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Reducing the deleterious effect of Vortex Induced Vibrations (VIV) in marine risers is an important task for ocean engineers; and many competing factors exist in the design of VIV suppression devices. This thesis explores the experimental minimization of the drag force and the disruption of the vortex formation by utilizing VIV suppression devices. Two series of tests are conducted- both utilizing separate testing designs. The first tests are the flexible cylinder experiments, detailed in Chapter 2, which determine the drag force and vibration amplitude of numerous, original testing configurations. The second series of tests are the rigid cylinder, PIV experiments, detailed in Chapter 3. These rests measure both the drag force on the cylinder and the oscillating component of the lift force, the latter of which is a good indication of vortex formation. The Chapter 3 tests also image the test section wake- providing helpful insight into the physical process of vortex formation. / Contract number: N62271-97-G-0026.

ABSTRACT: Background: Correlation of nutritional status with genital shedding of HIV-1 has not been described. Genital shedding patterns have not been described in Botswana previously. Methods: I conducted a cross-sectional study to describe genital shedding patterns in Botswana and to correlate nutritional status with genital shedding of HIV-1. Between July 2005 and December 2005, samples were collected and analyzed from 50 women participating in an ongoing micronutrient supplementation clinical trial that is examining the effect of supplementation on HIV disease progression. Results: HIV-1 RNA was isolated from both baseline and three months CVL in 24% of the study population, and these were labelled continuous shedders (CS). No HIV-1RNA was isolated from both baseline and three months CVL in 64% of the study population, and these were labelled non-shedders (NS). In 14% of women, HIV-1 RNA was either isolated from baseline CVL only (4/50) or from the three months CVL only (3/50) and these were labelled as Intermittent Shedders (IS). Women who had detectable genital HIV-1 RNA at baseline had lower haemoglobin compared to those who were not shedding (Hb11.7 (95% CI 10.8 ; 12.5) vs. Hb 12.5 (95% CI 12.0 ; 13) P = 0.0877), showing a strong trend, albeit a non significant haemoglobin difference. Women who had detectable genital HIV-1-RNA at baseline had significantly lower CD4 cell percentage compared to those not shedding (22% (95% CI 19 ; 24) vs. 30 % (95% CI 27 ; 34) P < 0.01) and a significantly higher log viral load (4.7 log (95% CI 4.2 ; 5.1) vs. 3.6 log; ((95% CI 3.5 ; 4.0) P < 0.01). Overall there was a non significant higher prevalence of genital infection in women who were shedding HIV-1 at baseline, compared to those who were not (73% vs. 46% P = 0.123). No HIV -1 RNA was isolated in all the19% of the women in the study who were using some form of contraception. Conclusions: The preliminary analysis showed three patterns of HIV shedding in this study population, namely Continuous shedders, Intermittent shedders and Non-shedders. Women with detectable genital HIV-1-RNA at baseline had more advanced disease, and by extension poor nutritional status, than those not shedding, as shown by higher plasma viral load, lower CD4 count, lower haemoglobin level and higher prevalence of genital infections. This study generates hypothesis on the role haemoglobin may play in genital shedding of HIV-1 in females. Recommendation: Due to the small sample size, these results will need to be validated by larger studies of appropriate design. Timely treatment of anaemia in HIV positive women may be important in reducing HIV transmission associated with presence of HIV-1RNA in genital secretions.

Circular cylinders in cross-flow have been extensively studied in the last century. However, there are still many unsolved problems in this area, one of which is the flow structure around two staggered finite circular cylinders. This thesis mainly focuses on an experimental investigation of the vortex shedding characteristics of two staggered finite circular cylinders of equal diameter in cross-flow. Wind tunnel experiments were conducted to measure the vortex shedding frequency at the mid-height of the two cylinders and along the height of the two cylinders. Two identical circular cylinders of aspect ratio AR = 9 were partially immersed in a flat-plate turbulent boundary layer, where the boundary layer thickness to cylinder height ratio at the location of the cylinders was δ/H = 0.4. The Reynolds number based on the cylinder diameter was Re<i>D</i> = 2.4z_x~104. Centre-to-centre pitch ratios of <i>P/D</i> = 1.125, 1.25, 1.5, 2, 2.5, 3, 4 and 5 were examined and the incidence angle was incremented in small steps from á = 0° to 180°. For each configuration of the cylinders, the vortex shedding frequency, represented in dimensionless form as the Strouhal number, St, was measured with a single-component hot-wire anemometer. Also, a seven-hole pressure probe was used to measure the time-averaged wake velocity field behind the cylinders at selected configurations in order to get a better understanding of the wake structure.<p>The vortex shedding frequencies measured at the mid-height of the cylinders clearly showed the similarities and differences of vortex shedding between two staggered finite and infinite circular cylinders. The Strouhal number behavior of the two finite circular cylinders is generally similar to that of two infinite circular cylinders, but the values of St for the two finite cylinders were found for most cases to be smaller than the case of the infinite cylinders.<p>The measurements of vortex shedding frequency along the heights of each finite cylinder revealed that, for most incidence angles, the value of the Strouhal number remains constant along the height of the cylinder, but a notable variation in the shape and strength of the vortex shedding peak along the heights of the cylinders is observed. Sharp and strong peaks in the power spectra are measured around the mid-height of the cylinder. Broader and weaker peaks are found both at the base of the cylinder and near the free end. At several particular configurations, the vortex shedding frequency changes along the height of the cylinder, caused by the varying flow pattern in the vertical direction.<p>Wake measurements showed the velocity field behind the two finite circular cylinders arranged in tandem configurations of P/D = 1.125, 2 and 5. The experimental data revealed that the flow structure behind two finite circular cylinders arranged in a tandem configuration is much more complicated than that of the single finite circular cylinder. The downwash flow from the tip of the downstream cylinder is weaker due to the flow interaction between the free ends of two cylinders, and this downwash flow becomes stronger with increasing P/D. A similar trend happens to the vorticity of the tip vortex structures. However, the upwash flow behind the downstream cylinder is not strongly affected by the existence of the upstream cylinder.

Circular cylinders in cross-flow have been extensively studied in the last century. However, there are still many unsolved problems in this area, one of which is the flow structure around two staggered finite circular cylinders. This thesis mainly focuses on an experimental investigation of the vortex shedding characteristics of two staggered finite circular cylinders of equal diameter in cross-flow. Wind tunnel experiments were conducted to measure the vortex shedding frequency at the mid-height of the two cylinders and along the height of the two cylinders. Two identical circular cylinders of aspect ratio AR = 9 were partially immersed in a flat-plate turbulent boundary layer, where the boundary layer thickness to cylinder height ratio at the location of the cylinders was δ/H = 0.4. The Reynolds number based on the cylinder diameter was Re<i>D</i> = 2.4z_x~104. Centre-to-centre pitch ratios of <i>P/D</i> = 1.125, 1.25, 1.5, 2, 2.5, 3, 4 and 5 were examined and the incidence angle was incremented in small steps from á = 0° to 180°. For each configuration of the cylinders, the vortex shedding frequency, represented in dimensionless form as the Strouhal number, St, was measured with a single-component hot-wire anemometer. Also, a seven-hole pressure probe was used to measure the time-averaged wake velocity field behind the cylinders at selected configurations in order to get a better understanding of the wake structure.<p>The vortex shedding frequencies measured at the mid-height of the cylinders clearly showed the similarities and differences of vortex shedding between two staggered finite and infinite circular cylinders. The Strouhal number behavior of the two finite circular cylinders is generally similar to that of two infinite circular cylinders, but the values of St for the two finite cylinders were found for most cases to be smaller than the case of the infinite cylinders.<p>The measurements of vortex shedding frequency along the heights of each finite cylinder revealed that, for most incidence angles, the value of the Strouhal number remains constant along the height of the cylinder, but a notable variation in the shape and strength of the vortex shedding peak along the heights of the cylinders is observed. Sharp and strong peaks in the power spectra are measured around the mid-height of the cylinder. Broader and weaker peaks are found both at the base of the cylinder and near the free end. At several particular configurations, the vortex shedding frequency changes along the height of the cylinder, caused by the varying flow pattern in the vertical direction.<p>Wake measurements showed the velocity field behind the two finite circular cylinders arranged in tandem configurations of P/D = 1.125, 2 and 5. The experimental data revealed that the flow structure behind two finite circular cylinders arranged in a tandem configuration is much more complicated than that of the single finite circular cylinder. The downwash flow from the tip of the downstream cylinder is weaker due to the flow interaction between the free ends of two cylinders, and this downwash flow becomes stronger with increasing P/D. A similar trend happens to the vorticity of the tip vortex structures. However, the upwash flow behind the downstream cylinder is not strongly affected by the existence of the upstream cylinder.

The objectives were to determine the association of hair shedding to performance in beef cattle and estimate genetic parameters for hair shedding scores. Dams were observed for shedding and given a score of 1 to 5. The month of first shedding (MFS) was determined when a female reached an average shedding score of 3.25 or less. Performance data included calf bw and d205wt and were considered as a trait of the dam. Hereford dams with a MFS of March weaned calves 18.37 + or - 8.85 kg heavier than dams with a MFS of June (P < 0.01). Angus dams with a MFS of March had calves with bw 7.75 + or - 1.64 kg greater than dams with a June MFS (P < 0.001). The heritability estimate for MFS was 0.11 + or - 0.06. Timing of hair shedding may have an influence on growth performance for certain breeds.

An experimental study in air has been performed to determine what effect fins have on the flow over circular cylinders. The tubes under investigation included one bare tube and three segmented-finned tubes of different fin densities with the same root diameter as the bare tube. The tests were performed at two Reynolds numbers (2.61 x 104 and 4.98 x 104) and two downstream distances (2.5 & 5 diameters) and involved the use of hotwire anemometry. Measurements of mean and fluctuating velocities were taken across the wake as well as two-point fluctuating velocity correlations. It was discovered that the use of fins can result in significant differences. Fins cause larger mean velocity deficits in the wake profiles and significant shape differences in the total turbulence intensity profiles. Fins also increase the strength of vortex shedding, contrary to what would be expected, and increase the number of harmonic frequency peaks in the frequency spectra as three harmonic peaks were observed for the bare tube, while as many as ten were seen for the densest finned tube. Correlation length measurements, and thus radiated sound intensity, proved to be inconclusive. It was discovered that correlation length changed with angular rotation suggesting that this phenomenon needs to be investigated further before making any comparisons. Based on the differences seen with increased fin density, it is thought that there may be a critical fin density which causes fundamental changes in the cylinder wake. Also, during the course of this investigation, it was concluded that while the use of an effective diameter, De, proved adequate in collapsing the finned tube data, this approximation could be improved. / Thesis / Master of Applied Science (MASc)

An experimental study in air has been performed to determine what effect fins have on the flow over circular cylinders. The tubes under investigation included one bare tube and three segmented-finned tubes of different fin densities with the same root diameter as the bare tube. The tests were performed at two Reynolds numbers (2.61 x 104 and 4.98 x 104) and two downstream distances (2.5 & 5 diameters) and involved the use of hotwire anemometry. Measurements of mean and fluctuating velocities were taken across the wake as well as two-point fluctuating velocity correlations. It was discovered that the use of fins can result in significant differences. Fins cause larger mean velocity deficits in the wake profiles and significant shape differences in the total turbulence intensity profiles. Fins also increase the strength of vortex shedding, contrary to what would be expected, and increase the number of harmonic frequency peaks in the frequency spectra as three harmonic peaks were observed for the bare tube, while as many as ten were seen for the densest finned tube. Correlation length measurements, and thus radiated sound intensity, proved to be inconclusive. It was discovered that correlation length changed with angular rotation suggesting that this phenomenon needs to be investigated further before making any comparisons. Based on the differences seen with increased fin density, it is thought that there may be a critical fin density which causes fundamental changes in the cylinder wake. Also, during the course of this investigation, it was concluded that while the use of an effective diameter, De, proved adequate in collapsing the finned tube data, this approximation could be improved. / Thesis / Master of Applied Science (MASc)

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 77-90).

Thesis (M.S.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 90-93).