Hopf bifurcation in wakes behind a rotating and translating circular cylinder

A low-dimensional Galerkin method, initiated by Noack and Eckelmann [Physica D 56, 151 (1992)], for the prediction of the flow field around a stationary two-dimensional circular cylinder in a uniform stream at low Reynolds number is generalized to the case of a rotating and translating cylinder. The Hopf bifurcation describing the transition from steady to time-periodic solution is investigated. A curve indicating the transitional boundary is given in the two-dimensional parameter plane of Reynolds number Re and rotating parameter alpha. Our results show that rotation may delay the onset of vortex street and decrease the vortex-shedding frequency. (C) 1996 American Institute of Physics.

Notch sensitivity of circular rings subjected to impact loading

'Notch-sensitive regions' have been observed during a series of experimental investigations into the dynamic plastic behaviour and failure of thin-walled metallic radially notched circular rings with are-shaped supports subjected to concentrated impact loads. The experimental results show that the exterior notches at some regions have no effect on the deformation of the rings, but do have effect at the remaining regions. The notch-sensitive region is theoretically determined by using the equivalent structures technique; fairly good agreement has been reached between the simple theory and the experimental results. Both dimensional and theoretical analyses prove that whether a plastic hinge formed or not at the notched section does not depend on the mean radius of the ring and the input kinetic energy. It depends on the weak coefficient of the notched section and the angle of the support. Generally speaking, there are mainly three failure modes for a notched circular ring with are-shaped support under impact loading: Mode I, large inelastic deformation when the notch is outside the sensitive region, in this case the ring deforms as a normal one; Mode II, large inelastic deformation only at some part of the ring and tearing occurred at the notched sections; Mode III, large inelastic deformation and total rupture occurred at the notched sections. It is believed that the present study could assist the understanding of the dynamic behaviour and failure of other kinds of nonstraight components with macroscopic imperfections under impulsive loading.

Circular brass foil failed by plugging opposite to direction of incident laser beam

The peripheries of circular foils of 30 mm in diameter and 0.1 mm thick are fixed while their surfaces are subjected to a long pulsed laser over a central region that may vary from 2 mm to 6 mm in diameter. Failure is observed and classified into three stages; they are referred to as thermal bulging, localized shear deformation, and perforation by plugging. A distinct feature of the failure mode is that bulging and plugging occurred in the direction opposite to the incident laser beam. Such a phenomenon can be expected to occur for a laser intensity threshold value of about 0.61 x 10(6) W/cm(2) beyond which local melting of the material begins to take place.

Stress-distribution at the rigid circular-arc inclusion end

The elastic plane problem of a rigid co-circular arc inclusion under arbitrary loads is dealt with. Applying Schwarz's reflection principle integrated with the analysis of the singularity of complex stress functions, the general solution of the problem is found and several closed-form solutions to some problems of practical importance are given. Finally, the stress distribution at the arc inclusion end is examined and a comparison is made with that of the rigid line inclusion end to show the effect of curvature.

Fatigue crack-growth from a circular notch under high-levels of biaxial stress

A series of experiments have been conducted on cruciform specimens to investigate fatigue crack growth from circular notches under high levels of biaxial stress. Two stress levels (Δσ₁= 380 and 560 MPa) and five stress biaxialities (λ=+1.0, +0.5, 0, −0.5 and −1.0; where λ=σ₂/σ₁ were adopted in the fatigue tests in type 316 stainless steel having a monotonic yield strength of 243 MPa. The results reveal that fatigue crack growth rates are markedly influenced by both the stress amplitude and the stress biaxiality. A modified model has been developed to describe fatigue crack growth under high levels of biaxial stress.

Standing wave of finite-amplitude in an circular basin with uneven bottom

The effect of the particle cover over the density interface between two layers of fluids and of the suspended solid particles in the upper turbulcnt layer on the turbulent entrainment has been studied experimentally. The entrainment distance D is a function of the time of power: D=kt, where =0.200-0.130p. For suspended particles in the upper layer and pure 2-layer fluid is equal to 0.200, but the value of k for the suspended particles is smaller than that for the pure 2-layer fluid. The non-dimensional entrainment velocity is E=KRiln, where n=1.50+0.93 p. It is shown that the particle cover over the interface changes the power of Ril in the entrainment and hinders the turbulent entrainment. The variation rule of E for the suspended particles is the same as that for the pure 2-layer fluid, but the K value of the former is smaller than that of the latter. The turbulent mixing mechanism has been discussed.

Vortex motion in the early stages of unsteady flow around a circular cylinder

In this paper, processes in the early stages of vortex motion and the development of flow structure behind an impulsively-started circular cylinder at high Reynolds number are investigated by combining the discrete vortex model with boundary layer theory, considering the separation of incoming flow boundary layer and rear shear layer in the recirculating flow region. The development of flow structure and vortex motion, particularly the formation and development of secondary vortex and a pair of secondary vortices and their effect on the flow field are calculated. The results clearly show that the flow structure and vortices motion went through a series of complicated processes before the symmetric main vortices change into asymmetric: development of main vortices induces secondary vortices; growth of the secondary vortices causes the main vortex sheets to break off and causes the symmetric main vortices to become “free” vortices, while a pair of secondary vortices is formed; then the vortex sheets, after breaking off, gradually extend downstream and the structure of a pair of secondary vortices becomes relaxed. These features of vortex motion look very much like the observed features in some available flow field visualizations. The action of the secondary vortices causes the main vortex sheets to break off and converts the main vortices into free vortices. This should be the immediate cause leading to the instability of the motion of the symmetric main vortices. The flow field structure such as the separation position of boundary layer and rear shear layer, the unsteady pressure distributions and the drag coefficient are calculated. Comparison with other results or experiments is also made.

Estudio empírico del endeudamiento, coste de la deuda y rentabilidades de la industria de calzado de La Rioja. Comparación por tamaño y sector

[ES] El presente trabajo tiene por objeto el estudio del nivel de endeudamiento, el coste de la deuda y las rentabilidades de la industria del calzado de la Comunidad Autónoma de La Rioja por sectores y tamaños. De acuerdo con la Economía Industrial, que considera el sector de actividad como el principal determinante de los resultados de las organizaciones, se analiza si las variables estudiadas son distintas en función de su pertenencia al sector del calzado en comparación con el de la industria agroalimentaria, por ser éste el más importante de la economía de la región. Por otro lado, de acuerdo con la Teoría de los Recursos y Capacidades, que considera que son los factores internos los que explican las diferentes rentabilidades, estudiaremos un recurso interno como es el tamaño, viendo su influencia sobre las variables comentadas. Por último, los resultados del estudio conjunto de la pertenencia a un sector de actividad por tamaños homogéneos nos permiten afirmar que el coste de la deuda de las pequeñas empresas es significativamente distinto en función de dicho sector de pertenencia.

Una valoración del sector vinícola riojano

Este trabajo es resultado de la investigación realizada en el marco de la Tesis Doctoral sobre Impacto socioeconómico del sector del vino en Rioja, que elabora M. Larreina.

Efectos tamaño y sector sobre la rentabilidad, endeudamiento y coste de la deuda de las empresas familiares riojanas

Ponencia presentada y defendida en las XIV jornadas Hispano Lusas de Gestión Científica celebradas en Azores en febrero de 2004.

La percepción de la calidad en el sector de la mensajería urgente

[ES] Esta investigación muestra como, en el servicio de transporte urgente y mensajería, el operador público «Correos» es percibido con una calidad inferior a varios de sus competidores más cercanos: Seur, MRW y Nacex. A pesar de los esfuerzos realizados por esta entidad pública en la mejora de la calidad del servicio, éstos no se ven reflejados en las evaluaciones de los consumidores, al menos al mismo nivel que sus competidores. Estos resultados han sido obtenidos tras la utilización de diferentes metodologías, como la regresión ordinal, la comparación entre grupos o los modelos multinivel. Asimismo, diversas propuestas para futuras investigaciones son comentadas al final del estudio.

El análisis del entorno político y legal en el marco de la planificación estratégica en el sector turístico y hotelero

[ES] Las empresas turísticas se encuentran inmersas en un entorno cambiante, caracterizado por los avances tecnológicos, al aumento de la competencia global y a las consecuencias derivadas de la crisis económica mundial. Ante estas circunstancias, las empresas turísticas se ven obligadas a diseñar estrategias de marketing y llevar a cabo planes estratégicos. Pues bien, para entender el marketing y desarrollar estrategias eficaces, es fundamental entender el contexto en el que opera la empresa, puesto que en él se generan las oportunidades del mercado y se presentan las amenazas que van a condicionar su futuro. Entre las fuerzas que integran el entorno empresarial se encuentran la economía, la sociedad, la política o la demografía, entre otras.