99,661 research outputs found
Improving the Accuracy and Scope of Control-Oriented Vapor Compression Cycle System Models
The benefits of applying advanced control techniques to vapor compression cycle systems are well know.
The main advantages are improved performance and efficiency, the achievement of which brings both economic and
environmental gains. One of the most significant hurdles to the practical application of advanced control techniques
is the development of a dynamic system level model that is both accurate and mathematically tractable. Previous
efforts in control-oriented modeling have produced a class of heat exchanger models known as moving-boundary
models. When combined with mass flow device models, these moving-boundary models provide an excellent
framework for both dynamic analysis and control design. This thesis contains the results of research carried out to
increase both the accuracy and scope of these system level models.
The improvements to the existing vapor compression cycle models are carried out through the application
of various modeling techniques, some static and some dynamic, some data-based and some physics-based. Semiempirical
static modeling techniques are used to increase the accuracy of both heat exchangers and mass flow
devices over a wide range of operating conditions. Dynamic modeling techniques are used both to derive new
component models that are essential to the simulation of very common vapor compression cycle systems and to
improve the accuracy of the existing compressor model. A new heat exchanger model that accounts for the effects
of moisture in the air is presented. All of these model improvements and additions are unified to create a simple but
accurate system level model with a wide range of application. Extensive model validation results are presented,
providing both qualitative and quantitative evaluation of the new models and model improvements.Air Conditioning and Refrigeration Project 17
Nucleon in a periodic magnetic field: Finite-volume aspects
The paper presents an extension and a refinement of our previous work on the
extraction of the doubly virtual forward Compton scattering amplitude on the
lattice by using the background field technique, Phys. Rev. D 95, 031502 (2017)
(arXiv:1610.05545). The zero frequency limit for the periodic background field
is discussed, in which the well-known result is reproduced. Further, an upper
limit for the magnitude of the external field is established for which the
perturbative treatment is still possible. Finally, the framework is set for the
evaluation of the finite-volume corrections allowing for the analysis of
upcoming lattice results.Comment: 42 pages, 5 figures; version accepted for publication in Physical
Review
Model-driven design of context-aware applications
In many cases, in order to be effective, software applications need to allow sensitivity to context changes. This implies however additional complexity associated with the need for applications’ adaptability (being capable of capturing context, interpreting it and reacting on it). Hence, we envision 3 ‘musts’ that, in combination, are especially relevant to the design of context-aware applications. Firstly, at the business modeling level, it is considered crucial that the different possible context states can be properly captured and modeled, states that correspond to certain desirable behaviors. Secondly, it must be known what are the dependencies between the two, namely between states and behaviors. And finally, what is valid for application design in general, business needs are to be aligned to application solutions. In this work, we address the mentioned challenges, by approaching the notion of context and extending from this perspective a previously proposed business-software alignment approach. We illustrate our achieved results by means of a small example. It is expected that this research contribution will be useful as an additional result concerning the alignment between business modeling and software design
Utilization-Based Scheduling of Flexible Mixed-Criticality Real-Time Tasks
Mixed-criticality models are an emerging paradigm for the design of real-time
systems because of their significantly improved resource efficiency. However,
formal mixed-criticality models have traditionally been characterized by two
impractical assumptions: once \textit{any} high-criticality task overruns,
\textit{all} low-criticality tasks are suspended and \textit{all other}
high-criticality tasks are assumed to exhibit high-criticality behaviors at the
same time. In this paper, we propose a more realistic mixed-criticality model,
called the flexible mixed-criticality (FMC) model, in which these two issues
are addressed in a combined manner. In this new model, only the overrun task
itself is assumed to exhibit high-criticality behavior, while other
high-criticality tasks remain in the same mode as before. The guaranteed
service levels of low-criticality tasks are gracefully degraded with the
overruns of high-criticality tasks. We derive a utilization-based technique to
analyze the schedulability of this new mixed-criticality model under EDF-VD
scheduling. During runtime, the proposed test condition serves an important
criterion for dynamic service level tuning, by means of which the maximum
available execution budget for low-criticality tasks can be directly determined
with minimal overhead while guaranteeing mixed-criticality schedulability.
Experiments demonstrate the effectiveness of the FMC scheme compared with
state-of-the-art techniques.Comment: This paper has been submitted to IEEE Transaction on Computers (TC)
on Sept-09th-201
Seismic Vulnerability of the Italian Roadway Bridge Stock
This study focuses on the seismic vulnerability evaluation of the Italian roadway bridge stock, within the framework of a Civil Protection sponsored project. A comprehensive database of existing bridges (17,000 bridges with different level of knowledge) was implemented. At the core of the study stands a procedure for automatically carrying out state-of-the-art analytical evaluation of fragility curves for two performance levels – damage and collapse – on an individual bridge basis. A webGIS was developed to handle data and results. The main outputs are maps of bridge seismic risk (from the fragilities and the hazard maps) at the national level and real-time scenario damage-probability maps (from the fragilities and the scenario shake maps). In the latter case the webGIS also performs network analysis to identify routes to be followed by rescue teams. Consistency of the fragility derivation over the entire bridge stock is regarded as a major advantage of the adopted approach
- …