4,192 research outputs found
The History of Wake Forest College, Volume IV, 1943-1967
No full textThe Shaw volume contains much information, although it is not as detailed as the first three books. It is also more readable and wanders less often than the earlier ones. It covers the years of World War II, the admission of female students, the return of the veterans, the decision to move to Winston-Salem, the move itself, and the "fruitful years of the Tribble administration." One reviewer summarized: "Scores of names and dozens of pictures, as well as sections on student life, athletics and departmental histories complete the fabric of life at Wake Forest." A review by Linda Brinson (WFU '69) in the Winston-Salem Journal September 4, 1988, H6 concluded: "Perhaps the greatest strength of Vol. IV is that Shaw does what he states as his purpose in the preface: 'to give the whole picture of the life of the college.'" Wake Forest should be well pleased with this chronicle of the years that did so much to shape its future. Anyone with an interest in the college would find this new history a valuable source of both information and understanding. (J. Edwin Hendricks)Biographical information about the author is available in Linda Brinson, "Gentle Man of the Press," Wake Forest University Magazine, September 2, 2002. p. 46
Analytical solution for the cumulative wake of yawed wind turbines
No full textThis thesis sets out to improve the physical grounding and predictive accuracy of cumulative wake effect modelling within wind farms with yawed turbines. It derives an analytical solution for the lateral velocity field within a wind farm and compares its predictions to those of computational fluid dynamics.A parametric study is performed using a Reynolds-averaged Navier-Stokes (RANS) solver with the k-ε-fP turbulence model, Joukowsky rotor-based actuator disc, and neutral log-law inflow within the PyWakeEllipSys framework to determine the effects of yaw angle, thrust coefficient, and turbulence intensity on the lateral wake.The results of this parametric study are used to solve an approximate form of conservation of mass and momentum in the lateral direction for a turbine within a wind farm. The solution is an explicit equation predicting the lateral velocity distribution and lateral wake deflection within a wind farm of arbitrary layout and with arbitrarily yawed turbines. It also provides a first mathematical proof of secondary wake steering. The solution is implemented in Python and used to predict the velocity distributions in several wind farm cases, including for a single turbine, a two-turbine arrangement, and two wind farm cases with aligned and staggered layouts. These predictions are then compared against those of the RANS setup. The model significantly overestimates wake deflections unless corrected to neglect the near wake, but the corrected version shows promise, particularly in predicting wind farm power of the staggered layout, where the prediction is 19% closer to the RANS result than the prediction that considers lateral velocities equal to zero.https://github.com/NilsGaukroger/Analytical-solution-for-the-cumulative-wake-of-yawed-wind-turbinesEuropean Wind Energy Masters (EWEM) | Rotor Design Trac
Amphibian diversity, distribution and conservation in the Ethiopian highlands : morphological, molecular and biogeographic investigation on Leptopelis and Ptychadena (Anura)
No full textLittle is known about the diversity, distribution and population status of Ethiopian amphibians in general, and most of the existing knowledge is based on field data recorded about three decades ago or earlier. There are almost no genetic data available for molecular systematics studies. Species of the Tree Frogs (Leptopelis Günther 1859) and Grassland Frogs (Ptychadena Boulenger 1917) are solely distributed in Africa (mainly sub-Saharan), with 52 and 53 known species, respectively. Six species of Leptopelis and thirteen species of Ptychadena were recorded in Ethiopia. Together these two genera comprise 30% of all known species of amphibians in Ethiopia. Many of these species (five Leptopelis and five Ptychadena) are said to be endemic to the Ethiopian Highlands that are part of the Eastern Afromontane Biodiversity Hotspot. Geographically, the Ethiopian Highlands are bisected by the Rift Valley, and further fragmented by valleys and gorges, and comprise the highest concentration of elevated ground in Africa. Earlier taxonomic studies were mainly based on morphological and ecological studies, making it difficult to identify most species in museum collections or during field work. In addition, limited sampling from the geographic areas of each species made it difficult to make good estimates of the ranges of species, and to prioritize them for conservation.
The main objectives of this study are, using Leptopelis and Ptychadena as model taxa, 1) to explore the diversity and phylogeography of some amphibians in the Ethiopian Highlands and parts of the Rift Valley; 2) to preliminarily explain the geo-climatic events that are associated with the evolutionary history of these taxa; and 3) to re-evaluate the conservation status of species and their habitats by associating phylogenetic, biogeographic and ecological information. We tested hypotheses pertaining to correspondence of traditional morphological taxonomy versus molecular phylogeny, biogeographic distinctness of distribution patterns, evolutionary history of diversification, and evaluation of conservation status of species and populations in the highlands.
The field sampling conducted between 2006 and 2010 from several localities across and within the Ethiopian Rift Valley was substantial, but not enough, to fully assess the phylogeography of the above genera. This assessment, conducted for the first time for Ethiopian Leptopelis and Ptychadena, was done using partial mitochondrial DNA sequences of the 12S and 16S genes. Estimation of phylogenetic relationships and divergence times was made using Maximum Likelihood and Maximum Parsimony methods. Morphological observations were made on fresh collections, holotypes and non-type museum materials. Biogeographic patterns were assessed using geographic distribution data. Geographic and spatial data were combined with new phylogenetic groupings to assess geographic ranges and habitat status of populations and species. We followed a new approach of ‘elevation-based’ extent of occurrence (instead of the simple polygons applied in the IUCN Red List maps) to estimate geographic ranges. Results were compared and evaluated with previous reports and online database.
Despite the wide taxonomic variation between the studied genera (Leptopelis and Ptychaena), we found similarities in some of their major taxonomic problems, as well as evolutionary, biogeographic and conservation aspects. The similarities are in: overlaps in many morphological characters (conservatism) among different species; misleading variation in some physical features within a population/species (homoplasy); monophyly of highland endemic species; cryptic phylo-groups embedded within known clades; relatively low genetic distance between species and recent evolutionary divergence times; habitat status and threats for survival of populations.
In both genera, the reconstructed phylogenetic relationships showed that the highland endemic species form well-supported monophyletic groups: the ‘Ethiopian Highland Leptopelis species group’, and the ‘Ptychadena cooperi species group’. Cryptic diversity of highland endemics was revealed, highlighting the possibility of having six candidate species (at least two Leptopelis and four Ptychadena) awaiting description. Two presumed lowland endemic species of Ptychadena (P. filwoha and P. harenna) were genetically found to be conspecific with other widely distributed (non-endemic) lowland species (P. mascareniensis and P. anchietae, respectively).
Wide overlaps in several morphological features made identification of some closely related species populations difficult. New diagnostic features were identified to characterize some of the most difficult groups (e.g., presence of spicules in males of P. neumanni contrasted with absence in P. erlangeri or P. nana).
As compared with some other African species for which molecular data are available, relatively small evolutionary distances were found among the highland species within each genus, explained by a possibly very recent radiation as estimated in the corresponding divergence times. Diversification of the highland endemics was probably associated with formation of the Ethiopian Highlands by volcanic activities and uplifting, and accompanying climatic changes between 30 and 6 Mya.
We observed congruence of phylogenetic groups with clear patterns of geographic distribution, allowing us to identify distinct biogeographic categories that can potentially serve as units for conservation of Ethiopian amphibians. The Rift Valley and major river gorges appear important horizontal barriers delimiting geographic ranges of most species. There is no considerable vertical (altitudinal) segregation of the highland populations in the two genera.
The highland Leptopelis and Ptychadena comprise more diverse endemic species (16) than known before (10), contributing substantially to the biodiversity value of the Ethiopian Highlands. While range extension is revealed for some species in the current study, there is unfortunately a substantial reduction for others from what has been proposed previously. Land cover data and our field observation of many parts of the country for about two decades indicate that large parts of the suitable highland habitats for most species of Leptopelis and Ptychadena are severely degraded and fragmented by human activities. Lakes are drying, levels of rivers are decreasing, and the wooded and grassland vegetation of the highlands and the Rift Valley is being lost. Our revised assessment of populations showed that nine of the 16 studied species appear to be threatened at different levels. This implies an urgent need for revision of existing conservation status of these taxa to protect them in rapidly changing environments. Further work is needed in the areas of phylogeography, taxonomy, and natural history of populations and species in areas that are not covered in this study
Hybrid simulation of wake vortices of landing aircraft in a turbulent environment
No full textWake-vortex evolution during landing of a long range aircraft is investigated in a turbulent environment. The simulations cover final approach, touchdown on the tarmac, and the evolution of the wake after touchdown. An ambient turbulent crosswind and headwind field is generated in a pre-simulation. The wake is initialized using a RANS-LES coupling approach. The further development of the vortical wake is investigated by large-eddy simulation until final decay. Strong three-dimensional deformations appearing after touchdown and linkings with the ground are studied. The downwind vortex is strongly advected with crosswind and decays quickly. The interaction of plate line disturbances and end effects in a turbulent environment leads to irregular decay pattern
Vortex Dynamics in The Transitional and Turbulent Wake of 6:1 Prolate Spheroid at 45-deg incidence angle
No full textThe incompressible flow past a 6:1 prolate spheroid with an inclination angle of 45o at Re = 3,000 has been studied by means of direct numerical simulations (DNS). The Reynolds number is based on the inflow velocity and minor-axis length. The preliminary results presented here are focused mainly on vortex dynamics and vortical structures in the wake. The wake behind this configuration starts almost symmetric but is soon strongly deflected and bent as it evolves to the intermediate wake. A pair of unequal-strength vortices dominates the intermediate wake, of which one exhibits the shape of a long vortex tube while the other rapidly breaks down into turbulent-like vortical structures
Investigation of Lagrangian coherent structures in a wake-induced boundary layer transition
No full textThe evolution of coherent structures in a flat plate boundary layer transition induced by the cylinder wake is investigated using the particle image velocimetry (PIV) technique. The finite-time Lyapunov exponent (FTLE), which characterizes the amount of stretching about the flow trajectory, is used to extract the Lagrangian coherent structures. It is revealed that secondary vortex is induced by the cylinder wake vortices in the near wall region,which would evolve into hairpin vortex as it convects downstream. The subsequent evolvement of the hairpin vortex, characterized by the regeneration of offspring hairpin vortex upstream of it, leads to the appearance of the hairpin packet and the boundary layer finally reaches a turbulent state
Dispersive to nondispersive transition in the plane wake and channel flows
No full textBy varying the wavenumber over a large and finely discretized interval of values, we analyse the phase and group velocity of linear three-dimensional travelling waves both in the plane wake and channel flows to get the transition between dispersive and non-dispersive behaviour. The dispersion relation is computed from the Orr-Sommerfeld and Squire eigenvalue problem by observing the least stable mode, see figure 2, panels (a,b) and the comparison with [1, 2, 4–11, 15, 16]. The group velocity vg is also shown. The Reynolds number varies in the 20-100, 1000-8000 ranges for the wake and the channel flow, respectively, while we consider wavenumbers in the range 0.1-10. The wake basic flow consists of the first two orders of the Navier-Stokes matched asymptotic expansion described in [3, 13, 14]. At low wavenumbers we observe a dispersive behaviour where the phase speed and the group velocity substantially differ. The relevant perturbed solution is amenable to the typical solution belonging to the left branch of the eigenvalue spectrum, see the two examples shown in figure 1 (channel flow: Re = 6000; k = 1; wake Re = 100; k = 0:7). By rising the wave number value, we observe a sharp transition from the dispersive to the nondispersive regime. This transition is located at a critical wave number kd which is a function of the Reynolds number Re, the wave angle _, and the wake downstream observation point x0. Precisely, kd increases with Re and decreases with _ for the wake flow, while these trends are reversed for the channel flow, see tables 1,2. Beyond the wavenumber threshold, the observed least-stable mode belongs to the right branch of the spectrum. The asymptotic solutions in the dispersive region are wall modes for the channel flow , and in-wake modes for the wake flow. This means that, for both the flows, the dispersive behaviour is related to perturbations with high momentum variations (high vorticity) in correspondence to the base flow high-shear region. On the contrary, if k > kd the solutions are central modes for the channel case, and out-of-wake modes for the wake flow. In these cases, the disturbance has high variations outside the base flow high-shear region. To understand the physical mechanism of the dispersive-nondispersive transition we focused on time variation of the wave kinetic energy associated to the convective transport. Figure 2 (c,d) shows the convective term as a function of the wavenumber for the two least stable modes. We observe that the dispersive-nondisperive transition allows waves k > kd to keep the lowest possible temporal variation of kinetic energy, i.e. the lowest decay. This remains true also when all the other more stable modes are considered. In practice nondispersive waves maintain their convective energy with k
History of Wake Forest College, Volume II, 1865-1905
No full textThe Paschal histories are encyclopedic, listing every faculty member, trustee, staff, and most students known to have been associated with the institution. In the preface to volume one, Paschal indicated that he had followed the advice of prolific North Carolina historian R. D. W. Connor, Chief Archivist of the National Archives, to "Put in everything; no one will ever work over again the documents from which you draw your account, and what you omit will be permanently lost to the history of the College and the State." One reviewer observed that the Paschal volumes "contain more details of people and events, activities of students and of relationships of denominational and private colleges to the state institutions than any other college histories." (Wake Forest College Alumni News, May 1945, 5-6) The same review continues: "The volumes will constitute an excellent reference set. They contain names of every professor who has ever taught in the college, names of numerous students, lists of gifts, detailed data about organizations and activities, etc. In fact there is nothing about the college, good or bad, controversial or otherwise, that Dr. Paschal has not handled." The books are great sources of information, but not necessarily the type of history that one is likely sit down to read. Earlier attitudes and perceptions produced long sections which may not be of interest to today's readers. Even so, the detail in recounting the history of Wake Forest University in these books make them valuable for research and insight about the early years of the history of the institution. (J. Edwin Hendricks)Biographical information about the author is available in Henry S. Stroupe, "George Washington Paschal," Dictionary of North Carolina Biography, volume 5 edited by William S. Powell. Copyright 1994 by the University of North Carolina Press
History of Wake Forest College, Volume I, 1834-1865
No full textThe Paschal histories are encyclopedic, listing every faculty member, trustee, staff, and most students known to have been associated with the institution. In the preface to volume one, Paschal indicated that he had followed the advice of prolific North Carolina historian R. D. W. Connor, Chief Archivist of the National Archives, to "Put in everything; no one will ever work over again the documents from which you draw your account, and what you omit will be permanently lost to the history of the College and the State." One reviewer observed that the Paschal volumes "contain more details of people and events, activities of students and of relationships of denominational and private colleges to the state institutions than any other college histories." (Wake Forest College Alumni News, May 1945, 5-6) The same review continues: "The volumes will constitute an excellent reference set. They contain names of every professor who has ever taught in the college, names of numerous students, lists of gifts, detailed data about organizations and activities, etc. In fact there is nothing about the college, good or bad, controversial or otherwise, that Dr. Paschal has not handled." The books are great sources of information, but not necessarily the type of history that one is likely sit down to read. Earlier attitudes and perceptions produced long sections which may not be of interest to today's readers. Even so, the detail in recounting the history of Wake Forest University in these books make them valuable for research and insight about the early years of the history of the institution. (J. Edwin Hendricks)Biographical information about the author is available in Henry S. Stroupe, "George Washington Paschal," Dictionary of North Carolina Biography, volume 5 edited by William S. Powell. Copyright 1994 by the University of North Carolina Press
Ram-jet combustion based on shock/flame interaction
No full textAn experimental investigation into the effects of shock/wake and
shock/flame interaction on the base pressure of axisymmetric bodies at
Mach 2 has been carried out. This investigation has determined the
effects of various forms of shock generator (axisymmetric cowls, twodimensional
wedges and 'delta' wings) on the base pressure. Shock
waves generated by over-expanding the airflow in an open-jet wind tunnel
have been used to determine the effect of shock strength on the base
pressure of an axisymmetric fuel injector. Both peripheral bleed and
axial bleed of hydrogen fuel have been examined and the effect of shock
compression on the resulting flame has been determined. In the axial
bleed case nitrogen and hydrogen bleed without combustion has also been
examined. The effect of varying the airflow stagnation temperature has
also beeninvestigated.
It is demonstrated herein that there is a distinct shock/wake
interaction position that maximises the base pressure, that with
interaction at this optimal position the static pressure rise across
the shock wave can be communicated in full to the base of the centrebody,
and that favourable aerodynamic interference between the wake and a
cowl of 50 convergent-divergent internal section can give rise to a net
drag reduction. The shock/wake and shock/flame experiments demonstrate
that a significant base thrust can be generated, however, the fuel
efficiency decreases with increasing shock strength. It is shown that
the fuel specific impulse is a function of shock strength, interaction
position and bleed mode (peripheral or axial). The onset of boundary
layer separation due to the adverse pressure gradient encountered when
the base pressure is high appears to limit the useful addition of wake
combustion. Finally, it is demonstrated that the base pressure, with
and without combustion, is only a weak function of airflow stagnation
temperature
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