This project was made by student from UmeåUniversity and a request from the universityETH in Zürich, Switzerland. In this research project the electrical strengthof different natural gases and mixtures was investigated, and the aim was to finda gas or gas mixture with a natural origin or strongly attaching gases that couldreplace SF6 (Sulfur Hexafluoride). The gases were tested with breakdown experiments,one of those test was called lightning impulse breakdown test. The mainpart of this project was to investigate triggered spark gaps, which could be used inlightning impulse breakdown test. These spark gaps were made in a previous thesis,but have proved to not be reliable, therefore an investigation was needed. In thelab, a breakdown test setup, made up of a rectifying circuit and a transformer, wasused. In this project voltages up to 140kV were used. The two main parts of theproject were the spark gap unit and circuit analyzing and the spark gap characterization.These two parts contained test to see if the spark gap worked as it shouldor if there were any problems with it. The results from the tests showed that therewere problems with the spark gap, but these problems could be corrected or avoidedthrough controls of the spark gap before use.

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Ester liquids including both natural ester and synthetic ester are being considered as potential alternatives to mineral oil, due to their better environmental performance and for some liquids their higher fire point. Although these liquids have been widely used in distribution and traction transformers, it is still a significant step to adopt ester liquids in high-voltage power transformers because the high cost and severe consequence of a factory test failure and the high level of safety and reliability required in service for these units, tend to lead to a cautious approach to any step change in technology. Lightning impulse strength as basic insulation level is of importance for insulation design of power transformers and lightning impulse test is commonly required in the factory routine tests for high-voltage power transformers, so this thesis is aimed to investigate the electrical performances including pre-breakdown and breakdown of natural ester and synthetic ester under impulse voltage. Two types of field geometry were considered in the study, one is sphere-sphere configuration which represents the quasi-uniform fields inside a transformer and another is strongly non-uniform point-plane configuration which represents the situation of a defect or a source of discharge. In quasi-uniform field study, standard breakdown tests were carried out under negative lightning and switching impulse voltages. Influence of various testing methods on the measured lightning breakdown voltage was studied and the 1% lightning withstand voltage was obtained based on Weibull distribution fitting on the cumulative probability plot built up using the approximately 1000 impulse shots. As for strongly non-uniform field study, streamer propagation and breakdown event in ester liquids either with or without pressboard interface were investigated at various gap distances under both positive and negative lightning impulse voltages. A relationship between the results under lightning impulse and previously published results under step voltage was built up to predict the lightning breakdown voltage of ester liquids at very large gaps. The results indicated that impulse strengths of ester liquids for both breakdown and withstand in a quasi-uniform field, are comparable to those of mineral oil. In a strongly non-uniform field, streamers in ester liquids propagate faster and further, than in mineral oil at the same voltage level. Thus breakdown voltages of ester liquids are generally lower than those of mineral oil, which could be as low as 40% at a large gap distance of approximately 1000 mm. Introduction of parallel pressboard interface has no influence on the streamer propagation and thus does not weaken the breakdown voltage, but it tends to reduce the acceleration voltage particularly for mineral oil under positive polarity. Last but not least, a unique phenomenon of secondary reverse streamer (SRS) was observed in ester liquids, which occurs subsequently and well after the extinction of the primary streamer (PS) propagation within a single shot of impulse voltage and has the reverse polarity to the PS. The formation mechanism of SRS is explained mainly due to the reverse electric field induced by the residual space charges left by the PS.

The escalating cost of claims for Noise Induced Hearing Loss (NIHL) in the Canadian Armed Forces (CAF) supports the need to review and upgrade current hearing conservation practices. The rise of these escalating costs and the need to protect the military personnel when training in extreme noise conditions has initiated an engineering investigation within the Department of National Defence (DND) and in collaboration with the University of Ottawa, to review the existing standards in the field of hearing protection test and evaluation, to propose technical recommendations and to identify the possible technical problems and gaps impacting the quality of the existing procedures. This study dealt with the estimation of the protection capability of Hearing Protection Devices (HPDs) in the case of high-level impulse noise from small firearms weapons that are a particularly damaging source of noise in military environments, representing an important cause of NIHL. Testing and evaluation based on a system engineering approach have been used in this work introducing: - A new testing approach, based on ANSI/ASA S12.42-2010, for testing HPDs when the impulse noise is generated by a small firearm; - A new evaluation approach for HPD performance, introducing a characterization approach using a sub-band analysis for dealing with impulse noise generated by a small firearm. The effectiveness of HPDs, taking into account the physiological human limitations induced by Bone Conduction (BC), is computed by using an innovative method attempting to better prevent the risk of NIHL when using small firearms.

PART I Hollow-sphere (HS) steel foam is a relatively new material whose cellular morphology and material properties qualify it as a metallic foam. This is an innovative foam-like material that exhibits high stiffness paired with low relative densities. Technological advancements in the past few decades have enabled the manufacturing of this material by a sintering process and, as a result, research has begun to accelerate as a multi-school collaboration effort for this particular work. Even though commercialization has been a challenge for metallic foams, it is imperative that researchers continue to prove and promote the advantages of metallic foams despite the current challenges posed by commercialization. One of the most promising characteristics of metallic foams is their energy absorption capacity. This work explores hollow-sphere steel foam’s ability to absorb energy at high strain rates under a dynamic impact load and builds upon an earlier work of quasi-static compression loading. Since most research in this field has been attributed to aluminum open-cell foams, the objective of this work seeks to build upon and apply existing methods to cultivate new research material for hollow-sphere steel foam. The premise of this work began with experimental research analyzing stress-strain relationships of a mass impacting samples of HS steel foam with different kinetic energies. As a result, material properties were extracted and quantified such as elastic modulus, yield stress, and energy absorption, among others. These properties set the foundation for the next set of research; finite element analysis whose objective is to develop a functional material model that could be used for a later application in structural engineering, such as a blast or crash impact. PART II The second part of this thesis applies structural engineering mechanics to a complex arboricultural project. A particular American elm (Ulmus americana L.) tree is the focus of analysis due to its usage for tree climbing competitions. Structurally, this work is relevant to structural engineering by involving finite element analysis of a branch of this American elm tree. This particular work has the objective of understanding how a particular American elm branch behaves structurally under a variety of dynamic loads with different input parameters. Before any of the analyses can be implemented, the definite geometry of the tree has to be measured and material properties have to be calculated. Field experimental data are imperative for this project so that the idealized model can represent the real system as best as possible. Following the data acquisition and modeling of the tree, loads that were either measured or calculated are applied. These loads can be idealized as an impulse load and a cyclic load, with variability imposed within each of them. It is within this variability of the parameters within the loads that the purpose of this work arises. By applying extreme loads upon this tree branch, critical points along the branch can be identified by calculating maximum bending and axial stresses. These stresses indicate not only the critical points along the primary branch but in addition, they indicate the magnitude and severity of these potential stresses, which can be compared directly with the mechanical properties of the wood in the branch. The final intent of this work is to contribute to the knowledge of how a particular branch behaves dynamically in order to better equip tree climbers, academics, and professionals by integrating structural mechanics and arboriculture.

This work deals with acoustics of rooms for sound post-production activities and their simulations, in order to reduce the need for acoustic room treatment and specialized monitoring equipment to a hardware unit and headphones - specifcally by creating hardware product for auralization of rooms impulse resp

This diploma thesis deals with the determination of the Young’s modulus of coatings using the impulse excitation technique (IET). The theoretical part of the thesis describes Cold and Thermal Spray technology, theoretical foundations of the impulse excitation technique and models of composite materials. The experimental part of the thesis deals with the determination of the tensile modulus of copper coating created by Cold Spray technology. The impulse excitation technique has been used to measure fifteen samples with coating thickness ranging approximately from 0,4 to 2 mm. Results from this measurement were evaluated using five composite models to establish the Young’s modulus of the applied coating. The best results were achieved by using the composite model based on rule of mixtures (ROM).

Topic of this diploma thesis is thermodynamical recalculation of turbine TG3 for different parameters and new design of its blading. Introduction deals with theoretical basics of turbines and their components. Second part explains general reasons for retrofit and then specifically for Heating plant Olomouc, where TG3 is located. Third part includes used calculating methods and formulas. Last part presents results, which were calculated in software MS Excel. A cross section drawing is attachment of this thesis.

This diploma thesis deals with impact of room acoustics on automatic speech recognition (ASR) accuracy. Experiments were evaluated on speech corpus LibriSpeech and database of impulse responses and noise called ReverbDB. Used ASRs were based on Mini LibriSpeech recipe for Kaldi. First it was examined how well can ASR learn to transcribe in selected environments by using the same acoustic conditions during training and testing. Next, experiments were carried out with modifications of ASR architecture in order to achieve better robustness against new conditions by using methods for adapation to room acoustics - r-vectors and i-vectors. It was shown that recently proposed method of r-vectors is beneficial even when using real impulse responses for data augmentation.

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