1,720,993 research outputs found
Characterisation of the stability of compression corner geometries under supersonic flow conditions
Full text linkIdentifying the mechanism by which flow transitions to turbulence is of particular interest for the design and control of atmospheric flight vehicles. Compression corners are present on many key components of aerospace vehicles whose performance is essential for safe operation. Therefore, it is crucial to understand the transition mechanisms to avoid excessive thermal loading of the vehicle which is caused by separated flow and shock boundary layer interaction. The transition mechanisms involved in many high-speed separated boundary layer scenarios, are not fully understood. Linear stability theory, developed in the last century, describes the decomposition of a flow into a basic state and a small amplitude disturbance. The behaviour of these disturbances can be described as damped or growing. When growing disturbances are uncovered, these will begin to grow exponentially, leading to transition. This behaviour is known as modal. When a flow is subject to high external disturbance levels, it may cause a bypass of the modal amplification scenario, leading to the non-modal stability becoming a path to transition.
In order to truly represent flows for the purposes of stability analysis, highly accurate base states are required. Several methods for this are described; Direct Numerical Simulation (DNS) using second and high order methods, Direct Simulation Monte-Carlo (DSMC) used for rarefied gases, and triple deck theory used as a validation tool and method for characterising stability. The necessity for high order base-states is justified by the presence of unsteadiness in second order methods, in the form of small amplitude oscillations propagating throughout the domain even at low Reynolds numbers. These unsteady artefacts disappear when using high order methods, as well as the far greater decay and convergence of residuals achieved using these methods. These high order base-states show excellent agreement in the vicinity of separation with triple deck theory which provides confidence in the accuracy of these base-states.
Once appropriate base-states are calculated, modal and non-modal stability analysis can be undertaken. Throughout the planar and axisymmetric compression corners studied, an intimate link exists between the separation region and associated shocks through the modal mechanism. At high Reynolds numbers, a stationary unstable mode is identified, taking the form of the well documented separated boundary layer mode. This mode is studied over a wide range of Reynolds numbers characterising the neutral loop of this flow. An analogous mode is found using DSMC that is stable and on the hollow cylinder-flare that becomes unstable at high enough corner angles and Reynolds numbers. Further travelling modes are identified that are modally damped but show the potential to grow downstream out of the domain, which is corroborated using local spatial analysis. These structures are also compared with those of experimental work, showing a similar shape of periodic perturbations triggered in the separation region.
Non-modal analysis is performed on unstable planar ramp cases and describes significant short term growth which has the potential to bypass the modal mechanism, even when this modal behaviour is unstable. The large time required for the modal growth to achieve the same non-modal maximum gain suggests this modal behaviour will be bypassed in the transition mechanism. On the stable modal scenarios shown using high angle DSMC base-states, large energy gain is shown at short time suggesting that, in this case even a modally stable case may transition to turbulence
Influence of Fluid-Structure Interaction on Human Eye Biomechanics Under Air Puff Non-Contact Tonometry
Full text linkBiomechanical properties of biological tissues are important health indicators and multiple clinical decisions and surgical planning can be made based on their dynamic response to loading. But until now, some of the mechanical and dynamic responses are not fully understood due to the non-linearity and viscoelastic behaviour of biological tissues. The
relevant biological tissues of interest in the current study are the cornea and sclera of the human ocular globe. Cornea contributes with two-thirds of the optical focusing power of the eye beside intraocular lens and ocular fluids. The air puff tonometry test is a non-contact method with direct interaction to cornea in order to estimate the intraocular pressure which
helps with early Glaucoma diagnosis. The gab in research of this area is considering the fluid-structure interaction effect between cornea, the air puff and the eye internal fluid. Numerical model of the air puff test was constructed in the context of a coupled model between computational fluid dynamics (CFD) and finite element analysis (FEA) using Arbitrary
Lagrangian-Eulerian (ALE) deforming mesh. The time span of the jet is 30 ms and maximum Reynolds number (Re = 2.3×104), with jet orifice diameter 2.4 mm and impinging distance 11 mm. The present study was the first to take fluid-structure interaction between the air puff and cornea into account, in IOP and cornea material behaviour estimations
Advances in global instability computations: from incompressible to hypersonic flow
Full text linkEsta tesis constituye un gran avance en el conocimiento del estudio y análisis de inestabilidades hidrodinámicas desde un punto de vista físico y teórico, como consecuencia de haber desarrollado innovadoras técnicas para la resolución computacional eficiente y precisa de la parte principal del espectro correspondiente a los problemas de autovalores (EVP) multidimensionales que gobiernan la inestabilidad de flujos con dos o tres direcciones espaciales inhomogéneas, denominados problemas de estabilidad global lineal. En el contexto del trabajo de desarrollo de herramientas computacionales presentado en la tesis, la discretización mediante métodos de diferencias finitas estables de alto orden de los EVP bidimensionales y tridimensionales que se derivan de las ecuaciones de Navier-Stokes linealizadas sobre flujos con dos o tres direcciones espaciales inhomogéneas, ha permitido una aceleración de cuatro órdenes de magnitud en su resolución. Esta mejora de eficiencia numérica se ha conseguido gracias al hecho de que usando estos esquemas de diferencias finitas, técnicas eficientes de resolución de problemas lineales son utilizables, explotando el alto nivel de dispersión o alto número de elementos nulos en las matrices involucradas en los problemas tratados. Como más notable consecuencia cabe destacar que la resolución de EVPs multidimensionales de inestabilidad global, que hasta la fecha necesitaban de superordenadores, se ha podido realizar en ordenadores de sobremesa. Además de la solución de problemas de estabilidad global lineal, el mencionado desarrollo numérico facilitó la extensión de las ecuaciones de estabilidad parabolizadas (PSE) lineales y no lineales para analizar la inestabilidad de flujos que dependen fuertemente en dos direcciones espaciales y suavemente en la tercera con las ecuaciones de estabilidad parabolizadas tridimensionales (PSE-3D). Precisamente la capacidad de extensión del novedoso algoritmo PSE-3D para el estudio de interacciones no lineales de los modos de estabilidad, desarrollado íntegramente en esta tesis, permite la predicción de transición en flujos complejos de gran interés industrial y por lo tanto extiende el concepto clásico de PSE, el cuál ha sido empleado exitosamente durante las pasadas tres décadas en el mismo contexto para problemas de capa límite bidimensional. Típicos ejemplos de flujos incompresibles se han analizado en este trabajo sin la necesidad de recurrir a restrictivas presuposiciones usadas en el pasado. Se han estudiado problemas vorticales como es el caso de un vórtice aislado o sistemas de vórtices simulando la estela de alas, en los que la homogeneidad axial no se impone y así se puede considerar la difusión viscosa del flujo. Además, se ha estudiado el chorro giratorio turbulento, cuya inestabilidad se utiliza para mejorar las características de funcionamiento de combustores. En la tesis se abarcan adicionalmente problemas de flujos compresibles. Se presenta el estudio de inestabilidad de flujos de borde de ataque a diferentes velocidades de vuelo. También se analiza la estela formada por un elemento rugoso aislado en capa límite supersónica e hipersónica, mostrando excelentes comparaciones con resultados obtenidos mediante simulación numérica directa. Finalmente, nuevas inestabilidades se han identificado en el flujo hipersónico a Mach 7 alrededor de un cono elíptico que modela el vehículo de pruebas en vuelo HIFiRE-5. Los resultados comparan favorablemente con experimentos en vuelo, lo que subraya aún más el potencial de las metodologías de análisis de estabilidad desarrolladas en esta tesis. ABSTRACT The present thesis constitutes a step forward in advancing the frontiers of knowledge of fluid flow instability from a physical point of view, as a consequence of having been successful in developing groundbreaking methodologies for the efficient and accurate computation of the leading part of the spectrum pertinent to multi-dimensional eigenvalue problems (EVP) governing instability of flows with two or three inhomogeneous spatial directions. In the context of the numerical work presented in this thesis, the discretization of the spatial operator resulting from linearization of the Navier-Stokes equations around flows with two or three inhomogeneous spatial directions by variable-high-order stable finite-difference methods has permitted a speedup of four orders of magnitude in the solution of the corresponding two- and three-dimensional EVPs. This improvement of numerical performance has been achieved thanks to the high-sparsity level offered by the high-order finite-difference schemes employed for the discretization of the operators. This permitted use of efficient sparse linear algebra techniques without sacrificing accuracy and, consequently, solutions being obtained on typical workstations, as opposed to the previously employed supercomputers. Besides solution of the two- and three-dimensional EVPs of global linear instability, this development paved the way for the extension of the (linear and nonlinear) Parabolized Stability Equations (PSE) to analyze instability of flows which depend in a strongly-coupled inhomogeneous manner on two spatial directions and weakly on the third. Precisely the extensibility of the novel PSE-3D algorithm developed in the framework of the present thesis to study nonlinear flow instability permits transition prediction in flows of industrial interest, thus extending the classic PSE concept which has been successfully employed in the same context to boundary-layer type of flows over the last three decades. Typical examples of incompressible flows, the instability of which was analyzed in the present thesis without the need to resort to the restrictive assumptions used in the past, range from isolated vortices, and systems thereof, in which axial homogeneity is relaxed to consider viscous diffusion, as well as turbulent swirling jets, the instability of which is exploited in order to improve flame-holding properties of combustors. The instability of compressible subsonic and supersonic leading edge flows has been solved, and the wake of an isolated roughness element in a supersonic and hypersonic boundary-layer has also been analyzed with respect to its instability: excellent agreement with direct numerical simulation results has been obtained in all cases. Finally, instability analysis of Mach number 7 ow around an elliptic cone modeling the HIFiRE-5 flight test vehicle has unraveled flow instabilities near the minor-axis centerline, results comparing favorably with flight test predictions
Linear Instability Mechanisms on Airfoils at Low Reynolds Number: Massive Separation, Wingtip Vortex Formation and the Trailing Vortex System
No full textThe global linear instability analysis of separated flow on homogeneous infinite and finite wings are numerically investigated, including analysis of the wingtip vortex. Two- and three-dimensional modal and non-modal instability mechanisms of steady spanwise homogeneous laminar separated flows over airfoil profiles, placed at large angles of attack against the oncoming flow, have been investigated using linear global theory. Three NACA profiles of distinct thickness and camber were considered, in order to assess geometry effects on the laminar-turbulent transition paths discussed. At the conditions investigated large-scale steady separation occurs, such that Tollmien-Schlichting and crossflow mechanisms were not considered. I t is found that the leading modal instability on all three airfoils is that associated with the Kelvin-Helmholtz (KH) mechanism, taking the form of the eigenmodes known from analysis of generic bluff bodies. The three-dimensional stationary eigenmode of the two-dimensional laminar separation bubble, associated in earlier analyses with the formation on the airfoil surface of large-scale separation patterns akin to stall-cell, is shown to be stronger damped than the KH mode. Non-modal instability analysis reveals the potential of the flows to sustain transient growth which becomes stronger with increasing angle of attack and Reynolds number. Optimal initial conditions were computed and were found to be analogous to those on a cascade of Low Pressure Turbine blades. By changing the time-horizon of the analysis these linear optimal initial conditions are found to evolve into the KH mode. Steady Navier-Stokes equations for a high angle of attack and Reynolds number flow are achieved through selective damping frequency method, and its modal analysis is performed. The most unstable mode is oscillating after the airfoil and dominates about O(10) chord length. The sub-leading mode is a KH type as appeared in the low Reynolds number steady flow. The stationary mode starts immediately behind the airfoil and then decays into the wake. The time-periodic base flows ensuing linear amplification of the KH mode are analyzed here via temporal Floquet theory. Two amplified modes are discovered, having characteristic spanwise wavelengths of approximately 0.6 and 2 chord lengths, respectively. Unlike secondary instabilities on the circular cylinder, three-dimensional short-wavelength perturbations are the first to become linearly unstable on all airfoils. Long-wavelength perturbations are quasi-periodic, standing or traveling-wave perturbation that also become unstable as the Reynolds number is increased further. The dominant short-wavelength instability gives rise to spanwise periodic wall-shear patterns, akin to the separation cells encountered on airfoils at low angles of attack and the stall cells found in flight at conditions close to stall. Thickness and camber have quantitative but not qualitative effect on the secondary instability analysis results obtained. The previous analysis assums an idealistic wing flow which has a homogeneous boundary conditions in the spanwise direction. A generalized wingtip developed downstream should be taken into account. To this purpose, a finite wing laminar flow has been considered. Instability analysis of flow in the wake of a low aspect ratio three-dimensional wing of elliptic platform, constructed with appropriately scaled Eppler E387 airfoils, has been performed. The flow field over the airfoil and in its wake was computed by full threedimensional direct numerical simulation at a chord Reynolds number of Ree = — = 1750 and two angles of attack, AoA = 0° and 5°. The spatial eigenvalue problem governing linear global small-amplitude perturbations superposed upon this base flow has been solved and results were used to initialize a linear PSE-3D marching procedure without any simplifying assumptions regarding the form of the trailing vortex system, other than weak dependence of all flow quantities on the axial spatial direction. Two classes of linearly unstable perturbations were identified, namely stronger-amplified symmetric modes and weaker-amplified antisymmetric disturbances, both peaking at the vortex sheet which connects the trailing vortices. The amplitude functions of both classes of modes were documented and N-factor predictions for potential laminar breakdown have been computed. Resumen En esta tesis se investiga numéricamente el análisis global de estabilidad lineal en flujo desprendido sobre alas homogéneamente infinitas y finitas, incluyendo el análisis de los vórtices de punta de ala. Los mecanismos de inestabilidad modal y no modal, bidimensional y tridimensional, de flujos separados estacionarios laminares sobre superficies sustentadoras homogéneas a lo largo de la envergadura han sido investigados a altos ángulos de ataque, con respecto al flujo de entrada, mediante el uso de la teoría lineal global. Para ello se han considerado tres perfiles NACA de distinto grosor y curvatura con el fin de evaluar los efectos de la geometría en la ruta seguida por el flujo en la transición de flujo laminar a flujo turbulento. En las condiciones investigadas, no se considera la separación estacionaria a gran escala generada por mecanismos del tipo Tollmien-Schlichting o inestabilidad de flujo cruzado (crossflow). En estas condiciones se encontró que la inestabilidad modal dominante en las tres superficies sustentadoras están asociadas con el mecanismo de tipo Kelvin-Helmholtz (KH), siendo su forma similar a los modos propios obtenidos en la literatura del análisis de inestabilidad lineal alrededor de cuerpos romos. En este estudio se muestra que el modo propio estacionario tridimensional obtenido en la burbuja de separación laminar bidimensional (asociado en estudios previos con la formación de los patrones de separación de gran-escala parecidos a los “Stall-cells”) es más fuertemente amortiguado que los modos KH. El análisis de estabilidad no-modal revela el potencial que tienen estos flujos para permitir mecanismos de crecimiento transitorio los cuales son más fuertes cuanto mayor es el ángulo de ataque y el número de Reynolds. Se computaron las condiciones iniciales óptimas, las cuales se encontraron que son análogas a las que surgen en la cascada de álabes en turbinas de baja presión. Mediante el cambio del horizonte de tiempo en el análisis de estas condiciones iniciales óptimas se encontró que éstas evolucionan a modos de tipo KH. Por otro lado, las soluciones de Navier-Stokes estacionarias para ángulos de ataque y números de Reynolds considerados se calcularon mediante el uso de un método de amortiguación selectivo de frecuencias (“selective damping frequency method”), sobre las cuales se realizaron los análisis modales y no-modales. El modo más inestable es oscilante detrás de la superficie sustentadora y domina el comportamiento fluido sobre longitudes O(10) la longitud de la cuerda. El siguiente modo dominante es el modo de tipo KH que aparece en el flujo estacionario a números de Reynolds bajos. Finalmente, el modo estacionario comienza inmediatamente después de la superficie sustentadora y decae en la estela. El flujo base periódico en el tiempo resultante de la subsiguiente amplificación lineal del modo KH ha sido analizado aquí mediante la teoría temporal Floquet. Se descubrieron dos modos con longitudes típicas a lo largo de la envergadura del orden de 0.6 y 2 longitudes de cuerda, respectivamente. A diferencia de las inestabilidades secundarias sobre el cilindro, las inestabilidades tridimensionales de longitud de onda corta son las dominantes en todas las superficies sustentadoras. Las perturbaciones de longitud de onda larga son cuasi-periódicas, se vuelven también inestables cuando el número de Reynolds se incrementa. Las inestabilidades dominantes de corta longitud de onda dan lugar a patrones periódicos a lo largo de la envergadura de las líneas de corriente similares a las celdas de separación encontradas sobre las superficies sustentadoras a bajos ángulos de ataque, y las encontradas en condiciones de vuelo próximas a la entrada en pérdida (“Stall cells”). El espesor y la curvatura de las superficies tienen un efecto cuantitativo pero no cualitativo en el análisis de las inestabilidades secundarias realizado. El análisis anterior asume un flujo ideal sobre un ala homogénea en la dirección a lo largo de la envergadura. Un caso más general debería tener en cuenta el efecto de la punta del ala en el flujo aguas abajo. Para este objetivo se considero el flujo laminar entorno a un ala finita. Se realizo el análisis de inestabilidad del flujo en la estela de un ala tridimensional, de plataforma elíptica, con bajo ratio entre la cuerda y la envergadura construido a partir de perfiles Eppler E387 escalados apropiadamente. El flujo sobre el ala y sobre la estela fueron computados mediante simulación numérica directa tridimensional a número de Reynolds basado en la cuerda igual a 1750 y dos ángulos de ataque, AoA = 0• y 5• . El problema de valores propios espacial que gobierna las perturbaciones globales lineales de pequeña amplitud superpuestas al flujo base fue resuelto, y los resultados fueron usados para inicializar el PSE-3D linear el cuál utiliza un procedimiento de “marching” en el que no se realizaron ninguna hipótesis de simplificación en cuanto a la forma del sistema de vórtices de arrastre, que no sea la de la débil dependencia de todas la cantidades fluidas con respecto a la dirección espacial axial. De esta manera se identificaron dos clases de perturbaciones inestables, a saber, modos simétricos fuertemente amplificados y perturbaciones anti-simétricas débilmente amplificadas. Ambas alcanzan el máximo en la zona de la función de amplitud que conecta los vórtices de arrastre. Dichas funciones de amplitud han sido documentadas y las predicciones del “N-factor” para la ruptura potencial del flujo laminar fueron calculadas
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Stability analysis of the flow past a low-pressure turbine blade
Full text linkResults are presented of BiGlobal linear stability analysis of incompressible flow over a row of T-106/300 aircraft Low Pressure Turbine (LPT) blades. In particular the three-dimensional stability of two-dimensional steady and periodic states is investigated for Reynolds numbers below 10,000, where the primary two-dimensional instability leading the flow through a Hopf-bifurcation from steady to periodic has been identified to be at a chord Reynolds number of Rec = 905 ± 1. Structured and unstructured meshes have been used while variation of the polynomial order of the numerical methods as well as extension of the domain under consideration has ensured numerical convergence. Furthermore, consistency between linear stability analysis and full Navier-Stokes solution is shown. The leading Floquet- and eigenvalues of the LPT flow are observed at a range of Reynolds and span-wise wavenumber parameters. They show that the instability depends on the imposed periodicity in the two-dimensional plane of the computational model. Neglecting subharmonic effects the flow undergoes a three-dimensional transition caused by three-dimensional long wavelength disturbances immediately after its two-dimensional instability. The associated unstable mode is related to the wake of the basic state. A second short wavelength stable mode has been identified to be associated to the separation bubble at the trailing edge. A pseudospectra analysis has also been performed showing sensitivity of the eigenvalue problem and the associated potential for transient growth due to the non-orthogonal properties of the eigenmodes. Three-dimensional direct numerical simulation (DNS) shows that three-dimensional transition is susceptible to the modes identified. Finally, a subsequent two-dimensional optimum growth analysis based on a newly developed method related to the computation of the singular values of the eigenvalue problem has been performed for flow past a cylinder and the LPT flow. Optimum modes that exhibit strong energy growth were identified and compared with the adjoint modes as found in the literature. The maximum energy associated to sensitivity regions is located around the separation bubble at the trailing edge of the blade as they grow downstream. Demonstrating the potential of the developed method based on singular values, the purely two-dimensional results as presented in this work serve as a basis for future three-dimensional analyses.Open Acces
Flow physics and control of separation for low aspect ratio swept and tapered wings
No full textDecember 2023Flow separation is the last thing you want to happen over an aircraft wing: in most cases attached flow over the wing is the only thing keeping the plane in the air. The formation of 3D separated flows over wings and other control surfaces is an under-explored topic due to difficulties measuring or computing these phenomena. Despite this dearth in the literature, aircraft wings routinely encounter high-angle-of-attack scenarios either from transient gusts or intentional maneuvers. Unmanned aerial vehicles tend to operate at high angles of attack and low Reynolds numbers. The present experimental investigation seeks to provide a basis with which 3D separation can be characterized and controlled. Wind tunnel and water tunnel experiments were performed to show the effects of planform shape on the large scale flow structures over finite wings at high angles of attack. First, geometrically simple unswept planforms were considered. Wind tunnel experiments explored unswept planforms at the moderate Reynolds number , showing that these wings experience the owl-eye stall cell pattern at high angles of attack. The stall angle of attack increases with decreasing aspect ratio, as the end effects of the tip vortex and the horseshoe vortex at the wall get moved closer together and encourage attached flow. The surface foci of the stall cell are connected by an arch vortex which grows into the wake according to the spanwise distribution of the reversed flow region. At the midspan, the wake has some periodicity through the quasi-2D shedding of spanwise vortices into the wake. Next, the geometric complexity was systematically ramped up with a series of wind tunnel experiments on swept and tapered planforms at the moderate Reynolds number . For the untapered unswept wings, the stall cell pattern forms; for the swept back untapered wings the root-to-tip ram's horn forms, for the wings with forward swept trailing edge the inverted (tip-to-root) ram's horn forms and for swept back and tapered wings the ram's horn type surface spiral would form, though the 3D flow field shows some similarity to the arch type separation. When the leading edge is swept back, the reversed flow region and peak unsteadiness is shifted towards the wing tip, while when the trailing edge is swept forward, the reversed flow region and peak unsteadiness is shifted towards the root. Nine model wings were explored in water tunnel experiments at the very low Reynolds number . Some analogous topological patterns were identified between the wind tunnel and water tunnel tests in time-averaged volumetric velocity fields. Namely, the area of the reverse flow region as a function of the span showed very similar distributions at and as a function of sweep angle and taper ratio. The global flow structures like reverse flow region and spiraling 3D streamlines identified a ram's horn vortex for the swept back wing at both Reynolds numbers and an inverted (tip-to-root) ram's horn for the forward swept trailing edge wing at both Reynolds numbers. Finally, flow control using leading edge steady blowing with seven equally spaced rectangular jets was applied to two of the tapered wings in the wind tunnel at . Both wings had the same taper ratio and aspect ratio, but one had a forward swept trailing edge and the other had a swept back leading edge. The flow control for the trailing edge swept forward model was very effective, with beneficial aerodynamic augmentation being achieved when blowing is applied near the midspan. The flow control for the leading edge swept back model was less effective, as the leading-edge-normal blowing for the swept back leading edge angled the jet in a way that would increase the drag and fail to reattach the flow.Ph
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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