A distributed object-oriented simulator framework for marine power plants with weak power grids

In this work, we discuss and demonstrate how multi-engine marine power plants with weak power grids efficiently can be set up and simulated in a distributed co-simulation framework. To facilitate configuration switching such as starting and stopping, connecting and disconnecting arbitrary gensets online, the generator models are modelled as hybrid causality component models. This implementation enables seamless and energy conservative model switching. Also, the proposed simulator framework is scalable such that the number of gensets in the power plant can be set by a single parameter, which automatically scales the power management system and the tailored simulator master algorithm accordingly. To control the number of active gensets being connected to the power grid while running the simulation, a simple mixed integer linear programming formulation is proposed. A simulation case study including a marine power plant configuration with four equal-sized gensets is conducted in the end to demonstrate the features of the proposed simulator framework, which also can be applied to, e.g. a small wind farm, or an isolated number of islands with interconnected power generators.publishedVersio

En studie av flutterekko med hensyn på geometrisk akustikk og kantdiffraksjon

Flutterekko er et akustisk fenomen som oppstår når gjentatte refleksjoner oppstår mellom to eller flere flater. Dette eksiteres av pulssignal, som for eksempel klapping, og har en etterklang som ofte er lenger enn etterklangen i resten av rommet. Flutter oppstår gjerne i avlange rom med mye demping i gulv og himling. Dette oppfattes som svært forstyrrende. I denne oppgaven er det fokusert på å undersøke flutter med praktiske forsøk med to parallelle plater, samt undersøkelser med geometrisk og forenklede matematiske modeller som Kirchoff-Fresnel approksimasjon og fresnelsoner. speilkildeimplementering og diffraksjonsberegninger. I første eksperiment er responsen fra kun en plate undersøkt. Dette er gjort med praktiske forsøk, diffraksjonsberegninger og forenklede matematiske modeller. I andre eksperiment benyttes to parallelle plater i det praktiske forsøket for å undersøke flutter. Med fokus på impulsrespons, etterklang og Schroederkurver er disse resultatene undersøkt. I siste eksperiment er impulsrespons, frekvensrespons og Schroederkurver av flutter forsøkt simulert. Resultater viser at kantdiffraksjon for en plate kan beregnes bra med første ordens kantdiffraksjons. Det er også vist at diffraksjonsasymptoter og rippeleffekter av forsøket kan beskrives med Kirchoff-Fresnel approksimasjon og fresnelsoner. Flutterfenomenet er undersøkt med spekulære refleksjoner, og viser både sfærisk og eksponentiell demping. Impulsresponsen for vinklede plater har vist seg også mulig å simulere med speilkilder ved å plassere disse om en sirkulær geometri. Schroederkurvene av målt impulsrespons viser at dempingen ikke faller eksponentielt etter første 5[dB] demping, som tilsier at ISO3382 ikke er den beste metoden for å beregne etterklangstiden T30. Frekvensresponsen av simulert flutter viser skarpe frekvenstopper for samme frekvenser som den målte impulsresponsen, for både spekulære og første ordens kantdiffraksjonsberegninger. Sistnevnte viser også 6 [dB] økning av frekvenstopper med kantdiffraksjonsberegninger grunnet positive interferenseffekter fra diffraksjonspulsene. Dessverre antyder Schroederkurvene av simulert impulsrespons avvik fra målt impulsrespons ved lavere frekvenser, noe som indikerer at første ordens kantdiffraksjons ikke er tilstrekkelig for beregning av etterklangen av flutter ved lavere frekvenser. Det er også nødvendig med høyere ordens refleksjon for å øke lengden av impulsrespons

We Need to be Relevant : An Ethnography of Kenyan Anthropology Students

This thesis is based on seven months of ethnographic fieldwork among Kenyan anthropology students at the Institute of Anthropology, Gender & African Studies (IAGAS) at the University of Nairobi. I explore anthropology students 1) everyday life, interests, aspirations and motivations; 2) the relationship between their personal background and approach to anthropology; and 3) how they interpret society and assess their potential to contribute to it as social scientists. A prevalent theme of this thesis is an ambivalence toward anthropology in Kenya, which can be seen to be derived from a tension between traditionalism and modernism in the cultural politics of postcolonial Kenya. This ambivalence further manifests itself in current students evaluations of their academic endeavors. I begin my thesis with a historical overview of the emergence of anthropology in Kenya, assessed within a broader context of decolonization, Africanization of academia and concurrent shifts in developmental discourse. In chapter 2, I direct my focus to current anthropology students and how they perceive their education and prospects as anthropologists-to-be in a political-economic situation where education is becoming geared towards the market, and which questions the very relevance of the anthropological project. In chapter 3, I discuss the economics of Kenyan anthropology in more detail, with particular attention on the influence of political-economic conditions on research selection. In the final two chapters, I address the students worldviews and their ideas of work, discuss the ambivalence of their pursuits and multiple meanings of being relevant in Kenyan society. These chapters serve to illustrate that student aspirations reflect a transcendence of economic constraints and opportunistic self-interest to include a commitment to benefitting society and giving back to their own communities. While my thesis is limited to Kenyan students in 2014, triangulation with my own experiences as a student of social anthropology in a very different economic and cultural context suggests that the lessons learned from the Kenyan field site might have wider purchase for the discipline. In an increasingly globalized world where the logic of the market is propagated at all costs, the significance of all social science is called into question. An anthropologist in the making myself, I shared, across obvious contextual differences, many of these concerns and dreams about the future. In this sense, my ethnography is premised on an assertion of likeness rather than difference

An Uncertainty-aware Hybrid Approach for Sea State Estimation Using Ship Motion Responses

Situation awareness is essential for autonomous ships. One key aspect is to estimate the sea state in a real-time manner. Considering the ship as a large wave buoy, the sea state can be estimated from motion responses without extra sensors installed. This task is challenging since the relationship between the wave and the ship motion is hard to model. Existing methods include a wave buoyanalogy (WBA) method, which assumes linearity between wave and ship motion, and a machine learning (ML) approach. Since the data collected from a vessel in the real world is typically limited to a small range of sea states, the ML method might suffer from catastrophic failure when the encountered sea state is not in the training dataset. This paper proposes a hybrid approach that combined the two methods above. The ML method is compensated by the WBA method based on the uncertainty of estimation results and, thus, the catastrophic failure can be avoided. Real-world historical data from the Research Vessel (RV) Gunnerus are applied to validate the approach. Results show that the hybrid approach improves estimation accuracy.acceptedVersio

Data-driven sea state estimation for vessels using multi-domain features from motion responses

Situation awareness is of great importance for autonomous ships. One key aspect is to estimate the sea state in a real-time manner. Considering the ship as a large wave buoy, the sea state can be estimated from motion responses without extra sensors installed. However, it is difficult to associate waves with ship motion through an explicit model since the hydrodynamic effect is hard to model. In this paper, a data-driven model is developed to estimate the sea state based on ship motion data. The ship motion response is analyzed through statistical, temporal, spectral, and wavelet analysis. Features from multi-domain are constructed and an ensemble machine learning model is established. Real-world data is collected from a research vessel operating on the west coast of Norway. Through the validation with the real-world data, the model shows promising performance in terms of significant wave height and peak period.acceptedVersio

Ship and Offshore Structure Design in Climate Change Perspective

This book summarizes results of longstanding research and scientific contributions from many projects and relevant working groups. It collects and evaluates wind and wave climate projections under changing climate having design needs and marine safety in focus. Potential impact of projected climate change in met-ocean conditions on ships and offshore structures is discussed and illustrated by an example of the expected wave climate change on tanker design

Autonomous search and tracking of objects using model predictive control of unmanned aerial vehicle and gimbal: Hardware-in-the-loop simulation of payload and avionics

This paper describes the design of model predictive control (MPC) for an unmanned aerial vehicle (UAV) used to track objects of interest identified by a real-time camera vision (CV) module in a search and track (SAT) autonomous system. A fully functional UAV payload is introduced, which includes an infra-red (IR) camera installed in a two-axis gimbal system. Hardware-in-loop (HIL) simulations are performed to test the MPC's performance in the SAT system, where the gimbal attitude and the UAV's flight trajectory are optimized to place the object to be tracked in the center of the IR camera's image.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Management of harmonic propagation in a marine vessel by use of optimization

Advances in power electronics drive systems for variable speed operation has enabled extensive use of such solutions in the propulsion and thruster systems of marine vessels. These solutions however introduce current and voltage distortions that compromises the overall power quality of the onboard electrical system. This paper presents and discusses one approach for generating the harmonic current reference for an active filter based on optimization. Two relevant results are revealed by this study: 1) lower THD values are attained by performing system optimization compared to local compensation of one load, and 2) the lower THD values are achieved with a smaller active filter rating than the one required for local load compensation.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Optimal Compensation of Harmonic Propagation in a Multi-Bus Microgrid

This paper discusses how an Active Power Filter (APF) can be utilized for system-wide harmonic mitigation in a microgrid with multiple sources of harmonic distortion located at different buses. A two-bus microgrid system with independent nonlinear loads at both buses is first investigated analytically, and it is demonstrated that it is possible to derive a harmonic current injection from the APF that will minimize the harmonic distortion at both buses. However, analytical optimization of the APF current will be sensitive to parameter variations, will deteriorate when the APF reaches current saturation and cannot be easily extended to larger systems with many loads at different buses. A more practically applicable method for calculating the APF current references, by using the framework of Model Predictive Control (MPC) is instead proposed for the investigated system. Under realistic operating conditions, this approach can obtain further improvement in the system-level harmonic mitigation. The characteristics and performances that are obtained with the analytical solution and the MPC-based control are assessed by time domain simulations in the Matlab/Simulink environment. The results clearly indicate how an MPC-based system-oriented compensation can maximize the utilization of a single APF in a multi-bus Microgrid.© EA4EPQ. This is the authors’ accepted and refereed manuscript to the article