1,721,642 research outputs found
Beobachtungen über den Einfluss des Klimas auf Pflanzen und Thiere
No full textOriginaltitel: Some observations relative to the influence of climate on vegetable and animal bodie
Propagation of acoustic perturbations in non-uniform ducts with non-uniform mean flow using eigen analysis in general curvilinear coordinate systems
No full textA new framework, Eigen Analysis in General Curvilinear Coordinates (EAGCC), is presented for internal propagation of linear acoustic flow disturbances through irregular but smoothly varying duct geometries and non-uniform but smoothly varying mean flows. The framework is based on an eigen analysis of the linearised Euler equations for a perfect gas formulated in a general curvilinear coordinate system. A series of test cases are studied, from a simple uniform cylindrical annular duct with uniform mean flow to an axially and circumferentially non-uniform duct with non-uniform mean flow, which together validate the method for acoustic propagation through non-uniform annular ducts and non-uniform but irrotational and homentropic mean flow: although the framework provides for rotational and non-homentropic mean flow, and for modelling vortical and entropic flow perturbations, these features are not validated in this paper. Two propagation methods are presented. The first is a one-way “single sweep” calculation, in which only information travelling in the direction of propagation is retained. The second is an iterative “two-way sweep” method that accurately captures reflected waves and returns transmitted and reflected perturbations. Previous eigenvector analyses were subject to limitations on geometry and mean flow (for instance slowly-varying ducts) that are not required in the current method, for which the only limitations are that the duct and mean flow vary smoothly with position. This work extends the scope of the eigenvector approach to include acoustic problems previously limited to volumetric or surface-based methods.</p
A Qualitative Study Investigating the Positive Experiences of Therapy and Therapeutic Relationships of Late-Diagnosed Autistic Females
No full textBackground: Autistic adults face a paradox: they have a greater risk of developing mental health difficulties, while also experiencing increased barriers to accessing mental health care. Research on reducing these barriers has previously focused on physical adjustments such as providing quiet waiting rooms, and cognitive adaptations such as using unambiguous language. Approaches to building the therapeutic relationship have been under-researched.Methods: The researchers interviewed 12 UK-based late-diagnosed White autistic females about experiences of therapy that they identified as being particularly positive. The study adopted a critical realist and neuro-affirmative stance, with an insider researcher position. The researchers developed common themes and subthemes through reflexive thematic analysis.Findings: Three themes were developed from the interviews and incorporated eight subthemes. Theme 1: “Providing and delivering beneficial therapy for autistic clients” included “sourcing therapy” and “autistic expectations of positive therapy.” Theme 2: “Features of a positive therapeutic relationship from an autistic perspective” included “building trust and rapport,” “equitable power dynamics,” and “reciprocity and a collaborative approach.” Theme 3: “Understanding autism and using adaptation strategies” included “adaptation strategies,” “understanding autism,” and “positive autism.”Conclusions: While physical and cognitive adaptations improve the accessibility of therapeutic interventions, therapists must also focus on adapting the therapeutic relationship with autistic clients, particularly with an enhanced focus on power dynamics and collaborative approaches. All participants described positive experiences of connection when their therapists shared relevant insights and experiences to build common ground. Recognizing less stereotypical presentations of autism and exploring internalized ableism in both the therapist and client improved the positive experience of therapy
Photographic panorama of the site of Canberra [picture] /
No full textPhotograph in three sections a-c left to right.; Title from accession record.; Inscriptions at the back: From where present Parliament House stands looking towards where War Memorial is now, taken by A.B. Wilson
Fan buzz-saw noise under intake flow distortion: a computational study
No full textSteady intake flow distortion due to non-axisymmetric intake geometry and angle of attack of the flight stream can affect various fan tone noise, especially fan buzz-saw noise. In this paper, unsteady CFD simulations have been performed on fully coupled fan and intake models to study the effect of intake flow distortion on fan buzz-saw noise. Three cases have been investigated, namely a baseline case, an axisymmetric distorted case, and a drooped distorted case, and comparisons have been made on the intake noise data extracted from the CFD calculations. The distortion fields generated in the last two cases have been compared and characterised by Fourier-Bessel harmonics. The results show that the distortion generated in the drooped case is more significant and has resulted in stronger circumferential mode scattering appearing initially in the fan domain. The main effect of the distortions in both cases is to cause scattering of the rotor-locked modes into adjacent circumferential harmonics, as the shock waves propagate through the intake ducts.</p
Error analysis for 1D propagation using Eigen Analysis in General Curvilinear Coordinates
No full textThis paper provides a formal error analysis for acoustic propagation in one-dimension using the Eigen Analysis in General Curvilinear Coordinates (EAGCC) method. The method is shown to be second order accurate in mesh spacing. Different errors are observed in the forward and reverse direction relative to the input wave and equations have been derived that describe the error in each direction. They are composed of three leading order terms related to the first, second, and third derivatives of the Jacobian matrix with respect to distance in the direction of propagation. The EAGCC method has been successfully applied to a number of real engineering applications in three dimensions, but this is the first time a formal error analysis has been attempted. Although the analysis is in one dimension, a discussion is provided regarding the application of the results to three dimensional meshes. The analysis is supported by a range of numerical test-cases which confirm the predicted relationship between the wavenumber and mesh related parameters, and the error. It is demonstrated that local numerical errors act as sources of noise, such that the global error can be calculated as the cumulative effect of all of the local errors along the duct
A fast method For calculating sensitivities of acoustic propagation in ducts to small changes in geometry and mean flow
No full textThis paper introduces a computationally fast approximate method for calculating sensitivities of acoustic propagation in ducts to small changes in geometry and mean flow, although in this paper only changes to mean flow in one-dimensional and three-dimensional axisymmetric ducts are validated. A solution to the base (unperturbed) problem is first calculated by the eigen analysis in general curvilinear coordinates (EAGCC) method. The new method to calculate the sensitivities does not require any further eigen analysis beyond the base solution, and as a result is extremely fast to compute. The error in the method has been quantified for a range of test-cases and shown to be proportional to a single parameter combining the base flow Mach number, length of modified region, and a representative fractional increase in mean flow Mach number. As expected for a method based on linear approximation, the new method is shown to be accurate for small changes in mean flow over a limited region of the duct, but unsuitable for assessing widely varying geometries and mean flows. The new method is thus ideally suited to numerical optimisation and robust design studies, in which it can be used in an analogous manner to adjoint methods
Aeroacoustics research in Europe: The CEAS-ASC report on 2016 highlights
No full textThe Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on the European scale, and European aeronautics activities internationally. Each year, the committee highlights several of the research and development projects in Europe. This paper is the 2016 issue of this collection of Aeroacoustic Highlights, compiled from contributions submitted to the CEAS-ASC. The contributions are classified under three main headings; Aircraft and Turbomachinery Noise, Experimental and Numerical Methods and Further Applications of Aeroacoustics. A concise summary of the CEAS-ASC workshop held in Southampton, England, in September 2016 is also included in this report.</p
Calculation of acoustic transfer functions for smooth ducts of varying cross section and non-uniform mean flow using eigen analysis in general curvilinear coordinates
No full textThe EAGCC (Eigen Analysis in General Curvilinear Coordinates) method, based on the linearised Euler equations for isentropic perturbations, is extended to include an improved non-iterative solution methodology, an acoustic liner boundary condition and a Ffowcs-Williams/Hawkings surface for calculation of farfield acoustic pressures. Three validation cases are presented, testing the accuracy of the extended method to predict acoustic transmission across a geometric duct transition, an acoustically lined duct section, transition to external near-field flow at duct inlet and farfield acoustic pressure calculations. It is shown that there is a practical limit to the wavelengths that can be modelled. Taking a typical aeroengine inlet as an example, circumferential harmonics can be calculated up to between 40 or 60 depending on the complexity of the case. Under this limit the elapsed time for a complete calculation will range from a few minutes to a few hours on a current compute platform. All three testcases show good agreement between the EAGCC method and reference calculations. These test cases confirm that the EAGCC method has wide potential for industrial application to acoustic propagation, both in duct and to the farfield.</p
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