be composed of Fe, Ca, C, Al, and Mg rich shell with Si and O rich core opposed to those from urban environment consisting Hg, Ag, C, S and N rich shell with Cu and S rich core. Based on the homogeneous sphere/spheroid assumption, conventional SEM-EDS and FIB-SEM-EDS results, different particle model shapes [single species homogeneous sphere (S1) and spheroid (SPH1); multiple species homogeneously mixed sphere (S2) and spheroid (SPH2); and core-shell (CS)] were considered for simulating their respective optical properties; SSA (Single Scattering Albedo) and g (Asymmetric parameter). The effect of internal structure on SSA was found to be prominent in particles having low value of the imaginary part of refractive index (k). While the same was observed to be low (nearly negligible) for the particle with the high value of “k”. The particles rich in copper are found to be highly absorbing in nature which causes positive radiative forcing
On the relevance of detecting drugs in a fingerprint
No full textThis thesis explores the feasibility of testing for drugs from a fingerprint. Previous publications have reported drug detection in fingerprints from either drug users or after contact with a substance. There are possibilities to exploit these findings either for forensics (where a finger-mark is deposited at a crime scene to give intelligence about a donor) or for drug testing (where fingerprints are deposited under controlled conditions). In forensic science, it may be sufficient to know that a drug has been either handled or ingested within a specific time frame. In contrast, for drug testing, it may be necessary to exclude handling of drugs as a possible source. In either case, it is necessary to understand the significance of detecting a drug or its metabolite in a fingerprint.
This thesis explored the significance of detecting a selection of illicit drugs in fingerprints. In Chapter 4 and Chapter 5, a rapid analysis method based on paper spray high resolution mass spectrometry is developed and validated for cocaine and its metabolite, benzoylecgonine (BZE), and the method is applied to the fingerprints of non-drug users and drug users respectively. As a result, cocaine and BZE were found in samples from both non-drug users (set as environmental cut-off) and drug users. The detection rate from drug users was above 90 % and there were no false positive using this method. Moreover, handwashing involvement became indicative of either ingestion of cocaine OR recent contact with cocaine. In Chapter 6 and 7, imaging mass spectrometry techniques were employed to determine whether contact and ingestion scenarios can be distinguished via spatial distribution of analytes. Those results supported the hypothesis that hot spots would be formed in fingerprints after contact whereas analytes would be evenly distributed in fingerprints after ingestion. The presence of BZE was also used to in distinguishing fingerprint samples from the two scenarios. In Chapter 8 and 9, the paper spray mass spectrometry methodology was expanded to a selection of novel psychoactive substances (NPS) relevant to a prison environment using fingerprints for the first time. The method was applied to the fingerprints of prisoners before and after participants washed their hands. As a result, NPS substances were not detected from any participants, in agreement with their urine testing. Finally, in Chapter 10, the data collected in Chapter 4 and 5 was analysed retrospectively for detection of heroin and 6-AM in fingerprints to explore the possibility of carrying out an untargeted analysis. The sensitivity of the method was not as good as for cocaine and benzoylecgonine (BZE), which led to the lower detection rate of heroin and 6-AM than that of cocaine and BZE. However, this study proved that the paper spray method could still provide qualitative and quantitative results of heroin detection in fingerprints.
This study demonstrates that in the future with a suitable, deployable high resolution mass spectrometer, paper spray mass spectrometry could be used to detect cocaine, its metabolites and NPS for evidential purposes within the confines of a police station
A study on soil-structure interaction of offshore wind turbine foundations
No full textOffshore wind power is one of the most popular renewable sources of energy. However, there are many challenges during the design, construction and operation of offshore wind farms. One of these challenges is the stability of offshore wind turbines. The main loads on the foundations of wind turbines are from the environment (wind and wave) and there are other loads arising due to their operations (known as rotor frequency loads-1P and blade passing loads-2P/3P). All these 4 loads are unique in terms of magnitude, number of cycles and the strain they apply to the supporting soil.
Furthermore, due to innovation in turbine technology, the sizes of turbines also increased few folds (3MW to 12MW) in a span of about 5 years and these large turbines need customised foundations. Due to the attractiveness of this new technology and the reduction of LCOE (Levelized Cost of Energy), offshore wind turbines are also sited not only in deeper waters but also in seismic areas and other disaster-prone areas (typhoon and hurricane). Any new foundation must be validated using scaled model tests (i.e. study of Technology Readiness Level) to satisfy the industry requirements. This thesis developed techniques for scaled model testing to study different aspects of long-term performance of foundations.
The novel testing methodology and apparatus is based on understanding of the loads on the foundations. The apparatus consists of two eccentrically loaded gears which can be customised to apply cycloid loads. The apparatus can be easily upscaled to study bigger models and is very simple to assemble and operate. The apparatus can also apply millions of cycles of loading of different amplitude and frequency which is representative of a real wind turbine. Results from scaled model tests on few types of foundations are presented and they revealed interesting Soil-Structure Interaction. In a wind turbine system, long term performance is mainly governed by the SSI and this thesis summarised the limited field observations reported in the literature and compared with the laboratory observations.
One of the scientific challenges is the prediction of long-term performance of these relatively new and novel technologies. While scaled model tests can identify the physics, this is not a practical tool for routine design as it is difficult to create model tests for each of the sites. As a result, this thesis aimed to link the understanding of SSI to element testing of soil. This will allow to use the recovered sample from offshore wind farm location to carry laboratory tests to obtain design parameter. This thesis proposed a simple method to obtain the strain level in the soil which is beneficial for planning offshore Site Investigation.
Offshore wind turbines are currently designed for 25 to 30 tars and the number of cycles of loading are in the range of 100 million. This thesis presented data from element testing of soil where up to 50,000 cycles of loading were applied. The general trends of behaviour were noted, and it was observed that the soil behaviour was attaining a steady state. All the above helped to understand some SSI aspects of offshore wind turbines. Future work is also suggeste
Secure Millimeter Wave Cloud Radio Access Networks Relying on Microwave Multicast Fronthaul
No full textIn this paper, we investigate the downlink secure
beamforming (BF) design problem of cloud radio access networks (C-RANs) relying on multicast fronthaul, where millimeter-wave and microwave carriers are used for the access links and fronthaul links, respectively. The base stations (BSs) jointly serve users through cooperating hybrid analog/digital BF. We first develop an analog BF for cooperating BSs. On this basis, we formulate a secrecy rate maximization (SRM) problem subject
both to a realistic limited fronthaul capacity and to the total BS transmit power constraint. Due to the intractability of the non-convex problem formulated, advanced convex approximated techniques, constrained concave convex procedures and semidefinite
programming (SDP) relaxation are applied to transform it
into a convex one. Subsequently, an iterative algorithm of jointly optimizing multicast BF, cooperative digital BF and the artificial noise (AN) covariance is proposed. Next, we construct the solution of the original problem by exploiting both the primal and the dual optimal solution of the SDP-relaxed problem. Furthermore,
a per-BS transmit power constraint is considered, necessitating the reformulation of the SRM problem, which can be solved by an efficient iterative algorithm. We then eliminate the idealized simplifying assumption of having perfect channel state information (CSI) for the eavesdropper links and invoke realistic imperfect
CSI. Furthermore, a worst-case SRM problem is investigated. Finally, by combining the so-called S-Procedure and convex approximated
techniques, we design an efficient iterative algorithm
to solve it. Simulation results are presented to evaluate the secrecy rate and demonstrate the effectiveness of the proposed algorithms
Nanostructured materials plasma functionalised for electrochemical energy storage applications
No full textThe plasma treatment of few-layer graphene (FLG) was investigated for the effect on the performance in supercapacitors and microsupercapacitors. Modifications to the FLG surfaces were proven by comprehensive studies using characterisation techniques including elemental microanalysis, X-ray photoelectron spectroscopy, potentiometric titration, zeta-potential measurements and dispersion stability analysis.
A thermal pre-treatment to yield dried FLG was shown to increase the FLG surface charge and density due to the removal of adsorbed water and incorporation of carboxyl and phenolic functional groups. The thermal treatment was used before all characterisation methods were applied. An Ar gas plasma treatment on dried FLG was shown to introduce carboxyl and phenolic surface functional groups and reduce material variability. With increasing treatment time of Ar plasma, the FLG oxygen content increased by 1 at% due to the presence of a larger number of carboxyl functional groups.
The introduction of H2 gas at 3 wt% in Ar gas plasma produced a different functionalised FLG with a smaller quantity of carboxyl groups. Compared to the Ar gas plasma treated material, the H2/Ar gas treated material had a lower surface charge and density. NH3 gas plasma increased the nitrogen content of the FLG starting material two-fold according to XPS and elemental microanalysis. A multi-step treatment consisting of H2/Ar mixed gas plasma followed by NH3 gas plasma gave a further surface increase in nitrogen content by five times relative to the starting material.
Electrode films were manufactured using polytetrafluoroethylene (PTFE) and styrene-butadiene rubber (SBR) as non-conductive binders and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT/PSS) as a conductive binder. The electrode films were constructed into supercapacitors and microsupercapacitors. External testing with PTFE binder showed promise for the H2/Ar mixed gas plasma treated material with a specific capacitance of 195 F g-1 at 1 mA cm-2 in sulfuric acid electrolyte, a 50% increase relative to untreated FLG devices. The other treated materials did not match this performance because they did not contain low concentrations of oxygen surface functional groups and had large quantities of sp3 hybridised carbon atoms. The supercapacitor devices were studied with sulfuric acid and potassium hydroxide aqueous electrolytes. The devices with potassium hydroxide electrolyte did not match the performance of the materials in sulfuric acid electrolyte due to materials’ incompatibilities.
Supercapacitor testing was additionally carried out with SBR and carboxymethyl cellulose (CMC) in sandwiched devices alongside potassium hydroxide and sulfuric acid electrolytes. The manufacture of the electrode films required 20 wt% of SBR-CMC binder. The electrochemical results were indistinguishable and had large resistances.
An extensive investigation into the manufacture of flexible electrode films with FLG, multi-walled carbon nanotubes (MWCNT) and PEDOT/PSS in composite electrode materials was carried out. The electrode films were laser-etched into interdigitated patterns for planar micro-supercapacitor devices with the application of polyvinylalcohol-phosphoric acid gel electrolyte. These devices performed best with a mass ratio of 1:3:1 (PEDOT/PSS:FLG:MWCNT), and with NH3 functionalised FLG and acid functionalised MWCNT. Gravimetric capacitances of 120 F g-1 at 5 mV s-1 and volumetric capacitances of 20 F cm-3 at 5 mV s-1 were obtained for the NH3:MWCNT(Acid) combination during long cycling tests (10,000 cycles) and showed capacity retentions > 80%. In-situ Raman microscopy analysis suggested that the PEDOT/PSS component underwent pseudo-capacitive, reversible changes during cycling tests but the dominant electric-double layer capacitive-like response was due to the FLG and MWCNT materials, which were highly stable
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