3,534 research outputs found
Silicon Derived from Glass Bottles as Anode Materials for Lithium Ion Full Cell Batteries.
Every year many tons of waste glass end up in landfills without proper recycling, which aggravates the burden of waste disposal in landfill. The conversion from un-recycled glass to favorable materials is of great significance for sustainable strategies. Recently, silicon has been an exceptional anode material towards large-scale energy storage applications, due to its extraordinary lithiation capacity of 3579 mAh g-1 at ambient temperature. Compared with other quartz sources obtained from pre-leaching processes which apply toxic acids and high energy-consuming annealing, an interconnected silicon network is directly derived from glass bottles via magnesiothermic reduction. Carbon-coated glass derived-silicon (gSi@C) electrodes demonstrate excellent electrochemical performance with a capacity of ~1420 mAh g-1 at C/2 after 400 cycles. Full cells consisting of gSi@C anodes and LiCoO2 cathodes are assembled and achieve good initial cycling stability with high energy density
Design criteria of a transcutaneous power delivery system for implantable devices.
Implantable cardiac assist devices such as artificial hearts and blood pumps are a rapidly growing therapy used for treating moderate to severe congestive heart failure. While current treatments offer improved heart failure survival and increased patient functionality with enhanced quality of life, powering these devices are still constraining. In practice, percutaneous cables passing through skin are used for power and control data transmission requiring patients to maintain a sterile dressing on the skin cable-exit site. This contact site limits patient movement as it is vulnerable to wound infection due to trauma and poor healing. As a result, a sterile dressing has to be maintained and nursed regularly for treating the wound. Complications from the exit site infections are a leading cause of death in long-term support with these devices. Wireless power and control transmission systems have been studied and developed over years in order to avoid percutaneous cables while supplying power efficiently to the implanted device. These power systems, commonly named Transcutaneous Energy Transfer (TET) systems, enable power transmission across the skin without direct electrical connectivity to the power source. TET systems use time-varying electromagnetic induction produced by a primary coil that is usually placed near skin outside the body. The induced voltage in an implanted secondary coil is then rectified and regulated to transfer energy to an implanted rechargeable battery in order to power the biomedical load device. Efficient and optimum energy transfer using such transcutaneous methods is more complex for mobile patients due to coupling discrepancies caused by variations in the alignment of the coil. The research studies equivalent maximum power transfer topologies for evaluating voltage gain and coupling link efficiency of TET system. Also, this research adds to previous efforts by generalizing different scenarios of misalignments of different coil size that affects the coupling link. As a whole, this study of geometric coil misalignments reconsiders potential anatomic location for coil placement to optimize TET systems performance in anticipated environment for efficient and safe operation.--Abstract
Structural vibration energy harvesting via bistable nonlinear attachments
A vibration-based bistable electromagnetic energy harvester coupled to a directly excited host structure is theoretically and experimentally examined. The primary goal of the study is to investigate the potential benet of the bistable element for
harvesting broadband and low-amplitude vibration energy. The considered system consists of a grounded, weakly damped, linear oscillator (LO) coupled to a lightweight, damped oscillator by means of an element which provides for both cubic
nonlinear and negative linear stiness components and electromechanical coupling elements. Single and repeated impulses with varying amplitude applied to the LO are the vibration energy sources considered. A thorough sensitivity analysis of the
system's key parameters provides design insights for a bistable nonlinear energy harvesting (BNEH) device able to attain robust harvesting efficiency. Energy localization into the bistable attachment is achieved through the exploitation
of three BNEH main dynamical regimes; namely, periodic cross-well, aperiodic (chaotic) cross-well, and in-well oscillations.
For the experimental investigation on the performance of the bistable device, nonlinear and negative linear terms in the mechanical coupling are physically realized by exploiting the transverse displacement of a buckled slender steel beam;
the electromechanical coupling is accomplished by an electromagnetic transducer
A Detail Based Method for Linear Full Reference Image Quality Prediction
In this paper, a novel Full Reference method is proposed for image quality
assessment, using the combination of two separate metrics to measure the
perceptually distinct impact of detail losses and of spurious details. To this
purpose, the gradient of the impaired image is locally decomposed as a
predicted version of the original gradient, plus a gradient residual. It is
assumed that the detail attenuation identifies the detail loss, whereas the
gradient residuals describe the spurious details. It turns out that the
perceptual impact of detail losses is roughly linear with the loss of the
positional Fisher information, while the perceptual impact of the spurious
details is roughly proportional to a logarithmic measure of the signal to
residual ratio. The affine combination of these two metrics forms a new index
strongly correlated with the empirical Differential Mean Opinion Score (DMOS)
for a significant class of image impairments, as verified for three independent
popular databases. The method allowed alignment and merging of DMOS data coming
from these different databases to a common DMOS scale by affine
transformations. Unexpectedly, the DMOS scale setting is possible by the
analysis of a single image affected by additive noise.Comment: 15 pages, 9 figures. Copyright notice: The paper has been accepted
for publication on the IEEE Trans. on Image Processing on 19/09/2017 and the
copyright has been transferred to the IEE
Selection of the key earth observation sensors and platforms focusing on applications for Polar Regions in the scope of Copernicus system 2020-2030
An optimal payload selection conducted in the frame of the H2020 ONION project (id 687490) is presented based on the ability to cover the observation needs of the Copernicus system in the time period 2020–2030. Payload selection is constrained by the variables that can be measured, the power consumption, and weight of the instrument, and the required accuracy and spatial resolution (horizontal or vertical). It involved 20 measurements with observation gaps according to the user requirements that were detected in the top 10 use cases in the scope of Copernicus space infrastructure, 9 potential applied technologies, and 39 available commercial platforms. Additional Earth Observation (EO) infrastructures are proposed to reduce measurements gaps, based on a weighting system that assigned high relevance for measurements associated to Marine for Weather Forecast over Polar Regions. This study concludes with a rank and mapping of the potential technologies and the suitable commercial platforms to cover most of the requirements of the top ten use cases, analyzing the Marine for Weather Forecast, Sea Ice Monitoring, Fishing Pressure, and Agriculture and Forestry: Hydric stress as the priority use cases.Peer ReviewedPostprint (published version
Spatial mode storage in a gradient echo memory
Three-level atomic gradient echo memory (lambda-GEM) is a proposed candidate
for efficient quantum storage and for linear optical quantum computation with
time-bin multiplexing. In this paper we investigate the spatial multimode
properties of a lambda-GEM system. Using a high-speed triggered CCD, we
demonstrate the storage of complex spatial modes and images. We also present an
in-principle demonstration of spatial multiplexing by showing selective recall
of spatial elements of a stored spin wave. Using our measurements, we consider
the effect of diffusion within the atomic vapour and investigate its role in
spatial decoherence. Our measurements allow us to quantify the spatial
distortion due to both diffusion and inhomogeneous control field scattering and
compare these to theoretical models.Comment: 11 pages, 9 figure
Evaluation of optimised flight trajectories for conventional and novel aircraft and engine integrated systems
Today, the air transport industry has become an essential element of global society by
its great contributions to the wide exchanges of cultures/people and to the rapid growth
in the world economy.
However, on the other hand, the adverse impacts on the environment caused by air
transport, such as air pollution, noise and climate change, are drawing, increasingly,
growing public concern.
In order to address the steady growth in air-travel demand in the next decades through
an environmentally-friendly way and realise the ACARE 2020 environmental goals,
The Clean Sky programme has been launched by European Union over the period 2008
– 2013.
The project research, described in this thesis and sponsored by the Clean Sky
programme, aims at evaluating the feasibility of reducing the environmental impact of
commercial aviation through the introduction of changes in the aircraft operational rules
and procedures, as well as the application of the new-generation propfan (open rotor)
engine, based on flight trajectory multidisciplinary optimisation and analysis of
commercial aircraft.
In order to accomplish the above research objectives, a complete methodology to
achieve and realise optimum flight trajectories has been initially proposed. Then, 12
component-level models which function as simulating different disciplines, such as
aircraft performance, engine performance, engine gaseous emission, and flight noise,
have been developed or selected/adopted. Further, nine system-level integration and
optimisation models were built. These system-level models simulate flights from
Amsterdam Schiphol airport in the Netherlands to Munich airport in Germany flown by
different types of aircraft through different flight phases with different optimisation
objectives. Finally, detailed investigations into the flight trajectory optimisations were
performed, extensive optimisation results were achieved and corresponding description,
analysis and comparisons were provided.
The main contributions of this work to knowledge broadly comprise the following: 1)
the further development regarding the methodology of flight trajectory multidisciplinary
optimisation; 2) previous work on aircraft trajectory optimisation has often considered
fixed objectives over the complete flight trajectory. This research focused on
representative flight phases of a flight mission with different optimisation objectives,
namely, noise impact and fuel burn during the departure phase; fuel burn and flight time
during en route phase; and noise impact and NOx emission during the arrival phase; 3)
this research has extended the current flight trajectory optimisations to turboprop and
propfan equipped aircraft. As a result, a relative complete 2D flight trajectory
multidisciplinary optimisation spectrum, spanned by primary commercial aircraft types,
primary flight phases and primary optimisation objectives of interest, has been built.
Although encouraging progress have been achieved, this project research, as with any
other research activity, is also only ‘on the way’ rather than coming to the ‘end’ point.
There are still many aspects which can be improved further and there is still much new
research and exploration which can be investigated further. All these have also been
suggested in this thesis
Assessing the Dissipative Capacity of Particle Impact Dampers Based on their Nonlinear Bandwidth Characteristics
The dissipative capacity as quantified by the nonlinear bandwidth measure of
impulsively loaded primary structures (PSs) coupled to particle impact dampers
(PIDs) is assessed. The considered PIDs are designed by initially placing
different numbers of spherical, linearly viscoelastic granules at different 2D
initial topologies and clearances. The strongly nonlinear and highly
discontinuous dynamics of the PIDs are simulated via the discrete element
method taking Hertzian interactions, slipping friction and granular rotations
into account. The general definition of nonlinear bandwidth is used to evaluate
the energy dissipation capacity of the integrated PS-PID systems. Moreover, the
effect of the dynamics of the PIDs on the time-bandwidth product of these
systems is studied, as a measure of their capacity to store or dissipate
vibration energy. It is found that the initial topologies of the granules in
the PID drastically affect the time-bandwidth product, which, depending on
shock intensity, may break the classical limit of unity which holds for linear
time-invariant dissipative resonators. The optimal PS-PID systems composed of
multiple granules produce large nonlinear bandwidths, indicating strong
dissipative capacity of broadband input energy by the PIDs. Additionally, in
the optimal configurations, the time-bandwidth product, i.e., the measure of
the frequency bandwidth of the input shock that is stored in the PS-PID system,
in tandem with the amount of time it takes for the system to dissipate (1/e) of
the initial energy, can be tuned either above or below unity by varying the
applied shock intensity. The implications of these findings on the dissipative
capacity of the system considered are discussed, showing that it can be
predictively assessed so that PIDs can act as highly effective nonlinear energy
sinks capable of rapid and efficient suppression of vibration induced by
shocks
TERA for Rotating Equipment Selection
This thesis looks at creating a multidisciplinary simulation tool for rotating plant equipment
selection, specifically gas turbines, for the liquefaction of natural gas (LNG). This is a
collaborative project between Shell Global Solutions and Cranfield University in the UK. The
TERA LNG tool uses a Techno-economic, Environmental and Risk Analysis (TERA)
approach in order to satisfy the multidisciplinary nature of the investigation. The benefits of
the tool are to act as an aid to selection, operations and maintenance planning and it also acts
as a sensitivity tool for assessing the impact of changes in performance, environmental and
financial parameters to the overall economic impact of technology selection. The aim is to not
only select technology on the basis of techno-economics but also on the basis of risk analysis.
The LNG TERA tool is composed of a number of modules starting with the performance
simulation which calculates the thermodynamic conditions in the core of the engine. Next, life
estimates of the hot gas path components are made using a mixture of parametric and
probabilistic lifing models for the turbine first stage blades, coatings, and combustor liner.
This allows for a risk analysis to be conducted before maintenance and economics issues are
dealt with. In parallel, emissions estimations are made based on empirical correlations. The
modelling exemplifies a methodology which is uniquely applied to this application and there
are no studies previous to this which look at so many aspects before making conclusions on
plant machinery selection.
Comparisons have been done between industrial frame engines based on the General Electric
Frame 9E (130 MW) and Frame 7EA (87 MW) engines as well as more complex cycles
involving aero-derivation and inter-cooling such as the LM 6000 (42 MW) and LMS 100 (100
MW). Work has also been carried out to integrate the tool to Shell based systems in order to
utilise the database of information on failure and maintenance of machinery as well as its
performance.
The results of the integrated TERA show a clear favour for the aero-derivative engines and
the main benefit is the fuel saving, though the life of the hot gas path components is
deteriorated much faster. The risk results show that the industrial frame engines have a wider
variation in expected life compared to aero-derivatives, though the industrial frames have
longer component lives. In the context of maintenance and economics, the aero-derivative engines are better suited to LNG applications. The modular change out design of the aero-
derivatives also meant that time to repair was lower, thus reducing lost production.
Application of the LNG TERA tool was extended to power generation whereby a series of 6
engines were simulated. The changes required to the modelling were minimal and it shows
the flexibility of the TERA philosophy. This study was carried out assuming a given ratio of
load split between the engines and hence is sensitive to the way an operator demands power
of the engine as opposed to LNG application where the operator tries to drive the engine as
hard as possible to get the most production out of the train.
The study was limited in the modes of failure which were investigated, a major further work
would be to extend the methodology to more components and incorporate fatigue failure.
Further, the blade creep and probabilistic coating models were very sensitive to changes in
their respective control parameters such as coating thickness allowances and firing
temperature.
The contribution to the project from the MBA is the statistical techniques used to conduct the
risk analysis and data handling as well as financial management techniques such as the Net
Present Value (NPV) methodology for project evaluations
Analysis of a 115MW, 3 shaft, helium Brayton cycle
This research theme is originated from a development project that is going on in
South Africa, for the design and construction of a closed cycle gas turbine plant using
gas-cooled reactor as the heat source to generate 115 MW of electricity. South African
Power utility company, Eskom, promotes this developmental work through its
subsidiary called PBMR (Pebble Bed Modular Reactor). Some of the attractive features
of this plant are the inherent and passive safety features, modular geometry, small
evacuation area, small infrastructure requirements for the installation and running of the
plant, small construction time, quick starting and stopping and also low operational
cost.
This exercise is looking at the operational aspects of a closed cycle gas turbine,
the finding of which will have a direct input towards the successful development and
commissioning of the plant. A thorough understanding of the fluid dynamics in this
three-shaft system and its transient performance analysis were the two main objectives
of this research work. A computer programme called GTSI, developed by a previous
Cranfield University research student, has been used in this as a base programme for the
performance analysis. Some modifications were done on this programme to improve its
control abilities. The areas covered in the performance analysis are Start-up, Shutdown
and Load ramping. A detailed literature survey has been conducted to learn from the
helium Turbo machinery experiences, though it is very limited. A critical analysis on
the design philosophy of the PBMR is also carried out as part of this research work.
The performance analysis has shown the advantage, disadvantage and impact of
various power modulation methods suggested for the PBMR. It has tracked the effect of
the operations of the various valves included in the PBMR design. The start-up using a
hot gas injection has been analysed in detail and a successful start region has been
mapped. A start-up procedure is also written based on this. The analysis on the normal
and emergency load rejection using various power modulation devices has been done
and it stress the importance of more control facilities during full load rejection due to
generator faults.
A computational fluid dynamics (CFD) analysis, using commercial software, has
been carried out on some geometry of the PBMR design to find out whether its flow
characteristic will have any serious impact on the performance on the cycle during the
load control of the plant. The analysis has demonstrated that there will not be much
impact on the performance, during load control using pressure level changes, from this
geometry. However, some locations in the geometry have been identified as areas where
the flow is experiencing comparatively high pressure losses. Recommendations, which
include modification in the physical design, were made to improve this.
The CFD analysis has extended to a cascade to compare the flow behaviour of
Air and Helium with an objective of using air, being inexpensive, to test the helium
flow characteristic in a test rig to simulate the behavioural pattern of helium in the
PBMR pressure vessel. The specification of a hypothetical test rig and the necessary
scaling parameters has been derived from this exercise. This will be useful for designing
test rigs during the developmental and operational stage of the PBMR project
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