Modelling and scheduling of heterogeneous computing systems

Ph.DDOCTOR OF PHILOSOPH

Designing and Expanding Electrical Networks – Complexity and Combinatorial Algorithms

The transition from conventional to renewable power generation has a large impact on when and where electricity is generated. To deal with this change the electric transmission network needs to be adapted and expanded. Expanding the network has two benefits. Electricity can be generated at locations with high renewable energy potentials and then transmitted to the consumers via the transmission network. Without the expansion the existing transmission network may be unable to cope with the transmission needs, thus requiring power generation at locations closer to the energy demand, but at less well-suited locations. Second, renewable energy generation (e.g., from wind or solar irradiation) is typically volatile. Having strong interconnections between regions within a large geographical area allows to the smooth the generation and demand over that area. This smoothing makes them more predictable and the volatility of the generation easier to handle. In this thesis we consider problems that arise when designing and expanding electric transmission networks. As the first step we formalize them such that we have a precise mathematical problem formulation. Afterwards, we pursue two goals: first, improve the theoretical understanding of these problems by determining their computational complexity under various restrictions, and second, develop algorithms that can solve these problems. A basic formulation of the expansion planning problem models the network as a graph and potential new transmission lines as edges that may be added to the graph. We formalize this formulation as the problems Flow Expansion and Electrical Flow Expansion, which differ in the flow model (graph-theoretical vs. electrical flow). We prove that in general the decision variants of these problems are $\mathcal{NP}$-complete, even if the network structure is already very simple, e.g., a star. For certain restrictions, we give polynomial-time algorithms as well. Our results delineate the boundary between the $\mathcal{NP}$-complete cases and the cases that can be solved in polynomial time. The basic expansion planning problems mentioned above ignore that real transmission networks should still be able to operate if a small part of the transmission equipment fails. We employ a criticality measure from the literature, which measures the dynamic effects of the failure of a single transmission line on the whole transmission network. In a first step, we compare this criticality measure to the well-used $N-1$ criterion. Moreover, we formulate this criticality measure as a set of linear inequalities, which may be added to any formulation of a network design problem as a mathematical program. To exemplify this usage, we introduce the criticality criterion in two transmission network expansion planning problems, which can be formulated as mixed-integer linear programs (MILPs). We then evaluate the performance of solving the MILPs. Finally, we develop a greedy heuristic for one of the two problems, and compare its performance to solving the MILP. Microgrids play an important role in the electrification of rural areas. We formalize the design of the cable layout of a microgrid as a geometric optimization problem, which we call Microgrid Cable Layout. A key difference to the network design problems above is that there is no graph with candidate edges given. Instead, edges and new vertices may be placed anywhere in the plane. We present a hybrid genetic algorithm for Microgrid Cable Layout and evaluate it on a set of benchmark instances, which include a real microgrid in the Democratic Republic of the Congo. Finally, instead of expanding electrical networks one may place electric equipment such as FACTS (flexible AC transmission system). These influence the properties of the transmission lines such that the network can be used more efficiently. We apply a model of FACTS from the literature and study the problem whether a given network with given positions and properties of the FACTS admits an electrical flow provided that FACTS are set appropriately. We call such a flow a FACTS flow. In this thesis we prove that in general it is $\mathcal{NP}$-complete to determine whether a network admits a FACTS flow, and we present polynomial-time algorithms for two restricted cases

Data Structures & Algorithm Analysis in C++

This is the textbook for CSIS 215 at Liberty University.https://digitalcommons.liberty.edu/textbooks/1005/thumbnail.jp

Edge Cloud Computing for Geospatial Data Processing and Approximate Queries

Architecture for optimizing geospatial data processing pipelines in the cloud by making use of edge nodes deployed on containers in an urban moving taxi scenario (specifically Shenzhen, China). Edge nodes are using Geohash for efficient data preprocessing, including Geohash-based stratified sampling, and neighborhood location of incoming messages. Apache Kafka was then used to send data to a Spark cluster using a spatially-aware technique for data distribution. In particular, a Kafka topic for each neighborhood of the city considered was created, and each of these topics contained only messages originated in the same neighborhood

Scaling Up Delay Tolerant Networking

Delay Tolerant Networks (DTN) introduce a networking paradigm based on store, carry and forward. This makes DTN ideal for situations where nodes experience intermittent connectivity due to movement, less than ideal infrastructure, sparse networks or other challenging environmental conditions. Standardization efforts focused around the Bundle Protoocol (BP) (RFC 5050) aim to provide a generic set of protocols and technologies to build DTNs. However, there are several challenges when trying to apply the BP to the Internet as a whole that are tackled in this thesis: There is no DTN routing mechanism that can work in Internet-scale networks. Similarly, available discovery mechanisms for opportunistic contacts do not scale to the Internet. This work presents a solution offering pull-based name resolution that is able to represent the flat unstructured BP namespace in a distributed data structure and leaves routing through the Internet to the underlying IP layer. A second challenge is the large amount of data stored by DTN nodes in large-scale applications. Reconciling two large sets of data during an opportunistic contact without any previous state in a space efficient manner is a non-trivial problem. This thesis will present a very robust solution that is almost as efficient as Bloom filters while being able to avoid false positives that would prevent full reconciliation of the sets. Lastly, when designing networks that are based on agents willing to carry information, incentives are an important factor. This thesis proposes a financially sustainable system to incentive users to participate in a DTN with their private smartphones. A user study is conducted to get a lead on the main motivational factors that let people participate in a DTN. The study gives some insight under what conditions relying on continuous motivation and cooperation from private users is a reasonable assumption when designing a DTN.Delay Tolerant Networks (DTN) sind ein Konzept für Netzwerke, das auf der Idee beruht, Datenpakete bei Bedarf längere Zeit zu speichern und vor der Weiterleitung an einen anderen Knoten physikalisch zu transportieren. Diese Vorgehensweise erlaubt den Einsatz von DTN in Netzen, die häufige Unterbrechungen aufweisen. Mit dem Bundle Protocol (BP) (RFC 5050) wird ein Satz von Standardprotokollen für DTNs entwickelt. Wenn man das BP im Internet einsetzen möchte ergeben sich einige Herausforderungen: Es existiert kein DTN Routingverfahren, das skalierbar genug ist um im Internet eingesetzt zu werden. Das Gleiche trifft auf verfügbare Discovery Mechanismen für opportunistische Netze zu. In dieser Arbeit wird ein verteilter, reaktiver Mechanismus zur Namensauflösung im DTN vorgestellt, der den flachen, unstrukturierten Namensraum des BP abbilden kann und es ermöglicht das Routing komplett der IP Schicht zu überlassen. Eine weitere Herausforderung ist die große Menge an Nachrichten, die Knoten puffern müssen. Die effiziente Synchronisierung von zwei Datensets während eines opportunistischen Kontaktes, ohne Zustandsinformationen, ist ein komplexes Problem. Diese Arbeit schlägt einen robusten Algorithmus vor, der die Effizienz eines Bloom Filters hat, dabei jedoch die False Positives vermeidet, die normalerweise eine komplette Synchronisation verhindern würden. Ein DTN basiert darauf, dass Teilnehmer Daten puffern und transportieren. Wenn diese Teilnehmer z.B. private User mit Smarpthones sind, ist es essentiell diese Benutzer zu einer dauerhaften Teilnahme am Netzwerk zu motivieren. In dieser Arbeit wird ein finanziell tragfähiges System entwickelt, welches Benutzer für eine Teilnahme am DTN belohnt. Eine Benutzerstudie wurde durchgeführt, um herauszufinden, welche Faktoren Benutzer motivieren und unter welchen Umständen davon auszugehen ist, dass Benutzer wenn man das BP im Internet einsetzen möchte dauerhaft in einem DTN kooperieren und Resourcen zur Verfügung stellen