The boiling of water droplets on hot metal surfaces is studied experimentally and mathematically in order to establish the conditions necessary for droplets to enter a film boiling mode. The subsurface temperature history within a plate undergoing droplet boiling on the surface is measured. A numerical model of the heat transfer in the plate is then used to deduce from these data the following characteristics of droplet boiling: (1) the effective heat transfer coefficient between water droplet and plate during the initial transient forming the spherical droplet, (2) the apparent time period needed to establish the droplet in the film boiling mode, and (3) the minimum plate surface temperature reached during the initial formation of the boiling droplet. The effective heat transfer coefficient, formation time, and minimum surface temperature are sufficient to develop a calculation method which predicts the minimum initial plate temperature necessary for a water droplet to enter film boiling. This numerical conduction model accounts for the influence of plate material, plate thickness, oxidation of the plate surface, the boundary condition on the plate lower surface, and the size of the droplet. The prediction method is successfully used to estimate the minimum film boiling temperature for brass, graphite, Pyrex, copper, aluminum, stainless steel, and Zircalloy II. The findings of the experiments and numerical studies are applied to the rewetting phase of a loss-of-coolant-accident in a light water reactor. This application, in turn, provides explanations for some of the phenomena observed in studies of the prequench heat transfer within rod bundles including the effect of multiple droplet impacts, and suggests possible reasons for some of the difficulties experienced in attempts to establish the effective rewetting temperature on reactor fuel rod surfaces.

Electric power generation using wind turbines is on the rise in not only the United States but the entire globe. While the benefits from such methods of generation include clean and renewable energy, wind turbines may pose a potential risk to the stability of grid operation. Wind turbine generators are similar to conventional generators; however, the manner with which the wind turbine is coupled to the grid may reduce system inertia and increase the magnitude of transient stability problems. This study empirically examines the effect of wind generation on ERCOT system response characteristics following unit trips such as frequency drop, and phasor oscillation frequency and damping. It is shown with a high degree of certainty that an increase in wind generation is leading to a greater phasor oscillation frequency and lesser system inertia. Wind generation may also be leading to less system damping and smaller power frequency drops. / text

We have studied gas flow and particle deposition in a realistic three-dimensional model of the bronchial tree, extending from the trachea to the segmental bronchi (7th airway generation for the most distal ones) using Computational Fluid Dynamics (CFD). The model is based on the morphometrical data of Horsfield et al. [J. Appl. Physiol., 31: 207-217, 1971] and on bronchoscopic and CT images, which give the spatial 3D-orientation of the curved ducts. It incorporates realistic angles of successive branching planes. Steady inspiratory flow varying between 50cm³/s and 500cm³/s was simulated as well as deposition of spherical aerosol particles (1 to 7 m diameter, 1g/cm³ density). Flow simulations indicated non-fully developed flows in the branches because of their relative short lengths. Velocity flow profiles in the segmental bronchi, taken one diameter downstream the bifurcation, were distorted compared with the flow in a simple curved tube, and wide patterns of secondary flow fields were observed. Both were due to the asymmetrical 3D configuration of the bifurcating network. Viscous pressure drop in the model was compared with results obtained by Pedley et al. [Respir Physiol, 9: 387-405, 1970], which are shown to be a good first approximation. Particle deposition increased with particle size and was minimal for approximately 200cm³/s inspiratory flow but it was highly heterogeneous for branches of the same generation.

No description available.

Flying insects face challenging conditions such as rainfall, fog, and dew. In this theoretical and experimental thesis, we investigate the survival mechanisms of the mosquito, Anopheles, through particles of various size. Large particles such as falling raindrops can weigh up to fifty times a mosquito. Mosquitoes survive such impacts by virtue of their low mass and strong exoskeleton. Smaller particle sizes, as present in fog and insecticide, pose the greatest danger. Mosquitoes cannot fly through seemingly innocuous household humidifier fog or other gases with twice the density of air. Upon landing, fog accumulates on the mosquito body and wings, which in small quantities can be shaken off in the manner of a wet dog. Large amounts of dew on the wings create a coalescence cascade ultimately folding the wings into taco shapes, which are difficult to dry. The insights gained in this study will inform the nascent field of flapping micro-aerial vehicles.

Women are four to eight times more likely to injure their anterior cruciate ligament (ACL) compared to men. It is most commonly injured through a non-contact mechanism during game time situations. During landings, women display valgus collapse, where a less active gluteus medius muscle (GMed) may be unable to control the internal rotation of the thigh, causing an increase in knee joint abduction angle, augmenting the risk of ACL injury. This study’s purpose was to determine the difference between 12 male and 12 female athletes in muscle activity, specifically the GMed, and the 3D kinematics and kinetics of the lower-limb during drop jump landings from three heights; maximum vertical jump height, tibial length, and a commonly used height of 40cm. Results showed that females had greater hip adduction and knee abduction angles compared to men. The GMed activity showed no significant differences between sexes at each drop jump height.

A careful review of the literature showed that there is a serious lack of information (experimental or analytical) on the pressure losses during two-phase flow in combining tee junctions. Pipe networks in industrial applications involve combining and dividing junctions and knowledge of the pressure losses at these junctions is essential for analysis of the flow distribution in the network. To this end, the pressure losses of air-water mixtures passing through a horizontal, combining tee junction with a 37.8 mm diameter were experimentally studied with annular, wavy, and slug flow regimes in the outlet. The test matrix independently varied the outlet flow rates, the outlet mixture qualities, the gas distribution between the inlets, and the liquid distribution between the inlets. All experiments were conducted at room temperature and a nominal absolute pressure at the centre of the junction of 150 kPa. The pressure distribution in all three legs of the tee was determined using up to 49 pressure taps distributed among the three sides and monitored using pressure transducers to produce accurate measurements of the pressure losses. Time-averaged pressure measurements with annular and wavy flows are reported, while pressure measurements with slug flows were not repeatable. A new model and empirical coefficients is presented that allows accurate prediction of pressure losses for flows with either an annular or wavy outlet. Time-varying pressure measurements are presented and analyzed using probability density functions. Different distributions were found for differential measurements depending on whether or not slugging was present in the system. The probability density functions for cases with annular or wavy flow in the outlet followed Gaussian distributions, while cases with slug flow had skewed distributions. Time-varying pressure signals showed a time lag between slug events based on pressure tap locations. A visual study with slug flow present in the system showed upstream travelling waves induced in a stratified inlet when slug flow was present in the other, which led to unexpected slugging under certain flow conditions. / October 2016

Flight and drop tests of the Martin 270 (M270) seaplane were conducted in 1955. Theoretical and empirical pressures were determined by use of Wagner’s theory and also by the Code of Federal Regulations (CFR). The pressure results from the experimental tests on the hull were compared with pressures calculated from Wagner’s theory to determine how well the theory correlated with the measured pressures. The experimental pressure data was also compared with the CFR results to determine how the current industry standard of estimating impact loads compares with actual pressures a seaplane is subjected to. Using the structural design and geometry of the M270 the seaplane hull was modeled in Maestro with a coarse mesh finite element model. The pressures from Wagner’s theory and the CFR were applied to the model of the M270 hull. The structural reactions of the drop test section were compared with the reactions determined from Maestro.

The genetic profiles of evidentiary samples found at crime scenes are generated in order to determine the likelihood that a person contributed to DNA to the sample. One of the most challenging aspects of forensic deoxyribonucleic acid (DNA) analysis is that samples collected from crime scenes often contain only trace amounts of DNA; these samples are often referred to as low template DNA (LTDNA). Due to the low initial concentration of genetic material in LTDNA samples, substantive environmental insults will likely result in compromised DNA profiles that exhibit lower allele peak heights than expected, or in some cases, complete allele drop-out. The research detailed in this study investigates the impact various sources of compromise have on relative fluorescent unit (RFU) signal obtained from LTDNA samples. The potential for stochastic allele loss during a silica extraction of DNA prior to downstream processing is first considered using a dynamic systems model simulating the probability for allelic loss at each step in the procedure. Next, the impacts of damaging or degrading the DNA on the electropherogram signal are explored. Trends in RFU signal of LTDNA samples subjected to sonication by a sonic dismembrator probe, ultraviolet (UV) irradiation, and enzymatic digestion by two different enzymes are assessed, with the aim of creating a reference for typical behaviors in RFU signal data in compromised LTDNA. The distributions of electropherogram profile data from compromised LTDNA are then compared against one another in order to determine if the compromising methods explored in the study act on the samples in similar ways. The RFU signal data from the compromised LTDNA are then evaluated alongside the provided degradation index (DI) value resulting from quantification using the Quantifiler® Trio quantification kit (Thermo Fisher Scientific, Oyster Point, CA). The DI value acts as an early assessment of the quality of DNA samples and can be used to optimize downstream processing. Its ability to accurately predict behavior in compromised LTDNA samples is assessed through comparison of the DI value to the decrease in RFU signal as the samples are subjected to higher levels of simulated environmental insults.

Diploma thesis deals with numerical simulations of an air flow in a water cooled charge air cooler (WCAC), specifically with pressure drops in inlet/outlet chamber. The simulations have been performed in a proprietary software Star-CCM+. Physical phenomena have been solved by the Reynolds-averaged Navier-Stokes (RANS) equations and consequently a matrix of pressure drops for miscellaneous variations of chamber's geometry and the initial flow conditions has been created. Based on the CFD results, dependence between calculated pressure drops and changing parameters has been analyzed and finally a 1D solver has been developed and implemented into a software OpenModelica.