With the increase in complexity of modern electricity grids, the implementation of state-estimators has become a vital aspect of stability and contingency analyses for stable and secure power system operation. Transmission line reactance is an important component in the computation of state-estimators. Two models utilizing real-time synchrophasor data and ERCOT load information are proposed to compute Thevenin equivalent reactance. This thesis presents the results of implementing these methods to estimate the equivalent reactance of a transmission network between The University of Texas at Austin and The University of Texas, PanAm. / text

Many researchers have devoted their work to the development of modal analysis extraction techniques in order to obtain more reliable identification of the modal parameters. Also, as a consequence of all this work, there are some other works devoted to the evaluation and comparison of these methods in order to find which one is the most reliable method with respect to certain characteristics. In this thesis the Rational Fraction Polynomial (RFP) Method, the Prony or Complex Exponential Method (CEM), the Ibrahim Time Domain (ITD) Method, and Hilbert Envelope Method are used to evaluate how the accuracy of the damping ratio is affected with respect to various parameters and conditions. The investigation focuses in the estimation of damping ratio because among the modal parameters, it is the most difficult to model. Each method is evaluated individually in order to understand how the damping ratio estimation is affected with respect to each method when the characteristics of the FRF are changed. Also, they are compared to show that, in general, the Rational Fraction Polynomial Method is a more reliable method than the other methods. To investigate this, a simulated analytical data and an experimental data are processed to estimate the modal parameters, but focusing in the damping ratio. For the simulated analytical data the damping ratio's percent of error were calculated. The highest damping ratio's percent of error of the RFP was 0.0073501%. In the other hand, for the CEM, ITD, and Hilbert Envelope Method their highest damping ratio's percent of error were 83.02%, 99.82%, and 4.077%, respectively. / Master of Science

The work is focused in investigating the effectiveness of discretized damping tapes applied to a cantilever beam subjected to free and forced vibrations. The work is divided into three main sections. First, we performed material characterization of the viscoelastic (VE) pressure sensitive adhesive layer of the damping tapes. To do so, we designed a novel quad shear specimen to measure shear storage and loss moduli, and tan delta from dynamic mechanical analyzer measurements. Second, the optimal discretization length for different damping tapes was experimentally determined and analytically verified using linear viscoelasticity and basic strength of materials and vibrations principles. These results showed a mean to improve the damping of a structure without increasing the weight of the added damping layer. Third, a nonlinear analysis was performed for cantilever beams with damping layers subjected to parametric excitation. Comparison of the response amplitude of the parametrically excited beam was performed for different discretization lengths, and system identification of the nonlinear parameters was carried out. The effects of large deflections of a beam under parametric excitation were analyzed; large deflections were found to induce localized buckling of the stiff constraining layer of the damping tape that would invalidate some of the assumptions and analytical solutions that do not take such phenomena into account. / Master of Science

The dynamic properties of soil are normally inferred from laboratory tests on collected samples or from empirical relations. The soil properties measured in the field can be very different from those predicted from laboratory tests. It is very difficult to determine directly in the field the variation of the shear modulus and damping with the level of excitation (level of strains). This remains today a major gap in our knowledge and our ability to conduct reliable seismic analyses. The main objective of this study is to assess the feasibility of determining reliably in situ the shear modulus and damping of the soil as functions of the level of strains, developing a method to compute these properties from the measured data and providing practical recommendations for the use of the procedure. To achieve this objective, extensive and comprehensive sets of experimental and analytical studies were conducted in parallel. Some numerical analyses were performed to provide a better understanding for performing in situ tests with the newly developed vibroseis loading systems. In addition, the dynamic response of a surface foundation in vertical vibration were studied. This dissertation mostly focuses on the numerical aspects of the problem while some experimental data are also studied and utilized. Field tests were conducted to estimate shear moduli of silty sands at two sites, the Capital Aggregate Quarry and the Texas A&M University sites. Estimated nonlinear shear moduli presented very consistent trends regardless of the analysis methods and test sites. They showed larger elastic threshold shear strains, 1.5 × 10−3 % for the Capital Aggregate Quarry site and 2 × 10−3 % for the Texas A&M University site, than the mean of shear modulus curve for cohesionless soils proposed by Seed and Idriss (1970). Estimated moduli closely followed the mean of Seed and Idriss (1970) at strains larger than 6 × 10−3 % for both sites. Internal damping ratio can also be estimated if additional data are gathered from in situ tests in the future.

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This research investigates possible monitoring methods to non-invasively detect blockages in the cyclone of milk powder spray driers to avoid costly production shutdowns. Two possible solutions have been identified. These are guided wave and vibration analysis. This research focuses on vibration analysis method, based on variation in the natural frequencies and/or damping ratios caused by blockages. Experimental simulation studies the performance to assess the viability of the vibration analysis method in identifying blockage in the cyclone. To test this method, a 1.87m long vertical cylindrical steel tube with both ends simply supported was setup as a prototype and flour was used as the powder conveyed by the tube. Analytical, numerical and experimental methods were implemented on the prototype using vibration analysis techniques. Experimental resonant frequencies of the empty shell from the impact hammer excitation were compared with analytical and numerical solutions to analyse the modal shapes. The first bending mode was determined as 79 Hz, which decreased with the amount of added mass and location closer to the middle point. This was validated by the simulated mass experiment, which also matched with the beam-mass theory. Flour induced experiment further validated the variation of the first bending mode. Experimental 270Hz, 380Hz and 398Hz resonant frequencies increased with the amount of added mass, which was validated by the simulated mass and flour induced experiment. Besides the variation of the natural frequencies, the damping ratio was also studied and quantified using the Hilbert transform envelope curve method. Onsite monitoring of the vibration of the cyclone in a spray dryer was done at Fonterra Te Rapa and clear resonant frequencies were obtained. The research results from the prototype demonstrate that vibration analysis as a non-destructive method to detect the milk powder deposition or blockage in the cyclone is possible and promising. However, more work is required before industry application.

The aim of the submitted diploma thesis is the magnitude determination of the headlamp response to the dynamic excitation. Currently it is necessary to measure this response, because it is one of the assessed criteria of quality of the headlamp. When comparing results of the experimental measurement and the computational modelling, a good consensus of resonant frequencies is observed, but there are significant differences in acceleration amplitudes. The cause of this is the variable damping value. The theoretical part of the thesis deals with polymeric materials, basics of oscillation and damping. It serves to understand the mechanisms, which influence the results of the experimental measurement. The practical part is dedicated to the procedure of the computational modelling and the experimental measurement implementation. The analysis of the experimental measurement results leads to an ascertainment of nonlinearities, which influence the headlamp behaviour. The results of a sensitivity analysis of the computational modelling are used to create curves, on the basis of which the damping is estimated. The inclusion of the estimated damping into computational modelling leads to reduction of the compared differences of the acceleration amplitudes. The conclusion of the thesis contains the recommendation for the damping determination during the computational modelling of the headlamp.

This study separately investigates how temperature as well as two real load-situations affects the modal damping ratio and natural frequencies of a 64.9m span steel arch footbridge. Measurements of acceleration have been completed which covers a temperature span of  to . The natural frequencies of the five investigated modes were observed to decrease 2-6% as the temperature increased. This effect was with the help of beam-theory and finite element modelling deduced to originate mostly from changes in Young’s modulus of the materials, but also geometrical changes in steel because of thermal expansion. Further investigation included a static mass in the form of packed snow that was estimated to weigh 14 tons. The natural frequencies were observed to remain unchanged while the modal damping ratios decreased. The second load-case was an uncontrolled mass-event where a large group of pedestrians travelled over the bridge as two cars stood stationary at the quarter-point of the span. A large increase (146%) of the damping ratio was observed while the natural frequency of the first mode decreased 4%. This change was suggested come from the human structure interaction (HSI) partially because the natural frequency of the human body is close to the first vertical frequency of the bridge thus making humans act like dampers on the bridge when close to resonance, and that the number of pedestrians contribute to the modal mass of the system, thus decreasing the natural frequency. / Denna studie undersöker separat hur temperaturen såväl som två verkliga belastningssituationer påverkar de modala dämpnings kvoterna och egenfrekvenserna hos en 64,9 meter lång stål-bågs gångbro. Mätningar av accelerationen i bron har genomförts som täcker en temperatur på -10°C till 10°C. De naturliga frekvenserna hos de fem undersökta moderna observerades minska 2–6% när temperaturen ökade. Denna minskning var med hjälp av balk-teori och finita element-modellering härled att troligen komma från förändringar i Youngs modul av materialen, men även geometriska förändringar i stålet på grund av termisk expansion. Vidare undersökning innefattade en statisk massa i form av packad snö som uppskattades att väga 14 ton. Egenfrekvenserna observerades förbli oförändrade medan de modala dämpnings kvoterna minskade. Det andra lastfallet var ett okontrollerat massevenemang där en stor grupp fotgängare gick över bron medan två bilar var stationära en fjärdedel in på brons längd. En stor ökning (146%) av dämpnings kvoten för den första vertikala moden observerades medan egenfrekvensen minskade 4%. Denna förändring föreslogs komma från interaktionen mellan människan och bron, delvis för att människokroppens egenfrekvens ligger nära brons första vertikala frekvens vilket gör att människan agerar som en dämpare när de är nära resonans med bron, och att antalet fotgängare bidrar till den modala massan av systemet vilket sänker frekvensen.

The understanding of the impact of site effects on ground motions is crucial for improving the assessment of seismic hazards. Site response analyses (SRA) can numerically accommodate the mechanics behind the wave propagation phenomena near the surface as well as the variability associated with the input motion and soil properties. As a result, SRA constitute a key component of the assessment of site-specific seismic hazards within the probabilistic seismic hazard analysis framework. This work focuses on limitations in SRA, namely, the definition of the elastic half-space (EHS) boundary condition, the selection of input ground motions so that they are compatible with the assumed EHS properties, and the proper consideration of near-surface attenuation effects. Input motions are commonly selected based on similarities between the shear wave velocity (Vs) at the recording station and the materials below the reference depth at the study site (among other aspects such as the intensity of the expected ground motion, distance to rupture, type of source, etc.). This traditional approach disregards the influence of the attenuation in the shallow crust and the degree to which it can alter the estimates of site response. A Vs-κ correction framework for input motions is proposed to render them compatible with the properties of the assumed EHS at the site. An ideal EHS must satisfy the conditions of linearity and homogeneity. It is usually defined at a horizon where no strong impedance contrast will be found below that depth (typically the top of bedrock). However, engineers face challenges when dealing with sites where this strong impedance contrast takes place far beyond the depth of typical Vs measurements. Case studies are presented to illustrate potential issues associated with the selection of the EHS boundary in SRA. Additionally, the relationship between damping values as considered in geotechnical laboratory-based models, and as implied by seismological attenuation parameters measured using ground motions recorded in the field is investigated to propose alternative damping models that can match more closely the attenuation of seismic waves in the field. / Ph. D.

The liquefaction resistance of undisturbed soil samples collected from a selected location in Carbondale, Southern Illinois was evaluated by conducting cyclic triaxial tests. Index property tests were carried out on the sample for identification and classification of the soil. Cyclic triaxial tests were conducted on undisturbed sample after saturation, undisturbed sample at natural water content and remolded samples prepared by compaction in the lab. The results were used to evaluate the effect of saturation and remolding on liquefaction resistance of the local soil. Effect of effective confining pressure on dynamic properties of soil (Young's Modulus and Damping ratio) was also studied. Forty five stress controlled cyclic triaxial tests were performed. Three different values of initial effective confining pressure (5 psi, 10 psi and 15 psi) were used and cyclic stress ratio was varied from 0.1 to 0.5 in order to apply different cyclic shear stresses. The results show that the cyclic load resistance of soil decreases as a result of remolding. Saturated undisturbed samples show increase in resistance to liquefaction with increase in initial confining pressure. Remolded samples were prepared by compaction in the lab keeping unit weight and water content equal to that of undisturbed samples. Remolded samples show increase in liquefaction resistance with increase in confining pressure. Undisturbed samples at natural water content show increase in resistance to develop axial strain with increase in confining pressure. Both the rate of excess pressure development and axial strain development increase significantly as a result of remolding. While investigating the effect of saturation of undisturbed samples on liquefaction resistance of soil, interesting observations were made. The excess pressure buildup rate was faster in case of saturated undisturbed samples compared to that in samples with natural water content. On the other hand, rate of strain development was significantly high in case of sample with natural water content compared to that in saturated sample. Also, results obtained from cyclic triaxial tests on saturated undisturbed samples were compared with results obtained from similar tests on Ottawa Sand (Lama 2014) sample. The comparison shows that the saturated undisturbed soil samples of the selected local soil have very high resistance to liquefaction both in terms of initial liquefaction and development of 2.5% and 5% axial strain. Modulus of Elasticity and damping ratio were studied as important dynamic properties of soil. Young's Modulus was observed to decrease significantly at higher strain levels for all three types of samples. Young's modulus increased with increase in effective confining pressure, the effect of confining pressure being large at low strain level and almost insignificant at higher strain level. Damping ratio was highest in undisturbed sample at natural water content and smallest in remolded sample and damping ratio for saturated undisturbed sample falls in between. The damping ratio did not show any definite correlation with strain and confining pressure at lower strain level. But, for strain higher than 1% double amplitude axial strain, damping ratio significantly decreases with increase in strain. Damping ratio increases with increase in confining pressure as observed at high strain for all samples.