Bayesian Reconstruction of Gravitational-wave Signals from Binary Black Holes with Nonzero Eccentricities

We present a comprehensive study on how well gravitational-wave signals of binary black holes with nonzero eccentricities can be recovered with state of the art model-independent waveform reconstruction and parameter estimation techniques. For this we use BayesWave, a Bayesian algorithm used by the LIGO-Virgo Collaboration for unmodeled reconstructions of signal waveforms and parameters. We used two different waveform models to produce simulated signals of binary black holes with eccentric orbits and embed them in samples of simulated noise of design-sensitivity Advanced LIGO detectors. We studied the network overlaps and point estimates of central moments of signal waveforms recovered by BayesWave as a function of $e$, the eccentricity of the binary at 8 Hz orbital frequency. BayesWave recovers signals of near-circular ($e\lesssim0.2$) and highly eccentric ($e\gtrsim0.7$) binaries with network overlaps similar to that of circular ($e=0$) ones, however it produces lower network overlaps for binaries with $e\in[0.2,0.7]$. Estimation errors on central frequencies and bandwidths (measured relative to bandwidths) are nearly independent from $e$, while estimation errors on central times and durations (measured relative to durations) increase and decrease with $e$ above $e\gtrsim0.5$, respectively. We also tested how BayesWave performs when reconstructions are carried out using generalized wavelets with linear frequency evolution (chirplets) instead of sine-Gaussian wavelets. We have found that network overlaps improve by $\sim 10-20$ percent when chirplets are used, and the improvement is the highest at low ($e<0.5$) eccentricities. There is however no significant change in the estimation errors of central moments when the chirplet base is used.Comment: 16 pages, 9 figures, accepted for publication in CQ

Modeling the Impact of Piston Rings on Oil Consumption of Internal Combustion Engines

V rámci této práce byl vyvinut komplexní simulační nástroj, vycházející z výpočtového modelování fyzikálních a chemických dějů, který je doplněn vhodnými matematickými postupy. Výsledný software je schopen stanovit ztrátový výkon sady pístních kroužků pomocí účinků klíčových mechanismů a jejich vzájemné interakce při standardním provozu pístních kroužků. Simulační výstupy byly navrženy v souladu se zájmy průmyslové praxe, např. určení objemového toku plynů pístní skupinou, ztrátové výkony vlivem tření a spotřeba oleje, která je ovlivněna sadou pístních kroužků. Při vývoji simulačního modelu byly technické experimenty vykonány na tříválcovém zážehovém motoru za účelem získání vstupních dat a ověření výsledků. Možnosti navrženého simulačního nástroje jsou na tomto motoru dále demonstrovány v podobě parametrických studií, využitelných zejména při návrhovém procesu. Cílem dizertační práce bylo zaplnit mezeru ve výzkumné oblasti simulačních nástrojů, které mohou účinně propojit výpočtové modelování třecích ztrát a současně i spotřeby oleje, a podpořit tak výrobce pístních kroužků a vývojová oddělení spalovacích motorů.Within the frame of the present work a complex simulation tool was developed, built on strong physical and chemical foundations, supplemented with the appropriate mathematical approaches. The resulting software is capable of determining the performance of a piston ring pack by addressing all key mechanisms and their mutual influence during standard operating conditions of a piston ring. The outputs of the simulation were designed in accordance with industrial interest, like the volumetric gas flow through the piston assembly, the friction power losses and the lubricant oil consumption from the sources, which are affected by the piston ring pack. Besides the development of the simulation model, experiments were conducted with the intention of input data obtainment and results validation on an inline three-cylinder engine. Sample results were shown by applying the model to the parameters of the experimental engine. Possible industrial application of the source code is demonstrated with parameter studies. The work carried out within the frame of this doctoral dissertation was intended to fill the gap in the research area of combined simulation tools, able to support the needs of piston ring manufacturers and engine research centers, to calculate the impact of design parameter changes on friction losses and lubricant oil consumption simultaneously.

Car Door Handle FEM Model Creation and Validation for Crash Simulations

Cieľom tejto diplomovej práce bolo vytvoriť komponentný model multivýstuhy kľučky dverí, použitá v modeloch koncernu Volkswagen, ktorý je možný použiť v crashových výpočtoch. Naladiť jeho parametre tak, aby svojim chovaním najviac odpovedal skutočnej súčiastke. V teoretickej časti sa najprv predstavili súčasné predpisy organizácie Euro NCAP týkajúce sa testovania a hodnotenia pasívnej bezpečnosti nových vozidiel. Pozornosť sa zamerala na hodnotenie skúšok bočného nárazu, pri ktorých sa prejavili následky porušenia multivýstuhy v najväčšej miere. Ukázali sa dôvody snahy o simuláciu reálneho chovania multivýstuhy, faktory, ktoré iniciovali vznik danej témy. Praktická časť práce sa začína tvorbou FEM siete súčiastky na základe jej 3D CAD modelu, popisom požiadaviek na kvalitu siete, použitých nástrojov a postupov. Ďalej sa preskúmali charaktery skutočných namáhaní oblasti kľučky dverí pri bočnom náraze, na základe čoho sa navrhli komponentné skúšky na validáciu simulačného modelu. Experimentálny výskum zahrňoval skúšku zaťaženia multivýstuhy na ohyb a na krútenie, po troch vzorkách. Po vykonaní experimentov sa ich výsledky porovnali s hodnotami odpovedajúcich simulácií. Podľa odchýlok sa vykonali úpravy simulačného modelu: spresnila sa sieť konečných prvkov, nastavil sa nový materiálový model s mechanizmom porušení a nadefinovali sa skutočné materiálové vlastnosti použitého termoplastu. V záveru sa opäť porovnali miesta porušenia a závislosti nameraných hodnôt so simulačnými, obdŕžané výsledky sa vyhodnotili.The aim of this master’s thesis was to create a component model of a door handle stiffener used by the Volkswagen concern, which can be used for crash computations. Also to tune its parameters the way, its behavior corresponds the most to the real part’s. In the theoretical part the current regulations of the Euro NCAP are presented, concerning the testing and evaluation of the passive safety of new vehicles. Attention is focused on the evaluation of the side impact barrier tests, where the effect of the door handle stiffener’s damage is reflected the most. Shown are the reasons for the effort to simulate the real behavior of the stiffener, the factors, which initialized the born of the studied problem. The practical part starts with the creation of the FEM mesh of the part based on its 3D CAD model, also describes the requirements for the mesh quality, as well as the used tools and methods. Further on investigated are the characters of real damages of the door handle area during side impacts, based on which the component tests are proposed for the validation of the simulation model. Experimental research consists of the stiffener’s testing for simple bend and twist loads, three specimens each. After the execution of the tests the results get compared with the corresponding simulations. Modifications are made on the model according to the acquired results: refinement of the FEM mesh, new material model usage with failure for shell elements and definition of real material characteristics for the used thermoplastics. The latest obtained simulation dependencies are compared with the measured values again, the results are evaluated at last.

Modeling the Impact of Piston Rings on Oil Consumption of Internal Combustion Engines

V rámci této práce byl vyvinut komplexní simulační nástroj, vycházející z výpočtového modelování fyzikálních a chemických dějů, který je doplněn vhodnými matematickými postupy. Výsledný software je schopen stanovit ztrátový výkon sady pístních kroužků pomocí účinků klíčových mechanismů a jejich vzájemné interakce při standardním provozu pístních kroužků. Simulační výstupy byly navrženy v souladu se zájmy průmyslové praxe, např. určení objemového toku plynů pístní skupinou, ztrátové výkony vlivem tření a spotřeba oleje, která je ovlivněna sadou pístních kroužků. Při vývoji simulačního modelu byly technické experimenty vykonány na tříválcovém zážehovém motoru za účelem získání vstupních dat a ověření výsledků. Možnosti navrženého simulačního nástroje jsou na tomto motoru dále demonstrovány v podobě parametrických studií, využitelných zejména při návrhovém procesu. Cílem dizertační práce bylo zaplnit mezeru ve výzkumné oblasti simulačních nástrojů, které mohou účinně propojit výpočtové modelování třecích ztrát a současně i spotřeby oleje, a podpořit tak výrobce pístních kroužků a vývojová oddělení spalovacích motorů.Within the frame of the present work a complex simulation tool was developed, built on strong physical and chemical foundations, supplemented with the appropriate mathematical approaches. The resulting software is capable of determining the performance of a piston ring pack by addressing all key mechanisms and their mutual influence during standard operating conditions of a piston ring. The outputs of the simulation were designed in accordance with industrial interest, like the volumetric gas flow through the piston assembly, the friction power losses and the lubricant oil consumption from the sources, which are affected by the piston ring pack. Besides the development of the simulation model, experiments were conducted with the intention of input data obtainment and results validation on an inline three-cylinder engine. Sample results were shown by applying the model to the parameters of the experimental engine. Possible industrial application of the source code is demonstrated with parameter studies. The work carried out within the frame of this doctoral dissertation was intended to fill the gap in the research area of combined simulation tools, able to support the needs of piston ring manufacturers and engine research centers, to calculate the impact of design parameter changes on friction losses and lubricant oil consumption simultaneously.

Eccentricity distributions of eccentric binary black holes in galactic nuclei

Galactic nuclei are expected to be one of the main sites for formations of eccentric binary black holes (EBBHs), with an estimated detection rate of $\mathcal{O}(1-100$ yr$^{-1})$ with Advanced LIGO (aLIGO) detectors operating at design sensitivity. The two main formation channels of these binaries are gravitational capture and the secular Kozai-Lidov mechanism, with expectedly commensurable formation rates. We used Monte Carlo simulations to construct the eccentricity distributions of EBBHs formed through these channels in galactic nuclei, at the time their gravitational-wave signals enter the aLIGO band at $10$ Hz. We have found that the proportion of binary black holes entering the aLIGO band with eccentricities larger than $0.1$ is $\sim 10$ percent for the secular Kozai-Lidov mechanism, and $\sim 75$ percent for gravitational capture. We show that if future EBBH detection rates with aLIGO will be dominated by EBBHs formed in galactic nuclei, then the proportions of EBBHs formed through the two main channels can be constrained to a $\Delta \mathcal{F}= 0.2$ wide one-sigma confidence interval with a few tens of observations, even if parameter estimation errors are taken into account at realistic levels.Comment: 13 pages, 6 figures, typos correcte

Constraints on coasting cosmological models from gravitational-wave standard sirens

We present the first test of coasting cosmological models with gravitational-wave standard sirens observed in the first three observing runs of the LIGO-Virgo-KAGRA detector network. We apply the statistical galaxy catalog method adapted to coasting cosmologies and infer constraints on the $H_0$ Hubble constant for the three fixed values of the curvature parameter $k=\left\{ -1,0,+1 \right\}$ in $H_0^2 c^{-2}$ units. The maximum posteriors and $68.3\%$ highest density intervals we obtained from a combined analysis of $46$ dark siren detections and a single bright siren detection are $H_0=\left\{68.1^{+8.5}_{-5.6},67.5^{+8.3}_{-5.2},67.1^{+6.6}_{-5.8} \right\}~\mathrm{km\ s^{-1}\ Mpc^{-1}}$, respectively. All our constraints on $H_0$ are consistent within one sigma with the $H_0$ measured with the differential age method, which provides a constraint on $H_0$ in coasting cosmologies independently from $k$. Our results constrain all cosmological models with $a(t)\propto t$ linear expansion in the luminosity distance and redshift range of the $47$ LIGO-Virgo detections, i.e. $d_\mathrm{L}\lesssim 5~\mathrm{Gpc}$ and $z\lesssim 0.8$, which practically include all (both strictly linear and quasi-linear) models in the coasting model family. As we have found, the coasting models and the $\Lambda$CDM model fit equally well to the applied set of gravitational-wave detections.Comment: 7 pages, 3 figures, 1 tabl

Detecting Long-Duration Narrow-Band Gravitational Wave Transients Associated with Soft Gamma Repeater Quasi-Periodic Oscillations

We have performed an in-depth concept study of a gravitational wave data analysis method which targets repeated long quasi-monochromatic transients (triggers) from cosmic sources. The algorithm concept can be applied to multi-trigger data sets in which the detector-source orientation and the statistical properties of the data stream change with time, and does not require the assumption that the data is Gaussian. Reconstructing or limiting the energetics of potential gravitational wave emissions associated with quasi-periodic oscillations (QPOs) observed in the X-ray lightcurve tails of soft gamma repeater flares might be an interesting endeavour of the future. Therefore we chose this in a simplified form to illustrate the flow, capabilities, and performance of the method. We investigate performance aspects of a multi-trigger based data analysis approach by using O(100 s) long stretches of mock data in coincidence with the times of observed QPOs, and by using the known sky location of the source. We analytically derive the PDF of the background distribution and compare to the results obtained by applying the concept to simulated Gaussian noise, as well as off-source playground data collected by the 4-km Hanford detector (H1) during LIGO's fifth science run (S5). We show that the transient glitch rejection and adaptive differential energy comparison methods we apply succeed in rejecting outliers in the S5 background data. Finally, we discuss how to extend the method to a network containing multiple detectors, and as an example, tune the method to maximize sensitivity to SGR 1806-20 flare times.Comment: 11 pages, 8 figure

Global Optimization for Future Gravitational Wave Detectors' Sites

We consider the optimal site selection of future generations of gravitational wave detectors. Previously, Raffai et al. optimized a 2-detector network with a combined figure of merit. This optimization was extended to networks with more than two detectors in a limited way by first fixing the parameters of all other component detectors. In this work we now present a more general optimization that allows the locations of all detectors to be simultaneously chosen. We follow the definition of Raffai et al. on the metric that defines the suitability of a certain detector network. Given the locations of the component detectors in the network, we compute a measure of the network's ability to distinguish the polarization, constrain the sky localization and reconstruct the parameters of a gravitational wave source. We further define the `flexibility index' for a possible site location, by counting the number of multi-detector networks with a sufficiently high Figure of Merit that include that site location. We confirm the conclusion of Raffai et al., that in terms of flexibility index as defined in this work, Australia hosts the best candidate site to build a future generation gravitational wave detector. This conclusion is valid for either a 3-detector network or a 5-detector network. For a 3-detector network site locations in Northern Europe display a comparable flexibility index to sites in Australia. However for a 5-detector network, Australia is found to be a clearly better candidate than any other location.Comment: 30 pages, 23 figures, 2 table