Nya doktorsavhandlingar

Johan Forslund, "Studies of a Vertical Axis Turbine for Marine Current Energy Conversion: Electrical system and turbine performance", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1739

Abstract:

Ocean energy is a field of growing interest when it comes to renewable energy thanks to its high density of energy per unit area, and to the high predictability. Conversion of hydrokinetic energy, found in marine currents, is the utilization of the energy in free-flowing water for conversion to electric energy. This thesis presents experimental data from a test site with a marine current converter. The converter system features a vertical axis turbine directly connected to a permanent magnet synchronous generator placed on the riverbed. The converter is controlled by an electrical system. The focus of the work is to evaluate power control methods and turbine performance.  Results of a simple voltage control system is presented and compared with operation without control. The turbine type in the converter system is not self-starting. The startup power and energy has been investigated through experiments. The converter system has been connected to the local electric utility grid and the first experimental results are presented. [...] 

Flore Rémouit, "Automation of underwater operations on wave energy converters using remotely operated vehicles", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1695

Abstract:

In the last fifteen years, the Division of Electricity at Uppsala University has been developing a wave energy converter (WEC) concept. The concept is based on a point-absorbing buoy with a directly driven linear generator placed on the seabed. Several units are connected to a marine substation, whose role is to collect and smooth the power absorbed from the waves and then bring it to the shore through one single cable.

A big challenge in the project is to reduce the costs related to the deployment and maintenance of the WECs and substation. Currently, those operations are performed by divers, which is costly and entail considerable risks. A possibility is to replace divers with automated solutions using small robots called remotely operated vehicles (ROVs). This PhD thesis proposes and analyses a method for deployment and maintenance of underwater devices with no use of diving operations.[...] 

Nattakarn Suntornwipat, "Diamond devices based on valley polarization", Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214; 1670

Abstract:

Diamond is a wide bandgap semiconductor with extreme properties such as high thermal conductivity, high breakdown field, high carrier mobilities and chemical inertness. These properties together with the possibility to synthesize high purity Single-Crystalline (SC) diamond by Chemical Vapor Deposition (CVD), make it a very interesting material and a candidate for use in power electronics and in hazardous environments. The low impurity concentration achieved when fabricating diamond by CVD allows for a detailed study of the intrinsic electronic properties.

Diamond has six equivalent conduction band valleys oriented along the {100} axes with a uniquely low scattering rate between them. At low temperatures, the intervalley phonon scattering rate in diamond becomes negligible, which leads to a stable valley polarization state. We have observed non-equilibrium valley populations (valley-polarized electron ensembles), which in turn have been found to result in a Negative Differential Mobility (NDM).[...] 

Victor Mendoza, "Aerodynamic studies of vertical axis turbines using the actuator line model", Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1671

Abstract:

This thesis addresses the unsteady aerodynamics involved in the operation of vertical axis wind turbines (VAWTs). The main focus is to represent and understand the most relevant phenomena within the resulting flow pattern as the wake structure, loads on the different turbine components and the performance of the rotor. An actuator line model has been used for this purpose.

This model has been validated against experimental measurements from diverse cases with different operating conditions in both confined wind tunnels and open site locations. Numerical works were carried out considering a wide range of tip speed ratios (TSRs), and therefore covering from the no stall to the deep stall regime. The latter requires the implementation of a dynamic stall model for the proper representation of the unsteady forces on the blades. Also, different inlet conditions such as a uniform flow, a logarithmic wind shear and an atmospheric boundary layer (ABL) have been tested. The so-called recycling method technique was used to produce the fully developed ABL flow. Additionally, the resulting wake and performance of interacting turbines has been studied.[...] 

Kaspars Siliņš, "Plasma Enhanced Chemical- and Physical- Vapor Depositions Using Hollow Cathodes", Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1629

Abstract:

Development of coating deposition technologies, in terms of performance and costs, is an ongoing process. A promising class of deposition technologies are based on hollow cathode discharges.

This thesis investigates performance of selected hollow cathode plasma sources developed at the Plasma group, at Uppsala University for coating deposition at moderate pressures. Amorphous carbon film deposition was investigated by Radio frequency (RF) Hollow Cathode Plasma Jet (RHCPJ) and Magnets-in-Motion (M-M) linear hollow cathode plasma sources. Titanium nitride (TiN) films were deposited by a magnetized Hollow Cathode Enhanced magnetron Target (HoCET). Aluminium nitride (AlN) deposition by RHCPJ was compared with High Power Impulse Magnetron Sputtering (HiPIMS).[...] 

Pasan Hettiarachchi, "Measurements of X-ray emission from laboratory sparks and upward initiated lightning", Digital  Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1618

Abstract:

In 1925 Nobel laureate R. C. Wilson predicted that high electric fields of thunderstorms could accelerate electrons to relativistic energies which are capable of generating high energetic radiation. The first detection of X-rays from lightning was made in 2001 and from long sparks in 2005. Still there are gaps in our knowledge concerning the production of X-rays from lightning and long sparks, and the motivation of this thesis was to rectify this situation by performing new experiments to gather data in this subject.[...] 

Erik Hultman, "Robotized Production Methods for Special Electric Machines", Digital  Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1608

Abstract:

A research project on renewable energy conversion from ocean waves to electricity was started at the Division of Electricity at Uppsala University (UU) in 2001. The Wave Energy Converter (WEC) unit developed in this project is intended to be used in large offshore WEC farms and has therefore been designed with large-scale production in mind. The concept has now also been commercialized by the spin-off company Seabased Industry AB.

An essential part of the UU WEC is the linear direct-drive generator. This thesis presents the pilot work on developing robotized production methods for this special electric machine. The generator design is here investigated and four different backbreaking, monotone, potentially hazardous and time consuming manual production tasks are selected for automation. A robot cell with special automation equipment is then developed and constructed for each task. Simplicity, reliability and flexibility are prioritized and older model pre-owned industrial robots are used throughout the work. The robot cells are evaluated both analytically and experimentally, with focus on full scale experiments. It is likely that the developed production methods can be applied also for other similar electric machines. [...]