Continuous spectrum growth and modal instability in swirling duct flow

We present results on the stability of compressible inviscid swirling flows in an annular duct. Such flows are present in aeroengines, for example in the by-pass duct, and there are also similar flows in many aeroacoustic or aeronautical applications. The linearised Euler equations have a ('critical layer') singularity associated with pure convection of the unsteady disturbance by the mean flow, and we focus our attention on this region of the spectrum. By considering the critical layer singularity, we identify the continuous spectrum of the problem and describe how it contributes to the unsteady field. We find a very generic family of instability modes near to the continuous spectrum, whose eigenvalue wavenumbers form an infinite set and accumulate to a point in the complex plane. We study this accumulation process asymptotically, and find conditions on the flow to support such instabilities. It is also found that the continuous spectrum can cause a new type of instability, leading to algebraic growth with an exponent determined by the mean flow, given in the analysis. The exponent of algebraic growth can be arbitrarily large. Numerical demonstrations of the continuous spectrum instability, and also the modal instabilities are presented.

Modal scattering at an impedance transition in a lined flow duct

An explicit Wiener-Hopf solution is derived to describe the scattering of duct modes at a hard-soft wall impedance transition in a circular duct with uniform mean flow. Specifically, we have a circular duct r = 1, - ∞ < x < ∞ with mean flow Mach number M > 0 and a hard wall along x < 0 and a wall of impedance Z along x > 0. A minimum edge condition at x = 0 requires a continuous wall streamline r = 1 + h(x, t), no more singular than h = Ο(x1/2) for x ↓ 0. A mode, incident from x < 0, scatters at x = 0 into a series of reflected modes and a series of transmitted modes. Of particular interest is the role of a possible instability along the lined wall in combination with the edge singularity. If one of the "upstream" running modes is to be interpreted as a downstream-running instability, we have an extra degree of freedom in the Wiener-Hopf analysis that can be resolved by application of some form of Kutta condition at x = 0, for example a more stringent edge condition where h = Ο(x3/2) at the downstream side. The question of the instability requires an investigation of the modes in the complex frequency plane and therefore depends on the chosen impedance model, since Z = Z (ω) is essentially frequency dependent. The usual causality condition by Briggs and Bers appears to be not applicable here because it requires a temporal growth rate bounded for all real axial wave numbers. The alternative Crighton-Leppington criterion, however, is applicable and confirms that the suspected mode is usually unstable. In general, the effect of this Kutta condition is significant, but it is particularly large for the plane wave at low frequencies and should therefore be easily measurable. For ω → 0, the modulus fends to |R001| → (1 + M)/(1 -M) without and to 1 with Kutta condition, while the end correction tends to ∞ without and to a finite value with Kutta condition. This is exactly the same behaviour as found for reflection at a pipe exit with flow, irrespective if this is uniform or jet flow.

Frente Parlamentar Mista das Micro e Pequenas Empresas : lógica de funcionamento e resultados

Analisa o modo com que os parlamentares se organizam frente à estrutura institucional no Congresso Nacional. Tem como referências para discussão, contribuições de Barry Ames (2003) e Figueiredo e Limongi (2001) que apresentam dois modelos de funcionamento do Parlamento, o distributivista e o partidário. Analisa a atuação da Frente Parlamentar Mista das Micro e Pequenas Empresas. Enfatiza a segunda fase de funcionamento da Frente, os anos de 2008 e 2009, quando trabalhou pela regulamentação da Lei Geral das Micro e Pequenas Empresas (Lei Complementar nº 123/06) nos Estados e Municípios e seus aperfeiçoamentos por meio da aprovação de Leis Complementares nºs 127/07, 128/08 e 133/09.

Entre la epistemología y la lógica. Decisión y algoritmo de ordenación

[ES] Este trabajo en homenaje al Profesor Emilio Soldevilla trata de plantear algunos elementos de la matemática combinatoria, escogidos sin otro criterio que el de ser fácilmente visualizados para poner en evidencia el aspecto altamente significativo que poseen para la construcción de una epistemología de la economía y gestión de empresas. Y todo ello en torno a uno de los conceptos más destacados de este ámbito del conocimiento cual es el de decisión.

Aplicación de la Lógica Dominante del servicio (LDS) en el sector turístico: el marketing interno como antecedente de la cultura de co-creación de innovaciones con clientes y empleados

[ES] Este trabajo trata de profundizar en la comprensión del concepto de marketing interno (MI), considerado como un recurso operante desde la óptica de la Lógica Dominante del Servicio (LDS), así como en su influencia en la obtención de resultados empresariales superiores a los de la competencia. Para ello, se examina el efecto del MI en la predisposición de las empresas analizadas a que sus clientes y empleados de primera línea participen en el desarrollo de innovaciones de servicio, ampliando de este modo, de acuerdo con la LDS, las oportunidades de co-creación de valor disponibles para las organizaciones. Para contrastar las hipótesis planteadas se aplica un análisis de ecuaciones estructurales a la información facilitada por los gerentes de 240 hoteles de una muestra de ámbito nacional.

La LLanada Oriental hace mil años. ¿Qué hay del crecimiento agrario altomedieval? Hábitat y paisajes agrarios (entre la imaginación y la lógica)

Congreso 750 aniversario de la fundación de la villa de Salvatierra. Ana de Begoña Azcárraga y Henrike Knörr Borras in memorian.

Generalized modal identification of linear and nonlinear dynamic systems

This dissertation is concerned with the problem of determining the dynamic characteristics of complicated engineering systems and structures from the measurements made during dynamic tests or natural excitations. Particular attention is given to the identification and modeling of the behavior of structural dynamic systems in the nonlinear hysteretic response regime. Once a model for the system has been identified, it is intended to use this model to assess the condition of the system and to predict the response to future excitations.

A new identification methodology based upon a generalization of the method of modal identification for multi-degree-of-freedom dynaimcal systems subjected to base motion is developed. The situation considered herein is that in which only the base input and the response of a small number of degrees-of-freedom of the system are measured. In this method, called the generalized modal identification method, the response is separated into "modes" which are analogous to those of a linear system. Both parametric and nonparametric models can be employed to extract the unknown nature, hysteretic or nonhysteretic, of the generalized restoring force for each mode.

In this study, a simple four-term nonparametric model is used first to provide a nonhysteretic estimate of the nonlinear stiffness and energy dissipation behavior. To extract the hysteretic nature of nonlinear systems, a two-parameter distributed element model is then employed. This model exploits the results of the nonparametric identification as an initial estimate for the model parameters. This approach greatly improves the convergence of the subsequent optimization process.

The capability of the new method is verified using simulated response data from a three-degree-of-freedom system. The new method is also applied to the analysis of response data obtained from the U.S.-Japan cooperative pseudo-dynamic test of a full-scale six-story steel-frame structure.

The new system identification method described has been found to be both accurate and computationally efficient. It is believed that it will provide a useful tool for the analysis of structural response data.