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Authored by Bharadwaj Raj, Chetan Kulkarni, Kim Kyusung, and Gautam Biswas
Authored by Akshay Dabholkar and Aniruddha Gokhale
This paper proposes a model based approach to study the degradation effects of power supply converters on the avionics systems. Avionics systems combine physical processes, computational hardware, and software systems, and present unique challenges to performing root cause analysis when faults occur, and also for establishing the effects of faults on overall system behavior and performance. However, systematic analysis of these conditions are very important for analysis of safety and also to avoid catastrophic failures in navigation systems. A combined energy-based and physics of failure model approach is adopted for degradation analysis and prognosis of degrading components in DC-DC power converters. We have developed automated methods for generating Simulink models from bond graph representations of physical models. The bond graph models are also used to derive models for diagnostic and prognostic analysis. Further, we have also developed models of the software and hardware components of the GPS and INAV subsystems as Simulink™ modules. The complete system for studying the behaviors of the avionics system (both nominal and faulty) is implemented as a set of integrated Simulink modules. In avionics systems, degradations and faults in this unit propagates to the GPS and INAV systems. These can cause a variety of faults in these systems, e.g., ripple currents at the power supply output can cause glitches in the GPS position and velocity output, and this, in turn, produces errors in the Inertial Navigation (INAV) system calculations. One of the faults we have been studying in detail is electrolytic capacitor degradation in the power supply, and its effects on the functioning of the GPS unit. We apply qualitative fault signature methods for detecting and isolating faults in all three components of the avionics system. Fault signature generation is based on establishing causal relations between system parameters and measurements, and estimating the effect of a parameter value change (representing a fault) on the measured values. In the literature a number of operating conditions that cause capacitor degradation, such as High Voltage conditions, Transients, Reverse Bias, Strong Vibrations and high ripple current have been reported. Some of these conditions are observed by the power supplies embedded in the avionics systems. In this work, we study some of these conditions which lead to capacitor degradation i.e. due to thermal and electrical stresses. A topological energy based modeling scheme developed on the bond graph (BG) modeling language for building parametric models of multi-domain physical systems has been implemented. A model based approach to studying degradation phenomena enables us to combine the energy based modeling of the DC-DC converter with physics of failures models of capacitor degradation, and to predict using stochastic simulation methods how system performance deteriorates with time. This more systematic analysis may provide a more general and accurate method for computing the remaining useful life (RUL) of the component and the converter system. We adopt a physics of failure model (Arrhenius Law) for equivalent series resistance (ESR) increase in electrolytic capacitors subjected to electrical and thermal stresses. High ripple currents due to degradation lead to frequent resets and even damage in the systems that are downstream from the power supply. The literature indicates that the fluctuation in power supply voltage and excessive ripple currents could lead to various failures in the GPS receiver module. In this work we have simulated the GPS reset events due to voltage fluctuations. We have also simulated the loss of receiver lock due to excessive ripple current. We have demonstrated using our simulation models the effects of power supply faults on the overall performance of the GPS solution. Our methodology also provides a framework for developing efficient fault signature methods for fault detection and fault isolation. In future, we will conduct more detailed analysis of degradation effects, and their propagation to the different components of the system. We will also develop methods to quantify the effects of degradation on overall system performance.
Authored by Chetan Kulkarni, Gautam Biswas, Bharadwaj Raj, and Kim Kyusung
This paper presents the framework of a mobile air quality monitoring network, with an in-depth discussion of several new innovative techniques for web-based visualization. These techniques allow typical web users to access high-resolution pollution data gathered from a large number of vehicle-mounted mobile sensing devices coupled with highly-accurate static sensor data in an easy-to-use, intuitive interface. Additionally, this interface o ffers users a set of novel applications to promote health and pollution awareness, including a green trip planner, whereby users can plot routes between two locations based on a path of least exposure to specifi ed pollutants, and an exposure estimator, which allows users to calculate previous levels of exposure to harmful pollutants based only on a single timed GPS track.
Authored by Will Hedgecock, Peter Volgyesi, Akos Ledeczi, and Xenofon Koutsoukos
Authored by Tihamer Levendovszky and Gabor Karsai
This work-in-progress paper introduces a new hardware platform for wireless sensor networks, summarizes the new challenges it creates for software development and describes a toolchain being developed to meet those challenges. The hardware platform is based on a low-power FPGA as opposed to a traditional microcontroller. The FPGA confi guration includes a soft core microcontroller, but there are plenty of resources left to implement a subset of the operating system, middleware and application components directly on the FPGA. Instead of creating this partition early in the design phase, we advocate a flexible hardware/software boundary enabling "late binding" of components to the softcore or the hardware fabric. This increases the complexity of the design space mandating sophisticated tool support. The paper describes a toolchain that helps manage this complexity. The two main tools are a domain-speci c modeling environment and a symbolic design-space exploration tool.
Authored by Peter Volgyesi, Janos Sallai, Akos Ledeczi, P. Dutta, and Miklos Maroti
Authored by Tihamer Levendovszky, Daniel Balasubramanian, Anantha Narayanan, and Gabor Karsai
Authored by Gabor Karsai, F Massacci, L Osterweil, and I Schieferdecker
Authored by Heath LeBlanc, Emeka Eyisi, Nicholas Kottenstette, Xenofon Koutsoukos, and Janos Sztipanovits
Authored by Heath LeBlanc, Emeka Eyisi, Nicholas Kottenstette, Xenofon Koutsoukos, and Janos Sztipanovits
Authored by Janos Sallai, Akos Ledeczi, Isaac Amundson, Xenofon Koutsoukos, and Miklos Maroti
Authored by Janos Sallai, Akos Ledeczi, Xenofon Koutsoukos, and Peter Volgyesi
Authored by Peter Volgyesi, Janos Sallai, Sandor Szilvasi, Prabal Dutta, and Akos Ledeczi
Authored by Sandor Szilvasi and Peter Volgyesi
Authored by Himanshu Neema, Abhishek Dubey, and Gabor Karsai
Authored by Nilabja Roy, Aniruddha Gokhale, and Larry Dowdy
Interconnection damping assignment passivity based control (IDA-PBC) is an emerging control design method which allows an engineer to systematically design an advanced controller for complex non-linear systems. As a result specific gain ranges can be determined which can prevent an operator (adversary) from accidentally (maliciously) setting control gains which could potentially destabilize the system. However in order to generate the controller the engineer will have to resort to using symbolic numerical solvers in order to complete the design. This can be both a cumbersome and error-prone task which can be automated. We present initial results of a tool which simplifies IDA-PBC. In addition many fluid control problems posses tight operating regions in which pumps degrade over time. As a result actuator saturation may occur for given set-point profiles which will lead to integrator wind-up and more oscillatory behavior. We provide a non-linear anti-windup control-law which greatly improves system resilience to such degradation. Finally we demonstrate that IDA-PBC works reasonably well for moderately large sampling times by simply applying the bilinear transform to approximate any additional (non-linear) integral control terms.
Authored by Nicholas Kottenstette, Joseph Porter, Gabor Karsai, and Janos Sztipanovits
Authored by Ching-Kun Hsu, Gwo-Jen Hwang, and Chih-Kai Chang
Authored by Chetan Kulkarni, Gautam Biswas, Xenofon Koutsoukos, Celaya Jose, and Kai Goebel
Authored by Jonathan Wellons and Yuan Xue
Authored by Joseph Porter, Graham Hemingway, Harmon Nine, Chris vanBuskirk, Nicholas Kottenstette, Gabor Karsai, and Janos Sztipanovits
Service-Oriented Architectures (SOAs) are increasingly being used for designing and building large-scale networked and distributed systems. Catering to the complex and dynamically varying needs of business applications/clients, these systems must usually be realized by dynamically composing a variety of network-available services. Evaluation of large-scale SOAs, particularly on dynamic network platforms, such as Mobile Ad-hoc Networks (MANETs), is a non-trivial problem that requires not only a correct modeling of SOAs and the network platform, but also their relationships. This paper describes a new tool – SOAMANET – to design and rapidly synthesize simulations for the experimental evaluation of SOAs on MANET platforms. With its modeling techniques and analysis capabilities, SOAMANET allows simulationbased and system execution-based analysis of dynamic SOA and/or MANET designs and implementations.
Authored by Himanshu Neema, Anand Kashyap, Robert Kereskenyi, Yuan Xue, and Gabor Karsai
Modern software-defined radios are large, expensive, and power-hungry devices and this, we argue, hampers their more widespread deployment and use, particularly in low-power, size-constrained application settings like mobile phones and sensor networks. To rectify this problem, we propose to put the software-defined radio on a diet by redesigning it around just two core chips – an integrated RF transceiver and a Flash-based, mixed-signal FPGA. Modern transceivers integrate almost all RF front-end functions while emerging FPGAs integrate nearly all of required signal conditioning and processing functions. And, unlike conventional FPGAs, Flash-based FPGAs offer sleep mode power draws measured in the microamps and startup times measured in the microseconds, both of which are critical for low-power operation. If our platform architecture vision is realized, it will be possible to hold a software-defined radio in the palm of one’s hand, build it for $100, and power it for days using the energy in a typical mobile phone battery. This will make software radios deployable in high densities and broadly accessible for research and education.
Authored by Prabal Dutta, Ye-Sheng Kuo, Akos Ledeczi, Thomas Schmid, and Peter Volgyesi
Our previous work has explored the use of compositional stabilization techniques for embedded flight control software[9] based on passivity properties of controller components and systems. Zames[21] presented a compositional behavior-bounding technique for evaluating stability of nonlinear systems based on real intervals representing cones (sectors) that bound possible component behaviors. Many innovations in control theory have developed from his insights. We present a novel use of his sector bound theory to validate the stability of embedded control implementations online. The sector analysis can be implemented as a computationally efficient check of stability for different parts of a control design. The advantage of the online application of this technique is that it takes into account software platform effects that impact stability, such as time delays, quantization, and data integrity. We present a brief overview of the sector concept, our compatible control design approach, application of the technique to model-based embedded control software design, an example of its use to find design defects, and insights that may be drawn from our investigation so far. In the present work we only consider software (discrete-time) control of nonlinear continuous-time systems without switching.
Authored by Joseph Porter, Graham Hemingway, Nicholas Kottenstette, Gabor Karsai, and Janos Sztipanovits
Understanding the aging mechanisms of electronic components in an avionics system is extremely important as they are part of the critical sub-systems avionics which includes the GPS and INAV systems. Electrolytic capacitors and MOSFET’s have higher failure rates than the other components in DC-DC power converter systems. With increased use of electronics in avionics system, it becomes very much important to understand these components degradation mechanisms and their effects on the rest of the system. Our current work focuses on analyzing and modeling degradation phenomena in electrolytic capacitors and its effects on the output of DC-DC converter systems. The output degradation is typically measured by the increase in ripple current and the drop in output voltage at the load. Typically the ripple current effects dominate, and they can have adverse effects on downstream components. For example, in avionics systems where the power supply drives a GPS unit, ripple currents can cause glitches in the GPS position and velocity output, and this may cause errors in the Inertial Navigation (INAV) system causing the aircraft to fly off course. Literature reports a number of operating conditions that may cause capacitor degradation. These include High Voltage conditions, Transients, Reverse Bias, Strong Vibrations and high ripple current. In our work, we have studied the effects of capacitor degradation on DC-DC converter performance by developing a combination of converter system model and a physics of failure model of electrolytic capacitor degradation when subjected to thermal and electrical stresses. Thermal stress occurs when the capacitors operate in high temperature environments, while electrical stress conditions occur due to high operating voltages and even ripple currents above the rated values. In our work we are developing models to capture the failure phenomenon in these components. In this paper, we discuss two experiments to observe degradation in electrolytic capacitors. In the first ageing experiment study, the capacitor was subjected to degradation for over 1000 hours of capacitor operation time under nominal room temperature conditions, and the degradation was monitored at regular intervals. In the accelerated ageing methodology study, the capacitors were subjected to high electrical stress. During the accelerated testing we observed a faster degradation in the capacitors where we measured the ESR (Equivalent Series Resistance) which increased over the period of time. We also discuss the future accelerated ageing method and tests for capacitor degradation. In this paper we present the details of our aging methodology along with details of experiments and analysis of the results
Authored by Chetan Kulkarni, Gautam Biswas, Xenofon Koutsoukos, Kai Goebel, and Jose Celaya