1,809 research outputs found
Safety system design optimisation
This thesis investigates the efficiency of a design optimisation scheme that is
appropriate for systems which require a high likelihood of functioning on demand.
Traditional approaches to the design of safety critical systems follow the preliminary
design, analysis, appraisal and redesign stages until what is regarded as an acceptable
design is achieved. For safety systems whose failure could result in loss of life it is
imperative that the best use of the available resources is made and a system which is
optimal, not just adequate, is produced.
The object of the design optimisation problem is to minimise system unavailability
through manipulation of the design variables, such that limitations placed on them by
constraints are not violated.
Commonly, with mathematical optimisation problem; there will be an explicit
objective function which defines how the characteristic to be minimised is related to
the variables. As regards the safety system problem, an explicit objective function
cannot be formulated, and as such, system performance is assessed using the fault tree
method. By the use of house events a single fault tree is constructed to represent the
failure causes of each potential design to overcome the time consuming task of
constructing a fault tree for each design investigated during the optimisation
procedure. Once the fault tree has been constructed for the design in question it is
converted to a BDD for analysis.
A genetic algorithm is first employed to perform the system optimisation, where the
practicality of this approach is demonstrated initially through application to a High-Integrity
Protection System (HIPS) and subsequently a more complex Firewater
Deluge System (FDS).
An alternative optimisation scheme achieves the final design specification by solving
a sequence of optimisation problems. Each of these problems are defined by
assuming some form of the objective function and specifying a sub-region of the
design space over which this function will be representative of the system
unavailability.
The thesis concludes with attention to various optimisation techniques, which possess
features able to address difficulties in the optimisation of safety critical systems.
Specifically, consideration is given to the use of a statistically designed experiment
and a logical search approach
Transfer of Interactive Report Extracted Data (TIRED) requirements specification
There are no author-identified significant results in this report
Protocol for a mixed-methods exploratory investigation of care following intensive care discharge: the REFLECT study
© Author(s) 2019. Re-use permitted under CC BY. Published by BMJ.INTRODUCTION: A substantial number of patients discharged from intensive care units (ICUs) subsequently die without leaving hospital. It is unclear how many of these deaths are preventable. Ward-based management following discharge from ICU is an area that patients and healthcare staff are concerned about. The primary aim of REFLECT (Recovery Following Intensive Care Treatment) is to develop an intervention plan to reduce in-hospital mortality rates in patients who have been discharged from ICU. METHODS AND ANALYSIS: REFLECT is a multicentre mixed-methods exploratory study examining ward care delivery to adult patients discharged from ICU. The study will be made up of four substudies. Medical notes of patients who were discharged from ICU and subsequently died will be examined using a retrospective case records review (RCRR) technique. Patients and their relatives will be interviewed about their post-ICU care, including relatives of patients who died in hospital following ICU discharge. Staff involved in the care of patients post-ICU discharge will be interviewed about the care of this patient group. The medical records of patients who survived their post-ICU stay will also be reviewed using the RCRR technique. The analyses of the substudies will be both descriptive and use a modified grounded theory approach to identify emerging themes. The evidence generated in these four substudies will form the basis of the intervention development, which will take place through stakeholder and clinical expert meetings. ETHICS AND DISSEMINATION: Ethical approval has been obtained through the Wales Research and Ethics Committee 4 (17/WA/0107). We aim to disseminate the findings through international conferences, international peer-reviewed journals and social media. TRIAL REGISTRATION NUMBER: ISRCTN14658054.Peer reviewedFinal Published versio
Plot- and catchment-scale hydrological impacts of agricultural field boundary features
Natural flood management aims to reduce downstream flow levels by delaying the movement of water through
a catchment and increasing the amount of soil infiltration. Field boundary features such as hedgerows and dry
stone walls are common features in the rural landscape. It is hypothesised that there presence could reduce runoff
connectivity and change the soil moisture levels by altering the soil structure and porosity. The use of larger
agricultural machinery has resulted in the removal of field boundaries and the subsequent increase in field sizes
over the 20th Century. This change in the rural landscape is likely to have changed the partitioning of rainfall into
runoff and the hydrological pathways throughout the catchment. However, the link between field boundaries and
catchment scale flood risk has not yet been proven.
We aim to address this need for evidence to support natural flood management by focussing on these widespread
features in the rural landscape. Firstly, we quantify the change in the density of field boundaries over the past
120 years for the Skell catchment, Northern England using historical OS maps. The analysis has shown that
field size has approximately doubled in the Skell catchment since 1892, due to the removal of field boundaries.
Secondly, we assess the effect of field boundaries on local soil characteristics and hydrological processes through
plot scale continuous monitoring of the hydrological processes along a 20m transect through the linear boundary
features. For the summer period results show that soil moisture levels are lower immediately next to the hedgerow
compared to distances greater than 1m from the hedgerow. Finally, we use this data to parameterise and validate a
catchment scale hydrological model. The model is then applied to test the impact of a network of field boundaries
on river flow extremes at the catchment scale
Inter- and intra-field variations in soil compaction levels and subsequent impacts on hydrological extremes
The rural landscape in the UK is dominated by pastoral agriculture, with about 40% of land cover classified as
either improved or semi-natural grassland according to the Land Cover Map 2007. Intensification has resulted
in greater levels of compaction associated with higher stocking densities. However, there is likely to be a great
amount of variability in compaction levels within and between fields due to multiple controlling factors. This
research focusses in on two of these factors; firstly animal species, namely sheep, cattle and horses; and secondly
field zonation e.g. feeding areas, field gates, open field.
Field experiments have been conducted in multiple fields in the River Skell catchment, in Yorkshire, UK,
which has an area of 140km2. The effect on physical and hydrologic soil characteristics such as bulk density and
moisture contents have been quantified using a wide range of field and laboratory based experiments. Results
have highlighted statistically different properties between heavily compacted areas where animals congregate and
less-trampled open areas.
Furthermore, soil compaction has been hypothesised to contribute to increased flood risk at larger spatial
scales. Previous research (Pattison, 2011) on a 40km2 catchment (Dacre Beck, Lake District, UK) has shown
that when soil characteristics are homogeneously parameterised in a hydrological model, downstream peak
discharges can be 65% higher for a heavy compacted soil than for a lightly compacted soil. Here we report results
from spatially distributed hydrological modelling using soil parameters gained from the field experimentation.
Results highlight the importance of both the percentage of the catchment which is heavily compacted and also the
spatial distribution of these fields
Modifications to the soil-vegetation-atmosphere continuum by hedgerows: observations from a field site in Northern England [Abstract]
Modifications to the soil-vegetation-atmosphere continuum by hedgerows: observations from a field site in Northern England [Abstract
Upscaling spatially heterogeneous parameterisations of soil compaction to investigate catchment scale flood risk. [Abstract]
Upscaling spatially heterogeneous parameterisations of soil compaction to investigate catchment scale flood risk. [Abstract
Genetic algorithms in optimal safety system design
This paper describes a design optimization scheme for systems that require a high likelihood of functioning on demand. For safety systems whose failure could result in loss of life it is imperative that the best use of the available resources is made and that a system which is optimal and not just adequate is produced
Optimal safety system performance
This paper investigates the efficiency of a design
optimization scheme which is appropriate for systems which
require a high likelihood of functioning on demand. Traditional
approaches to the design of safety critical systems follows the
preliminary design, analysis, appraisal and redesign
stages until what is regarded as an acceptable design is
achieved. For safety systems whose failure could result in loss
of life it is imperative that the best use of the available
resources is made and a system which is optimal not just
adequate is produced.
The methodology presented in the paper retains the
commonly used fault tree method to analyse the individual
system designs. By the use of house events a single fault tree
is constructed to represent the failure causes of each potential
design to overcome the time consuming task of constructing a
fault tree for each design investigated during the optimization
procedure.
The final design specification is acheved using a
genetic algorithm to perform the optimization with the
constraints incorporated by penalising the fitness of infeasible
designs. To demonstrate the practicality of the method
developed it has been applied to a High Integrity Protection
System (HIPS)
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