Tarkvara arendamine vibratsioonikatsetuste andmeanalüüsiks

Kanderaketi üleslaskmise tagajärjel tekivad väga tugevad vibratsioonid ja põrutused. Igal süsteemil on oma loomulik sagedus. Kui väliste jõudude (vibratsioonide ja põrutuste) sagedus vastab terve süsteemi loomulikule sagedusele, tekivad resonantsid. Resonantsid suurendavad mitmekordselt jõude, mis süsteemile mõjuvad. Süsteemi struktuurid aga mõningatel juhtudel ka terved süsteemid võivad selle tagajärjel katki minna. Tagamaks, et kosmosesse saadetavad satelliidid kanderaketist tulenevatele jõududele vastu peavad, tuleb kõiki komponente erinevates keskkondades eelnevalt katsetada. Süsteemi iseloomustamiseks ja loomulike sageduste leidmiseks viiakse läbi resonantsanalüüs. See teostatakse vibratsioonisüsteemiga nii enne kui ka pärast süsteemi mehaanilisi katsetusi. Resonantsanalüüsi tulemusi võrreldes saab tuvastada, kas katseobjekt läbis katse või mitte. Käesolevas töös on tutvustatud Tartu Ülikooli Tartu observatooriumi vibratsiooni katsetamise süsteemi ja meetodit. Magistritöö eesmärgiks on arendada tarkvaralahendus, mis võimaldaks vibratsioonikatsetuste andmeid visualiseerida ja analüüsida. Luues kasutajaliides on tagatud, et tarkvaras tulemusi esitavad graafikud on kergesti kohandatavad vastavalt klientide nõuetele. Lisaks võimaldab tarkvara tuvastada katseandmetes resonantse, mida kuvatakse piikidena. Tarkvara suudab erinevate katsete puhul välja arvutada amplituudi ja sageduse erinevused ning võrreldes tulemusi omavahel järeldada, kas katseobjekt läbis katse või mitte. Arendatud tarkvaralahendus on olnud kasutusel Tartu Ülikooli Tartu observatooriumi kosmosetehnoloogia laboris 8 kuud. Katsetustunnistustel, mis klientidele peale vibratsiooni-katsetusi väljastatakse on esitatud käesoleva tarkvaraga loodud graafikud.Rocket launches are violent and involve harsh events such as vibrations and shocks. Every structural system has its own natural frequency. When the frequency of the external forces (shocks and vibrations) syncs up with the natural frequency of the whole system, it leads to resonance. This causes the forces acting on the system to be multiplied several folds. It can lead to a structural failure or even complete loss of the system in some cases. To ensure, that every spacecraft launched in to space is able to withstand these environments, every component undergoes environmental testing on ground. To characterize and find the natural frequencies of the system, a resonance survey is performed with the vibration testing system. This is done both, before and after the system is subjected to any mechanical environmental tests. The comparison of these resonance surveys helps to identify whether or not the Device Under Test (DUT) has passed the testing criteria. In this work the vibration testing system available at Tartu Observatory, University of Tartu has been introduced along with the method for vibration testing in use. The aim of this work was to develop a software that would perform visualization and analysis of the vibration testing data. It has been made sure that the resultant plots of the software are easily customizable with the help of a Graphical User Interface (GUI), to meet specific customer requirements. In addition, the software is capable of identifying the resonances in the data which show up as peaks. It calculates the amplitude and frequency shift in the resonances to easily show the user, whether the test object has passed the tests. The developed software has been in use in the Laboratory of Space Technology at Tartu Observatory, UT for 8 months. The test certificates handed over to the customers after vibration testing has been performed, contain the plots that are generated by this software

Towards open-ended crowd-powered data processing: a case study of clustering and counting

Due to the widespread use and importance of crowdsourcing in gathering training data at scale, the data management community has devoted its efforts in understanding and optimizing fundamental primitives like filters and joins. These primitive boolean operations, where the human responses come from a small, finite space of possible answers, are inadequate for a number of data analysis tasks, especially those involving images, videos and maps. There is, thus, a need for open-ended crowdsourcing in order to get more fine-grained information from humans that can be used in developing sophisticated AI systems. In this thesis, we study two popular open-ended crowdsourcing problems. The first, clustering, is the problem of organizing a collection of objects (images, videos) by allowing workers to form as many clusters as they would like and organize items across them. The second, counting, is the problem of counting objects in images. In this thesis, we develop models to reason about human behavior for both problems, and use these models to design provably cost-efficient algorithms that provide high-quality results, as compared to currently available approaches

Ultrashort-Laser-Pulse Multi-Photon Excitation Schemes for Combustion Diagnostics

Laser-based diagnostic approaches using ultra-short femtosecond (fs) laser pulses is a promising method for investigating complex chemically reacting flow fields such as flames. Femtosecond pulses offer several advantages over traditionally used nanosecond (ns) and picosecond (ps) pulses because of their broad spectral bandwidth, high peak power, and high repetition rates. They can be especially advantageous for efficient multi-photon excitation schemes. During the past decade, fs laser diagnostic has been developed and demonstrated primarily in gaseous flames and canonical geometries; however, their implementation for studying more practically relevant harsh combustion environments has been limited. Thus, the objective of this thesis research is to investigate methodologies to extend the applications of ultrashort, fs-pulse-based laser-induced fluorescence (LIF) techniques to imaging studies in realistic flame environments. This thesis consists of four main research tasks; (i) understanding the role of H-atoms in sooting formation by implementing ts two-photon LIF (fs-2pLIF) imaging, (ii) explore the applicability of fs imaging schemes in practically relevant hardware containing thick optical windows by using fs 3-photon LIF (fs-3pLIF) detection of H-atoms, (iii) extension of fs LIF methods for simultaneous multi-species detection using a single laser pulse by demonstrating H-atom and OH radicals imaging, and (iv) increasing imaging dimensionality by developing efficient, high-energy tunable laser source via direct frequency conversion. Under the first task, the previously demonstrated H-atom 2pLIF scheme ( = 205 nm) in laminar methane/air flames was extended to the harsh environment of heavily sooting flames for the first time. The implementation of several signal interference mitigation strategies enabled analyzing the relevance of H-atom concentration on soot formation pathways at atmospheric pressure ethylene/air flames. The experiments were performed on a series of sooting flames ranging from lean ( = 0.8) to very rich ( = 3.0). These studies revealed an inverse dependence of soot volume fraction (fV) on the H-atom number density ([H]), and a strong dependence of [H] and fV on flame temperature. In combustion test hardware such as optically accessible internal combustion (IC) engines and gas turbines test rigs, reactions take place at elevated pressures (10–50 bar) and hence involve test sections with thick optical windows. It has been realized that 205-nm deep UV (DUV) pulses can be problematic in cases with thick transmissive optics resulting in high absorption losses and other adverse nonlinear effects. Therefore, for detecting H atoms, red-shifting the excitation wavelength to 307-nm pulses and using 3pLIF excitation scheme can be beneficial in such situations. Under the second task, a detailed 2pLIF vs 3pLIF comparison was performed to characterize different levels of photolytic production, photoionization, and stimulated emission interferences. To the best of our knowledge, the H-atom 3pLIF scheme using = 307.7-nm photons was realized for the first time during this work. The implementation of the above 3pLIF scheme also enabled the extension of this diagnostic approach for simultaneous imaging of multiple species using a single excitation laser pulse. Under the third task, simultaneous detection of H-atom (via 3pLIF) and OH (via single-photon LIF) was achieved using the excitation wavelength of λ = 307.7 nm. This simultaneous detection provides an insight for understanding the effects of light species transport and preferential diffusion of H by revealing their spatial location with respect to the reaction zone marked by the OH radicals. The simultaneous H/OH detection is also important in understanding complex flame phenomena such as local extinction and reignition in turbulent flames and as soot formation pathways. In the last part of this thesis research, a more efficient wavelength generation scheme for acquiring high-energy tunable fs laser pulses was developed to generate high-energy UV pulsed for fs LIF imaging applications with increased dimensionality. The availability of high pulse energy is important for diagnosis in practical combustion systems to account for numerous transmission losses as well as increase the size of the field of view to discern turbulent structures. The high-efficiency third-harmonic generation (THG) scheme was implemented to generate tunable UV pulses near = 283 nm. The THG scheme was implemented for high-fidelity single-laser-shot planer LIF (PLIF) imaging of OH at 1-kHz data rate to study the flame structure and reaction zone in turbulent non-premixed flames using a high-speed imaging system. The above developments and the associated results discussed in this thesis is a significant step forward in implementing ultrashort pulse laser imaging techniques of intermediate chemical species for practically relevant combustion studies