1,699 research outputs found
Formal Synthesis of Control Strategies for Positive Monotone Systems
We design controllers from formal specifications for positive discrete-time
monotone systems that are subject to bounded disturbances. Such systems are
widely used to model the dynamics of transportation and biological networks.
The specifications are described using signal temporal logic (STL), which can
express a broad range of temporal properties. We formulate the problem as a
mixed-integer linear program (MILP) and show that under the assumptions made in
this paper, which are not restrictive for traffic applications, the existence
of open-loop control policies is sufficient and almost necessary to ensure the
satisfaction of STL formulas. We establish a relation between satisfaction of
STL formulas in infinite time and set-invariance theories and provide an
efficient method to compute robust control invariant sets in high dimensions.
We also develop a robust model predictive framework to plan controls optimally
while ensuring the satisfaction of the specification. Illustrative examples and
a traffic management case study are included.Comment: To appear in IEEE Transactions on Automatic Control (TAC) (2018), 16
pages, double colum
Formal methods for resilient control
Many systems operate in uncertain, possibly adversarial environments, and their successful operation is contingent upon satisfying specific requirements, optimal performance, and ability to recover from unexpected situations. Examples are prevalent in many engineering disciplines such as transportation, robotics, energy, and biological systems. This thesis studies designing correct, resilient, and optimal controllers for discrete-time complex systems from elaborate, possibly vague, specifications.
The first part of the contributions of this thesis is a framework for optimal control of non-deterministic hybrid systems from specifications described by signal temporal logic (STL), which can express a broad spectrum of interesting properties. The method is optimization-based and has several advantages over the existing techniques. When satisfying the specification is impossible, the degree of violation - characterized by STL quantitative semantics - is minimized. The computational limitations are discussed.
The focus of second part is on specific types of systems and specifications for which controllers are synthesized efficiently. A class of monotone systems is introduced for which formal synthesis is scalable and almost complete. It is shown that hybrid macroscopic traffic models fall into this class. Novel techniques in modular verification and synthesis are employed for distributed optimal control, and their usefulness is shown for large-scale traffic management. Apart from monotone systems, a method is introduced for robust constrained control of networked linear systems with communication constraints. Case studies on longitudinal control of vehicular platoons are presented.
The third part is about learning-based control with formal guarantees. Two approaches are studied. First, a formal perspective on adaptive control is provided in which the model is represented by a parametric transition system, and the specification is captured by an automaton. A correct-by-construction framework is developed such that the controller infers the actual parameters and plans accordingly for all possible future transitions and inferences. The second approach is based on hybrid model identification using input-output data. By assuming some limited knowledge of the range of system behaviors, theoretical performance guarantees are provided on implementing the controller designed for the identified model on the original unknown system
ARTIFICIAL INTELLIGENCE-BASED APPROACH TO MODELLING OF PIPE ORGANS
The aim of the project was to develop a new Artificial Intelligence-based method to aid
modeling of musical instruments and sound design. Despite significant advances in music
technology, sound design and synthesis of complex musical instruments is still time
consuming, error prone and requires expert understanding of the instrument attributes
and significant expertise to produce high quality synthesised sounds to meet the needs
of musicians and musical instrument builders. Artificial Intelligence (Al) offers an effective
means of capturing this expertise and for handling the imprecision and uncertainty
inherent in audio knowledge and data.
This thesis presents new techniques to capture and exploit audio expertise, following
extended knowledge elicitation with two renowned music technologist/audio experts, developed
and embodied into an intelligent audio system. The Al combined with perceptual
auditory modeling ba.sed techniques (ITU-R BS 1387) make a generic modeling framework
providing a robust methodology for sound synthesis parameters optimisation with
objective prediction of sound synthesis quality. The evaluation, carried out using typical
pipe organ sounds, has shown that the intelligent audio system can automatically design
sounds judged by the experts to be of very good quality, while significantly reducing the
expert's work-load by up to a factor of three and need for extensive subjective tests.
This research work, the first initiative to capture explicitly knowledge from audio
experts for sound design, represents an important contribution for future design of electronic
musical instruments based on perceptual sound quality will help to develop a new
sound quality index for benchmarking sound synthesis techniques and serve as a research
framework for modeling of a wide range of musical instruments.Musicom Lt
CRIKEY! ― It's co-ordination in temporal planning
Temporal planning contains aspects of both planning and scheduling. Many temporal planners assume a loose coupling between these two sub-problems in the form of "blackbox" durative actions, where the state of the world is not known during the action's execution. This reduces the size of the search space and so simplifies the temporal planning problem, restricting what can be modelled. In particular, the simplification makes it impossible to model co-ordination, where actions must be executed concurrently to achieve a desired effect. Coordination results from logical and temporal constraints that must both be met, and for this reason, the planner and scheduler must communicate in order to find a valid temporal plan. This communication effectively increases the size of the search space, so must be done intelligently and as little as possible to limit this increase. This thesis contributes a comprehensive analysis of where temporal constraints appear in temporal planning problems. It introduces the notions of minimum and maximum temporal constraints, and with these isolates where the planning and scheduling are coupled together tightly, in the form of co-ordination, it characterises this with the new concepts of envelopes and contents. A new temporal planner written, called СRIKЕҮ, uses this theory to solve temporal problems involving co-ordination that other planners are unable to solve. However, it does this intelligently, using this theory to minimise the communication between the sub-solvers, and so does not expand the search space unnecessarily. The novel search space that CRIKEY uses docs not specify the timings of future events and this allows for the handling of duration inequalities, which again, few other temporal planners are able to solve. Results presented show СRIKЕҮ to be a competitive planner, whilst not making the same simplifying assumptions that other temporal planners make as to the nature of temporal planning problems
Earth Observatory Satellite (EOS) system definition study
An executive summary of a study on the Earth Observatory Satellite (EOS) was presented. It was concluded that the overall costs of space systems could be reduced significantly by the development of a modular shuttle compatible standard spacecraft, and the use of that spacecraft with the Shuttle Transportation System. It was also demonstrated that the development of the standard spacecraft is feasible, desirable, and cost effective if applied to a series of missions. The ability to initially retrieve, refurbish, and reuse the spacecraft and its payload, and ultimately to perform in-orbit servicing, would result in significant cost savings. A number of specific conclusions and recommendations were also suggested
Joint University Program for Air Transportation Research, 1989-1990
Research conducted during the academic year 1989-90 under the NASA/FAA sponsored Joint University Program for Air Transportation research is discussed. Completed works, status reports and annotated bibliographies are presented for research topics, which include navigation, guidance and control theory and practice, aircraft performance, human factors, and expert systems concepts applied to airport operations. An overview of the year's activities for each university is also presented
Mixed-Criticality Systems on Commercial-Off-the-Shelf Multi-Processor Systems-on-Chip
Avionics and space industries are struggling with the adoption of technologies
like multi-processor system-on-chips (MPSoCs) due to strict safety requirements.
This thesis propose a new reference architecture for MPSoC-based mixed-criticality
systems (MCS) - i.e., systems integrating applications with different level of criticality - which are a common use case for aforementioned industries.
This thesis proposes a system architecture capable of granting partitioning -
which is, for short, the property of fault containment. It is based on the detection
of spatial and temporal interference, and has been named the online detection of
interference (ODIn) architecture.
Spatial partitioning requires that an application is not able to corrupt resources
used by a different application. In the architecture proposed in this thesis, spatial
partitioning is implemented using type-1 hypervisors, which allow definition of
resource partitions. An application running in a partition can only access resources
granted to that partition, therefore it cannot corrupt resources used by applications
running in other partitions.
Temporal partitioning requires that an application is not able to unexpectedly
change the execution time of other applications. In the proposed architecture, temporal partitioning has been solved using a bounded interference approach, composed of
an offline analysis phase and an online safety net.
The offline phase is based on a statistical profiling of a metric sensitive to
temporal interference’s, performed in nominal conditions, which allows definition of
a set of three thresholds:
1. the detection threshold TD;
2. the warning threshold TW ;
3. the α threshold.
Two rules of detection are defined using such thresholds:
Alarm rule When the value of the metric is above TD.
Warning rule When the value of the metric is in the warning region [TW ;TD] for
more than α consecutive times.
ODIn’s online safety-net exploits performance counters, available in many MPSoC architectures; such counters are configured at bootstrap to monitor the selected
metric(s), and to raise an interrupt request (IRQ) in case the metric value goes above
TD, implementing the alarm rule. The warning rule is implemented in a software detection module, which reads the value of performance counters when the monitored
task yields control to the scheduler and reset them if there is no detection.
ODIn also uses two additional detection mechanisms:
1. a control flow check technique, based on compile-time defined block signatures, is implemented through a set of watchdog processors, each monitoring
one partition.
2. a timeout is implemented through a system watchdog timer (SWDT), which is
able to send an external signal when the timeout is violated.
The recovery actions implemented in ODIn are:
• graceful degradation, to react to IRQs of WDPs monitoring non-critical applications or to warning rule violations; it temporarily stops non-critical applications
to grant resources to the critical application;
• hard recovery, to react to the SWDT, to the WDP of the critical application, or
to alarm rule violations; it causes a switch to a hot stand-by spare computer.
Experimental validation of ODIn was performed on two hardware platforms: the
ZedBoard - dual-core - and the Inventami board - quad-core.
A space benchmark and an avionic benchmark were implemented on both platforms, composed by different modules as showed in Table 1
Each version of the final application was evaluated through fault injection (FI)
campaigns, performed using a specifically designed FI system. There were three
types of FI campaigns:
1. HW FI, to emulate single event effects;
2. SW FI, to emulate bugs in non-critical applications;
3. artificial bug FI, to emulate a bug in non-critical applications introducing
unexpected interference on the critical application.
Experimental results show that ODIn is resilient to all considered types of faul
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