753 research outputs found
Damage to human hearing by airborne sound of very high frequency or ultrasonic frequency
No full textThis literature review examines the audiological, occupational hygiene and industrial safety literature on the subjective and auditory effects of audible sound in the very high frequency range (10-20 kHz) and also in the inaudible ultrasonic range (greater than 20 kHz, generally thought to be the upper frequency limit of young normal hearing). Exposure limits have been proposed, with the intent of avoiding any subjective effects and any auditory effects, in any exposed individuals. The evolution of these internationally recognised Damage Risk Criteria and Maximum Permitted Levels has been examined critically. Conclusions and recommendations are offered in respect of hearing damage and adverse subjective effects caused by sounds outside the customary frequency range for occupational noise exposure assessments. This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author and do not necessarily reflect HSE policy
Gender differences in self-reported late effects, quality of life and satisfaction with clinic in survivors of lymphoma
No full textObjectives: gender differences in perceived vulnerability to late effects and views about follow-up among cancer survivors have received little attention. As lymphoma affects both genders similarly, we compared the consequences of cancer (late effects, perceived vulnerability and quality of life (health-related quality of life (HRQoL)), and satisfaction with clinic visits between genders.Methods: a cohort of 115 younger adults (18–45 years, >5 years disease-free survival), who had been treated for lymphoma participated. Questionnaires (n = 91) were completed before and after (n = 62) routine consultant-led appointments. Survivors (n = 24) without appointments were recruited by post. Questionnaires included HRQoL, late effects, perceived vulnerability, issues survivors wanted to discuss and reported discussing in clinic, time waiting in clinic and consultation satisfaction.Results: there were no gender differences in number of self-reported late effects or perceived vulnerability. Men with more late effects reported worse psychological HRQoL (r = 0.50, p<0.001). While men wanted to discuss more topics than they did, women were able to discuss the topics they wanted (ANOVA, p = 0.01). Multiple regression analyses showed a shorter wait in clinic (r = ?0.46, p = 0.009) and discussing more topics (r = 0.34, p = 0.06) explained 30.6% of the variance in consultation satisfaction for men.Conclusions: issues surrounding follow-up provision are increasingly important given the length of survival in young adults following treatment for lymphoma. Men may experience poor psychological well-being due to distress about unanswered concerns. Consideration of their concerns should be prioritised, given that satisfaction and ultimately continued attendance at clinic and HRQoL may be dependent on the extent to which follow-up meets survivors' expectation
Instantaneous planar pressure determination from PIV in turbulent flow
No full textThis paper deals with the determination of instantaneous planar pressure fields from velocity data obtained by particle image velocimetry (PIV) in turbulent flow. The operating principles of pressure determination using a Eulerian or a Lagrangian approach are described together with theoretical considerations on its expected performance. These considerations are verified by a performance assessment on a synthetic flow field. Based on these results, guidelines regarding the temporal and spatial resolution required are proposed. The interrogation window size needs to be 5 times smaller than the flow structures and the acquisition frequency needs to be 10 times higher than the corresponding flow frequency (e.g. Eulerian time scales for the Eulerian approach). To further assess the experimental viability of the pressure evaluation methods, stereoscopic PIV and tomographic PIV experiments on a square cylinder flow (ReD = 9,500) were performed, employing surface pressure data for validation. The experimental results were found to support the proposed guidelines.Aerospace Engineerin
Dynamic pitching effect on a laminar separation bubble
No full textThe unsteady effect of a periodic pitching motion on the characteristic of a laminar separation bubble on the suction side of a SD7003 aerofoil is investigated by means of time-resolved planar and tomographic particle image velocimetry. The measurements provide information on the separation, transition and vortex roll-up onset as well as the spanwise distribution of vortical structures, for both the dynamic pitching between 4° and 8° and corresponding cases at a static pitch angle. During pitching, a clear hysteresis behaviour is observed for the vortex roll-up position and shedding frequency, showing a strongly delayed recovery of the shear layer with respect to the steady aerofoil case. The development of the shear layer transition exhibits initially 2D Kelvin–Helmholtz rollers that are interrupted, forming ?-shaped rollers, which eventually evolve into 3D arch-shaped hairpin structures. The 3D analysis of undulated rollers allowed the determination of the rollers streamwise spatial separation for both static and pitching aerofoil case
Assessment of flow around flying mosquito using computational fluid dynamics
No full textAerospace EngineeringAerodynamics, Wind Energy & PropulsionAerodynamic
Structural modelling and numerical analysis of dynamic passive flow control mechanisms in flight feathers
No full textWithin 100 years of the Wright Brother's first flight, we are already approaching the top of aviation’s technological S-curve. Breakthrough technical improvements have resulted in an undeniable increase in efficiency and range, but today’s aircrafts are still relatively inefficient resulting in a large amount of air and noise pollution. In order to aid further new advancements, in this thesis I set out drawing inspiration from nature - specifically birds; to understand how through more than 150 million years of evolution they came to be the most efficient flying creatures we know. The work presented in this thesis is related to the structural modeling and numerical analysis of the primary feather of the western jackdaw (Corvus monedula) to hypothesize its passive deformations under varying morphology and aerodynamic loading. Starting with Computed Micro-Tomograph scans of a primary feather, several techniques were devised towards realizing the detailed micro – and macro - structure of the feather. Modular capabilities of the model allow for rapidly creating morphological variants of the feather. This is the first attempt to model with such high detail the structural response of the micro-structures of flight feathers. Existing experimental or numerical investigations used highly simplified forms of the feathers structure, allowing the analysis of only stand-alone aspects of deformation dynamics of various avian species. Consequently, these low fidelity models failed to capture how individual sub-micron deformations collectively form the passive response of the feather. Passive dynamic deformation of the feathers micro-structures under increasing load revealed an initial decrease and then and increase in nose droop, overall profile camber and transmissivity of the vanes in order to limit flow separation. Response of feather structures due to change in microstructural morphology revealed high stresses at low loading conditions caused due to their reduced strength and rigidity. Buckling of the barbs at their kink zones was found and is attributed to aforementioned morphological changes and the large and unsteady pressure gradients caused as a result. Based on numerical quantification and evidences, the conclusion of this thesis presents a detailed hypothesis on the series of events and interactions which define the mechanics of dynamic passive flow control abilities of primary flight feathers.Aerospace EngineeringFlight Performance and Propulsio
Derivation of and Simulations with BiGlobal Stability Equations
No full textLaminar to turbulent transition has an important role in the aerospace domain in view of its impact on aerodynamic drag and, regarding the high velocity regime, heat transfer. State of the art computational methods, like DNS, LES and RANS are found to be too expensive or rely on case dependent turbulence models to be used for obtaining information regarding the transition phenomenon. Transition is typically initiated by the onset of instability of the laminar flow. Linear stability theory describes the eigenmode growth mechanism. Although this yields a restriction, because additional mechanisms play a role too, the eigenmode growth phase establishes an important base in many practical situations. However, the linearization provides a considerable step in the simplification of the analysis, while the stability theory can be adapted according to the structure of the given mean flow. At the Von Karman Institute (VKI), the VKI Extensible Stability and Transition Analysis (VESTA) toolkit has been developed, which mainly involves methods based on the linear stability theory. In the current project, the main goal was to extend the already present tools to incorporate the BiGlobal stability equations, which, together with appropriate boundary conditions, form an eigenvalue problem. This particular problem is solved for perturbations inhomogeneous in two spatial directions and their complex growth rate and frequency. This extension involved a new version of the tool for the derivation of the BiGlobal stability equations, a tool for their automatic implementation in Matlab via the spectral collocation method and a simulation tool to apply boundary conditions and execute the analysis corresponding to a prescribed mean flow. The derivation of the BiGlobal equations and their verification formed the first part of the project. Both incompressible and compressible versions are derived for different kinds of coordinate systems (e.g. Cartesian and cylindrical) and formulations in the compressible case (e.g. involving temperature and pressure and the energy equation based on static enthalpy). This allowed the verification of the tool with a large number of previously published references. All references, to the knowledge of the current author, that have thus far reported the compressible equations were found to contain errors and had to be cross-verified to yield the ultimate positive outcome. It is hence deemed that the present treatment is the first to report the full compressible BiGlobal stability equations in primitive variable formulation correctly. The second part of the project involved the verification of the performance of the combination of the derivation, implementation and simulation tools. This was done by considering three test cases (mean flows). In all cases, the eigenvalue problem was solved using the QZ algorithm. In cases that required high resolution, the Arnoldi algorithm was used in addition, because of its lean performance with respect to required memory. The first test case was the parallel Blasius boundary layer. Because of its one-dimensional nature, this flow has been intensively analysed in the past by means of the classic local stability analysis type (LST). This allowed the BiGlobal analysis of this mean flow to be thoroughly verified in both the incompressible and supersonic regime. The second case involved the developing incompressible Blasius boundary layer. This flow was chosen because of its better affinity with the actual Blasius boundary layer flow, which has an intrinsic developing nature. The BiGlobal approach involved artificial in- and outflow boundary conditions. Analyses were performed on a domain with a small and large streamwise extent to focus on a flow that is weakly and strongly developing, respectively. The former analyses were again compared to LST simulations to yield an internal verification and consistency check. The results of the analyses on the larger domain could be compared to the literature and were found to agree well in a qualitative sense. The Tollmien-Schlichting branch obtained in this study was found to lie too high with respect to the one reported in the literature. Although the exact reason for this could not yet be established, the most likely cause is a (small) difference in the prescribed mean flow. It is expected that the test case will yield identical results when exactly the same mean flow will be used, as some key differences can be identified in the literature in this regard. It was found that the artificial boundary conditions caused an odd/even effect with respect to the continuous eigenmode branches in the spectrum when the number of points in the streamwise direction was taken to be either odd or even. A similar behaviour was observed when consulting the literature, although the effect was never elaborated on explicitly. Lastly, the incompressible complex lamellar bidirectional vortex was considered. This mean flow is defined on a cylindrical coordinate system and is highly inhomogeneous in at least two spatial directions. Therefore, this case requires the BiGlobal approach and all power of the newly developed tools could be tested. A test case handled in the literature was very precisely reconstructed. Although it was found that no part of the spectrum was converged, the results were nearly identically retrieved. The solutions to all three test cases have been obtained successfully and compare reasonably well with the literature. It is therefore concluded that all capabilities of the newly developed tools have been tested successfully and the tools can be considered to be verified.AerodynamicsAerospace Engineerin
Characteristics of flow through orifices in pipes: An experimental investigation
No full textOrifice plates are key components used for flow measurement and control in several industries. For instance, they find applications in gas and liquid circuits of lithography machines, nuclear power plants and aerospace propulsion systems. They are used typically either for measuring flow-rate or to introduce a pressure drop for purposes of flow balancing. The present study focuses on the latter application. It is widely acknowledged in literature, that the turbulent, unsteady nature of the flow issuing through an orifice can also be a source of structural vibration. In order to understand the nature of the vibration source, the present experimental investigations analyze the time-varying flow field by means of unsteady wall-pressure measurements and time resolved, planar, particle-image-velocimetry (PIV). In addition to understanding the dynamics of the flow through a single-hole orifice, this study has assessed the possibility of using multiple-hole orifices as an alternative. It is observed that the overall magnitude and extent of the disturbance levels in the flow are reduced with the multiple-hole orifices, while maintaining similar levels of pressure drop. It is hypothesized that these lower disturbances are a result of the small-scale flow structures associated with the multiple-hole orifice flow (multiple jets as opposed to one). The measurements give detailed insights into the flow behavior downstream of orifice plates. Results indicate a low frequency flapping motion of the single-hole orifice jet, which is sustained by the surrounding large recirculation regions. For the geometries of the sharp-edged single-hole orifices investigated, the flapping frequency was observed to increase with flow speed and is found to occur at a Strouhal number = 0.02 based on the orifice jet velocity and the difference in internal diameters of the pipe and orifice.AerodynamicsAerospace Engineerin
Rowing Blade Design using CFD
No full textHow water and air ow around a rowing blade during a rowing stroke is poorly understood by the scientific community. Since important rowing races are won by time differences of only 0.4%, having a sound understanding of the ow will become more and more significant when it comes to rowing blade optimization. It is therefore the purpose of this Master Thesis project to investigate the ow around rowing blades using Computational Fluid Dynamics (CFD) in order to acquire enough knowledge and understanding of the ow to design a rowing blade.Aerospace Engineerin
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